|
The
InteractiveFly: Drosophila as a Model for
Human Diseases |
| Drosophila
genes associated with Parkinson's disease
mask milton miro ND-42 parkin Pink1 Rab11 sicily |
Related
terms Autophagy Gaucher's disease Mitochondria and mitochondrial function Neuromuscular junction Vesicles |
| Relevant
studies of Parkinson's disease Suzuki, M., Fujikake, N., Takeuchi, T., Kohyama-Koganeya, A., Nakajima, K., Hirabayashi, Y., Wada, K. and Nagai, Y. (2015). Glucocerebrosidase deficiency accelerates the accumulation of proteinase K-resistant α-synuclein and aggravates neurodegeneration in a Drosophila model of Parkinson's disease. Hum Mol Genet 24: 6675-6686. PubMed ID: 26362253 Abstract Highlights
Discussion The phenotypic aggravation by GCase deficiency in αSyn flies was associated with the accumulation of PK-resistant αSyn, rather than with changes in the total amount of αSyn, suggesting that the production of this PK-resistant αSyn species might play a key role in the neurotoxicity. Although the toxicity of PK-resistant αSyn was not directly demonstrated, there was a tight association between the neurotoxicity of αSyn and its PK resistance. PK-resistant αSyn oligomers that are formed as an intermediate conformer in the course of in vitro αSyn fibrillization have been shown to cause oxidative stress in primary neurons at much higher levels than non-PK-resistant oligomers. It has been shown that two kinds of αSyn fibrils exhibiting different vulnerabilities to PK digestion can be isolated from repetitive seeded fibrillization, and the αSyn strain more resistant to PK digestion is more toxic to neurons. In addition, αSyn fibril strains produced using different buffers show different vulnerabilities to PK digestion, and their toxicities are associated with their resistance to PK digestion. Interestingly, αSyn fibrils with different levels of PK resistance have different structures, cross-seeding abilities and propagation properties both in vitro and in vivo, all of which are reminiscent of the properties of prions. Therefore, it is possible that the accelerated formation of PK-resistant αSyn that was observed in the GCase-deficient flies represents the ‘prion-like conversion’ of αSyn and that this toxic species leads to phenotypic aggravation by promoting the prion-like seeding and propagation of αSyn (Suzuki, 2015). The idea that αSyn is degraded in lysosomes has led to several studies on the basis of the hypothesis that loss of GCase activity compromises the αSyn-degrading function of lysosomes, resulting in αSyn accumulation. Several groups have demonstrated that decreased GCase activity results in increased amounts of αSyn, using cultured neurons, human iPSC-derived neurons from GBA1 mutation carriers and mice treated with a GCase inhibitor. In contrast, two other groups have reported that GCase activity does not correlate with the amount of αSyn in neuronal cells, whereas the expression of a mutant GCase that maintains its enzyme activity increases the amount of αSyn, favoring a gain-of-function mechanism in the pathogenesis of GBA1-associated PD. In the fly model, the amount of total αSyn was not significantly increased by GCase deficiency, despite the phenotypic aggravation. However, a recent study using PD model mice with a GBA1 mutation has shown that the total amount of αSyn in the brain lysates is not increased, but the rate of αSyn degradation assessed by pulse-chase experiments is decreased in primary neurons from the same mice. Thus, the possibility that αSyn degradation is compromised by lysosomal dysfunction can not be completely excluded, even though changes in the total amount of αSyn are not detected (Suzuki, 2015). In addition to the fly model experiments, it was demonstrated by in vitro experiments that GlcCer directly promotes the formation of PK-resistant αSyn, as a mechanism for the increased accumulation of PK-resistant αSyn in the dGBA1a-RNAi flies. These results are consistent with a previous report showing a direct effect of GlcCer on the stability of αSyn oligomers. Moreover, a significant increase in αSyn dimers by the incubation of αSyn with GlcCer-containing liposomes was also found, which is consistent with the finding that the amount of αSyn dimers is significantly increased in GD patients. It was also shown that β-Gal knockdown exacerbates the locomotor dysfunction of αSyn flies, and GM1 directly promotes the PK resistance of αSyn, supporting the hypothesis that aberrant interactions of αSyn with glycolipids trigger the toxic conversion of αSyn, resulting in increased neurotoxicity in vivo. It has been demonstrated that GM1 specifically binds to αSyn and induces its oligomerization, thereby inhibiting its fibrillation. Interestingly, a recent report shows that iPSC-derived neurons from GBA1-associated PD patients exhibit not only decreased GCase activity, but also decreased β-Gal activity, which can be rescued by zinc-finger nuclease-mediated gene correction, implying a crosstalk between GCase and β-Gal activities. Taken together, it is possible that a loss of β-Gal activity also contributes to the acceleration of αSyn toxicity in GBA1-associated PD. It is noted that the direct binding of GM1 to the amyloid β protein also triggers its toxic conversion, implying a common or similar role of glycolipids in the conversion of neurodegenerative disease-related proteins from their non-toxic to toxic forms (Suzuki, 2015). Then, where in a cell does the accumulated GlcCer interact with αSyn to convert it into a PK-resistant form? One possibility is that αSyn is transported into lysosomes via macroautophagy or chaperone-mediated autophagy, where it interacts with accumulated GlcCer. Then, GlcCer-associated αSyn is secreted from the cells, taken up by itself or by the surrounding cells and accumulates in the cytosol. The other possibility is that the accumulated GlcCer in the lysosome leaks into the cytosol and interacts with αSyn in the cytosol, as the leakage of GlcCer into the cytosol has been reported in both GD patients and GD model mice. There have been no reports to date of the level of GlcCer in the brain of PD patients with a GBA1 mutation. However, in iPSC-derived neurons from two PD patients with a heterozygous GBA1 mutation (RecNcil/wt and N370S/wt), which causes an approximately 50% decrease in GCase activity, the amount of GlcCer has been reported to be about 2-fold higher than that of isogenic gene-corrected iPSC-derived neurons. Furthermore, GlcCer has been reported to accumulate in the brains of GD patients, in which GCase activity decreases (by 80–90%). GCase activity has also been found to be moderately decreased in the brains of GBA1 mutant carrier PD patients (58% decrease in the substantia nigra). Collectively, these data suggest that GlcCer accumulates in the brains of GBA1 mutation carrier PD patients (Suzuki, 2015). This study focused on the loss-of-function aspect of GBA1 mutations, but there is another possibility arguing the gain-of-function toxicity of mutant GCase, because most mutant GCases are prone to misfold in the endoplasmic reticulum (ER). Human skin fibroblasts derived from GD patients and carriers are reported to induce the unfolded protein response, which is also observed in Drosophila models of GD expressing human mutant GCase. Ambroxol, a potential pharmacological chaperone for mutant GCase, has been shown to ameliorate both ER stress and the phenotypes of these Drosophila models. Interestingly, ambroxol treatment also suppresses the misfolding of mutant GCase, subsequently resulting in an enhancement of cellular GCase activity. Therefore, chemical chaperone therapy can be expected to exert beneficial effects against GD, via the amelioration of both the gain-of-function aspect through ER stress and the loss-of-function aspect through decreased GCase activity. As ER stress has been suggested to be involved in the neurodegeneration that occurs in PD, the synergistic effects of chemical chaperone therapy would also be effective for GBA1-associated PD patients, through the suppression of both ER stress and the toxic conversion of αSyn by GlcCer accumulation (Suzuki, 2015). Wang, X., Winter, D., Ashrafi, G., Schlehe, J., Wong, Y.L., Selkoe, D., Rice, S., Steen, J., LaVoie, M..J and Schwarz, T.L. (2011). PINK1 and Parkin target Miro for phosphorylation and degradation to arrest mitochondrial motility. Cell 147: 893-906. PubMed ID: 22078885 Abstract Highlights
Discussion Mitochondrial motility is especially critical to neurons where it may take days for a mitochondrion to move between the cell body and a distant axonal or dendritic ending. The need for mitochondria to undergo turnover, as well as their redistribution to balance changes in local energy demand, make mitochondrial movement an important on-going and regulated process. The mitochondrion-specific adaptor proteins, Miro and Milton, are control points for this motility. Damaged mitochondria in cell lines selectively recruit Parkin and are in turn targeted for mitophagy. In contrast to an earlier report, it was found that this recruitment also occurs in axons; when highly expressed, YFP-Parkin is observed on mitochondria without depolarization (consistent with its ability to arrest mitochondrial motility upon overexpression), but with lower expression levels it is recruited to mitochondria by treatment with Antimycin A. Parkin recruitment is initiated by the depolarization-induced stabilization of PINK1 on the mitochondrial surface and PINK1 is also upstream of Parkin in regulating mitochondrial morphology. This relationship also holds for mitochondrial motility. PINK1 arrests mitochondrial motility in wildtype but not Parkin−/− mice or Parkin RNAi flies. Mitochondrial depolarization with CCCP causes the degradation of Miro in a Parkin-dependent manner. Similarly, PINK1 expression causes the degradation of Miro in Parkin expressing cells, but not in Parkin-lacking HeLa cells (Wang, 2011). In previous genetic studies of PINK1 and Parkin, differences are noted between mice and Drosophila. Drosophila loss of function mutants exhibit profound defects in mitochondrial morphology that are seen in knockout mice only when neurons are additionally stressed. Differences were also observed in this study between Drosophila and murine models. In both, PINK1 or Parkin overexpression arrests mitochondria and in both Parkin is required downstream of PINK1. However, in Drosophila neurons, RNAi knockdown of PINK1 or Parkin increases mitochondrial motility whereas differences of motility in murine Parkin−/− neurons are not statistically significant. These differences may reflect a difference in how the species employ the pathway: in mammals, it may be strictly reserved for the response to mitochondrial depolarization whereas in the fly, whose short lifespan may make mitochondrial damage less critical, it may contribute to the ongoing turnover of proteins that participate in mitochondrial dynamics (Wang, 2011). The ability of Parkin overexpression to alter mitochondrial motility in the presence of PINK1 RNAi or mitochondrial morphology in a PINK1 null background indicates that, although PINK1 can stimulate Parkin function, Parkin can act independently as well. Results from this study do not show if Parkin is effective because of residual PINK1 in the RNAi-expressing cells, because other kinases can also activate Miro as a Parkin substrate, or because elevated levels of Parkin can lead to Miro degradation even in the absence of a phosphorylation. Thus, PINK1 is likely to enhance Parkin function but probably is not required (Wang, 2011). The observation that two PD-associated genes encode regulators of mitochondrial motility is consistent with other findings linking misregulation of mitochondrial dynamics to neurodegeneration. Changes in mitochondrial distribution, transport, and dynamics are implicated in Charcot-Marie-Tooth, Amyotrophic Lateral Sclerosis, Alzheimer’s and Huntington’s diseases. These findings underscore the importance of mitochondrial dynamics for supplying distal regions with sufficient energy and Ca2+-buffering capacity, compensating for changes in energy demand, refreshing older mitochondria through fusion with newly-synthesized mitochondria, and clearing damaged mitochondria (Wang, 2011). Clarification of the relationship of PINK1 and Parkin supports the view that PD is a mitochondrial disorder. In the etiology of PD, the regulation of Miro levels may be significant. Either through a specific sorting pathway or as a consequence of the random reassortment of mitochondrial proteins that occur with repeated fusion and fission, some organelles or fragments of the organelle will arise in which the burden of dysfunctional proteins is sufficient to compromise the membrane potential. The resulting stabilization of PINK1 on the surface and targeting of Miro, mitofusin, and other proteins for Parkin action and degradation, will bring about the sequestration and eventual engulfment of that dysfunctional organelle. Sequestration and mitophagy thereby prevent further cellular damage due to reactive oxygen species and enable the cellular complement of mitochondria to be replenished by healthier organelles. The greater the stresses on mitochondria, the more acute the need for this clearance pathway. The heightened sensitivity of the dopaminergic neurons in the substantia nigra to disruption of this ubiquitous pathway may therefore reflect exceptional challenges for mitochondria in these cells. Those stresses may include the susceptibility of dopamine to oxidation and high rates of Ca2+ influx. When this quality control mechanism is defective in patients carrying mutations in either gene, damaged mitochondria will retain Miro and mitofusin, and therefore may move about in the neuron and, through fusion reactions, reintroduce damaged components to otherwise healthy organelles rather than undergo mitophagy (Wang, 2011). Liang, Z., Chan, H. Y. E., Lee, M. M. and Chan, M. K. (2021). A SUMO1-derived peptide targeting SUMO-interacting motif inhibits alpha-synuclein aggregation. Cell Chem Biol. PubMed ID: 33444530
Abstract The accumulation of α-synuclein amyloid fibrils in the brain is linked to Parkinson's disease and other synucleinopathies. The intermediate species in the early aggregation phase of α-synuclein are involved in the emergence of amyloid toxicity and considered to be the most neurotoxic. The N-terminal region flanking the non-amyloid-β component domain of α-synuclein has been implicated in modulating its aggregation. This study reports the development of a SUMO1-derived peptide inhibitor (SUMO1(15-55); see Drosophila Sumo), which targets two SUMO-interacting motifs (SIMs) within this aggregation-regulating region and suppresses α-synuclein aggregation. Molecular modeling, site-directed mutagenesis, and binding studies are used to elucidate the mode of interaction, namely, via the binding of either of the two SIM sequences on α-synuclein to a putative hydrophobic binding groove on SUMO1(15-55). Subsequent studies show that SUMO1(15-55) also reduces α-synuclein-induced cytotoxicity in cell-based and Drosophila disease models (Liang, 2021).
Jewett, K. A., Thomas, R. E., Phan, C. Q., Lin, B., Milstein, G., Yu, S., Bettcher, L. F., Neto, F. C., Djukovic, D., Raftery, D., Pallanck, L. J. and Davis, M. Y. (2021). Glucocerebrosidase reduces the spread of protein aggregation in a Drosophila melanogaster model of neurodegeneration by regulating proteins trafficked by extracellular vesicles. PLoS Genet 17(2): e1008859. PubMed ID: 33539341
Abstract Abnormal protein aggregation within neurons is a key pathologic feature of Parkinson's disease (PD). The spread of brain protein aggregates is associated with clinical disease progression, but how this occurs remains unclear. Mutations in glucosidase, beta acid 1 (GBA), which encodes glucocerebrosidase (GCase), are the most penetrant common genetic risk factor for PD and dementia with Lewy bodies and associate with faster disease progression. To explore how GBA mutations influence pathogenesis, Drosophila model of GBA deficiency (Gba1b) was created that manifests neurodegeneration and accelerated protein aggregation. Proteomic analysis of Gba1b mutants revealed dysregulation of proteins involved in extracellular vesicle (EV) biology, and altered protein composition of EVs was found from Gba1b mutants. Accordingly, it was hypothesized that GBA may influence pathogenic protein aggregate spread via EVs. It was found that accumulation of ubiquitinated proteins and Ref(2)P, Drosophila homologue of mammalian p62, were reduced in muscle and brain tissue of Gba1b flies by ectopic expression of wildtype GCase in muscle. Neuronal GCase expression also rescued protein aggregation both cell-autonomously in brain and non-cell-autonomously in muscle. Muscle-specific GBA expression reduced the elevated levels of EV-intrinsic proteins and Ref(2)P found in EVs from Gba1b flies. Perturbing EV biogenesis through neutral sphingomyelinase (nSMase), an enzyme important for EV release and ceramide metabolism, enhanced protein aggregation when knocked down in muscle, but did not modify Gba1b mutant protein aggregation when knocked down in neurons. Lipidomic analysis of nSMase knockdown on ceramide and glucosylceramide levels suggested that Gba1b mutant protein aggregation may depend on relative depletion of specific ceramide species often enriched in EVs. Finally, ectopically expressed GCase was identified within isolated EVs. Together, these findings suggest that GCase deficiency promotes accelerated protein aggregate spread between cells and tissues via dysregulated EVs, and EV-mediated trafficking of GCase may partially account for the reduction in aggregate spread (Jewett, 2021).
Many genetic influences of PD have now been identified, and much work has been focused on how these genes lead to protein aggregation through mechanisms such as protein misfolding and autophagy defects. However, none of these genes have been implicated in cell-to-cell spread of pathogenic protein aggregates, which closely correlates with clinical disease progression. Proteomic analysis and non-cell-autonomous rescue of protein aggregation in Gba1b mutants has led to the hypothesize that GBA mutations may influence the rate of propagation of protein aggregates between neurons. This work suggests a link between GBA mutations and faster spread of intracellular protein aggregates via a novel EV-mediated mechanism, possibly explaining the recent clinical finding that GBA mutations accelerate the progression of clinical disease. Using a Drosophila model of GBA deficiency that manifests accelerated protein aggregation, this study found that expressing WT GCase in specific tissues of a GBA-deficient fly can not only rescue protein aggregation cell-autonomously and in distant tissues, but also rescue alterations in protein cargo observed in EVs isolated from Gba1b mutant hemolymph. Interestingly, ectopically expressed WT GCase itself was found within EVs of GBA-deficient flies, suggesting that the non-cell-autonomous rescue due to GCase expression is mediated by both reduction in aggregated proteins in EVs and trafficking of GCase via EVs to distant cells and tissues. Perturbing EV biogenesis through decreased expression of ESCRT-independent nSMase affected protein aggregation in local tissues in a tissue-dependent manner, and further decreased a subset of Cer species already reduced in Gba1b mutants. Interestingly, this subset of Cer species is known to be enriched in EV membranes. Together, these findings suggest that mutations in GBA result in the accelerated spread of protein aggregates through changes in cellular lipid composition and dysregulation of proteins trafficked by EVs (Jewett, 2021).
Although the model of GBA mutations promoting spread of protein aggregates via EVs is novel, the idea that proteostasis can be maintained in a non-cell-autonomous fashion is well supported in the literature. For example, in C. elegans, misfolded α-synuclein accumulating in endo-lysosomal vesicles was found to be transmitted from muscle to the hypodermis, a nearby tissue, for degradation. It is possible that a non-cell-autonomous mechanism is necessary because certain tissues may be more efficient in reducing protein aggregation. This has been previously described, where overexpression of FOXO in Drosophila muscle decreased aging-related protein aggregates in muscle as well as brain and other distant tissues, but FOXO overexpression in adipose tissue was unable to prevent protein aggregation in muscle. In the curren model, overexpressing dGba1b in Drosophila muscle or neuronal tissue prevented accumulation of protein aggregates throughout the organism, however overexpression of WT GCase in midgut and fat body did not significantly reduce protein aggregation in the brain. These discrepancies could be due to tissue-specific biogenesis of EVs, which could depend on factors such as metabolic rate or endovesicular trafficking. Although dGba1b is expressed in all tissues, a second homologue of human GBA1, dGba1a, is expressed only in the midgut. Gba1b mutants retain ~25% expression of dGba1a. Deficiency of dGba1a was found to extend lifespan and does not result in significant accumulation of GlcCer, suggesting that there can be significant tissue-specific differences in function for GCase that could influence EV biogenesis (Jewett, 2021).
The unexpected results from perturbation of EV biogenesis suggest that the EV-mediated regulation of protein aggregation is tissue-specific and complex. Because an increase in EV-intrinsic proteins and alteration of protein cargo were observed in Gba1b mutants, it is anticipated that genetic perturbations decreasing the biogenesis of EVs might rescue protein aggregation non-cell-autonomously by reducing the production of dysregulated EVs. However, decreased expression of ESCRT-independent nSMase in muscle did not rescue protein aggregation in heads, suggesting that a tissue-specific decrease in biogenesis of dysregulated EVs is not sufficient to reduce protein aggregation in the rest of the organism, and the cargo of EVs may need to be corrected to reduce spread of protein aggregation. In contrast, decreased expression of nSMase in the nervous system had no effect on protein aggregation in the head. This difference in outcome in perturbation of EV biogenesis in muscle and neurons could be due to cell-specific compensatory mechanisms or intrinsic metabolic demands and solicits further investigation (Jewett, 2021).
A possible explanation for why decreased muscle expression of nSMase enhanced cell-autonomous protein aggregation and EV protein cargo alterations is that both GCase and nSMase enzymatically produce Cer. If GCase-deficient phenotypes are dependent on a relative reduction in Cer, decreased nSMase expression could exacerbate Gba1b mutant phenotypes. Indeed, lipidomic analysis of alterations in Cer metabolism due to nSMase knockdown revealed a further decrease in a subset of Cer species that were already significantly decreased in Gba1b mutants compared to controls. The further reduction in Cer species due to nSMase knockdown correlates with enhancement of cell-autonomous protein aggregation and EV cargo alterations, suggesting that accelerated protein aggregation in Gba1b mutants is mediated by Cer deficiency rather than GlcCer accumulation, as nSMase knockdown had a much more modest effect on the significantly increased levels of GlcCer species in Gba1b mutants compared to controls (Jewett, 2021).
Cer has been implicated in the composition and biogenesis of EVs, and nSMase knockdown further altered EV cargo in Gba1b mutants, suggesting that decreased Cer levels may directly influence EV biogenesis in Gba1b mutants. However, Cer species were not globally decreased, suggesting that the regulation of Cer metabolism is complex and may be more dependent on specific Cer species. Interestingly, only 1 of the 9 Cer species significantly increased in Gba1b mutants versus controls had a monounsaturated fatty acyl group, while all 5 of the Cer species significantly decreased in Gba1b mutants versus controls had a monounsaturated fatty acyl group, suggesting GBA influences the metabolism of specific subset of Cer species that may be implicated in Gba1b mutant phenotypes. This subset of Cer species is enriched in species with long chain monounsaturated fatty acyl chains. Interestingly, lipids with monounsaturated fatty acyl groups are an abundant component in mammalian exosome membranes. Investigating the alterations in lipid composition of EVs resulting from GCase deficiency and nSMase knockdown will be important in elucidating the role of Cer metabolism in Gba1b mutant phenotypes (Jewett, 2021).
