Effects of phosphatidylcholine membrane fluidity on the conformation and aggregation of N-terminally acetylated α-synuclein

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.

α-synuclein overexpression and the microbiome shape the gut and brain metabolome in mice

Pathological forms of α-synuclein contribute to synucleinopathies, including Parkinson's disease (PD). Most cases of PD arise from gene-environment interactions. Microbiome composition is altered in PD, and gut bacteria are causal to symptoms in animal models. We quantitatively profiled nearly 630 metabolites in the gut, plasma, and brain of α-synuclein-overexpressing (ASO) mice, compared to wild-type (WT) animals, and comparing germ-free (GF) to specific pathogen-free (SPF) animals (n = 5 WT-SPF; n = 6 ASO-SPF; n = 6 WT-GF; n = 6 ASO-GF). Many differentially expressed metabolites in ASO mice are also dysregulated in human PD patients, including amine oxides, bile acids and indoles. The microbial metabolite trimethylamine N-oxide (TMAO) strongly correlates from the gut to the plasma to the brain in mice, notable since TMAO is elevated in the blood and cerebrospinal fluid of PD patients. These findings uncover broad metabolomic changes that are influenced by the intersection of host genetics and microbiome in a mouse model of PD.

Pore Formation by Amyloid-like Peptides: Effects of the Nonpolar-Polar Sequence Pattern

One of the mechanisms accounting for the toxicity of amyloid peptides in diseases like Alzheimer's and Parkinson's is the formation of pores on the plasma membrane of neurons. Here, we perform unbiased all-atom simulations of the full membrane damaging pathway, which includes adsorption, aggregation, and perforation of the lipid bilayer accounting for pore-like structures. Simulations are performed using four peptides made with the same amino acids. Differences in the nonpolar-polar sequence pattern of these peptides prompt them to adsorb into the membrane with the extended conformations oriented either parallel [peptide labeled F1, Ac-(FKFE)2-NH2], perpendicular (F4, Ac-FFFFKKEE-NH2), or with an intermediate orientation (F2, Ac-FFKKFFEE-NH2, and F3, Ac-FFFKFEKE-NH2) in regard to the membrane surface. At the water-lipid interface, only F1 fully self-assembles into β-sheets, and F2 peptides partially fold into an α-helical structure. The β-sheets of F1 emerge as electrostatic interactions attract neighboring peptides to intermediate distances where nonpolar side chains can interact within the dry core of the bilayer. This complex interplay between electrostatic and nonpolar interactions is not observed for the other peptides. Although β-sheets of F1 peptides are mostly parallel to the membrane, some of their edges penetrate deep inside the bilayer, dragging water molecules with them. This precedes pore formation, which starts with the flow of two water layers through the membrane that expand into a stable cylindrical pore delimited by polar faces of β-sheets spanning both leaflets of the bilayer.

Clinical, mechanistic, biomarker, and therapeutic advances in GBA1-associated Parkinson's disease

Parkinson's disease (PD) is the second most common neurodegenerative disease. The development of PD is closely linked to genetic and environmental factors, with GBA1 variants being the most common genetic risk. Mutations in the GBA1 gene lead to reduced activity of the coded enzyme, glucocerebrosidase, which mediates the development of PD by affecting lipid metabolism (especially sphingolipids), lysosomal autophagy, endoplasmic reticulum, as well as mitochondrial and other cellular functions. Clinically, PD with GBA1 mutations (GBA1-PD) is characterized by particular features regarding the progression of symptom severity. On the therapeutic side, the discovery of the relationship between GBA1 variants and PD offers an opportunity for targeted therapeutic interventions. In this review, we explore the genotypic and phenotypic correlations, etiologic mechanisms, biomarkers, and therapeutic approaches of GBA1-PD and summarize the current state of research and its challenges.

Role of Lipids in the Pathogenesis of Parkinson's Disease

Aggregation of α-synuclein (αSyn) and its accumulation as Lewy bodies play a central role in the pathogenesis of Parkinson's disease (PD). However, the mechanism by which αSyn aggregates in the brain remains unclear. Biochemical studies have demonstrated that αSyn interacts with lipids, and these interactions affect the aggregation process of αSyn. Furthermore, genetic studies have identified mutations in lipid metabolism-associated genes such as glucocerebrosidase 1 (GBA1) and synaptojanin 1 (SYNJ1) in sporadic and familial forms of PD, respectively. In this review, we focus on the role of lipids in triggering αSyn aggregation in the pathogenesis of PD and propose the possibility of modulating the interaction of lipids with αSyn as a potential therapy for PD.

αvβ3 Integrin and Folate-Targeted pH-Sensitive Liposomes with Dual Ligand Modification for Metastatic Breast Cancer Treatment

The advent of pH-sensitive liposomes (pHLips) has opened new opportunities for the improved and targeted delivery of antitumor drugs as well as gene therapeutics. Comprising fusogenic dioleylphosphatidylethanolamine (DOPE) and cholesteryl hemisuccinate (CHEMS), these nanosystems harness the acidification in the tumor microenvironment and endosomes to deliver drugs effectively. pH-responsive liposomes that are internalized through endocytosis encounter mildly acidic pH in the endosomes and thereafter fuse or destabilize the endosomal membrane, leading to subsequent cargo release into the cytoplasm. The extracellular tumor matrix also presents a slightly acidic environment that can lead to the enhanced drug release and improved targeting capabilities of the nano-delivery system. Recent studies have shown that folic acid (FA) and iRGD-coated nanocarriers, including pH-sensitive liposomes, can preferentially accumulate and deliver drugs to breast tumors that overexpress folate receptors and αvβ3 and αvβ5 integrins. This study focuses on the development and characterization of 5-Fluorouracil (5-FU)-loaded FA and iRGD surface-modified pHLips (FA-iRGD-5-FU-pHLips). The novelty of this research lies in the dual targeting mechanism utilizing FA and iRGD peptides, combined with the pH-sensitive properties of the liposomes, to enhance selective targeting and uptake by cancer cells and effective drug release in the acidic tumor environment. The prepared liposomes were small, with an average diameter of 152 ± 3.27 nm, uniform, and unilamellar, demonstrating efficient 5-FU encapsulation (93.1 ± 2.58%). Despite surface functionalization, the liposomes maintained their pH sensitivity and a neutral zeta potential, which also conferred stability and reduced aggregation. Effective pH responsiveness was demonstrated by the observation of enhanced drug release at pH 5.5 compared to physiological pH 7.4. (84.47% versus 46.41% release at pH 5.5 versus pH 7.4, respectively, in 72 h). The formulations exhibited stability for six months and were stable when subjected to simulated biological settings. Blood compatibility and cytotoxicity studies on MDA-MB-231 and SK-BR3 breast cancer cell lines revealed an enhanced cytotoxicity of the liposomal formulation that was modified with FA and iRGD compared to free 5-FU and minimal hemolysis. Collectively, these findings support the potential of FA and iRGD surface-camouflaged, pH-sensitive liposomes as a promising drug delivery strategy for breast cancer treatment.

