Abstract: BACKGROUND: Oligomerization and aggregation of alpha-synuclein molecules play a major role in neuronal dysfunction and loss in Parkinson's disease [1]. However, alpha-synuclein oligomerization and aggregation have mostly been detected indirectly in cells using detergent extraction methods [2], [3], [4]. A number of in vitro studies showed that dopamine can modulate the aggregation of alpha-synuclein by inhibiting the formation of or by disaggregating amyloid fibrils [5], [6], [7]. METHODOLOGY/PRINCIPAL FINDINGS: Here, we show that alpha-synuclein adopts a variety of conformations in primary neuronal cultures using fluorescence lifetime imaging microscopy (FLIM). Importantly, we found that dopamine, but not dopamine agonists, induced conformational changes in alpha-synuclein which could be prevented by blocking dopamine transport into the cell. Dopamine also induced conformational changes in alpha-synuclein expressed in neuronal cell lines, and these changes were also associated with alterations in oligomeric/aggregated species. CONCLUSION/SIGNIFICANCE: Our results show, for the first time, a direct effect of dopamine on the conformation of alpha-synuclein in neurons, which may help explain the increased vulnerability of dopaminergic neurons in Parkinson's disease.
Abstract: The heterogeneity of symptoms and disease progression observed in synucleinopathies, of which Parkinson's disease (PD) is the most common representative, poses large problems for its treatment and for the discovery of novel therapeutics. The molecular basis for pathology is currently unclear, both in familial and in sporadic cases. While the therapeutic effects of L-DOPA and dopamine receptor agonists are still the gold standards for symptomatic treatment in PD, the development of neuroprotective and/or neurorestorative treatments for these disorders faces significant challenges due to the poor knowledge of the putative targets involved. Recent experimental evidence strongly suggests a central role for neurotoxic -synuclein oligomeric species in neurodegeneration. The events leading to protein oligomerization, as well as the oligomeric species themselves, are likely amenable to modulation by small molecules, which are beginning to emerge in high throughput compound screens in a variety of model organisms. The therapeutic potential of small molecule modulators of oligomer formation demands further exploration and validation in cellular and animal disease models in order to accelerate human drug development.
Abstract: Protein misfolding and aggregation are central events in many disorders including several neurodegenerative diseases. This suggests that alterations in normal protein homeostasis may contribute to pathogenesis, but the exact molecular mechanisms involved are still poorly understood. The budding yeast Saccharomyces cerevisiae is one of the model systems of choice for studies in molecular medicine. Modeling human neurodegenerative diseases in this simple organism has already shown the incredible power of yeast to unravel the complex mechanisms and pathways underlying these pathologies. Indeed, this work has led to the identification of several potential therapeutic targets and drugs for many diseases, including the neurodegenerative diseases. Several features associated with these diseases, such as formation of protein aggregates, cellular toxicity mediated by misfolded proteins, oxidative stress and hallmarks of apoptosis have been faithfully recapitulated in yeast, enabling researchers to take advantage of this powerful model to rapidly perform genetic and compound screens with the aim of identifying novel candidate therapeutic targets and drugs. Here we review the work undertaken to model human brain disorders in yeast, and how these models provide insight into novel therapeutic approaches for these diseases.
Abstract: The heterogeneity of symptoms and disease progression observed in synucleinopathies, of which Parkinson's disease (PD) is the most common representative, poses large problems for the discovery of novel therapeutics. The molecular basis for pathology is currently unclear, both in familial and in sporadic cases. While the therapeutic effects of L-DOPA and dopamine receptor agonists constitute good options for symptomatic treatment in PD, the development of neuroprotective and/or neurorestorative treatments for PD and other synucleinopathies faces significant challenges due to the poor knowledge of the putative targets. Recent experimental evidence strongly suggests a central role for neurotoxic alpha-synuclein oligomeric species in neurodegeneration. The events leading to protein oligomerization, as well as the oligomeric species themselves, are likely amenable to modulation by small molecules, which are beginning to emerge in high throughput compound screens in a variety of model organisms. The therapeutic potential of small molecule modulators of oligomer formation demands further exploration and validation in cellular and animal disease models in order to accelerate human drug development.
