Yeast reveals similar molecular mechanisms underlying alpha- and beta-synuclein toxicity

Targeting protein aggregation using a cocoa-bean shell extract to reduce α-synuclein toxicity in models of Parkinson's disease

Neurodegenerative diseases are among the major challenges in modern medicine, due to the progressive aging of the world population. Among these, Parkinson's disease (PD) affects 10 million people worldwide and is associated with the aggregation of the presynaptic protein α-synuclein (α-syn). Here we use two different PD models, yeast cells and neuroblastoma cells overexpressing α-syn, to investigate the protective effect of an extract from the cocoa shell, which is a by-product of the roasting process of cocoa beans. The LC-ESI-qTOF-MS and NMR analyses allow the identification of amino acids (including the essential ones), organic acids, lactate and glycerol, confirming also the presence of the two methylxanthines, namely caffeine and theobromine. The present study demonstrates that the supplementation with the cocoa bean shell extract (CBSE) strongly improves the longevity of yeast cells expressing α-syn, reducing the level of reactive oxygen species, activating autophagy and reducing the intracellular protein aggresomes. These anti-aggregation properties are confirmed also in neuroblastoma cells, where CBSE treatment leads to activation of AMPK kinase and to a significant reduction of toxic α-syn oligomers. Results obtained by surface plasmon resonance (SPR) assay highlights that CBSE binds α-syn protein in a concentration-dependent manner, supporting its inhibitory role on the amyloid aggregation of α-syn. These findings suggest that the supplementation with CBSE in the form of nutraceuticals may represent a promising way to prevent neurodegenerative diseases associated with α-syn aggregation.

Understanding Genetic Risks: Computational Exploration of Human β-Synuclein nsSNPs and their Potential Impact on Structural Alteration

Synucleins are pivotal in neurodegenerative conditions. Beta-synuclein (β-synuclein) is part of the synuclein protein family alongside alpha-synuclein (α-synuclein) and gamma-synuclein (γ-synuclein). These proteins, found mainly in brain tissue and cancers, are soluble and unstructured. β-synuclein shares significant similarity with α-synuclein, especially in their N-terminus, with a 90% match. However, their aggregation tendencies differ significantly. While α-synuclein aggregation is believed to be counteracted by β-synuclein, which occurs in conditions like Parkinson's disease, β-synuclein may counteract α-synuclein's toxic effects on the nervous system, offering potential treatment for neurodegenerative diseases. Under normal circumstances, β-synuclein may guard against disease by interacting with α-synuclein. Yet, in pathological environments with heightened levels or toxic substances, it might contribute to disease. Our research aims to explore potential harmful mutations in the β-synuclein using computational tools to predict their destabilizing impact on protein structure. Consensus analysis revealed rs1207608813 (A63P), rs1340051870 (S72F), and rs1581178262 (G36C) as deleterious. These findings highlight the intricate relationship between nsSNPs and protein function, shedding light on their potential implications in disease pathways. Understanding the structural consequences of nsSNPs is crucial for elucidating their role in pathogenesis and developing targeted therapeutic interventions. Our results offer a robust computational framework for identifying neurodegenerative disorder-related mutations from SNP datasets, potentially reducing the costs associated with experimental characterization.

Age-Related Changes of the Synucleins Profile in the Mouse Retina

Alpha-synuclein (aSyn) plays a central role in Parkinson's disease (PD) and has been extensively studied in the brain. This protein is part of the synuclein family, which is also composed of beta-synuclein (bSyn) and gamma-synuclein (gSyn). In addition to its neurotoxic role, synucleins have important functions in the nervous system, modulating synaptic transmission. Synucleins are expressed in the retina, but they have been poorly characterized. However, there is evidence that they are important for visual function and that they can play a role in retinal degeneration. This study aimed to profile synucleins in the retina of naturally aged mice and to correlate their patterns with specific retinal cells. With aging, we observed a decrease in the thickness of specific retinal layers, accompanied by an increase in glial reactivity. Moreover, the aSyn levels decreased, whereas bSyn increased with aging. The colocalization of both proteins was decreased in the inner plexiform layer (IPL) of the aged retina. gSyn presented an age-related decrease at the inner nuclear layer but was not significantly changed in the ganglion cell layer. The synaptic marker synaptophysin was shown to be preferentially colocalized with aSyn in the IPL with aging. At the same time, aSyn was found to exist at the presynaptic endings of bipolar cells and was affected by aging. Overall, this study suggests that physiological aging can be responsible for changes in the retinal tissue, implicating functional alterations that could affect synuclein family function.

