About this Journal Submit a Manuscript Table of Contents
Parkinson's Disease
Volume 2011 (2011), Article ID 212706, 7 pages
http://dx.doi.org/10.4061/2011/212706
Review Article

α-Synuclein Transgenic Drosophila As a Model of Parkinson's Disease and Related Synucleinopathies

1School of Pharmaceutical Sciences, Mukogawa Women's University, Nishinomiya, Hyogo 663-8179, Japan
2Department of Degenerative Neurological Diseases, National Institute of Neuroscience, National Center of Neurology and Psychiatry, 4-1-1 Ogawa-Higashi, Kodaira, Tokyo 187-8502, Japan

Received 5 October 2010; Accepted 2 December 2010

Academic Editor: Enrico Schmidt

Copyright © 2011 Hideya Mizuno et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

α-Synuclein (α-Syn) is a major component of protein inclusions known as Lewy bodies, which are hallmarks of synucleinopathies such as Parkinson's disease (PD). The α-Syn gene is one of the familial PD-causing genes and is also associated with an increased risk of sporadic PD. Numerous studies using α-Syn expressing transgenic animals have indicated that α-Syn plays a critical role in the common pathogenesis of synucleinopathies. Drosophila melanogaster has several advantages for modeling human neurodegenerative diseases and is widely used for studying their pathomechanisms and therapies. In fact, Drosophila models expressing α-Syn have already been established and proven to replicate several features of human PD. In this paper, we review the current research on synucleinopathies using α-Syn Drosophila models and, moreover, explore the possibilities of these models for comprehensive genetic analyses and large-scale drug screening towards elucidating the molecular pathogenesis and developing therapies for synucleinopathies.

1. Introduction

Protein inclusions known as Lewy Bodies (LBs) are one of the hallmarks of Parkinson’s disease (PD), in which the major component is now known to be α-synuclein (α-Syn) [1, 2]. LBs are found in the substantia nigra in PD and also more extensively in other brain regions in other synucleinopathies including multiple system atrophy and dementia with Lewy bodies (DLB) [3, 4]. The α-Syn encoding gene, SNCA, is the first gene in which missense mutations such as A30P and A53T were found to cause familial PD [5, 6]. Furthermore, the multiplication mutations of α-Syn gene were also found to cause familial PD [7]. Most importantly, single nucleotide polymorphisms (SNPs) of α-Syn have been reported to associate with an increased risk of sporadic PD, which comprises the majority of PD patients [811]. α-Syn expression has been experimentally shown to mimic several aspects of PD in transgenic animals, such as motor dysfunction, α-Syn aggregation/accumulation, and neurodegeneration [1214]. These phenotypes are manifested not only by mutations in the α-Syn gene but also by overexpression of wild-type α-Syn [15], indicating that α-Syn plays a critical role in the common pathogenesis of synucleinopathies.

Drosophila melanogaster, commonly known as the fruit fly, has been recognized as a powerful organism for modeling human neurodegenerative diseases [16]. At least ~75% of human disease genes have Drosophila homologues [17]. Using Drosophila for modeling human neurodegenerative diseases has various advantages as follows: (1) analysis of gene functions in vivo, (2) rapid generation cycle (10–14 days) with a short life span (50–60 days), (3) suitability for genetic analysis, (4) abundant genetic information, and (5) little labor and cost-effective to maintain fly stocks (Table 1). In fact, Drosophila models of several neurodegenerative diseases including PD, Alzheimer’s disease, and the polyglutamine diseases have already been established and have successfully provided valuable insights into the elucidation of pathomechanisms and development of therapies for these diseases.

tab1
Table 1: Advantages of using Drosophila for modeling human neurodegenerative diseases.

Feany and Bender first developed transgenic Drosophila models expressing either wild-type or familial PD-linked mutants (A53T and A30P) of human α-Syn [12]. These α-Syn expressing flies replicate several features of human PD, including (1) locomotor dysfunction, (2) LB-like inclusion body formation, and (3) age-dependent loss of dopaminergic neurons and are therefore widely used for studying the molecular pathogenesis of α-Syn-induced neurodegeneration in not only PD but also synucleinopathies. In this paper, we will discuss what has been revealed in the pathogenesis of synucleinopathies using α-Syn Drosophila models, focusing on “misfolding and aggregation of α-Syn”, “posttranslational modifications of α-Syn”, and “oxidative stress” (Table 2).

tab2
Table 2: Summary of studies on α-Syn-induced neurodegeneration using Drosophila models.

2. Misfolding and Aggregation of α-Synuclein

Recent accumulating evidence has implicated that misfolding and subsequent aggregation of α-Syn play a central role in the pathogenesis of synucleinopathies [37]. Indeed, α-Syn has been demonstrated to be aggregated and deposited as inclusion bodies in flies expressing either wild-type or mutant α-Syn (A53T and A30P), the latter of which has accelerated aggregation propensity. Recently, Karpinar et al. showed that structurally-engineered α-Syn mutants with an increased propensity to form soluble oligomers exhibit enhanced neurotoxicity in Drosophila [18]. Moreover, a recent study demonstrated that histone deacetylase 6 (HDAC6) suppresses α-Syn-induced dopaminergic neuron loss and locomotor dysfunction by reducing α-Syn oligomers and instead promoting inclusion formation in α-Syn flies, further supporting a critical role of toxic oligomers in α-Syn-induced neurodegeneration in the pathogenesis of synucleinopathies [19].

