The formation of highly soluble oligomers of alpha-synuclein is regulated by fatty acids and enhanced in Parkinson's disease

α-Synuclein facilitates endocytosis by elevating the steady-state levels of phosphatidylinositol 4,5-bisphosphate

α-Synuclein (α-Syn) is a protein implicated in the pathogenesis of Parkinson's disease (PD). It is an intrinsically disordered protein that binds acidic phospholipids. Growing evidence supports a role for α-Syn in membrane trafficking, including, mechanisms of endocytosis and exocytosis, although the exact role of α-Syn in these mechanisms is currently unclear. Here we investigate the associations of α-Syn with the acidic phosphoinositides (PIPs), phosphatidylinositol 4,5-bisphosphate (PI(4,5)P2) and phosphatidylinositol 3,4-bisphosphate (PI(3,4)P2). Our results show that α-Syn colocalizes with PIP2 and the phosphorylated active form of the clathrin adaptor protein 2 (AP2) at clathrin-coated pits. Using endocytosis of transferrin as an indicator for clathrin-mediated endocytosis (CME), we find that α-Syn involvement in endocytosis is specifically mediated through PI(4,5)P2 levels on the plasma membrane. In accord with their effects on PI(4,5)P2 levels, the PD associated A30P, E46K, and A53T mutations in α-Syn further enhance CME in neuronal and nonneuronal cells. However, lysine to glutamic acid substitutions at the KTKEGV repeat domain of α-Syn, which interfere with phospholipid binding, are ineffective in enhancing CME. We further show that the rate of synaptic vesicle (SV) endocytosis is differentially affected by the α-Syn mutations and associates with their effects on PI(4,5)P2 levels, however, with the exception of the A30P mutation. This study provides evidence for a critical involvement of PIPs in α-Syn-mediated membrane trafficking.

Isotope-reinforced polyunsaturated fatty acids improve Parkinson's disease-like phenotype in rats overexpressing α-synuclein

Lipid peroxidation is a key to a portfolio of neurodegenerative diseases and plays a central role in α-synuclein (α-syn) toxicity, mitochondrial dysfunction and neuronal death, all key processes in the pathogenesis of Parkinson’s disease (PD). Polyunsaturated fatty acids (PUFAs) are important constituents of the synaptic and mitochondrial membranes and are often the first molecular targets attacked by reactive oxygen species (ROS). The rate-limiting step of the chain reaction of ROS-initiated PUFAs autoxidation involves hydrogen abstraction at bis-allylic sites, which can be slowed down if hydrogens are replaced with deuteriums. In this study, we show that targeted overexpression of human A53T α-syn using an AAV vector unilaterally in the rat substantia nigra reproduces some of pathological features seen in PD patients. Chronic dietary supplementation with deuterated PUFAs (D-PUFAs), specifically 0.8% D-linoleic and 0.3% H-linolenic, produced significant disease-modifying beneficial effects against α-syn-induced motor deficits, synaptic pathology, oxidative damage, mitochondrial dysfunction, disrupted trafficking along axons, inflammation and DA neuronal loss. These findings support the clinical evaluation of D-PUFAs as a neuroprotective therapy for PD.

MMP13 Expression Is Increased Following Mutant α-Synuclein Exposure and Promotes Inflammatory Responses in Microglia

α-Synuclein is a 140-amino acid protein that readily misfolds and is associated with the Lewy body pathology found in sporadic and genetic forms of Parkinson's disease. We and others have shown that wild-type α-synuclein is a damage-associated molecular pattern that directly elicits a proinflammatory response in microglia through toll-like receptor activation. Here we investigated the direct effect of oligomeric mutant α-synuclein (A53T) on microglia morphology and activation. We found that misfolded A53T increased quantitative measures of amoeboid cell morphology, NFκB nuclear translocation and the expression of prototypical proinflammatory molecules. We also demonstrated that A53T increased expression of MMP13, a matrix metalloproteinase that remodels the extracellular matrix. To better understand the role of MMP13 in synucleinopathies, we further characterized the role of MMP13 in microglial signaling. We showed exposure of microglia to MMP13 induced a change in morphology and promoted the release of TNFα and MMP9. Notably, IL1β was not released indicating that the pathway involved in MMP13 activation of microglia may be different than the A53T pathway. Lastly, MMP13 increased the expression of CD68 suggesting that the lysosomal pathway might be altered by this MMP. Taken together this study shows that mutant α-synuclein directly induces a proinflammatory phenotype in microglia, which includes the expression of MMP13. In turn, MMP13 directly alters microglia supporting the need for multi-target therapies to treat Parkinson's disease patients.

Modeling Parkinson's Disease Neuropathology and Symptoms by Intranigral Inoculation of Preformed Human α-Synuclein Oligomers

The accumulation of aggregated α-synuclein (αSyn) is a hallmark of Parkinson's disease (PD). Current evidence indicates that small soluble αSyn oligomers (αSynOs) are the most toxic species among the forms of αSyn aggregates, and that size and topological structural properties are crucial factors for αSynOs-mediated toxicity, involving the interaction with either neurons or glial cells. We previously characterized a human αSynO (H-αSynO) with specific structural properties promoting toxicity against neuronal membranes. Here, we tested the neurotoxic potential of these H-αSynOs in vivo, in relation to the neuropathological and symptomatic features of PD. The H-αSynOs were unilaterally infused into the rat substantia nigra pars compacta (SNpc). Phosphorylated αSyn (p129-αSyn), reactive microglia, and cytokine levels were measured at progressive time points. Additionally, a phagocytosis assay in vitro was performed after microglia pre-exposure to αsynOs. Dopaminergic loss, motor, and cognitive performances were assessed. H-αSynOs triggered p129-αSyn deposition in SNpc neurons and microglia and spread to the striatum. Early and persistent neuroinflammatory responses were induced in the SNpc. In vitro, H-αSynOs inhibited the phagocytic function of microglia. H-αsynOs-infused rats displayed early mitochondrial loss and abnormalities in SNpc neurons, followed by a gradual nigrostriatal dopaminergic loss, associated with motor and cognitive impairment. The intracerebral inoculation of structurally characterized H-αSynOs provides a model of progressive PD neuropathology in rats, which will be helpful for testing neuroprotective therapies.

Upregulation of Cellular Palmitoylation Mitigates α-Synuclein Accumulation and Neurotoxicity

BACKGROUND

Synucleinopathies, including Parkinson's disease (PD), are characterized by α-synuclein (αS) cytoplasmic inclusions. αS-dependent vesicle-trafficking defects are important in PD pathogenesis, but their mechanisms are not well understood. Protein palmitoylation, post-translational addition of the fatty acid palmitate to cysteines, promotes trafficking by anchoring specific proteins to the vesicle membrane. αS itself cannot be palmitoylated as it lacks cysteines, but it binds to membranes, where palmitoylation occurs, via an amphipathic helix. We hypothesized that abnormal αS membrane-binding impairs trafficking by disrupting palmitoylation. Accordingly, we investigated the therapeutic potential of increasing cellular palmitoylation.

OBJECTIVES

We asked whether upregulating palmitoylation by inhibiting the depalmitoylase acyl-protein-thioesterase-1 (APT1) ameliorates pathologic αS-mediated cellular phenotypes and sought to identify the mechanism.

METHODS

Using human neuroblastoma cells, rat neurons, and iPSC-derived PD patient neurons, we examined the effects of pharmacologic and genetic downregulation of APT1 on αS-associated phenotypes.

RESULTS

APT1 inhibition or knockdown decreased αS cytoplasmic inclusions, reduced αS serine-129 phosphorylation (a PD neuropathological marker), and protected against αS-dependent neurotoxicity. We identified the APT1 substrate microtubule-associated-protein-6 (MAP6), which binds to vesicles in a palmitoylation-dependent manner, as a key mediator of these effects. Mechanistically, we found that pathologic αS accelerated palmitate turnover on MAP6, suggesting that APT1 inhibition corrects a pathological αS-dependent palmitoylation deficit. We confirmed the disease relevance of this mechanism by demonstrating decreased MAP6 palmitoylation in neurons from αS gene triplication patients.

CONCLUSIONS

Our findings demonstrate a novel link between the fundamental process of palmitoylation and αS pathophysiology. Upregulating palmitoylation represents an unexplored therapeutic strategy for synucleinopathies. © 2020 International Parkinson and Movement Disorder Society.