Yeast red pigment, protein aggregates, and amyloidoses: a review

Estimating the amyloid level in yeast Saccharomyces, we found out that the red pigment (product of polymerization of aminoimidazole ribotide) accumulating in ade1 and ade2 mutants leads to drop of the amyloid content. We demonstrated in vitro that fibrils of several proteins grown in the presence of the red pigment stop formation at the protofibril stage and form stable aggregates due to coalescence. Also, the red pigment inhibits reactive oxygen species accumulation in cells. This observation suggests that red pigment is involved in oxidative stress response. We developed an approach to identify the proteins whose aggregation state depends on prion (amyloid) or red pigment presence. These sets of proteins overlap and in both cases involve many different chaperones. Red pigment binds amyloids and is supposed to prevent chaperone-mediated prion propagation. An original yeast-Drosophila model was offered to estimate the red pigment effect on human proteins involved in neurodegeneration. As yeast cells are a natural feed of Drosophila, we could compare the data on transgenic flies fed on red and white yeast cells. Red pigment inhibits aggregation of human Amyloid beta and α-synuclein expressed in yeast cells. In the brain of transgenic flies, the red pigment diminishes amyloid beta level and the area of neurodegeneration. An improvement in memory and viability accompanied these changes. In transgenic flies expressing human α-synuclein, the pigment leads to a decreased death rate of dopaminergic neurons and improves mobility. The obtained results demonstrate yeast red pigment potential for the treatment of neurodegenerative diseases.

β-Synuclein: An Enigmatic Protein with Diverse Functionality

α-Synuclein (αS) is a small, unstructured, presynaptic protein expressed in the brain. Its aggregated form is a major component of Lewy bodies, the large proteinaceous deposits in Parkinson's disease. The closely related protein, β-Synuclein (βS), is co-expressed with αS. In vitro, βS acts as a molecular chaperone to inhibit αS aggregation. As a result of this assignation, βS has been largely understudied in comparison to αS. However, recent reports suggest that βS promotes neurotoxicity, implying that βS is involved in other cellular pathways with functions independent of αS. Here, we review the current literature pertaining to human βS in order to understand better the role of βS in homeostasis and pathology. Firstly, the structure of βS is discussed. Secondly, the ability of βS to (i) act as a molecular chaperone; (ii) regulate synaptic function, lipid binding, and the nigrostriatal dopaminergic system; (iii) mediate apoptosis; (iv) participate in protein degradation pathways; (v) modulate intracellular metal levels; and (vi) promote cellular toxicity and protein aggregation is explored. Thirdly, the P123H and V70M mutations of βS, which are associated with dementia with Lewy bodies, are discussed. Finally, the importance of post-translational modifications on the structure and function of βS is reviewed. Overall, it is concluded that βS has both synergistic and antagonistic interactions with αS, but it may also possess important cellular functions independent of αS.