Protein quality control systems function as a defense mechanism against protein misfolding and aggregation, which consist of molecular chaperones and protein degradation systems [38]. Molecular chaperones assist proper protein folding and hence are considered as essential proteins for protecting cells against the detrimental effects of the misfolding and aggregation of proteins such as α-Syn. Most molecular chaperones are induced upon heat stress to promote the refolding of misfolded proteins, and hence they are called heat shock proteins (HSPs) [39]. On the other hand, once proper protein folding has been altered, the resulting misfolded and aggregated proteins must be eliminated by their degradation. Two major protein degradation systems are the ubiquitin-proteasome system (UPS) and the autophagy-lysosome system [40]. UPS degrades short-lived and misfolded proteins through selective deubiquitination of substrate proteins and their targeting to the proteasome, whereas the autophagy-lysosome system is a nonselective bulk degradation system for long-lived and misfolded proteins, which involves engulfment of substrate proteins into the autophagosome and their delivery to the lysosome. The role of molecular chaperones and protein degradation systems in protecting against α-Syn misfolding in the pathogenesis of synucleinopathies has been investigated using α-Syn Drosophila models.

2.1. Molecular Chaperones

As molecular chaperones are expected to protect against protein misfolding and aggregation, their roles in the pathogenesis of PD have been investigated so far [41]. Extensive colocalization with LBs has been demonstrated for several HSPs [42], and expression levels of HSPs have been reported to be elevated in synucleinopathy brains [43]. HSP70 has been shown to inhibit α-Syn aggregation in vitro [44], and HSPs, such as HSP27 or HSP70, have been reported to protect against α-Syn-induced neurotoxicity in cultured cells and transgenic mice [45, 46], suggesting an important role of HSPs in PD pathology.

Indeed, Auluck et al. demonstrated that coexpression of HSP70 ameliorated the toxicity of α-Syn to dopaminergic neurons without changing the number of inclusions [20]. They also confirmed that coexpression of Hsc4.K71S, a dominant negative form of Drosophila HSP70, accelerated dopaminergic neuron loss in α-Syn expressing flies. Furthermore, they subsequently showed that geldamamycin, an Hsp90 inhibitor and heat shock transcription factor 1-activator compound, protects against neurotoxicity through induction of Hsp70 in α-Syn flies [21]. Taken together, these results confirmed that the molecular chaperone HSP70 suppresses α-Syn toxicity in vivo by using the Drosophila system.

2.2. Protein Degradation

The UPS and the autophagy-lysosome system can degrade misfolded proteins, and impairment of these systems has been reported to cause neurodegeneration [40, 47]. Furthermore, the UPS has been suggested to coordinate with the autophagy system to eliminate misfolded proteins. Lee et al. have shown protective effects of the UPS on α-Syn-induced toxicity using cell culture and Drosophila models [22]. A cell culture-based study indicated that K48-linked polyubiquitination is protective against α-Syn-induced toxicity in a UPS-dependent manner. In α-Syn flies, coexpression of ubiquitin has been shown to suppress loss of dopaminergic neurons and locomotor dysfunction and to extend life-span. These results suggest that UPS-mediated degradation of α-Syn is a potential therapeutic approach for synucleinopathies including PD.

Cathepsin D (CathD) is a major lysosomal aspartyl protease and its defect results in fatal neurodegenerative diseases [48]. CathD has been shown to efficiently degrade recombinant α-Syn in in vitro experiments, and knockdown of CathD in cultured cells increased α-Syn levels, indicating a role of CathD in α-Syn degradation [49]. Using α-Syn expressing flies, Cullen et al. demonstrated that a CathD defect enhanced α-Syn-induced neurodegeneration in vivo [23]. CathD knock-out mice have also been shown to facilitate insoluble α-Syn accumulation and α-Syn-induced neurotoxicity, confirming that CathD may protect neurons against α-Syn-induced toxicity through degradation.

3. Posttranslational Modifications of α-Synuclein

Posttranslational modifications including phosphorylation, ubiquitination, or C-terminal truncation of α-Syn have been observed in LBs in the postmortem brain of synucleinopathy patients [37]. In vitro studies suggest that these modifications can accelerate oligomerization or aggregation of α-Syn. Accordingly, the role of posttranslational modifications of α-Syn on toxicity has been studied using α-Syn expressing flies.

3.1. α-Synuclein Phosphorylation

Phosphorylation at Ser129 has been identified in α-Syn deposited as LBs in synucleinopathy brains [50]. To explore the pathological role of this phosphorylation in vivo, accumulation and phosphorylation of α-Syn was studied in flies expressing wild-type or mutant α-Syn. Indeed, α-Syn accumulated in these flies was phosphorylated at Ser129 as reported in human patients, and the order of the degree of phosphorylation was A53T > A30P > wild-type [51]. Mutagenesis studies demonstrated that the phosphomimic S129D mutant increases α-Syn-induced toxicity, whereas the phospho-resistant S129A mutant reduces the toxicity accompanied with an increased number of inclusion bodies [24]. Furthermore, GPRK2 has been shown to be responsible for the α-Syn phosphorylation in Drosophila. These studies revealed that Ser129 phosphorylation plays an important role for α-Syn-induced neurotoxicity and inclusion body formation.

