Glial cytoplasmic inclusions in white matter oligodendrocytes of multiple system atrophy brains contain insoluble alpha-synuclein

A characterization of Gaucher iPS-derived astrocytes: Potential implications for Parkinson's disease

While astrocytes, the most abundant cells found in the brain, have many diverse functions, their role in the lysosomal storage disorder Gaucher disease (GD) has not been explored. GD, resulting from the inherited deficiency of the enzyme glucocerebrosidase and subsequent accumulation of glucosylceramide and its acylated derivative glucosylsphingosine, has both non-neuronopathic (GD1) and neuronopathic forms (GD2 and 3). Furthermore, mutations in GBA1, the gene mutated in GD, are an important risk factor for Parkinson's disease (PD). To elucidate the role of astrocytes in the disease pathogenesis, we generated iAstrocytes from induced pluripotent stem cells made from fibroblasts taken from controls and patients with GD1, with and without PD. We also made iAstrocytes from an infant with GD2, the most severe and progressive form, manifesting in infancy. Gaucher iAstrocytes appropriately showed deficient glucocerebrosidase activity and levels and substrate accumulation. These cells exhibited varying degrees of astrogliosis, Glial Fibrillary Acidic Protein (GFAP) up-regulation and cellular proliferation, depending on the level of residual glucocerebrosidase activity. Glutamte uptake assays demonstrated that the cells were functionally active, although the glutamine transporter EEAT2 was upregulated and EEAT1 downregulated in the GD2 samples. GD2 iAstrocytes were morphologically different, with severe cytoskeletal hypertrophy, overlapping of astrocyte processes, pronounced up-regulation of GFAP and S100β, and significant astrocyte proliferation, recapitulating the neuropathology observed in patients with GD2. Although astrocytes do not express α-synuclein, when the iAstrocytes were co-cultured with dopaminergic neurons generated from the same iPSC lines, excessive α-synuclein released from neurons was endocytosed by astrocytes, translocating into lysosomes. Levels of aggregated α-synuclein increased significantly when cells were treated with monomeric or fibrillar α-synuclein. GD1-PD and GD2 iAstrocytes also exhibited impaired Cathepsin D activity, leading to further α-synuclein accumulation. Cytokine and chemokine profiling of the iAstrocytes demonstrated an inflammatory response. Thus, in patients with GBA1-associated parkinsonism, astrocytes appear to play a role in α-synuclein accumulation and processing, contributing to neuroinflammation.

Prion-Like Propagation of Protein Misfolding and Aggregation in Amyotrophic Lateral Sclerosis

The discovery that prion protein can misfold into a pathological conformation that encodes structural information capable of both propagation and inducing severe neuropathology has revolutionized our understanding of neurodegenerative disease. Many neurodegenerative diseases with a protein misfolding component are now classified as “prion-like” owing to the propagation of both symptoms and protein aggregation pathology in affected individuals. The neuromuscular disorder amyotrophic lateral sclerosis (ALS) is characterized by protein inclusions formed by either TAR DNA-binding protein of 43 kDa (TDP-43), Cu/Zn superoxide dismutase (SOD1), or fused in sarcoma (FUS), in both upper and lower motor neurons. Evidence from in vitro, cell culture, and in vivo studies has provided strong evidence to support the involvement of a prion-like mechanism in ALS. In this article, we review the evidence suggesting that prion-like propagation of protein aggregation is a primary pathomechanism in ALS, focusing on the key proteins and genes involved in disease (TDP-43, SOD1, FUS, and C9orf72). In each case, we discuss the evidence ranging from biophysical studies to in vivo examinations of prion-like spreading. We suggest that the idiopathic nature of ALS may stem from its prion-like nature and that elucidation of the specific propagating protein assemblies is paramount to developing effective therapies.

Selective vulnerability in α-synucleinopathies

Parkinson's disease, dementia with Lewy bodies, and multiple system atrophy are neurodegenerative disorders resulting in progressive motor/cognitive deficits among other symptoms. They are characterised by stereotypical brain cell loss accompanied by the formation of proteinaceous aggregations of the protein α-synuclein (α-syn), being, therefore, termed α-synucleinopathies. Although the presence of α-syn inclusions is a common hallmark of these disorders, the exact nature of the deposited protein is specific to each disease. Different neuroanatomical regions and cellular populations manifest a differential vulnerability to the appearance of protein deposits, cell dysfunction, and cell death, leading to phenotypic diversity. The present review describes the multiple factors that contribute to the selective vulnerability in α-synucleinopathies. We explore the intrinsic cellular properties in the affected regions, including the physiological and pathophysiological roles of endogenous α-syn, the metabolic and genetic build-up of the cells and their connectivity. These factors converge with the variability of the α-syn conformational strains and their spreading capacity to dictate the phenotypic diversity and regional vulnerability of each disease. Finally, we describe the exogenous and environmental factors that potentially contribute by igniting and modulating the differential pathology in α-synucleinopathies. In conclusion, we think that it is the confluence of this disruption of the cellular metabolic state and α-syn structural equilibrium through the anatomical connectivity which appears to initiate cascades of pathological processes triggered by genetic, environmental, or stochastic events that result in the "death by a thousand cuts" profile of α-synucleinopathies.

Converging Patterns of α-Synuclein Pathology in Multiple System Atrophy

We aimed to determine patterns of α-synuclein (α-syn) pathology in multiple system atrophy (MSA) using 70-µm-thick sections of 20 regions of the central nervous system of 37 cases with striato-nigral degeneration (SND) and 10 cases with olivo-ponto-cerebellar atrophy (OPCA). In SND cases with the shortest disease duration (phase 1), α-syn pathology was observed in striatum, lentiform nucleus, substantia nigra, brainstem white matter tracts, cerebellar subcortical white matter as well as motor cortex, midfrontal cortex, and sensory cortex. SND with increasing duration of disease (phase 2) was characterized by involvement of spinal cord and thalamus, while phase 3 was characterized by involvement of hippocampus and amygdala. Cases with the longest disease duration (phase 4) showed involvement of the visual cortex. We observed an increasing overlap of α-syn pathology with increasing duration of disease between SND and OPCA, and noted increasingly similar regional distribution patterns of α-syn pathology. The GBA variant, p.Thr408Met, was found to have an allele frequency of 6.94% in SND cases which was significantly higher compared with normal (0%) and other neurodegenerative disease pathologies (0.74%), suggesting that it is associated with MSA. Our findings indicate that SND and OPCA show distinct early foci of α-syn aggregations, but increasingly converge with longer disease duration to show overlapping patterns of α-syn pathology.

Slow Progressive Accumulation of Oligodendroglial Alpha-Synuclein (α-Syn) Pathology in Synthetic α-Syn Fibril-Induced Mouse Models of Synucleinopathy

Synucleinopathies are composed of Parkinson disease (PD), dementia with Lewy bodies (DLB), and multiple system atrophy (MSA). Alpha-synuclein (α-Syn) forms aggregates mainly in neurons in PD and DLB, while oligodendroglial α-Syn aggregates are characteristic of MSA. Recent studies have demonstrated that injections of synthetic α-Syn preformed fibrils (PFFs) into the brains of wild-type (WT) animals induce intraneuronal α-Syn aggregates and the subsequent interneuronal transmission of α-Syn aggregates. However, injections of α-Syn PFFs or even brain lysates of patients with MSA have not been reported to induce oligodendroglial α-Syn aggregates, raising questions about the pathogenesis of oligodendroglial α-Syn aggregates in MSA. Here, we report that WT mice injected with mouse α-Syn (m-α-Syn) PFFs develop neuronal α-Syn pathology after short postinjection (PI) intervals on the scale of weeks, while oligodendroglial α-Syn pathology emerges after longer PI intervals of several months. Abundant oligodendroglial α-Syn pathology in white matter at later time points is reminiscent of MSA. Furthermore, comparison between young and aged mice injected with m-α-Syn PFFs revealed that PI intervals rather than aging correlate with oligodendroglial α-Syn aggregation. These results provide novel insights into the pathological mechanisms of oligodendroglial α-Syn aggregation in MSA.

Conjugal multiple system atrophy: Chance, shared risk factors, or evidence of transmissibility?

OBJECTIVE

To describe conjugal multiple system atrophy (MSA) in a couple married for 44 years, and to report environmental risk factors possibly contributing to the occurrence.

METHODS

Case description of conjugal MSA with report of shared environmental risk factors and retrospective review of consecutively diagnosed MSA patients between 1998 and 2012 with autonomic reflex screen at Mayo Clinic, Rochester (clinical series). Probability calculation was based on the age-specific point prevalence of MSA.

