Does α-synuclein have a dual and opposing effect in preclinical vs. clinical Parkinson's disease?

Viral overexpression of human alpha-synuclein in mouse substantia nigra dopamine neurons results in hyperdopaminergia but no neurodegeneration

Loss of select neuronal populations such as midbrain dopamine (DA) neurons is a pathological hallmark of Parkinson's disease (PD). The small neuronal protein α-synuclein has been related both genetically and neuropathologically to PD, yet how and if it contributes to selective vulnerability remains elusive. Here, we describe the generation of a novel adeno-associated viral vector (AAV) for Cre-dependent overexpression of wild-type human α-synuclein. Our strategy allows us to restrict α-synuclein to select neuronal populations and hence investigate the cell-autonomous effects of elevated α-synuclein in genetically-defined cell types. Since DA neurons in the substantia nigra pars compacta (SNc) are particularly vulnerable in PD, we investigated in more detail the effects of increased α-synuclein in these cells. AAV-mediated overexpression of wildtype human α-synuclein in SNc DA neurons increased the levels of α-synuclein within these cells and augmented phosphorylation of α-synuclein at serine-129, which is considered a pathological feature of PD and other synucleinopathies. However, despite abundant α-synuclein overexpression and hyperphosphorylation we did not observe any dopaminergic neurodegeneration up to 90 days post virus infusion. In contrast, we noticed that overexpression of α-synuclein resulted in increased locomotor activity and elevated striatal DA levels suggesting that α-synuclein enhanced dopaminergic activity. We therefore conclude that cell-autonomous effects of elevated α-synuclein are not sufficient to trigger acute dopaminergic neurodegeneration.

Research Priorities on the Role of α-Synuclein in Parkinson's Disease Pathogenesis

Various forms of Parkinson's disease, including its common sporadic form, are characterized by prominent α-synuclein (αSyn) aggregation in affected brain regions. However, the role of αSyn in the pathogenesis and evolution of the disease remains unclear, despite vast research efforts of more than a quarter century. A better understanding of the role of αSyn, either primary or secondary, is critical for developing disease-modifying therapies. Previous attempts to hone this research have been challenged by experimental limitations, but recent technological advances may facilitate progress. The Scientific Issues Committee of the International Parkinson and Movement Disorder Society (MDS) charged a panel of experts in the field to discuss current scientific priorities and identify research strategies with potential for a breakthrough. © 2024 The Author(s). Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

Viral overexpression of human alpha-synuclein in mouse substantia nigra dopamine neurons results in hyperdopaminergia but no neurodegeneration

Loss of select neuronal populations such as midbrain dopamine (DA) neurons is a pathological hallmark of Parkinson's disease (PD). The small neuronal protein α-synuclein has been related both genetically and neuropathologically to PD, yet how it contributes to selective vulnerability remains elusive. Here, we describe the generation of a novel adeno-associated viral vector (AAV) for Cre-dependent overexpression of wild-type human α-synuclein. Our strategy allows us to restrict α-synuclein to select neuronal populations and hence investigate the cell-autonomous effects of elevated α-synuclein in genetically-defined cell types. Since DA neurons in the substantia nigra pars compacta (SNc) are particularly vulnerable in PD, we investigated in more detail the effects of increased α-synuclein in these cells. AAV-mediated overexpression of wildtype human α-synuclein in SNc DA neurons increased the levels of α-synuclein within these cells and augmented phosphorylation of α-synuclein at serine-129, which is considered a pathological feature of PD and other synucleinopathies. However, despite abundant α-synuclein overexpression and hyperphosphorylation we did not observe any DA neurodegeneration up to 90 days post virus infusion. In contrast, we noticed that overexpression of α-synuclein resulted in increased locomotor activity and elevated striatal DA levels suggesting that α-synuclein enhanced dopaminergic activity. We therefore conclude that cell-autonomous effects of elevated α-synuclein are not sufficient to trigger acute DA neurodegeneration.

Loss of monomeric alpha-synuclein (synucleinopenia) and the origin of Parkinson's disease

These facts argue against the gain-of-function synucleinopathy hypothesis, which proposes that Lewy pathology causes Parkinson's disease: (1) most brains from people without neurological symptoms have multiple pathologies; (2) neither pathology type nor distribution correlate with disease severity or progression in Parkinson's disease; (3) aggregated α-synuclein in the form of Lewy bodies is not a space-occupying lesion but the insoluble fraction of its precursor, soluble monomeric α-synuclein; (4) pathology spread is passive, occurring by irreversible nucleation, not active replication; and (5) low cerebrospinal fluid α-synuclein levels predict brain atrophy and clinical disease progression. The transformation of α-synuclein into Lewy pathology may occur as a response to biological, toxic, or infectious stressors whose persistence perpetuates the nucleation process, depleting normal α-synuclein and eventually leading to Parkinson's symptoms from neuronal death. We propose testing the loss-of-function synucleinopenia hypothesis by evaluating the clinical and neurodegenerative rescue effect of replenishing the levels of monomeric α-synuclein.

Nonintuitive Immunogenicity and Plasticity of Alpha-Synuclein Conformers: A Paradigm for Smart Delivery of Neuro-Immunotherapeutics

