The Role of Lipids in the Initiation of α-Synuclein Misfolding

Synaptic and cognitive impairment associated with L444P heterozygous glucocerebrosidase mutation

Cognitive impairment is a common but poorly understood non-motor aspect of Parkinson's disease, negatively affecting the patient's functional capacity and quality of life. The mechanisms underlying cognitive impairment in Parkinson's disease remain elusive, limiting treatment and prevention strategies. This study investigates the molecular and cellular basis of cognitive impairment associated with heterozygous mutations in GBA1, the strongest risk gene for Parkinson's disease, which encodes glucocerebrosidase, a lysosome enzyme that degrades the glycosphingolipid glucosylceramide into glucose and ceramide. Using a Gba1L444P/+ mouse model, we provide evidence that L444P heterozygous Gba1 mutation (L444P/+) causes hippocampus-dependent spatial and reference memory deficits independently of α-synuclein (αSyn) accumulation, glucocerebrosidase lipid substrate accumulation, dopaminergic dysfunction and motor deficits. The mutation disrupts hippocampal synaptic plasticity and basal synaptic transmission by reducing the density of hippocampal CA3-CA1 synapses, a mechanism that is dissociated from αSyn-mediated presynaptic neurotransmitter release. Using a well-characterized Thy1-αSyn pre-manifest Parkinson's disease mouse model overexpressing wild-type human αSyn, we find that the L444P/+ mutation exacerbates hippocampal synaptic αSyn accumulation, synaptic and cognitive impairment in young Gba1L444P/+:Thy1-αSyn double mutant animals. With age, Thy1-αSyn mice manifest motor symptoms, and the double mutant mice exhibit more exacerbated synaptic and motor impairment than the Thy1-αSyn mice. Taken together, our results suggest that heterozygous L444P GBA1 mutation alone perturbs hippocampal synaptic structure and function, imposing a subclinical pathological burden for cognitive impairment. When co-existing αSyn overexpression is present, heterozygous L444P GBA1 mutation interacts with αSyn pathology to accelerate Parkinson's disease-related cognitive impairment and motor symptoms.

Synaptic vesicle-omics in mice captures signatures of aging and synucleinopathy

Neurotransmitter release occurs through exocytosis of synaptic vesicles. α-Synuclein's function and dysfunction in Parkinson's disease and other synucleinopathies is thought to be tightly linked to synaptic vesicle binding. Age is the biggest risk factor for synucleinopathy, and ~15% of synaptic vesicle proteins have been linked to central nervous system diseases. Yet, age- and disease-induced changes in synaptic vesicles remain unexplored. Via systematic analysis of synaptic vesicles at the ultrastructural, protein, and lipid levels, we reveal specific changes in synaptic vesicle populations, proteins, and lipids over age in wild-type mice and in α-synuclein knockout mice with and without expression of human α-synuclein. Strikingly, we find several previously undescribed synaptic changes in mice lacking α-synuclein, suggesting that loss of α-synuclein function contributes to synaptic dysfunction. These findings not only provide insights into synaptic vesicle biology and disease mechanisms in synucleinopathy, but also serve as a baseline for further mechanistic exploration of age- and disease-related alterations in synaptic vesicles.

Salt-Induced Membrane-Bound Conformation of the NAC Domain of α-Synuclein Leads to Structural Polymorphism of Amyloid Fibrils

α-Synuclein (αS) interacts with lipid membranes in neurons to form amyloid fibrils that contribute to Parkinson's disease, and its non-amyloid-β component domain is critical in the fibrillation. In this study, the salt (NaCl) effect on the membrane interaction and fibril formation of αS57-102 peptide (containing the non-amyloid-β component domain) was characterized at the molecular level because the αS57-102 fibrils exhibited structural polymorphism with two morphologies (thin and thick) in the presence of NaCl but showed one morphology (thin) in the absence of NaCl. The membrane-bound conformation (before fibrillation) of αS57-102 had two helical regions (first and second) on the membrane regardless of salt, but the length of the first region largely shortened when NaCl was present, exposing its hydrophobic area to the solvent. The exposed region induced two distinct pathways of fibril nucleation, depending on the molar ratios of free and membrane-bound αS57-102: one from the association of free αS57-102 with membrane-bound αS57-102 and the other from the assembly among membrane-bound αS57-102. The differences mainly affected the β-strand orientation and helical content within the fibril conformations, probably contributing to the thickness degree, leading to structural polymorphism.

Exploring glycolytic enzymes in disease: potential biomarkers and therapeutic targets in neurodegeneration, cancer and parasitic infections

Glycolysis, present in most organisms, is evolutionarily one of the oldest metabolic pathways. It has great relevance at a physiological level because it is responsible for generating ATP in the cell through the conversion of glucose into pyruvate and reducing nicotinamide adenine dinucleotide (NADH) (that may be fed into the electron chain in the mitochondria to produce additional ATP by oxidative phosphorylation), as well as for producing intermediates that can serve as substrates for other metabolic processes. Glycolysis takes place through 10 consecutive chemical reactions, each of which is catalysed by a specific enzyme. Although energy transduction by glucose metabolism is the main function of this pathway, involvement in virulence, growth, pathogen-host interactions, immunomodulation and adaptation to environmental conditions are other functions attributed to this metabolic pathway. In humans, where glycolysis occurs mainly in the cytosol, the mislocalization of some glycolytic enzymes in various other subcellular locations, as well as alterations in their expression and regulation, has been associated with the development and progression of various diseases. In this review, we describe the role of glycolytic enzymes in the pathogenesis of diseases of clinical interest. In addition, the potential role of these enzymes as targets for drug development and their potential for use as diagnostic and prognostic markers of some pathologies are also discussed.

