It is also possible that SAM amount in host cells is recognized
as a hallmark of nutrition availability. Thus, SAM reduction
triggers the ‘fasting’ response. For example, in
yeast, nutrient poor diet induces autophagy, which is inhibited by
methionine at least partially through the regulation of
SAM-dependent PP2A methylation by ppm1
methyltransferase. Autophagy, induced by MR, has been reported to
be a direct cause of lifespan extension, suggesting that SAM
reduction-induced autophagy extends longevity, although no
orthologue of ppm1 is found in Drosophila.
SAM-dependent transmethylation, including ribosomal RNA
methylation, that affects lifespan through modulating translation
is another possible connection between SAM and longevity. The
exact molecular mechanisms behind the SAM effect on lifespan need
to be investigated (Obata and Miura, 2015).
Ames dwarf mice are long-lived mutants that have defects in the
production of growth hormone (GH) with consequent reductions in
IGF-1 levels. Interestingly, Ames dwarf mice also show elevated
GNMT expression and activity in addition to reduced SAM levels in
their liver. Administration of GH to Ames dwarf reduces GNMT
activity while GH receptor knockout mice show increased GNMT
expression, indicating that GH signalling negatively regulates
GNMT. Although the contribution of GNMT in longevity has not been
not studied, MR does not further extend lifespan in Ames dwarf
mice, suggesting that altered methionine metabolism is responsible
for longevity in these animals. gnmt is one of seven
genes commonly upregulated under DR (or resveratrol treatment)
conditions in flies and mice, further demonstrating that the
positive effects of enhanced gnmt activity on longevity
in mammals is conserved (Obata and Miura, 2015).
The Drosophila genome encodes eight insulin/IGF-like peptide (dilp) paralogs, including tandem-encoded dilp1 and dilp2. This study finds that dilp1 is highly expressed in adult dilp2 mutants under nondiapause conditions. The inverse expression of dilp1 and dilp2 suggests these genes interact to regulate aging. Dilp1 and dilp2 single and double mutants were used to describe interactions affecting longevity, metabolism, and adipokinetic hormone (AKH), the functional homolog of glucagon. Mutants of dilp2 extend lifespan and increase Akh mRNA and protein in a dilp1-dependent manner. Loss of dilp1 alone has no impact on these traits, whereas transgene expression of dilp1 increases lifespan in dilp1 - dilp2 double mutants. dilp1 and dilp2 interact to control circulating sugar, starvation resistance, and compensatory dilp5 expression. Repression or loss of dilp2 slows aging because its depletion induces dilp1, which acts as a pro-longevity factor. Likewise, dilp2 regulates Akh through epistatic interaction with dilp1. Akh and glycogen affect aging in Caenorhabditis elegans and Drosophila. The data suggest that dilp2 modulates lifespan in part by regulating Akh, and by repressing dilp1, which acts as a pro-longevity insulin-like peptide (Post, 2018).
Furthermore, DILP1 production is associated with adult reproductive diapause. IIS regulates adult reproductive diapause in Drosophila, a somatic state that prolongs survival during inclement seasons. DILP1 may stimulate these diapause pro-longevity pathways, while expression in nondiapause adults is sufficient to extend survival even in optimal environments (Post, 2018).
Does DILP1 act as an insulin receptor agonist or inhibitor? Inhibitory DILP1 could directly interact with the insulin receptor to suppress IIS, potentially even in the presence of other insulin peptides. Such action could induce programs for longevity assurance that are associated with activated FOXO. Alternatively, DILP1 may act as a typical insulin receptor agonist that induces autophosphorylation and represses FOXO. In this case, to extend lifespan, DILP1 should stimulate cellular responses distinct from those produced by other insulin peptides such as DILP2 or DILP5. Through a third potential mechanism, DILP1 may interact with binding proteins such as IMPL2 or dALS to indirectly inhibit IIS output. These distinctions may be resolvednin a future study using synthetic DILP1 applied to cells in culture (Post, 2018).
While dFOXO and DAF-16 are intimately associated with how reduced IIS regulates aging in Drosophila and C. elegans, in the current work, the behavior of FOXO does not correspond with how longevity is controlled epistatically by dilp1 and dilp2. Mutation of dilp2 did not impact FOXO activity, as measured by expression of target genes InR and 4eBP, and interactions with dilp1 did not modify this result. Some precedence suggests only a limited role for dfoxo as the mediator of reduced IIS in aging, as dfoxo only partially rescues longevity benefits of chico mutants, revealing that IIS extends lifespan through some FOXO-independent pathways. On the other hand, dilp1 expression from a transgene in the dilp1-2 double mutant background did induce FOXO targets. Differences among these results might arise if whole animal analysis of dFOXO targets obscures its role when IIS regulates aging through actions in specific tissues. In this vein, this study found that dilp2 controls thorax ERK signaling but not AKT, suggesting that dilp2 mutants may activate muscle-specific ERK/MAPK anti-aging programs (Post, 2018).
Neurodegeneration in the central nervous system (CNS) is a defining feature of organismal aging that is influenced by peripheral tissues. Clinical observations indicate that skeletal muscle influences CNS aging, but the underlying muscle-to-brain signaling remains unexplored. In Drosophila, this study found that moderate perturbation of the proteasome in skeletal muscle induces compensatory preservation of CNS proteostasis during aging. Such long-range stress signaling depends on muscle-secreted Amyrel amylase. Mimicking stress-induced Amyrel upregulation in muscle reduces age-related accumulation of poly-ubiquitinated proteins in the brain and retina via chaperones. Preservation of proteostasis stems from the disaccharide maltose, which is produced via Amyrel amylase activity. Correspondingly, RNAi for SLC45 maltose transporters reduces expression of Amyrel-induced chaperones and worsens brain proteostasis during aging. Moreover, maltose preserves proteostasis and neuronal activity in human brain organoids challenged by thermal stress. Thus, proteasome stress in skeletal muscle hinders retinal and brain aging by mounting an adaptive response via amylase/maltose (Rai, 2021).
The decline of neuronal synapses is an established feature of ageing accompanied by the diminishment of neuronal function, and in the motor system at least, a reduction of behavioural capacity. This study has investigated Drosophila motor neuron synaptic terminals during ageing. Cumulative fragmentation of presynaptic structures was observed, accompanied by diminishment of both evoked and miniature neurotransmission occurring in tandem with reduced motor ability. Through discrete manipulation of each neurotransmission modality, it was found that miniature but not evoked neurotransmission is required to maintain presynaptic architecture and that increasing miniature events can both preserve synaptic structures and prolong motor ability during ageing. These results establish that miniature neurotransmission, formerly viewed as an epiphenomenon, is necessary for the long-term stability of synaptic connections (Banerjee, 2021).
Spermidine is a natural polyamine, central to cellular homeostasis and growth, that promotes macroautophagy/autophagy. The polyamine pathway is highly conserved from bacteria to mammals and spermidine (prominently found in some kinds of aged cheese, wheat germs, nuts, soybeans, and fermented products thereof, among others) is an intrinsic part of the human diet. Apart from nutrition, spermidine is available to mammalian organisms from intracellular biosynthesis and microbial production in the gut. Importantly, externally supplied spermidine (via drinking water or food) prolongs lifespan, activates autophagy, improves mitochondrial function, and refills polyamine pools that decline during aging in various tissues of model organisms, including mice. In two adjacent studies, how dietary spermidine supplementation enhances eEF5/EIF5A hypusination, cerebral mitochondrial function and cognition in aging Drosophila melanogaster and mice was explored (Hofer, 2021).
Sarcopenia is a syndrome characterized by progressive loss of muscle mass and function during aging. Although mitochondrial dysfunction and related metabolic defects precede age-related changes in muscle, their contributions to muscle aging are still not well known. This study used a Drosophila model to investigate the role of lipophorin receptors (LpRs), a Drosophila homologue of the mammalian very low-density lipoprotein receptor (VLDLR), in mitochondrial dynamics and muscle aging. Muscle-specific knockdown of LpR1 or LpR2 resulted in mitochondrial dysfunction and reduced proteostasis, which contributed to muscle aging. Activation of AMP-activated protein kinase (AMPK) ameliorated muscle dysfunction induced by LpR1 knockdown. These results suggest that LpR1/VLDLR is a novel key target that modulates age-dependent lipid remodeling and muscle homeostasis (Kim, 2021).
Erez, N., Israitel, L., Bitman-Lotan, E., Wong, W. H., Raz, G., Cornelio-Parra, D. V., Danial, S., Flint Brodsly, N., Belova, E., Maksimenko, O., Georgiev, P., Druley, T., Mohan, R. D. and Orian, A. (2021). A Non-stop identity complex (NIC) supervises enterocyte identity and protects from premature aging. Elife 10. PubMed ID: 33629655
A hallmark of aging is loss of differentiated cell identity. Aged Drosophila midgut differentiated enterocytes (ECs) lose their identity, impairing tissue homeostasis. To discover identity regulators, an RNAi screen targeting ubiquitin-related genes was performed in ECs. Seventeen genes were identified, including the deubiquitinase Non-stop (CG4166). Lineage tracing established that acute loss of Non-stop in young ECs phenocopies aged ECs at cellular and tissue levels. Proteomic analysis unveiled that Non-stop maintains identity as part of a Non-stop identity complex (NIC) containing E(y)2, Sgf11, Cp190, (Mod) mdg4, and Nup98. Non-stop ensured chromatin accessibility, maintaining the EC-gene signature, and protected NIC subunit stability. Upon aging, the levels of Non-stop and NIC subunits declined, distorting the unique organization of the EC nucleus. Maintaining youthful levels of Non-stop in wildtype aged ECs safeguards NIC subunits, nuclear organization, and suppressed aging phenotypes. Thus, Non-stop and NIC, supervise EC identity and protects from premature aging (Erez, 2021).
Differentiated cell states are actively established and maintained through action of 'identity supervisors'. Identity supervisors safeguard the expression of genes that enable differentiated cells to respond to environmental cues and perform required physiological tasks. Concomitantly, they ensure silencing/repression of previous fate and non-relevant gene programs and reduce transcriptional noise. Inability to safeguard cell identity is a hallmark of aging and results in diseases such as neurodegeneration, diabetes, and cancer. In many cases, transcription factors (TFs) together with chromatin regulators and architectural/scaffold proteins establish and maintain large-scale chromatin and nuclear organization that is unique to the differentiated state of the cell (Erez, 2021).
In adult Drosophila midgut epithelia, the transcription factor Hey [Hairy/E(spl)-related with YRPW motif], together with Drosophila nuclear type A lamin, Lamin C (LamC), co-supervise identity of fully differentiated enterocytes (ECs). Highly similar to the vertebrate gut, Drosophila midgut epithelia intestinal stem cells (ISC) either self-renew or differentiate into progenitor cells that mature into enteroendocrine cells (EEs) or give rise to enteroblast (EB) progenitors. EBs mature into fully polyploid differentiated enterocytes (ECs) that carry out many critical physiological tasks of the intestine. Aging affects the entire midgut, and is associated with loss of EC identity, mis-differentiation of progenitors, pathological activation of the immune system, and loss of the physiological properties of the gut and its integrity. It also results in loss of intestinal compartmentalization, and microbiota-dysbiosis, all leading to reduced lifespan. During aging, the protein levels of identity supervisors such as Hey and LamC decline, resulting in inability to maintain EC-gene programs and ectopic expression of previous- and non-relevant gene programs. Indeed, continuous expression of Hey in aged ECs restores and protects EC identity, gut integrity, and tissue homeostasis (Flint Brodsly, 2019; Erez, 2021 and references therein).
Regulation of EC identity requires signaling to the nucleus to communicate physiological changes in the gut environment. An important mechanism involves changes in post-transcriptional modifications (PTMs) which may propagate, amplify, or conduct signals, ultimately leading to differential gene regulation. One type of PTM is the covalent attachment of ubiquitin or ubiquitin-like (Ub/UbL) molecules, that affect protein stability, function, localization, as well as modulatex chromatin structure. Recent works suggest an intimate link between ubiquitin, proteostasis, and aging. A RNAi screen was performed in this study to search for Ub/UbL-related genes within ECs that supervise identity. Screening of 362 genes, 17 were identified whose conditional elimination in fully differentiated ECs resulted in loss of EC identity. Further analysis revealed one of them, the deubiquitinating isopeptidase (DUB) Non-stop (Non-stop/dUSP22) is a key EC identity supervisor. Purification and proteomic analysis identified Non-stop as part of a CP190/Nup98/Sgf11/e(y)2/mdg4 protein complex, termed Non-stop identity complex (NIC), that is essential for maintenance of EC identity. In part, Non-stop protects NIC proteins from age-dependent decline, safeguarding the EC-gene expression signature, as well as large-scale nuclear organization in these cells, preventing premature aging. Over lifespan, Non-stop protein levels in ECs declined, leading to loss of NIC subunits. This decline is associated with loss of gut identity and physiology at the cellular and tissue levels. Maintaining youthful levels of Non-stop prevented loss of the NIC and prevented aging of the gut (Erez, 2021).
Based on cell-specific secondary tests, this study identified three categories of supervisors; 1. EC-specific identity regulators 2. Genes that are required for differentiated cell identity (both EEs and ECs) 3. Genes that are required for identity of all cell types (general identity regulators). Of specific interest were a group of genes (CG1490; CG2926; CG4080) whose elimination in EEs resulted in a loss of EC, but not EE, identity, acting as inductive identity regulators. Likely their effect on ECs involves cell~cell communication via diffusible factors. While loss of each individual gene identified in the screen resulted in loss of EC identity, the molecular and genetic connections between different identity regulators requires further studies (Erez, 2021).
The observation that Ub/UbL-related genes protect the differentiated identity is conserved across species. Screens in mammalian systems identified enzymes within the SUMO and ubiquitin pathways acting as a barrier against forced reprogramming of differentiated cell. Among these genes were Ubc9 (Drosophila Lesswright), the sole SUMO conjugating enzyme, that was also identified in this screen and the isopeptidase Psmd14. In addition to Non-stop, the screen identified the iso-isopeptidase UTO6-like (CG7857), Usp7, and Rpn11 as regulators of EC identity. Rpn11 is part of the lid particle of the 26S proteasome, involved in deubiquitinating proteins undergoing proteasomal degradation (Erez, 2021).
Genes regulating identity are likely to serve as a barrier to tumorigenesis having a tumor suppressive function. The human ortholog of Non-stop, USP22 has mixed oncogenic and tumor-suppressive functions. Relevant to the current study is the observation that USP22 has tumor suppressive functions in colon cancer by reducing mTor activity. Along this line it is interesting to note that 10/17 of human orthologs to genes discovered in the screen are either mutated or silenced in cancer. Thus, future studies of these human orthologs may identify potent tumor suppressors in cancer (Erez, 2021).
The proteomic, biochemical, and genetic analyses established that to maintain identity Non-stop acts as part of the NIC protein complex. Like SAGA, NIC contained the entire DUB module including Non-stop, E(y)two and Sgf11. Within SAGA, Sgf11 is critical for Non-stop activity. However, loss of Sgf11 did not result in loss of EC identity. While this may reflect intrinsic differences between the complexes it may also be possible that knock-down of Sgf11 transcripts in ECs did not reduce Sgf11 protein levels sufficiently enough to result in a phenotype (Erez, 2021).
The BTB domain of Mod(mdg4) interacts with the M domain of Cp190, and together they enable the recruitment of NIC to the promoter/enhancer regions. There are more than 30 Mod(mdg4) isoforms with different C-ends, each of which interacts with different DNA-binding TF. Cp190 can also be able to recruit different TFs and interacts with Chromo and Zinc-finger 4, that are co-localized with Nup98-96. The Mod(mdg4)/CP190 sub-complex is bound to promoters through interactions with many promoter specific C2H2 proteins including dCTCF, Su(Hw), and possibly via other TFs enriched in the ATAC-seq analysis (Erez, 2021).
Prominent phenotypes of loss of Non-stop were the reduced protein level of Nup98 and its miss-localization from the nuclear periphery to an intranuclear punctate distribution. Nup98 was shown to recruit Set1~COMPASS to enhance histone H3K4me2-3 methylations in hematopoietic progenitors. Thus, a possible function of the NIC may be the recruitment of the H3K4me2/3 COMPASS methylases to catalyze H3K9 di- and tri-methylation at enhancers and promotors, which are fundamental for gene activation. Members of the NIC complex were previously shown to form a Nuclear pore complex that enhances transcriptional memory upon exposure to ecdysone, raising the possibility that NIC is required for enhancing transcriptional memory promoting the transcription of EC-related genes and prevents Polycomb-dependent transcriptional repression (Erez, 2021).
In addition to NIC subunits the complex described by Pascual-Garcia (2017) contained Trithorax-like protein (Trl)/GAF and the boundary/architectural proteins CTCF, Suppressor of Hairy Wing (SuHw) and Mtor, but not Non-stop or E(y)2. Interestingly, the DNA binding site of Trl/GAF/ was enriched in EC genes that their expression required Non-stop for maintaining chromatin accessibility. However, Trl, CTCF, SuHw, or Mtor that interact with Cp190 were not detected as Non-stop bound proteins in the proteomic analysis, and RNAi-mediated elimination of Trl/GAF, or SuHw from ECs did not result in loss of EC identity. Thus, suggesting that these are likely separate regulatory complexes with shared subunits (Erez, 2021).
Non-stop was found to be required for the stability of NIC in ECs. RNA-seq analysis established that Non-stop did not regulate the mRNA level of NIC subunits. Suggesting that Nonstop acts by deubiquitinating NIC subunits in ECs. In this regard, it is possible that the stabilization of NIC subunits may also require the EC-related lamin, LamC. It was noticed that Lamin C protein levels (but not mRNA) decline upon loss of Non-stop. Moreover, LamC expression partially restored the protein levels of NIC subunits and their intranuclear localization, potentially by serving as a scaffold for NIC at the nuclear periphery. Therefore, additional experiments are required to establish whether NIC subunits are directly deubiquitinated and stabilized by Non-stop iso-peptidase activity and the potential contribution of LamC to stabilization of NIC subunits (Erez, 2021).
Thus, Non-stop may function at two levels; One is a direct role in transcription safeguarding chromatin accessibility at EC genes, while a second function is the stabilization of identity supervisors including NIC subunits and LamC (Erez, 2021).
Both Non-stop and the transcription factor Hey are bona-fide regulators of EC identity required for the expression of EC-related genes. A significant number of EC-related genes required both Non-stop and Hey for their expression, suggesting that Hey and Non-stop may co-regulate these genes. However, functional and epistatic tests suggest that Hey also acts upstream or in additional pathways to Non-stop. Hey binds to enhancers in lamin genes repressing the expression of the ISC-related lamin, LamDm0 and enhances the expression of LamC. In contrast, Non-stop does not regulate the accessibility, or expression of either LamDm0 or LamC at mRNA level. However, Non-stop is required for maintaining the levels of LamC protein. Therefore, loss of Non-stop results in a decline in LamC but not in the ectopic expression of LamDm0, which is observed upon acute loss of Hey or aging. This discrepancy may be due to the presence of Hey on its repressed targets in young ECs where Non-stop is targeted, and directly repressing their expression as maybe in the case of LamDm0. Moreover, EC-specific expression of Non-stop did not suppress the phenotypes associated with acute loss of Hey in young ECs further supporting for Hey-dependent, but Non-stop independent functions. However, the ECs-specific expression of either Non-stop or Hey in aging midguts restores expression of LamC and repressed ectopic LamDm0 expression (Erez, 2021).
Changes in large-scale nuclear organization are hallmarks of aging. Expression of identity supervisors can prevent age-related distortion of the nucleus EC identity and protect overall the epithelial tissue). However, to accomplish this, Non-stop or Hey were continuously expressed in ECs and temporal expression of Hey or Non-stop in already aged ECs was not sufficient to suppress aging phenotypes. Thus, if the levels of identity supervisors are kept at youthful levels, they can continue to maintain cell identity and prevent signs of aging, effectively keeping the gut organization and structure similar to young tissue (Erez, 2021).
Furthermore, it is not clear how expression of a single regulator like Non-stop has an extensive impact on the entire nucleus. Recent studies suggest that Non-stop functions in additional multiprotein complexes that may regulate large-scale cellular organization. For example, Non-stop is part of an Arp2/3 and WAVE regulatory (WRC) actin-cytoskeleton organization complex where it deubiquitinates the subunit SCAR. In this regard, a nuclear actin organizing complex, WASH, interacted with nuclear Lamin and was required for large scale nuclear organization. Thus, it is tempting to suggest that such complexes are required to maintain cell identity, and that subunits within these complexes are deubiquitinated by Non-stop (Erez, 2021).
In this regard many nuclear proteins are extremely long-lived proteins (LLPs) among them are nuclear pore complex proteins (NPCs) and core histones. The extended stability of LLPs may originate from intrinsic properties of LLPs, or due to sequestration and evading degradation. However, increased stability may be also actively maintained by constitutive de-ubiquitination. Indeed, post-translational modification by ubiquitin and SUMO were shown to regulate lamin stability and their intranuclear localization. Specifically, type-A lamin and its splice variant Progerin, the cause of Hutchinson Gilford progeria syndrome (HGPS), a premature aging syndrome, are degraded by the HECT-type E3 ligase Smurf2 via ubiquitin-dependent autophagy. The elimination of Progerin by expression of Smurf2 in HGSP-fibroblasts reduced the deformation observed in these cells. Thus, it is possible that enhancing Progerin degradation by inhibiting the human ortholog of Non-stop, USP22, will restore nuclear architecture, and suppress the premature aging phenotypes observed in HGPS cells (Erez, 2021).
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Pallares, L. F., Lea, A. J., Han, C., Filippova, E. V., Andolfatto, P. and Ayroles, J. F. (2023). Dietary stress remodels the genetic architecture of lifespan variation in outbred Drosophila. Nat Genet 55(1): 123-129. PubMed ID: 36550361
Summary:
Evolutionary theory suggests that lifespan-reducing alleles should be purged from the gene pool, and yet decades of genome-wide association and model organism studies have shown that they persist. One potential explanation is that alleles that regulate lifespan do so only in certain environmental contexts. This study exposed outbred Drosophila to control and high-sugar diets and genotyped more than 10,000 adult flies to track allele frequency changes over the course of a single adult lifespan. Thousands of lifespan-associated alleles associated with early versus late-life trade-offs, late-onset effects and genotype-by-environment interactions. Remarkably, a third of lifespan-associated genetic variation had environmentally dependent effects on lifespan. Lifespan-reducing alleles are often recently derived, have stronger effects on a high-sugar diet and show signatures of selection in wild Drosophila populations, consistent with the evolutionary mismatch hypothesis. These results provide insight into the highly polygenic and context-dependent genetic architecture of lifespan variation and the evolutionary processes that shape this key trait.
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Merino, M. M. (2023). Azot expression in the Drosophila gut modulates organismal lifespan. Commun Integr Biol 16(1): 2156735. PubMed ID: 36606245
Summary:
Cell Competition emerged in Drosophila as an unexpected phenomenon, when confronted clones of fit vs unfit cells genetically induced. During the last decade, it has been shown that this mechanism is physiologically active in Drosophila and higher organisms. In Drosophila, Flower (Fwe) eliminates unfit cells during development, regeneration and disease states. Furthermore, studies suggest that Fwe signaling is required to eliminate accumulated unfit cells during adulthood extending Drosophila lifespan. Indeed, ahuizotl (azot) mutants accumulate unfit cells during adulthood and after physical insults in the brain and other epithelial tissues, showing a decrease in organismal lifespan. On the contrary, flies carrying three functional copies of the gene, unfit cell culling seems to be more efficient and show an increase in lifespan. During aging, Azot is required for the elimination of unfit cells, however, the specific organs modulating organismal lifespan by Azot remain unknown. This study found a potential connection between gut-specific Azot expression and lifespan which may uncover a more widespread organ-specific mechanism modulating organismal survival.
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Witt, E., Langer, C. B., Svetec, N. and Zhao, L. (2023. Transcriptional and mutational signatures of the Drosophila ageing germline. Nat Ecol Evol. PubMed ID: 36635344
Summary:
Ageing is a complex biological process that is accompanied by changes in gene expression and mutational load. In many species, including humans, older fathers pass on more paternally derived de novo mutations; however, the cellular basis and cell types driving this pattern are still unclear. To explore the root causes of this phenomenon, this study performed single-cell RNA sequencing on testes from young and old male Drosophila and genomic sequencing (DNA sequencing) on somatic tissues from the same flies. Early germ cells from old and young flies were found to enter spermatogenesis with similar mutational loads but older flies are less able to remove mutations during spermatogenesis. Mutations in old cells may also increase during spermatogenesis. These data reveal that old and young flies have distinct mutational biases. Many classes of genes show increased postmeiotic expression in the germlines of older flies. Late spermatogenesis-biased genes have higher dN/dS (ratio of non-synonymous to synonymous substitutions) than early spermatogenesis-biased genes, supporting the hypothesis that late spermatogenesis is a source of evolutionary innovation. Surprisingly, genes biased in young germ cells show higher dN/dS than genes biased in old germ cells. These results provide new insights into the role of the germline in de novo mutation.
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Shaposhnikov, M. V., Gorbunova, A. A., Zemskaya, N. V., Ulyasheva, N. S., Pakshina, N. R., Yakovleva, D. V. and Moskalev, A. (2023). Simultaneous activation of the hydrogen sulfide biosynthesis genes (CBS and CSE) induces sex-specific geroprotective effects in Drosophila melanogaster. Biogerontology. PubMed ID: 36662374
Summary:
Hydrogen sulfide (H(2)S) is one of the most important gasotransmitters that affect lifespan and provide resistance to adverse environmental conditions. This study investigated geroprotective effects of the individual and simultaneous overexpression of genes encoding key enzymes of H(2)S biosynthesis - cystathionine-β-synthase (CBS) and cystathionine-γ-lyase (CSE) on D. melanogaster model. Simultaneous overexpression of CBS and CSE resulted in additive (in males) and synergistic (in females) beneficial effects on median lifespan. Individual overexpression of CBS was associated with increased thermotolerance and decreased transcription level of genes encoding stress-responsive transcription factors HIF1 and Hsf, while individual overexpression of CSE was associated with increased resistance to paraquat. Simultaneous overexpression of both genes increased resistance to hyperthermia in old females or paraquat in old males. The obtained results suggest sex-specific epistatic interaction of CBS and CSE overexpression effects on longevity and stress resistance.
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Tang, X., Liu, N., Qi, H. and Lin, H. (2023). Piwi maintains homeostasis in the Drosophila adult intestine. Stem Cell Reports. PubMed ID: 36736325
Summary:
PIWI genes are well known for their germline but not somatic functions. This study reports the function of the Drosophila piwi gene in the adult gut, where intestinal stem cells (ISCs) produce enteroendocrine cells and enteroblasts that generate enterocytes. piwi is expressed in ISCs and enteroblasts. Piwi deficiency reduced ISC number, compromised enteroblasts maintenance, and induced apoptosis in enterocytes, but did not affect ISC proliferation and its differentiation to enteroendocrine cells. In addition, deficiency of zygotic but not maternal piwi mildly de-silenced several retrotransposons in the adult gut. Importantly, either piwi mutations or piwi knockdown specifically in ISCs and enteroblasts shortened the Drosophila lifespan, indicating that intestinal piwi contributes to longevity. Finally, mRNA sequencing data implied that Piwi may achieve its intestinal function by regulating diverse molecular processes involved in metabolism and oxidation-reduction reaction.
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Zanco, B., Rapley, L., Johnstone, J. N., Dedman, A., Mirth, C. K., Sgro, C. M. and Piper, M. D. W. (2023). Drosophila melanogaster females prioritise dietary sterols for producing viable eggs. J Insect Physiol 144: 104472. PubMed ID: 36549582
Summary:
Limiting calories or specific nutrients without malnutrition, otherwise known as dietary restriction (DR), has been shown to extend lifespan and reduce reproduction across a broad range of taxa. Recent findings in Drosophila melanogaster show that supplementing flies on macronutrient-rich diets with additional cholesterol can extend lifespan to the same extent as DR, while also sustaining high egg production. Thus, DR may be beneficial for lifespan because it reduces egg production which in turn reduces the mother's demand for sterols, thus supporting longer lifespan. It is also possible that mothers live longer and lay more eggs on high sterol diets because the diet triggers enhanced somatic maintenance and promotes egg production, but at the cost of diminished egg quality. To test this, the viability of eggs was measure and development of offspring from mothers fed either cholesterol-sufficient or cholesterol-limiting diets. Even when the mother's diet was completely devoid of cholesterol, viable egg production persisted for ~10 days. Furthermore, it was shown that sterol-supplemented flies with long lives lay eggs that have high viability and the same developmental potential as those laid by shorter lived mothers on sterol limiting diets. These findings suggest that offspring viability is not a hidden cost of lifespan extension seen in response to dietary sterol supplementation.
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Hwangbo, D. S., Kwon, Y. J., Iwanaszko, M., Jiang, P., Abbasi, L., Wright, N., Alli, S., Hutchison, A. L., Dinner, A. R., Braun, R. I. and Allada, R. (2023). Dietary Restriction Impacts Peripheral Circadian Clock Output Important for Longevity in Drosophila. bioRxiv. PubMed ID: 36711760
Summary:
Circadian clocks may mediate lifespan extension by caloric or dietary restriction (DR). The core clock transcription factor Clock is crucial for a robust longevity and fecundity response to DR in Drosophila. To identify clock-controlled mediators, RNA-sequencing was performed from abdominal fat bodies across the 24 h day after just 5 days under control or DR diets. In contrast to more chronic DR regimens, no significant changes were detected in the rhythmic expression of core clock genes. Yet it was discovered that DR induced de novo rhythmicity or increased expression of rhythmic clock output genes. Network analysis revealed that DR increased network connectivity in one module comprised of genes encoding proteasome subunits. Adult, fat body specific RNAi knockdown demonstrated that proteasome subunits contribute to DR-mediated lifespan extension. Thus, clock control of output links DR-mediated changes in rhythmic transcription to lifespan extension.
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Sakakibara, Y., Yamashiro, R., Chikamatsu, S., Hirota, Y., Tsubokawa, Y., Nishijima, R., Takei, K., Sekiya, M. and Iijima, K. M. (2023). Drosophila Toll-9 is induced by aging and neurodegeneration to modulate stress signaling and its deficiency exacerbates tau-mediated neurodegeneration. iScience 26(2): 105968. PubMed ID: 36718365
Summary:
Drosophila Toll-9 is most closely related to mammalian Toll-like receptors; however, physiological functions of Toll-9 remain elusive. This study examined the roles of Toll-9 in fly brains in aging and neurodegeneration. Toll-9 mRNA levels were increased in aged fly heads accompanied by activation of nuclear factor-kappa B (NF-kB) and stress-activated protein kinase (SAPK; Jun-N-terminal Kinase pathway) signaling, and many of these changes were modulated by Toll-9 in glial cells. The loss of Toll-9 did not affect lifespan or brain integrity, whereas it exacerbated hydrogen peroxide-induced lethality. Toll-9 expression was also induced by nerve injury but did not affect acute stress response or glial engulfment activity, suggesting Toll-9 may modulate subsequent neurodegeneration. In a fly tauopathy model, Toll-9 deficiency enhanced neurodegeneration and disease-related tau phosphorylation with reduced SAPK activity, and blocking SAPK enhanced tau phosphorylation and neurodegeneration. In sum, Toll-9 is induced upon aging and nerve injury and affects neurodegeneration by modulating stress kinase signaling.
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Ramakrishnan, P., Joshi, A., Tulasi, M. and Yadav, P. (2022). Monochromatic visible lights modulate the timing of pre-adult developmental traits in Drosophila melanogaster. Photochem Photobiol Sci. PubMed ID: 36583814
Summary:
Light exposure impacts several aspects of Drosophila development including the establishment of circadian rhythms, neuroendocrine regulation, life-history traits, etc. Introduction of artificial lights in the environment has caused almost all animals to develop ecological and physiological adaptations. White light which comprises different lights of differing wavelengths shortens the lifespan in fruit flies Drosophila melanogaster. The wavelength-specific effects of white light on Drosophila development remains poorly understood. This study shows that different wavelengths of white light differentially modulate Drosophila development in all its concomitant stages when maintained in a 12-h light: 12-h dark photoperiod. It was observed that exposure to different monochromatic lights significantly alters larval behaviours such as feeding rate and phototaxis that influence pre-adult development. Larvae grown under shorter wavelengths of light experienced an altered feedingrate. Similarly, larvae were found to avoid shorter wavelengths of light but were highly attracted to the longer wavelengths of light. Most of the developmental processes were greatly accelerated under the green light regime while in other light regimes, the effects were highly varied. Interestingly, pre-adult survivorship remained unaltered across all light regimes but light exposure was found to show its impact on sex determination. This study for the first time reveals how different wavelengths of white light modulate Drosophila development which in the future might help in developing non-invasive therapies and effective pest measures.
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Symonenko, A. V., Roshina, N. V., Krementsova, A. V., Rybina, O. Y. and Pasyukova, E. G. (2022). Shuttle craft Gene Affects Lifespan of Drosophila melanogaster by Controlling Early Development and Modifying Aging Program. Biochemistry (Mosc) 87(12): 1611-1621. PubMed ID: 36717450
Summary:
Fundamental mechanisms underlying genetic control of lifespan are intensively studied and discussed due to the increasing importance of extending healthy human life. The stc gene of the model organism Drosophila melanogaster encodes a transcription factor, homolog of the human transcription factor NF-X1, involved in regulation of neuronal development and other processes, as well as in control of lifespan. This work demonstrates that the stc knockdown in embryonic and nerve cells leads to changes in lifespan, with the nature of changes depending on the cell type and sex of individuals. Based on these results, it is suggested that stc gene is involved in transcription regulation throughout life, and, as a result, also affects a complex integral trait, lifespan. At the same time, it was shown that the reduction of stc expression in neurons can alleviate the negative effect of glutamate on longevity, possibly preventing development of glutamate excitotoxicity, thus modifying the cell death program and preventing death of individuals due to phenoptosis.
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Morgunova, V. V., Sokolova, O. A., Sizova, T. V., Malaev, L. G., Babaev, D. S., Kwon, D. A. and Kalmykova, A. I. (2022). Dysfunction of Lamin B and Physiological Aging Cause Telomere Instability in Drosophila Germline. Biochemistry (Mosc) 87(12): 1600-1610. PubMed ID: 36717449
Summary:
Chromatin spatial organization in the nucleus is essential for the genome functioning and regulation of gene activity. The nuclear lamina and lamina-associated proteins, lamins, play a key role in this process. Lamin dysfunction leads to the decompaction and transcriptional activation of heterochromatin, which is associated with the premature aging syndrome. In many cell types, telomeres are located at the nuclear periphery, where their replication and stability are ensured by the nuclear lamina. Moreover, diseases associated with defects in lamins and telomeres have similar manifestations and resemble physiological aging. Understanding molecular changes associated with aging at the organismal level is especially important. This study compared the effects caused by the mutation in lamin B and physiological aging in the germline of the model organism Drosophila melanogaster. The impaired localization of lamin B was shown to lead to the heterochromatin decompaction and transcriptional activation of some transposable elements and telomeric repeats. Both DNA damage and activation of homologous recombination in the telomeres were observed in the germ cells of lamin B mutants. The instability of repeat-enriched heterochromatin can be directly related to the genome destabilization, germ cell death, and sterility observed in lamin B mutants. Similar processes were observed in Drosophila germline in the course of physiological aging, which indicates a close link between the maintenance of the heterochromatin stability at the nuclear periphery and mechanisms of aging.
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Lushchak, O., Strilbytska, O. and Storey, K. B. (2023). Gender-specific effects of pro-longevity interventions in Drosophila. Mech Ageing Dev 209: 111754. PubMed ID: 36375654
Summary:
Sex differences in lifespan are well recognized in the majority of animal species. For example, in male versus female Drosophila melanogaster there are significant differences in behavior and physiology. However, little is known about the underlying mechanisms of gender differences in responses to pro-longevity interventions in this model organism. This study summarized the existing data on the effects of nutritional and pharmacological anti-aging interventions such as nutrition regimens, diet and dietary supplementation on the lifespan of male and female Drosophila. It was demonstrated that males and females have different sensitivities to interventions and that the effects are highly dependent on genetic background, mating, dose and exposure duration. This work highlights the importance of understanding the mechanisms that underlie the gender-specific effect of anti-aging manipulations. This will provide insight into how these benefits may be valuable for elucidating the primary physiological and molecular targets involved in aging and lifespan determination.
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Merino, M. M. (2023). Azot expression in the Drosophila gut modulates organismal lifespan. Commun Integr Biol 16(1): 2156735. PubMed ID: 36606245
Summary:
Cell Competition emerged in Drosophila as an unexpected phenomenon, when confronted clones of fit vs unfit cells genetically induced. During the last decade, it has been shown that this mechanism is physiologically active in Drosophila and higher organisms. In Drosophila, Flower (Fwe) eliminates unfit cells during development, regeneration and disease states. Furthermore, studies suggest that Fwe signaling is required to eliminate accumulated unfit cells during adulthood extending Drosophila lifespan. Indeed, ahuizotl (azot) mutants accumulate unfit cells during adulthood and after physical insults in the brain and other epithelial tissues, showing a decrease in organismal lifespan. On the contrary, flies carrying three functional copies of the gene, unfit cell culling seems to be more efficient and show an increase in lifespan. During aging, Azot is required for the elimination of unfit cells, however, the specific organs modulating organismal lifespan by Azot remain unknown. This study found a potential connection between gut-specific Azot expression and lifespan which may uncover a more widespread organ-specific mechanism modulating organismal survival.
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Hwangbo, D. S., Kwon, Y. J., Iwanaszko, M., Jiang, P., Abbasi, L., Wright, N., Alli, S., Hutchison, A. L., Dinner, A. R., Braun, R. I. and Allada, R. (2023). Dietary Restriction Impacts Peripheral Circadian Clock Output Important for Longevity in Drosophila. bioRxiv. PubMed ID: 36711760
Summary:
Circadian clocks may mediate lifespan extension by caloric or dietary restriction (DR). This study found that the core clock transcription factor Clock is crucial for a robust longevity and fecundity response to DR in Drosophila. To identify clock-controlled mediators, RNA-sequencing was performed from abdominal fat bodies across the 24 h day after just 5 days under control or DR diets. In contrast to more chronic DR regimens, no significant changes were detected in the rhythmic expression of core clock genes. Yet it was discovered that DR induced de novo rhythmicity or increased expression of rhythmic clock output genes. Network analysis revealed that DR increased network connectivity in one module comprised of genes encoding proteasome subunits. Adult, fat body specific RNAi knockdown demonstrated that proteasome subunits contribute to DR-mediated lifespan extension. Thus, clock control of output links DR-mediated changes in rhythmic transcription to lifespan extension.
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Huang, S., Piao, C., Beuschel, C. B., Zhao, Z. and Sigrist, S. J. (2022). A brain-wide form of presynaptic active zone plasticity orchestrates resilience to brain aging in Drosophila. PLoS Biol 20(12): e3001730. PubMed ID: 36469518
Summary:
The brain as a central regulator of stress integration determines what is threatening, stores memories, and regulates physiological adaptations across the aging trajectory. While sleep homeostasis seems to be linked to brain resilience, how age-associated changes intersect to adapt brain resilience to life history remains enigmatic. This study provides evidence that a brain-wide form of presynaptic active zone plasticity ("PreScale"), characterized by increases of active zone scaffold proteins and synaptic vesicle release factors, integrates resilience by coupling sleep, longevity, and memory during early aging of Drosophila. PreScale increased over the brain until mid-age, to then decreased again, and promoted the age-typical adaption of sleep patterns as well as extended longevity, while at the same time it reduced the ability of forming new memories. Genetic induction of PreScale also mimicked early aging-associated adaption of sleep patterns and the neuronal activity/excitability of sleep control neurons. Spermidine supplementation, previously shown to suppress early aging-associated PreScale, also attenuated the age-typical sleep pattern changes. Pharmacological induction of sleep for 2 days in mid-age flies also reset PreScale, restored memory formation, and rejuvenated sleep patterns. The data suggest that early along the aging trajectory, PreScale acts as an acute, brain-wide form of presynaptic plasticity to steer trade-offs between longevity, sleep, and memory formation in a still plastic phase of early brain aging.
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Munneke, A. S., Chakraborty, T. S., Porter, S. S., Gendron, C. M. and Pletcher, S. D. (2022). The serotonin receptor 5-HT2A modulates lifespan and protein feeding in Drosophila melanogaster. Front Aging 3: 1068455. PubMed ID: 36531741
Summary:
The conserved neurotransmitter serotonin has been shown to be an important modulator of lifespan in specific nutritional contexts; however, it remained unclear how serotonin signaling influences lifespan under normal conditions. This study shows that serotonin signaling through the 5-HT2A receptor influences lifespan, behavior, and physiology in Drosophila. Loss of the 5-HT2A receptor extends lifespan and induces a resistance to changes in dietary protein that are normally detrimental to lifespan. 5-HT2A-/- null mutant flies also display decreased protein feeding and protein content in the body. Therefore, serotonin signaling through receptor 5-HT2A is likely recruited to promote motivation for protein intake, and chronic reduction of protein-drive through loss of 5-HT2A signaling leads to a lower protein set-point adaptation, which influences physiology, decreases feeding, and increases lifespan. These findings reveal insights into the mechanisms by which organisms physiologically adapt in response to perceived inability to satisfy demand.
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Johnson, J. C., Munneke, A. S., Richardson, H. M., Gendron, C. M. and Pletcher, S. D. (2023). Light modulates Drosophila lifespan via perceptual systems independent of circadian rhythms. Aging (Albany NY) 15. PubMed ID: 36622279
Summary:
Across taxa, sensory perception modulates aging in response to important ecological cues, including food, sex, and danger. The range of sensory cues involved, and their mechanism of action, are largely unknown. This study therefore sought to better understand how one potential cue, that of light, impacts aging in Drosophila melanogaster. In accordance with recently published data, it was found that flies lived significantly longer in constant darkness. Extended lifespan was not accompanied by behavioral changes that might indirectly slow aging such as activity, feeding, or fecundity, nor were circadian rhythms necessary for the effect. The lifespans of flies lacking eyes or photoreceptor neurons were unaffected by light kept at normal housing conditions, and transgenic activation of these same neurons was sufficient to phenocopy the effects of environmental light on lifespan. The relationship between light and lifespan was not correlated with its intensity, duration, nor the frequency of light-dark transitions. Furthermore, high-intensity light reduced lifespan in eyeless flies, indicating that the effects observed were largely independent of the known, non-specific damaging effects associated with light. These results suggest that much like other environmental cues, light may act as a sensory stimulus to modulate aging.
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Jiao, J., Curley, M., Graca, F. A., Robles-Murguia, M., Shirinifard, A., Finkelstein, D., Xu, B., Fan, Y. and Demontis, F. (2023). Modulation of protease expression by the transcription factor Ptx1/PITX regulates protein quality control during aging. Cell Rep 42(1): 111970. PubMed ID: 36640359
Summary:
Protein quality control is important for healthy aging and is dysregulated in age-related diseases. The autophagy-lysosome and ubiquitin-proteasome are key for proteostasis, but it remains largely unknown whether other proteolytic systems also contribute to maintain proteostasis during aging. This study finds that expression of proteolytic enzymes (proteases/peptidases) distinct from the autophagy-lysosome and ubiquitin-proteasome systems declines during skeletal muscle aging in Drosophila. Age-dependent protease downregulation undermines proteostasis, as demonstrated by the increase in detergent-insoluble poly-ubiquitinated proteins and pathogenic huntingtin-polyQ levels in response to protease knockdown. Computational analyses identify the transcription factor Ptx1 (homologous to human PITX1/2/3) as a regulator of protease expression. Consistent with this model, Ptx1 protein levels increase with aging, and Ptx1 RNAi counteracts the age-associated downregulation of protease expression. Moreover, Ptx1 RNAi improves muscle protein quality control in a protease-dependent manner and extends lifespan. These findings indicate that proteases and their transcriptional modulator Ptx1 ensure proteostasis during aging.
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Chen, Y., Liu, T. T., Niu, M., Li, X., Wang, X., Liu, T. and Li, Y. (2023). Epilepsy gene prickle ensures neuropil glial ensheathment through regulating cell adhesion molecules. iScience 26(1): 105731. PubMed ID: 36582832
Summary:
Human PRICKLE1 gene has been associated with epilepsy. However, the underlying pathogenetic mechanisms remain elusive. A Drosophila prickle mutant pk IG1-1 exhibiting strong epileptic seizures and, intriguingly, abnormal glial wrapping. pk was found to be required in both neurons and glia, particularly neuropil ensheathing glia (EGN), the fly analog of oligodendrocyte, for protecting the animal from seizures. It was further revealed that Pk directly binds to the membrane skeleton binding protein Ankyrin 2 (Ank2), thereby regulating the cell adhesion molecule Neuroglian (Nrg). Such protein interactions also apply to their human homologues. Moreover, nrg and ank2 mutant flies also display seizure phenotypes, and expression of either Nrg or Ank2 rescues the seizures of pk IG1-1) flies. Therefore, these findings indicate that Prickle ensures neuron-glial interaction within neuropils through regulating cell adhesion between neurons and ensheathing glia. Dysregulation of this process may represent a conserved pathogenic mechanism underlying PRICKLE1-associated epilepsy.
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Martinez, P., Patel, H., You, Y., Jury, N., Perkins, A., Lee-Gosselin, A., Taylor, X., You, Y., Viana Di Prisco, G., Huang, X., Dutta, S., Wijeratne, A. B., Redding-Ochoa, J., Shahid, S. S., Codocedo, J. F., Min, S., Landreth, G. E., Mosley, A. L., Wu, Y. C., McKinzie, D. L., Rochet, J. C., Zhang, J., Atwood, B. K., Troncoso, J. and Lasagna-Reeves, C. A. (2022). Bassoon contributes to tau-seed propagation and neurotoxicity. Nat Neurosci 25(12): 1597-1607. PubMed ID: 36344699
Summary:
Tau aggregation is a defining histopathological feature of Alzheimer's disease and other tauopathies. However, the cellular mechanisms involved in tau propagation remain unclear. In this study an unbiased quantitative proteomic study was performed to identify proteins that specifically interact with this tau seed. Bassoon (BSN), a presynaptic scaffolding protein, was identified as an interactor of the tau seed isolated from a mouse model of tauopathy, and from Alzheimer's disease and progressive supranuclear palsy postmortem samples. BSN was shown to exacerbate tau seeding and toxicity in both mouse and Drosophila models for tauopathy, and that BSN downregulation decreases tau spreading and overall disease pathology, rescuing synaptic and behavioral impairments and reducing brain atrophy. These findings improve the understanding of how tau seeds can be stabilized by interactors such as BSN. Inhibiting tau-seed interactions is a potential new therapeutic approach for neurodegenerative tauopathies.
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Cormier, R. J., Doiron, J. A., Touaibia, M., Surette, M. E. and Pichaud, N. (2023). Time-dependent metabolome and fatty acid profile changes following a high-fat diet exposure in Drosophila melanogaster. Insect Biochem Mol Biol 152: 103892. PubMed ID: 36493963
Summary:
High-fat diets (HFDs) are often used to study metabolic disorders using different animal models. However, the underlying cellular mechanisms pertaining to the concurrent loss of metabolic homeostasis characteristics of these disorders are still unclear mainly because the effects of such diets are also dependent on the time frame of the experiments. This study used the fruit fly, Drosophila melanogaster, to investigate the metabolic dynamic effects following 0, 2, 4, 7 and 9 days of an exposure to a HFD (standard diet supplemented with 20% w/v coconut oil, rich in 12:0 and 14:0) by combining NMR metabolomics and GC-FID fatty acid profiling. The results show that after 2 days, the ingested 12:0 and 14:0 fatty acids are used for both lipogenesis and fatty acid oxidation. After 4 days, metabolites from several different pathways are highly modulated in response to the HFD, and an accumulation of 12:0 is also observed, suggesting that the balance of lipid, amino acid and carbohydrate metabolism is profoundly perturbed at this specific time point. Following a longer exposure to the HFD (and notably after 9 days), an accumulation of many metabolites is observed indicating a clear dysfunction of the metabolic system. Overall, this study highlights the relevance of the Drosophila model to study metabolic disorders and the importance of the duration of the exposure to a HFD to study the dynamics of the fundamental mechanisms that control metabolism following exposure to dietary fats. This knowledge is crucial to understand the development and progression of metabolic diseases.
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Carney, T. D., Hebalkar, R. Y., Edeleva, E., Cicek, I. and Shcherbata, H. R. (2023). Signaling through the dystrophin glycoprotein complex affects the stress-dependent transcriptome in Drosophila. Dis Model Mech 16(1). PubMed ID: 36594281
Summary:
Deficiencies in the human dystrophin glycoprotein complex (DGC), which links the extracellular matrix with the intracellular cytoskeleton, cause muscular dystrophies, a group of incurable disorders associated with heterogeneous muscle, brain and eye abnormalities. Stresses such as nutrient deprivation and aging cause muscle wasting, which can be exacerbated by reduced levels of the DGC in membranes, the integrity of which is vital for muscle health and function. Moreover, the DGC operates in multiple signaling pathways, demonstrating an important function in gene expression regulation. To advance disease diagnostics and treatment strategies, this study strived to understand the genetic pathways that are perturbed by DGC mutations. A Drosophila model was used to investigate the transcriptomic changes in mutants of four DGC components under temperature and metabolic stress. DGC-dependent genes, stress-dependent genes and genes dependent on the DGC for a proper stress response were identified, confirming a novel function of the DGC in stress-response signaling. This perspective yields new insights into the etiology of muscular dystrophy symptoms, possible treatment directions and a better understanding of DGC signaling and regulation under normal and stress conditions.
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Cao, Y., He, S., Ding, M., Gu, W., Wang, T., Zhang, S., Feng, J., Li, Q. and Zheng, L. (2023). Regular Exercise in Drosophila Prevents Age-Related Cardiac Dysfunction Caused by High Fat and Heart-Specific Knockdown of skd. Int J Mol Sci 24(2). PubMed ID: 36674733
Summary:
Skuld (skd) is a subunit of the Mediator complex subunit complex. In the heart, skd controls systemic obesity, is involved in systemic energy metabolism, and is closely linked to cardiac function and aging. However, it is unclear whether the effect of cardiac skd on cardiac energy metabolism affects cardiac function. This study found that cardiac-specific knockdown of skd showed impaired cardiac function, metabolic impairment, and premature aging. Drosophila was subjected to an exercise and high-fat diet (HFD) intervention to explore the effects of exercise on cardiac skd expression and cardiac function in HFD Drosophila. Hand-Gal(4)>skd RNAi (KC) Drosophila had impaired cardiac function, metabolic impairment, and premature aging. Regular exercise significantly improved cardiac function and metabolism and delayed aging in HFD KC Drosophila. Thus, this study found that the effect of skd on cardiac energy metabolism in the heart affected cardiac function. Exercise may counteract age-related cardiac dysfunction and metabolic disturbances caused by HFD and heart-specific knockdown of skd. Skd may be a potential therapeutic target for heart disease.
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Gupta, H. P., Pandey, R. and Ravi Ram, K. (2023). Altered sperm fate in the reproductive tract milieu due to oxidative stress leads to sub-fertility in type 1 diabetes females: A Drosophila-based study. Life Sci 313: 121306. PubMed ID: 36543282
Summary:
Female sub-fertility, a prominent complication due to Type 1 diabetes (T1D), is generally attributed to disturbances in menstrual cycles and/or ovarian defects/disorders. T1D women, however, are high in oxidative stress, although the impact of the same on their reproduction and associated events remains unknown. Therefore, the repercussions of elevated oxidative stress on the sperm fate (storage/utilization) in the reproductive tract milieu of T1D females and their fertility using the Drosophila T1D model (Df[dilp1-5]), which lacks insulin-like peptides and displays reduced female fertility. Df[dilp1-5] females were mated to normal males and thereafter sperm storage and/or utilization were examined in conjunction with oxidative stress parameters in mated Df[dilp1-5] females at different time points. Also, the impact of antioxidant (Amla or Vitamin C) supplementation on the above oxidative stress parameters in Df[dilp1-5] females and the consequences on their sperm and fertility levels were examined. Df[dilp1-5] females showed elevated oxidative stress parameters and a few of their reproductive tract proteins are oxidatively modified. Also, these females stored significantly fewer sperm and also did not utilize sperm as efficiently as their controls. Surprisingly, amelioration of the oxidative stress in Df[dilp1-5] females' milieu through antioxidant (Amla or vitamin C) supplementation enhanced sperm storage and improved fertility. Hyperglycemia coupled with elevated oxidative stress within the female reproductive tract environment affects the sperm fate, thereby reducing female fertility in T1D. In addition, these findings suggest that antioxidant supplementation may substantially aid in the mitigation of sub-fertility in T1D females
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Huang, Z. (2023). A Function of Amyloid-β in Mediating Activity-Dependent Axon/Synapse Competition May Unify Its Roles in Brain Physiology and Pathology. J Alzheimers Dis. PubMed ID: 36710681
Summary:
Amyloid-β protein precursor (AβPP) gives rise to amyloid-β (Aβ), a peptide at the center of Alzheimer's disease (AD). AβPP, however, is also an ancient molecule dating back in evolution to some of the earliest forms of metazoans. This suggests a possible ancestral function that may have been obscured by those that evolve later. Based on literature from the functions of Aβ/AβPP in nervous system development, plasticity, and disease, to those of anti-microbial peptides (AMPs) in bacterial competition as well as mechanisms of cell competition uncovered first by Drosophila genetics, this paper proposes that Aβ/AβPP may be part of an ancient mechanism employed in cell competition, which is subsequently co-opted during evolution for the regulation of activity-dependent neural circuit development and plasticity. This hypothesis is supported by foremost the high similarities of Aβ to AMPs, both of which possess unique, opposite (i.e., trophic versus toxic) activities as monomers and oligomers. A large body of data further suggests that the different Aβ oligomeric isoforms may serve as the protective and punishment signals long predicted to mediate activity-dependent axonal/synaptic competition in the developing nervous system and that the imbalance in their opposite regulation of innate immune and glial cells in the brain may ultimately underpin AD pathogenesis. This hypothesis can not only explain the diverse roles observed of Aβ and AβPP family molecules, but also provide a conceptual framework that can unify current hypotheses on AD. Furthermore, it may explain major clinical observations not accounted for and identify approaches for overcoming shortfalls in AD animal modeling.
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Hudson, J., Paul, S., Veraksa, A., Ghabrial, A., Harvey, K. F. and Poon, C. (2023). NDR kinase Tricornered genetically interacts with Ccm3 and metabolic enzymes in Drosophila melanogaster tracheal development. G3 (Bethesda). PubMed ID: 36653023
Summary:
The Germinal Center Kinase III (GckIII) pathway is a Hippo-like kinase module defined by sequential activation of Ste20 kinases Thousand and One (Tao) and GckIII, followed by nuclear dbf2-related (NDR) kinase Tricornered (Trc). Previous work uncovered a role for the GckIII pathway in Drosophila melanogaster tracheal (respiratory) tube morphology. The trachea form a network of branched epithelial tubes essential for oxygen transport, and are structurally analogous to branched tubular organs in vertebrates, such as the vascular system. In the absence of GckIII pathway function, aberrant dilations form in tracheal tubes characterised by mislocalized junctional and apical proteins, suggesting that the pathway is important in maintaining tube integrity in development. This study observed a genetic interaction between trc and Cerebral cavernous malformations 3 (Ccm3), the Drosophila ortholog of a human vascular disease gene, supporting the hypothesis that the GckIII pathway functions downstream of Ccm3 in trachea, and potentially in the vertebrate cerebral vasculature. However, how GckIII pathway signalling is regulated and the mechanisms that underpin its function in tracheal development are unknown. This study undertook biochemical and genetic approaches to identify proteins that interact with Trc, the most downstream GckIII pathway kinase. Known GckIII and NDR scaffold proteins are likely to control GckIII pathway signalling in tracheal development, consistent with their conserved roles in Hippo-like modules. Furthermore, this study showed genetic interactions between trc and multiple enzymes in glycolysis and oxidative phosphorylation, suggesting a potential function of the GckIII pathway in integrating cellular energy requirements with maintenance of tube integrity.
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Katzenberger, R. J., Ganetzky, B. and Wassarman, D. A. (2023). Lissencephaly-1 mutations enhance traumatic brain injury outcomes in Drosophila. Genetics. PubMed ID: 36683334
Summary:
Traumatic brain injury (TBI) outcomes vary greatly among individuals, but most of the variation remains unexplained. Using a Drosophila melanogaster TBI model and 178 genetically diverse lines from the Drosophila Genetic Reference Panel (DGRP), this study investigated the role that genetic variation plays in determining TBI outcomes. Following injury at 20-27 days old, DGRP lines varied considerably in mortality within 24 hours ('early mortality'). Additionally, the disparity in early mortality resulting from injury at 20-27 versus 0-7 days old differed among DGRP lines. These data support a polygenic basis for differences in TBI outcomes, where some gene variants elicit their effects by acting on aging-related processes. The genome-wide association study of DGRP lines identified associations between single nucleotide polymorphisms in Lissencephaly-1 (Lis-1) and Patronin and early mortality following injury at 20-27 days old. Lis-1 regulates dynein, a microtubule motor required for retrograde transport of many cargoes, and Patronin protects microtubule minus ends against depolymerization. While Patronin mutants did not affect early mortality, Lis-1 compound heterozygotes (Lis-1x/Lis-1y) had increased early mortality following injury at 20-27 or 0-7 days old compared with Lis-1 heterozygotes (Lis-1x/+), and flies that survived 24 hours after injury had increased neurodegeneration but an unaltered lifespan, indicating that Lis-1 affects TBI outcomes independently of effects on aging. These data suggest that Lis-1 activity is required in the brain to ameliorate TBI outcomes through effects on axonal transport, microtubule stability, and other microtubule proteins such as tau, implicated in chronic traumatic encephalopathy, a TBI-associated neurodegenerative disease in humans.
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Kim, Y. A., Siddiqui, T., Blaze, J., Cosacak, M. I., Winters, T., Kumar, A., Tein, E., Sproul, A. A., Teich, A. F., Bartolini, F., Akbarian, S., Kizil, C., Hargus, G. and Santa-Maria, I. (2023). RNA methyltransferase NSun2 deficiency promotes neurodegeneration through epitranscriptomic regulation of tau phosphorylation. Acta Neuropathol 145(1): 29-48. PubMed ID: 36357715
Summary:
Epitranscriptomic regulation adds a layer of post-transcriptional control to brain function during development and adulthood. The identification of RNA-modifying enzymes has opened the possibility of investigating the role epitranscriptomic changes play in the disease process. NOP2/Sun RNA methyltransferase 2 (NSun2) is one of the few known brain-enriched methyltransferases able to methylate mammalian non-coding RNAs. NSun2 loss of function due to autosomal-recessive mutations has been associated with neurological abnormalities in humans. This study shows NSun2 is expressed in adult human neurons in the hippocampal formation and prefrontal cortex. Strikingly, this study unraveled decreased NSun2 protein expression and an increased ratio of pTau/NSun2 in the brains of patients with Alzheimer's disease (AD) as demonstrated by Western blotting and immunostaining, respectively. In a well-established Drosophila melanogaster model of tau-induced toxicity, reduction of NSun2 exacerbated tau toxicity, while overexpression of NSun2 partially abrogated the toxic effects. Conditional ablation of NSun2 in the mouse brain promoted a decrease in the miR-125b m6A levels and tau hyperphosphorylation. Utilizing human induced pluripotent stem cell (iPSC)-derived neuronal cultures, it was confirmed that NSun2 deficiency results in tau hyperphosphorylation. This study also found that neuronal NSun2 levels decrease in response to amyloid-beta oligomers (AβO). Notably, AβO-induced tau phosphorylation and cell toxicity in human neurons could be rescued by overexpression of NSun2. Altogether, these results indicate that neuronal NSun2 deficiency promotes dysregulation of miR-125b and tau phosphorylation in AD and highlights a novel avenue for therapeutic targeting.
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Lin, G., Tepe, B., McGrane, G., Tipon, R. C., Croft, G., Panwala, L., Hope, A., Liang, A. J. H., Zuo, Z., Byeon, S. K., Wang, L., Pandey, A. and Bellen, H. J. (2023). Exploring therapeutic strategies for infantile neuronal axonal dystrophy (INAD/PARK14) Elife 12. PubMed ID: 36645408
Summary:
Infantile neuroaxonal dystrophy (INAD) is caused by recessive variants in PLA2G6 and is a lethal pediatric neurodegenerative disorder. Loss of the Drosophila homolog of PLA2G6, leads to ceramide accumulation, lysosome expansion, and mitochondrial defects. This study reports that retromer function, ceramide metabolism, the endolysosomal pathway, and mitochondrial morphology are affected in INAD patient-derived neurons. In INAD mouse models, the same features are affected in Purkinje cells, arguing that the neuropathological mechanisms are evolutionary conserved and that these features can be used as biomarkers. 20 drugs that target these pathways were tested and Ambroxol, Desipramine, Azoramide, and Genistein were found to alleviate neurodegenerative phenotypes in INAD flies and INAD patient-derived neural progenitor cells. This study also developed an AAV-based gene therapy approach that delays neurodegeneration and prolongs lifespan in an INAD mouse model.