Transient transfection of WT-αS and A53T-αS brought about a mild apoptosis due to degradation of released cytochrome c through PARC

α-Synuclein (αS) aggregates plays a pivotal role in the pathogenesis of synucleinopathies including Parkinson's Disease. The toxicity of αS aggregates has been broadly studied and variant defects have been reported through which these aggregates lead in cell death. Although cell death through apoptosis pathway has been proposed in many studies, the molecular details underlying in this pathway have not been uncovered. To shed a light on the relationships between αS aggregates and apoptotic cell death, changes in levels and behavior of molecular indicators of the intrinsic apoptotic pathway was investigated in HEK-293T cells overexpressing wild-type α-synuclein and A53T-α-synuclein. Overexpression of both WT-αS and A53T-αS resulted in the increase of caspase-9 activity, and rise in Cytochrome c (Cyt c) and PARC content, concurrently. We assume that rising in PARC level may result in Cyt c degradation, and consequently suppressing/attenuating intrinsic apoptosis pathway. Besides, increasing of Casp-9 activity can be related to αS aggregates and subsequent degradation of Cyt c. To understand the mechanisms behind this using theoretical model, molecular dynamic simulation was also applied to investigate the possible interaction of Casp-9 with α-synuclein aggregates. The results showed that the interaction between Casp-9 with αS aggregates could activate Casp-9 by changing the conformation of some crucial residues.

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

Arylsulfatase A (ASA) in Parkinson's Disease: From Pathogenesis to Biomarker Potential

Parkinson's disease (PD), the second most common neurodegenerative disorder after Alzheimer's disease, is a clinically heterogeneous disorder, with obscure etiology and no disease-modifying therapy to date. Currently, there is no available biomarker for PD endophenotypes or disease progression. Accumulating evidence suggests that mutations in genes related to lysosomal function or lysosomal storage disorders may affect the risk of PD development, such as GBA1 gene mutations. In this context, recent studies have revealed the emerging role of arylsulfatase A (ASA), a lysosomal hydrolase encoded by the ARSA gene causing metachromatic leukodystrophy (MLD) in PD pathogenesis. In particular, altered ASA levels have been detected during disease progression, and reduced enzymatic activity of ASA has been associated with an atypical PD clinical phenotype, including early cognitive impairment and essential-like tremor. Clinical evidence further reveals that specific ARSA gene variants may act as genetic modifiers in PD. Recent in vitro and in vivo studies indicate that ASA may function as a molecular chaperone interacting with α-synuclein (SNCA) in the cytoplasm, preventing its aggregation, secretion and cell-to-cell propagation. In this review, we summarize the results of recent preclinical and clinical studies on the role of ASA in PD, aiming to shed more light on the potential implication of ASA in PD pathogenesis and highlight its biomarker potential.

Interaction of Alpha-Synuclein With Lipids: Mitochondrial Cardiolipin as a Critical Player in the Pathogenesis of Parkinson's Disease

Alpha-Synuclein (α-Syn) is a central protein in the pathogenesis of synucleinopathies, a group of neurodegenerative disorders including Parkinson’s disease (PD). Although its role in neurotransmission is well established, the precise role of this protein in disease pathogenesis is still not fully understood. It is, however, widely regarded to be associated with the misfolding and accumulation of toxic intracellular aggregates. In fact, α-Syn is the most abundant protein component of Lewy bodies and Lewy neurites, which are also characterized by a high lipid content. Lipids, the main constituents of cellular membranes, have been implicated in many aspects of PD-related processes. α-Syn interacts with membrane phospholipids and free fatty acids via its N-terminal domain, and altered lipid-protein complexes might enhance both its binding to synaptic and mitochondrial membranes and its oligomerization. Several studies have highlighted a specific interaction of α-Syn with the phospholipid cardiolipin (CL), a major constituent of mitochondrial membranes. By interacting with CL, α-Syn is able to disrupt mitochondrial membrane integrity, leading to mitochondrial dysfunction. Additionally, externalized CL is able to facilitate the refolding of toxic α-Syn species at the outer mitochondrial membrane. In this review, we discuss how α-Syn/lipid interactions, in particular the α-Syn/CL interaction at the mitochondrial membrane, may affect α-Syn aggregation and mitochondrial dysfunction and may thus represent an important mechanism in the pathogenesis of PD.

Prolyl oligopeptidase inhibition by KYP-2407 increases alpha-synuclein fibril degradation in neuron-like cells

Growing evidence emphasizes insufficient clearance of pathological alpha-synuclein (αSYN) aggregates in the progression of Parkinson's disease (PD). Consequently, cellular degradation pathways represent a potential therapeutic target. Prolyl oligopeptidase (PREP) is highly expressed in the brain and has been suggested to increase αSYN aggregation and negatively regulate the autophagy pathway. Inhibition of PREP with a small molecule inhibitor, KYP-2407, stimulates autophagy and reduces the oligomeric species of αSYN aggregates in PD mouse models. However, whether PREP inhibition has any effects on intracellular αSYN fibrils has not been studied before. In this study, the effect of KYP2407 on αSYN preformed fibrils (PFFs) was tested in SH-SY5Y cells and human astrocytes. Immunostaining analysis revealed that both cell types accumulated αSYN PFFs intracellularly but KYP-2047 decreased intracellular αSYN deposits only in SH-SY5Y cells, as astrocytes did not show any PREP activity. Western blot analysis confirmed the reduction of high molecular weight αSYN species in SH-SY5Y cell lysates, and secretion of αSYN from SH-SY5Y cells also decreased in the presence of KYP-2407. Accumulation of αSYN inside the SH-SY5Y cells resulted in an increase of the auto-lysosomal proteins p62 and LC3BII, as well as calpain 1 and 2, which have been shown to be associated with PD pathology. Notably, treatment with KYP-2407 significantly reduced p62 and LC3BII levels, indicating an increased autophagic flux, and calpain 1 and 2 levels returned to normal in the presence of KYP-2407. Our findings indicate that PREP inhibition can potentially be used as therapy to reduce the insoluble intracellular αSYN aggregates.

How specific are the conformation-specific α-synuclein antibodies? Characterization and validation of 16 α-synuclein conformation-specific antibodies using well-characterized preparations of α-synuclein monomers, fibrils and oligomers with distinct structures and morphology

Increasing evidence suggests that alpha-synuclein (α-syn) oligomers are obligate intermediates in the pathway involved in α-syn fibrillization and Lewy body (LB) formation, and may also accumulate within LBs in Parkinson's disease (PD) and other synucleinopathies. Therefore, the development of tools and methods to detect and quantify α-syn oligomers has become increasingly crucial for mechanistic studies to understand their role in PD, and to develop new diagnostic methods and therapies for PD and other synucleinopathies. The majority of these tools and methods rely primarily on the use of aggregation state-specific or conformation-specific antibodies. Given the impact of the data and knowledge generated using these antibodies on shaping the foundation and directions of α-syn and PD research, it is crucial that these antibodies are thoroughly characterized, and their specificity or ability to capture diverse α-syn species is tested and validated. Herein, we describe an antibody characterization and validation pipeline that allows a systematic investigation of the specificity of α-syn antibodies using well-defined and well-characterized preparations of various α-syn species, including monomers, fibrils, and different oligomer preparations that are characterized by distinct morphological, chemical and secondary structure properties. This pipeline was used to characterize 18 α-syn antibodies, 16 of which have been reported as conformation- or oligomer-specific antibodies, using an array of techniques, including immunoblot analysis (slot blot and Western blot), a digital ELISA assay using single molecule array technology and surface plasmon resonance. Our results show that i) none of the antibodies tested are specific for one particular type of α-syn species, including monomers, oligomers or fibrils; ii) all antibodies that were reported to be oligomer-specific also recognized fibrillar α-syn; and iii) a few antibodies showed high specificity for oligomers and fibrils but did not bind to monomers. These findings suggest that the great majority of α-syn aggregate-specific antibodies do not differentiate between oligomers and fibrils, thus highlighting the importance of exercising caution when interpreting results obtained using these antibodies. Our results also underscore the critical importance of the characterization and validation of antibodies before their use in mechanistic studies and as diagnostic tools or therapeutic agents. This will not only improve the quality and reproducibility of research and reduce costs but will also reduce the number of therapeutic antibody failures in the clinic.