From onset to advancement: the temporal spectrum of α-synuclein in synucleinopathies

This review provides an in-depth analysis of the complex role of alpha-synuclein (α-Syn) in the development of α-synucleinopathies, with a particular focus on its structural diversity and the resulting clinical variability. The ability of α-Syn to form different strains or polymorphs and undergo various post-translational modifications significantly contributes to the wide range of symptoms observed in disorders such as Parkinson's disease (PD), dementia with Lewy bodies (DLB), and multiple system atrophy (MSA), as well as in lesser-known non-classical α-synucleinopathies. The interaction between genetic predispositions and environmental factors further complicates α-synucleinopathic disease pathogenesis, influencing the disease-specific onset and progression. Despite their common pathological hallmark of α-Syn accumulation, the clinical presentation and progression of α-synucleinopathies differ significantly, posing challenges for diagnosis and treatment. The intricacies of α-Syn pathology highlight the critical need for a deeper understanding of its biological functions and interactions within the neuronal environment to develop targeted therapeutic strategies. The precise point at which α-Syn aggregation transitions from being a byproduct of initial disease triggers to an active and independent driver of disease progression - through the propagation and acceleration of pathogenic processes - remains unclear. By examining the role of α-Syn across various contexts, we illuminate its dual role as both a marker and a mediator of disease, offering insights that could lead to innovative approaches for managing α-synucleinopathies.

α-Synuclein fibrils enhance HIV-1 infection of human T cells, macrophages and microglia

HIV-associated neurocognitive disorders (HAND) and viral reservoirs in the brain remain a significant challenge. Despite their importance, the mechanisms allowing HIV-1 entry and replication in the central nervous system (CNS) are poorly understood. Here, we show that α-synuclein and (to a lesser extent) Aβ fibrils associated with neurological diseases enhance HIV-1 entry and replication in human T cells, macrophages, and microglia. Additionally, an HIV-1 Env-derived amyloidogenic peptide accelerated amyloid formation by α-synuclein and Aβ peptides. Mechanistic studies show that α-synuclein and Aβ fibrils interact with HIV-1 particles and promote virion attachment and fusion with target cells. Despite an overall negative surface charge, these fibrils facilitate interactions between viral and cellular membranes. The enhancing effects of human brain extracts on HIV-1 infection correlated with their binding to Thioflavin T, a dye commonly used to stain amyloids. Our results suggest a detrimental interplay between HIV-1 and brain amyloids that may contribute to the development of neurodegenerative diseases.

Targeting the glymphatic system to promote α-synuclein clearance: a novel therapeutic strategy for Parkinson's disease

ABSTRACT

The excessive buildup of neurotoxic α-synuclein plays a pivotal role in the pathogenesis of Parkinson's disease, highlighting the urgent need for innovative therapeutic strategies to promote α-synuclein clearance, particularly given the current lack of disease-modifying treatments. The glymphatic system, a recently identified perivascular fluid transport network, is crucial for clearing neurotoxic proteins. This review aims to synthesize current knowledge on the role of the glymphatic system in α-synuclein clearance and its implications for the pathology of Parkinson's disease while emphasizing potential therapeutic strategies and areas for future research. The review begins with an overview of the glymphatic system and details its anatomical structure and physiological functions that facilitate cerebrospinal fluid circulation and waste clearance. It summarizes emerging evidence from neuroimaging and experimental studies that highlight the close correlation between the glymphatic system and clinical symptom severity in patients with Parkinson's disease, as well as the effect of glymphatic dysfunction on α-synuclein accumulation in Parkinson's disease models. Subsequently, the review summarizes the mechanisms of glymphatic system impairment in Parkinson's disease, including sleep disturbances, aquaporin-4 impairment, and mitochondrial dysfunction, all of which diminish glymphatic system efficiency. This creates a vicious cycle that exacerbates α-synuclein accumulation and worsens Parkinson's disease. The therapeutic perspectives section outlines strategies for enhancing glymphatic activity, such as improving sleep quality and pharmacologically targeting aquaporin-4 or its subcellular localization. Promising interventions include deep brain stimulation, melatonin supplementation, γ-aminobutyric acid modulation, and non-invasive methods (such as exercise and bright-light therapy), multisensory γ stimulation, and ultrasound therapy. Moreover, identifying neuroimaging biomarkers to assess glymphatic flow as an indicator of α-synuclein burden could refine Parkinson's disease diagnosis and track disease progression. In conclusion, the review highlights the critical role of the glymphatic system in α-synuclein clearance and its potential as a therapeutic target in Parkinson's disease. It advocates for further research to elucidate the specific mechanisms by which the glymphatic system clears misfolded α-synuclein and the development of imaging biomarkers to monitor glymphatic activity in patients with Parkinson's disease. Findings from this review suggest that enhancing glymphatic clearance is a promising strategy for reducing α-synuclein deposits and mitigating the progression of Parkinson's disease.

Folding of N-terminally acetylated α-synuclein upon interaction with lipid membranes

α-Synuclein (α-syn) is an abundant presynaptic neuronal protein whose aggregation is strongly associated with Parkinson's disease. It has been proposed that lipid membranes significantly affect α-syn's aggregation process. Extensive studies have been conducted to understand the interactions between α-syn and lipid membranes and have demonstrated that the N-terminus plays a critical role. However, the dynamics of the interactions and the conformational transitions of the N-terminus of α-syn at the atomistic scale details are still highly desired. In this study, we performed extensive enhanced sampling molecular dynamics simulations to quantify the folding and interactions of wild-type and N-terminally acetylated α-syn when interacting with lipid structures. We found that N-terminal acetylation significantly increases the helicity of the first few residues in solution or when interacting with lipid membranes. The observations in simulations showed that the binding of α-syn with lipid membranes mainly follows the induced-fit model, where the disordered α-syn binds with the lipid membrane through the electrostatic interactions and hydrophobic contacts with the packing defects; after stable insertion, N-terminal acetylation promotes the helical folding of the N-terminus to enhance the anchoring, thus increasing the binding affinity. We have shown the critical role of the first N-terminal residue methionine for recognition and anchoring to the negatively charged membrane. Although N-terminal acetylation neutralizes the positive charge of Met1 that may affect the electrostatic interactions of α-syn with membranes, the increase in helicity of the N-terminus should compensate for the binding affinity. This study provides detailed insight into the folding dynamics of α-syn's N-terminus with or without acetylation in solution and upon interaction with lipids, which clarifies how the N-terminal acetylation regulates the affinity of α-syn binding to lipid membranes. It also shows how packing defects and electrostatic effects coregulate the N-terminus of α-syn folding and its interaction with membranes.