This work suggests that GCase deficiency influences EV biogenesis to promote faster propagation of pathogenic protein aggregates throughout the tissues of an organism, which may be a compensatory response to cell-autonomous lysosomal stress. In the initial characterization of the Drosophila GBA-deficient model, accelerated insoluble ubiquitinated protein aggregates, accumulation of Ref(2)P, and oligomerization of ectopically expressed human α-synuclein in was found Gba1b mutants, suggesting an impairment in lysosomal degradation. A similar GBA-deficient Drosophila model also found evidence of lysosomal dysfunction, including enlarged lysosomes in GBA-deficient brains. However, proteomic analysis of Gba1b mutants did not support a profound impairment in autophagy, but instead suggested dysregulation of EVs with altered protein cargo which could be suppressed locally with knockdown of genes encoding ESCRT machinery important for EV biogenesis. Based on these results, it is believed that the initial observations of increased insoluble ubiquitinated proteins and Ref(2)P in Gba1b mutants are due to lysosomal stress. One possible explanation for the proteomic findings is that there may be a compensatory increase in EV biogenesis and packaging of autophagy substrates within EVs for discard outside of the cell in Gba1b mutants. Such an increase may have prevented detection od defects in autophagy. Upregulation of EV biogenesis may be cell-autonomously neuroprotective in the setting of lysosomal stress, particularly in aggregation-prone neurodegenerative diseases such as PD. It was recently demonstrated in a human neuronal cell culture model of PD that inhibiting macroautophagy protects against α-synuclein-induced cell death by promoting the release of α-synuclein-containing EVs. However, it remains possible that upregulating EV biogenesis may relieve lysosomal stress within cells containing aggregate-prone proteins, while simultaneously promoting the spread of protein aggregates between cells and throughout the organism (Jewett, 2021).
This work suggests a novel mechanism for GBA in reducing the spread of pathogenic protein aggregation from cell-to-cell via regulation of EV protein cargo, but many key questions remain. To better understand the progression of neurodegenerative diseases, it is important to uncover the mechanisms by which GCase deficiency alters EV protein content and biogenesis, identify the specific changes in EVs facilitating propagation of pathogenic protein aggregates, and determine how these changes influence recipient cells internalizing dysregulated EVs. GCase is a critical enzyme in ceramide metabolism, hydrolyzing glucosylceramide into glucose and ceramide. Ceramides are a key component of EV membranes, and alterations in ceramide metabolism due to GCase deficiency may directly influence EV biogenesis and protein cargo trafficked via EVs. Further studies using this Drosophila model and mammalian cell culture models should better elucidate how GCase deficiency alters the protein cargo of EVs to induce propagation of pathogenic protein aggregates, as well as whether endogenous GCase is enzymatically functional when trafficked to distant tissues via EVs. Understanding this mechanism could have broad implications in understanding the pathogenesis of aggregate-prone neurodegenerative diseases and reveal new therapeutic targets to slow or halt disease progression (Jewett, 2021).
O'Hanlon, M. E., Tweedy, C., Scialo, F., Bass, R., Sanz, A. and Smulders-Srinivasan, T. K. (2022). Mitochondrial electron transport chain defects modify Parkinson's disease phenotypes in a Drosophila model. Neurobiol Dis 171: 105803. PubMed ID: 35764292
Abstract Xue, J., Zhu, Y., Wei, L., Huang, H., Li, G., Huang, W., Zhu, H. and Duan, R. (2022). Loss of Drosophila NUS1 results in cholesterol accumulation and Parkinson's disease-related neurodegeneration. Faseb j 36(7): e22411. PubMed ID: 35695805
Abstract NgBR is the Nogo-B receptor, encoded by NUS1 gene. As NgBR contains a C-terminal domain that is similar to cis-isoprenyltransferase (cis-IPTase), NgBR was speculated to stabilize nascent Niemann-Pick type C 2 (NPC2) to facilitate cholesterol transport out of lysosomes. Mutations in the NUS1 were known as risk factors for Parkinson's disease (PD). In a previous study, it was shown that knockdown of Drosophila NUS1 orthologous gene tango14 causes decreased climbing ability, loss of dopaminergic neurons, and decreased dopamine contents. In this study, tango14 mutant flies were generated with a mutation in the C-terminal enzyme activity region using CRISPR/Cas9. tango14 mutant showed a reduced lifespan with locomotive defects and cholesterol accumulation in Malpighian tubules and brains, especially in dopaminergic neurons. Multilamellar bodies were found in tango14 mutants using electron microscopy. Neurodegenerative-related brain vacuolization was also detected in tango14 knockdown flies in an age-dependent manner. In addition, tango14 knockdown increased α-synuclein (α-syn) neurotoxicity in α-syn-overexpressing flies, with decreased locomotive activities, dopamine contents, and the numbers of dopaminergic neurons in aging flies. Thus, these observations suggest a role of NUS1, the ortholog of tango14, in PD-related pathogenesis.
Neves, P. F. R., Milanesi, B. B., Paz, L. V., de Miranda Monteiro, V. A. C., Neves, L. T., da Veiga, L. C., da Silva, R. B., Sulzbach, J. H., Knijkik, G. P., de Revoredo Ribeiro, E. C., de Souza Silva, E. L., Vieira, M. Q., Bagatini, P. B., Wieck, A., Mestriner, R. G. and Xavier, L. L. (2022). Age-related tolerance to paraquat-induced parkinsonism in Drosophila melanogaster. Toxicol Lett 361: 43-53. PubMed ID: 35367327
Abstract Paraquat (PQ) is a widely used herbicide that can cross the dopaminergic neuronal membrane, accumulate in mitochondria and damage complex I of the electron transport chain, leading to neuronal death. In Drosophila melanogaster, PQ exposure leads to the development of parkinsonism and is a classical model for studying Parkinson's Disease (PD). Muscle mitochondrial dysfunction, affecting survival and locomotion, is described in familial PD in D. melanogaster mutants. However, no study has shown the effects of PQ-induced parkinsonism in D. melanogaster regarding muscle ultrastructure and locomotor behavior at different ages. Thus, this study evaluated survival, locomotion, and morphological parameters of mitochondria and myofibrils using transmission electron microscopy in 2 and 15-day-old D. melanogaster, treated with different PQ doses: control, 10, 50, 100, 150, and 200 mM. PQ100mM presented 100% lethality in 15-day-old D. melanogaster, while in 2-day-old animals PQ150mM produced 20% lethality. Bradykinesia was only observed in 15-day-old D. melanogaster treated with PQ10 mM and PQ50 mM. However, these results are unlikely to be associated with changes to morphology. Taken together, these data indicate pathophysiological differences between PQ-induced parkinsonism and familial parkinsonism in D. melanogaster (resultant from gene mutations), demonstrating for the first time a differential susceptibility to PQ in two developmental stages.
O'Hanlon, M. E., Tweedy, C., Scialo, F., Bass, R., Sanz, A. and Smulders-Srinivasan, T. K. (2022). Mitochondrial electron transport chain defects modify Parkinson's disease phenotypes in a Drosophila model. Faseb j 36(8): e22432. Neurobiol Dis 171: 105803. PubMed ID: 35764292
Abstract Mitochondrial defects have been implicated in Parkinson's disease (PD) More evidence of mitochondrial involvement arose when many of the genes whose mutations caused inherited PD were discovered to be subcellularly localized to mitochondria or have mitochondrial functions. The aim of this study was to better understand mitochondrial dysfunction in PD by evaluating mitochondrial respiratory complex mutations in a Drosophila model of PD. This study conducted a targeted heterozygous enhancer/suppressor screen using Drosophila mutations within mitochondrial electron transport chain (ETC) genes against a null PD mutation in parkin. The interactions were assessed by climbing assays at 2-5 days as an indicator of motor function. A strong enhancer mutation in COX5A was examined further for L-dopa rescue, oxygen consumption, mitochondrial content, and reactive oxygen species. A later timepoint of 16-20 days was also investigated for both COX5A and a suppressor mutation in cyclope. Mutations in individual genes for subunits within the mitochondrial respiratory complexes were found to have interactions with parkin, while others do not, irrespective of complex. One intriguing mutation in a complex IV subunit (cyclope) shows a suppressor rescue effect at early time points, improving the gross motor defects caused by the PD mutation, providing a strong candidate for drug discovery. Most mutations, however, show varying degrees of enhancement or slight suppression of the PD phenotypes. Thus, individual mitochondrial mutations within different oxidative phosphorylation complexes have different interactions with PD with regard to degree and direction. Upon further investigation of the strongest enhancer (COX5A), the mechanism by which these interactions occur initially does not appear to be based on defects in ATP production, but rather may be related to increased levels of reactive oxygen species. This work highlights some key subunits potentially involved in mechanisms underlying PD pathogenesis, implicating ETC complexes other than complex I in PD.
Fevga, C., Tesson, C., Mascaro, A. C., ..., Mandemakers, W., Brice, A. and Bonifati, V. (2022). PTPA variants and impaired PP2A activity in early-onset parkinsonism with intellectual disability. Brain. PubMed ID: 36073231 Abstract The protein phosphatase 2A complex (PP2A), the major Ser/Thr phosphatase in the brain, is involved in a number of signaling pathways and functions, including the regulation of crucial proteins for neurodegeneration, such as alpha-synuclein, tau, and LRRK2. This study reports the identification of variants in the PTPA/PPP2R4 gene, encoding a major PP2A activator, in two families with early-onset parkinsonism and intellectual disability. Functional studies were performed on the disease-associated variants in cultured cells and knock-down of ptpa in Drosophila melanogaster. A homozygous PTPA variant, c.893T > G (p.Met298Arg), was identified in patients from a South African family with early-onset parkinsonism and intellectual disability. Screening of a large series of additional families yielded a second homozygous variant, c.512C > A (p.Ala171Asp), was identified in a Libyan family with a similar phenotype. Both variants co-segregate with disease in the respective families. The affected subjects display juvenile-onset parkinsonism and intellectual disability. The motor symptoms were responsive to treatment with levodopa and deep brain stimulation of the subthalamic nucleus. In overexpression studies, both the PTPA p.Ala171Asp and p.Met298Arg variants were associated with decreased PTPA RNA stability and decreased PTPA protein levels; the p.Ala171Asp variant additionally displayed decreased PTPA protein stability. Crucially, expression of both variants was associated with decreased PP2A complex levels and impaired PP2A phosphatase activation. PTPA ortholog knock-down in Drosophila neurons induced a significant impairment of locomotion in the climbing test. This defect was age-dependent and fully reversed by L-DOPA treatment. It is conclude that bi-allelic missense PTPA variants associated with impaired activation of the PP2A phosphatase cause autosomal recessive early-onset parkinsonism with intellectual disability. Thee findings might also provide new insights for understanding the role of the PP2A complex in the pathogenesis of more common forms of neurodegeneration.
Zhou, Z. D., Saw, W. T., Ho, P. G. H., Zhang, Z. W., Zeng, L., Chang, Y. Y., Sun, A. X. Y., Ma, D. R., Wang, H. Y., Zhou, L., Lim, K. L. and Tan, E. K. (2022). The role of tyrosine hydroxylase-dopamine pathway in Parkinson's disease pathogenesis. Cell Mol Life Sci 79(12): 599. PubMed ID: 36409355
Abstract Parkinson's disease (PD) is characterized by selective and progressive dopamine (DA) neuron loss in the substantia nigra and other brain regions, with the presence of Lewy body formation. Most PD cases are sporadic, whereas monogenic forms of PD have been linked to multiple genes, including Leucine kinase repeat 2 (LRRK2) and PTEN-induced kinase 1 (PINK1), two protein kinase genes involved in multiple signaling pathways. There is increasing evidence to suggest that endogenous DA and DA-dependent neurodegeneration have a pathophysiologic role in sporadic and familial PD. This study generated patient-derived dopaminergic neurons and human midbrain-like organoids (hMLOs), transgenic (TG) mouse and Drosophila models, expressing both mutant and wild-type (WT) LRRK2 and PINK1. Using these models,the effect of LRRK2 and PINK1 on tyrosine hydroxylase (TH)-DA pathway was studied. PD-linked LRRK2 mutations were able to modulate TH-DA pathway, resulting in up-regulation of DA early in the disease which subsequently led to neurodegeneration. The LRRK2-induced DA toxicity and degeneration were abrogated by wild-type (WT) PINK1 (but not PINK1 mutations), and early treatment with a clinical-grade drug, α-methyl-L-tyrosine (α-MT), a TH inhibitor, was able to reverse the pathologies in human neurons and TG Drosophila models. Opposing effects between LRRK2 and PINK1 on TH expression were also identified, suggesting that functional balance between these two genes may regulate the TH-DA pathway. These findings highlight the vital role of the TH-DA pathway in PD pathogenesis. LRRK2 and PINK1 have opposing effects on the TH-DA pathway, and its balance affects DA neuron survival. LRRK2 or PINK1 mutations can disrupt this balance, promoting DA neuron demise. These findings provide support for potential clinical trials using TH-DA pathway inhibitors in early or prodromic PD.
Tibashailwa, N., Stephano, F., Shadrack, D. M., Munissi, J. J. E. and Nyandoro, S. S. (2022). Neuroprotective potential of cinnamoyl derivatives against Parkinson's disease indicators in Drosophila melanogaster and in silico models. Neurotoxicology. PubMed ID: 36410467
Abstract Parkinson's disease (PD) is a movement disorder resulting from the loss of dopaminergic neurons over time. While there is no cure for PD, available conventional therapies aid to manage the motor symptoms. Natural products (NPs) derived from plants are among the most potent alternative therapies for PD. This study explored the neuroprotective potential of selected cinnamoyl derivatives namely toussaintine A (1), E-toussaintine E (2), asperphenamate (3) and julocrotine (4) against PD indicators using rotenone-challenged Drosophila melanogaster and in silico models. The compounds were first assessed for their toxicity preceding treatment experiments. Adult flies (aged 1-4 days) were exposed to varying concentrations of the compounds for 7 days. During the experiment, the mortality of flies was observed, and the lethal concentration (LC(50)) of each tested compound was determined. The LC(50) values were found to be 50.1, 55.6, 513.5, and 101.0μM for compounds 1, 2, 3, and 4, respectively. For seven days, flies were exposed to 500μM of rotenone and co-fed with a chosen dose of 40μM of each test compound in the diet. Using a negative geotaxis test, rotenone-challenged flies exhibited compromised climbing ability in comparison to control flies, the condition that was reversed by the action of studied compounds. Rotenone exposure also elevated malondialdehyde levels in the brain tissues, as measured by lipid peroxidation, when compared to control flies. In flies exposed to rotenone and co-fed with the compounds, this effect was lessened. In flies exposed to rotenone, mRNA levels of antioxidant enzymes such as superoxide dismutase and catalase were raised but were normalized in flies treated with the investigated compounds. Moreover, in-silico studies examined the inhibitory ability of compounds 1 - 4 against selected PD molecular targets, revealing the strong power of toussaintine A (1) against Adenosine receptor 2 (A2AR) and monoamine oxidase B. Thus, theser findings suggest that cinnamoyl derivatives have neuroprotective potential via reducing the oxidative burden and improving locomotor ability after toxin invectives. In particular, compound 1 at lower doses can simultaneously be a potential inhibitor of A2AR and an anti-oxidative mediator in the development of anti-PD agents.
Inoshita, T., Liu, J. Y., Taniguchi, D., Ishii, R., Shiba-Fukushima, K., Hattori, N. and Imai, Y. (2022). Parkinson disease-associated Leucine-rich repeat kinase regulates UNC-104-dependent axonal transport of Arl8-positive vesicles in Drosophila. iScience 25(12): 105476. PubMed ID: 36404922
Abstract Some Parkinson's disease (PD)-causative/risk genes, including the PD-associated kinase leucine-rich repeat kinase 2 (LRRK2), are involved in membrane dynamics. Although LRRK2 and other PD-associated genes are believed to regulate synaptic functions, axonal transport, and endolysosomal activity, it remains unclear whether a common pathological pathway exists. This study reports that the loss of Lrrk, an ortholog of human LRRK2, leads to the accumulation of the lysosome-related organelle regulator, Arl8 along with dense core vesicles at the most distal boutons of the neuron terminals in Drosophila. Moreover, the inactivation of a small GTPase Rab3 and altered Auxilin activity phenocopied Arl8 accumulation. The accumulation of Arl8-positive vesicles is UNC-104-dependent and modulated by PD-associated genes, Auxilin, VPS35, RME-8, and INPP5F, indicating that VPS35, RME-8, and INPP5F are upstream regulators of Lrrk. These results indicate that certain PD-related genes, along with LRRK2, drive precise neuroaxonal transport of dense core vesicles.
Liu, W., Lim, K. L. and Tan, E. K. (2022). Intestine-derived α-synuclein initiates and aggravates pathogenesis of Parkinson's disease in Drosophila. Transl Neurodegener 11(1): 44. PubMed ID: 36253844 Abstract
Aberrant aggregation of α-synuclein (α-syn) is a key pathological feature of Parkinson's disease (PD), but the precise role of intestinal α-syn in the progression of PD is unclear. In a number of genetic Drosophila models of PD, α-syn was frequently ectopically expressed in the neural system to investigate the pathobiology. This study investigated the potential role of intestinal α-syn in PD pathogenesis using a Drosophila model. Human α-syn was overexpressed in Drosophila guts, and life span, survival, immunofluorescence and climbing were evaluated. Immunofluorescence, Western blotting and reactive oxygen species (ROS) staining were performed to assess the effects of intestinal α-syn on intestinal dysplasia. High-throughput RNA and 16S rRNA gene sequencing, quantitative RT-PCR, immunofluorescence, and ROS staining were performed to determine the underlying molecular mechanism. It was found that the midgut α-syn alone recapitulated many phenotypic and pathological features of PD, including impaired life span, loss of dopaminergic neurons, and progressive motor defects. The intestine-derived α-syn disrupted intestinal homeostasis and accelerated the onset of intestinal ageing. Moreover, intestinal expression of α-syn induced dysbiosis, while microbiome depletion was efficient to restore intestinal homeostasis and ameliorate the progression of PD. Intestinal α-syn triggered ROS, and eventually led to the activation of the dual oxidase (DUOX)-ROS-Jun N-terminal Kinase (JNK) pathway. In addition, α-syn from both the gut and the brain synergized to accelerate the progression of PD. The intestinal expression of α-syn recapitulates many phenotypic and pathologic features of PD, and induces dysbiosis that aggravates the pathology through the DUOX-ROS-JNK pathway in Drosophila. These findings provide new insights into the role of intestinal α-syn in PD pathophysiology (Liu, 2022).
Ayajuddin, M., Phom, L., Koza, Z., Modi, P., Das, A., Chaurasia, R., Thepa, A., Jamir, N., Neikha, K. and Yenisetti, S. C. (2022). Adult health and transition stage-specific rotenone-mediated Drosophila model of Parkinson's disease: Impact on late-onset neurodegenerative disease models. Front Mol Neurosci 15: 896183. PubMed ID: 36017079
Abstract Parkinson's disease (PD) affects almost 1% of the population worldwide over the age of 50 years. Exposure to environmental toxins like paraquat and rotenone is a risk factor for sporadic PD which constitutes 95% of total cases. Herbicide rotenone has been shown to cause Parkinsonian symptoms in multiple animal models. Drosophila is an excellent model organism for studying neurodegenerative diseases (NDD) including PD. The aging process is characterized by differential expression of genes during different life stages. Hence it is necessary to develop life-stage-matched animal models for late-onset human disease(s) such as PD. Such animal models are critical for understanding the pathophysiology of age-related disease progression and important to understand if a genotropic drug/nutraceutical can be effective during late stages. With this idea, an adult life stage-specific (health and transition phase, during which late-onset NDDs such as PD sets in) rotenone-mediated Drosophila model of idiopathic PD was developed. Drosophila is susceptible to rotenone in dose-time dependent manner. Rotenone-mediated fly model of sporadic PD exhibits mobility defects (independent of mortality), inhibited mitochondrial complex I activity, dopaminergic (DAergic) neuronal dysfunction (no loss of DAergic neuronal number; however, reduction in rate-limiting enzyme tyrosine hydroxylase (TH) synthesis), and alteration in levels of dopamine (DA) and its metabolites; 3,4-Dihydroxyphenylacetic acid (DOPAC) and Homovanilic acid (HVA) in brain-specific fashion. These PD-linked behaviors and brain-specific phenotypes denote the robustness of the present fly model of PD. This novel model will be of great help to decipher life stage-specific genetic targets of small molecule mediated DAergic neuroprotection; understanding of which is critical for formulating therapeutic strategies for PD.
Rai, P. and Roy, J. K. (2022). Rab11 regulates mitophagy signaling pathway of Parkin and Pink1 in the Drosophila model of Parkinson's disease. Biochem Biophys Res Commun 626: 175-186. PubMed ID: 35994827
Abstract Parkinson's disease (PD) is a common neurodegenerative disorder caused by the loss of dopaminergic neurons in the substantia nigra. The pathophysiology of this disease is the formation of the Lewy body, mostly consisting of alpha-synuclein and dysfunctional mitochondria. There are two common PD-associated genes, Pink1 (encoding a mitochondrial ser/thr kinase) and Parkin (encoding cytosolic E3-ubiquitin ligase), involved in the mitochondrial quality control pathway. They assist in removing damaged mitochondria via selective autophagy (mitophagy) which if unchecked, results in the formation of protein aggregates in the cytoplasm. The role of Rab11, a small Ras-like GTPase associated with recycling endosomes, in PD is still unclear. The present study used the PD model of Drosophila melanogaster and found that Rab11 has a crucial role in the regulation of mitochondrial quality control and endo-lysosomal pathways in association with Parkin and Pink1 and Rab11 acting downstream of Parkin. Additionally, overexpression of Rab11 in parkin mutant rescued the mitochondrial impairment, suggesting the therapeutic potential of Rab11 in PD pathogenesis.
Sanz, F. J., Solana-Manrique, C., Lilao-Garzon, J., Brito-Casillas, Y., Muñoz-Descalzo, S. and Paricio, N. (2022). Exploring the link between Parkinson's disease and type 2 diabetes mellitus in Drosophila. Faseb j 36(8): e22432. PubMed ID: 35766235
Abstract Parkinson's disease (PD) is the second most common neurodegenerative disease. Diabetes mellitus (DM) is a metabolic disease characterized by high levels of glucose in blood. Recent epidemiological studies have highlighted the link between both diseases; it is even considered that DM might be a risk factor for PD. To further investigate the likely relation of these diseases, a Drosophila PD model was used based on inactivation of the DJ-1β gene (ortholog of human DJ-1), and diet-induced Drosophila and mouse type 2 DM (T2DM) models, together with human neuron-like cells. T2DM models were obtained by feeding flies with a high sugar-containing medium, and mice with a high fat diet. The results showed that both fly models exhibit common phenotypes such as alterations in carbohydrate homeostasis, mitochondrial dysfunction or motor defects, among others. In addition, it was demonstrated that T2DM might be a risk factor of developing PD since the diet-induced fly and mouse T2DM models present DA neuron dysfunction, a hallmark of PD. This study also confirmed that neurodegeneration is caused by increased glucose levels, which has detrimental effects in human neuron-like cells by triggering apoptosis and leading to cell death. Besides, the observed phenotypes were exacerbated in DJ-1β mutants cultured in the high sugar medium, indicating that DJ-1 might have a role in carbohydrate homeostasis. Finally, it was confirmed that metformin, an antidiabetic drug, is a potential candidate for PD treatment and that it could prevent PD onset in T2DM model flies. This result supports antidiabetic compounds as promising PD therapeutics.