Despite the extensive research successes and continuous developments in modern medicine in terms of diagnosis, prevention, and treatment, the lack of clinically useful disease-modifying drugs or immunotherapeutic agents that can successfully treat or prevent neurodegenerative diseases is an ongoing challenge. To date, only one of the 244 drugs in clinical trials for the treatment of neurodegenerative diseases has been approved in the past decade, indicating a failure rate of 99.6%. In corollary, the approved monoclonal antibody did not demonstrate significant cognitive benefits. Thus, the prevalence of neurodegenerative diseases is increasing rapidly. Therefore, there is an urgent need for creative approaches to identifying and testing biomarkers for better diagnosis, prevention, and disease-modifying strategies for the treatment of neurodegenerative diseases. Overexpression of the endogenous α-synuclein has been identified as the driving force for the formation of the pathogenic α-synuclein (α-Syn) conformers, resulting in neuroinflammation, hypersensitivity, endogenous homeostatic responses, oxidative dysfunction, and degeneration of dopaminergic neurons in Parkinson's disease (PD). However, the conformational plasticity of α-Syn proffers that a certain level of α-Syn is essential for the survival of neurons. Thus, it exerts both neuroprotective and neurotoxic (regulatory) functions on neighboring neuronal cells. Furthermore, the aberrant metastable α-Syn conformers may be subtle and difficult to detect but may trigger cellular and molecular events including immune responses. It is well documented in literature that the misfolded α-Syn and its conformers that are released into the extracellular space from damaged or dead neurons trigger the innate and adaptive immune responses in PD. Thus, in this review, we discuss the nonintuitive plasticity and immunogenicity of the α-Syn conformers in the brain immune cells and their physiological and pathological consequences on the neuroimmune responses including neuroinflammation, homeostatic remodeling, and cell-specific interactions that promote neuroprotection in PD. We also critically reviewed the novel strategies for immunotherapeutic delivery interventions in PD pathogenesis including immunotherapeutic targets and potential nanoparticle-based smart drug delivery systems. It is envisioned that a greater understanding of the nonintuitive immunogenicity of aberrant α-Syn conformers in the brain's microenvironment would provide a platform for identifying valid therapeutic targets and developing smart brain delivery systems for clinically effective disease-modifying immunotherapeutics that can aid in the prevention and treatment of PD in the future.

Neurocognitive Impairment and Social Cognition in Parkinson's Disease Patients

In addition to motor symptoms, neurocognitive impairment (NCI) affects patients with prodromal Parkinson's disease (PD). NCI in PD ranges from subjective cognitive complaints to dementia. The purpose of this review is to present the available evidence of NCI in PD and highlight the heterogeneity of NCI phenotypes as well as the range of factors that contribute to NCI onset and progression. A review of publications related to NCI in PD up to March 2023 was performed using PubMed/Medline. There is an interconnection between the neurocognitive and motor symptoms of the disease, suggesting a common underlying pathophysiology as well as an interconnection between NCI and non-motor symptoms, such as mood disorders, which may contribute to confounding NCI. Motor and non-motor symptom evaluation could be used prognostically for NCI onset and progression in combination with imaging, laboratory, and genetic data. Additionally, the implications of NCI on the social cognition of afflicted patients warrant its prompt management. The etiology of NCI onset and its progression in PD is multifactorial and its effects are equally grave as the motor effects. This review highlights the importance of the prompt identification of subjective cognitive complaints in PD patients and NCI management.

Alpha-synuclein in skin as a high-quality biomarker for Parkinson's disease

Parkinson's disease (PD), the most common neurological motor system disorder, which characterised by the irreversible loss of dopaminergic neurones in the substantia nigra pars compacta, and leads to the deficiency of dopamine in the striatum. Deposited Lewy bodies (LBs) in diseased neurones and nerve terminals are the pathological hallmark of PD, and alpha-synuclein (α-Syn) is the most prominent protein in LBs. The tight association between α-Syn and the molecular pathology of PD has generatly increaed the interest in using the α-Syn species as biomarkers to diagnose early PD. α-Syn is not confined to the central nervous system, it is also present in the peripheral tissues, such as human skin. The assessment of skin α-Syn has the potential to be a diagnostic method that not only has excellent sensitivity, specificity, and reproducibility, but also convenient and acceptable to patients. In this review, we (i) integrate the biochemical, aggregation and structural features of α-Syn; (ii) map the distribution of the α-Syn species present in the brain, biological fluids, and peripheral tissues; and (iii) present a critical and comparative analysis of previous studies that have measured α-Syn in the skin. Finally, we provide an outlook on the future of skin biopsy as a diagnostic approach for PD, and highlight its potential implications for clinical trials, clinical decision-making, treatment strategies as well as the development of new therapies.

Alpha-synuclein and the Parkinson's disease drug pipeline

The process of protein aggregation involves the transformation of soluble peptides into insoluble cross-beta amyloids. In Parkinson's disease (PD), soluble monomeric α-synuclein transforms into the amyloid state known as Lewy pathology. Monomeric (functional) α-synuclein depletes as the fraction of Lewy pathology increases. We examined the allocation of disease-modifying projects in the PD therapeutic pipeline classified based on whether they aimed to reduce directly or indirectly the insoluble or increase the soluble α-synuclein. A project was defined as a drug development program that may include more than one registered clinical trial, according to the Parkinson's Hope List, a database of therapies under development for PD. Of 67 projects, 46 aimed to reduce α-synuclein, 15 (22.4%) directly and 31 (46.3%) indirectly, amounting to 68.7% of all disease-modifying projects. No projects explicitly aimed to increase soluble α-synuclein levels. Altogether, α-synuclein is the target of more than two-thirds of the disease-modifying pipeline, with treatments aimed at reducing or preventing an increase in its insoluble fraction. As no treatments aim to restore soluble α-synuclein levels within a normal range, we propose rebalancing the therapeutic PD pipeline.

Unraveling the Complex Interplay between Alpha-Synuclein and Epigenetic Modification

Alpha-synuclein (αS) is a small, presynaptic neuronal protein encoded by the SNCA gene. Point mutations and gene multiplication of SNCA cause rare familial forms of Parkinson’s disease (PD). Misfolded αS is cytotoxic and is a component of Lewy bodies, which are a pathological hallmark of PD. Because SNCA multiplication is sufficient to cause full-blown PD, gene dosage likely has a strong impact on pathogenesis. In sporadic PD, increased SNCA expression resulting from a minor genetic background and various environmental factors may contribute to pathogenesis in a complementary manner. With respect to genetic background, several risk loci neighboring the SNCA gene have been identified, and epigenetic alterations, such as CpG methylation and regulatory histone marks, are considered important factors. These alterations synergistically upregulate αS expression and some post-translational modifications of αS facilitate its translocation to the nucleus. Nuclear αS interacts with DNA, histones, and their modifiers to alter epigenetic status; thereby, influencing the stability of neuronal function. Epigenetic changes do not affect the gene itself but can provide an appropriate transcriptional response for neuronal survival through DNA methylation or histone modifications. As a new approach, publicly available RNA sequencing datasets from human midbrain-like organoids may be used to compare transcriptional responses through epigenetic alterations. This informatic approach combined with the vast amount of transcriptomics data will lead to the discovery of novel pathways for the development of disease-modifying therapies for PD.