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Su, M. T., Lu, C. W., Wu, W. J., Jheng, Y. S., Yang, S. Y., Chuang, W. C., Lee, M. C. and Wu, C. H. (2022). Applications of Immunomagnetic Reduction Technology as a Biosensor in Therapeutic Evaluation of Chinese Herbal Medicine in Tauopathy Alleviation of an AD Drosophila Model. Biosensors (Basel) 12(10). PubMed ID: 36291020
Summary:
Alzheimer's disease (AD) is the most common form of dementia. The most convincing biomarkers in the blood for AD are currently β-amyloid (Aβ) and Tau protein because amyloid plaques and neurofibrillary tangles are pathological hallmarks in the brains of patients with AD. The development of assay technologies in diagnosing early-stage AD is very important. The study of human AD subjects is hindered by ethical and technical limitations. Thus, many studies have therefore turned to AD animal models, such as Drosophila melanogaster, to explore AD pathology. However, AD biomarkers such as Aβ and p-Tau protein in Drosophila melanogaster occur at extremely low levels and are difficult to detect precisely. This study applied the immunomagnetic reduction (IMR) technology of nanoparticles for the detection of p-Tau expressions in hTau(R406W) flies, an AD Drosophila model. Furthermore, IMR technology was used as a biosensor in the therapeutic evaluation of Chinese herbal medicines in hTau(R406W) flies with Tau-induced toxicity. To uncover the pathogenic pathway and identify therapeutic interventions of Chinese herbal medicines in Tau-induced toxicity, tauopathy was modeled in the notum of hTau(R406W) flies. IMR data showed that the selected Chinese herbal medicines can significantly reduce p-Tau expressions in hTau(R406W) flies. Using evidence of notal bristle quantification and Western blotting analysis, the IMR data was confirmed and validated. Thus, it is suggested that IMR can serve as a new tool for measuring tauopathy and therapeutic evaluation of Chinese herbal medicine in an AD Drosophila model.
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Yu, J., Liufu, T., Zheng, Y., Xu, J., Meng, L., Zhang, W., Yuan, Y., Hong, D., Charlet-Berguerand, N., Wang, Z. and Deng, J. (2022). CGG repeat expansion in NOTCH2NLC causes mitochondrial dysfunction and progressive neurodegeneration in Drosophila model. Proc Natl Acad Sci U S A 119(41): e2208649119. PubMed ID: 36191230
Summary:
Neuronal intranuclear inclusion disease (NIID) is a neuromuscular/neurodegenerative disease caused by the expansion of CGG repeats in the 5' untranslated region (UTR) of the NOTCH2NLC gene. These repeats can be translated into a polyglycine-containing protein, uN2CpolyG, which forms protein inclusions and is toxic in cell models, albeit through an unknown mechanism. This study established a transgenic Drosophila model expressing uN2CpolyG in multiple systems, which resulted in progressive neuronal cell loss, locomotor deficiency, and shortened lifespan. Interestingly, electron microscopy revealed mitochondrial swelling both in transgenic flies and in muscle biopsies of individuals with NIID. Immunofluorescence and immunoelectron microscopy showed colocalization of uN2CpolyG with mitochondria in cell and patient samples, while biochemical analysis revealed that uN2CpolyG interacted with a mitochondrial RNA binding protein, LRPPRC (leucine-rich pentatricopeptide repeat motif-containing protein). Furthermore, RNA sequencing (RNA-seq) analysis and functional assays showed down-regulated mitochondrial oxidative phosphorylation in uN2CpolyG-expressing flies and NIID muscle biopsies. Finally, idebenone treatment restored mitochondrial function and alleviated neurodegenerative phenotypes in transgenic flies. Overall, these results indicate that transgenic flies expressing uN2CpolyG recapitulate key features of NIID and that reversing mitochondrial dysfunction might provide a potential therapeutic approach for this disorder.
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Riccardi, C., D'Aria, F., Fasano, D., Digilio, F. A., Carillo, M. R., Amato, J., De Rosa, L., Paladino, S., Melone, M. A. B., Montesarchio, D. and Giancola, C. (2022). Truncated Analogues of a G-Quadruplex-Forming Aptamer Targeting Mutant Huntingtin: Shorter Is Better!. Int J Mol Sci 23(20). PubMed ID: 36293267
Summary:
Two analogues of the MS3 aptamer, which was previously shown to have an exquisite capability to selectively bind and modulate the activity of mutant huntingtin (mHTT), have been designed and evaluated in this study for their physicochemical and biological properties. Featured by a distinctive propensity to form complex G-quadruplex structures, including large multimeric aggregates, the original 36-mer MS3 has been truncated to give a 33-mer (here named MS3-33) and a 17-mer (here named MS3-17). A combined use of different techniques (UV, CD, DSC, gel electrophoresis) allowed a detailed physicochemical characterization of these novel G-quadruplex-forming aptamers, tested in vitro on SH-SY5Y cells and in vivo on a Drosophila Huntington's disease model, in which these shorter MS3-derived oligonucleotides proved to have improved bioactivity in comparison with the parent aptamer.
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Siddique, Y. H., Rahul, Ara, G., Afzal, M., Varshney, H., Gaur, K., Subhan, I., Mantasha, I. and Shahid, M. (2022). Beneficial effects of apigenin on the transgenic Drosophila model of Alzheimer's disease. Chem Biol Interact 366: 110120. PubMed ID: 36027948
Summary:
Alzheimer's disease (AD) is a progressive neurodegenerative disorder. The available drugs improve the symptoms but do not play role in modifying disease effects. Currently, the treatment strategies focus on inhibiting the production of Aβ-42 aggregates and tau filaments. In this context the natural plant products could act as a potent candidate. Therefore, the effect was studied of apigenin, a free-radical scavenger and antioxidant, on the transgenic Drosophila model of AD i.e., expressing Aβ-42 in the neurons. The AD flies were allowed to feed on the diet having 25, 50, 75 and 100 μM of apigenin for 30 days. The exposure of AD flies to apigenin showed a dose dependent significant decrease in the oxidative stress and delay in the loss of climbing ability. Apigenin also inhibits the activity of acetylcholinesterase. The immunostaining and molecular docking studies suggest that apigenin inhibits the formation of Aβ-42 aggregates. Apigenin is potent in reducing the AD symptoms being mimicked in the transgenic Drosophila model of AD.
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Dyson, A., Ryan, M., Garg, S., Evans, D. G. and Baines, R. A. (2022). Loss of NF1 in Drosophila larvae causes tactile hypersensitivity and impaired synaptic transmission at the neuromuscular junction. J Neurosci. PubMed ID: 36344265
Summary:
Autism Spectrum Disorder (ASD) is a neurodevelopmental condition in which the mechanisms underlying its core symptomatology are largely unknown. Studying animal models of monogenic syndromes associated with ASD, such as neurofibromatosis type 1 (NF1), can offer insights into its aetiology. This study shows that loss of function of the Drosophila NF1 ortholog results in tactile hypersensitivity following brief mechanical stimulation in the larva (mixed sexes), paralleling the sensory abnormalities observed in individuals with ASD. Mutant larvae also exhibit synaptic transmission deficits at the glutamatergic neuromuscular junction (NMJ), with increased spontaneous but reduced evoked release. While the latter is homeostatically compensated for by a postsynaptic increase in input resistance, the former is consistent with neuronal hyperexcitability. Indeed, diminished expression of NF1 specifically within central cholinergic neurons induces both excessive neuronal firing and tactile hypersensitivity, suggesting the two may be linked. Furthermore, both impaired synaptic transmission and behavioural deficits are fully rescued via knockdown of Ras proteins. These findings validate NF1(-/-) Drosophila as a tractable model of ASD with the potential to elucidate important pathophysiological mechanisms.
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Shrivastava, N. K., Chauhan, N. and Shakarad, M. N. (2022). Heightened immune surveillance in Drosophila melanogaster populations selected for faster development and extended longevity. Heliyon 8(12): e12090. PubMed ID: 36544838
Summary:
Maximization of life-history traits is under constraints due to both, limitations of resource acquisition and the restricted pathways of resource allocation. Drosophila melanogaster has served as an excellent model organism to not only unravel various trade-offs among life history traits but also numerous aspects of host immune response. Drosophila larvae are semi-aquatic that live, feed and excrete inside the food source-often over-ripe fruits and vegetables that are rich in both commensal and pathogenic microbiota that can impact the larval survival. This study used six populations of D. melanogaster, three of which are selected for faster pre-adult development and extended adult longevity, and their three ancestral controls, to explore the impact of selection on the basal immune activity in the larval stage. The larvae from selected populations had nearly significantly upregulated plasmatocyte density, significantly higher percent phagocytosis, phagocytic index and higher transcript levels of Tep3, eater and NimC1. Selected populations also had significantly upregulated crystal cell number along with higher transcript of PPO2. Out of seven tested AMPs level, Drosomycin was significantly upregulated in selected populations while Drosocin was significantly higher in control populations. ROS levels were comparable in the selected and control populations. The results strongly suggest that enhanced basal immune activity during larval stage manages the faster development and could be responsible for comparable larval survival of selected and control populations.
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Ding, M., Li, Q. F., Peng, T. H., Wang, T. Q., Yan, H. H., Tang, C., Wang, X. Y., Guo, Y. and Zheng, L. (2022). Early life exercise training and inhibition of apoLpp mRNA expression to improve age-related arrhythmias and prolong the average lifespan in Drosophila melanogaster. Aging (Albany NY) 14(24): 9908-9923. PubMed ID: 36470666
Summary:
Cardiovascular disease (CVD) places a heavy burden on older patients and the global healthcare system. A large body of evidence suggests that exercise training is essential in preventing and treating cardiovascular disease, but the underlying mechanisms are not well understood. This study used the Drosophila melanogaster animal model to study the effects of early-life exercise training (Exercise) on the aging heart and lifespan. It was found in flies that age-induced arrhythmias are conserved across different genetic backgrounds. The fat body is the primary source of circulating lipoproteins in flies. Inhibition of fat body apoLpp (Drosophila apoB homolog) demonstrated that low expression of apoLpp reduced the development of arrhythmias in aged flies but did not affect average lifespan. At the same time, exercise can also reduce the expression of apoLpp mRNA in aged flies and have a protective effect on the heart, which is similar to the inhibition of apoLpp mRNA. Although treatment of UAS-apoLpp(RNAi) and exercise alone had no significant effect on lifespan, the combination of UAS-apoLpp(RNAi) and exercise extended the average lifespan of flies. Therefore, it is concluded that UAS-apoLpp(RNAi) and exercise are sufficient to resist age-induced arrhythmias, which may be related to the decreased expression of apoLpp mRNA, and that UAS-apoLpp(RNAi) and exercise have a combined effect on prolonging the average lifespan.
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Semaniuk, U. V., Gospodaryov, D. V., Strilbytska, O. M., Kucharska, A. Z., Sokol-Lętowska, A., Burdyliuk, N. I., Storey, K. B., Bayliak, M. M. and Lushchak, O. (2022). Chili-supplemented food decreases glutathione-S-transferase activity in Drosophila melanogaster females without a change in other parameters of antioxidant system. Redox Rep 27(1): 221-229. PubMed ID: 36200601
Summary:
Many plant-derived anti-aging preparations influence antioxidant defense system. Consumption of food supplemented with chili pepper powder was found to extend lifespan in the fruit fly, Drosophila melanogaster. The present study aimed to test a connection between life-extending effect of chili powder and antioxidant defense system of D. melanogaster. Flies were reared for 15 days in the mortality cages on food with 0% (control), 0.04%, 0.12%, 0.4%, or 3% chili powder. Antioxidant and related enzymes, as well as oxidative stress indices were measured. Female flies that consumed chili-supplemented food had a 40-60% lower glutathione-S-transferase (GST) activity as compared with the control cohort. Activity of superoxide dismutase (SOD) was about 37% higher in males that consumed food with 3% chili powder in comparison with the control cohort. Many of the parameters studied were sex-dependent. It is concluded that consumption of chili-supplemented food extends lifespan in fruit fly cohorts in a concentration- and gender-dependent manner. However, this extension is not mediated by a strengthening of antioxidant defenses. Consumption of chili-supplemented food does not change the specific relationship between antioxidant and related enzymes in D. melanogaster, and does not change the linkage of the activities of these enzymes to fly gender (Semaniuk, 2022).
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Srinivasan, A. R., Tran, T. T. and Bonini, N. M.(2022). The Clock:Cycle complex is a major transcriptional regulator of Drosophila photoreceptors that protects the eye from retinal degeneration and oxidative stress. PLoS Genet 18(1): e1010021. PubMed ID: 35100266
Summary:
Aging is a risk factor for neurodegenerative disease, but precise mechanisms that influence this relationship are still under investigation. Work in Drosophila melanogaster identified the microRNA miR-34 as a modifier of aging and neurodegeneration in the brain. MiR-34 mutants present aspects of early aging, including reduced lifespan, neurodegeneration, and a buildup of the repressive histone mark H3K27me3. To better understand how miR-34 regulated pathways contribute to age-associated phenotypes in the brain, here we transcriptionally profiled the miR-34 mutant brain. This identified that genes associated with translation are dysregulated in the miR-34 mutant. The brains of these animals show increased translation activity, accumulation of protein aggregation markers, and altered autophagy activity. To determine if altered H3K27me3 was responsible for this proteostasis dysregulation, the effects of increased H3K27me3 was studied by mutating the histone demethylase Utx. Reduced Utx activity enhanced neurodegeneration and mimicked the protein accumulation seen in miR-34 mutant brains. However, unlike the miR-34 mutant, Utx mutant brains did not show similar altered autophagy or translation activity, suggesting that additional miR-34-targeted pathways are involved. Transcriptional analysis of predicted miR-34 targets identified Lst8, a subunit of Tor Complex 1 (TORC1), as a potential target. We confirmed that miR-34 regulates the 3' UTR of Lst8 and identified several additional predicted miR-34 targets that may be critical for maintaining proteostasis and brain health. Together, these results present novel understanding of the brain and the role of the conserved miRNA miR-34 in impacting proteostasis in the brain with age.
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Tonoki, A., Nagai, S., Yu, Z., Yue, T., Lyu, S., Hou, X., Onuki, K., Yabana, K., Takahashi, H. and Itoh, M.(2022). Nitric oxide-soluble guanylyl cyclase pathway as a contributor to age-related memory impairment in Drosophila. Aging Cell 21(9): e13691. PubMed ID: 35963012
Summary:
Age-related changes in the transcriptome lead to memory impairment. Several genes have been identified to cause age-dependent memory impairment (AMI) by changes in their expression, but genetic screens to identify genes critical for AMI have not been performed. The fruit fly is a useful model for studying AMI due to its short lifespan and the availability of consistent techniques and environments to assess its memory ability. A list of candidate genes that act as AMI regulators was generated by performing a comprehensive analysis of RNA sequencing data from young and aged fly heads and genome-wide RNAi screening data to identify memory-regulating genes. A candidate screen using temporal and panneuronal RNAi expression was performed to identify genes critical for AMI. The guanylyl cyclase β-subunit at 100B (gycβ) gene, which encodes a subunit of soluble guanylyl cyclase (sGC), the only intracellular nitric oxide (NO) receptor in fruit flies, as a negative regulator of AMI. RNAi knockdown of gycβ in neurons and NO synthase (NOS) in glia or neurons enhanced the performance of intermediate-term memory (ITM) without apparent effects on memory acquisition. This study also showed that pharmacological inhibition of sGC and NOS enhanced ITM in aged individuals, suggesting the possibility that age-related enhancement of the NO-sGC pathway causes memory impairment.
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Malacrino, A., Brengdahl, M. I., Kimber, C. M., Mital, A., Shenoi, V. N., Mirabello, C. and Friberg, U.(2022). Ageing desexualizes the Drosophila brain transcriptome. Proc Biol Sci 289(1980): 20221115. PubMed ID: 35946149
Summary:
General evolutionary theory predicts that individuals in low condition should invest less in sexual traits compared to individuals in high condition. Whether this positive association between condition and investment also holds between young (high condition) and senesced (low condition) individuals is however less clear, since elevated investment into reproduction may be beneficial when individuals approach the end of their life. To address how investment into sexual traits changes with age, genes were studied with sex-biased expression in the brain, the tissue from which sexual behaviours are directed. Across two distinct populations of Drosophila melanogaster, it was found that old brains display fewer sex-biased genes, and that expression of both male-biased and female-biased genes converges towards a sexually intermediate phenotype owing to changes in both sexes with age. It was further found that sex-biased genes in general show heightened age-dependent expression in comparison to unbiased genes and that age-related changes in the sexual brain transcriptome are commonly larger in males than females.The results hence show that ageing causes a desexualization of the fruit fly brain transcriptome and that this change mirrors the general prediction that low condition individuals should invest less in sexual phenotypes.
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Jauregui-Lozano, J., Hall, H., Stanhope, S. C., Bakhle, K., Marlin, M. M. and Weake, V. M.(2022). The Clock:Cycle complex is a major transcriptional regulator of Drosophila photoreceptors that protects the eye from retinal degeneration and oxidative stress. PLoS Genet 18(1): e1010021. PubMed ID: 35100266
Summary:
The aging eye experiences physiological changes that include decreased visual function and increased risk of retinal degeneration. Although there are transcriptomic signatures in the aging retina that correlate with these physiological changes, the gene regulatory mechanisms that contribute to cellular homeostasis during aging remain to be determined. This study integrated ATAC-seq and RNA-seq data to identify 57 transcription factors that showed differential activity in aging Drosophila photoreceptors. These 57 age-regulated transcription factors include two circadian regulators, Clock and Cycle, that showed sustained increased activity during aging. When the Clock:Cycle complex was disrupted by expressing a dominant negative version of Clock (ClkDN) in adult photoreceptors, changes were observed in expression of 15-20% of genes including key components of the phototransduction machinery and many eye-specific transcription factors. Using ATAC-seq, expression of ClkDN in photoreceptors was shown to lead to changes in activity of 37 transcription factors and causes a progressive decrease in global levels of chromatin accessibility in photoreceptors. Supporting a key role for Clock-dependent transcription in the eye, expression of ClkDN in photoreceptors also induced light-dependent retinal degeneration and increased oxidative stress, independent of light exposure. Together, these data suggests that the circadian regulators Clock and Cycle act as neuroprotective factors in the aging eye by directing gene regulatory networks that maintain expression of the phototransduction machinery and counteract oxidative stress.
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Krittika, S. and Yadav, P. (2022). Trans-generational effect of protein restricted diet on adult body and wing size of Drosophila melanogaster. R Soc Open Sci 9(1): 211325. PubMed ID: 35116152
Summary:
Protein restriction (PR) has established feasible trade-offs in Drosophila melanogaster to understand lifespan or ageing in a nutritionally challenged environment. However, the phenotypes of body size, weight and wing length respond according to factors such as flies' genotype, environmental exposure and parental diet, and hence their understanding is essential. This study demonstrates the effect of long-term PR diet on body size, weight, normal and dry wing length of flies subjected to PR50 and PR70 (50% and 70% protein content present in control food, respectively) for 20 generations from the pre-adult stage. PR-fed flies were found to have lower body weight, relative water content (in males), unaltered (PR50%) and higher (PR70%) relative fat content in males, smaller normal and dry body size when compared with control and generations 1 and 2. Interestingly, the wing size and pupal size of PR flies are smaller and showed significant effects on diet and generation. Thus, these traits are sex and generation dependent along with a diet interaction, which is capable of modulating these results variably. Taken together, the trans-generational effect of PR on fitness and fitness-related traits might be helpful to understand the underpinning mechanisms of evolution and ageing in fruit flies D. melanogaster.
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Jauregui-Lozano, J., Escobedo, S., Easton, A., Lanman, N. A., Weake, V. M. and Hall, H. (2022). Proper control of R-loop homeostasis is required for maintenance of gene expression and neuronal function during aging. Aging Cell 21(2): e13554. PubMed ID: 35048512
Summary:
Age-related loss of cellular function and increased cell death are characteristic hallmarks of aging. While defects in gene expression and RNA metabolism have been linked with age-associated human neuropathies, it is not clear how the changes that occur in aging neurons contribute to loss of gene expression homeostasis. R-loops are RNA-DNA hybrids that typically form co-transcriptionally via annealing of the nascent RNA to the template DNA strand, displacing the non-template DNA strand. Dysregulation of R-loop homeostasis has been associated with both transcriptional impairment and genome instability. Importantly, a growing body of evidence links R-loop accumulation with cellular dysfunction, increased cell death, and chronic disease onset. This study characterized the R-loop landscape in aging Drosophila melanogaster photoreceptor neurons and showed that bulk R-loop levels increased with age. Further, genome-wide mapping of R-loops revealed that transcribed genes accumulated R-loops over gene bodies during aging, which correlated with decreased expression of long and highly expressed genes. Importantly, while photoreceptor-specific down-regulation of Top3β, a DNA/RNA topoisomerase associated with R-loop resolution, lead to decreased visual function, over-expression of Top3β or nuclear-localized RNase H1, which resolves R-loops, enhanced positive light response during aging. Together, these studies highlight the functional link between dysregulation of R-loop homeostasis, gene expression, and visual function during aging.
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Shukla, N. and Kolthur-Seetharam, U. (2022). Drosophila Sirtuin 6 mediates developmental diet-dependent programming of adult physiology and survival. Aging Cell 21(3): e13576. PubMed ID: 35233942
Summary:
Organisms in the wild experience unpredictable and diverse food availability throughout their lifespan. Over-/under-nutrition during development and in adulthood is known to dictate organismal survival and fitness. Studies using model systems have also established long-term effects of developmental dietary alterations on life-history traits. However, the underlining genetic/molecular factors, which differentially couple nutrient inputs during development with fitness later in life are far less understood. Using Drosophila and loss/gain of function perturbations, serendipitous findings demonstrate an essential role of Sirtuin 6 in regulating larval developmental kinetics, in a nutrient-dependent manner. The absence of Sirt6 affected ecdysone and insulin signalling and led to accelerated larval development. Moreover, varying dietary glucose and yeast during larval stages resulted in enhanced susceptibility to metabolic and oxidative stress in adults. This study also demonstrated an evolutionarily conserved role for Sirt6 in regulating physiological homeostasis, physical activity and organismal lifespan, known only in mammals until now. These results highlight gene-diet interactions that dictate thresholding of nutrient inputs and physiological plasticity, operative across development and adulthood. In summary, besides showing its role in invertebrate ageing, this study also identifies Sirt6 as a key factor that programs macronutrient-dependent life-history traits.
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Overman, K. E., Choi, D. M., Leung, K., Shaevitz, J. W. and Berman, G. J.. (2022). Measuring the repertoire of age-related behavioral changes in Drosophila melanogaster. PLoS Comput Biol 18(2): e1009867. PubMed ID: 35202388
Summary:
Aging affects almost all aspects of an organism-its morphology, its physiology, its behavior. Isolating which biological mechanisms are regulating these changes, however, has proven difficult, potentially due to our inability to characterize the full repertoire of an animal's behavior across the lifespan. Using data from fruit flies (D. melanogaster) this study measured the full repertoire of behaviors as a function of age. A sexually dimorphic pattern of changes was observed in the behavioral repertoire during aging. Although the stereotypy of the behaviors and the complexity of the repertoire overall remains relatively unchanged, evidence was found that the observed alterations in behavior can be explained by changing the fly's overall energy budget, suggesting potential connections between metabolism, aging, and behavior.
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Phillips, M. A., Arnold, K. R., Vue, Z., Beasley, H. K., Garza-Lopez, E., Marshall, A. G., Morton, D. J., McReynolds, M. R., Barter, T. T. and Hinton, A., Jr. (2022). <Combining Metabolomics and Experimental Evolution Reveals Key Mechanisms Underlying Longevity Differences in Laboratory Evolved Drosophila melanogaster Populations. Int J Mol Sci 23(3). PubMed ID: 35162994
Summary:
Experimental evolution with Drosophila melanogaster has been used extensively for decades to study aging and longevity. In recent years, the addition of DNA and RNA sequencing to this framework has allowed researchers to leverage the statistical power inherent to experimental evolution to study the genetic basis of longevity itself. Here, we incorporated metabolomic data into to this framework to generate even deeper insights into the physiological and genetic mechanisms underlying longevity differences in three groups of experimentally evolved D. melanogaster populations with different aging and longevity patterns. Metabolomic analysis found that aging alters mitochondrial metabolism through increased consumption of NAD(+) and increased usage of the TCA cycle. Combining the genomic and metabolomic data produced a list of biologically relevant candidate genes. Among these candidates, significant enrichment was found for genes and pathways associated with neurological development and function, and carbohydrate metabolism. While enrichment for aging canonical genes was not specifically found, neurological dysregulation and carbohydrate metabolism are both known to be associated with accelerated aging and reduced longevity. Taken together, these results provide plausible genetic mechanisms for what might be driving longevity differences in this experimental system. More broadly, these findings demonstrate the value of combining multiple types of omic data with experimental evolution when attempting to dissect mechanisms underlying complex and highly polygenic traits such as aging.
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Yamamoto, R., Palmer, M., Koski, H., Curtis-Joseph, N. and Tatar, M. (2021). Aging modulated by the Drosophila insulin receptor through distinct structure-defined mechanisms. Genetics 217(2). PubMed ID: 33724413
Summary:
Mutations of the Drosophila melanogaster insulin/IGF signaling system slow aging, while also affecting growth and reproduction. To understand this pleiotropy, an allelic series of single codon substitutions was produced in the Drosophila insulin receptor, InR. Substitutions were generated using homologous recombination, and each was related to emerging models of receptor tyrosine kinase structure and function. Three mutations when combined as trans-heterozygotes extended lifespan while retarding growth and fecundity. These genotypes reduced insulin-stimulated Akt phosphorylation, suggesting they impede kinase catalytic domain function. Among these genotypes, longevity was negatively correlated with egg production, consistent with life-history trade-off theory. In contrast, one mutation (InR353) was located in the kinase insert domain, a poorly characterized element found in all receptor tyrosine kinases. Remarkably, wild-type heterozygotes with InR353 robustly extended lifespan without affecting growth or reproduction and retained capacity to fully phosphorylate Akt. The Drosophila insulin receptor kinase insert domain contains a previously unrecognized SH2 binding motif. It is proposed the kinase insert domain interacts with SH2-associated adapter proteins to affect aging through mechanisms that retain insulin sensitivity and are independent of reproduction (Yamamoto, 2021).
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Wong, C. O., Karagas, N. E., Jung, J., Wang, Q., Rousseau, M. A., Chao, Y., Insolera, R., Soppina, P., Collins, C. A., Zhou, Y., Hancock, J. F., Zhu, M. X. and Venkatachalam, K. (2021). Regulation of longevity by depolarization-induced activation of PLC-beta-IP(3)R signaling in neurons. Proc Natl Acad Sci U S A 118(16). PubMed ID: 33859040
Summary:
Mitochondrial ATP production is a well-known regulator of neuronal excitability. The reciprocal influence of plasma-membrane potential on ATP production, however, remains poorly understood. This study describes a mechanism by which depolarized neurons elevate the somatic ATP/ADP ratio in Drosophila glutamatergic neurons. Depolarization increased phospholipase-Cβ (PLC-β) activity by promoting the association of the enzyme with its phosphoinositide substrate. Augmented PLC-β activity led to greater release of endoplasmic reticulum Ca(2+) via the inositol trisphosphate receptor (IP(3)R), increased mitochondrial Ca(2+) uptake, and promoted ATP synthesis. Perturbations that decoupled membrane potential from this mode of ATP synthesis led to untrammeled PLC-β-IP(3)R activation and a dramatic shortening of Drosophila lifespan. Upon investigating the underlying mechanisms, this study found that increased sequestration of Ca(2+) into endolysosomes was an intermediary in the regulation of lifespan by IP(3)Rs. Manipulations that either lowered PLC-β/IP(3)R abundance or attenuated endolysosomal Ca(2+) overload restored animal longevity. Collectively, these findings demonstrate that depolarization-dependent regulation of PLC-β-IP(3)R signaling is required for modulation of the ATP/ADP ratio in healthy glutamatergic neurons, whereas hyperactivation of this axis in chronically depolarized glutamatergic neurons shortens animal lifespan by promoting endolysosomal Ca(2+) overload (Wong, 2021).
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Yu, R., Cao, X., Sun, L., Zhu, J. Y., Wasko, B. M., Liu, W., Crutcher, E., Liu, H., Jo, M. C., Qin, L., Kaeberlein, M., Han, Z. and Dang, W. (2021). Inactivating histone deacetylase HDA promotes longevity by mobilizing trehalose metabolism. Nat Commun 12(1): 1981. PubMed ID: 33790287
Summary:
Histone acetylations are important epigenetic markers for transcriptional activation in response to metabolic changes and various stresses. Using the high-throughput SEquencing-Based Yeast replicative Lifespan screen method and the yeast knockout collection, this study demonstrate that the HDA complex, a class-II histone deacetylase (HDAC), regulates aging through its target of acetylated H3K18 at storage carbohydrate genes. In addition to longer lifespan, disruption of HDA results in resistance to DNA damage and osmotic stresses. This study shows that these effects are due to increased promoter H3K18 acetylation and transcriptional activation in the trehalose metabolic pathway in the absence of HDA. Furthermore, it was determined that the longevity effect of HDA is independent of the Cyc8-Tup1 repressor complex known to interact with HDA and coordinate transcriptional repression. Silencing the HDA homologs in C. elegans and Drosophila increases their lifespan and delays aging-associated physical declines in adult flies. Hence, this study has demonstrated that this HDAC controls an evolutionarily conserved longevity pathway (Yu, 2021).
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Wang, Y., Burra, S. and Galko, M. J. (2021). Drosophila larval epidermal cells only exhibit epidermal aging when they persist to the adult stage. J Exp Biol. PubMed ID: 33795421
Summary:
Holometabolous insects undergo a complete transformation of the body plan from the larval to the adult stage. In Drosophila, this transformation includes replacement of larval epidermal cells (LECs) by adult epidermal cells (AECs). AECs in Drosophila undergo a rapid and stereotyped aging program where they lose both cell membranes and nuclei. Whether LECs are capable of undergoing aging in a manner similar to AECs remains unknown. This question was addressed in two ways. First, hallmarks were sought of epidermal aging in larvae that have a greatly extended third instar and/or carry mutations that would cause premature epidermal aging at the adult stage. Such larvae, irrespective of genotype, did not show any of the signs of epidermal aging observed in the adult. Second, a procedure was developed to effect a heterochronic persistence of LECs into the adult epidermal sheet. Lineage tracing verified that presumptive LECs in the adult epidermis are not derived from imaginal epidermal histoblasts. LECs embedded within the adult epidermal sheet undergo clear signs of epidermal aging; they form multinucleate cells with each other and with the surrounding AECs. The incidence of adult cells with mixed AEC nuclei (small) and persistent LEC nuclei (large) increased with age. These data reveals that epidermal aging in holometabolous Drosophila is a stage-specific phenomenon and that the capacity of LECs to respond to aging signals does exist (Wang, 2021).
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Tain, L. S., Sehlke, R., Meilenbrock, R. L., Leech, T., Paulitz, J., Chokkalingam, M., Nagaraj, N., Gronke, S., Frohlich, J., Atanassov, I., Mann, M., Beyer, A. and Partridge, L. (2021). Tissue-specific modulation of gene expression in response to lowered insulin signalling in Drosophila. Elife 10. PubMed ID: 33879316
Summary:
Reduced activity of the insulin/IGF signalling network increases health during ageing in multiple species. Diverse and tissue-specific mechanisms drive the health improvement. Tissue-specific transcriptional and proteomic profiling were performed of long-lived Drosophila dilp2-3,5 mutants, and tissue-specific regulation was identified of &gy;3600 transcripts and >3700 proteins. Most expression changes were regulated post-transcriptionally in the fat body, and only in mutants infected with the endosymbiotic bacteria, Wolbachia pipientis, which increases their lifespan. Bioinformatic analysis identified reduced co-translational ER targeting of secreted and membrane-associated proteins and increased DNA damage/repair response proteins. Accordingly, age-related DNA damage and genome instability were lower in fat body of the mutant, and overexpression of a minichromosome maintenance protein subunit extended lifespan. Proteins involved in carbohydrate metabolism showed altered expression in the mutant intestine, and gut-specific overexpression of a lysosomal mannosidase increased autophagy, gut homeostasis, and lifespan. These processes are candidates for combatting ageing-related decline in other organisms (Tain, 2021).
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Privalova, V., Szlachcic, E., Sobczyk, L., Szabla, N. and Czarnoleski, M. (2021). Oxygen Dependence of Flight Performance in Ageing Drosophila melanogaster. Biology (Basel) 10(4). PubMed ID: 33919761
Summary:
Similar to humans, insects lose their physical and physiological capacities with age, which makes them a convenient study system for human ageing. Although insects have an efficient oxygen-transport system, little is known about how their flight capacity changes with age and environmental oxygen conditions. Two types of locomotor performance in ageing Drosophila melanogaster flies: the frequency of wing beats and the capacity to climb vertical surfaces. Flight performance was measured under normoxia and hypoxia. As anticipated, ageing flies showed systematic deterioration of climbing performance, and low oxygen impeded flight performance. Against predictions, flight performance did not deteriorate with age, and younger and older flies showed similar levels of tolerance to low oxygen during flight. It is suggested that among different insect locomotory activities, flight performance deteriorates slowly with age, which is surprising, given that insect flight is one of the most energy-demanding activities in animals. Apparently, the superior capacity of insects to rapidly deliver oxygen to flight muscles remains little altered by ageing, but this study showed that insects can become oxygen limited in habitats with a poor oxygen supply (e.g., those at high elevations) during highly oxygen-demanding activities such as flight (Privalova, 2021).
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Ulgherait, M., Midoun, A. M., Park, S. J., Gatto, J. A., Tener, S. J., Siewert, J., Klickstein, N., Canman, J. C., Ja, W. W. and Shirasu-Hiza, M. (2021). Circadian autophagy drives iTRF-mediated longevity. Nature 598(7880): 353-358. PubMed ID: 34588695
Summary:
Time-restricted feeding (TRF) has recently gained interest as a potential anti-ageing treatment for organisms from Drosophila to humans. TRF restricts food intake to specific hours of the day. Because TRF controls the timing of feeding, rather than nutrient or caloric content, TRF has been hypothesized to depend on circadian-regulated functions; the underlying molecular mechanisms of its effects remain unclear. To exploit the genetic tools and well-characterized ageing markers of Drosophila, this study developed an intermittent TRF (iTRF) dietary regimen that robustly extended fly lifespan and delayed the onset of ageing markers in the muscles and gut. iTRF enhanced circadian-regulated transcription, and iTRF-mediated lifespan extension required both circadian regulation and autophagy, a conserved longevity pathway. Night-specific induction of autophagy was both necessary and sufficient to extend lifespan on an ad libitum diet and also prevented further iTRF-mediated lifespan extension. By contrast, day-specific induction of autophagy did not extend lifespan. Thus, these results identify circadian-regulated autophagy as a critical contributor to iTRF-mediated health benefits in Drosophila. Because both circadian regulation and autophagy are highly conserved processes in human ageing, this work highlights the possibility that behavioural or pharmaceutical interventions that stimulate circadian-regulated autophagy might provide people with similar health benefits, such as delayed ageing and lifespan extension (Ulgherait, 2021).
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Harrison, B. R., Hoffman, J. M., Samuelson, A., Raftery, D. and Promislow, D. E. L. (2021). Modular Evolution of the Drosophila Metabolome.
Mol Biol Evol. PubMed ID: 34662414
Summary:
Comparative phylogenetic studies offer a powerful approach to study the evolution of complex traits. While much effort has been devoted to the evolution of the genome and to organismal phenotypes, until now relatively little work has been done on the evolution of the metabolome, despite the fact that it is composed of the basic structural and functional building blocks of all organisms. This study explored variation in metabolite levels across 50 million years of evolution in the genus Drosophila, employing a common garden design to measure the metabolome within and among 11 species of Drosophila. This study found that both sex and age have dramatic and evolutionarily conserved effects on the metabolome. This study also found substantial evidence that many metabolite pairs covary after phylogenetic correction, and that such metabolome coevolution is modular. Some of these modules are enriched for specific biochemical pathways and show different evolutionary trajectories, with some showing signs of
stabilizing selection. Both observations suggest that functional relationships may ultimately cause such modularity. These coevolutionary patterns also differ between sexes and are affected by age. This study also explored the relevance of modular evolution to fitness by associating modules with lifespan variation measured in the same common garden. Several modules associated with lifespan were found, particularly in the metabolome of older flies. Oxaloacetate levels in older females appear to coevolve with lifespan, and a lifespan-associated module in older females suggests that metabolic associations could underlie 50 million years of lifespan evolution (Harrison, 2021).
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Zhu, Y., Cai, Q., Zheng, X., Liu, L., Hua, Y., Du, B., Zhao, G., Yu, J., Zhuo, Z., Xie, Z. and Ji, S. (2021). Aspirin Positively Contributes to Drosophila Intestinal Homeostasis and Delays Aging through Targeting Imd.
Aging Dis 12(7): 1821-1834. PubMed ID: 34631223
Summary:
The intestine, a high-turnover tissue, plays a critical role in regulating aging and health in both vertebrates and invertebrates. Maintaining the epithelial barrier function of the intestine by preserving innate immune homeostasis significantly delays aging and prevents mortality. In an effort to explore effective chemicals and materials that can improve intestinal integrity, a nonbiased screen was performed utilizing Drosophila as an animal model. Long-term uptake of aspirin markedly prevented age-onset gut leakage, the over-proliferation of intestinal stem cells, and the dysbiosis of commensal microbiota in fruit flies. Mechanistically, aspirin efficiently downregulated chronic activation of intestinal immune deficiency signaling during aging. Furthermore, in vivo and in vitro biochemical analyses indicated that aspirin is a negative modulator in control of the K63-linked ubiquitination of Imd. These findings uncover a novel regulatory mechanism by which aspirin positively modulates intestinal homeostasis, thus delaying aging, in Drosophila (Zhu, 2021).
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Bouska, M. J. and Bai, H. (2021). Loxl2 is a mediator of cardiac aging in Drosophila melanogaster; genetically examining the role of aging clock genes.
G3 (Bethesda). PubMed ID: 34734976
Summary:
Transcriptomic, proteomic, and methylation aging clocks demonstrate that aging has a predictable preset program, while Transcriptome Trajectory Turning Points indicate that the 20 to 40 age range in humans is the likely stage at which the progressive loss of homeostatic control, and in turn aging, begins to have detrimental effects. Turning points in this age range overlapping with human aging clock genes revealed five candidates that were hypothesized could play a role in aging or age-related physiological decline. To examine these gene's effects on lifespan and health-span, this study utilized whole body and heart specific gene knockdown of human orthologs in Drosophila melanogaster. Whole body Loxl2, fz3, and Glo1 RNAi positively affected lifespan as did heart-specific Loxl2 knockdown. Loxl2 inhibition concurrently reduced age-related cardiac arrythmia and collagen (Pericardin) fiber width. Loxl2 binds several transcription factors in humans and RT-qPCR confirmed that a conserved transcriptional target CDH1 (Drosophila CadN2), has expression levels which correlate with Loxl2 reduction in Drosophila. These results point to conserved pathways and multiple mechanisms by which inhibition of Loxl2 can be beneficial to heart health and organismal aging (Bouska, 2021).
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Ebanks, B., Wang, Y., Katyal, G., Sargent, C., Ingram, T. L., Bowman, A., Moisoi, N. and Chakrabarti, L. (2021). Exercising D. melanogaster Modulates the Mitochondrial Proteome and Physiology. The Effect on Lifespan Depends upon Age and Sex. Int J Mol Sci 22(21). PubMed ID: 34769041
Summary:
Ageing is a major risk factor for many of the most prevalent diseases, including neurodegenerative diseases, cancer, and heart disease. As the global population continues to age, behavioural interventions that can promote healthy ageing will improve quality of life and relieve the socioeconomic burden that comes with an aged society. Exercise is recognised as an effective intervention against many diseases of ageing, but we do not know the stage in an individual's lifetime at which exercise is most effective at promoting healthy ageing, and whether or not it has a direct effect on lifespan. This study exercised w(1118) Drosophila melanogaster, investigating the effects of sex and group size at different stages of their lifetime, and recorded their lifespan. Climbing scores at 30 days were measured to record differences in fitness in response to exercise. The mitochondrial proteome was assessed of w(1118) Drosophila that had been exercised for one week, alongside mitochondrial respiration measured using high-resolution respirometry, to determine changes in mitochondrial physiology in response to exercise. This study found that age-targeted exercise interventions improved the lifespan of both male and female Drosophila, and grouped males exercised in late life had improved climbing scores when compared with those exercised throughout their entire lifespan. The proteins of the electron transport chain were significantly upregulated in expression after one week of exercise, and complex-II-linked respiration was significantly increased in exercised Drosophila. Taken together, our findings provide a basis to test specific proteins, and complex II of the respiratory chain, as important effectors of exercise-induced healthy ageing (Ebanks, 2021).
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Azpurua, J., El-Karim, E. G., Tranquille, M. and Dubnau, J. (2021). A behavioral screen for mediators of age-dependent TDP-43 neurodegeneration identifies SF2/SRSF1 among a group of potent suppressors in both neurons and glia.
PLoS Genet 17(11): e1009882. PubMed ID: 34723963
Summary:
Cytoplasmic aggregation of Tar-DNA/RNA binding protein 43 (TDP-43) occurs in 97 percent of amyotrophic lateral sclerosis (ALS), ~40% of frontotemporal dementia (FTD) and in many cases of Alzheimer's disease (AD). Cytoplasmic TDP-43 inclusions are seen in both sporadic and familial forms of these disorders, including those cases that are caused by repeat expansion mutations in the C9orf72 gene. To identify downstream mediators of TDP-43 toxicity, This study expressed human TDP-43 in a subset of Drosophila motor neurons. Such expression causes age-dependent deficits in negative geotaxis behavior. Using this behavioral readout of locomotion, this study conducted an shRNA suppressor screen and identified 32 transcripts whose knockdown was sufficient to ameliorate the neurological phenotype. The majority of these suppressors also substantially suppressed the negative effects on lifespan seen with glial TDP-43 expression. In addition to identification of a number of genes whose roles in neurodegeneration were not previously known, this screen also yielded genes involved in chromatin regulation and nuclear/import export - pathways that were previously identified in the context of cell based or neurodevelopmental suppressor screens. A notable example is SF2, a conserved orthologue of mammalian SRSF1, an RNA binding protein with roles in splicing and nuclear export. The identification SF2/SRSF1 as a potent suppressor of both neuronal and glial TDP-43 toxicity also provides a convergence with C9orf72 expansion repeat mediated neurodegeneration, where this gene also acts as a downstream mediator (Azpurua, 2021).
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Parkhitko, A. A., Wang, L., Filine, E., Jouandin, P., Leshchiner, D., Binari, R., Asara, J. M., Rabinowitz, J. D. and Perrimon, N. (2021). A genetic model of methionine restriction extends Drosophila health- and lifespan.
Proc Natl Acad Sci U S A 118(40). PubMed ID: 34588310
Summary:
Loss of metabolic homeostasis is a hallmark of aging and is characterized by dramatic metabolic reprogramming. To analyze how the fate of labeled methionine is altered during aging, This study applied C5-Methionine labeling to Drosophila and demonstrated significant changes in the activity of different branches of the methionine metabolism as flies age. Whether targeted degradation of methionine metabolism components would "reset" methionine metabolism flux and extend the fly lifespan was tested. Specifically, this study created transgenic flies with inducible expression of Methioninase, a bacterial enzyme capable of degrading methionine and revealed methionine requirements for normal maintenance of lifespan. Also demonstrated was the microbiota-derived methionine is an alternative and important source in addition to food-derived methionine. In this genetic model of methionine restriction (MetR), this study also demonstrate that either whole-body or tissue-specific Methioninase expression can dramatically extend Drosophila health- and lifespan and exerts physiological effects associated with MetR. Interestingly, while previous dietary MetR extended lifespan in flies only in low amino acid conditions, MetR from Methioninase expression extends lifespan independently of amino acid levels in the food. Finally, because impairment of the methionine metabolism has been previously associated with the development of Alzheimer's disease, this study compared methionine metabolism reprogramming between aging flies and a Drosophila model relevant to Alzheimer's disease, and found that overexpression of human Tau caused methionine metabolism flux reprogramming similar to the changes found in aged flies. Altogether, this study highlights Methioninase as a potential agent for health- and lifespan extension (Parkhitko, 2021).
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Landis, G. N., Hilsabeck, T. A. U., Bell, H. S., Ronnen-Oron, T., Wang, L., Doherty, D. V., Tejawinata, F. I., Erickson, K., Vu, W., Promislow, D. E. L., Kapahi, P. and Tower, J. (2021). Mifepristone Increases Life Span of Virgin Female Drosophila on Regular and High-fat Diet Without Reducing Food Intake. Front Genet 12: 751647. PubMed ID: 34659367.
Summary:
The synthetic steroid mifepristone is reported to have anti-obesity and anti-diabetic effects in mammals on normal and high-fat diets (HFD). Previous work showed that mifepristone blocks the negative effect on life span caused by mating in female Drosophila melanogaster. This study asked if mifepristone could protect virgin females from the life span-shortening effect of HFD. Mifepristone increased life span of virgin females on regular media, as well as on media supplemented with either 2.5 or 5% coconut oil. Food intake was not reduced in any assay, and was significantly increased by mifepristone in half of the assays. To ask if mifepristone might rescue virgin females from all life span-shortening stresses, the oxidative stressor paraquat was tested, and mifepristone produced little to no rescue. Analysis of extant metabolomics and transcriptomics data suggested similarities between effects of mifepristone in virgin and mated females, including reduced tryptophan breakdown and similarities to dietary restriction. Bioinformatics analysis identified candidate mifepristone targets, including transcription factors Paired and Extra-extra. In addition to shortening life span, mating also causes midgut hypertrophy and activation of the lipid metabolism regulatory factor SREBP. Mifepristone blocked the increase in midgut size caused by mating, but did not detectably affect midgut size in virgins. Finally, mating increased activity of a SREBP reporter in abdominal tissues, as expected, but reporter activity was not detectably reduced by mifepristone in either mated or virgin females. Mifepristone increases life span of virgin females on regular and HFD without reducing food intake. Metabolomics and transcriptomics analyses suggest some similar effects of mifepristone between virgin and mated females, however reduced midgut size was observed only in mated females (Landis, 2021).
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Goh, G. H., Blache, D., Mark, P. J., Kennington, W. J. and Maloney, S. K. (2021). Daily temperature cycles prolong lifespan and have sex-specific effects on peripheral clock gene expression in Drosophila melanogaster. J Exp Biol. PubMed ID: 33758022
Summary:
Circadian rhythms optimize health by coordinating the timing of physiological processes to match predictable daily environmental challenges. The circadian rhythm of body temperature is thought to be an important modulator of molecular clocks in peripheral tissues, but how daily temperature cycles impact physiological function is unclear. This study examined the effect of constant (25°C, T(CON)) and cycling (28°C/22°C during light/dark, T(CYC)) temperature paradigms on lifespan of Drosophila melanogaster, and the expression of clock genes, Heat shock protein 83 (Hsp83), Frost (Fst), and Senescence-associated protein 30 (smp-30). Male and female Drosophila housed at T(CYC) had longer median lifespans than those housed at T(CON) T(CYC) induced robust Hsp83 rhythms and rescued the age-related decrease in smp-30 expression that was observed in flies at T(CON), potentially indicating an increased capacity to cope with age-related cellular stress. Ageing under T(CON) led to a decrease in the amplitude of expression of all clock genes in the bodies of male flies, except for cyc, which was non-rhythmic, and for per and cry in female flies. Strikingly, housing under T(CYC) conditions rescued the age-related decrease in amplitude of all clock genes, and generated rhythmicity in cyc expression, in the male flies, but not the female flies. The results suggest that ambient temperature rhythms modulate Drosophila lifespan, and that the amplitude of clock gene expression in peripheral body clocks may be a potential link between temperature rhythms and longevity in male Drosophila Longevity due to T(CYC) appeared predominantly independent of clock gene amplitude in female Drosophila (Goh, 2021).
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Schroeder, S., Hofer, S. J., et al. (2021). Dietary spermidine improves cognitive function. Cell Rep 35(2): 108985. PubMed ID: 33852843
Summary:
Decreased cognitive performance is a hallmark of brain aging, but the underlying mechanisms and potential therapeutic avenues remain poorly understood. Recent studies have revealed health-protective and lifespan-extending effects of dietary spermidine, a natural autophagy-promoting polyamine. This study shows that dietary spermidine passes the blood-brain barrier in mice and increases hippocampal eIF5A hypusination and mitochondrial function. Spermidine feeding in aged mice affects behavior in homecage environment tasks, improves spatial learning, and increases hippocampal respiratory competence. In a Drosophila aging model, spermidine boosts mitochondrial respiratory capacity, an effect that requires the autophagy regulator Atg7 and the mitophagy mediators Parkin and Pink1. Neuron-specific Pink1 knockdown abolishes spermidine-induced improvement of olfactory associative learning. This suggests that the maintenance of mitochondrial and autophagic function is essential for enhanced cognition by spermidine feeding. Finally, this study showed large-scale prospective data linking higher dietary spermidine intake with a reduced risk for cognitive impairment in humans (Schroeder, 2021).
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Liang, Y., T., Piao, C., Beuschel, C. B., Toppe, D., Kollipara, L., Bogdanow, B., Maglione, M., Lutzkendorf, J., See, J. C. K., Huang, S., Conrad, T. O. F., Kintscher, U., Madeo, F., Liu, F., Sickmann, A. and Sigrist, S. J. (2021). eIF5A hypusination, boosted by dietary spermidine, protects from premature brain aging and mitochondrial dysfunction. Cell Rep 35(2): 108941. PubMed ID: 33852845
Summary:
Recent evidence indicates that the composition of the ribosome is heterogeneous and that multiple types of specialized ribosomes regulate the synthesis of specific protein subsets. In Drosophila, expression of the ribosomal RpS28 protein variants RpS28a and RpS28-like were found to preferentially occurs in the germline, a tissue resistant to aging; it significantly declines in skeletal muscle during aging. Muscle-specific overexpression of RpS28a at levels similar to those seen in the germline decreases early mortality and promotes the synthesis of a subset of proteins with known anti-aging roles, some of which have preferential expression in the germline. These findings indicate a contribution of specialized ribosomal proteins to the regulation of the muscle proteome during aging (Liang, 2021).
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Lu, Y. X., Regan, J. C., Esser, J., Drews, L. F., Weinseis, T., Stinn, J., Hahn, O., Miller, R. A., Gronke, S. and Partridge, L. (2021). A TORC1-histone axis regulates chromatin organisation and non-canonical induction of autophagy to ameliorate ageing. Elife 10. PubMed ID: 33988501
Summary:
Summary:
Age-related changes to histone levels are seen in many species. However, it is unclear whether changes to histone expression could be exploited to ameliorate the effects of ageing in multicellular organisms. This study shows that inhibition of mTORC1 by the lifespan-extending drug rapamycin increases expression of histones H3 and H4 post-transcriptionally, through eIF3-mediated translation. Elevated expression of H3/H4 in intestinal enterocytes in Drosophila alters chromatin organization, induces intestinal autophagy through transcriptional regulation, prevents age-related decline in the intestine. Importantly, it also mediates rapamycin-induced longevity and intestinal health. Histones H3/H4 regulate expression of an autophagy cargo adaptor Blue Cheese (Bchs (WDFY3 in mammals), increased expression of which in enterocytes mediates increased H3/H4-dependent healthy longevity. In mice, rapamycin treatment increases expression of histone proteins and Wdfy3 transcription, and alters chromatin organisation in the small intestine, suggesting the mTORC1-histone axis is at least partially conserved in mammals and may offer new targets for anti-ageing interventions.
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Nguyen, A. H. and Bachtrog, D. (2021). Toxic Y chromosome: Increased repeat expression and age-associated heterochromatin loss in male Drosophila with a young Y chromosome. PLoS Genet 17(4): e1009438. PubMed ID: 33886541
Summary:
Summary:
Sex-specific differences in lifespan are prevalent across the tree of life and influenced by heteromorphic sex chromosomes. In species with XY sex chromosomes, females often outlive males. Males and females can differ in their overall repeat content due to the repetitive Y chromosome, and repeats on the Y might lower survival of the heterogametic sex (toxic Y effect). This study takes advantage of the well-assembled young Y chromosome of Drosophila miranda to study the sex-specific dynamics of chromatin structure and repeat expression during aging in male and female flies. Male D. miranda have about twice as much repetitive DNA compared to females, and live shorter than females. Heterochromatin is crucial for silencing of repetitive elements, yet old D. miranda flies lose H3K9me3 modifications in their pericentromere, with heterochromatin loss being more severe during aging in males than females. Satellite DNA becomes de-repressed more rapidly in old vs. young male flies relative to females. In contrast to what is observed in D. melanogaster, it was found that transposable elements (TEs) are expressed at higher levels in male D. miranda throughout their life. Epigenetic silencing via heterochromatin formation is ineffective on the TE-rich neo-Y chromosome, presumably due to active transcription of a large number of neo-Y linked genes, resulting in up-regulation of Y-linked TEs already in young males. This is consistent with an interaction between the evolutionary age of the Y chromosome and the genomic effects of aging. These data support growing evidence that "toxic Y chromosomes" can diminish male fitness and a reduction in heterochromatin can contribute to sex-specific aging.
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Gabrawy, M. M., Khosravian, N., Morcos, G. S., Morozova, T. V., Jezek, M., Walston, J. D., Huang, W., Abadir, P. M. and Leips, J. (2022). Genome-Wide Analysis in Drosophila Reveals the Genetic Basis of Variation in Age-Specific Physical Performance and Response to ACE Inhibition. Genes (Basel) 13(1). PubMed ID: 35052483
Summary:
Despite impressive results in restoring physical performance in rodent models, treatment with renin-angiotensin system (RAS) inhibitors, such as Lisinopril, have highly mixed results in humans, likely, in part, due to genetic variation in human populations. To date, the genetic determinants of responses to drugs, such as RAS inhibitors, remain unknown. Given the complexity of the relationship between physical traits and genetic background, genomic studies which predict genotype- and age-specific responses to drug treatments in humans or vertebrate animals are difficult. Using 126 genetically distinct lines of Drosophila melanogaster, this study tested the effects of Lisinopril on age-specific climbing speed and endurance. The data show that functional response and sensitivity to Lisinopril treatment ranges from significant protection against physical decline to increased weakness depending on genotype and age. Furthermore, genome-wide analyses led to identification of evolutionarily conserved genes in the WNT signaling pathway as being significantly associated with variations in physical performance traits and sensitivity to Lisinopril treatment. Genetic knockdown of genes in the WNT signaling pathway, Axin, frizzled, nemo, and wingless, diminished or abolished the effects of Lisinopril treatment on climbing speed traits. These results implicate these genes as contributors to the genotype- and age-specific effects of Lisinopril treatment and because they have orthologs in humans, they are potential therapeutic targets for improvement of resiliency. This approach should be widely applicable for identifying genomic variants that predict age- and sex-dependent responses to any type of pharmaceutical treatment.
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Cortot, J., Farine, J. P., Ferveur, J. F. and Everaerts, C. (2022). Aging-Related Variation of Cuticular Hydrocarbons in Wild Type and Variant Drosophila melanogaster. J Chem Ecol. PubMed ID: 35022940
Summary:
The cuticle of all insects is covered with hydrocarbons which have multiple functions. Cuticular hydrocarbons (CHCs) basically serve to protect insects against environmental harm and reduce dehydration. In many species, some CHCs also act as pheromones. CHCs have been intensively studied in Drosophila species and more especially in D. melanogaster. In this species, flies produce about 40 CHCs forming a complex sex- and species-specific bouquet. The quantitative and qualitative pattern of the CHC bouquet was characterized during the first days of adult life but remains unexplored in aging flies. This study characterized CHCs during the whole-or a large period of-adult life in males and females of several wild type and transgenic lines. Both types of lines included standard and variant CHC profiles. Some of the genotypes tested in this study showed very dramatic and unexpected aging-related variation based on their early days' profile. This study provides a concrete dataset to better understand the mechanisms underlying the establishment and maintenance of CHCs on the fly cuticle. It could be useful to determine physiological parameters, including age and response to climate variation, in insects collected in the wild.
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Cheng, X., Xie, M., Luo, L., Tian, Y., Yu, G., Wu, Q., Fan, X., Yang, D., Mao, X., Gaur, U. and Yang, M. (2022). Inhibitor GSK690693 extends Drosophila lifespan via reduce AKT signaling pathway. Mech Ageing Dev 202: 111633. PubMed ID: 35065134
Summary:
Aging is a process involving physiological changes that lead to the decline of biological functions of various tissues and organs of the body. Therefore, it is crucial to find anti-aging drugs that can intervene with the changes induced because of aging and slow down the degeneration of the biological functions. Among many signaling pathways linked with aging and aging-related diseases, PI3K-AKT signaling pathway has attracted major attention in aging biology. This paper demonstrates that AKT inhibitor GSK690693 can extend lifespan in Drosophila irrespective of start of the treatment from the beginning of life or the mid-life. Effect of GSK690693 for lifespan extension has been primarily related to the improvements in oxidative resistance, intestinal integrity and increased autophagy, but not in physical activity or starvation resistance. Furthermore, GSK690693 treatment reduced the activation of AKT and ERK, consequently activating FOXO, GSK-3β and apoptosis to modulate longevity of flies. Remarkably, GSK690693 did not induce hyperglycemia after treatment. The results indicate that GSK690693 may become an effective compound for anti-aging intervention.
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Wang, Y. and Westermark, G. T. (2021). The Amyloid Forming Peptides Islet Amyloid Polypeptide and Amyloid beta Interact at the Molecular Level. Int J Mol Sci 22(20). PubMed ID: 34681811
Summary:
Epidemiological studies support a connection between the two common disorders, type-2 diabetes and Alzheimer's disease. Both conditions have local amyloid formation in their pathogenesis, and cross-seeding between islet amyloid polypeptide (IAPP) and amyloid β (Aβ) could constitute the link. The bimolecular fluorescence complementation (BiFC) assay was used to investigate the occurrence of heterologous interactions between IAPP and Aβ and to compare the potential toxic effects of IAPP/Aβ, IAPP/IAPP, and Aβ/Aβ expression in living cells. Microscopy was used to confirm the fluorescence and determine the lysosomal, mitochondrial areas and mitochondrial membrane potential, and a FACS analysis was used to determine ROS production and the role for autophagy. Drosophila melanogaster expressing IAPP and Aβ was used to study their co-deposition and effects on longevity. Co-expression of IAPP and Aβ resulted in fluorophore reconstitution to the same extent as determined for homologous IAPP/IAPP or Aβ/Aβ expression. The BiFC(+)/BiFC(-) ratio of lysosomal area calculations increased in transfected cells independent of the vector combinations, while only Aβ/Aβ expression increased mitochondrial membrane potential. Expression combinations containing Aβ were necessary for the formation of a congophilic amyloid. In Drosophila melanogaster expressing IAPP/Aβ, co-deposition of the amyloid-forming peptides caused reduced longevity. The BiFC results confirmed a heterologous interaction between IAPP and Aβ, while co-deposits in the brain of Drosophila suggest mixed amyloid aggregates.
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Ngian, Z. K., Lin, W. Q. and Ong, C. T.(2021). NELF-A controls Drosophila healthspan by regulating heat-shock protein-mediated cellular protection and heterochromatin maintenance. Aging Cell: e13348. PubMed ID: 33788376
Summary:
NELF-mediated pausing of RNA polymerase II (RNAPII) constitutes a crucial step in transcription regulation. However, it remains unclear how control release of RNAPII pausing can affect the epigenome and regulate important aspects of animal physiology like aging. This study found that NELF-A dosage regulates Drosophila healthspan: Halving NELF-A level in the heterozygous mutants or via neuronal-specific RNAi depletion improves their locomotor activity, stress resistance, and lifespan significantly. Conversely, NELF-A overexpression shortens fly lifespan drastically. Mechanistically, lowering NELF-A level facilitates the release of paused RNAPII for productive transcription of the heat-shock protein (Hsp) genes. The elevated HSPs expression in turn attenuates the accumulation of insoluble protein aggregates, reactive oxidative species, DNA damage and systemic inflammation in the brains of aging NELF-A depleted flies as compared to their control siblings. This pro-longevity effect is unique to NELF-A due to its higher expression level and more efficient pausing of RNAPII than other NELF subunits. Importantly, enhanced resistance to oxidative stress in NELF-A heterozygous mutants is highly conserved such that knocking down its level in human SH-SY5Y cells attenuates hydrogen peroxide-induced DNA damage and apoptosis. Depleting NELF-A reconfigures the epigenome through the maintenance of H3K9me2-enriched heterochromatin during aging, leading to the repression of specific retrotransposons like Gypsy-1 in the brains of NELF-A mutants. Taken together, this study showed that the dosage of neuronal NELF-A affects multiple aspects of aging in Drosophila by regulating transcription of Hsp genes in the brains, suggesting that targeting transcription elongation might be a viable therapeutic strategy against age-onset diseases like neurodegeneration.
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Sasaki, A., Nishimura, T., Takano, T., Naito, S. and Yoo, S. K.(2021). White regulates proliferative homeostasis of intestinal stem cells during ageing in Drosophila. Nat Metab 3(4): 546-557. PubMed ID: 33820991
Summary:
Tissue integrity is contingent on maintaining stem cells. Intestinal stem cells (ISCs) over-proliferate during ageing, leading to tissue dysplasia in Drosophila melanogaster. This study describes a role for white, encoding the evolutionarily conserved ATP-binding cassette transporter subfamily G, with a particularly well-characterized role in eye colour pigmentation, in ageing-induced ISC proliferation in the midgut. ISCs increase expression of white during ageing. ISC-specific inhibition of white suppresses ageing-induced ISC dysregulation and prolongs lifespan. Of the proteins that form heterodimers with White, Brown mediates ISC dysregulation during ageing. Metabolomics analyses reveal previously unappreciated, profound metabolic impacts of white inhibition on organismal metabolism. Among the metabolites affected by White, tetrahydrofolate is transported by White, is accumulated in ISCs during ageing and is indispensable for ageing-induced ISC over-proliferation. Since Thomas Morgan's isolation of a white mutant as the first Drosophila mutant, white mutants have been used extensively as genetic systems and often as controls. These findings provide insights into metabolic regulation of stem cells mediated by the classic gene white.
