Reducing C-terminal-truncated alpha-synuclein by immunotherapy attenuates neurodegeneration and propagation in Parkinson's disease-like models

Autoantibodies targeting neuronal proteins as biomarkers for neurodegenerative diseases

Neurodegenerative diseases (NDDs) are associated with the accumulation of a range of misfolded proteins across the central nervous system and related autoimmune responses, including the generation of antibodies and the activation of immune cells. Both innate and adaptive immunity become mobilized, leading to cellular and humoral effects. The role of humoral immunity in disease onset and progression remains to be elucidated with rising evidence suggestive of positive (protection, repair) and negative (injury, toxicity) outcomes. In this study, we review advances in research of neuron-targeting autoantibodies in the most prevalent NDDs. We discuss their biological origin, molecular diversity and changes in the course of diseases, consider their relevance to the initiation and progression of pathology as well as diagnostic and prognostic significance. It is suggested that the emerging autoimmune aspects of NDDs not only could facilitate the early detection but also might help to elucidate previously unknown facets of pathobiology with relevance to the development of precision medicine.

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

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

Conformation-specific Antibodies Targeting Aggregated Forms of α-synuclein Block the Propagation of Synucleinopathy

Abnormal aggregation of α-synuclein is a key element in the pathogenesis of several neurodegenerative diseases, including Parkinson's disease (PD), dementia with Lewy bodies, and multiple system atrophy. α-synuclein aggregation spreads through various brain regions during the course of disease progression, a propagation that is thought to be mediated by the secretion and subsequent uptake of extracellular α-synuclein aggregates between neuronal cells. Thus, aggregated forms of this protein have emerged as promising targets for disease-modifying therapy for PD and related diseases. Here, we generated and characterized conformation-specific antibodies that preferentially recognize aggregated forms of α-synuclein. These antibodies promoted phagocytosis of extracellular α-synuclein aggregates by microglial cells and interfered with cell-to-cell propagation of α-synuclein. In an α-synuclein transgenic model, passive immunization with aggregate-specific antibodies significantly ameliorated pathological phenotypes, reducing α-synuclein aggregation, gliosis, inflammation, and neuronal loss. These results suggest that conformation-specific antibodies targeting α-synuclein aggregates are promising therapeutic agents for PD and related synucleinopathies.

The C-terminal tail of α-synuclein protects against aggregate replication but is critical for oligomerization

Aggregation of the 140-residue protein α-synuclein (αSN) is a key factor in the etiology of Parkinson’s disease. Although the intensely anionic C-terminal domain (CTD) of αSN does not form part of the amyloid core region or affect membrane binding ability, truncation or reduction of charges in the CTD promotes fibrillation through as yet unknown mechanisms. Here, we study stepwise truncated CTDs and identify a threshold region around residue 121; constructs shorter than this dramatically increase their fibrillation tendency. Remarkably, these effects persist even when as little as 10% of the truncated variant is mixed with the full-length protein. Increased fibrillation can be explained by a substantial increase in self-replication, most likely via fragmentation. Paradoxically, truncation also suppresses toxic oligomer formation, and oligomers that can be formed by chemical modification show reduced membrane affinity and cytotoxicity. These remarkable changes correlate to the loss of negative electrostatic potential in the CTD and highlight a double-edged electrostatic safety guard.

Farzadfard et al. present a comprehensive analysis of a range of C-terminal truncations of aSN, linking the importance of high C-terminus charge for decreased fibrillation rates. The ability to formation oligomers, to disrupt synthetic vesicles and cell toxicity was reduced with truncated aSN, aiding in understanding of the intramolecular interactions of aSN which promote/inhibit aggregation.

Passive Immunization in Alpha-Synuclein Preclinical Animal Models

Alpha-synucleinopathies include Parkinson’s disease, dementia with Lewy bodies, pure autonomic failure and multiple system atrophy. These are all progressive neurodegenerative diseases that are characterized by pathological misfolding and accumulation of the protein alpha-synuclein (αsyn) in neurons, axons or glial cells in the brain, but also in other organs. The abnormal accumulation and propagation of pathogenic αsyn across the autonomic connectome is associated with progressive loss of neurons in the brain and peripheral organs, resulting in motor and non-motor symptoms. To date, no cure is available for synucleinopathies, and therapy is limited to symptomatic treatment of motor and non-motor symptoms upon diagnosis. Recent advances using passive immunization that target different αsyn structures show great potential to block disease progression in rodent studies of synucleinopathies. However, passive immunotherapy in clinical trials has been proven safe but less effective than in preclinical conditions. Here we review current achievements of passive immunotherapy in animal models of synucleinopathies. Furthermore, we propose new research strategies to increase translational outcome in patient studies, (1) by using antibodies against immature conformations of pathogenic αsyn (monomers, post-translationally modified monomers, oligomers and protofibrils) and (2) by focusing treatment on body-first synucleinopathies where damage in the brain is still limited and effective immunization could potentially stop disease progression by blocking the spread of pathogenic αsyn from peripheral organs to the brain.

T cells, α-synuclein and Parkinson disease

The notion that autoimmune responses to α-synuclein may be involved in the pathogenesis of this disorder stems from reports that mutations in α-synuclein or certain alleles of the major histocompatibility complex (MHC) are associated with the disease and that dopaminergic and norepinephrinergic neurons in the midbrain can present antigenic epitopes. Here, we discuss recent evidence that a defined set of peptides derived from α-synuclein act as antigenic epitopes displayed by specific MHC alleles and drive helper and cytotoxic T cell responses in patients with PD. Moreover, phosphorylated α-synuclein may activate T cell responses in a less restricted manner in PD. While the roles for the acquired immune system in disease pathogenesis remain unknown, preclinical animal models and in vitro studies indicate that T cells may interact with neurons and exert effects related to neuronal death and neuroprotection. These findings suggest that therapeutics that target T cells and ameliorate the incidence or disease severity of inflammatory bowel disorders or CNS autoimmune diseases such as multiple sclerosis may be useful in PD.

Efficacy and immunogenicity of MultiTEP-based DNA vaccines targeting human α-synuclein: prelude for IND enabling studies

Accumulation of misfolded proteins such as amyloid-β (Aβ), tau, and α-synuclein (α-Syn) in the brain leads to synaptic dysfunction, neuronal damage, and the onset of relevant neurodegenerative disorder/s. Dementia with Lewy bodies (DLB) and Parkinson’s disease (PD) are characterized by the aberrant accumulation of α-Syn intracytoplasmic Lewy body inclusions and dystrophic Lewy neurites resulting in neurodegeneration associated with inflammation. Cell to cell propagation of α-Syn aggregates is implicated in the progression of PD/DLB, and high concentrations of anti-α-Syn antibodies could inhibit/reduce the spreading of this pathological molecule in the brain. To ensure sufficient therapeutic concentrations of anti-α-Syn antibodies in the periphery and CNS, we developed four α-Syn DNA vaccines based on the universal MultiTEP platform technology designed especially for the elderly with immunosenescence. Here, we are reporting on the efficacy and immunogenicity of these vaccines targeting three B-cell epitopes of hα-Syn aa85–99 (PV-1947D), aa109–126 (PV-1948D), aa126–140 (PV-1949D) separately or simultaneously (PV-1950D) in a mouse model of synucleinopathies mimicking PD/DLB. All vaccines induced high titers of antibodies specific to hα-Syn that significantly reduced PD/DLB-like pathology in hα-Syn D line mice. The most significant reduction of the total and protein kinase resistant hα-Syn, as well as neurodegeneration, were observed in various brain regions of mice vaccinated with PV-1949D and PV-1950D in a sex-dependent manner. Based on these preclinical data, we selected the PV-1950D vaccine for future IND enabling preclinical studies and clinical development.