RESULTS

A husband and wife both developed MSA symptoms at age 63. The husband's onset was of imbalance, followed by falls and genitourinary failure; parkinsonism and antecollis was evident on examination. Autonomic testing showed widespread autonomic failure. The patient died 2.25 years after onset. The wife initially developed urinary symptoms progressing to incontinence. Parkinsonism, dysphonia, and falls began within 1 year. Autonomic testing revealed severe autonomic failure. Interview with the surviving wife and son revealed substantial chemical exposure, in particular pesticides. In our clinical series, there were no other cases of conjugal MSA. Assuming an age-specific point prevalence of MSA based on population studies and independence of the two events, the probability of both individuals developing MSA by chance is 6.08 e-9.

CONCLUSION

Based on the population point prevalence of MSA, conjugal MSA is rare but possible. We conclude that this case of conjugal MSA likely occurred by chance; however, exposure to shared risk factors (pesticides) may be contributory. Because this is the first reported case of conjugal MSA, to our best knowledge, evidence for transmissibility between spouses is lacking.

Silver staining (Campbell-Switzer) of neuronal α-synuclein assemblies induced by multiple system atrophy and Parkinson's disease brain extracts in transgenic mice

Synucleinopathies [Parkinson’s disease (PD), dementia with Lewy bodies (DLB) and multiple system atrophy (MSA)] share filamentous α-synuclein assemblies in nerve cells and glial cells. We compared the abilities of brain extracts from MSA and PD patients to induce neuronal α-synuclein assembly and neurodegeneration following intracerebral injection in heterozygous mice transgenic for human mutant A53T α-synuclein. MSA extracts were more potent than PD extracts in inducing α-synuclein assembly and in causing neurodegeneration. MSA assemblies were Campbell-Switzer- and Gallyas-silver-positive, whereas PD assemblies were only Campbell-Switzer-positive, in confirmation of previous findings. However, induced α-synuclein inclusions were invariably Campbell-Switzer-positive and Gallyas-negative, irrespective of whether MSA or PD brain extracts were injected. The α-synuclein inclusions of non-injected homozygous mice transgenic for A53T α-synuclein were also Campbell-Switzer-positive and Gallyas-negative. These findings demonstrate that transgene expression and its intracellular environment dominated over the silver staining properties of the conformers of assembled α-synuclein.

Ultrasensitive Detection of Aggregated α-Synuclein in Glial Cells, Human Cerebrospinal Fluid, and Brain Tissue Using the RT-QuIC Assay: New High-Throughput Neuroimmune Biomarker Assay for Parkinsonian Disorders

Adult-onset neurodegenerative disorders, like Parkinson's disease (PD) and dementia with Lewy bodies (DLB), that share the accumulation of aggregated α-synuclein (αSynagg) as their hallmark molecular pathology are collectively known as α-synucleinopathies. Diagnosing α-synucleinopathies requires the post-mortem detection of αSynagg in various brain regions. Recent efforts to measure αSynagg in living patients include quantifying αSynagg in different biofluids as a biomarker for PD. We adopted the real-time quaking-induced conversion (RT-QuIC) assay to detect very low levels of αSynagg. We first optimized RT-QuIC for sensitivity, specificity, and reproducibility by using monomeric recombinant human wild-type αSyn as a substrate and αSynagg as the seed. Next, we exposed mouse microglia to αSyn pre-formed fibrils (αSynPFF) for 24 h. RT-QuIC assay revealed that the αSynPFF is taken up rapidly by mouse microglia, within 30 min, and cleared within 24 h. We then evaluated the αSyn RT-QuIC assay for detecting αSynagg in human PD, DLB, and Alzheimer's disease (AD) post-mortem brain homogenates (BH) along with PD and progressive supranuclear palsy (PSP) cerebrospinal fluid (CSF) samples and then determined protein aggregation rate (PAR) for αSynagg. The PD and DLB BH samples not only showed significantly higher αSynagg PAR compared to age-matched healthy controls and AD, but RT-QuIC was also highly reproducible with 94% sensitivity and 100% specificity. Similarly, PD CSF samples demonstrated significantly higher αSynagg PAR compared to age-matched healthy controls, with 100% sensitivity and specificity. Overall, the RT-QuIC assay accurately detects αSynagg seeding activity, offering a potential tool for antemortem diagnosis of α-synucleinopathies and other protein-misfolding disorders. Graphical Abstract A schematic representation of αSyn RT-QuIC assay.

Endogenous oligodendroglial alpha-synuclein and TPPP/p25α orchestrate alpha-synuclein pathology in experimental multiple system atrophy models

Multiple system atrophy (MSA) is characterized by the presence of distinctive glial cytoplasmic inclusions (GCIs) within oligodendrocytes that contain the neuronal protein alpha-synuclein (aSyn) and the oligodendroglia-specific phosphoprotein TPPP/p25α. However, the role of oligodendroglial aSyn and p25α in the formation of aSyn-rich GCIs remains unclear. To address this conundrum, we have applied human aSyn (haSyn) pre-formed fibrils (PFFs) to rat wild-type (WT)-, haSyn-, or p25α-overexpressing oligodendroglial cells and to primary differentiated oligodendrocytes derived from WT, knockout (KO)-aSyn, and PLP-haSyn-transgenic mice. HaSyn PFFs are readily taken up by oligodendroglial cells and can recruit minute amounts of endogenous aSyn into the formation of insoluble, highly aggregated, pathological assemblies. The overexpression of haSyn or p25α accelerates the recruitment of endogenous protein and the generation of such aberrant species. In haSyn PFF-treated primary oligodendrocytes, the microtubule and myelin networks are disrupted, thus recapitulating a pathological hallmark of MSA, in a manner totally dependent upon the seeding of endogenous aSyn. Furthermore, using oligodendroglial and primary cortical cultures, we demonstrated that pathology-related S129 aSyn phosphorylation depends on aSyn and p25α protein load and may involve different aSyn “strains” present in oligodendroglial and neuronal synucleinopathies. Importantly, this hypothesis was further supported by data obtained from human post-mortem brain material derived from patients with MSA and dementia with Lewy bodies. Finally, delivery of haSyn PFFs into the mouse brain led to the formation of aberrant aSyn forms, including the endogenous protein, within oligodendroglia and evoked myelin decompaction in WT mice, but not in KO-aSyn mice. This line of research highlights the role of endogenous aSyn and p25α in the formation of pathological aSyn assemblies in oligodendrocytes and provides in vivo evidence of the contribution of oligodendroglial aSyn in the establishment of aSyn pathology in MSA.

α-Synuclein Trafficking in Parkinson's Disease: Insights From Fly and Mouse Models

Protein aggregation and accumulation are common pathological hallmarks in neurodegenerative diseases. To efficiently clear and eliminate such aggregation becomes an important cellular strategy for cell survival. Lewy bodies inclusion and aggregation of α-Synuclein (α-Syn) during the pathogenesis of Parkinson's disease (PD) serve as a good example and are potentially linked to other pathological PD features such as progressive dopaminergic neuron cell death, behavioral defects, and nonmotor symptoms like anosmia, cognitive impairment, and depression. Years of research have revealed a variety of mechanisms underlying α-Syn aggregation, clearance, and spread. Particularly, vesicular routes associated with the trafficking of α-Syn, leading to its aggregation and accumulation, have been shown to play vital roles in PD pathogenesis. How α-Syn proteins propagate among cells in a prion-like manner, either from or to neurons and glia, via means of uptake or secretion, are questions under active investigation and have been of central interest in the field of PD study. This review covers components and pathways of possible vesicular routes involved in α-Syn trafficking. Events including but not limited to exocytosis and endocytosis will be discussed within the context of an overall cellular trafficking theme. Recent advances on α-Syn trafficking mechanisms and their significance in mediating PD pathogenesis will be thoroughly reviewed, ending with a discussion on the advantages and limitations of different animal PD models.

Transmission of α-synuclein seeds in neurodegenerative disease: recent developments

Cell-to-cell transmission of proteopathic alpha-synuclein (α-syn) seeds is increasingly thought to underlie the progression of neurodegenerative diseases including Parkinson's disease, dementia with Lewy bodies, multiple system atrophy, and related synucleinopathies. As such, it is important to understand the chemical and biological relationships between cells and pathological aggregates of α-syn. This brief review updates our understanding of the templated spread of α-syn pathology in neurodegenerative disease from the perspective of proteopathic α-syn seeds, including how these seeds are processed by cells as well as their effects on cellular function. Recent advances in understanding the conformations of α-syn seeds are highlighted, and the possible structural basis for the observed heterogeneity of synucleinopathies is discussed. Finally, we propose the possibility that some known risk factors for synucleinopathies may in fact potentiate the cell-to-cell transmission of α-syn pathology via imbalances in interrelated cell biological processes.