Small molecule modulators of alpha-synuclein aggregation and toxicity: Pioneering an emerging arsenal against Parkinson's disease

Parkinson's disease (PD) is primarily characterized by loss of dopaminergic neurons in the substantia nigra pars compacta region of the brain and accumulation of aggregated forms of alpha-synuclein (α-Syn), an intrinsically disordered protein, in the form of Lewy Bodies and Lewy Neurites. Substantial evidences point to the aggregated/fibrillar forms of α-Syn as a central event in PD pathogenesis, underscoring the modulation of α-Syn aggregation as a promising strategy for PD treatment. Consequently, numerous anti-aggregation agents, spanning from small molecules to polymers, have been scrutinized for their potential to mitigate α-Syn aggregation and its associated toxicity. Among these, small molecule modulators like osmoprotectants, polyphenols, cellular metabolites, metals, and peptides have emerged as promising candidates with significant potential in PD management. This article offers a comprehensive overview of the effects of these small molecule modulators on the aggregation propensity and associated toxicity of α-Syn and its PD-associated mutants. It serves as a valuable resource for identifying and developing potent, non-invasive, non-toxic, and highly specific small molecule-based therapeutic arsenal for combating PD. Additionally, it raises pertinent questions aimed at guiding future research endeavours in the field of α-Syn aggregation remodelling.

Salt-Induced Hydrophobic C-Terminal Region of α-Synuclein Triggers Its Fibrillation under the Mimic Physiologic Condition

α-Synuclein (αS) causes Parkinson's disease due to the structural alteration into amyloid fibrils that form after the interaction with synaptic membranes in neurons. To understand the alternation mechanism, the effect of salt (NaCl) on the interaction of αS with synaptic mimic membrane was characterized at the molecular level because salt triggered the amyloid fibril formation. The membrane-bound conformation (or the initial conformation before fibrillation) showed that NaCl decreased the number of helical structures and Tyr residues interacting with the membrane surface compared to when NaCl was absent, implying an increase in solvent-exposed regions. The N-terminal region of αS interacted with the membrane, forming the helical structures regardless of NaCl, while the C-terminal region formed a random structure with weak membrane interaction, but NaCl inhibited the interaction of its hydrophobic area, suggesting that salt promoted amyloid fibril formations by exposing the hydrophobic C-terminal region, which can intermolecularly interact with free αS.

Identification of SYNJ1 in a Complex Case of Juvenile Parkinsonism Using a Multiomics Approach

This study aimed to elucidate the genetic causes underlying the juvenile parkinsonism (JP) diagnosed in a girl with several family members diagnosed with spinocerebellar ataxia type 2 (SCA2). To achieve this, whole-exome sequencing, analysis of CAG repeats, RNA sequencing analysis on fibroblasts, and metabolite identification were performed. As a result, a homozygous missense mutation SNP T>C (rs2254562) in synaptojamin 1 (SYNJ1), which has been implicated in the regulation of membrane trafficking in the synaptic vesicles, was identified. Additionally, we observed overexpression of L1 cell adhesion molecule (L1CAM), Cdc37, GPX1, and GPX4 and lower expression of ceruloplasmin in the patient compared to the control. We also found changes in sphingolipid, inositol, and inositol phosphate metabolism. These findings help to clarify the mechanisms of JP and suggest that the etiology of JP in the patient may be multifactorial. This is the first report of the rs2254562 mutation in the SYNJ gene identified in a JP patient with seizures and cognitive impairment.

Molecular mechanism of α-synuclein aggregation on lipid membranes revealed

The central hallmark of Parkinson's disease pathology is the aggregation of the α-synuclein protein, which, in its healthy form, is associated with lipid membranes. Purified monomeric α-synuclein is relatively stable in vitro, but its aggregation can be triggered by the presence of lipid vesicles. Despite this central importance of lipids in the context of α-synuclein aggregation, their detailed mechanistic role in this process has not been established to date. Here, we use chemical kinetics to develop a mechanistic model that is able to globally describe the aggregation behaviour of α-synuclein in the presence of DMPS lipid vesicles, across a range of lipid and protein concentrations. Through the application of our kinetic model to experimental data, we find that the reaction is a co-aggregation process involving both protein and lipids and that lipids promote aggregation as much by enabling fibril elongation as by enabling their initial formation. Moreover, we find that the primary nucleation of lipid-protein co-aggregates takes place not on the surface of lipid vesicles in bulk solution but at the air-water and/or plate interfaces, where lipids and proteins are likely adsorbed. Our model forms the basis for mechanistic insights, also in other lipid-protein co-aggregation systems, which will be crucial in the rational design of drugs that inhibit aggregate formation and act at the key points in the α-synuclein aggregation cascade.