Aging AdipoR2-deficient mice are hyperactive with enlarged brains excessively rich in saturated fatty acids

To investigate how the fatty acid composition of brain phospholipids influences brain-specific processes, we leveraged the AdipoR2 (adiponectin receptor 2) knockout mouse model in which the brain is enlarged, and cellular membranes are excessively rich in saturated fatty acids. Lipidomics analysis of brains at 2, 7, and 18 months of age showed that phosphatidylcholines, which make up about two-thirds of all cerebrum membrane lipids, contain a gross excess of saturated fatty acids in AdipoR2 knockout mice, and that this is mostly attributed to an excess palmitic acid (C16:0) at the expense of oleic acid (C18:1), consistent with a defect in fatty acid desaturation and elongation in the mutant. Specifically, there was a ~12% increase in the overall saturated fatty acid content within phosphatidylcholines and a ~30% increase in phosphatidylcholines containing two palmitic acids. Phosphatidylethanolamines, sphingomyelins, ceramides, lactosylceramides, and dihydroceramides also showed an excess of saturated fatty acids in the AdipoR2 knockout mice while nervonic acid (C24:1) was enriched at the expense of shorter saturated fatty acids in glyceroceramides. Similar defects were found in the cerebellum and myelin sheaths. Histology showed that cell density is lower in the cerebrum of AdipoR2 knockout mice, but electron microscopy did not detect reproducible defects in the ultrastructure of cerebrum neurons, though proteomics analysis showed an enrichment of electron transport chain proteins in the cerebellum. Behavioral tests showed that older (33 weeks old) AdipoR2 knockout mice are hyperactive and anxious compared to control mice of a similar age. Also, in contrast to control mice, the AdipoR2 knockout mice do not gain weight in old age but do have normal lifespans. We conclude that an excess fatty acid saturation in brain phospholipids is accompanied by hyperactivity but seems otherwise well tolerated.

α-Synuclein Overexpression and the Microbiome Shape the Gut and Brain Metabolome in Mice

Pathological forms of the protein α-synuclein contribute to a family of disorders termed synucleinopathies, which includes Parkinson's disease (PD). Most cases of PD are believed to arise from gene-environment interactions. Microbiome composition is altered in PD, and gut bacteria are causal to symptoms and pathology in animal models. To explore how the microbiome may impact PD-associated genetic risks, we quantitatively profiled nearly 630 metabolites from 26 biochemical classes in the gut, plasma, and brain of α-synuclein-overexpressing (ASO) mice with or without microbiota. We observe tissue-specific changes driven by genotype, microbiome, and their interaction. Many differentially expressed metabolites in ASO mice are also dysregulated in human PD patients, including amine oxides, bile acids and indoles. Notably, levels of the microbial metabolite trimethylamine N-oxide (TMAO) strongly correlate from the gut to the plasma to the brain, identifying a product of gene-environment interactions that may influence PD-like outcomes in mice. TMAO is elevated in the blood and cerebral spinal fluid of PD patients. These findings uncover broad metabolomic changes that are influenced by the intersection of host genetics and the microbiome in a mouse model of PD.

GDE5/Gpcpd1 activity determines phosphatidylcholine composition in skeletal muscle and regulates contractile force in mice

Glycerophosphocholine (GPC) is an important precursor for intracellular choline supply in phosphatidylcholine (PC) metabolism. GDE5/Gpcpd1 hydrolyzes GPC into choline and glycerol 3-phosphate; this study aimed to elucidate its physiological function in vivo. Heterozygous whole-body GDE5-deficient mice reveal a significant GPC accumulation across tissues, while homozygous whole-body knockout results in embryonic lethality. Skeletal muscle-specific GDE5 deletion (Gde5 skKO) exhibits reduced passive force and improved fatigue resistance in electrically stimulated gastrocnemius muscles in vivo. GDE5 deficiency also results in higher glycolytic metabolites and glycogen levels, and glycerophospholipids alteration, including reduced levels of phospholipids that bind polyunsaturated fatty acids (PUFAs), such as DHA. Interestingly, this PC fatty acid compositional change is similar to that observed in skeletal muscles of denervated and Duchenne muscular dystrophy mouse models. These are accompanied by decrease of GDE5 expression, suggesting a regulatory role of GDE5 activity for glycerophospholipid profiles. Furthermore, a DHA-rich diet enhances contractile force and lowers fatigue resistance, suggesting a functional relationship between PC fatty acid composition and muscle function. Finally, skinned fiber experiments show that GDE5 loss increases the probability of the ryanodine receptor opening and lowers the maximum Ca2+-activated force. Collectively, GDE5 activity plays roles in PC and glucose/glycogen metabolism in skeletal muscle.

Unveiling the role of iPLA2β in neurodegeneration: From molecular mechanisms to advanced therapies

Calcium-independent phospholipase A2β (iPLA2β), a member of the phospholipase A2 (PLA2s) superfamily, is encoded by the PLA2G6 gene. Mutations in the PLA2G6 gene have been identified as the primary cause of infantile neuroaxonal dystrophy (INAD) and, less commonly, as a contributor to Parkinson's disease (PD). Recent studies have revealed that iPLA2β deficiency leads to neuroinflammation, iron accumulation, mitochondrial dysfunction, lipid dysregulation, and other pathological changes, forming a complex pathogenic network. These discoveries shed light on potential mechanisms underlying PLA2G6-associated neurodegeneration (PLAN) and offer valuable insights for therapeutic development. This review provides a comprehensive analysis of the fundamental characteristics of iPLA2β, its association with neurodegeneration, the pathogenic mechanisms involved in PLAN, and potential targets for therapeutic intervention. It offers an overview of the latest advancements in this field, aiming to contribute to ongoing research endeavors and facilitate the development of effective therapies for PLAN.

The Effects of Lipids on α-Synuclein Aggregation In Vitro

The small neuronal protein α-synuclein (αS) is found in pre-synaptic terminals and plays a role in vesicle recycling and neurotransmission. Fibrillar aggregates of αS are the hallmark of Parkinson's disease and related neurodegenerative disorders. In both health and disease, interactions with lipids influence αS's structure and function, prompting much study of the effects of lipids on αS aggregation. A comprehensive collection (126 examples) of aggregation rate data for various αS/lipid combinations was presented, including combinations of lipid variations and mutations or post-translational modifications of αS. These data were interpreted in terms of lipid structure to identify general trends. These tabulated data serve as a resource for the community to help in the interpretation of aggregation experiments with lipids and to be potentially used as inputs for computational models of lipid effects on aggregation.

Exploring the use of niosomes in cosmetics for efficient dermal drug delivery

Dermal drug delivery has emerged as a promising alternative to traditional methods of drug administration due to its non-invasive nature and ease of use. However, the stratum corneum, the outermost layer of the skin, presents a significant barrier to drug penetration. Niosomes, self-assembled vesicular structures composed of nonionic surfactants and cholesterol, have been extensively investigated as a means of overcoming this barrier and improving the efficacy of dermal drug delivery. This review summarizes the current state of research on the use of niosomes in dermal drug delivery in cosmetics, with a particular focus on their formulation, characterization, and application in the delivery of various drug classes. The review highlights the advantages of niosomes over conventional drug delivery methods, including improved solubility and stability of drugs, controlled release, and enhanced skin permeation. The review also discusses the challenges associated with niosome-based drug delivery, such as their complex formulation and optimization, and the need for further studies on their long-term safety and toxicity.