Abstract: The sirtuins are a family of enzymes which control diverse and vital cellular functions, including metabolism and aging. Manipulations of sirtuin activities cause activation of anti-apoptotic, anti-inflammatory, anti-stress responses, and the modulation of an aggregation of proteins involved in neurodegenerative disorders. Recently, sirtuins were found to be disease-modifiers in various models of neurodegeneration. However, almost in all instances, the exact mechanisms of neuroprotection remain elusive. Nevertheless, the manipulation of sirtuin activities is appealing as a novel therapeutic strategy for the treatment of currently fatal human disorders such as Alzheimer's and Parkinson's diseases. Here, we review current data which support the putative therapeutic roles of sirtuin in aging and in neurodegenerative diseases and the feasibility of the development of sirtuin-based therapies.
Abstract: Recent studies implicate a disruption in Rab-mediated protein trafficking as a possible contributing factor to neurodegeneration in Parkinson's disease (PD). Misfolding of the neuronal protein alpha-synuclein (asyn) is implicated in PD. Overexpression of asyn results in cell death in a wide variety of model systems, and in several organisms, including yeast, worms, flies, and rodent primary neurons, this toxicity is suppressed by the overproduction of Rab proteins. These and other findings suggest that asyn interferes with Rab function and provide new avenues for PD drug discovery. This chapter describes two assay formats that have been used successfully to identify small molecules that rescue asyn toxicity in yeast. The 96-well format monitors rescue by optical density and is suitable for screening thousands of compounds. A second format measures viable cells by reduction of the dye alamarBlue, a readout that is compatible with 96-, 384-, and 1536-well plates allowing the screening of large libraries (>100,000 compounds). A secondary assay to eliminate mechanistically undesirable hits is also described.
Abstract: Because accumulation of alpha-synuclein (alphaS) in the brain is a hallmark of Parkinson disease (PD) and related disorders, we examined its occurrence in human cerebrospinal fluid (CSF). Following affinity enrichment and trypsin digestion of CSF collected from a neurologically healthy donor, we identified several alphaS-derived peptides by mass spectrometry. The concentration of alphaS amounted to <0.001% of the CSF proteome. We then built, validated and optimized a sandwich-type, enzyme-linked immunoadsorbent assay (ELISA) to measure total alphaS levels in unconcentrated CSF. In a cross-sectional study of 100 living donors, we examined cell-free CSF samples from subjects clinically diagnosed with advanced PD, dementia with Lewy bodies (DLB), Alzheimer disease (AD), and a group of non-neurodegenerative disease controls (NCO). In these four groups the CSF alphaS concentrations ranged from 0.8 to 16.2 pg/microl. Mean CSF alphaS values were lower in donors with a primary synucleinopathy (PD, DLB: n=57) than in the other two groups (AD, NCO: n=35; p=0.025). By contrast, living Creutzfeldt-Jakob disease patients showed markedly elevated CSF alphaS levels (n=8; mean, 300 pg/microl; p<0.001). Our results unequivocally confirm the presence of alphaS in adult human CSF. In a first feasibility study employing a novel ELISA, we found relatively low CSF alphaS concentrations in subjects with parkinsonism linked to synucleinopathy, PD and DLB. In definite prion disease cases, we recorded a marked rise in total CSF alphaS resulting from rapid cell death. Our results will likely aid future biomarker explorations in neurodegenerative conditions and facilitate target validation studies.
Abstract: alpha-Synuclein (alphaSyn) can self-associate, forming oligomers, fibrils, and Lewy bodies, the pathological hallmark of Parkinson disease. Current dogma suggests that oligomeric alphaSyn intermediates may represent the most toxic alphaSyn species. Here, we studied the effect of a potent molecular chaperone, CHIP (carboxyl terminus of Hsp70-interacting protein), on alphaSyn oligomerization using a novel bimolecular fluorescence complementation assay. CHIP is a multidomain chaperone, utilizing both a tetratricopeptide/Hsp70 binding domain and a U-box/ubiquitin ligase domain to differentially impact the fate of misfolded proteins. In the current study, we found that co-expression of CHIP selectively reduced alphaSyn oligomerization and toxicity in a tetratricopeptide domain-dependent, U-box-independent manner by specifically degrading toxic alphaSyn oligomers. We conclude that CHIP preferentially recognizes and mediates degradation of toxic, oligomeric forms of alphaSyn. Further elucidation of the mechanisms of CHIP-induced degradation of oligomeric alphaSyn may contribute to the successful development of drug therapies that target oligomeric alphaSyn by mimicking or enhancing the powerful effects of CHIP.