α-Synuclein in synaptic function and dysfunction

α-Synuclein is a neuronal protein that is enriched in presynaptic terminals. Under physiological conditions, it binds to synaptic vesicle membranes and functions in neurotransmitter release, although the molecular details remain unclear, and it is controversial whether α-synuclein inhibits or facilitates neurotransmitter release. Pathologically, in synucleinopathies including Parkinson's disease (PD), α-synuclein forms aggregates that recruit monomeric α-synuclein and spread throughout the brain, which triggers neuronal dysfunction at molecular, cellular, and organ levels. Here, we present an overview of the effects of α-synuclein on SNARE-complex assembly, neurotransmitter release, and synaptic vesicle pool homeostasis, and discuss how the observed divergent effects of α-synuclein on neurotransmitter release can be reconciled. We also discuss how gain-of-function versus loss-of-function of α-synuclein may contribute to pathogenesis in synucleinopathies.

Abandoning the Proteinopathy Paradigm in Parkinson Disease

This Viewpoint makes a case for changing the approach in Parkinson disease research efforts from one of proteinopathy (accrual of amyloids) to proteinopenia (depletion of normal proteins).

Synaptic vesicle binding of α-synuclein is modulated by β- and γ-synucleins

α-synuclein, β-synuclein, and γ-synuclein are abundantly expressed proteins in the vertebrate nervous system. α-synuclein functions in neurotransmitter release by binding to and clustering synaptic vesicles and chaperoning SNARE-complex assembly. Pathologically, aggregates originating from soluble pools of α-synuclein are deposited into Lewy bodies in Parkinson's disease and related synucleinopathies. The functions of β-synuclein and γ-synuclein in presynaptic terminals remain poorly studied. Using in vitro liposome binding studies, circular dichroism spectroscopy, immunoprecipitation, and fluorescence resonance energy transfer (FRET) experiments on isolated synaptic vesicles in combination with subcellular fractionation of brains from synuclein mouse models, we show that β-synuclein and γ-synuclein have a reduced affinity toward synaptic vesicles compared with α-synuclein, and that heteromerization of β-synuclein or γ-synuclein with α-synuclein results in reduced synaptic vesicle binding of α-synuclein in a concentration-dependent manner. Our data suggest that β-synuclein and γ-synuclein are modulators of synaptic vesicle binding of α-synuclein and thereby reduce α-synuclein's physiological activity at the neuronal synapse.

Parkinsonism and dementia

The aim of the present review is to summarize literature data on dementia in parkinsonian disorders. Cognitive decline and the gradual development of dementia are considered to be key features in the majority of parkinsonian conditions. The burden of dementia in everyday life of parkinsonian patients and their caregivers is vast and can be even more challenging to handle than the motor component of the disease. Common pathogenetic mechanisms involve the aggregation and spreading of abnormal proteins like alpha-synuclein, tau or amyloid in cortical and subcortical regions with subsequent dysregulation of multiple neurotransmitter systems. The degree of cognitive deterioration in these disorders is variable and ranges from mild cognitive impairment to severe cognitive dysfunction. There is also variation in the number and type of affected cognitive domains which can involve either a single domain like executive or visuospatial function or multiple ones. Novel genetic, biological fluid or imaging biomarkers appear promising in facilitating the diagnosis and staging of dementia in parkinsonian conditions. A significant part of current research in Parkinson's disease and other parkinsonian syndromes is targeted towards the cognitive aspects of these disorders. Stabilization or amelioration of cognitive outcomes represents a primary endpoint in many ongoing clinical trials for novel disease modifying treatments in this field. This article is part of the Special Issue "Parkinsonism across the spectrum of movement disorders and beyond" edited by Joseph Jankovic, Daniel D. Truong and Matteo Bologna.

The Impact of SNCA Variations and Its Product Alpha-Synuclein on Non-Motor Features of Parkinson's Disease

Parkinson’s disease (PD) is a common and progressive neurodegenerative disease, caused by the loss of dopaminergic neurons in the substantia nigra pars compacta in the midbrain, which is clinically characterized by a constellation of motor and non-motor manifestations. The latter include hyposmia, constipation, depression, pain and, in later stages, cognitive decline and dysautonomia. The main pathological features of PD are neuronal loss and consequent accumulation of Lewy bodies (LB) in the surviving neurons. Alpha-synuclein (α-syn) is the main component of LB, and α-syn aggregation and accumulation perpetuate neuronal degeneration. Mutations in the α-syn gene (SNCA) were the first genetic cause of PD to be identified. Generally, patients carrying SNCA mutations present early-onset parkinsonism with severe and early non-motor symptoms, including cognitive decline. Several SNCA polymorphisms were also identified, and some of them showed association with non-motor manifestations. The functional role of these polymorphisms is only partially understood. In this review we explore the contribution of SNCA and its product, α-syn, in predisposing to the non-motor manifestations of PD.

Alpha-synuclein research: defining strategic moves in the battle against Parkinson's disease

With the advent of the genetic era in Parkinson's disease (PD) research in 1997, α-synuclein was identified as an important player in a complex neurodegenerative disease that affects >10 million people worldwide. PD has been estimated to have an economic impact of $51.9 billion in the US alone. Since the initial association with PD, hundreds of researchers have contributed to elucidating the functions of α-synuclein in normal and pathological states, and these remain critical areas for continued research. With this position paper the authors strive to achieve two goals: first, to succinctly summarize the critical features that define α-synuclein's varied roles, as they are known today; and second, to identify the most pressing knowledge gaps and delineate a multipronged strategy for future research with the goal of enabling therapies to stop or slow disease progression in PD.