The Bidirectional Interplay of α-Synuclein with Lipids in the Central Nervous System and Its Implications for the Pathogenesis of Parkinson's Disease

The alteration and aggregation of alpha-synuclein (α-syn) play a crucial role in neurodegenerative diseases collectively termed as synucleinopathies, including Parkinson's disease (PD). The bidirectional interaction of α-syn with lipids and biomembranes impacts not only α-syn aggregation but also lipid homeostasis. Indeed, lipid composition and metabolism are severely perturbed in PD. One explanation for lipid-associated alterations may involve structural changes in α-syn, caused, for example, by missense mutations in the lipid-binding region of α-syn as well as post-translational modifications such as phosphorylation, acetylation, nitration, ubiquitination, truncation, glycosylation, and glycation. Notably, different strategies targeting the α-syn-lipid interaction have been identified and are able to reduce α-syn pathology. These approaches include the modulation of post-translational modifications aiming to reduce the aggregation of α-syn and modify its binding properties to lipid membranes. Furthermore, targeting enzymes involved in various steps of lipid metabolism and exploring the neuroprotective potential of lipids themselves have emerged as novel therapeutic approaches. Taken together, this review focuses on the bidirectional crosstalk of α-syn and lipids and how alterations of this interaction affect PD and thereby open a window for therapeutic interventions.

Lipid Metabolism Disorder in Cerebrospinal Fluid Related to Parkinson's Disease

BACKGROUND

Abnormal accumulation of lipids is found in dopamine neurons and resident microglia in the substantia nigra of patients with Parkinson's disease (PD). The accumulation of lipids is an important risk factor for PD. Previous studies have mainly focussed on lipid metabolism in peripheral blood, but little attention has been given to cerebrospinal fluid (CSF). We drew the lipidomic signature in CSF from PD patients and evaluated the role of lipids in CSF as biomarkers for PD diagnosis.

METHODS

Based on lipidomic approaches, we investigated and compared lipid metabolism in CSF from PD patients and healthy controls without dyslipidaemia in peripheral blood and explored the relationship of lipids between CSF and serum by Pearson correlation analysis.

RESULTS

A total of 231 lipid species were detected and classified into 13 families in the CSF. The lipid families, including phosphatidylcholine (PC), sphingomyelin (SM) and cholesterol ester (CE), had significantly increased expression compared with the control. Hierarchical clustering was performed to distinguish PD patients based on the significantly changed expression of 34 lipid species. Unsupervised and supervised methods were used to refine this classification. A total of 12 lipid species, including 3-hydroxy-dodecanoyl-carnitine, Cer(d18:1/24:1), CE(20:4), CE(22:6), PC(14:0/18:2), PC(O-18:3/20:2), PC(O-20:2/24:3), SM(d18:0/16:0), SM(d18:2/14:0), SM(d18:2/24:1), SM(d18:1/20:1) and SM(d18:1/12:0), were selected to draw the lipidomic signature of PD. Correlation analysis was performed and showed that the CE family and CE (22:6) in CSF had a positive association with total cholesterol in the peripheral blood from PD patients but not from healthy controls.

CONCLUSIONS

Our results revealed that the lipidomic signature in CSF may be considered a potential biomarker for PD diagnosis, and increased CE, PC and SM in CSF may reveal pathological changes in PD patients, such as blood-brain barrier leakage.

Influence of Cholesterol on the Membrane Binding and Conformation of α-Synuclein

The α-Synuclein (α-Syn) plays an important role in the pathology of Parkinson's disease (PD), and its oligomers and fibrils are toxic to the nervous system. As organisms age, the cholesterol content in biological membranes increases, which is a potential cause of PD. Cholesterol may affect the membrane binding of α-Syn and its abnormal aggregation, but the mechanism remains unclear. Here, we present our molecular dynamics simulation studies on the interaction between α-Syn and lipid membranes, with or without cholesterol. It is demonstrated that cholesterol provides additional hydrogen bond interaction with α-Syn; however, the coulomb interaction and hydrophobic interaction between α-Syn and lipid membranes could be weakened by cholesterol. In addition, cholesterol leads to the shrinking of lipid packing defects and the decrease of lipid fluidity, thereby shortening the membrane binding region of α-Syn. Under these multifaceted effects of cholesterol, membrane-bound α-Syn shows signs of forming a β-sheet structure, which may further induce the formation of abnormal α-Syn fibrils. These results provide important information for the understanding of membrane binding of α-Syn, and they are expected to promote the bridging between cholesterol and the pathological aggregation of α-Syn.

Changes in Liver Lipidomic Profile in G2019S-LRRK2 Mouse Model of Parkinson's Disease

The identification of Parkinson's disease (PD) biomarkers has become a main goal for the diagnosis of this neurodegenerative disorder. PD has not only been intrinsically related to neurological problems, but also to a series of alterations in peripheral metabolism. The purpose of this study was to identify metabolic changes in the liver in mouse models of PD with the scope of finding new peripheral biomarkers for PD diagnosis. To achieve this goal, we used mass spectrometry technology to determine the complete metabolomic profile of liver and striatal tissue samples from WT mice, 6-hydroxydopamine-treated mice (idiopathic model) and mice affected by the G2019S-LRRK2 mutation in LRRK2/PARK8 gene (genetic model). This analysis revealed that the metabolism of carbohydrates, nucleotides and nucleosides was similarly altered in the liver from the two PD mouse models. However, long-chain fatty acids, phosphatidylcholine and other related lipid metabolites were only altered in hepatocytes from G2019S-LRRK2 mice. In summary, these results reveal specific differences, mainly in lipid metabolism, between idiopathic and genetic PD models in peripheral tissues and open up new possibilities to better understand the etiology of this neurological disorder.

The Consequences of GBA Deficiency in the Autophagy-Lysosome System in Parkinson's Disease Associated with GBA

GBA gene variants were the first genetic risk factor for Parkinson's disease. GBA encodes the lysosomal enzyme glucocerebrosidase (GBA), which is involved in sphingolipid metabolism. GBA exhibits a complex physiological function that includes not only the degradation of its substrate glucosylceramide but also the metabolism of other sphingolipids and additional lipids such as cholesterol, particularly when glucocerebrosidase activity is deficient. In the context of Parkinson's disease associated with GBA, the loss of GBA activity has been associated with the accumulation of α-synuclein species. In recent years, several hypotheses have proposed alternative and complementary pathological mechanisms to explain why lysosomal enzyme mutations lead to α-synuclein accumulation and become important risk factors in Parkinson's disease etiology. Classically, loss of GBA activity has been linked to a dysfunctional autophagy-lysosome system and to a subsequent decrease in autophagy-dependent α-synuclein turnover; however, several other pathological mechanisms underlying GBA-associated parkinsonism have been proposed. This review summarizes and discusses the different hypotheses with a special focus on autophagy-dependent mechanisms, as well as autophagy-independent mechanisms, where the role of other players such as sphingolipids, cholesterol and other GBA-related proteins make important contributions to Parkinson's disease pathogenesis.