Autonomic dysfunction in genetic forms of synucleinopathies

The discovery of genetic links between alpha-synuclein and PD has opened unprecedented opportunities for research into a new group of diseases, now collectively known as synucleinopathies. Autonomic dysfunction, including cardiac sympathetic denervation, has been reported in familial forms of synucleinopathies that have Lewy bodies at the core of their pathogenesis. SNCA mutations and multiplications, LRRK2 disease with Lewy bodies as well as other common, sporadic forms of idiopathic PD, MSA, pure autonomic failure, and dementia with Lewy bodies have all been associated with dysautonomia. By contrast, in familial cases of parkinsonism without Lewy bodies, such as in PARK2, the autonomic profile remains normal throughout the course of the disease. The degeneration of the central and peripheral autonomic systems in genetic as well as sporadic forms of neurodegenerative synucleinopathies correlates with the accumulation of alpha-synuclein immunoreactive-containing inclusions. Given that dysautonomia has a significant impact on the quality of life of sufferers and autonomic symptoms are generally treatable, a prompt diagnostic testing and treatment should be provided. Moreover, new evidence suggests that autonomic dysfunction can be used as an outcome prediction factor in some forms of synucleinopathies or premotor diagnostic markers that could be used in the future to define further research avenues. In this review, we describe the autonomic dysfunction of genetic synucleinopathies in comparison to the dysautonomia of sporadic forms of alpha-synuclein accumulation and provide the reader with an up-to-date overview of the current understanding in this fast-growing field. © 2018 International Parkinson and Movement Disorder Society.

A cullin-RING ubiquitin ligase targets exogenous α-synuclein and inhibits Lewy body-like pathology

Parkinson's disease (PD) is a neurological disorder characterized by the progressive accumulation of neuronal α-synuclein (αSyn) inclusions called Lewy bodies. It is believed that Lewy bodies spread throughout the nervous system due to the cell-to-cell propagation of αSyn via cycles of secretion and uptake. Here, we investigated the internalization and intracellular accumulation of exogenous αSyn, two key steps of Lewy body pathogenesis, amplification and spreading. We found that stable αSyn fibrils substantially accumulate in different cell lines upon internalization, whereas αSyn monomers, oligomers, and dissociable fibrils do not. Our data indicate that the uptake-mediated accumulation of αSyn in a human-derived neuroblastoma cell line triggered an adaptive response that involved proteins linked to ubiquitin ligases of the S-phase kinase-associated protein 1 (SKP1), cullin-1 (Cul1), and F-box domain-containing protein (SCF) family. We found that SKP1, Cul1, and the F-box/LRR repeat protein 5 (FBXL5) colocalized and physically interacted with internalized αSyn in cultured cells. Moreover, the SCF containing the F-box protein FBXL5 (SCFFBXL5) catalyzed αSyn ubiquitination in reconstitution experiments in vitro using recombinant proteins and in cultured cells. In the human brain, SKP1 and Cul1 were recruited into Lewy bodies from brainstem and neocortex of patients with PD and related neurological disorders. In both transgenic and nontransgenic mice, intracerebral administration of exogenous αSyn fibrils triggered a Lewy body-like pathology, which was amplified by SKP1 or FBXL5 loss of function. Our data thus indicate that SCFFXBL5 regulates αSyn in vivo and that SCF ligases may constitute targets for the treatment of PD and other α-synucleinopathies.

α-Synuclein pathology in Parkinson's disease and related α-synucleinopathies

Over 20 years ago, the synaptic protein α-synuclein was identified as the primary component of the Lewy bodies (LBs) that are a sine qua non of Parkinson's disease (PD). Since that time, extensive research has demonstrated that α-synuclein pathology is not only a hallmark of PD, but can also cause neuronal dysfunction and death. Detailed staging of α-synuclein pathology in the brains of patients has revealed a progressive pattern of pathology that correlates with the symptoms of disease. Early in the disease course, PD patients exhibit motor dysfunction, and α-synuclein pathology at this stage is primarily found in regions controlling motor function. At later stages of disease as patients' cognitive function deteriorates, α-synuclein pathology can be found in cortical structures responsible for higher cognitive processing. The stereotypical progression of α-synuclein pathology through the brain over time suggests that there may be a physical transmission of pathological α-synuclein from one area of the brain to another. The transmission hypothesis posits that an initial seed of pathological α-synuclein in one neuron may be released and taken up by another vulnerable neuron and thereby initiate pathological misfolding of α-synuclein in the recipient neuron. In recent years, convergent evidence from various studies has indicated that pathological protein transmission can occur in the human brain. Cell and animal models based on the transmission hypothesis have shown not only that pathological α-synuclein can be transmitted from cell-to-cell, but that this pathology can lead to neuronal dysfunction and degeneration. The α-synuclein transmission hypothesis has profound implications for treatment of what is currently an intractable neurodegenerative disease. In this review, we explore the evidence for cell-to-cell transmission of pathological α-synuclein, the current understanding of how pathological α-synuclein can move to a new cell and template misfolding, and the therapeutic implications of α-synuclein transmission.

Fyn kinase regulates misfolded α-synuclein uptake and NLRP3 inflammasome activation in microglia

Persistent microglia-mediated neuroinflammation is a major pathophysiological contributor to the progression of Parkinson's disease (PD), but the cell-signaling mechanisms governing chronic neuroinflammation are not well understood. Here, we show that Fyn kinase, in conjunction with the class B scavenger receptor CD36, regulates the microglial uptake of aggregated human α-synuclein (αSyn), which is the major component of PD-associated Lewy bodies. αSyn can effectively mediate LPS-independent priming and activation of the microglial NLRP3 inflammasome. Fyn kinase regulates both of these processes; it mediates PKCδ-dependent NF-κB-p65 nuclear translocation, leading to inflammasome priming, and facilitates αSyn import into microglia, contributing to the generation of mitochondrial reactive oxygen species and consequently to inflammasome activation. In vivo experiments using A53T and viral-αSyn overexpression mouse models as well as human PD neuropathological results further confirm the role of Fyn in NLRP3 inflammasome activation. Collectively, our study identifies a novel Fyn-mediated signaling mechanism that amplifies neuroinflammation in PD.

Replication of multiple system atrophy prions in primary astrocyte cultures from transgenic mice expressing human α-synuclein

Glial cytoplasmic inclusions (GCIs) containing aggregated and hyperphosphorylated α-synuclein are the signature neuropathological hallmark of multiple system atrophy (MSA). Native α-synuclein can adopt a prion conformation that self-propagates and spreads throughout the brain ultimately resulting in neurodegeneration. A growing body of evidence argues that, in addition to oligodendrocytes, astrocytes contain α-synuclein inclusions in MSA and other α-synucleinopathies at advanced stages of disease. To study the role of astrocytes in MSA, we added MSA brain homogenate to primary cultures of astrocytes from transgenic (Tg) mouse lines expressing human α-synuclein. Astrocytes from four Tg lines, expressing either wild-type or mutant (A53T or A30P) human α-synuclein, propagated and accumulated α-synuclein prions. Furthermore, we found that MSA-infected astrocytes formed two morphologically distinct α-synuclein inclusions: filamentous and granular. Both types of cytoplasmic inclusions shared several features characteristic of α-synuclein inclusions in synucleinopathies: hyperphosphorylation preceded by aggregation, ubiquitination, thioflavin S–positivity, and co-localization with p62. Our findings demonstrate that human α-synuclein forms distinct inclusion morphologies and propagates within cultured Tg astrocytes exposed to MSA prions, indicating that α-synuclein expression determines the tropism of inclusion formation in certain cells. Thus, our work may prove useful in elucidating the role of astrocytes in the pathogenic mechanisms that feature in neurodegeneration caused by MSA prions.