Chen et al. recently reported that Tyr125 of α-Syn is also phosphorylated in α-Syn expressing flies [25]. This phosphorylation occurs at a young age but diminishes during the aging process in both humans and flies. They showed that soluble oligomers of α-Syn were increased by phosphorylation at Ser129 and decreased by phosphorylation at Tyr125. In addition, blocking Tyr125 phosphorylation increased α-Syn toxicity. Taken together, these studies suggest that α-Syn toxicity in synucleinopathies results from an imbalance between the detrimental action of Ser129 phosphorylation by accelerating toxic oligomer formation and a neuroprotective action of Tyr125 phosphorylation by suppressing oligomer formation.

3.2. α-Synuclein Truncation

Truncated small species of α-Syn have been detected in purified LBs and insoluble fractions from synucleinopathy brains [52, 53], suggesting that truncation of α-Syn contributes to aggregation and LB formation. Several studies have implicated that C-terminal truncation of α-Syn accelerates its aggregation [54, 55], and the NAC domain (residues 61–95) of α-Syn has been demonstrated to be essential for α-Syn aggregation in vitro [56, 57]. Indeed, flies expressing α-Syn with an NAC domain deletion (α-Syn Δ71–82) did not show any loss of dopaminergic neurons with no evidence of α-Syn aggregation, confirming an essential role of the NAC domain in α-Syn aggregation and toxicity in vivo [26]. On the other hand, expression of C-terminal truncated α-Syn (α-Syn 1–120) resulted in increased α-Syn aggregation and significantly greater loss of dopaminergic neurons than wild-type in Drosophila, suggesting a potential role of the C-terminal region of α-Syn in suppressing aggregation.

α-Syn has been shown to be a substrate for proteolytic cleavage by calpain in vitro, which is one of a family of intracellular calcium-dependent proteases [58, 59]. The calpain-cleaved α-Syn species exhibit a similar molecular size to truncated α-Syn fragments that have been shown to promote aggregation and to enhance toxicity [54, 55, 60]. Dufty et al. have identified calpain I-cleaved α-Syn fragments in the brains of human PD/DLB patients as well as α-Syn expressing flies using a specific antibody [27]. These results suggest that calpain I-mediated cleavage of α-Syn may be involved in the disease-linked aggregation of α-Syn in synucleinopathies.

4. Oxidative Stress and Antioxidants

Oxidative stress has been believed to play a central role in the progression of neurodegenerative diseases although its relationship with α-Syn toxicity has not been well elucidated. Dopaminergic neurons of α-Syn expressing flies have been shown to be sensitive to hyperoxia-induced oxidative stress [28]. Importantly, overexpression of Cu/Zn superoxide dismutase rescued both the dopaminergic neuron loss and locomotor dysfunction in mutant α-Syn flies. The same group also demonstrated that reduction of dopamine levels by RNAi silencing of the tyrosine hydroxylase gene decreases the neurotoxicity in α-Syn expressing flies, implying that dopamine which produces reactive oxygen species might be involved in the α-Syn-induced neurotoxicity through oxidative stress [29]. These results suggest that oxidative stress plays a significant role in the pathogenesis of PD in vivo.

Trinh et al. examined the involvement of the phase II detoxification pathway, specifically glutathione metabolism, in α-Syn-induced neurotoxicity in Drosophila models [30]. They found that the loss-of-function gene mutations affecting glutathione metabolism pathways enhance dopaminergic neuron loss in α-Syn expressing flies. Moreover, the dopaminergic neuron loss can be rescued by genetic or pharmacological interventions that increase glutathione biosynthesis or glutathione conjugation activity, suggesting that oxidative stress is involved in α-Syn-induced neurotoxicity and that induction of the phase II detoxification pathway may be a potential therapy for synucleinopathies.

In addition, feeding Nicotinamide, the principal form of niacin (vitamin B3), has been shown to improve the motor dysfunction in α-Syn expressing flies through improvement of oxidative mitochondrial dysfunction [31]. Grape extracts, which contain various polyphenols and exhibit scavenging effects on reactive oxygen species, also showed a significant improvement in locomotor function and average lifespan in α-Syn flies [32].

5. Association with Other PD-Causing Genes

Loss of function gene mutations of Parkin, an E3 ubiquitin ligase, is responsible for a rare familial form of PD, autosomal recessive juvenile Parkinsonism, which develops typical Parkinsonian symptoms as a result of midbrain dopaminergic neuron loss, but usually lacks LBs [61]. Although a direct molecular interaction between Parkin and α-Syn remains controversial, several studies have shown that coexpression of Parkin rescues α-Syn-induced dopaminergic neurodegeneration and motor dysfunction in α-Syn flies. These studies suggest that up-regulation of Parkin expression may provide a novel therapy for PD [3335].