Serum Metabolomics of Benign Essential Blepharospasm Using Liquid Chromatography and Orbitrap Mass Spectrometry

Background

Benign essential blepharospasm (BEB) is a form of focal dystonia that causes excessive involuntary spasms of the eyelids. Currently, the pathogenesis of BEB remains unclear. This study is aimed at investigating the serum metabolites profiles in patients with BEB and healthy control and to identify the mechanism and biomarkers of this disease.

Methods

30 patients with BEB and 33 healthy controls were recruited for this study. We conducted the quantitative and nontargeted metabolomics analysis of the serum samples from 63 subjects by using liquid chromatography and Orbitrap mass spectrometry (LC-Orbitrap MS). Multivariate statistical analysis was performed to detect and identify different metabolites between the two groups. The Kyoto Encyclopedia of Genes and Genomes (KEGG) and receiver operating characteristic (ROC) curve analysis of the altered metabolites were performed.

Results

A total of 134 metabolites were found and identified. The metabolites belonged to several metabolic pathways including phenylalanine metabolism, phenylalanine, tyrosine and tryptophan biosynthesis, arginine biosynthesis, linoleic acid metabolism, tryptophan metabolism, aminoacyl-tRNA biosynthesis, sphingolipid metabolism, glycosphingolipid biosynthesis, leucine and isoleucine biosynthesis, and vitamin B6 metabolism. Eight metabolites were identified as the potential biomarkers.

Conclusions

These results demonstrated that serum metabolic profiling of BEB patients was significantly different from healthy controls based on LC-Orbitrap MS. Besides, metabolomics might provide useful information for a better understanding of BEB.

How important is the N-terminal acetylation of alpha-synuclein for its function and aggregation into amyloids?

N-α-acetylation is a frequently occurring post-translational modification in eukaryotic proteins. It has manifold physiological consequences on the regulation and function of several proteins, with emerging studies suggesting that it is a global regulator of stress responses. For decades, in vitro biochemical investigations into the precise role of the intrinsically disordered protein alpha-synuclein (αS) in the etiology of Parkinson's disease (PD) were performed using non-acetylated αS. The N-terminus of α-synuclein is now unequivocally known to be acetylated in vivo, however, there are many aspects of this post-translational modifications that are not understood well. Is N-α-acetylation of αS a constitutive modification akin to most cellular proteins, or is it spatio-temporally regulated? Is N-α-acetylation of αS relevant to the as yet elusive function of αS? How does the N-α-acetylation of αS influence the aggregation of αS into amyloids? Here, we provide an overview of the current knowledge and discuss prevailing hypotheses on the impact of N-α-acetylation of αS on its conformational, oligomeric, and fibrillar states. The extent to which N-α-acetylation of αS is vital for its function, membrane binding, and aggregation into amyloids is also explored here. We further discuss the overall significance of N-α-acetylation of αS for its functional and pathogenic implications in Lewy body formation and synucleinopathies.

Serum Phospholipid Profile Changes in Gaucher Disease and Parkinson's Disease

Alterations in the levels of serum sphingolipids and phospholipids have been reported in Gaucher disease and in Parkinson's disease, suggesting a potential role of these lipids as biomarkers. This project's objective is to detect novel associations and novel candidate biomarkers in the largest Spanish Gaucher and Parkinson diseases of the Iberian Peninsula. For that, 278 participants were included: 100 sporadic Parkinson's patients, 70 Gaucher patients, 15 GBA1-mutation-carrier Parkinson's patients and 93 controls. A serum lipidomics array including 10 phospholipid groups, 368 species, was performed using high-performance liquid chromatography-mass spectrometry. Lipid levels were compared between groups via multiple-regression analyses controlling for clinical and demographic parameters. Additionally, lipid levels were compared within the Gaucher and Parkinson's groups controlling for medication and/or disease severity. Results were controlled for robustness by filtering of non-detectable lipid values. There was an increase in the levels of phosphatidylcholine, with a simultaneous decrease in lyso-phosphatidylcholine, in the Gaucher, Parkinson's and GBA1-mutation-carrier Parkinson's patients vs. controls. Phosphatidylethanolamine, lyso- and plasmalogen-phosphatidylethanolamine were also increased in Gaucher and Parkinson's. Gaucher patients also showed an increase in lyso-phosphatidylserine and phosphatidylglycerol. While in the Gaucher and Parkinson's groups, velaglucerase alpha and dopamine agonists, respectively, showed positive associations with the lipid changes, miglustat treatment in Gaucher patients normalized the altered phosphatidylcholine/lyso-phosphatidylcholine ratio. In conclusion, Gaucher and Parkinson's patients showed changes in various serum phospholipid levels when compared with healthy controls, further supporting the role of such lipids in disease development and, possibly, as putative biomarkers. This hypothesis was reinforced by the normalizing effect of miglustat, and by controlling for data robustness, even though the limited number of participants, especially in the sub-distribution by treatment groups in GD requires validation in a larger number of patients.

N-Terminal Acetylation of α-Synuclein Slows down Its Aggregation Process and Alters the Morphology of the Resulting Aggregates

Parkinson's disease is associated with the aberrant aggregation of α-synuclein. Although the causes of this process are still unclear, post-translational modifications of α-synuclein are likely to play a modulatory role. Since α-synuclein is constitutively N-terminally acetylated, we investigated how this post-translational modification alters the aggregation behavior of this protein. By applying a three-pronged aggregation kinetics approach, we observed that N-terminal acetylation results in a reduced rate of lipid-induced aggregation and slows down both elongation and fibril-catalyzed aggregate proliferation. An analysis of the amyloid fibrils produced by the aggregation process revealed different morphologies for the acetylated and non-acetylated forms in both lipid-induced aggregation and seed-induced aggregation assays. In addition, we found that fibrils formed by acetylated α-synuclein exhibit a lower β-sheet content. These findings indicate that N-terminal acetylation of α-synuclein alters its lipid-dependent aggregation behavior, reduces its rate of in vitro aggregation, and affects the structural properties of its fibrillar aggregates.

Dual Effects of Presynaptic Membrane Mimetics on α-Synuclein Amyloid Aggregation

Aggregation of intrinsically disordered α-synuclein (αSN) under various conditions is closely related to synucleinopathies. Although various biological membranes have shown to alter the structure and aggregation propensity of αSN, a thorough understanding of the molecular and mechanical mechanism of amyloidogenesis in membranes remains unanswered. Herein, we examined the structural changes, binding properties, and amyloidogenicity of three variations of αSN mutants under two types of liposomes, 1,2-Dioleoyl-sn-glycero-3-Phosphocholine (DOPC) and presynaptic vesicle mimetic (Mimic) membranes. While neutrally charged DOPC membranes elicited marginal changes in the structure and amyloid fibrillation of αSNs, negatively charged Mimic membranes induced dramatic helical folding and biphasic amyloid generation. At low concentration of Mimic membranes, the amyloid fibrillation of αSNs was promoted in a dose-dependent manner. However, further increases in the concentration constrained the fibrillation process. These results suggest the dual effect of Mimic membranes on regulating the amyloidogenesis of αSN, which is rationalized by the amyloidogenic structure of αSN and condensation-dilution of local αSN concentration. Finally, we propose physicochemical properties of αSN and membrane surfaces, and their propensity to drive electrostatic interactions as decisive factors of amyloidogenesis.