Fellgett, A., Middleton, C. A., Munns, J., Ugbode, C., Jaciuch, D., Wilson, L., Chawla, S. and Elliott, C. J. H. (2021). Multiple Pathways of LRRK2-G2019S/Rab10 Interaction in Dopaminergic Neurons. J Parkinsons Dis. PubMed ID: 34250948
Abstract Inherited mutations in the LRRK2 protein are the common causes of Parkinson's disease, but the mechanisms by which increased kinase activity of mutant LRRK2 leads to pathological events remain to be determined. In vitro assays (heterologous cell culture, phospho-protein mass spectrometry) suggest that several Rab proteins might be directly phosphorylated by LRRK2-G2019S. An in vivo screen of Rab expression in dopaminergic neurons in young adult Drosophila demonstrated a strong genetic interaction between LRRK2-G2019S and Rab10. To determine if Rab10 is necessary for LRRK2-induced pathophysiological responses in the neurons that control movement, vision, circadian activity, and memory. These four systems were chosen because they are modulated by dopaminergic neurons in both humans and flies. LRRK2-G2019S was expressed in Drosophila dopaminergic neurons and the effects of Rab10 depletion on Proboscis Extension, retinal neurophysiology, circadian activity pattern ('sleep'), and courtship memory determined in aged flies. Rab10 loss-of-function rescued LRRK2-G2019S induced bradykinesia and retinal signaling deficits. Rab10 knock-down, however, did not rescue the marked sleep phenotype which results from dopaminergic LRRK2-G2019S. Courtship memory is not affected by LRRK2, but is markedly improved by Rab10 depletion. Anatomically, both LRRK2-G2019S and Rab10 are seen in the cytoplasm and at the synaptic endings of dopaminergic neurons. It is concluded that, in Drosophila dopaminergic neurons, Rab10 is involved in some, but not all, LRRK2-induced behavioral deficits. Therefore, variations in Rab expression may contribute to susceptibility of different dopaminergic nuclei to neurodegeneration seen in people with Parkinson's disease (Fellgett, 2021).
Pallos, J., Jeng, S., McWeeney, S. and Martin, I. (2015). Dopamine neuron-specific LRRK2 G2019S effects on gene expression revealed by translatome profiling. Neurobiol Dis: 105390. PubMed ID: 33984508
Abstract Leucine-rich repeat kinase 2 (LRRK2) mutations are the most common genetic cause of late-onset autosomal dominant Parkinson's disease. The pathogenic G2019S mutation enhances LRRK2 kinase activity and induces neurodegeneration in C. elegans, Drosophila and rodent models through unclear mechanisms. Gene expression profiling has the potential to provide detailed insight into the biological pathways modulated by LRRK2 kinase activity in vivo. Prior studies have surveyed the effects of LRRK2 G2019S on genome-wide mRNA expression in complex brain tissues with high cellular heterogeneity, limiting their power to detect more restricted gene expression changes occurring in a cell type-specific manner. This study used translating ribosome affinity purification (TRAP) coupled to RNA-seq to profile dopamine neuron-specific gene expression changes caused by LRRK2 G2019S in the Drosophila CNS. A modest number of genes were differentially expressed in the presence of mutant LRRK2 that represent a broad range of molecular functions including DNA repair (RfC3), mRNA metabolism and translation (Ddx1 and lin-28), calcium homeostasis (MCU), and other categories (Ugt37c1, disp, l(1)G0196, CG6602, CG1126 and CG11068). Further analysis on a subset of these genes revealed that LRRK2 G2019S did not alter their expression across the whole brain, consistent with dopamine neuron-specific effects uncovered by the TRAP approach that may offer insight into the neurodegenerative process. This is the first study to profile the effects of LRRK2 G2019S on DA neuron gene expression in vivo. Beyond providing a set of differentially expressed gene candidates relevant to LRRK2, this study demonstrates the effective use of TRAP to perform high-resolution assessment of dopamine neuron gene expression for the study of PD (Pallos, 2021).
Sen, A., Kalvakuri, S., Bodmer, R. and Cox, R. T. (2015). Clueless, a protein required for mitochondrial function, interacts with the PINK1-Parkin complex in Drosophila. Dis Model Mech 8: 577-589. PubMed ID: 26035866
Abstract Loss of mitochondrial function often leads to neurodegeneration and is thought to be one of the underlying causes of neurodegenerative diseases such as Parkinson's disease. However, the precise events linking mitochondrial dysfunction to neuronal death remain elusive. PTEN-induced putative kinase 1 (PINK1) and Parkin (Park), either of which, when mutated, are responsible for early-onset PD, mark individual mitochondria for destruction at the mitochondrial outer membrane. The specific molecular pathways that regulate signaling between the nucleus and mitochondria to sense mitochondrial dysfunction under normal physiological conditions are not well understood. This study shows that Drosophila Clueless (Clu), a highly conserved protein required for normal mitochondrial function, can associate with Translocase of the outer membrane (TOM) 20, Porin and PINK1, and is thus located at the mitochondrial outer membrane. Previous studies have found that clu genetically interacts with park in Drosophila female germ cells. This study shows that clu also genetically interacts with PINK1, and epistasis analysis places clu downstream of PINK1 and upstream of park. In addition, Clu forms a complex with PINK1 and Park, further supporting that Clu links mitochondrial function with the PINK1-Park pathway. Lack of Clu causes PINK1 and Park to interact with each other, and clu mutants have decreased mitochondrial protein levels, suggesting that Clu can act as a negative regulator of the PINK1-Park pathway. Taken together, these results suggest that Clu directly modulates mitochondrial function, and that Clu's function contributes to the PINK1-Park pathway of mitochondrial quality control (Sen, 2015).
Discussion Mitochondrial function is intimately linked to cellular health. These organelles provide the majority of ATP for the cell in addition to being the sites for major metabolic pathways such as fatty acid β-oxidation and heme biosynthesis. In addition, mitochondria are crucial for apoptosis, and they can irreparably damage the cell via oxidation when their biochemistry is abnormally altered. Given these many roles, tissues and cell types with high energy demands, such as neurons, are particularly sensitive to changes in mitochondrial function. This is also true for germ cell mitochondria because mitochondria are inherited maternally from the egg's cytoplasm and are thus the sole source of energy for the newly developing embryo (Sen, 2015).
Mitochondrial biology is complex owing to the dynamic nature of the organelle and the fact that most of the proteins required for function are encoded in the nucleus. In addition to the metabolites they provide, mitochondria undergo regulated fission, fusion and transport along microtubules. Because mitochondria cannot be made de novo, and tend to accumulate oxidative damage due to their biochemistry, they are subject to organelle and protein quality-control measures that involve mitochondrial and cytoplasmic proteases, as well as a specialized organelle-specific autophagy called mitophagy. However, the specific molecular signaling pathways between the nucleus and mitochondria that are used to sense which individual mitochondria are damaged during normal cellular homeostasis in vivo are not well understood.
This study used the Drosophila ovary to identify genes regulating mitochondrial function and have characterized mitochondrial dynamics during Drosophila oogenesis. Germ cells contain large numbers of mitochondria that can be visualized at the single organelle level, making this system useful for studying genes that control mitochondrial function (Sen, 2015).
The gene clueless (clu) is crucial for mitochondrial localization in germ cells. Clu has homologs in many different species, and shows 53% amino acid identity to the human homolog, CLUH. The molecular role of Clu is not known. The yeast homolog, Clu1p, was found to interact with the eukaryotic initiation factor 3 (eIF3) complex in yeast and bind mRNA; however, the significance of this is not clear. CLUH has also been shown to bind mRNA. Flies mutant for clu are weak, uncoordinated, short-lived, and male and female sterile. Lack of Clu causes a sharp decrease in ATP, increased mitochondrial oxidative damage and changes in mitochondrial ultrastructure. Levels of Clu protein are homogeneously high in the cytoplasm and it is also found in large mitochondrially-associated particles. Although Clu clearly has an effect on mitochondria function, whether this is direct or indirect has not yet been established (Sen, 2015).
Parkin (Park), an E3 ubiquitin ligase, acts with PTEN-induced putative kinase 1 (PINK1) to target mitochondria for mitophagy. clu genetically interacts with park, and Clu particles are absent in park mutants, indicating that Clu might play a role in Park's mechanism. park and PINK1 have been identified as genes that, when mutated, cause early-onset forms of Parkinson's disease. Upon mitochondrial depolarization, PINK1 is stabilized on the mitochondrial outer membrane, recruiting Park, which then goes on to ubiquitinate many surface proteins, thus marking and targeting that mitochondrion for mitophagy. Before their biochemical interaction was recognized, PINK1 was placed upstream of park in a genetic pathway in Drosophila. Understanding Park and PINK1's role in mitochondrial quality control has shed light on the neurodegeneration underlying Parkinson's disease (Sen, 2015).
This study shows that Clu's mitochondrial role is well conserved, because the human homolog, CLUH, can rescue the fly mutant. Clu peripherally associates with mitochondria because it forms a complex with the mitochondrial outer-membrane proteins Porin and Translocase of the outer membrane (TOM) 20, supporting that the loss of mitochondrial function caused by lack of Clu is a direct effect. In addition, this study found that clu genetically interacts with PINK1 and, using epistasis, clu was placed upstream of park, but downstream of PINK1. Clu forms a complex with PINK1, and is able to interact with Park after the mitochondrial membrane potential is disrupted. Finally, lack of Clu causes PINK1 and Park to interact with each other, as well as causing a decrease in mitochondrial proteins, which suggests that Clu negatively regulates PINK1-Park function. Taken together, these data identify Clu as a mitochondrially-associated protein that plays a direct role in maintaining mitochondrial function and that binds TOM20, and support a role for Clu linking mitochondrial function to the PINK1-Park pathway (Sen, 2015).
Drosophila Clu is a large, highly conserved protein that shares its Clu and tetratricopeptide repeat (TPR) domains with its human homolog, CLUH. Expressing CLUH in flies that are mutant for clu rescues the mutant phenotypes; thus, the human protein can use the fly machinery to fulfill the role of Clu. To date, all the evidence supports the idea that Clu has a role in mitochondrial function; however, it has been unclear how direct it is. In this study, using IPs showed that Clu can associate with three proteins located on the mitochondrial outer membrane, TOM20, Porin and PINK1. Thus, Clu is not only a cytoplasmic protein, but can also be a peripherally associated mitochondrial protein, supporting the idea that this highly conserved protein directly affects mitochondrial function (Sen, 2015).
clu mutants share many phenotypes with park and PINK1 mutant flies, including flight muscle defects and sterility. Mitochondria are also mislocalized in PINK1 mutant germ cells, similarly to park mutants, and form large knotted clumps that include circularized mitochondria, which is consistent with increased fusion events. Mitochondria in clu mutant germ cells, on the other hand, do not show any signs of changes in fission or fusion. clu also genetically interacts with PINK1 and park, with double heterozygotes having clumped mitochondria in germ cells and a loss of Clu particles, and double knockdown of clu with PINK1 or park in flight muscle causing an increase in abnormal wing posture. Park functions in a pathway with PINK1 to elicit a mitophagic response, and overexpressing park can rescue PINK1 phenotypes in Drosophila. Using S2R+ cells and clu RNAi knockdown, this study found that overexpressing Park, but not PINK1, causes mitochondria to disperse. In adult flies, overexpressing full-length clu rescues the abnormal wing phenotype as well as mitochondrial phenotypes of PINK1 mutants, and overexpressing full-length clu or CLUH in PINK1, but not park, mutants rescues their thoracic indentation. These results place clu upstream of park, but downstream of PINK1. PINK1 stabilization on the mitochondrial outer membrane signals for Park to translocate to the organelle and subsequently ubiquitinate different proteins on the mitochondrial surface. Thus, it is somewhat surprising in Drosophila that loss of PINK1 can be rescued by increased amounts of Park, and suggests that there might be additional roles that Park plays in the cell. The data support the idea that an excess of Park overcomes deficits in mitochondrial function because it can rescue a loss of Clu as well. Mitochondrial clumping seems to be one of the responses to mitochondrial damage, in this system and in human tissue culture cells; thus, the dispersal upon Park overexpression in clu-RNAi-treated S2R+ cells is likely a sign of better mitochondrial health (Sen, 2015).
This study shows that Clu reciprocally immunoprecipitates with overexpressed PINK1 under normal cell culture conditions. PINK1 has been shown to directly bind TOM20, and Clu can also form a complex with TOM20, suggesting that all three proteins are found in close proximity at the mitochondrial membrane. Clu still immunoprecipitates with PINK1 when PINK1 is no longer targeted to the mitochondrial outer membrane (PINK1ΔMTS). This result indicates that Clu forms a complex with PINK1 independent of TOM20 or any other mitochondrial outer membrane proteins. Under normal conditions, PINK1 degradation happens so quickly that there are undetectable levels found at the outer mitochondrial membrane. Therefore, how is it possible that Clu is found in a complex with PINK1 in the absence of mitochondrial damage? It is likely that overexpressed PINK1 overwhelms the normal degradation process, thus becoming aberrantly stabilized at the outer mitochondrial membrane. Alternatively, it is possible that low levels of mitochondrial damage could account for the PINK1 being stabilized at the outer membrane, and then being able to interact with Clu (Sen, 2015).
Mitophagy ultimately leads to mitochondrial degradation in the lysosome. Currently, the literature involving Park and PINK1 uses mitochondrial protein levels as a read-out of mitophagy. However, recent data shows that different mitochondrial proteins have different half-lives, likely depending on what type of protein quality-control mechanism they use. Recent papers have examined protein half-life and found that Drosophila and yeast mitochondrial proteins, particularly those of Complex I in the case of flies, have increased half-lives when mitophagy proteins are missing. In addition, mitochondrial protein quality control does not always require destruction of the entire mitochondrion, but can selectively destroy certain proteins. For the mitochondrial proteins examined, all were greatly reduced in clu and PINK1 mutants, but not substantially altered in park mutants. This suggests that the turnover of the mitochondrial proteinsexamined is more sensitive to the absence of clu and PINK1 than park. This study found that Park and PINK1 form a complex in the absence of Clu. Thus, Clu is not necessary for this interaction, and loss of Clu causes a PINK1-Park interaction. This, plus the fact that Clu can be found at the outer mitochondrial membrane in a complex with both PINK1 and Park, suggests that Clu can influence mitochondrial quality or function, perhaps by regulating mitochondrial protein levels (Sen, 2015).
Yeast Clu1p was identified as a component of the eukaryotic initiation factor 3 (eIF3) complex and as an mRNA-binding protein. From IP and mass spectrometry data of the current study, there evidence that Clu can associate with the ribosome as well. Although CCCP is commonly used to force mitophagy and mitochondrial protein turnover, this treatment might not mimic the more subtle damage and changes mitochondria likely face in vivo. Mitochondrial protein import, for example, requires an intact mitochondrial membrane potential. Given the curent data, it is possible that Clu could function in co-translational import of proteins, as well as act as a sensor to couple PINK1-Park complex activation to how well protein import occurs. This would help explain why this study found that loss of Clu triggers a PINK1-Park interaction. In addition, Park and PINK1 directly interact with Porin and TOM20, respectively, placing them and Clu at the same place at the outer mitochondrial membrane. Recently, CLUH has been found to bind mRNAs for nuclear-encoded mitochondrial proteins, supporting a potential role in co-translational import. Further experiments are required to understand the precise relationship between Clu, TOM20, PINK1 and Park (Sen, 2015).
Mitochondria clearly undergo targeted destruction and require robust quality-control mechanisms, which are very active areas of investigation. PINK1 and Park's molecular mechanisms are particularly relevant to Parkinson's disease, given that inherited mutations in PARK2 and PINK1 can cause early-onset Parkinsonism. The molecular mechanisms that control mitophagy are becoming increasingly complex, involving membrane and cell biology; however, to date, the field has yet to visualize and understand the role of basal mitophagy levels in vivo. In the future, studying mitochondria and Clu function in Drosophila germ cells could lead to a better understand the role of mitochondrial protein turnover and quality control in the normal life cycle of tissues (Sen, 2015).
Ham, S. J., Lee, D., Xu, W. J., Cho, E., Choi, S., Min, S., Park, S. and Chung, J. (2021). (2021). Loss of UCHL1 rescues the defects related to Parkinson's disease by suppressing glycolysis. Sci Adv 7(28). PubMed ID: 34244144
The role of ubiquitin carboxyl-terminal hydrolase L1 (UCHL1; also called PARK5) in the pathogenesis of Parkinson's disease (PD) has been controversial. This study finds that the loss of UCHL1 destabilizes pyruvate kinase (PKM) and mitigates the PD-related phenotypes induced by PTEN-induced kinase 1 (PINK1) or Parkin loss-of-function mutations in Drosophila and mammalian cells. In UCHL1 knockout cells, cellular pyruvate production and ATP levels are diminished, and the activity of AMP-activated protein kinase (AMPK) is highly induced. Consequently, the activated AMPK promotes the mitophagy mediated by Unc-51-like kinase 1 (ULK1) and FUN14 domain-containing 1 (FUNDC1), which underlies the effects of UCHL1 deficiency in rescuing PD-related defects. Furthermore, this study identified tripartite motif-containing 63 (TRIM63) as a previously unknown E3 ligase of PKM and demonstrate its antagonistic interaction with UCHL1 to regulate PD-related pathologies. These results suggest that UCHL1 is an integrative factor for connecting glycolysis and PD pathology (Ham, 2021).
Inoue, E., Suzuki, T., Shimizu, Y., Sudo, K., Kawasaki, H. and Ishida, N. (2021). Saffron ameliorated motor symptoms, short life span and retinal degeneration in Parkinson's disease fly models. Gene 799: 145811. PubMed ID: 34224829
Parkinson's disease (PD) is a common neurodegenerative disorder with motor symptoms linked to the loss of dopaminergic neurons in the brain. α-Synuclein is an aggregation-prone neural protein that plays a role in the pathogenesis of PD. In a previous paper, it was found that saffron; the stigma of Crocus sativus Linne (Iridaceae), and its constituents (crocin and crocetin) suppressed aggregation of α-synuclein and promoted the dissociation of α-synuclein fibrils in vitro. This study investigated the effect of dietary saffron and its constituent, crocetin, in vivo on a fly PD model overexpressing several mutant α-synuclein in a tissue-specific manner. Saffron and crocetin significantly suppressed the decrease of climbing ability in the Drosophila overexpressing A30P (A30P fly PD model) or G51D (G51D fly PD model) mutated α-synuclein in neurons. Saffron and crocetin extended the life span in the G51D fly PD model. Saffron suppressed the rough-eyed phenotype and the dispersion of the size histogram of the ocular long axis in the eye of A30P fly PD model. Saffron had a cytoprotective effect on a human neuronal cell line with α-synuclein fibrils. These data showed that saffron and its constituent crocetin have protective effects on the progression of PD disease in animals in vivo and suggest that saffron and crocetin can be used to treat PD (Inoue, 2021).
Sarkar, S., Olsen, A. L., Sygnecka, K., Lohr, K. M. and Feany, M. B. (2021). alpha-synuclein impairs autophagosome maturation through abnormal actin stabilization. PLoS Genet 17(2): e1009359. PubMed ID: 33556113
Vesicular trafficking defects, particularly those in the autophagolysosomal system, have been strongly implicated in the pathogenesis of Parkinson's disease and related α-synucleinopathies. However, mechanisms mediating dysfunction of membrane trafficking remain incompletely understood. Using a Drosophila model of α-synuclein neurotoxicity with widespread and robust pathology, this study found that human α-synuclein expression impairs autophagic flux in aging adult neurons. Genetic destabilization of the actin cytoskeleton rescues F-actin accumulation, promotes autophagosome clearance, normalizes the autophagolysosomal system, and rescues neurotoxicity in α-synuclein transgenic animals through an Arp2/3 dependent mechanism. Similarly, mitophagosomes accumulate in human α-synuclein-expressing neurons, and reversal of excessive actin stabilization promotes both clearance of these abnormal mitochondria-containing organelles and rescue of mitochondrial dysfunction. These results suggest that Arp2/3 dependent actin cytoskeleton stabilization mediates autophagic and mitophagic dysfunction and implicate failure of autophagosome maturation as a pathological mechanism in Parkinson's disease and related α-synucleinopathies (Sarkar, 2021).
Reiszadeh S. J., Ramesh, S. R., Finkelstein, D. I. and Haddadi, M. (2020). alpha-Synuclein E46K Mutation and Involvement of Oxidative Stress in a Drosophila Model of Parkinson's Disease. Parkinsons Dis 2021: 6621507. PubMed ID: 34285796
Parkinson's disease (PD) is an age-associated neurodegenerative condition in which some genetic variants are known to increase disease susceptibility on interaction with environmental factors inducing oxidative stress. Different mutations in the SNCA gene (synuclein α) are reported as the major genetic contributors to PD. E46K mutation pathogenicity has not been investigated as intensive as other SNCA gene mutations including A30P and A53T. In this study, based on the GAL4-UAS binary genetic tool, transgenic Drosophila melanogaster flies expressing wild-type and E46K-mutated copies of the human SNCA gene were constructed. Overexpression of human α-synuclein in the central nervous system of these transgenic flies led to disorganized ommatidia structures and loss of dopaminergic neurons. E46K α-synuclein caused remarkable climbing defects, reduced survivorship, higher ethanol sensitivity, and increased PQ-mediated mortality. A noticeable decline in activity of catalase and superoxide dismutase enzymes besides considerable increase in the levels of lipid peroxidation and reactive oxygen species was observed in head capsule homogenates of α-synuclein-expressing flies, which indicates obvious involvement of oxidative stress as a causal factor in SNCA (E46K) neurotoxicity. In all the investigations, E46K copy of the SNCA gene was found to impose more severe defects when compared to wild-type SNCA. It can be concluded that the constructed Drosophila models developed PD-like symptoms that facilitate comparative studies of molecular and cellular pathways implicated in the pathogenicity of different α-synuclein mutations (Reiszadeh, 2021).