A systematic review of associations between common SNCA variants and clinical heterogeneity in Parkinson's disease

There is great heterogeneity in both the clinical presentation and rate of disease progression among patients with Parkinson’s disease (PD). This can pose prognostic difficulties in a clinical setting, and a greater understanding of the risk factors that contribute to modify disease course is of clear importance for optimizing patient care and clinical trial design. Genetic variants in SNCA are an established risk factor for PD and are candidates to modify disease presentation and progression. This systematic review aimed to summarize all available primary research reporting the association of SNCA polymorphisms with features of PD. We systematically searched PubMed and Web of Science, from inception to 1 June 2020, for studies evaluating the association of common SNCA variants with age at onset (AAO) or any clinical feature attributed to PD in patients with idiopathic PD. Fifty-eight studies were included in the review that investigated the association between SNCA polymorphisms and a broad range of outcomes, including motor and cognitive impairment, sleep disorders, mental health, hyposmia, or AAO. The most reproducible findings were with the REP1 polymorphism or rs356219 and an earlier AAO, but no clear associations were identified with an SNCA polymorphism and any individual clinical outcome. The results of this comprehensive summary suggest that, while there is evidence that genetic variance in the SNCA region may have a small impact on clinical outcomes in PD, the mechanisms underlying the association of SNCA polymorphisms with PD risk may not be a major factor driving clinical heterogeneity in PD.

Genome-wide survival study identifies a novel synaptic locus and polygenic score for cognitive progression in Parkinson's disease

A key driver of patients' well-being and clinical trials for Parkinson's disease (PD) is the course that the disease takes over time (progression and prognosis). To assess how genetic variation influences the progression of PD over time to dementia, a major determinant for quality of life, we performed a longitudinal genome-wide survival study of 11.2 million variants in 3,821 patients with PD over 31,053 visits. We discover RIMS2 as a progression locus and confirm this in a replicate population (hazard ratio (HR) = 4.77, P = 2.78 × 10-11), identify suggestive evidence for TMEM108 (HR = 2.86, P = 2.09 × 10-8) and WWOX (HR = 2.12, P = 2.37 × 10-8) as progression loci, and confirm associations for GBA (HR = 1.93, P = 0.0002) and APOE (HR = 1.48, P = 0.001). Polygenic progression scores exhibit a substantial aggregate association with dementia risk, while polygenic susceptibility scores are not predictive. This study identifies a novel synaptic locus and polygenic score for cognitive disease progression in PD and proposes diverging genetic architectures of progression and susceptibility.

"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.

Variable Effects of PD-Risk Associated SNPs and Variants in Parkinsonism-Associated Genes on Disease Phenotype in a Community-Based Cohort

Genetic risk factors for Parkinson's disease (PD) risk and progression have been identified from genome-wide association studies (GWAS), as well as studies of familial forms of PD, implicating common variants at more than 90 loci and pathogenic or likely pathogenic variants at 16 loci. With the goal of understanding whether genetic variants at these PD-risk loci/genes differentially contribute to individual clinical phenotypic characteristics of PD, we used structured clinical documentation tools within the electronic medical record in an effort to provide a standardized and detailed clinical phenotypic characterization at the point of care in a cohort of 856 PD patients. We analyzed common SNPs identified in previous GWAS studies, as well as low-frequency and rare variants at parkinsonism-associated genes in the MDSgene database for their association with individual clinical characteristics and test scores at baseline assessment in our community-based PD patient cohort: age at onset, disease duration, Unified Parkinson's Disease Rating Scale I-VI, cognitive status, initial and baseline motor and non-motor symptoms, complications of levodopa therapy, comorbidities and family history of neurological disease with one or more than one affected family members. We find that in most cases an individual common PD-risk SNP identified in GWAS is associated with only a single clinical feature or test score, while gene-level tests assessing low-frequency and rare variants reveal genes associated in either a unique or partially overlapping manner with the different clinical features and test scores. Protein-protein interaction network analysis of the identified genes reveals that while some of these genes are members of already identified protein networks others are not. These findings indicate that genetic risk factors for PD differentially affect the phenotypic presentation and that genes associated with PD risk are also differentially associated with individual disease phenotypic characteristics at baseline. These findings raise the intriguing possibility that different SNPs/gene effects impact discrete phenotypic characteristics. Furthermore, they support the hypothesis that different gene and protein-protein interaction networks that underlie PD risk, the PD phenotype, and the neurodegenerative process leading to the disease phenotype, and point to the significance of the genetic background on disease phenotype.

Genome-Wide Association Studies of Cognitive and Motor Progression in Parkinson's Disease

BACKGROUND

There are currently no treatments that stop or slow the progression of Parkinson's disease (PD). Case-control genome-wide association studies have identified variants associated with disease risk, but not progression. The objective of the current study was to identify genetic variants associated with PD progression.

METHODS

We analyzed 3 large longitudinal cohorts: Tracking Parkinson's, Oxford Discovery, and the Parkinson's Progression Markers Initiative. We included clinical data for 3364 patients with 12,144 observations (mean follow-up 4.2 years). We used a new method in PD, following a similar approach in Huntington's disease, in which we combined multiple assessments using a principal components analysis to derive scores for composite, motor, and cognitive progression. These scores were analyzed in linear regression in genome-wide association studies. We also performed a targeted analysis of the 90 PD risk loci from the latest case-control meta-analysis.

RESULTS

There was no overlap between variants associated with PD risk, from case-control studies, and PD age at onset versus PD progression. The APOE ε4 tagging variant, rs429358, was significantly associated with composite and cognitive progression in PD. Conditional analysis revealed several independent signals in the APOE locus for cognitive progression. No single variants were associated with motor progression. However, in gene-based analysis, ATP8B2, a phospholipid transporter related to vesicle formation, was nominally associated with motor progression (P = 5.3 × 10^-6 ).