Peripheral Upregulation of Parkinson's Disease-Associated Genes Encoding α-Synuclein, β-Glucocerebrosidase, and Ceramide Glucosyltransferase in Major Depression

Due to the high comorbidity of Parkinson's disease (PD) with major depressive disorder (MDD) and the involvement of sphingolipids in both conditions, we investigated the peripheral expression levels of three primarily PD-associated genes: α-synuclein (SNCA), lysosomal enzyme β-glucocerebrosidase (GBA1), and UDP-glucose ceramide glucosyltransferase (UGCG) in a sex-balanced MDD cohort. Normalized gene expression was determined by quantitative PCR in patients suffering from MDD (unmedicated n = 63, medicated n = 66) and controls (remitted MDD n = 39, healthy subjects n = 61). We observed that expression levels of SNCA (p = 0.036), GBA1 (p = 0.014), and UGCG (p = 0.0002) were higher in currently depressed patients compared to controls and remitted patients, and expression of GBA1 and UGCG decreased in medicated patients during three weeks of therapy. Additionally, in subgroups, expression was positively correlated with the severity of depression and anxiety. Furthermore, we identified correlations between the gene expression levels and PD-related laboratory parameters. Our findings suggest that SNCA, GBA1, and UGCG analysis could be instrumental in the search for biomarkers of MDD and in understanding the overlapping pathological mechanisms underlying neuro-psychiatric diseases.

Integrated metabolomics and proteomics analysis of plasma lipid metabolism in Parkinson's disease

INTRODUCTION

Metabolomics and proteomics are two growing fields of science which may shed light on the molecular mechanisms that contribute to neurodegenerative diseases. Studies focusing on these aspects can reveal specific metabolites and proteins that can halt or reverse the progressive neurodegenerative process leading to dopaminergic cell death in the brain.

AREAS COVERED

In this article, an overview of the current status of metabolomic and proteomic profiling in the neurodegenerative disease such as Parkinson's disease (PD) is presented. We discuss the importance of state-of-the-art metabolomics and proteomics using advanced analytical methodologies and their potential for discovering new biomarkers in PD. We critically review the research to date, highlighting how metabolomics and proteomics can have an important impact on early disease diagnosis, future therapy development and the identification of new biomarkers. Finally, we will discuss interactions between lipids and α-synuclein (SNCA) and also consider the role of SNCA in lipid metabolism.

EXPERT OPINION

Metabolomic and proteomic studies contribute to understanding the biological basis of PD pathogenesis, identifying potential biomarkers and introducing new therapeutic strategies. The complexity and multifactorial nature of this disease requires a comprehensive approach, which can be achieved by integrating just these two omic studies.

Length and saturation of fatty acids in phosphatidylserine determine the rate of lysozyme aggregation simultaneously altering the structure and toxicity of amyloid oligomers and fibrils

Abrupt aggregation of misfolded proteins is the underlying molecular cause of numerous severe pathologies including Alzheimer's and Parkinson's diseases. Protein aggregation yields small oligomers that can later propagate into amyloid fibrils, β-sheet-rich structures with a variety of topologies. A growing body of evidence suggests that lipids play an important role in abrupt aggregation of misfolded proteins. In this study, we investigate the roles of length and saturation of fatty acids (FAs) in phosphatidylserine (PS), an anionic lipid that is responsible for the recognition of apoptotic cells by macrophages, in lysozyme aggregation. We found that both the length and saturation of FAs in PS contribute to the aggregation rate of insulin. PS with 14-carbon-long FAs (14:0) enabled a much stronger acceleration of protein aggregation compared to PS with 18-carbon-long FAs (18:0). Our results demonstrate that the presence of double bonds in FAs accelerated the rate of insulin aggregation relative to PS with fully saturated FAs. Biophysical methods revealed morphological and structural differences in lysozyme aggregates grown in the presence of PS with varying lengths and FA saturation. We also found that such aggregates exerted diverse cell toxicities. These results demonstrate that the length and saturation of FAs in PS can uniquely alter the stability of misfolded proteins on lipid membranes.

The role of the PLA2G6 gene in neurodegenerative diseases

PLA2G6-associated neurodegeneration (PLAN) represents a continuum of clinically and genetically heterogeneous neurodegenerative disorders with overlapping features. Usually, it encompasses three autosomal recessive diseases, including infantile neuroaxonal dystrophy or neurodegeneration with brain iron accumulation (NBIA) 2A, atypical neuronal dystrophy with childhood-onset or NBIA2B, and adult-onset dystonia-parkinsonism form named PARK14, and possibly a certain subtype of hereditary spastic paraplegia. PLAN is caused by variants in the phospholipase A2 group VI gene (PLA2G6), which encodes an enzyme involved in membrane homeostasis, signal transduction, mitochondrial dysfunction, and α-synuclein aggregation. In this review, we discuss PLA2G6 gene structure and protein, functional findings, genetic deficiency models, various PLAN disease phenotypes, and study strategies in the future. Our primary aim is to provide an overview of genotype-phenotype correlations of PLAN subtypes and speculate on the role of PLA2G6 in potential mechanisms underlying these conditions.

Inhibition of Protein Aggregation and Endoplasmic Reticulum Stress as a Targeted Therapy for α-Synucleinopathy

α-synuclein (α-syn) is an intrinsically disordered protein abundant in the central nervous system. Physiologically, the protein regulates vesicle trafficking and neurotransmitter release in the presynaptic terminals. Pathologies related to misfolding and aggregation of α-syn are referred to as α-synucleinopathies, and they constitute a frequent cause of neurodegeneration. The most common α-synucleinopathy, Parkinson's disease (PD), is caused by abnormal accumulation of α-syn in the dopaminergic neurons of the midbrain. This results in protein overload, activation of endoplasmic reticulum (ER) stress, and, ultimately, neural cell apoptosis and neurodegeneration. To date, the available treatment options for PD are only symptomatic and rely on dopamine replacement therapy or palliative surgery. As the prevalence of PD has skyrocketed in recent years, there is a pending issue for development of new disease-modifying strategies. These include anti-aggregative agents that target α-syn directly (gene therapy, small molecules and immunization), indirectly (modulators of ER stress, oxidative stress and clearance pathways) or combine both actions (natural compounds). Herein, we provide an overview on the characteristic features of the structure and pathogenic mechanisms of α-syn that could be targeted with novel molecular-based therapies.

