A Saccharomyces cerevisiae strain unable to store neutral lipids is tolerant to oxidative stress induced by α-synuclein

Serum lipid levels are associated with orthostatic hypotension in multiple system atrophy patients

OBJECTIVES

Orthostatic hypotension (OH) is one of the most important autonomic features of multiple system atrophy (MSA). This study was established to confirm the correlation between lipid levels and OH in MSA.

METHODS

A total of 580 patients with probable or possible MSA from neurological wards in six hospitals in Tianjin, Beijing, Hebei Province, and Henan Province, China, were included in this study. The tilt test or stand test was used to assess the severity of OH. Lipid contents, including total cholesterol, low-density-lipoprotein cholesterol (LDL-C), high-density-lipoprotein cholesterol (HDL-C), and triglyceride were evaluated.

RESULTS

Serum levels of total cholesterol, LDL-C, and triglyceride in MSA-OH patients were significantly lower than those in MSA without OH. The risks of OH were significantly higher in the lowest quartiles of triglyceride and LDL-C than in the highest quartiles, after adjusting for confounders (OR = 2.17, 95% CI: 1.23-3.82, P = 0.008 and OR = 2.02, 95% CI: 1.16-3.47, P = 0.012). The risk of severe OH was significantly higher in the lowest quartile and the second quartile of triglyceride than in the highest quartile after adjusting for confounders (OR = 2.16, 95% CI: 1.20-3.87, P = 0.010 and OR = 2.25, 95% CI: 1.24-4.07, P = 0.007). Moreover, the risk of OH was significantly higher in the lowest quartile, and the third quartile of TC than in the highest quartile after adjusting for confounders (OR = 2.04, 95% CI: 1.18-3.52, P = 0.010 and OR = 2.06, 95% CI: 1.19-3.56, P = 0.010).

CONCLUSION

Low levels of TC, LDL-C, and triglyceride increased the risk of OH in MSA. A low level of triglyceride predicted severe OH in MSA.

Artificial intelligence-based clustering and characterization of Parkinson's disease trajectories

Parkinson's disease (PD) is a highly heterogeneous disease both with respect to arising symptoms and its progression over time. This hampers the design of disease modifying trials for PD as treatments which would potentially show efficacy in specific patient subgroups could be considered ineffective in a heterogeneous trial cohort. Establishing clusters of PD patients based on their progression patterns could help to disentangle the exhibited heterogeneity, highlight clinical differences among patient subgroups, and identify the biological pathways and molecular players which underlie the evident differences. Further, stratification of patients into clusters with distinct progression patterns could help to recruit more homogeneous trial cohorts. In the present work, we applied an artificial intelligence-based algorithm to model and cluster longitudinal PD progression trajectories from the Parkinson's Progression Markers Initiative. Using a combination of six clinical outcome scores covering both motor and non-motor symptoms, we were able to identify specific clusters of PD that showed significantly different patterns of PD progression. The inclusion of genetic variants and biomarker data allowed us to associate the established progression clusters with distinct biological mechanisms, such as perturbations in vesicle transport or neuroprotection. Furthermore, we found that patients of identified progression clusters showed significant differences in their responsiveness to symptomatic treatment. Taken together, our work contributes to a better understanding of the heterogeneity encountered when examining and treating patients with PD, and points towards potential biological pathways and genes that could underlie those differences.

Alteration in the Cerebrospinal Fluid Lipidome in Parkinson's Disease: A Post-Mortem Pilot Study

Lipid metabolism is clearly associated to Parkinson's disease (PD). Although lipid homeostasis has been widely studied in multiple animal and cellular models, as well as in blood derived from PD individuals, the cerebrospinal fluid (CSF) lipidomic profile in PD remains largely unexplored. In this study, we characterized the post-mortem CSF lipidomic imbalance between neurologically intact controls (n = 10) and PD subjects (n = 20). The combination of dual extraction with ultra-performance liquid chromatography-electrospray ionization quadrupole-time-of-flight mass spectrometry (UPLC-ESI-qToF-MS/MS) allowed for the monitoring of 257 lipid species across all samples. Complementary multivariate and univariate data analysis identified that glycerolipids (mono-, di-, and triacylglycerides), saturated and mono/polyunsaturated fatty acids, primary fatty amides, glycerophospholipids (phosphatidylcholines, phosphatidylethanolamines), sphingolipids (ceramides, sphingomyelins), N-acylethanolamines and sterol lipids (cholesteryl esters, steroids) were significantly increased in the CSF of PD compared to the control group. Interestingly, CSF lipid dyshomeostasis differed depending on neuropathological staging and disease duration. These results, despite the limitation of being obtained in a small population, suggest extensive CSF lipid remodeling in PD, shedding new light on the deployment of CSF lipidomics as a promising tool to identify potential lipid markers as well as discriminatory lipid species between PD and other atypical parkinsonisms.