Mutations in the PTEN-induced putative kinase 1 (PINK1) gene cause another form of autosomal recessive PD [62]. PINK1 has been shown to be located in mitochondria and is thought to be involved in cellular protection. Overexpression of PINK1 has been shown to rescue loss of climbing ability and neurodegeneration induced by α-Syn expression in Drosophila [36]. Furthermore, it has been suggested that Parkin and PINK1 function in a common pathway in maintaining mitochondrial integrity and morphology, as demonstrated using Drosophila models [63, 64].

6. Genomics and Proteomics Studies

One of the advantages of using Drosophila models in studying human diseases is the easiness to handle numerous samples at one time, which can provide us with reliable amounts of data for unbiased statistical analyses. In addition, shortness of their life span makes it convenient to perform time course analyses in relatively short time periods.

Scherzer et al. performed expression profiling analysis of α-Syn A30P flies at different disease stages using microarray and found that expression of genes involved in lipid processing, energy production, and membrane transport is significantly altered by α-Syn expression [65]. Xun et al. performed proteomic analysis of α-Syn flies at different disease stages using liquid chromatography coupled with mass spectrometry [66, 67]. They found cytoskeletal and mitochondrial protein changes in the presymptomatic and early disease stages in the α-Syn A30P expressing flies [66]. They further reported dysregulated expression of proteins associated with membrane, endoplasmic reticulum, actin cytoskeleton, mitochondria, and ribosome in the presymptomatic α-Syn A53T flies, consistent with the α-Syn A30P flies [67]. These unbiased genomics and proteomics studies especially in the presymptomatic α-Syn flies will provide us with further insight into pathomechanisms and potential therapeutic targets of synucleinopathies.

7. Concluding Remarks

As described above, α-Syn Drosophila models have been widely employed to uncover the molecular pathogenesis of synucleinopathies (Table 2). Most of the results reviewed here have indeed been confirmed in transgenic mouse models expressing α-Syn. As we described in the introduction, Drosophila is a powerful in vivo model to study human neurodegenerative diseases with various advantages (Table 1), especially its short life span since human neurodegenerative diseases gradually appear and progress in middle-late ages.

Genetic analyses using α-Syn expressing flies have revealed pathological associations between α-Syn and various synucleinopathy-related genes and have provided novel insights into the molecular pathogenesis of synucleinopathies. Drosophila models of other neurodegenerative diseases such as the polyglutamine diseases have also been established, and numerous comprehensive genetic screenings have been conducted and have elucidated previously unknown pathomechanisms, taking advantage of the characteristics of Drosophila [68]. Similarly, comprehensive genetic screenings using Drosophila models will further lead to the elucidation of the pathomechanisms of synucleinopathies including PD in the future.

On the other hand, Drosophila models are also suited for drug screening. Indeed, L-DOPA and dopamine agonists have been shown to exert therapeutic effects against α-Syn-induced neurotoxicity using α-Syn flies [69]. In addition, HDAC inhibitors such as sodium butyrate or SAHA, and SIRT2 inhibitors have been identified as novel therapeutic agents that protect against α-Syn-induced neurotoxicity using Drosophila [70, 71]. In the future, novel therapeutic candidates for synucleinopathies are expected to be developed by extensive large-scale drug screening using Drosophila models.

Acknowledgments

The authors thank Dr. H. Akiko Popiel for critical reading of the manuscript. This work was supported by the Intramural Research Grant (21B-4) for Neurological and Psychiatric Disorders of National Center of Neurology and Psychiatry, Japan.