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Hunt, L. C. and Demontis, F. (2021). Age-Related Increase in Lactate Dehydrogenase Activity in Skeletal Muscle Reduces Lifespan in Drosophila. J Gerontol A Biol Sci Med Sci. PubMed ID: 34477202
Summary:
Metabolic adaptations occur with aging but the significance and causal roles of such changes are only partially known. In Drosophila, this study found that skeletal muscle aging is paradoxically characterized by increased readouts of glycolysis (lactate, NADH/NAD+) but reduced expression of most glycolytic enzymes. This conundrum is explained by lactate dehydrogenase (LDH), an enzyme necessary for anaerobic glycolysis and whose expression increases with aging. Experimental Ldh overexpression in skeletal muscle of young flies increases glycolysis and shortens lifespan, suggesting that age-related increases in muscle LDH contribute to mortality. Similar results are also found with overexpression of other glycolytic enzymes (Pfrx/PFKFB, Pgi/GPI). Conversely, hypomorphic mutations in Ldh extend lifespan whereas reduction in PFK, Pglym78/PGAM, Pgi/GPI, and Ald/ALDO levels shorten lifespan to various degrees, indicating that glycolysis needs to be tightly controlled for optimal aging. Altogether, these findings indicate a role for muscle LDH and glycolysis in aging.
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Feng, X., Hong, X., Fan, Q., Chen, L., Li, J., Deng, J., Gong, S., Hou, F. F. and Zhang, F. (2021). dCubilin/dAMN- mediated protein reabsorption in Drosophila nephrocytes modulates longevity. Dis Model Mech. PubMed ID: 34437681
Summary:
Aging is a multi-faceted process regulated by multiple cellular pathways, including the proteostasis network. Pharmacological or genetic enhancement of the intracellular proteostasis network extends lifespan and prevents age-related diseases. However, how proteostasis is regulated in different tissues throughout the aging process remains unclear. This study shows that Drosophila homologs for Cubilin/Amnionless (dCubilin/dAMN)-mediated protein reabsorption from hemolymph (fly equivalent of blood) by nephrocytes modulates longevity through regulating proteostasis in muscle and brain tissues in Drosophila. Overexpression of dAMN receptor in nephrocytes extends lifespan, whereas nephrocyte-specific dCubilin or dAMN RNAi knockdown results in a protein reabsorption defect and shortens lifespan in flies. dCubilin/dAMN-mediated protein reabsorption in nephrocytes regulates proteostasis in hemolymph and improves healthspan. In addition, it was shown that enhanced dCubilin/dAMN-mediated protein reabsorption in nephrocytes slows down the aging process in muscle and brain by maintaining the proteostasis network in these tissues. Furthermore, this study shows that dCubilin/dAMN -mediated protein reabsorption in nephrocytes affects proteasome activity in the whole body and muscle tissues. Altogether, this work has revealed an inter-organ communication network across nephrocytes and muscle/neuronal tissue which is essential to maintain proteostasis and to delay senescence in these organs. The findings have provided insights into the role of renal protein reabsorption in the aging process via this tele-proteostasis network.
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Saito, T., Chiku, T., Oka, M., Wada-Kakuda, S., Nobuhara, M., Oba, T., Shinno, K., Abe, S., Asada, A., Sumioka, A., Takashima, A., Miyasaka, T. and Ando, K. (2021). Disulfide bond formation in microtubule-associated tau protein promotes tau accumulation and toxicity in vivo. Hum Mol Genet. PubMed ID: 34137825
Summary:
Accumulation of microtubule-associated tau protein is thought to cause neuron loss in a group of neurodegenerative diseases called tauopathies. In diseased brains, tau molecules adopt pathological structures that propagate into insoluble forms with disease-specific patterns. Several types of posttranslational modifications in tau are known to modulate its aggregation propensity in vitro, but their influence on tau accumulation and toxicity at the whole-organism level has not been fully elucidated. This study utilized a series of transgenic Drosophila models to compare systematically the toxicity induced by five tau constructs with mutations or deletions associated with aggregation, including substitutions at seven disease-associated phosphorylation sites (S7A and S7E), deletions of PHF6 and PHF6* sequences (ΔPHF6 and ΔPHF6*), and substitutions of cysteine residues in the microtubule binding repeats (C291/322A). Substitutions and deletions resulted in different patterns of neurodegeneration and accumulation, with C291/322A having a dramatic effect on both tau accumulation and neurodegeneration. These cysteines formed disulfide bonds in mouse primary cultured neurons and in the fly retina, and stabilized tau proteins. Additionally, they contributed to tau accumulation under oxidative stress. This study also found that each of these cysteine residues contributes to the microtubule polymerization rate and microtubule levels at equilibrium, but none of them affected tau binding to polymerized microtubules. Since tau proteins expressed in the Drosophila retina are mostly present in the early stages of tau filaments self-assembly, these results suggest that disulfide bond formation by these cysteine residues could be attractive therapeutic targets.
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Wang, L. J., Hsu, T., Lin, H. L. and Fu, C. Y. (2021). Modulation of mitochondrial nucleoid structure during aging and by mtDNA content in Drosophila. Biol Open 10(6). PubMed ID: 34180963
Summary:
Mitochondrial DNA (mtDNA) encodes gene products that are essential for oxidative phosphorylation. They organize as higher order nucleoid structures (mtNucleoids) that were shown to be critical for the maintenance of mtDNA stability and integrity. While mtNucleoid structures are associated with cellular health, how they change in situ under physiological maturation and aging requires further investigation. This study investigated the mtNucleoid assembly at an ultrastructural level in situ using the TFAM-Apex2 Drosophila model. Smaller and more compact TFAM-nucleoids are populated in the mitochondria of indirect flight muscle of aged flies. Furthermore, mtDNA transcription and replication were cross-regulated in the mtTFB2-knockdown flies as in the mtRNAPol-knockdown flies that resulted in reductions in mtDNA copy numbers and nucleoid-associated TFAM. Overall, this study reveals that the modulation of TFAM-nucleoid structure under physiological aging, which is critically regulated by mtDNA content.
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Wu, K., Tang, Y., Zhang, Q., Zhuo, Z., Sheng, X., Huang, J., Ye, J., Li, X., Liu, Z. and Chen, H. (2021). Aging-related upregulation of the homeobox gene caudal represses intestinal stem cell differentiation in Drosophila. PLoS Genet 17(7): e1009649. PubMed ID: 34228720
Summary:
The differentiation efficiency of adult stem cells undergoes a significant decline in aged animals, which is closely related to the decline in organ function and age-associated diseases. However, the underlying mechanisms that ultimately lead to this observed decline of the differentiation efficiency of stem cells remain largely unclear. This study investigated Drosophila midguts and identified an obvious upregulation of caudal (cad), which encodes a homeobox transcription factor. This factor is traditionally known as a central regulator of embryonic anterior-posterior body axis patterning. This study reports that depletion of cad in intestinal stem/progenitor cells promotes quiescent intestinal stem cells (ISCs) to become activate and produce enterocytes in the midgut under normal gut homeostasis conditions. However, overexpression of cad results in the failure of ISC differentiation and intestinal epithelial regeneration after injury. Moreover, this study suggests that cad prevents intestinal stem/progenitor cell differentiation by modulating the Janus kinase/signal transducers and activators of the transcription pathway and Sox21a-GATAe signaling cascade. Importantly, the reduction of cad expression in intestinal stem/progenitor cells restrained age-associated gut hyperplasia in Drosophila. This study identified a function of the homeobox gene cad in the modulation of adult stem cell differentiation and suggested a potential gene target for the treatment of age-related diseases induced by age-related stem cell dysfunction.
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Gao, Y., Zhu, C., Li, K., Cheng, X., Du, Y., Yang, D., Fan, X., Gaur, U. and Yang, M. (2020). Comparative proteomics analysis of dietary restriction in Drosophila. PLoS One 15(10): e0240596. PubMed ID: 33064752
Summary:
To explore the underlying mechanism of dietary restriction (DR) induced lifespan extension in fruit flies at protein level, proteome sequencing was performed in Drosophila at day 7 (young) and day 42 (old) under DR and ad libitum (AL) conditions. A total of 18629 unique peptides were identified in Uniprot, corresponding to 3,662 proteins. Among them, 383 and 409 differentially expressed proteins (DEPs) were identified from comparison between DR vs AL at day 7 and 42, respectively. Bioinformatics analysis revealed that membrane-related processes, post-transcriptional processes, spliceosome and reproduction related processes, were highlighted significantly. In addition, expression of proteins involved in pathways such as spliceosomes, oxidative phosphorylation, lysosomes, ubiquitination, and riboflavin metabolism was relatively higher during DR. A relatively large number of DEPs were found to participate in longevity and age-related disease pathways. 20 proteins were identified that were consistently regulated during DR and some of which are known to be involved in ageing, such as mTORC1, antioxidant, DNA damage repair and autophagy. In the integration analysis, 15 genes were found that were stably regulated by DR at both transcriptional as well as translational levels. These results provided a useful dataset for further investigations on the mechanism of DR and aging (Gao, 2020).
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McCracken, A. W., Buckle, E. and Simons, M. J. P. (2020). The relationship between longevity and diet is genotype dependent and sensitive to desiccation in Drosophila melanogaster. J Exp Biol. PubMed ID: 33109715
Summary:
Dietary restriction (DR) is a key focus in ageing research. Specific conditions and genotypes were recently found to negate lifespan extension by DR, questioning its universal relevance. However, the concept of dietary reaction norms explains why DR's effects might be obscured in some situations. This study tested the importance of dietary reaction norms by measuring longevity and fecundity on five diets in five genotypes, with and without water supplementation in female Drosophila melanogaster (N>25,000). Substantial genetic variation was found in the response of lifespan to diet. Flies supplemented with water rescued putative desiccation stress at the richest diets, suggesting water availability can be an experimental confound. Fecundity declined at these richest diets, but was unaffected by water, and this reduction is thus most likely caused by nutritional toxicity. These results demonstrate empirically that a range of diets need to be considered to conclude an absence of the DR longevity effect (McCracken, 2020).
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Zanco, B., Mirth, C. K., Sgro, C. M. and Piper, M. D. (2021). A dietary sterol trade-off determines lifespan responses to dietary restriction in Drosophila melanogaster females. Elife 10. PubMed ID: 33494859
Summary:
Diet plays a significant role in maintaining lifelong health. In particular, lowering the dietary protein: carbohydrate ratio can improve lifespan. This has been interpreted as a direct effect of these macronutrients on physiology. Using Drosophila melanogaster, this study shows that the role of protein and carbohydrate on lifespan is indirect, acting by altering the partitioning of limiting amounts of dietary sterols between reproduction and lifespan. Shorter lifespans in flies fed on high protein: carbohydrate diets can be rescued by supplementing their food with cholesterol. Not only does this fundamentally alter the way we interpret the mechanisms of lifespan extension by dietary restriction, these data highlight the important principle that life histories can be affected by nutrient-dependent trade-offs that are indirect and independent of the nutrients (often macronutrients) that are the focus of study. This brings us closer to understanding the mechanistic basis of dietary restriction (Zanco, 2021).
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Dai, Z., Li, D., Du, X., Ge, Y., Hursh, D. A. and Bi, X. (2020). Drosophila Caliban preserves intestinal homeostasis and lifespan through regulating mitochondrial dynamics and redox state in enterocytes. PLoS Genet 16(10): e1009140. PubMed ID: 33057338
Summary:
Precise regulation of stem cell activity is crucial for tissue homeostasis. In Drosophila, intestinal stem cells (ISCs) maintain the midgut epithelium and respond to oxidative challenges. However, the connection between intestinal homeostasis and redox signaling remains obscure. This study found that Caliban (Clbn), a component of the ribosome quality control complex (RQC), functions as a regulator of mitochondrial dynamics in enterocytes (ECs) and is required for intestinal homeostasis. The clbn knock-out flies have a shortened lifespan and lose the intestinal homeostasis. Clbn is highly expressed and localizes to the outer membrane of mitochondria in ECs. Mechanically, Clbn mediates mitochondrial dynamics in ECs and removal of clbn leads to mitochondrial fragmentation, accumulation of reactive oxygen species, ECs damage, activation of JNK and JAK-STAT signaling pathways. Moreover, multiple mitochondria-related genes are differentially expressed between wild-type and clbn mutated flies by a whole-genome transcriptional profiling. Furthermore, loss of clbn promotes tumor growth in gut generated by activated Ras in intestinal progenitor cells. These findings reveal an EC-specific function of Clbn in regulating mitochondrial dynamics, and provide new insight into the functional link among mitochondrial redox modulation, tissue homeostasis and longevity (Cai, 2020).
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Cui, L., Song, W., Zeng, Y., Wu, Q., Fan, Z., Huang, T., Zeng, B., Zhang, M., Ni, Q., Li, Y., Wang, T., Li, D., Mao, X., Lian, T., Yang, D., Yang, M. and Fan, X. (2020). Deubiquitinase USP7 regulates Drosophila aging through ubiquitination and autophagy. Aging (Albany NY) 12(22): 23082-23095. PubMed ID: 33221768
Ubiquitination-mediated protein degradation is the selective degradation of diverse forms of damaged proteins that are tagged with ubiquitin, while deubiquitinating enzymes reverse ubiquitination-mediated protein degradation by removing the ubiquitin chain from the target protein. The interactions of ubiquitinating and deubiquitinating enzymes are required to maintain protein homeostasis. The ubiquitin-specific protease USP7 is a deubiquitinating enzyme that indirectly plays a role in repairing DNA damage and development. However, the mechanism of its participation in aging has not been fully explored. Regarding this issue, this study found that USP7 was necessary to maintain the normal lifespan of Drosophila melanogaster, and knockdown of dusp7 shortened the lifespan and reduced the ability of Drosophila to cope with starvation, oxidative stress and heat stress. Furthermore, this study showed that the ability of USP7 to regulate aging depends on the autophagy and ubiquitin signaling pathways. Furthermore, 2,5-dimethyl-celecoxib (DMC), a derivative of celecoxib, can partially restore the shortened lifespan and aberrant phenotypes caused by dusp7 knockdown. These results suggest that USP7 is an important factor involved in the regulation of aging, and related components in this regulatory pathway may become new targets for anti-aging treatments (Cui, 2020).
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Thompson, J. B., Su, O. O., Yang, N. and Bauer, J. H. (2020). Sleep-length differences are associated with altered longevity in the fruit fly Drosophila melanogaster. Biol Open 9(9). PubMed ID: 32938639
Summary:
Sleep deprivation has been shown to negatively impact health outcomes, leading to decreased immune responses, memory loss, increased activity of stress and inflammatory pathways, weight gain, and even behavioral changes. These observations suggest that sleep deprivation substantially interferes with important physiological functions, including metabolic pathways of energy utilization. Many of those phenotypes are correlated with age, suggesting that disrupted sleep may interfere with the aging process. However, little is known about how sleep disruption affects aging and longevity. This study investigated this relationship using eight representative fruit fly lines from the Sleep Inbred Panel (SIP). The SIP consists of 39 inbred lines that display extreme short- and long-sleep patterns, and constitutes a crucial Drosophila community resource for investigating the mechanisms of sleep regulation. The data show that flies with short-sleep periods have ∼16% longer life span, as well as reduced aging rate, compared to flies with long-sleep. In contrast, disrupting normal circadian rhythm reduces fly longevity. Short-sleep SIP flies moreover show slight metabolic differences to long-sleep lines, and to flies with disrupted circadian rhythm. These data suggest that the inbred SIP lines engage sleep mechanisms that are distinct from the circadian clock system (Thompson, 2020).
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Brengdahl, M. I., Kimber, C. M., Elias, P., Thompson, J. and Friberg, U. (2020). Deleterious mutations show increasing negative effects with age in Drosophila melanogaster. BMC Biol 18(1): 128. PubMed ID: 32993647
Summary:
In order for aging to evolve in response to a declining strength of selection with age, a genetic architecture that allows for mutations with age-specific effects on organismal performance is required. Understanding of how selective effects of individual mutations are distributed across ages is however poor. Established evolutionary theories assume that mutations causing aging have negative late-life effects, coupled to either positive or neutral effects early in life. New theory now suggests evolution of aging may also result from deleterious mutations with increasing negative effects with age, a possibility that has not yet been empirically explored. To directly test how the effects of deleterious mutations are distributed across ages, age-specific effects on fecundity were separately measure for each of 20 mutations in Drosophila melanogaster. Deleterious mutations in general were found to have a negative effect that increases with age, and the rate of increase depends on how deleterious a mutation is early in life. These findings suggest that aging does not exclusively depend on genetic variants assumed by the established evolutionary theories of aging. Instead, aging can result from deleterious mutations with negative effects that amplify with age. If increasing negative effect with age is a general property of deleterious mutations, the proportion of mutations with the capacity to contribute towards aging may be considerably larger than previously believed (Brengdahl, 2020).
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Soule, S., Mellottee, L., Arab, A., Chen, C. and Martin, J. R. (2020). Jouvence a small nucleolar RNA required in the gut extends lifespan in Drosophila. Nat Commun 11(1): 987. PubMed ID: 32080190
Summary:
Longevity is influenced by genetic and environmental factors, but the underlying mechanisms remain elusive. This study functionally characterise a Drosophila small nucleolar RNA (snoRNA), named jouvence whose loss of function reduces lifespan. The genomic region of jouvence rescues the longevity in mutant, while its overexpression in wild-type increases lifespan. Jouvence is required in enterocytes. In mutants, the epithelium of the gut presents more hyperplasia, while the overexpression of jouvence prevents it. Molecularly, the mutant lack pseudouridylation on 18S and 28S-rRNA, a function rescued by targeted expression of jouvence in the gut. A transcriptomic analysis performed from the gut reveals that several genes are either up- or down-regulated, while restoring the mRNA level of two genes (ninaD or CG6296) rescue the longevity. Since snoRNAs are structurally and functionally well conserved throughout evolution, this study identified a putative jouvence orthologue in mammals including humans, suggesting that its function in longevity could be conserved (Soule, 2020).
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Cho, L. C., Yu, C. C. and Kao, C. F. (2021). Social perception of young adults prolongs the lifespan of aged Drosophila. NPJ Aging Mech Dis 7(1): 21. PubMed ID: 34471134
Summary:
Lifespan is modulated at distinct levels by multiple factors, including genetic backgrounds, the environment, behavior traits, metabolic status, and more interestingly, sensory perceptions. However, the effects of social perception between individuals living in the same space remain less clear. This study used the Drosophila model to study the influences of social perception on the lifespan of aged fruit flies. The lifespan of aged Drosophila was found to be markedly prolonged after being co-housed with young adults of the same gender. Moreover, the changes of lifespan were affected by several experimental contexts: (1) the ratios of aged and young adults co-housed, (2) the chronological ages of two populations, and (3) the integrity of sensory modalities. Together, it is hypothesize the chemical/physical stimuli derived from the interacting young adults are capable of interfering with the physiology and behavior of aged flies, ultimately leading to the alteration of lifespan (Cho, 2021).
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Sasaki, A., Nishimura, T., Takano, T., Naito, S. and Yoo, S. K. (2020). White regulates proliferative homeostasis of intestinal stem cells during ageing in Drosophila. Nat Metab 3(4): 546-557. PubMed ID: 33820991
Summary:
Tissue integrity is contingent on maintaining stem cells. Intestinal stem cells (ISCs) over-proliferate during ageing, leading to tissue dysplasia in Drosophila melanogaster. This study describes a role for white, encoding the evolutionarily conserved ATP-binding cassette transporter subfamily G, with a particularly well-characterized role in eye colour pigmentation, in ageing-induced ISC proliferation in the midgut. ISCs increase expression of white during ageing. ISC-specific inhibition of white suppresses ageing-induced ISC dysregulation and prolongs lifespan. Of the proteins that form heterodimers with White, Brown mediates ISC dysregulation during ageing. Metabolomics analyses reveal previously unappreciated, profound metabolic impacts of white inhibition on organismal metabolism. Among the metabolites affected by White, tetrahydrofolate is transported by White, is accumulated in ISCs during ageing and is indispensable for ageing-induced ISC over-proliferation. Since Thomas Morgan's isolation of a white mutant as the first Drosophila mutant, white mutants have been used extensively as genetic systems and often as controls. These findings provide insights into metabolic regulation of stem cells mediated by the classic gene white (Sasaki, 2021).
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Wang, L. J., Hsu, T., Lin, H. L. and Fu, C. Y. (2020). Modulation of mitochondrial nucleoid structure during aging and by mtDNA content in Drosophila. Biol Open 10(6). PubMed ID: 34180963
Summary:
Mitochondrial DNA (mtDNA) encodes gene products that are essential for oxidative phosphorylation. They organize as higher order nucleoid structures (mtNucleoids) that were shown to be critical for the maintenance of mtDNA stability and integrity. While mtNucleoid structures are associated with cellular health, how they change in situ under physiological maturation and aging requires further investigation. This study investigated the mtNucleoid assembly at an ultrastructural level in situ using the TFAM-Apex2 Drosophila model. Smaller and more compact TFAM-nucleoids are populated in the mitochondria of indirect flight muscle of aged flies. Furthermore, mtDNA transcription and replication were cross-regulated in the mtTFB2-knockdown flies as in the mtRNAPol-knockdown flies that resulted in reductions in mtDNA copy numbers and nucleoid-associated TFAM. Overall, this study reveals that the modulation of TFAM-nucleoid structure under physiological aging, which is critically regulated by mtDNA content (Wang, 2021).
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Long, D. M., Frame, A. K., Reardon, P. N., Cumming, R. C., Hendrix, D. A., Kretzschmar, D. and Giebultowicz, J. M. (2020). Lactate dehydrogenase expression modulates longevity and neurodegeneration in Drosophila melanogaster. Aging (Albany NY) 12. PubMed ID: 32484787
Summary:
Lactate dehydrogenase (LDH) catalyzes the conversion of glycolysis-derived pyruvate to lactate. Lactate has been shown to play key roles in brain energetics and memory formation. However, lactate levels are elevated in aging and Alzheimer's disease patients, and it is not clear whether lactate plays protective or detrimental roles in these contexts. This study shows that Ldh transcript levels are elevated and cycle with diurnal rhythm in the heads of aged flies and this is associated with increased LDH protein, enzyme activity, and lactate concentrations. To understand the biological significance of increased Ldh gene expression, Ldh levels were genetically manipulated in adult neurons or glia. Overexpression of Ldh in both cell types caused a significant reduction in lifespan whereas Ldh down-regulation resulted in lifespan extension. Moreover, pan-neuronal overexpression of Ldh disrupted circadian locomotor activity rhythms and significantly increased brain neurodegeneration. In contrast, reduction of Ldh in neurons delayed age-dependent neurodegeneration. Thus, this unbiased genetic approach identified Ldh and lactate as potential modulators of aging and longevity in flies (Long, 2020).
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Yurkevych, I. S., Gray, L. J., Gospodaryov, D. V., Burdylyuk, N. I., Storey, K. B., Simpson, S. J. and Lushchak, O. (2020). Development of fly tolerance to consuming a high-protein diet requires physiological, metabolic and transcriptional changes. Biogerontology. PubMed ID: 32468146
Summary:
Mortality in insects consuming high-protein-and-low-carbohydrate diets resembles a type III lifespan curve with increased mortality at an early age and few survivors that live a relatively long lifespan. A Drosophila line was selected for ability to live for a long time on an imbalanced high-protein-low-carbohydrate diet by carrying out five rounds of breeding to select for the most long-lived survivors. Adaptation to this diet in the selected line was studied at the biochemical, physiological and transcriptomic levels. The selected line of flies consumed less of the imbalanced food but also accumulated more storage metabolites: glycogen, triacylglycerides, and trehalose. Selected flies also had a higher activity of alanine transaminase and a higher urea content. Adaptation of the selected line on the transcriptomic level was characterized by down-regulation of genes encoding serine endopeptidases (Jon25i, Jon25ii, betaTry, and others) but up-regulation of genes encoding proteins related to the immune system, such as antimicrobial peptides, Turandot-family humoral factors, hexamerin isoforms, and vitellogenin. These sets of down- and up-regulated genes were similar to those observed in fruit flies with suppressed juvenile hormone signaling. These data show that the physiological adaptation of fruit flies to a high-protein-low-carbohydrate diet occurs via intuitive pathways, namely a decrease in food consumption, conversion of amino acids into ketoacids to compensate for the lack of carbohydrate, and accumulation of storage metabolites to eliminate the negative effects of excess amino acids. Nevertheless, transcriptomic adaptation occurs in a counter-intuitive way, likely via an influence of gut microbiota on food digestion (Yurkevych, 2020).
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Ruzzi, L. R., Schilman, P. E., San Martin, A., Lew, S. E., Gelb, B. D. and Pagani, M. R. (2020). The Phosphatase CSW Controls Life Span by Insulin Signaling and Metabolism Throughout Adult Life in Drosophila. Front Genet 11: 364. PubMed ID: 32457793
Summary:
Noonan syndrome and related disorders are caused by mutations in genes encoding for proteins of the RAS-ERK1/2 signaling pathway, which affect development by enhanced ERK1/2 activity. However, the mutations' effects throughout adult life are unclear. This study identified that the protein most commonly affected in Noonan syndrome, the phosphatase SHP2, known in Drosophila as corkscrew (CSW), controls life span, triglyceride levels, and metabolism without affecting ERK signaling pathway. This study found that CSW loss-of-function mutations extended life span by interacting with components of the insulin signaling pathway and impairing AKT activity in adult flies. By expressing csw-RNAi in different organs, it was determined that CSW extended life span by acting in organs that regulate energy availability, including gut, fat body and neurons. In contrast to that in control animals, loss of CSW leads to reduced homeostasis in metabolic rate during activity. Clinically relevant gain-of-function csw allele reduced life span, when expressed in fat body, but not in other tissues. However, overexpression of a wild-type allele did not affect life span, showing a specific effect of the gain-of-function allele independently of a gene dosage effect. It is concluded that CSW normally regulates life span and that mutations in SHP2 are expected to have critical effects throughout life by insulin-dependent mechanisms in addition to the well-known RAS-ERK1/2-dependent developmental alterations.
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Liao, S., Amcoff, M. and Nassel, D. R. (2020). Impact of high-fat diet on lifespan, metabolism, fecundity and behavioral senescence in Drosophila. Insect Biochem Mol Biol: 103495. PubMed ID: 33171202
Summary:
Excess consumption of high-fat diet (HFD) is likely to result in obesity and increases the predisposition to associated health disorders. Drosophila melanogaster has emerged as an important model to study the effects of HFD on metabolism, gut function, behavior, and ageing. In this study, the effects of HFD on physiology and behavior of female flies was investigated at different time-points over several weeks. HFD was found to decrease lifespan, and also with age leads to accelerated decline of climbing ability in both virgins and mated flies. In virgins HFD also increased sleep fragmentation with age. Furthermore, long-term exposure to HFD results in elevated adipokinetic hormone (AKH) transcript levels and an enlarged crop with increased lipid stores. No long-term effects of HFD were detected on body mass, or levels of triacylglycerides (TAG), glycogen or glucose, although fecundity was diminished. However, one week of HFD resulted in decreased body mass and elevated TAG levels in mated flies. Finally, this study investigated the role of AKH in regulating effects of HFD during aging. Both with normal diet (ND) and HFD, Akh mutant flies displayed increased longevity compared to control flies. However, both mutants and controls showed shortened lifespan on HFD compared to ND. In flies exposed to ND, fecundity is decreased in Akh mutants compared to controls after one week, but increased after three weeks. However, HFD leads to a similar decrease in fecundity in both genotypes after both exposure times. Thus, long-term exposure to HFD increases AKH signaling, impairs lifespan and fecundity and augments age-related behavioral senescence (Liao, 2020).
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Bakalov, V., Reyes-Uribe, L., Deshpande, R., Maloy, A. L., Shapiro, S. D., Angus, D. C., Chang, C. H., Le Moyec, L., Wendell, S. G. and Kaynar, A. M. (2020). Dichloroacetate-induced metabolic reprogramming improves lifespan in a Drosophila model of surviving sepsis. PLoS One 15(11): e0241122. PubMed ID: 33151963
Summary:
Sepsis is the leading cause of death in hospitalized patients and beyond the hospital stay and these long-term sequelae are due in part to unresolved inflammation. Metabolic shift from oxidative phosphorylation to aerobic glycolysis links metabolism to inflammation and such a shift is commonly observed in sepsis under normoxic conditions. By shifting the metabolic state from aerobic glycolysis to oxidative phosphorylation, it was hypothesized that the shift would reverse unresolved inflammation and subsequently improve outcome. This study proposes that a shift from aerobic glycolysis to oxidative phosphorylation as a sepsis therapy by targeting the pathways involved in the conversion of pyruvate into acetyl-CoA via pyruvate dehydrogenase (PDH). Chemical manipulation of PDH using dichloroacetic acid (DCA) will promote oxidative phosphorylation over glycolysis and decrease inflammation. This hypothesis was tested in a Drosophila melanogaster model of surviving sepsis infected with Staphylococcus aureus. Drosophila were divided into 3 groups: unmanipulated, sham and sepsis survivors, all treated with linezolid; each group was either treated or not with DCA for one week following sepsis. Lifespan, measured gene expression of Toll, defensin, cecropin A, and drosomycin, and levels of lactate, pyruvate, acetyl-CoA was studied as well as TCA metabolites. In this model, metabolic effects of sepsis are modified by DCA with normalized lactate, TCA metabolites, and was associated with improved lifespan of sepsis survivors, yet had no lifespan effects on unmanipulated and sham flies. While Drosomycin and cecropin A expression increased in sepsis survivors, DCA treatment decreased both and selectively increased defensin (Bakalov, 2020).
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Weigelt, C. M., Sehgal, R., Tain, L. S., Cheng, J., Esser, J., Pahl, A., Dieterich, C., Gronke, S. and Partridge, L. (2020). An insulin-sensitive circular RNA that regulates lifespan in Drosophila. Mol Cell 79(2): 268-279. PubMed ID: 32592682
Summary:
Circular RNAs (circRNAs) are abundant and accumulate with age in neurons of diverse species. However, only few circRNAs have been functionally characterized, and their role during aging has not been addressed. This study uses transcriptome profiling during aging and find that accumulation of circRNAs is slowed down in long-lived insulin mutant flies. Next, the in vivo function was tested of a circRNA generated by the sulfateless gene (circSfl), which is consistently upregulated, particularly in the brain and muscle, of diverse long-lived insulin mutants. Strikingly, lifespan extension of insulin mutants is dependent on circSfl, and overexpression of circSfl alone is sufficient to extend the lifespan. Moreover, circSfl is translated into a protein that shares the N terminus and potentially some functions with the full-length Sfl protein encoded by the host gene. This study demonstrates that insulin signaling affects global circRNA accumulation and reveals an important role of circSfl during aging in vivo (Weigelt, 2020).
Circular RNAs (circRNAs) were originally identified more than 30 years ago, but for a long time they were thought to be by-products of the mRNA splicing process without a specific function; hence, they were not investigated further. Recently, circRNAs have been discovered in fungi, protists, and plants; C. elegans; Drosophila; mice; and humans. The majority of circRNA are generated by backsplicing of exons of protein-coding genes ('host genes'), and reverse complementary regions in the introns flanking circRNA-producing exons are crucial for circularization. Despite the high abundance and expression of certain circRNAs, only a few circRNAs have been functionally characterized; for instance, human CDR1as, which acts as an effective microRNA sponge. More recently, two independent reports have shown that a subset of circRNAs might be translated. circRNAs are enriched in neuronal tissues such as Drosophila heads and the mammalian brain. Furthermore, circRNAs have been shown to accumulate with age in C. elegans, in Drosophila heads and photoreceptor neurons, and in the mouse cortex and hippocampus but not in mouse heart tissue. However, a function of circRNAs in the aging process has not yet been revealed (Weigelt, 2020).
The nutrient-sensing insulin/insulin-like growth factor signaling (IIS) pathway is a key regulator of aging, metabolism, reproduction, and growth and is evolutionarily conserved from worms and flies to mice and humans. Downregulation of IIS pathway activity pharmacologically or by genetic modification extends the lifespan in C. elegans, Drosophila, and mice. In Drosophila, simultaneous knockout of three of the seven insulin-like peptides (dilp2-3,5) results in a robust lifespan extension of 30%-50% and ameliorates the age-related decline in sleep quality, suggesting that the healthspan is also extended. Proteome analysis of long-lived insulin mutants (genetic ablation of insulin-producing cells) revealed that the response to reduced insulin signaling and lifespan extension are highly tissue specific (Weigelt, 2020).
This study has characterized the functional link between circRNAs and insulin-mediated lifespan extension and aging. Tissue-specific, genome-wide, next-generation sequencing was used of wild-type and dilp2-3,5 mutant flies and hundreds of differentially expressed circRNAs were identified, including the circRNA encoded by the sulfateless (sfl) gene (hereafter referred to as circSfl). circSfl was highly upregulated in all tissues of several long-lived insulin mutants, and overexpression of circSfl alone was sufficient to extend the lifespan. Finally, evidence is provided that circSfl is translated into a small protein that may share some function with the protein encoded by the linear sfl transcripts. Importantly, overexpression of just the circSfl open reading frame (ORF) from a linear transcript was sufficient to extend longevity, implicating the protein encoded by circSfl in lifespan regulation. This study demonstrated that circRNAs are actively involved in the aging process and can influence the lifespan (Weigelt, 2020).
One of the most striking discoveries about circRNAs is the observation that they accumulate with age in neuronal tissues of diverse species. Several hypotheses regarding why circRNAs accumulate with age have been proposed. First, circRNAs are more stable compared with linear RNA molecules. Second, it has been suggested that circRNAs accumulate with age specifically in neuronal tissue because neurons are mostly post-mitotic, and, therefore, the more stable circRNAs are not degraded by proliferation or cell death. However, if this theory holds true, then circRNAs should accumulate in most tissues of the fruit fly because Drosophila is a mainly post-mitotic organism. Third, alternative splicing is increased and more error prone with age, potentially resulting in more backsplicing of circRNAs. This study showed that circRNA accumulation with age is slowed down in long-lived insulin mutants. This might point toward the third theory of why circRNAs accumulate with age and is supported by the finding that the splicing factor SFA-1 is required for dietary restriction-induced longevity in nematodes, highlighting the importance of splicing for lifespan extension upon deregulated nutrient sensing. These findings demonstrated that accumulation of circRNAs with age is malleable, suggesting that accumulation of circRNAs might be a potential aging biomarker (Weigelt, 2020).
This study identified several circRNAs that were differentially regulated in response to reduced insulin signaling in dilp 2-3,5 mutants, including circSfl. circSfl was also upregulated in two other insulin mutant flies that have an extended lifespan, and the upregulation is dependent on the dFoxo transcription factor, an essential mediator of longevity downstream of IIS. Notably, the magnitude of upregulation of circSfl in these mutants was correlated with the magnitude of the lifespan extension, with strong, up to 7-fold upregulation in the very long-lived dilp 2-3,5 mutants and only mildly upregulated in MNC-ablated flies and dFoxo overexpression flies (1.5- to 2-fold), which show a more mild lifespan extension. Similarly, the linear transcript Sfl RB was only upregulated in dilp2-3,5 mutant flies and not in the two other insulin mutants, suggesting that longevity and expression of the linear isoform can be uncoupled. Interestingly, neither circSfl nor the linear Sfl isoforms are upregulated upon rapamycin treatment or dietary restriction or in mth1 mutant flies, suggesting that upregulation of circSfl is not a general hallmark of lifespan-extending interventions in flies but specific to IIS-mediated longevity (Weigelt, 2020).
To overexpress circRNAs in vivo, different UAS constructs were tested. As expected, overexpression of the circRNA exon without its flanking introns did not lead to increased circRNA expression because flanking introns are required for biogenesis of circRNAs. In contrast, introducing reverse complementary matching flanking introns strongly increased biogenesis of circRNAs in vivo. These results are in line with previous studies that expressed circRNAs by engineering reverse complementary introns in zebrafish and in vitro. However, the first study that overexpressed a circRNA (circMbl) in vivo in Drosophila used a minigene construct including the circMbl exon and around 100 bp of the natural flanking introns but no inverted repeats. CircMbl overexpression led to a 4-fold increase in the circMbl expression level, much less than the strong overexpression achieved by engineered flanking introns. In summary, the mutants demonstrate that circRNAs can be efficiently overexpressed in Drosophila using engineered, reverse complementary matches in flanking introns that increase circRNA biogenesis in vivo (Weigelt, 2020).
Furthermore, sflΔex2 mutant flies were generated that lacked the Sfl RA-specific exon 2, and it was demonstrated that circSfl biogenesis is dependent on Sfl RA. Combination of sflΔex2 mutants with dilp 2-3,5 mutants revealed that the lifespan extension of dilp 2-3,5 mutants is partly dependent on the presence of this exon. The biogenesis of circRNAs is poorly understood, but several RNA binding proteins have been shown recently to inhibit or promote circularization, including Muscleblind, Quaking, and Adar1. It is tempting to speculate that an RNA binding protein might bind to the Sfl RA-specific exon and promote biogenesis of circSfl, which is abolished in sflΔex2 mutant flies. Because sflΔex2 mutants affect biogenesis of circSfl and expression of the linear Sfl RA isoform, it is currently not possible to formally exclude a role of the linear splice variant in insulin-mediated longevity. However, several lines of evidence suggest circSfl as the causal factor in this context. First, although Sfl RA expression was lost in sflΔex2 mutants, overall expression of linear Sfl was not affected. This is consistent with the finding that Sfl protein levels were not changed in dilp 2-3,5 mutant flies despite differential alternative splicing of the RA and RB isoforms. Thus, modifying exon 2 expression levels does not seem to affect Sfl protein levels, which can affect the lifespan. In addition, overexpression of circSfl and a linear transcript encoding the circSfl protein was sufficient to extend the lifespan, directly linking circSfl expression with longevity regulation. Given that most circRNAs are embedded in a host gene, generation of specific circRNA mutants that do not affect the host gene has been very challenging in the field. Because siRNA-mediated knockdown was not efficient in the case of circSfl, in new strategies should be tested in the future (e.g., by modification or deletion of the flanking introns that affect circRNA biogenesis), which can then be used to verify the hypothesis (Weigelt, 2020).
This study presented several lines of evidence showing that circSfl might be translated into a protein that is identical to the N terminus arising from linear Sfl transcripts. Sequence homology analysis showed that the in-frame stop codon after the circRNA-specific backsplice junction is conserved within Drosophila species that are separated by 10-20 million years of evolution, suggesting that the protein encoded by circSfl might also be conserved between these species. However, the identical stop codon could not be detected in more distantly related insect species, like honeybees or mosquitoes, which could indicate that the circlSfl protein is specific to Drosophila species or that other stop codons more downstream are used in other insects. A previous study identified 37 potentially translated circRNAs in Drosophila using ribosome footprinting on wild-type Drosophila heads; however, they failed to detect circSfl. Similarly, in the polysome profiling experiment, only very few circSfl reads were detected in wild-type fat bodies. In contrast, in dilp 2-3,5 mutant fat bodies, circSfl was one of the most abundant circRNAs, consistent with the insulin-dependent increase in circSfl transcript and protein levels. Furthermore, this study has shown that the protein encoded by circSfl and the protein arising from the linear Sfl transcripts can positively affect the lifespan of flies. This finding might indicate that both proteins affect the lifespan through overlapping mechanisms or by interacting with each other. Because the protein encoded by circSfl lacks the catalytic domain, it is unlikely that it acts as an active enzyme. Thus, circSfl may interact with proteins similar to the Sfl full-length protein in the cytoplasm or the membrane. For example, one could imagine that circSfl might interact with a repressor of the Sfl full-length protein, promoting the activity of Sfl and extending the lifespan. Alternatively, the truncated circSfl protein could also act as a dominant-negative protein because Sfl overexpression has also been suggested to cause a loss-of-function phenotype. Noteworthy is that overexpression of circSfl and Sfl caused tissue-specific effects on longevity, which could indicate that they work via different mechanisms or that different expression levels in different tissues are needed for the beneficial effects of the two proteins on lifespan. Interestingly, overexpression of circSfl and Sfl only extended the female but not the male lifespan despite upregulation of circSfl in dilp2-3,5 mutant males. This might reflect the gender bias in insulin-mediated longevity, in which females often show stronger effects than males (Weigelt, 2020).
The sfl gene in Drosophila encodes an Ndst and catalyzes synthesis of heparan sulfate (a glycosaminoglycan) by sulfation of the N and 6-O position of GlcNAc. Heparan sulfate is essential for wingless and fibroblast growth factor (FGF) receptor signaling, and full knockout of sfl is embryonic lethal. Sfl has been suggested to be localized to the Golgi apparatus and may be involved in the unfolded protein response. Furthermore, knockdown of Sfl increased the autophagy machinery and ubiquitinated proteins and reduced the climbing ability of flies, suggesting that Sfl is required for protein homeostasis and health. Similarly, this study has demonstrated that neuron-specific knockdown of Sfl is detrimental for the lifespan but that neuron-specific overexpression of Sfl extends the lifespan. Furthermore, this suty demonstrated, by genetic epistasis experiments, that Dally might contribute to the Sfl-mediated lifespan extension. Previous studies have demonstrated that overexpression of Sfl increases heparan sulfate levels and disrupts normal Wingless (Wg) and Decapentaplegic (Dpp) signaling, with the latter being controlled by Dally. However, similar to Sfl, the role of Dally has been characterized extensively during development but has not yet been implicated in aging (Weigelt, 2020).
In summary, this study demonstrated that neuronal circRNA accumulation with age is malleable and reduced in long-lived insulin mutants. Furthermore, this study established an efficient method to overexpress circRNAs in vivo by using reverse complementary introns. Interestingly, this study showed that a single circRNA (circSfl) can extend the lifespan in Drosophila. It is proposed that circSfl is translated into a protein that shares the same N terminus with the full-length protein arising from linear transcripts and potentially similar functions. This study will help to further elucidate the molecular mechanisms underlying longevity and provides unique insights into the in vivo function of circRNAs (Weigelt, 2020).
A limitation of this study is that it is currently unclear whether the circRNA-derived peptide and the full-length Sfl protein affect the lifespan by the same or by independent mechanisms. Lifespan extension by the full-length Sfl protein is dependent on its direct downstream target, the Dally protein. Thus, to address whether lifespan extension upon circSfl overexpression works in a similar way and also requires Dally, epistasis experiments were performed by co-overexpression of the circSfl protein and dally RNAi and the lifespan of these flies was measured. These experiments had to be terminated because of the current coronavirus crisis. In the future, it will be very interesting to further elucidate the mechanism of lifespan extension by circSfl and Sfl using genetic epistasis experiments (Weigelt, 2020).
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Veselkina, E. R., Trostnikov, M. V., Roshina, N. V. and Pasyukova, E. G. (2023). The Effect of the Tau Protein on D. melanogaster Lifespan Depends on GSK3 Expression and Sex. Int J Mol Sci 24(3). PubMed ID: 36768490
Summary:
The microtubule-associated conserved protein tau has attracted significant attention because of its essential role in the formation of pathological changes in the nervous system, which can reduce longevity. The study of the effects caused by tau dysfunction and the molecular mechanisms underlying them is complicated because different forms of tau exist in humans and model organisms, and the changes in protein expression can be multidirectional. This article shows that an increase in the expression of the main isoform of the Drosophila melanogaster Tau protein in the nervous system has differing effects on lifespan depending on the sex of individuals but has no effect on the properties of the nervous system, in particular, the synaptic activity and distribution of another microtubule-associated protein, Futsch, in neuromuscular junctions. Reduced expression of tau in the nervous system does not affect the lifespan of wild-type flies, but it does increase the lifespan dramatically shortened by overexpression of the shaggy gene encoding the GSK3 (Glycogen Synthase Kinase 3) protein kinase, which is one of the key regulators of tau phosphorylation levels. This effect is accompanied by the normalization of the Futsch protein distribution impaired by shaggy overexpression. The results presented in this article demonstrate that multidirectional changes in tau expression can lead to effects that depend on the sex of individuals and the expression level of GSK3.
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Sheng, L., Shields, E. J., Gospocic, J., Sorida, M., Ju, L., Byrns, C. N., Carranza, F., Berger, S. L., Bonini, N. and Bonasio, R. (2023). Ensheathing glia promote increased lifespan and healthy brain aging. Aging Cell: e13803. PubMed ID: 36840361
Summary:
Glia have an emergent role in brain aging and disease. In the Drosophila melanogaster brain, ensheathing glia function as phagocytic cells and respond to acute neuronal damage, analogous to mammalian microglia. Changes in glia composition over the life of ants and fruit flies have been reported, including a decline in the relative proportion of ensheathing glia with time. How these changes influence brain health and life expectancy is unknown. This study shows that ensheathing glia but not astrocytes decrease in number during Drosophila melanogaster brain aging. The remaining ensheathing glia display dysregulated expression of genes involved in lipid metabolism and apoptosis, which may lead to lipid droplet accumulation, cellular dysfunction, and death. Inhibition of apoptosis rescued the decline of ensheathing glia with age, improved the neuromotor performance of aged flies, and extended lifespan. Furthermore, an expanded ensheathing glia population prevented amyloid-beta accumulation in a fly model of Alzheimer's disease and delayed the premature death of the diseased animals. These findings suggest that ensheathing glia play a vital role in regulating brain health and animal longevity.
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Sidisky, J. M., de Paula Moreira, D., Okumus, M., Caratenuto, R., Drost, C., Connors, B., Hussain, S., Alkhatib, S. and Babcock, D. T. (2023). Genome-wide analysis reveals novel regulators of synaptic maintenance in Drosophila. Genetics 223(4). PubMed ID: 36799927
Summary:
Maintaining synaptic communication is required to preserve nervous system function as an organism ages. While much work has been accomplished to understand synapse formation and development, Relatively little is understood regarding maintaining synaptic integrity throughout aging. To better understand the mechanisms responsible for maintaining synaptic structure and function, an unbiased forward genetic screen was performed to identify genes required for synapse maintenance of adult Drosophila neuromuscular junctions. Using flight behavior as a screening tool, this study evaluated flight ability in 198 lines from the Drosophila Genetic Reference Panel to identify single nucleotide polymorphisms (SNPs) that are associated with a progressive loss of flight ability with age. Among the many candidate genes identified from this screen, this study focussed on 10 genes with clear human homologs harboring SNPs that are most highly associated with synaptic maintenance. Functional validation of these genes using mutant alleles revealed a progressive loss of synaptic structural integrity. Tissue-specific knockdown of these genes using RNA interference (RNAi) uncovered important roles for these genes in either presynaptic motor neurons, postsynaptic muscles, or associated glial cells, highlighting the importance of each component of tripartite synapses. These results offer greater insight into the mechanisms responsible for maintaining structural and functional integrity of synapses with age.
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Li, Q., Wang, L., Cao, Y., Wang, X., Tang, C. and Zheng, L. (2023). Stable Expression of dmiR-283 in the Brain Promises Positive Effects in Endurance Exercise on Sleep-Wake Behavior in Aging Drosophila. Int J Mol Sci 24(4). PubMed ID: 36835595
Summary:
Sleep-wake stability is imbalanced with natural aging, and microRNAs (miRNAs) play important roles in cell proliferation, apoptosis, and aging; however, the biological functions of miRNAs in regulating aging-related sleep-wake behavior remain unexplored. This study varied the expression pattern of dmiR-283 in Drosophila and the result showed that the aging decline in sleep-wake behavior was caused by the accumulation of brain dmiR-283 expression, whereas the core clock genes cwo and Notch signaling pathway might be suppressed, which regulate the aging process. In addition, to identify exercise intervention programs of Drosophila that promote healthy aging, mir-283SP/+ (mir-23SP referes to mir-283sponge) and Pdf > mir-283SP flies were driven to perform endurance exercise for a duration of 3 weeks starting at 10 and 30 days, respectively. The results showed that exercise starting in youth leads to an enhanced amplitude of sleep-wake rhythms, stable periods, increased activity frequency upon awakening, and the suppression of aging brain dmiR-283 expression in mir-283SP/+ middle-aged flies. Conversely, exercise performed when the brain dmiR-283 reached a certain accumulation level showed ineffective or negative effects. In conclusion, the accumulation of dmiR-283 expression in the brain induced an age-dependent decline in sleep-wake behavior. Endurance exercise commencing in youth counteracts the increase in dmiR-283 in the aging brain, which ameliorates the deterioration of sleep-wake behavior during aging.
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Dyson, A., Ryan, M., Garg, S., Evans, D. G. and Baines, R. A. (2022). Loss of NF1 in Drosophila larvae causes tactile hypersensitivity and impaired synaptic transmission at the neuromuscular junction. J Neurosci. PubMed ID: 36344265
Summary:
Mechanisms underlying the depletion of NAD(+) and accumulation of reactive oxygen species (ROS) in aging and age-related disorders remain poorly defined. This study shows that reverse electron transfer (RET) at mitochondrial complex I, which causes increased ROS production and NAD(+) to NADH conversion and thus lowered NAD(+) /NADH ratio, is active during aging. Genetic or pharmacological inhibition of RET decreases ROS production and increases NAD(+) /NADH ratio, extending the lifespan of normal flies. The lifespan-extending effect of RET inhibition is dependent on NAD(+) -dependent Sirtuin, highlighting the importance of NAD(+) /NADH rebalance, and on longevity-associated Foxo and autophagy pathways. RET and RET-induced ROS and NAD(+) /NADH ratio changes are prominent in human induced pluripotent stem cell (iPSC) model and fly models of Alzheimer's disease (AD). Genetic or pharmacological inhibition of RET prevents the accumulation of faulty translation products resulting from inadequate ribosome-mediated quality control, rescues relevant disease phenotypes, and extends the lifespan of Drosophila and mouse AD models. Deregulated RET is therefore a conserved feature of aging, and inhibition of RET may open new therapeutic opportunities in the context of aging and age-related diseases including AD.
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Jauregui-Lozano, J., McGovern, S. E., Bakhle, K. M., Hagins, A. C. and Weake, V. M. (2023). Establishing the contribution of active histone methylation marks to the aging transcriptional landscape of Drosophila photoreceptors. Sci Rep 13(1): 5105. PubMed ID: 36991154
Summary:
Studies in multiple organisms have shown that aging is accompanied by several molecular phenotypes that include dysregulation of chromatin. Since chromatin regulates DNA-based processes such as transcription, alterations in chromatin modifications could impact the transcriptome and function of aging cells. In flies, as in mammals, the aging eye undergoes changes in gene expression that correlate with declining visual function and increased risk of retinal degeneration. However, the causes of these transcriptome changes are poorly understood. This study profiled chromatin marks associated with active transcription in the aging Drosophila eye to understand how chromatin modulates transcriptional outputs. Both H3K4me3 and H3K36me3 globally decrease across all actively expressed genes with age. However, no correlation was found with changes in differential gene expression. Downregulation of the H3K36me3 methyltransferase Set2 in young photoreceptors revealed significant changes in splicing events that overlapped significantly with those observed in aging photoreceptors. These overlapping splicing events impacted multiple genes involved in phototransduction and neuronal function. Since proper splicing is essential for visual behavior, and because aging Drosophila undergo a decrease in visual function, these data suggest that H3K36me3 could play a role in maintaining visual function in the aging eye through regulating alternative splicing.
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Frame, A. K., Robinson, J. W., Mahmoudzadeh, N. H., Tennessen, J. M., Simon, A. F. and Cumming, R. C. (2023). Genome-wide analysis reveals novel regulators of synaptic maintenance in Drosophila. Genetics 223(4). PubMed ID: 36799927
Summary:
The astrocyte-neuron lactate shuttle hypothesis posits that glial-generated lactate is transported to neurons to fuel metabolic processes required for long-term memory. Although studies in vertebrates have revealed that lactate shuttling is important for cognitive function, it is uncertain if this form of metabolic coupling is conserved in invertebrates or is influenced by age. Lactate dehydrogenase (Ldh) is a rate limiting enzyme that interconverts lactate and pyruvate. This study genetically manipulated expression of Drosophila melanogaster Lactate dehydrogenase (dLdh) in neurons or glia to assess the impact of altered lactate metabolism on invertebrate aging and long-term courtship memory at different ages. Survival, negative geotaxis, brain neutral lipids (the core component of lipid droplets) and brain metabolites were also examined. Both upregulation and downregulation of dLdh in neurons resulted in decreased survival and memory impairment with age. Glial downregulation of dLdh expression caused age-related memory impairment without altering survival, while upregulated glial dLdh expression lowered survival without disrupting memory. Both neuronal and glial dLdh upregulation increased neutral lipid accumulation. Evidence is provided that altered lactate metabolism with age affects the tricarboxylic acid (TCA) cycle, 2-hydroxyglutarate (2HG), and neutral lipid accumulation. Collectively, these findings indicate that the direct alteration of lactate metabolism in either glia or neurons affects memory and survival but only in an age-dependent manner.
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Hanson, M. A. and Lemaitre, B. (2023). Antimicrobial peptides do not directly contribute to aging in Drosophila, but improve lifespan by preventing dysbiosis. Dis Model Mech. PubMed ID: 36847474
Summary:
Antimicrobial peptides (AMPs) are innate immune effectors first studied for their role in host defense. Recent studies have implicated these peptides in the clearance of aberrant cells and in neurodegenerative syndromes. In Drosophila, many AMPs are produced downstream of Toll and Imd NF-κB pathways upon infection. Upon aging, AMPs are upregulated, drawing attention to these molecules as possible causes of age-associated inflammatory diseases. However, functional studies overexpressing or silencing these genes have been inconclusive. Using an isogenic set of AMP gene deletions, this study investigated the net impact of AMPs on aging. Overall, no major effect of individual AMPs on lifespan was found, with the possible exception of Defensin. However, ΔAMP14 flies lacking seven AMP gene families display reduced lifespan. Increased bacterial load in the food of aged ΔAMP14 flies suggests their lifespan reduction is due to microbiome dysbiosis, consistent with a previous study. Moreover, germ-free conditions extends the lifespan of ΔAMP14 flies. Overall, these results do not point to an overt role of individual AMPs in lifespan. Instead, this study found that AMPs collectively impact lifespan by preventing dysbiosis during aging.
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Pant, A., Melkani, Y. and Melkani, G. (2023). Automated evaluation of cardiac contractile dynamics and aging prediction using machine learning in a Drosophila model. Res Sq. PubMed ID: 36993511
Summary:
The Drosophila model has proven tremendously powerful for understanding pathophysiological bases of several human disorders including aging and cardiovascular disease. Relevant high-speed imaging and high-throughput lab assays generate large volumes of high-resolution videos, necessitating next-generation methods for rapid analysis. This study presents a platform for deep learning-assisted segmentation applied to optical microscopy of Drosophila hearts and the first to quantify cardiac physiological parameters during aging. An experimental test dataset is used to validate a Drosophila aging model. Then two novel methods were used to predict fly aging: deep-learning video classification and machine-learning classification via cardiac parameters. Both models suggest excellent performance, with an accuracy of 83.3% (AUC 0.90) and 77.1% (AUC 0.85), respectively. Furthermore, beat-level dynamics are reported for predicting the prevalence of cardiac arrhythmia. The presented approaches can expedite future cardiac assays for modeling human diseases in Drosophila and can be extended to numerous animal/human cardiac assays under multiple conditions. Significance Current analysis of Drosophila cardiac recordings is capable of limited cardiac physiological parameters and are error-prone and time-consuming. This study presents the first deep-learning pipeline for high-fidelity automatic modeling of Drosophila contractile dynamics. Methods are presented for automatically calculating all relevant parameters for diagnosing cardiac performance in aging model. Using the machine and deep learning age-classification approach, aging hearts can be predicted with an accuracy of 83.3% (AUC 0.90) and 77.1% (AUC 0.85), respectively.
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Zakharenko, L. P., Petrovskii, D. V., Bobrovskikh, M. A., Gruntenko, N. E., Yakovleva, E. Y., Markov, A. V. and Putilov, A. A. (2023). Motus Vita Est: Fruit Flies Need to Be More Active and Sleep Less to Adapt to Either a Longer or Harder Life. Clocks Sleep 5(1): 98-115. PubMed ID: 36975551
Summary:
Activity plays a very important role in keeping bodies strong and healthy, slowing senescence, and decreasing morbidity and mortality. Drosophila models of evolution under various selective pressures can be used to examine whether increased activity and decreased sleep duration are associated with the adaptation of this nonhuman species to longer or harder lives. For several years, descendants of wild flies were reared in a laboratory without and with selection pressure. To maintain the "salt" and "starch" strains, flies from the wild population (called "control") were reared on two adverse food substrates. The "long-lived" strain was maintained through artificial selection for late reproduction. The 24 h patterns of locomotor activity and sleep in flies from the selected and unselected strains (902 flies in total) were studied in constant darkness for at least, 5 days. Compared to the control flies, flies from the selected strains demonstrated enhanced locomotor activity and reduced sleep duration. The most profound increase in locomotor activity was observed in flies from the starch (short-lived) strain. Additionally, the selection changed the 24 h patterns of locomotor activity and sleep. For instance, the morning and evening peaks of locomotor activity were advanced and delayed, respectively, in flies from the long-lived strain. Flies become more active and sleep less in response to various selection pressures. These beneficial changes in trait values might be relevant to trade-offs among fitness-related traits, such as body weight, fecundity, and longevity.
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Yang, D., Xiao, F., Li, J., Wang, S., Fan, X., Ni, Q., Li, Y., Zhang, M., Yan, T., Yang, M. and He, Z. (2023). Age-related ceRNA networks in adult Drosophila ageing. Front Genet 14: 1096902. PubMed ID: 36926584
Summary:
As Drosophila is an extensively used genetic model system, understanding of its regulatory networks has great significance in revealing the genetic mechanisms of ageing and human diseases. Competing endogenous RNA (ceRNA)-mediated regulation is an important mechanism by which circular RNAs (circRNAs) and long non-coding RNAs (lncRNAs) regulate ageing and age-related diseases. However, extensive analyses of the multiomics (circRNA/miRNA/mRNA and lncRNA/miRNA/mRNA) characteristics of adult Drosophila during ageing have not been reported. This study, differentially expressed circRNAs and microRNAs (miRNAs) between 7 and 42-day-old flies were screened and identified. Then, the differentially expressed mRNAs, circRNAs, miRNAs, and lncRNAs between the 7- and 42-day old flies were analysed to identify age-related circRNA/miRNA/mRNA and lncRNA/miRNA/mRNA networks in ageing Drosophila. Several key ceRNA networks were identified, such as the dme_circ_0009500/dme_miR-289-5p/CG31064, dme_circ_0009500/dme_miR-289-5p/frizzled, dme_circ_0009500/dme_miR-985-3p/Abl, and XLOC_027736/dme_miR-985-3p/Abl XLOC_189909/dme_miR-985-3p/Abl networks. Furthermore, real-time quantitative PCR (qPCR) was used to verify the expression level of those genes. Those results suggest that the discovery of these ceRNA networks in ageing adult Drosophila provide new information for research on human ageing and age-related diseases.
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Wei, J. J., Li, X. J., Liu, W., Chai, X. J., Zhu, X. Y., Sun, P. H., Liu, F., Zhao, Y. K., Huang, J. L., Liu, Y. F. and Zhao, S. T. (2023). Eucommia Polysaccharides Ameliorate Aging-Associated Gut Dysbiosis: A Potential Mechanism for Life Extension in Drosophila. Int J Mol Sci 24(6). PubMed ID: 36982954
Summary:
The gut microbiota is increasingly considered to play a key role in human immunity and health. The aging process alters the microbiota composition, which is associated with inflammation, reactive oxygen species (ROS), decreased tissue function, and increased susceptibility to age-related diseases. It has been demonstrated that plant polysaccharides have beneficial effects on the gut microbiota, particularly in reducing pathogenic bacteria abundance and increasing beneficial bacteria populations. However, there is limited evidence of the effect of plant polysaccharides on age-related gut microbiota dysbiosis and ROS accumulation during the aging process. To explore the effect of Eucommiae polysaccharides (EPs) on age-related gut microbiota dysbiosis and ROS accumulation during the aging process of Drosophila, a series of behavioral and life span assays of Drosophila with the same genetic background in standard medium and a medium supplemented with EPs were performed. Next, the gut microbiota composition and protein composition of Drosophila in standard medium and the medium supplemented with EPs were detected using 16S rRNA gene sequencing analysis and quantitative proteomic analysis. This study shows that supplementation of Eucommiae polysaccharides (EPs) during development leads to the life span extension of Drosophila. Furthermore, EPs decreased age-related ROS accumulation and suppressed Gluconobacter, Providencia, and Enterobacteriaceae in aged Drosophila. Increased Gluconobacter, Providencia, and Enterobacteriaceae in the indigenous microbiota might induce age-related gut dysfunction in Drosophila and shortens their life span. This study demonstrates that EPs can be used as prebiotic agents to prevent aging-associated gut dysbiosis and reactive oxidative stress.
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Li, H., Yu, Z., Niu, Z., Cheng, Y., Wei, Z., Cai, Y., Ma, F., Hu, L., Zhu, J. and Zhang, W. (2023). A neuroprotective role of Ufmylation through Atg9 in the aging brain of Drosophila. Cell Mol Life Sci 80(5): 129. PubMed ID: 37086384
Summary:
Ufmylation is a recently identified small ubiquitin-like modification, whose biological function and relevant cellular targets are poorly understood. This study presents evidence of a neuroprotective role for Ufmylation involving Autophagy-related gene 9 (Atg9) during Drosophila aging. The Ufm1 system ensures the health of aged neurons via Atg9 by coordinating autophagy and mTORC1, and maintaining mitochondrial homeostasis and JNK (c-Jun N-terminal kinase) activity. Neuron-specific expression of Atg9 suppresses the age-associated movement defect and lethality caused by loss of Ufmylation. Furthermore, Atg9 is identified as a conserved target of Ufm1 conjugation mediated by Ddrgk1, a critical regulator of Ufmylation. Mammalian Ddrgk1 was shown to be indispensable for the stability of endogenous Atg9A protein in mouse embryonic fibroblast (MEF) cells. Taken together, these findings might have important implications for neurodegenerative diseases in mammals.