The role of lipids in α-synuclein misfolding and neurotoxicity

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

Parkinson's and Lewy body dementia CSF biomarkers

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

Cerebral mitochondrial electron transport chain dysfunction in multiple system atrophy and Parkinson's disease

Multiple system atrophy (MSA) is a neurodegenerative disease characterised by glial cytoplasmic inclusions (GCIs), containing α-synuclein. Mutated COQ2, encoding an enzyme essential for co-enzyme Q10 (CoQ10) biosynthesis, has been associated with MSA. CoQ10 is an electron carrier in the mitochondrial electron transport chain (ETC) and antioxidant. It has been shown to be deficient in MSA brain tissue, thus implicating mitochondrial dysfunction in MSA. To investigate mitochondrial dysfunction in MSA further we examined ETC activity in MSA and control brain tissue, compared with Parkinson's disease (PD) where mitochondrial dysfunction is known to be important. Using cerebellar and occipital white matter ETC complex I, II/III and IV activities were measured spectrophotometrically, selected individual components of the ETC were assessed by immunoblotting and cellular complex IV activity was analysed by enzyme histochemistry. We show decreased complex II/III activity with increased complex I and IV activity in MSA cerebellar white matter. This corresponds with the deficit in CoQ10 previously described in MSA and reflects the high regional pathological burden of GCIs. This study highlights mitochondrial dysfunction in MSA pathogenesis, suggests an influence on selective regional vulnerability to disease and points to shared disease mechanisms in α-synucleinopathies.

Marine-Derived Natural Compounds for the Treatment of Parkinson's Disease

Parkinson’s disease (PD) is a neurodegenerative disorder caused by the loss of dopaminergic neurons, leading to the motor dysfunctions of patients. Although the etiology of PD is still unclear, the death of dopaminergic neurons during PD progress was revealed to be associated with the abnormal aggregation of α-synuclein, the elevation of oxidative stress, the dysfunction of mitochondrial functions, and the increase of neuroinflammation. However, current anti-PD therapies could only produce symptom-relieving effects, because they could not provide neuroprotective effects, stop or delay the degeneration of dopaminergic neurons. Marine-derived natural compounds, with their novel chemical structures and unique biological activities, may provide anti-PD neuroprotective effects. In this study, we have summarized anti-PD marine-derived natural products which have shown pharmacological activities by acting on various PD targets, such as α-synuclein, monoamine oxidase B, and reactive oxygen species. Moreover, marine-derived natural compounds currently evaluated in the clinical trials for the treatment of PD are also discussed.

Emerging Developments in Targeting Proteotoxicity in Neurodegenerative Diseases

The most common neurodegenerative diseases are Alzheimer's disease (AD), Parkinson's disease (PD), Huntington's disease, frontotemporal lobar degeneration, and the motor neuron diseases, with AD affecting approximately 6% of people aged 65 years and older, and PD affecting approximately 1% of people aged over 60 years. Specific proteins are associated with these neurodegenerative diseases, as determined by both immunohistochemical studies on post-mortem tissue and genetic screening, where protein misfolding and aggregation are key hallmarks. Many of these proteins are shown to misfold and aggregate into soluble non-native oligomers and large insoluble protein deposits (fibrils and plaques), both of which may exert a toxic gain of function. Proteotoxicity has been examined intensively in cell culture and in in vivo models, and clinical trials of methods to attenuate proteotoxicity are relatively new. Therapies to enhance cellular protein quality control mechanisms such as upregulation of chaperones and clearance/degradation pathways, as well as immunotherapies against toxic protein conformations, are being actively pursued. In this article, we summarize the common pathophysiology of neurodegenerative disease, and review therapies in early-phase clinical trials that target the proteotoxic component of several neurodegenerative diseases.

Characterization of the metal status of natively purified alpha-synuclein from human blood, brain tissue, or recombinant sources using size exclusion ICP-MS reveals no significant binding of Cu, Fe or Zn

The binding of Cu, Fe or Zn to alpha-synuclein has been implicated in neurodegenerative disease, such as Parkinson's.

Quantification of brain-derived extracellular vesicles in plasma as a biomarker to diagnose Parkinson's and related diseases

INTRODUCTION

There is still a substantial unmet need for blood-based biomarkers to make an objective diagnosis of Parkinson's disease (PD) and the parkinsonism-plus syndromes. This study is aimed to determine whether enumeration of brain-derived exosomes (BDEs) in plasma is informative in the diagnosis of those diseases.

METHODS

We have developed a specific method to enumerate the plasma levels of neuron-derived, astrocyte-derived, and oligodendrocyte-derived exosomes (NDEs, ADEs and ODEs, respectively), and quantified them individually in patients with PD (n = 15), multiple system atrophy (MSA, n = 15), progressive supranuclear palsy (PSP, n = 7) and disease controls (n = 15). Our assays employ specific antibodies against molecules expressed by neurons, astrocytes and oligodendrocytes, respectively, combined with an antibody to the exosome common marker CD81.

RESULTS

The plasma levels of NDEs showed significant increase in PD compared to control (p < 0.01) and MSA (p < 0.05) (one-way ANOVA, Bonferroni post hoc test). The plasma levels of ODEs and the ratio of ODE/NDE showed a significant correlation with UPDRS part III scores in the patients with MSA with predominant parkinsonism (MSA-P) (r² = 0.57, n = 6, p = 0.048) and in the patients with PD (r² = 0.51, n = 14, p = 0.0041), respectively.

CONCLUSIONS

This is the first paper that enumerated NDE, ADE, and ODE in human plasma and showed the usefulness of those levels as biomarkers for PD. Our results suggest the capability of the plasma levels of NDE and ODE as a diagnostic and surrogate biomarker for PD and MSA-P, respectively.

Anle138b modulates α-synuclein oligomerization and prevents motor decline and neurodegeneration in a mouse model of multiple system atrophy

Background

MSA is a fatal neurodegenerative disease characterized by autonomic failure and severe motor impairment. Its main pathological hallmark is the accumulation of α‐synuclein in oligodendrocytes, leading to glial and neuronal dysfunction and neurodegeneration. These features are recapitulated in the PLP‐hαSyn mouse model expressing human α‐synuclein in oligodendrocytes. At present, there is no effective disease‐modifying therapy. Previous experiments have shown that the aggregation inhibitor, anle138b, reduces neurodegeneration and behavioral deficits in mouse models of other proteinopathies.

Objectives

To test the therapeutic potential of anle138b in a mouse model of MSA.

Methods

Two‐month‐old PLP‐hαSyn mice were fed over a period of 4 months with pellets containing anle138b at two different doses (0.6 and 2 g/kg) and compared to healthy controls and PLP‐hαSyn mice fed with placebo pellets. At the end of the treatment, behavioral and histological analyses were performed.

Results

We observed a reversal of motor function to healthy control levels when PLP‐hαSyn mice were treated with both doses of anle138b. Histological and molecular analyses showed a significant reduction in α‐synuclein oligomers and glial cytoplasmic inclusions in animals fed with anle138b compared to nontreated mice. These animals also present preservation of dopaminergic neurons and reduction in microglial activation in SN correlating with the α‐synuclein reduction observed.

Conclusions

Anle138b reduces α‐synuclein accumulation in PLP‐hαSyn mice, leading to neuroprotection, reduction of microglial activation, and preservation of motor function supporting the use of anle138b in a future clinical trial for MSA. © 2018 The Authors. Movement Disorders published by Wiley Periodicals, Inc. on behalf of International Parkinson and Movement Disorder Society.

Converging Patterns of α-Synuclein Pathology in Multiple System Atrophy

We aimed to determine patterns of α-synuclein (α-syn) pathology in multiple system atrophy (MSA) using 70-µm-thick sections of 20 regions of the central nervous system of 37 cases with striato-nigral degeneration (SND) and 10 cases with olivo-ponto-cerebellar atrophy (OPCA). In SND cases with the shortest disease duration (phase 1), α-syn pathology was observed in striatum, lentiform nucleus, substantia nigra, brainstem white matter tracts, cerebellar subcortical white matter as well as motor cortex, midfrontal cortex, and sensory cortex. SND with increasing duration of disease (phase 2) was characterized by involvement of spinal cord and thalamus, while phase 3 was characterized by involvement of hippocampus and amygdala. Cases with the longest disease duration (phase 4) showed involvement of the visual cortex. We observed an increasing overlap of α-syn pathology with increasing duration of disease between SND and OPCA, and noted increasingly similar regional distribution patterns of α-syn pathology. The GBA variant, p.Thr408Met, was found to have an allele frequency of 6.94% in SND cases which was significantly higher compared with normal (0%) and other neurodegenerative disease pathologies (0.74%), suggesting that it is associated with MSA. Our findings indicate that SND and OPCA show distinct early foci of α-syn aggregations, but increasingly converge with longer disease duration to show overlapping patterns of α-syn pathology.