Alterations of Sphingolipid and Phospholipid Pathways and Ornithine Level in the Plasma as Biomarkers of Parkinson's Disease

The biomarkers of Parkinson’s disease (PD) remain to be investigated. This work aimed to identify blood biomarkers for PD using targeted metabolomics analysis. We quantified the plasma levels of 255 metabolites in 92 PD patients and 60 healthy controls (HC). PD patients were sub-grouped into early (Hoehn–Yahr stage ≤ 2, n = 72) and advanced (Hoehn–Yahr stage > 2, n = 20) stages. Fifty-nine phospholipids, 3 fatty acids, 3 amino acids, and 7 biogenic amines, demonstrated significant alterations in PD patients. Six of them, dihydro sphingomyelin (SM) 24:0, 22:0, 20:0, phosphatidylethanolamine-plasmalogen (PEp) 38:6, and phosphatidylcholine 38:5 and 36:6, demonstrated lowest levels in PD patients in the advanced stage, followed by those in the early stage and HC. By contrast, the level of ornithine was highest in PD patients at the advanced stage, followed by those at the early stage and HC. These biomarker candidates demonstrated significant correlations with scores of motor disability, cognitive dysfunction, depression, and quality of daily life. The support vector machine algorithm using α-synuclein, dihydro SM 24:0, and PEp 38:6 demonstrated good ability to separate PD from HC (AUC: 0.820). This metabolomic analysis demonstrates new plasma biomarker candidates for PD and supports their role in participating PD pathogenesis and monitoring disease progression.

The Crucial Roles of Phospholipids in Aging and Lifespan Regulation

Phospholipids are major membrane lipids that consist of lipid bilayers. This basic cellular structure acts as a barrier to protect the cell against various environmental insults and more importantly, enables multiple cellular processes to occur in subcellular compartments. Numerous studies have linked the complexity of membrane lipids to signal transductions, organelle functions, as well as physiological processes, and human diseases. Recently, crucial roles for membrane lipids in the aging process are beginning to emerge. In this study, we summarized current advances in our understanding of the relationship between membrane lipids and aging with an emphasis on phospholipid species. We surveyed how major phospholipid species change with age in different organisms and tissues, and some common patterns of membrane lipid change during aging were proposed. Further, the functions of different phospholipid molecules in regulating healthspan and lifespan, as well as their potential mechanisms of action, were also discussed.

α-Synuclein-mediated neurodegeneration in Dementia with Lewy bodies: the pathobiology of a paradox

Dementia with Lewy bodies (DLB) is epitomized by the pathognomonic manifestation of α-synuclein-laden Lewy bodies within selectively vulnerable neurons in the brain. By virtue of prion-like inheritance, the α-synuclein protein inexorably undergoes extensive conformational metamorphoses and culminate in the form of fibrillar polymorphs, instigating calamitous damage to the brain's neuropsychological networks. This epiphenomenon is nebulous, however, by lingering uncertainty over the quasi "pathogenic" behavior of α-synuclein conformers in DLB pathobiology. Despite numerous attempts, a monolithic "α-synuclein" paradigm that is able to untangle the enigma enshrouding the clinicopathological spectrum of DLB has failed to emanate. In this article, we review conceptual frameworks of α-synuclein dependent cell-autonomous and non-autonomous mechanisms that are likely to facilitate the transneuronal spread of degeneration through the neuraxis. In particular, we describe how the progressive demise of susceptible neurons may evolve from cellular derangements perpetrated by α-synuclein misfolding and aggregation. Where pertinent, we show how these bona fide mechanisms may mutually accentuate α-synuclein-mediated neurodegeneration in the DLB brain.

Glycoconjugate journal special issue on: the glycobiology of Parkinson's disease

Parkinson's disease (PD) is a neurodegenerative disorder that affects over 10 million aging people worldwide. This condition is characterized by the degeneration of dopaminergic neurons in the pars compacta region of the substantia nigra (SNpc) and by aggregation of proteins, commonly α-synuclein (SNCA). The formation of Lewy bodies that encapsulate aggregated proteins in lipid vesicles is a hallmark of PD. Glycosylation of proteins and neuroinflammation are involved in the pathogenesis. SNCA has many posttranslational modifications and interacts with components of membranes that affect aggregation. The large membrane lipid dolichol accumulates in the brain upon age and has a significant effect on membrane structure. The replacement of dopamine and dopaminergic neurons are at the forefront of therapeutic development. This review examines the role of membrane lipids, glycolipids, glycoproteins and dopamine in the aggregation of SNCA and development of PD. We discuss the SNCA-dopamine-neuromelanin-dolichol axis and the role of membranes in neuronal stem cells that could be a regenerative therapy for PD patients.

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.

Wild-type GBA1 increases the α-synuclein tetramer-monomer ratio, reduces lipid-rich aggregates, and attenuates motor and cognitive deficits in mice

The mechanisms responsible for brain α-synuclein (αS) dyshomeostasis, caused by Gaucher’s GBA1 mutations that increase Parkinson’s disease (PD) risk, are largely unknown. We previously showed that abrogating physiological αS tetramers by a familial PD-E46K–amplified 3K mutation produces PD-like syndrome in mice and that treatment with stearoyl-CoA desaturase inhibitors increased a portion of the αS tetramers, benefitting the motor phenotypes. Here, we show that—similar to previous findings in GBA1-mutant PD culture—GCase elevation prolonged the stabilization of wild-type and 3K mutant αS tetramers in wtGBA1–transduced mouse brains, improving lysosomal integrity and motor and cognitive phenotypes. These data help elucidating lipid modulators that impact the αS physiological state in vivo and the development of PD therapeutic approaches.

Loss-of-function mutations in acid beta-glucosidase 1 (GBA1) are among the strongest genetic risk factors for Lewy body disorders such as Parkinson’s disease (PD) and Lewy body dementia (DLB). Altered lipid metabolism in PD patient–derived neurons, carrying either GBA1 or PD αS mutations, can shift the physiological α-synuclein (αS) tetramer–monomer (T:M) equilibrium toward aggregation-prone monomers. A resultant increase in pSer129+ αS monomers provides a likely building block for αS aggregates. 3K αS mice, representing a neuropathological amplification of the E46K PD–causing mutation, have decreased αS T:M ratios and vesicle-rich αS+ aggregates in neurons, accompanied by a striking PD-like motor syndrome. We asked whether enhancing glucocerebrosidase (GCase) expression could benefit αS dyshomeostasis by delivering an adeno-associated virus (AAV)–human wild-type (wt) GBA1 vector into the brains of 3K neonates. Intracerebroventricular AAV-wtGBA1 at postnatal day 1 resulted in prominent forebrain neuronal GCase expression, sustained through 6 mo. GBA1 attenuated behavioral deficits both in working memory and fine motor performance tasks. Furthermore, wtGBA1 increased αS solubility and the T:M ratio in both 3K-GBA mice and control littermates and reduced pS129+ and lipid-rich aggregates in 3K-GBA. We observed GCase distribution in more finely dispersed lysosomes, in which there was increased GCase activity, lysosomal cathepsin D and B maturation, decreased perilipin-stabilized lipid droplets, and a normalized TFEB translocation to the nucleus, all indicative of improved lysosomal function and lipid turnover. Therefore, a prolonged increase of the αS T:M ratio by elevating GCase activity reduced the lipid- and vesicle-rich aggregates and ameliorated PD-like phenotypes in mice, further supporting lipid modulating therapies in PD.