CONCLUSIONS

We provide early evidence that this new method in PD improves measurement of symptom progression. We show that the APOE ε4 allele drives progressive cognitive impairment in PD. Replication of this method and results in independent cohorts are needed. © 2020 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

Effect of polygenic load on striatal dopaminergic deterioration in Parkinson disease

OBJECTIVE

To investigate the effect of polygenic load on the progression of striatal dopaminergic dysfunction in patients with Parkinson disease (PD).

METHODS

Using data from 335 patients with PD in the Parkinson's Progression Markers Initiative (PPMI) database, we investigated the longitudinal association of PD-associated polygenic load with changes in striatal dopaminergic activity as measured by ¹²³I-N-3-fluoropropyl-2-β-carboxymethoxy-3β-(4-iodophenyl) nortropane (¹²³I-FP-CIT) SPECT over 4 years. PD-associated polygenic load was estimated by calculating weighted genetic risk scores (GRS) using 1) all available 27 PD-risk single nucleotide polymorphisms (SNPs) in the PPMI database (GRS1) and 2) 23 SNPs with minor allele frequency >0.05 (GRS2).

RESULTS

GRS1 and GRS2 were correlated with younger age at onset in patients with PD (GRS1, Spearman ρ = -0.128, p = 0.019; GRS2, Spearman ρ = -0.109, p = 0.047). Although GRS1 did not show an association with changes in striatal ¹²³I-FP-CIT availability, GRS2 was associated with a slower decline of striatal dopaminergic activity (interactions with disease duration in linear mixed model; caudate nucleus, estimate = 0.399, SE = 0.165, p = 0.028; putamen, estimate = 0.396, SE = 0.137, p = 0.016).

CONCLUSIONS

Our results suggest that genetic factors for PD risk may have heterogeneous effects on striatal dopaminergic degeneration, and some factors may be associated with a slower decline of dopaminergic activity. Composition of PD progression-specific GRS may be useful in predicting disease progression in patients.

SNCA Rep1 promoter variability influences cognition in Parkinson's disease

BACKGROUND

While the association between alpha-synuclein gene promoter (Rep1) variability and risk of PD is well established, its association with cognition is unclear.

OBJECTIVES

To investigate the association between Rep1 and motor and cognitive outcomes in PD.

METHODS

Rep1 allele lengths were determined in 172 PD patients who were grouped into "long" and "short" carriers according to previous methods. Multivariable regression analysis was performed to investigate the effect of Rep1 length on cognitive and motor scores.

RESULTS

Long Rep1 allele carriers had significantly lower MMSE (P = 0.010) and higher UPDRS Part III (P = 0.026) and H & Y (P = 0.008) scores compared to short allele carriers (controlled for age, sex, and disease duration). Interaction analyses of Rep1 with apolipoprotein 4 revealed no significant effect on clinical outcomes.

CONCLUSIONS

PD patients carrying long Rep1 alleles are more impaired on cognitive and motor function independent of apolipoprotein 4 genotype. © 2019 International Parkinson and Movement Disorder Society.

Alpha-synuclein gene polymorphism affects risk of dementia in Han Chinese with Parkinson's disease

BACKGROUND

Single-nucleotide polymorphisms (SNPs) in the SNCA gene encoding alpha-synuclein have been shown to affect the PD phenotype. However, whether such polymorphisms can influence risk of dementia in PD remains unclear.

OBJECTIVES

To investigate possible associations between SNCA gene polymorphisms and dementia in patients with PD.

MATERIALS AND METHODS

A consecutive series of 291 PD patients with dementia (n = 45, 15.5%) or without it (n = 246, 84.5%) were genotyped at four SNPs in the SNCA gene. As controls, 615 healthy Han Chinese were also genotyped.

RESULTS

Three SNPs (rs11931074, rs7684318 and rs356219) were in strong linkage disequilibrium. The GG genotype at rs11931074 significantly reduced risk of PD (p = 0.023), but it significantly increased risk of dementia after PD onset (p = 0.015) based on the recessive genetic model. Logistic regression identified the following risk factors for dementia among patients with PD: age ≥65 years (odds ratio [OR] 2.69, 95% confidence interval [CI] 1.25-5.77, p = 0.011), education ≤6 years (OR 4.66, 95% CI 2.21-9.83, p < 0.001), part III score on the Unified Parkinson's Disease Rating Scale ≥40 (OR 5.01, 95% CI 2.40-10.45, p < 0.001), and GG genotype at rs11931074 (OR 2.81, 95% CI 1.16-6.83, p = 0.022).

CONCLUSIONS

PD patients carrying the protective GG genotype at SNCA rs11931074 may be at significantly higher risk of dementia than patients with other genotypes. Our results support the view that SNCA polymorphisms can have opposite effects on preclinical and clinical PD.

Global, Yet Incomplete Overview of Cohort Studies in Parkinson's disease

BACKGROUND

Parkinson's disease (PD) is characterized by heterogeneity and multifactorial longitudinal changes. To identify PD subtypes and factors influencing the disease course, multiple cohort studies have been designed globally. Knowledge about existing cohorts is pivotal to foster collaboration, which may help to advance the understanding of PD.

OBJECTIVE

To raise the awareness about PD cohorts and potential global collaboration opportunities.

METHODS

Observational cohort studies in clinical PD were identified by a European working group (JPND BioLoC-PD) and through literature search. Using a structured survey investigators of 44 cohorts provided basic information on cohorts and assessments performed.

RESULTS

For the 44 cohorts (32% on early/de-novo PD), 14.666 participants (cohorts' median: 138; range: 23-3.090), a median 1.5-year follow-up interval (0.5-4 years) and a median (planned) observational period of 5 years (1-20 years) were indicated. All studies have assessed motor functions often using rating scales (UPDRS-III; 93% of studies) and less frequently quantitative gait/balance (25%) or fine motor assessments (27%). Cognitive (100%), neuropsychiatric (91%), daily living (78%), sleep (70%), sensory (63%), and gastrointestinal/autonomic (55%) assessments were common and often comparable. Neuroimaging data (82%) and biomaterial (69%) have been collected in many studies. Surprisingly, possible disease modifiers, such as sport/physical activity (11%), have rarely been assessed.