Sarkar, S., Murphy, M. A., Dammer, E. B., Olsen, A. L., Rangaraju, S., Fraenkel, E. and Feany, M. B. (2020). Comparative proteomic analysis highlights metabolic dysfunction in α-synucleinopathy. NPJ Parkinsons Dis 6(1): 40. PubMed ID: 33311497
The synaptic protein α-synuclein is linked through genetics and neuropathology to the pathogenesis of Parkinson's disease and related disorders. However, the mechanisms by which α-synuclein influences disease onset and progression are incompletely understood. To identify pathogenic pathways and therapeutic targets proteomic analysis was performed in a highly penetrant new Drosophila model of α-synucleinopathy. 476 significantly upregulated and 563 significantly downregulated proteins were identified in heads from α-synucleinopathy model flies compared to controls. Multiple complementary analyses was used to identify and prioritize genes and pathways within the large set of differentially expressed proteins for functional studies. Gene Ontology enrichment analysis was performed, the proteomic changes were integrated with human Parkinson's disease genetic studies, and the α-synucleinopathy proteome was compared with that of tauopathy model flies, which are relevant to Alzheimer's disease and related disorders. These approaches identified GTP cyclohydrolase (GCH1) and folate metabolism as candidate mediators of α-synuclein neurotoxicity. In functional validation studies, it was found that the knockdown of Drosophila Gch1 enhanced locomotor deficits in α-synuclein transgenic flies, while folate supplementation protected from α-synuclein toxicity. This integrative analysis suggested that mitochondrial dysfunction was a common downstream mediator of neurodegeneration. Accordingly, Gch1 knockdown enhanced metabolic dysfunction in α-synuclein transgenic fly brains while folate supplementation partially normalized brain bioenergetics. An integrative approach was outlined and implemented to identify and validate potential therapeutic pathways using comparative proteomics and genetics and capitalizing on the facile genetic and pharmacological tools available in Drosophila (Sarkar, 2020).
Liu, Q., Bautista-Gomez, J., Higgins, D. A., Yu, J. and Xiong, Y. (2021). Dysregulation of the AP2M1 phosphorylation cycle by LRRK2 impairs endocytosis and leads to dopaminergic neurodegeneration. Sci Signal 14(693). PubMed ID: 34315807
Mutations in the kinase LRRK2 and impaired endocytic trafficking are both implicated in the pathogenesis of Parkinson's disease (PD). Expression of the PD-associated LRRK2 mutant in mouse dopaminergic neurons was shown to disrupt clathrin-mediated endocytic trafficking. This study explored the molecular mechanism linking LRRK2 to endocytosis and found that LRRK2 bound to and phosphorylated the μ2 subunit of the adaptor protein AP2 (AP2M1), a core component of the clathrin-mediated endocytic machinery. Analysis of human SH-SY5Y cells and mouse neurons and tissues revealed that loss of LRRK2 abundance or kinase function resulted in decreased phosphorylation of AP2M1, which is required for the initial formation of clathrin-coated vesicles (CCVs). In contrast, overexpression of LRRK2 or expression of a Parkinson's disease-associated gain-of-function mutant LRRK2 (G2019S) inhibited the uncoating of AP2M1 from CCVs at later stages and prevented new cycles of CCV formation. Thus, the abundance and activity of LRRK2 must be calibrated to ensure proper endocytosis. Dysregulated phosphorylation of AP2M1 from the brain but not thyroid tissues of LRRK2 knockout and G2019S-knockin mice suggests a tissue-specific regulatory mechanism of endocytosis. Furthermore, this study found that LRRK2-dependent phosphorylation of AP2M1 mediated dopaminergic neurodegeneration in a Drosophila model of PD. Together, these findings provide a mechanistic link between LRRK2, AP2, and endocytosis in the pathogenesis of PD.
Xie, J., Chen, S., Bopassa, J. C. and Banerjee, S. (2021). Drosophila tubulin polymerization promoting protein mutants reveal pathological correlates relevant to human Parkinson's disease. Sci Rep. 11(1):13614. PubMed ID: 34193896
Parkinson's disease (PD) is a progressive neurodegenerative disorder with no known cure. PD is characterized by locomotion deficits, nigrostriatal dopaminergic neuronal loss, mitochondrial dysfunctions and formation of α-Synuclein aggregates. A well-conserved and less understood family of Tubulin Polymerization Promoting Proteins (TPPP) is also implicated in PD and related disorders, where TPPP exists in pathological aggregates in neurons in patient brains. However, there are no in vivo studies on mammalian TPPP to understand the genetics and neuropathology linking TPPP aggregation or neurotoxicity to PD. The only Drosophila homolog of human TPPP is named Ringmaker (Ringer). This study reports that adult ringer mutants display progressive locomotor disabilities, reduced lifespan and neurodegeneration. Importantly, the findings reveal that Ringer is associated with mitochondria and ringer mutants have mitochondrial structural damage and dysfunctions. Adult ringer mutants also display progressive loss of dopaminergic neurons. Together, these phenotypes of ringer mutants recapitulate some of the salient features of human PD patients, thus allowing utilization of ringer mutants as a fly model relevant to PD, and further exploration of its genetic and molecular underpinnings to gain insights into the role of human TPPP in PD (Xie, 2021)
Terriente-Felix, A., Wilson, E. L. and Whitworth, A. J. (2020). Drosophila phosphatidylinositol-4 kinase fwd promotes mitochondrial fission and can suppress Pink1/parkin phenotypes. PLoS Genet 16(10): e1008844. PubMed ID: 33085661
Balanced mitochondrial fission and fusion play an important role in shaping and distributing mitochondria, as well as contributing to mitochondrial homeostasis and adaptation to stress. In particular, mitochondrial fission is required to facilitate degradation of damaged or dysfunctional units via mitophagy. Two Parkinson's disease factors, PINK1 and Parkin, are considered key mediators of damage-induced mitophagy, and promoting mitochondrial fission is sufficient to suppress the pathological phenotypes in Drosophila Pink1/parkin mutants. Additional factors were sought that impinge on mitochondrial dynamics and which may also suppress Pink1/parkin phenotypes. The Drosophila phosphatidylinositol 4-kinase IIIβ homologue, Four wheel drive (Fwd), promotes mitochondrial fission downstream of the pro-fission factor Drp1. Previously described only as male sterile, this study identified several new phenotypes in fwd mutants, including locomotor deficits and shortened lifespan, which are accompanied by mitochondrial dysfunction. Finally, fwd overexpression can suppress locomotor deficits and mitochondrial disruption in Pink1/parkin mutants, consistent with its function in promoting mitochondrial fission. Together these results shed light on the complex mechanisms of mitochondrial fission and further underscore the potential of modulating mitochondrial fission/fusion dynamics in the context of neurodegeneration (Terriente-Felix, 2020).
Mitochondria are dynamic organelles that are transported to the extremities of the cell and frequently undergo fusion and fission events that influence their size, branching and degradation. Many of the core components of the mitochondrial fission and fusion machineries have been well characterised. There include the pro-fusion factors Mfn1/2 and Opa1, and pro-fission factors Drp1 and Mff. Maintaining an appropriate balance of fission and fusion, as well as transport dynamics, is crucial for cellular health and survival as mutations in many of the core components cause severe neurological conditions in humans and model organisms. Recently, a role for phosphatidylinositol 4-phosphate [PI(4)P] in mitochondrial fission has been elucidated in cultured cells (Nagashima, 2020; Science 367(6484): 1366-1371), but the in vivo consequences have not yet been described (Terriente-Felix, 2020).
The mitochondrial fission/fusion cycle has been linked to the selective removal of damaged mitochondria through the process of autophagy (termed mitophagy), in which defective mitochondria are engulfed into autophagosomes and degraded by lysosomes. Two genes that have been firmly linked to the mitophagy process are PINK1 and PRKN. Mutations in these genes cause autosomal-recessive juvenile parkinsonism, associated with degeneration of midbrain dopaminergic neurons and motor impairments, among other symptoms and pathologies. Studies from a wide variety of model systems have shown various degrees of mitochondrial dysfunction associated with mutation of PINK1/PRKN homologues including disrupted fission/fusion. Drosophila have proven to be a fruitful model for investigating the function of the conserved homologues Pink1 and parkin, with these mutants exhibiting robust mitochondrial disruption and neuromuscular phenotypes. Importantly, several studies have shown that the pathological consequences of loss of Pink1 or parkin can be largely suppressed by genetic manipulations that increase mitochondrial fission or reduce fusion (Terriente-Felix, 2020).
To identify genes involved in mitochondrial quality control and homeostasis, an RNAi screen was performed in Drosophila S2 cells to identify kinases and phosphatases that phenocopy or suppress hyperfused mitochondria caused by loss of Pink1 (Pogson, 2014). This study identified the phosphatidylinositol 4-kinase IIIβ homologue, four wheel drive (fwd), whose knockdown phenocopied Pink1 RNAi, resulting in excess mitochondrial fusion. Drosophila mutant for fwd have been reported to be viable but male sterile due to incomplete cytokinesis during spermatogenesis. While muscle-specific knockdown has shown to impact neuromuscular junction formation (Forrest, 2013), no other organismal phenotypes or mitochondrial involvement have been described to date. Thus, this study sought to better understand the role of Fwd in mitochondrial homeostasis (Terriente-Felix, 2020).
This study has characterised fwd mutants for organismal phenotypes associated with Pink1/parkindysfunction and analysed the impact on mitochondrial form and function. Genetic interactions were investigated between fwd and Pink1/parkin, as well as with mitochondrial fission/fusion factors. It was found that loss of fwd inhibited mitochondrial function, causing increased mitochondrial length and branching, and decreased respiratory capacity. These effects were associated with shortened lifespan and dramatically reduced locomotor ability, similar to Pink1 and parkin mutants. Furthermore, fwd overexpression was sufficient to significantly suppress Pink1/parkin mutant locomotor deficits and mitochondrial phenotypes. Interestingly, it was found that the mitochondrial and locomotion phenotypes in fwd mutants can be rescued by loss of pro-fusion factors Marf and Opa1, but the pro-fission activity of Drp1 appears to require fwd. These results support a role for fwd in regulating mitochondrial morphology, specifically in facilitating mitochondrial fission, and further substantiate the important contribution of aberrant mitochondrial fission/fusion dynamics in Pink1/parkinphenotypes (Terriente-Felix, 2020).
Previous work identified fwd as a gene whose knockdown induces mitochondrial hyperfusion in cultured cells, similar to loss of Pink1. This study has validated that the genetic loss or knockdown of fwd also causes excess mitochondrial fusion in neuronal cells in vivo, leading to increased mitochondrial length and branching. As mitochondrial fission/fusion dynamics have been shown to be important for mitochondrial homeostasis, it is not surprising that this also has an impact on respiration at the organismal level and on organismal fitness and vitality. While fwd mutants have mainly been characterised for their male sterility phenotype, this study describes new organismal phenotypes associated with loss of fwd: profound locomotor deficits and shortened lifespan. Interestingly, while the data reveal a stronger requirement for fwd in the nervous system compared to the musculature to maintain normal motor behaviour, fwd is required in muscle for neuromuscular junction formation. Furthermore, consistent with the observations on lifespan, Fwd overexpression has previously been shown to confer increased lifespan. Thus, Fwd clearly has a more widespread role in organismal vitality than previously appreciated (Terriente-Felix, 2020).
The robust locomotor phenotype allowed a test of the genetic relationship between fwd and core components of the mitochondrial fission/fusion machinery. Given the excess mitochondrial fusion upon loss of fwd, suppression of the organismal phenotypes by reduction of fusion factors Marf and Opa1 was expected. However, it was surprising that overexpression of the fission factor Drp1 was unable to ameliorate organismal phenotypes or even the increased mitochondrial length, though it was able to revert the increased branching caused by loss of fwd. These results suggested that Drp1 requires Fwd to drive mitochondrial fission. Consistent with this, Drp1 overexpression was no longer able to rescue Pink1/parkin mutant phenotypes in the absence of fwd. These genetic experiments strongly hint at a functional link between Drp1 and Fwd but do not illuminate the molecular mechanism underpinning it. Fwd is the Drosophila homologue of phosphatidylinositol 4-kinase IIIβ [PI(4)KB], which mediates the phosphorylation of phosphatidylinositol to generate phosphatidylinositol 4-phosphate [PI(4)P]. PI(4)P is one of the most abundant phosphoinositides, which is usually concentrated in the trans-Golgi network; thus, the mechanism by which PI(4)P may influence mitochondrial dynamics is not immediately obvious. However, while this manuscript was in preparation, Godi, 1999 (Nat Cell Biol 1(5): 280-287) reported that Golgi-derived PI(4)P-containing vesicles were required for the final stages of mitochondrial fission (Nagashima, 2020; Science 367(6484): 1366-1371). In that study, the authors found that loss of PI(4)KIIIβ led to hyperfusion and increased branching of the mitochondrial network, consistent with what was observed in this study. Moreover, Nagashima described that while Drp1 was still recruited, it was unable to fully execute the scission event, although the reason is unclear, leading to extended mitochondrial constriction sites. Genetic evidence that the action of Drp1 requires Fwd is consistent with these findings, and provides an in vivo validation of Nagashima's results. Currently, it is unclear why Drp1 overexpression was able to revert the increased branching caused by loss of fwd but the mechanisms of branch formations are not well understood. It is interesting to note that while Nagashima suggest a universal role for PI(4)P in mitochondrial fission, the current in vivo analysis reveals that while fwd affected mitochondrial morphology in the nervous system, it appeared to have a much more limited role in the musculature. These tissue-specific requirements were borne out in the strong locomotor deficits caused by neuronal loss of fwd but much less so by knockdown in muscles. Clearly, further work is required to better understand the complexities of regulated fission/fusion events in different cell contexts in vivo (Terriente-Felix, 2020).
A key role of mitochondrial fission/fusion dynamics is in contributing to a quality control mechanism of mitochondrial sorting to eliminate dysfunctional units via mitophagy. A substantial body of evidence from cellular models indicates that mammalian PINK1 and Parkin act to promote damage-induced mitophagy, and some in vivo evidence from Drosophila also supports this. However, the precise nature of PINK1/Parkin-mediated mitochondrial turnover in vivo is debated with contradictory results emerging. Nevertheless, interventions to combat the decline in mitochondrial homeostasis remain a key challenge to combatting PINK1/PRKN related pathologies. One mechanism that seems to provide substantial benefit in physiological contexts is through augmenting mitochondrial fission, which presumably facilitates the flux of damaged mitochondrial components towards turnover. This study, provide further evidence that augmenting a pro-fission pathway is beneficial against Pink1 and parkin dysfunction. As phosphoinositides can be interconverted by the action of multiple enzymes that may be druggable, these findings suggest another potential route towards a therapeutic intervention (Terriente-Felix, 2020).
Abstract Abstract Abstract Abstract Abstract Abstract Abstract Abstract Abstract Abstract Heremans, I. P., Caligiore, F., Gerin, I., Bury, M., Lutz, M., Graff, J., Stroobant, V., Vertommen, D., Teleman, A. A., Van Schaftingen, E. and Bommer, G. T. (2022). Parkinson's disease protein PARK7 prevents metabolite and protein damage caused by a glycolytic metabolite. Proc Natl Acad Sci U S A 119(4). PubMed ID: 35046029
Abstract Adedara, A. O., Babalola, A. D., Stephano, F., Awogbindin, I. O., Olopade, J. O., Rocha, J. B. T., Whitworth, A. J. and Abolaji, A. O. (2022). An assessment of the rescue action of resveratrol in parkin loss of function-induced oxidative stress in Drosophila melanogaster. Sci Rep 12(1): 3922. PubMed ID: 35273283
Abstract Hernandez-Diaz, S., Ghimire, S., Sanchez-Mirasierra, I., Montecinos-Oliva, C., Swerts, J., Kuenen, S., Verstreken, P. and Soukup, S. F. (2022). Endophilin-B regulates autophagy during synapse development and neurodegeneration. Neurobiol Dis 163: 105595. PubMed ID: 34933093
Abstract Girard, V., Jollivet, F., Knittelfelder, O., Celle, M., Arsac, J. N., Chatelain, G., Van den Brink, D. M., Baron, T., Shevchenko, A., Kuhnlein, R. P., Davoust, N. and Mollereau, B. (2021). Abnormal accumulation of lipid droplets in neurons induces the conversion of alpha-Synuclein to proteolytic resistant forms in a Drosophila model of Parkinson's disease. PLoS Genet 17(11): e1009921. PubMed ID: 34788284
Parkinson's disease (PD) is a neurodegenerative disorder characterized by alpha-synuclein (αSyn) aggregation and associated with abnormalities in lipid metabolism. The accumulation of lipids in cytoplasmic organelles called lipid droplets (LDs) was observed in cellular models of PD. To investigate the pathophysiological consequences of interactions between αSyn and proteins that regulate the homeostasis of LDs, a transgenic Drosophila model of PD was used in which human αSyn is specifically expressed in photoreceptor neurons. It was first found that overexpression of the LD-coating proteins Perilipin 1 or 2 (dPlin1/2), which limit the access of lipases to LDs, markedly increased triacylglyclerol (TG) loaded LDs in neurons. However, dPlin-induced-LDs in neurons are independent of lipid anabolic, and catabolic enzymes, indicating that alternative mechanisms regulate neuronal LD homeostasis. Interestingly, the accumulation of LDs induced by various LD proteins (dPlin1, dPlin2, CG7900 or KlarsichtLD-BD) was synergistically amplified by the co-expression of αSyn, which localized to LDs in both Drosophila photoreceptor neurons and in human neuroblastoma cells. Finally, the accumulation of LDs increased the resistance of αSyn to proteolytic digestion, a characteristic of αSyn aggregation in human neurons. It is proposed that αSyn cooperates with LD proteins to inhibit lipolysis and that binding of αSyn to LDs contributes to the pathogenic misfolding and aggregation of αSyn in neurons (Girard, 2021).
This study has investigated the mechanisms that regulate LD homeostasis in neurons, the contribution of αSyn to LD homeostasis, and whether αSyn-LD binding influences the pathogenic potential of αSyn. Expression of the LD proteins, dPlin1 and dPlin2, CG7900 or of the LD-binding domain of Klarsicht increased LD accumulation in Drosophila photoreceptor neurons and that this phenotype was amplified by co-expressing the PD-associated protein αSyn. Transfected and endogenous αSyn co-localized with PLINs on the LD surface in human neuroblastoma cells, as demonstrated by confocal microscopy and PLA assays. Neuronal accumulation of LDs was not dependent on the canonical enzymes of TG synthesis (Mdy, dFatp), Bmm/dATGL-dependent lipolysis or lipophagy inhibition. One possible explanation for LD accumulation is that LD proteins inhibit an unknown lipase in Drosophila photoreceptor neurons. Finally, it was observed that LD accumulation in photoreceptor neurons was associated with increased resistance of αSyn to proteinase K digestion, suggesting that LD accumulation might promote αSyn misfolding, an important step in the progression towards PD. Thus, this study has uncovered a potential novel role for LDs in the pathogenicity of αSyn in PD (Girard, 2021).
Understanding of the mechanisms of LD homeostasis in neurons under physiological or pathological conditions is far from complete. Neurons predominantly synthesize ATP through aerobic metabolism of glucose, rather than through FA β-oxidation, which likely explains the relative scarcity of LDs in neurons compared with glial cells. This study used the Drosophila adult retina that is composed of photoreceptor neurons and glial cells to explore the mechanism regulating LD homeostasis in the nervous system. The canonical mechanisms regulating TG turnover and LD formation are dependent on evolutionary conserved regulators of lipogenesis and lipolysis in the fly adipose tissue, called fat body, or in other non-fat cells, such as glial cells. Indeed, it has been shown that de novo TG-synthesis enzymes Dgat1/Mdy and dFatp, are required for LD biogenesis in the fat body and glial cells. This is in contrast to dPlin-induced neuronal accumulation of LDs (this study), which occurs through a mechanism, independent of Mdy- and dFatp-mediated de novo TG synthesis. One possibility is that LD biogenesis depends on Dgat2 in neurons. However, the fact that there are three Dgat2 paralogs encoded by the fly genome and that no triple mutant is available, precluded its functional analysis in the current study (Girard, 2021).
The evolutionarily conserved and canonical TG lipase Bmm, otholog of mammalian adipose triglyceride lipase (ATGL) regulates lipolysis in the fat body. This study shows that Bmm regulates LD abundance in glial cells but not in photoreceptor neurons. Interestingly, in both bmm-mutant Drosophila (this study) and ATGL-mutant mice, neurons do not accumulate LDs. This suggests the existence of an unknown and possibly cell type specific lipase regulating the degradation of LDs in neurons. This is supported by the fact that the overexpression of dPlins proteins, which are known inhibitors of lipolysis, promotes LD accumulation in photoreceptor neurons. In further support of a neuron-specific TG lipase, the human hereditary spastic paraplegia gene DDHD2, a member of the iPLA1/PAPLA1 family, was proposed to be the main lipase regulating TG metabolism in the mammalian brain. A recent study, showed that Bmm plays a role in the somatic cells of the gonad and in neurons to regulate systemic TG breakdown. It was also suggested that Bmm may play a role in regulating LD turnover in neurons, although this was not directly tested in this study. The results using bmm knock-down and bmm mutants do not support a role of Bmm in the regulation of LD accumulation in photoreceptor neurons. However, the possibility cannot be excluded that Bmm would be required in a subpopulation of neurons to regulate LD content but this would require further analyses. Finally, the possibility cannot be excluded that the overexpression of LD proteins, such as dPlins but also CG7900 or the Klarsicht lipid-binding domain promotes LD accumulation by shielding and stabilizing LDs rather than limiting the access of lipases to LDs. Indeed, stabilization of LDs could well be an ancestral function of PLINs, as reported for yeast and Drosophila adipose tissue. Thus, inhibiting lipolysis and/or stabilizing LDs, allows the formation of LDs, which would be otherwise actively degraded in photoreceptor neurons. This opens avenues to further study LD homeostasis but also their pathophysiological role in diseases of the nervous system (Girard, 2021).
Earlier studies have observed the accumulation of LDs in cellular models of PD. For example, LDs form in SH-SY5Y cells exposed to 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), a dopaminergic neurotoxin prodrug that causes PD-like symptoms in animal and cellular models. In addition, studies in yeast, rat dopaminergic neurons, and human induced pluripotent stem cells have proposed that αSyn expression induces lipid dysregulation and LD accumulation, but the underlying mechanisms remained unclear. Low levels of αSyn accumulation were hypothezised to perturb lipid homeostasis by enhancing unsaturated FA synthesis and the subsequent accumulation of DGs and TGs. The present study showed that αSyn expression alone did not enhance the accumulation of LDs but instead required concomitant overexpression of a LD protein. Moreover, αSyn expression alone had no effect on DG, TG, or LD content in Drosophila photoreceptor neurons, which indicates that αSyn-induced LDs are not driven by increased TG biosynthesis in this cellular context. Instead, the fact that endogenous αSyn and PLIN3 proteins co-localized at the LD surface in human neuroblastoma cells, suggests that LD-associated αSyn have a direct physiological function in promoting neutral lipid accumulation by inhibiting lipolysis. This hypothesis is supported by experiments in HeLa cells transfected with αSyn, loaded with fatty acids, in which the overexpression of αSyn protects LDs from lipolysis (Girard, 2021).