Genetic modifiers of synucleinopathies-lessons from experimental models

α-Synuclein is a pleiotropic protein underlying a group of progressive neurodegenerative diseases, including Parkinson's disease and dementia with Lewy bodies. Together, these are known as synucleinopathies. Like all neurological diseases, understanding of disease mechanisms is hampered by the lack of access to biopsy tissues, precluding a real-time view of disease progression in the human body. This has driven researchers to devise various experimental models ranging from yeast to flies to human brain organoids, aiming to recapitulate aspects of synucleinopathies. Studies of these models have uncovered numerous genetic modifiers of α-synuclein, most of which are evolutionarily conserved. This review discusses what we have learned about disease mechanisms from these modifiers, and ways in which the study of modifiers have supported ongoing efforts to engineer disease-modifying interventions for synucleinopathies.

Development of Small Molecules Targeting α-Synuclein Aggregation: A Promising Strategy to Treat Parkinson's Disease

Parkinson's disease, the second most common neurodegenerative disorder worldwide, is characterized by the accumulation of protein deposits in the dopaminergic neurons. These deposits are primarily composed of aggregated forms of α-Synuclein (α-Syn). Despite the extensive research on this disease, only symptomatic treatments are currently available. However, in recent years, several compounds, mainly of an aromatic character, targeting α-Syn self-assembly and amyloid formation have been identified. These compounds, discovered by different approaches, are chemically diverse and exhibit a plethora of mechanisms of action. This work aims to provide a historical overview of the physiopathology and molecular aspects associated with Parkinson's disease and the current trends in small compound development to target α-Syn aggregation. Although these molecules are still under development, they constitute an important step toward discovering effective anti-aggregational therapies for Parkinson's disease.

Anti-Parkinson Effects of Holothuria leucospilota-Derived Palmitic Acid in Caenorhabditis elegans Model of Parkinson’s Disease

Parkinson’s disease (PD) is the second most common neurodegenerative disease which is still incurable. Sea cucumber-derived compounds have been reported to be promising candidate drugs for treating age-related neurological disorders. The present study evaluated the beneficial effects of the Holothuria leucospilota (H. leucospilota)-derived compound 3 isolated from ethyl acetate fraction (HLEA-P3) using Caenorhabditis elegans PD models. HLEA-P3 (1 to 50 µg/mL) restored the viability of dopaminergic neurons. Surprisingly, 5 and 25 µg/mL HLEA-P3 improved dopamine-dependent behaviors, reduced oxidative stress and prolonged lifespan of PD worms induced by neurotoxin 6-hydroxydopamine (6-OHDA). Additionally, HLEA-P3 (5 to 50 µg/mL) decreased α-synuclein aggregation. Particularly, 5 and 25 µg/mL HLEA-P3 improved locomotion, reduced lipid accumulation and extended lifespan of transgenic C. elegans strain NL5901. Gene expression analysis revealed that treatment with 5 and 25 µg/mL HLEA-P3 could upregulate the genes encoding antioxidant enzymes (gst-4, gst-10 and gcs-1) and autophagic mediators (bec-1 and atg-7) and downregulate the fatty acid desaturase gene (fat-5). These findings explained the molecular mechanism of HLEA-P3-mediated protection against PD-like pathologies. The chemical characterization elucidated that HLEA-P3 is palmitic acid. Taken together, these findings revealed the anti-Parkinson effects of H. leucospilota-derived palmitic acid in 6-OHDA induced- and α-synuclein-based models of PD which might be useful in nutritional therapy for treating PD.

Lysophospholipids: A Potential Drug Candidates for Neurodegenerative Disorders

Neurodegenerative diseases (NDs) commonly present misfolded and aggregated proteins. Considerable research has been performed to unearth the molecular processes underpinning this pathological aggregation and develop therapeutic strategies targeting NDs. Fibrillary deposits of α-synuclein (α-Syn), a highly conserved and thermostable protein, are a critical feature in the development of NDs such as Alzheimer's disease (AD), Lewy body disease (LBD), Parkinson's disease (PD), and multiple system atrophy (MSA). Inhibition of α-Syn aggregation can thus serve as a potential approach for therapeutic intervention. Recently, the degradation of target proteins by small molecules has emerged as a new therapeutic modality, gaining the hotspot in pharmaceutical research. Additionally, interest is growing in the use of food-derived bioactive compounds as intervention agents against NDs via functional foods and dietary supplements. According to reports, dietary bioactive phospholipids may have cognition-enhancing and neuroprotective effects, owing to their abilities to influence cognition and mental health in vivo and in vitro. However, the mechanisms by which lipids may prevent the pathological aggregation of α-Syn warrant further clarification. Here, we review evidence for the potential mechanisms underlying this effect, with a particular focus on how porcine liver decomposition product (PLDP)-derived lysophospholipids (LPLs) may inhibit α-Syn aggregation.

Cu2+ ions modulate the interaction between α-synuclein and lipid membranes

α-synuclein protein aggregates are the major constituent of Lewy bodies, which is a main pathogenic hallmark of Parkinson's disease. Both lipid membranes and Cu²⁺ ions can bind to α-synuclein and modulate its aggregation propensity and toxicity. However, the synergistic effect of copper ions and lipid membranes on α-synuclein remains to be explored. Here, we investigate how Cu²⁺ and α-synuclein simultaneously influence the lipidic structure of lipidic cubic phase(LCP) matrix by using small-angle X-ray scattering. α-Syn proteins destabilize the cubic-Pn3m phase of LCP that can be further recovered after the addition of Cu² ions even at a low stoichiometric ratio. By using circular dichroism and nuclear magnetic resonance, we also study how lipid membranes and Cu²⁺ ions impact the secondary structures of α-synuclein at an atomic level. Although the secondary structure of α-synuclein with lipid membranes is not significantly changed to a large extent in the presence of Cu²⁺ ions, lipid membranes promote the interaction between α-synuclein C-terminus and Cu²⁺ ions. The modulation of Cu²⁺ ions and lipid membranes on α-synuclein dynamics and structure may play an important role in the molecular pathogenesis of Parkinson's disease.