CONCLUSIONS

Existing data of PD cohorts provide vast collaboration opportunities. We propose to establish a comprehensive, up-to-date, open-access internet platform with easy-to-use search tools of PD cohort descriptions and potentially available data. Bringing researchers together to enable collaborative joint, meta- and replication analyses is timely and necessary to advance PD research ultimately required for an understanding of PD that can be translated into more effective therapies.

The Length of SNCA Rep1 Microsatellite May Influence Cognitive Evolution in Parkinson's Disease

Background

Alpha-synuclein is a constituent of Lewy bodies and mutations of its gene cause familial Parkinson's disease (PD). A previous study showed that a variant of the alpha-synuclein gene (SNCA), namely the 263 bp allele of Rep1 was associated with faster motor progression in PD. On the contrary, a recent report failed to detect a detrimental effect of Rep1 263 on both motor and cognitive outcomes in PD. Aim of this study was to evaluate the influence of the Rep1 variants on disease progression in PD patients.

Methods

We recruited and genotyped for SNCA Rep1 426 PD patients with age at onset ≥40 years and disease duration ≥4 years. We then analyzed frequency and time of occurrence of wearing-off, dyskinesia, freezing of gait, visual hallucinations, and dementia using a multivariate Cox's proportional hazards regression model.

Results

SNCA Rep1 263 carriers showed significantly increased risk of both dementia (HR = 3.03) and visual hallucinations (HR = 2.69) compared to 263 non-carriers. Risk of motor complications did not differ in the two groups.

Conclusion

SNCA Rep1 263 allele is associated with a worse cognitive outcome in PD.

Silencing Alpha Synuclein in Mature Nigral Neurons Results in Rapid Neuroinflammation and Subsequent Toxicity

Human studies and preclinical models of Parkinson’s disease implicate the involvement of both the innate and adaptive immune systems in disease progression. Further, pro-inflammatory markers are highly enriched near neurons containing pathological forms of alpha synuclein (α-syn), and α-syn overexpression recapitulates neuroinflammatory changes in models of Parkinson’s disease. These data suggest that α-syn may initiate a pathological inflammatory response, however the mechanism by which α-syn initiates neuroinflammation is poorly understood. Silencing endogenous α-syn results in a similar pattern of nigral degeneration observed following α-syn overexpression. Here we aimed to test the hypothesis that loss of α-syn function within nigrostriatal neurons results in neuronal dysfunction, which subsequently stimulates neuroinflammation. Adeno-associated virus (AAV) expressing an short hairpin RNA (shRNA) targeting endogenous α-syn was unilaterally injected into the substantia nigra pars compacta (SNc) of adult rats, after which nigrostriatal pathology and indices of neuroinflammation were examined at 7, 10, 14 and 21 days post-surgery. Removing endogenous α-syn from nigrostriatal neurons resulted in a rapid up-regulation of the major histocompatibility complex class 1 (MHC-1) within transduced nigral neurons. Nigral MHC-1 expression occurred prior to any overt cell death and coincided with the recruitment of reactive microglia and T-cells to affected neurons. Following the induction of neuroinflammation, α-syn knockdown resulted in a 50% loss of nigrostriatal neurons in the SNc and a corresponding loss of nigrostriatal terminals and dopamine (DA) concentrations within the striatum. Expression of a control shRNA did not elicit any pathological changes. Silencing α-syn within glutamatergic neurons of the cerebellum did not elicit inflammation or cell death, suggesting that toxicity initiated by α-syn silencing is specific to DA neurons. These data provide evidence that loss of α-syn function within nigrostriatal neurons initiates a neuronal-mediated neuroinflammatory cascade, involving both the innate and adaptive immune systems, which ultimately results in the death of affected neurons.

Cell-Specific RNA Quantification in Human SN DA Neurons from Heterogeneous Post-mortem Midbrain Samples by UV-Laser Microdissection and RT-qPCR

Cell specificity of gene expression analysis is from particular relevance when the abundance of target cells is not homogeneous in the compared tissue samples, like it is the case, e.g., when comparing brain tissues from controls and in neurodegenerative disease states. While single-cell gene expression profiling is already a methodological challenge per se, it becomes even more prone to artifacts when analyzing individual cells from human post-mortem samples. Not only because human samples can never be matched as precisely as those from animal models, but also, because the RNA-quality that can be obtained from human samples usually displays a high range of variability. Here, we detail our most actual method for combining contact-free UV-laser microdissection (UV-LMD) with reverse transcription and quantitative PCR (RT-qPCR) that addresses all these issues. We specifically optimized our protocols to quantify and compare mRNA as well as miRNA levels in human neurons from post-mortem brain tissue. As human post-mortem tissue samples are never perfectly matched (e.g., in respect to distinct donor ages and RNA integrity numbers RIN), we refined data analysis by applying a linear mixed effects model to RT-qPCR data, which allows dissecting and subtracting linear contributions of distinct confounders on detected gene expression levels (i.e., RIN, age). All these issues were considered for comparative gene expression analysis in dopamine (DA) midbrain neurons of the Substantia nigra (SN) from controls and Parkinson's disease (PD) specimens, as the preferential degeneration of SN DA neurons in the pathological hallmark of PD. By utilizing the here-described protocol we identified that a variety of genes-encoding for ion channels, dopamine metabolism proteins, and PARK gene products-display a transcriptional dysregulation in remaining human SN DA neurons from PD brains compared to those of controls. We show that the linear mixed effects model allows further stratification of RT-qPCR data, as it indicated that differential gene expression of some genes was rather correlated with different ages of the analyzed human brain samples than with the disease state.

Inventory of real world data sources in Parkinson's disease

Background

Real world data have an important role to play in the evaluation of epidemiology and burden of disease; and in assisting health-care decision-makers, especially related to coverage and payment decisions. However, there is currently no overview of the existing longitudinal real world data sources in Parkinson’s disease (PD) in the USA. Such an assessment can be very helpful, to support a future effort to harmonize real world data collection and use the available resources in an optimal way.