Abstract: BACKGROUND: Misfolding, oligomerization, and fibrillization of alpha-synuclein are thought to be central events in the onset and progression of Parkinson's disease (PD) and related disorders. Although fibrillar alpha-synuclein is a major component of Lewy bodies (LBs), recent data implicate prefibrillar, oligomeric intermediates as the toxic species. However, to date, oligomeric species have not been identified in living cells. METHODOLOGY/PRINCIPAL FINDINGS: Here we used bimolecular fluorescence complementation (BiFC) to directly visualize alpha-synuclein oligomerization in living cells, allowing us to study the initial events leading to alpha-synuclein oligomerization, the precursor to aggregate formation. This novel assay provides us with a tool with which to investigate how manipulations affecting alpha-synuclein aggregation affect the process over time. Stabilization of alpha-synuclein oligomers via BiFC results in increased cytotoxicity, which can be rescued by Hsp70 in a process that reduces the formation of alpha-synuclein oligomers. Introduction of PD-associated mutations in alpha-synuclein did not affect oligomer formation but the biochemical properties of the mutant alpha-synuclein oligomers differ from those of wild type alpha-synuclein. CONCLUSIONS/SIGNIFICANCE: This novel application of the BiFC assay to the study of the molecular basis of neurodegenerative disorders enabled the direct visualization of alpha-synuclein oligomeric species in living cells and its modulation by Hsp70, constituting a novel important tool in the search for therapeutics for synucleinopathies.
Abstract: Several transgenic mouse lines with altered alpha-synuclein expression have been developed that show a variety of Parkinson's disease-like symptoms without specific loss of dopaminergic neurons. Targeted over-expression of human alpha-synuclein using viral-vector mediated gene delivery into the substantia nigra of rats and non-human primates leads to dopaminergic cell loss and the formation of alpha-synuclein aggregates reminiscent of Lewy bodies. In the context of these recent findings, we used adeno-associated virus (AAV) to over-express wild type human alpha-synuclein in the substantia nigra of mice. We hypothesized that this over-expression would recapitulate pathological hallmarks of Parkinson's disease, creating a mouse model to further characterize the disease pathogenesis. Recombinant AAV expressing alpha-synuclein was stereotaxically injected into the substantia nigra of mice, leading to a 25% reduction of dopaminergic neurons after 24 weeks of transduction. Furthermore, examination of mRNA levels of stress-related proteins using laser capture microdissection and quantitative PCR revealed a positive correlation of Hsp27 expression with the extent of viral transduction at 4 weeks and a positive correlation of Hsp40, Hsp70 and caspase 9 with the extent of viral transduction at 24 weeks. Taken together, our findings suggest that targeted over-expression of alpha-synuclein can induce pathology at the gross anatomical and molecular level in the substantia nigra, providing a mouse model in which upstream changes in Parkinson's disease pathogenesis can be further elucidated.
Abstract: Treatments based on pharmacological inhibition of poly(ADP-ribose) polymerase-1 (PARP-1) have been suggested for a broad variety of human disorders, including Parkinson's disease (PD). The neuroprotective effects underlying the efficacy of PARP-1 inhibitors in PD models suggest a role for PARP-1 in neurodegeneration. In this study, we assessed the efficacy of PARP-1 inhibition in two distinct PD models. First, we tested a panel of small molecule PARP-1 inhibitors in alpha-synuclein (aSyn) cytotoxicity assay, where we observed compound-dependent ameliorating effects. Next, we tested the same panel in primary ventral mesencephalic neuronal cultures, treated with MPP(+). Dopaminergic neurons, the primary cells affected in PD, were selected and subjected to analysis. A significant ameliorating effect was achieved only with a highly potent PARP-1 inhibitor. Our data implicates aberrant PARP-1 function in different pathways of neurodegeneration. Further, our results suggest a rationale for the development of highly potent, bio-available, brain-penetrable PARP-1 inhibitors to provide therapeutic benefits for Parkinson's patients.
Abstract: Protein misfolding and aggregation are common to many disorders, including neurodegenerative diseases referred to as "conformational disorders," suggesting that alterations in the normal protein homeostasis might contribute to pathogenesis. Cells evolved 2 major components of the protein quality control system to deal with misfolded and/or aggregated proteins: molecular chaperones and the ubiquitin proteasome pathway. Recent studies have implicated components of both systems in neurodegenerative diseases such as Alzheimer's, Parkinson's, Huntington's, or the prion diseases. A detailed understanding of how the cellular quality control systems relate to neurodegeneration might lead to the development of novel therapeutic approaches for disorders associated with protein misfolding and aggregation.