Modulation of the Interactions Between α-Synuclein and Lipid Membranes by Post-translational Modifications

Parkinson's disease is characterised by the presence in brain tissue of aberrant inclusions known as Lewy bodies and Lewy neurites, which are deposits composed by α-synuclein and a variety of other cellular components, including in particular lipid membranes. The dysregulation of the balance between lipid homeostasis and α-synuclein homeostasis is therefore likely to be closely involved in the onset and progression of Parkinson's disease and related synucleinopathies. As our understanding of this balance is increasing, we describe recent advances in the characterisation of the role of post-translational modifications in modulating the interactions of α-synuclein with lipid membranes. We then discuss the impact of these advances on the development of novel diagnostic and therapeutic tools for synucleinopathies.

Lipid droplets in the nervous system

Lipid droplets are dynamic intracellular lipid storage organelles that respond to the physiological state of cells. In addition to controlling cell metabolism, they play a protective role for many cellular stressors, including oxidative stress. Despite prior descriptions of lipid droplets appearing in the brain as early as a century ago, only recently has the role of lipid droplets in cells found in the brain begun to be understood. Lipid droplet functions have now been described for cells of the nervous system in the context of development, aging, and an increasing number of neuropathologies. Here, we review the basic mechanisms of lipid droplet formation, turnover, and function and discuss how these mechanisms enable lipid droplets to function in different cell types of the nervous system under healthy and pathological 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.

Paradigm shift: the primary function of the "Adiponectin Receptors" is to regulate cell membrane composition

The ADIPOR1 and ADIPOR2 proteins (ADIPORs) are generally considered as adiponectin receptors with anti-diabetic properties. However, studies on the yeast and C. elegans homologs of the mammalian ADIPORs, and of the ADIPORs themselves in various mammalian cell models, support an updated/different view. Based on findings in these experimental models, the ADIPORs are now emerging as evolutionarily conserved regulators of membrane homeostasis that do not require adiponectin to act as membrane fluidity sensors and regulate phospholipid composition. More specifically, membrane rigidification activates ADIPOR signaling to promote fatty acid desaturation and incorporation of polyunsaturated fatty acids into membrane phospholipids until fluidity is restored. The present review summarizes the evidence supporting this new view of the ADIPORs, and briefly examines physiological consequences.

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.

Cholesterol-containing lipid nanodiscs promote an α-synuclein binding mode that accelerates oligomerization

Dysregulation of the biosynthesis of cholesterol and other lipids has been implicated in many neurological diseases, including Parkinson's disease. Misfolding of α-synuclein (α-Syn), the main actor in Parkinson's disease, is associated with changes in a lipid environment. However, the exact molecular mechanisms underlying cholesterol effect on α-Syn binding to lipids as well as α-Syn oligomerization and fibrillation remain elusive, as does the relative importance of cholesterol compared to other factors. We probed the interactions and fibrillation behaviour of α-Syn using styrene-maleic acid nanodiscs, containing zwitterionic and anionic lipid model systems with and without cholesterol. Surface plasmon resonance and thioflavin T fluorescence assays were employed to monitor α-Syn binding, as well as fibrillation in the absence and presence of membrane models. 1 H-15 N-correlated NMR was used to monitor the fold of α-Syn in response to nanodisc binding, determining individual residue apparent affinities for the nanodisc-contained bilayers. The addition of cholesterol inhibited α-Syn interaction with lipid bilayers and, however, significantly promoted α-Syn fibrillation, with a more than a 20-fold reduction of lag times before fibrillation onset. When α-Syn bilayer interactions were analysed at an individual residue level by solution-state NMR, we observed two different effects of cholesterol. In nanodiscs made of DOPC, the addition of cholesterol modulated the NAC part of α-Syn, leading to stronger interaction of this region with the lipid bilayer. In contrast, in the nanodiscs comprising DOPC, DOPE and DOPG, the NAC part was mostly unaffected by the presence of cholesterol, while the binding of the N and the C termini was both inhibited.

The Potential for Phospholipids in the Treatment of Airway Inflammation: An Unexplored Solution

Asthma, chronic obstructive pulmonary disease (COPD), and cystic fibrosis (CF) are major inflammatory respiratory diseases. Current mainstay therapy for asthma, and chronic obstructive pulmonary disease are corticosteroids, which have well-established side effect profiles. Phospholipids (PLs) are ubiquitous, diverse compounds with varying functions such as their structural role incell membrane, energy storage, and cell signaling.Recent advances in understanding PLs role as inflammatory mediators in the body as well as their widespread long-standing use as carrier molecules in drug delivery demonstrate the potential application of phospholipids in modulating inflammatory conditions. This review briefly explains the main mechanisms of inflammation in chronic respiratory diseases, currentanti-inflammatory treatments and areas of unmet need. The structural features, roles of endogenous and exogenous phospholipids, including their use as pharmaceutical excipients are reviewed. Current research on the immunomodulatory properties of PLs and their potentialapplication in inflammatory diseasesis the major section of this review. Considering the roles of PLs as inflammatory mediators and their safety profile established in pharmaceutical formulations, these small molecules demonstrate great potential as candidates in respiratory inflammation. Future studies need to focus on the immunomodulatory properties and the underlying mechanisms of phospholipids in respiratory inflammatory diseases.

Tunable Electromechanical Nanopore Trap Reveals Populations of Peripheral Membrane Protein Binding Conformations

We demonstrate that a naturally occurring nanopore, the voltage-dependent anion channel (VDAC) of the mitochondrion, can be used to electromechanically trap and interrogate proteins bound to a lipid surface at the single-molecule level. Electromechanically probing α-synuclein (αSyn), an intrinsically disordered neuronal protein intimately associated with Parkinson's pathology, reveals wide variation in the time required for individual proteins to unbind from the same membrane surface. The observed distributions of unbinding times span up to 3 orders of magnitude and depend strongly on the lipid composition of the membrane; surprisingly, lipid membranes to which αSyn binds weakly are most likely to contain subpopulations in which electromechanically driven unbinding is very slow. We conclude that unbinding of αSyn from the membrane surface depends not only on membrane binding affinity but also on the conformation adopted by an individual αSyn molecule on the membrane surface.