References

  1. M. G. Spillantini, R. A. Crowther, R. Jakes, M. Hasegawa, and M. Goedert, “α-synuclein in filamentous inclusions of Lewy bodies from Parkinson's disease and dementia with Lewy bodies,” Proceedings of the National Academy of Sciences of the United States of America, vol. 95, no. 11, pp. 6469–6473, 1998. View at Publisher · View at Google Scholar · View at Scopus
  2. M. G. Spillantini, M. L. Schmidt, V. M. Y. Lee, J. Q. Trojanowski, R. Jakes, and M. Goedert, “α-synuclein in Lewy bodies,” Nature, vol. 388, no. 6645, pp. 839–840, 1997. View at Publisher · View at Google Scholar · View at PubMed · View at Scopus
  3. K. Beyer and A. Ariza, “Protein aggregation mechanisms in synucleinopathies: commonalities and differences,” Journal of Neuropathology and Experimental Neurology, vol. 66, no. 11, pp. 965–974, 2007. View at Publisher · View at Google Scholar · View at PubMed · View at Scopus
  4. T. Iwatsubo, “Pathological biochemistry of α-synucleinopathy,” Neuropathology, vol. 27, no. 5, pp. 474–478, 2007. View at Publisher · View at Google Scholar · View at Scopus
  5. R. Krüger, W. Kuhn, T. Müller et al., “Ala30Pro mutation in the gene encoding α-synuclein in Parkinson's disease,” Nature Genetics, vol. 18, no. 2, pp. 106–108, 1998. View at Scopus
  6. M. H. Polymeropoulos, C. Lavedan, E. Leroy et al., “Mutation in the α-synuclein gene identified in families with Parkinson's disease,” Science, vol. 276, no. 5321, pp. 2045–2047, 1997. View at Publisher · View at Google Scholar · View at Scopus
  7. A. B. Singleton, M. Farrer, J. Johnson et al., “α-synuclein locus triplication causes Parkinson's disease,” Science, vol. 302, no. 5646, p. 841, 2003. View at Publisher · View at Google Scholar · View at PubMed · View at Scopus
  8. J. C. Mueller, J. Fuchs, A. Hofer et al., “Multiple regions of α-synuclein are associated with Parkinson's disease,” Annals of Neurology, vol. 57, no. 4, pp. 535–541, 2005. View at Publisher · View at Google Scholar · View at PubMed · View at Scopus
  9. I. Mizuta, W. Satake, Y. Nakabayashi et al., “Multiple candidate gene analysis identifies α-synuclein as a susceptibility gene for sporadic Parkinson's disease,” Human Molecular Genetics, vol. 15, no. 7, pp. 1151–1158, 2006. View at Publisher · View at Google Scholar · View at PubMed · View at Scopus
  10. W. Satake, Y. Nakabayashi, I. Mizuta et al., “Genome-wide association study identifies common variants at four loci as genetic risk factors for Parkinson's disease,” Nature Genetics, vol. 41, no. 12, pp. 1303–1307, 2009. View at Publisher · View at Google Scholar · View at PubMed · View at Scopus
  11. J. Simón-Sánchez, C. Schulte, J. M. Bras et al., “Genome-wide association study reveals genetic risk underlying Parkinson's disease,” Nature Genetics, vol. 41, no. 12, pp. 1308–1312, 2009. View at Publisher · View at Google Scholar · View at PubMed · View at Scopus
  12. M. B. Feany and W. W. Bender, “A Drosophila model of Parkinson's disease,” Nature, vol. 404, no. 6776, pp. 394–398, 2000. View at Publisher · View at Google Scholar · View at PubMed · View at Scopus
  13. M. K. Lee, W. Stirling, Y. Xu et al., “Human α-synuclein-harboring familial Parkinson's disease-linked Ala-53 → Thr mutation causes neurodegenerative disease with α-synuclein aggregation in transgenic mice,” Proceedings of the National Academy of Sciences of the United States of America, vol. 99, no. 13, pp. 8968–8973, 2002. View at Publisher · View at Google Scholar · View at PubMed · View at Scopus
  14. E. Masliah, E. Rockenstein, I. Veinbergs et al., “Dopaminergic loss and inclusion body formation in α-synuclein mice: implications for neurodegenerative disorders,” Science, vol. 287, no. 5456, pp. 1265–1269, 2000. View at Publisher · View at Google Scholar · View at Scopus
  15. M. Farrer, J. Kachergus, L. Forno et al., “Comparison of kindreds with Parkinsonism and α-synuclein genomic multiplications,” Annals of Neurology, vol. 55, no. 2, pp. 174–179, 2004. View at Publisher · View at Google Scholar · View at PubMed · View at Scopus
  16. J. Bilen and N. M. Bonini, “Drosophila as a model for human neurodegenerative disease,” Annual Review of Genetics, vol. 39, pp. 153–171, 2005. View at Publisher · View at Google Scholar · View at PubMed · View at Scopus
  17. L. T. Reiter, L. Potocki, S. Chien, M. Gribskov, and E. Bier, “A systematic analysis of human disease-associated gene sequences in Drosophila melanogaster,” Genome Research, vol. 11, no. 6, pp. 1114–1125, 2001. View at Publisher · View at Google Scholar · View at PubMed · View at Scopus
  18. D. P. Karpinar, M. B. G. Balija, S. Kügler et al., “Pre-fibrillar α-synuclein variants with impaired β-structure increase neurotoxicity in parkinson's disease models,” EMBO Journal, vol. 28, no. 20, pp. 3256–3268, 2009. View at Publisher · View at Google Scholar · View at PubMed