Amino acid starvation inhibits autophagy in lipid droplet-deficient cells through mitochondrial dysfunction

Lipid droplets are ubiquitous organelles in eukaryotes that act as storage sites for neutral lipids. Under normal growth conditions, they are not required in the yeast Saccharomyces cerevisiae. However, recent works have shown that lipid droplets are required for autophagy to proceed in response to nitrogen starvation and that they play an essential role in maintaining ER homeostasis. Autophagy is a major catabolic pathway that helps degradation and recycling of potentially harmful proteins and organelles. It can be pharmacologically induced by rapamycin even in the absence of lipid droplets. Here, we show that amino acid starvation is responsible for autophagy failure in lipid droplet-deficient yeast. It not only fails to induce autophagy but also inhibits rapamycin-induced autophagy. The general amino acid control pathway is not involved in this paradoxical effect of amino acid shortage. We correlate the autophagy failure with mitochondria aggregation and we show that amino acid starvation-induced autophagy is restored in lipid droplet-deficient yeast by increasing mitochondrial biomass physiologically (respiration) or genetically (REG1 deletion). Our results establish a new functional link between lipid droplets, ER and mitochondria during nitrogen starvation-induced autophagy.

Proteomics-Based Monitoring of Pathway Activity Reveals that Blocking Diacylglycerol Biosynthesis Rescues from Alpha-Synuclein Toxicity

Proteinaceous inclusions containing alpha-synuclein (α-Syn) have been implicated in neuronal toxicity in Parkinson's disease, but the pathways that modulate toxicity remain enigmatic. Here, we used a targeted proteomic assay to simultaneously measure 269 pathway activation markers and proteins deregulated by α-Syn expression across a panel of 33 Saccharomyces cerevisiae strains that genetically modulate α-Syn toxicity. Applying multidimensional linear regression analysis to these data predicted Pah1, a phosphatase that catalyzes conversion of phosphatidic acid to diacylglycerol at the endoplasmic reticulum membrane, as an effector of rescue. Follow-up studies demonstrated that inhibition of Pah1 activity ameliorates the toxic effects of α-Syn, indicate that the diacylglycerol branch of lipid metabolism could enhance α-Syn neuronal cytotoxicity, and suggest a link between α-Syn toxicity and the biology of lipid droplets.

Lipids at the Crossroad of α-Synuclein Function and Dysfunction: Biological and Pathological Implications

Since its discovery, the study of the biological role of α-synuclein and its pathological implications has been the subject of increasing interest. The propensity to adopt different conformational states governing its aggregation and fibrillation makes this small 14-kDa cytosolic protein one of the main etiologic factors associated with degenerative disorders known as synucleinopathies. The structure, function, and toxicity of α-synuclein and the possibility of different therapeutic approaches to target the protein have been extensively investigated and reviewed. One intriguing characteristic of α-synuclein is the different ways in which it interacts with lipids. Though in-depth studies have been carried out in this field, the information they have produced is puzzling and the precise role of lipids in α-synuclein biology and pathology and vice versa is still largely unknown. Here we provide an overview and discussion of the main findings relating to α-synuclein/lipid interaction and its involvement in the modulation of lipid metabolism and signaling.

The Role of Lipids in Parkinson's Disease

Parkinson’s disease (PD) is a neurodegenerative disease characterized by a progressive loss of dopaminergic neurons from the nigrostriatal pathway, formation of Lewy bodies, and microgliosis. During the past decades multiple cellular pathways have been associated with PD pathology (i.e., oxidative stress, endosomal-lysosomal dysfunction, endoplasmic reticulum stress, and immune response), yet disease-modifying treatments are not available. We have recently used genetic data from familial and sporadic cases in an unbiased approach to build a molecular landscape for PD, revealing lipids as central players in this disease. Here we extensively review the current knowledge concerning the involvement of various subclasses of fatty acyls, glycerolipids, glycerophospholipids, sphingolipids, sterols, and lipoproteins in PD pathogenesis. Our review corroborates a central role for most lipid classes, but the available information is fragmented, not always reproducible, and sometimes differs by sex, age or PD etiology of the patients. This hinders drawing firm conclusions about causal or associative effects of dietary lipids or defects in specific steps of lipid metabolism in PD. Future technological advances in lipidomics and additional systematic studies on lipid species from PD patient material may improve this situation and lead to a better appreciation of the significance of lipids for this devastating disease.