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Sanchez, J. A., Ingaramo, M. C., Gerve, M. P., Thomas, M. G., Boccaccio, G. L. and Dekanty, A. (2023). FOXO-mediated repression of Dicer1 regulates metabolism, stress resistance, and longevity in Drosophila. Proc Natl Acad Sci U S A 120(15): e2216539120. PubMed ID: 37014862
Summary:
The adipose tissue plays a crucial role in metabolism and physiology, affecting animal lifespan and susceptibility to disease. This study presents evidence that adipose Dicer1 (Dcr-1), a conserved type III endoribonuclease involved in miRNA processing, plays a crucial role in the regulation of metabolism, stress resistance, and longevity. The results indicate that the expression of Dcr-1 in murine 3T3L1 adipocytes is responsive to changes in nutrient levels and is subject to tight regulation in the Drosophila fat body, analogous to human adipose and hepatic tissues, under various stress and physiological conditions such as starvation, oxidative stress, and aging. The specific depletion of Dcr-1 in the Drosophila fat body leads to changes in lipid metabolism, enhanced resistance to oxidative and nutritional stress, and is associated with a significant increase in lifespan. Moreover, mechanistic evidence is provided showing that the JNK-activated transcription factor FOXO binds to conserved DNA-binding sites in the dcr-1 promoter, directly repressing its expression in response to nutrient deprivation. These findings emphasize the importance of FOXO in controlling nutrient responses in the fat body by suppressing Dcr-1 expression. This mechanism coupling nutrient status with miRNA biogenesis represents a novel and previously unappreciated function of the JNK-FOXO axis in physiological responses at the organismal level.
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Hagedorn, E., Bunnell, D., Henschel, B., Smith, D. L., Dickinson, S., Brown, A. W., De Luca, M., Turner, A. N. and Chtarbanova, S. (2023). RNA virus-mediated changes in organismal oxygen consumption rate in young and old Drosophila melanogaster males. Aging (Albany NY) 15(6): 1748-1767. PubMed ID: 36947702
Summary:
Aging is accompanied by increased susceptibility to infections including with viral pathogens resulting in higher morbidity and mortality among the elderly. Significant changes in host metabolism can take place following virus infection. Efficient immune responses are energetically costly, and viruses divert host molecular resources to promote their own replication. Virus-induced metabolic reprogramming could impact infection outcomes, however, how this is affected by aging and impacts organismal survival remains poorly understood. RNA virus infection of Drosophila melanogaster with Flock House virus (FHV) is an effective model to study antiviral responses with age, where older flies die faster than younger flies due to impaired disease tolerance. Using this aged host-virus model, longitudinal, single-fly respirometry studies were conducted to determine if metabolism impacts infection outcomes. Analysis using linear mixed models on Oxygen Consumption Rate (OCR) following the first 72-hours post-infection showed that FHV modulates respiration, but age has no significant effect on OCR. However, the longitudinal assessment revealed that OCR in young flies progressively and significantly decreases, while OCR in aged flies remains constant throughout the three days of the experiment. Furthermore, it was found that the OCR signature at 24-hours varied in response to both experimental treatment and survival status. FHV-injected flies that died prior to 48- or 72-hours measurements had a lower OCR compared to survivors at 48-hours. These findings suggest the host's metabolic profile could influence the outcome of viral infections.
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Golubev, D. A., Zemskaya, N. V., Gorbunova, A. A., Kukuman, D. V., Moskalev, A. and Shaposhnikov, M. V. (2023). Studying the Geroprotective Properties of YAP/TAZ Signaling Inhibitors on Drosophila melanogaster Model. Int J Mol Sci 24(6). PubMed ID: 36983079
Summary:
The transcriptional coactivators Yes-associated protein (YAP) and transcriptional coactivator with PDZ-binding motif (TAZ) are the main downstream effectors of the evolutionarily conserved Hippo signaling pathway. YAP/TAZ are implicated in the transcriptional regulation of target genes that are involved in a wide range of key biological processes affecting tissue homeostasis and play dual roles in the aging process, depending on the cellular and tissue context. The aim of the present study was to investigate whether pharmacological inhibitors of Yap/Taz increase the lifespan of Drosophila melanogaster. Real-time qRT-PCR was performed to measure the changes in the expression of Yki (Yorkie, the Drosophila homolog of YAP/TAZ) target genes. This study has revealed a lifespan-increasing effect of YAP/TAZ inhibitors that was mostly associated with decreased expression levels of the wg and E2f1 genes. However, further analysis is required to understand the link between the YAP/TAZ pathway and aging.
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Onuma, T., Yamauchi, T., Kosakamoto, H., Kadoguchi, H., Kuraishi, T., Murakami, T., Mori, H., Miura, M. and Obata, F. (2023). Recognition of commensal bacterial peptidoglycans defines Drosophila gut homeostasis and lifespan. PLoS Genet 19(4): e1010709. PubMed ID: 37023169
Summary:
Commensal microbes in animals have a profound impact on tissue homeostasis, stress resistance, and ageing. Previous work has shown in Drosophila melanogaster that Acetobacter persici is a member of the gut microbiota that promotes ageing and shortens fly lifespan. However, the molecular mechanism by which this specific bacterial species changes lifespan and physiology remains unclear. The difficulty in studying longevity using gnotobiotic flies is the high risk of contamination during ageing. To overcome this technical challenge, a bacteria-conditioned diet was used, enriched with bacterial products and cell wall components. This study demonstrated that an A. persici-conditioned diet shortens lifespan and increases intestinal stem cell (ISC) proliferation. Feeding adult flies a diet conditioned with A. persici, but not with Lactiplantibacillus plantarum, can decrease lifespan but increase resistance to paraquat or oral infection of Pseudomonas entomophila, indicating that the bacterium alters the trade-off between lifespan and host defence. A transcriptomic analysis using fly intestine revealed that A. persici preferably induces antimicrobial peptides (AMPs), while L. plantarum upregulates amidase peptidoglycan recognition proteins (PGRPs). The specific induction of these Imd target genes by peptidoglycans from two bacterial species is due to the stimulation of the receptor PGRP-LC in the anterior midgut for AMPs or PGRP-LE from the posterior midgut for amidase PGRPs. Heat-killed A. persici also shortens lifespan and increases ISC proliferation via PGRP-LC, but it is not sufficient to alter the stress resistance. this study emphasizes the significance of peptidoglycan specificity in determining the gut bacterial impact on healthspan. It also unveils the postbiotic effect of specific gut bacterial species, which turns flies into a "live fast, die young" lifestyle.
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Zhao, Y., Xuan, H., Shen, C., Liu, P., Han, J. J. and Yu, W. (2022). Immunosuppression Induced by Brain-Specific HDAC6 Knockdown Improves Aging Performance in Drosophila melanogaster. Phenomics 2(3): 194-200. PubMed ID: 36939772
Summary:
HDAC6 is involved in several biological processes related to aging-associated diseases. However, it was unknown whether HDAC6 could directly regulate lifespan and healthspan. This study found that HDAC6 knockdown induced transcriptome changes to attenuate the aging changes in the Drosophila head, particularly on the inflammation and innate immunity-related genes. Whole-body knockdown of HDAC6 extended lifespan in the fly, furthermore brain-specific knockdown of HDAC6 extended both lifespan and healthspan in the fly. These results established HDAC6 as a lifespan regulator and provided a potential anti-aging target.
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Schneider, B. K., Sun, S., Lee, M., Li, W., Skvir, N., Neretti, N., Vijg, J. and Secombe, J. (2023). Expression of retrotransposons contributes to aging in Drosophila. Genetics. PubMed ID: 37084379
Summary:
Retrotransposons are a class of transposable elements capable of self-replication and insertion into new genomic locations. Across species, the mobilization of retrotransposons in somatic cells has been suggested to contribute to the cell and tissue functional decline that occurs during aging. Retrotransposons are broadly expressed across cell types, and de novo insertions have been observed to correlate with tumorigenesis. However, the extent to which new retrotransposon insertions occur during normal aging and their effect on cellular and animal function remains understudied. This study used a single nucleus whole genome sequencing approach in Drosophila to directly test whether transposon insertions increase with age in somatic cells. Analyses of nuclei from thoraces and indirect flight muscles using a newly developed pipeline, Retrofind, revealed no significant increase in the number of transposon insertions with age. Despite this, reducing the expression of two different retrotransposons, 412 and Roo, extended lifespan, but did not alter indicators of health such as stress resistance. This suggests a key role for transposon expression and not insertion in regulating longevity. Transcriptomic analyses revealed similar changes to gene expression in 412 and Roo knockdown flies and highlighted changes to genes involved in proteolysis and immune function as potential contributors to the observed changes in longevity. Combined, these data show a clear link between retrotransposon expression and aging.
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Wen, D. T., Gao, Y. H., Wang, J., Wang, S., Zhong, Q. and Hou, W. Q. (2023). Role of muscle FOXO gene in exercise against the skeletal muscle and cardiac age-related defects and mortality caused by high-salt intake in Drosophila. Genes Nutr 18(1): 6. PubMed ID: 36997839
Summary:
FOXO has long been associated with aging, exercise, and tissue homeostasis, but it remains unclear what the role is of the muscle FOXO gene in exercise (E) against high-salt intake(HSI)-induced age-related defects of the skeletal muscle, heart, and mortality. In this research, overexpression and RNAi of the FOXO gene in the skeletal and heart muscle of Drosophila were constructed by building Mhc-GAL4/FOXO-UAS-overexpression and Mhc-GAL4/FOXO-UAS-RNAi system. The skeletal muscle and heart function, the balance of oxidation and antioxidant, and mitochondrial homeostasis were measured. The results showed that exercise reversed the age-related decline in climbing ability and downregulation of muscle FOXO expression induced by HSI. Muscle-specific FOXO-RNAi (FOXO-RNAi) and -overexpression (FOXO-OE) promoted or slowed the age-related decline in climbing ability, heart function, and skeletal muscle and heart structure damage, which was accompanied by the inhibition or activation of FOXO/PGC-1α/SDH and FOXO/SOD pathway activity, and oxidative stress (ROS) increased or decreased in both skeletal muscle and heart. The protective effect of exercise on the skeletal muscle and heart was blocked by FOXO-RNAi in aged HSI flies. FOXO-OE prolonged its lifespan, but it did not resist the HSI-induced lifespan shortening. Exercise did not improve HSI-induced lifespan shortening in FOXO-RNAi flies. Therefore, current results confirmed that the muscle FOXO gene played a vital role in exercise against age-related defects of the skeletal muscle and heart induced by HSI because it determined the activity of muscle FOXO/SOD and FOXO/PGC-1α/SDH pathways. The muscle FOXO gene also played an important role in exercise against HSI-induced mortality in aging flies.
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Escobedo, S. E., Stanhope, S. C., Dong, Z. and Weake, V. M. (2022). Aging and Light Stress Result in Overlapping and Unique Gene Expression Changes in Photoreceptors. Genes (Basel) 13(2). PubMed ID: 35205309
Summary:
The extended photoreceptor cell lifespan, in addition to its high metabolic needs due to phototransduction, makes it critical for these neurons to continually respond to the stresses associated with aging by mounting an appropriate gene expression response. This study sought to untangle the more general neuronal age-dependent transcriptional signature of photoreceptors with that induced by light stress. To do this, flies were aged or exposed to various durations of blue light, followed by photoreceptor nuclei-specific transcriptome profiling. Using this approach, genes were identified that are both common and uniquely regulated by aging and light induced stress. Whereas both age and blue light induce expression of DNA repair genes and a neuronal-specific signature of death, both conditions result in downregulation of phototransduction. Interestingly, blue light uniquely induced genes that directly counteract the overactivation of the phototransduction signaling cascade. Lastly, unique gene expression changes in aging photoreceptors included the downregulation of genes involved in membrane potential homeostasis and mitochondrial function, as well as the upregulation of immune response genes. It is proposed that light stress contributes to the aging transcriptome of photoreceptors, but that there are also other environmental or intrinsic factors involved in age-associated photoreceptor gene expression signatures.
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Taylor, J. R., Wood, J. G., Mizerak, E., Hinthorn, S., Liu, J., Finn, M., Gordon, S., Zingas, L., Chang, C., Klein, M. A., Denu, J. M., Gorbunova, V., Seluanov, A., Boeke, J. D., Sedivy, J. M. and Helfand, S. L. (2022). Sirt6 regulates lifespan in Drosophila melanogaster. Proc Natl Acad Sci U S A 119(5). PubMed ID: 35091469
Summary:
Sirt6 is a multifunctional enzyme that regulates diverse cellular processes such as metabolism, DNA repair, and aging. Overexpressing Sirt6 extends lifespan in mice, but the underlying cellular mechanisms are unclear. Drosophila melanogaster are an excellent model to study genetic regulation of lifespan; however, despite extensive study in mammals, very little is known about Sirt6 function in flies. This study characterized the Drosophila ortholog of Sirt6, dSirt6, and examined its role in regulating longevity; dSirt6 is a nuclear and chromatin-associated protein with NAD(+)-dependent histone deacetylase activity. dSirt6 overexpression (OE) in flies produces robust lifespan extension in both sexes, while reducing dSirt6 levels shortens lifespan. dSirt6 OE flies have normal food consumption and fertility but increased resistance to oxidative stress and reduced protein synthesis rates. Transcriptomic analyses reveal that dSirt6 OE reduces expression of genes involved in ribosome biogenesis, including many dMyc target genes. dSirt6 OE partially rescues many effects of dMyc OE, including increased nuclear size, up-regulation of ribosome biogenesis genes, and lifespan shortening. Last, dMyc haploinsufficiency does not convey additional lifespan extension to dSirt6 OE flies, suggesting dSirt6 OE is upstream of dMyc in regulating lifespan. These results provide insight into the mechanisms by which Sirt6 OE leads to longer lifespan.
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Krittika, S. and Yadav, P.. Alterations in lifespan and sleep/wake duration under selective monochromes of visible light in Drosophila melanogaster. Biol Open. PubMed ID: 35735020
Summary:
Rapid technology development, exposure to gadgets, and artificial lights (with different monochromes) have disturbed lifestyles and the circadian clock, which otherwise confers better regulation of behavioral patterns and sleep/wake cycles in most organisms including Drosophila melanogaster. This study assayed the effect of LD12:12 hr (light: dark) monochromatic lights (violet, blue, green, yellow, orange, and red) on the lifespan, activity, and sleep of the D. melanogaster. A shortened lifespan was observed under 12h of violet, blue, green, and yellow lights, while significantly reduced activity levels under the light phase of blue and green light as compared to their dark phase is observed. Significant increase in the evening anticipation index of flies under blue and green light alongside increased and decreased sleep depth during the day and night respectively suggests the light avoidance, while there is no effect of colored light on the waking time, daily active time, and sleep time. Thus, this study shows short and long-term exposure to certain colored lights in terms of reduced lifespan and locomotor activity, which cause qualitative as well as quantitative changes in the sleep of flies; probably as a sign of aversion towards a specific light.
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Du, X., Wang, Y., Wang, J., Liu, X., Chen, J., Kang, J., Yang, X. and Wang, H. (2022). d-Chiro-Inositol extends the lifespan of male Drosophila melanogaster better than d-Pinitol through insulin signaling and autophagy pathways. Exp Gerontol 165: 111856. PubMed ID: 35644418
Summary:
d-Pinitol (DP) is the methylated product of d-Chiro-Inositol (DCI), which is one of the nine isomers of inositol with optical activity. Both substances possess antioxidant activity. This study was conducted to investigate and compare the antioxidant and life-prolonging effects of DCI and DP on male Drosophila melanogaster. Results showed that DCI and DP prolonged the lifespan and improved the climbing, anti-stress, and antioxidant activities. After treatment with DCI and DP, intestinal homeostasis was improved and the abnormal proliferation of intestinal stem cells (ISCs) was attenuated. Furthermore, real-time PCR revealed downregulated expression levels of PI3K and Akt and upregulated expression levels of Dilp5 and FOXO, which consequently activated Atg1, Atg5, Atg8a, and Atg8b and increased the number of lysosomes. Altogether, DCI exerts a slightly better effect than DP based on various indicators. RNAi D. melanogaster lifespan and molecular docking results further suggested that DCI and DP could prolong longevity through insulin signaling (IIS) and autophagy pathways.
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Mlih, M. and Karpac, J. (2022). Integrin-ECM interactions and membrane-associated Catalase cooperate to promote resilience of the Drosophila intestinal epithelium. PLoS Biol 20(5): e3001635. PubMed ID: 35522719
Summary:
Balancing cellular demise and survival constitutes a key feature of resilience mechanisms that underlie the control of epithelial tissue damage. These resilience mechanisms often limit the burden of adaptive cellular stress responses to internal or external threats. Diedel, a secreted protein/cytokine, has been identified as a potent antagonist of apoptosis-induced regulated cell death in the Drosophila intestinal midgut epithelium during aging. This study shows that Diedel is a ligand for RGD-binding Integrins and is thus required for maintaining midgut epithelial cell attachment to the extracellular matrix (ECM)-derived basement membrane. Exploiting this function of Diedel, a resilience mechanism was uncovered of epithelial tissues, mediated by Integrin-ECM interactions, which shapes cell death spreading through the regulation of cell detachment and thus cell survival. Moreover, It was found that resilient epithelial cells, enriched for Diedel-Integrin-ECM interactions, are characterized by membrane association of Catalase, thus preserving extracellular reactive oxygen species (ROS) balance to maintain epithelial integrity. Intracellular Catalase can relocalize to the extracellular membrane to limit cell death spreading and repair Integrin-ECM interactions induced by the amplification of extracellular ROS, which is a critical adaptive stress response. Membrane-associated Catalase, synergized with Integrin-ECM interactions, likely constitutes a resilience mechanism that helps balance cellular demise and survival within epithelial tissues.
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Malacrida, S., De Lazzari, F., Mrakic-Sposta, S., Vezzoli, A., Zordan, M. A., Bisaglia, M., Menti, G. M., Meda, N., Frighetto, G., Bosco, G., Dal Cappello, T., Strapazzon, G., Reggiani, C., Gussoni, M. and Megighian, A. (2022). Lifespan and ROS levels in different Drosophila melanogaster strains after 24 h hypoxia exposure. Biol Open 11(6). PubMed ID: 35616023
Summary:
During recent decades, model organisms such as Drosophila melanogaster have made it possible to study the effects of different environmental oxygen conditions on lifespan and oxidative stress. In this study, longevity and ROS levels were compared in young, unmated males of three laboratory wild-type lines (Canton-S, Oregon-R and Berlin-K) and one mutant line (Sod1n1) as a positive control of redox imbalance, under both normoxic and hypoxic (2% oxygen for 24 h) conditions. The genetic background was found to be a relevant factor involved in D. melanogaster longevity and ROS levels. Indeed, as expected, in normoxia Sod1n1 are the shortest-lived, while the wild-type strains, despite a longer lifespan, show some differences, with the Canton-S line displaying the lowest mortality rate. After hypoxic stress these variances are amplified, with Berlin-K flies showing the highest mortality rate and most evident reduction of lifespan. Moreover, this analysis highlighted differential effects of hypoxia on redox balance/unbalance. Canton-S flies had the lowest increase of ROS level compared to all the other strains, confirming it to be the less sensitive to hypoxic stress. Sod1n1 flies displayed the highest ROS levels in normoxia and after hypoxia. These results should be used to further standardize future Drosophila research models designed to investigate genes and pathways that may be involved in lifespan and/or ROS, as well as comparative studies on specific mutant strains.
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Mlih, M. and Karpac, J. (2022). Integrin-ECM interactions and membrane-associated Catalase cooperate to promote resilience of the Drosophila intestinal epithelium. PLoS Biol 20(5): e3001635. PubMed ID: 35522719
Summary:
Balancing cellular demise and survival constitutes a key feature of resilience mechanisms that underlie the control of epithelial tissue damage. These resilience mechanisms often limit the burden of adaptive cellular stress responses to internal or external threats. Diedel, a secreted protein/cytokine, has been identified as a potent antagonist of apoptosis-induced regulated cell death in the Drosophila intestinal midgut epithelium during aging. This study shows that Diedel is a ligand for RGD-binding Integrins and is thus required for maintaining midgut epithelial cell attachment to the extracellular matrix (ECM)-derived basement membrane. Exploiting this function of Diedel, a resilience mechanism was uncovered of epithelial tissues, mediated by Integrin-ECM interactions, which shapes cell death spreading through the regulation of cell detachment and thus cell survival. Moreover, It was found that resilient epithelial cells, enriched for Diedel-Integrin-ECM interactions, are characterized by membrane association of Catalase, thus preserving extracellular reactive oxygen species (ROS) balance to maintain epithelial integrity. Intracellular Catalase can relocalize to the extracellular membrane to limit cell death spreading and repair Integrin-ECM interactions induced by the amplification of extracellular ROS, which is a critical adaptive stress response. Membrane-associated Catalase, synergized with Integrin-ECM interactions, likely constitutes a resilience mechanism that helps balance cellular demise and survival within epithelial tissues.
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Hayashi, Y., Kashio, S., Murotomi, K., Hino, S., Kang, W., Miyado, K., Nakao, M., Miura, M., Kobayashi, S. and Namihira, M. (2022). Serotonin and dopamine modulate aging in response to food odor and availability. Nat Commun 13(1): 3271. PubMed ID: 35672307
Summary:
An organism's ability to perceive and respond to changes in its environment is crucial for its health and survival. This study reveals how the most well-studied longevity intervention, dietary restriction, acts in-part through a cell non-autonomous signaling pathway that is inhibited by the presence of attractive smells. Using an intestinal reporter for a key gene induced by dietary restriction but suppressed by attractive smells, this study identified three compounds that block food odor effects in C. elegans, thereby increasing longevity as dietary restriction mimetics. These compounds clearly implicate serotonin and dopamine in limiting lifespan in response to food odor. A chemosensory neuron that likely perceives food odor, an enteric neuron that signals through the serotonin receptor 5-HT1A/SER-4, and a dopaminergic neuron that signals through the dopamine receptor DRD2/DOP-3. Aspects of this pathway are conserved in D. melanogaster. Thus, blocking food odor signaling through antagonism of serotonin or dopamine receptors is a plausible approach to mimic the benefits of dietary restriction.
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Shaposhnikov, M. V., Guvatova, Z. G., Zemskaya, N. V., Koval, L. A., Schegoleva, E. V., Gorbunova, A. A., Golubev, D. A., Pakshina, N. R., Ulyasheva, N. S., Solovev, I. A., Bobrovskikh, M. A., Gruntenko, N. E., Menshanov, P. N., Krasnov, G. S., Kudryavseva, A. V. and Moskalev, A. A. (2022). Molecular mechanisms of exceptional lifespan increase of Drosophila melanogaster with different genotypes after combinations of pro-longevity interventions. Commun Biol 5(1): 566. PubMed ID: 35681084
Summary:
Aging is one of the current global challenges. The search for new anti-aging interventions is also an issue of great actuality. This report describes the success of Drosophila melanogaster lifespan extension under the combined influence of dietary restriction, co-administration of berberine, fucoxanthin, and rapamycin, photodeprivation, and low-temperature conditions up to 185 days in w(1118) strain and up to 213 days in long-lived E(z)/w mutants. The trade-off was found between longevity and locomotion. The transcriptome analysis showed an impact of epigenetic alterations, lipid metabolism, cellular respiration, nutrient sensing, immune response, and autophagy in the registered effect.
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Delventhal, R., Wooder, E. R., Basturk, M., Sattar, M., Lai, J., Bolton, D., Muthukumar, G., Ulgherait, M. and Shirasu-Hiza, M. M (2022). Dietary restriction ameliorates TBI-induced phenotypes in Drosophila melanogaster. Sci Rep 12(1): 9523. PubMed ID: 35681073
Summary:
Traumatic brain injury (TBI) affects millions annually and is associated with long-term health decline. TBI also shares molecular and cellular hallmarks with neurodegenerative diseases (NDs), typically increasing in prevalence with age, and is a major risk factor for developing neurodegeneration later in life. While understanding of genes and pathways that underlie neurotoxicity in specific NDs has advanced, a complete understanding of early molecular and physiological changes that drive neurodegeneration, particularly as an individual ages following a TBI, is lacking. Recently Drosophila has been introduced as a model organism for studying closed-head TBI. In this paper, a TBI is delivered to flies early in adult life, and then molecular and physiological phenotypes were measured at short-, mid-, and long-term timepoints following the injury. The aim was to identify the timing of changes that contribute to neurodegeneration. Prior work is confirmed demonstrating a TBI-induced decline in lifespan, and evidence is presented of a progressive decline in locomotor function, robust acute and modest chronic neuroinflammation, and a late-onset increase in protein aggregation. Evidence is also presented of metabolic dysfunction, in the form of starvation sensitivity and decreased lipids, that persists beyond the immediate injury response, but does not differ long-term. An intervention of dietary restriction (DR) partially ameliorates some TBI-induced phenotypes, including lifespan and locomotor function, though it does not alter the pattern of starvation sensitivity of injured flies. In the future, molecular pathways identified as altered following TBI-particularly in the short-, or mid-term-could present potential therapeutic targets.
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Gautrey, S. L. and Simons, M. J. P.
(2022). Amino acid availability is not essential for lifespan extension by dietary restriction in the fly. J Gerontol A Biol Sci Med Sci. PubMed ID: 35486979
Summary:
Dietary restriction (DR) is one of the most potent ways to extend health- and lifespan. Key progress in understanding the mechanisms of DR, and ageing more generally, was made when dietary protein, and more specifically essential amino acids (EAA), were identified as the dietary component to restrict to obtain DR's health and lifespan benefits. This role of dietary amino acids has influenced work on ageing mechanisms, especially in nutrient sensing, e.g. Tor and insulin(-like) signalling networks. Experimental biology in Drosophila melanogaster has been instrumental in generating and confirming the hypothesis that EAA availability is important in ageing. This study expanded on previous work testing the involvement of EAA in DR through large scale (N=6,238) supplementation experiments across four diets and two genotypes in female flies. Surprisingly, it was found that EAA are not essential to DR's lifespan benefits. Importantly, the fecundity benefits of EAA supplementation were not identified suggesting the supplemented EAA were bioavailable. Furthermore, it was found that the effects of amino acids on lifespan vary by diet and genetic line studied and that, at the most restricted diet, fecundity is constrained by other nutrients than EAA. It is suggested that DR for optimal health is a concert of nutritional effects, orchestrated by genetic, dietary and other environmental interactions. These results question the universal importance of amino acid availability in the biology of ageing and DR.
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Hodge, B. A., Meyerhof, G. T., Katewa, S. D., Lian, T., Lau, C., Bar, S., Leung, N. Y., Li, M., Li-Kroeger, D., Melov, S., Schilling, B., Montell, C. and Kapahi, P.. Dietary restriction and the transcription factor clock delay eye aging to extend lifespan in Drosophila Melanogaster. Nat Commun 13(1): 3156. PubMed ID: 35672419
Summary:
Many vital processes in the eye are under circadian regulation, and circadian dysfunction has emerged as a potential driver of eye aging. Dietary restriction is one of the most robust lifespan-extending therapies and amplifies circadian rhythms with age. This study demonstrates that dietary restriction extends lifespan in Drosophila melanogaster by promoting circadian homeostatic processes that protect the visual system from age- and light-associated damage. Altering the positive limb core molecular clock transcription factor, CLOCK, or CLOCK-output genes, accelerates visual senescence, induces a systemic immune response, and shortens lifespan. Flies subjected to dietary restriction are protected from the lifespan-shortening effects of photoreceptor activation. Inversely, photoreceptor inactivation, achieved via mutating rhodopsin or housing flies in constant darkness, primarily extends the lifespan of flies reared on a high-nutrient diet. These findings establish the eye as a diet-sensitive modulator of lifespan and indicates that vision is an antagonistically pleiotropic process that contributes to organismal aging.
Hayashi, Y., Kashio, S., Murotomi, K., Hino, S., Kang, W., Miyado, K., Nakao, M., Miura, M., Kobayashi, S. and Namihira, M. (2022). Biosynthesis of S-adenosyl-methionine enhances aging-related defects in Drosophila oogenesis. Sci Rep 12(1): 5593. PubMed ID: 35379840
Summary:
Exposing sires to various environmental manipulations has demonstrated that paternal effects can be non-trivial also in species where male investment in offspring is almost exclusively limited to sperm. Whether paternal effects also have a genetic component (i.e. paternal indirect genetic effects (PIGEs)) in such species is however largely unknown, primarily because of methodological difficulties separating indirect from direct effects of genes. PIGEs may nevertheless be important since they have the capacity to contribute to evolutionary change. This studyd used Drosophila genetics to construct a breeding design that allows testing nearly complete haploid genomes (more than 99%) for PIGEs. Using this technique, the variance was estimated in male lifespan due to PIGEs among four populations and compare this to the total paternal genetic variance (the sum of paternal indirect and direct genetic effects). These results indicate that a substantial part of the total paternal genetic variance results from PIGEs. A screen of 38 haploid genomes, randomly sampled from a single population, suggests that PIGEs also influence variation in lifespan within populations. Collectively, these results demonstrate that PIGEs may constitute an underappreciated source of phenotypic variation.
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Piper, M. D. W., Zanco, B., Sgro, C. M., Adler, M. I., Mirth, C. K. and Bonduriansky, R. (2022). Dietary restriction and lifespan: adaptive reallocation or somatic sacrifice?. Febs j. PubMed ID: 35466532
Summary:
Reducing overall food intake, or lowering the proportion of protein relative to other macronutrients, can extend the lifespan of diverse organisms. A number of mechanistic theories have been developed to explain this phenomenon, mostly assuming that the molecules connecting diet to lifespan are evolutionarily conserved. A recent study using Drosophila melanogaster females has pinpointed a single essential micronutrient that can explain how lifespan is changed by dietary restriction. This study proposes a likely mechanism for this observation, which involves a trade-off between lifespan and reproduction, but in a manner that is conditional on the dietary supply of an essential micronutrient - a sterol. Importantly, these observations argue against previous evolutionary theories that rely on constitutive resource reallocation or damage directly inflicted by reproduction. Instead, they are compatible with a model in which the inverse relationship between lifespan and food level is caused by the consumer suffering from varying degrees of malnutrition when maintained on lab food. The data also indicate that animals on different lab foods may suffer from different nutritional imbalances and that the mechanisms by which dietary restriction benefits the lifespan of different species may vary. This means that translating the mechanistic findings from lab animals to humans will not be simple and should be interpreted in light of the range of challenges that have shaped each organism's lifespan in the wild and the composition of the natural diets upon which they would feed.
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Butsch, T. J., Dubuisson, O., Johnson, A. E. and Bohnert, K. A. (2022). A meiotic switch in lysosome activity supports spermatocyte development in young flies but collapses with age. iScience 25(6): 104382. PubMed ID: 35620438
Summary:
Gamete development ultimately influences animal fertility. Identifying mechanisms that direct gametogenesis, and how they deteriorate with age, may inform ways to combat infertility. Recentl work has shown that lysosomes acidify during oocyte maturation in Caenorhabditis elegans, suggesting that a meiotic switch in lysosome activity promotes female germ-cell health. Using Drosophila melanogaster, this study reports that lysosomes likewise acidify in male germ cells during meiosis. Inhibiting lysosomes in young-male testes causes E-cadherin accumulation and loss of germ-cell partitioning membranes. Notably, analogous changes occur naturally during aging; in older testes, a reduction in lysosome acidity precedes E-cadherin accumulation and membrane dissolution, suggesting one potential cause of age-related spermatocyte abnormalities. Consistent with lysosomes governing the production of mature sperm, germ cells with homozygous-null mutations in lysosome-acidifying machinery fail to survive through meiosis. Thus, lysosome activation is entrained to meiotic progression in developing sperm, as in oocytes, and lysosomal dysfunction may instigate male reproductive aging.
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Li, Y., Pan, L., Li, P., Yu, G., Li, Z., Dang, S., Jin, F. and Nan, Y. (2022). Microbiota aggravates the pathogenesis of Drosophila acutely exposed to vehicle exhaust. Heliyon 8(9): e10382. PubMed ID: 36060467
Summary:
Vehicle exhaust (VE) is the primary cause of urban air pollution, which adversely affects the respiratory system, exacerbates lung diseases, and results in high mortality rates. However, the underlying mechanism of the pathogenesis is largely unclear. This study developed a Drosophila model to systematically investigate the effects of VE on their health and physiology. VE was found to significantly impaired life span and locomotion in Drosophila. Interestingly, there was an increase in bacterial load in the guts upon VE exposure, suggesting VE is able to induce dysbiosis in the guts. Microbiota depletion can ameliorate the impairment of life span and locomotion. VE causes permeability of intestinal epithelial cells and increases proliferation of intestinal cells, suggesting VE disrupts intestinal homeostasis. This study elucidated the underlying mechanism by which VE triggers Imd and DUOX gene expression. Taken together, this Drosophila model provides insight into the pathogenesis of Drosophila exposure to VE, enabling better understanding of the specific role of microbiota.
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Li, Y., Pan, L., Li, P., Yu, G., Li, Z., Dang, S., Jin, F. and Nan, Y. (2022). Microbiota aggravates the pathogenesis of Drosophila acutely exposed to vehicle exhaust. Heliyon 8(9): e10382. PubMed ID: 36060467
Summary:
Vehicle exhaust (VE) is the primary cause of urban air pollution, which adversely affects the respiratory system, exacerbates lung diseases, and results in high mortality rates. However, the underlying mechanism of the pathogenesis is largely unclear. This study developed a Drosophila model to systematically investigate the effects of VE on their health and physiology. VE was found to significantly impaired life span and locomotion in Drosophila. Interestingly, there was an increase in bacterial load in the guts upon VE exposure, suggesting VE is able to induce dysbiosis in the guts. Microbiota depletion can ameliorate the impairment of life span and locomotion. VE causes permeability of intestinal epithelial cells and increases proliferation of intestinal cells, suggesting VE disrupts intestinal homeostasis. This study elucidated the underlying mechanism by which VE triggers Imd and DUOX gene expression. Taken together, this Drosophila model provides insight into the pathogenesis of Drosophila exposure to VE, enabling better understanding of the specific role of microbiota.
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Hewitt, V. L., Miller-Fleming, L., Twyning, M. J., Andreazza, S., Mattedi, F., Prudent, J., Polleux, F., Vagnoni, A. and Whitworth, A. J. (2022). Decreasing pdzd8-mediated mito-ER contacts improves organismal fitness and mitigates Aβ(42) toxicity. Life Sci Alliance 5(11). PubMed ID: 35831024
Summary:
Mitochondria<>/a-ER contact sites (MERCs) orchestrate many important cellular functions including regulating mitochondrial quality control through mitophagy and mediating mitochondrial calcium uptake. This study identified and functionally characterize the Drosophila ortholog of the recently identified mammalian MERC protein, Pdzd8. Reducing pdzd8-mediated MERCs in neurons slows age-associated decline in locomotor activity and increases lifespan in Drosophila. The protective effects of pdzd8 knockdown in neurons correlate with an increase in mitophagy, suggesting that increased mitochondrial turnover may support healthy aging of neurons. In contrast, increasing MERCs by expressing a constitutive, synthetic ER-mitochondria tether disrupts mitochondrial transport and synapse formation, accelerates age-related decline in locomotion, and reduces lifespan. Although depletion of pdzd8 prolongs the survival of flies fed with mitochondrial toxins, it is also sufficient to rescue locomotor defects of a fly model of Alzheimer's disease expressing Amyloid β(42) (Aβ(42)). Together, these results provide the first in vivo evidence that MERCs mediated by the tethering protein pdzd8 play a critical role in the regulation of mitochondrial quality control and neuronal homeostasis.
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Strilbytska, O., Strutynska, T., Semaniuk, U., Burdyliyk, N., Bubalo, V. and Lushchak, O. (2022). Dietary Sucrose Determines Stress Resistance, Oxidative Damages, and Antioxidant Defense System in Drosophila. Scientifica (Cairo) 2022: 7262342. PubMed ID: 35547569/a>
Summary:
Varied nutritional interventions affect lifespan and metabolic health. Abundant experimental evidence indicates that the carbohydrate restriction in the diet induces changes to support long-lived phenotypes. Reactive oxygen species (ROS) are among the main mechanisms that mediate the effect of nutrient consumption on the aging process. This study tested the influence of sucrose concentration in the diet on stress resistance, antioxidant defense systems, and oxidative stress markers in D. melanogaster. High sucrose concentration in the fly medium was found to lead to enhanced resistance to starvation, oxidative, heat, and cold stresses. However, flies that were raised on low sucrose food displayed increased levels of low-molecular-mass thiols, lipid peroxides in females, and higher activity of antioxidant enzymes, indicating that the consumption of a low carbohydrate diet could induce oxidative stress in the fruit fly. The consumption of sucrose-enriched diet increased protein carbonyl level, which may indicate about the activation of glycation processes. The results highlight a strong dependence of oxidative metabolism in D. melanogaster from dietary carbohydrates.
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Aiello, G., Sabino, C., Pernici, D., Audano, M., Antonica, F., Gianesello, M., Ballabio, C., Quattrone, A., Mitro, N., Romanel, A., Soldano, A. and Tiberi, L. (2022). Transient rapamycin treatment during developmental stage extends lifespan in Mus musculus and Drosophila melanogaster. EMBO Rep 23(9): e55299. PubMed ID: 35796299
Summary:
Lifespan is determined by complex and tangled mechanisms that are largely unknown. The early postnatal stage has been proposed to play a role in lifespan, but its contribution is still controversial. This show that a short rapamycin treatment during early life can prolong lifespan in Mus musculus and Drosophila melanogaster. Notably, the same treatment at later time points has no effect on lifespan, suggesting that a specific time window is involved in lifespan regulation. It was also found that sulfotransferases are upregulated during early rapamycin treatment both in newborn mice and in Drosophila larvae, and transient dST1 overexpression in Drosophila larvae extends lifespan. These findings unveil a novel link between early-life treatments and long-term effects on lifespan.
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Shit, B., Prakash, A., Sarkar, S., Vale, P. F. and Khan, I. (2022). Ageing leads to reduced specificity of antimicrobial peptide responses in Drosophila melanogaster. Proc Biol Sci 289(1987): 20221642. PubMed ID: 36382522
Summary:
Evolutionary theory predicts a late-life decline in the force of natural selection, possibly leading to late-life deregulations of the immune system. A potential outcome of such deregulations is the inability to produce specific immunity against target pathogens. This possibility was tested by infecting multiple Drosophila melanogaster lines (with bacterial pathogens) across age groups, where either individual or different combinations of Imd- and Toll-inducible antimicrobial peptides (AMPs) were deleted using CRISPR gene editing. A high degree of non-redundancy and pathogen-specificity of AMPs was demonstrated in young flies: in some cases, even a single AMP could confer complete resistance. However, ageing led to drastic reductions in such specificity to target pathogens, warranting the action of multiple AMPs across Imd and Toll pathways. Moreover, use of diverse AMPs either lacked survival benefits or even accompanied survival costs post-infection. These features were also sexually dimorphic: females required a larger repertoire of AMPs than males but extracted equivalent survival benefits. Finally, age-specific expansion of the AMP-repertoire was accompanied with ageing-induced downregulation of negative-regulators of the Imd pathway and damage to renal function post-infection, as features of poorly regulated immunity. Overall, this study highlights the potentially non-adaptive role of ageing in producing less-specific AMP responses, across sexes and pathogens.
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Hoedjes, K. M., Kostic, H., Keller, L. and Flatt, T. (2022). Natural alleles at the Doa locus underpin evolutionary changes in Drosophila lifespan and fecundity. Proc Biol Sci 289(1986): 20221989. PubMed ID: 36350205
Summary:
'Evolve and resequence' (E&R) studies in Drosophila melanogaster have identified many candidate loci underlying the evolution of ageing and life history, but experiments that validate the effects of such candidates remain rare. In a recent E&R study several alleles were identified of the LAMMER kinase Darkener of apricot (Doa) as candidates for evolutionary changes in lifespan and fecundity. This study used two complementary approaches to confirm a functional role of Doa in life-history evolution. First, transgenic RNAi was used to study the effects of Doa at the whole-gene level. Ubiquitous silencing of expression in adult flies reduced both lifespan and fecundity, indicating pleiotropic effects. Second, to characterize segregating variation at Doa, four candidate single nucleotide polymorphisms (SNPs; Doa-1, -2, -3, -4) were examined using a genetic association approach. Three candidate SNPs had effects that were qualitatively consistent with expectations based on the E&R study: Doa-2 pleiotropically affected both lifespan and late-life fecundity; Doa-1 affected lifespan (but not fecundity); and Doa-4 affected late-life fecundity (but not lifespan). Finally, the last candidate allele (Doa-3) also affected lifespan, but in the opposite direction from predicted.
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Lushchak, O., Strilbytska, O. and Storey, K. B. (2022). Gender-Specific Effects of Pro-longevity Interventions in Drosophila. Mech Ageing Dev: 111754. PubMed ID: 36375654
Summary:
Sex differences in lifespan are well recognized in the majority of animal species. For example, in male versus female Drosophila melanogaster there are significant differences in behavior and physiology. However, little is known about the underlying mechanisms of gender differences in responses to pro-longevity interventions in this model organism. This study summarized the existing data on the effects of nutritional and pharmacological anti-aging interventions such as nutrition regimens, diet and dietary supplementation on the lifespan of male and female Drosophila. Males and females have different sensitivities to interventions, and the effects are highly dependent on genetic background, mating, dose and exposure duration. Thia work highlights the importance of understanding the mechanisms that underlie the gender-specific effect of anti-aging manipulations. This will provide insight into how these benefits may be valuable for elucidating the primary physiological and molecular targets involved in aging and lifespan determination.
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G, N. L., Ko, S., Peng, O., Bognar, B., Khmelkov, M., H, S. B. and Tower, J. (2022) (2022). A screen of small molecule and genetic modulators of life span in female Drosophila identifies etomoxir, RH5849 and unanticipated temperature effects. Fly (Austin) 16(1): 397-413. PubMed ID: 36412257
Summary:
Mifepristone increases life span in female Drosophila melanogaster, and its molecular target(s) remain unclear. Small molecule and genetic interventions were tested for ability to mimic mifepristone, or to decrease life span in a way that can be rescued by mifepristone. Etomoxir inhibits lipid metabolism, and significantly increased life span in virgin and mated females, but not males, at 50 μM concentration. Pioglitazone is reported to activate both mammalian PPAR γ and its Drosophila homolog Eip75B. Pioglitazone produced minor and inconsistent benefits for female Drosophila life span, and only at the lowest concentrations tested. Ecdysone is a Drosophila steroid hormone reported to regulate responses to mating, and RH5849 is a potent mimic of ecdysone. RH5849 reduced virgin female life span, and this was partly rescued by mifepristone. Mifepristone did not compete with RH5849 for activation of an ecdysone receptor (EcR)-responsive transgenic reporter, indicating that the relevant target for mifepristone is not EcR. The conditional GAL4/GAL80ts system was used in attempt to test the effect of an Eip75B RNAi construct on female life span. However, the 29C temperature used for induction reduced or eliminated mating-induced midgut hypertrophy, the negative life span effects of mating, and the positive life span effects of mifepristone. Even when applied after mating was complete, a shift to 29°C temperature reduced mating-induced midgut hypertrophy by half, and the life span effects of mating by 4.8-fold. Taken together, these results identify promising small molecules for further analysis, and inform the design of experiments involving the GAL4/GAL80ts system.
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Wang, R., Zhang, P., Wang, J., Ma, L., E, W., Suo, S., Jiang, M., Li, J., Chen, H., Sun, H., Fei, L., Zhou, Z., Zhou, Y., Chen, Y., Zhang, W., Wang, X., Mei, Y., Sun, Z., Yu, C., Shao, J., Fu, Y., Xiao, Y., Ye, F., Fang, X., Wu, H., Guo, Q., Fang, X., Li, X., Gao, X., Wang, D., Xu, P. F., Zeng, R., Xu, G., Zhu, L., Wang, L., Qu, J., Zhang, D., Ouyang, H., Huang, H., Chen, M., Ng, S. C., Liu, G. H., Yuan, G. C., Guo, G. and Han, X.(2022). Construction of a cross-species cell landscape at single-cell level. Nucleic Acids Res. PubMed ID: 35929025
Summary:
Individual cells are basic units of life. Despite extensive efforts to characterize the cellular heterogeneity of different organisms, cross-species comparisons of landscape dynamics have not been achieved. This study applied single-cell RNA sequencing (scRNA-seq) to map organism-level cell landscapes at multiple life stages for mice, zebrafish and Drosophila. By integrating the comprehensive dataset of > 2.6 million single cells, a cross-species cell landscape was developed, and signatures and common pathways were identified that changed throughout the life span. structural inflammation and mitochondrial dysfunction were identified as the most common hallmarks of organism aging, and pharmacological activation of mitochondrial metabolism was found to alleviated aging phenotypes in mice. The cross-species cell landscape with other published datasets were stored in an integrated online portal-Cell Landscape. This work provides a valuable resource for studying lineage development, maturation and aging.
How many cell types are there in nature? How do they change during the life cycle? These are two fundamental questions that researchers have been trying to understand in the area of biology. In this study, single-cell mRNA sequencing data were used to profile over 2.6 million individual cells from mice, zebrafish and Drosophila at different life stages, 1.3 million of which were newly collected. The comprehensive datasets allow investigators to construct a cross-species cell landscape that helps to reveal the conservation and diversity of cell taxonomies at genetic and regulatory levels. The resources in this study are assembled into a publicly available at website
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Ozaki, M., Le, T. D. and Inoue, Y. H. (2022). Downregulating Mitochondrial DNA Polymerase γ in the Muscle Stimulated Autophagy, Apoptosis, and Muscle Aging-Related Phenotypes in Drosophila Adults. Biomolecules 12(8). PubMed ID: 36008999
Summary:
Reactive oxygen species, generated as by-products of mitochondrial electron transport, can induce damage to mitochondrial DNA (mtDNA) and proteins. This study investigated whether the moderate accumulation of mtDNA damage in adult muscles resulted in accelerated aging-related phenotypes in Drosophila. DNA polymerase γ (Polγ) is the sole mitochondrial DNA polymerase. The muscle-specific silencing of the genes encoding the polymerase subunits resulted in the partial accumulation of mtDNA with oxidative damage and a reduction in the mtDNA copy number. This subsequently resulted in the production of abnormal mitochondria with reduced membrane potential and, consequently, a partially reduced ATP quantity in the adult muscle. Immunostaining indicated a moderate increase in autophagy and mitophagy in adults with RNA interference of Polγ (PolγRNAi) muscle cells with abnormal mitochondria. In adult muscles showing continuous silencing of Polγ, malformation of both myofibrils and mitochondria was frequently observed. This was associated with the partially enhanced activation of pro-apoptotic caspases in the muscle. Adults with muscle-specific PolγRNAi exhibited a shortened lifespan, accelerated age-dependent impairment of locomotor activity, and disturbed circadian rhythms. These findings in this Drosophila model contribute to understanding how the accumulation of mtDNA damage results in impaired mitochondrial activity and how this contributes to muscle aging.
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Ozaki, M., Le, T. D. and Inoue, Y. H. (2022). Downregulating Mitochondrial DNA Polymerase γ in the Muscle Stimulated Autophagy, Apoptosis, and Muscle Aging-Related Phenotypes in Drosophila Adults. Biomolecules 12(8). PubMed ID: 36008999
Summary:
Reactive oxygen species, generated as by-products of mitochondrial electron transport, can induce damage to mitochondrial DNA (mtDNA) and proteins. This study investigated whether the moderate accumulation of mtDNA damage in adult muscles resulted in accelerated aging-related phenotypes in Drosophila. DNA polymerase γ (Polγ) is the sole mitochondrial DNA polymerase. The muscle-specific silencing of the genes encoding the polymerase subunits resulted in the partial accumulation of mtDNA with oxidative damage and a reduction in the mtDNA copy number. This subsequently resulted in the production of abnormal mitochondria with reduced membrane potential and, consequently, a partially reduced ATP quantity in the adult muscle. Immunostaining indicated a moderate increase in autophagy and mitophagy in adults with RNA interference of Polγ (PolγRNAi) muscle cells with abnormal mitochondria. In adult muscles showing continuous silencing of Polγ, malformation of both myofibrils and mitochondria was frequently observed. This was associated with the partially enhanced activation of pro-apoptotic caspases in the muscle. Adults with muscle-specific PolγRNAi exhibited a shortened lifespan, accelerated age-dependent impairment of locomotor activity, and disturbed circadian rhythms. These findings in this Drosophila model contribute to understanding how the accumulation of mtDNA damage results in impaired mitochondrial activity and how this contributes to muscle aging.
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Hayashi, Y., Kashio, S., Murotomi, K., Hino, S., Kang, W., Miyado, K., Nakao, M., Miura, M., Kobayashi, S. and Namihira, M. (2022). Biosynthesis of S-adenosyl-methionine enhances aging-related defects in Drosophila oogenesis. Sci Rep 12(1): 5593. PubMed ID: 35379840
Summary:
Over recent decades, increased longevity has not been paralleled by extended health span, resulting in more years spent with multiple diseases in older age. As such, interventions to improve health span are urgently required. Zoledronate (Zol) is a nitrogen-containing bisphosphonate, which inhibits the farnesyl pyrophosphate synthase enzyme, central to the mevalonate pathway. It is already used clinically to prevent fractures in osteoporotic patients, who have been reported to derive unexpected and unexplained survival benefits. Using Drosophila as a model the effects were determined of Zol on life span, parameters of health span (climbing ability and intestinal dysplasia), and the ability to confer resistance to oxidative stress using a combination of genetically manipulated Drosophila strains and Western blotting. This study study shows that Zol extended life span, improved climbing activity, and reduced intestinal epithelial dysplasia and permeability with age. Mechanistic studies showed that Zol conferred resistance to oxidative stress and reduced accumulation of X-ray-induced DNA damage via inhibition of farnesyl pyrophosphate synthase. Moreover, Zol was associated with inhibition of phosphorylated AKT in the mammalian target of rapamycin pathway downstream of the mevalonate pathway and required dFOXO for its action, both molecules associated with increased longevity. Taken together, this work indicates that Zol, a drug already widely used to prevent osteoporosis and dosed only once a year, modulates important mechanisms of aging. Its repurposing holds great promise as a treatment to improve health span.
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Hayashi, Y., Kashio, S., Murotomi, K., Hino, S., Kang, W., Miyado, K., Nakao, M., Miura, M., Kobayashi, S. and Namihira, M. (2022). Biosynthesis of S-adenosyl-methionine enhances aging-related defects in Drosophila oogenesis. Sci Rep 12(1): 5593. PubMed ID: 35379840
Summary:
cAMP Responsible Element Binding Protein (CREB) is an evolutionarily conserved transcriptional factor that regulates cell growth, synaptic plasticity and so on. This study unexpectedly found proteasome inhibitors, such as MLN2238, robustly increase CREB activity in adult flies through a large-scale compound screening. Mechanistically, reactive oxidative species (ROS) generated by proteasome inhibition are required and sufficient to promote CREB activity through c-Jun N-terminal kinase (JNK). In 293 T cells, JNK activation by MLN2238 is also required for increase of CREB phosphorylation at Ser(133). Meanwhile, transcriptome analysis in fly intestine identified a group of genes involved in redox and proteostatic regulation are augmented by overexpressing CRTC (CREB-regulated transcriptional coactivator). Intriguingly, CRTC overexpression in muscles robustly restores protein folding and proteasomal activity in a fly Huntington's disease (HD) model, and ameliorates HD related pathogenesis, such as protein aggregates, motility, and lifespan. Moreover, CREB activity increases during aging, and further enhances its activity can suppress protein aggregates in aged muscles. Together, these results identified CRTC/CREB downstream ROS/JNK signaling as a conserved sensor to tackle oxidative and proteotoxic stresses. Boosting CRTC/CREB activity is a potential therapeutic strategy to treat aging related protein aggregation diseases.
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Hayashi, Y., Kashio, S., Murotomi, K., Hino, S., Kang, W., Miyado, K., Nakao, M., Miura, M., Kobayashi, S. and Namihira, M. (2022). Biosynthesis of S-adenosyl-methionine enhances aging-related defects in Drosophila oogenesis. Sci Rep 12(1): 5593. PubMed ID: 35379840
Summary:
Tissue aging is a major cause of aging-related disabilities and a shortened life span. Understanding how tissue aging progresses and identifying the factors underlying tissue aging are crucial; however, the mechanism of tissue aging is not fully understood. This study shows that the biosynthesis of S-adenosyl-methionine (SAM), the major cellular donor of methyl group for methylation modifications, potently accelerates the aging-related defects during Drosophila oogenesis. An aging-related increase in the SAM-synthetase (Sam-S) levels in the germline leads to an increase in ovarian SAM levels. Sam-S-dependent biosynthesis of SAM controls aging-related defects in oogenesis through two mechanisms, decreasing the ability to maintain germline stem cells and accelerating the improper formation of egg chambers. Aging-related increases in SAM commonly occur in mouse reproductive tissue and the brain. Therefore, these results raise the possibility suggesting that SAM is the factor related to tissue aging beyond the species and tissues.
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Lee, H. Y., Lee, S. H. and Min, K. J. (2022). The Increased Abundance of Commensal Microbes Decreases Drosophila melanogaster Lifespan through an Age-Related Intestinal Barrier Dysfunction. Insects 13(2). PubMed ID: 35206792
Summary:
Commensal microbiota live in their host with a symbiotic relationship that affects the host's health and physiology. Many studies showed that microbial load and composition were changed by aging and have observed that increasing the abundance and changing the composition of commensal microbes had detrimental effects on host lifespan. It was hypothesized that dysbiosis of the intestinal microbiota leads to systemic effects in aging flies as a result of the increased intestinal permeability. The fruit fly laboratory strain w(1118) was used as a model system. The incidence of intestinal dysfunction was increased with age, and intestinal dysfunction increased the permeability of the fly intestine to resident microbes. The lifespan of flies with an intestinal barrier dysfunction was increased by removal of the microbes. Interestingly, some bacteria were also found in the hemolymph of flies with intestinal barrier dysfunction. These findings suggest the possibility that, as the host ages, there is an increase in intestinal permeability, which leads to an increased intestinal microbial load and a reduction in the host lifespan. These data therefore indicate a connection between commensal microbes and host lifespan.
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Hayashi, Y., Kashio, S., Murotomi, K., Hino, S., Kang, W., Miyado, K., Nakao, M., Miura, M., Kobayashi, S. and Namihira, M. (2022). Biosynthesis of S-adenosyl-methionine enhances aging-related defects in Drosophila oogenesis. Sci Rep 12(1): 5593. PubMed ID: 35379840
Summary:
Tissue aging is a major cause of aging-related disabilities and a shortened life span. Understanding how tissue aging progresses and identifying the factors underlying tissue aging are crucial; however, the mechanism of tissue aging is not fully understood. This study showed that the biosynthesis of S-adenosyl-methionine (SAM), the major cellular donor of methyl group for methylation modifications, potently accelerates the aging-related defects during Drosophila oogenesis. An aging-related increase in the SAM-synthetase (Sam-S) levels in the germline leads to an increase in ovarian SAM levels. Sam-S-dependent biosynthesis of SAM controls aging-related defects in oogenesis through two mechanisms, decreasing the ability to maintain germline stem cells and accelerating the improper formation of egg chambers. Aging-related increases in SAM commonly occur in mouse reproductive tissue and the brain. Therefore, these results raise the possibility suggesting that SAM is the factor related to tissue aging beyond the species and tissues.
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Maslov, D. L., Zemskaya, N. V., Trifonova, O. P., Lichtenberg, S., Balashova, E. E., Lisitsa, A. V., Moskalev, A. A. and Lokhov, P. G. (2021). Comparative Metabolomic Study of Drosophila Species with Different Lifespans. Int J Mol Sci 22(23). PubMed ID: 34884677
The increase in life expectancy, leading to a rise in the proportion of older people, is accompanied by a prevalence of age-related disorders among the world population, the fight against which today is one of the leading biomedical challenges. Exploring the biological insights concerning the lifespan is one of the ways to provide a background for designing an effective treatment for the increase in healthy years of life. Untargeted direct injection mass spectrometry-based metabolite profiling of 12 species of Drosophila with significant variations in natural lifespans was conducted in this research. A cross-comparison study of metabolomic profiles revealed lifespan signatures of flies. These signatures indicate that lifespan extension is associated with the upregulation of amino acids, phospholipids, and carbohydrate metabolism. Such information provides a metabolome-level view on longevity and may provide a molecular measure of organism age in age-related studies.
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Pan, H. Y., Ye, Z. W., Zheng, Q. W., Yun, F., Tu, M. Z., Hong, W. G., Chen, B. X., Guo, L. Q. and Lin, J. F. (2022). Ergothioneine exhibits longevity-extension effect in Drosophila melanogaster via regulation of cholinergic neurotransmission, tyrosine metabolism, and fatty acid oxidation. Food Funct 13(1): 227-241. PubMed ID: 34877949
Summary:
Many studies have demonstrated the protective effect of ergothioneine (EGT), the unique sulfur-containing antioxidant found in mushrooms, on several aging-related diseases. Nevertheless, to date, no single study has explored the potential role of EGT in the lifespan of animal models. This study shows that EGT consistently extends fly lifespan in diverse genetic backgrounds and both sexes, as well as in a dose and gender-dependent manner. Additionally, EGT is shown to increases the climbing activity of flies, enhance acetylcholinesterase (AchE) activity, and maintain the ratio of reduced glutathione (GSH) to oxidized glutathione (GSSG) of aged flies. The increase in lifespan by EGT is gut microorganism dependent. This study proposed potential mechanisms of lifespan extension in Drosophila by EGT through RNA-seq analysis: preservation of the normal status of the central nervous system via the coordination of cholinergic neurotransmission, tyrosine metabolism, and peroxisomal proteins, regulation of autophagic activity by altering the lysosomal protein CTSD, and the preservation of normal mitochondrial function through controlled substrate feeding into the tricarboxylic acid (TCA) cycle, the major energy-yielding metabolic process in cells.
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Iyengar, A., Ruan, H. and Wu, C. F. (2022). Distinct Aging-Vulnerable and -Resilient Trajectories of Specific Motor Circuit Functions in Oxidation- and Temperature-Stressed Drosophila. eNeuro 9(1). PubMed ID: 34876473
Summary:
In Drosophila, molecular pathways affecting longevity have been extensively studied. However, corresponding neurophysiological changes underlying aging-related functional and behavioral deteriorations remain to be fully explored. This study examined different motor circuits in Drosophila across the life span and uncovered distinctive age-resilient and age-vulnerable trajectories in their established functional properties. In the giant fiber (GF) and downstream circuit elements responsible for the jump-and-flight escape reflex, relatively mild deterioration was observed toward the end of the life span. In contrast, more substantial age-dependent modifications were seen in the plasticity of GF afferent processing, specifically in use dependence and habituation properties. In addition, there were profound changes in different afferent circuits that drive flight motoneuron activities, including flight pattern generation and seizure spike discharges evoked by electroconvulsive stimulation. Importantly, in high-temperature (HT)-reared flies (29°C), the general trends in these age-dependent trajectories were largely maintained, albeit over a compressed time scale, lending support for the common practice of HT rearing for expediting Drosophila aging studies. It was discovered that shortened life spans in Cu/Zn superoxide dismutase (Sod) mutant flies were accompanied by altered aging trajectories in motor circuit properties distinct from those in HT-reared flies, highlighting differential effects of oxidative versus temperature stressors. This work helps to identify several age-vulnerable neurophysiological parameters that may serve as quantitative indicators for assessing genetic and environmental influences on aging progression in Drosophila.
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Graham, L. C., Kline, R. A., Lamont, D. J., Gillingwater, T. H., Mabbott, N. A., Skehel, P. A. and Wishart, T. M. (2021). Temporal Profiling of the Cortical Synaptic Mitochondrial Proteome Identifies Ageing Associated Regulators of Stability. Cells 10(12). PubMed ID: 34943911
Summary:
Synapses are particularly susceptible to the effects of advancing age, and mitochondria have long been implicated as organelles contributing to this compartmental vulnerability. Despite this, the mitochondrial molecular cascades promoting age-dependent synaptic demise remain to be elucidated. This study sought to examine how the synaptic mitochondrial proteome (including strongly mitochondrial associated proteins) was dynamically and temporally regulated throughout ageing to determine whether alterations in the expression of individual candidates can influence synaptic stability/morphology. Proteomic profiling of wild-type mouse cortical synaptic and non-synaptic mitochondria across the lifespan revealed significant age-dependent heterogeneity between mitochondrial subpopulations, with aged organelles exhibiting unique protein expression profiles. Recapitulation of aged synaptic mitochondrial protein expression at the Drosophila neuromuscular junction has the propensity to perturb the synaptic architecture, demonstrating that temporal regulation of the mitochondrial proteome may directly modulate the stability of the synapse in vivo.
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Kanel, P., Noll, G. A., Schroedter, K., Naffin, E., Kronenberg, J., Busswinkel, F., Twyman, R. M., Klambt, C. and Prufer, D. (2022). The tobacco phosphatidylethanolamine-binding protein NtFT4 increases the lifespan of Drosophila melanogaster by interacting with the proteostasis network. Aging (Albany NY) 14. PubMed ID: 35396341
Summary:
Proteostasis reflects the well-balanced synthesis, trafficking and degradation of cellular proteins. This is a fundamental aspect of the dynamic cellular proteome, which integrates multiple signaling pathways, but it becomes increasingly error-prone during aging. Phosphatidylethanolamine-binding proteins (PEBPs) are highly conserved regulators of signaling networks and could therefore affect aging-related processes. To test this hypothesis, this study expressed PEPBs in a heterologous context to determine their ectopic activity. Heterologous expression of the tobacco (Nicotiana tabacum) PEBP NtFT4 in Drosophila melanogaster significantly increased the lifespan of adult flies and reduced age-related locomotor decline. Similarly, overexpression of the Drosophila ortholog CG7054 increased longevity, whereas its suppression by RNA interference had the opposite effect. In tobacco, NtFT4 acts as a floral regulator by integrating environmental and intrinsic stimuli to promote the transition to reproductive growth. In Drosophila, NtFT4 engaged distinct targets related to proteostasis, such as HSP26. In older flies, it also prolonged Hsp26 gene expression, which promotes longevity by maintaining protein integrity. In NtFT4-transgenic flies, deregulated genes were identified encoding proteases that may contribute to proteome stability at equilibrium. The results demonstrate that the expression of NtFT4 influences multiple aspects of the proteome maintenance system via both physical interactions and transcriptional regulation, potentially explaining the aging-related phenotypes that were observed.