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

The aggregation of α-synuclein (α-syn) is inseparably connected to Parkinson’s disease (PD). It is now well-established that certain forms of α-syn aggregates, oligomers and fibrils, can exert neurotoxicity in synucleinopathies. With the exception of rare familial forms, the vast majority of PD cases are idiopathic. Understanding the earliest molecular mechanisms that cause initial α-syn misfolding could help to explain why PD affects only some individuals and others not. Factors that chaperone the transition of α-syn’s physiological to pathological function are of particular interest, since they offer opportunities for intervention. The relationship between α-syn and lipids represents one of those factors. Membrane interaction is crucial for normal cellular function, but lipids also induce the aggregation of α-syn, causing cell toxicity. Also, disease-causing or risk-factor mutations in genes related to lipid metabolism like PLA2G6, SCARB2 or GBA1 highlight the close connection between PD and lipids. Despite the clear link, the ambivalent interaction has not been studied sufficiently so far. In this review, we address how α-syn interacts with lipids and how they can act as key factor for orchestrating toxic conversion of α-syn. Furthermore, we will discuss a scenario in which initial α-syn aggregation is determined by shifts in lipid/α-syn ratio as well as by dyshomeostasis of membrane bound/unbound state of α-syn.

Metabolomics Fingerprint Induced by the Intranigral Inoculation of Exogenous Human Alpha-Synuclein Oligomers in a Rat Model of Parkinson's Disease

Parkinson’s disease (PD) is considered a synucleinopathy because of the intraneuronal accumulation of aggregated α-synuclein (αSyn). Recent evidence points to soluble αSyn-oligomers (αSynO) as the main cytotoxic species responsible for cell death. Given the pivotal role of αSyn in PD, αSyn-based models are crucial for the investigation of toxic mechanisms and the identification of new therapeutic targets in PD. By using a metabolomics approach, we evaluated the metabolic profile of brain and serum samples of rats infused unilaterally with preformed human αSynOs (HαSynOs), or vehicle, into the substantia nigra pars compacta (SNpc). Three months postinfusion, the striatum was dissected for striatal dopamine (DA) measurements via High Pressure Liquid Chromatography (HPLC) analysis and mesencephalon and serum samples were collected for the evaluation of metabolite content via gas chromatography mass spectrometry analysis. Multivariate, univariate and correlation statistics were applied. A 40% decrease of DA content was measured in the HαSynO-infused striatum as compared to the contralateral and the vehicle-infused striata. Decreased levels of dehydroascorbic acid, myo-inositol, and glycine, and increased levels of threonine, were found in the mesencephalon, while increased contents of fructose and mannose, and a decrease in glycine and urea, were found in the serum of HαSynO-infused rats. The significant correlation between DA and metabolite content indicated that metabolic variations reflected the nigrostriatal degeneration. Collectively, the metabolomic fingerprint of HαSynO-infused rats points to an increase of oxidative stress markers, in line with PD neuropathology, and provides hints for potential biomarkers of PD.

Brain region-specific lipid alterations in the PLB4 hBACE1 knock-in mouse model of Alzheimer's disease

BACKGROUND

Lipid dysregulation is associated with several key characteristics of Alzheimer's disease (AD), including amyloid-β and tau neuropathology, neurodegeneration, glucose hypometabolism, as well as synaptic and mitochondrial dysfunction. The β-site amyloid precursor protein cleavage enzyme 1 (BACE1) is associated with increased amyloidogenesis, and has been affiliated with diabetes via its role in metabolic regulation.

METHODS

The research presented herein investigates the role of hBACE1 in lipid metabolism and whether specific brain regions show increased vulnerability to lipid dysregulation. By utilising advanced mass spectrometry techniques, a comprehensive, quantitative lipidomics analysis was performed to investigate the phospholipid, sterol, and fatty acid profiles of the brain from the well-known PLB4 hBACE1 knock-in mouse model of AD, which also shows a diabetic phenotype, to provide insight into regional alterations in lipid metabolism.

RESULTS

Results show extensive region - specific lipid alterations in the PLB4 brain compared to the wild-type, with decreases in the phosphatidylethanolamine content of the cortex and triacylglycerol content of the hippocampus and hypothalamus, but increases in the phosphatidylcholine, phosphatidylinositol, and diacylglycerol content of the hippocampus. Several sterol and fatty acids were also specifically decreased in the PLB4 hippocampus.

CONCLUSION

Collectively, the lipid alterations observed in the PLB4 hBACE1 knock-in AD mouse model highlights the regional vulnerability of the brain, in particular the hippocampus and hypothalamus, to lipid dysregulation, hence supports the premise that metabolic abnormalities have a central role in both AD and diabetes.

α-Synuclein BAC transgenic mice exhibit RBD-like behaviour and hyposmia: a prodromal Parkinson's disease model

Parkinson's disease is one of the most common movement disorders and is characterized by dopaminergic cell loss and the accumulation of pathological α-synuclein, but its precise pathogenetic mechanisms remain elusive. To develop disease-modifying therapies for Parkinson's disease, an animal model that recapitulates the pathology and symptoms of the disease, especially in the prodromal stage, is indispensable. As subjects with α-synuclein gene (SNCA) multiplication as well as point mutations develop familial Parkinson's disease and a genome-wide association study in Parkinson's disease has identified SNCA as a risk gene for Parkinson's disease, the increased expression of α-synuclein is closely associated with the aetiology of Parkinson's disease. In this study we generated bacterial artificial chromosome transgenic mice harbouring SNCA and its gene expression regulatory regions in order to maintain the native expression pattern of α-synuclein. Furthermore, to enhance the pathological properties of α-synuclein, we inserted into SNCA an A53T mutation, two single-nucleotide polymorphisms identified in a genome-wide association study in Parkinson's disease and a Rep1 polymorphism, all of which are causal of familial Parkinson's disease or increase the risk of sporadic Parkinson's disease. These A53T SNCA bacterial artificial chromosome transgenic mice showed an expression pattern of human α-synuclein very similar to that of endogenous mouse α-synuclein. They expressed truncated, oligomeric and proteinase K-resistant phosphorylated forms of α-synuclein in the regions that are specifically affected in Parkinson's disease and/or dementia with Lewy bodies, including the olfactory bulb, cerebral cortex, striatum and substantia nigra. Surprisingly, these mice exhibited rapid eye movement (REM) sleep without atonia, which is a key feature of REM sleep behaviour disorder, at as early as 5 months of age. Consistent with this observation, the REM sleep-regulating neuronal populations in the lower brainstem, including the sublaterodorsal tegmental nucleus, nuclei in the ventromedial medullary reticular formation and the pedunculopontine nuclei, expressed phosphorylated α-synuclein. In addition, they also showed hyposmia at 9 months of age, which is consistent with the significant accumulation of phosphorylated α-synuclein in the olfactory bulb. The dopaminergic neurons in the substantia nigra pars compacta degenerated, and their number was decreased in an age-dependent manner by up to 17.1% at 18 months of age compared to wild-type, although the mice did not show any related locomotor dysfunction. In conclusion, we created a novel mouse model of prodromal Parkinson's disease that showed RBD-like behaviour and hyposmia without motor symptoms.

α-Synuclein facilitates endocytosis by elevating the steady-state levels of phosphatidylinositol 4,5-bisphosphate.. [DOI: 10.1101/2020.06.18.158709] [Citation(s) in RCA: 0] [Impact Index Per Article: 0]

α-Synuclein (α-Syn) is a protein implicated in the pathogenesis of Parkinson’s disease (PD). It is an intrinsically disordered protein that binds acidic phospholipids. Growing evidence supports a role for α-Syn in membrane trafficking, including, mechanisms of endocytosis and exocytosis, although the exact role of α-Syn in these mechanisms is currently unclear. Here we have investigated the role of α-Syn in membrane trafficking through its association with acidic phosphoinositides (PIPs), such as phosphatidylinositol 4,5-bisphosphate (PI4,5P2) and phosphatidylinositol 3,4-bisphosphate (PI3,4P2). Our results show that α-Syn colocalizes with PIP2 and the phosphorylated active form of the clathrin adaptor AP2 at clathrin-coated pits. Using endocytosis of transferrin, an indicator of clathrin mediated endocytosis (CME), we find that α-Syn involvement in endocytosis is specifically mediated through PI4,5P2 levels. We further show that the rate of synaptic vesicle (SV) endocytosis is differentially affected by α-Syn mutations. In accord with their effects on PI4,5P2 levels at the plasma membrane, the PD associated E46K and A53T mutations further enhance SV endocytosis. However, neither A30P mutation, nor Lysine to Glutamic acid substitutions at the KTKEGV repeat domain of α-Syn, that interfere with phospholipid binding, affect SV endocytosis. This study provides evidence for a critical involvement of PIPs in α-Syn-mediated membrane trafficking.