Targeting alpha-synuclein via the immune system in Parkinson's disease: Current vaccine therapies

Parkinson's disease (PD) is the second most common neurodegenerative disorder and is defined pathologically by the abnormal accumulation of the presynaptic protein alpha-synuclein (aSyn) in the form of Lewy bodies and Lewy neurites and loss of midbrain dopaminergic neurons in the substantia nigra pars compacta. Because of aSyn's involvement in both sporadic and familial forms of PD, it has become a key target for the development of novel therapeutics. Aberrant aSyn is associated with multiple mechanisms of neuronal dysfunction and degeneration including inflammation, impaired mitochondrial function, altered protein degradation systems, and oxidative stress. Inflammation, in particular, has emerged as a potential significant contributor early in the disease making it an attractive target for disease modification and neuroprotection. Thus, immunotherapies targeting aSyn are currently being investigated in pre-clinical and clinical trials. The focus of this review is to highlight the role of aSyn in neuroinflammation and discuss the current status of aSyn-directed immunotherapies in pre-clinical and clinical trials for PD.

Pathophysiology of neurodegenerative diseases: An interplay among axonal transport failure, oxidative stress, and inflammation?

Neurodegenerative diseases (NDs) are heterogeneous neurological disorders characterized by a progressive loss of selected neuronal populations. A significant risk factor for most NDs is aging. Considering the constant increase in life expectancy, NDs represent a global public health burden. Axonal transport (AT) is a central cellular process underlying the generation and maintenance of neuronal architecture and connectivity. Deficits in AT appear to be a common thread for most, if not all, NDs. Neuroinflammation has been notoriously difficult to define in relation to NDs. Inflammation is a complex multifactorial process in the CNS, which varies depending on the disease stage. Several lines of evidence suggest that AT defect, axonopathy and neuroinflammation are tightly interlaced. However, whether these impairments play a causative role in NDs or are merely a downstream effect of neuronal degeneration remains unsettled. We still lack reliable information on the temporal relationship between these pathogenic mechanisms, although several findings suggest that they may occur early during ND pathophysiology. This article will review the latest evidence emerging on whether the interplay between AT perturbations and some aspects of CNS inflammation can participate in ND etiology, analyze their potential as therapeutic targets, and the urge to identify early surrogate biomarkers.

Therapeutics in the Pipeline Targeting α-Synuclein for Parkinson's Disease

Parkinson's disease (PD) is the second most common neurodegenerative disorder and the fastest growing neurologic disease in the world, yet no disease-modifying therapy is available for this disabling condition. Multiple lines of evidence implicate the protein α-synuclein (α-Syn) in the pathogenesis of PD, and as such, there is intense interest in targeting α-Syn for potential disease modification. α-Syn is also a key pathogenic protein in other synucleionpathies, most commonly dementia with Lewy bodies. Thus, therapeutics targeting this protein will have utility in these disorders as well. Here we discuss the various approaches that are being investigated to prevent and mitigate α-Syn toxicity in PD, including clearing its pathologic aggregates from the brain using immunization strategies, inhibiting its misfolding and aggregation, reducing its expression level, enhancing cellular clearance mechanisms, preventing its cell-to-cell transmission within the brain and perhaps from the periphery, and targeting other proteins associated with or implicated in PD that contribute to α-Syn toxicity. We also discuss the therapeutics in the pipeline that harness these strategies. Finally, we discuss the challenges and opportunities for the field in the discovery and development of therapeutics for disease modification in PD. SIGNIFICANCE STATEMENT: PD is the second most common neurodegenerative disorder, for which disease-modifying therapies remain a major unmet need. A large body of evidence points to α-synuclein as a key pathogenic protein in this disease as well as in dementia with Lewy bodies, making it of leading therapeutic interest. This review discusses the various approaches being investigated and progress made to date toward discovering and developing therapeutics that would slow and stop progression of these disabling diseases.

Therapeutic Strategies for Immune Transformation in Parkinson's Disease

Dysregulation of innate and adaptive immunity can lead to alpha-synuclein (α-syn) misfolding, aggregation, and post-translational modifications in Parkinson's disease (PD). This process is driven by neuroinflammation and oxidative stress, which can contribute to the release of neurotoxic oligomers that facilitate dopaminergic neurodegeneration. Strategies that promote vaccines and antibodies target the clearance of misfolded, modified α-syn, while gene therapy approaches propose to deliver intracellular single chain nanobodies to mitigate α-syn misfolding, or to deliver neurotrophic factors that support neuronal viability in an otherwise neurotoxic environment. Additionally, transformative immune responses provide potential targets for PD therapeutics. Anti-inflammatory drugs represent one strategy that principally affects innate immunity. Considerable research efforts have focused on transforming the balance of pro-inflammatory effector T cells (Teffs) to favor regulatory T cell (Treg) activity, which aims to attenuate neuroinflammation and support reparative and neurotrophic homeostasis. This approach serves to control innate microglial neurotoxic activities and may facilitate clearance of α-syn aggregates accordingly. More recently, changes in the intestinal microbiome have been shown to alter the gut-immune-brain axis leading to suppressed leakage of bacterial products that can promote peripheral inflammation and α-syn misfolding. Together, each of the approaches serves to interdict chronic inflammation associated with disordered immunity and neurodegeneration. Herein, we examine research strategies aimed at improving clinical outcomes in PD.

Immunotherapeutic interventions in Parkinson's disease: Focus on α-Synuclein

Parkinson's disease (PD) is a neurodegenerative disorder characterized classically by motor manifestations. However, nonmotor symptoms appear early in the course of the disease progression, making both diagnosis and treatment difficult. The pathology of PD is complicated by the accumulation and aggregation of misfolded proteins in intracellular cytoplasmic inclusions called Lewy bodies (LBs). The main toxic component of LBs is the protein α-Synuclein which plays a pivotal role in PD pathogenesis. α-Synuclein can propagate from cell-to-cell exhibiting prion-like properties and spread PD pathology throughout the central nervous system. Immunotherapeutic interventions in PD, both active and passive immunization, have targeted α-Synuclein in both experimental models and clinical trials. In addition, targeting the hyperactive inflammation in PD also holds promise in designing potential immunotherapeutics. The inflammatory and proteotoxic pathways are interlinked and contribute immensely to the disease pathology. In this chapter, we critically review the targets of immunotherapeutic interventions in PD, focusing on the pathogenetic mechanisms of PD, particularly neuroinflammation and α-Synuclein misfolding, aggregation, and propagation. We thoroughly summarized the various immunotherapeutic strategies designed to treat PD-in vitro, in vivo, and clinical trials. The development of these targeted immunotherapies could open a new avenue in the treatment of patients with PD.

Toward a Disease-Modifying Therapy of Alpha-Synucleinopathies: New Molecules and New Approaches Came into the Limelight

The accumulation of the various products of alpha-synuclein aggregation has been associated with the etiology and pathogenesis of several neurodegenerative conditions, including both familial and sporadic forms of Parkinson’s disease (PD) and dementia with Lewy bodies (DLB). It is now well established that the aggregation and spread of alpha-synuclein aggregation pathology activate numerous pathogenic mechanisms that contribute to neurodegeneration and, ultimately, to disease progression. Therefore, the development of a safe and effective disease-modifying therapy that limits or prevents the accumulation of the toxic intermediate products of alpha-synuclein aggregation and the spread of alpha-synuclein aggregation pathology could provide significant positive clinical outcomes in PD/DLB cohorts. It has been suggested that this goal can be achieved by reducing the intracellular and/or extracellular levels of monomeric and already aggregated alpha-synuclein. The principal aim of this review is to critically evaluate the potential of therapeutic strategies that target the post-transcriptional steps of alpha-synuclein production and immunotherapy-based approaches to alpha-synuclein degradation in PD/DLB patients. Strategies aimed at the downregulation of alpha-synuclein production are at an early preclinical stage of drug development and, although they have shown promise in animal models of alpha-synuclein aggregation, many limitations need to be resolved before in-human clinical trials can be seriously considered. In contrast, many strategies aimed at the degradation of alpha-synuclein using immunotherapeutic approaches are at a more advanced stage of development, with some in-human Phase II clinical trials currently in progress. Translational barriers for both strategies include the limitations of alpha-synuclein aggregation models, poor understanding of the therapeutic window for the alpha-synuclein knockdown, and variability in alpha-synuclein pathology across patient cohorts. Overcoming such barriers should be the main focus of further studies. However, it is already clear that these strategies do have the potential to achieve a disease-modifying effect in PD and DLB.