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Akinade, T. C., Babatunde, O. O., Adedara, A. O., Adeyemi, O. E., Otenaike, T. A., Ashaolu, O. P., Johnson, T. O., Terriente-Felix, A., Whitworth, A. J. and Abolaji, A. O. (2022). Protective capacity of carotenoid trans-astaxanthin in rotenone-induced toxicity in Drosophila melanogaster. Sci Rep 12(1): 4594. PubMed ID: 35301354
Summary:
Trans-astaxanthin (TA), a keto-carotenoid found in aquatic invertebrates, possesses anti-oxidative and anti-inflammatory activities. Rotenone is used to induce oxidative stress-mediated Parkinson's disease (PD) in animals. Probes were performed to see if TA would protect against rotenone-induced toxicity in Drosophila melanogaster. Trans-astaxanthin and rotenone were separately orally exposed to flies in the diet to evaluate longevity and survival rates, respectively. Consequently, the ameliorative actions of TA on rotenone -induced toxicity was evaluated in Drosophila after 7 days' exposure. Additionally, molecular docking of TA was performed against selected pro-inflammatory protein targets. It was observed that TA increased the lifespan of D. melanogaster by 36.36%. Moreover, TA ameliorated rotenone-mediated inhibition of Catalase, Glutathione-S-transferase and Acetylcholinesterase activities, and depletion of Total Thiols and Non-Protein Thiols contents. Trans-astaxanthin prevented behavioural dysfunction and accumulation of Hydrogen Peroxide, Malondialdehyde, Protein Carbonyls and Nitric Oxide in D. melanogaster. Trans-astaxanthin showed higher docking scores against the pro-inflammatory protein targets evaluated than the standard inhibitors. Conclusively, the structural features of TA might have contributed to its protective actions against rotenone-induced toxicity.
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Narayan, V. P., Wilson, A. J. and Chenoweth, S. F. (2022). Genetic and social contributions to sex differences in lifespan in Drosophila serrata. J Evol Biol 35(4): 657-663. PubMed ID: 35290690
Summary:
Sex differences in lifespan remain an intriguing puzzle in evolutionary biology. While explanations range from sex differences in selection to sex differences in the expression of recessive lifespan-altering mutations (via X-linkage), little consensus has been reached. One unresolved issue is the extent to which genetic influences on lifespan dimorphism are modulated by the environment. For example, studies have shown that sex differences in lifespan can either increase or decrease depending upon the social environment. This study took an experimental approach, manipulating multiple axes of the social environment across inbred long- and short-lived genotypes and their reciprocal F1s in the fly Drosophila serrata. The results reveal strong genetic effects and subtle yet significant genotype-by-environment interactions for male and female lifespan, specifically due to both population density and mating status. Further, the data do not support the idea that unconditional expression of deleterious X-linked recessive alleles in heterogametic males accounts for lower male lifespan.
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Takeuchi, K. I., Honda, D., Okumura, M., Miura, M. and Chihara, T. (2021). Systemic innate immune response induces death of olfactory receptor neurons in Drosophila. Genes Cells PubMed ID: 34921694
Summary:
Neural functions are known to decline during normal aging and neurodegenerative diseases. However, the mechanisms of functional impairment owing to the normal aging of the brain are poorly understood. It was previously reported that caspase-3-like protease, the protease responsible for inducing apoptosis, is activated in a subset of olfactory receptor neurons (ORNs), especially in Drosophila Or42b neurons, during normal aging. This study investigated the molecular mechanism underlying age-related caspase-3-like protease activation and cell death in Or42b neurons. Gene expression profiling of young and aged fly antenna showed that the expression of antimicrobial peptides was significantly upregulated, suggesting an activated innate immune response. Consistent with this observation, inhibition or activation of the innate immune pathway caused delayed or precocious cell death, respectively, in Or42b neurons. Accordingly, autonomous cell activation of the innate immune pathway in Or42b neurons is not likely required for their age-related death, whereas the systemic innate immune response induces caspase-3-like protease activation in Or42b neurons; this indicated that the death of these neurons is regulated non-cell autonomously. A possible link between the innate immune response and the death of olfactory neurons during normal aging is proposed.
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Sheshadri, D., Onkar, A. and Ganesh, S. (2021). Alterations in brain glycogen levels influence life-history traits and reduce the lifespan in female Drosophila melanogaster. Biol Open 10(12). PubMed ID: 34817590
Summary:
Sexual dimorphism in lifespan, wherein females outlive males, is evident across all animal taxa. The longevity difference between sexes is controlled by multiple physiological processes with complex relationships to one another. In recent years, glycogen, the storage form of glucose, has been shown to cause rapid aging upon forced synthesis in healthy neurons. Glycogen in the form of corpora amylacea in the aging brain is also widely reported. While these studies did suggest a novel role for glycogen in aging, most of them have focused on pooled samples, and have not looked at sex-specific effects, if any. Given the widespread occurrence of sex-biased expression of genes and the underlying physiology, it is important to look at the sex-specific effects of metabolic processes. Using transgenic fly lines for the human glycogen synthase, this study investigated the sex-specific effects of glycogen on stress resistance, fitness, and survival. Drosophila melanogaster females with altered levels of glycogen in the brain were shown to display a shortened lifespan, increased resistance to starvation, and higher oxidative stress than male flies. The present study thus provides a novel insight into the sex-specific effect of glycogen in survival and aging and how differences in metabolic processes could contribute to sex-specific traits.
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Ortega-Arellano, H. F., Jimenez-Del-Rio, M. and Velez-Pardo, C. (2021). Melatonin Increases Life Span, Restores the Locomotor Activity, and Reduces Lipid Peroxidation (LPO) in Transgenic Knockdown Parkin Drosophila
melanogaster Exposed to Paraquat or Paraquat/Iron. Neurotox Res. PubMed ID: 34339012
Summary:
Parkinson's disease (PD)
is a complex progressive neurodegenerative disorder involving
impairment of bodily movement caused by the specific destruction of
dopaminergic (DAergic) neurons. Mounting evidence suggests that PD might
be triggered by an interplay between environmental neurotoxicants
(e.g., paraquat, PQ), heavy metals (e.g., iron), and gene alterations
(e.g., PARKIN gene). Unfortunately, there are no therapies currently
available that protect, slow, delay, or prevent the progression of PD.
Melatonin (Mel, N-acetyl-5-methoxy tryptamine) is a natural hormone with
pleiotropic functions including receptor-independent pathways which
might be useful in the treatment of PD. Therefore, as a chemical
molecule, it has been shown that Mel prolonged the lifespan and
locomotor activity, and reduced lipid peroxidation (LPO) in wild-type
Canton-S flies exposed to PQ, suggesting antioxidant and neuroprotective
properties. However, it is not yet known whether Mel can protect or
prevent the genetic model parkin
deficient in flies against oxidative stress (OS) stimuli. This study
shows that Mel (0.5, 1, 3 mM) significantly extends the life span
and locomotor activity of TH > parkin-RNAi/ + Drosophila melanogaster flies (> 15 days) compared to untreated flies. Knock-down (K-D) parkin
flies treated with PQ (1 mM) or PQ (1 mM)/iron (1 mM)
significantly diminished the survival index and climbing abilities
(e.g., 50% of flies were dead and locomotor impairment by days 4 and 3,
respectively). Remarkably, Mel reverted the noxious effect of PQ or
PQ/iron combination in K-D parkin. Indeed, Mel protects TH > parkin-RNAi/
+ Drosophila melanogaster flies against PQ- or PQ/iron-induced diminish
survival, locomotor impairment, and LPO (e.g., 50% of flies were death
and locomotor impairment by days 6 and 9, respectively). Similarly, Mel
prevented K-D parkin flies against both PQ and PQ/iron. Taken together,
these findings suggest that Mel can be safely used as an antioxidant and
neuroprotectant agent against OS-stimuli in selective individuals at
risk to suffer early-onset Parkinsonism and PD (Ortega-Arellano, 2021).
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Banerjee, S. J., Schonbrun, A., Eizadshenass, S., Benji, S., Cantor, Y. T., Eliach, L., Lubin, M., Narrowe, Z., Purow, J., Shulman, B., Wiener, L. and Steinhauer, J. (2021). iPLA2-VIA is required for healthy aging of neurons, muscle, and the female germline in Drosophila melanogaster. PLoS One 16(9): e0256738. PubMed ID: 34506510
Summary:
Neurodegenerative disease (ND) is a growing health burden worldwide, but its causes and treatments remain elusive. Although most cases of ND are sporadic, rare familial cases have been attributed to single genes, which can be investigated in animal models. This study generated a new mutation in the calcium-independent phospholipase A2 (iPLA2) VIA gene CG6718, the Drosophila melanogaster ortholog of human PLA2G6/PARK14, mutations in which cause a suite of NDs collectively called PLA2G6-associated neurodegeneration (PLAN). The mutants display age-related loss of climbing ability, a symptom of neurodegeneration in flies. Although phospholipase activity commonly is presumed to underlie iPLA2-VIA function, locomotor decline in the mutants used in this study is rescued by a transgene carrying a serine-to-alanine mutation in the catalytic residue, suggesting that important functional aspects are independent of phospholipase activity. Additionally, it was found that iPLA2-VIA knockdown in either muscle or neurons phenocopies locomotor decline with age, demonstrating its necessity in both neuronal and non-neuronal tissues. Furthermore, RNA in situ hybridization shows high endogenous iPLA2-VIA mRNA expression in adult germ cells, and transgenic HA-tagged iPLA2-VIA colocalizes with mitochondria there. Mutant males are fertile with normal spermatogenesis, while fertility is reduced in mutant females. Mutant female germ cells display age-related mitochondrial aggregation, loss of mitochondrial potential, and elevated cell death. These results suggest that iPLA2-VIA is critical for mitochondrial integrity in the Drosophila female germline, which may provide a novel context to investigate its functions with parallels to PLAN.
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Webb, J. L., Moe, S. M., Bolstad, A. K. and McNeill, E. M. (2021). Identification of conserved transcriptome features between humans and Drosophila in the aging brain utilizing machine learning on combined data from the NIH Sequence Read Archive. PLoS One 16(8): e0255085. PubMed ID: 34379632
Summary:
Aging is universal, yet characterizing the molecular changes that occur in aging which lead to an increased risk for neurological disease remains a challenging problem. Aging affects the prefrontal cortex (PFC), which governs executive function, learning, and memory. Previous sequencing studies have demonstrated that aging alters gene expression in the PFC, however the extent to which these changes are conserved across species and are meaningful in neurodegeneration is unknown. Identifying conserved, age-related genetic and morphological changes in the brain allows application of the wealth of tools available to study underlying mechanisms in model organisms such as Drosophila melanogaster. RNA sequencing data from human PFC and fly heads were analyzed to determine conserved transcriptome signatures of age. This analysis revealed that expression of 50 conserved genes can accurately determine age in Drosophila (R2 = 0.85) and humans (R2 = 0.46). These transcriptome signatures were also able to classify Drosophila into three age groups with a mean accuracy of 88% and classify human samples with a mean accuracy of 69%. Overall, this work identifies 50 highly conserved aging-associated genetic changes in the brain that can be further studied in model organisms and demonstrates a novel approach to uncovering genetic changes conserved across species from multi-study public databases.
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Brooks, D. S., Vishal, K., Bawa, S., Alder, A. and Geisbrecht, E. R. (2021). Integration of proteomic and genetic approaches to assess developmental muscle atrophy. Faseb j 35(10): e21914 J Exp Biol. PubMed ID: 34547132
Summary:
Muscle atrophy, or a decline in muscle protein mass, is a significant problem in the aging population and in numerous disease states. Unraveling molecular signals that trigger and promote atrophy may lead to a better understanding of treatment options; however, there is no single cause of atrophy identified to date. To gain insight into this problem, changes in protein profiles during muscle atrophy were investigated in Manduca sexta and Drosophila melanogaster. The use of insect models provides an interesting parallel to probe atrophic mechanisms since these organisms undergo a normal developmental atrophy process during the pupal transition stage. Leveraging the inherent advantages of each model organism, protein signature changes during Manduca intersegmental muscle (ISM) atrophy were defubed and then genetic approaches were used to confirm their functional importance in the Drosophila dorsal internal oblique muscles (DIOMs). The data reveal an upregulation of proteasome and peptidase components and a general downregulation of proteins that regulate actin filament formation. Surprisingly, thick filament proteins that comprise the A band are increased in abundance, providing support for the ordered destruction of myofibrillar components during developmental atrophy. The actin filament regulator Ciboulot (Cib) was uncovered as a novel regulator of muscle atrophy. These insights provide a framework towards a better understanding of global changes that occur during atrophy and may lead to eventual therapeutic targets (Brooks, 2021).
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Deepashree, S., Shivanandappa, T. and Ramesh, S. R. (2021). Genetic repression of the antioxidant enzymes reduces the lifespan in Drosophila melanogaster. J Comp Physiol B. PubMed ID: 34625818
Summary:
Aging is a biological process associated with gradual loss of function caused by cellular and molecular damages ultimately leading to mortality. Free radicals are implicated in oxidative damage which affects the longevity of organisms. Natural cellular defenses involving antioxidant enzymes delay or prevent oxidative damage and, therefore, influence the aging process and longevity has been shown in many species including Drosophila. Oxidative resistance has been shown to be an important mechanism in the aging process in Drosophila. Therefore, it was hypothesized that repressing endogenous antioxidant defenses shortens longevity in Drosophila. To study the influence of natural defense mechanisms against oxidative stress in aging, this study has investigated the effect of genetic repression of the antioxidant enzymes, superoxide dismutase (SOD) and catalase (CAT), on longevity in Drosophila using transgenic RNAi flies and in vivo inhibition of the enzymes with chemical inhibitors. RNAi lines of Drosophila viz., UAS-sod1-IR and UAS-cat-IR, are driven ubiquitously using Act5C-Gal4 and Tubulin-Gal4 to achieve the suppression of SOD1 and CAT activities, respectively. Genetic repression of SOD1 and CAT by RNAi in transgenic flies led to drastically reduced longevity (SOD1, 77%; CAT, 83%), presenting the evidence for the role of endogenous antioxidant defenses in lifespan extension in Drosophila. Further, this study shows that the enzyme inhibitors, diethyldithiocarbamate and 3-amino-1,2,4-triazole, although lower the enzyme activities in vivo in flies, but did not affect longevity, which could be attributed to the factors such as bioavailability and metabolism of the inhibitors and adaptive mechanisms involving de novo synthesis of the enzymes. This study of genetic repression using transgenic RNAi provides experimental evidence that extended longevity is associated with endogenous antioxidant defenses and aging is correlated with oxidative stress resistance (Deepashree, 2021).
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Yamashita, K., Oi, A., Kosakamoto, H., Yamauchi, T., Kadoguchi, H., Kuraishi, T., Miura, M. and Obata, F. (2021). Activation of innate immunity during development induces unresolved dysbiotic inflammatory gut and shortens lifespan. Dis Model Mech 14(9). PubMed ID: 34448472
Summary:
An early-life inflammatory response is associated with risks of
age-related pathologies. How transient immune signalling activity during
animal development influences life-long fitness is not well understood.
Using Drosophila as a model, this study found that activation of innate
immune pathway Immune deficiency (Imd) signalling in the developing larvae increases adult starvation resistance, decreases food intake and shortens organismal lifespan.
Interestingly, lifespan is shortened by Imd activation in the larval
gut and fat body, whereas starvation resistance and food intake are
altered by that in neurons. The adult flies that developed with Imd
activation show sustained Imd activity in the gut, despite complete
tissue renewal during metamorphosis. The larval Imd activation increases
an immunostimulative bacterial species, Gluconobacter sp., in the gut
microbiome, and this dysbiosis is persistent to adulthood. Removal of
gut microbiota by antibiotics in the adult fly mitigates intestinal
immune activation and rescues the shortened lifespan. This study
demonstrates that early-life immune activation triggers long-term
physiological changes, highlighted as an irreversible alteration in gut
microbiota, prolonged inflammatory intestine and concomitant shortening
of the organismal lifespan.
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Lee, B., Shin, C., Shin, M., Choi, B., Yuan, C. and Cho, K. S. (2021). The linear ubiquitin E3 ligase-Relish pathway is involved in the regulation of proteostasis in Drosophila muscle during aging. Biochem Biophys Res Commun 550: 184-190. PubMed ID: 33706102
Summary:
Linear ubiquitination is an atypic ubiquitination process that directly connects the N- and C-termini of ubiquitin and is catalyzed by HOIL-1-interacting protein (HOIP). It is involved in the immune response or apoptosis by activating the nuclear factor-κB pathway and is associated with polyglucosan body myopathy 1, an autosomal recessive disorder with progressive muscle weakness and cardiomyopathy. However, little is currently known regarding the function of linear ubiquitination in muscles. This study investigated the role of linear ubiquitin E3 ligase (LUBEL), a Drosophila HOIP ortholog, in the development and aging of muscles. The muscles of the flies with down-regulation of LUBEL or its downstream factors, kenny and Relish, developed normally, and there were no obvious abnormalities in function in young flies. However, the locomotor activity of the LUBEL RNAi flies was reduced compared to age-matched control, while LUBEL RNAi did not affect the increased mitochondrial fusion or myofiber disorganization during aging. Interestingly, the accumulation of polyubiquitinated protein aggregation during aging decreased in muscles by silencing LUBEL, kenny, or Relish. Meanwhile, the levels of autophagy and global translation, which are implicated in the maintenance of proteostasis, did not change due to LUBEL down-regulation. In conclusion, a new role of linear ubiquitination is proposed in proteostasis in the muscle aging (Lee, 2021).
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Shi, D., Han, T., Chu, X., Lu, H., Yang, X., Zi, T., Zhao, Y., Wang, X., Liu, Z., Ruan, J., Liu, X., Ning, H., Wang, M., Tian, Z., Wei, W., Sun, Y., Li, Y., Guo, R., Wang, Y., Ling, F., Guan, Y., Shen, D., Niu, Y., Li, Y. and Sun, C. (2021). An isocaloric moderately high-fat diet extends lifespan in male rats and Drosophila. Cell Metab. PubMed ID: 33440166
Summary:
The health effect of dietary fat has been one of the most vexing issues in the field of nutrition. Few animal studies have examined the impact of high-fat diets on lifespan by controlling energy intake. This study found that compared to a normal diet, an isocaloric moderately high-fat diet (IHF) significantly prolonged lifespan by decreasing the profiles of free fatty acids (FFAs) in serum and multiple tissues via downregulating FFA anabolism and upregulating catabolism pathways in rats and flies. Proteomics analysis in rats identified PPRC1 as a key protein that was significantly upregulated by nearly 2-fold by IHF, and among the FFAs, only palmitic acid (PA) was robustly and negatively associated with the expression of PPRC1. Using PPRC1 transgenic RNAi/overexpression flies and in vitro experiments, IHF was demonstrated to significantly reduced PA, which could upregulate PPRC1 through PPARG, resulting in improvements in oxidative stress and inflammation and prolonging the lifespan (Shi, 2021).
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Fabian, D. K., Melike Donertaş, H., Fuentealba, M., Partridge, L. and Thornton, J. M. (2021). Transposable element landscape in Drosophila populations selected for longevity. Genome Biol Evol. PubMed ID: 33595657
Summary:
Transposable elements (TEs) inflict numerous negative effects on health and fitness as they replicate by integrating into new regions of the host genome. Even though organisms employ powerful mechanisms to demobilize TEs, transposons gradually lose repression during aging. The rising TE activity causes genomic instability and was implicated in age-dependent neurodegenerative diseases, inflammation and the determination of lifespan. It is therefore conceivable that long-lived individuals have improved TE silencing mechanisms resulting in reduced TE expression relative to their shorter-lived counterparts and fewer genomic insertions. This study tested this hypothesis by performing the first genome-wide analysis of TE insertions and expression in populations of Drosophila melanogaster selected for longevity through late-life reproduction for 50-170 generations from four independent studies. Contrary to expectation, TE families were generally more abundant in long-lived populations compared to non-selected controls. Although simulations showed that this was not expected under neutrality, little evidence was found for selection driving TE abundance differences. Additional RNA-seq analysis revealed a tendency for reducing TE expression in selected populations, which might be more important for lifespan than regulating genomic insertions. Limited evidence was found of parallel selection on genes related to TE regulation and transposition. However, telomeric TEs were genomically and transcriptionally more abundant in long-lived flies, suggesting improved telomere maintenance as a promising TE-mediated mechanism for prolonging lifespan. The results provide a novel viewpoint indicating that reproduction at old age increases the opportunity of TEs to be passed on to the next generation with little impact on longevity (Fabian, 2021).
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Akan, I., Halim, A., Vakhrushev, S. Y., Clausen, H. and Hanover, J. A. (2021). Drosophila O-GlcNAcase Mutants Reveal an Expanded Glycoproteome and Novel Growth and Longevity Phenotypes. Cells 10(5). PubMed ID: 33925313
Summary:
The reversible posttranslational O-GlcNAc modification of serine or threonine residues of intracellular proteins is involved in many cellular events from signaling cascades to epigenetic and transcriptional regulation. O-GlcNAcylation is a conserved nutrient-dependent process involving two enzymes, with O-GlcNAc transferase (OGT) adding O-GlcNAc and with O-GlcNAcase (OGA) removing it in a manner that's protein- and context-dependent. O-GlcNAcylation is essential for epigenetic regulation of gene expression through its action on Polycomb and Trithorax and COMPASS complexes. However, the important role of O-GlcNAc in adult life and health span has been largely unexplored, mainly due the lack of available model systems. Cataloging the O-GlcNAc proteome has proven useful in understanding the biology of this modification in vivo. In this study, a recently developed oga knockout fly mutant was leveraged to identify the O-GlcNAcylated proteins in adult Drosophila melanogaster. The adult O-GlcNAc proteome revealed many proteins related to cell and organismal growth, development, differentiation, and epigenetics. Many O-GlcNAcylated proteins were identified that play a role in increased growth and decreased longevity, including HCF, SIN3A, LOLA, KISMET, ATX2, SHOT, and FOXO. Interestingly, oga mutant flies are larger and have a shorter life span compared to wild type flies, suggesting increased O-GlcNAc results in increased growth. These results suggest that O-GlcNAc alters the function of many proteins related to transcription, epigenetic modification and signaling pathways that regulate growth rate and longevity. Therefore, these findings highlight the importance of O-GlcNAc in growth and life span in adult Drosophila.
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Oka, M., Suzuki, E., Asada, A., Saito, T., Iijima, K. M. and Ando, K. (2021). Increasing neuronal glucose uptake attenuates brain aging and promotes life span under dietary restriction in Drosophila. iScience 24(1): 101979. PubMed ID: 33490892
Summary:
Brain neurons play a central role in organismal aging, but there is conflicting evidence about the role of neuronal glucose availability because glucose uptake and metabolism are associated with both aging and extended life span. This study analyzed metabolic changes in the brain neurons of Drosophila during aging. Using a genetically encoded fluorescent adenosine triphosphate (ATP) biosensor, decreased ATP concentration was found in the neuronal somata of aged flies, correlated with decreased glucose content, expression of glucose transporter and glycolytic enzymes and mitochondrial quality. The age-associated reduction in ATP concentration did not occur in brain neurons with suppressed glycolysis or enhanced glucose uptake, suggesting these pathways contribute to ATP reductions. Despite age-associated mitochondrial damage, increasing glucose uptake maintained ATP levels, suppressed locomotor deficits, and extended the life span. Increasing neuronal glucose uptake during dietary restriction resulted in the longest life spans, suggesting an additive effect of enhancing glucose availability during a bioenergetic challenge on aging (Oka, 2021).
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Vincow, E. S., Thomas, R. E., Merrihew, G. E., MacCoss, M. J. and Pallanck, L. J. (2021). Slowed protein turnover in aging Drosophila reflects a shift in cellular priorities. J Gerontol A Biol Sci Med Sci. PubMed ID: 33453098
Summary:
The accumulation of protein aggregates and dysfunctional organelles as organisms age has led to the hypothesis that aging involves general breakdown of protein quality control. This hypothesis was tested using a proteomic and informatic approach in the fruit fly Drosophila melanogaster. Turnover of most proteins was markedly slower in old flies. However, ribosomal and proteasomal proteins maintained high turnover rates, suggesting that the observed slowdowns in protein turnover might not be due to a global failure of quality control. As protein turnover reflects the balance of protein synthesis and degradation, whether decreases in synthesis or decreases in degradation would best explain the observed slowdowns in protein turnover was investigated. It was found that while many individual proteins in old flies showed slower turnover due to decreased degradation, an approximately equal number showed slower turnover due to decreased synthesis, and enrichment analyses revealed that translation machinery itself was less abundant. Mitochondrial complex I subunits and glycolytic enzymes were decreased in abundance as well, and proteins involved in glutamine-dependent anaplerosis were increased, suggesting that old flies modify energy production to limit oxidative damage. Together, these findings suggest that age-related proteostasis changes in Drosophila represent a coordinated adaptation rather than a systems collapse (Vincow, 2021).
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Strilbytska, O. M., Zayachkivska, A., Koliada, A., Galeotti, F., Volpi, N., Storey, K. B., Vaiserman, A. and Lushchak, O. (2020). Anise Hyssop Agastache foeniculum Increases Lifespan, Stress Resistance, and Metabolism by Affecting Free Radical Processes in Drosophila. Front Physiol 11: 596729. PubMed ID: 33391017
Summary:
Anise hyssop, Agastache foeniculum, is a widely used medicinal herb with known antioxidant properties. This study examined how dietary supplementation with dried A. foeniculum leaf powder affected physiological and metabolic traits as well as activities of antioxidant enzymes and markers of oxidative stress in Drosophila melanogaster. Dietary hyssop extended the lifespan in a sex and genotype independent manner over a broad range of concentrations up to 30 mg/ml. Dietary supplementation with the herb significantly increased fecundity, resistance to oxidative stress and starvation. Higher transcript levels of Drosophila insulin-like peptide (dilp2) and decreased dilp3 and dilp6 transcripts together with increased levels of glycogen and triacylglycerols support an alteration of insulin signaling by the plant extract. Increased enzymatic activities of superoxide dismutase and aconitase as well as elevated protein and low molecular mass thiols also supported an alteration of free radical process in flies treated with dietary A. foeniculum leaf powder. Thus, physiological and metabolic traits as well as free radical processed may be affected by active compounds detected in extracts of anise hyssop leaves and contribute to the increased lifespan and reproductive (egg-laying) activity observed (Strilbytska, 2020).
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Savola, E., Montgomery, C., Waldron, F. M., Monteith, K. M., Vale, P. and Walling, C. (2020). Testing evolutionary explanations for the lifespan benefit of dietary restriction in fruit flies (Drosophila melanogaster). Evolution. PubMed ID: 33320333
Summary:
Dietary restriction (DR), limiting calories or specific nutrients without malnutrition, extends lifespan across diverse taxa. Traditionally, this lifespan extension has been explained as a result of diet-mediated changes in the trade-off between lifespan and reproduction, with survival favored when resources are scarce. However, a recently proposed alternative suggests that the selective benefit of the response to DR is the maintenance of reproduction. This hypothesis predicts that lifespan extension is a side effect of benign laboratory conditions, and DR individuals would be frailer and unable to deal with additional stressors, and thus lifespan extension should disappear under more stressful conditions. This was tested by rearing outbred female fruit flies (Drosophila melanogaster) on 10 different protein:carbohydrate diets. Flies were either infected with a bacterial pathogen (Pseudomonas entomophila), injured with a sterile pinprick, or unstressed. Lifespan, fecundity, and measures of aging were monitored. DR extended lifespan and reduced reproduction irrespective of injury and infection. Infected flies on lower protein diets had particularly poor survival. Exposure to infection and injury did not substantially alter the relationship between diet and aging patterns. These results do not provide support for lifespan extension under DR being a side effect of benign laboratory conditions (Savola, 2020).
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Krittika, S. and Yadav, P. (2020). Dietary protein restriction deciphers new relationships between lifespan, fecundity and activity levels in fruit flies Drosophila melanogaster. Sci Rep 10(1): 10019. PubMed ID: 32572062
Summary:
Drosophila melanogaster has been used in Diet Restriction (DR) studies for a few decades now, due to easy diet implementation and its short lifespan. Since the concentration of protein determines the trade-offs between lifespan and fecundity, it is important to understand the level of protein and the extent of its influence on lifespan, fecundity and activity of fruit flies. This study intended to assess the effect of a series of protein restricted diets from age 1 day of the adult fly on these traits to understand the possible variations in trade-off across tested diets. Lifespan under different protein concentrations remains unaltered, even though protein restricted diets exerted an age-specific influence on fecundity. Interestingly, there was no difference in lifetime activity of the flies in most of the tested protein restricted (PR) diets, even though a sex-dependent influence of protein concentrations was observed. Additionally, it is reported that not all concentrations of PR diet increase activity, thereby suggesting that the correlation between lifespan and the lifetime activity can be challenged under protein-restricted condition. Therefore, the PR does not need to exert its effect on lifespan and fecundity only but can also influence activity levels of the flies, thereby emphasizing the role of nutrient allotment between lifespan, fecundity and activity (Krittika, 2020).
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Wilson, K. A., Beck, J. N., Nelson, C. S., Hilsabeck, T. A., Promislow, D., Brem, R. B. and Kapahi, P. (2020). GWAS for Lifespan and Decline in Climbing Ability in Flies upon Dietary Restriction Reveal decima as a Mediator of Insulin-like Peptide Production. Curr Biol. PubMed ID: 32502405
Summary:
Dietary restriction (DR) is the most robust means to extend lifespan and delay age-related diseases across species. An underlying assumption in the aging field is that DR enhances both lifespan and physical activity through similar mechanisms, but this has not been rigorously tested in different genetic backgrounds. Furthermore, nutrient response genes responsible for lifespan extension or age-related decline in functionality remain underexplored in natural populations. To address this, nutrient-dependent changes were measured in lifespan and age-related decline in climbing ability in the Drosophila Genetic Reference Panel fly strains. On average, DR extended lifespan and delayed decline in climbing ability, but there was a lack of correlation between these traits across individual strains, suggesting that distinct genetic factors modulate these traits independently and that genotype determines response to diet. Only 50% of strains showed positive response to DR for both lifespan and climbing ability, 14% showed a negative response for one trait but not both, and 35% showed no change in one or both traits. Through GWAS, a number of genes were uncovered previously not known to be diet responsive nor to influence lifespan or climbing ability. decima/CG34351 was validated as a gene that alters lifespan and daedalus/CG33690 as one that influences age-related decline in climbing ability. decima was found to influences insulin-like peptide transcription in the GABA receptor neurons downstream of short neuropeptide F precursor (sNPF) signaling. Modulating these genes produced independent effects on lifespan and physical activity decline, which suggests that these age-related traits can be regulated through distinct mechanisms (Wilson, 2020).
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Fan, X., Zeng, Y., Fan, Z., Cui, L., Song, W., Wu, Q., Gao, Y., Yang, D., Mao, X., Zeng, B., Zhang, M., Ni, Q., Li, Y., Wang, T., Li, D. and Yang, M. (2020). Dihydromyricetin promotes longevity and activates the transcription factors FOXO and AOP in Drosophila. Aging (Albany NY) 12. PubMed ID: 33291074
Summary:
Drugs or compounds have been shown to promote longevity in various approaches. This study used Drosophila to explore novel natural compounds can be applied to anti-aging. A flavonoid named Dihydromyricetin can increase stress tolerance and lipid levels, slow down gut dysfunction and extend Drosophila lifespan. Dihydromyricetin can also lessen pERK and pAKT signaling, consequently activating FOXO and AOP to modulate longevity. These results suggested that DHM could be used as an effective compound for anti-aging intervention, which could likely be applied to both mammals and humans (Fan, 2020).
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Parkhitko, A. A., Ramesh, D., Wang, L., Leshchiner, D., Filine, E., Binari, R., Olsen, A. L., Asara, J. M., Cracan, V., Rabinowitz, J. D., Brockmann, A. and Perrimon, N. (2020). Downregulation of the tyrosine degradation pathway extends Drosophila lifespan. Elife 9. PubMed ID: 33319750
Summary:
Lipid homeostasis is essential for insects to maintain phospholipid (PL)-based membrane integrity and to provide on-demand energy supply throughout life. Triacylglycerol (TAG) is the major lipid class used for energy production and is stored in lipid droplets, the universal cellular fat storage organelles. Accumulation and mobilization of TAG are strictly regulated since excessive accumulation of TAG leads to obesity and has been correlated with adverse effects on health- and lifespan across phyla. Little is known, however, about when during adult life and why excessive storage lipid accumulation restricts lifespan. This study used genetically obese Drosophila mutant males, which were all shown to be short-lived compared to control males and applied single fly mass spectrometry-based lipidomics to profile TAG, diacylglycerol and major membrane lipid signatures throughout adult fly life from eclosion to death. This comparative approach revealed distinct phases of lipidome remodeling throughout aging. Quantitative and qualitative compositional changes of TAG and PL species, which are characterized by the length and saturation of their constituent fatty acids, were pronounced during young adult life. In contrast, lipid signatures of adult and senescent flies were remarkably stable. Genetically obese flies displayed both quantitative and qualitative changes in TAG species composition, while PL signatures were almost unaltered compared to normal flies at all ages. Collectively, this suggests a tight control of membrane composition throughout lifetime largely uncoupled from storage lipid metabolism. Finally, evidence is presented for a characteristic lipid signature of moribund flies, likely generated by a rapid and selective storage lipid depletion close to death. Of note, the analytical power to monitor lipid species profiles combined with high sensitivity of this single fly lipidomics approach is universally applicable to address developmental or behavioral lipid signature modulations of importance for insect life (Hofbauer, 2020).
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Khor, S. and Cai, D. (2020). Control of lifespan and survival by Drosophila NF-κB signaling through neuroendocrine cells and neuroblasts. Aging (Albany NY) 12(24): 24604-24622. PubMed ID: 33232282
Summary:
This paper reports a comparative analysis of the effects of immune activation in the fly nervous system using genetic activation models to target Drosophila NF-κB within Toll versus Imd pathways. Genetic gain-of-function models for either pathway pan-neuronally, as well as in discrete subsets of neural cells including neuroendocrine insulin-producing cells (IPCs) or neuroblasts, reduce fly lifespan, however, these phenotypes in IPCs and neuroblasts are stronger with Toll activation than Imd activation. Of note, while aging is influenced more by Toll/NF-κB activation in IPCs during adulthood, neuroblasts influence aging more substantially during development. The study then focused on Toll/NF-κB inhibition, revealing that IPCs or neuroblasts are important for the effects of lifespan and healthspan extension but in a life stage-dependent manner while some of these effects display sexual dimorphism. Importantly, co-inhibition of Toll/NF-κB pathway in IPCs and neuroblasts increased fly lifespan greater than either cell population, suggesting that independent mechanisms might exist. Toll/NF-κB inhibition in IPCs was also sufficient to enhance survival under various fatal stresses, supporting the additional benefits to fly healthspan. In conclusion, IPCs and neuroblasts are important for Drosophila NF-κB for controlling lifespan (Khor, 2020).
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Bjedov, I., Cocheme, H. M., Foley, A., Wieser, D., Woodling, N. S., Castillo-Quan, J. I., Norvaisas, P., Lujan, C., Regan, J. C., Toivonen, J. M., Murphy, M. P., Thornton, J., Kinghorn, K. J., Neufeld, T. P., Cabreiro, F. and Partridge, L. (2020). Fine-tuning autophagy maximises lifespan and is associated with changes in mitochondrial gene expression in Drosophila. PLoS Genet 16(11): e1009083. PubMed ID: 33253201
Summary:
Increased cellular degradation by autophagy is a feature of many interventions that delay ageing. This paper reports that increased autophagy is necessary for reduced insulin-like signalling (IIS) to extend lifespan in Drosophila and is sufficient on its own to increase lifespan. It was first established that the well-characterised lifespan extension associated with deletion of the insulin receptor substrate chico was completely abrogated by downregulation of the essential autophagy gene Atg5. Next autophagy was directly induced by over-expressing the major autophagy kinase Atg1; a mild increase in autophagy extended lifespan. Interestingly, strong Atg1 up-regulation was detrimental to lifespan. Transcriptomic and metabolomic approaches identified specific signatures mediated by varying levels of autophagy in flies. Transcriptional upregulation of mitochondrial-related genes was the signature most specifically associated with mild Atg1 upregulation and extended lifespan, whereas short-lived flies, possessing strong Atg1 overexpression, showed reduced mitochondrial metabolism and up-regulated immune system pathways. Increased proteasomal activity and reduced triacylglycerol levels were features shared by both moderate and high Atg1 overexpression conditions. These contrasting effects of autophagy on ageing and differential metabolic profiles highlight the importance of fine-tuning autophagy levels to achieve optimal healthspan and disease prevention (Bjedov, 2020).
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Parkhitko, A. A., Ramesh, D., Wang, L., Leshchiner, D., Filine, E., Binari, R., Olsen, A. L., Asara, J. M., Cracan, V., Rabinowitz, J. D., Brockmann, A. and Perrimon, N. (2020). Downregulation of the tyrosine degradation pathway extends Drosophila lifespan. Elife 9. PubMed ID: 33319750
Summary:
To identify metabolic pathways associated with aging, age-dependent changes in the metabolomes of long-lived Drosophila were examined. Among the metabolites that changed, levels of tyrosine were increased with age in long-lived flies. The levels of enzymes in the tyrosine degradation pathway increase with age in wild-type flies. Whole-body and neuronal-specific downregulation of enzymes in the tyrosine degradation pathway significantly extends Drosophila lifespan, causes alterations of metabolites associated with increased lifespan, and upregulates the levels of tyrosine-derived neuromediators. Moreover, feeding wild-type flies with tyrosine increased their lifespan. Mechanistically, it was shown that suppression of ETC complex I drives the upregulation of enzymes in the tyrosine degradation pathway, an effect that can be rescued by tigecycline, an FDA-approved drug that specifically suppresses mitochondrial translation. In addition, tyrosine supplementation partially rescued lifespan of flies with ETC complex I suppression. Altogether, this study highlights the tyrosine degradation pathway as a regulator of longevity (Parkhitko, 2020).
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Sheng, L., Shields, E. J., Gospocic, J., Glastad, K. M., Ratchasanmuang, P., Berger, S. L., Raj, A., Little, S. and Bonasio, R. (2020). Social reprogramming in ants induces longevity-associated glia remodeling. Sci Adv 6(34): eaba9869. PubMed ID: 32875108
Summary:
In social insects, workers and queens arise from the same genome but display profound differences in behavior and longevity. In Harpegnathos saltator ants, adult workers can transition to a queen-like state called gamergate, which results in reprogramming of social behavior and life-span extension. Using single-cell RNA sequencing, the distribution of neuronal and glial populations was compared before and after the social transition. This study found that the conversion of workers into gamergates resulted in the expansion of neuroprotective ensheathing glia. Brain injury assays revealed that activation of the damage response gene Mmp1 was weaker in old workers, where the relative frequency of ensheathing glia also declined. On the other hand, long-lived gamergates retained a larger fraction of ensheathing glia and the ability to mount a strong Mmp1 response to brain injury into old age. Molecular and cellular changes were observed suggestive of age-associated decline in ensheathing glia in Drosophila (Sheng, 2020).
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Nandakumar, S., Grushko, O. and Buttitta, L. A. (2020). Polyploidy in the adult Drosophila brain. Elife 9. PubMed ID: 32840209
Summary:
Long-lived cells such as terminally differentiated postmitotic neurons and glia must cope with the accumulation of damage over the course of an animal's lifespan. How long-lived cells deal with ageing-related damage is poorly understood. This study shows that polyploid cells accumulate in the adult fly brain and that polyploidy protects against DNA damage-induced cell death. Multiple types of neurons and glia that are diploid at eclosion, become polyploid in the adult Drosophila brain. The optic lobes exhibit the highest levels of polyploidy, associated with an elevated DNA damage response in this brain region. Inducing oxidative stress or exogenous DNA damage leads to an earlier onset of polyploidy, and polyploid cells in the adult brain are more resistant to DNA damage-induced cell death than diploid cells. These results suggest polyploidy may serve a protective role for neurons and glia in adult Drosophila melanogaster brains (Nandakumar, 2020).
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Yamauchi, T., Oi, A., Kosakamoto, H., Akuzawa-Tokita, Y., Murakami, T., Mori, H., Miura, M. and Obata, F. (2020). Gut Bacterial Species Distinctively Impact Host Purine Metabolites during Aging in Drosophila. iScience 23(9): 101477. PubMed ID: 32916085
Summary:
Gut microbiota impacts the host metabolome and affects its health span. How bacterial species in the gut influence age-dependent metabolic alteration has not been elucidated. This study shows in Drosophila melanogaster that allantoin, an end product of purine metabolism, is increased during aging in a microbiota-dependent manner. Allantoin levels are low in young flies but are commonly elevated upon lifespan-shortening dietary manipulations such as high-purine, high-sugar, or high-yeast feeding. Removing Acetobacter persici in the Drosophila microbiome attenuated age-dependent allantoin increase. Mono-association with A. persici, but not with Lactobacillus plantarum, increased allantoin in aged flies. A. persici increased allantoin via activation of innate immune signaling IMD pathway in the renal tubules. On the other hand, analysis of bacteria-conditioned diets revealed that L. plantarum can decrease allantoin by reducing purines in the diet. These data together demonstrate species-specific regulations of host purine levels by the gut microbiome (Yamauchi, 2020).
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Lien, W. Y., Chen, Y. T., Li, Y. J., Wu, J. K., Huang, K. L., Lin, J. R., Lin, S. C., Hou, C. C., Wang, H. D., Wu, C. L., Huang, S. Y. and Chan, C. C. (2020). Lifespan regulation in alpha/beta posterior neurons of the fly mushroom bodies by Rab27. Aging Cell: e13179. PubMed ID: 32627932
Summary:
Brain function has been implicated to control the aging process and modulate lifespan. However, continuous efforts remain for the identification of the minimal sufficient brain region and the underlying mechanism for neuronal regulation of longevity. This study shows that the Drosophila lifespan is modulated by rab27 functioning in a small subset of neurons of the mushroom bodies (MB), a brain structure that shares analogous functions with mammalian hippocampus and hypothalamus. Depleting rab27 in the α/βp neurons of the MB is sufficient to extend lifespan, enhance systemic stress responses, and alter energy homeostasis, all without trade-offs in major life functions. Within the α/βp neurons, rab27KO causes the mislocalization of phosphorylated S6K thus attenuates TOR signaling, resulting in decreased protein synthesis and reduced neuronal activity. Consistently, expression of dominant-negative S6K in the α/βp neurons increases lifespan. Furthermore, the expression of phospho-mimetic S6 in α/βp neurons of rab27KO rescued local protein synthesis and reversed lifespan extension. These findings demonstrate that inhibiting TOR-mediated protein synthesis in α/βp neurons is sufficient to promote longevity (Lien, 2020).
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Yamakawa-Kobayashi, K., Ohhara, Y., Kawashima, T., Ohishi, Y. and Kayashima, Y. (2020). Loss of CNDP causes a shorter lifespan and higher sensitivity to oxidative stress in Drosophila melanogaster. Biomed Res 41(3): 131-138. PubMed ID: 32522930
Summary:
Increasing oxidative stress seems to be the result of an imbalance between free radical production and antioxidant defenses. During the course of aging, oxidative stress causes tissue/cellular damage, which is implicated in numerous age-related diseases. Carnosinase (CN or CNDP) is dipeptidase, which is associated with carnosine and/or glutathione (GSH) metabolism, those are the most abundant naturally occurring endogenous dipeptide and tripeptides with antioxidant and free radical scavenger properties. This study generated Drosophila cndp (dcndp) mutant flies using the CRISPR/Cas9 system to study the roles of dcndp in vivo. dcndp mutant flies exhibit shorter lifespan and increased sensitivity to paraquat or hydrogen peroxide induced oxidative stress. These results suggest that dcndp maintains homeostatic conditions, protecting cells and tissues against the harmful effects of oxidative stress in the course of aging.
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Brown, E. J., Nguyen, A. H. and Bachtrog, D. (2020). The Y chromosome may contribute to sex-specific ageing in Drosophila. Nat Ecol Evol. PubMed ID: 32313175
Summary:
Heterochromatin suppresses repetitive DNA, and a loss of heterochromatin has been observed in aged cells of several species, including humans and Drosophila. Males often contain substantially more heterochromatic DNA than females, due to the presence of a large, repeat-rich Y chromosome, and male flies generally have a shorter average lifespan than females. This study shows that repetitive DNA becomes de-repressed more rapidly in old male flies relative to females, and repeats on the Y chromosome are disproportionally mis-expressed during ageing. This is associated with a loss of heterochromatin at repetitive elements during ageing in male flies, and a general loss of repressive chromatin in aged males away from pericentromeric regions and the Y. By generating flies with different sex chromosome karyotypes (XXY females and X0 and XYY males), this study shows that repeat de-repression and average lifespan is correlated with the number of Y chromosomes. This suggests that sex-specific chromatin differences may contribute to sex-specific ageing in flies (Brown, 2020).
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Huang, W., Campbell, T., Carbone, M. A., Jones, W. E., Unselt, D., Anholt, R. R. H. and Mackay, T. F. C. (2020). Context-dependent genetic architecture of Drosophila life span. PLoS Biol 18(3): e3000645. PubMed ID: 32134916
Summary:
Understanding the genetic basis of variation in life span is a major challenge that is difficult to address in human populations. Evolutionary theory predicts that alleles affecting natural variation in life span will have properties that enable them to persist in populations at intermediate frequencies, such as late-life-specific deleterious effects, antagonistic pleiotropic effects on early and late-age fitness components, and/or sex- and environment-specific or antagonistic effects. This study quantified variation in life span in males and females reared in 3 thermal environments for the sequenced, inbred lines of the Drosophila melanogaster Genetic Reference Panel (DGRP) and an advanced intercross outbred population derived from a subset of DGRP lines. Quantitative genetic analyses of life span and the micro-environmental variance of life span in the DGRP revealed significant genetic variance for both traits within each sex and environment, as well as significant genotype-by-sex interaction (GSI) and genotype-by-environment interaction (GEI). Genome-wide association (GWA) mapping in both populations implicates over 2,000 candidate genes with sex- and environment-specific or antagonistic pleiotropic allelic effects. Over 1,000 of these genes are associated with variation in life span in other D. melanogaster populations. The effects of 15 candidate genes were functionally assessed using RNA interference (RNAi): all affected life span and/or micro-environmental variance of life span in at least one sex and environment and exhibited sex-and environment-specific effects. These results implicate novel candidate genes affecting life span and suggest that variation for life span may be maintained by variable allelic effects in heterogeneous environments (Huang, 2020).
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Wu, Q., Yu, G., Cheng, X., Gao, Y., Fan, X., Yang, D., Xie, M., Wang, T., Piper, M. D. W. and Yang, M. (2020). Sexual dimorphism in the nutritional requirement for adult lifespan in Drosophila melanogaster. Aging Cell 19(3): e13120. PubMed ID: 32069521
Summary:
The nutritional requirements of Drosophila have mostly been studied for development and reproduction, but the minimal requirements for adult male and female flies for lifespan have not been established. Following development on a complete diet, this study found substantial sex difference in the basic nutritional requirement of adult flies for full length of life. Relative to females, males require less of each nutrient, and for some nutrients that are essential for development, adult males have no requirement at all for lifespan. The most extreme (and surprising) sex differences were that chronic cholesterol and vitamin deficiencies had no effect on the lifespan of adult males, but they greatly decreased lifespan in females. Female oogenesis rather than chromosomal karyotype and mating status is the key cause of this gender difference in life-sustaining nutritional requirements. These data are important to the way the mechanisms are understood by which diet modifies lifespan (Wu, 2020).
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Obata, F., Fons, C. O. and Gould, A. P. (2018). Early-life exposure to low-dose oxidants can increase longevity via microbiome remodelling in Drosophila. Nat Commun 9(1): 975. PubMed ID: 29515102
Summary:
Envronmental stresses experienced during development exert many long-term effects upon health and disease. For example, chemical oxidants or genetic perturbations that induce low levels of reactive oxygen species can extend lifespan in several species. In some cases, the beneficial effects of low-dose oxidants are attributed to adaptive protective mechanisms such as mitohormesis, which involve long-term increases in the expression of stress response genes. This study shows in Drosophila that transient exposure to low concentrations of oxidants during development leads to an extension of adult lifespan. Surprisingly, this depends upon oxidants acting in an antibiotic-like manner to selectively deplete the microbiome of Acetobacter proteobacteria. The presence of Acetobacter species, such as A. aceti, in the indigenous microbiota increases age-related gut dysfunction and shortens lifespan. This study demonstrates that low-dose oxidant exposure during early life can extend lifespan via microbiome remodelling rather than mitohormesis (Obata, 2018).
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Matsuno, M., Horiuchi, J., Ofusa, K., Masuda, T. and Saitoe, M. (2019). Inhibiting glutamate activity during consolidation suppresses age-related long-term memory impairment in Drosophila. iScience 15: 55-65. PubMed ID: 31030182
Summary:
In Drosophila, long-term memory (LTM) formation requires increases in glial gene expression. Klingon (Klg), a cell adhesion molecule expressed in both neurons and glia, induces expression of the glial transcription factor, Repo. However, glial signaling downstream of Repo has been unclear. This study demonstrates that Repo increases expression of the glutamate transporter, EAAT1, and EAAT1 is required during consolidation of LTM. The expressions of Klg, Repo, and EAAT1 decrease upon aging, suggesting that age-related impairments in LTM are caused by dysfunction of the Klg-Repo-EAAT1 pathway. Supporting this idea, overexpression of Repo or EAAT1 rescues age-associated impairments in LTM. Pharmacological inhibition of glutamate activity during consolidation improves LTM in klg mutants and aged flies. Altogether, the results indicate that LTM formation requires glial-dependent inhibition of glutamate signaling during memory consolidation, and aging disrupts this process by inhibiting the Klg-Repo-EAAT1 pathway (Matsuno, 2019).
Changes in glial transcription due to neuronal activity have been studied previously, but a specific role of glial transcription in LTM has been less characterized. Expression of the glial transcription factor, Repo, increases shortly after spaced training, and this increase is required for LTM formation. This report has identified Eaat1 as a Repo-regulated glial gene required for LTM consolidation. Eaat1 encodes a glial glutamate transporter that removes glutamate from synaptic sites and transports it into astrocytes. Thus, the data indicate that glutamate signaling needs to be inhibited during LTM consolidation (Matsuno, 2019).
To identify Eaat1, a screen was performed for various genes regulating glial physiology for altered expression during LTM formation. Expression of Eaat1 and crammer was found to increase after spaced training. As Eaat1, but not crammer, is expressed exclusively in glia, focus was placed on Eaat1 as a likely Repo-regulated gene. Indeed, spaced-training-induced increases in EAAT1 depend on Repo and Klg activity. Interestingly, expression of the glial gene, genderblind, which encodes another glial glutamate transporter, required Repo activity for expression, but was not affected by spaced training, suggesting that other transcriptional regulatory factors besides Repo are likely necessary to differentially regulate genes required for memory consolidation from those required for other glial functions (Matsuno, 2019).
Because only screened selected genes were screened, it is possible that Repo induces the expression of other unidentified genes after spaced training. However, somewhat unexpectedly, it was found that overexpression of Eaat1 alone in glial cells is sufficient to rescue the LTM defects of klg and repo mutants. This indicates that the major function of the Klg/Repo signaling pathway is to induce glial expression of Eaat1. It further suggests that one function of astrocytes is to decrease glutamate signaling during LTM consolidation (Matsuno, 2019).
Combined with results from previous studies, this work identifies a putative pathway linking neuronal activity to glial inhibition of glutamate signaling. In flies, the homophilic cell adhesion molecule, Klingon, is expressed in both neurons and glia, and needs to be expressed in both cell types for normal LTM. Repo expression normally increases after spaced training, whereas it fails to do so in klg mutants, indicating that Klg-mediated neuron-glia communication is necessary for this increase. Thus, it is proposed that spaced training increases neuronal activity, which induces signaling to glia via the cell adhesion molecule Klg. This results in increased Repo activity in glia, which increases Eaat1 expression, and subsequently decreases glutamate signaling (Matsuno, 2019).
Previous work from various groups including has shown that glutamate signaling through NMDA-type receptors (NRs) is necessary for learning and memory. Overexpression of NRs in mice enhances learning and memory formation, and it has been shown that glial production of D-serine, a neuromodulator that functions as a coactivator of NRs, is necessary for short-lasting memory. In the current study, focus was placed on glutamate activity specifically during memory consolidation, instead of during initial learning and memory formation. Considering the current findings with those of previous studies, it is proposed that NR-dependent glutamate signaling needs to be initially high, during formation of short-lasting memories, but low during a later phase where short-lasting memories are consolidated into LTM. This suggests that glia play at least two roles in memory. They produce D-serine that contributes to high NR activity during memory formation and also produce EAAT1 after learning, which functions to reduce glutamate signaling during memory consolidation (Matsuno, 2019).
Age-related impairments in Drosophila memory do not consist of a general decrease in all forms of learning and memory, but instead consist of decreases in two specific phases of memory, MTM and LTM. The current results suggest that both these memory effects are caused by age-related glial dysfunction. Glia in young flies are able to produce sufficient amounts of D-serine for normal MTM, whereas D-serine amounts decrease 2-fold in aged flies. This decrease is responsible for age-related impairments in 1-h memory, because increasing glial production of D-serine, or directly feeding of D-serine to aged flies, rescues this impairment. Likewise, glial dysfunction is also responsible for age-related impairments in LTM because aged glia are unable to inhibit glutamate signaling during consolidation. Thus, in contrast to young flies, aged flies are unable to modulate glutamate activity during learning and consolidation, leading to defects in the two memory phases (Matsuno, 2019).
The model that EAAT1 inhibits glutamate activity during consolidation stems from EAAT1's role in clearing glutamate from synaptic sites and transporting it into astrocytes. This model is consistent with several mammalian studies that demonstrated decreased expression of astrocytic glutamate transporters upon aging, with a consequent reduction of glutamate uptake. Further supporting this model, it was found that feeding flies memantine or MK801, NMDA receptor antagonists, after spaced training, restores normal LTM in klg mutants and restores LTM in aged flies to youthful levels. This effect requires feeding after training during the consolidation phase. Similar results were obtained by feeding riluzole, a glutamate modulator, which decreases glutamate release and increases astrocytic glutamate uptake. Riluzole has also been reported to ameliorate age-related cognitive decline in mammals, suggesting that the mechanisms of AMI may be conserved between species. In contrast, this study found that D-serine feeding, which rescues age-related declines in short-lasting (1-h) memory, does not improve declines in LTM, but rather attenuates it. This is consistent with the model wherein declines in short-lasting memory and LTM are caused by distinct or opposing mechanisms and glutamate signaling needs to be suppressed during consolidation. Somewhat unexpectedly, it was also found that (s)-4C3HPG, the mGluR1 antagonist/mGluR2 agonist, also ameliorated age-related impairments in LTM. This result indicates that glutamate activity through both ionotropic and metabotropic glutamate receptors antagonizes memory consolidation (Matsuno, 2019).
Currently, it is unclear why glutamate signaling needs to be inhibited during consolidation, but a previous study has shown that Mg2+ block mutations in NMDA-type glutamate receptors (NRs) cause specific defects in LTM in Drosophila. Although Mg2+ block mutations have various effects, one effect is to increase NR activity. Increased NR activity results in increased activity of dCREB2b, an inhibitory isoform of CREB. CREB-dependent gene expression is required during consolidation of LTM, suggesting that consolidation may be preferentially sensitive to NR activity (Matsuno, 2019).
Alternatively, it is possible that neuronal activity needs to be inhibited globally during memory consolidation. Sleep is known to be important for LTM. Sleep deprivation during consolidation prevents LTM formation, whereas artificially inducing sleep after training has been reported to improve LTM. Thus a second possibility is suggested that inhibition of glutamate signaling after spaced training may be a brain-wide phenomenon that promotes consolidation by inducing the organism to sleep. Thus far, gross alterations in sleep duration in klg and repo mutants have not been detected, although this does not preclude minor disruptions in sleep quality that may not be detectable by motion-based sleep assays. Finally, a third possibility is envisioned wherein neuronal inhibition may be required as a neuroprotective mechanism that may be necessary to prevent cell death in neurons that were extensively stimulated during spaced training (Matsuno, 2019).
Mapping the glutamatergic neurons whose activity is inhibited during consolidation will be of great interest in the future. As aversive olfactory memories are formed and stored in the Drosophila MBs, it is possible that specific glutamatergic MB output neurons (MBONs) are inhibited during consolidation. Several glutamatergic MBONs are involved in feedback networks with the lobes of the MBs, suggesting that altering the activity of these neurons may modulate memory consolidation and memory-associated behavioral responses (Matsuno, 2019).
This study has demonstrate that increased expression of Eaat1 is required for LTM consolidation. Based on numerous results from other groups, it is hypothesized that Eaat1 functions to reduce glutamate signaling, and support for this model is provided by demonstrating that pharmacological inhibition of glutamate signaling during consolidation improves LTM under various conditions. However, due to technical limitations, it was not possible to actually measure glutamate concentrations at synapses during memory consolidation and it is not known where and how much glutamate signaling has to be inhibited for optimal LTM consolidation (Matsuno, 2019).
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Dobson, A. J., Boulton-McDonald, R., Houchou, L., Svermova, T., Ren, Z., Subrini, J., Vazquez-Prada, M., Hoti, M., Rodriguez-Lopez, M., Ibrahim, R., Gregoriou, A., Gkantiragas, A., Bahler, J., Ezcurra, M. and Alic, N. (2019). Longevity is determined by ETS transcription factors in multiple tissues and diverse species. PLoS Genet 15(7): e1008212. PubMed ID: 31356597
Summary:
Ageing populations pose a major public health crises. Reprogramming gene expression by altering the activities of sequence-specific transcription factors (TFs) can ameliorate deleterious effects of age. This explore how a circuit of TFs coordinates pro-longevity transcriptional outcomes, which reveals a multi-tissue and multi-species role for an entire protein family: the E-twenty-six (ETS) TFs. In Drosophila, reduced insulin/IGF signalling (IIS) extends lifespan by coordinating activation of Aop, an ETS transcriptional repressor, and Foxo, a Forkhead transcriptional activator. Aop and Foxo bind the same genomic loci, and this study shows that, individually, they effect similar transcriptional programmes in vivo. In combination, Aop can both moderate or synergise with Foxo, dependent on promoter context. Moreover, Foxo and Aop oppose the gene-regulatory activity of Pnt, an ETS transcriptional activator. Directly knocking down Pnt recapitulates aspects of the Aop/Foxo transcriptional programme and is sufficient to extend lifespan. The lifespan-limiting role of Pnt appears to be balanced by a requirement for metabolic regulation in young flies, in which the Aop-Pnt-Foxo circuit determines expression of metabolic genes, and Pnt regulates lipolysis and responses to nutrient stress. Molecular functions are often conserved amongst ETS TFs, prompting examination of whether other Drosophila ETS-coding genes may also affect ageing. This study shows that five out of eight Drosophila ETS TFs play a role in fly ageing, acting from a range of organs and cells including the intestine, adipose and neurons. This study expands the repertoire of lifespan-limiting ETS TFs in C. elegans, confirming their conserved function in ageing and revealing that the roles of ETS TFs in physiology and lifespan are conserved throughout the family, both within and between species (Dodson, 2019).
Ageing is characterised by a steady systematic decline in biological function, and increased likelihood of disease. Understanding the basic biology of ageing therefore promises to help improve the overall health of older people, who constitute an ever-increasing proportion of populations. In experimental systems, healthy lifespan can be extended by altered transcriptional regulation, coordinated by sequence-specific TFs. Thus, understanding TFs' functions can reveal how to promote health in late life. Forkhead family TFs, especially Forkhead Box O (Foxo) orthologues, have been studied extensively in this context. This effort has been driven by the association of Foxo3a alleles with human longevity; and the findings that the activation of Foxos is necessary and sufficient to explain the extension of lifespan observed following reduced insulin/IGF signalling (IIS) in model organisms. Foxos interact with additional TFs in regulatory circuits, and it is in this context that their function must be understood. For example, in Caenorhabditis elegans, the pro-longevity activity of Daf-16 is orchestrated with further TFs including Hsf, Elt-2, Skn-1, Pqm-1 and Hlh-30/Tfeb. Examining regions bound by Foxos across animals has highlighted the conserved presence of sites to bind ETS family TFs. In Drosophila, two members of this family, namely Aop (a.k.a. Yan) and Pnt, have been linked to ageing via genetic interactions with Foxo and IIS, and similar interactions are evident in C. elegans. These findings raise questions of the overall roles of ETS factors in ageing, and their relationship to the activities of Foxos (Dodson, 2019).
The ETS TFs are conserved across animals, including 28 representatives in humans. Their shared, defining feature is a core helix-turn-helix DNA-binding domain, which binds DNA on 5'-GGA(A/T)-3' ETS-binding motifs (EBMs). They are differentiated by tissue-specific expression, and variation in peripheral amino acid residues which, along with variation in nucleotides flanking the core EBM, confers DNA-binding specificity. ETS TFs generally function as transcriptional activators, but a few repress transcription. Aop is one such repressor in Drosophila. Aop and its human orthologue Tel are thought to repress transcription by competing with activators for binding sites, recruiting co-repressors, and forming homo-oligomers that limit activator access to euchromatin. Consequently, Aop's role in physiology must be explored in the context of its interactions with additional TFs, especially activators. Foxo is one such activator. Both Foxo and Aop are required for longevity by IIS inhibition, each is individually sufficient to extend lifespan, and both are recruited to the same genomic loci in vivo. Whilst activating either in the gut and fat body extends lifespan, the effect of activating both is not additive. Furthermore, if Aop is knocked down, activating Foxo not only ceases to extend lifespan, but even becomes deleterious for lifespan. Overall, these findings suggest that gene expression downstream of IIS is orchestrated by the coordinated activity of Aop and Foxo, and that there is a redundancy in the function of the two TFs, even though Foxo is a transcriptional activator and Aop a transcriptional repressor. This study started by characterising Aop and its relationship with relevant transcriptional activators, including Foxo. This led revealing that roles in ageing are widespread throughout the ETS TF family, extending across multiple fly tissues and diverse animal taxa (Dodson, 2019).