The results show that LDs contribute to αSyn conversion to proteinase K resistant forms, which indicates that LDs may be involved in the progression of PD pathology. This is an apparent discrepancy with the results in a previous study, in which LDs protect from lipotoxicity cells expressing αSyn. That study used cellular models including yeast cells, and rat cortical neuron primary cultures exposed or not to oleic acid. In such cellular context, it was proposed that αSyn induces the accumulation of toxic diacylglycerol (DG), which is subsequently converted to TG and sequestered into LDs. LDs are thus protective by allowing the sequestration of toxic lipids. In the fly retina study, αSyn expression did not induce TG accumulation. In the Drosophila nervous system, toxic DG may not reach sufficient level to promote photoreceptor toxicity. Interestingly, this difference allowed study of the binding of αSyn to LD and examine their contribution to pathological conversion of αSyn. Indeed, the results suggest an alternative but not mutually exclusive role for LDs in promoting αSyn misfolding and conversion to a proteinase K-resistant form. The increased LD surface could provide a physical platform for αSyn deposition and conversion. In support of this hypothesis, it was previously proposed that αSyn aggregation is facilitated in the presence of synthetic phospholipid vesicles. Thus, the current results point to a direct role of LDs on αSyn resistance to proteinase K digestion (Girard, 2021).
This study showed that the accumulation of LD proteins, such as dPlins, is a prerequisite for the increased LD accumulation induced by αSyn in neurons. This raises the possibility that some physiological or pathological conditions will favor the expression and/or accumulation of LD proteins, which triggers the neuronal accumulation of LDs. Interestingly, it was proposed that age-dependent accumulation of fat and dPlin2 is dependent on the histone deacetylase (HDAC6) in Drosophila. Moreover, an accumulation of LD-containing cells (lipid-laden cells), associated with PLIN2 expression, was observed in meningeal, cortical and neurogenic brain regions of the aging mice. Finally, a recent expression study on all human perlipin proteins (PLIN1-5), found that PLIN2 accumulates, particularly in neurons, in brains of old subjects and of patients with Alzheimer disease. As an alternative putative mechanism regulating LD level, it was shown that targeted degradation of PLIN2 and PLIN3 occurs by chaperone-mediated autophagy (CMA). Thus, in aging tissue with decreased HDAC6 or reduced basal CMA, the accumulation of PLINs may initiate LD accumulation, hence favoring αSyn-induced LD production. In this study, mutations in the central autophagy gene Atg8 did not lead to LD accumulation in Drosophila retina. Thus a more systematic analysis will be required to identify the proteolytic mechanisms regulating dPlins degradation and LD accumulation in the aged Drosophila nervous system (Girard, 2021).
Based on a combination of the current results and these observations, a model is proposed of LD homeostasis in healthy and diseased neurons. In healthy neurons, relatively few LDs are detected due to a combination of low basal rate of TG synthesis, active lipolysis and limited LD shielding capacity. In pathological conditions such as PD, possibly in combination with an age-dependent ectopic fat accumulation and Plin proteins increased expression, αSyn and Plins could cooperate to limit lipolysis and promote the accumulation of LDs in neurons. This could set a vicious cycle in which αSyn enhances Plin-dependent LD stabilization, which, in turn, would increase αSyn conversion to a proteinase K-resistant form, culminating in αSyn aggregation and formation of cytoplasmic inclusion bodies. Collectively, these results raise the possibility that αSyn binding to LDs could be an important step in the pathogenesis of PD (Girard, 2021).
Hung, Y. C., Huang, K. L., Chen, P. L., Li, J. L., Lu, S. H., Chang, J. C., Lin, H. Y., Lo, W. C., Huang, S. Y., Lee, T. T., Lin, T. Y., Imai, Y., Hattori, N., Liu, C. S., Tsai, S. Y., Chen, C. H., Lin, C. H. and Chan, C. C. (2021). UQCRC1 engages cytochrome c for neuronal apoptotic cell death. Cell Rep 36(12): 109729. PubMed ID: 34551295
Human ubiquinol-cytochrome c reductase core protein 1 (UQCRC1) is an evolutionarily conserved core subunit of mitochondrial respiratory chain complex III. This study recently identified the disease-associated variants of UQCRC1 from patients with familial parkinsonism, but its function remains unclear. This study investigates the endogenous function of UQCRC1 in the human neuronal cell line and the Drosophila nervous system. Flies with neuronal knockdown of uqcrc1 exhibit age-dependent parkinsonism-resembling defects, including dopaminergic neuron reduction and locomotor decline, and are ameliorated by UQCRC1 expression. Lethality of uqcrc1-KO is also rescued by neuronally expressing UQCRC1, but not the disease-causing variant, providing a platform to discern the pathogenicity of this mutation. Furthermore, UQCRC1 associates with the apoptosis trigger cytochrome c (cyt-c), and uqcrc1 deficiency increases Cyt-c in the cytoplasmic fraction and activates the caspase cascade. Depleting cyt-c or expression of the anti-apoptotic p35 ameliorates uqcrc1-mediated neurodegeneration. The findings identified a role for UQCRC1 in regulating cyt-c-induced apoptosis (Hung, 2021).
Parker-Character, J., Hager, D. R., Call, T. B., Pickup, Z. S., Turnbull, S. A., Marshman, E. M., Korch, S. B., Chaston, J. M. and Call, G. B. (2021). An altered microbiome in a Parkinson's disease model Drosophila melanogaster has a negative effect on development. Sci Rep 11(1): 23635. PubMed ID: 34880269
Abstract 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 Abstract Li, J., Lim, R. G., Kaye, J. A., Dardov, V., Coyne, A. N., Wu, J., Milani, P., Cheng, A., Thompson, T. G., Ornelas, L., Frank, A., Adam, M., Banuelos, M. G., Casale, M., Cox, V., Escalante-Chong, R., Daigle, J. G., Gomez, E., Hayes, L., Holewenski, R., Lei, S., Lenail, A., Lima, L., Mandefro, B., Matlock, A., Panther, L., Patel-Murray, N. L., Pham, J., Ramamoorthy, D., Sachs, K., Shelley, B., Stocksdale, J., Trost, H., Wilhelm, M., Venkatraman, V., Wassie, B. T., Wyman, S., Yang, S., Van Eyk, J. E., Lloyd, T. E., Finkbeiner, S., Fraenkel, E., Rothstein, J. D., Sareen, D., Svendsen, C. N. and Thompson, L. M. (2021). An integrated multi-omic analysis of iPSC-derived motor neurons from C9ORF72 ALS patients. iScience 24(11): 103221. PubMed ID: 34746695 Abstract Manivannan, S. N., Roovers, J., Smal, N., Myers, C. T., Turkdogan, D., Roelens, F., Kanca, O., Chung, H. L., Scholz, T., Hermann, K., Bierhals, T., Caglayan, H. S., Stamberger, H., Mefford, H., de Jonghe, P., Yamamoto, S., Weckhuysen, S. and Bellen, H. J. (2021) Abstract Pant, C., Chakrabarti, M., Mendonza, J. J., Ganganna, B., Pabbaraja, S. and Pal Bhadra, M. (2021) Abstract Kowada, R., Kodani, A., Ida, H., Yamaguchi, M., Lee, I. S., Okada, Y. and Yoshida, H. (2021). The function of Scox in glial cells is essential for locomotive ability in Drosophila. Sci Rep 11(1): 21207. PubMed ID: 34707123 Abstract Licata, N. V., Cristofani, R., Salomonsson, S., Wilson, K. M., Kempthorne, L., Vaizoglu, D., D'Agostino, V. G., Pollini, D., Loffredo, R., Pancher, M., Adami, V., Bellosta, P., Ratti, A., Viero, G., Quattrone, A., Isaacs, A. M., Poletti, A. and Provenzani, A. (2021). C9orf72 ALS/FTD dipeptide repeat protein levels are reduced by small molecules that inhibit PKA or enhance protein degradation. EMBO J: e105026. PubMed ID: 34791698 Abstract Lee, H., Lee, J. J., Park, N. Y., Dubey, S. K., Kim, T., Ruan, K., Lim, S. B., Park, S. H., Ha, S., Kovlyagina, I., Kim, K. T., Kim, S., Oh, Y., Kim, H., Kang, S. U., Song, M. R., Lloyd, T. E., Maragakis, N. J., Hong, Y. B., Eoh, H. and Lee, G. (2021). Multi-omic analysis of selectively vulnerable motor neuron subtypes implicates altered lipid metabolism in ALS. Nat Neurosci. PubMed ID: 34782793 Abstract Rivera, M. J., Contreras, A., Nguyen, L. T., Eldon, E. D. and Klig, L. S. (2021). Regulated inositol synthesis is critical for balanced metabolism and development in Drosophila melanogaster. Biol Open 10(10). PubMed ID: 34710213 Abstract Scharenbrock, A. R., Katzenberger, R. J., Fischer, M. C., Ganetzky, B. and Wassarman, D. A. (2021). Beta-blockers reduce intestinal permeability and early mortality following traumatic brain injury in Drosophila. MicroPubl Biol 2021. PubMed ID: 34723144 Abstract 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 Abstract Yamazoe, T., Nakahara, Y., Katsube, H. and Inoue, Y. H. (2021). Expression of Human Mutant Preproinsulins Induced Unfolded Protein Response, Gadd45 Expression, JAK-STAT Activation, and Growth Inhibition in Drosophila. Int J Mol Sci 22(21). PubMed ID: 34769468 Abstract Yap, Z. Y., Efthymiou, S., Seiffert, S., ..., Houlden, H. and Yoon, W. H. (2021). Bi-allelic variants in OGDHL cause a neurodevelopmental spectrum disease featuring epilepsy, hearing loss, visual impairment, and ataxia. Am J Hum Genet. PubMed ID: 34800363 Abstract Xiao, G., Zhao, M., Liu, Z., Du, F. and Zhou, B. (2021). Zinc antagonizes iron-regulation of tyrosine hydroxylase activity and dopamine production in Drosophila melanogaster. BMC Biol 19(1): 236. PubMed ID: 34732185 Abstract AYazar, V., Kang, S. U., Ha, S., Dawson, V. L. and Dawson, T. M. (2021). Integrative genome-wide analysis of dopaminergic neuron-specific PARIS expression in Drosophila dissects recognition of multiple PPAR-γ associated gene regulation. Sci Rep 11(1): 21500. PubMed ID: 34728675
Abstract 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
Abstract De Lazzari, F., Agostini, F., Plotegher, N., Sandre, M., Greggio, E., Megighian, A., Bubacco, L., Sandrelli, F., Whitworth, A. J. and Bisaglia, M. (2023). DJ-1 promotes energy balance by regulating both mitochondrial and autophagic homeostasis. Neurobiol Dis 176: 105941. PubMed ID: 36473592
Abstract Agostini, F., Bubacco, L., Chakrabarti, S. and Bisaglia, M. (2023). α-Synuclein Toxicity in Drosophila melanogaster Is Enhanced by the Presence of Iron: Implications for Parkinson's Disease. Antioxidants (Basel) 12(2). PubMed ID: 36829820
Abstract Carvajal-Oliveros, A., Dominguez-Baleon, C., Sanchez-Diaz, I., Zambrano-Tipan, D., Hernandez-Vargas, R., Campusano, J. M., Narváez-Padilla, V. and Reynaud, E. (2023). Parkinsonian phenotypes induced by Synphilin-1 expression are differentially contributed by serotonergic and dopaminergic circuits and suppressed by nicotine treatment. PLoS One 18(3): e0282348. PubMed ID: 36857384
Abstract Agostini, F., Bubacco, L., Chakrabarti, S. and Bisaglia, M. (2023). α-Synuclein Toxicity in Drosophila melanogaster Is Enhanced by the Presence of Iron: Implications for Parkinson's Disease. Antioxidants (Basel) 12(2). PubMed ID: 36829820
Abstract Usher, J. L., Sanchez-Martinez, A., Terriente-Felix, A., Chen, P. L., Lee, J. J., Chen, C. H. and Whitworth, A. J. (2022). Parkin drives pS65-Ub turnover independently of canonical autophagy in Drosophila. EMBO Rep: e202153552. PubMed ID: 36250243
Abstract Wang, X., Rimal, S., Tantray, I., Geng, J., Bhurtel, S., Khaket, T. P., Li, W., Han, Z. and Lu, B. (2022). Prevention of ribosome collision-induced neuromuscular degeneration by SARS CoV-2-encoded Nsp1. Proc Natl Acad Sci U S A 119(42): e2202322119. PubMed ID: 36170200
Abstract Li, J., Amoh, B. K., McCormick, E., Tarkunde, A., Zhu, K. F., Perez, A., Mair, M., Moore, J., Shulman, J. M., Al-Ramahi, I. and Botas, J. (2023). Integration of transcriptome-wide association study with neuronal dysfunction assays provides functional genomics evidence for Parkinson's disease genes. Hum Mol Genet 32(4): 685-695. PubMed ID: 36173927
Abstract Maor, G., Dubreuil, R. R. and Feany, M. B. (2023). α-synuclein promotes neuronal dysfunction and death by disrupting the binding of ankyrin to β-spectrin. J Neurosci. PubMed ID: 36653193
Abstract De Lazzari, F., Agostini, F., Plotegher, N., Sandre, M., Greggio, E., Megighian, A., Bubacco, L., Sandrelli, F., Whitworth, A. J. and Bisaglia, M. (2023). DJ-1 promotes energy balance by regulating both mitochondrial and autophagic homeostasis. Neurobiol Dis 176: 105941. PubMed ID: 36473592
Abstract Dhanushkodi, N. R., Abul Khair, S. B., Ardah, M. T. and Haque, M. E. (2023). ATP13A2 Gene Silencing in Drosophila Affects Autophagic Degradation of A53T Mutant α-Synuclein. Int J Mol Sci 24(2). PubMed ID: 36675288
Abstract Dumitrescu, E., Copeland, J. M. and Venton, B. J. (2023). Parkin Knockdown Modulates Dopamine Release in the Central Complex, but Not the Mushroom Body Heel, of Aging Drosophila. ACS Chem Neurosci 14(2): 198-208. PubMed ID: 36576890
Abstract Ren, M., Yang, Y., Heng, K. H. Y., Ng, L. Y., Chong, C. Y., Ng, Y. T., Gorur-Shandilya, S., Lee, R. M. Q., Lim, K. L., Zhang, J. and Koh, T. W. (2022). MED13 and glycolysis are conserved modifiers of alpha-synuclein-associated neurodegeneration. Cell Rep 41(12): 111852. PubMed ID: 36543134
Abstract Ren, M., Yang, Y., Heng, K. H. Y., Ng, L. Y., Chong, C. Y., Ng, Y. T., Gorur-Shandilya, S., Lee, R. M. Q., Lim, K. L., Zhang, J. and Koh, T. W. (2022). MED13 and glycolysis are conserved modifiers of alpha-synuclein-associated neurodegeneration. Cell Rep 41(12): 111852. PubMed ID: 36543134
Abstract 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
Abstract De Groef, S., Wilms, T., Balmand, S., Calevro, F. and Callaerts, P. (2021). Sexual Dimorphism in Metabolic Responses to Western Diet in Drosophila melanogaster. Biomolecules 12(1). PubMed ID: 35053181
Abstract Casale, A. M., Liguori, F., Ansaloni, F., Cappucci, U., Finaurini, S., Spirito, G., Persichetti, F., Sanges, R., Gustincich, S. and Piacentini, L. (2022). Transposable element activation promotes neurodegeneration in a Drosophila model of Huntington's disease. iScience 25(1): 103702. PubMed ID: 35036881
Abstract Kim, Y. W., Al-Ramahi, I., Koire, A., Wilson, S. J., Konecki, D. M., Mota, S., Soleimani, S., Botas, J. and Lichtarge, O. (2020). Harnessing the paradoxical phenotypes of APOE epsilon2 and APOE epsilon4 to identify genetic modifiers in Alzheimer's disease. Alzheimers Dement. PubMed ID: 33576571
Abstract 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) Abstract Yazar, V., Kang, S. U., Ha, S., Dawson, V. L. and Dawson, T. M. (2021). Integrative genome-wide analysis of dopaminergic neuron-specific PARIS expression in Drosophila dissects recognition of multiple PPAR-γ associated gene regulation. Sci Rep 11(1): 21500. PubMed ID: 34728675
Abstract Xiao, G., Zhao, M., Liu, Z., Du, F. and Zhou, B. (2021). Zinc antagonizes iron-regulation of tyrosine hydroxylase activity and dopamine production in Drosophila melanogaster. BMC Biol 19(1): 236. PubMed ID: 34732185 Abstract Pant, C., Chakrabarti, M., Mendonza, J. J., Ganganna, B., Pabbaraja, S. and Pal Bhadra, M. (2021). Aza-Flavanone Diminishes Parkinsonism in the Drosophila melanogaster Parkin Mutant. ACS Chem Neurosci. PubMed ID: 34763419
Abstract Hung, Y. C., Huang, K. L., Chen, P. L., Li, J. L., Lu, S. H., Chang, J. C., Lin, H. Y., Lo, W. C., Huang, S. Y., Lee, T. T., Lin, T. Y., Imai, Y., Hattori, N., Liu, C. S., Tsai, S. Y., Chen, C. H., Lin, C. H. and Chan, C. C. (2021). UQCRC1 engages cytochrome c for neuronal apoptotic cell death. Cell Rep 36(12): 109729. PubMed ID: 34551295
Human ubiquinol-cytochrome c reductase core protein 1 (UQCRC1) is an evolutionarily conserved core subunit of mitochondrial respiratory chain complex III. This study recently identified the disease-associated variants of UQCRC1 from patients with familial parkinsonism, but its function remains unclear. This study investigates the endogenous function of UQCRC1 in the human neuronal cell line and the Drosophila nervous system. Flies with neuronal knockdown of uqcrc1 exhibit age-dependent parkinsonism-resembling defects, including dopaminergic neuron reduction and locomotor decline, and are ameliorated by UQCRC1 expression. Lethality of uqcrc1-KO is also rescued by neuronally expressing UQCRC1, but not the disease-causing variant, providing a platform to discern the pathogenicity of this mutation. Furthermore, UQCRC1 associates with the apoptosis trigger cytochrome c (cyt-c), and uqcrc1 deficiency increases Cyt-c in the cytoplasmic fraction and activates the caspase cascade. Depleting cyt-c or expression of the anti-apoptotic p35 ameliorates uqcrc1-mediated neurodegeneration. The findings identified a role for UQCRC1 in regulating cyt-c-induced apoptosis (Hung, 2021).
Solana-Manrique, C., Sanz, F. J., Ripolles, E., Bano, M. C., Torres, J., Munoz-Soriano, V. and Paricio, N. (2020). Enhanced activity of glycolytic enzymes in Drosophila and human cell models of Parkinson's disease based on DJ-1 deficiency. Free Radic Biol Med. PubMed ID: 32726690
Parkinson's disease (PD) is a neurodegenerative debilitating disorder characterized by progressive disturbances in motor, autonomic and psychiatric functions. One of the genes involved in familial forms of the disease is DJ-1, whose mutations cause early-onset PD. Besides, it has been shown that an over-oxidized and inactive form of the DJ-1 protein is found in brains of sporadic PD patients. Interestingly, the DJ-1 protein plays an important role in cellular defense against oxidative stress and also participates in mitochondrial homeostasis. Flies mutant for the DJ-1β gene, the Drosophila ortholog of human DJ-1, exhibited disease-related phenotypes such as motor defects, increased reactive oxygen species production and high levels of protein carbonylation. The present study demonstrated that DJ-1β mutants also show a significant increase in the activity of several regulatory glycolytic enzymes. Similar results were obtained in DJ-1-deficient SH-SY5Y neuroblastoma cells, thus suggesting that loss of DJ-1 function leads to an increase in the glycolytic rate. In such a scenario, an enhancement of the glycolytic pathway could be a protective mechanism to decrease ROS production by restoring ATP levels, which are decreased due to mitochondrial dysfunction. The results also show that meclizine and dimethyl fumarate, two FDA-approved compounds with different clinical applications, are able to attenuate PD-related phenotypes in both models. Moreover, it was found that they may exert their beneficial effect by increasing glycolysis through the activation of key glycolytic enzymes. Taken together, these results are consistent with the idea that increasing glycolysis could be a potential disease-modifying strategy for PD, as recently suggested. Besides, they also support further evaluation and potential repurposing of meclizine and dimethyl fumarate as modulators of energy metabolism for neuroprotection in PD.
Fernandez-Cruz, I., Sanchez-Diaz, I., Narvaez-Padilla, V. and Reynaud, E. (2020). Rpt2 proteasome subunit reduction causes Parkinson's disease like symptoms in Drosophila, IBRO Rep 9: 65-77. PubMed ID: 32715147
The dysfunction of the proteasome-ubiquitin system is commonly reported in several neurodegenerative diseases. Post mortem samples of brains of patients with Parkinson´s disease present cytoplasmic inclusions that are rich in proteins such as ubiquitin, Tau, and α-synuclein. In Parkinson´s disease, a specific reduction of some of the proteasome subunits has also been reported. However, the specific role of the different proteasome subunits in dopaminergic neuron degeneration has not been thoroughly explored. In this work, the Gal4/UAS system was used to test fourteen Drosophila melanogaster RNAi lines from the Bloomington Drosophila Stock Center. Each of these lines targets a different proteasome subunit. To identify the strains that were able to induce neurodegeneration, the expression of these lines was driven to the eye, and they were catagorized as a function of the extent of neurodegeneration that they induced. The targeted proteasomal subunits are conserved in mammals and therefore may be relevant to study proteasome related diseases. The RNAi line among the regulatory subunits with the most penetrant phenotype targeted the proteasomal subunit Rpt2 and its phenotypes were further characterized. Rpt2 knockdown in the Drosophila central nervous system reduced the activity of the proteasome, augmented the amount of insoluble ubiquitinated protein, and elicited motor and non-motor phenotypes that were similar to the ones found in Drosophila and other models for Parkinson's disease. When Rpt2 is silenced pan-neurally, third instar larvae have locomotion dysfunctions and die during pupation. Larval lethality was avoided using the Gal80-Gal4 system to induce the expression of the Rpt2 RNAi to dopaminergic neurons only after pupation. The reduction of Rpt2 in adult dopaminergic neurons causes reduced survival, hyperactivity, neurodegeneration, and sleep loss; probably recapitulating some of the sleep disorders that Parkinson's disease patients have before the appearance of locomotion disorders (Fernandez-Cruz, 2020).