Alpha-Synuclein Induced Immune Cells Activation and Associated Therapy in Parkinson's Disease

Parkinson's disease (PD) is a neurodegenerative disorder closely related to immunity. An important aspect of the pathogenesis of PD is the interaction between α-synuclein and a series of immune cells. Studies have shown that accumulation of α-synuclein can induce an autoimmune response that accelerates the progression of PD. This study discusses the mechanisms underlying the interaction between α-synuclein and the immune system. During the development of PD, abnormally accumulated α-synuclein becomes an autoimmune antigen that binds to Toll-like receptors (TLRs) that activate microglia, which differentiate into the microglia type 1 (M1) subtype. The microglia activate intracellular inflammatory pathways, induce the release of proinflammatory cytokines, and promote the differentiation of cluster of differentiation 4 + (CD4 +) T cells into proinflammatory T helper type 1 (Th1) and T helper type 17 (Th17) subtypes. Given the important role of α-synuclein in the immune system of the patients with PD, identifying potential targets of immunotherapy related to α-synuclein is critical for slowing disease progression. An enhanced understanding of immune-associated mechanisms in PD can guide the development of associated therapeutic strategies in the future.

ABBV-0805, a novel antibody selective for soluble aggregated α-synuclein, prolongs lifespan and prevents buildup of α-synuclein pathology in mouse models of Parkinson's disease

A growing body of evidence suggests that aggregated α-synuclein, the major constituent of Lewy bodies, plays a key role in the pathogenesis of Parkinson's disease and related α-synucleinopathies. Immunotherapies, both active and passive, against α-synuclein have been developed and are promising novel treatment strategies for such disorders. Here, we report on the humanization and pharmacological characteristics of ABBV-0805, a monoclonal antibody that exhibits a high selectivity for human aggregated α-synuclein and very low affinity for monomers. ABBV-0805 binds to a broad spectrum of soluble aggregated α-synuclein, including small and large aggregates of different conformations. Binding of ABBV-0805 to pathological α-synuclein was demonstrated in Lewy body-positive post mortem brains of Parkinson's disease patients. The functional potency of ABBV-0805 was demonstrated in several cellular assays, including Fcγ-receptor mediated uptake of soluble aggregated α-synuclein in microglia and inhibition of neurotoxicity in primary neurons. In vivo, the murine version of ABBV-0805 (mAb47) displayed significant dose-dependent decrease of α-synuclein aggregates in brain in several mouse models, both in prophylactic and therapeutic settings. In addition, mAb47 treatment of α-synuclein transgenic mice resulted in a significantly prolonged survival. ABBV-0805 selectively targets soluble toxic α-synuclein aggregates with a picomolar affinity and demonstrates excellent in vivo efficacy. Based on the strong preclinical findings described herein, ABBV-0805 has been progressed into clinical development as a potential disease-modifying treatment for Parkinson's disease.

A Phase II Study to Evaluate the Safety and Efficacy of Prasinezumab in Early Parkinson's Disease (PASADENA): Rationale, Design, and Baseline Data

Background: Currently available treatments for Parkinson's disease (PD) do not slow clinical progression nor target alpha-synuclein, a key protein associated with the disease. Objective: The study objective was to evaluate the efficacy and safety of prasinezumab, a humanized monoclonal antibody that binds aggregated alpha-synuclein, in individuals with early PD. Methods: The PASADENA study is a multicenter, randomized, double-blind, placebo-controlled treatment study. Individuals with early PD, recruited across the US and Europe, received monthly intravenous doses of prasinezumab (1,500 or 4,500 mg) or placebo for a 52-week period (Part 1), followed by a 52-week extension (Part 2) in which all participants received active treatment. Key inclusion criteria were: aged 40-80 years; Hoehn & Yahr (H&Y) Stage I or II; time from diagnosis ≤2 years; having bradykinesia plus one other cardinal sign of PD (e.g., resting tremor, rigidity); DAT-SPECT imaging consistent with PD; and either treatment naïve or on a stable monoamine oxidase B (MAO-B) inhibitor dose. Study design assumptions for sample size and study duration were built using a patient cohort from the Parkinson's Progression Marker Initiative (PPMI). In this report, baseline characteristics are compared between the treatment-naïve and MAO-B inhibitor-treated PASADENA cohorts and between the PASADENA and PPMI populations. Results: Of the 443 patients screened, 316 were enrolled into the PASADENA study between June 2017 and November 2018, with an average age of 59.9 years and 67.4% being male. Mean time from diagnosis at baseline was 10.11 months, with 75.3% in H&Y Stage II. Baseline motor and non-motor symptoms (assessed using Movement Disorder Society-Unified Parkinson's Disease Rating Scale [MDS-UPDRS]) were similar in severity between the MAO-B inhibitor-treated and treatment-naïve PASADENA cohorts (MDS-UPDRS sum of Parts I + II + III [standard deviation (SD)]; 30.21 [11.96], 32.10 [13.20], respectively). The overall PASADENA population (63.6% treatment naïve and 36.4% on MAO-B inhibitor) showed a similar severity in MDS-UPDRS scores (e.g., MDS-UPDRS sum of Parts I + II + III [SD]; 31.41 [12.78], 32.63 [13.04], respectively) to the PPMI cohort (all treatment naïve). Conclusions: The PASADENA study population is suitable to investigate the potential of prasinezumab to slow disease progression in individuals with early PD. Trial Registration: NCT03100149.

Amyloid-β and α-Synuclein Immunotherapy: From Experimental Studies to Clinical Trials

Alzheimer’s disease and Lewy body diseases are the most common causes of neurodegeneration and dementia. Amyloid-beta (Aβ) and alpha-synuclein (αSyn) are two key proteins involved in the pathogenesis of these neurodegenerative diseases. Immunotherapy aims to reduce the harmful effects of protein accumulation by neutralising toxic species and facilitating their removal. The results of the first immunisation trial against Aβ led to a small percentage of meningoencephalitis cases which revolutionised vaccine design, causing a shift in the field of immunotherapy from active to passive immunisation. While the vast majority of immunotherapies have been developed for Aβ and tested in Alzheimer’s disease, the field has progressed to targeting other proteins including αSyn. Despite showing some remarkable results in animal models, immunotherapies have largely failed final stages of clinical trials to date, with the exception of Aducanumab recently licenced in the US by the FDA. Neuropathological findings translate quite effectively from animal models to human trials, however, cognitive and functional outcome measures do not. The apparent lack of translation of experimental studies to clinical trials suggests that we are not obtaining a full representation of the effects of immunotherapies from animal studies. Here we provide a background understanding to the key concepts and challenges involved in therapeutic design. This review further provides a comprehensive comparison between experimental and clinical studies in Aβ and αSyn immunotherapy and aims to determine the possible reasons for the disconnection in their outcomes.

Promising drug targets and associated therapeutic interventions in Parkinson's disease

Parkinson's disease (PD) is one of the most debilitating brain diseases. Despite the availability of symptomatic treatments, response towards the health of PD patients remains scarce. To fulfil the medical needs of the PD patients, an efficacious and etiological treatment is required. In this review, we have compiled the information covering limitations of current therapeutic options in PD, novel drug targets for PD, and finally, the role of some critical beneficial natural products to control the progression of PD.