  19. G. Du, X. Liu, X. Chen et al., “Drosophila histone deacetylase 6 protects dopaminergic neurons against α-synuclein toxicity by promoting inclusion formation,” Molecular Biology of the Cell, vol. 21, no. 13, pp. 2128–2137, 2010. View at Publisher · View at Google Scholar · View at PubMed
  20. P. K. Auluck, H. Y. E. Chan, J. Q. Trojanowski, V. M. Y. Lee, and N. M. Bonini, “Chaperone suppression of α-synuclein toxicity in a Drosophila model for Parkinson's disease,” Science, vol. 295, no. 5556, pp. 865–868, 2002. View at Publisher · View at Google Scholar · View at PubMed
  21. P. K. Auluck and N. M. Bonini, “Pharmacological prevention of Parkinson disease in Drosophila,” Nature Medicine, vol. 8, no. 11, pp. 1185–1186, 2002. View at Publisher · View at Google Scholar · View at PubMed
  22. F. K. M. Lee, A. K. Y. Wong, Y. W. Lee, OI. W. Wan, H. Y. Edwin Chan, and K. K. K. Chung, “The role of ubiquitin linkages on α-synuclein induced-toxicity in a Drosophila model of Parkinson's disease,” Journal of Neurochemistry, vol. 110, no. 1, pp. 208–219, 2009. View at Publisher · View at Google Scholar · View at PubMed
  23. V. Cullen, M. Lindfors, J. Ng et al., “Cathepsin D expression level affects alpha-synuclein processing, aggregation, and toxicity in vivo,” Molecular Brain, vol. 2, no. 1, article 5, 2009. View at Publisher · View at Google Scholar · View at PubMed
  24. LI. Chen and M. B. Feany, “α-synuclein phosphorylation controls neurotoxicity and inclusion formation in a Drosophila model of Parkinson disease,” Nature Neuroscience, vol. 8, no. 5, pp. 657–663, 2005. View at Publisher · View at Google Scholar · View at PubMed
  25. L. Chen, M. Periquet, X. Wang et al., “Tyrosine and serine phosphorylation of α-synuclein have opposing effects on neurotoxicity and soluble oligomer formation,” Journal of Clinical Investigation, vol. 119, no. 11, pp. 3257–3265, 2009. View at Publisher · View at Google Scholar · View at PubMed
  26. M. Periquet, T. Fulga, L. Myllykangas, M. G. Schlossmacher, and M. B. Feany, “Aggregated α-synuclein mediates dopaminergic neurotoxicity in vivo,” Journal of Neuroscience, vol. 27, no. 12, pp. 3338–3346, 2007. View at Publisher · View at Google Scholar · View at PubMed
  27. B. M. Dufty, L. R. Warner, S. T. Hou et al., “Calpain-cleavage of α-synuclein: connecting proteolytic processing to disease-linked aggregation,” American Journal of Pathology, vol. 170, no. 5, pp. 1725–1738, 2007. View at Publisher · View at Google Scholar · View at PubMed
  28. J. A. Botella, F. Bayersdorfer, and S. Schneuwly, “Superoxide dismutase overexpression protects dopaminergic neurons in a Drosophila model of Parkinson's disease,” Neurobiology of Disease, vol. 30, no. 1, pp. 65–73, 2008. View at Publisher · View at Google Scholar · View at PubMed
  29. F. Bayersdorfer, A. Voigt, S. Schneuwly, and J. A. Botella, “Dopamine-dependent neurodegeneration in Drosophila models of familial and sporadic Parkinson's disease,” Neurobiology of Disease, vol. 40, no. 1, pp. 113–119, 2010. View at Publisher · View at Google Scholar · View at PubMed
  30. K. Trinh, K. Moore, P. D. Wes et al., “Induction of the phase II detoxification pathway suppresses neuron loss in Drosophila models of Parkinson's disease,” Journal of Neuroscience, vol. 28, no. 2, pp. 465–472, 2008. View at Publisher · View at Google Scholar · View at PubMed
  31. H. Jia, X. Li, H. Gao et al., “High doses of nicotinamide prevent oxidative mitochondrial dysfunction in a cellular model and improve motor deficit in a Drosophila model of Parkinson's disease,” Journal of Neuroscience Research, vol. 86, no. 9, pp. 2083–2090, 2008. View at Publisher · View at Google Scholar · View at PubMed
  32. J. Long, H. Gao, L. Sun, J. Liu, and X. Zhao-Wilson, “Grape extract protects mitochondria from oxidative damage and improves locomotor dysfunction and extends lifespan in a Drosophila Parkinson's disease model,” Rejuvenation Research, vol. 12, no. 5, pp. 321–331, 2009. View at Publisher · View at Google Scholar · View at PubMed
  33. A. F. M. Haywood and B. E. Staveley, “Parkin counteracts symptoms in a Drosophila model of Parkinson's disease,” BMC Neuroscience, vol. 5, article 14, 2004. View at Publisher · View at Google Scholar · View at PubMed
  34. A. F. M. Haywood and B. E. Staveley, “Mutant α-synuclein-induced degeneration is reduced by parkin in a fly model of Parkinson's disease,” Genome, vol. 49, no. 5, pp. 505–510, 2006. View at Publisher · View at Google Scholar · View at PubMed
  35. Y. Yang, I. Nishimura, Y. Imai, R. Takahashi, and B. Lu, “Parkin suppresses dopaminergic neuron-selective neurotoxicity induced by Pael-R in Drosophila,” Neuron, vol. 37, no. 6, pp. 911–924, 2003. View at Publisher · View at Google Scholar