Ingles-Prieto, A., Furthmann, N., Crossman, S. H., Tichy, A. M., Hoyer, N., Petersen, M., Zheden, V., Biebl, J., Reichhart, E., Gyoergy, A., Siekhaus, D. E., Soba, P., Winklhofer, K. F. and Janovjak, H. (2021). Optogenetic delivery of trophic signals in a genetic model of Parkinson's disease. PLoS Genet 17(4): e1009479. PubMed ID: 33857132
Optogenetics has been harnessed to shed new mechanistic light on current and future therapeutic strategies. This has been to date achieved by the regulation of ion flow and electrical signals in neuronal cells and neural circuits that are known to be affected by disease. In contrast, the optogenetic delivery of trophic biochemical signals, which support cell survival and are implicated in degenerative disorders, has never been demonstrated in an animal model of disease. This study reengineered the human and Drosophila melanogaster REarranged during Transfection (hRET and dRET) receptors to be activated by light, creating one-component optogenetic tools termed Opto-hRET and Opto-dRET. Upon blue light stimulation, these receptors robustly induced the MAPK/ERK proliferative signaling pathway in cultured cells. In PINK1B9 flies that exhibit loss of PTEN-induced putative kinase 1 (PINK1), a kinase associated with familial Parkinson's disease (PD), light activation of Opto-dRET suppressed mitochondrial defects, tissue degeneration and behavioral deficits. In human cells with PINK1 loss-of-function, mitochondrial fragmentation was rescued using Opto-dRET via the PI3K/NF-kappaB pathway. These results demonstrate that a light-activated receptor can ameliorate disease hallmarks in a genetic model of PD. The optogenetic delivery of trophic signals is cell type-specific and reversible and thus has the potential to inspire novel strategies towards a spatio-temporal regulation of tissue repair.
Arsac, J. N., Sedru, M., Dartiguelongue, M., Vulin, J., Davoust, N., Baron, T. and Mollereau, B. (2021). Chronic Exposure to Paraquat Induces Alpha-Synuclein Pathogenic Modifications in Drosophila. Int J Mol Sci 22(21). PubMed ID: 34769043
Parkinson's disease (PD) is characterized by the progressive accumulation of neuronal intracellular aggregates largely composed of α-Synuclein (αSyn) protein. The process of αSyn aggregation is induced during aging and enhanced by environmental stresses, such as the exposure to pesticides. Paraquat (PQ) is an herbicide which has been widely used in agriculture and associated with PD. PQ is known to cause an increased oxidative stress in exposed individuals but the consequences of such stress on αSyn conformation remains poorly understood. To study Syn pathogenic modifications in response to PQ, Drosophila expressing human αSyn were exposedto a chronic PQ protocol. It was first shown that PQ exposure and αSyn expression synergistically induced fly mortality. The exposure to PQ was also associated with increased levels of total and phosphorylated forms of αSyn in the Drosophila brain. Interestingly, PQ increased the detection of soluble αSyn in highly denaturating buffer but did not increase αSyn resistance to proteinase K digestion. These results suggest that PQ induces the accumulation of toxic soluble and misfolded forms of αSyn but that these toxic forms do not form fibrils or aggregates that are detected by the proteinase K assay. Collectively, these results demonstrate that Drosophila can be used to study the effect of PQ or other environmental neurotoxins on Syn driven pathology (Arsac, 2021).
Olsen, A. L. and Feany, M. B. (2021). Parkinson's disease risk genes act in glia to control neuronal alpha-synuclein toxicity. Neurobiol Dis 159: 105482. PubMed ID: 34390834
Idiopathic Parkinson's disease is the second most common neurodegenerative disease and is estimated to be approximately 30% heritable. Genome wide association studies have revealed numerous loci associated with risk of development of Parkinson's disease. The majority of genes identified in these studies are expressed in glia at either similar or greater levels than their expression in neurons, suggesting that glia may play a role in Parkinson's disease pathogenesis. The role of individual glial risk genes in Parkinson's disease development or progression is unknown, however. It was hypothesized that some Parkinson's disease risk genes exert their effects through glia. A Drosophila model of α-synucleinopathy was developed in which gene expression can be individually expressed in neurons and glia. Human wild type α-synuclein is expressed in all neurons, and these flies develop the hallmarks of Parkinson's disease, including motor impairment, death of dopaminergic and other neurons, and α-synuclein aggregation. In these flies, a candidate genetic screen was performed, using RNAi to knockdown 14 well-validated Parkinson's disease risk genes in glia, and the effect on locomotion was measured in order to identify glial modifiers of the &alpha-synuclein phenotype. Four modifiers were identified: aux, Lrrk, Ric, and Vps13, orthologs of the human genes GAK, LRRK2, RIT2, and VPS13C, respectively. Knockdown of each gene exacerbated neurodegeneration as measured by total and dopaminergic neuron loss. Knockdown of each modifier also increased α-synuclein oligomerization. These results suggest that some Parkinson's disease risk genes exert their effects in glia and that glia can influence neuronal α-synuclein proteostasis in a non-cell-autonomous fashion. Further, this study provides proof of concept that this novel Drosophila α-synucleinopathy model can be used to study glial modifier genes, paving the way for future large unbiased screens to identify novel glial risk factors that contribute to PD risk and progression.
Han, Y., Zhuang, N. and Wang, T. (2021). Roles of PINK1 in regulation of systemic growth inhibition induced by mutations of PTEN in Drosophila. Cell Rep 34(12): 108875. PubMed ID: 33761355
The maintenance of mitochondrial homeostasis requires PTEN-induced kinase 1 (PINK1)-dependent mitophagy, and mutations in PINK1 are associated with Parkinson's disease (PD). PINK1 is also downregulated in tumor cells with PTEN mutations. However, there is limited information concerning the role of PINK1 in tissue growth and tumorigenesis. This study shows that the loss of pink1 caused multiple growth defects independent of its pathological target, Parkin. Moreover, knocking down pink1 in muscle cells induced hyperglycemia and limited systemic organismal growth by the induction of Imaginal morphogenesis protein-Late 2 (ImpL2). Similarly, disrupting PTEN activity in multiple tissues impaired systemic growth by reducing pink1 expression, resembling wasting-like syndrome in cancer patients. Furthermore, the re-expression of PINK1 fully rescued defects in carbohydrate metabolism and systemic growth induced by the tissue-specific pten mutations. These data suggest a function for PINK1 in regulating systemic growth in Drosophila and shed light on its role in wasting in the context of PTEN mutations.
Krzystek, T. J., Banerjee, R., Thurston, L., Huang, J., Swinter, K., Rahman, S. N., Falzone, T. L. and Gunawardena, S. (2021). Differential mitochondrial roles for alpha-synuclein in DRP1-dependent fission and PINK1/Parkin-mediated oxidation. Cell Death Dis 12(9): 796. PubMed ID: 34404758
Abstract Guo, Q., Wang, B., Wang, X., Smith, W. W., Zhu, Y. and Liu, Z. (2021). Activation of Nrf2 in Astrocytes Suppressed PD-Like Phenotypes via Antioxidant and Autophagy Pathways in Rat and Drosophila Models. Cells 10(8). PubMed ID: 34440619
Abstract Putz, S. M., Kram, J., Rauh, E., Kaiser, S., Toews, R., Lueningschroer-Wang, Y., Rieger, D. and Raabe, T. (2021). Loss of p21-activated kinase Mbt/PAK4 causes Parkinson-like phenotypes in Drosophila. Dis Model Mech 14(6). PubMed ID: 34125184
Abstract Bhat, S., Guthrie, D. A., Kasture, A., El-Kasaby, A., Cao, J., Bonifazi, A., Ku, T., Giancola, J. B., Hummel, T., Freissmuth, M. and Newman, A. H. (2021). Tropane-Based Ibogaine Analog Rescues Folding-Deficient Serotonin and Dopamine Transporters. ACS Pharmacol Transl Sci 4(2): 503-516. PubMed ID: 33860180
Abstract Missense mutations that give rise to protein misfolding are rare, but collectively, defective protein folding diseases are consequential. Folding deficiencies are amenable to pharmacological correction (pharmacochaperoning), but the underlying mechanisms remain enigmatic. Ibogaine and its active metabolite noribogaine correct folding defects in the dopamine transporter (DAT), but they rescue only a very limited number of folding-deficient DAT mutant proteins, which give rise to infantile Parkinsonism and dystonia. In this study, a series of analogs was generated by reconfiguring the complex ibogaine ring system and exploring the structural requirements for binding to wild-type transporters, as well as for rescuing two equivalent synthetic folding-deficient mutants, SERT-PG(601,602)AA and DAT-PG(584,585)AA. The most active tropane-based analog (9b) was also an effective pharmacochaperone in vivo in Drosophila harboring the DAT-PG(584,585)AA mutation and rescued 6 out of 13 disease-associated human DAT mutant proteins in vitro. Hence, a novel lead pharmacochaperone has been identified that demonstrates medication development potential for patients harboring DAT mutations.
Buck, S. A., Steinkellner, T., Aslanoglou, D., Villeneuve, M., Bhatte, S. H., Childers, V. C., Rubin, S. A., De Miranda, B. R., O'Leary, E. I., Neureiter, E. G., Fogle, K. J., Palladino, M. J., Logan, R. W., Glausier, J. R., Fish, K. N., Lewis, D. A., Greenamyre, J. T., McCabe, B. D., Cheetham, C. E. J., Hnasko, T. S. and Freyberg, Z. (2021).Vesicular glutamate transporter modulates sex differences in dopamine neuron vulnerability to age-related neurodegeneration.. Aging Cell: e13365. PubMed ID: 33909313
Abstract Age is the greatest risk factor for Parkinson's disease (PD) which causes progressive loss of dopamine (DA) neurons, with males at greater risk than females. Intriguingly, some DA neurons are more resilient to degeneration than others. Increasing evidence suggests that vesicular glutamate transporter (VGLUT) expression in DA neurons plays a role in this selective vulnerability. We investigated the role of DA neuron VGLUT in sex- and age-related differences in DA neuron vulnerability using the genetically tractable Drosophila model. This study found sex differences in age-related DA neurodegeneration and its associated locomotor behavior, where males exhibit significantly greater decreases in both DA neuron number and locomotion during aging compared with females. Dynamic changes in DA neuron VGLUT expression mediate these age- and sex-related differences, as a potential compensatory mechanism for diminished DA neurotransmission during aging. Importantly, female Drosophila possess higher levels of VGLUT expression in DA neurons compared with males, and this finding is conserved across flies, rodents, and humans. Moreover, this study showed that diminishing VGLUT expression in DA neurons eliminates females' greater resilience to DA neuron loss across aging. This offers a new mechanism for sex differences in selective DA neuron vulnerability to age-related DA neurodegeneration. Finally, in mice, this study showed that the ability of DA neurons to achieve optimal control over VGLUT expression is essential for DA neuron survival. These findings lay the groundwork for the manipulation of DA neuron VGLUT expression as a novel therapeutic strategy to boost DA neuron resilience to age- and PD-related neurodegeneration.
Yamaguchi, A., Ishikawa, K. I., Inoshita, T., Shiba-Fukushima, K., Saiki, S., Hatano, T., Mori, A., Oji, Y., Okuzumi, A., Li, Y., Funayama, M., Imai, Y., Hattori, N. and Akamatsu, W. (2020). Identifying Therapeutic Agents for Amelioration of Mitochondrial Clearance Disorder in Neurons of Familial Parkinson Disease. Stem Cell Reports 14(6): 1060-1075. PubMed ID: 32470327
Abstract Parkinson disease (PD) is a neurodegenerative disorder caused by the progressive loss of midbrain dopaminergic neurons, and mitochondrial dysfunction is involved in its pathogenesis. This study aimed to establish an imaging-based, semi-automatic, high-throughput system for the quantitative detection of disease-specific phenotypes in dopaminergic neurons from induced pluripotent stem cells (iPSCs) derived from patients with familial PD having Parkin or PINK1 mutations, which exhibit abnormal mitochondrial homeostasis. The proposed system recapitulates the deficiency of mitochondrial clearance, ROS accumulation, and increasing apoptosis in these familial PD-derived neurons. 320 compounds were screened for their ability to ameliorate multiple phenotypes, and four candidate drugs were identified. Some of these drugs improved the locomotion defects and reduced ATP production caused by PINK1 inactivation in Drosophila and were effective for idiopathic PD-derived neurons with impaired mitochondrial clearance. These findings suggest that the proposed high-throughput system has potential for identifying effective drugs for familial and idiopathic PD (Yamaguchi, 2020).
Xie, J., Chen, S., Bopassa, J. C. and Banerjee, S. (2021).Drosophila tubulin polymerization promoting protein mutants reveal pathological correlates relevant to human Parkinson's disease. Sci Rep. 11(1):13614. PubMed ID: 34193896
Abstract Carvajal-Oliveros, A., Domínguez-Baleon, C., Zarate, R. V., Campusano, J. M., Narvaez-Padilla, V. and Reynaud, E. (2021). Nicotine suppresses Parkinson's disease like phenotypes induced by Synphilin-1 overexpression in Drosophila melanogaster by increasing tyrosine hydroxylase and dopamine levels. Sci Rep 11(1): 9579. PubMed ID: 33953275
It has been observed that there is a lower Parkinson's disease (PD) incidence in tobacco users. Nicotine is a cholinergic agonist and is the principal psychoactive compound in tobacco linked to cigarette addiction. Different studies have shown that nicotine has beneficial effects on sporadic and genetic models of PD. This work evaluated nicotine's protective effect in a Drosophila melanogaster model for PD where Synphilin-1 (Sph-1) is expressed in dopaminergic neurons. Nicotine has a moderate effect on dopaminergic neuron survival that becomes more evident as flies age. Nicotine is beneficial on fly survival and motility increasing tyrosine hydroxylase and dopamine levels, suggesting that cholinergic agonists may promote survival and metabolic function of the dopaminergic neurons that express Sph-1. The Sph-1 expressing fly is a good model for the study of early-onset phenotypes such as olfaction loss one of the main non-motor symptom related to PD. Thd data suggest that nicotine is an interesting therapeutic molecule whose properties should be explored in future research on the phenotypic modulators of the disease and for the development of new treatments.
Qiao, J. D. and Mao, Y. L. (2020). Knockout of PINK1 altered the neural connectivity of Drosophila dopamine PPM3 neurons at input and output sites. Invert Neurosci 20(3): 11. PubMed ID: 32766952
Abstract
Impairment of the dopamine system is the main cause of Parkinson disease (PD). PTEN-induced kinase 1 (PINK1) is possibly involved in pathogenesis of PD. However, its role in dopaminergic neurons has not been fully established yet. In the present investigation, the PINK1 knockout Drosophila model to explore the role of PINK1 in dopaminergic neurons. Electrophysiological and behavioral tests indicated that PINK1 elimination enhances the neural transmission from the presynaptic part of dopaminergic neurons in the protocerebral posterior medial region 3 (PPM3) to PPM3 neurons (which are homologous to those in the substantia nigra in humans). Firing properties of the action potential in PPM3 neurons were also altered in the PINK1 knockout genotypes. Abnormal motor ability was also observed in these PINK1 knockout animals. These results indicate that knockout of PINK1 could alter both the input and output properties of PPM3 neurons (Qiao, 2020).
Wan, Z., Xu, J., Huang, Y., Zhai, Y., Ma, Z., Zhou, B. and Cao, Z. (2020). Elevating bioavailable iron levels in mitochondria suppresses the defective phenotypes caused by PINK1 loss-of-function in Drosophila melanogaster. Biochem Biophys Res Commun 532(2): 285-291. PubMed ID: 32873392
Abstract Parkinson's disease (PD) is the second most common progressive neurodegenerative disease, which is characterized by the loss of dopaminergic neurons in the substantia nigra pars compacta (SNpc). Iron deposit was found in the SNpc of PD patients and animal models, however, the mechanisms involved in disturbed iron metabolism remain unknown. Identifying the relationship between iron metabolism and PD is important for finding new therapeutic strategies. This study found that transgenic overexpression (OE) of Drosophila mitoferrin (dmfrn) or knockdown of Fer3HCH significantly mitigated the reduced mitochondrial aconitase activity, abnormal wing posture, flight deficits and mitochondrial morphology defects associated with PINK1 loss-of-function (LOF). Further work demonstrated that dmfrn OE or Fer3HCH knockdown significantly rescued the impaired mitochondrial respiration in PINK1 LOF flies, indicating that dmfrn or Fer3HCH may rescue PINK1 LOF phenotypes through elevating mitochondrial bioavailable iron levels to promote mitochondrial respiration (Wan, 2020).
Rahul, Naz, F., Jyoti, S. and Siddique, Y. H. (2020). Effect of kaempferol on the transgenic Drosophila model of Parkinson's disease. Sci Rep 10(1): 13793. PubMed ID: 32796885
Abstract
The present study was aimed to study the effect of kaempferol, on the transgenic Drosophila model of Parkinson's disease. Kaempferol was added in the diet at final concentration of 10, 20, 30 and 40 µM and the effect was studied on various cognitive and oxidative stress markers. The results of the study showed that kaempferol, delayed the loss of climbing ability as well as the activity of PD flies in a dose dependent manner compared to unexposed PD flies. A dose-dependent reduction in oxidative stress markers was also observed. Histopathological examination of fly brains using anti-tyrosine hydroxylase immunostaining has revealed a significant dose-dependent increase in the expression of tyrosine hydroxylase in PD flies exposed to kaempferol. Molecular docking results revealed that kaempferol binds to human alpha synuclein at specific sites that might results in the inhibition of alpha synuclein aggregation and prevents the formation of Lewy bodies (Rahul, 2020).
Blosser, J. A., Podolsky, E. and Lee, D. (2020). L-DOPA-Induced Dyskinesia in a Genetic Drosophila Model of Parkinson's Disease. Exp Neurobiol 29(4): 273-284. PubMed ID: 32921640
Abstract Motor symptoms in Parkinson's disease (PD) are directly related to the reduction of a neurotransmitter dopamine. Therefore, its precursor L-DOPA became the gold standard for PD treatment. However, chronic use of L-DOPA causes uncontrollable, involuntary movements, called L-DOPA-induced dyskinesia (LID) in the majority of PD patients. LID is complicated and very difficult to manage. Current rodent and non-human primate models have been developed to study LID mainly using neurotoxins. Therefore, it is necessary to develop a LID animal model with defects in genetic factors causing PD in order to study the relation between LID and PD genes such as α-synuclein. This study first showed that a low concentration of L-DOPA (100 μM) rescues locomotion defects (i.e., speed, angular velocity, pause time) in Drosophila larvae expressing human mutant α-synuclein (A53T). This A53T larval model of PD was used to further examine dyskinetic behaviors. High concentrations of L-DOPA (5 or 10 mM) causes hyperactivity such as body bending behavior (BBB) in A53T larva, which resembles axial dyskinesia in rodents. Using ImageJ plugins and other third party software, dyskinetic BBB has been accurately and efficiently quantified. Further, a dopamine agonist pramipexole (PRX) partially rescues BBB caused by high L-DOPA. This Drosophila genetic LID model will provide an important experimental platform to examine molecular and cellular mechanisms underlying LID, to study the role of PD causing genes in the development of LID, and to identify potential targets to slow/reverse LID pathology (Blosser, 2020).
Sun, L., Zhang, J., Chen, W., Chen, Y., Zhang, X., Yang, M., Xiao, M., Ma, F., Yao, Y., Ye, M., Zhang, Z., Chen, K., Chen, F., Ren, Y., Ni, S., Zhang, X., Yan, Z., Sun, Z. R., Zhou, H. M., Yang, H., Xie, S., Haque, M. E., Huang, K. and Yang, Y. (2020). Attenuation of epigenetic regulator SMARCA4 and ERK-ETS signaling suppresses aging-related dopaminergic degeneration. Aging Cell 19(9): e13210. PubMed ID: 32749068
Abstract How complex interactions of genetic, environmental factors and aging jointly contribute to dopaminergic degeneration in Parkinson's disease (PD) is largely unclear. This study applied frequent gene co-expression analysis on human patient substantia nigra-specific microarray datasets to identify potential novel disease-related genes. In vivo Drosophila studies validated two of 32 candidate genes, a chromatin-remodeling factor SMARCA4 and a biliverdin reductase BLVRA. Inhibition of SMARCA4 was able to prevent aging-dependent dopaminergic degeneration not only caused by overexpression of BLVRA but also in four most common Drosophila PD models. Furthermore, down-regulation of SMARCA4 specifically in the dopaminergic neurons prevented shortening of life span caused by α-synuclein and LRRK2. Mechanistically, aberrant SMARCA4 and BLVRA converged on elevated ERK-ETS activity, attenuation of which by either genetic or pharmacological manipulation effectively suppressed dopaminergic degeneration in Drosophila in vivo. Down-regulation of SMARCA4 or drug inhibition of MEK/ERK also mitigated mitochondrial defects in PINK1 (a PD-associated gene)-deficient human cells. These findings underscore the important role of epigenetic regulators and implicate a common signaling axis for therapeutic intervention in normal aging and a broad range of age-related disorders including PD (Sun, 2020).
Chauhan, N., Shrivastava, N. K., Agrawal, N. and Shakarad, M. N. (2020). Wnt2 overexpression protects against PINK1 mutant induced mitochondrial dysfunction and oxidative stress. Wing patterning in faster developing Drosophila is associated with high ecdysone titer and wingless expression. Mech Dev: 103626. PubMed ID: 32526278
Abstract Xia, S. R., Wen, X. Y., Fan, X. L., Chen, X. R., Wei, Z. W., Li, Q. H. and Sun, L. (2020). Wnt2 overexpression protects against PINK1 mutant induced mitochondrial dysfunction and oxidative stress. Mol Med Rep 21(6): 2633-2641. PubMed ID: 32323790
Abstract The PTEN induced putative kinase 1 (PINK1) mutation is the second most common cause of autosomal recessive adolescent Parkinson's disease (PD). Furthermore, mitochondrial disorders and oxidative stress are important mechanisms in the pathogenesis of PD. Numerous members of the Wnt family have been found to be associated with neurodegenerative diseases. Therefore, the present study investigated the role of the Wnt2 gene in PINK1B9 transgenic flies, which is a PD model, and its underlying mechanism. It was identified that overexpression of Wnt2 reduced the abnormality rate of PD transgenic Drosophila and improved their flight ability, while other intervention groups had no significant effect. Furthermore, an increase in ATP concentration normalized mitochondrial morphology, and increased the mRNA expression levels of NADHubiquinone oxidoreductase chain 1 (ND1), ND42, ND75, succinate dehydrogenase complex subunits B, Cytochrome b and Cyclooxygenase 1, which are associated with Wnt2 overexpression. Moreover, overexpression of Wnt2 in PD transgenic Drosophila resulted in the downregulation of reactive oxygen species and malondialdehyde production, and increased manganese superoxide dismutase (MnSOD), while glutathione was not significantly affected. It was found that overexpression of Wnt2 did not alter the protein expression of betacatenin in PINK1B9 transgenic Drosophila, but did increase the expression levels of PPARG coactivator 1alpha (PGC1alpha) and forkhead box subgroup O (FOXO). Collectively, the present results indicated that the Wnt2 gene may have a protective effect on PD PINK1B9 transgenic Drosophila. Thus, it was speculated that the reduction of oxidative stress and the restoration of mitochondrial function via Wnt2 overexpression may be related to the PGC1alpha/FOXO/MnSOD signaling pathway in PINK1 mutant transgenic Drosophila (Xia, 2020).