Significance Statement

α-Synuclein (α-Syn) protein is known for its causative role in Parkinson’s disease. α-Syn is normally involved in mechanisms of membrane trafficking, including endocytosis, exocytosis and synaptic vesicles cycling. However, a certain degree of controversy regarding the exact role of α-Syn in these mechanisms persists. Here we show that α-Syn acts to increase plasma membrane levels PI4,5P2 and PI3,4P2 to facilitate clathrin mediated and synaptic vesicles endocytosis. Based on the results, we suggest that α-Syn interactions with the acidic phosphoinositides facilitate a shift in their homeostasis to support endocytosis.

LRRK2 and α-Synuclein: Distinct or Synergistic Players in Parkinson's Disease?

Parkinson's disease (PD) is the most common neurodegenerative movement disorder, characterized by prominent degeneration of dopaminergic neurons in the substantia nigra and aggregation of the protein α-synuclein within intraneuronal inclusions known as Lewy bodies. Ninety percent of PD cases are idiopathic while the remaining 10% are associated with gene mutations that affect cellular functions ranging from kinase activity to mitochondrial quality control, hinting at a multifactorial disease process. Mutations in LRRK2 and SNCA (the gene coding for α-synuclein) cause monogenic forms of autosomal dominant PD, and polymorphisms in either gene are also associated with increased risk of idiopathic PD. Although Lewy bodies are a defining neuropathological feature of PD, an appreciable subset of patients with LRRK2 mutations present with a clinical phenotype indistinguishable from idiopathic PD but lack Lewy pathology at autopsy, suggesting that LRRK2-mediated PD may occur independently of α-synuclein aggregation. Here, we examine whether LRRK2 and α-synuclein, as mediators of neurodegeneration in PD, exist in common or distinct pathways. Specifically, we review evidence from preclinical models and human neuropathological studies examining interactions between the two proteins. Elucidating the degree of interplay between LRRK2 and α-synuclein will be necessary for treatment stratification once effective targeted disease-modifying therapies are developed.

Quantitative Characterization of α-Synuclein Aggregation in Living Cells through Automated Microfluidics Feedback Control

Aggregation of α-synuclein and formation of inclusions are hallmarks of Parkinson’s disease (PD). Aggregate formation is affected by cellular environment, but it has been studied almost exclusively in cell-free systems. We quantitatively analyzed α-synuclein inclusion formation and clearance in a yeast cell model of PD expressing either wild-type (WT) α-synuclein or the disease-associated A53T mutant from the galactose (Gal)-inducible promoter. A computer-controlled microfluidics device regulated α-synuclein in cells by means of closed-loop feedback control. We demonstrated that inclusion formation is strictly concentration dependent and that the aggregation threshold of the A53T mutant is about half of the WT α-synuclein (56%). We chemically modulated the proteasomal and autophagic pathways and demonstrated that autophagy is the main determinant of A53T α-synuclein inclusions’ clearance. In addition to proposing a technology to overcome current limitations in dynamically regulating protein expression levels, our results contribute to the biology of PD and have relevance for therapeutic applications.

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In silico feedback control enables regulation of α-synuclein expression in yeast

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α-Synuclein inclusion formation is strictly concentration, but not time, dependent

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The aggregation threshold of the α-synuclein A53T mutant is 56% of the wild-type

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Autophagy induction speeds up inclusion clearance in the A53T α-synuclein strain

Polymorphic α-Synuclein Strains Modified by Dopamine and Docosahexaenoic Acid Interact Differentially with Tau Protein

The pathological hallmark of synucleinopathies, including Parkinson’s disease (PD), is the aggregation of α-synuclein (α-Syn) protein. Even so, tau protein pathology is abundantly found in these diseases. Both α-Syn and tau can exist as polymorphic aggregates, a phenomenon that has been widely studied, mostly in their fibrillar assemblies. We have previously discovered that in addition to α-Syn oligomers, oligomeric tau is also present in the brain tissues of patients with PD and dementia with Lewy bodies (DLB). However, the effect of interaction between polymorphic α-Syn oligomers and tau has not been scrupulously studied. Here, we have explored the structural and functional diversity of distinct α-Syn oligomers, prepared by modifying the protein with dopamine (DA) and docosahexaenoic acid (DHA). The two α-Syn oligomers differed in aggregate size, conformation, sensitivity to proteinase K digestion, tryptic digestion, and toxicity, suggesting them as distinct α-Syn oligomeric strains. We examined their internalization mechanisms in primary neurons and seeding propensity in inducing α-Syn aggregation. Using a combined approach of molecular and cellular techniques, we observed that the tau aggregates cross-seeded with the individual α-Syn oligomeric strains differed in their biochemical and biological properties, suggesting two distinct tau strains. The tau aggregate cross-seeded with the DA-modified α-Syn oligomeric strain possessed a potent intracellular tau seeding propensity. This study provides a comprehensive analysis of unique strain-specific interaction between oligomeric α-Syn and tau. Furthermore, this study allows us to speculate that distinct α-Syn-tau interactions inducing tau aggregation might be an underlying mechanism of neurodegeneration in PD.

α-Synuclein Translocates to the Nucleus to Activate Retinoic-Acid-Dependent Gene Transcription

α-Synuclein (α-Syn) protein is implicated in the pathogenesis of Parkinson disease (PD). It is primarily cytosolic and interacts with cell membranes. α-Syn also occurs in the nucleus. Here we investigated the mechanisms involved in nuclear translocation of α-Syn. We analyzed alterations in gene expression following induced α-Syn expression in SH-SY5Y cells. Analysis of upstream regulators pointed at alterations in transcription activity of retinoic acid receptors (RARs) and additional nuclear receptors. We show that α-Syn binds RA and translocates to the nucleus to selectively enhance gene transcription. Nuclear translocation of α-Syn is regulated by calreticulin and is leptomycin-B independent. Importantly, nuclear translocation of α-Syn following RA treatment enhances its toxicity in cultured neurons and the expression levels of PD-associated genes, including ATPase cation transporting 13A2 (ATP13A2) and PTEN-induced kinase1 (PINK1). The results link a physiological role for α-Syn in the regulation of RA-mediated gene transcription and its toxicity in the synucleinopathies.

Fatty Acid Binding Protein 3 Enhances the Spreading and Toxicity of α-Synuclein in Mouse Brain

Oligomerization and/or aggregation of α-synuclein (α-Syn) triggers α-synucleinopathies such as Parkinson’s disease and dementia with Lewy bodies. It is known that α-Syn can spread in the brain like prions; however, the mechanism remains unclear. We demonstrated that fatty acid binding protein 3 (FABP3) promotes propagation of α-Syn in mouse brain. Animals were injected with mouse or human α-Syn pre-formed fibrils (PFF) into the bilateral substantia nigra pars compacta (SNpc). Two weeks after injection of mouse α-Syn PFF, wild-type (WT) mice exhibited motor and cognitive deficits, whereas FABP3 knock-out (Fabp3^−/−) mice did not. The number of phosphorylated α-Syn (Ser-129)-positive cells was significantly decreased in Fabp3^−/− mouse brain compared to that in WT mice. The SNpc was unilaterally infected with AAV-GFP/FABP3 in Fabp3^−/− mice to confirm the involvement of FABP3 in the development of α-Syn PFF toxicity. The number of tyrosine hydroxylase (TH)- and phosphorylated α-Syn (Ser-129)-positive cells following α-Syn PFF injection significantly decreased in Fabp3^−/− mice and markedly increased by AAV-GFP/FABP3 infection. Finally, we confirmed that the novel FABP3 inhibitor MF1 significantly antagonized motor and cognitive impairments by preventing α-Syn spreading following α-Syn PFF injection. Overall, FABP3 enhances α-Syn spreading in the brain following α-Syn PFF injection, and the FABP3 ligand MF1 represents an attractive therapeutic candidate for α-synucleinopathy.

The role of glia in Parkinson's disease: Emerging concepts and therapeutic applications

Originally believed to primarily affect neurons, Parkinson's disease (PD) has recently been recognized to also affect the functions and integrity of microglia and astroglia, two cell categories of fundamental importance to brain tissue homeostasis, defense, and repair. Both a loss of glial supportive-defensive functions and a toxic gain of glial functions are implicated in the neurodegenerative process. Moreover, the chronic treatment with L-DOPA may cause maladaptive glial plasticity favoring a development of therapy complications. This chapter focuses on the pathophysiology of PD from a glial point of view, presenting this rapidly growing field from the first discoveries made to the most recent developments. We report and compare histopathological and molecular findings from experimental models of PD and human studies. We moreover discuss the important role played by astrocytes in compensatory adaptations taking place during presymptomatic disease stages. We finally describe examples of potential therapeutic applications stemming from an increased understanding of the important roles of glia in PD.