Membrane Interactions of α-Synuclein Probed by Neutrons and Photons

α-Synuclein (α-syn) is a key protein in the etiology of Parkinson's disease. In a disease state, α-syn accumulates as insoluble amyloid fibrils enriched in β-sheet structure. However, in its functional state, α-syn adopts an amphipathic helix upon membrane association and plays a role in synaptic vesicle docking, fusion, and clustering. In this Account, we describe our contributions made in the past decade toward developing a molecular understanding of α-syn membrane interactions, which are crucial for function and have pathological implications. Three topics are covered: α-syn membrane binding probed by neutron reflectometry (NR), the effects of membrane on α-syn amyloid formation, and interactions of α-syn with cellular membranes.NR offers a unique perspective by providing direct measurements of protein penetration depth. By the use of segmentally deuterated α-syn generated through native chemical ligation, the spatial resolution of specific membrane-bound polypeptide regions was determined by NR. Additionally, we used NR to characterize the membrane-bound complex of α-syn and glucocerebrosidase, a lysosomal hydrolase whose mutations are a common genetic risk factor for Parkinson's disease. Although phosphatidylcholine (PC) is the most abundant lipid species in mammalian cells, interactions of PC with α-syn have been largely ignored because they are substantially weaker compared with the electrostatically driven binding of negatively charged lipids. We discovered that α-syn tubulates zwitterionic PC membranes, which is likely related to its involvement in synaptic vesicle fusion by stabilization of membrane curvature. Interestingly, PC lipid tubules inhibit amyloid formation, in contrast to anionic phosphatidylglycerol lipid tubules, which stimulate protein aggregation. We also found that membrane fluidity influences the propensity of α-synuclein amyloid formation. Most recently, we obtained direct evidence of binding of α-syn to exocytic sites on intact cellular membranes using a method called cellular unroofing. This method provides direct access to the cytosolic plasma membrane. Importantly, measurements of fluorescence lifetime distributions revealed that α-syn is more conformationally dynamic at the membrane interface than previously appreciated. This exquisite responsiveness to specific lipid composition and membrane topology is important for both its physiological and pathological functions. Collectively, our work has provided insights into the effects of the chemical nature of phospholipid headgroups on the interplay among membrane remodeling, protein structure, and α-syn amyloid formation.

α-Synuclein and neuronal membranes: Conformational flexibilities in health and disease

Parkinson's disease (PD) is the second most common neurodegenerative disease. Currently, PD has no treatment. The neuronal protein α-synuclein (αS) plays an important role in PD. However, the molecular mechanisms governing its physiological and pathological roles are not fully understood. It is becoming widely acknowledged that the biological roles of αS involve interactions with biological membranes. In these biological processes there is a fine-tuned interplay between lipids affecting the properties of αS and αS affecting lipid metabolism, αS binding to membranes, and membrane damage. In this review, the intricate interactions between αS and membranes will be reviewed and a discussion of the relationship between αS and neuronal membrane structural plasticity in health and disease will be made. It is proposed that in healthy neurons the conformational flexibilities of αS and the neuronal membranes are coupled to assist the physiological roles of αS. However, in circumstances where their conformational flexibilities are decreased or uncoupled, there is a shift toward cell toxicity. Strategies to modulate toxic αS-membrane interactions are potential approaches for the development of new therapies for PD. Future work using specific αS molecular species as well as membranes with specific physicochemical properties should widen our understanding of the intricate biological roles of αS which, in turn, would propel the development of new strategies for the treatment of PD.

Neutral lipids as early biomarkers of cellular fate: the case of α-synuclein overexpression

α-synuclein (α-syn) accumulation and aggregation is a common pathological factor found in synucleinopathies, a group of neurodegenerative disorders that includes Parkinson´s disease (PD). It has been proposed that lipid dyshomeostasis is responsible for the occurrence of PD-related processes, however, the precise role of lipids in the onset and progression of neurodegenerative disorders remains unclear. Our aim was to investigate the effect of α-syn overexpression on neutral lipid metabolism and how this impacts on neuronal fate. We found lipid droplet (LD) accumulation in cells overexpressing α-syn to be associated with a rise in triacylglycerol (TAG) and cholesteryl ester (CE) levels. α-syn overexpression promoted diacylglycerol acyltransferase 2 upregulation and acyl-CoA synthetase activation, triggering TAG buildup, that was accompanied by an increase in diacylglycerol acylation. Moreover, the CE increment was associated with higher activity of acyl-CoA:cholesterol acyltransferase. Interestingly, α-syn overexpression increased cholesterol lysosomal accumulation. We observed that sterol regulatory element-binding protein (SREBP)-1 and SREBP-2 were differentially regulated by α-syn overexpression. The latter gave rise to a reduction in SREBP-1 nuclear translocation and consequently in fatty acid synthase expression, whereas it produced an increase in SREBP-2 nuclear localization. Surprisingly, and despite increased cholesterol levels, SREBP-2 downstream genes related to cholesterolgenesis were not upregulated as expected. Notably, phospholipid (PL) levels were diminished in cells overexpressing α-syn. This decrease was related to the activation of phospholipase A2 (PLA2) with a concomitant imbalance of the PL deacylation-acylation cycle. Fatty acids released from PLs by iPLA2 and cPLA2 action were esterified into TAGs, thus promoting a biological response to α-syn overexpression with uncompromised cell viability. When the described steady-state was disturbed under conditions favoring higher levels of α-syn, the response was an enhanced LD accumulation, this imbalance ultimately leading to neuronal death.

Interactions of α-synuclein oligomers with lipid membranes

Parkinson's disease is an increasingly prevalent and currently incurable neurodegenerative disorder. At the molecular level, this disease is characterized by the formation of aberrant intracellular protein deposits known as Lewy bodies. Oligomeric forms of the protein α-synuclein (αS), which are believed to be both intermediates and by-products of Lewy body formation, are considered to be the main pathogenic species. Interactions of such oligomers with lipid membranes are increasingly emerging as a major molecular pathway underpinning their toxicity. Here we review recent progress in our understanding of the interactions of αS oligomers with lipid membranes. We highlight key structural and biophysical features of αS oligomers, the effects of these features on αS oligomer membrane binding properties, and resultant implications for understanding the etiology of Parkinson's disease. We discuss mechanistic modes of αS oligomer-lipid membrane interactions and the effects of environmental factors to such modes. Finally, we provide an overview of the current understanding of the main molecular determinants of αS oligomer toxicity in vivo.

The interplay between Glucocerebrosidase, α-synuclein and lipids in human models of Parkinson's disease

Mutations in the gene GBA, encoding glucocerebrosidase (GCase), are the highest genetic risk factor for Parkinson's disease (PD). GCase is a lysosomal glycoprotein responsible for the hydrolysis of glucosylceramide into glucose and ceramide. Mutations in GBA cause a decrease in GCase activity, stability and protein levels which in turn lead to the accumulation of GCase lipid substrates as well as α-synuclein (αS) in vitro and in vivo. αS is the main constituent of Lewy bodies found in the brain of PD patients and an increase in its levels was found to be associated with a decrease in GCase activity/protein levels in vitro and in vivo. In this review, we describe the reported biophysical and biochemical changes that GBA mutations can induce in GCase activity and stability as well as the current overview of the levels of GCase protein/activity, αS and lipids measured in patient-derived samples including post-mortem brains, stem cell-derived neurons, cerebrospinal fluid, blood and fibroblasts as well as in SH-SY5Y cells. In particular, we report how the levels of αS and lipids are affected by/correlated to significant changes in GCase activity/protein levels and which cellular pathways are activated or disrupted by these changes in each model. Finally, we review the current strategies used to revert the changes in the levels of GCase activity/protein, αS and lipids in the context of PD.