Methods

The objective of this comprehensive literature review is to systematically identify and describe the longitudinal, real world data sources in PD in the USA, and to provide a summary of their measurements (categorized into 8 main dimensions: motor and neurological functions, cognition, psychiatry, activities of daily living, sleep, quality of life, autonomic symptoms and other). The literature search was performed using MEDLINE, EMBASE and internet key word search.

Results

Of the 53 data sources identified between May and August 2016, 16 were still ongoing. Current medications (81%) and comorbidities (79%) were frequently collected, in comparison to medical imaging (36%), genetic information (30%), caregiver burden (11%) and healthcare costs (2%). Many different measurements (n = 108) were performed and an interesting variability among used measurements was revealed.

Conclusions

Many longitudinal real world data sources on PD exist. Different types of measurements have been performed over time. To allow comparison and pooling of these multiple data sources, it will be essential to harmonize practices in terms of types of measurements.

Genetic Variants in SNCA and the Risk of Sporadic Parkinson's Disease and Clinical Outcomes: A Review

There is increasing evidence of the contribution of genetic susceptibility to the etiology of Parkinson's disease (PD). Genetic variations in the SNCA gene are well established by linkage and genome-wide association studies. Positive associations of single nucleotide polymorphisms (SNPs) in SNCA and increased risk for PD were found. However, the role of SNCA variants in individual traits or phenotypes of PD is unknown. Here, we reviewed the current literature and identified 57 studies, performed in fourteen different countries, that investigated SNCA variants and susceptibility to PD. We discussed the findings based on environmental factors, history of PD, clinical outcomes, and ethnicity. In conclusion, SNPs within the SNCA gene can modify the susceptibility to PD, leading to increased or decreased risk. The risk associations of some SNPs varied among samples. Of notice, no studies in South American or African populations were found. There is little information about the effects of these variants on particular clinical aspects of PD, such as motor and nonmotor symptoms. Similarly, evidence of possible interactions between SNCA SNPs and environmental factors or disease progression is scarce. There is a need to expand the clinical applicability of these data as well as to investigate the role of SNCA SNPs in populations with different ethnic backgrounds.

Variants in SNCA Gene Are Associated with Parkinson's Disease Risk and Cognitive Symptoms in a Brazilian Sample

Genetic susceptibility contributes to the etiology of sporadic Parkinson's Disease (PD) and worldwide studies have found positive associations of polymorphisms in the alpha-synuclein gene (SNCA) with the risk for PD. However, little is known about the influence of variants of SNCA in individual traits or phenotypical aspects of PD. Further, there is a lack of studies with Latin-American samples. We evaluated the association between SNCA single nucleotide polymorphisms (single nucleotide polymorphisms, SNPs - rs2583988, rs356219, rs2736990, and rs11931074) and PD risk in a Brazilians sample. In addition, we investigated their potential interactions with environmental factors and specific clinical outcomes (motor and cognitive impairments, depression, and anxiety). A total of 105 PD patients and 101 controls participated in the study. Single locus analysis showed that the risk allele of all SNPs were more frequent in PD patients (p < 0.05), and the associations of SNPs rs2583988, rs356219, and rs2736990 with increased PD risk were confirmed. Further, the G-rs356219 and C-rs2736990 alleles were associated with early onset PD. T-rs2583988, G-rs356219 and C-2736990 alleles were significantly more frequent in PD patients with cognitive impairments than controls in this condition. In addition, in a logistic regression model, we found an association of cognitive impairment with PD, and the practice of cognitive activity and smoking habits had a protective effect. This study shows for the first time an association of SNCA polymorphism and PD in a South-American sample. In addition, we found an interaction between SNP rs356219 and a specific clinical outcome, i.e., the increased risk for cognitive impairment in PD patients.

Common variant rs356182 near SNCA defines a Parkinson's disease endophenotype

Objective

Parkinson's disease (PD) presents clinically with several motor subtypes that exhibit variable treatment response and prognosis. Here, we investigated genetic variants for their potential association with PD motor phenotype and progression.

Methods

We screened 10 SNPs, previously associated with PD risk, for association with tremor‐dominant (TD) versus postural‐instability gait disorder (PIGD) motor subtypes. SNPs that correlated with the TD/PIGD ratio in a discovery cohort of 251 PD patients were then evaluated in a multi‐site replication cohort of 559 PD patients. SNPs associated with motor phenotype in both cross‐sectional cohorts were next evaluated for association with (1) rates of motor progression in a longitudinal subgroup of 230 PD patients and (2) brain alpha‐synuclein (SNCA) expression in the GTEx (Genotype‐Tissue Expression project) consortium database.

Results

Genotype at rs356182, near SNCA, correlated with the TD/PIGD ratio in both the discovery (Bonferroni‐corrected P = 0.04) and replication cohorts (P = 0.02). The rs356182 GG genotype was associated with a more tremor‐predominant phenotype and predicted a slower rate of motor progression (1‐point difference in annual rate of UPDRS‐III motor score change, P = 0.01). The rs356182 genotype was associated with SNCA expression in the cerebellum (P = 0.005).

Interpretation

Our study demonstrates that the GG genotype at rs356182 provides molecular definition for a clinically important endophenotype associated with (1) more tremor‐predominant motor phenomenology, (2) slower rates of motor progression, and (3) decreased brain expression of SNCA. Such molecularly defined endophenotyping in PD may benefit both clinical trial design and tailoring of clinical care as we enter the era of precision medicine.