The pathogenesis linked to coenzyme Q10 insufficiency in iPSC-derived neurons from patients with multiple-system atrophy

Multiple-system atrophy (MSA) is a neurodegenerative disease characterized by autonomic failure with various combinations of parkinsonism, cerebellar ataxia, and pyramidal dysfunction. We previously reported that functionally impaired variants of COQ2, which encodes an essential enzyme in the biosynthetic pathway of coenzyme Q10, are associated with MSA. Here, we report functional deficiencies in mitochondrial respiration and the antioxidative system in induced pluripotent stem cell (iPSC)-derived neurons from an MSA patient with compound heterozygous COQ2 mutations. The functional deficiencies were rescued by site-specific CRISPR/Cas9-mediated gene corrections. We also report an increase in apoptosis of iPSC-derived neurons from MSA patients. Coenzyme Q10 reduced apoptosis of neurons from the MSA patient with compound heterozygous COQ2 mutations. Our results reveal that cellular dysfunctions attributable to decreased coenzyme Q10 levels are related to neuronal death in MSA, particularly in patients with COQ2 variants, and may contribute to the development of therapy using coenzyme Q10 supplementation.

The effect of truncation on prion-like properties of α-synuclein

Increasing evidence suggests that α-synuclein (αS) aggregates in brains of individuals with Parkinson's disease and dementia with Lewy bodies can spread in a prion-like manner. Although the initial αS nuclei are pivotal in determining αS fibril polymorphs and resulting phenotypes, it is not clear how the initial fibril seeds are generated. Previous studies have shown that αS truncation might have an important role in αS aggregation. However, little is known about how this truncation influences αS's propagation properties. In the present study, we generated αS fibrils from a series of truncated human αS constructs, characterized their structures and conformational stabilities, and investigated their ability to convert the conformation of full-length αS in vitro, in cultured cells, and in WT mice. We show that both C- and N-terminal truncations of human αS induce fibril polymorphs and exhibit different cross-seeding activities. N-terminally 10- or 30-residue-truncated human αS fibrils induced more abundant αS pathologies than WT fibrils in mice, whereas other truncated fibrils induced less abundant pathologies. Biochemical analyses of these truncated fibrils revealed that N-terminal 10- or 30-residue truncations of human αS change the fibril conformation in a manner that increases their structural compatibility with WT mouse αS fibrils and reduces their stability. C-terminally 20-residue-truncated fibrils displayed enhanced seeding activity in vitro Our findings imply that truncation of αS can influence its prion-like pathogenicity, resulting in phenotypic diversity of α-synucleinopathies.

Intercellular Spread of Protein Aggregates in Neurodegenerative Disease

Most neurodegenerative diseases are characterized by the accumulation of protein aggregates, some of which are toxic to cells. Mounting evidence demonstrates that in several diseases, protein aggregates can pass from neuron to neuron along connected networks, although the role of this spreading phenomenon in disease pathogenesis is not completely understood. Here we briefly review the molecular and histopathological features of protein aggregation in neurodegenerative disease, we summarize the evidence for release of proteins from donor cells into the extracellular space, and we highlight some other mechanisms by which protein aggregates might be transmitted to recipient cells. We also discuss the evidence that supports a role for spreading of protein aggregates in neurodegenerative disease pathogenesis and some limitations of this model. Finally, we consider potential therapeutic strategies to target spreading of protein aggregates in the treatment of neurodegenerative diseases.

Comparison of the in vivo induction and transmission of α-synuclein pathology by mutant α-synuclein fibril seeds in transgenic mice

Parkinson's disease (PD) is one of many neurodegenerative diseases termed synucleinopathies, neuropathologically defined by inclusions containing aggregated α-synuclein (αS). αS gene (SNCA) mutations can directly cause autosomal dominant PD. In vitro studies demonstrated that SNCA missense mutations may either enhance or diminish αS aggregation but cross-seeding of mutant and wild-type αS proteins appear to reduce aggregation efficiency. Here, we extended these studies by assessing the effects of seeded αS aggregation in αS transgenic mice through intracerebral or peripheral injection of various mutant αS fibrils. We observed modestly decreased time to paralysis in mice transgenic for human A53T αS (line M83) intramuscularly injected with H50Q, G51D or A53E αS fibrils relative to wild-type αS fibrils. Conversely, E46K αS fibril seeding was significantly delayed and less efficient in the same experimental paradigm. However, the amount and distribution of αS inclusions in the central nervous system were similar for all αS fibril muscle injected mice that developed paralysis. Mice transgenic for human αS (line M20) injected in the hippocampus with wild-type, H50Q, G51D or A53E αS fibrils displayed induction of αS inclusion pathology that increased and spread over time. By comparison, induction of αS aggregation following the intrahippocampal injection of E46K αS fibrils in M20 mice was much less efficient. These findings show that H50Q, G51D or A53E can efficiently cross-seed and induce αS pathology in vivo. In contrast, E46K αS fibrils are intrinsically inefficient at seeding αS inclusion pathology. Consistent with previous in vitro studies, E46K αS polymers are likely distinct aggregated conformers that may represent a unique prion-like strain of αS.

Cryo-EM structure of alpha-synuclein fibrils

Parkinson’s disease is a progressive neuropathological disorder that belongs to the class of synucleinopathies, in which the protein alpha-synuclein is found at abnormally high concentrations in affected neurons. Its hallmark are intracellular inclusions called Lewy bodies and Lewy neurites. We here report the structure of cytotoxic alpha-synuclein fibrils (residues 1–121), determined by cryo-electron microscopy at a resolution of 3.4 Å. Two protofilaments form a polar fibril composed of staggered β-strands. The backbone of residues 38 to 95, including the fibril core and the non-amyloid component region, are well resolved in the EM map. Residues 50–57, containing three of the mutation sites associated with familial synucleinopathies, form the interface between the two protofilaments and contribute to fibril stability. A hydrophobic cleft at one end of the fibril may have implications for fibril elongation, and invites for the design of molecules for diagnosis and treatment of synucleinopathies.

People with Parkinson’s disease have damaged cells in a part of the brain involved in movement, learning and reward-seeking behaviors. These cells contain blob-like aggregates that contain abnormally high amounts of a protein called alpha-synuclein. It is generally believed that, within these blobs, this protein clusters together into small needles called fibrils.

Discerning the structure of a fibril could help researchers to understand both how alpha-synuclein damages brain cells and how diseases like Parkinson’s spread. Biophysicists have attempted to reveal the fibril structure previously. But many of these efforts only looked at short segments of the alpha-synuclein protein. Researchers still need more detailed imagery of the fibrils to confirm previous findings regarding their architecture and ultimately to identify ways to counteract the damage they cause.

Guerrero-Ferreira et al. used a technique called cryo-electron microscopy to capture images of frozen fibrils made from a version of human alpha-synuclein that readily aggregates and that is only slightly shorter than the full-length protein. Processing these high-resolution images with computer software then revealed a three-dimensional model of the fibril structure, in which fine details are clearly visible. In the fibril, the proteins cluster to form a helix, similar to a flight of stairs. Each turn of the helix is formed by two alpha-synuclein molecules, facing each other but rotated by almost 180 degrees from one another. The three-dimensional model displays which parts of the protein lie at the core of the helix and thereby stabilize the fibril structure. Guerrero-Ferreira et al. speculate that fibrils may also take alternative forms because common alpha-synuclein mutations, which correlate with disease, would destabilize the observed helical structure.

In the future, researchers may be able to use the features of this three-dimensional model to help design molecules that would make the fibrils detectable via medical imaging. This could help doctors to diagnose people with Parkinson’s disease at an earlier stage. Further research is also needed to understand where and how fibrils form, if differences in fibril structures exist within or between patients, possibly leading to different sub-classes of the disease, and how such fibrils interact with and possibly damage human brain cells.

Neurodegeneration and the ordered assembly of α-synuclein

In 2017, it was 200 years since James Parkinson published 'An Essay on the Shaking Palsy' and 20 years since α-synuclein aggregation came to the fore. In 1998, multiple system atrophy joined Parkinson's disease and dementia with Lewy bodies as the third major synucleinopathy. Here, we describe the work that led to the identification of α-synuclein in Lewy bodies, Lewy neurites and Papp-Lantos bodies. We also review some of the findings reported since 1997.