Physical mechanisms of amyloid nucleation on fluid membranes

Biological membranes can dramatically accelerate the aggregation of normally soluble protein molecules into amyloid fibrils and alter the fibril morphologies, yet the molecular mechanisms through which this accelerated nucleation takes place are not yet understood. Here, we develop a coarse-grained model to systematically explore the effect that the structural properties of the lipid membrane and the nature of protein-membrane interactions have on the nucleation rates of amyloid fibrils. We identify two physically distinct nucleation pathways-protein-rich and lipid-rich-and quantify how the membrane fluidity and protein-membrane affinity control the relative importance of those molecular pathways. We find that the membrane's susceptibility to reshaping and being incorporated into the fibrillar aggregates is a key determinant of its ability to promote protein aggregation. We then characterize the rates and the free-energy profile associated with this heterogeneous nucleation process, in which the surface itself participates in the aggregate structure. Finally, we compare quantitatively our data to experiments on membrane-catalyzed amyloid aggregation of α-synuclein, a protein implicated in Parkinson's disease that predominately nucleates on membranes. More generally, our results provide a framework for understanding macromolecular aggregation on lipid membranes in a broad biological and biotechnological context.

Lipid-Chaperone Hypothesis: A Common Molecular Mechanism of Membrane Disruption by Intrinsically Disordered Proteins

An increasing number of human diseases has been shown to be linked to aggregation and amyloid formation by intrinsically disordered proteins (IDPs). Amylin, amyloid-β, and α-synuclein are, indeed, involved in type-II diabetes, Alzheimer's, and Parkinson's, respectively. Despite the correlation of the toxicity of these proteins at early aggregation stages with membrane damage, the molecular events underlying the process is quite complex to understand. In this study, we demonstrate the crucial role of free lipids in the formation of lipid-protein complex, which enables an easy membrane insertion for amylin, amyloid-β, and α-synuclein. Experimental results from a variety of biophysical methods and molecular dynamics results reveal that this common molecular pathway in membrane poration is shared by amyloidogenic (amylin, amyloid-β, and α-synuclein) and nonamyloidogenic (rat IAPP, β-synuclein) proteins. Based on these results, we propose a "lipid-chaperone" hypothesis as a unifying framework for protein-membrane poration.

Aquaporin-5 regulation of cell-cell adhesion proteins: an elusive "tail" story

Aquaporins (AQPs) are water channels that facilitate transport of water across cellular membranes. AQPs are overexpressed in several cancers. Especially in breast cancer, AQP5 overexpression correlates with spread to lymph nodes and poor prognosis. Previously, we showed that AQP5 expression reduced cell-cell adhesion by reducing levels of adherens and tight-junction proteins (e.g., ZO-1, plakoglobin, and β-catenin) at the actual junctions. Here, we show that, when targeted to the plasma membrane, the AQP5 COOH-terminal tail domain regulated junctional proteins and, moreover, that AQP5 interacted with ZO-1, plakoglobin, β-catenin, and desmoglein-2, which were all reduced at junctions upon AQP5 overexpression. Thus, our data suggest that AQP5 mediates the effect on cell-cell adhesion via interactions with junctional proteins independently of AQP5-mediated water transport. AQP5 overexpression in cancers may thus contribute to carcinogenesis and cancer spread by two independent mechanisms: reduced cell-cell adhesion, a characteristic of epithelial-mesenchymal transition, and increased cell migration capacity via water transport.

A Stearoyl-Coenzyme A Desaturase Inhibitor Prevents Multiple Parkinson Disease Phenotypes in α-Synuclein Mice

Objective

Parkinson disease (PD) has useful symptomatic treatments that do not slow the neurodegenerative process, and no significant disease‐modifying treatments are approved. A key therapeutic target in PD is α‐synuclein (αS), which is both genetically implicated and accumulates in Lewy bodies rich in vesicles and other lipid membranes. Reestablishing αS homeostasis is a central goal in PD. Based on previous lipidomic analyses, we conducted a mouse trial of a stearoyl–coenzyme A desaturase (SCD) inhibitor (“5b”) that prevented αS‐positive vesicular inclusions and cytotoxicity in cultured human neurons.

Methods

Oral dosing and brain activity of 5b were established in nontransgenic mice. 5b in drinking water was given to mice expressing wild‐type human αS (WT) or an amplified familial PD αS mutation (E35K + E46K + E61K ["3K"]) beginning near the onset of nigral and cortical neurodegeneration and the robust PD‐like motor syndrome in 3K. Motor phenotypes, brain cytopathology, and SCD‐related lipid changes were quantified in 5b‐ versus placebo‐treated mice. Outcomes were compared to effects of crossing 3K to SCD1^−/− mice.

Results

5b treatment reduced αS hyperphosphorylation in E46K‐expressing human neurons, in 3K neural cultures, and in both WT and 3K αS mice. 5b prevented subtle gait deficits in WT αS mice and the PD‐like resting tremor and progressive motor decline of 3K αS mice. 5b also increased αS tetramers and reduced proteinase K‐resistant lipid‐rich aggregates. Similar benefits accrued from genetically deleting 1 SCD allele, providing target validation.

Interpretation

Prolonged reduction of brain SCD activity prevented PD‐like neuropathology in multiple PD models. Thus, an orally available SCD inhibitor potently ameliorates PD phenotypes, positioning this approach to treat human α‐synucleinopathies. ANN NEUROL 2021;89:74–90

Molecular mechanism of olesoxime-mediated neuroprotection through targeting α-synuclein interaction with mitochondrial VDAC

An intrinsically disordered neuronal protein α-synuclein (αSyn) is known to cause mitochondrial dysfunction, contributing to loss of dopaminergic neurons in Parkinson's disease. Through yet poorly defined mechanisms, αSyn crosses mitochondrial outer membrane and targets respiratory complexes leading to bioenergetics defects. Here, using neuronally differentiated human cells overexpressing wild-type αSyn, we show that the major metabolite channel of the outer membrane, the voltage-dependent anion channel (VDAC), is a pathway for αSyn translocation into the mitochondria. Importantly, the neuroprotective cholesterol-like synthetic compound olesoxime inhibits this translocation. By applying complementary electrophysiological and biophysical approaches, we provide mechanistic insights into the interplay between αSyn, VDAC, and olesoxime. Our data suggest that olesoxime interacts with VDAC β-barrel at the lipid-protein interface thus hindering αSyn translocation through the VDAC pore and affecting VDAC voltage gating. We propose that targeting αSyn translocation through VDAC could represent a key mechanism for the development of new neuroprotective strategies.