Promoting healthy ageing by transcriptional control is an attractive prospect, because targeting one specific protein can restructure global gene expression to provide broad-scale benefits. This study suggests key roles for ETS TFs in such optimisation. The results show dual roles for Aop: balancing Foxo's outputs, and opposing Pnt's outputs. These functions coordinate transcriptional changes that correspond to lifespan. Repressing transcription from the ETS site appears to be the key longevity-promoting step, and indeed lifespan was extended by limiting multiple ETS TFs, in multiple fly tissues, and in multiple taxa. Altogether, these results show that inhibiting lifespan is a general feature of ETS transcriptional activators. Presumably the expression of these TFs is maintained, despite costs in late life, because of benefits in other contexts. For example, Pnt is important during development, and expression may simply run-on into adulthood. This study now shows that Pnt is also important for adults facing nutritional variation or stress, and genomic evidence suggests equivalent functions for Ets-4 in C. elegans. In addition, Ets21C is required to mount an effective immune response, and both Ets21C and Pnt control gut homeostasis. Tissue environment appears to be another important contextual factor that determines the lifespan effects of specific ETS TFs. Differences between tissues in chromatin architecture are likely to alter the capacity of a given TF to bind a given site, and the current results show that a given TF, and also upstream RTKs, do not necessarily lead to the same lifespan effect across all tissues. The tissue-specific functions that are shown for ETS TFs, Foxo and RTKs, suggests that transcription is locally coordinated by distinct receptors and TFs in distinct tissues, but that lifespan-regulatory signalling nevertheless converges on the ETS site. This differentiation makes it all the more remarkable that roles in lifespan appear to be conserved amongst ETS family TFs, even in diverse tissue contexts (Dodson, 2019).
The structure of molecular networks and their integration amongst tissues underpins phenotype, including into old age. Unravelling the basics of these networks is a critical step in identifying precise anti-ageing molecular targets. Identifying the least disruptive perturbation of these networks, by targeting the 'correct' effector, is a key goal in order to achieve desirable outcomes without undesirable trade-offs that may ensue from broader-scale perturbation. This targeting can be at the level of specific proteins, cell types, points in the life-course, or a combination of all three. The tissue-specific expression pattern of ETS TFs, and the apparent conservation of their roles in longevity, highlights them as important regulators of tissue-specific programs that may be useful in precise medical targeting of specific senescent pathologies (Dodson, 2019).
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Suh, Y. S., Yeom, E., Nam, J. W., Min, K. J., Lee, J. and Yu, K. (2020). Methionyl-tRNA Synthetase Regulates Lifespan in Drosophila. Mol Cells. PubMed ID: 31940717
Summary:
Methionyl-tRNA synthetase (MRS) is essential for translation. MRS mutants reduce global translation, which usually increases lifespan in various genetic models. However, this study found that inhibition of MRS in Drosophila reduced lifespan despite of the reduced protein synthesis. Microarray analysis with MRS inhibited Drosophila revealed significant changes in inflammatory and immune response genes. Especially, the expression of anti-microbial peptides (AMPs) genes was reduced. When the expression levels of AMP genes during aging was measured, those were getting increased in the control flies but reduced in MRS inhibition flies age dependently. Interestingly, in the germ-free condition, the maximum lifespan was increased in MRS inhibition flies compared with that of the conventional condition. These findings suggest that the lifespan of MRS inhibition flies is reduced due to the down-regulated AMPs expression in Drosophila (Suh, 2020).
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Parker, G. A., Kohn, N., Spirina, A., McMillen, A., Huang, W. and Mackay, T. F. C. (2020). Genetic Basis of Increased Lifespan and Postponed Senescence in Drosophila melanogaster. G3 (Bethesda). PubMed ID: 31969430
Summary:
Limited lifespan and senescence are near-universal phenomena. These quantitative traits exhibit variation in natural populations due to the segregation of many interacting loci and from environmental effects. Due to the complexity of the genetic control of lifespan and senescence, understanding of the genetic basis of variation in these traits is incomplete. This study analyzed the pattern of genetic divergence between long-lived (O) Drosophila melanogaster lines selected for postponed reproductive senescence and unselected control (B) lines. The productivity of the O and B lines were quantified, and reproductive senescence was found to be maternally controlled. 57 candidate genes were selected that are expressed in ovaries, 49 of which have human orthologs, and the effects of RNA interference in ovaries and accessary glands on lifespan and reproduction were assessed. All but one candidate gene affected at least one life history trait in one sex or productivity week. In addition, 23 genes had antagonistic pleiotropic effects on lifespan and productivity. Identifying evolutionarily conserved genes affecting increased lifespan and delayed reproductive senescence is the first step towards understanding the evolutionary forces that maintain segregating variation at these loci in nature and may provide potential targets for therapeutic intervention to delay senescence while increasing lifespan (Parker, 2020).
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Tonoki, A., Ogasawara, M., Yu, Z. and Itoh, M. (2020). Appetitive memory with survival benefit is robust across aging in Drosophila. J Neurosci. PubMed ID: 31992587
Summary:
The formation of memory declines with advancing age. However, susceptibility to memory impairments depends on several factors, including the robustness of memory, the responsible neural circuits, and the internal state of aged individuals. How age-dependent changes in internal states and neural circuits affect memory formation remains unclear. This study showed in Drosophila melanogaster that aged flies of both sexes form robust appetitive memory conditioned with nutritious sugar, which suppresses their high mortality rates during starvation. In contrast, aging impairs the formation of appetitive memory conditioned with non-nutritious sugar that lacks survival benefits for the flies. Aging was found to enhanced the preference for nutritious sugar over non-nutritious sugar correlated with an age-dependent increase in the expression of Drosophila neuropeptide F, an ortholog of mammalian neuropeptide Y. Furthermore, a subset of dopaminergic neurons that signal the sweet taste of sugar decreases its function with aging, while a subset of dopaminergic neurons that signal the nutritional value of sugar maintains its function with age. These results suggest that aging impairs the ability to form memories without survival benefits; however, the ability to form memories with survival benefits is maintained through age-dependent changes in the neural circuits and neuropeptides (Tonoki, 2020).
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Martinez Corrales, G., Filer, D., Wenz, K. C., Rogan, A., Phillips, G., Li, M., Feseha, Y., Broughton, S. J. and Alic, N. (2020). Partial Inhibition of RNA Polymerase I Promotes Animal Health and Longevity. Cell Rep 30(6): 1661-1669. PubMed ID: 32049000
Summary:
Health and survival in old age can be improved by changes in gene expression. RNA polymerase (Pol) I is the essential, conserved enzyme whose task is to generate the pre-ribosomal RNA (rRNA). Pol I is the fundamental structurally and functionally conserved eukaryotic enzyme that transcribes a single gene, ribosomal DNA (rDNA) (Vannini and Cramer, 2012). It generates the pre-rRNA that is processed into the mature 18S, 5.8S, and 28S rRNAs, the key structural and catalytic components of the ribosome. Reducing the levels of Pol I activity is sufficient to extend lifespan in the fruit fly. This effect can be recapitulated by partial, adult-restricted inhibition, with both enterocytes and stem cells of the adult midgut emerging as important cell types. In stem cells, Pol I appears to act in the same longevity pathway as Pol III, implicating rRNA synthesis in these cells as the key lifespan determinant. Importantly, reduction in Pol I activity delays broad, age-related impairment and pathology, improving the function of diverse organ systems. Hence, this study shows that Pol I activity in the adult drives systemic, age-related decline in animal health and anticipates mortality (Martinez Corrales, 2020).
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Tain, L. S., Jain, C., Nespital, T., Froehlich, J., Hinze, Y., Gronke, S. and Partridge, L. (2019). Longevity in response to lowered insulin signaling requires glycine N-methyltransferase-dependent spermidine production. Aging Cell: e13043. PubMed ID: 31721422
Summary:
Reduced insulin/IGF signaling (IIS) extends lifespan in multiple organisms. Different processes in different tissues mediate this lifespan extension, with a set of interplays that remain unclear. This study shows that, in Drosophila, reduced IIS activity modulates methionine metabolism, through tissue-specific regulation of glycine N-methyltransferase (Gnmt), and that this regulation is required for full IIS-mediated longevity. Furthermore, fat body-specific expression of Gnmt was sufficient to extend lifespan. Targeted metabolomics showed that reducing IIS activity led to a Gnmt-dependent increase in spermidine levels. It was also shown that both spermidine treatment and reduced IIS activity are sufficient to extend the lifespan of Drosophila, but only in the presence of Gnmt. This extension of lifespan was associated with increased levels of autophagy. Finally, this study found that increased expression of Gnmt occurs in the liver of liver-specific IRS1 KO mice and is thus an evolutionarily conserved response to reduced IIS. The discovery of Gnmt and spermidine as tissue-specific modulators of IIS-mediated longevity may aid in developing future therapeutic treatments to ameliorate aging and prevent disease.
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Gospodaryov, D. V., Strilbytska, O. M., Semaniuk, U. V., Perkhulyn, N. V., Rovenko, B. M., Yurkevych, I. S., Barata, A. G., Dick, T. P., Lushchak, O. V. and Jacobs, H. T. (2019). Alternative NADH dehydrogenase extends lifespan and increases resistance to xenobiotics in Drosophila. Biogerontology. PubMed ID: 31749111
Summary:
Mitochondrial alternative NADH dehydrogenase (aNDH) was found to extend lifespan when expressed in the fruit fly. This study has found that fruit flies expressing aNDH from Ciona intestinalis (NDX) had 17-71% lifespan prolongation on media with different protein-to-carbohydrate ratios except NDX-expressing males that had 19% shorter lifespan than controls on a high protein diet. NDX-expressing flies were more resistant to organic xenobiotics, 2,4-dichlorophenoxyacetic acid and alloxan, and inorganic toxicant potassium iodate, and partially to sodium molybdate treatments. On the other hand, NDX-expressing flies were more sensitive to catechol and sodium chromate. Enzymatic analysis showed that NDX-expressing males had higher glucose 6-phosphate dehydrogenase activity, whilst both sexes showed increased glutathione S-transferase activity (Gospodaryov, 2019).
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Nash, T. R., Chow, E. S., Law, A. D., Fu, S. D., Fuszara, E., Bilska, A., Bebas, P., Kretzschmar, D. and Giebultowicz, J. M. (2019). Daily blue-light exposure shortens lifespan and causes brain neurodegeneration in Drosophila. NPJ Aging Mech Dis 5: 8. PubMed ID: 31636947
Summary:
Light is necessary for life, but prolonged exposure to artificial light is a matter of increasing health concern. Humans are exposed to increased amounts of light in the blue spectrum produced by light-emitting diodes (LEDs), which can interfere with normal sleep cycles. The LED technologies are relatively new; therefore, the long-term effects of exposure to blue light across the lifespan are not understood. This study investigated the effects of light in the model organism, Drosophila melanogaster, and determined that flies maintained in daily cycles of 12-h blue LED and 12-h darkness had significantly reduced longevity compared with flies maintained in constant darkness or in white light with blue wavelengths blocked. Exposure of adult flies to 12 h of blue light per day accelerated aging phenotypes causing damage to retinal cells, brain neurodegeneration, and impaired locomotion. Brain damage and locomotor impairments do not depend on the degeneration in the retina, as these phenotypes were evident under blue light in flies with genetically ablated eyes. Blue light induces expression of stress-responsive genes in old flies but not in young, suggesting that cumulative light exposure acts as a stressor during aging. This study also determined that several known blue-light-sensitive proteins are not acting in pathways mediating detrimental light effects. This study reveals the unexpected effects of blue light on fly brain and establishes Drosophila as a model in which to investigate long-term effects of blue light at the cellular and organismal level (Nash, 2019).
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Hoedjes, K. M., van den Heuvel, J., Kapun, M., Keller, L., Flatt, T. and Zwaan, B. J. (2019). Distinct genomic signals of lifespan and life history evolution in response to postponed reproduction and larval diet in Drosophila. Evol Lett 3(6): 598-609. PubMed ID: 31867121
Summary:
Reproduction and diet are two major factors controlling the physiology of aging and life history, but how they interact to affect the evolution of longevity is unknown. Moreover, although studies of large-effect mutants suggest an important role of nutrient sensing pathways in regulating aging, the genetic basis of evolutionary changes in lifespan remains poorly understood. To address these questions, the genomes of experimentally evolved Drosophila melanogaster populations were subjected to a factorial combination of two selection regimes: reproductive age (early versus postponed), and diet during the larval stage ("low," "control," "high"), resulting in six treatment combinations with four replicate populations each. Selection on reproductive age consistently affected lifespan, with flies from the postponed reproduction regime having evolved a longer lifespan. In contrast, larval diet affected lifespan only in early-reproducing populations: flies adapted to the "low" diet lived longer than those adapted to control diet. This study found genomic evidence for strong independent evolutionary responses to either selection regime, as well as loci that diverged in response to both regimes, thus representing genomic interactions between the two. Overall, the genomic basis of longevity was found to be largely independent of dietary adaptation. Differentiated loci were not enriched for "canonical" longevity genes, suggesting that naturally occurring genic targets of selection for longevity differ qualitatively from variants found in mutant screens. Comparing the candidate loci to those from other "evolve and resequence" studies of longevity demonstrated significant overlap among independent experiments. This suggests that the evolution of longevity, despite its presumed complex and polygenic nature, might be to some extent convergent and predictable (Hoedjes, 2019).
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Erwin, A. A. and Blumenstiel, J. P. (2019). Aging in the Drosophila ovary: contrasting changes in the expression of the piRNA machinery and mitochondria but no global release of transposable elements. BMC Genomics 20(1): 305. PubMed ID: 31014230
Summary:
Evolutionary theory indicates that the dynamics of aging in the soma and reproductive tissues may be distinct. Using mRNA sequencing data from late-stage egg chambers in Drosophila melanogaster, this study characterized the landscape of altered gene and transposable element expression in aged reproductive tissues. This allowed a test of the hypothesis that reproductive tissues may differ from somatic tissues in their response to aging. This study shows that age-related expression changes in late-stage egg chambers tend to occur in genes residing in heterochromatin, particularly on the largely heterochromatic 4th chromosome. However, these expression differences are seen as both decreases and increases during aging, inconsistent with a general loss of heterochromatic silencing. This study also identified an increase in expression of the piRNA machinery, suggesting an age-related increased investment in the maintenance of genome stability. A strong age-related reduction in the expression of mitochondrial transcripts was identified. However, no evidence was foud for global TE derepression in reproductive tissues. Rather, the observed effects of aging on TEs are primarily strain and family specific. These results identify unique responses in somatic versus reproductive tissue with regards to aging. As in somatic tissues, female reproductive tissues show reduced expression of mitochondrial genes. In contrast, the piRNA machinery shows increased expression during aging. Overall, these results also indicate that global loss of TE control observed in other studies may be unique to the soma and sensitive to genetic background and TE family (Erwin, 2019).
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Schinaman, J. M., Rana, A., Ja, W. W., Clark, R. I. and Walker, D. W. (2019). Rapamycin modulates tissue aging and lifespan independently of the gut microbiota in Drosophila. Sci Rep 9(1): 7824. PubMed ID: 31127145
Summary:
The FDA approved drug rapamycin can prolong lifespan in diverse species and delay the onset of age-related disease in mammals. However, a number of fundamental questions remain unanswered regarding the mechanisms by which rapamycin modulates age-related pathophysiology and lifespan. Alterations in the gut microbiota can impact host physiology, metabolism and lifespan. While recent studies have shown that rapamycin treatment alters the gut microbiota in aged animals, the causal relationships between rapamycin treatment, microbiota dynamics and aging are not known. Using Drosophila as a model organism, this study shows that rapamycin-mediated alterations in microbiota dynamics in aged flies are associated with improved markers of intestinal and muscle aging. Critically, however, this study shows that the beneficial effects of rapamycin treatment on tissue aging and lifespan are not dependent upon the microbiota. Indeed, germ-free flies show delayed onset of intestinal barrier dysfunction, improved proteostasis in aged muscles and a significant lifespan extension upon rapamycin treatment. In contrast, genetic inhibition of autophagy impairs the ability of rapamycin to mediate improved gut health and proteostasis during aging. These results indicate that rapamycin-mediated modulation of the microbiota in aged animals is not causally required to slow tissue and organismal aging (Schinaman, 2019).
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Kristensen, T. N., Loeschcke, V., Tan, Q., Pertoldi, C. and Mengel-From, J. (2019). Sex and age specific reduction in stress resistance and mitochondrial DNA copy number in Drosophila melanogaster. Sci Rep 9(1): 12305. PubMed ID: 31444377
Summary:
Environmental stresses such as extreme temperatures, dehydration and food deprivation may have distinct consequences for different age-classes and for males and females across species. This study investigated a natural population of the model organism Drosophila melanogaster. Males and females at ages 3, 19 and 35 days were tested for stress resistance; i.e. the ability of flies to cope with starvation and both cold and hot temperatures. Further, a measure of metabolic efficiency, namely mitochondrial DNA copy number (mtDNA CN), was tested in both sexes at all three age-classes. It was hypothesized that stress resistance is reduced at old age and more so in males, and that mtDNA CN is a biomarker for sex- and age-dependent reductions in the ability to cope with harsh environments. This study showed that: (1) males exhibit reduced starvation tolerance at old age, whereas older females are better in coping with periods without food compared to younger females, (2) heat tolerance decreases with increasing age in males but not in females, (3) cold tolerance is reduced at old age in both sexes, and (4) old males have reduced mtDNA CN whereas mtDNA CN slightly increases with age in females. In conclusion, these data provide strong evidence for trait and sex specific consequences of aging with females generally being better at coping with environmental stress at old age. The reduced mtDNA CN in old males suggests reduced metabolic efficiency and this may partly explain why males are less stress tolerant at old age than females. It is suggested that mtDNA CN might be a suitable biomarker for physiological robustness. These findings likely extend to other taxa than Drosophila and therefore the observations are discussed in relation to aging and sex specific lifespan across species (Kristensen, 2019).
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Duxbury, E. M. L. and Chapman, T. (2019) (2019). Sex-specific responses of lifespan and fitness to variation in developmental versus adult diets in D. melanogaster. J Gerontol A Biol Sci Med Sci. PubMed ID: 31362304
Summary:
Nutritional variation across the lifetime can have significant and sex-specific impacts upon fitness. Using Drosophila melanogaster, these impacts were measured by testing the effects on lifespan and reproductive success of high or low yeast content in developmental versus adult diets, separately for each sex. Two hypotheses were tested: that dietary mismatches between development and adulthood are costly and that any such costs are sex-specific. Overall, the results revealed the rich and complex responses of each sex to dietary variation across the lifetime. Contrary to the first hypothesis, dietary mismatches between developmental and adult life stages were not universally costly. Where costs of nutritional variation across the life course did occur, they were sex-, context- and trait-specific, consistent with hypothesis 2. Effects of mismatches between developmental and adult diets on reproductive success were found in females but not males. Adult diet was the main determinant of survival, and lifespan was significantly longer on high yeast adult food, in comparison to low, in both sexes. Developing on a high yeast diet also benefited adult female lifespan and reproductive success, regardless of adult diet. In contrast, a high yeast developmental diet was only beneficial for male lifespan when it was followed by low yeast adult food. Adult diet affected mating frequency in opposing directions, with males having higher mating frequency on high and females on low, with no interaction with developmental diet for either sex. The results emphasize the importance of sex differences and of the directionality of dietary mismatches in the responses to nutritional variation (Duxbury, 2019).
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Castillo-Quan, J. I., Tain, L. S., Kinghorn, K. J., Li, L., Gronke, S., Hinze, Y., Blackwell, T. K., Bjedov, I. and Partridge, L. (2019). A triple drug combination targeting components of the nutrient-sensing network maximizes longevity. Proc Natl Acad Sci U S A 116(42): 20817-20819. PubMed ID: 31570569
Summary:
Increasing life expectancy is causing the prevalence of age-related diseases to rise, and there is an urgent need for new strategies to improve health at older ages. Reduced activity of insulin/insulin-like growth factor signaling (IIS) and mechanistic target of rapamycin (mTOR) nutrient-sensing signaling network can extend lifespan and improve health during aging in diverse organisms. However, the extensive feedback in this network and adverse side effects of inhibition imply that simultaneous targeting of specific effectors in the network may most effectively combat the effects of aging. This study shows that the mitogen-activated protein kinase kinase (MEK) inhibitor trametinib, the mTOR complex 1 (mTORC1) inhibitor rapamycin, and the glycogen synthase kinase-3 (GSK-3) inhibitor lithium act additively to increase longevity in Drosophila. Remarkably, the triple drug combination increased lifespan by 48%. Furthermore, the combination of lithium with rapamycin cancelled the latter's effects on lipid metabolism. In conclusion, a polypharmacology approach of combining established, prolongevity drug inhibitors of specific nodes may be the most effective way to target the nutrient-sensing network to improve late-life health (Castillo-Quan, 2019).
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Wen, D. T., Zheng, L., Li, J. X., Lu, K. and Hou, W. Q. (2019). The activation of cardiac dSir2-related pathways mediates physical exercise resistance to heart aging in old Drosophila. Aging (Albany NY) 11. PubMed ID: 31503544
Summary:
Cardiac aging is notably characterized by increased diastolic dysfunction, lipid accumulation, oxidative stress, and contractility debility. The Sir2/Sirt1 gene overexpression delays cell aging and reduces obesity and oxidative stress. Exercise improves heart function and delays heart aging. However, it remains unclear whether exercise delaying heart aging is related to cardiac Sir2/Sirt1-related pathways. In this study, cardiac dSir2 overexpression or knockdown was regulated using the UAS/hand-Gal4 system in Drosophila. Flies underwent exercise interventions from 4 weeks to 5 weeks old. Results showed that either cardiac dSir2 overexpression or exercise remarkably increased the cardiac period, systolic interval, diastolic interval, fractional shortening, SOD activity, dSIR2 protein, Foxo, dSir2, Nmnat, and bmm expression levels in the aging flies; they also notably reduced the cardiac triacylglycerol level, malonaldehyde level, and the diastolic dysfunction index. Either cardiac dSir2 knockdown or aging had almost opposite effects on the heart as those of cardiac dSir2 overexpression. Therefore, this study claims that cardiac dSir2 overexpression or knockdown delayed or promoted heart aging by reducing or increasing age-related oxidative stress, lipid accumulation, diastolic dysfunction, and contractility debility. The activation of cardiac dSir2/Foxo/SOD and dSir2/Foxo/Bmm pathways may be two important molecular mechanisms through which exercise works against heart aging in Drosophila (Wen, 2019).
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Qiu, W., Chen, X., Tian, Y., Wu, D., Du, M. and Wang, S. (2019). Protection against oxidative stress and anti-aging effect in Drosophila of royal jelly-collagen peptide. Food Chem Toxicol: 110881. PubMed ID: 31622731
Summary:
Dietary peptide has been of great interest because of its perspective in nutrition and health of human body. The aim of this study was to develop a dietary nutritional supplement exerting both antioxidant and anti-aging effects. Peptide, named as ERJ-CP, was prepared by mixing enzyme-treated royal jelly (ERJ) with collagen peptide (CP), showing stronger antioxidant activity in vitro. Drosophila was used as model animal to investigate anti-aging effect of ERJ-CP in vivo. ERJ-CP significantly prolonged the average life span of Drosophila treated with H2O2 and paraquat, reducing malondialdehyde (MDA) and protein carbonyl (PCO) levels in Drosophila. In addition, 3mg/mL of ERJ-CP could prolong the lifespan of natural aging Drosophila by 11.16%. ERJ-CP could up-regulate the levels of total superoxide dismutase (T-SOD), glutathione peroxidase (GSH-Px), catalase (CAT) and down-regulate the contents of MDA and PCO. Moreover, the intake of ERJ-CP increased the food consumption, weight gain and exercise capacity of Drosophila. The results showed that ERJ-CP played a protective role in both antioxidant and anti-aging effects on Drosophila, and the anti-aging effect may be achieved by alleviating oxidative damage. It suggests that ERJ-CP could be developed as a health-promoting ingredient with antioxidant and anti-aging effects for human body (Qiu, 2019).
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Xiao, C., Hull, D., Qiu, S., Yeung, J., Zheng, J., Barwell, T., Robertson, R. M. and Seroude, L. (2019). Expression of Heat shock protein 70 is insufficient to extend Drosophila melanogaster longevity. G3 (Bethesda). PubMed ID: 31624139
Summary:
It has been known for over 20 years that Drosophila melanogaster flies with twelve additional copies of the hsp70 gene encoding the 70 kDa heat shock protein lives longer after a non-lethal heat treatment. Since the heat treatment also induces the expression of additional heat shock proteins, the biological effect can be due either to HSP70 acting alone or in combination. This study used the UAS/GAL4 system to determine whether hsp70 is sufficient to affect the longevity and the resistance to thermal, oxidative or desiccation stresses of the whole organism. It was observed that HSP70 expression in the nervous system or muscles has no effect on longevity or stress resistance but ubiquitous expression reduces the life span of males. It was also observed that the down-regulation of Hsp70 using RNAi did not affect longevity (Xiao, 2019).
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Li, J. Q., Duan, D. D., Zhang, J. Q., Zhou, Y. Z., Qin, X. M., Du, G. H. and Gao, L. (2019). Bioinformatic prediction of critical genes and pathways involved in longevity in Drosophila melanogaster. Mol Genet Genomics. PubMed ID: 31327054
Summary:
The pursuit of longevity has been the goal of humanity since ancient times. Genetic alterations have been demonstrated to affect lifespan. As increasing numbers of pro-longevity genes and anti-longevity genes have been discovered in Drosophila, screening for functionally important genes among the large number of genes has become difficult. The aim of this study was to explore critical genes and pathways affecting longevity in Drosophila melanogaster. In this study, 168 genes associated with longevity in D. melanogaster were collected from the Human Ageing Genomic Resources (HAGR) database. Network clustering analysis, network topological analysis, and pathway analysis were integrated to identify key genes and pathways. Quantitative real-time PCR (qRT-PCR) was applied to verify the expression of genes in representative pathways and of predicted genes derived from the gene-gene sub-network. The results revealed that six key pathways might be associated with longevity, including the longevity-regulating pathway, the peroxisome pathway, the mTOR-signalling pathway, the FOXO-signalling pathway, the AGE-RAGE-signalling pathway in diabetic complications, and the TGF-beta-signalling pathway. Moreover, the results revealed that six key genes in representative pathways, including Cat, Ry, S6k, Sod, Tor, and Tsc1, and the predicted genes Jra, Kay, and Rheb exhibited significant expression changes in ageing D. melanogaster strain w(1118) compared to young ones. Overall, these results revealed that six pathways and six key genes might play pivotal roles in regulating longevity, and three interacting genes might be implicated in longevity. The results will not only provide new insight into the mechanisms of longevity, but also provide novel ideas for network-based approaches for longevity-related research (Li, 2019).
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Keebaugh, E. S., Yamada, R. and Ja, W. W. (2019). The nutritional environment influences the impact of microbes on Drosophila melanogaster life span. MBio 10(4). PubMed ID: 31289176
Summary:
Microbes can extend Drosophila melanogaster life span by contributing to the nutritional value of malnourishing fly culture medium. The beneficial effect of microbes during malnutrition is dependent on their individual ability to proliferate in the fly environment and is mimicked by lifelong supplementation of equivalent levels of heat-killed microbes or dietary protein, suggesting that microbes can serve directly as a protein-rich food source. This study used nutritionally rich fly culture medium to demonstrate how changes in dietary composition influence monocolonized fly life span; microbes that extend fly life span on malnourishing diets can shorten life on rich diets. The mechanisms employed by microbes to affect host health likely differ on low- or high-nutrient diets. The results demonstrate how Drosophila-associated microbes can positively or negatively influence fly life span depending on the nutritional environment. Although controlled laboratory environments allow focused investigations on the interaction between fly microbiota and nutrition, the relevance of these studies is not straightforward, because it is difficult to mimic the nutritional ecology of natural Drosophila-microbe interactions. As such, caution is needed in designing and interpreting fly-microbe experiments and before categorizing microbes into specific symbiotic roles based on results obtained from experiments testing limited conditions (Keebaugh, 2019).
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Munkacsy, E., Chocron, E. S., Quintanilla, L., Gendron, C. M., Pletcher, S. D. and Pickering, A. M. (2019). Neuronal-specific proteasome augmentation via Prosbeta5 overexpression extends lifespan and reduces age-related cognitive decline. Aging Cell: e13005. PubMed ID: 31334599
Summary:
Cognitive function declines with age throughout the animal kingdom, and increasing evidence shows that disruption of the proteasome system contributes to this deterioration. The proteasome has important roles in multiple aspects of the nervous system, including synapse function and plasticity, as well as preventing cell death and senescence. Previous studies have shown neuronal proteasome depletion and inhibition can result in neurodegeneration and cognitive deficits, but it is unclear if this pathway is a driver of neurodegeneration and cognitive decline in aging. This study reports that overexpression of the proteasome beta5 subunit enhances proteasome assembly and function. Significantly, it was shown that neuronal-specific proteasome augmentation slows age-related declines in measures of learning, memory, and circadian rhythmicity. Surprisingly, neuronal-specific augmentation of proteasome function also produces a robust increase of lifespan in Drosophila melanogaster. These findings appear specific to the nervous system; ubiquitous proteasome overexpression increases oxidative stress resistance but does not impact lifespan and is detrimental to some healthspan measures. These findings demonstrate a key role of the proteasome system in brain aging (Munkacsy, 2019).
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Hunt, L. C., Stover, J., Haugen, B., Shaw, T. I., Li, Y., Pagala, V. R., Finkelstein, D., Barton, E. R., Fan, Y., Labelle, M., Peng, J. and Demontis, F. (2019). A key role for the ubiquitin ligase UBR4 in myofiber hypertrophy in Drosophila and mice. Cell Rep 28(5): 1268-1281. PubMed ID: 31365869
Summary:
Skeletal muscle cell (myofiber) atrophy is a detrimental component of aging and cancer that primarily results from muscle protein degradation via the proteasome and ubiquitin ligases. Transcriptional upregulation of some ubiquitin ligases contributes to myofiber atrophy, but little is known about the role that most other ubiquitin ligases play in this process. To address this question, RNAi screening in Drosophila was used to identify the function of > 320 evolutionarily conserved ubiquitin ligases in myofiber size regulation in vivo. Whereas RNAi for some ubiquitin ligases induces myofiber atrophy, loss of others (including the N-end rule ubiquitin ligase UBR4) promotes hypertrophy. In Drosophila and mouse myofibers, loss of UBR4 induces hypertrophy via decreased ubiquitination and degradation of a core set of target proteins, including the HAT1/RBBP4/RBBP7 histone-binding complex. Together, this study defines the repertoire of ubiquitin ligases that regulate myofiber size and the role of UBR4 in myofiber hypertrophy (Hunt, 2019).
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Andreazza, S., Samstag, C. L., Sanchez-Martinez, A., Fernandez-Vizarra, E., Gomez-Duran, A., Lee, J. J., Tufi, R., Hipp, M. J., Schmidt, E. K., Nicholls, T. J., Gammage, P. A., Chinnery, P. F., Minczuk, M., Pallanck, L. J., Kennedy, S. R. and Whitworth, A. J. (2019). Mitochondrially-targeted APOBEC1 is a potent mtDNA mutator affecting mitochondrial function and organismal fitness in Drosophila. Nat Commun 10(1): 3280. PubMed ID: 31337756
Summary:
Somatic mutations in the mitochondrial genome (mtDNA) have been linked to multiple disease conditions and to ageing itself. In Drosophila, knock-in of a proofreading deficient mtDNA polymerase (POLG) generates high levels of somatic point mutations and also small indels, but surprisingly limited impact on organismal longevity or fitness. This study describes a new mtDNA mutator model based on a mitochondrially-targeted cytidine deaminase, APOBEC1. mito-APOBEC1 acts as a potent mutagen which exclusively induces C:G>T:A transitions with no indels or mtDNA depletion. In these flies, the presence of multiple non-synonymous substitutions, even at modest heteroplasmy, disrupts mitochondrial function and dramatically impacts organismal fitness. A detailed analysis of the mutation profile in the POLG and mito-APOBEC1 models reveals that mutation type (quality) rather than quantity is a critical factor in impacting organismal fitness. The specificity for transition mutations and the severe phenotypes make mito-APOBEC1 an excellent mtDNA mutator model for ageing research (Andreazza, 2019).
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Niraula, P. and Kim, M. S. (2019). N-Acetylcysteine extends lifespan of Drosophila via modulating ROS scavenger gene expression. Biogerontology 20(4): 533-543. PubMed ID: 31115735
Summary:
N-Acetylcysteine (NAc) has been shown to play a diversity of favorable health-related roles (e.g., antioxidant, paracetamol antidote, mucolytics, neuroprotective agent). This study evaluated the health-promoting properties of NAc, particularly its ability to modulate organismal longevity. It is noted that 1 mg/ml NAc prolonged the lifespan of Drosophila. Furthermore, it was observed that NAc increased the capability of these flies to resist environmental stresses measured by starvation and paraquat stress assays. In an effort to reveal cellular mechanisms behind this interesting phenomenon, qPCR was performed, uncovering that transcript levels of catalase and phospholipid hydroperoxide glutathione peroxidase-key enzymes to fend off reactive oxygen species (ROS) assaults, were up-regulated. Correspondingly, enzyme activities of catalase and glutathione peroxidase were increased as well. Combined, it is hoped that this research helps broaden the spectrum of clinical application for NAc so that one may eventually determine if NAc is a potentially useful anti-aging agent by encouraging others to scrutinize the hidden health benefits of NAc (Niraula, 2019).
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Deepashree, S., Niveditha, S., Shivanandappa, T. and Ramesh, S. R. (2019). Oxidative stress resistance as a factor in aging: evidence from an extended longevity phenotype of Drosophila melanogaster. Biogerontology. PubMed ID: 31054025
Summary:
Longevity of a species is a multifactorial quantitative trait influenced by genetic background, sex, age and environment of the organism. Extended longevity phenotypes (ELP) from experimental evolution in the laboratory can be used as model systems to investigate the mechanisms underlying aging and senescence. This study investigated the hypothesis that enhanced oxidative stress resistance and elevated antioxidant defense system play a positive role in longevity using an ELP of Drosophila melanogaster. An ELP of D. melanogaster isolated and characterized through artificial selection (inbred laboratory strain of Oregon K) was employed in this study. This ELP, designated long lifespan (LLS) flies, shows marked extension in lifespan when compared to the progenitor population (normal lifespan, NLS) and makes a suitable model to study the role of mitochondrial genome in longevity because of its least heterogeneity. In this study, sensitivity to ethanol with age was employed as a measure of resistance to oxidative stress in NLS and LLS flies. Effect of age and oxidative stress on longevity was examined by employing NLS and LLS flies of different age groups against ethanol-induced oxidative stress. Results show that the lower mortality against ethanol was associated with enhanced oxidative stress resistance, higher antioxidant defenses, lower reactive oxygen species (ROS) levels, enhanced alcohol dehydrogenase activity and better locomotor ability attributes of LLS flies. In addition, age-related changes like locomotor impairments, decreased antioxidant defenses, higher ROS levels and sensitivity to oxidative stress were delayed in LLS flies when compared to NLS. This study supports the hypothesis that higher oxidative stress resistance and enhanced antioxidant defenses are significant factors in extending longevity (Deepashree, 2019).
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Su, Y., Wang, T., Wu, N., Li, D., Fan, X., Xu, Z., Mishra, S. K. and Yang, M. (2019). Alpha-ketoglutarate extends Drosophila lifespan by inhibiting mTOR and activating AMPK. Aging (Albany NY) 11. PubMed ID: 31242135
Summary:
Alpha-ketoglutarate (AKG) is a key metabolite of the tricarboxylic acid (TCA) cycle, an essential process influencing the mitochondrial oxidative respiration rate. Recent studies have shown that dietary AKG reduces mTOR pathway activation by inhibiting ATP synthase, thereby extending the lifespan of nematodes. Although AKG also extends lifespan in fruit flies, the antiaging mechanisms of AKG in these organisms remain unclear. This study explored changes in gene expression associated with the extension of Drosophila lifespan mediated by dietary AKG. Supplementation of the flies' diets with 5 &mi;M AKG extended their lifespan but reduced their reproductive performance. Dietary AKG also enhanced vertical climbing ability, but did not protect against oxidative stress or increase tolerance to starvation. AKG-reared flies were resistant to heat stress and demonstrated higher expression of heat shock protein genes (Hsp22 and Hsp70) than control flies. In addition, AKG significantly upregulated mRNA expression of cry, FoxO, HNF4, p300, Sirt1 and AMPKalpha, and downregulated expression of HDAC4, PI3K, TORC, PGC, and SREBP. The metabolic effects of AKG supplementation included a reduction in the ATP/ADP ratio and increased autophagy. Collectively, these observations indicate that AKG extends Drosophila lifespan by activating AMPK signaling and inhibiting the mTOR pathway (Su, 2019).
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Flintham, E. O., Yoshida, T., Smith, S., Pavlou, H. J., Goodwin, S. F., Carazo, P. and Wigby, S. (2018).
Interactions between the sexual identity of the nervous system and the social environment mediate lifespan in Drosophila melanogaster. Proc Biol Sci 285(1892). PubMed ID: 30487307
Summary:
Sex differences in lifespan are ubiquitous, but the underlying causal factors remain poorly understood. Inter- and intrasexual social interactions are well known to influence lifespan in many taxa, but it has proved challenging to separate the role of sex-specific behaviours from wider physiological differences between the sexes. To address this problem, the sexual identity of the nervous system - and hence sexual behaviour - was genetically manipulated in Drosophila melanogaster, and lifespan was measured under varying social conditions. Consistent with previous studies, masculinization of the nervous system in females induced male-specific courtship behaviour and aggression, while nervous system feminization in males induced male-male courtship and reduced aggression. Control females outlived males, but masculinized female groups displayed male-like lifespans and male-like costs of group living. By varying the mixture of control and masculinized females within social groups, male-specific behaviours were shown to be costly to recipients, even when received from females. However, consistent with recent findings, the data suggest courtship expression to be surprisingly low cost. Overall, this study indicates that nervous system-mediated expression of sex-specific behaviour per se-independent of wider physiological differences between the sexes, or the receipt of aggression or courtship-plays a limited role in mediating sex differences in lifespan (Flintham, 2018).
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Pacifico, R., MacMullen, C. M., Walkinshaw, E., Zhang, X. and Davis, R. L. (2018). Brain transcriptome changes in the aging Drosophila melanogaster accompany olfactory memory performance deficits. PLoS One 13(12): e0209405. PubMed ID: 30576353
Summary:
Cognitive decline is a common occurrence of the natural aging process in animals and studying age-related changes in gene expression in the brain might shed light on disrupted molecular pathways that play a role in this decline. The fruit fly is a useful neurobiological model for studying aging due to its short generational time and relatively small brain size. This study investigated age-dependent changes in the Drosophila melanogaster whole-brain transcriptome by comparing 5-, 20-, 30- and 40-day-old flies of both sexes. RNA-sequencing of dissected brain samples followed by differential expression, temporal clustering, co-expression network and gene ontology enrichment analyses were performed. An overall decline was observed in expression of genes from the mitochondrial oxidative phosphorylation pathway that occurred as part of aging. In females, a pattern of continuously declining expression was detected for many neuronal function genes, which was unexpectedly reversed later in life. This group of genes was highly enriched in memory-impairing genes previously identified through an RNAi screen. Deficits in short-term olfactory memory performance was observed in older flies of both sexes, some of which matched the timing of certain changes in the brain transcriptome. This study provides the first transcriptome profile of aging brains from fruit flies of both sexes, and it will serve as an important resource for those who study aging and cognitive decline in this model (Pacifico, 2018).
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Nguyen, N. N., Rana, A., Goldman, C., Moore, R., Tai, J., Hong, Y., Shen, J., Walker, D. W. and Hur, J. H.(2019). Proteasome beta5 subunit overexpression improves proteostasis during aging and extends lifespan in Drosophila melanogaster. Sci Rep 9(1): 3170. PubMed ID: 30816680
Summary:
The beta5 subunit of the proteasome has been shown in worms and in human cell lines to be regulatory. In these models, beta5 overexpression results in upregulation of the entire proteasome complex which is sufficient to increase proteotoxic stress resistance, improve metabolic parameters, and increase longevity. However, fundamental questions remain unanswered, including the temporal requirements for beta5 overexpression and whether beta5 overexpression can extend lifespan in other species. To determine if adult-only overexpression of the beta5 subunit can increase proteasome activity in a different model, this study characterized phenotypes associated with beta5 overexpression in Drosophila melanogaster adults. Adult-only overexpression of the beta5 subunit does not result in transcriptional upregulation of the other subunits of the proteasome as they do in nematodes and human cell culture. Despite this lack of a regulatory role, boosting beta5 expression increases the chymotrypsin-like activity associated with the proteasome, reduces both the size and number of ubiquitinated protein aggregates in aged flies, and increases longevity. Surprisingly, these phenotypes were not associated with increased resistance to acute proteotoxic insults or improved metabolic parameters (Nguyen, 2019).
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Bhukel, A., Beuschel, C. B., Maglione, M., Lehmann, M., Juhasz, G., Madeo, F. and Sigrist, S. J.(2019). Autophagy within the mushroom body protects from synapse aging in a non-cell autonomous manner. Nat Commun 10(1): 1318. PubMed ID: 30899013
Summary:
Macroautophagy is an evolutionarily conserved cellular maintenance program, meant to protect the brain from premature aging and neurodegeneration. How neuronal autophagy, usually loosing efficacy with age, intersects with neuronal processes mediating brain maintenance remains to be explored. This study shows that impairing autophagy in the Drosophila learning center (mushroom body, MB) but not in other brain regions triggered changes normally restricted to aged brains: impaired associative olfactory memory as well as a brain-wide ultrastructural increase of presynaptic active zones (metaplasticity), a state non-compatible with memory formation. Mechanistically, decreasing autophagy within the MBs reduced expression of an NPY-family neuropeptide, and interfering with autocrine NPY signaling of the MBs provoked similar brain-wide metaplastic changes. The results in an exemplary fashion show that autophagy-regulated signaling emanating from a higher brain integration center can execute high-level control over other brain regions to steer life-strategy decisions such as whether or not to form memories (Bhukel, 2019).
The maintenance of neuronal homeostasis is severely threatened by aging. The strictly postnatal character of deficits observed after KD of core autophagy machinery triggered the hope that autophagy might have a specific relation to the aging process. The last few years have indeed seen an accumulation of evidences that the efficiency of autophagic clearance in neurons declines with age on organismal level. Hence, rejuvenating autophagy in aging neurons is considered a promising strategy to restore cognitive performance. Successfully exploring this direction will, however, depend on deepening insights at the intersection of autophagy, the relevant neuronal sub-cellular compartments, importantly synaptic specializations, and relevant neuron populations/brain regions (Bhukel, 2019).
The endogenous polyamine spermidine has prominent cardio-protective and neuro-protective effects and recent work finds spermidine restoration to counteract otherwise deteriorating health in aging mice in an autophagy-dependent manner. In Drosophila, restoring spermidine specifically suppressed age-induced decay in their ability to form olfactory memories, again in an autophagy-dependent manner. Concomitantly, in the aged Drosophila brain, previous work found a brain-wide, age-induced upshift in the ultrastructural size (EM: larger T-bars; STED: increased diameter of BRP scaffold) of presynaptic AZs (metaplasticity). Two findings causally linked this upshift to decreased olfactory memory performance. First, when continuously fed with spermidine, flies of 30 days of age (normally suffering from a complete loss of age-sensitive component of memory) were largely protected from these changes. Secondly, genetically provoking this up-shift eliminated the normally age-sensitive memory component in young animals already. An upshift in the AZ size should increase synaptic strength, evident in increased SV release in response to natural odors observed in aged but not aged-spermidine-fed flies. Presynaptic plasticity is crucial for forming memory traces in Drosophila. Previous work thus suggests that this presynaptic metaplasticity shifts the operational range of synapses in a way that they become unable to execute the plastic changes faithfully in response to conditioning stimuli (Bhukel, 2019).
This study further addressed the relation between defective autophagy, presynaptic ultrastructure and plasticity and olfactory memory formation. Autophagosome biogenesis is very dominant close to presynaptic specializations in distal axons in compartmentalized fashion and efficient macro-autophagy is essential for neuronal homeostasis and survival. Retrograde transport of autophagosomes might play a role in broader neuronal signaling processes, promoting neuronal complexity and preventing neurodegeneration. Surprisingly, however, the data do not favor a direct substrate relationship between AZ proteins and autophagy. Instead, evidence was found for a seemingly non-cell autonomous relation between brain-wide synapse organization and the autophagic status of the mere MB. After genetic impairment of autophagy (via atg5 or atg9 KD) using two different MB-specific Gal4-driver lines, the presynaptic metaplasticity was observed across the Drosophila olfactory system and beyond. While the autophagic arrest (p62 staining) was largely limited to the expression domain of these drivers, the synapses were pushed towards a state of metaplasticity. Since the ultrastructural size of AZs and the per AZ BRP levels increased equally in aged and MB-autophagy-challenged animals, it is concluded that the autophagic status of the MB neuron population executes a signaling process, which can control the per AZ amounts of BRP and other AZ proteins. Further studies are warranted to dissect the nature of these signaling processes (Bhukel, 2019).
Notably, accumulating evidences support the important role of neuropeptide Y (NPY) in aging and lifespan determination. NPY levels decrease with age in mice and re-substituting NPY is able to counteract age-induced changes of the brain at several levels. A cross-talk between autophagy and NPY in regulating the feeding behavior has been demonstrated in mice (Bhukel, 2019).
This study found that transcript expression level of an NPY family member (sNPF) are controlled by autophagy within the MBs. snpf hypomorph allele mimicking the MB reduction of sNPF of the MB-specific autophagy KD situations as well as the sNPF expression in aged animals. In this hypomorph allele a similar up regulation was observed in BRP Nc82 signal. KD of the snpfr using an MB-specific driver drove the brain-wide metaplastic change even stronger than the sNPF hypomorph (obviously only partially affecting the sNPF-specific signaling). This scenario in ultrastructural detail resembled both the age-induced and MB-specific autophagy-KD-induced metaplasticity phenotypes. These results, therefore, support the essential role of MB in integrating the metabolic state of Drosophila in an autocrine fashion to modulate the presynaptic release scaffold state throughout the fly brain. The mechanistic basis of this exciting regulation warrants further investigation. Interestingly, elevated cAMP signaling is generally driving plasticity in Drosophila neurons, while sNPF signaling is meant to reduce cAMP and thus potentially might be able to reset plastic changes such as increased BRP levels. In apparent contradiction to sNPF signaling directly widely controlling metaplasticity is the finding that MB-specific KD of the sNPFR sufficed to increase BRP levels. At this moment, it can only be speculated as to why KD of sNPF-receptor also results in extended metaplastic changes. Potentially, sNPF-receptor signaling within the MB might be important to control sNPF secretion in a physiological manner via a quasi-autocrine mechanism (Bhukel, 2019).
Intriguingly, the metaplastic state characterized both aged and MB-specific autophagy KD animals, and in both cases provoked a specific loss of the ASM component of memory. Notably, olfactory MTM measured in this study, are considered to be the direct precursor of olfactory LTM, which in turn have been shown to be energetically costly. Notably, autophagy and NPY signaling are prime candidate mechanisms for the therapy of age-induced cognitive processes (Bhukel, 2019).
Recent research has uncovered several examples connecting autophagy and hormonal-type regulations interacting between organ systems in non-cell autonomous regimes. For instance, Atg18 acts non-cell autonomously both in neurons and in intestines to firstly, maintain the wild-type lifespan of C.elegans and secondly, to respond to the dietary restriction and DAF-2 longevity signals. Atg18 in chemosensory neurons and intestines acts in parallel and converges on unidentified neurons that secrete neuropeptides to mediate the influence of Daf-2 on C.elegans lifespan through the transcription factor DAF-16/FOXO in response to reduced IGF signaling. In Drosophila, neuronal up-regulation of AMPK induces autophagy, via up-regulation of Atg1 non-cell autonomously in intestines and slows intestinal aging and vice versa. Moreover, up-regulation of Atg1 in neurons extends lifespan and maintains intestinal homeostasis during aging and these inter-tissue effects of AMPK/Atg1 were linked to altered insulin-like signaling. On the contrary, this study found the insulin producing cells (IPCs) themselves to not mediate the observed metaplastic state, as neither the KD of atg9 nor the KD of snpfr in Pars intercerebralis had any impact on the synaptic status of these flies (Bhukel, 2019).
Autophagy regulation is tightly connected to cellular energetics, nutrient recycling, and the maintenance of cellular energy status. The fruit fly can evaluate its metabolic state by integrating hunger and satiety signals at the very KC-to-MBON synapses in MB under control of dopaminergic neurons to control hunger-driven food-seeking behavior. At the same time, long-term memory encoding necessitates an increase in MB energy flux with dopamine signaling mediating this energy switch in the MB. In line with these findings, this study now provides a modeling basis to study these delicate relations in an exemplary fashion. Taken together, these data suggest that MB integrates the metabolic state of the flies via cross talk between autophagy and sNPF signaling with the decision whether to form memories or not and a block in this cross talk with aging gives rise to synaptic metaplasticity which initiates the age-induced memory impairment in Drosophila. It is tempting to speculate that the MB executes hierarchically, a high-level control integrating the metabolic and caloric situation with a life-strategy decision of whether or not to form mid-term memories (Bhukel, 2019).
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Wang, M. and Lemos, B. (2019). Ribosomal DNA harbors an evolutionarily conserved clock of biological aging. Genome Res. PubMed ID: 30765617
Summary:
The ribosomal DNA (rDNA) is the most evolutionarily conserved segment of the genome and gives origin to the nucleolus, an energy intensive nuclear organelle and major hub influencing myriad molecular processes from cellular metabolism to epigenetic states of the genome. The rDNA/nucleolus has been directly and mechanistically implicated in aging and longevity in organisms as diverse as yeasts, Drosophila, and humans. The rDNA is also a significant target of DNA methylation that silences supernumerary rDNA units and regulates nucleolar activity. This study introduced an age clock built exclusively with CpG methylation within the rDNA. The ribosomal clock is sufficient to accurately estimate individual age within species, is responsive to genetic and environmental interventions that modulate life-span, and operates across species as distant as humans, mice, and dogs. Further analyses revealed a significant excess of age-associated hypermethylation in the rDNA relative to other segments of the genome, and which forms the basis of the rDNA clock. These observations identified an evolutionarily conserved marker of aging that is easily ascertained, grounded on nucleolar biology, and could serve as a universal marker to gauge individual age and response to interventions in humans as well as laboratory and wild organisms across a wide diversity of species (Wang, 2019).
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Kennerdell, J. R., Liu, N. and Bonini, N. M. (2018).
MiR-34 inhibits polycomb repressive complex 2 to modulate chaperone expression and promote healthy brain aging. Nat Commun 9(1): 4188. PubMed ID: 30305625
Summary:
Aging is a prominent risk factor for neurodegenerative disease. Defining gene expression mechanisms affecting healthy brain aging should lead to insight into genes that modulate susceptibility to disease. To define such mechanisms, analysis of miR-34 mutants have been pursued in Drosophila. The miR-34 mutant brain displays a gene expression profile of accelerated aging, and miR-34 upregulation is a potent suppressor of polyglutamine-induced neurodegeneration. Pcl and Su(z)12, two components of polycomb repressive complex 2, (PRC2), are targets of miR-34, with implications for age-associated processes. Because PRC2 confers the repressive H3K27me3 mark, it is hypothesized that miR-34 modulates PRC2 activity to relieve silencing of genes promoting healthful aging. Gene expression profiling of the brains of hypomorphic mutants in Enhancer of zeste (E(z)), the enzymatic methyltransferase component of PRC2, revealed a younger brain transcriptome profile and identified the small heat shock proteins as key genes reduced in expression with age (Kennerdell, 2018).
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Joseph, N. M., Elphick, N. Y., Mohammad, S. and Bauer, J. H. (2018). Altered pheromone biosynthesis is associated with sex-specific changes in life span and behavior in Drosophila melanogaster. Mech Ageing Dev. PubMed ID: 30312624
Summary:
Many insect behaviors, including foraging, aggression, mating or group behavior, are tightly regulated by pheromones. Recently, it has been shown that pheromones may influence extreme longevity in the honeybee Apis mellifera, while changes in pheromone profile have been observed during ageing in Drosophila melanogaster. These data suggest a potential link between the pheromone system, behavior and longevity in insects. This study investigated this potential link by examining changes in behavior and longevity in fruit flies with altered pheromone profiles. Oenocyte-specific reduction of desaturase activity was shown to be sufficient to dramatically alter the composition of the hydrocarbon mix displayed by the flies. In addition, flies with altered desaturase activity display changes in fecundity and stereotypical mating behavior, and, importantly, extended longevity. These data provide evidence for a potential link between hydrocarbon synthesis and life span, and suggest that longevity may be influenced by behavior (Joseph, 2018).
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Westfall, S., Lomis, N. and Prakash, S. (2018).
Longevity extension in Drosophila through gut-brain communication. Sci Rep 8(1): 8362. Pubmed ID: 29849035
Summary:
Aging and chronic disease development are multifactorial processes involving the cumulative effects of metabolic distress, inflammation, oxidative stress and mitochondrial dynamics. Recently, variations in the gut microbiota have been associated with age-related phenotypes and probiotics have shown promise in managing chronic disease progression. In this study, novel probiotic and synbiotic formulations are shown to combinatorially extend longevity in male Drosophila melanogaster through mechanisms of gut-brain-axis communication with implications in chronic disease management. Both the probiotic and synbiotic formulations rescued markers of metabolic stress by managing insulin resistance and energy regulatory pathways. Both formulations also ameliorated elevations in inflammation, oxidative stress and the loss of mitochondrial complex integrity. In almost all the measured pathways, the synbiotic formulation has a more robust impact than its individual components insinuating its combinatorial effect. The concomitant action of the gut microbiota on each of the key risk factors of aging and makes it a powerful therapeutic tool against neurodegeneration, diabetes, obesity, cardiovascular disease and other age-related chronic diseases (Westfall, 2018).
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Davie, K., Janssens, J., Koldere, D., De Waegeneer, M., Pech, U., Kreft, L., Aibar, S., Makhzami, S., Christiaens, V., Bravo Gonzalez-Blas, C., Poovathingal, S., Hulselmans, G., Spanier, K. I., Moerman, T., Vanspauwen, B., Geurs, S., Voet, T., Lammertyn, J., Thienpont, B., Liu, S., Konstantinides, N., Fiers, M., Verstreken, P. and Aerts, S. (2018). A single-cell transcriptome atlas of the aging Drosophila brain. Cell. PubMed ID: 29909982
Summary:
The diversity of cell types and regulatory states in the brain, and how these change during aging, remains largely unknown. This paper presents a single-cell transcriptome atlas of the entire adult Drosophila melanogaster brain sampled across its lifespan. Cell clustering identified 87 initial cell clusters that are further subclustered and validated by targeted cell-sorting. The data show high granularity and identify a wide range of cell types. Gene network analyses using SCENIC revealed regulatory heterogeneity linked to energy consumption. During aging, RNA content declines exponentially without affecting neuronal identity in old brains. This single-cell brain atlas covers nearly all cells in the normal brain and provides the tools to study cellular diversity alongside other Drosophila and mammalian single-cell datasets in this unique single-cell analysis platform: SCope (http://scope.aertslab.org). These results, together with SCope, allow comprehensive exploration of all transcriptional states of an entire aging brain (Davie, 2018).
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Catterson, J. H., Khericha, M., Dyson, M. C., Vincent, A. J., Callard, R., Haveron, S. M., Rajasingam, A., Ahmad, M. and Partridge, L. (2018). Short-term, intermittent fasting induces long-lasting gut health and TOR-independent lifespan extension. Curr Biol. PubMed ID: 29779873
Summary:
Intermittent fasting (IF) can improve function and health during aging in laboratory model organisms, but the mechanisms at work await elucidation. This study subjected fruit flies (Drosophila melanogaster) to varying degrees of IF and found that just one month of a 2-day fed:5-day fasted IF regime at the beginning of adulthood was sufficient to extend lifespan. This long-lasting, beneficial effect of early IF was not due to reduced fecundity. Starvation resistance and resistance to oxidative and xenobiotic stress were increased after IF. Early-life IF also led to higher lipid content in 60-day-old flies, a potential explanation for increased longevity. Guts of flies 40 days post-IF showed a significant reduction in age-related pathologies and improved gut barrier function. Improved gut health was also associated with reduced relative bacterial abundance. Early IF thus induced profound long-term changes. Pharmacological and genetic epistasis analysis showed that IF acted independently of the TOR pathway because rapamycin and IF acted additively to extend lifespan, and global expression of a constitutively active S6K did not attenuate the IF-induced lifespan extension. It is concluded that short-term IF during early life can induce long-lasting beneficial effects, with robust increase in lifespan in a TOR-independent manner, probably at least in part by preserving gut health (Catterson, 2018).
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Liang, Y., Liu, C., Lu, M., Dong, Q., Wang, Z., Wang, Z., Xiong, W., Zhang, N., Zhou, J., Liu, Q., Wang, X. and Wang, Z. (2018). Calorie restriction is the most reasonable anti-ageing intervention: a meta-analysis of survival curves. Sci Rep 8(1): 5779. PubMed ID: 29636552
Summary:
Despite technological advances, the survival records from longevity experiments remain the most indispensable tool in ageing-related research. A variety of interventions, including medications, genetic manipulations and calorie restriction (CR), have been demonstrated to extend the lifespan of several species. Surprisingly, few systematic studies have investigated the differences among these anti-ageing strategies using survival data. This study conductd a comprehensive and comparative meta-analysis of numerous published studies on Caenorhabditis elegans and Drosophila. CR and genetic manipulations were found to be generally more effective than medications at extending the total lifespan in both models, and CR can improve the ageing pattern of C. elegans. The survival variation for different anti-ageing medications was examined and determined that hypoglycaemic agents and antioxidants are advantageous despite only moderately increasing the overall lifespan; therefore, these two types of medications are promising CR mimetics. Analysis of genetic manipulations also indicated that the genes or pathways that extend lifespan in a healthier pattern are associated with CR. These results suggest that CR or CR mimetics may be the most reasonable and potentially beneficial anti-ageing strategy (Liang, 2018).
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Yan, Y., Wang, H., Hu, M., Jiang, L., Wang, Y., Liu, P., Liang, X., Liu, J., Li, C.,
Lindstrom-Battle, A., Lam, S. M., Shui, G., Deng, W. M. and Jiao, R. (2017). HDAC6 suppresses age-dependent ectopic fat accumulation by maintaining the proteostasis of PLIN2 in Drosophila.
Dev Cell 43(1): 99-111.e115. PubMed ID: 28966044
Summary:
Age-dependent ectopic fat accumulation (EFA) in animals contributes to
the progression of tissue aging and diseases such as obesity, diabetes,
and cancer. However, the primary causes of age-dependent EFA remain largely elusive. This study characterized the occurrence of age-dependent EFA in Drosophila and identified HDAC6, a cytosolic histone deacetylase, as a suppressor of EFA. Loss
of HDAC6 leads to significant age-dependent EFA, lipid composition imbalance,
and reduced animal longevity on a high-fat diet. The EFA and longevity
phenotypes are ameliorated by a reduction of the lipid-droplet-resident
protein PLIN2. HDAC6 was found to be associated physically with the
chaperone protein dHsc4/Hsc70 to
maintain the proteostasis of PLIN2. These findings indicate that
proteostasis collapse serves as an intrinsic cue to cause age-dependent
EFA. This study suggests that manipulation of proteostasis could be an
alternative approach to the treatment of age-related metabolic diseases
such as obesity and diabetes (Yan, 2017).
Age-dependent EFA occurs in mammals as a hallmark of aging and contributes to age-related tissue deterioration and dysfunction. This study used a Drosophila model to assess the molecular basis of age-dependent EFA formation. Age-dependent EFA appears mainly in the thoracic jump muscles of adult flies in an age-dependent manner. Further, proteostatic regulators, dHDAC6 and dHs4, are identified to suppress age-dependent EFA. The genetic and biochemical data indicate that dHDAC6 maintains the proteostasis of lipid droplet protein PLIN2 by modulating the acetylation level of dHsc4. The dHDAC6-dHsc4-PLIN2 axis links proteostasis to fat metabolism during aging. These results also highlight that it is the protein quality rather than the protein quantity of PLIN2 that controls age-dependent EFA (Yan, 2017).
PLIN2, belonging to the PAT family, is an lipid droplet (LD) coating protein that has been shown to play important roles in the formation and turnover of LDs in non-adipose tissues such as the skeletal muscle, pancreas, gonads, and gut. PLIN2 accumulates in human muscle with age and is associated with muscle weakness, obesity, and diabetes. Since the activity of both ubiquitin-proteasome and lysosome weakens during aging, it is plausible to infer that the increase in PLIN2 protein levels in aged individuals are caused by lowered activity of either ubiquitin-proteasome or lysosome. The results demonstrate that the degradation of PLIN2 is mediated by dHDAC6 through chaperone dHsc4-assisted autophagy but not macro-autophagy, and that the quality but not the quantity of PLIN2 plays an important role in EFA formation and tissue dysfunction during aging. The substrates of chaperone Hsc70/dHsc4 exhibit a consensus pentapeptide KFERQ motif, and Hsc70 has been reported to mediate the degradation of PAT family proteins, PLIN2 and PLIN3, in mouse. This study excluded the possibility that dHsc4/Hsc70 mediates the degradation of PLIN2 through the CMA machinery based on the following evidence: First, no conserved KREFQ motif specific for CMA degradation was found in Drosophila PLIN2; second, a mutant form of Drosophila PLIN2 was made in the non-canonical KREFQ motif region, which did not show any decreased degradation rate; Third, CMA degradation in mammals requires the lysosome receptor LAMP2A, however, Lamp1, the Drosophila homolog of LAMP2A, is not involved in age-dependent EFA. Therefore, it is speculated that dHsc4/Hsc70 may mediate the degradation of PLIN2 through chaperone-assisted selective autophagy, which involves co-chaperones and ubiquitination to degrade mainly insoluble proteins. Supporting this hypothesis, a significant amount of ubiquitinated aggregates were detected to accumulate on the surface of LDs in the jump muscles of dHDAC6 mutants, which colocalize with PLIN2. On the other hand, several co-chaperones (Dnaj-1, HspB8, Dnaj-2, mrj, and CG5001) and the E3 ligase CHIP were tested, but none of them were required for the chaperone-assisted selective autophagy process to lead to EFA. It is speculated that there may be another unknown co-chaperone(s) that functions with dHDAC6/dHsc4 in Drosophila (Yan, 2017).