Shiba-Fukushima, K., Inoshita, T., Sano, O., Iwata, H., Ishikawa, K. I., Okano, H., Akamatsu, W., Imai, Y. and Hattori, N. (2020). A Cell-Based High-Throughput Screening Identified Two Compounds that Enhance PINK1-Parkin Signaling. iScience 23(5): 101048. PubMed ID: 32335362
Abstract Early-onset Parkinson's disease-associated PINK1-Parkin signaling maintains mitochondrial health. Therapeutic approaches for enhancing PINK1-Parkin signaling present a potential strategy for treating various diseases caused by mitochondrial dysfunction. This study reports two chemical enhancers of PINK1-Parkin signaling, identified using a robust cell-based high-throughput screening system. These small molecules, T0466 and T0467, activate Parkin mitochondrial translocation in dopaminergic neurons and myoblasts at low doses that do not induce mitochondrial accumulation of PINK1. Moreover, both compounds reduce unfolded mitochondrial protein levels, presumably through enhanced PINK1-Parkin signaling. These molecules also mitigate the locomotion defect, reduced ATP production, and disturbed mitochondrial Ca(2+) response in the muscles along with the mitochondrial aggregation in dopaminergic neurons through reduced PINK1 activity in Drosophila. These results suggested that T0466 and T0467 may hold promise as therapeutic reagents in Parkinson's disease and related disorders (Shiba-Fukushima, 2020).
Petridi, S., Middleton, C. A., Ugbode, C., Fellgett, A., Covill, L. and Elliott, C. J. H. (2020). In Vivo Visual Screen for Dopaminergic Rab <--> LRRK2-G2019S Interactions in Drosophila Discriminates Rab10 from Rab3. G3 (Bethesda). PubMed ID: 32321836
Abstract LRRK2 mutations cause Parkinson's, but the molecular link from increased kinase activity to pathological neurodegeneration remains undetermined. Previous in vitro assays indicate that LRRK2 substrates include at least 8 Rab GTPases. This hypothesis was examined in vivo in a functional, electroretinogram screen, expressing each Rab with/without LRRK2-G2019S in selected Drosophila dopaminergic neurons. The screen discriminated Rab10 from Rab3. The strongest Rab/LRRK2-G2019S interaction is with Rab10; the weakest with Rab3. Rab10 is expressed in a different set of dopaminergic neurons from Rab3. Thus, anatomical and physiological patterns of Rab10 are related. It is concluded that Rab10 is a valid substrate of LRRK2 in dopaminergic neurons in vivo. It is proposed that variations in Rab expression contribute to differences in the rate of neurodegeneration recorded in different dopaminergic nuclei in Parkinson's (Petridi, 2020).
Xu, Y., Xie, M., Xue, J., Xiang, L., Li, Y., Xiao, J., Xiao, G. and Wang, H. L. (2020). EGCG ameliorates neuronal and behavioral defects by remodeling gut microbiota and TotM expression in Drosophila models of Parkinson's disease. Faseb j. PubMed ID: 32157731
Abstract Parkinson's disease (PD) is the second most common neurodegenerative disease. Eigallocatechin-3-gallate (EGCG), the major polyphenol in green tea, is known to exert a beneficial effect on PD patients. Although some mechanisms were suggested to underlie this intervention, it remains unknown if the EGCG-mediated protection was achieved by remodeling gut microbiota. In the present study, 0.1 mM or 0.5 mM EGCG was administered to the Drosophila melanogaster with PINK1 (PTEN induced putative kinase 1) mutations, a prototype PD model, and their behavioral performances, as well as neuronal/mitochondrial morphology (only for 0.5 mM EGCG treatment) were determined. According to the results, the mutant PINK1(B9) flies exhibited dopaminergic, survival, and behavioral deficits, which were rescued by EGCG supplementation. Meanwhile, EGCG resulted in profound changes in gut microbial compositions in PINK1(B9) flies, restoring the abundance of a set of bacteria. Notably, EGCG protection was blunted when gut microbiota was disrupted by antibiotics. Four bacterial strains were isolated from fly guts and the supplementation of individual Lactobacillus plantarum or Acetobacter pomorum strain exacerbated the neuronal and behavioral dysfunction of PD flies, which could not be rescued by EGCG. Transcriptomic analysis identified TotM as the central gene responding to EGCG or microbial manipulations. Genetic ablation of TotM blocked the recovery activity of EGCG, suggesting that EGCG-mediated protection warrants TotM. Apart from familial form, EGCG was also potent in improving sporadic PD symptoms induced by rotenone treatment, wherein gut microbiota shared regulatory roles. Together, these results suggest the relevance of the gut microbiota-TotM pathway in EGCG-mediated neuroprotection, providing insight into indirect mechanisms underlying nutritional intervention of Parkinson's disease (Xu, 2020).
Pirooznia, S. K., Yuan, C., Khan, M. R., Karuppagounder, S. S., Wang, L., Xiong, Y., Kang, S. U., Lee, Y., Dawson, V. L. and Dawson, T. M. (2020). PARIS induced defects in mitochondrial biogenesis drive dopamine neuron loss under conditions of parkin or PINK1 deficiency. Mol Neurodegener 15(1): 17. PubMed ID: 32138754
Abstract Mutations in PINK1 and parkin cause autosomal recessive Parkinson's disease (PD). Evidence placing PINK1 and parkin in common pathways regulating multiple aspects of mitochondrial quality control is burgeoning. However, compelling evidence to causatively link specific PINK1/parkin dependent mitochondrial pathways to dopamine neuron degeneration in PD is lacking. This study examined how PINK1/parkin mediated regulation of the pathogenic substrate PARIS impacts dopaminergic mitochondrial network homeostasis and neuronal survival in Drosophila. The UAS-Gal4 system was employed for cell-type specific expression of the various transgenes. Effects on dopamine neuronal survival and function were assessed by anti-TH immunostaining and negative geotaxis assays. Defects in mitochondrial biogenesis were shown to drive adult onset progressive loss of dopamine neurons and motor deficits in Drosophila models of PINK1 or parkin insufficiency. Such defects result from PARIS dependent repression of dopaminergic PGC-1alpha and its downstream transcription factors NRF1 and TFAM that cooperatively promote mitochondrial biogenesis. Dopaminergic accumulation of human or Drosophila PARIS recapitulates these neurodegenerative phenotypes that are effectively reversed by PINK1, parkin or PGC-1alpha overexpression in vivo. PARIS is the only co-substrate of PINK1 and parkin to specifically accumulate in the DA neurons and cause neurodegeneration and locomotor defects stemming from disrupted dopamine signaling. These findings identify a highly conserved role for PINK1 and parkin in regulating mitochondrial biogenesis and promoting mitochondrial health via the PARIS/ PGC-1alpha axis. The Drosophila models described in this study effectively recapitulate the cardinal PD phenotypes and thus will facilitate identification of novel regulators of mitochondrial biogenesis for physiologically relevant therapeutic interventions (Pirooznia, 2020).
Casu, M. A., Mocci, I., Isola, R., Pisanu, A., Boi, L., Mulas, G., Greig, N. H., Setzu, M. D. and Carta, A. R. (2020). Neuroprotection by the Immunomodulatory Drug Pomalidomide in the Drosophila LRRK2(WD40) Genetic Model of Parkinson's Disease. Front Aging Neurosci 12: 31. PubMed ID: 32116655
Abstract The search for new disease-modifying drugs for Parkinson's disease (PD) is a slow and highly expensive process, and the repurposing of drugs already approved for different medical indications is becoming a compelling alternative option for researchers. Genetic variables represent a predisposing factor to the disease and mutations in leucine-rich repeat kinase 2 (LRRK2) locus have been correlated to late-onset autosomal-dominant PD. The common fruit fly Drosophila melanogaster carrying the mutation LRRK2 loss-of-function in the WD40 domain (LRRK2(WD40)), is a simple in vivo model of PD and is a valid tool to first evaluate novel therapeutic approaches to the disease. Recent studies have suggested a neuroprotective activity of immunomodulatory agents in PD models. In this study the immunomodulatory drug Pomalidomide (POM), a Thalidomide derivative, was examined in the Drosophila LRRK2(WD40) genetic model of PD. Mutant and wild type flies received increasing POM doses (1, 0.5, 0.25 mM) through their diet from day 1 post eclosion, until postnatal day (PN) 7 or 14, when POM's actions were evaluated by quantifying changes in climbing behavior as a measure of motor performance, the number of brain dopaminergic neurons and T-bars, mitochondria integrity. LRRK2(WD40) flies displayed a spontaneous age-related impairment of climbing activity, and POM significantly and dose-dependently improved climbing performance both at PN 7 and PN 14. LRRK2(WD40) fly motor disability was underpinned by a progressive loss of dopaminergic neurons in posterior clusters of the protocerebrum, which are involved in the control of locomotion, by a low number of T-bars density in the presynaptic bouton active zones. POM treatment fully rescued the cell loss in all posterior clusters at PN 7 and PN 14 and significantly increased the T-bars density. Moreover, several damaged mitochondria with dilated cristae were observed in LRRK2(WD40) flies treated with vehicle but not following POM. This study demonstrates the neuroprotective activity of the immunomodulatory agent POM in a genetic model of PD. POM is an FDA-approved clinically available and well-tolerated drug used for the treatment of multiple myeloma. If further validated in mammalian models of PD, POM could rapidly be clinically tested in humans (Casu, 2020).
Ham, S. J., Lee, D., Yoo, H., Jun, K., Shin, H. and Chung, J. (2020). Decision between mitophagy and apoptosis by Parkin via VDAC1 ubiquitination. Proc Natl Acad Sci U S A. PubMed ID: 32047033
Abstract VDAC1 is a critical substrate of Parkin responsible for the regulation of mitophagy and apoptosis. This study demonstrates that VDAC1 can be either mono- or polyubiquitinated by Parkin in a PINK1-dependent manner. VDAC1 deficient with polyubiquitination (VDAC1 Poly-KR) hampers mitophagy, but VDAC1 deficient with monoubiquitination (VDAC1 K274R) promotes apoptosis by augmenting the mitochondrial calcium uptake through the mitochondrial calcium uniporter (MCU) channel. The transgenic flies expressing Drosophila Porin K273R, corresponding to human VDAC1 K274R, show Parkinson disease (PD)-related phenotypes including locomotive dysfunction and degenerated dopaminergic neurons, which are relieved by suppressing MCU and mitochondrial calcium uptake. To further confirm the relevance of these findings in PD, a missense mutation of Parkin was discovered in PD patients, T415N, which lacks the ability to induce VDAC1 monoubiquitination but still maintains polyubiquitination. Interestingly, Drosophila Parkin T433N, corresponding to human Parkin T415N, fails to rescue the PD-related phenotypes of Parkin-null flies. Taken together, these results suggest that VDAC1 monoubiquitination plays important roles in the pathologies of PD by controlling apoptosis (Ham, 2020).
Lee, J. J., Andreazza, S. and Whitworth, A. J. (2020). The STING pathway does not contribute to behavioural or mitochondrial phenotypes in Drosophila Pink1/parkin or mtDNA mutator models. Sci Rep 10(1): 2693. PubMed ID: 32060339
Abstract Mutations in PINK1 and Parkin/PRKN cause the degeneration of dopaminergic neurons in familial forms of Parkinson's disease but the precise pathogenic mechanisms are unknown. The PINK1/Parkin pathway has been described to play a central role in mitochondrial homeostasis by signalling the targeted destruction of damaged mitochondria, however, how disrupting this process leads to neuronal death was unclear until recently. An elegant study in mice revealed that the loss of Pink1 or Prkn coupled with an additional mitochondrial stress resulted in the aberrant activation of the innate immune signalling, mediated via the cGAS/Relish, was insufficient to suppress the behavioural deficits or mitochondria disruption in the Pink1/parkin mutants. Thus, it is concluded that phenotypes associated with loss of Pink1/parkin are not universally due to aberrant activation of the STING pathway (Lee, 2020).
Diana, A., Collu, M., Casu, M. A., Mocci, I., Aguilar-Santelises, M. and Setzu, M. D. (2020). Improvements of motor performances in the Drosophila LRRK2 loss-of-function model of Parkinson's disease: Effects of dialyzed leucocyte Extracts from Human Serum. Brain Sci 10(1). PubMed ID: 31947539
Abstract Within neurodegenerative syndromes, Parkinson's disease (PD) is typically associated with its locomotor defects, sleep disturbances and related dopaminergic (DA) neuron loss. The fruit fly, Drosophila melanogaster, with leucine-rich repeat kinase 2 mutants (LRRK2) loss-of-function in the WD40 domain, provides mechanistic insights into corresponding human behaviour, possibly disclosing some physiopathologic features of PD in both genetic and sporadic forms. Moreover, several data support the boosting impact of innate and adaptive immunity pathways for driving the progression of PD. In this context, human dialyzable leukocyte extracts (DLE) have been extensively used to transfer antigen-specific information that influences the activity of various immune components, including inflammatory cytokines. Hence, the main goal of this study was to ascertain the therapeutic potential of DLE from male and female donors on D. melanogaster LRRK2 loss-of-function, as compared to D. melanogaster wild-type (WT), in terms of rescuing physiological parameters, such as motor and climbing activities, which are severely compromised in the mutant flies. Finally, in search of the anatomical structures responsible for restored functions in parkinsonian-like mutant flies, this study found a topographical correlation between improvement of locomotor performances and an increased number of dopaminergic neurons in selective areas of LRRK2 mutant brains (Diana, 2020).
Imai, Y., Inoshita, T., Meng, H., Shiba-Fukushima, K., Hara, K. Y., Sawamura, N. and Hattori, N. (2019). Light-driven activation of mitochondrial proton-motive force improves motor behaviors in a Drosophila model of Parkinson's disease. Commun Biol 2: 424. PubMed ID: 31799427
Abstract Mitochondrial degeneration is considered one of the major causes of Parkinson's disease (PD). Improved mitochondrial functions are expected to be a promising therapeutic strategy for PD. This study introduced a light-driven proton transporter, Delta-rhodopsin (dR), to Drosophila mitochondria, where the mitochondrial proton-motive force (Deltap) and mitochondrial membrane potential are maintained in a light-dependent manner. The loss of the PD-associated mitochondrial gene CHCHD2 resulted in reduced ATP production, enhanced mitochondrial peroxide production and lower Ca(2+)-buffering activity in dopaminergic (DA) terminals in flies. These cellular defects were improved by the light-dependent activation of mitochondrion-targeted dR (mito-dR). Moreover, mito-dR reversed the pathology caused by the CHCHD2 deficiency to suppress alpha-synuclein aggregation, DA neuronal loss, and elevated lipid peroxidation in brain tissue, improving motor behaviors. This study suggests the enhancement of Deltap by mito-dR as a therapeutic mechanism that ameliorates neurodegeneration by protecting mitochondrial functions (Imai, 2019).
Chung, H. J., Islam, M. S., Rahman, M. M. and Hong, S. T. (2019).Neuroprotective function of Omi to alpha-synuclein-induced neurotoxicity. Neurobiol Dis: 104706. PubMed ID: 31837423
Abstract Yedlapudi, D., Xu, L., Luo, D., Marsh, G. B., Todi, S. V. and Dutta, A. K. (2019). Targeting alpha synuclein and amyloid beta by a multifunctional, brain-penetrant dopamine D2/D3 agonist D-520: Potential therapeutic application in Parkinson's disease with dementia. Sci Rep 9(1): 19648. PubMed ID: 31873106
Abstract Sim, J. P. L., Ziyin, W., Basil, A. H., Lin, S., Chen, Z., Zhang, C., Zeng, L., Cai, Y. and Lim, K. L. (2019). Identification of PP2A and S6 kinase as modifiers of Leucine-rich repeat kinase-induced neurotoxicity. Neuromolecular Med. PubMed ID: 31664682
Abstract Mutations in LRRK2 are currently recognized as the most common monogenetic cause of Parkinsonism. The elevation of kinase activity of LRRK2 that frequently accompanies its mutations is widely thought to contribute to its toxicity. Accordingly, many groups have developed LRRK2-specific kinase inhibitors as a potential therapeutic strategy. Given that protein phosphorylation is a reversible event, this study sought to elucidate the phosphatase(s) that can reverse LRRK2-mediated phosphorylation, with the view that targeting this phosphatase(s) may similarly be beneficial. Using an unbiased RNAi phosphatase screen conducted in a Drosophila LRRK2 model, PP2A was identified as a genetic modulator of LRRK2-induced neurotoxicity. Further, ribosomal S6 kinase (S6K), a target of PP2A, was also identified as a novel regulator of LRRK2 function. Finally, modulation of PP2A or S6K activities were shown to ameliorate LRRK2-associated disease phenotype in Drosophila.
Man Anh, H., Linh, D. M., My Dung, V. and Thi Phuong Thao, D. (2019). Evaluating dose- and time-dependent effects of vitamin C treatment on a Parkinson's disease fly model. Parkinsons Dis 2019: 9720546. PubMed ID: 30719278
Abstract
Parkinson's disease (PD) is a common neurodegenerative disorder and characterized by progressive locomotive defects and loss of dopaminergic neurons (DA neuron). Currently, there is no potent therapy to cure PD, and the medications merely support to control the symptoms. It is difficult to develop an effective treatment, since the PD onset mechanism of PD is still unclear. Oxidative stress is considered as a major cause of neurodegenerative diseases, and there is increasing evidence for the association between PD and oxidative stress. Therefore, antioxidant treatment may be a promising therapy for PD. Drosophila with knockdown of dUCH, a homolog of UCH-L1 which is a PD-related gene, exhibited PD-like phenotypes including progressive locomotive impairments and DA neuron degeneration. Moreover, knockdown of dUCH led to elevated level of ROS. Thus, dUCH knockdown flies can be used as a model for screening of potential antioxidants for treating PD. Previous studies demonstrated that curcumin at 1 mM and vitamin C at 0.5 mM could improve PD-like phenotypes induced by this knockdown. With the purpose of further investigating the efficiency of vitamin C in PD treatment, dUCH knockdown Drosophila model was used to examine the dose- and time-dependent effects of vitamin C on PD-like phenotypes. The results showed that although vitamin C exerted neuroprotective effects, high doses of vitamin C and long-term treatment with this antioxidant also resulted in side effects on physiology. It is suggested that dose-dependent effects of vitamin C should be considered when used for treating PD (Man Anh, 2019).
Aggarwal, A., Reichert, H. and VijayRaghavan, K. (2019). A locomotor assay reveals deficits in heterozygous Parkinson's disease model and proprioceptive mutants in adult Drosophila. Proc Natl Acad Sci U S A. PubMed ID: 31748267
Abstract Severe locomotor impairment is a common phenotype of neurodegenerative disorders such as Parkinson's disease (PD). Drosophila models of PD, studied for more than a decade, have helped in understanding the interaction between various genetic factors, such as parkin and PINK1, in this disease. To characterize locomotor behavioral phenotypes for these genes, fly climbing assays have been widely used. While these simple current assays for locomotor defects in Drosophila mutants measure some locomotor phenotypes well, it is possible that detection of subtle changes in behavior is important to understand the manifestation of locomotor disorders. This study introduces a climbing behavior assay which provides such fine-scale behavioral data and tests this proposition for the Drosophila model. This inexpensive, fully automated assay was used to quantitatively characterize the climbing behavior at high parametric resolution in 3 contexts. First, wild-type flies were characterized, and a hitherto unknown sexual dimorphism in climbing behavior was uncovered. Second, climbing behavior was studied of heterozygous mutants of genes implicated in the fly PD model, and previously unreported prominent locomotor defects were revealed in some of these heterozygous fly lines. Finally, locomotor defects were studied in a homozygous proprioceptory mutation (Trp-gamma1) known to affect fine motor control in Drosophila. Moreover, aberrant geotactic behavior was identified in Trp-gamma1 mutants, thereby opening up a finer assay for geotaxis and its genetic basis. This assay is therefore a cost-effective, general tool for measuring locomotor behaviors of wild-type and mutant flies in fine detail and can reveal subtle motor defects (Aggarwal, 2019).
Mori, A., Hatano, T., Inoshita, T., Shiba-Fukushima, K., Koinuma, T., Meng, H., Kubo, S. I., Spratt, S., Cui, C., Yamashita, C., Miki, Y., Yamamoto, K., Hirabayashi, T., Murakami, M., Takahashi, Y., Shindou, H., Nonaka, T., Hasegawa, M., Okuzumi, A., Imai, Y. and Hattori, N. (2019). Parkinson's disease-associated iPLA2-VIA/PLA2G6 regulates neuronal functions and alpha-synuclein stability through membrane remodeling. Proc Natl Acad Sci U S A 116(41): 20689-20699. PubMed ID: 31548400
Abstract Mutations in the iPLA2-VIA/PLA2G6 gene are responsible for PARK14-linked Parkinson's disease (PD) with alpha-synucleinopathy. However, it is unclear how iPLA2-VIA mutations lead to alpha-synuclein (alpha-Syn) aggregation and dopaminergic (DA) neurodegeneration. This study reports that iPLA2-VIA-deficient Drosophila exhibits defects in neurotransmission during early developmental stages and progressive cell loss throughout the brain, including degeneration of the DA neurons. Lipid analysis of brain tissues reveals that the acyl-chain length of phospholipids is shortened by iPLA2-VIA loss, which causes endoplasmic reticulum (ER) stress through membrane lipid disequilibrium. The introduction of wild-type human iPLA2-VIA or the mitochondria-ER contact site-resident protein C19orf12 in iPLA2-VIA-deficient flies rescues the phenotypes associated with altered lipid composition, ER stress, and DA neurodegeneration, whereas the introduction of a disease-associated missense mutant, iPLA2-VIA A80T, fails to suppress these phenotypes. The acceleration of alpha-Syn aggregation by iPLA2-VIA loss is suppressed by the administration of linoleic acid, correcting the brain lipid composition. These findings suggest that membrane remodeling by iPLA2-VIA is required for the survival of DA neurons and alpha-Syn stability (Mori, 2019).