Methods for detecting toxic α-synuclein species as a biomarker for Parkinson's disease

Parkinson's disease (PD) is the most common neurodegenerative movement disorder and is characterized by the accumulation of α-synuclein (α-syn) into insoluble aggregates known as Lewy bodies and Lewy neurites in the brain. However, prior to the formation of these large aggregates, α-syn forms oligomers and small fibrils, which are believed to be the pathogenic species leading to the death of neurons in the substantia nigra in disease. The majority of aggregated α-syn is phosphorylated, and it is thought that this post-translational modification may be critical in disease pathogenesis. Thus, early detection of the toxic forms of α-syn may provide a window of opportunity for an intervention to halt or slow the progression of neurodegeneration in PD. Expression of α-syn is not restricted to the central nervous system and the protein can be found elsewhere, including bodily fluids and peripheral tissues. This review will examine current methods for detecting toxic forms of α-syn in accessible biospecimens and outline emerging techniques that may provide reliable identification of biomarkers for PD.

Propofol Attenuates α-Synuclein Aggregation and Neuronal Damage in a Mouse Model of Ischemic Stroke

α-Synuclein is a soluble monomer abundant in the central nervous system. Aggregates of α-synuclein, consisting of higher-level oligomers and insoluble fibrils, have been observed in many chronic neurological diseases and are implicated in neurotoxicity and neurodegeneration. α-Synuclein has recently been shown to aggregate following acute ischemic stroke, exacerbating neuronal damage. Propofol is an intravenous anesthetic that is commonly used during intravascular embolectomy following acute ischemic stroke. While propofol has demonstrated neuroprotective properties following brain injury, the mechanism of protection in the setting of ischemic stroke is unclear. In this study, propofol administration significantly reduced the neurotoxic aggregation of α-synuclein, decreased the infarct area, and attenuated the neurological deficits after ischemic stroke in a mouse model. We then demonstrated that the propofol-induced reduction of α-synuclein aggregation was associated with increased mammalian target of rapamycin/ribosomal protein S6 kinase beta-1 signaling pathway activity and reduction of the excessive autophagy occurring after acute ischemic stroke.

Novel fatty acid-binding protein 3 ligand inhibits dopaminergic neuronal death and improves motor and cognitive impairments in Parkinson's disease model mice

The main symptom of Parkinson's disease (PD) is motor dysfunction and remarkably approximately 30-40% of PD patients exhibit cognitive impairments. Recently, we have developed MF8, a heart-type fatty acid-binding protein (FABP3)-specific ligand, which can inhibit α-synuclein (α-syn) oligomerization induced by arachidonic acid in FABP3 overexpressing neuro2A cells. The present study aimed to determine whether MF8 attenuates dopaminergic neuronal death and motor and cognitive impairments in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced PD mice model. MF8 can penetrate the blood-brain barrier and its peak brain concentration (21.5 ± 2.1 nM) was achieved 6 h after the oral administration (1.0 mg/kg). We also compared its effects and pharmacological action with those of L-DOPA (3,4-dihydroxy-l-phenylalanine). PD model mice were developed by administering MPTP (25 mg/kg, i.p.) once a day for five consecutive days. Twenty-four hours after the final MPTP injection, mice were administered MF8 (0.3, 1.0 mg/kg, p.o.) or L-DOPA (25 mg/kg, i.p.) once a day for 28 consecutive days and subjected to behavioral and histochemical studies. MF8 (1.0 mg/kg, p.o.), but not L-DOPA, inhibited the dopaminergic neuronal death in the ventral tegmental area and the substantia nigra pars compacta region of the MPTP-treated mice. MF8 also improved both, motor and cognitive functions, while L-DOPA ameliorated only motor dysfunction. Taken together, our results showed that MF8 attenuated the MPTP-induced dopaminergic neuronal death associated with PD pathology. We present MF8 as a novel disease-modifying therapeutic molecule for PD, which acts via a mechanism different from that of L-DOPA.

Analysis of α-synuclein species enriched from cerebral cortex of humans with sporadic dementia with Lewy bodies

Since researchers identified α-synuclein as the principal component of Lewy bodies and Lewy neurites, studies have suggested that it plays a causative role in the pathogenesis of dementia with Lewy bodies and other ‘synucleinopathies’. While α-synuclein dyshomeostasis likely contributes to the neurodegeneration associated with the synucleinopathies, few direct biochemical analyses of α-synuclein from diseased human brain tissue currently exist. In this study, we analysed sequential protein extracts from a substantial number of patients with neuropathological diagnoses of dementia with Lewy bodies and corresponding controls, detecting a shift of cytosolic and membrane-bound physiological α-synuclein to highly aggregated forms. We then fractionated aqueous extracts (cytosol) from cerebral cortex using non-denaturing methods to search for soluble, disease-associated high molecular weight species potentially associated with toxicity. We applied these fractions and corresponding insoluble fractions containing Lewy-type aggregates to several reporter assays to determine their bioactivity and cytotoxicity. Ultimately, high molecular weight cytosolic fractions enhances phospholipid membrane permeability, while insoluble, Lewy-associated fractions induced morphological changes in the neurites of human stem cell-derived neurons. While the concentrations of soluble, high molecular weight α-synuclein were only slightly elevated in brains of dementia with Lewy bodies patients compared to healthy, age-matched controls, these observations suggest that a small subset of soluble α-synuclein aggregates in the brain may drive early pathogenic effects, while Lewy body-associated α-synuclein can drive neurotoxicity.

A Role of Cholesterol in Modulating the Binding of α-Synuclein to Synaptic-Like Vesicles

α-Synuclein (αS) is a presynaptic protein whose aggregation is associated with Parkinson's disease (PD). Although the physiological function of αS is still unclear, several lines of evidence indicate that this protein may play a role in the trafficking of synaptic vesicles (SVs) during neurotransmitter release, a task associated with its ability to bind SVs and promote their clustering. It is therefore crucial to identify the cellular factors that modulate this process. To address this question, using nuclear magnetic resonance (NMR) spectroscopy we have characterized the role of cholesterol, a major component of the membrane of SVs, in the binding of αS with synaptic-like vesicles. Our results indicate that cholesterol can act as a modulator of the overall affinity of αS for SVs by reducing the local affinity of the region spanning residues 65-97 in the non-amyloid-β component (NAC) of the protein. The increased population of bound states that expose the region 65-97 to the solvent was found to induce stronger vesicle-vesicle interactions by αS. These results provide evidence that cholesterol modulates the clustering of synaptic vesicles induced by (α)S, and supports the role of the disorder-to-order equilibrium of the NAC region in the modulation of the biological properties of the membrane-bound state of αS.

Alpha-Synuclein Physiology and Pathology: A Perspective on Cellular Structures and Organelles

Alpha-synuclein (α-syn) is localized in cellular organelles of most neurons, but many of its physiological functions are only partially understood. α-syn accumulation is associated with Parkinson's disease, dementia with Lewy bodies, and multiple system atrophy as well as other synucleinopathies; however, the exact pathomechanisms that underlie these neurodegenerative diseases remain elusive. In this review, we describe what is known about α-syn function and pathophysiological changes in different cellular structures and organelles, including what is known about its behavior as a prion-like protein. We summarize current knowledge of α-syn and its pathological forms, covering its effect on each organelle, including aggregation and toxicity in different model systems, with special interest on the mitochondria due to its relevance during the apoptotic process of dopaminergic neurons. Moreover, we explore the effect that α-syn exerts by interacting with chromatin remodeling proteins that add or remove histone marks, up-regulate its own expression, and resume the impairment that α-syn induces in vesicular traffic by interacting with the endoplasmic reticulum. We then recapitulate the events that lead to Golgi apparatus fragmentation, caused by the presence of α-syn. Finally, we report the recent findings about the accumulation of α-syn, indirectly produced by the endolysosomal system. In conclusion, many important steps into the understanding of α-syn have been made using in vivo and in vitro models; however, the time is right to start integrating observational studies with mechanistic models of α-syn interactions, in order to look at a more complete picture of the pathophysiological processes underlying α-synucleinopathies.