Small Molecule Fisetin Modulates Alpha-Synuclein Aggregation

Phenolic compounds are thought to be important to prevent neurodegenerative diseases (ND). Parkinson's Disease (PD) is a neurodegenerative disorder known for its typical motor features, the deposition of α-synuclein (αsyn)-positive inclusions in the brain, and for concomitant cellular pathologies that include oxidative stress and neuroinflammation. Neuroprotective activity of fisetin, a dietary flavonoid, was evaluated against main hallmarks of PD in relevant cellular models. At physiologically relevant concentrations, fisetin protected SH-SY5Y cells against oxidative stress overtaken by tert-butyl hydroperoxide (t-BHP) and against methyl-4-phenylpyridinuim (MPP+)-induced toxicity in dopaminergic neurons, the differentiated Lund human Mesencephalic (LUHMES) cells. In this cellular model, fisetin promotes the increase of the levels of dopamine transporter. Remarkably, fisetin reduced the percentage of cells containing αsyn inclusions as well as their size and subcellular localization in a yeast model of αsyn aggregation. Overall, our data show that fisetin exerts modulatory activities toward common cellular pathologies present in PD; remarkably, it modulates αsyn aggregation, supporting the idea that diets rich in this compound may prove beneficial.

Hydrogen Sulfide: Novel Endogenous and Exogenous Modulator of Oxidative Stress in Retinal Degeneration Diseases

Oxidative stress (OS) damage can cause significant injury to cells, which is related to the occurrence and development of many diseases. This pathological process is considered to be the first step to trigger the death of outer retinal neurons, which is related to the pathology of retinal degenerative diseases. Hydrogen sulfide (H₂S) has recently received widespread attention as a physiological signal molecule and gas neuromodulator and plays an important role in regulating OS in eyes. In this article, we reviewed the OS responses and regulatory mechanisms of H₂S and its donors as endogenous and exogenous regulators in retinal degenerative diseases. Understanding the relevant mechanisms will help to identify the therapeutic potential of H₂S in retinal degenerative diseases.

Bioprospection of Natural Sources of Polyphenols with Therapeutic Potential for Redox-Related Diseases

Plants are a reservoir of high-value molecules with underexplored biomedical applications. With the aim of identifying novel health-promoting attributes in underexplored natural sources, we scrutinized the diversity of (poly)phenols present within the berries of selected germplasm from cultivated, wild, and underutilized Rubus species. Our strategy combined the application of metabolomics, statistical analysis, and evaluation of (poly)phenols' bioactivity using a yeast-based discovery platform. We identified species as sources of (poly)phenols interfering with pathological processes associated with redox-related diseases, particularly, amyotrophic lateral sclerosis, cancer, and inflammation. In silico prediction of putative bioactives suggested cyanidin-hexoside as an anti-inflammatory molecule which was validated in yeast and mammalian cells. Moreover, cellular assays revealed that the cyanidin moiety was responsible for the anti-inflammatory properties of cyanidin-hexoside. Our findings unveiled novel (poly)phenolic bioactivities and illustrated the power of our integrative approach for the identification of dietary (poly)phenols with potential biomedical applications.

Hydrogen Sulfide and β-Synuclein Are Involved and Interlinked in the Aging Glaucomatous Retina

Purpose

Glaucoma, one of the leading causes of irreversible blindness worldwide, is a group of disorders characterized by progressive retinal ganglion cell (RGC) loss. Synucleins, a family of small proteins, have been of interest in studies of neurodegeneration and CNS. However, their roles and functions in glaucoma are still not completely understood and remain to be explored. Our previous studies showed that α-synuclein and H₂S play a pivotal role in glaucoma. This study aims to (1) elucidate the potential roles and functions of synucleins in glaucoma throughout aging, (2) investigate the interaction between the synucleins and H₂S, and better understand the mechanism of H₂S in neuroprotection.

Methods

The chronic IOP elevation model was carried out in 12 animals at different ages (3 months and 14 months), and RGCs were quantified by Brn3a staining. Mass spectrometric-assisted proteomics analysis was employed to measure synuclein levels and H₂S producing proteins in retina. Secondly, the acute IOP elevation model was carried out in 12 juvenile animals, with or without intravitreal injection of GYY4137 (a H₂S donor). RGCs were quantified along with the abundancy of synucleins.

Results

RGCs and β-synuclein (SNCB) are significantly changed in old animals. Under chronic IOP elevation, there is a significant RGC loss in old animals, whereas no significant change in young animals; SNCB is significantly downregulated and 3MST is significantly upregulated in young animals due to IOP, while no significant changes in old ones are notable. Under acute IOP elevation (approx. 55 mmHg), a significant RGC loss is observed; exogenous H₂S significantly reduced RGC loss and downregulated SNCB levels.