Abstract: The sirtuins are members of the histone deacetylase family of proteins that participate in a variety of cellular functions and play a role in aging. We identified a potent inhibitor of sirtuin 2 (SIRT2) and found that inhibition of SIRT2 rescued alpha-synuclein toxicity and modified inclusion morphology in a cellular model of Parkinson's disease. Genetic inhibition of SIRT2 via small interfering RNA similarly rescued alpha-synuclein toxicity. Furthermore, the inhibitors protected against dopaminergic cell death both in vitro and in a Drosophila model of Parkinson's disease. The results suggest a link between neurodegeneration and aging.
Abstract: In this study, we examined the effects of angiotensin II (AngII) in a genetic in vitro PD model produced by alpha-synuclein (alpha-syn) overexpression in the human neuroglioma H4 cell line. We observed a maximal decrease in alpha-syn-induced toxicity of 85% and reduction in inclusion formation by 19% when cultures were treated with AngII in the presence of the angiotensin type 1 (AT1) receptor antagonist losartan and AT2 receptor antagonist PD123319. When compared to AngII, the AT4 receptor agonist AngIV was moderately effective in protecting H4 cells against alpha-syn toxicity and did not significantly reduce inclusion formation. Here we show that AngII is protective against genetic, as well as neurotoxic models of PD. These data support the view that agents acting on the renin-angiotensin-system (RAS) may be useful in the prevention and/or treatment of Parkinson's disease.
Abstract: The high degree of conservation of cellular and molecular processes between the budding yeast Saccharomyces cerevisiae and higher eukaryotes have made it a valuable system for numerous studies of the basic mechanisms behind devastating illnesses such as cancer, infectious disease, and neurodegenerative disorders. Several studies in yeast have already contributed to our basic understanding of cellular dysfunction in both Huntington's and Parkinson's disease. Functional genomics approaches currently being undertaken in yeast may lead to novel insights into the genes and pathways that modulate neuronal cell dysfunction and death in these diseases. In addition, the budding yeast constitutes a valuable system for identification of new drug targets, both via target-based and non-target-based drug screening. Importantly, yeast can be used as a cellular platform to analyze the cellular effects of candidate compounds, which is critical for the development of effective therapeutics. While the molecular mechanisms that underlie neurodegeneration will ultimately have to be tested in neuronal and animal models, there are several distinct advantages to using simple model organisms to elucidate fundamental aspects of protein aggregation, amyloid toxicity, and cellular dysfunction. Here, we review recent studies that have shown that amyloid formation by disease-causing proteins and many of the resulting cellular deficits can be faithfully recapitulated in yeast. In addition, we discuss new yeast-based techniques for screening candidate therapeutic compounds for Huntington's and Parkinson's diseases.
Abstract: Misfolded proteins accumulate in many neurodegenerative diseases, including huntingtin in Huntington's disease and alpha-synuclein in Parkinson's disease. The disease-causing proteins can take various conformations and are prone to aggregate and form larger cytoplasmic or nuclear inclusions. One approach to the development of therapeutic intervention for these diseases has been to identify chemical compounds that reduce the size or number of inclusions. We have, however, identified a compound that promotes inclusion formation in cellular models of both Huntington's disease and Parkinson's disease. Of particular interest, this compound prevents huntingtin-mediated proteasome dysfunction and reduces alpha-synuclein-mediated toxicity. These results demonstrate that compounds that increase inclusion formation may actually lessen cellular pathology in both Huntington's and Parkinson's diseases, suggesting a therapeutic approach for neurodegenerative diseases caused by protein misfolding.