Misfolded α-synuclein causes hyperactive respiration without functional deficit in live neuroblastoma cells

The misfolding and aggregation of the largely disordered protein, α-synuclein, is a central pathogenic event that occurs in the synucleinopathies, a group of neurodegenerative disorders that includes Parkinson's disease. While there is a clear link between protein misfolding and neuronal vulnerability, the precise pathogenic mechanisms employed by disease-associated α-synuclein are unresolved. Here, we studied the pathogenicity of misfolded α-synuclein produced using the protein misfolding cyclic amplification (PMCA) assay. To do this, previous published methods were adapted to allow PMCA-induced protein fibrillization to occur under non-toxic conditions. Insight into potential intracellular targets of misfolded α-synuclein was obtained using an unbiased lipid screen of 15 biologically relevant lipids that identified cardiolipin (CA) as a potential binding partner for PMCA-generated misfolded α-synuclein. To investigate whether such an interaction can impact the properties of α-synuclein misfolding, protein fibrillization was carried out in the presence of the lipid. We show that CA both accelerates the rate of α-synuclein fibrillization and produces species that harbour enhanced resistance to proteolysis. Because CA is virtually exclusively expressed in the inner mitochondrial membrane, we then assessed the ability of these misfolded species to alter mitochondrial respiration in live non-transgenic SH-SY5Y neuroblastoma cells. Extensive analysis revealed that misfolded α-synuclein causes hyperactive mitochondrial respiration without causing any functional deficit. These data give strong support for the mitochondrion as a target for misfolded α-synuclein and reveal persistent, hyperactive respiration as a potential upstream pathogenic event associated with the synucleinopathies.This article has an associated First Person interview with the first author of the paper.

The N-terminal Acetylation of α-Synuclein Changes the Affinity for Lipid Membranes but not the Structural Properties of the Bound State

The aggregation of α-synuclein (αS), a protein abundant at presynaptic terminals, is associated with a range of highly debilitating neurodegenerative conditions, including Parkinson’s disease (PD), dementia with Lewy bodies (DLB) and multiple system atrophy (MSA). Emerging evidence indicates that the interaction of αS with lipid membranes defines both its physiological function and pathological effects. The characterisation of the modes of membrane binding by αS is therefore crucial to clarify the balance between normal and aberrant behaviour of this protein. Here we used solid-state nuclear magnetic resonance (ssNMR) spectroscopy to probe the nature of the N-terminally acetylated form of αS (NTAc-αS) bound to synaptic-like lipid vesicles. This post-translational modification is prevalent for the physiological form of αS and modulates the binding to lipid bilayers. By probing the structure, dynamics and membrane topology of NTAc-αS, we found that N-terminal acetylation does not alter significantly the conformational and topological properties of the membrane-bound state of αS, despite increasing its propensity for binding. Taken together, our data and previous characterisations of the cytosolic state of NTAc-αS clarify that the role of the N-terminal acetylation is to regulate the binding affinity of αS for synaptic vesicles without altering the structural properties of the bound state.

Parkinson's disease: proteinopathy or lipidopathy?

Lipids play a more significant role in Parkinson’s disease and its related brain disorders than is currently recognized, supporting a “lipid cascade”. The 14 kDa protein α-synuclein (αS) is strongly associated with Parkinson’s disease (PD), dementia with Lewy bodies (DLB), other synucleinopathies such as multiple system atrophy, and even certain forms of Alzheimer’s disease. Rigorously deciphering the biochemistry of αS in native systems is the key to developing treatments. αS is highly expressed in the brain, the second most lipid-rich organ, and has been proposed to be a lipid-binding protein that physiologically interacts with phospholipids and fatty acids (FAs). αS-rich cytoplasmic inclusions called Lewy bodies and Lewy neurites are the hallmark lesions of synucleinopathies. Excess αS–membrane interactions may trigger proteinaceous αS aggregation by stimulating its primary nucleation. However, αS may also exert its toxicity prior to or independent of its self-aggregation, e.g., via excessive membrane interactions, which may be promoted by certain lipids and FAs. A complex αS-lipid landscape exists, which comprises both physiological and pathological states of αS. As novel insights about the composition of Lewy lesions occur, new lipid-related PD drug candidates emerge, and genome-wide association studies (GWAS) increasingly validate new hits in lipid-associated pathways, it seems timely to review our current knowledge of lipids in PD and consider the roles for these pathways in synucleinopathies.Fig. 1

Mechanisms of alpha-synuclein toxicity: An update and outlook

Alpha-synuclein (aSyn) was identified as the main component of inclusions that define synucleinopathies more than 20 years ago. Since then, aSyn has been extensively studied in an attempt to unravel its roles in both physiology and pathology. Today, studying the mechanisms of aSyn toxicity remains in the limelight, leading to the identification of novel pathways involved in pathogenesis. In this chapter, we address the molecular mechanisms involved in synucleinopathies, from aSyn misfolding and aggregation to the various cellular effects and pathologies associated. In particular, we review our current understanding of the mechanisms involved in the spreading of aSyn between different cells, from the periphery to the brain, and back. Finally, we also review recent studies on the contribution of inflammation and the gut microbiota to pathology in synucleinopathies. Despite significant advances in our understanding of the molecular mechanisms involved, we still lack an integrated understanding of the pathways leading to neurodegeneration in PD and other synucleinopathies, compromising our ability to develop novel therapeutic strategies.

Inhibiting Stearoyl-CoA Desaturase Ameliorates α-Synuclein Cytotoxicity

The lack of disease-modifying treatments for neurodegenerative disease stems in part from our rudimentary understanding of disease mechanisms and the paucity of targets for therapeutic intervention. Here we used an integrated discovery paradigm to identify a new therapeutic target for diseases caused by α-synuclein (α-syn), a small lipid-binding protein that misfolds and aggregates in Parkinson's disease and other disorders. Using unbiased phenotypic screening, we identified a series of compounds that were cytoprotective against α-syn-mediated toxicity by inhibiting the highly conserved enzyme stearoyl-CoA desaturase (SCD). Critically, reducing the levels of unsaturated membrane lipids by inhibiting SCD reduced α-syn toxicity in human induced pluripotent stem cell (iPSC) neuronal models. Taken together, these findings suggest that inhibition of fatty acid desaturation has potential as a therapeutic approach for the treatment of Parkinson's disease and other synucleinopathies.

α-Synuclein oligomers mediate the aberrant form of spike-induced calcium release from IP3 receptor

Emerging evidence implicates α-synuclein oligomers as potential culprits in the pathogenesis of Lewy body disease (LBD). Soluble oligomeric α-synuclein accumulation in cytoplasm is believed to modify neuronal activities and intraneural Ca²⁺ dynamics, which augment the metabolic burden in central neurons vulnerable to LBD, although this hypothesis remains to be fully tested. We evaluated how intracellular α-synuclein oligomers affect the neuronal excitabilities and Ca²⁺ dynamics of pyramidal neurons in neocortical slices from mice. Intracellular application of α-synuclein containing stable higher-order oligomers (αSNo) significantly reduced spike frequency during current injection, elongated the duration of spike afterhyperpolarization (AHP), and enlarged AHP current charge in comparison with that of α-synuclein without higher-order oligomers. This αSNo-mediated alteration was triggered by spike-induced Ca²⁺ release from inositol trisphosphate receptors (IP₃R) functionally coupled with L-type Ca²⁺ channels and SK-type K⁺ channels. Further electrophysiological and immunochemical observations revealed that α-synuclein oligomers greater than 100 kDa were directly associated with calcium-binding protein 1, which is responsible for regulating IP₃R gating. They also block Ca²⁺-dependent inactivation of IP₃R, and trigger Ca²⁺-induced Ca²⁺ release from IP₃R during multiple spikes. This aberrant machinery may result in intraneural Ca²⁺ dyshomeostasis and may be the molecular basis for the vulnerability of neurons in LBD brains.