Conclusion

The present study indicates a strong link between ageing and SNCB regulation. In young animals SNCB is downregulated going along with less RGC loss. Furthermore, increasing endogenous H₂S is effective to downregulate SNCB and is neuroprotective against acute IOP elevation.

Characterization of the activity, aggregation, and toxicity of heterodimers of WT and ALS-associated mutant Sod1

Aggregation of the antioxidant enzyme Sod1 represents common factors of both familial (fALS) and sporadic cases of ALS, a fatal neurodegenerative disease. Although many ALS studies have focused on Sod1 homodimers/homomers, the investigation of Sod1 heterodimers/heteromers remains controversial and has mostly been performed with recombinant proteins in vitro, in the absence of a cellular environment. By using living cells, this study sheds light into a critical issue in the context of fALS, the high toxicity of the WT–mutant heteromeric inclusions, especially WT–A4V heteromers which accumulate both in human cells as well as in chronologically aged yeast cells. Besides the aggregation, we proposed that an inefficient heteromer response against oxidative conditions might contribute to fALS-linked mutant hSod1 toxicity.

Mutations in Cu/Zn superoxide dismutase (Sod1) have been reported in both familial and sporadic amyotrophic lateral sclerosis (ALS). In this study, we investigated the behavior of heteromeric combinations of wild-type (WT) and mutant Sod1 proteins A4V, L38V, G93A, and G93C in human cells. We showed that both WT and mutant Sod1 formed dimers and oligomers, but only mutant Sod1 accumulated in intracellular inclusions. Coexpression of WT and hSod1 mutants resulted in the formation of a larger number of intracellular inclusions per cell than that observed in cells coexpressing WT or mutant hSod1. The number of inclusions was greater in cells expressing A4V hSod1. To eliminate the contribution of endogenous Sod1, and better evaluate the effect of ALS-associated mutant Sod1 expression, we expressed human Sod1 WT and mutants in human cells knocked down for endogenous Sod1 (Sod1-KD), and in sod1Δ yeast cells. Using Sod1-KD cells we found that the WT–A4V heteromers formed higher molecular weight species compared with A4V and WT homomers. Using the yeast model, in conditions of chronological aging, we concluded that cells expressing Sod1 heterodimers showed decreased antioxidant activity, increased oxidative damage, reduced longevity, and oxidative stress-induced mutant Sod1 aggregation. In addition, we also found that ALS-associated Sod1 mutations reduced nuclear localization and, consequently, impaired the antioxidant response, suggesting this change in localization may contribute to disease in familial ALS. Overall, our study provides insight into the molecular underpinnings of ALS and may open avenues for the design of future therapeutic strategies.

Carbon monoxide released by CORM-A1 prevents yeast cell death via autophagy stimulation

Autophagy is an autodigestive process, promoting cytoprotection by the elimination of dysfunctional organelles, misfolded proteins and toxic aggregates. Carbon monoxide (CO) is an endogenous gasotransmitter that under low concentrations prevents cell death and inflammation. For the first time, the role of autophagy in CO-mediated cytoprotection against oxidative stress was evaluated in the model yeast Saccharomyces cerevisiae. The boron-based CO-releasing molecule, CORM-A1, was used to deliver CO. CORM-A1 partially prevented oxidative stress-induced cell death in yeast. Likewise, CORM-A1 activated autophagy under basal physiological conditions, which were assessed by autophagic flux and the expression of mCherry-Atg8 or GFP-Atg8. Inhibition of autophagy by knocking out key autophagic genes in yeast (ATG8 or ATG11) blocked CORM-A1 cytoprotective effect, indicating the critical role of autophagy in CO-induced cytoprotection. The CO-mediated cytoprotection via autophagy induction observed in yeast was validated in primary cultures of astrocytes, a well-characterized model for CO's cytoprotective functions. As in yeast, CORM-A1 prevented oxidative stress-induced cell death in an autophagy-dependent manner in astrocytes. Overall, our data support the cytoprotective action of CO against oxidative stress. CO promotes cytoprotection in yeast via autophagy, opening new possibilities for the study of molecular mechanisms of CO's biological functions using this powerful eukaryotic model.