Ding, Y., Kong, D., Zhou, T., Yang, N. D., Xin, C., Xu, J., Wang, Q., Zhang, H., Wu, Q., Lu, X., Lim, K., Ma, B., Zhang, C., Li, L. and Huang, W. (2019). alpha-Arbutin protects against Parkinson's disease-associated mitochondrial dysfunction in vitro and in vivo. Neuromolecular Med. PubMed ID: 31401719
Abstract Parkinson's disease (PD), the most common neurodegenerative movement disorder, is characterized by the progressive loss of dopaminergic neurons in substantia nigra. The underlying mechanisms of PD pathogenesis have not been fully illustrated and currently PD remains incurable. Accumulating evidences suggest that mitochondrial dysfunction plays pivotal role in the dopaminergic neuronal death. Therefore, discovery of novel and safe agent for rescuing mitochondrial dysfunction would benefit PD treatment. This study demonstrated that alpha-Arbutin (Arb), a natural polyphenol extracted from Ericaceae species, displayed significant protective effect on the rotenone (Rot)-induced mitochondrial dysfunction and apoptosis of human neuroblastoma cell (SH-SY5Y). It was further found that the neuroprotective effect of Arb was associated with ameliorating oxidative stress, stabilizing of mitochondrial membrane potential, and enhancing adenosine triphosphate production. To investigate the underlying mechanism, the AMP-activated protein kinase and autophagy pathway was checked, were found to be involved in the neuroprotection of Arb. Moreover, the protective effect of Arb was explored in Drosophila PD model, and Arb was found to rescue parkin deficiency-induced motor function disability and mitochondrial abnormality of Drosophila. Taken together, this study demonstrated that Arb got excellent neuroprotective effect on PD models both in vitro and in vivo and Arb might serve as a potent therapeutic agent for the treatment of PD (DingY, 2019).
Wu, S., Tan, K. J., Govindarajan, L. N., Stewart, J. C., Gu, L., Ho, J. W. H., Katarya, M., Wong, B. H., Tan, E. K., Li, D., Claridge-Chang, A., Libedinsky, C., Cheng, L. and Aw, S. S. (2019). Fully automated leg tracking of Drosophila neurodegeneration models reveals distinct conserved movement signatures. PLoS Biol 17(6): e3000346. PubMed ID: 31246996
Abstract Some neurodegenerative diseases, like Parkinsons Disease (PD) and Spinocerebellar ataxia 3 (SCA3), are associated with distinct, altered gait and tremor movements that are reflective of the underlying disease etiology. Drosophila melanogaster models of neurodegeneration have led to understanding of the molecular mechanisms of disease. However, it is unknown whether specific gait and tremor dysfunctions also occur in fly disease mutants. To answer this question, a machine-learning image-analysis program, Feature Learning-based LImb segmentation and Tracking (FLLIT), was developed that automatically tracks leg claw positions of freely moving flies recorded on high-speed video, producing a series of gait measurements. Notably, unlike other machine-learning methods, FLLIT generates its own training sets and does not require user-annotated images for learning. Using FLLIT, high-throughput and high-resolution analysis of gait and tremor features were carried out in Drosophila neurodegeneration mutants for the first time. Fly models of PD and SCA3 exhibited markedly different walking gait and tremor signatures, which recapitulated characteristics of the respective human diseases. Selective expression of mutant SCA3 in dopaminergic neurons led to a gait signature that more closely resembled those of PD flies. This suggests that the behavioral phenotype depends on the neurons affected rather than the specific nature of the mutation. Different mutations produced tremors in distinct leg pairs, indicating that different motor circuits were affected. Using this approach, fly models can be used to dissect the neurogenetic mechanisms that underlie movement disorders (Wu, 2019).
Doktor, B., Damulewicz, M. and Pyza, E. (2019). Effects of MUL1 and PARKIN on the circadian clock, brain and behaviour in Drosophila Parkinson's disease models. BMC Neurosci 20(1): 24. PubMed ID: 31138137
Abstract Mutants which carry mutations in genes encoding mitochondrial ligases MUL1 and PARKIN are convenient Drosophila models of Parkinson's disease (PD). In several studies it has been shown that in Parkinson's disease sleep disturbance occurs, which may be the result of a disturbed circadian clock. This study found that the ROS level was higher, while the anti-oxidant enzyme SOD1 level was lower in mul1(A6) and park(1) mutants than in the white mutant used as a control. Moreover, mutations of both ligases affected circadian rhythms and the clock. The expression of clock genes per, tim and clock and the level of PER protein were changed in the mutants. Moreover, expression of ATG5, an autophagy protein also involved in circadian rhythm regulation, was decreased in the brain and in PDF-immunoreactive large ventral lateral clock neurons. The observed changes in the molecular clock resulted in a longer period of locomotor activity rhythm, increased total activity and shorter sleep at night. Finally, the lack of both ligases led to decreased longevity and climbing ability of the flies. It is concluded that all of the changes observed in the brains of these Drosophila models of PD, in which mitochondrial ligases MUL1 and PARKIN do not function, may explain the mechanisms of some neurological and behavioural symptoms of PD (Doktor, 2019).
Sakai, R., Suzuki, M., Ueyama, M., Takeuchi, T., Minakawa, E. N., Hayakawa, H., Baba, K., Mochizuki, H. and Nagai, Y. (2019). E46K mutant alpha-synuclein is more degradation resistant and exhibits greater toxic effects than wild-type alpha-synuclein in Drosophila models of Parkinson's disease. PLoS One 14(6): e0218261. PubMed ID: 31242217
Abstract Alpha-synuclein (alphaSyn) plays key roles in the pathogenesis of Parkinson's disease (PD). The mechanisms underlying the variance in the clinical phenotypes of familial PD caused by missense mutations in the alphaSyn gene remain elusive. This study established novel Drosophila models expressing either wild-type (WT) alphaSyn or one of five alphaSyn mutants (A30P, E46K, H50Q, G51D, and A53T) using site-specific transgenesis, which express transgenes at equivalent levels. Expression of either WT or mutant alphaSyn in the compound eyes by the GMR-GAL4 driver caused mild rough eye phenotypes with no obvious difference among the mutants. Upon pan-neuronal expression by the nSyb-GAL4 driver, these alphaSyn-expressing flies showed a progressive decline in locomotor function. Notably, it was found that E46K, H50Q, G51D, and A53T alphaSyn-expressing flies showed earlier onset of locomotor dysfunction than WT alphaSyn-expressing flies, suggesting their enhanced toxic effects. Whereas mRNA levels of WT and mutant alphaSyn were almost equivalent, it was found that protein expression levels of E46K alphaSyn were higher than those of WT alphaSyn. In vivo chase experiments using the drug-inducible GMR-GeneSwitch driver demonstrated that degradation of E46K alphaSyn protein was significantly slower than WT alphaSyn protein, indicating that the E46K alphaSyn mutant gains resistance to degradation in vivo. It is therefore conclude that the novel site-specific transgenic fly models expressing either WT or mutant alphaSyn are useful to explore the mechanisms by which different alphaSyn mutants gain toxic functions in vivo (Sakai, 2019).
Cackovic, J., Gutierrez-Luke, S., Call, G. B., Juba, A., O'Brien, S., Jun, C. H. and Buhlman, L. M. (2018). Vulnerable parkin loss-of-function Drosophila dopaminergic neurons have advanced mitochondrial aging, mitochondrial network loss and transiently reduced autophagosome recruitment. Front Cell Neurosci 12: 39. PubMed ID: 29497364
Abstract Selective degeneration of substantia nigra dopaminergic (DA) neurons is a hallmark pathology of familial Parkinson's disease (PD). While the mechanism of degeneration is elusive, abnormalities in mitochondrial function and turnover are strongly implicated. An Autosomal Recessive-Juvenile Parkinsonism (AR-JP) Drosophila melanogaster model exhibits DA neurodegeneration as well as aberrant mitochondrial dynamics and function. Disruptions in mitophagy have been observed in parkin loss-of-function models, and changes in mitochondrial respiration have been reported in patient fibroblasts. Whether loss of parkin causes selective DA neurodegeneration in vivo as a result of lost or decreased mitophagy is unknown. This study employs the use of fluorescent constructs expressed in Drosophila DA neurons that are functionally homologous to those of the mammalian substantia nigra. Evidence is provided that degenerating DA neurons in parkin loss-of-function mutant flies have advanced mitochondrial aging and that mitochondrial networks are fragmented and contain swollen organelles. This study also found that mitophagy initiation is decreased in park (Drosophila parkin/PARK2 ortholog) homozygous mutants, but autophagosome formation is unaffected, and mitochondrial network volumes are decreased. As the fly ages, autophagosome recruitment becomes similar to control, while mitochondria continue to show signs of damage, and climbing deficits persist. Interestingly, aberrant mitochondrial morphology, aging and mitophagy initiation were not observed in DA neurons that do not degenerate. These results suggest that parkin is important for mitochondrial homeostasis in vulnerable Drosophila DA neurons, and that loss of parkin-mediated mitophagy may play a role in degeneration of relevant DA neurons or motor deficits in this model (Cackovic, 2018).
Ran, D., Xie, B., Gan, Z., Sun, X., Gu, H. and Yang, J. (2018). Melatonin attenuates hLRRK2-induced long-term memory deficit in a Drosophila model of Parkinson's disease. Biomed Rep 9(3): 221-226. PubMed ID: 30271597
Abstract As the most common genetic cause of Parkinson's disease (PD), the role of human leucine-rich repeat kinase 2 (hLRRK2) in the efficacy of PD treatment is a focus of study. A previous study demonstrated that mushroom body (MB) expression of hLRRK2 in Drosophila could recapitulate the clinical feature of sleep disturbances observed in PD patients, and melatonin (MT) treatment could attenuate the hLRRK2-induced sleep disorders and synaptic dysfunction, suggesting the therapeutic potential of MT in PD patients carrying hLRRK2 mutations; however, no further study into the impacts on memory deficit was conducted. Therefore, in the current paper, the study of the effects of MT on hLRRK2 flies was continued, to determine its potential role in the improvement of memory deficit in PD. To achieve this, the Drosophila learning and memory phases, including short- and long-term memory, were recorded; furthermore, the effect of MT on calcium channel activity during neurotransmission was detected using electrophysiology patch clamp recordings. It was demonstrated that MT treatment reversed hLRRK2-induced long-term memory deficits in Drosophila; furthermore, MT reduced MB calcium channel activities. These findings suggest that MT may exerts therapeutic effects on the long-term memory of PD patients via calcium channel modulation, thus providing indication of its potential to maintain cognitive function in PD patients (Ran, 2018).
Himmelberg, M. M., West, R. J. H., Elliott, C. J. H. and Wade, A. R. (2018). Abnormal visual gain control and excitotoxicity in early-onset Parkinson's disease Drosophila models. J Neurophysiol. 119(3):957-970 PubMed ID: 29142100
Abstract The excitotoxic theory of Parkinson's disease (PD) hypothesises that a pathophysiological degeneration of dopaminergic neurons stems from neural hyperactivity at early stages of disease, leading to mitochondrial stress and cell death. Recent research has harnessed the visual system of Drosophila PD models to probe this hypothesis. This study investigated whether abnormal visual sensitivity and excitotoxicity occur in early-onset PD Drosophila models DJ-1Delta72, DJ1-Delta93, and PINK15. An electroretinogram was used to record steady state visually evoked potentials driven by temporal contrast stimuli. At 1 day of age, all early-onset PD mutants had a twofold increase in response amplitudes when compared to w- controls. Further, excitotoxicity was found to occur in older early-onset PD models after increased neural demand is applied via visual stimulation. In an additional analysis, a linear discriminant analysis was used to test whether there were subtle variations in neural gain control that could be used to classify Drosophila into their correct age and genotype. The discriminant analysis was highly accurate, classifying Drosophila into their correct genotypic class at all age groups at 50-70% accuracy (20% chance baseline). Differences in cellular processes link to subtle alterations in neural network operation in young flies, all of which lead to the same pathogenic outcome. These data are the first to demonstrate abnormal gain control and excitotoxicity in early-onset PD Drosophila mutants. It is concluded that early-onset PD mutations may be linked to more sensitive neuronal signalling in prodromal animals that may cause the expression of PD symptomologies later in life (Himmelberg, 2017).
Valadas, J. S., Esposito, G., Vandekerkhove, D., Miskiewicz, K., Deaulmerie, L., Raitano, S., Seibler, P., Klein, C. and Verstreken, P. (2018). ER lipid defects in neuropeptidergic neurons impair sleep patterns in Parkinson's disease. Neuron 98(6): 1155-1169.e1156. PubMed ID: 29887339
Abstract Parkinson's disease patients report disturbed sleep patterns long before motor dysfunction. In parkin and pink1 models, this study has identified circadian rhythm and sleep pattern defects and has mapped these to specific neuropeptidergic neurons in fly models and in hypothalamic neurons differentiated from patient induced pluripotent stem cells (iPSCs). Parkin and Pink1 control the clearance of mitochondria by protein ubiquitination. Although major defects were not observed in mitochondria of mutant neuropeptidergic neurons, excess of endoplasmic reticulum-mitochondrial contacts was found. These excessive contact sites cause abnormal lipid trafficking that depletes phosphatidylserine from the endoplasmic reticulum (ER) and disrupts the production of neuropeptide-containing vesicles. Feeding mutant animals phosphatidylserine rescues neuropeptidergic vesicle production and acutely restores normal sleep patterns in mutant animals. Hence, sleep patterns and circadian disturbances in Parkinson's disease models are explained by excessive ER-mitochondrial contacts, and blocking their formation or increasing phosphatidylserine levels rescues the defects in vivo (Valadas, 2018).
Prasad, V., Wasser, Y., Hans, F., Goswami, A., Katona, I., Outeiro, T. F., Kahle, P. J., Schulz, J. B. and Voigt, A. (2018). Monitoring alpha-synuclein multimerization in vivo. Faseb j: fj201800148RRR. PubMed ID: 30252534
Abstract The pathophysiology of Parkinson's disease is characterized by the abnormal accumulation of alpha-synuclein (alpha-Syn), eventually resulting in the formation of Lewy bodies and neurites in surviving neurons in the brain. Although alpha-Syn aggregation has been extensively studied in vitro, there is limited in vivo knowledge on alpha-Syn aggregation. This study used the powerful genetics of Drosophila melanogaster and developed an in vivo assay to monitor alpha-Syn accumulation by using a bimolecular fluorescence complementation assay. Both genetic and pharmacologic manipulations affected alpha-Syn accumulation. Interestingly, it was also found that alterations in the cellular protein degradation mechanisms strongly influenced alpha-Syn accumulation. Administration of compounds identified as risk factors for Parkinson's disease, such as rotenone or heavy metal ions, had only mild or even no impact on alpha-Syn accumulation in vivo. Finally, this study showed that increasing phosphorylation of alpha-Syn at serine 129 enhances the accumulation and toxicity of alpha-Syn. Altogether, this study establishes a novel model to study alpha-Syn accumulation and illustrates the complexity of manipulating proteostasis in vivo (Prasad, 2018).
Lee, K. S., Huh, S., Lee, S., Wu, Z., Kim, A. K., Kang, H. Y. and Lu, B. (2018). Altered ER-mitochondria contact impacts mitochondria calcium homeostasis and contributes to neurodegeneration in vivo in disease models. Proc Natl Acad Sci U S A. PubMed ID: 30185553
Abstract Calcium (Ca(2+)) homeostasis is essential for neuronal function and survival. Altered Ca(2+) homeostasis has been consistently observed in neurological diseases. How Ca(2+) homeostasis is achieved in various cellular compartments of disease-relevant cell types is not well understood. This study shows in Drosophila Parkinson's disease (PD) models that Ca(2+) transport from the endoplasmic reticulum (ER) to mitochondria through the ER-mitochondria contact site (ERMCS) critically regulates mitochondrial Ca(2+) (mito-Ca(2+)) homeostasis in dopaminergic (DA) neurons, and that the PD-associated PINK1 protein modulates this process. In PINK1 mutant DA neurons, the ERMCS is strengthened and mito-Ca(2+) level is elevated, resulting in mitochondrial enlargement and neuronal death. Miro, a well-characterized component of the mitochondrial trafficking machinery, mediates the effects of PINK1 on mito-Ca(2+) and mitochondrial morphology, apparently in a transport-independent manner. Miro overexpression mimics PINK1 loss-of-function effect, whereas inhibition of Miro or components of the ERMCS, or pharmacological modulation of ERMCS function, rescued PINK1 mutant phenotypes. Mito-Ca(2+) homeostasis is also altered in the LRRK2-G2019S model of PD and the PAR-1/MARK model of neurodegeneration, and genetic or pharmacological restoration of mito-Ca(2+) level is beneficial in these models. Our results highlight the importance of mito-Ca(2+) homeostasis maintained by Miro and the ERMCS to mitochondrial physiology and neuronal integrity. Targeting this mito-Ca(2+) homeostasis pathway holds promise for a therapeutic strategy for neurodegenerative diseases (Lee, 2018).
Issa, A. R., Sun, J., Petitgas, C., Mesquita, A., Dulac, A., Robin, M., Mollereau, B., Jenny, A., Cherif-Zahar, B. and Birman, S. (2018). The lysosomal membrane protein LAMP2A promotes autophagic flux and prevents SNCA-induced Parkinson disease-like symptoms in the Drosophila brain. Autophagy. PubMed ID: 29989488
Abstract The autophagy-lysosome pathway plays a fundamental role in the clearance of aggregated proteins and protection against cellular stress and neurodegenerative conditions. Alterations in autophagy processes, including macroautophagy and chaperone-mediated autophagy (CMA), have been described in Parkinson disease (PD). CMA is a selective autophagic process that depends on LAMP2A (Lysosomal associated membrane protein 2A), a mammal and bird-specific membrane glycoprotein that translocates cytosolic proteins containing a KFERQ-like peptide motif across the lysosomal membrane. Drosophila reportedly lack CMA and use endosomal microautophagy (eMI) as an alternative selective autophagic process. This study reports that neuronal expression of human LAMP2A protected Drosophila against starvation and oxidative stress, and delayed locomotor decline in aging flies without extending their lifespan. LAMP2A also prevented the progressive locomotor and oxidative defects induced by neuronal expression of PD-associated human SNCA (synuclein alpha) with alanine-to-proline mutation at position 30 (SNCA(A30P)). LAMP2A expression stimulated selective autophagy in the adult brain and not in the larval fat body. Noteworthy, neurally expressed LAMP2A markedly upregulated levels of Drosophila Atg5, a key macroautophagy initiation protein, and of the Atg5-containing complex, and that it increased the density of Atg8a/LC3-positive puncta, which reflects the formation of autophagosomes. Furthermore, LAMP2A efficiently prevented accumulation of the autophagy defect marker Ref(2)P/p62 in the adult brain under acute oxidative stress. These results indicate that LAMP2A can promote autophagosome formation and potentiate autophagic flux in the Drosophila brain, leading to enhanced stress resistance and neuroprotection (Issa, 2018).
Basso, V., Marchesan, E., Peggion, C., Chakraborty, J., von Stockum, S., Giacomello, M., Ottolini, D., Debattisti, V., Caicci, F., Tasca, E., Pegoraro, V., Angelini, C., Antonini, A., Bertoli, A., Brini, M. and Ziviani, E. (2018). Regulation of ER-mitochondria contacts by Parkin via Mfn2. Pharmacol Res. PubMed ID: 30219582
Abstract Parkin, an E3 ubiquitin ligase and a Parkinson's disease (PD) related gene, translocates to impaired mitochondria and drives their elimination via autophagy, a process known as mitophagy. Mitochondrial pro-fusion protein Mitofusins (Mfn1 and Mfn2) were found to be a target for Parkin mediated ubiquitination. Mfns are transmembrane GTPase embedded in the outer membrane of mitochondria, which are required on adjacent mitochondria to mediate fusion. In mammals, Mfn2 also forms complexes that are capable of tethering mitochondria to endoplasmic reticulum (ER), a structural feature essential for mitochondrial energy metabolism, calcium (Ca(2+)) transfer between the organelles and Ca(2+) dependent cell death. Despite its fundamental physiological role, the molecular mechanisms that control ER-mitochondria cross talk are obscure. Ubiquitination has recently emerged as a powerful tool to modulate protein function, via regulation of protein subcellular localization and protein ability to interact with other proteins. Ubiquitination is also a reversible mechanism, which can be actively controlled by opposing ubiquitination-deubiquitination events. This work found that in Parkin deficient cells and parkin mutant human fibroblasts, the tether between ER and mitochondria is decreased. The site of Parkin dependent ubiquitination was identified, and it was shown that the non-ubiquitinatable Mfn2 mutant fails to restore ER-mitochondria physical and functional interaction. Finally, advantage was taken of an established in vivo model of PD to demonstrate that manipulation of ER-mitochondria tethering by expressing an ER-mitochondria synthetic linker is sufficient to rescue the locomotor deficit associated to an in vivo Drosophila model of PD (Basso, 2018).
Kim, E. Y., Kang, K. H. and Koh, H. (2018). Cyclophilin 1 (Cyp1) mutation ameliorates oxidative stress-induced defects in a Drosophila DJ-1 null mutant. Biochem Biophys Res Commun. PubMed ID: 30297105
Abstract Drosophila cyclophilin 1 (Cyp1) is a structural and functional homolog of mammalian cyclophilin D (CypD), a unique mitochondrial cyclophilin (Cyp) that regulates the inner mitochondrial membrane permeability transition and cell survival under cellular stresses such as oxidative damage. This study generated and characterized a Drosophila Cyp1 mutant. Cyp1 mutant flies successfully developed into adults and showed no significant defects in mitochondrial morphology, function, and content. However, oxidative damage significantly decreased in Cyp1 mutant flies, and inhibition of Cyp1 expression substantially increased the survival under various oxidative stress paradigms. Moreover, Cyp1 mutation successfully ameliorated survival rates, locomotor activity, and dopaminergic neuron quantity in a Drosophila DJ-1 mutant under oxidative stress, further confirming the protective role of Cyp1 mutation against oxidative stress. In conclusion, these results suggest Cyp1 and its human homolog CypD as putative molecular targets for the treatment of DJ-1 deficiency-associated diseases, including Parkinson's disease (Kim, 2018).
Cunningham, P. C., Waldeck, K., Ganetzky, B. and Babcock, D. T. (2018) |