Fatty Acid-Binding Protein 3 is Critical for α-Synuclein Uptake and MPP+-Induced Mitochondrial Dysfunction in Cultured Dopaminergic Neurons

α-Synuclein is an abundant neuronal protein that accumulates in insoluble inclusions in Parkinson′s disease and other synucleinopathies. Fatty acids partially regulate α-Synuclein accumulation, and mesencephalic dopaminergic neurons highly express fatty acid-binding protein 3 (FABP3). We previously demonstrated that FABP3 knockout mice show decreased α-Synuclein oligomerization and neuronal degeneration of tyrosine hydroxylase (TH)-positive neurons in vivo. In this study, we newly investigated the importance of FABP3 in α-Synuclein uptake, 1-methyl-4-phenylpyridinium (MPP⁺)-induced axodendritic retraction, and mitochondrial dysfunction. To disclose the issues, we employed cultured mesencephalic neurons derived from wild type or FABP3^−/− C57BL6 mice and performed immunocytochemical analysis. We demonstrated that TH⁺ neurons from FABP3^+/+ mice take up α-Synuclein monomers while FABP3^−/− TH⁺ neurons do not. The formation of filamentous α-Synuclein inclusions following treatment with MPP⁺ was observed only in FABP3^+/+, and not in FABP3^−/− neurons. Notably, detailed morphological analysis revealed that FABP^−/− neurons did not exhibit MPP⁺-induced axodendritic retraction. Moreover, FABP3 was also critical for MPP⁺-induced reduction of mitochondrial activity and the production of reactive oxygen species. These data indicate that FABP3 is critical for α-Synuclein uptake in dopaminergic neurons, thereby preventing synucleinopathies, including Parkinson′s disease.

Cell models of lipid-rich α-synuclein aggregation validate known modifiers of α-synuclein biology and identify stearoyl-CoA desaturase

Misfolding and accumulation of the protein α-synuclein (αS) inside nerve cells characterize Parkinson’s disease (PD) and related brain diseases, for which no disease-modifying therapies exist. Robust cell models are needed that recapitulate abnormal αS folding/accumulation in real time, especially for compound screening. We took advantage of the engineered αS “3K” (E35K+E46K+E61K) mutation, which amplifies the familial PD-causing E46K and readily forms round inclusions. We rescued the inclusions with known αS modulators and then screened a ∼2,000-compound library. We identified the potential therapeutic target stearoyl-CoA desaturase; its inhibition cleared αS inclusions, in accord with the effects of conditioning in saturated fatty acids. We propose a model for how fatty acids serve as key modulators of cellular αS homeostasis.

Microscopy of Lewy bodies in Parkinson’s disease (PD) suggests they are not solely filamentous deposits of α-synuclein (αS) but also contain vesicles and other membranous material. We previously reported the existence of native αS tetramers/multimers and described engineered mutations of the αS KTKEGV repeat motifs that abrogate the multimers. The resultant excess monomers accumulate in lipid membrane-rich inclusions associated with neurotoxicity exceeding that of natural familial PD mutants, such as E46K. Here, we use the αS “3K” (E35K+E46K+E61K) engineered mutation to probe the mechanisms of reported small-molecule modifiers of αS biochemistry and then identify compounds via a medium-throughput automated screen. αS 3K, which forms round, vesicle-rich inclusions in cultured neurons and causes a PD-like, l-DOPA–responsive motor phenotype in transgenic mice, was fused to YFP, and fluorescent inclusions were quantified. Live-cell microscopy revealed the highly dynamic nature of the αS inclusions: for example, their rapid clearance by certain known modulators of αS toxicity, including tacrolimus (FK506), isradipine, nilotinib, nortriptyline, and trifluoperazine. Our automated 3K cellular screen identified inhibitors of stearoyl-CoA desaturase (SCD) that robustly prevent the αS inclusions, reduce αS 3K neurotoxicity, and prevent abnormal phosphorylation and insolubility of αS E46K. SCD inhibition restores the E46K αS multimer:monomer ratio in human neurons, and it actually increases this ratio for overexpressed wild-type αS. In accord, conditioning 3K cells in saturated fatty acids rescued, whereas unsaturated fatty acids worsened, the αS phenotypes. Our cellular screen allows probing the mechanisms of synucleinopathy and refining drug candidates, including SCD inhibitors and other lipid modulators.

Blunting neuroinflammation with resolvin D1 prevents early pathology in a rat model of Parkinson's disease

Neuroinflammation is one of the hallmarks of Parkinson’s disease (PD) and may contribute to midbrain dopamine (DA) neuron degeneration. Recent studies link chronic inflammation with failure to resolve early inflammation, a process operated by specialized pro-resolving mediators, including resolvins. However, the effects of stimulating the resolution of inflammation in PD – to modulate disease progression – still remain unexplored. Here we show that rats overexpressing human α-synuclein (Syn) display altered DA neuron properties, reduced striatal DA outflow and motor deficits prior to nigral degeneration. These early alterations are coupled with microglia activation and perturbations of inflammatory and pro-resolving mediators, namely IFN-γ and resolvin D1 (RvD1). Chronic and early RvD1 administration in Syn rats prevents central and peripheral inflammation, as well as neuronal dysfunction and motor deficits. We also show that endogenous RvD1 is decreased in human patients with early-PD. Our results suggest there is an imbalance between neuroinflammatory and pro-resolving processes in PD.

Resolvins are endogenous lipids with pro-resolving activity. Here the authors find that rats overexpressing human α-synuclein show defects in dopamine signalling before dopamine cell loss, and that this is associated with low Resolvin D1 levels and neuroinflammation.

Lipid and Lipid Raft Alteration in Aging and Neurodegenerative Diseases: A Window for the Development of New Biomarkers

Lipids in the brain are major components playing structural functions as well as physiological roles in nerve cells, such as neural communication, neurogenesis, synaptic transmission, signal transduction, membrane compartmentalization, and regulation of gene expression. Determination of brain lipid composition may provide not only essential information about normal brain functioning, but also about changes with aging and diseases. Indeed, deregulations of specific lipid classes and lipid homeostasis have been demonstrated in neurodegenerative disorders such as Alzheimer's disease (AD) and Parkinson's disease (PD). Furthermore, recent studies have shown that membrane microdomains, named lipid rafts, may change their composition in correlation with neuronal impairment. Lipid rafts are key factors for signaling processes for cellular responses. Lipid alteration in these signaling platforms may correlate with abnormal protein distribution and aggregation, toxic cell signaling, and other neuropathological events related with these diseases. This review highlights the manner lipid changes in lipid rafts may participate in the modulation of neuropathological events related to AD and PD. Understanding and characterizing these changes may contribute to the development of novel and specific diagnostic and prognostic biomarkers in routinely clinical practice.

XBP-1 Remodels Lipid Metabolism to Extend Longevity

The endoplasmic reticulum unfolded protein response (UPRER) is a cellular stress response that maintains homeostasis within the secretory pathway, regulates glucose and lipid metabolism, and influences longevity. To ask whether this role in lifespan determination depends upon metabolic intermediaries, we metabotyped C. elegans expressing the active form of the UPRER transcription factor XBP-1, XBP-1s, and found many metabolic changes. These included reduced levels of triglycerides and increased levels of oleic acid (OA), a monounsaturated fatty acid associated with lifespan extension in C. elegans. Here, we show that constitutive XBP-1s expression increases the activity of lysosomal lipases and upregulates transcription of the Δ9 desaturase FAT-6, which is required for the full lifespan extension induced by XBP-1s. Dietary OA supplementation increases the lifespan of wild-type, but not xbp-1s-expressing animals and enhances proteostasis. These results suggest that modulation of lipid metabolism by XBP-1s contributes to its downstream effects on protein homeostasis and longevity.

Antibodies against alpha-synuclein: tools and therapies

Synucleinopathies including Parkinson's disease, dementia with Lewy bodies and multiple system atrophy are characterized by the abnormal accumulation and propagation of α-synuclein (α-syn) pathology in the central and peripheral nervous system as Lewy bodies or glial cytoplasmic inclusions. Several antibodies against α-syn have been developed since it was first detected as the major component of Lewy bodies and glial cytoplasmic inclusions. Over the years, researchers have generated specific antibodies that alleviate the accumulation of intracellular aggregated α-syn and associated pathology in cellular and preclinical models of synucleinopathies. So far, antibodies have been the first choice as tools for research and diagnosis and currently, a wide variety of antibody fragments have been developed as an alternative to full-length antibodies for increasing its therapeutic usefulness. Recently, conformation specific antibody-based approaches have been found to be promising as therapeutic strategies, both to block α-syn aggregation and ameliorate the resultant cytotoxicity, and as diagnostic tools. In this review, we summarize different α-syn specific antibodies and provide their usefulness in tackling synucleinopathies. This article is part of the Special Issue "Synuclein".