Yeast-Based Screens to Target Alpha-Synuclein Toxicity

The budding yeast Saccharomyces cerevisiae (S. cerevisiae) has been a remarkable experimental model for the discovery of fundamental biological processes. The high degree of conservation of cellular and molecular processes between the budding yeast and higher eukaryotes has made it a valuable system for the investigation of the molecular mechanisms behind various types of devastating human pathologies. Genetic screens in yeast provided important insight into the toxic mechanisms associated with the accumulation of misfolded proteins. Thus, using yeast genetics and high-throughput screens, novel molecular targets with therapeutic potential have been identified. Here, we describe a yeast screen protocol for the identification of genetic modifiers of alpha-synuclein (aSyn) toxicity, thereby accelerating the identification of novel potential targets for intervention in Parkinson's disease (PD) and other synucleinopathies.

Interactions between the Intrinsically Disordered Proteins β-Synuclein and α-Synuclein

Several intrinsically disordered proteins have been implicated in the process of amyloid fibril formation in neurodegenerative disease, and developing approaches to inhibit the aggregation of these intrinsically disordered proteins is critical for establishing effective therapies against disease progression. The aggregation pathway of the intrinsically disordered protein alpha-synuclein, which is implicated in several neurodegenerative diseases known as synucleinopathies, has been extensively characterized. Less attention has been leveraged on beta-synuclein, a homologous intrinsically disordered protein that co-localizes with alpha-synuclein and is known to delay alpha-synuclein fibril formation. In this review, we focus on beta-synuclein and the molecular-level interactions between alpha-synuclein and beta-synuclein that underlie the delay of fibril formation. We highlight studies that begin to define alpha-synuclein and beta-synuclein interactions at the monomer, oligomer, and surface levels, and suggest that beta-synuclein plays a role in regulation of inhibition at many different stages of alpha-synuclein aggregation.

The yeast stress inducible Ssa Hsp70 reduces α-synuclein toxicity by promoting its degradation through autophagy

The mechanism underlying the role of Hsp70s in toxicity associated with intracellular accumulation of toxic protein inclusions is under intense investigation. In current study, we examined the roles of all different isoforms of yeast cytosolic Ssa Hsp70 on α-synuclein mediated cellular toxicity. The study showed that yeast cells expressing stress-inducible Ssa3 or Ssa4 as sole Ssa Hsp70 isoforms, reduced α-synuclein toxicity better than those expressing a constitutive counterpart. The protective effect of stress-inducible Ssa Hsp70s was not α-syn specific, but more general to other inclusion forming proteins such as polyQ. We show that the protective effect is not by induction of a general stress response in Ssa3 cells rather by promoting α-synuclein degradation through autophagy. The present study revealed that effect of Hsp70s was isoform dependent, and that autophagy protects Ssa3 cells from the deleterious effects of toxic protein inclusions.

Yeast red pigment modifies cloned human α-synuclein pathogenesis in Parkinson disease models in Saccharomyces cerevisiae and Drosophila melanogaster

Recently, we identified the yeast red pigment (RP), a polymer of 1-(5'-Phosphoribosyl)-5-aminoimidazole, as a novel potential anti-amyloid agent for the therapy of neurodegenerative diseases. The purpose of this study was to further validate RP for treatment of Parkinson's disease (PD) and to clarify molecular mechanisms involved in the reduction of amyloid cytotoxicity. We investigated RP effects in vivo using Saccharomyces cerevisiae and Drosophila melanogaster PD models. Western blot analysis revealed reduction in the levels of insoluble α-synuclein in both models, while soluble α-synuclein decreased only in Drosophila. In both models RP significantly reduced α-synuclein cytotoxicity, as was revealed by immunohistochemistry in Drosophila (p < 0.001, n = 27 flies per genotype/assay) and by flow cytometry in yeast (p < 0.05). Data obtained from the yeast PD model suggests that RP antitoxic effects are associated with a drop in ROS accumulation, and slower cellular transition from the early to late apoptotic stage. Using Drosophila brain tissue sections, we have demonstrated that RP helps to compensate for an α-synuclein-mediated reduction in the number of dopaminergic neurons and leads to better performance in animal climbing tests (p < 0.001, n = 120-150 flies per genotype/assay). Taken together, these results demonstrate the potential of RP for the treatment of PD, at least in model systems.