The subcellular arrangement of alpha-synuclein proteoforms in the Parkinson's disease brain as revealed by multicolor STED microscopy

Various post-translationally modified (PTM) proteoforms of alpha-synuclein (aSyn)-including C-terminally truncated (CTT) and Serine 129 phosphorylated (Ser129-p) aSyn-accumulate in Lewy bodies (LBs) in different regions of the Parkinson's disease (PD) brain. Insight into the distribution of these proteoforms within LBs and subcellular compartments may aid in understanding the orchestration of Lewy pathology in PD. We applied epitope-specific antibodies against CTT and Ser129-p aSyn proteoforms and different aSyn domains in immunohistochemical multiple labelings on post-mortem brain tissue from PD patients and non-neurological, aged controls, which were scanned using high-resolution 3D multicolor confocal and stimulated emission depletion (STED) microscopy. Our multiple labeling setup highlighted a consistent onion skin-type 3D architecture in mature nigral LBs in which an intricate and structured-appearing framework of Ser129-p aSyn and cytoskeletal elements encapsulates a core enriched in CTT aSyn species. By label-free CARS microscopy we found that enrichments of proteins and lipids were mainly localized to the central portion of nigral aSyn-immunopositive (aSyn+) inclusions. Outside LBs, we observed that 122CTT aSyn+ punctae localized at mitochondrial membranes in the cytoplasm of neurons in PD and control brains, suggesting a physiological role for 122CTT aSyn outside of LBs. In contrast, very limited to no Ser129-p aSyn immunoreactivity was observed in brains of non-neurological controls, while the alignment of Ser129-p aSyn in a neuronal cytoplasmic network was characteristic for brains with (incidental) LB disease. Interestingly, Ser129-p aSyn+ network profiles were not only observed in neurons containing LBs but also in neurons without LBs particularly in donors at early disease stage, pointing towards a possible subcellular pathological phenotype preceding LB formation. Together, our high-resolution and 3D multicolor microscopy observations in the post-mortem human brain provide insights into potential mechanisms underlying a regulated LB morphogenesis.

Disease-, region- and cell type specific diversity of α-synuclein carboxy terminal truncations in synucleinopathies

Synucleinopathies, including Parkinson's disease (PD), Lewy body dementia (LBD), Alzheimer's disease with amygdala restricted Lewy bodies (AD/ALB), and multiple system atrophy (MSA) comprise a spectrum of neurodegenerative disorders characterized by the presence of distinct pathological α-synuclein (αSyn) inclusions. Experimental and pathological studies support the notion that αSyn aggregates contribute to cellular demise and dysfunction with disease progression associated with a prion-like spread of αSyn aggregates via conformational templating. The initiating event(s) and factors that contribute to diverse forms of synucleinopathies remain poorly understood. A major post-translational modification of αSyn associated with pathological inclusions is a diverse array of specific truncations within the carboxy terminal region. While these modifications have been shown experimentally to induce and promote αSyn aggregation, little is known about their disease-, region- and cell type specific distribution. To this end, we generated a series of monoclonal antibodies specific to neo-epitopes in αSyn truncated after residues 103, 115, 119, 122, 125, and 129. Immunocytochemical investigations using these new tools revealed striking differences in the αSyn truncation pattern between different synucleinopathies, brain regions and specific cellular populations. In LBD, neuronal inclusions in the substantia nigra and amygdala were positive for αSyn cleaved after residues 103, 119, 122, and 125, but not 115. In contrast, in the same patients' brain αSyn cleaved at residue 115, as well as 103, 119 and 122 were abundant in the dorsal motor nucleus of the vagus. In patients with AD/ALB, these modifications were only weakly or not detected in amygdala αSyn inclusions. αSyn truncated at residues 103, 115, 119, and 125 was readily present in MSA glial cytoplasmic inclusions, but 122 cleaved αSyn was only weakly or not present. Conversely, MSA neuronal pathology in the pontine nuclei was strongly reactive to the αSyn x-122 neo-epitope but did not display any reactivity for αSyn 103 cleavage. These studies demonstrate significant disease-, region- and cell type specific differences in carboxy terminal αSyn processing associated with pathological inclusions that likely contributes to their distinct strain-like prion properties and promotes the diversity displayed in the degrees of these insidious diseases.

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.

Potent inhibitors of toxic alpha-synuclein identified via cellular time-resolved FRET biosensors

We have developed a high-throughput drug discovery platform, measuring fluorescence resonance energy transfer (FRET) with fluorescent alpha-synuclein (αSN) biosensors, to detect spontaneous pre-fibrillar oligomers in living cells. Our two αSN FRET biosensors provide complementary insight into αSN oligomerization and conformation in order to improve the success of drug discovery campaigns for the treatment of Parkinson's disease. We measure FRET by fluorescence lifetime, rather than traditional fluorescence intensity, providing a structural readout with greater resolution and precision. This facilitates identification of compounds that cause subtle but significant conformational changes in the ensemble of oligomeric states that are easily missed using intensity-based FRET. We screened a 1280-compound small-molecule library and identified 21 compounds that changed the lifetime by >5 SD. Two of these compounds have nanomolar potency in protecting SH-SY5Y cells from αSN-induced death, providing a nearly tenfold improvement over known inhibitors. We tested the efficacy of several compounds in a primary mouse neuron assay of αSN pathology (phosphorylation of mouse αSN pre-formed fibrils) and show rescue of pathology for two of them. These hits were further characterized with biophysical and biochemical assays to explore potential mechanisms of action. In vitro αSN oligomerization, single-molecule FRET, and protein-observed fluorine NMR experiments demonstrate that these compounds modulate αSN oligomers but not monomers. Subsequent aggregation assays further show that these compounds also deter or block αSN fibril assembly.

"Janus-Faced" α-Synuclein: Role in Parkinson's Disease

Parkinson's disease (PD) is a pathological condition characterized by the aggregation and the resultant presence of intraneuronal inclusions termed Lewy bodies (LBs) and Lewy neurites which are mainly composed of fibrillar α-synuclein (α-syn) protein. Pathogenic aggregation of α-syn is identified as the major cause of LBs deposition. Several mutations in α-syn showing varied aggregation kinetics in comparison to the wild type (WT) α-syn are reported in PD (A30P, E46K, H 50Q, G51D, A53E, and A53T). Also, the cell-to-cell spread of pathological α-syn plays a significant role in PD development. Interestingly, it has also been suggested that the pathology of PD may begin in the gastrointestinal tract and spread via the vagus nerve (VN) to brain proposing the gut-brain axis of α-syn pathology in PD. Despite multiple efforts, the behavior and functions of this protein in normal and pathological states (specifically in PD) is far from understood. Furthermore, the etiological factors responsible for triggering aggregation of this protein remain elusive. This review is an attempt to collate and present latest information on α-syn in relation to its structure, biochemistry and biophysics of aggregation in PD. Current advances in therapeutic efforts toward clearing the pathogenic α-syn via autophagy/lysosomal flux are also reviewed and reported.

Immunotherapies for Parkinson's disease: Progression of Clinical Development

Parkinson's disease is a common neurodegenerative disease affecting the movement and wellbeing of most elderlies. The manifestations of Parkinson's disease often include resting tremor, stiffness, bradykinesia and muscular rigidity. The typical hallmark of Parkinson's disease is the destruction of neurons in the substantia nigra and the presence of Lewy bodies in different compartments of the central nervous system. Due to various limitations to the currently available treatments, immunotherapies have emerged to be the new approach to Parkinson's disease treatment. This approach shows some positive outcomes on the efficacy in removing the aggregated species of alpha-synuclein, which is believed to be one of the causes of Parkinson's disease. In this review, an overview of how alpha-synuclein contributes to Parkinson's disease and the effects of a few new immunotherapeutic treatments, including BIIB054 (cinpanemab), MEDI1341, AFFITOPE and PRX002 (prasinezumab) that are currently under clinical development, will be discussed.

The Contribution of Microglia to Neuroinflammation in Parkinson's Disease

With the world's population ageing, the incidence of Parkinson's disease (PD) is on the rise. In recent years, inflammatory processes have emerged as prominent contributors to the pathology of PD. There is great evidence that microglia have a significant neuroprotective role, and that impaired and over activated microglial phenotypes are present in brains of PD patients. Thereby, PD progression is potentially driven by a vicious cycle between dying neurons and microglia through the instigation of oxidative stress, mitophagy and autophagy dysfunctions, a-synuclein accumulation, and pro-inflammatory cytokine release. Hence, investigating the involvement of microglia is of great importance for future research and treatment of PD. The purpose of this review is to highlight recent findings concerning the microglia-neuronal interplay in PD with a focus on human postmortem immunohistochemistry and single-cell studies, their relation to animal and iPSC-derived models, newly emerging technologies, and the resulting potential of new anti-inflammatory therapies for PD.