Untwisted α-Synuclein Filaments Formed in the Presence of Lipid Vesicles

Accumulation of filamentous aggregates of α-synuclein is a pathological hallmark of several neurodegenerative diseases, including Parkinson's disease (PD). The interaction between α-synuclein and phospholipids has been shown to play a critical role in the aggregation of α-synuclein. Most structural studies have, however, been focused on α-synuclein filaments formed in the absence of lipids. Here, we report the structural investigation of α-synuclein filaments assembled under the quiescent condition in the presence of anionic lipid vesicles using electron microscopy (EM), including cryogenic electron microscopy (cryo-EM). Our transmission electron microscopy (TEM) analyses reveal that α-synuclein forms curly protofilaments at an early stage of aggregation. The flexible protofilaments were then converted to long filaments after a longer incubation of 30 days. More detailed structural analyses using cryo-EM reveal that the long filaments adopt untwisted structures with different diameters, which have not been observed in previous α-synuclein fibrils formed in vitro. The untwisted filaments are rather similar to straight filaments with no observable twist that are extracted from patients with dementia with Lewy bodies. Our structural studies highlight the conformational diversity of α-synuclein filaments, requiring additional structural investigation of not only more ex vivo α-synuclein filaments but also in vitro α-synuclein filaments formed in the presence of diverse cofactors to better understand the molecular basis of diverse molecular conformations of α-synuclein filaments.

Loss of Drosophila NUS1 results in cholesterol accumulation and Parkinson's disease-related neurodegeneration

NgBR is the Nogo-B receptor, encoded by NUS1 gene. As NgBR contains a C-terminal domain that is similar to cis-isoprenyltransferase (cis-IPTase), NgBR was speculated to stabilize nascent Niemann-Pick type C 2 (NPC2) to facilitate cholesterol transport out of lysosomes. Mutations in the NUS1 were known as risk factors for Parkinson's disease (PD). In our previous study, it was shown that knockdown of Drosophila NUS1 orthologous gene tango14 causes decreased climbing ability, loss of dopaminergic neurons, and decreased dopamine contents. In this study, tango14 mutant flies were generated with a mutation in the C-terminal enzyme activity region using CRISPR/Cas9. Tango14 mutant showed a reduced lifespan with locomotive defects and cholesterol accumulation in Malpighian tubules and brains, especially in dopaminergic neurons. Multilamellar bodies were found in tango14 mutants using electron microscopy. Neurodegenerative-related brain vacuolization was also detected in tango14 knockdown flies in an age-dependent manner. In addition, tango14 knockdown increased α-synuclein (α-syn) neurotoxicity in α-syn-overexpressing flies, with decreased locomotive activities, dopamine contents, and the numbers of dopaminergic neurons in aging flies. Thus, these observations suggest a role of NUS1, the ortholog of tango14, in PD-related pathogenesis.

The Degree of Unsaturation of Fatty Acids in Phosphatidylserine Alters the Rate of Insulin Aggregation and the Structure and Toxicity of Amyloid Aggregates

Phosphatidylserine (PS) in the plasma membrane plays an important role in cell signaling and apoptosis. Cell degeneration is also linked to numerous amyloid diseases, pathologies that are associated with aggregation of misfolded proteins. In this work, we examine the effect of both saturated PS (DMPS) and unsaturated PS (DOPS and POPS) on the aggregation properties of insulin, as well as the structure and toxicity of insulin aggregates formed in the presence of these phospholipids. We found that the degree of unsaturation of fatty acids in PS alters the rate of insulin aggregation. We also found that toxicity of insulin-DMPS aggregates is significantly lower than the toxicity of DOPS- and POPS-insulin fibrils, whereas all these lipid-containing aggregates exert lower cell toxicity than insulin fibrils grown in a lipid-free environment.

α-Synuclein Impacts on Intrinsic Neuronal Network Activity Through Reduced Levels of Cyclic AMP and Diminished Numbers of Active Presynaptic Terminals

α-synuclein (α-Syn) is intimately linked to synucleinopathies like Parkinson’s disease and dementia with Lewy bodies. However, the pathophysiological mechanisms that are triggered by this protein are still largely enigmatic. α-Syn overabundance may cause neurodegeneration through protein accumulation and mitochondrial deterioration but may also result in pathomechanisms independent from neuronal cell death. One such proposed pathological mechanism is the influence of α-Syn on non-stimulated, intrinsic brain activity. This activity is responsible for more than 90% of the brain’s energyconsumption, and is thus thought to play an eminent role in basic brain functionality. Here we report that α-Syn substantially disrupts intrinsic neuronal network burst activity in a long-term neuronal cell culture model. Mechanistically, the impairment of network activity originates from reduced levels of cyclic AMP and cyclic AMP-mediated signaling as well as from diminished numbers of active presynaptic terminals. The profound reduction of network activity due to α-Syn was mediated only by intracellularly expressed α-Syn, but not by α-Syn that is naturally released by neurons. Conversely, extracellular pre-formed fibrils of α-Syn mimicked the effect of intracellular α-Syn, suggesting that they trigger an off-target mechanism that is not activated by naturally released α-Syn. A simulation-based model of the network activity in our cultures demonstrated that even subtle effect sizes in reducing outbound connectivity, i.e., loss of active synapses, can cause substantial global reductions in non-stimulated network activity. These results suggest that even low-level loss of synaptic output capabilities caused by α-Syn may result in significant functional impairments in terms of intrinsic neuronal network activity. Provided that our model holds true for the human brain, then α-Syn may cause significant functional lesions independent from neurodegeneration.