High-level recombinant production of squalene using selected Saccharomyces cerevisiae strains

For recombinant production of squalene, which is a triterpenoid compound with increasing industrial applications, in microorganisms generally recognized as safe, we screened Saccharomyces cerevisiae strains to determine their suitability. A strong strain dependence was observed in squalene productivity among Saccharomyces cerevisiae strains upon overexpression of genes important for isoprenoid biosynthesis. In particular, a high level of squalene production (400 ± 45 mg/L) was obtained in shake flasks with the Y2805 strain overexpressing genes encoding a bacterial farnesyl diphosphate synthase (ispA) and a truncated form of hydroxyl-3-methylglutaryl-CoA reductase (tHMG1). Partial inhibition of squalene epoxidase by terbinafine further increased squalene production by up to 1.9-fold (756 ± 36 mg/L). Furthermore, squalene production of 2011 ± 75 or 1026 ± 37 mg/L was obtained from 5-L fed-batch fermentations in the presence or absence of terbinafine supplementation, respectively. These results suggest that the Y2805 strain has potential as a new alternative source of squalene production.

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.

Phosphatidylinositol-3-phosphate regulates response of cells to proteotoxic stress

Human Nedd4 ubiquitin ligase, or its variants, inhibit yeast cell growth by disturbing the actin cytoskeleton organization and dynamics, and lead to an increase in levels of ubiquitinated proteins. In a screen for multicopy suppressors which rescue growth of yeast cells producing Nedd4 ligase with an inactive WW4 domain (Nedd4w4), we identified a fragment of ATG2 gene encoding part of the Atg2 core autophagy protein. Expression of the Atg2-C1 fragment (aa 1074-1447) improved growth, actin cytoskeleton organization, but did not significantly change the levels of ubiquitinated proteins in these cells. The GFP-Atg2-C1 protein in Nedd4w4-producing cells primarily localized to a single defined structure adjacent to the vacuole, surrounded by an actin filament ring, containing Hsp42 and Hsp104 chaperones. This localization was not affected in several atg deletion mutants, suggesting that it might be distinct from the phagophore assembly site (PAS). However, deletion of ATG18 encoding a phosphatidylinositol-3-phosphate (PI3P)-binding protein affected the morphology of the GFP-Atg2-C1 structure while deletion of ATG14 encoding a subunit of PI3 kinase suppressed toxicity of Nedd4w4 independently of GFP-Atg2-C1. Further analysis of the Atg2-C1 revealed that it contains an APT1 domain of previously uncharacterized function. Most importantly, we showed that this domain is able to bind phosphatidylinositol phosphates, especially PI3P, which is abundant in the PAS and endosomes. Together our results suggest that human Nedd4 ubiquitinates proteins in yeast and causes proteotoxic stress and, with some Atg proteins, leads to formation of a perivacuolar structure, which may be involved in sequestration, aggregation or degradation of proteins.

Yeast reveal a "druggable" Rsp5/Nedd4 network that ameliorates α-synuclein toxicity in neurons

α-Synuclein (α-syn) is a small lipid-binding protein implicated in several neurodegenerative diseases, including Parkinson's disease, whose pathobiology is conserved from yeast to man. There are no therapies targeting these underlying cellular pathologies, or indeed those of any major neurodegenerative disease. Using unbiased phenotypic screens as an alternative to target-based approaches, we discovered an N-aryl benzimidazole (NAB) that strongly and selectively protected diverse cell types from α-syn toxicity. Three chemical genetic screens in wild-type yeast cells established that NAB promoted endosomal transport events dependent on the E3 ubiquitin ligase Rsp5/Nedd4. These same steps were perturbed by α-syn itself. Thus, NAB identifies a druggable node in the biology of α-syn that can correct multiple aspects of its underlying pathology, including dysfunctional endosomal and endoplasmic reticulum-to-Golgi vesicle trafficking.

Lipid droplets and peroxisomes: key players in cellular lipid homeostasis or a matter of fat--store 'em up or burn 'em down

Lipid droplets (LDs) and peroxisomes are central players in cellular lipid homeostasis: some of their main functions are to control the metabolic flux and availability of fatty acids (LDs and peroxisomes) as well as of sterols (LDs). Both fatty acids and sterols serve multiple functions in the cell—as membrane stabilizers affecting membrane fluidity, as crucial structural elements of membrane-forming phospholipids and sphingolipids, as protein modifiers and signaling molecules, and last but not least, as a rich carbon and energy source. In addition, peroxisomes harbor enzymes of the malic acid shunt, which is indispensable to regenerate oxaloacetate for gluconeogenesis, thus allowing yeast cells to generate sugars from fatty acids or nonfermentable carbon sources. Therefore, failure of LD and peroxisome biogenesis and function are likely to lead to deregulated lipid fluxes and disrupted energy homeostasis with detrimental consequences for the cell. These pathological consequences of LD and peroxisome failure have indeed sparked great biomedical interest in understanding the biogenesis of these organelles, their functional roles in lipid homeostasis, interaction with cellular metabolism and other organelles, as well as their regulation, turnover, and inheritance. These questions are particularly burning in view of the pandemic development of lipid-associated disorders worldwide.