Epigenetic Modulation in Parkinson's Disease and Potential Treatment Therapies

In the recent past, huge emphasis has been given to the epigenetic alterations of the genes responsible for the cause of neurological disorders. Earlier, the scientists believed somatic changes and modifications in the genetic makeup of DNA to be the main cause of the neurodegenerative diseases. With the increase in understanding of the neural network and associated diseases, it was observed that alterations in the gene expression were not always originated by the change in the genetic sequence. For this reason, extensive research has been conducted to understand the role of epigenetics in the pathophysiology of several neurological disorders including Alzheimer's disease, Parkinson's disease and, Huntington's disease. In a healthy person, the epigenetic modifications play a crucial role in maintaining the homeostasis of a cell by either up-regulating or down-regulating the genes. Therefore, improved understanding of these modifications may provide better insight about the diseases and may serve as potential therapeutic targets for their treatment. The present review describes various epigenetic modifications involved in the pathology of Parkinson's Disease (PD) backed by multiple researches carried out to study the gene expression regulation related to the epigenetic alterations. Additionally, we will briefly go through the current scenario about the various treatment therapies including small molecules and multiple phytochemicals potent enough to reverse these alterations and the future directions for a better management of PD.

Soluble α-synuclein-antibody complexes activate the NLRP3 inflammasome in hiPSC-derived microglia

Parkinson's disease is characterized by accumulation of α-synuclein (αSyn). Release of oligomeric/fibrillar αSyn from damaged neurons may potentiate neuronal death in part via microglial activation. Heretofore, it remained unknown if oligomeric/fibrillar αSyn could activate the nucleotide-binding oligomerization domain (NOD)-like receptor (NLR) family pyrin domain-containing 3 (NLRP3) inflammasome in human microglia and whether anti-αSyn antibodies could prevent this effect. Here, we show that αSyn activates the NLRP3 inflammasome in human induced pluripotent stem cell (hiPSC)-derived microglia (hiMG) via dual stimulation involving Toll-like receptor 2 (TLR2) engagement and mitochondrial damage. In vitro, hiMG can be activated by mutant (A53T) αSyn secreted from hiPSC-derived A9-dopaminergic neurons. Surprisingly, αSyn-antibody complexes enhanced rather than suppressed inflammasome-mediated interleukin-1β (IL-1β) secretion, indicating these complexes are neuroinflammatory in a human context. A further increase in inflammation was observed with addition of oligomerized amyloid-β peptide (Aβ) and its cognate antibody. In vivo, engraftment of hiMG with αSyn in humanized mouse brain resulted in caspase-1 activation and neurotoxicity, which was exacerbated by αSyn antibody. These findings may have important implications for antibody therapies aimed at depleting misfolded/aggregated proteins from the human brain, as they may paradoxically trigger inflammation in human microglia.

Effects of α-Synuclein-Associated Post-Translational Modifications in Parkinson's Disease

α-Synuclein (α-syn), a small highly conserved presynaptic protein containing 140 amino acids, is thought to be the main pathological hallmark in related neurodegenerative disorders. Although the normal function of α-syn is closely involved in the regulation of vesicular neurotransmission in these diseases, the underlying mechanisms of post-translational modifications (PTMs) of α-syn in the pathogenesis of Parkinson's disease (PD) have not been fully characterized. The pathological accumulation of misfolded α-syn has a critical role in PD pathogenesis. Recent studies of factors contributing to α-syn-associated aggregation and misfolding have expanded our understanding of the PD disease process. In this Review, we summarize the structure and physiological function of α-syn, and we further highlight the major PTMs (namely phosphorylation, ubiquitination, nitration, acetylation, truncation, SUMOylation, and O-GlcNAcylation) of α-syn and the effects of these modifications on α-syn aggregation, which may elucidate mechanisms for PD pathogenesis and lay a theoretical foundation for clinical treatment of PD.

α-Synuclein antisense oligonucleotides as a disease-modifying therapy for Parkinson's disease

Parkinson's disease (PD) is a prevalent neurodegenerative disease with no approved disease-modifying therapies. Multiplications, mutations, and single nucleotide polymorphisms in the SNCA gene, encoding α-synuclein (aSyn) protein, either cause or increase risk for PD. Intracellular accumulations of aSyn are pathological hallmarks of PD. Taken together, reduction of aSyn production may provide a disease-modifying therapy for PD. We show that antisense oligonucleotides (ASOs) reduce production of aSyn in rodent preformed fibril (PFF) models of PD. Reduced aSyn production leads to prevention and removal of established aSyn pathology and prevents dopaminergic cell dysfunction. In addition, we address the translational potential of the approach through characterization of human SNCA-targeting ASOs that efficiently suppress the human SNCA transcript in vivo. We demonstrate broad activity and distribution of the human SNCA ASOs throughout the nonhuman primate brain and a corresponding decrease in aSyn cerebral spinal fluid (CSF) levels. Taken together, these data suggest that, by inhibiting production of aSyn, it may be possible to reverse established pathology; thus, these data support the development of SNCA ASOs as a potential disease-modifying therapy for PD and related synucleinopathies.

Neuroinflammation in Parkinson's Disease: Triggers, Mechanisms, and Immunotherapies

Parkinson's disease (PD) is a heterogeneous neurodegenerative disease involving multiple etiologies and pathogenesis, in which neuroinflammation is a common factor. Both preclinical experiments and clinical studies provide evidence for the involvement of neuroinflammation in the pathophysiology of PD, although there are a number of key issues related to neuroinflammatory processes in PD that remain to be addressed. In this review, we highlight the relationship between the common pathological mechanisms of PD and neuroinflammation, including aggregation of α-synuclein, genetic factors, mitochondrial dysfunction, and gut microbiome dysbiosis. We also describe the two positive feedback loops initiated in PD after the immune system is activated, and their role in the pathogenesis of PD. In addition, the interconnections and differences between the central and peripheral immune systems are discussed. Finally, we review the latest progress in immunotherapy research for PD patients, and propose future directions for clinical research.

Treating Parkinson's Disease with Antibodies: Previous Studies and Future Directions

Parkinson's disease is a neurodegenerative disorder mainly characterized by the degeneration of dopaminergic neurons in the substantia nigra. Degenerating neurons contain abnormal aggregates called Lewy bodies, that are predominantly composed of the misfolded and/or mutated alpha-synuclein protein. Post-translational modifications, cellular stress, inflammation and gene mutations are thought to trigger its pathological misfolding and aggregation. With alpha-synuclein pathology being strongly associated with dopaminergic neuronal toxicity, strategies aimed to reduce its burden are expected to be beneficial in slowing disease progression. Moreover, multiple sources of evidence suggest a cell-to-cell transmission of pathological alpha-synuclein in a prion-like manner. Therefore, antibodies targeting extra- or intracellular alpha-synuclein could be efficient in limiting the aggregation and transmission. Several active and passive immunization strategies have been explored to target alpha-synuclein. Here, we summarize immunotherapeutic approaches that were tested in pre-clinical or clinical studies in the last two decades in an attempt to treat Parkinson's disease.

Harnessing the immune system for the treatment of Parkinson's disease

Current treatment options for Parkinson's disease (PD) typically aim to replace dopamine, and hence only provide symptomatic relief. However, in the long run, this approach alone loses its efficacy as it is associated with debilitating side effects. Hence there is an unmet clinical need for addressing levodopa resistant symptoms, and an urgency to develop therapies that can halt or prevent the course of PD. The premise that α-syn can transmit from cell-to-cell in a prion like manner has opened up the possibility for the use of immunotherapy in PD. There is evidence for inflammation in PD as is evidenced by microglial activation, as well as the involvement of the peripheral immune system in PD, and peripheral inflammation can exacerbate dopaminergic degeneration as seen in animal models of the disease. However, mechanisms that link the immune system with PD are not clear, and the sequence of immune responses with respect to PD are still unknown. Nevertheless, our present knowledge offers avenues for the development of immune-based therapies for PD. In order to successfully employ such strategies, we must comprehend the state of the peripheral immune system during the course of PD. This review describes the developments in the field of both active and passive immunotherapies in the treatment of PD, and highlights the crucial need for future research for clarifying the role of inflammation and immunity in this debilitating disease.