Sumoylation Protects Against β-Synuclein Toxicity in Yeast

Aggregation of α-synuclein (αSyn) plays a central role in the pathogenesis of Parkinson’s disease (PD). The budding yeast Saccharomyces cerevisiae serves as reference cell to study the interplay between αSyn misfolding, cytotoxicity and post-translational modifications (PTMs). The synuclein family includes α, β and γ isoforms. β-synuclein (βSyn) and αSyn are found at presynaptic terminals and both proteins are presumably involved in disease pathogenesis. Similar to αSyn, expression of βSyn leads to growth deficiency and formation of intracellular aggregates in yeast. Co-expression of αSyn and βSyn exacerbates the cytotoxicity. This suggests an important role of βSyn homeostasis in PD pathology. We show here that the small ubiquitin-like modifier SUMO is an important determinant of protein stability and βSyn-induced toxicity in eukaryotic cells. Downregulation of sumoylation in a yeast strain, defective for the SUMO-encoding gene resulted in reduced yeast growth, whereas upregulation of sumoylation rescued growth of yeast cell expressing βSyn. This corroborates a protective role of the cellular sumoylation machinery against βSyn-induced toxicity. Upregulation of sumoylation significantly reduced βSyn aggregate formation. This is an indirect molecular process, which is not directly linked to βSyn sumoylation because amino acid substitutions in the lysine residues required for βSyn sumoylation decreased aggregation without changing yeast cellular toxicity. αSyn aggregates are more predominantly degraded by the autophagy/vacuole than by the 26S ubiquitin proteasome system. We demonstrate a vice versa situation for βSyn, which is mainly degraded in the 26S proteasome. Downregulation of sumoylation significantly compromised the clearance of βSyn by the 26S proteasome and increased protein stability. This effect is specific, because depletion of functional SUMO did neither affect βSyn aggregate formation nor its degradation by the autophagy/vacuolar pathway. Our data support that cellular βSyn toxicity and aggregation do not correlate in their cellular impact as for αSyn but rather represent two distinct independent molecular functions and molecular mechanisms. These insights into the relationship between βSyn-induced toxicity, aggregate formation and degradation demonstrate a significant distinction between the impact of αSyn compared to βSyn on eukaryotic cells.

Alternative Splicing of Alpha- and Beta-Synuclein Genes Plays Differential Roles in Synucleinopathies

The synuclein family is composed of three members, two of which, α- and β-synuclein, play a major role in the development of synucleinopathies, including Parkinson’s disease (PD) as most important movement disorder, dementia with Lewy bodies (DLB) as the second most frequent cause of dementia after Alzheimer’s disease and multiple system atrophy. Whereas abnormal oligomerization and fibrillation of α-synuclein are now well recognized as initial steps in the development of synucleinopathies, β-synuclein is thought to be a natural α-synuclein anti-aggregant. α-synuclein is encoded by the SNCA gene, and β-synuclein by SNCB. Both genes are homologous and undergo complex splicing events. On one hand, in-frame splicing of coding exons gives rise to at least three shorter transcripts, and the functional properties of the corresponding protein isoforms are different. Another type of alternative splicing is the alternative inclusion of at least four initial exons in the case of SNCA, and two in the case of SNCB. Finally, different lengths of 3’ untranslated regions have been also reported for both genes. SNCB only expresses in the brain, but some of the numerous SNCA transcripts are also brain-specific. With the present article, we aim to provide a systematic review of disease related changes in the differential expression of the various SNCA and SNCB transcript variants in brain, blood, and non-neuronal tissue of synucleinopathies, but especially PD and DLB as major neurodegenerative disorders.