Abstract: Oligomerization and aggregation of alpha-synuclein molecules are believed to play a major role in neuronal dysfunction and loss in Parkinson's disease (PD) and dementia with Lewy bodies. However, alpha-synuclein oligomerization and aggregation have been detected only indirectly in cells using detergent extraction methods. Here, we show for the first time intracellular alpha-synuclein oligomerization using fluorescence lifetime imaging (FLIM). Two forms of alpha-synuclein homomeric interactions were detected: an antiparallel amino terminus-carboxyl terminus interaction between alpha-synuclein molecules, and a close amino terminus-carboxy terminus interaction within single alpha-synuclein molecules. Coexpression of the chaperone protein Hsp70, which can block alpha-synuclein toxicity in several systems, causes alpha-synuclein to adopt a different, open conformation, but Hsp70 does not alter alpha-synuclein-alpha-synuclein interactions. Thus, the neuroprotective effect of Hsp70 can be explained by its chaperone activity on alpha-synuclein molecules, rather than alteration of alpha-synuclein-alpha-synuclein interactions.
Abstract: Protein misfolding and inclusion formation are common events in neurodegenerative diseases, such as Parkinson's disease (PD), Alzheimer's disease (AD) or Huntington's disease (HD). Alpha-synuclein (aSyn) is the main protein component of inclusions called Lewy bodies (LB) which are pathognomic of PD, Dementia with Lewy bodies (DLB), and other diseases collectively known as LB diseases. Heat shock proteins (HSPs) are one class of the cellular quality control system that mediate protein folding, remodeling, and even disaggregation. Here, we investigated the role of the small heat shock proteins Hsp27 and alphaB-crystallin, in LB diseases. We demonstrate, via quantitative PCR, that Hsp27 messenger RNA levels are approximately 2-3-fold higher in DLB cases compared to control. We also show a corresponding increase in Hsp27 protein levels. Furthermore, we found that Hsp27 reduces aSyn-induced toxicity by approximately 80% in a culture model while alphaB-crystallin reduces toxicity by approximately 20%. In addition, intracellular inclusions were immunopositive for endogenous Hsp27, and overexpression of this protein reduced aSyn aggregation in a cell culture model.
Abstract: Parkinson's disease (PD) is a neurologic disorder resulting from the loss of dopaminergic neurons in the brain. Two lines of evidence suggest that the protein alpha-synuclein plays a role in the pathogenesis of PD: Fibrillar alpha-synuclein is a major component of Lewy bodies in diseased neurons, and two mutations in alpha-synuclein are linked to early-onset disease. Accordingly, the fibrillization of alpha-synuclein is proposed to contribute to neurodegeneration in PD. In this report, we provide evidence that oligomeric intermediates of the alpha-synuclein fibrillization pathway, termed protofibrils, might be neurotoxic. Analyses of protofibrillar alpha-synuclein by atomic force microscopy and electron microscopy indicate that the oligomers consist of spheres, chains, and rings. alpha-Synuclein protofibrils permeabilize synthetic vesicles and form pore-like assemblies on the surface of brain-derived vesicles. Dopamine reacts with alpha-synuclein to form a covalent adduct that slows the conversion of protofibrils to fibrils. This finding suggests that cytosolic dopamine in dopaminergic neurons promotes the accumulation of toxic alpha-synuclein protofibrils, which might explain why these neurons are most vulnerable to degeneration in PD. Finally, we note that aggregation of alpha-synuclein likely occurs via different mechanisms in the cell versus the test tube. For example, the binding of alpha-synuclein to cellular membranes might influence its self-assembly. To address this point, we have developed a yeast model that might enable the selection of random alpha-synuclein mutants with different membrane-binding affinities. These variants might be useful to test whether membrane binding by alpha-synuclein is necessary for neurodegeneration in transgenic animal models of PD.
Abstract: The occurrence of protein aggregates in ordered fibrillar structures known as amyloid, found inside and outside of brain cells, is a feature shared by many neurodegenerative disorders, including Alzheimer's, Parkinson's, and Huntington's diseases. Although the molecular mechanisms that underlie neurodegeneration will ultimately have to be tested in neuronal and animal models, there are several distinct advantages in using model organisms to elucidate fundamental aspects of protein aggregation, amyloid formation, and toxicity. Here, we review recent studies indicating that amyloid formation by disease-causing proteins can be faithfully recapitulated in simple yeast-based models in Saccharomyces cerevisiae. These studies have already contributed to our basic understanding of molecular chaperone function/dysfunction in Huntington's disease, and functional genomics approaches being undertaken currently will likely bear novel insights into the genes and pathways that modulate neuronal cell dysfunction and death in these devastating diseases. A final advantage of using yeast to study amyloid formation and toxicity is the ease and rapidity with which large-scale drug-screening efforts can be conducted in this model organism.