Electrochemical biosensors for biometal-protein interactions in neurodegenerative diseases

Electrochemical biosensors have been adopted into a wide range of applications in the study of biometal-protein interactions in neurodegenerative diseases. Transition metals such as zinc, copper, and iron that are significant to biological functions have been shown to have strong implications in the progressive neural degeneration in Alzheimer's disease (AD), Parkinson's disease (PD), and prion protein diseases. This review presents a summative examination of the progress made in the design, fabrication, and applications of electrochemical biosensors in recent literature at understanding the metal-protein interactions in neurodegenerative diseases. The focus will be drawn on disease-causing biomarkers such as amyloid-β (Aβ) and tau proteins for AD, α-synuclein (α-syn) for PD, and prion proteins (PrP). Topics such as the use of electrochemical biosensing in monitoring biometal-induced conformational changes, elucidation of complexation motifs, production of reactive oxygen species (ROS) as well as the influence on downstream biomolecular interactions will be discussed. Major results and important concepts presented in these studies will be summarized in the hope to spark inspiration for the next generation of electrochemical sensors.

Parkinson's disease and translational research

Parkinson’s disease (PD) is diagnosed when patients exhibit bradykinesia with tremor and/or rigidity, and when these symptoms respond to dopaminergic medications. Yet in the last years there was a greater recognition of additional aspects of the disease including non-motor symptoms and prodromal states with associated pathology in various regions of the nervous system. In this review we discuss current concepts of two major alterations found during the course of the disease: cytoplasmic aggregates of the protein α-synuclein and the degeneration of dopaminergic neurons. We provide an overview of new approaches in this field based on current concepts and latest literature. In many areas, translational research on PD has advanced the understanding of the disease but there is still a need for more effective therapeutic options based on the insights into the basic biological phenomena.

Novel antibodies detect additional α-synuclein pathology in synucleinopathies: potential development for immunotherapy

BACKGROUND

Alpha-synuclein (α-Syn) aggregation is the primary characteristic of synucleinopathies including Parkinson's disease (PD), dementia with Lewy bodies (DLB) and multiple system atrophy (MSA). Immunotherapy targeting α-Syn has shown promising results in animal models of the disease. This study investigates the target specificity of three different active vaccines for pathological α-Syn aggregates found in human brain tissue from synucleinopathies.

METHODS

Guinea pigs were immunised with 3 vaccines developed by United Neuroscience, and IgG fractions purified from the resulting immune sera (IGG-1, IGG-2 or IGG-3) were used to perform immunohistochemical staining of human cases of PD, DLB and MSA. The resulting immunoreactivity was compared to a commercially available α-Syn antibody from Novacastra (NOV) commonly used for diagnostic purposes. Images were captured from the substantia nigra (SN), temporal lobe, internal capsule, insular cortex and putamen and quantified for the percentage area with α-Syn immunoreactivity. Lewy bodies (LB) and Lewy neurites (LN) were further analysed in PD and DLB cases.

RESULTS

Vaccine-generated antibodies detected more α-Syn pathology compared to NOV. The levels of α-Syn immunoreactivity varied between brain region and disease type with IGG-3 recognising the highest levels of α-Syn in most cases and in all brain regions that are affected early in disease progression. IGG-3 had a high recognition for glial inclusions found in MSA which are known to have a more compact conformation. Slot blot analysis confirmed the specificity of IGG-3 for native oligomers and fibrillar α-Syn. Higher levels of α-Syn were recognised by IGG-2 in cortical regions, and by IGG-3 in SN of PD and DLB cases. This was due to increased immunolabelling of LNs in these brain regions suggesting that IGG-2 and IGG-3 recognised additional α-Syn pathology compared to IGG-1 and NOV. Whether the unique binding properties of the antibodies produced in guinea pigs will translate in the clinic remains to be addressed, which is the main limitation of this study.

CONCLUSIONS

These vaccines induce antibodies that bind α-Syn oligomers and aggregates in the human brain and specifically support the choice of the vaccine generating IGG-3 (i.e. UB-312) as a candidate for clinical trials for synucleinopathies.

Low serum Α-SYNUCLEIN and oligomer Α-SYNUCLEIN levels in multiple sclerosis patients

INTRODUCTION

Multiple sclerosis (MS) is an autoimmune, inflammatory, demyelinating neurodegenerative disease progressing with attacks. Alpha-synuclein (α-Syn), a neuronal protein, has been previously associated with the inflammation and development of neurodegenerative diseases. Although the cause of neurodegeneration in multiple sclerosis is mainly associated with inflammation, α-Syn may play a role in the pathogenesis of MS, as in other classical neurodegenerative diseases such as synucleinopathies. In multiple sclerosis, α-Syn has been directly studied in central nervous system lesions and cerebrospinal fluid (CSF). However, there are few studies approaching variations in peripheral α-Syn in MS. The aim of our study was to investigate the correlation between disease progression and other clinical parameters by measuring serum α-Syn and oligomer α-Syn levels in MS patients.

MATERIAL AND METHOD

The study included 60 MS patients aged 18 years or older who were admitted to the Department of Neurology between 01.02.2020-01.04.2020 and diagnosed with MS according to the 2010 MC Donald criteria, and 60 age- and sex-matched healthy controls. Those who were in the MS attack period and received cortisone treatment in the past three months were excluded from the study. The serum α-Syn and oligomer α-Syn levels of the individuals in both groups were measured. The correlation between the serum α-Syn, oligomer α-Syn, oligomer α-Syn/α-Syn ratio levels of the MS patients and their age, disease duration, number of attacks, annualized relapse rate (ARR), disease type, EDSS scores and immunomodulatory drug type used was investigated. Statistical analysis was performed using the SPSS 22.0 software.

RESULTS

In our study, 73.3% of the MS patients were female and the mean age of the patients was 36.18 ± 9.5 years. The most common MS disease type was RRMS with 83.3%. Serum α-Syn (79.52 ± 34.81) and oligomer α-Syn (18.79 ± 10.48) levels were significantly lower in the MS patients compared to the control group (p < 0.001). Serum oligomer α-Syn/α-Syn ratio was higher in the MS patients compared to the control group and in SPMS compared to RRMS, but was not statistically significant. There was no significant correlation between the serum α-Syn, oligomer α-Syn and oligomer α-Syn/α-Syn ratio ratio of the MS patients and their age, disease duration, disease type, EDDS, ARR and immunomodulatory treatments. There was a significant positive correlation between α-Syn and oligomer α-Syn in MS patients (r: 0.29, p: 0.02).

CONCLUSION

In our study, serum α-Syn and oligomer α-Syn levels were lower in the MS patients compared to the control group. Low levels of α-Syn in MS may play a role in the development of neuroinflammation and may be a result of the diffuse neuronal and synaptic loss. There is a need for further studies on this subject.

Current Management and Emerging Therapies in Multiple System Atrophy

Multiple system atrophy (MSA) is a progressive neurodegenerative disease variably associated with motor, nonmotor, and autonomic symptoms, resulting from putaminal and cerebellar degeneration and associated with glial cytoplasmic inclusions enriched with α-synuclein in oligodendrocytes and neurons. Although symptomatic treatment of MSA can provide significant improvements in quality of life, the benefit is often partial, limited by adverse effects, and fails to treat the underlying cause. Consistent with the multisystem nature of the disease and evidence that motor symptoms, autonomic failure, and depression drive patient assessments of quality of life, treatment is best achieved through a coordinated multidisciplinary approach driven by the patient's priorities and goals of care. Research into disease-modifying therapies is ongoing with a particular focus on synuclein-targeted therapies among others. This review focuses on both current management and emerging therapies for this devastating disease.