Recently, studies show that PLIN2 is associated with the progression of age-related diseases, such as insulin resistance, fatty liver, type 2 diabetes, sarcopenia, and cancer. All the diseases reported thus far that are associated with PLIN2 are linked to aging, implying that the changes in PLIN2 during aging might have a pivotal contribution to the severity of these age-related diseases. This study assessed the changes in soluble and insoluble PLIN2 protein levels during aging and showed that only the insoluble PLIN2 protein level was increased and associated with the increase in age-dependent EFA in the jump muscle. The results suggest a possibility of improving the proteostasis of PLIN2 as an efficient way to ameliorate the progressive defects of age-related metabolic diseases (Yan, 2017).
Another question is how increased insoluble PLIN2 can cause increased EFA in aging muscle. Insoluble proteins exhibit hydrophobic aggregation properties and LDs containing a hydrophobic core are prone to act as an anchoring site for hydrophobic proteins. Thus, it is proposed that insoluble PLIN2 is prone to be anchored on the LDs to sequester more hydrophobic lipases. Anchored insoluble PLIN2 or insoluble PLIN2 aggregates prevent triglyceride lipases from reaching the LD surface to mediate lipid breakdown. In support of this hypothesis, the data show that increased LD accumulation in the jump muscle of the dHDAC6 mutant could not be reverted by overexpression of lipases such as Bmm or dHSL. However, more investigations are needed to explore precisely how the proteostasis of PLIN2 affects LD turnover in the aging process and whether the proteostasis of PLIN2 may also be involved in other physiological processes (Yan, 2017).
The maintenance of proteostasis in organelles, such as the endoplasmic reticulum, mitochondrion, and the nucleus, involves specialized cellular compartments. Mitochondrial proteostasis requires mitochondrial chaperones, ATFS-1 signaling, and GCN2 signaling to activate mitochondrial unfolded protein response (UPRmt); whereas nuclear proteostasis requires nuclear envelope, nuclear pore complexes, and transport pathways. In Drosophila, proteostasis of the muscles controls systemic aging and requires Foxo/4E-BP signaling and Activin signaling. As the primary site of lipid metabolism, LDs are considered as dynamic organelles, but little is known about how proteostasis of LDs is maintained. This study identified that the chaperone dHsc4 and the deacetylase dHDAC6 play key roles in maintaining LD proteostasis. More importantly, proteostasis of the LD protein PLIN2 links the proteostasis network to age-dependent EFA (Yan, 2017).
Age-dependent EFA appears mainly in the tubular jump muscle, but not in the fibrous indirect flight muscle, which is a large part of adult thoracic muscles, indicating LD accumulation is more sensitive to aging in jump muscle than in indirect flight muscle. Age-dependent EFA was also detected in other regions of an aging fly particularly in the posterior midgut and the tip region of testis. However, EFA in these tissues appears to be regulated in a non-tissue autonomous manner, since muscle-specific expression of dHDAC6 in the dHDAC6 mutants reverted the EFA-increase phenotype not only in the jump muscle but also in the posterior midgut and the testis. Recently, fat accumulation has also been shown to occur in other conditions, such as in the niche glia of stem cells of larval CNS under oxidant/oxidative stress and in the adult pigment cells of mitochondrial mutants. LD formation in the niche glia functions as a protective organelle to sequester polyunsaturated fatty acids and to reduce the levels of reactive oxygen species, whereas LD accumulation in adult pigment cells appears to increase lipid peroxidation and to promote neurodegenerative disease. LD accumulation in either the niche glia cells or the pigment cells can be reverted by overexpression of triglyceride lipases, indicating that the LDs formed in such conditions are an 'active' organelle. However, the LD accumulation in the aging jump muscle described in this study could not be reverted by overexpression of lipases, implying that the LDs in aging jump muscle seem to be a 'steady' organelle. This 'steady' LD formation can only be ameliorated by improving the proteostasis of LD-resident protein PLIN2. LD accumulation could also be induced by altering some of the fat-metabolism-related genes, but not in an age-dependent manner; thus, age-dependent EFA occurs in a distinct way contributing to the dysfunction of muscle aging. This study suggests that improvement of proteostasis of PLIN2 may be a new approach to ameliorate age-related metabolic diseases such as obesity (Yan, 2017).
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Lee, B. C., Lee, H. M., Kim, S., Avanesov, A. S., Lee, A., Chun, B. H., Vorbruggen, G. and Gladyshev, V. N. (2018). Expression of the methionine sulfoxide reductase lost during evolution extends Drosophila lifespan in a methionine-dependent manner. Sci Rep 8(1): 1010. PubMed ID: 29343716
Summary:
Accumulation of oxidized amino acids, including methionine, has been implicated in aging. The ability to reduce one of the products of methionine oxidation, free methionine-R-sulfoxide (Met-R-SO), is widespread in microorganisms, but during evolution this function, conferred by the enzyme fRMsr, was lost in metazoa. This study examined whether restoration of the fRMsr function in an animal can alleviate the consequences of methionine oxidation. Ectopic expression of yeast fRMsr supported the ability of Drosophila to catalyze free Met-R-SO reduction without affecting fecundity, food consumption, and response to starvation. fRMsr expression also increased resistance to oxidative stress. Moreover, it extended lifespan of flies in a methionine-dependent manner. Thus, expression of an oxidoreductase lost during evolution can enhance metabolic and redox functions and lead to an increase in lifespan in an animal model. More broadly, this study exposes the potential of a combination of genetic and nutritional strategies in lifespan control (Lee, 2018).
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Pyo, J. H., Jeon, H. J., Park, J. S., Lee, J. S., Chung, H. Y. and Yoo, M. A. (2018). Drosophila PEBP1 inhibits intestinal stem cell aging via suppression of ERK pathway. Oncotarget 9(26): 17980-17993. PubMed ID: 29719584
Summary:
The intestine is a high cellular turnover tissue largely dependent on the regenerative function of stem cell throughout life, and a signaling center for the health and viability of organisms. Therefore, better understanding of the mechanisms underlying the regulation of intestinal stem cell (ISC) regenerative potential is essential for the possible intervention of aging process and age-related diseases. Drosophila midgut is a well-established model system for studying the mechanisms underlying ISC regenerative potential during aging. This study reporta the requirement of Drosophila phosphatidylethanolamine binding protein 1 (PEBP1) in ISC regenerative potential. PEBP1 was strongly expressed in enterocytes (ECs) of guts and its decrease with age and oxidative stress. Furthermore, the downregulation of PEBP1 in ECs accelerates ISC aging, as evidenced by ISC hyper-proliferation, gammaH2AX accumulation, and centrosome amplification, and intestinal hyperplasia. The decrease in PEBP1 expression was associated with increased extracellular signal-regulated kinase (ERK) activity in ECs. All these phenotypes by EC-specific depletion of PEBP1 were rescued by the concomitant inhibition of ERK signaling. These findings evidence that the age-related downregulation of PEBP1 in ECs is a novel cause accelerating ISC aging and that PEBP1 is an EC-intrinsic suppressor of epidermal growth factor receptor (EGFR)/ERK signaling. This study provides molecular insights into the tight regulation of EGFR/ERK signaling in niches for stem cell regenerative potential (Pyo, 2018).
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Brenman-Suttner, D. B., Long, S. Q., Kamesan, V., de Belle, J. N., Yost, R. T., Kanippayoor, R. L. and Simon, A. F. (2018). Progeny of old parents have increased social space in Drosophila melanogaster. Sci Rep 8(1): 3673. PubMed ID: 29487349
Summary:
This study report the effects of aging and parental age in Drosophila melanogaster on two types of responses to social cues: the choice of preferred social spacing in an undisturbed group and the response to the Drosophila stress odorant (dSO) emitted by stressed flies. The patterns of changes during aging were notably different for these two social responses. Flies were initially closer in space and then became further apart. However, the pattern of change in response to dSO followed a more typical decline in performance, similarly to changes in locomotion. Interestingly, the increased social space of old parents, as well as their reduced performance in avoiding dSO, was passed on to their progeny, such that young adults adopted the behavioural characteristic of their old parents. While the response to social cues was inherited, the changes in locomotion were not. It was possible to scale the changes in the social space of parents and their progeny by accelerating or decelerating the physiological process of aging by increasing temperatures and exposure to oxidative stress, or via caloric restriction, respectively. Finally, when only one parent was aged, only the male progeny of old fathers and the progeny of very old mothers were more distant (Brenman-Suttner, 2018).
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Becker, L., Nogueira, M. S., Klima, C., de Angelis, M. H. and Peleg, S. (2018). Rapid and transient oxygen consumption increase following acute HDAC/KDAC inhibition in Drosophila tissue. Sci Rep 8(1): 4199. PubMed ID: 29520020
Summary:
Epigenetic deregulation, such as the reduction of histone acetylation levels, is thought to be causally linked to various maladies associated with aging. Consequently, histone deacetylase inhibitors are suggested to serve as epigenetic therapy by increasing histone acetylation. However, previous work suggests that many non-histone proteins, including metabolic enzymes, are also acetylated and that post transitional modifications may impact their activity. Furthermore, deacetylase inhibitors were recently shown to impact the acetylation of a variety of proteins. By utilizing a novel technique to measure oxygen consumption rate from whole living tissue, this study demonstrated that treatment of whole living fly heads by the HDAC/KDAC inhibitors sodium butyrate and Trichostatin A, induces a rapid and transient increase of oxygen consumption rate. In addition, this study indicates that the rate increase is markedly attenuated in midlife fly head tissue. Overall, this data suggest that HDAC/KDAC inhibitors may induce enhanced mitochondrial activity in a rapid manner. This observed metabolic boost provides further, but novel evidence, that treating various maladies with deacetylase inhibitors may be beneficial (Becker, 2018).
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Wen, D. T., Zheng, L., Yang, F., Li, H. Z. and Chen, J. (2018). Endurance exercise prevents high-fat-diet induced locomotor impairment, cardiac dysfunction, lifespan shortening, and dSir2 expression decline in aging Drosophila. Exp Gerontol [Epub ahead of print]. PubMed ID: 29355704
Summary:
High-Fat-Diet (HFD)-induced obesity is a major contributor to premature senescence in both Drosophila and humans, which includes locomotor impairment, cardiac dysfunction, and decrease in lifespan. While, few studies have shown that HFD could affect the expression dSir2 genes since the dSir2 genes are closely related to aging. Endurance exercise can efficiently prevent obesity and delay age-related functional decline in Drosophila and humans. However, few directed reports showing that exercise can resist HFD-induced locomotor impairment, cardiac dysfunction and decrease in lifespan. It is also unclear whether exercise training can relieve the harmful HFD-induced influence on the dSir2 gene and prevent premature senescence in flies. In this study, flies were fed a HFD and trained from when they were one week old until they were five weeks old. Then, TAG levels, climbing index, cardiac function, lifespan, and dSir2 mRNA expressions were measured. It was found that endurance exercise could protect Drosophila from HFD-induced and age-related body lipid accumulation, locomotor impairment, cardiac contraction dysfunction, heart fibrillation rise, lifespan shortening, and dSir2 expression decline in aging flies. Therefore, this study confirmed that exercise effectively prevented flies from HFD-induced premature aging (Wen, 2018).
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Romey-Glusing, R., Li, Y., Hoffmann, J., von Frieling, J., Knop, M., Pfefferkorn, R., Bruchhaus, I., Fink, C. and Roeder, T. (2017). Nutritional regimens with periodically recurring phases of dietary restriction extend lifespan in Drosophila. Faseb J. PubMed ID: 29196499
Summary:
Nutritional interventions such as caloric and dietary restriction increase lifespan in various animal models. To identify alternative and less demanding nutritional interventions that extend lifespan, fruit flies (Drosophila melanogaster) were subjected to weekly nutritional regimens that involved alternating a conventional diet with dietary restriction. Short periods of dietary restriction (up to 2 d) followed by longer periods of a conventional diet yielded minimal increases in lifespan. Three or more days of contiguous dietary restriction (DR) was necessary to yield a lifespan extension similar to that observed with persistent DR. Female flies were more responsive to these interventions than males. Physiologic changes known to be associated with prolonged DR, such as reduced metabolic rates, showed the same time course as lifespan extension. Moreover, concurrent transcriptional changes indicative of reduced insulin signaling were identified with DR. These physiologic and transcriptional changes were sustained, as they were detectable several days after switching to conventional diets. Taken together, diets with longer periods of DR extended lifespan concurrently with physiologic and transcriptional changes that may underlie this increase in lifespan (Romey-Glusing, 2017).
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Filer, D., Thompson, M. A., Takhaveev, V., Dobson, A. J., Kotronaki, I., Green, J. W. M., Heinemann, M., Tullet, J. M. A. and Alic, N. (2017). RNA polymerase III limits longevity downstream of TORC1. Nature 552(7684): 263-267. PubMed ID: 29186112
Summary:
Three distinct RNA polymerases transcribe different classes of genes in the eukaryotic nucleus. RNA polymerase (Pol) III is the essential, evolutionarily conserved enzyme that generates short, non-coding RNAs, including tRNAs and 5S rRNA. The historical focus on transcription of protein-coding genes has left the roles of Pol III in organismal physiology relatively unexplored. Target of rapamycin kinase complex 1 (TORC1) regulates Pol III activity, and is also an important determinant of longevity. This raises the possibility that Pol III is involved in ageing. This study shows that Pol III limits lifespan downstream of TORC1. A reduction in Pol III extends chronological lifespan in yeast and organismal lifespan in worms and flies. Inhibiting the activity of Pol III in the gut of adult worms or flies is sufficient to extend lifespan; in flies, longevity can be achieved by Pol III inhibition specifically in intestinal stem cells. The longevity phenotype is associated with amelioration of age-related gut pathology and functional decline, dampened protein synthesis and increased tolerance of proteostatic stress. Pol III acts on lifespan downstream of TORC1, and limiting Pol III activity in the adult gut achieves the full longevity benefit of systemic TORC1 inhibition. Hence, Pol III is a pivotal mediator of this key nutrient-signalling network for longevity; the growth-promoting anabolic activity of Pol III mediates the acceleration of ageing by TORC1. The evolutionary conservation of Pol III affirms its potential as a therapeutic target (Filer, 2017).
The task of carrying out transcription in the eukaryotic nucleus is divided among RNA Pol I, II and III. This specialization is evident in the biogenesis of the translation machinery, a task that requires the co-ordinated activity of all three polymerases: Pol I generates the 45S pre-rRNA that is subsequently processed into mature rRNAs, Pol II transcribes various RNAs including mRNAs encoding ribosomal proteins, while Pol III provides the tRNAs and 5S rRNA. This costly process of generating protein synthetic capacity is tightly regulated to match the extrinsic conditions and the intrinsic need for protein synthesis by the key driver of cellular anabolism, TORC1. The central position of TORC1 in the control of fundamental cellular processes is mirrored by the notable effect of its activity on organismal physiology: following its initial discovery in worms, inhibition of TORC1 has been demonstrated to extend lifespan in all tested organisms, from yeast to mice, with beneficial effects on a range of age-related diseases and dysfunctions. TORC1 strongly activates Pol III transcription and this relationship suggests the possibility that inhibition of Pol III promotes longevity (Filer, 2017).
In Saccharomyces cerevisiae, each of the 17 Pol III subunits is encoded by an essential gene. This study generated a yeast strain in which the largest Pol III subunit (C160, encoded by RPC160, also known as RPO31) is fused to the auxin-inducible degron (AID). The fusion protein can be targeted for degradation by the ectopically expressed E3 ubiquitin ligase (OsTir) in the presence of indole-3-acetic acid (IAA) to achieve conditional inhibition of Pol III. It was confirmed that IAA treatment triggered degradation of the fusion protein, and it was observed that IAA treatment also improved the survival of the RPC160-AID strain upon prolonged culture. In addition, IAA treatment of the control strain lacking the AID fusion reduced its survival relative to both the same strain in the absence of IAA and to the RPC160-AID strain in the presence of IAA. Hence, Pol III depletion appears to extend the chronological lifespan in yeast. While IAA had no substantial effect on the survival of a strain carrying the AID domain fused to the largest subunit of Pol II (RPB220, also known as RP021), this strain appeared to survive better than the control strain did in the presence of IAA, indicating that inhibition of Pol II may also extend chronological lifespan. Chronological lifespan of yeast is a measure of survival in a nutritionally limited, quiescent population, whereas replicative lifespan measures the number of daughters produced by a single mother cell in its lifetime. No evidence was found that inhibition of Pol III causes an increase in the replicative lifespan in yeast (Filer, 2017).
The observed increase in chronological lifespan may simply indicate increased stress resistance and hence be of limited relevance to organismal ageing. To examine the role of Pol III in organismal ageing directly, animal models were examined. RNA-mediated interference (RNAi) was initiated against rpc-1, the Caenorhabditis elegans orthologue of RPC160, in worms from the L4 stage, causing a partial knockdown of rpc-1 mRNA. This consistently extended the lifespan of worms at both 20°C and 25°C. To reduce Pol III activity in Drosophila melanogaster, a P-element insertion that deletes the transcriptional start site of the gene encoding the Pol III-specific subunit C53 (CG5147EY22749, henceforth called dC53EY, was backcrossed into a healthy, outbred population of flies. Homozygous dC53EY/EY mutants were not viable, but heterozygous females had reduced dC53 mRNA levels and lived longer than controls. Taken together, these data strongly indicate that Pol III limits lifespan in multiple model organisms and conversely, that partial inhibition of its activity is an intervention that increases longevity in multiple species (Filer, 2017).
The longevity of an animal can be governed from a single organ. In the worm, this role is often played by the gut. To restrict the rpc-1 knockdown to the gut, worms were used that were deficient in rde-1, in which the RNAi machinery deficiency is restored in the gut by gut-specific rde-1 rescue. rpc-1 RNAi extended the lifespan of this strain, both at 20°C and 25°C. Similarly, in the adult fly, driving an RNAi construct targeting the RPC160 orthologue (CG17209, henceforth called dC160,with the mid-gut-specific, RU486-inducible driver TIGS extended the lifespan of females, while the presence of the inducer (RU486) did not affect survival of the control strains. The longevity phenotype could also be recapitulated with RNAi against dC53, another Pol III subunit, indicating that the phenotype was not subunit-specific or due to off-target effects. As well as the gut, longevity can also be associated with the fat body and neurons in flies. However, the longevity phenotype caused by dC160 RNAi appears to be specific to the gut, since no significant lifespan extension was observed upon induction of dC160 RNAi in the fat body of the adult fly, and only a modest, albeit significant, extension resulted from neuronal induction of dC160 RNAi (Filer, 2017).
The worm gut is composed of only post-mitotic cells. In flies, as in mammals, the adult gut epithelium contains mitotically active intestinal stem cells, and the mid-gut-specific driver TIGS appears to be active in at least some ISCs, prompting restricting of dC160 RNAi induction to this cell type. ISC-specific dC160 RNAi, achieved with the GS5961 driver, was sufficient to promote longevity. In summary, Pol III activity in the gut limits survival in worms and flies, and in the fly, Pol III can drive ageing specifically from the gut stem-cell compartment (Filer, 2017).
The consequences of Pol III inhibition in the fly gut was assessed. Pol III acts to generate precursor tRNAs (pre-tRNAs) that are processed rapidly to mature tRNAs. Owing to their short half-lives, pre-tRNAs are useful as readouts of in vivo Pol III activity. Profiling the levels of specific pre-tRNAs, pre-tRNAHis, pre-tRNAAla and pre-tRNALeu, relative to the levels of U3 (a small nucleolar RNA transcribed by Pol II) revealed a moderate but significant reduction in Pol III activity upon gut-specific induction of dC160 RNAi. The three polymerases can be directly coordinated to generate the translation machinery. Indeed, Pol III inhibition had knock-on effects on Pol I- but not Pol II-generated transcripts, revealing partial cross-talk. dC160 RNAi also reduced protein synthesis in the gut, consistent with reduced Pol III activity. These effects (reduction in pre-tRNAs or protein synthesis) were not observed after feeding RU486 to the driver-only control. The reduction in protein synthesis was not pathological: total protein content of the gut was unaltered; fecundity, a sensitive readout of a female's nutritional status, was unaffected; and the flies' weight, triacylglycerol and protein levels remained unchanged. Reduced protein synthesis can liberate protein-folding machinery from protein production and increase homeostatic capacity. Indeed, induction of dC160 RNAi in the gut increased the resistance of adult flies to proteostatic challenge with tunicamycin for TIGS-only control. Hence, Pol III can fine-tune the rate of protein synthesis in the adult fly gut without obvious detrimental outcomes, while increasing resistance to proteotoxic stress (Filer, 2017).
Having demonstrated the relevance of Pol III for ageing, whether it acts on lifespan downstream of TORC1 was investigated in Drosophila. Numerous observations in several organisms support the model in which TORC1 localizes on Pol III-transcribed loci and promotes phosphorylation of the components of the Pol III transcriptional machinery to activate transcription, in part by inhibition of the Pol III repressor, Maf1. Using chromatin immunoprecipitation (ChIP) with two independently generated antibodies against Drosophila TOR (target of rapamycin), TOR enrichment was observed on Pol III-target genes in the adult fly, relative to Pol II targets. Inhibition of TORC1 by feeding rapamycin to flies reduced the levels of pre-tRNAs in whole flies. Rapamycin also reduced pre-tRNA levels specifically in the gut relative to U3. Since rapamycin results in re-scaling of the gut, evidenced by the reduction in the total RNA content of the organ, it was also confirmed that the drug reduced pre-tRNA levels relative to total RNA. Interestingly, rapamycin did not cause a decrease in 45S pre-rRNA in the gut, suggesting a lack of sustained Pol I inhibition. Additionally, gut-specific overexpression of Maf1 reduced the levels of pre-tRNAs and extended lifespan, confirming that Maf1 acts on Pol III in the adult gut. These data are consistent with TORC1 driving systemic and gut-specific Pol III activity in the adult fruitfly (Filer, 2017).
To examine whether the lifespan effects of Pol III are downstream of TORC1, adult-onset Pol III inhibition was combined with rapamycin treatment. Rapamycin feeding or gut-specific dC160 RNAi resulted in the same magnitude of lifespan extension. The two treatments were not additive, consistent with their acting on the same longevity pathway. The same effect was observed with RNAi against dC53 in the gut, as well as when dC160 RNAi was restricted to the ISCs. Importantly, rapamycin feeding also inhibited phosphorylation of the TORC1 substrate, S6 kinase (S6K), in both the gut and the whole fly, and decreased fecundity, while gut-specific C160 RNAi did not have these effects. This confirms that Pol III inhibition does not impact TORC1 activity locally or systemically, and therefore, Pol III acts downstream of TORC1 in ageing (Filer, 2017).
TORC1 inhibition is known to ameliorate age-related pathology and functional decline of the gut. Whether inhibition of Pol III was sufficient to block the dysplasia resulting from hyperproliferation and aberrant differentiation of ISCs was examined by assessing the characteristic, age-dependent increase in dividing phospho-histone H3 (pH3)-positive cells. Inducing dC160 RNAi in the fly gut or solely in the ISCs ameliorated this pathology. These treatments also counteracted the age-related loss of gut barrier function, decreasing the number of flies displaying extra-intestinal accumulation of a blue food dye (the 'Smurf' phenotype). It as also found that rpc-1 RNAi reduced the severity of age-related loss of gut-barrier function in worms. In Drosophila, gut health and TORC1 inhibition are specifically linked to female survival. Indeed, induction of dC160 RNAi in the gut had a sexually dimorphic effect on lifespan, as the effect on males, although significant, was lower in magnitude relative to the effect on females. Overall, the data show that gut- or ISC-specific inhibition of Pol III, which extends lifespan, is sufficient to ameliorate age-related impairments in gut health, which may be causative of or correlate with this longevity (Filer, 2017).
This study demonstrates that the adult-onset decrease in the growth-promoting anabolic function mediated by Pol III in the gut, and specifically in the intestinal stem-cell compartment, is sufficient to recapitulate the longevity benefits of rapamycin treatment. Pol III activity is essential for growth; its detrimental effects on ageing suggest an antagonistic pleiotropy in which wild-type levels of Pol III activity are optimised for growth and reproductive fitness in early life but prove detrimental for later health. This study reveals a fundamental role for Pol III in adult physiology, implicating wild-type Pol III activity in age-related stem-cell dysfunction, declining gut health and organismal survival downstream of nutrient signalling pathways. The longevity resulting from partial Pol III inhibition in adulthood is likely to result from the reduced provision of protein synthetic machinery; however, differential regulation of tRNA genes or Pol III-mediated changes to chromatin organization may also be involved, as has been suggested in other contexts (Arimbasseri, 2016). The strong structural and functional conservation of Pol III in eukaryotes suggests that studies of its influence on mammalian ageing are warranted and could lead to important therapies (Filer, 2017).
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Kayashima, Y., Katayanagi, Y., Tanaka, K., Fukutomi, R., Hiramoto, S. and Imai, S. (2017). Alkylresorcinols activate SIRT1 and delay ageing in Drosophila melanogaster. Sci Rep 7: 43679. PubMed ID: 28252007
Summary:
Sirtuins are enzymes that catalyze NAD+ dependent protein deacetylation. The natural polyphenolic compound resveratrol received renewed interest when recent findings implicated resveratrol as a potent SIRT1 activator capable of mimicking the effects of calorie restriction. However, resveratrol directly interacts with fluorophore-containing peptide substrates. It was demonstrated that the SIRT1 activation of resveratrol is affected by the amino acid composition of the substrate. Resveratrol did increase the enzyme activity in cases in which hydrophobic amino acids are at the +1 position to the acetylated lysine in the substrate. Alkylresorcinols (ARs) are compounds that belong to the family of phenolic lipids, and they are found in numerous biological species. This study shows that the natural activators ARs increased the Vmax of recombinant SIRT1 for NAD+ and peptide substrate, and that ARs decreased acetylated histone in human monocyte cells by stimulating SIRT1-dependent deacetylation of substrates. ARs also extended the lifespan of Drosophila melanogaster, which was shown to be dependent on functional Sir2. These results demonstrated that ARs are natural catalytic activators for sirtuin (Kayashima, 2017).
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Klassen, M. P., Peters, C. J., Zhou, S., Williams, H. H., Jan, L. Y. and Jan, Y. N. (2017). Age-dependent diastolic heart failure in an in vivo Drosophila model. Elife 6 [Epub ahead of print]. PubMed ID: 28328397
Summary:
While the signals and complexes that coordinate the heartbeat are well established, how the heart maintains its electromechanical rhythm over a lifetime remains an open question with significant implications to human health. Reasoning that this homeostatic challenge confronts all pulsatile organs, this study developed a high resolution imaging and analysis toolset for measuring cardiac function in intact, unanesthetized Drosophila melanogaster. As in humans, normal aging primarily manifests as defects in relaxation (diastole) while preserving contractile performance. Using this approach, it was discovered that a pair of two-pore potassium channel (K2P) subunits (FlyBase gene: sandman), largely dispensable early in life, are necessary for terminating contraction (systole) in aged animals, where their loss culminates in fibrillatory cardiac arrest. As the pumping function of its heart is acutely dispensable for survival, Drosophila represents a uniquely accessible model for understanding the signaling networks maintaining cardiac performance during normal aging (Klassen, 2017).
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Stefana, M. I., Driscoll, P. C., Obata, F., Pengelly, A. R., Newell, C. L., MacRae, J. I. and Gould, A. P. (2017). Developmental diet regulates Drosophila lifespan via lipid autotoxins. Nat Commun 8(1): 1384. PubMed ID: 29123106
Summary:
Early-life nourishment exerts long-term influences upon adult physiology and disease risk. These lasting effects of diet are well established but the underlying mechanisms are only partially understood. This study shows that restricting dietary yeast during Drosophila development can, depending upon the subsequent adult environment, more than double median lifespan. Developmental diet acts via a long-term influence upon the adult production of toxic molecules, which are termed autotoxins, that are shed into the environment and shorten the lifespan of both sexes. Autotoxins are synthesised by oenocytes and some of them correspond to alkene hydrocarbons that also act as pheromones. This study identifies a mechanism by which the developmental dietary history of an animal regulates its own longevity and that of its conspecific neighbours. It also has important implications for the design of lifespan experiments as autotoxins can influence the regulation of longevity by other factors including diet, sex, insulin signalling and population density (Stefana, 2017).
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Garschall, K., Dellago, H., Galikova, M., Schosserer, M., Flatt, T. and Grillari, J. (2017). Ubiquitous overexpression of the DNA repair factor dPrp19 reduces DNA damage and extends Drosophila life span. NPJ Aging Mech Dis 3: 5. PubMed ID: 28649423
Summary:
Mechanisms that ensure and maintain the stability of genetic information are fundamentally important for organismal function and can have a large impact on disease, aging, and life span. While a multi-layered cellular apparatus exists to detect and respond to DNA damage, various insults from environmental and endogenous sources continuously affect DNA integrity. Over time this can lead to the accumulation of somatic mutations, which is thought to be one of the major causes of aging. Previous work has found that overexpression of the essential human DNA repair and splicing factor SNEV, also called PRP19 or hPso4, extends replicative life span of cultured human endothelial cells and impedes accumulation of DNA damage. This study show that adult-specific overexpression of dPrp19, the D. melanogaster ortholog of human SNEV/PRP19/hPso4, robustly extends life span in female fruit flies. This increase in life span is accompanied by reduced levels of DNA damage and improved resistance to oxidative and genotoxic stress. These findings suggest that dPrp19 plays an evolutionarily conserved role in aging, life span modulation and stress resistance, and support the notion that superior DNA maintenance is key to longevity (Garschall, 2017).
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Ruth Archer, C., Basellini, U., Hunt, J., Simpson, S. J., Lee, K. P. and Baudisch, A. (2017). Diet has independent effects on the pace and shape of aging in Drosophila melanogaster. Biogerontology [Epub ahead of print]. PubMed ID: 28914388
Summary:
Studies examining how diet affects mortality risk over age typically characterise mortality using parameters such as aging rates, which condense how much and how quickly the risk of dying changes over time into a single measure. Demographers have suggested that decoupling the tempo and the magnitude of changing mortality risk may facilitate comparative analyses of mortality trajectories, but it is unclear what biologically meaningful information this approach offers. This study has determined how the amount and ratio of protein and carbohydrate ingested by female Drosophila melanogaster affects how much mortality risk increases over a time-standardised life-course (the shape of aging) and the tempo at which animals live and die (the pace of aging). Pace values increased as flies consumed more carbohydrate but declined with increasing protein consumption. Shape values were independent of protein intake but were lowest in flies consuming ~90 mug of carbohydrate daily. As protein intake only affected the pace of aging, varying protein intake rescaled mortality trajectories (i.e. stretched or compressed survival curves), while varying carbohydrate consumption caused deviation from temporal rescaling (i.e. changed the topography of time-standardised survival curves), by affecting pace and shape. Clearly, the pace and shape of aging may vary independently in response to dietary manipulation. This suggests that there is the potential for pace and shape to evolve independently of one another and respond to different physiological processes. Understanding the mechanisms responsible for independent variation in pace and shape, may offer insight into the factors underlying diverse mortality trajectories (Ruth Archer, 2017).
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Bloch Qazi, M. C., Miller, P. B., Poeschel, P. M., Phan, M. H., Thayer, J. L. and Medrano, C. L. (2017). Transgenerational effects of maternal and grandmaternal age on offspring viability and performance in Drosophila melanogaster. J Insect Physiol 100: 43-52. PubMed ID: 28529156
Summary:
In non-social insects, fitness is determined by relative lifetime fertility. Fertility generally declines with age as a part of senescence. For females, senescence has profound effects on fitness by decreasing viability and fertility as well as those of her offspring. However, important aspects of these maternal effects, including the cause(s) of reduced offspring performance and carry-over effects of maternal age, are poorly understood. Drosophila melanogaster is a useful system for examining potential transgenerational effects of increasing maternal age, because of their use as a model system for studying the physiology and genetic architecture of both reproduction and senescence. To test the hypothesis that female senescence has transgenerational effects on offspring viability and development, this study measured the effects of maternal age on offspring survival over two generations and under two larval densities in two laboratory strains of flies (Oregon-R and Canton-S). Transgenerational effects of maternal age influence embryonic viability and embryonic to adult viability in both strains. However, the generation causing the effects, and the magnitude and direction of those effects differed by genotype. The effects of maternal age on embryonic-to-adult viability when larvae are stressed was also genotype-specific. Maternal effects involve provisioning: older females produced smaller eggs and larger offspring. These results show that maternal age has profound, complex, and multigenerational consequences on several components of offspring fitness and traits. This study contributes to a body of work demonstrating that female age is an important condition affecting phenotypic variation and viability across multiple generations (Bloch Qazi, 2017).
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Lucchetta, E.M. and Ohlstein, B. (2017). Amitosis of polyploid cells regenerates functional stem cells in the Drosophila intestine. Cell
Stem Cell [Epub ahead of print]. PubMed ID: 28343984
Summary:
Organ fitness depends on appropriate maintenance of stem cell populations,
and aberrations in functional stem cell numbers are associated with
malignancies and aging. Symmetrical division is the best characterized
mechanism of stem cell replacement, but other mechanisms could also be
deployed, particularly in situations of high stress. This study shows that
after severe depletion, intestinal stem cells (ISCs) in the Drosophila
midgut are replaced by
spindle-independent ploidy reduction of cells in the enterocyte lineage
through a process known as amitosis. Amitosis is also induced by the
functional loss of ISCs coupled with tissue demand and in aging flies, underscoring the generality of this mechanism. However, random
homologous chromosome segregation during ploidy reduction can expose
deleterious mutations through loss of heterozygosity. Together, these data
highlight amitosis as an unappreciated mechanism for restoring stem cell
homeostasis, but one with some associated risk in animals carrying mutations (Lucchetta, 2017).
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Garcia, J. F., Carbone, M. A., Mackay, T. F. C. and Anholt, R. R. H. (2017). Regulation of Drosophila lifespan by bellwether promoter alleles. Sci Rep 7(1): 4109. PubMed ID: 28646164
Summary:
Longevity varies among individuals, but how natural genetic variation contributes to variation in lifespan is poorly understood. Drosophila melanogaster presents an advantageous model system to explore the genetic underpinnings of longevity, since its generation time is brief and both the genetic background and rearing environment can be precisely controlled. The bellwether (blw) gene encodes the alpha subunit of mitochondrial ATP synthase. Since metabolic rate may influence lifespan, this study investigated whether alternative haplotypes in the blw promoter affect lifespan when expressed in a co-isogenic background. 521 bp upstream promoter sequences containing the alternative SNP haplotypes (G/T and A/G)
were amplified, and promoter activity was assessed both in vitro and in vivo using a luciferase reporter system. The AG haplotype showed significantly greater expression of luciferase than the GT haplotype. A blw cDNA construct driven by either the AG or GT haplotype promoter was driven in transgenic flies, and the AG haplotype was shown to results in greater blw cDNA expression and a significant decrease in lifespan relative to the GT promoter haplotype, in male flies only. Thus, the results show that naturally occurring regulatory variants of blw affect lifespan in a sex-specific manner (Garcia, 2017).
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Carazo, P., Green, J., Sepil, I., Pizzari, T. and Wigby, S. (2016). Inbreeding removes sex differences in lifespan in a population of Drosophila melanogaster Biol Lett 12. PubMed ID: 27354712
Summary:
Sex differences in ageing rates and lifespan are common in nature, and an enduring puzzle for evolutionary biology. One possibility is that sex-specific mortality rates may result from recessive deleterious alleles in 'unguarded' heterogametic X or Z sex chromosomes (the unguarded X hypothesis). Empirical evidence for this is, however, limited. This study tests a fundamental prediction of the unguarded X hypothesis in Drosophila melanogaster, namely that inbreeding shortens lifespan more in females (the homogametic sex in Drosophila) than in males. To test for additional sex-specific social effects, the lifespan of males and females kept in isolation was studied, in related same-sex groups, and in unrelated same-sex groups. As expected, outbred females outlive outbred males and inbreeding shortens lifespan. However, inbreeding-mediated reductions in lifespan are stronger for females, such that lifespan is similar in inbred females and males. It was also shown that the social environment, independent of inbreeding, affects male, but not female lifespan. In conjunction with recent studies, these data suggest that asymmetric inheritance mechanisms may play an important role in the evolution of sex-specific lifespan and that social effects must be considered explicitly when studying these fundamental patterns (Carazo, 2016).
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Moskalev, A., Shaposhnikov, M., Proshkina, E., Belyi, A., Fedintsev, A., Zhikrivetskaya, S., Guvatova, Z., Sadritdinova, A., Snezhkina, A., Krasnov, G. and Kudryavtseva, A. (2016). The influence of pro-longevity gene Gclc overexpression on the age-dependent changes in Drosophila transcriptome and biological functions. BMC Genomics 17(Suppl 14): 1046. PubMed ID: 28105938
Summary:
Transcriptional changes that contribute to the organism's longevity and prevent the age-dependent decline of biological functions are not well understood. This study overexpressed pro-longevity gene encoding glutamate-cysteine ligase catalytic subunit (Gclc) and analyzed age-dependent changes in transcriptome that associated with the longevity, stress resistance, locomotor activity, circadian rhythmicity, and fertility. The life extension effect of neuronal overexpression of the Gclc gene were reproduced, and its influence on the age-depended dynamics of transcriptome and biological functions such as fecundity, spontaneous locomotor activity and circadian rhythmicity were investigated, as well as on the resistance to oxidative, proteotoxic and osmotic stresses. It was shown that Gclc overexpression reduces locomotor activity in the young and middle ages compared to control flies. Gclc overexpression slowed down the age-dependent decline of locomotor activity and circadian rhythmicity, and resistance to stress treatments. Gclc level demonstrated associations with the expression of genes involved in a variety of cellular processes including Jak-STAT, MAPK, FOXO, Notch, mTOR, TGF-beta signaling pathways, translation, protein processing in endoplasmic reticulum, proteasomal degradation, glycolysis, oxidative phosphorylation, apoptosis, regulation of circadian rhythms, differentiation of neurons, synaptic plasticity and transmission. This study revealed that Gclc overexpression induces transcriptional changes associated with the lifespan extension and uncovered pathways that may be associated with the age-dependent decline of biological functions.
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Vonk, J. J., et al. (2017). Drosophila Vps13 Is required for protein homeostasis in the brain. PLoS One 12(1): e0170106. PubMed ID: 28107480
Summary:
Chorea-Acanthocytosis is a rare, neurodegenerative disorder characterized by progressive loss of locomotor and cognitive function. It is caused by loss of function mutations in the Vacuolar Protein Sorting 13A (VPS13A) gene. This study characterized a Drosophila Vps13 mutant line. The data suggest that Vps13 is a peripheral membrane protein located to endosomal membranes and enriched in the fly head. Vps13 mutant flies showed a shortened life span and age associated neurodegeneration. Vps13 mutant flies were sensitive to proteotoxic stress and accumulated ubiquitylated proteins. Levels of Ref(2)P, the Drosophila orthologue of p62, were increased and protein aggregates accumulated in the central nervous system. Overexpression of the human Vps13A protein in the mutant flies partly rescued apparent phenotypes. This suggests a functional conservation of human VPS13A and Drosophila Vps13. The results demonstrate that Vps13 is essential to maintain protein homeostasis in the larval and adult Drosophila brain. Drosophila Vps13 mutants are suitable to investigate the function of Vps13 in the brain, to identify genetic enhancers and suppressors and to screen for potential therapeutic targets for Chorea-Acanthocytosis (Vonk, 2017).
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M'Angale, P. G. and Staveley, B. E. (2016). Inhibition of Atg6 and Pi3K59F autophagy genes in neurons decreases lifespan and locomotor ability in Drosophila melanogaster. Genet Mol Res 15. PubMed ID: 27813607
Summary:
Autophagy is a cellular mechanism implicated in the pathology of Parkinson's disease. The proteins Atg6 (Beclin 1) and Pi3K59F are involved in autophagosome formation, a key step in the initiation of autophagy. This study used the GMR-Gal4 driver to determine the effect of reducing the expression of the genes encoding these proteins on the developing Drosophila eye. Subsequently, their expression in D. melanogaster neurons was inhibited under the direction of a Dopa decarboxylase (Ddc) transgene, and the effects on longevity and motor function were examined. Decreased longevity coupled with an age-dependent loss of climbing ability was observed. In addition, the roles of these genes were investigated in the well-studied alpha-synuclein-induced Drosophila model of Parkinson's disease. In this context, lowered expression of Atg6 or Pi3K59F in Ddc-Gal4-expressing neurons results in decreased longevity and associated age-dependent loss of locomotor ability. Inhibition of Atg6 or Pi3K59F together with overexpression of the sole pro-survival Bcl-2 Drosophila homolog Buffy in Ddc-Gal4-expressing neurons resulted in further decrease in the survival and climbing ability of Atg6-RNAi flies, whereas these measures were ameliorated in Pi3K59F-RNAi flies (M'Angale, 2016).
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Delabaere, L., et al. (2016). Aging impairs double-strand break repair by homologous recombination in Drosophila germ cells. Aging Cell [Epub ahead of print]. PubMed ID: 28000382
Summary:
Aging is characterized by genome instability, which contributes to cancer formation and cell lethality leading to organismal decline. The high levels of DNA double-strand breaks (DSBs) observed in old cells and premature aging syndromes are likely a primary source of genome instability. This study shows that premeiotic germline cells of young and old flies have distinct differences in their ability to repair DSBs by the error-free pathway homologous recombination (HR). Repair of DSBs induced by either ionizing radiation (IR) or the endonuclease I-SceI is markedly defective in older flies. This correlates with a remarkable reduction in HR repair measured with the DR-white DSB repair reporter assay. Strikingly, most of this repair defect is already present at 8 days of age. Finally, HR defects correlate with increased expression of early HR components and increased recruitment of Rad51 to damage in older organisms. Thus, it is proposed that the defect in the HR pathway for germ cells in older flies occurs following Rad51 recruitment. These data reveal that DSB repair defects arise early in the aging process and suggest that HR deficiencies are a leading cause of genome instability in germ cells of older animals (Delabaere, 2016).
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Vienne, J., Spann, R., Guo, F. and Rosbash, M. (2016). Age-related reduction of recovery sleep and arousal threshold in Drosophila. Sleep [Epub ahead of print]. PubMed ID: 27306274
Summary:
Physiological studies show that aging affects both sleep quality and quantity in humans, and sleep complaints increase with age. Along with knowledge about the negative effects of poor sleep on health, understanding the enigmatic relationship between sleep and aging is important. Because human sleep is similar to Drosophila (fruit fly) sleep in many ways, this study addressed the effects of aging on sleep in this model organism. Baseline sleep was recorded in five different Drosophila genotypes raised at either 21 ° C or 25 ° C. The amount of sleep recovered was then investigated after a nighttime of sleep deprivation (12 h) and after chronic sleep deprivation (3 h every night for multiple nights). Finally, the effects of aging on arousal, namely, sensitivity to neuronal and mechanical stimuli, were studied. Fly sleep was shown to be affected by age in a manner similar to that of humans and other mammals. Not only do older flies of several genotypes have more fragmented sleep and reduced total sleep time compared to young flies, but older flies also fail to recover as much sleep after sleep deprivation. This suggests either lower sleep homeostasis and/or a failure to properly recover sleep. Older flies also show a decreased arousal threshold, i.e., an increased response to neuronal and mechanical wake-promoting stimuli. The reduced threshold may either reflect or cause the reduced recovery sleep of older flies compared to young flies after sleep deprivation. It is concluded that further studies are certainly needed, but it is suggested that the lower homeostatic sleep drive of older flies causes their decreased arousal threshold (Vienne, 2016).
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Wu, Q., Lian, T., Fan, X., Song, C., Gaur, U., Mao, X., Yang, D., Piper, M. D. and Yang, M. (2016). 2,5-Dimethyl-Celecoxib extends Drosophila life span via a mechanism that requires insulin and Target of rapamycin signaling. J Gerontol A Biol Sci Med Sci [Epub ahead of print]. PubMed ID: 28025308
Summary:
The search for antiaging drugs is a key component of gerontology research. A few drugs with positive effects on life span in model organisms have been found. This study reports that 2,5-dimethyl-celecoxib, a derivative of the anti-inflammatory drug celecoxib, can extend Drosophila life span and delay aging by a mechanism involving insulin signaling and target of rapamycin signaling. Importantly, its positive effects were apparent when the treatment window was restricted to the beginning of life or the later half. 2,5-Dimethyl-celecoxib-induced longevity was also associated with improvements in physical activity, intestinal integrity, and increased autophagy. In addition, 2,5-dimethyl-celecoxib exhibited protective effects against several kinds of stress such as starvation and heat. The generally positive effects of 2,5-dimethyl-celecoxib on both health and life span, combined with its mode of action via evolutionarily conserved signaling pathways, indicate that it has the potential to become an effective antiaging drug (Wu, 2016).
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Heintz, C., et al. (2016). Splicing factor 1 modulates dietary restriction and TORC1 pathway longevity in C. elegans. Nature [Epub ahead of print]. PubMed ID: 27919065
Summary:
Ageing is driven by a loss of transcriptional and protein homeostasis and is the key risk factor for multiple chronic diseases. Interventions that attenuate or reverse systemic dysfunction associated with age therefore have the potential to reduce overall disease risk in the elderly. Precursor mRNA (pre-mRNA) splicing is a fundamental link between gene expression and the proteome, and deregulation of the splicing machinery is linked to several age-related chronic illnesses. However, the role of splicing homeostasis in healthy ageing remains unclear. This study demonstrates that pre-mRNA splicing homeostasis is a biomarker and predictor of life expectancy in Caenorhabditis elegans. Using transcriptomics and in-depth splicing analysis in young and old animals fed ad libitum or subjected to dietary restriction, this study found defects in global pre-mRNA splicing with age that are reduced by dietary restriction via splicing factor 1 (SFA-1; the C. elegans homologue of SF1, also known as branchpoint binding protein, BBP; see Drosophila SF1). SFA-1 is specifically required for lifespan extension by dietary restriction and by modulation of the TORC1 pathway components AMPK, RAGA-1 and RSKS-1/S6 kinase. It was also demonstrated that overexpression of SFA-1 is sufficient to extend lifespan. Together, these data demonstrate a role for RNA splicing homeostasis in dietary restriction longevity and suggest that modulation of specific spliceosome components may prolong healthy ageing (Heintz, 2016).
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Johnson, J. L., Huang, W., Roman, G. and Costa-Mattioli, M. (2016). TORC2: a novel target for treating age-associated memory impairment. Sci Rep 5: 15193. PubMed ID: 26489398
Summary:
Memory decline is one of the greatest health threats of the twenty-first century. Because of the widespread increase in life expectancy, 20 percent of the global population will be over 60 in 2050 and the problems caused by age-related memory loss will be dramatically aggravated. However, the molecular mechanisms underlying this inevitable process are not well understood. This study shows that the activity of the recently discovered mechanistic target of rapamycin (mTOR) complex 2 (mTORC2, see Drosophila TOR and Rictor) declines with age in the brain of both fruit flies and rodents and that the loss of mTORC2-mediated actin polymerization contributes to age-associated memory loss. Intriguingly, treatment with a small molecule that activates mTORC2 (A-443654; a specific Akt inhibitor that activates mTORC2-mediated phosphorylation of Akt) reverses long-term memory (LTM) deficits in both aged mice and flies. In addition, pharmacologically boosting either mTORC2 or actin polymerization enhances LTM. In contrast to the current approaches to enhance memory that have primarily targeted the regulation of gene expression (epigenetic, transcriptional, and translational), the data points to a novel, evolutionarily conserved mechanism for restoring memory that is dependent on structural plasticity. These insights into the molecular basis of age-related memory loss may hold promise for new treatments for cognitive disorders (Johnson, 2016).
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Gupta, V. K., Pech, U., Bhukel, A., Fulterer, A., Ender, A., Mauermann, S. F., Andlauer, T. F., Antwi-Adjei, E., Beuschel, C., Thriene, K., Maglione, M., Quentin, C., Bushow, R., Schwarzel, M., Mielke, T., Madeo, F., Dengjel, J., Fiala, A. and Sigrist, S. J. (2016). Spermidine Suppresses Age-Associated Memory Impairment by Preventing Adverse Increase of Presynaptic Active Zone Size and Release. PLoS Biol 14: e1002563. PubMed ID: 27684064
Summary:
Memories are assumed to be formed by sets of synapses changing their structural or functional performance. The efficacy of forming new memories declines with advancing age, but the synaptic changes underlying age-induced memory impairment remain poorly understood. Spermidine feeding has been found to specifically suppress age-dependent impairments in forming olfactory memories, providing a mean to search for synaptic changes involved in age-dependent memory impairment. This study shows that a specific synaptic compartment, the presynaptic active zone (AZ) of the adult brain, increases the size of its ultrastructural elaboration and releases significantly more synaptic vesicles with advancing age. These age-induced AZ changes, however, were fully suppressed by spermidine feeding. A genetically enforced enlargement of AZ scaffolds (four gene-copies of BRP) impaired memory formation in young animals. Thus, in the Drosophila nervous system, aging AZs seem to steer towards the upper limit of their operational range, limiting synaptic plasticity and contributing to impairment of memory formation. Spermidine feeding suppresses age-dependent memory impairment by counteracting these age-dependent changes directly at the synapse. The results suggest that the integrity of the autophagic system is crucial for the spermidine-mediated protection from age-associated increase in AZ scaffold components (Gupta, 2016).
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Wen, D. T., Zheng, L., Ni, L., Wang, H., Feng, Y. and Zhang, M. (2016). The expression of CG9940 affects the adaptation of cardiac function, mobility, and lifespan to exercise in aging Drosophila. Exp Gerontol 83: 6-14. PubMed ID: 27448710
Summary:
The CG9940 gene, which encodes the NAD+ synthase protein in Drosophila, is conserved in human, zebra fish, and mosquito. NAD+ synthase is a homodimer, which catalyzes the final step in de novo nicotinamide adenine dinucleotide (NAD+) biosynthesis, an amide transfer from either ammonia or glutamine to nicotinic acid adenine dinucleotide (NaAD). Both the CG9940 and exercise are closely relative to NAD+ level, and NAD+ plays important roles not only in energy metabolism and mitochondrial functions but also in aging. This study changed expression of CG9940 by UAS/GAL4 system in Drosophila. Flies were trained by a training device. Cardiac function was analyzed by M-mode traces, climbing index was measured through negative geotaxis assay, and lifespan was measured via lifespan assays. The important new findings from this study included the following: (1) the expression of the CG9940 could affect cardiac function, mobility, and lifespan in Drosophila. Over-expression of the CG9940 gene had positive effects on Drosophila, such as enhanced aging cardiac output, reduced heart failure, delayed age-related mobility decline, and prolonged lifespan, but lower-expression of the CG9940 had negative effects on them. (2) Different expressions of the CG9940 resulted in different influences on the adaptation of cardiac function, mobility, and lifespan to exercise in aging Drosophila. Both normal-expression and over-expression of the CG9940 resulted in positive influences on the adaptation of cardiac functions, mobility, and lifespan to exercise in aging Drosophila such as exercise slowed age-related decline of cardiac function, mobility and extent of lifespan in these flies, while lower-expression of the CG9940 led to negative impacts on the adaptation of mobility and lifespan to exercise in Drosophila (Wen, 2016).
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Parkhitko, A.A., Binari, R., Zhang, N., Asara, J.M., Demontis, F. and Perrimon, N. (2016). Tissue-specific down-regulation of S-adenosyl-homocysteine via suppression of dAhcyL1/dAhcyL2 extends health span and life span in Drosophila. Genes Dev [Epub ahead of print]. PubMed ID: 27313316
Summary:
Aging is a risk factor for many human pathologies and is characterized by extensive metabolic changes. Using targeted high-throughput metabolite profiling in Drosophila melanogaster at different ages, this study demonstrates that methionine metabolism changes strikingly during aging. Methionine generates the methyl donor S-adenosyl-methionine (SAM), which is converted via methylation to S-adenosyl-homocysteine (SAH), which accumulates during aging. A targeted RNAi screen against methionine pathway components reveals significant life span extension in response to down-regulation of two noncanonical Drosophila homologs of the SAH hydrolase Ahcy (S-adenosyl-L-homocysteine hydrolase [SAHH]), CG9977/dAhcyL1 and Ahcy89E/CG8956/dAhcyL2, which act as dominant-negative regulators of canonical AHCY. Importantly, tissue-specific down-regulation of dAhcyL1/L2 in the brain and intestine extends health and life span. Furthermore, metabolomic analysis of dAhcyL1-deficient flies reveals its effect on age-dependent metabolic reprogramming and H3K4 methylation. Altogether, reprogramming of methionine metabolism in young flies and suppression of age-dependent SAH accumulation lead to increased life span. These studies highlight the role of noncanonical Ahcy enzymes as determinants of healthy aging and longevity (Parkhitko, 2006).
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Regan, J.C., Khericha, M., Dobson, A.J., Bolukbasi, E., Rattanavirotkul, N. and Partridge, L. (2016). Sex difference in pathology of the ageing gut mediates the greater response of female lifespan to dietary restriction. Elife 5:e10956. PubMed ID: 26878754
Summary:
Women live on average longer than men, but have greater levels of late-life morbidity. This study uncovers a substantial sex difference in the pathology of the ageing gut in Drosophila. The intestinal epithelium of the ageing female undergoes major deterioration, driven by intestinal stem cell (ISC) division, while lower ISC activity in males associates with delay or absence of pathology, and better barrier function, even at old ages. Males succumb to intestinal challenges to which females are resistant, associated with fewer proliferating ISCs, suggesting a trade-off between highly active repair mechanisms and late-life pathology in females. Dietary restriction reduces gut pathology in ageing females, and extends female lifespan more than male. By genetic sex reversal of a specific gut region, female-like ageing pathologies were induced in males, associated with decreased lifespan, but also with a greater increase in longevity in response to dietary restriction (Regan, 2016).
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Xia, B. and de Belle, S. (2016). Transgenerational programming of longevity and reproduction by post-eclosion dietary manipulation in Drosophila. Aging 8(5):1115-34. PubMed ID: 27025190
Summary:
Accumulating evidence suggests that early-life diet may program one's health status by causing permanent alternations in specific organs, tissues, or metabolic or homeostatic pathways, and such programming effects may propagate across generations through heritable epigenetic modifications. However, it remains uninvestigated whether postnatal dietary changes may program longevity across generations. To address this question of important biological and public health implications, newly-born flies (F0) were collected and subjected to various post-eclosion dietary manipulations (PDMs) with different protein-carbohydrate (i.e., LP, IP or HP for low-, intermediate- or high-protein) contents or a control diet (CD). Longevity and fecundity analyses were performed with these treated F0 flies and their F1, F2 and F3 offspring, while maintained on CD at all times. The LP and HP PDMs were found to shorten longevity, while the IP PDM extends longevity significantly up to the F3 generation. Furthermore, the LP reduces while the IP PDM increases lifetime fecundity across the F0-F2 generations. These observations establish the first animal model for studying transgenerational inheritance of nutritional programming of longevity, making it possible to investigate the underlying epigenetic mechanisms and identify gene targets for drug discovery in future studies (Xia, 2006).
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Slade, J. D. and Staveley, B. E.(2016). Enhanced survival of Drosophila Akt1 hypomorphs during amino-acid starvation requires foxo. Genome 59(2):87-93. PubMed ID: 26783834
Summary:
Disordered eating includes any pattern of irregular eating that may lead to either extreme weight loss or obesity. The conserved Aging is the primary risk factor for many major human pathologies, including cancer, diabetes, cardiovascular disorders, and neurodegenerative diseases. Previous studies of the transcriptional changes that occur during Drosophila aging have revealed that genes encoding members of metabolic pathways are among the most affected. In addition, analyses of changes associated with dietary restriction (DR) that slows down the aging process have also demonstrated dramatic changes in the expression of different metabolic genes. Similarly, studies in worms, mice, and humans have documented changes in the metabolome during the aging process. Recently, untargeted metabolomics analysis in flies (Hoffman, 2014) has suggested that DR might reverse age-dependent metabolic reprogramming at the tissue (Laye, 2015) and whole-organism (Avanesov, 2014) levels. Despite these studies, the mechanisms underlying age-dependent metabolic reprogramming, the nature of the metabolites that change with time, and their effect on life span are still poorly characterized (Parkhitko, 2016).
A number of alterations in metabolic pathway activities are known to extend life span in flies and other organisms. Among them, perturbation of components of the mitochondrial respiratory complexes I, III, IV, and V; increased mitochondrial uncoupling via expression of human UCP2; heterozygous mutations of AMP biosynthetic enzymes; reduced levels of Enigma, the enzyme responsible for β-oxidation of fatty acids; and reduced levels of Indy, which functions as a cation-independent electroneutral transporter for a variety of tricarboxylic acid cycle intermediates extend life span in Drosophila. In addition, key longevity regulators such as insulin receptor substrate (IRS)/chico and JNK are known to reprogram whole-body metabolism, but it is unknown whether this reprogramming is responsible for life span extension (Parkhitko, 2016).
Another level of complexity between metabolism and aging arises from the observation that different tissues have different metabolic requirements and that alterations of different metabolic components or upstream regulators of metabolism in one tissue can affect aging of other tissues and life span. For example, muscle-specific FOXO/4E-BP signaling retards muscle aging in Drosophila in a cell-autonomous manner and nonautonomously extends life span and preserves proteostasis in other aging tissues such as the brain, the retina, and adipose tissue. Similarly, overexpression of AMPK in the adult Drosophila nervous system nonautonomously maintains proteostasis during muscle aging and extends organismal life span. In addition, muscle-specific mitochondrial injury promotes organismal life span via activation of mtUPR and increased production of ImpL2, an insulin growth factor-binding protein (IGFBP)-like protein. Moreover, muscle-specific expression of the transcription factor Mnt extends life span by reducing ribosome biogenesis and promoting the expression of the myokine Myoglianin (Parkhitko, 2016).
To expand knowledge of the regulation of life span by metabolism, high-throughput metabolite profiling of Drosophila melanogaster was performed to identify changes that may correlate with aging. Strikingly, methionine metabolism emerged as one of the most regulated metabolic pathways with age. To test the role of the methionine pathway in life span determination, a targeted RNAi screen against most of the methionine pathway components and related enzymes was performed. Unexpectedly, ubiquitous down-regulation of two Drosophila homologs of S-adenosyl-homocysteine (SAH) hydrolase-like proteins, CG9977/dAhcyL1 (S-adenosyl-L-homocysteine hydrolase [SAHH]) and CG8956/Ahcy89E/dAhcyL2, significantly extended life span. Moreover, brain-specific down-regulation of dAhcyL1 and intestine-specific down-regulation of both dAhcyL1 and dAhcyL2 increased life span. Importantly, down-regulation of dAhcyL1 extended not only life span but also health span. Finally, suppression of dAhcyL1 activities decreased the level of SAH, as determined by tandem mass spectrometry (MS/MS), and suppressed H3K4 trimethylation (H3K4me3), thus phenocopying methionine starvation. Altogether, these data demonstrate that dAhcyL1 and dAhcyL2 encode new key regulators of age-dependent metabolic reprogramming and control both health span and life span (Parkhitko, 2016).
By studying metabolic changes during fly aging, two potential targets for health and life span extension were identified, CG9977/dAhcyL1 and Ahcy89E/CG8956/dAhcyL2. Whole-body and tissue-specific down-regulation of these two noncanonical, dominant-negative Drosophila homologs of Ahcy (AHCY is the rate-limiting enzyme in methionine metabolism that hydrolyzes SAH to adenosine and homocysteine) significantly extended life span, decreased levels of SAH, and suppressed H3K4me3 (Parkhitko, 2016).
Fly metabolome changes caused by aging were sought and it was hypothesized that preventing some of these changes would increase life span and prevent age-dependent health deterioration. Metabolite profiling revealed striking changes in the metabolome of aged flies, including altered levels of multiple methionine metabolism intermediates as well as several other previously known pathways affected by aging, including glutamate metabolism, glutathione metabolism, and the mitochondrial electron transport chain (Parkhitko, 2016).
Restriction of a single amino acid, either methionine or tryptophan, extends life span in rodents. In addition, methionine restriction extends life span in yeast, flies, rodents, and human diploid fibroblasts. Methionine metabolism consists of three branches: salvage, de novo, and transsulfuration pathways. Methionine is converted into glutathione and taurine via the transsulfuration pathway supplying cells with antioxidant defense. In accordance, overexpression of CBS, the rate-limiting enzyme in the transsulfuration pathway, extends life span. Moreover, CBS is one of the primary sources of hydrogen sulfide production, which has been shown to function as an evolutionarily conserved mediator of DR-mediated longevity (Parkhitko, 2016).
This study identified two novel members of methionine metabolism (located upstream of the transsulfuration pathway) that can extend life span when down-regulated. Both dAhcyL1/CG9977 and dAhcyL2/Ahcy89E/CG8956 encode noncanonical AHCY/SAHH enzymes that most likely suppress the function of the canonical AHCY enzyme. A possible explanation for their effects on life span extension is that down-regulation of dAhcyL1 and dAhcyL2 would enhance flux into the transsulfuration pathway. However, cycloleucine, an upstream inhibitor of Sam-S, also increases life span, suggesting that life span extension is most likely due to the clearance of metabolites between Sam-S and Ahcy13 (SAM and SAH) (Parkhitko, 2016).