Yeast models of Parkinson's disease-associated molecular pathologies

The aging of the human population is resulting in an increase in the number of people afflicted by neurodegenerative disorders such as Parkinson's disease (PD), creating tremendous socio-economic challenges. This requires the urgent for the development of effective therapies, and of tools for early diagnosis of the disease. However, our understanding of the molecular mechanisms underlying PD pathogenesis is still incomplete, hampering progress in those areas. In recent years, the progression made in genetics has considerably contributed to our knowledge, by identifying several novel PD genes. Furthermore, many cellular and animal models have proven their value to decipher pathways involved in PD development. In this review we highlight the value of the yeast Saccharomyces cerevisiae as a model for PD. This unicellular eukaryote has contributed to our understanding of the cellular mechanisms targeted by most important PD genes and offers an excellent tool for discovering novel players via powerful and informative high throughput screens that accelerate further validation in more complex models.

Melatonin improves survival and respiratory activity of yeast cells challenged by alpha-synuclein and menadione

One of the hallmarks of Parkinson disease is α-synuclein aggregate deposition that leads to endoplasmic reticulum stress, Golgi fragmentation and impaired energy metabolism with consequent redox imbalance. In the last decade, many studies have used Saccharomyces cerevisiae as a model in order to explore the intracellular consequences of α-synuclein overexpression. In this study we propose to evaluate the respiratory outcome of yeast cells expressing α-synuclein. Cell viability or growth on selective media for respiratory activity was mainly affected in the α-synuclein-expressing cells if they were also treated with menadione, which stimulates reactive oxygen species production. We also tested whether melatonin, a natural antioxidant, would counteract the deleterious effects of α-synuclein and menadione. In fact, melatonin addition improved the respiratory growth of α-synuclein/menadione-challenged cells, presented a general improvement in the enzymatic activity of the respiratory complexes and finally elevated the rate of mitophagy, an important cellular process necessary for the clearance of damaged mitochondria. Altogether, our data confirms that α-synuclein impairs respiration in yeast, which can be rescued by melatonin addition.

Randomized CRISPR-Cas Transcriptional Perturbation Screening Reveals Protective Genes against Alpha-Synuclein Toxicity

The genome-wide perturbation of transcriptional networks with CRISPR-Cas technology has primarily involved systematic and targeted gene modulation. Here, we developed PRISM (Perturbing Regulatory Interactions by Synthetic Modulators), a screening platform that uses randomized CRISPR-Cas transcription factors (crisprTFs) to globally perturb transcriptional networks. By applying PRISM to a yeast model of Parkinson's disease (PD), we identified guide RNAs (gRNAs) that modulate transcriptional networks and protect cells from alpha-synuclein (αSyn) toxicity. One gRNA identified in this screen outperformed the most protective suppressors of αSyn toxicity reported previously, highlighting PRISM's ability to identify modulators of important phenotypes. Gene expression profiling revealed genes differentially modulated by this strong protective gRNA that rescued yeast from αSyn toxicity when overexpressed. Human homologs of top-ranked hits protected against αSyn-induced cell death in a human neuronal PD model. Thus, high-throughput and unbiased perturbation of transcriptional networks via randomized crisprTFs can reveal complex biological phenotypes and effective disease modulators.

Yeast and other lower eukaryotic organisms for studies of Vps13 proteins in health and disease

Human Vps13 proteins are associated with several diseases, including the neurodegenerative disorder Chorea-acanthocytosis (ChAc), yet the biology of these proteins is still poorly understood. Studies in Saccharomyces cerevisiae, Dictyostelium discoideum, Tetrahymena thermophila and Drosophila melanogaster point to the involvement of Vps13 in cytoskeleton organization, vesicular trafficking, autophagy, phagocytosis, endocytosis, proteostasis, sporulation and mitochondrial functioning. Recent findings show that yeast Vps13 binds to phosphatidylinositol lipids via 4 different regions and functions at membrane contact sites, enlarging the list of Vps13 functions. This review describes the great potential of simple eukaryotes to decipher disease mechanisms in higher organisms and highlights novel insights into the pathological role of Vps13 towards ChAc.