ω-3 fatty acid eicosapentaenoic acid attenuates MPP+-induced neurodegeneration in fully differentiated human SH-SY5Y and primary mesencephalic cells

Eicosapentaenoic acid (EPA), a neuroactive omega-3 fatty acid, has been demonstrated to exert neuroprotective effects in experimental models of Parkinson's disease (PD), but the cellular mechanisms of protection are unknown. Here, we studied the effects of EPA in fully differentiated human SH-SY5Y cells and primary mesencephalic neurons treated with MPP(+) . In both in-vitro models of PD, EPA attenuated an MPP(+) -induced reduction in cell viability. EPA also prevented the presence of electron-dense cytoplasmic inclusions in SH-SY5Y cells. Then, possible mechanisms of the neuroprotection were studied. In primary neurons, EPA attenuated an MPP(+) -induced increase in Tyrosine-related kinase B (TrkB) receptors. In SH-SY5Y cells, EPA down-regulated reactive oxygen species and nitric oxide. This antioxidant effect of EPA may have been mediated by its inhibition of neuronal NADPH oxidase and cyclo-oxygenase-2 (COX-2), as MPP(+) increased the expression of these enzymes. Furthermore, EPA prevented an increase in cytosolic phospholipase A2 (cPLA2), an enzyme linked with COX-2 in the potentially pro-inflammatory arachidonic acid cascade. Lastly, EPA attenuated an increase in the bax:bcl-2 ratio, and cytochrome c release. However, EPA did not prevent mitochondrial enlargement or a decrease in mitochondrial membrane potential. This study demonstrated cellular mechanisms by which EPA provided neuroprotective effects in experimental PD.

Contribution of yeast models to neurodegeneration research

As a model organism Saccharomyces cerevisiae has greatly contributed to our understanding of many fundamental aspects of cellular biology in higher eukaryotes. More recently, engineered yeast models developed to study endogenous or heterologous proteins that lay at the root of a given disease have become powerful tools for unraveling the molecular basis of complex human diseases like neurodegeneration. Additionally, with the possibility of performing target-directed large-scale screenings, yeast models have emerged as promising first-line approaches in the discovery process of novel therapeutic opportunities against these pathologies. In this paper, several yeast models that have contributed to the uncovering of the etiology and pathogenesis of several neurodegenerative diseases are described, including the most common forms of neurodegeneration worldwide, Alzheimer's, Parkinson's, and Huntington's diseases. Moreover, the potential input of these cell systems in the development of more effective therapies in neurodegeneration, through the identification of genetic and chemical suppressors, is also addressed.

Oxidative stress in Alzheimer's and Parkinson's diseases: insights from the yeast Saccharomyces cerevisiae

Alzheimer's (AD) and Parkinson's (PD) diseases are the two most common causes of dementia in aged population. Both are protein-misfolding diseases characterized by the presence of protein deposits in the brain. Despite growing evidence suggesting that oxidative stress is critical to neuronal death, its precise role in disease etiology and progression has not yet been fully understood. Budding yeast Saccharomyces cerevisiae shares conserved biological processes with all eukaryotic cells, including neurons. This fact together with the possibility of simple and quick genetic manipulation highlights this organism as a valuable tool to unravel complex and fundamental mechanisms underlying neurodegeneration. In this paper, we summarize the latest knowledge on the role of oxidative stress in neurodegenerative disorders, with emphasis on AD and PD. Additionally, we provide an overview of the work undertaken to study AD and PD in yeast, focusing the use of this model to understand the effect of oxidative stress in both diseases.

Influence of RNA interference on the mitochondrial subcellular localization of alpha-synuclein and on the formation of Lewy body-like inclusions in the cytoplasm of human embryonic kidney 293 cells induced by the overexpression of alpha-synuclein

The specific and effective α-synuclein RNA interference (RNAi) plasmids, and the α-synuclein-pEGFP recombinant plasmids were co-transfected into human embryonic kidney 293 (HEK293) cells using the lipofectamine method. Using an inverted fluorescence microscope, α-synuclein proteins were observed to aggregate in the cytoplasm and nucleus. Wild-type α-synuclein proteins co-localized with mitochondria. Hematoxylin-eosin staining revealed round eosinophilic bodies (Lewy body-like inclusions) in the cytoplasm of some cells transfected with α-synuclein-pEGFP plasmid. However, the formation of Lewy body-like inclusions was not observed following transfection with the RNAi pSYN-1 plasmid. RNAi blocked Lewy body-like inclusions in the cytoplasm of HEK293 cells induced by wild-type α-synuclein overexpression, but RNAi did not affect the subcellular localization of wild-type α-synuclein in mitochondria.