Are We Ready for Detecting α-Synuclein Prone to Aggregation in Patients? The Case of "Protein-Misfolding Cyclic Amplification" and "Real-Time Quaking-Induced Conversion" as Diagnostic Tools

The accumulation and deposition of α-synuclein aggregates in brain tissue is the main event in the pathogenesis of different neurodegenerative disorders grouped under the term of synucleinopathies. They include Parkinson's disease, dementia with Lewy bodies and multiple system atrophy. To date, the diagnosis of any of these disorders mainly relies on the recognition of clinical symptoms, when the neurodegeneration is already in an advanced phase. In the last years, several efforts have been carried out to develop new diagnostic tools for early diagnosis of synucleinopathies, with special interest to Parkinson's disease. The Protein-Misfolding Cyclic Amplification (PMCA) and the Real-Time Quaking-Induced Conversion (RT-QuIC) are ultrasensitive protein amplification assays for the detection of misfolded protein aggregates. Starting from the successful application in the diagnosis of human prion diseases, these techniques were recently tested for the detection of misfolded α-synuclein in brain homogenates and cerebrospinal fluid samples of patients affected by synucleinopathies. So far, only a few studies on a limited number of samples have been performed to test PMCA and RT-QuIC diagnostic reliability. Neverthless, these assays have shown very high sensitivity and specificity in detecting synucleinopathies even at the pre-clinical stage. Despite the application of PMCA and RT-QuIC for α-synuclein detection in biological fluids is very recent, these techniques seem to have the potential for identifying subjects that will be likely to develop synucleinopathies.

Cellular milieu imparts distinct pathological α-synuclein strains in α-synucleinopathies

In Lewy body (LB) diseases, including Parkinson’s disease (PD), without and with dementia (PDD), dementia with Lewy bodies (DLB) and Alzheimer’s disease (AD) patients with LB co-pathology¹, α-synuclein (α-Syn) aggregates in neurons as LBs and Lewy neurites (LNs)², while in multiple system atrophy (MSA), α-Syn mainly accumulates in oligodendrocytes as glial cytoplasmic inclusions (GCIs)³. Here, we report that pathological α-Syn in GCIs and LBs (GCI-α-Syn and LB-α-Syn) are conformationally and biologically distinct. GCI-α-Syn forms more compact structures and is ~1,000-fold more potent than LB-α-Syn in seeding α-Syn aggregation, consistent with the highly aggressive nature of MSA. Surprisingly, GCI-α-Syn and LB-α-Syn show no cell type preference in seeding α-Syn pathology, raising the question of why they demonstrate different cell type distributions in LB disease versus MSA. Strikingly, we found that oligodendrocytes but not neurons transform misfolded α-Syn into a GCI-like strain, highlighting that distinct α-Syn strains are generated by different intracellular milieus. Moreover, GCI-α-Syn maintains its high seeding activity when propagated in neurons. Thus, α-Syn strains are determined by both misfolded seeds and intracellular environments.

Epothilone D inhibits microglia-mediated spread of alpha-synuclein aggregates

Multiple System Atrophy (MSA) is a progressive neurodegenerative disease characterized by chronic neuroinflammation and widespread α-synuclein (α-syn) cytoplasmic inclusions. Neuroinflammation associated with microglial cells is typically located in brain regions with α-syn deposits. The potential link between microglial cell migration and the transport of pathological α-syn protein in MSA was investigated. Qualitative analysis via immunofluorescence of MSA cases (n = 4) revealed microglial cells bearing α-syn inclusions distal from oligodendrocytes bearing α-syn cytoplasmic inclusions, as well as close interactions between microglia and oligodendrocytes bearing α-syn, suggestive of a potential transfer mechanism between microglia and α-syn bearing cells in MSA and the possibility of microglia acting as a mobile vehicle to spread α-syn between anatomically connected brain regions. Further In vitro experiments using microglial-like differentiated THP-1 cells were conducted to investigate if microglial cells could act as potential transporters of α-syn. Monomeric or aggregated α-syn was immobilized at the centre of glass coverslips and treated with either cell free medium, undifferentiated THP-1 cells or microglial-like phorbol-12-myristate-13-acetate differentiated THP-1 cells (48 h; n = 3). A significant difference in residual immobilized α-syn density was observed between cell free controls and differentiated (p = 0.016) as well as undifferentiated and differentiated THP-1 cells (p = 0.032) when analysed by quantitative immunofluorescence. Furthermore, a significantly greater proportion of differentiated cells were observed bearing α-syn aggregates distal from the immobilized protein than their non-differentiated counterparts (p = 0.025). Similar results were observed with Highly Aggressive Proliferating Immortalised (HAPI) microglial cells, with cells exposed to aggregated α-syn yielding lower residual immobilized α-syn (p = 0.004) and a higher proportion of α-syn positive distal cells (p = 0.001) than cells exposed to monomeric α-syn. Co-treatment of THP-1 groups with the tubulin depolymerisation inhibitor, Epothilone D (EpoD; 10 nM), was conducted to investigate if inhibition of microtubule activity had an effect on cell migration and residual immobilized α-syn density. There was a significant increase in both residual immobilized α-syn between EpoD treated and non-treated differentiated cells exposed to monomeric (p = 0.037) and aggregated (p = 0.018) α-syn, but not with undifferentiated cells. Differentiated THP-1 cells exposed to immobilized aggregated α-syn showed a significant difference in the proportion of distal aggregate bearing cells between EpoD treated and untreated (p = 0.027). The results suggest microglia could play a role in α-syn transport in MSA, a role which could potentially be inhibited therapeutically by EpoD.

Detecting Alpha Synuclein Seeding Activity in Formaldehyde-Fixed MSA Patient Tissue by PMCA

Alpha synuclein (α-syn) is central to the pathogenesis of a group of neurodegenerative disorders known as synucleinopathies, including Parkinson’s disease (PD), dementia with Lewy bodies (DLB), and multiple system atrophy (MSA). Aggregation of α-syn is the pathologic hallmark of these disorders and is intimately associated with the pathogenic changes. The prion-like hypothesis postulates that the aggregated α-syn provides a template to seed the aggregation of normal α-syn and spread the pathology. Thus far, it remains unclear whether aggregated α-syn can be a useful biomarker for diagnosis and/or tracking disease progression, which is mainly due to the lack of a suitable biochemical assay. The protein misfolding cyclic amplification (PMCA) technique is known for its enormous amplification power to detect the seeding activity of protein aggregates such as prions. In this study, we adapted PMCA for detecting the seeding activity of α-syn. By extensively optimizing the PMCA parameters, we developed a protocol that is able to sensitively and quantitatively detect the seeding activity of as little as 100 attomoles (10⁻¹⁶ mol) of α-syn aggregate. Using our protocol, we detected α-syn seeding activity from a histologically positive, formaldehyde-fixed MSA sample, but not with the histologically negative, formaldehyde-fixed control sample. Our results confirmed that the α-syn in MSA patient’s brain does contain seeding activity, which remains active even after fixation. Moreover, we also established that PMCA with sonication is a sensitive and quantitative method for detecting α-syn seeding activity, which can be further adapted to more accessible patients’ samples to evaluate α-syn aggregates as a biomarker for synucleinopathies.

Alpha-synuclein levels in patients with multiple system atrophy: a meta-analysis

PURPOSE

This study evaluates the relationship between multiple system atrophy and α-synuclein levels in the cerebrospinal fluid, plasma and neural tissue.

METHOD

Literature search for relevant research articles was undertaken in electronic databases and study selection was based on a priori eligibility criteria. Random-effects meta-analyses of standardized mean differences in α-synuclein levels between multiple system atrophy patients and normal controls were conducted to obtain the overall and subgroup effect sizes. Meta-regression analyses were performed to evaluate the effect of age, gender and disease severity on standardized mean differences.

RESULTS

Data were obtained from 11 studies involving 378 multiple system atrophy patients and 637 healthy controls (age: multiple system atrophy patients 64.14 [95% confidence interval 62.05, 66.23] years; controls 64.16 [60.06, 68.25] years; disease duration: 44.41 [26.44, 62.38] months). Cerebrospinal fluid α-synuclein levels were significantly lower in multiple system atrophy patients than in controls but in plasma and neural tissue, α-synuclein levels were significantly higher in multiple system atrophy patients (standardized mean difference: -0.99 [-1.65, -0.32]; p = 0.001). Percentage of male multiple system atrophy patients was significantly positively associated with the standardized mean differences of cerebrospinal fluid α-synuclein levels (p = 0.029) whereas the percentage of healthy males was not associated with the standardized mean differences of cerebrospinal fluid α-synuclein levels (p = 0.920).

CONCLUSION

In multiple system atrophy patients, α-synuclein levels were significantly lower in the cerebrospinal fluid and were positively associated with the male gender.