  36. A. M. Todd and B. E. Staveley, “Pink1 suppresses α-synuclein-induced phenotypes in a Drosophila model of Parkinson's disease,” Genome, vol. 51, no. 12, pp. 1040–1046, 2008. View at Publisher · View at Google Scholar · View at PubMed
  37. V. N. Uversky, “Neuropathology, biochemistry, and biophysics of α-synuclein aggregation,” Journal of Neurochemistry, vol. 103, no. 1, pp. 17–37, 2007. View at Publisher · View at Google Scholar · View at PubMed
  38. H. Naiki and Y. Nagai, “Molecular pathogenesis of protein misfolding diseases: pathological molecular environments versus quality control systems against misfolded proteins,” Journal of Biochemistry, vol. 146, no. 6, pp. 751–756, 2009. View at Publisher · View at Google Scholar · View at PubMed
  39. J. C. Young, V. R. Agashe, K. Siegers, and F. U. Hartl, “Pathways of chaperone-mediated protein folding in the cytosol,” Nature Reviews Molecular Cell Biology, vol. 5, no. 10, pp. 781–791, 2004. View at Publisher · View at Google Scholar · View at PubMed
  40. D. C. Rubinsztein, “The roles of intracellular protein-degradation pathways in neurodegeneration,” Nature, vol. 443, no. 7113, pp. 780–786, 2006. View at Publisher · View at Google Scholar · View at PubMed
  41. R. Bandopadhyay and J. de Belleroche, “Pathogenesis of Parkinson's disease: emerging role of molecular chaperones,” Trends in Molecular Medicine, vol. 16, no. 1, pp. 27–36, 2010. View at Publisher · View at Google Scholar · View at PubMed
  42. P. J. McLean, H. Kawamata, S. Shariff et al., “TorsinA and heat shock proteins act as molecular chaperones: suppression of α-synuclein aggregation,” Journal of Neurochemistry, vol. 83, no. 4, pp. 846–854, 2002. View at Publisher · View at Google Scholar
  43. T. F. Outeiro, J. Klucken, K. E. Strathearn et al., “Small heat shock proteins protect against α-synuclein-induced toxicity and aggregation,” Biochemical and Biophysical Research Communications, vol. 351, no. 3, pp. 631–638, 2006. View at Publisher · View at Google Scholar · View at PubMed
  44. M. M. Dedmon, J. Christodoulou, M. R. Wilson, and C. M. Dobson, “Heat shock protein 70 inhibits α-synuclein fibril formation via preferential binding to prefibrillar species,” Journal of Biological Chemistry, vol. 280, no. 15, pp. 14733–14740, 2005. View at Publisher · View at Google Scholar · View at PubMed
  45. J. Klucken, Y. Shin, E. Masliah, B. T. Hyman, and P. J. McLean, “Hsp70 reduces α-synuclein aggregation and toxicity,” Journal of Biological Chemistry, vol. 279, no. 24, pp. 25497–25502, 2004. View at Publisher · View at Google Scholar · View at PubMed
  46. A. Zourlidou, M. D. Payne Smith, and D. S. Latchman, “HSP27 but not HSP70 has a potent protective effect against α-synuclein-induced cell death in mammalian neuronal cells,” Journal of Neurochemistry, vol. 88, no. 6, pp. 1439–1448, 2004.
  47. T. Pan, S. Kondo, W. Le, and J. Jankovic, “The role of autophagy-lysosome pathway in neurodegeneration associated with Parkinson's disease,” Brain, vol. 131, no. 8, pp. 1969–1978, 2008. View at Publisher · View at Google Scholar · View at PubMed
  48. J. Tyynelä, I. Sohar, D. E. Sleat et al., “A mutation in the ovine cathepsin D gene causes a congenital lysosomal storage disease with profound neurodegeneration,” EMBO Journal, vol. 19, no. 12, pp. 2786–2792, 2000.
  49. D. Sevlever, P. Jiang, and S. H. C. Yen, “Cathepsin D is the main lysosomal enzyme involved in the degradation of α-synuclein and generation of its carboxy-terminally truncated species,” Biochemistry, vol. 47, no. 36, pp. 9678–9687, 2008. View at Publisher · View at Google Scholar · View at PubMed
  50. H. Fujiwara, M. Hasegawa, N. Dohmae et al., “α-synuclein is phosphorylated in synucleinopathy lesions,” Nature Cell Biology, vol. 4, no. 2, pp. 160–164, 2002. View at Publisher · View at Google Scholar · View at PubMed
  51. M. Takahashi, H. Kanuka, H. Fujiwara et al., “Phosphorylation of α-synuclein characteristic of synucleinopathy lesions is recapitulated in α-synuclein transgenic Drosophila,” Neuroscience Letters, vol. 336, no. 3, pp. 155–158, 2003. View at Publisher · View at Google Scholar
  52. M. Baba, S. Nakajo, P. H. Tu et al., “Aggregation of α-synuclein in Lewy bodies of sporadic Parkinson's disease and dementia with Lewy bodies,” American Journal of Pathology, vol. 152, no. 4, pp. 879–884, 1998.
  53. W. P. Gai, J. H. T. Power, P. C. Blumbergs, J. G. Culvenor, and P. H. Jensen, “α-synuclein immunoisolation of glial inclusions from multiple system atrophy brain tissue reveals multiprotein components,” Journal of Neurochemistry, vol. 73, no. 5, pp. 2093–2100, 1999.
  54. I. V. J. Murray, B. I. Giasson, S. M. Quinn et al., “Role of α-synuclein carboxy-terminus on fibril formation in vitro,” Biochemistry, vol. 42, no. 28, pp. 8530–8540, 2003. View at Publisher · View at Google Scholar · View at PubMed