Gnmt catalyzes the conversion of glycine to sarcosine using SAM as a donor of the methyl group, and recent studies have shown that Gnmt overexpression decreases levels of SAM and extends life span in flies. Although Gnmt overexpression extends life span, its product, sarcosine, was identified as a metabolite contributing to prostate cancer progression, and high cytoplasmic GNMT expression in patient tumor samples correlated with more aggressive forms of prostate cancer. Based on these data, dAhcyL1 and dAhcyL2 could represent better targets for developing methionine restriction mimetics, as they affect methionine indirectly via regulation of AHCY activity (Parkhitko, 2016).
AHCY (Ahcy13 in flies) is a tetrameric enzyme that catalyzes the reversible hydrolysis of SAH to adenosine and L-homocysteine. SAH is formed as a by-product of SAM through methylation reactions, and hydrolysis of SAH is required to maintain proper concentrations of SAH, which serves as an inhibitor of SAM-dependent methylation reactions. Accordingly, inhibition of AHCY, which is associated with decreased life span, results in the intracellular accumulation of SAH (whole-body adult-onset Ahcy13 RNAi expression caused an ~15-fold increase in whole-body SAH level). In contrast, down-regulation of dAhcyL1 moderately suppressed levels of SAH (approximately twofold decrease) and increased life span. Interestingly, the level of SAH was increased with age in OreR flies and was significantly lower in naturally selected long-lived flies compared with control flies at 7 wk of age. The mechanisms underlying the age-dependent changes of SAH and which of them affect the age-dependent changes in Ahcy13 activity and methionine pathway activity are unknown. Possibly, age-dependent increased oxidative stress can redirect methionine flux into the transsulfuration pathway for glutathione production. It is also worth noting that alterations in SAH levels do not equally affect the activity of methyltransferases, an observation that warrants further investigation (Parkhitko, 2016).
dAHCYL1/dAHCYL2 proteins consist of a C-terminal AHCY domain and an N-terminal IRBIT domain. Due to the fact that dAHCYL1/dAHCYL2 proteins likely have lost their enzyme activity, they can suppress Ahcy13 function via heteromultimerization. As the presence of an N-terminal IRBIT domain gives dAHCYL1/dAHCYL2 proteins new functions in Ca2+ signaling, intracellular pH regulation, and production of deoxyribonucleotides (which are referred as noncanonical functions), tests were performed to see which downstream effectors of dAHCYL1/dAHCYL2 proteins are responsible for life span extension. Down-regulation of dAhcyL1 in the whole body did not affect the levels of deoxyribonucleotides, and the down-regulation of RnrL and Itp-r83A or overexpression of Itp-r83A had no effect on life span. Furthermore, dAhcyL1 down-regulation suppressed the levels of SAH and increased life span, contrary to Ahcy13 function. Altogether, these results suggest that down-regulation of dAhcyL1 promotes life span via modulating Ahcy13 function but not through noncanonical functions. The modular structure of AHCYL proteins suggests that they integrate different signals from Ca2+ signaling, pH regulation, production of deoxyribonucleotides, SAH clearance, and life span regulation (Parkhitko, 2016).
Several studies have shown that specific heterochromatin regions are remodeled during aging and that life span-extending interventions such as calorie restriction suppress age-dependent heterochromatin remodeling. Moreover, heterochromatin formation prolongs life span, and its status depends on the levels of HP1 and H3K9me. As the status of methionine metabolism is sufficient to determine the H3K4me3 (but not H3K9me3 or H3K27me3) levels in human cells, it was hypothesized that down-regulation of dAhcyL1 and dAhcyL2 would mimic methionine starvation and affect H3K4me3 levels and the level of heterochromatinization. Accordingly, it was found that down-regulation of dAhcyL1 suppressed H3K4me3 levels. In contrast, no effect of down-regulation of dAhcyL1 was observed on expression of a LacZ reporter gene located in the heterochromatin, which could be explained by differences in the effects of calorie restriction and methionine starvation (Parkhitko, 2016).
Interestingly, the mammalian homolog of Ahcy13 (SAHH) was recovered in a loss-of-function genetic screen as a putative tumor suppressor gene, and its mRNA was lost in 50% of tumor tissues studied in comparison with normal tissue. Moreover, elevated homocysteine levels have been reported as a risk factor for dementia and Alzheimer's disease. As it was proposed that down-regulation of dAhcyL1 and dAhcyL2 activates Ahcy13 (SAHH), it will be important to examine whether dAhcyL1/2 can affect carcinogenesis. In addition, methionine metabolism and SAM levels have been shown to be critical for the maintenance and differentiation of human embryonic stem cells (ESCs) and induced pluripotent stem cells (iPSCs). Interestingly, wild-type flies exhibit age-dependent intestine stem cell (ISC) hyperproliferation and misdifferentiation, causing loss of intestinal integrity, whereas genetic manipulations that improve proliferative homeostasis extend life span. The current data suggest that down-regulation of dAhcyL1 and dAhcyL2 suppresses age-dependent SAH accumulation and prevents lossof intestinal integrity (as revealed by the 'Smurf' assay) and that their ubiquitous and tissue-specific down-regulation extends life span. The precise mechanisms of ISC regulation by methionine metabolism and SAH are interesting subjects for further studies (Parkhitko, 2016).
In their lifetime, all organisms experience environments that change both temporally and spatially in their nutrient availability and energy content. The optimal utilization and storage of available energy is a physiological challenge that shapes variation in life-history phenotypes, and in principle sets the trade-off between lifespan and reproduction. Failing to allocate energy optimally to the changing availability of nutrients would be expected to have significant fitness costs. As a consequence, nutrient sensing and response networks are strongly conserved pathways. Since there are optimal physiological responses that reset internal energy balance for different environments, genetic variation associated with these responses would be expected (Talbert, 2015).
As potential modifiers of cell energy state through their action on metabolite levels, the genes of central metabolism are potential sources for this genetic variation. The response to changing nutrient input results in intercellular signals that drive a cascade of downstream gene transcription shifts that facilitate energy utilization and storage. The proximal signal is generally derived from specific metabolite levels as they change under shifting nutrient load. There is considerable precedent for this general mechanism; for example, the well-known action of glucose on insulin secretion in vertebrates, and the signals associated with the secretion and action of adipokinetic hormone (AKH) in insects. The effect of energy balance on longevity in yeast is well known. Since metabolite concentrations act as proximal signals and also appear to correlate with the associated gene expression levels of the component steps in metabolism, this relationship clearly implicates the natural genetic variation in expression (or activity) of the central metabolic genes as potential sources of genetic variation in setting metabolite levels, and thus play a role in sensing and setting responses. Moreover, specific enzymes are expected to emerge as the targets of natural selection where genetic expression or activity level will act as an 'energy-stat'. Different genotypes will bracket and set the nutrient levels involved in triggering downstream responses that affect traits associated with fitness, such as lifespan variation and fecundity (Talbert, 2015).
The well-established observation that nutritional or dietary restriction (DR) extends lifespan in many species is mechanistically related to energy-state signalling. In Drosophila, many studies have shown DR to extend lifespan, and using genetic manipulation, many of the signalling pathways have been identified that extend lifespan and thus effectively mimic DR. Experimental work has shown connections between energy-signalling steps and other energy correlated phenotypes such as starvation resistance, nutrient storage and stress resistance that have connections to DR (Talbert, 2015).
In both plants and animals, it is becoming apparent that many metabolic genes and their enzyme products are associated with roles other than simple processing of metabolites. Based on evidence from RNAi reduction screens of central metabolic genes in Caenorhabditis elegans, it is estimated that as much as 25% of the genes screened implicate metabolism in longevity extension. RNAi knockdown of expression of several genes in the mitochondrial respiratory chain has been shown to extend lifespan in Drosophila. In yeast, the overexpression of several of the genes involved in cofactor shuttles actually extends lifespan. Despite its importance as a model in lifespan studies, and the connection between metabolism and lifespan seen in other models, no studies in Drosophila have examined the mutational perturbation of central metabolic gene activity and their effects on longevity (Talbert, 2015).
Natural populations of Drosophila melanogaster vary in both average lifespan and response of lifespan to dietary challenge. In D. melanogaster, the genes of the central metabolic pathway harbour considerable sequence and expression variation, which often shows change with latitude and season. In this regard, unlike the other experimental models used in aging studies, Drosophila offers the unique opportunity to associate aging and signalling pathways with their population genetics (Talbert, 2015).
The long-term goal of these studies is to integrate geographical and seasonal variation in metabolic genes with life-history phenotypes, such as longevity and its fitness correlates. This report used matched sets of P-element excision alleles in D. melanogaster to create genotypes that possess modest reductions in gene expression and subsequently examined the impact of these perturbations on lifespan under normal and restricted diets. Seven metabolic genes were studied: Idh, Mdh2, Hex-C, Hex-A, Gpdh, Gdh and Men. These enzymes involve possible signalling via glucose, ATP/ADP, NAD/NADH and NADP/NADPH ratios, citrate, pyruvate, malate and glutamate, and they also involve genes with primary expression restricted to the cytoplasm or the mitochondria. A range of effects was observed on lifespan, from none at all to very significant increases in lifespan that can depend on diet (Talbert, 2015).
This study observed that the genetic perturbation of central metabolic genes has significant effects on lifespan. Moreover, the general observation is that low-activity genotypes show extension of lifespan. Perhaps not surprisingly, some genotype effects are also diet dependent. Some genes (Idh, Mdh2, Hex-C) show an increase in lifespan under DR, but no effect of genotype, while others show a strong (Gdh, Men) genotype dependence in their response to DR. Finally, Gpdh shows a strong dependence on genotype activity, yet no effect of DR. These differences are expected because the observations represent seven enzymes that act on different metabolites and cofactors, and are limited to mitochondrial or cytosolic function (Talbert, 2015).
In this work, experimental outcomes across genes are not strictly comparable. First, while single gene effects are being studied within identical genetic backgrounds, the backgrounds differ across the seven gene sets. The P-element progenitor lines differ in the type of element used in the excision series (e.g. KG versus EP), and while the replacement backgrounds possess some chromosomes in common (often the 6326 chromosomes), they generally differ in others. Second, while all of the genotype comparisons involve reductions of activity of 50% or less, the same level of flux control across enzymes cannot be expected. Thus, cytosolic IDH may possess little flux control over NADPH/NADP levels, while MEN may exercise greater control over these metabolites, especially at reduced nutrient levels. It should be pointed out that in the Raleigh population the cytosolic Idh gene bears little molecular polymorphism and the few SNPs seen show little cis-based expression effect or clinal change (Talbert, 2015).
It should also be emphasized that unlike many gene-targeted lifespan studies, this study was not using full knockout genotypes, or genotypes where the relative functional reduction is unknown, and precise estimates of genotype activity are available. Moreover, these activity differences are representative of the range of much of the cis-associated SNP expression variation seen in natural populations. The observation that metabolic genes, when perturbed modestly in activity, have an effect on lifespan is certainly relevant to discussions of the maintenance of genetic variation in these genes in natural populations, especially as nutrient levels vary geographically and seasonally (Talbert, 2015).
Gpdh, Gdh and Hex-A were highlighted in this study study of clinal SNP expression variation in the pathway. These genes, among others, showed significant changes in gene transcript expression with latitude. The observations in this study add a fitness component to the causes of genetic expression variation of metabolic genes in natural populations of Drosophila. Also, the expectation that the gene-specific extension of lifespan can depend on dietary level adds complexity, since nutritional background is expected to shift locally and seasonally in this species. The effect of reduced activity is incrementally small in terms of daily survival, but when integrated over the average lifespan of a fly this can be very significant. This relationship is in contrast to flight metabolism, where similar activity changes have no effects on flight performance (Talbert, 2015).
The enzymes were targeted because they act on different metabolites and cofactors, and are limited to either mitochondrial or cytosolic function. Both IDH and MEN are cytosolic enzymes and NADPH dependent, and, along with the pentose shunt enzymes, provide a significant contribution to the NADPH/NADP pool. Both glutamate (GDH) and malate dehydrogenase (MDH2) are limited to mitochondrial function and, like GPDH, are dependent on NAD/NADH, and will impact that redox balance and its effect on signalling and aging. The two hexokinases, HEX-A and HEX-C, potentially affect the ADP/ATP ratio and have different tissue expressions. They could vary the ADP/ATP content, and in that fashion set energy-state response via regulating AMPK signalling. This AMP-activated kinase is a sensor that has effects in Drosophila, which provides a link between lifespan and caloric restriction (Talbert, 2015).
The observations for the Gpdh and Gdh genes implicate mitochondrial function and the redox balance with lifespan extension. GPDH is part of the essential mitochondrial phosphoglycerol shuttle in insects and is often considered a point of ROS production. The NAD/NADH redox balance is emerging as an important element of lifespan extension in yeast and is often considered a direct readout of metabolic state. Moreover, the lifespan extension associated with these genes might also act through the Sir-like enzymes, which are NAD-dependent histone deacetylases that silence chromatin and thus control transcription in a fashion directly coupled to energy-state imbalance. This relationship is important because starvation in Drosophila has been clearly shown to significantly raise the NAD/NADH ratio, although the role of Sir2 in lifespan extension in Drosophila has been questioned. GDH is also limited to mitochondrial function, and potentially affects the redox balance and NAD/NADH ratio. It connects glutamate, a key energy-state signalling molecule, to metabolic control, and sits at the important crossroads of carbohydrate and amino acid metabolism. As well, glutamate is at the hub of connectivity in the large central metabolic network. Both of these enzymes show significant extension of lifespan with only 40% reductions in whole-body activity. However, all mitochondrial or NAD-dependent genes are not similar in affecting lifespan; comparable activity changes in mitochondrial and NAD-dependent MDH (Mdh2) have little effect on lifespan in either dietary condition (Talbert, 2015).
The dependence of the results on diet is important. Over the past two decades, DR has been shown to impose a trade-off where it extends lifespan and reduces reproduction fecundity. It has gained prominence because of its association with aging research in general, but the phenomenon of DR has obvious relevance to studies of life-history evolution because it will be associated with plastic responses to nutritional challenges in nature, and the potential maintenance of genetic variation. Studies on model organisms have led to the discovery of many genes where mutational perturbation extends lifespan and thus mimics DR restriction. This is most notable in the parallel effects of disruption of genes specifically associated with energy-sensing pathways and signalling of dietary state and DR. Despite its general occurrence in D. melanogaster, an effect of DR on lifespan is not seen in some of the experimental lines. Two (Gpdh, Hex-A) of the seven genes show no DR effect in general. For Gdh, DR is seen just for the low-activity genotype. This different response to DR is suggested by studies where line-by-diet interactions are noted, but is shown more definitively in studies in mice and yeast, where it becomes clear that genetic background affects the response to DR. In another study, 166 single, non-essential genes were made deficient in yeast, and a large proportion of genes showed loss of DR extension capability, as well as an enhanced DR response. Clearly, DR response can be modified genetically and it would not be surprising if genetic variation in natural populations were to reflect this observation (Talbert, 2015).
Does the failure of some expression modified genotypes to respond to DR imply a mechanistic connection to the signalling associated with DR? An interaction between genotype and diet would suggest that the lifespan responses to DR may be coupled to metabolic signals associated with these enzymes or pathways. For example, the full-activity Men genotype shows a significant DR lifespan response, yet the Men low-activity genotype appears resistant to lifespan extension under DR. This may suggest that the NADPH/NADP ratio in the case of MEN is a signal associated with DR. However, the NADPH-dependent IDH shows no genotypic effect on DR, which may contradict this suggestion or simply be because IDH possesses low control over cofactor pool levels. Conversely, the Gdh normal activity genotype shows no DR response, while a genotype reduction in Gdh activity strongly enhances a DR response. Perhaps the reduction in amino acids that is associated with DR in Drosophila is enhanced by reduction of Gdh activity, since glutamate and GDH sit at the crossover of carbohydrate and amino acid metabolism in the mitochondria. However, this interaction must be interpreted with caution, since tests of genotype dependence of DR should be tested by using a range of diet changes (Talbert, 2015).
Where might the mechanism of action reside that extends lifespan or is associated with a genotype-dependent response to DR for these metabolic genes? Discussions of energy-signalling pathways typically start with the statement that nutrient levels are first 'sensed' and then the pathway of interest is addressed (e.g. the insulin receptor insulin/TOR pathway in Drosophila). Presumably, this initial sensing must emanate from direct immediate readouts of the cell's metabolic state (i.e., metabolites). In Drosophila, dietary sugars induce significant metabolite changes. These metabolite levels changes trigger the secretion of neuropeptides from specialized neurosecretory cells. This model of sensing is similar to the regulation of glucagon in mammalian pancreatic cells, and a similar case has been made for the sensing and regulation of AKH by the corpora cardiac cells in Drosophila. It is possible that either these cell-specific or just systemic metabolite levels initiate the signalling process. Genetic variation will regulate these metabolite levels in conjunction with nutrient inputs. In this sense, lifespan extension by some metabolic genes is top-down (Talbert, 2015).
Over the past two decades, a large number of genes in several model species have been observed to extend lifespan when mutated. In Drosophila, most studies have emphasized the signalling cascades emanating from neurosecretory cells. However, the most proximal steps of central metabolism must set the signalling environments because their metabolite levels respond immediately to nutrient inputs. This study places the metabolic pathway in the discussion of energy signalling and looked at the impact of genetic perturbation of some key genes on lifespan. The outcome is that there are numerous examples where reductions in activity extend lifespan. Perhaps not surprisingly, this extension depends on the nutrient environment. It is proposed that this setting of lifespan response to gene expression variation also provides a selective context for naturally segregating metabolic gene variation, and moreover may contribute to unravelling the patterns of genetic variation observed in natural populations (Talbert, 2015).
The data showed that decreased Rpd3 expression in Drosophila has a benefit for stress resistance against the environment. To downregulate the rpd3 gene in whole body, two ways were approached using the heterozygous rpd3 mutant (P{PZ}rpd3[04556]/+) and the UAS/Gal4 system to carry out RNAi (rpd3Ri/armG4). Both flies showed higher survivorship under oxidative stress compared to the control flies. However, the flies differed in increased survivorship percent (rpd3-/+: 31% and rpd3Ri/armG4: 22%). Considering that the downregulation yield of the rpd3 gene was different between the two approaches (rpd3-/+: 54% and rpd3Ri/armG4: 40%), it is possible that more downregulation of the rpd3 gene may induce higher resistance to stress. In the heart-specific Rpd3 downregulation, a similar pattern was observed between the rpd3Ri/tinG4 and rpd3RiS/tinG4 flies. The 21bp target sequence of rpd3RiS transgene was less effective at rpd3 downregulation compared to the 482bp sequences of rpd3Ri transgene when tested in the whole body. Thus, the rpd3RiS/tinG4 flies showed a 23% increase in survivorship compared to a 35% increase in rpd3Ri/tinG4 flies (Fig. 3A). Those data let to a speculation that the content of rpd3 downregulation determines the consequent stress-resistance enhancement (Kopp, 2015).
It was found that heart-specific Rpd3 downregulation systemically increases expression of anti-aging genes such as Sod2 and dFOXO. It was also shown that more downregulation of the rpd3 gene in a heart induces higher expression of anti-aging genes. This may provide an explanation of how Rpd3 downregulation in the heart enhances stress resistance mechanism, particularly since dFOXO is considered to activate sod2 gene. In response to cellular stresses, such as nutrient deprivation or increased levels of reactive oxygen species, dFOXO is activated and inhibits growth through acting on target genes such as Thor (d4E-BP). As a translational repressor, 4E-BP activity is shown to be critical for survival under dietary restriction and oxidative stress, and is linked to lifespan. This dFOXO/4E-BP signaling is also revealed to play a key role in the coordination of organismal and tissue aging through an organism-wide regulation of proteostasis in response to muscle aging. Interestingly, this Drosophila forkhead transcription factor (dFOXO) activates d4E-BP transcription, which is upregulated under stressed conditions. Consistent with increased foxo expression in flies with heart-specific Rpd3 downregulation, the data also showed that Thor was significantly upregulated with heart-specific Rpd3 downregulation. When induced by stress, fat body antimicrobial peptide (AMP) genes are activated in response to nuclear dFOXO activity. Upregulation of both foxo and DptB (one of target AMP) genes in heart-specific Rpd3 downregulation illustrates that Rpd3 downregulation in the heart modulates gene expression in other tissues such as fat body for stress adaption. One possible mechanism of this modulation is that heart-specific Rpd3 downregulation produces secreted proteins through Rpd3 deacetylase activity from heart, which thus regulates gene expression in other tissues (Kopp, 2015).
A positive correlation between stress resistance and lifespan extension was shown in several long-lived mutant flies. Previous findings have also suggested that enhanced stress resistance may extend lifespan in Drosophila. The data indicated that downregulating the rpd3 gene in the whole body or heart enhances both stress resistance and lifespan with improved cardiac function. However, insufficient heart-specific Rpd3 downregulation in older aged flies failed to prolong lifespan or improve cardiac condition, implying that throughout lifetime, Rpd3 in the heart influences both cardiac function and lifespan. Currently, although a conclusion of whether improved cardiac function from heart-specific Rpd3 modulation directly impacts longevity mechanism cannot yet be made, it is reported that enhanced cardiac capability could extend the lifespan of Drosophila (Kopp, 2015).
Old age is associated with a progressive decline of mitochondrial function and changes in nuclear chromatin. However, little is known about how metabolic activity and epigenetic modifications change as organisms reach their midlife. This study assessed how cellular metabolism and protein acetylation change during early aging in Drosophila melanogaster. Contrary to common assumptions, it was found that flies increase oxygen consumption and become less sensitive to histone deacetylase inhibitors as they reach midlife. Further, midlife flies show changes in the metabolome, elevated acetyl-CoA levels, alterations in protein-notably histone-acetylation, as well as associated transcriptome changes. Based on these observations, the activity of the acetyl-CoA-synthesizing enzyme ATP citrate lyase (ATPCL) or the levels of the histone H4 K12-specific acetyltransferase Chameau were decreased. It was found that these targeted interventions both alleviate the observed aging-associated changes and promote longevity. These findings reveal a pathway that couples changes of intermediate metabolism during aging with the chromatin-mediated regulation of transcription and changes in the activity of associated enzymes that modulate organismal life span (Peleg, 2016).
The process of aging is characterized by a deterioration of multiple interconnected cellular pathways, which makes the identification of molecular mechanisms of phenotypic aging and death particularly difficult. Many molecular analyses have focused on the comparison of young and old organisms, which resulted in the formulation of nine hallmarks of aging ranging from telomere shortening and epigenetic alterations, to differences in nutrient sensing and stem cell depletion. While many of these experiments have identified valuable paths toward life span extension, such studies face the complication that old individuals suffer from the progressive deterioration of multiple cellular systems, which can make it challenging to distinguish primary from secondary effects. To identify changes involved in the onset of aging, this study compared D. melanogaster flies at young age and during midlife at the onset of a premortality plateau, when most individuals of a population are still alive (Peleg, 2016).
Surprisingly, heads from midlife flies consume more oxygen than the young ones. This is in apparent contradiction to the general observation of a reduced metabolism when animals age, which this study also observe in old flies. There are several possible explanations for this unexpected finding. In many studies, the oxygen consumption rate was extrapolated from measurements of isolated mitochondria, which may lack crucial extra-mitochondrial signals when investigated in isolation, whereas this study has measured activity in isolated fly heads. Alternatively, flies may change their feeding behavior when reaching midlife, or switch from an anaerobic to a more aerobic metabolism due to their decreased activity, which is consistent with higher levels of metabolites generated by oxidative processes in midlife flies. Finally, the metabolic changes may be due to a feed-forward activation of metabolic enzymes that become stimulated by hyper-acetylation. The observation that the treatment of isolated fly heads with lysine deacetylase (KDAC) inhibitors increases oxygen consumption rate (OCR) within minutes suggests that such a direct feed-forward mechanism might indeed exist. The finding that midlife flies have a higher ground state of acetylation and are less susceptible to a stimulation by KDAC inhibitors argues for similar acetylation events triggered by KDAC inhibitor treatment and aging (Peleg, 2016).
The increased level of acetyl-CoA in midlife flies correlates with a very specific change in the histone modification pattern as flies reach midlife. As it is not possible to distinguish between mitochondrial and cytosolic acetyl-CoA, the substrate for acetyltransferases, the observed correlation may not be causal. However, an increased activity of the main enzyme was also observed for the synthesis of cytosolic acetyl-CoA, ATPCL, in midlife flies, and therefore it was assumed that the cytosolic acetyl-CoA level is indeed higher when flies reach midlife. Interestingly, this increased activity is not caused by increased protein synthesis of ATPCL, but potentially by posttranslational mechanisms such as a hyper-acetylation. This is also supported by the observation that a fly strain heterozygous for an atpcl mutation shows only a 15% reduction in ATPCL activity, suggesting that there is a substantial degree of posttranscriptional regulation of this enzymatic activity. Such a regulation of ATPCL has also been proposed to stimulate lipid synthesis and tumor growth in rats. The current findings that a fly strain carrying a mutation in the ATPCL gene has an extended life span and a delayed onset of aging further confirm the importance of extra-mitochondrial acetyl-CoA for the regulation of aging. Interestingly, the reduction in ATPCL has a much stronger effect on the metabolism of midlife animals when compared to young animals. The effects observed analyzing head tissue of Drosophila melanogaster are in line with earlier reports that the targeted depletion of an unrelated acetyl-CoA synthase in fly neurons extends life span. It will be interesting to resolve the physiological effects of ATPCL mutation on the metabolome, the histone acetylation, and the transcriptome in isolated neurons (Peleg, 2016).
Previous studies demonstrated that old flies show an impaired transcriptome surveillance, as manifested in increased transcriptional noise and expression of aberrant or immature mRNAs. This study found substantial changes in the transcriptional profile as flies reach midlife, suggesting that the differential regulation of gene expression is one of the early hallmarks of the aging process. It remains to be explored how specific changes in gene expression integrate with regulatory modifications and metabolic activity. Chameau appears to promote the expression of a large number of genes particularly during the midlife period genes. Conceivably, the enhanced H4K12 acetylation leads to widespread chromatin opening, with positive effects for the transcription of specific genes. A side effect of this loosening of chromatin structure may be the increased transcriptional noise, which might compromise a variety of physiological functions. Considering the localization of H4K12ac at the gene body of highly expressed genes, it will be interesting to investigate whether the increased transcription during midlife is due to a higher rate of transcript elongation or a higher activity of cryptic promoters. It is hypothesized that the attenuation of this effect in chm mutant flies is the cause for their extended life span. A similar effect is also seen in ATPCL mutant flies, and the observation that life span is not further extended if the ATPCL and chm alleles are combined suggests that the two enzymes may act in the same pathway (Peleg, 2016).
These data provide an overview of the metabolic, proteomic, and transcriptomic changes that occur as flies reach the premortality plateau phase. Conceivably, metabolic processes are linked to changes in gene expression through differential protein acetylation, in general, and histone acetylation, in particular. Currently it cannot be unambiguously distinguish whether the shift in metabolic activity upon fly aging precedes the increases in protein/histone acetylation, or whether increases in protein/histone acetylation result in specific metabolic changes. Most likely, both principles affect each other in a complex network of feedback and feed-forward loops. Indeed, many mitochondrial enzymes that have been shown to be acetylated in response to metabolic changes either gain or lose enzymatic activity (Peleg, 2016).
Considering the high conservation of central metabolism, metabolic regulation, and epigenetics between flies and humans, these data raise the possibility that small molecule regulators of acetyl-CoA production or consumption, or changes in the activity of selective acetyltransferase functions, could prolong a healthy midlife also in humans. These model organism data reveal a potential alternative strategy that could extend midlife and delay aging-associated homeostatic decline in humans (Peleg, 2016).
It was found that the performance index decreased gradually with
the increase of extinction cycle numbers. Furthermore, when equal
or more than four cycles of PCOP was performed, the ratio of
memory reduction was more than 30%, which was a more significant
decrease than previous paradigm. These findings suggested that the
presenting time of PCOP and the unconditioned odor affected
extinction efficiency. By adjusting the sequence of 4 cycles of
PCOP and the unconditioned odor, it was found that the earlier
presentation of PCOP, the more significant memory extinction
induced. Therefore, four cycles of PCOP before the unconditioned
odor were used in all subsequent experiments (Chen, 2015)
To investigate the effect of aging on extinction, the memory index
upon extinction procedures in flies at 2, 10, 20, 30 and 50 days
of age was measured. It was found that the aversive olfactory
memory was reduced significantly by PCOP among these flies.
Strikingly, the memory reduction ratio in flies at 20, 30 and 50
days of age was statistically higher than the younger flies. These
results indicated that memory extinction in aging flies was more
severe than in younger flies, in accordance with the faster
extinction performance in aging rats (Chen, 2015).
Several earlier reports showed that extinguished memory can be
restored in the presence of an unconditioned stimulus. To test
whether the extinction effect changed over time in flies, the
memory 3 h post conditioning was evaluated. It was found that
PCOP-induced memory reduction was spontaneously recovered within 3
h in flies at 2 days or 10 days of age. Strikingly, this memory
restoration was not observed in flies at 20, 30 and 50 days of
age, suggesting more severe memory deficiencies in aging flies
(Chen, 2015).
It has been reported that aging specifically impaired
anesthesia-sensitive memory (ASM) while leaving
anesthesia-resistant memory (ARM) intact. Given these findings
that aging flies exhibited higher ratios of memory extinction, it
was then examined whether extinction affected ARM and ASM
differently, using amnX8 and rsh1 mutant
flies. It was found that amnX8 mutant flies exhibited
significant memory extinction, with a reduction comparable to that
in wild-type flies. Unexpectedly, little memory extinction was
observed in rsh1 mutant flies. These results suggested
that PCOP specifically suppressed ARM, whereas ASM was unaffected
(Chen, 2015).
Bruchpilot (Brp), a ubiquitous presynaptic active zone protein,
has been reported to be specifically required in the MB for ARM
formation. Similar to rsh1 mutant flies, MB-specific brp-knocking
down flies exhibited no significant memory extinction in the PCOP
assay. Taken together, these results suggested that prolonged odor
presentation specifically impaired ARM, but not ASM (Chen, 2015).
To test if the impaired ARM was restored, or whether ASM was
elevated after 3 h, a 2-min cold shock 2 h after the conditioning
step was introduced to examine ARM. In young wild-type flies, the
PCOP group showed comparable ARM to that in the air control group,
indicating that the extinction-induced impairment of ARM was
restored. In contrast, amnX8 mutant flies still
exhibited significant PCOP-induced reduction of ARM, and showed
almost no detectable ARM in the PCOP group. Since amnX8
mutant flies were deficient in ASM, the study proposed that
recovery of the suppressed ARM required the presence of ASM.
Overall, these findings reveal that upon aging, memory extinction
is becoming more and more severe, and once in place, this
reduction cannot be restored (Chen, 2015).
The normal synaptic transmission from DPM neurons onto follower
neurons during spaced training that is required for generating LTM
is lost with age. This is attributable to the reduction of
synaptic contacts between DPM neuron processes and MB axons
specifically in the tip of the α lobe neuropil as revealed
by GRASP signals. The loss of synaptic contacts between DPM and MB
neurons in this region also may explain why synaptic blockade of
DPM neurons during acquisition disrupts
protein-synthesis-dependent LTM in young but not old flies.
Therefore, a second major finding is that neural contacts and
subsequent synaptic activity between DPM and α/β MB
neurons are required for generating protein-synthesis-dependent
LTM, and aging impairs this process. Consistent with this model,
it is found that aging blocks the formation of a calcium-based,
protein-synthesis-dependent memory trace in the α/β MB
neurons (Tonoki, 2015).
It has been found previously that ITM is impaired in flies of 30
d of age along with the capacity to form an ITM trace in the DPM
neurons. Nevertheless, aging does not compromise the capacity to
form an STM trace in the α'/β' MB neurons. Therefore,
aging disrupts specific temporal forms of memory, including ITM
and protein synthesis LTM, but not STM and
protein-synthesis-independent LTM. It is possible that the loss of
connectivity of DPM neurons with the α tip neuropil is
responsible for the loss of both ITM and
protein-synthesis-dependent LTM, along with their respective
memory traces. Previous and this study's data indicate that STM
appears to bypass the DPM neurons, whereas the reciprocal activity
between DPM and MB neurons is required for ITM and LTM. Aging puts
a kink in this neural system by impairing connectivity (Tonoki,
2015)
The study offers a model to explain the neural circuitry involved
in protein-synthesis-dependent LTM formation and how aging impairs
this form of memory. Although DPM neurons make contacts widely
throughout the MB lobe neuropil with processes of many cell types,
the critical interaction for LTM formation occurs in the vertical
lobes of the MB through contacts onto the axons of α/β
MB neurons. DPM neuron synaptic activity during spaced training,
which occurs due to their stimulation by MB neurons, promotes
synaptic changes in the postsynaptic α/β MB neurons and
leads to the formation of memory trace in the α/β MB
neurons. Aging impairs protein-synthesis-dependent LTM along with
a LTM trace that normally forms in the α/β MB neurons
by lessening the connectivity of DPM and α/β MB
neurons. Identifying the mechanisms by which the DPM neurons lose
their connectivity with only the tips of α/β MB neurons
might reveal how aging impairs protein-synthesis-dependent LTM
(Tonoki, 2015).
Identifying the molecular mechanisms that underlie aging and
their pharmacological manipulation are key aims for improving
lifelong human health. This study has identified a critical role
for Ras-Erk-ETS signaling in aging in Drosophila. Inhibition of
Ras was shown to be sufficient for lifespan extension downstream
of reduced insulin/IGF-1 (IIS) signaling. Moreover, direct
reduction of Ras or Erk activity leads to increased lifespan. ETS
transcriptional repressor Anterior open (Aop) was identified as
central to lifespan extension caused by reduced IIS or Ras
attenuation. Importantly, it was demonstrates that adult-onset
administration of the drug trametinib, a highly specific inhibitor
of Ras-Erk-ETS signaling, can extend lifespan. This discovery of
the Ras-Erk-ETS pathway as a pharmacological target for animal
aging, together with the high degree of evolutionary conservation
of the pathway, suggests that inhibition of Ras-Erk-ETS signaling
may provide an effective target for anti-aging interventions in
mammals (Slack, 2015).
The key role of IIS in determining animal lifespan has been well
appreciated for more than two decades and shows strong
evolutionary conservation. Alleles of genes encoding components of
this pathway have also been linked to longevity in humans.
Multiple studies have demonstrated the importance of the
PI3K-Akt-Foxo branch of IIS, while this study has identified an
equally important role for Ras-Erk-ETS signaling in IIS-dependent
lifespan extension (Slack, 2015).
A simple model integrates the role of Ras-Erk-ETS signaling with
the PI3K-Akt-Foxo branch in extension of lifespan by reduced IIS.
It is proposed that, downstream of Chico, the IIS pathway
bifurcates into branches delineated by Erk and Akt, with
inhibition of either sufficient to extend lifespan, as is
activation of either responsive TF, Aop or Foxo. The two branches
are not redundant, because mutation of chico or the loss
of its ability to activate either branch results in the same
magnitude of lifespan extension. Furthermore, Aop and Foxo are
each individually required downstream of chico mutation
for lifespan extension. At the same time, the effects of the two
branches are not additive, as simultaneous activation of Aop and
Foxo does not extend lifespan more than activation of either TF
alone. Taken together, these data suggest that the two pathways
re-join for transcriptional regulation, where Aop and Foxo
co-operatively regulate genes required for lifespan extension. The
model is corroborated by a previous finding that, in the adult gut
and fat body, some 60% of genomic locations bound by Foxo overlap
with regions of activated-Aop binding (Slack, 2015).
It is proposed that functional interactions of Aop and Foxo at
these sites may be such that each factor is both necessary and
sufficient to achieve the beneficial changes in target gene
expression upon reduced IIS. It remains to be determined how
promoter-based Foxo and Aop interactions produce such
physiologically relevant, transcriptional changes. It is, however,
curious that activation of either TF alone promotes longevity when
one is known as a transcriptional activator (Foxo) and the other
as a transcriptional repressor (Aop). A subset of Foxo-bound
genes, albeit a minority, has been consistently observed that are
transcriptionally repressed when Foxo is activated. Furthermore,
the Foxo target gene myc is downregulated in larval muscle
when Foxo is active under low insulin conditions, while deletion
of foxo or its binding site within the myc
promoter results in de-repression of myc expression in adipose of
fed larvae (Teleman, 2008). Thus, on some promoters under certain
conditions, Drosophila Foxo appears to act as a transcriptional
repressor. Mammalian Foxo3a may also directly repress some genes.
It will therefore be important to test whether the
lifespan-relevant interactions between Foxo and Aop occur on
promoters where Foxo acts as a repressor with Foxo possibly acting
as a cofactor for Aop or vice versa (Slack, 2015).
In mediating the effects of IIS on lifespan, the Ras-Erk-ETS- and
PI3K-Akt-Foxo-signaling pathways both appear to inhibit Aop/Foxo.
To understand why signaling might be so wired, it is important to
consider that the two pathways are also regulated by other
stimuli, such as other growth factors, stress signals, and
nutritional cues. The re-joining of the two branches at the
transcriptional level would therefore allow for their outputs to
be integrated, producing a concerted transcriptional response, a
feature that is also seen in other contexts. For example,
stability of the Myc transcription factor is differentially
regulated in response to Erk and PI3K signals, allowing it to
integrate signals from the two kinases. Transcriptional
integration in response to RTK signaling also confers specificity
during cell differentiation, with combinatorial effects of
multiple transcriptional modulators inducing tissue-specific
responses to inductive Ras signals. Similar integrated responses
of lifespan could be orchestrated by transcriptional coordination
of Aop and Foxo (Slack, 2015).
Direct inhibition of Ras in Drosophila can extend lifespan,
suggesting that the role of Ras in aging is evolutionarily
conserved. In budding yeast, deletion of RAS1 extends
replicative lifespan, and deletion of RAS2 increases
chronological lifespan by altering signaling through
cyclic-AMP/protein kinase A (cAMP/PKA), downregulation of which is
sufficient to extend both replicative and chronological lifespan.
This role of cAMP/PKA in aging may be conserved in mammals, as
disruption of adenylyl cyclase 5' and PKA function extend murine
lifespan. However, cAMP/PKA are not generally considered mediators
of Ras function in metazoa. Instead, the data suggest that
signaling through Erk and the ETS TFs mediates the longevity
response to Ras. Interestingly, fibroblasts isolated from
long-lived mutant strains of mice and long-lived species of
mammals and birds show altered dynamics of Erk phosphorylation in
response to stress, further suggesting a link between Erk activity
and longevity. Importantly, the ETS TFs are conserved mediators of
Ras-Erk signaling in mammals. Investigation of the effects of Ras
inhibition on mammalian lifespan and the role of the mammalian Aop
ortholog Etv6 are now warranted (Slack, 2015).
A role for Ras-Erk-ETS signaling in lifespan offers multiple
potential targets for small-molecule inhibitors that could
function as anti-aging interventions. Importantly, due to the key
role of this pathway in cancer, multiple such inhibitors exist or
are in development (Slack, 2015).
This study has shown that trametinib, a highly specific
allosteric inhibitor of the Mek kinase, prolongs Drosophila
lifespan, thus validating the Ras-Erk-ETS pathway as a
pharmacological target for anti-aging therapeutics. Trametinib
joins a very exclusive list of FDA-approved drugs that promote
longevity in animals, the most convincing other example being
rapamycin (Slack, 2015).
Rapamycin not only increases lifespan in multiple organisms,
including mammals, but also improves several indices of function
during aging. While rapamycin can protect against tumor growth,
the effects on longevity appear to be independent of cancer
prevention, as rapamcyin-treated animals still develop tumors and
rapamycin can increase lifespan in tumor-free species.
Furthermore, increased activity of certain tumor suppressors such
as lnk4a/Arf and PTEN as well as the RasGrf1 deficiency
all increase lifespan independently of anti-tumor activity. The
findings that trametinib can increase lifespan inDrosophila, which
are mainly post-mitotic in adulthood, and that doses of trametinib
that increase lifespan do not alter proliferation rates of ISCs
inDrosophila suggest that the anti-aging effects of trametinib are
separable from its anti-cancer activity (Slack, 2015).
Finally, due to the high degree of evolutionary conservation in
the Ras-Erk-ETS pathway, this study suggests the intriguing
possibility that pharmacological inhibition of Ras-Erk-ETS may
also increase lifespan in mammal (Slack, 2015).
As neither cysteine nor methionine exhibited evidence for diurnal
rhythms in either young or old flies, it appears that the
contribution of the trans-sulfuration pathway to glutathione
homeostasis is not regulated by circadian clocks. Consistent with
these findings, methionine was found to be arrhythmic in the study
of the human metabolome of blood plasma and saliva although the
analyses were performed with healthy but older (57–61 years)
males, where age-dependent effects might have influenced the
oscillations. In contrast, mouse hepatic metabolome and
transcriptome studies revealed rhythmicity in metabolic
sub-pathways, where oscillations in glutathione were ascertained
by oscillations in its precursors, cysteine and methionine, albeit
with a lower amplitude for the latter (Klichko, 2015).
Another important finding of this study is that the diurnal
fluctuations in GSH levels were not followed by similar changes in
the products of its degradation (Cys-Gly) and oxidation (GSSG).
While Cys-Gly was completely arrhythmic, changes in GSSG profile
did not mirror those observed for GSH. Even though both shared the
same slow drop-off from ZT0 to ZT8 as well as the ZT8 trough,
their peaks were quite distinct (ZT12 for GSSG and ZT20 for GSH).
Also in old flies, a certain degree of rhythmicity is maintained
for GSSG in contrast to the absence of any diurnal GSH patterns
(Klichko, 2015).
An additional important finding of this study is that the rhythms
in glutathione levels observed in young flies were lost in old
flies, presumably due to the loss of diurnal fluctuations of GCLc,
GCLm as well as GCL activity, in response to the weakening of the
circadian clocks. In contrast, GSSG rhythms were largely preserved
in older flies, suggesting that the daily changes in glutathione
disulfide levels are supported by enzymatic reactions that are not
under clock control (Klichko, 2015)
Despite loss of circadian regulation, average daily levels of GSH
remained unchanged during aging, while the levels of GSSG were
slightly higher, mainly due to lesser drop in the early morning.
In Drosophila, it has been established that whole body
GSH levels were either relatively constant or slightly decreased
during aging while GSSG rose 2–3 fold. Similar age-related
changes were documented in different mammalian tissues with the
most significant reduction in GSH and accumulation of GSSG in the
brain, indicative of a more pro-oxidative cellular environment. As
such changes in GSH and GSSG were frequently associated with
increases in enzyme activities related to GSH usage, the
relatively steady glutathione concentrations observed in the heads
of old flies could point to less efficient GSH utilization
(Klichko, 2015).
The rather unexpected finding of this study is that the
expression of Gclc at both mRNA and protein levels significantly
increased in the heads of old flies, and this increase was
associated with about 25% higher average daily GCL activity.
Despite this increase, the average daily levels of GSH remained
unchanged suggesting a loss in GCL catalytic efficiency or an
age-related increase in GSH utilization. One possible scenario is
that the efficiency of GSH synthesis can be induced by oxidative
stress, in part through the well-documented increase in H2O2
signaling that accompanies aging. For instance, post-translational
control of γ-glutamylcysteine (γ-Glu-Cys) synthesis is
influenced by oxidative stress, which can dramatically affect
formation of GCL holoenzyme and its stabilization (Klichko, 2015).
Consistent with induction of GCL by stress, it was previously
reported that per-null
mutants with disrupted clock displayed arrhythmic as well as
elevated GCL activity, which was also reflected in arrhythmic and
elevated ROS levels relative to the control. It should be noted
that previous studies comparing GCL activity and GSH levels in
young and old rats showed a decrease of both parameters in liver,
while in aging brain and heart GSH decreased but GCL activity
remained unchanged, pointing again to catalytic deficiency of the
enzyme (Klichko, 2015).
Other aminothiols that did not show cycling in young flies also
remained arrhythmic in old flies, but displayed changes in their
steady state levels. Consistent with previous reports, the amounts
of Cys-Gly were ∼50% higher in older flies. Cys-Gly, derived
from the breakdown of glutathione, is required for GSH synthesis
as a precursor of cysteine, but at the same time it is also a
prooxidant generated during the catabolism of glutathione. The
requirement of Cys-Gly for GSH synthesis justifies its increase
with age, as the tissues require an increased supply of precursors
for GSH biosynthesis in older flies. However, an increase in
cysteine levels during aging was not observed. A more plausible
explanation is that the increase in Cys-Gly is indicative of an
increase in oxidative stress and GSH degradation. In agreement
with this view, the average daily levels of methionine were about
35% lower in old flies suggesting the likelihood of an increase in
oxidation of methionine to methionine sulfoxide by ROS rather than
an increase in methionine consumption for cysteine biosynthesis.
Together, these changes indicate a shift in redox homeostasis in
the heads of older flies, consistent with the earlier reports in
whole flies. Similar alterations in the redox components were also
indicative of heightened oxidative stress in pathologies like
systemic lupus erythematosus (Klichko, 2015).
While this study reports that the loss of behavioral rhythms
after manipulation of dBACE is associated with reduced expression
of clock genes in the central pacemaker, other recent work shows
that expression of human Aβ peptides leads to disruption of
rest activity rhythms without interfering with PER oscillations in
the central pacemaker. Even strongly neurotoxic Aβ peptides,
such as Aβ42 arctic, do not cause rhythm disruption when
expressed in central pacemaker neurons; rather, pan-neuronal
expression is required. The fact that even the most neurotoxic
Aβ peptides are not capable of dampening PER oscillation in
pacemaker neurons suggests that Aβ production does not affect
clock oscillations and that it is not Aβ production that
causes the phenotype observed in this study upon over-expression
of dBACE. This was confirmed by expression of KUZ,
whose activity does not increase dAβ production; however, it
also leads to disruption of rest-activity rhythms. Similar rhythm
disruption by dBACE and KUZ suggests that an excess cleavage
product of both pathways might be responsible for the disruption.
Like in the mammalian APP cleavage pathway, in Drosophila
cleavage of APPL by KUZ or dBACE results in a C-terminal fragment
(CTF) that is subsequently cleaved by the ϒ-secretase
resulting in the production of dAICD. Indeed, it was shown that
expression of dAICD results in an age-dependent decline in
rhythmic locomotor activity. As with dBACE and KUZ expression,
dAICD expression causes weakening or complete loss of behavioral
rhythms while age-matched control flies remain highly rhythmic. In
this context, it is worth noting that α-secretase activators
are considered for clinical trials to reduce Aβ production in
AD patients. However, according to results in this study, this
could lead to disruptions of circadian rhythms and sleep patterns
thus negatively impacting the lives of patients and their
caretakers (Blake, 2015).
This study's data suggest that increased dAICD may be the
proximal cause of decay in rest-activity rhythms. The role of AICD
in AD is increasingly evident but poorly understood. AICD is able
to enter the nucleus and has been implicated in transcriptional
regulation that may affect cell death, neurite outgrowth and
neuronal excitability. Interestingly, transgenic mice expressing
AICD have increased activity of GSK-3, which in flies affects the
circadian clock. Over-expression of GSK-3
in Drosophila leads to altered circadian behavior by
hyper-phosphorylation of
TIMELESS (TIM), a key circadian protein which forms dimers
with PER that enter the nucleus and regulate the clock mechanism.
Of further interest, increased GSK-3 activity has been implicated
in AD, and in Drosophila, increased GSK-3 activity
mediates the toxicity of Aβ peptides (Blake, 2015).
Cleavage of APPL likely results in a significant decline in
intact APPL, and this could be detrimental as APPL has
neuroprotective effects. It was also recently shown that loss of
full-length APPL induces cognitive deficits in memory. This study
reports that flies over-expressing full-length APPL in central
pacemaker neurons maintain stronger behavioral rest-activity
rhythms during aging than control flies; however this effect is
not observed when APPL is expressed pan-neuronally. This could be
caused by negative effects of APPL when expressed in other
unspecified neurons, or could be related to driver strength.
Overall, the study suggests that the loss of full-length APPL
might negatively affect circadian behavior by way of the central
pacemaker neurons (Blake, 2015).
Over-expression of dAICD induces a severe phenotype, disrupting
rest-activity rhythms as early as age 5d when expressed in central
pacemaker neurons and by age 35d with pan-neuronal expression.
Taken together these results suggest that while loss of
full-length APPL by over-expression of its secretases might
negatively impact circadian behavior, the cleavage product dAICD
induces the most severe behavioral rest-activity disruption.
Interestingly, the observed effect is not likely a product of
neurodegeneration as it was previously shown that dAICD has no
effect on neurodegeneration, and this study shows that the
pacemaker cells appear intact in pdf > dAICD flies.
In addition, it was shown that dAICD, like the vertebrate AICD,
can be found in the nucleus. Therefore, this study suggests that
dAICD may directly or indirectly affect the expression of clock
genes. This offers a novel entry point toward understanding the
mechanism of circadian rhythm disruption in Alzheimer's disease
(Blake, 2015).
This study highlights the interaction between cell-autonomous and
non-autonomous events in the ER stress response of ISCs and
supports the notion that improving proteostasis by boosting ER
folding capacity in stem cells improves long-term tissue
homeostasis and can impact lifespan. The regulation of PERK
activity in ISCs by the JAK/Stat signaling pathway provides a
tentative mechanism for the interaction between IECs experiencing
ER stress and ISCs: the study proposes that JNK-mediated release
of JAK/Stat ligands from stressed IECs results in JAK/Stat
mediated activation of PERK in ISCs, and that this activation is
required for the proliferative response of ISCs to epithelial
dysfunction. The activation of JAK/Stat signaling in the
intestinal epithelium of animals in which Xbp1 is knocked down in
ECs, the requirement for JNK activation and Upd
expression in ECs for ISC proliferation in response to stress, and
the requirement for Stat (and Hop
and Dome)
in ISCs for the activation of
eIF2α phosphorylation and stress-induced ISC
proliferation, support this model. The mechanisms by which Stat
mediates activation of PERK remain unclear, and will be
interesting topics of further study (Wang, 2015).
Studies in worms have established the UPRER as a critical
determinant of longevity, and Xbp1 extends lifespan by improving
ER stress resistance. This study's data further support the notion
that regulating ER stress response pathways is critical to
increase health- and lifespan. Here, chronic PERK activation can
be considered a downstream readout of the buildup of proteotoxic
stress in the intestinal epithelium during aging, which then
perturbs proliferative homeostasis by continuously providing
pro-mitotic signals to ISCs. Knocking down PERK in ISCs limits
these pro-mitotic signals, improving homeostasis and barrier
function, and extending lifespan. Lifespan is generally extended
when ISC proliferation is limited in older flies, but not when it
is completely inhibited. Accordingly, lifespan extension is
observed when PERK is knocked down using an RNAi approach that
does not completely ablate PERK function (Wang, 2015).
ER stress has been documented as tightly associated with
intestinal inflammation and the development of IBDs in mice and
humans. Genetic variants in Xbp1 are associated with higher
susceptibility to IBD and a recent study indicates that Xbp1 can
act as a tumor suppressor in the intestinal epithelium, by
limiting intestinal proliferative responses and tumor development
through the control of local inflammation. In this context, the
specific role of PERK in the control of ISC proliferation in the
fly gut is consistent with the function of PERK in the intestinal
epithelium of mice, where activation of PERK can promote
transition of ISCs into the transient amplifying cell population.
While the Drosophila midgut epithelium does not contain
a transit amplifying cell population, this study's data suggest
that a role for PERK in the proliferative response of the ISC
lineage to ER stress is conserved (Wang, 2015)
Due to the importance of the UPRER in the maintenance of tissue
homeostasis in aging organisms, therapies targeting the UPRER are
promising strategies to delay the aging process. Accordingly,
pharmaceuticals that can limit ER stress (such as
Tauroursodeoxycholic acid, TUDCA and 4-phenylbutyrate, PBA) have
had therapeutic success in various human disorders. Interestingly,
flies fed PBA show increased lifespan, yet the effects of PBA on
intestinal homeostasis have not yet been explored. Based on this
work, it is likely that further characterization of the effects of
UPRER-targeting drugs on ISC function and intestinal homeostasis
will help develop clinically relevant strategies to limit human
aging and extend healthspan (Wang, 2015).
Surprisingly, it was observed that there was a 65% increase of
aged tufeatm−8/+ GSCs in S phase (1.98-fold
increase relative to young tufeatm−8/+ GSCs), as
compared to its sibling controls at the same age (1.33-fold
increase relative to young control GSCs). Coincidently, a recent
publication on Drosophila reported that ATM functions in
DNA damage repair and exerts negative feedback control over the
level of programmed double strand breaks (DSBs) during meiosis,
and thus the number of H2AX foci (a marker of DNA damage) is
dramatically increased in tufeatm−8 mutant germ
cells. This study speculates that tufeatm−8/+ GSCs
may induce more DNA damage via feedback regulation, thereby
causing more severe S phase delay. However, in mice, Atm−/−
undifferentiated spermatogonia are not maintained in the testis
due to DNA damage-induced cell cycle G1 arrest, suggesting that
ATM may function in the G1 phase in response to DNA damage.
Nevertheless, it remains to be elucidated whether ATM mediates
different cell cycle regulators in different cell contexts or in
response to different types of stress-induced DNA damage (Kao,
2015).
With age, cells may accumulate DNA mutations that allow them to
escape normal regulatory processes and become tumor cells.
Although tumorigenesis is harmful to health in the long term, it
may also serve as a survival and protective mechanism when the
body is highly threatened. While the germarium normally houses
differentiating 8- or 16-germ cell cysts interconnected with
branched fusomes, this study found that the middle portion of the
aged germarium was occupied by tumor-like GSCs, which express pMad
(a Dpp
signaling effector) and possess rounded fusomes. This result
recalls an earlier report that forced stemness Dpp signaling
causes differentiating germ cell cysts to revert into functional
stem cells in Drosophila ovaries, through the induction
of ring canal closure and fusome scission (Kao, 2015).
It has also been reported that aged human epidermal cells can
dedifferentiate into stem cell-like cells via Wnt/β-catenin
signaling, and injury can drive the dedifferentiation of epidermal
cells via the β-integrin-mediated signaling pathway; these
findings suggest that dedifferentiation is a process by which
organisms address aging or tissue damage. Given that GSCs play a
fundamental role in producing the next generation, this study
suspects that these tumor-like GSCs may be derived from germ cell
cysts through a dedifferentiation process triggered by aging;
however, they cannot rule out the possibility that these
tumor-like GSCs are derived from the transformation of normal GSCs
(Kao, 2015).
In outbred sexually reproducing populations, age-specific mortality rates reach a plateau in late life following the exponential increase in mortality rates that marks aging. Little is known about what happens to physiology when cohorts transition from aging to late life. Age-specific values were measured for starvation resistance, desiccation resistance, time-in-motion and geotaxis in ten Drosophila melanogaster populations: five populations selected for rapid development and five control populations. Adulthood was divided into two stages, the aging phase and the late-life phase according to demographic data. Consistent with previous studies, populations selected for rapid development entered the late-life phase at an earlier age than the controls. Age-specific rates of change for all physiological phenotypes showed differences between the aging phase and the late-life phase. This result suggests that late life is physiologically distinct from aging. The ages of transitions in physiological characteristics from aging to late life statistically match the age at which the demographic transition from aging to late life occurs, in all cases but one. These experimental results support evolutionary theories of late life that depend on patterns of decline and stabilization in the forces of natural selection (Shahrestani, 2016).
One of the hallmarks of CR-mediated longevity extension is
increased mitochondrial biogenesis mediated by dPGC-1.
Increased dPGC-1 levels and mitochondrial biogenesis
have been described in the muscle of Indy mutant flies,
the liver of mIndy−/− mice, and this study
describes it in the midgut of Indy mutant flies. One
possible mechanism for these effects can be attributed to the
physiological effects of reduced INDY transport activity. Reduced
INDY-mediated transport activity could lead to reduced
mitochondrial substrates, an increase in the ADP/ATP ratio,
activation of AMPK, and dPGC-1 synthesis. This is
consistent with findings in CR flies and the livers of
mINDY−/− mice. This study's analysis of
mitochondrial physiology in the Indy mutant midgut shows
upregulation of respiratory proteins, maintenance of mitochondrial
potential and increased mitochondrial biogenesis, all of which are
signs of enhanced mitochondrial health. The observed increase in dPGC-1
levels in Indy mutant midgut therefore appears to
promote mitochondrial biogenesis and functional efficiency,
representing a protective mechanism activated in response to
reduced energy availability (Rogers, 2014).
Genetic interventions that conserve mitochondrial energetic
capacity have been shown to maintain a favorable redox state and
regenerative tissue homeostasis. This is particularly beneficial
in the fly midgut, which facilitates nutrient uptake, waste
removal and response to bacterial infection. Indy mutant
flies have striking increases in the steady-state expression of
the GstE1 and GstD5 ROS detoxification genes.
As a result, any increase in ROS levels, whether from
mitochondrial demise or exposure to external ROS sources can be
readily metabolized to prevent accumulation of oxidative damage.
Such conditions not only promote oxidative stress resistance, but
also preserve ISC homeostasis as demonstrated by consistent
proliferation rates throughout Indy mutant lifespan and
preserved intestinal architecture in aged Indy mutant
midguts. Thus, enhanced ROS detoxification mechanisms induced by Indy
reduction and subsequent elevation of dPGC-1 contributes
to preservation of ISC functional efficiency, and may be a
contributing factor to the long-lived phenotype of Indy
mutant flies (Rogers, 2014).
This study suggests that INDY may function as a physiological
regulator of mitochondrial function and related metabolic
pathways, by modulating nutrient flux in response to nutrient
availability and energetic demands. Given the localization of INDY
in metabolic tissues, and importance of regulated tissue
homeostasis during aging, these studies highlight INDY as a
potential target to improved health and longevity. Reduced Indy
expression causes similar physiological changes in flies, worms
and mice indicating its regulatory role would be conserved.
Further work should examine the interplay between Indy
mutation and metabolic pathways, such as insulin signaling, which
have been shown to promote stem cell maintenance and healthy aging
in flies and mice. In doing so, the molecular mechanisms, which
underlie Indy mutant longevity may provide insight for
anti-aging therapies (Rogers, 2014).
The study proposes that by implementing a cell-fitness
checkpoint, multicellular communities became more robust and less
sensitive to several mutations that create viable but potentially
harmful cells. Moreover, azot is not involved in other
types of apoptosis, suggesting a dedicated function, and- given
the evolutionary conservation of Azot- pointing to the existence
of central cell selection pathways in multicellular animals
(Merino, 2015).
Tauopathies, including Alzheimer's disease, are a group of neurodegenerative diseases characterized by abnormal tau hyperphosphorylation that leads to formation of neurofibrillary tangles. Drosophila models of tauopathy display prominent features of the human disease including compromised lifespan, impairments of learning, memory and locomotor functions and age-dependent neurodegeneration visible as vacuolization. This study used a Drosophila model of frontotemporal dementia with parkinsonism linked to chromosome 17 (FTDP-17), in order to study the neuroprotective capacity of a recently identified neuronal maintenance factor, nicotinamide mononucleotide (NAD) adenylyl transferase (NMNAT), a protein that has both NAD synthase and chaperone function. NMNAT is essential for maintaining neuronal integrity under normal conditions and has been shown to protect against several neurodegenerative conditions. However, its protective role in tauopathy has not been examined. This study shows that overexpression of NMNAT significantly suppresses both behavioral and morphological deficits associated with tauopathy by means of reducing the levels of hyperphosphorylated tau oligomers. Importantly, the protective activity of NMNAT protein is independent of its NAD synthesis activity, indicating a role for direct protein-protein interaction. Next, it was shown that NMNAT interacts with phosphorylated tau in vivo and promotes the ubiquitination and clearance of toxic tau species. Consequently, apoptosis activation was significantly reduced in brains overexpressing NMNAT, and neurodegeneration was suppressed. This report on the molecular basis of NMNAT-mediated neuroprotection in tauopathies opens future investigation of this factor in other protein foldopathies (Ali, 2012).
Interestingly, GO analyses revealed a significant enrichment of
immune responsive genes in Lamin-associated domains (LADs) in four
different mammalian cell types and Drosophila Kc cells.
Since the large-scale pattern of LADs is conserved in different
cell types in mammals, it is possible that the immune-responsive
genes are also enriched in LADs in the fly fat body cells.
Supporting this notion, the IKKγ, key, which is one of the
two derepressed IMD regulators and was found to exhibit H3K9me3
reduction and gene activation, is localized to LADs in Kc cells.
It is speculated that lamin-B might play an evolutionarily
conserved role in repressing a subset of inflammatory genes in
certain tissues, such as the immune organs, in the absence of
infection or injury. Consistently, senescence-associated lamin-B1
loss in mammalian fibroblasts is correlated with
senescence-associated secretory phenotype (SASP). Although the in
vivo relevance of fibroblast SASP in chronic inflammation and
aging-associated diseases in mammals remains to be established,
the findings in Drosophila provide insights and impetus
to investigate the role of lamins in immunosenescence and systemic
inflammation in mammals (Chen, 2014).
Lamin-B gradually decreases in fat body cells of aging flies,
whereas lamin-C amount remains the same. Since it has been
recently shown that the assembly of an even and dense nuclear
lamina is dependent on the total lamin concentration, the
age-associated appearance of lamin-B and lamin-C gaps around the
nuclear periphery of fat body cells is likely caused by the drop
of the lamin-B level. How aging triggers lamin-B loss is unknown,
but it appears to be posttranscriptional, because lamin-B
transcripts in fat bodies remain unchanged upon aging.
Interestingly, among the tissues examined, no changes of lamin-B
and lamin-C proteins were found in cells in the heart tube,
oenocytes, or gut epithelia in old flies. Therefore, the
age-associated lamin-B loss does not occur in all cell types in
vivo. A systematic survey to establish the cell/tissue types that
undergo age-associated reduction of lamins in both flies and
mammals should provide clues to the cause of loss. Deciphering how
advanced age leads to lamin loss should open the door to further
investigate the cellular mechanism that contributes to chronic
systemic inflammation and how it in turn promotes age-associated
diseases in humans (Chen, 2014).