Abstract: Prions are infectious protein conformations that are generally ordered protein aggregates. In the absence of prions, newly synthesized molecules of these same proteins usually maintain a conventional soluble conformation. However, prions occasionally arise even without a homologous prion template. The conformational switch that results in the de novo appearance of yeast prions with glutamine/aspargine (Q/N)-rich prion domains (e.g., [PSI+]), is promoted by heterologous prions with a similar domain (e.g., [RNQ+], also known as [PIN+]), or by overexpression of proteins with prion-like Q-, N-, or Q/N-rich domains. This finding led to the hypothesis that aggregates of heterologous proteins provide an imperfect template on which the new prion is seeded. Indeed, we show that newly forming Sup35 and preexisting Rnq1 aggregates always colocalize when [PSI+] appearance is facilitated by the [RNQ+] prion, and that Rnq1 fibers enhance the in vitro formation of fibers by the prion domain of Sup35 (NM). The proteins do not however form mixed, interdigitated aggregates. We also demonstrate that aggregating variants of the polyQ-containing domain of huntingtin promote the de novo conversion of Sup35 into [PSI+]; whereas nonaggregating variants of huntingtin and aggregates of non-polyQ amyloidogenic proteins, transthyretin, alpha-synuclein, and synphilin do not. Furthermore, transthyretin and alpha-synuclein amyloids do not facilitate NM aggregation in vitro, even though in [PSI+] cells NM and transthyretin aggregates also occasionally colocalize. Our data, especially the in vitro reproduction of the highly specific heterologous seeding effect, provide strong support for the hypothesis of cross-seeding in the spontaneous initiation of prion states.
Abstract: The yeast Saccharomyces cerevisiae genome encodes several proteins that, in laboratory strains, can take up a stable, transmissible prion form. In each case, this requires the Asn/Gln-rich prion-forming domain (PrD) of the protein to be intact. In order to further understand the evolutionary significance of this unusual property, we have examined four different prion genes and their corresponding PrDs, from a number of naturally occurring strains of S. cerevisiae. In 4 of the 16 strains studied we identified a new allele of the SUP35 gene (SUP35delta19) that contains a 19-amino-acid deletion within the N-terminal PrD, a deletion that eliminates the prion property of Sup35p. In these strains a second prion gene, RNQ1, was found to be highly polymorphic, with eight different RNQ1 alleles detected in the six diploid strains studied. In contrast, for one other prion gene (URE2) and the sequence of the NEW1 gene encoding a PrD, no significant degree of DNA polymorphism was detected. Analysis of the naturally occurring alleles of RNQ1 and SUP35 indicated that the various polymorphisms identified were associated with DNA tandem repeats (6, 12, 33, 42 or 57 bp) within the coding sequences. The expansion and contraction of DNA repeats within the RNQ1 gene may provide an evolutionary mechanism that can ensure rapid change between the [PRION+] and [prion-] states.
Abstract: Alpha-synuclein is implicated in several neurodegenerative disorders, such as Parkinson's disease and multiple system atrophy, yet its functions remain obscure. When expressed in yeast, alpha-synuclein associated with the plasma membrane in a highly selective manner, before forming cytoplasmic inclusions through a concentration-dependent, nucleated process. Alpha-synuclein inhibited phospholipase D, induced lipid droplet accumulation, and affected vesicle trafficking. This readily manipulable system provides an opportunity to dissect the molecular pathways underlying normal alpha-synuclein biology and the pathogenic consequences of its misfolding.
Abstract: Genome-wide screens were performed in yeast to identify genes that enhance the toxicity of a mutant huntingtin fragment or of alpha-synuclein. Of 4850 haploid mutants containing deletions of nonessential genes, 52 were identified that were sensitive to a mutant huntingtin fragment, 86 that were sensitive to alpha-synuclein, and only one mutant that was sensitive to both. Genes that enhanced toxicity of the mutant huntingtin fragment clustered in the functionally related cellular processes of response to stress, protein folding, and ubiquitin-dependent protein catabolism, whereas genes that modified alpha-synuclein toxicity clustered in the processes of lipid metabolism and vesicle-mediated transport. Genes with human orthologs were overrepresented in our screens, suggesting that we may have discovered conserved and nonoverlapping sets of cell-autonomous genes and pathways that are relevant to Huntington's disease and Parkinson's disease.