Amphiphilic surface chemistry of fullerenols is necessary for inhibiting the amyloid aggregation of alpha-synuclein NACore

Featuring small sizes, caged structures, low cytotoxicity and the capability to cross biological barriers, fullerene hydroxy derivatives named fullerenols have been explored as nanomedicinal candidates for amyloid inhibition. Understanding the surface chemistry effect of hydroxylation extents and the corresponding amyloid inhibition mechanisms is necessary for enabling applications of fullerenols and also future designs of nanomedicines in mitigating amyloid aggregation. Here, we investigated effects of C60(OH)n with n = 0-40 on the aggregation of NACore (the amyloidogenic core region of the non-amyloid-β component in α-synuclein), the amyloidogenic core of α-synuclein, by computational simulations, transmission electron microscopy (TEM), Fourier transform infrared (FTIR) spectroscopy, thioflavin-T (ThT) fluorescence kinetics and viability assays. Computationally, NACore assembled into cross-β aggregates via intermediates including β-barrels, which are postulated as toxic oligomers of amyloid aggregation. Hydrophobic C60 preferred to self-assemble, and NACore bound to the surface of C60 nano-clusters formed β-sheet rich aggregates - i.e., having little inhibition effect. Amphiphilic C60(OH)n with n = 4-20 displayed significant inhibition effects on NACore aggregation, where hydrogen bonding between hydroxyls and peptide backbones interrupted the formation of β-sheets between peptides adsorbed onto the surfaces of fullerenols or fullerenol nano-assemblies due to hydrophobic interactions. Thus, both cross-β aggregates and β-barrel intermediates were significantly suppressed. With hydroxyls increased to 40, fullerenols became highly hydrophilic with reduced peptide binding and thus an inhibition effect on amyloid aggregation. ThT, FTIR and TEM characterization of C60(OH)n with n = 0, 24, & 40 confirmed the computational predictions. Our results and others underscore the importance of amphiphilic surface chemistry and the capability of polar groups in forming hydrogen bonds with peptide backbones to render amyloid inhibition, offering a new insight for de-novo design of anti-amyloid inhibitors.

Glatiramer Acetate Reverses Motor Dysfunction and the Decrease in Tyrosine Hydroxylase Levels in a Mouse Model of Parkinson's Disease

Parkinson's disease (PD) is the second most common neurodegenerative disease and there are no effective treatments that either slow or reverse the degeneration of the dopamine (DA) pathway. Using a 4-week progressive MPTP (1-methyl-1,2,3,6-tetrahydropyridine) neurotoxin model of PD, which is characterized by neuroinflammation, loss of nigrostriatal DA, and motor dysfunction, as seen in patients with PD, we tested whether post-MPTP treatment with glatiramer acetate (GA), an immunomodulatory drug, could reverse these changes. GA restored the grip dysfunction and gait abnormalities that were evident in the MPTP treated group. The reversal of the motor dysfunction was attributable to the substantial recovery in tyrosine hydroxylase (TH) protein expression in the striatum. Within the substantia nigra pars compacta, surface cell count analysis showed a slight increase in TH+ cells following GA treatment in the MPTP group, which was not statistically different from the vehicle (VEH) group. This was associated with the recovery of BDNF (brain derived neurotrophic factor) protein levels and a reduction in the microglial marker, IBA1, protein expression within the midbrain. Alpha synuclein (syn-1) levels within the midbrain and striatum were decreased following MPTP, while GA facilitated recovery to VEH levels in the striatum in the MPTP group. Although DA tissue analysis revealed no significant increase in striatal DA or 3,4-Dihydroxyphenylacetic acid levels (DOPAC) in the MPTP group treated with GA, DA turnover (DOPAC/DA) recovered back to VEH levels following GA treatment. GA treatment effectively reversed clinical (motor dysfunction) and pathology (TH, IBA1, BDNF expression) of PD in a murine model.

Dysfunction of Cellular Proteostasis in Parkinson's Disease

Despite decades of research, current therapeutic interventions for Parkinson’s disease (PD) are insufficient as they fail to modify disease progression by ameliorating the underlying pathology. Cellular proteostasis (protein homeostasis) is an essential factor in maintaining a persistent environment for neuronal activity. Proteostasis is ensured by mechanisms including regulation of protein translation, chaperone-assisted protein folding and protein degradation pathways. It is generally accepted that deficits in proteostasis are linked to various neurodegenerative diseases including PD. While the proteasome fails to degrade large protein aggregates, particularly alpha-synuclein (α-SYN) in PD, drug-induced activation of autophagy can efficiently remove aggregates and prevent degeneration of dopaminergic (DA) neurons. Therefore, maintenance of these mechanisms is essential to preserve all cellular functions relying on a correctly folded proteome. The correlations between endoplasmic reticulum (ER) stress and the unfolded protein response (UPR) that aims to restore proteostasis within the secretory pathway are well-established. However, while mild insults increase the activity of chaperones, prolonged cell stress, or insufficient adaptive response causes cell death. Modulating the activity of molecular chaperones, such as protein disulfide isomerase which assists refolding and contributes to the removal of unfolded proteins, and their associated pathways may offer a new approach for disease-modifying treatment. Here, we summarize some of the key concepts and emerging ideas on the relation of protein aggregation and imbalanced proteostasis with an emphasis on PD as our area of main expertise. Furthermore, we discuss recent insights into the strategies for reducing the toxic effects of protein unfolding in PD by targeting the ER UPR pathway.

The role of lipids in α-synuclein misfolding and neurotoxicity

The misfolding and aggregation of α-synuclein (αsyn) in the central nervous system is associated with a group of neurodegenerative disorders referred to as the synucleinopathies. In addition to being a pathological hallmark of disease, it is now well-established that upon misfolding, αsyn acquires pathogenic properties, such as neurotoxicity, that can contribute to disease development. The mechanisms that produce αsyn misfolding and the molecular events underlying the neuronal damage caused by these misfolded species are not well-defined. A consistent observation that may be relevant to αsyn's pathogenicity is its ability to associate with lipids. This appears important not only to how αsyn aggregates, but also to the mechanism by which the misfolded protein causes intracellular damage. This review discusses the current literature reporting a role of lipids in αsyn misfolding and neurotoxicity in various synucleinopathy disorders and provides an overview of current methods to assess protein misfolding and pathogenicity both in vitro and in vivo.

Inhibiting and catalysing amyloid fibrillation at dynamic lipid interfaces

Proteins are naturally exposed to diverse interfaces in living organisms, from static solid to dynamic fluid. Solid interfaces can enrich proteins as corona, and then catalyze, retard or hinder amyloid fibrillation. But fluid interfaces abundant in biology have rarely been studied for their correlation with protein fibrillation. Unsaturated fatty acids own growing essential roles in diet, whose fluid interfaces are found in vitro to catalyze amyloid fibrillation under certain physiologic conditions. It is determined by the location of double bonds within alkyl chains as well as the presence of physical shear. Docosahexaenoic acid (DHA) shows low catalysis because its unique alkyl chain does not favor to stabilize cross-β nucleus. Mixtures of different fatty acids also decelerate their catalytic activity. High catalysis poses an unprecedented approach to synthesize biologic nanofibrils as one-dimensional (1D) building blocks of functional hybrids. Fibrillation inhibition implied that appropriate diet would be a preventive strategy for amyloid-related diseases. Thus these results may find their significances in diverse fields of science as chemistry, biotechnology, nanotechnology, nutrition, amyloid pathobiology and nanomedicine.

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

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

Parkinson's and Lewy body dementia CSF biomarkers

The clinical diagnosis of Parkinson's disease (PD) and Dementia with Lewy bodies (DLB) is challenging due to highly variable clinical presentation and clinical and pathological overlap with other neurodegenerative diseases. Since cerebrospinal fluid (CSF) mirrors the pathological changes taking place in the brain, it represents a promising source of biomarkers. With respect to classical AD biomarkers, low CSF Aβ₄₂ levels have shown a robust prognostic value in terms of development of cognitive impairment in PD and DLB. In the differential diagnosis between AD and DLB, a potential role of t-tau, p-tau and Aβ₄₂/Aβ₃₈ ratio has been demonstrated. Regarding CSF α-synuclein (α-syn) species, lower levels of total α-synuclein (t-α-syn) and higher concentration of oligomeric-α-synuclein (o-α-syn) and phosphorylated α-synuclein (p-α-syn) have been observed in PD. Furthermore, the detection of "pro-aggregating" α-synuclein has enabled the discrimination of patients affected by synucleinopathies with high sensitivity and specificity. New promising biomarkers are emerging: GCase activity (reduced in PD and DLB patients vs. controls), CSF/serum albumin ratio (increased in PD and DLB), fatty-acid-binding protein (increased in AD and DLB vs. PD), visinin-like protein-1 (increased in AD vs. DLB) and monoamines (useful in differential diagnosis among PD and DLB). These encouraging results need to be confirmed by future studies.