A pH-dependent switch promotes β-synuclein fibril formation via glutamate residues

α-Synuclein (αS) is the primary protein associated with Parkinson's disease, and it undergoes aggregation from its intrinsically disordered monomeric form to a cross-β fibrillar form. The closely related homolog β-synuclein (βS) is essentially fibril-resistant under cytoplasmic physiological conditions. Toxic gain-of-function by βS has been linked to dysfunction, but the aggregation behavior of βS under altered pH is not well-understood. In this work, we compare fibril formation of αS and βS at pH 7.3 and mildly acidic pH 5.8, and we demonstrate that pH serves as an on/off switch for βS fibrillation. Using αS/βS domain-swapped chimera constructs and single residue substitutions in βS, we localized the switch to acidic residues in the N-terminal and non-amyloid component domains of βS. Computational models of βS fibril structures indicate that key glutamate residues (Glu-31 and Glu-61) in these domains may be sites of pH-sensitive interactions, and variants E31A and E61A show dramatically altered pH sensitivity for fibril formation supporting the importance of these charged side chains in fibril formation of βS. Our results demonstrate that relatively small changes in pH, which occur frequently in the cytoplasm and in secretory pathways, may induce the formation of βS fibrils and suggest a complex role for βS in synuclein cellular homeostasis and Parkinson's disease.

The effects of the novel A53E alpha-synuclein mutation on its oligomerization and aggregation

α-synuclein (aSyn) is associated with both sporadic and familial forms of Parkinson’s disease (PD), the second most common neurodegenerative disorder after Alzheimer’s disease. In particular, multiplications and point mutations in the gene encoding for aSyn cause familial forms of PD. Moreover, the accumulation of aSyn in Lewy Bodies and Lewy neurites in disorders such as PD, dementia with Lewy bodies, or multiple system atrophy, suggests aSyn misfolding and aggregation plays an important role in these disorders, collectively known as synucleinopathies. The exact function of aSyn remains unclear, but it is known to be associated with vesicles and membranes, and to have an impact on important cellular functions such as intracellular trafficking and protein degradation systems, leading to cellular pathologies that can be readily studied in cell-based models. Thus, understanding the molecular effects of aSyn point mutations may provide important insight into the molecular mechanisms underlying disease onset.

We investigated the effect of the recently identified A53E aSyn mutation. Combining in vitro studies with studies in cell models, we found that this mutation reduces aSyn aggregation and increases proteasome activity, altering normal proteostasis.

We observed that, in our experimental paradigms, the A53E mutation affects specific steps of the aggregation process of aSyn and different cellular processes, providing novel ideas about the molecular mechanisms involved in synucleinopathies.

Exploring the power of yeast to model aging and age-related neurodegenerative disorders

Aging is a multifactorial process determined by molecular, cellular and systemic factors and it is well established that advancing age is a leading risk factor for several neurodegenerative diseases. In fact, the close association of aging and neurodegenerative disorders has placed aging as the greatest social and economic challenge of the 21st century, and age-related diseases have also become a key priority for countries worldwide. The growing need to better understand both aging and neurodegenerative processes has led to the development of simple eukaryotic models amenable for mechanistic studies. Saccharomyces cerevisiae has proven to be an unprecedented experimental model to study the fundamental aspects of aging and to decipher the intricacies of neurodegenerative disorders greatly because the molecular mechanisms underlying these processes are evolutionarily conserved from yeast to human. Moreover, yeast offers several methodological advantages allowing a rapid and relatively easy way of establishing gene-protein-function associations. Here we review different aging theories, common cellular pathways driving aging and neurodegenerative diseases and discuss the major contributions of yeast to the state-of-art knowledge in both research fields.