Apoptosis, Induced by Human α-Synuclein in Yeast, Can Occur Independent of Functional Mitochondria

Human α-synuclein expression in baker’s yeast reportedly induces mitochondria-dependent apoptosis. Surprisingly, we find that, under de-repressing conditions of the inducible MET25/GAL1 promoters, yeast cells expressing chromosomally-integrated copies of the human α-synuclein gene are not killed, but spontaneously form respiration-deficient rho-minus (ρ⁻) petites. Although yeast cells can undergo cell death (apoptosis) from loss of mitochondrial function, they can also survive without functional mitochondria. Such cells are referred to as ρ⁰ or ρ⁻ petites. This study reports that minimal expression of human α-synuclein in yeast, from MET25/GAL1 promoter, gives rise to ρ⁻ petites. Interestingly, the full expression of α-synuclein, from the same promoters, in α-synuclein-triggered ρ⁻ petites and also in ρ⁰ petites (produced by treating ρ⁺ cells with the mutagen ethidium bromide) initiates apoptosis. The percentages of petites increase with increasing α-synuclein gene copy-number. ρ⁻ petites expressing α-synuclein from fully-induced MET25/GAL1 promoters exhibit increased ROS levels, loss of mitochondrial membrane potential, and nuclear DNA fragmentation, with increasing copies of α-synuclein. Our results indicate that, for the first time in yeast, α-synuclein-triggered apoptosis can occur independently of functional mitochondria. The observation that α-synuclein naturally forms petites and that they can undergo apoptosis may have important implications in understanding the pathogenesis of Parkinson’s disease.

Targeting α-synuclein by PD03 AFFITOPE® and Anle138b rescues neurodegenerative pathology in a model of multiple system atrophy: clinical relevance

Background

Misfolded oligomeric α-synuclein plays a pivotal role in the pathogenesis of α-synucleinopathies including Parkinson’s disease and multiple system atrophy, and its detection parallels activation of microglia and a loss of neurons in the substantia nigra pars compacta. Here we aimed to analyze the therapeutic efficacy of PD03, a new AFFITOPE® immunotherapy approach, either alone or in combination with Anle138b, in a PLP-α-syn mouse model.

Methods

The PLP-α-syn mice were treated with PD03 immunotherapy, Anle138b, or a combination of two. Five months after study initiation, the mice underwent behavioral testing and were sacrificed for neuropathological analysis. The treatment groups were compared to the vehicle group with regard to motor performance, nigral neuronal loss, microglial activation and α-synuclein pathology.

Results

The PLP-α-syn mice receiving the PD03 or Anle138b single therapy showed improvement of gait deficits and preservation of nigral dopaminergic neurons associated with the reduced α-synuclein oligomer levels and decreased microglial activation. The combined therapy with Anle138b and PD03 resulted in lower IgG binding in the brain as compared to the single immunotherapy with PD03.

Conclusions

PD03 and Anle138b can selectively target oligomeric α-synuclein, resulting in attenuation of neurodegeneration in the PLP-α-syn mice. Both approaches are potential therapies that should be developed further for disease modification in α-synucleinopathies.

Safety and immunogenicity of the α-synuclein active immunotherapeutic PD01A in patients with Parkinson's disease: a randomised, single-blinded, phase 1 trial

BACKGROUND

Robust evidence supports the role of α-synuclein pathology as a driver of neuronal dysfunction in Parkinson's disease. PD01A is a specific active immunotherapy with a short peptide formulation targeted against oligomeric α-synuclein. This phase 1 study assessed the safety and tolerability of the PD01A immunotherapeutic in patients with Parkinson's disease.

METHODS

We did a first-in-human, randomised, phase 1 study of immunisations with PD01A, followed by three consecutive study extensions. Patients aged 45-65 years with a clinical diagnosis of Parkinson's disease (≤4 years since diagnosis and Hoehn and Yahr Stage 1 to 2), imaging results (dopamine transporter single photon emission CT and MRI) consistent with their Parkinson's disease diagnosis, and on stable doses of Parkinson's disease medications for at least 3 months were recruited at a single private clinic in Vienna, Austria. Patients were randomly assigned (1:1), using a computer-generated sequence with varying block size, to receive four subcutaneous immunisations with either 15 μg or 75 μg PD01A injected into the upper arms and followed up initially for 52 weeks, followed by a further 39 weeks' follow-up. Patients were then randomly assigned (1:1) again to receive the first booster immunisation at 15 μg or 75 μg and were followed up for 24 weeks. All patients received a second booster immunisation of 75 μg and were followed up for an additional 52 weeks. Patients were masked to dose allocation. Primary (safety) analyses included all treated patients. These four studies were registered with EU Clinical Trials Register, EudraCT numbers 2011-002650-31, 2013-001774-20, 2014-002489-54, and 2015-004854-16.

FINDINGS

32 patients were recruited between Feb 14, 2012, and Feb 6, 2013, and 24 were deemed eligible and randomly assigned to receive four PD01A priming immunisations. One patient had a diagnosis change to multiple system atrophy and was withdrawn and two patients withdrew consent during the studies. 21 (87%) of 24 patients received all six immunisations and completed 221-259 weeks in-study (two patients in the 15 μg dose group and one patient in the 75 μg dose group discontinued). All patients experienced at least one adverse event, but most of them were considered unrelated to study treatment (except for transient local injection site reactions, which affected all but one patient). Serial MRI assessments also ruled out inflammatory processes. Systemic treatment-related adverse events were fatigue (n=4), headache (n=3), myalgia (n=3), muscle rigidity (n=2), and tremor (n=2). The geometric group mean titre of antibodies against the immunising peptide PD01 increased from 1:46 at baseline to 1:3580 at week 12 in the 15 μg dose group, and from 1:76 to 1:2462 at week 12 in the 75 μg dose group. Antibody titres returned to baseline over 2 years, but could be rapidly reactivated after booster immunisation from week 116 onwards, reaching geometric group mean titres up to 1:20218.

INTERPRETATION

Repeated administrations of PD01A were safe and well tolerated over an extended period. Specific active immunotherapy resulted in a substantial humoral immune response with target engagement. Phase 2 studies are needed to further assess the safety and efficacy of PD01A for the treatment of Parkinson's disease.

FUNDING

AFFiRiS, Michael J Fox Foundation.

In Search of Effective Treatments Targeting α-Synuclein Toxicity in Synucleinopathies: Pros and Cons

Parkinson's disease (PD), multiple system atrophy (MSA) and Dementia with Lewy bodies (DLB) represent pathologically similar, progressive neurodegenerative disorders characterized by the pathological aggregation of the neuronal protein α-synuclein. PD and DLB are characterized by the abnormal accumulation and aggregation of α-synuclein in proteinaceous inclusions within neurons named Lewy bodies (LBs) and Lewy neurites (LNs), whereas in MSA α-synuclein inclusions are mainly detected within oligodendrocytes named glial cytoplasmic inclusions (GCIs). The presence of pathologically aggregated α-synuclein along with components of the protein degradation machinery, such as ubiquitin and p62, in LBs and GCIs is considered to underlie the pathogenic cascade that eventually leads to the severe neurodegeneration and neuroinflammation that characterizes these diseases. Importantly, α-synuclein is proposed to undergo pathogenic misfolding and oligomerization into higher-order structures, revealing self-templating conformations, and to exert the ability of "prion-like" spreading between cells. Therefore, the manner in which the protein is produced, is modified within neural cells and is degraded, represents a major focus of current research efforts in the field. Given that α-synuclein protein load is critical to disease pathogenesis, the identification of means to limit intracellular protein burden and halt α-synuclein propagation represents an obvious therapeutic approach in synucleinopathies. However, up to date the development of effective therapeutic strategies to prevent degeneration in synucleinopathies is limited, due to the lack of knowledge regarding the precise mechanisms underlying the observed pathology. This review critically summarizes the recent developed strategies to counteract α-synuclein toxicity, including those aimed to increase protein degradation, to prevent protein aggregation and cell-to-cell propagation, or to engage antibodies against α-synuclein and discuss open questions and unknowns for future therapeutic approaches.