Progressive striatonigral degeneration in a transgenic mouse model of multiple system atrophy: translational implications for interventional therapies

Multiple system atrophy (MSA) is a rapidly progressive neurodegenerative disorder characterized by widespread oligodendroglial cytoplasmic inclusions of filamentous α-synuclein, and neuronal loss in autonomic centres, basal ganglia and cerebellar circuits. It has been suggested that primary oligodendroglial α-synucleinopathy may represent a trigger in the pathogenesis of MSA, but the mechanisms underlying selective vulnerability and disease progression are unclear. The post-mortem analysis of MSA brains provides a static final picture of the disease neuropathology, but gives no clear indication on the sequence of pathogenic events in MSA. Therefore, alternative methods are needed to address these issues. We investigated selective vulnerability and disease progression in the transgenic PLP-α-syn mouse model of MSA characterized by targeted oligodendroglial α-synuclein overexpression aiming to provide a neuropathological correlate of motor deterioration. We show progressive motor deficits that emerge at 6 months of age and deteriorate up to 18 months of follow-up. The motor phenotype was associated with dopaminergic cell loss in the substantia nigra pars compacta at 6 months, followed by loss of striatal dopaminergic terminals and DARPP32-positive medium sized projection neurons at 12 months. Olivopontocerebellar motor loops remained spared in the PLP-α-syn model of MSA. These findings replicate progressive striatonigral degeneration underlying Parkinson-variant MSA. The initiation of the degenerative process was linked to an increase of soluble oligomeric α-synuclein species between 2 and 6 months. Early region-specific α-synuclein-associated activation profile of microglia was found in MSA substantia nigra. The role of abnormal neuroinflammatory signalling in disease progression was further supported by increased levels of CD68, CCL3, CCL5 and M-CSF with a peak in aged PLP-α-syn mice. In summary, transgenic PLP-α-syn mice show a distinctive oligodendroglial α-synucleinopathy that is associated with progressive striatonigral degeneration linked to abnormal neuroinflammatory response. The model provides a relevant tool for preclinical therapeutic target discovery for human Parkinson-variant MSA.

MSA prions exhibit remarkable stability and resistance to inactivation

In multiple system atrophy (MSA), progressive neurodegeneration results from the protein α-synuclein misfolding into a self-templating prion conformation that spreads throughout the brain. MSA prions are transmissible to transgenic (Tg) mice expressing mutated human α-synuclein (TgM83^+/-), inducing neurological disease following intracranial inoculation with brain homogenate from deceased patient samples. Noting the similarities between α-synuclein prions and PrP scrapie (PrP^Sc) prions responsible for Creutzfeldt-Jakob disease (CJD), we investigated MSA transmission under conditions known to result in PrP^Sc transmission. When peripherally exposed to MSA via the peritoneal cavity, hind leg muscle, and tongue, TgM83^+/- mice developed neurological signs accompanied by α-synuclein prions in the brain. Iatrogenic CJD, resulting from PrP^Sc prion adherence to surgical steel instruments, has been investigated by incubating steel sutures in contaminated brain homogenate before implantation into mouse brain. Mice studied using this model for MSA developed disease, whereas wire incubated in control homogenate had no effect on the animals. Notably, formalin fixation did not inactivate α-synuclein prions. Formalin-fixed MSA patient samples also transmitted disease to TgM83^+/- mice, even after incubating in fixative for 244 months. Finally, at least 10% sarkosyl was found to be the concentration necessary to partially inactivate MSA prions. These results demonstrate the robustness of α-synuclein prions to denaturation. Moreover, they establish the parallel characteristics between PrP^Sc and α-synuclein prions, arguing that clinicians should exercise caution when working with materials that might contain α-synuclein prions to prevent disease.

SUMOylation and ubiquitination reciprocally regulate α-synuclein degradation and pathological aggregation

α-Synuclein accumulation is a pathological hallmark of Parkinson's disease (PD). Ubiquitinated α-synuclein is targeted to proteasomal or lysosomal degradation. Here, we identify SUMOylation as a major mechanism that counteracts ubiquitination by different E3 ubiquitin ligases and regulates α-synuclein degradation. We report that PIAS2 promotes SUMOylation of α-synuclein, leading to a decrease in α-synuclein ubiquitination by SIAH and Nedd4 ubiquitin ligases, and causing its accumulation and aggregation into inclusions. This was associated with an increase in α-synuclein release from the cells. A SUMO E1 inhibitor, ginkgolic acid, decreases α-synuclein levels by relieving the inhibition exerted on α-synuclein proteasomal degradation. α-Synuclein disease mutants are more SUMOylated compared with the wild-type protein, and this is associated with increased aggregation and inclusion formation. We detected a marked increase in PIAS2 expression along with SUMOylated α-synuclein in PD brains, providing a causal mechanism underlying the up-regulation of α-synuclein SUMOylation in the disease. We also found a significant proportion of Lewy bodies in nigral neurons containing SUMO1 and PIAS2. Our observations suggest that SUMOylation of α-synuclein by PIAS2 promotes α-synuclein aggregation by two mutually reinforcing mechanisms. First, it has a direct proaggregatory effect on α-synuclein. Second, SUMOylation facilitates α-synuclein aggregation by blocking its ubiquitin-dependent degradation pathways and promoting its accumulation. Therefore, inhibitors of α-synuclein SUMOylation provide a strategy to reduce α-synuclein levels and possibly aggregation in PD.

Alpha-synuclein oligomer-selective antibodies reduce intracellular accumulation and mitochondrial impairment in alpha-synuclein exposed astrocytes

Background

Due to its neurotoxic properties, oligomeric alpha-synuclein (α-syn) has been suggested as an attractive target for passive immunization against Parkinson’s disease (PD). In mouse models of PD, antibody treatment has been shown to lower the levels of pathogenic α-syn species, including oligomers, although the mechanisms of action remain unknown. We have previously shown that astrocytes rapidly engulf α-syn oligomers that are intracellularly stored, rather than degraded, resulting in impaired mitochondria.

Methods

The aim of the present study was to investigate if the accumulation of α-syn in astrocytes can be affected by α-syn oligomer-selective antibodies. Co-cultures of astrocytes, neurons, and oligodendrocytes were derived from embryonic mouse cortex and exposed to α-syn oligomers or oligomers pre-incubated with oligomer-selective antibodies.

Results

In the presence of antibodies, the astrocytes displayed an increased clearance of the exogenously added α-syn, and consequently, the α-syn accumulation in the culture was markedly reduced. Moreover, the addition of antibodies rescued the astrocytes from the oligomer-induced mitochondrial impairment.

Conclusions

Our results demonstrate that oligomer-selective antibodies can prevent α-syn accumulation and mitochondrial dysfunction in cultured astrocytes.

Human Astrocytes Transfer Aggregated Alpha-Synuclein via Tunneling Nanotubes

Many lines of evidence suggest that the Parkinson's disease (PD)-related protein α-synuclein (α-SYN) can propagate from cell to cell in a prion-like manner. However, the cellular mechanisms behind the spreading remain elusive. Here, we show that human astrocytes derived from embryonic stem cells actively transfer aggregated α-SYN to nearby astrocytes via direct contact and tunneling nanotubes (TNTs). Failure in the astrocytes' lysosomal digestion of excess α-SYN oligomers results in α-SYN deposits in the trans-Golgi network followed by endoplasmic reticulum swelling and mitochondrial disturbances. The stressed astrocytes respond by conspicuously sending out TNTs, enabling intercellular transfer of α-SYN to healthy astrocytes, which in return deliver mitochondria, indicating a TNT-mediated rescue mechanism. Using a pharmacological approach to inhibit TNT formation, we abolished the transfer of both α-SYN and mitochondria. Together, our results highlight the role of astrocytes in α-SYN cell-to-cell transfer, identifying possible pathophysiological events in the PD brain that could be of therapeutic relevance.

SIGNIFICANCE STATEMENT Astrocytes are the major cell type in the brain, yet their role in Parkinson's disease progression remains elusive. Here, we show that human astrocytes actively transfer aggregated α-synuclein (α-SYN) to healthy astrocytes via direct contact and tunneling nanotubes (TNTs), rather than degrade it. The astrocytes engulf large amounts of oligomeric α-SYN that are subsequently stored in the trans-Golgi network region. The accumulation of α-SYN in the astrocytes affects their lysosomal machinery and induces mitochondrial damage. The stressed astrocytes respond by sending out TNTs, enabling intercellular transfer of α-SYN to healthy astrocytes. Our findings highlight an unexpected role of astrocytes in the propagation of α-SYN pathology via TNTs, revealing astrocytes as a potential target for therapeutic intervention.