The contribution of alpha synuclein to neuronal survival and function - Implications for Parkinson's disease

The aggregation of alpha synuclein (α-syn) is a neuropathological feature that defines a spectrum of disorders collectively termed synucleinopathies, and of these, Parkinson's disease (PD) is arguably the best characterized. Aggregated α-syn is the primary component of Lewy bodies, the defining pathological feature of PD, while mutations or multiplications in the α-syn gene result in familial PD. The high correlation between α-syn burden and PD has led to the hypothesis that α-syn aggregation produces toxicity through a gain-of-function mechanism. However, α-syn has been implicated to function in a diverse range of essential cellular processes such as the regulation of neurotransmission and response to cellular stress. As such, an alternative hypothesis with equal explanatory power is that the aggregation of α-syn results in toxicity because of a toxic loss of necessary α-syn function, following sequestration of functional forms α-syn into insoluble protein aggregates. Within this review, we will provide an overview of the literature linking α-syn to PD and the knowledge gained from current α-syn-based animal models of PD. We will then interpret these data from the viewpoint of the α-syn loss-of-function hypothesis and provide a potential mechanistic model by which loss of α-syn function could result in at least some of the neurodegeneration observed in PD. By providing an alternative perspective on the etiopathogenesis of PD and synucleinopathies, this may reveal alternative avenues of research in order to identify potential novel therapeutic targets for disease modifying strategies. The correlation between α-synuclein burden and Parkinson's disease pathology has led to the hypothesis that α-synuclein aggregation produces toxicity through a gain-of-function mechanism. However, in this review, we discuss data supporting the alternative hypothesis that the aggregation of α-synuclein results in toxicity because of loss of necessary α-synuclein function at the presynaptic terminal, following sequestration of functional forms of α-synuclein into aggregates.

Is Alpha-Synuclein Loss-of-Function a Contributor to Parkinsonian Pathology? Evidence from Non-human Primates

Accumulation of alpha-synuclein (α-syn) in Lewy bodies and neurites of midbrain dopamine neurons is diagnostic for Parkinson's disease (PD), leading to the proposal that PD is a toxic gain-of-function synucleinopathy. Here we discuss the alternative viewpoint that α-syn displacement from synapses by misfolding and aggregation results in a toxic loss-of-function. In support of this hypothesis we provide evidence from our pilot study demonstrating that knockdown of endogenous α-syn in dopamine neurons of non-human primates reproduces the pattern of nigrostriatal degeneration characteristic of PD.

Variants in the SNCA gene associate with motor progression while variants in the MAPT gene associate with the severity of Parkinson's disease

INTRODUCTION

It is well known that α-synuclein (SNCA) and microtubule associated protein (MAPT) genes predispose individuals to develop Parkinson's disease (PD). However, whether these genes contribute to differences in the variable progression observed in PD is obscure. This study aims to evaluate the association of common variants in SNCA (rs11931074, rs894278) and MAPT (rs242557_H1c haplotype, rs3744456) genes with the severity and duration of motor and cognitive performance.

METHODS

296 Chinese patients with PD were recruited from Shanghai Ruijin Hospital. Motor performance was assessed using the Unified Parkinson's Disease Rating Scale (UPDRS-III) and Hoehn &Yahar (H&Y) stages and cognitive performance using the Mini-Mental Status Examination (MMSE). Genetic associations were analysed using general linear modelling for severity and Cox regression analysis for duration to motor (UPDRS-III≥36 or H&Y ≥ 3, average duration 13 years) and cognitive (MMSE<27, average duration 8 years) cutoffs, covarying for age and gender.

RESULTS

The severity of motor function associated with synergic interaction of SNCA (rs11931074) and MAPT (rs3744456) (p ≤ 0.05) while longer survival to the motor cutoff associated with SNCA (rs11931074/T, HR = 0.4, p = 0.03). Increased severity of cognitive function associated with MAPT (H1c haplotype, p = 0.05) with none of the risk alleles chosen associated with survival to the cognitive cutoff (p > 0.05).

CONCLUSION

Our findings add further data showing that common variants in SNCA and MAPT genes contribute to variability in progression of PD, with SNCA variants associating with motor progression while MAPT variants associated with clinical severity.

Clinically meaningful parameters of progression and long-term outcome of Parkinson disease: An international consensus statement

Parkinson disease (PD) is associated with a clinical course of variable duration, severity, and a combination of motor and non-motor features. Recent PD research has focused primarily on etiology rather than clinical progression and long-term outcomes. For the PD patient, caregivers, and clinicians, information on expected clinical progression and long-term outcomes is of great importance. Today, it remains largely unknown what factors influence long-term clinical progression and outcomes in PD; recent data indicate that the factors that increase the risk to develop PD differ, at least partly, from those that accelerate clinical progression and lead to worse outcomes. Prospective studies will be required to identify factors that influence progression and outcome. We suggest that data for such studies is collected during routine office visits in order to guarantee high external validity of such research. We report here the results of a consensus meeting of international movement disorder experts from the Genetic Epidemiology of Parkinson's Disease (GEO-PD) consortium, who convened to define which long-term outcomes are of interest to patients, caregivers and clinicians, and what is presently known about environmental or genetic factors influencing clinical progression or long-term outcomes in PD. We propose a panel of rating scales that collects a significant amount of phenotypic information, can be performed in the routine office visit and allows international standardization. Research into the progression and long-term outcomes of PD aims at providing individual prognostic information early, adapting treatment choices, and taking specific measures to provide care optimized to the individual patient's needs.

Differential Co-Expression between α-Synuclein and IFN-γ Signaling Genes across Development and in Parkinson's Disease

Expression patterns of the alpha-synuclein gene (SNCA) were studied across anatomy, development, and disease to better characterize its role in the brain. In this postmortem study, negative spatial co-expression between SNCA and 73 interferon-γ (IFN-γ) signaling genes was observed across many brain regions. Recent animal studies have demonstrated that IFN-γ induces loss of dopamine neurons and nigrostriatal degeneration. This opposing pattern between SNCA and IFN-γ signaling genes increases with age (rho = −0.78). In contrast, a meta-analysis of four microarray experiments representing 126 substantia nigra samples reveals a switch to positive co-expression in Parkinson’s disease (p<0.005). Use of genome-wide testing demonstrates this relationship is specific to SNCA (p<0.002). This change in co-expression suggests an immunomodulatory role of SNCA that may provide insight into neurodegeneration. Genes showing similar co-expression patterns have been previously linked to Alzheimer’s (ANK1) and Parkinson’s disease (UBE2E2, PCMT1, HPRT1 and RIT2).