Cathepsin K is a potent disaggregase of α-synuclein fibrils

The intracellular accumulation of α-synuclein (α-syn) amyloid fibrils is a hallmark of Parkinson's disease. Because lysosomes are responsible for degrading aggregated species, enhancing lysosomal function could alleviate the overburden of α-syn. Previously, we showed that cysteine cathepsins (Cts) is the main class of lysosomal proteases that degrade α-syn, and in particular, CtsL was found to be capable of digesting α-syn fibrils. Here, we report that CtsK is a more potent protease for degrading α-syn amyloids. Using peptide mapping by liquid chromatography with mass spectrometry, critical cleavage sites involved in destabilizing fibril structure are identified. CtsK is only able to devour the internal regions after the removal of both N- and C-termini, indicating their protective role of the amyloid core from proteolytic attack. Our results suggest that if overexpressed in lysosomes, CtsK has the potential to ameliorate α-syn pathology.

Therapeutic innovation in Parkinson's disease: a 2020 update on disease-modifying approaches

INTRODUCTION

Parkinson's disease (PD) is the second most common neurodegenerative disorder affecting more than 10 million patients worldwide. Despite increasing improvements in disease management, a huge medical need still exists as its relentless progression cannot be delayed by current treatments. Therefore, scientists, clinicians, and pharmaceutical companies are hunting new drugs with 'disease-modifying' properties.

AREAS COVERED

This review concentrates on new therapeutics - excluding cell and gene therapies - under investigation for PD with 'disease-modifying' potential. This is a global, comprehensive picture of the current innovative drug pipeline, where the main preclinical and clinical data available are provided. Drug candidates presented include α-synuclein modulating agents, neuroprotective agents and neuroinflammation modulators, kinase modulators, neurotrophic factors, and drugs acting on emerging targets.

EXPERT OPINION

There is excitement for agents with 'disease-modifying' properties and the authors found more than 130 assets, not including cell and gene therapies under investigation - most of them still in preclinical development - meaning that the science is progressing multiple, diverse new opportunities. Many limitations hamper the successful development of these drug candidates such as the translational accuracy of preclinical models, the current clinical development paradigm as well as the lack of biomarkers to be used in diagnosis and therapy management.

Immunotherapies for Aging-Related Neurodegenerative Diseases-Emerging Perspectives and New Targets

Neurological disorders such as Alzheimer's disease (AD), Lewy body dementia (LBD), frontotemporal dementia (FTD), and vascular dementia (VCID) have no disease-modifying treatments to date and now constitute a dementia crisis that affects 5 million in the USA and over 50 million worldwide. The most common pathological hallmark of these age-related neurodegenerative diseases is the accumulation of specific proteins, including amyloid beta (Aβ), tau, α-synuclein (α-syn), TAR DNA-binding protein 43 (TDP43), and repeat-associated non-ATG (RAN) peptides, in the intra- and extracellular spaces of selected brain regions. Whereas it remains controversial whether these accumulations are pathogenic or merely a byproduct of disease, the majority of therapeutic research has focused on clearing protein aggregates. Immunotherapies have garnered particular attention for their ability to target specific protein strains and conformations as well as promote clearance. Immunotherapies can also be neuroprotective: by neutralizing extracellular protein aggregates, they reduce spread, synaptic damage, and neuroinflammation. This review will briefly examine the current state of research in immunotherapies against the 3 most commonly targeted proteins for age-related neurodegenerative disease: Aβ, tau, and α-syn. The discussion will then turn to combinatorial strategies that enhance the effects of immunotherapy against aggregating protein, followed by new potential targets of immunotherapy such as aging-related processes.

Immunization therapies for Parkinson's disease: state of the art and considerations for future clinical trials

INTRODUCTION

Advances in the understanding of the mechanisms that lead to Lewy body pathology in Parkinson's disease (PD) have yielded rationales for tackling neurodegeneration associated with α-Synuclein (α-Syn) misfolding, aggregation, and/or its related spreading. Immunization therapies targeting distinct α-Syn epitopes (conformational and linear) that aim to limit extracellular spread in the brain are now in development. Completed and ongoing studies have enrolled early PD patients without considering individual clinical differences and assume a common pathogenetic mechanism of the disease. Such approaches have led to disappointing results; this is most likely attributed to trial methodology and inadequate patient selection rather than underlying target biology.

AREAS COVERED

This review presents the status of immunotherapies that target α-Syn epitopes in PD. Mechanisms associated with neurodegeneration are examined along with the limitations of current antibody research strategies and ongoing clinical trials. Patient stratification based on disease progression is discussed and the article culminates with author suggestions on how to progress future clinical trials.

EXPERT OPINION

The efficacy of passive and active immunotherapies is inadequately evaluated in ongoing clinical trials where participating patients have various progression rates, genetic backgrounds, and clinical phenotypes. Future disease-modifying studies can overcome these limitations by enrolling patients based on progression pathways and genotypic contribution to disease manifestations.

The emerging role of α-synuclein truncation in aggregation and disease

α-Synuclein (αsyn) is an abundant brain neuronal protein that can misfold and polymerize to form toxic fibrils coalescing into pathologic inclusions in neurodegenerative diseases, including Parkinson's disease, Lewy body dementia, and multiple system atrophy. These fibrils may induce further αsyn misfolding and propagation of pathologic fibrils in a prion-like process. It is unclear why αsyn initially misfolds, but a growing body of literature suggests a critical role of partial proteolytic processing resulting in various truncations of the highly charged and flexible carboxyl-terminal region. This review aims to 1) summarize recent evidence that disease-specific proteolytic truncations of αsyn occur in Parkinson's disease, Lewy body dementia, and multiple system atrophy and animal disease models; 2) provide mechanistic insights on how truncation of the amino and carboxyl regions of αsyn may modulate the propensity of αsyn to pathologically misfold; 3) compare experiments evaluating the prion-like properties of truncated forms of αsyn in various models with implications for disease progression; 4) assess uniquely toxic properties imparted to αsyn upon truncation; and 5) discuss pathways through which truncated αsyn forms and therapies targeted to interrupt them. Cumulatively, it is evident that truncation of αsyn, particularly carboxyl truncation that can be augmented by dysfunctional proteostasis, dramatically potentiates the propensity of αsyn to pathologically misfold into uniquely toxic fibrils with modulated prion-like seeding activity. Therapeutic strategies and experimental paradigms should operate under the assumption that truncation of αsyn is likely occurring in both initial and progressive disease stages, and preventing truncation may be an effective preventative strategy against pathologic inclusion formation.

Cell-to-Cell Transmission of Tau and α-Synuclein

The stereotypical spread of pathological protein inclusions and clinicopathological heterogeneity are well described in neurodegenerative diseases. Accumulating evidence suggests that the former can be attributed to consecutive cell-to-cell transmission of pathological proteins between anatomically connected brain regions, while the latter has been hypothesized to result from the spread of conformationally distinct pathological protein aggregates, or strains. These emerging concepts have dramatically changed our understanding of neurodegenerative diseases. In this review, we first summarize the background and recent findings underpinning these concepts with a focus on two major pathological proteins: tau and α-synuclein. We then discuss their clinical implications for tauopathies and synucleinopathies and propose a working hypothesis for future research.

New hopes for disease modification in Parkinson's Disease

To date, despite numerous clinical trials, no intervention has been demonstrated to modify the progression of Parkinson's disease (PD). However, over the past decades encouraging progress has been made towards a better understanding of molecular pathways relevant for the neurodegenerative process in PD. This is also based on new insights into the genetic architecture of the disease, revealing multiple novel targets for potentially disease-modifying interventions. Important achievements have also been made in the field of risk markers and combinations thereof, in the form of risk algorithms, will hopefully soon provide the possibility to identify affected individuals at yet prediagnostic or prodromal stages of the illness. Such phases of the disease would provide an ideal window for neuroprotection trials. Taken together, these developments offer hope that a breakthrough towards modifying the course of PD might be reached. In this article we summarize various approaches currently pursued in this quest. This article is part of the special issue entitled 'The Quest for Disease-Modifying Therapies for Neurodegenerative Disorders'.