Lipid level alteration in human and cellular models of alpha synuclein mutations

Lipid profiles in biological fluids from patients with Parkinson's disease (PD) are increasingly investigated in search of biomarkers. However, the lipid profiles in genetic PD remain to be determined, a gap of knowledge of particular interest in PD associated with mutant α-synuclein (SNCA), given the known relationship between this protein and lipids. The objective of this research is to identify serum lipid composition from SNCA A53T mutation carriers and to compare these alterations to those found in cells and transgenic mice carrying the same genetic mutation. We conducted an unbiased lipidomic analysis of 530 lipid species from 34 lipid classes in serum of 30 participants with SNCA mutation with and without PD and 30 healthy controls. The primary analysis was done between 22 PD patients with SNCA+ (SNCA+/PD+) and 30 controls using machine-learning algorithms and traditional statistics. We also analyzed the lipid composition of human clonal-cell lines and tissue from transgenic mice overexpressing the same SNCA mutation. We identified specific lipid classes that best discriminate between SNCA+/PD+ patients and healthy controls and found certain lipid species, mainly from the glycerophosphatidylcholine and triradylglycerol classes, that are most contributory to this discrimination. Most of these alterations were also present in human derived cells and transgenic mice carrying the same mutation. Our combination of lipidomic and machine learning analyses revealed alterations in glycerophosphatidylcholine and triradylglycerol in sera from PD patients as well as cells and tissues expressing mutant α-Syn. Further investigations are needed to establish the pathogenic significance of these α-Syn-associated lipid changes.

α-Synuclein at the Presynaptic Axon Terminal as a Double-Edged Sword

α-synuclein (α-syn) is a presynaptic, lipid-binding protein strongly associated with the neuropathology observed in Parkinson’s disease (PD), dementia with Lewy bodies (DLB), and Alzheimer’s Disease (AD). In normal physiology, α-syn plays a pivotal role in facilitating endocytosis and exocytosis. Interestingly, mutations and modifications of precise α-syn domains interfere with α-syn oligomerization and nucleation that negatively affect presynaptic vesicular dynamics, protein expressions, and mitochondrial profiles. Furthermore, the integration of the α-syn oligomers into the presynaptic membrane results in pore formations, ion influx, and excitotoxicity. Targeted therapies against specific domains of α-syn, including the use of small organic molecules, monoclonal antibodies, and synthetic peptides, are being screened and developed. However, the prospect of an effective α-syn targeted therapy is still plagued by low permeability across the blood–brain barrier (BBB), and poor entry into the presynaptic axon terminals. The present review proposes a modification of current strategies, which includes the use of novel encapsulation technology, such as lipid nanoparticles, to bypass the BBB and deliver such agents into the brain.

Intermediates of α-synuclein aggregation: Implications in Parkinson's disease pathogenesis

Cytoplasmic deposition of aberrantly misfolded α-synuclein (α-Syn) is a common feature of synucleinopathies, including Parkinson's disease (PD). However, the precise pathogenic mechanism of α-Syn in synucleinopathies remains elusive. Emerging evidence has suggested that α-Syn may contribute to PD pathogenesis in several ways; wherein the contribution of fibrillar species, for exerting toxicity and disease transmission, cannot be neglected. Further, the oligomeric species could be the most plausible neurotoxic species causing neuronal cell death. However, understanding the structural and molecular insights of these oligomers are very challenging due to the heterogeneity and transient nature of the species. In this review, we discuss the recent advancements in understanding the formation and role of α-Syn oligomers in PD pathogenesis. We also summarize the different types of α-Syn oligomeric species and potential mechanisms to exert neurotoxicity. Finally, we address the possible ways to target α-Syn as a promising approach against PD and the possible future directions.

Alpha-Synuclein and Lipids: The Elephant in the Room?

Since the initial identification of alpha-synuclein (α-syn) at the synapse, numerous studies demonstrated that α-syn is a key player in the etiology of Parkinson's disease (PD) and other synucleinopathies. Recent advances underline interactions between α-syn and lipids that also participate in α-syn misfolding and aggregation. In addition, increasing evidence demonstrates that α-syn plays a major role in different steps of synaptic exocytosis. Thus, we reviewed literature showing (1) the interplay among α-syn, lipids, and lipid membranes; (2) advances of α-syn synaptic functions in exocytosis. These data underscore a fundamental role of α-syn/lipid interplay that also contributes to synaptic defects in PD. The importance of lipids in PD is further highlighted by data showing the impact of α-syn on lipid metabolism, modulation of α-syn levels by lipids, as well as the identification of genetic determinants involved in lipid homeostasis associated with α-syn pathologies. While questions still remain, these recent developments open the way to new therapeutic strategies for PD and related disorders including some based on modulating synaptic functions.

Genetic ablation of Gpnmb does not alter synuclein-related pathology

The gene GPNMB is known to play roles in phagocytosis and tissue repair, and is upregulated in microglia in many mouse models of neurodegenerative disease as well as in human patients. Nearby genomic variants are associated with both elevated Parkinson's disease (PD) risk and higher expression of this gene, suggesting that inhibiting GPNMB activity might be protective in Parkinson's disease. We tested this hypothesis in three different mouse models of neurological diseases: a remyelination model and two models of alpha-synuclein pathology. We found that Gpnmb deletion had no effect on histological, cellular, behavioral, neurochemical or gene expression phenotypes in any of these models. These data suggest that Gpnmb does not play a major role in the development of pathology or functional defects in these models and that further work is necessary to study its role in the development or progression of Parkinson's disease.