  55. L. C. Serpell, J. Berriman, R. Jakes, M. Goedert, and R. A. Crowther, “Fiber diffraction of synthetic α-synuclein filaments shows amyloid-like cross-β conformation,” Proceedings of the National Academy of Sciences of the United States of America, vol. 97, no. 9, pp. 4897–4902, 2000. View at Publisher · View at Google Scholar
  56. A. M. Bodles, D. J. S. Guthrie, B. Greer, and G. Brent Irvine, “Identification of the region of non-Aβ component (NAC) of Alzheimer's disease amyloid responsible for its aggregation and toxicity,” Journal of Neurochemistry, vol. 78, no. 2, pp. 384–395, 2001. View at Publisher · View at Google Scholar
  57. B. I. Giasson, I. V. J. Murray, J. Q. Trojanowski, and V. M. Y. Lee, “A hydrophobic stretch of 12 amino acid residues in the middle of α-synuclein is essential for filament assembly,” Journal of Biological Chemistry, vol. 276, no. 4, pp. 2380–2386, 2001. View at Publisher · View at Google Scholar · View at PubMed
  58. A. J. Mishizen-Eberz, R. P. Guttmann, B. I. Giasson et al., “Distinct cleavage patterns of normal and pathologic forms of α-synuclein by calpain I in vitro,” Journal of Neurochemistry, vol. 86, no. 4, pp. 836–847, 2003. View at Publisher · View at Google Scholar
  59. A. J. Mishizen-Eberz, E. H. Norris, B. I. Giasson et al., “Cleavage of α-synuclein by calpain: potential role in degradation of fibrillized and nitrated species of α-synuclein,” Biochemistry, vol. 44, no. 21, pp. 7818–7829, 2005. View at Publisher · View at Google Scholar · View at PubMed
  60. W. Li, N. West, E. Colla et al., “Aggregation promoting C-terminal truncation of α-synuclein is a normal cellular process and is enhanced by the familial Parkinson's disease-linked mutations,” Proceedings of the National Academy of Sciences of the United States of America, vol. 102, no. 6, pp. 2162–2167, 2005. View at Publisher · View at Google Scholar · View at PubMed
  61. T. Kitada, S. Asakawa, N. Hattori et al., “Mutations in the parkin gene cause autosomal recessive juvenile parkinsonism,” Nature, vol. 392, no. 6676, pp. 605–608, 1998. View at Publisher · View at Google Scholar · View at PubMed
  62. E. M. Valente, P. M. Abou-Sleiman, V. Caputo et al., “Hereditary early-onset Parkinson's disease caused by mutations in PINK1,” Science, vol. 304, no. 5674, pp. 1158–1160, 2004. View at Publisher · View at Google Scholar · View at PubMed
  63. I. E. Clark, M. W. Dodson, C. Jiang et al., “Drosophila pink1 is required for mitochondrial function and interacts genetically with parkin,” Nature, vol. 441, no. 7097, pp. 1162–1166, 2006. View at Publisher · View at Google Scholar · View at PubMed · View at Scopus
  64. J. Park, S. B. Lee, S. Lee et al., “Mitochondrial dysfunction in Drosophila PINK1 mutants is complemented by parkin,” Nature, vol. 441, no. 7097, pp. 1157–1161, 2006. View at Publisher · View at Google Scholar · View at PubMed · View at Scopus
  65. C. R. Scherzer, R. V. Jensen, S. R. Gullans, and M. B. Feany, “Gene expression changes presage neurodegeneration in a Drosophila model of Parkinson's disease,” Human Molecular Genetics, vol. 12, no. 19, pp. 2457–2466, 2003. View at Publisher · View at Google Scholar · View at PubMed · View at Scopus
  66. Z. Xun, R. A. Sowell, T. C. Kaufman, and D. E. Clemmer, “Lifetime proteomic profiling of an A30P α-synuclein Drosophila model of Parkinson's disease,” Journal of Proteome Research, vol. 6, no. 9, pp. 3729–3738, 2007. View at Publisher · View at Google Scholar · View at PubMed · View at Scopus
  67. Z. Xun, R. A. Sowell, T. C. Kaufman, and D. E. Clemmer, “Quantitative proteomics of a presymptomatic A53T α-synuclein Drosophila model of Parkinson disease,” Molecular and Cellular Proteomics, vol. 7, no. 7, pp. 1191–1203, 2008. View at Publisher · View at Google Scholar · View at PubMed · View at Scopus
  68. P. Fernandez-Funez, M. L. Nino-Rosales, B. de Gouyon et al., “Identification of genes that modify ataxin-1-induced neurodegeneration,” Nature, vol. 408, no. 6808, pp. 101–106, 2000. View at Publisher · View at Google Scholar · View at PubMed · View at Scopus
  69. R. G. Pendleton, F. Parvez, M. Sayed, and R. Hillman, “Effects of pharmacological agents upon a transgenic model of Parkinson's disease in Drosophila melanogaster,” Journal of Pharmacology and Experimental Therapeutics, vol. 300, no. 1, pp. 91–96, 2002. View at Publisher · View at Google Scholar · View at Scopus
  70. E. Kontopoulos, J. D. Parvin, and M. B. Feany, “α-synuclein acts in the nucleus to inhibit histone acetylation and promote neurotoxicity,” Human Molecular Genetics, vol. 15, no. 20, pp. 3012–3023, 2006. View at Publisher · View at Google Scholar · View at PubMed · View at Scopus
  71. T. F. Outeiro, E. Kontopoulos, S. M. Altmann et al., “Sirtuin 2 inhibitors rescue α-synuclein-mediated toxicity in models of Parkinson's disease,” Science, vol. 317, no. 5837, pp. 516–519, 2007. View at Publisher · View at Google Scholar · View at PubMed · View at Scopus