The Diagnosis and Natural History of Multiple System Atrophy, Cerebellar Type

The objective of this study was to identify key features differentiating multiple system atrophy cerebellar type (MSA-C) from idiopathic late-onset cerebellar ataxia (ILOCA). We reviewed records of patients seen in the Massachusetts General Hospital Ataxia Unit between 1992 and 2013 with consensus criteria diagnoses of MSA-C or ILOCA. Twelve patients had definite MSA-C, 53 had possible/probable MSA-C, and 12 had ILOCA. Autonomic features, specifically urinary urgency, frequency, and incontinence with erectile dysfunction in males, differentiated MSA-C from ILOCA throughout the disease course (p = 0.005). Orthostatic hypotension developed later and differentiated MSA-C from ILOCA (p < 0.01). REM sleep behavior disorder (RBD) occurred early in possible/probable MSA-C (p < 0.01). Late MSA-C included pathologic laughing and crying (PLC, p < 0.01), bradykinesia (p = 0.01), and corticospinal findings (p = 0.01). MRI distinguished MSA-C from ILOCA by atrophy of the brainstem (p < 0.01) and middle cerebellar peduncles (MCP, p = 0.02). MSA-C progressed faster than ILOCA: by 6 years, MSA-C walker dependency was 100 % and ILOCA 33 %. MSA-C survival was 8.4 ± 2.5 years. Mean length of ILOCA illness to date is 15.9 ± 6.4 years. A sporadic onset, insidiously developing cerebellar syndrome in midlife, with autonomic features of otherwise unexplained bladder dysfunction with or without erectile dysfunction in males, and atrophy of the cerebellum, brainstem, and MCP points strongly to MSA-C. RBD and postural hypotension confirm the diagnosis. Extrapyramidal findings, corticospinal tract signs, and PLC are helpful but not necessary for diagnosis. Clarity in early MSA-C diagnosis can prevent unnecessary investigations and facilitate therapeutic trials.

The ER retention protein RER1 promotes alpha-synuclein degradation via the proteasome

Abnormal accumulation of α-synuclein (αSyn) has been linked to endoplasmic-reticulum (ER) stress, defective intracellular protein/vesicle trafficking, and cytotoxicity. Targeting factors involved in ER-related protein processing and trafficking may, therefore, be a key to modulating αSyn levels and associated toxicity. Recently retention in endoplasmic reticulum 1 (RER1) has been identified as an important ER retrieval/retention factor for Alzheimer's disease proteins and negatively regulates amyloid-β peptide levels. Here, we hypothesized that RER1 might also play an important role in retention/retrieval of αSyn and mediate levels. We expressed RER1 and a C-terminal mutant RER1Δ25, which lacks the ER retention/retrieval function, in HEK293 and H4 neuroglioma cells. RER1 overexpression significantly decreased levels of both wild type and A30P, A53T, and E46K disease causal mutants of αSyn, whereas the RER1Δ25 mutant had a significantly attenuated effect on αSyn. RER1 effects were specific to αSyn and had little to no effect on either βSyn or the Δ71-82 αSyn mutant, which both lack the NAC domain sequence critical for synuclein fibrillization. Tests with proteasomal and macroautophagy inhibitors further demonstrate that RER1 effects on αSyn are primarily mediated through the ubiquitin-proteasome system. RER1 also appears to interact with the ubiquitin ligase NEDD4. RER1 in human diseased brain tissues co-localizes with αSyn-positive Lewy bodies. Together, these findings provide evidence that RER1 is a novel and potential important mediator of elevated αSyn levels. Further investigation of the mechanism of RER1 and downstream effectors on αSyn may yield novel therapeutic targets for modulation in Parkinson disease and related synucleinopathies.

Preclinical development of a vaccine against oligomeric alpha-synuclein based on virus-like particles

Parkinson's disease (PD) is a progressive and currently incurable neurological disorder characterised by the loss of midbrain dopaminergic neurons and the accumulation of aggregated alpha-synuclein (a-syn). Oligomeric a-syn is proposed to play a central role in spreading protein aggregation in the brain with associated cellular toxicity contributing to a progressive neurological decline. For this reason, a-syn oligomers have attracted interest as therapeutic targets for neurodegenerative conditions such as PD and other alpha-synucleinopathies. In addition to strategies using small molecules, neutralisation of the toxic oligomers by antibodies represents an attractive and highly specific strategy for reducing disease progression. Emerging active immunisation approaches using vaccines are already being trialled to induce such antibodies. Here we propose a novel vaccine based on the RNA bacteriophage (Qbeta) virus-like particle conjugated with short peptides of human a-syn. High titres of antibodies were successfully and safely generated in wild-type and human a-syn over-expressing (SNCA-OVX) transgenic mice following vaccination. Antibodies from vaccine candidates targeting the C-terminal regions of a-syn were able to recognise Lewy bodies, the hallmark aggregates in human PD brains. Furthermore, antibodies specifically targeted oligomeric and aggregated a-syn as they exhibited 100 times greater affinity for oligomeric species over monomer a-syn proteins in solution. In the SNCA-OVX transgenic mice used, vaccination was, however, unable to confer significant changes to oligomeric a-syn bioburden. Similarly, there was no discernible effect of vaccine treatment on behavioural phenotype as compared to control groups. Thus, antibodies specific for oligomeric a-syn induced by vaccination were unable to treat symptoms of PD in this particular mouse model.

Clinical and genetic characteristics of sporadic adult-onset degenerative ataxia

Objective:

To define the clinical phenotype and natural history of sporadic adult-onset degenerative ataxia and to identify putative disease-causing mutations.

Methods:

The primary measure of disease severity was the Scale for the Assessment and Rating of Ataxia (SARA). DNA samples were screened for mutations using a high-coverage ataxia-specific gene panel in combination with next-generation sequencing.

Results:

The analysis was performed on 249 participants. Among them, 83 met diagnostic criteria of clinically probable multiple system atrophy cerebellar type (MSA-C) at baseline and another 12 during follow-up. Positive MSA-C criteria (4.94 ± 0.74, p < 0.0001) and disease duration (0.22 ± 0.06 per additional year, p = 0.0007) were associated with a higher SARA score. Forty-eight participants who did not fulfill MSA-C criteria and had a disease duration of >10 years were designated sporadic adult-onset ataxia of unknown etiology/non-MSA (SAOA/non-MSA). Compared with MSA-C, SAOA/non-MSA patients had lower SARA scores (13.6 ± 6.0 vs 16.0 ± 5.8, p = 0.0200) and a slower annual SARA increase (1.1 ± 2.3 vs 3.3 ± 3.2, p = 0.0013). In 11 of 194 tested participants (6%), a definitive or probable genetic diagnosis was made.

Conclusions:

Our study provides quantitative data on the clinical phenotype and progression of sporadic ataxia with adult onset. Screening for causative mutations with a gene panel approach yielded a genetic diagnosis in 6% of the cohort.

ClinicalTrials.gov registration:

NCT02701036.

Multiple System Atrophy: Many Lessons from the Transcriptome

Multiple system atrophy (MSA) is a complex, multifactorial, debilitating neurodegenerative disease that is often misdiagnosed and misunderstood. MSA has two subclasses, MSA-P and MSA-C, defined by the dominance of parkinsonism or cerebellar dysfunction in the earlier stages of disease, coupled with dysautonomia. This distinction between subclasses becomes largely redundant as the disease progresses. Aggregation of α-synuclein is a clinical marker used to confirm MSA diagnoses, which can only be performed postmortem. Transcriptome profiling provides in-depth information about the diseased state and can contribute to further understanding of MSA, enabling easier and more rapid diagnosis as well as contributing to improving the quality of life of people with MSA. Currently, there is no method of diagnosing MSA with certainty, and there is no cure for this disease. This review provides an update on current advances in investigations of molecular pathology of MSA with particular focus on perturbation of individual gene expression and MSA transcriptome.

Distinct α-Synuclein strains and implications for heterogeneity among α-Synucleinopathies

The deposition of misfolded β-sheet enriched amyloid protein is a shared feature of many neurodegenerative diseases. Recent studies demonstrated the existence of conformationally diverse strains as a common property for multiple amyloidogenic proteins including α-Synuclein (α-Syn). α-Syn is misfolded and aggregated in a group of neurodegenerative diseases collectively known as α-Synucleinopathies, which include Parkinson's disease (PD), dementia with Lewy body, multiple system atrophy and also a subset of Alzheimer's disease patients with concomitant PD-like Lewy bodies and neurites. While sharing the same pathological protein, different α-Synucleinopathies demonstrate distinct clinical and pathological phenotypes, which could result from the existence of diverse pathological α-Syn strains in patients. In this review, we summarized the characteristics of different α-Synucleinopathies and α-Syn strains generated with recombinant α-Syn monomers. We also make predictions of α-Syn strains that could potentially exist in patients based on the knowledge from other amyloid proteins and the clinical and pathological features of different α-Synucleinopathies.