Innovative treatment targeting gangliosides aimed at blocking the formation of neurotoxic α-synuclein oligomers in Parkinson's disease

Parkinson's disease (PD) is a major neurodegenerative disorder which exhibits many of the characteristics of a pandemic. Current therapeutic strategies are centered on the dopaminergic system, with limited efficacy, so that a treatment that has a direct impact on the underlying disease pathogenesis is urgently needed. Although α-synuclein is a privileged target for such therapies, this protein has been in the past wrongly considered as exclusively intracellular, so that the impact of paracrine neurotoxicity mechanisms in PD have been largely ignored. In this article we review the data showing that lipid rafts act as plasma membrane machineries for the formation of α-synuclein pore-like oligomers which trigger an increase of intracellular Ca²⁺. This Ca²⁺ influx is responsible for a self-sustained cascade of neurotoxic events, including mitochondrial oxidative stress, tau phosphorylation, Ca²⁺ release from the endoplasmic reticulum, Lewy body formation, and extracellular release of α-synuclein in exosomes. The first step of this cascade is the binding of α-synuclein to lipid raft gangliosides, suggesting that PD should be considered as both a proteinopathy and a ganglioside membrane disorder lipidopathy. Accordingly, blocking α-synuclein-ganglioside interactions should annihilate the whole neurotoxic cascade and stop disease progression. A pipeline of anti-oligomer molecules is under development, among which an in-silico designed synthetic peptide AmyP53 which is the first drug targeting gangliosides and thus able to prevent the formation of α-synuclein oligomers and all downstream neurotoxicity. These new therapeutic avenues challenge the current symptomatic approaches by finally targeting the root cause of PD through a long-awaited paradigm shift.

α-Synuclein: An All-Inclusive Trip Around its Structure, Influencing Factors and Applied Techniques

Alpha-synuclein (αSyn) is a highly expressed and conserved protein, typically found in the presynaptic terminals of neurons. The misfolding and aggregation of αSyn into amyloid fibrils is a pathogenic hallmark of several neurodegenerative diseases called synucleinopathies, such as Parkinson’s disease. Since αSyn is an Intrinsically Disordered Protein, the characterization of its structure remains very challenging. Moreover, the mechanisms by which the structural conversion of monomeric αSyn into oligomers and finally into fibrils takes place is still far to be completely understood. Over the years, various studies have provided insights into the possible pathways that αSyn could follow to misfold and acquire oligomeric and fibrillar forms. In addition, it has been observed that αSyn structure can be influenced by different parameters, such as mutations in its sequence, the biological environment (e.g., lipids, endogenous small molecules and proteins), the interaction with exogenous compounds (e.g., drugs, diet components, heavy metals). Herein, we review the structural features of αSyn (wild-type and disease-mutated) that have been elucidated up to present by both experimental and computational techniques in different environmental and biological conditions. We believe that this gathering of current knowledge will further facilitate studies on αSyn, helping the planning of future experiments on the interactions of this protein with targeting molecules especially taking into consideration the environmental conditions.

Triple-Knockout, Synuclein-Free Mice Display Compromised Lipid Pattern

Recent studies have implicated synucleins in several reactions during the biosynthesis of lipids and fatty acids in addition to their recognised role in membrane lipid binding and synaptic functions. These are among aspects of decreased synuclein functions that are still poorly acknowledged especially in regard to pathogenesis in Parkinson's disease. Here, we aimed to add to existing knowledge of synuclein deficiency (i.e., the lack of all three family members), with respect to changes in fatty acids and lipids in plasma, liver, and two brain regions in triple synuclein-knockout (TKO) mice. We describe changes of long-chain polyunsaturated fatty acids (LCPUFA) and palmitic acid in liver and plasma, reduced triacylglycerol (TAG) accumulation in liver and non-esterified fatty acids in plasma of synuclein free mice. In midbrain, we observed counterbalanced changes in the relative concentrations of phosphatidylcholine (PC) and cerebrosides (CER). We also recorded a notable reduction in ethanolamine plasmalogens in the midbrain of synuclein free mice, which is an important finding since the abnormal ether lipid metabolism usually associated with neurological disorders. In summary, our data demonstrates that synuclein deficiency results in alterations of the PUFA synthesis, storage lipid accumulation in the liver, and the reduction of plasmalogens and CER, those polar lipids which are principal compounds of lipid rafts in many tissues. An ablation of all three synuclein family members causes more profound changes in lipid metabolism than changes previously shown to be associated with γ-synuclein deficiency alone. Possible mechanisms by which synuclein deficiency may govern the reported modifications of lipid metabolism in TKO mice are proposed and discussed.

Cell Death via Lipid Peroxidation and Protein Aggregation Diseases

Lipid peroxidation of cellular membranes is a complicated cellular event, and it is both the cause and result of various diseases, such as ischemia-reperfusion injury, neurodegenerative diseases, and atherosclerosis. Lipid peroxidation causes non-apoptotic cell death, which is associated with cell fate determination: survival or cell death. During the radical chain reaction of lipid peroxidation, various oxidized lipid products accumulate in cells, followed by organelle dysfunction and the induction of non-apoptotic cell death. Highly reactive oxidized products from unsaturated fatty acids are detected under pathological conditions. Pathological protein aggregation is the general cause of these diseases. The cellular response to misfolded proteins is well-known as the unfolded protein response (UPR) and it is partially concomitant with the response to lipid peroxidation. Moreover, the association between protein aggregation and non-apoptotic cell death by lipid peroxidation is attracting attention. The link between lipid peroxidation and protein aggregation is a matter of concern in biomedical fields. Here, we focus on lethal protein aggregation in non-apoptotic cell death via lipid peroxidation. We reviewed the roles of protein aggregation in the initiation and execution of non-apoptotic cell death. We also considered the relationship between protein aggregation and oxidized lipid production. We provide an overview of non-apoptotic cell death with a focus on lipid peroxidation for therapeutic targeting during protein aggregation diseases.