p25alpha relocalizes in oligodendroglia from myelin to cytoplasmic inclusions in multiple system atrophy

The Golgi Outpost Protein TPPP Nucleates Microtubules and Is Critical for Myelination

Oligodendrocytes extend elaborate microtubule arbors that contact up to 50 axon segments per cell, then spiral around myelin sheaths, penetrating from outer to inner layers. However, how they establish this complex cytoarchitecture is unclear. Here, we show that oligodendrocytes contain Golgi outposts, an organelle that can function as an acentrosomal microtubule-organizing center (MTOC). We identify a specific marker for Golgi outposts-TPPP (tubulin polymerization promoting protein)-that we use to purify this organelle and characterize its proteome. In in vitro cell-free assays, recombinant TPPP nucleates microtubules. Primary oligodendrocytes from Tppp knockout (KO) mice have aberrant microtubule branching, mixed microtubule polarity, and shorter myelin sheaths when cultured on 3-dimensional (3D) microfibers. Tppp KO mice exhibit hypomyelination with shorter, thinner myelin sheaths and motor coordination deficits. Together, our data demonstrate that microtubule nucleation outside the cell body at Golgi outposts by TPPP is critical for elongation of the myelin sheath.

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.

Induced pluripotent stem cells in multiple system atrophy: recent developments and scientific challenges

Multiple system atrophy (MSA) is a rare and fatal neurodegenerative disease, with no known genetic cause to date. Oligodendroglial α-synuclein accumulation, neuroinflammation, and early myelin dysfunction are hallmark features of the disease and have been modeled in part in various preclinical models of MSA, yet the pathophysiology of MSA remains elusive. Here, we review the role and scientific challenges of induced pluripotent stem cells in the detection of novel biomarkers and druggable targets in MSA.

Pharmacological targeting of α-synuclein and TPPP/p25 in Parkinson's disease: challenges and opportunities in a Nutshell

With the aging of population, neurological disorders, and especially disorders involving defects in protein conformation (also known as proteopathies) pose a serious socio-economic problem. So far there is no effective treatment for most proteopathies, including Parkinson's disease (PD). The mechanism underlying PD pathogenesis is largely unknown, and the hallmark proteins, α-synuclein (SYN) and tubulin polymerization promoting protein (TPPP/p25) are challenging drug targets. These proteins are intrinsically disordered with high conformational plasticity, and have diverse physiological and pathological functions. In the healthy brain, SYN and TPPP/p25 occur in neurons and oligodendrocytes, respectively; however, in PD and multiple system atrophy, they are co-enriched and co-localized in both cell types, thereby marking pathogenesis. Although large inclusions appear at a late disease stage, small, soluble assemblies of SYN promoted by TPPP/p25 are pathogenic. In the light of these issues, we established a new innovative strategy for the validation of a specific drug target based upon the identification of contact surfaces of the pathological SYN-TPPP/p25 complex that may lead to the development of peptidomimetic foldamers suitable for pharmaceutical intervention.

An emerging role of dysfunctional axon-oligodendrocyte coupling in neurodegenerative diseases

Myelin is made by highly specialized glial cells and enables fast axonal impulse propagation. Recent studies show that oligodendrocytes in the central nervous system are, in addition to myelination, required for the integrity and survival of axons, independent of the presence or absence of myelin itself. The underlying mechanism of this support is given by glycolytic oligodendrocytes which provide axons with energy-rich metabolites. These findings represent a paradigm shift for the physiological function of axon-associated glia, and open the intriguing possibility that oligodendrocytes are important contributors to neurodegenerative diseases in which myelinated axons are lost, such as in Alzheimer disease, amyotrophic lateral sclerosis, and multiple system atrophy. Understanding the role of axon-oligodendrocyte coupling in neurodegenerative diseases may pave the way for the development of metabolism-based therapeutic approaches.

Treatment of multiple system atrophy - the past, present and future

Multiple system atrophy is a sporadic progressive degenerative disease which is characterized by multiple central nervous systems involved. So far, there is no effective medicine to cure MSA. The main research direction of treatment includes immunization transplantation and cytotherapy. Human umbilical cord blood is the residue of blood in the placenta and umbilical cord after fetal delivery. It is the most abundant cell bank and its usage is not limited to treat hematological diseases. The researches about hUCB-MNC treatment on MSA are increasing gradually. The potential of other MSC is also discussed. Lateral atlanto-occipital space puncture is an ingenious way created by Professor Dianrong Gong. More than 30 cases of MSA have been treated by this method with fine clinical effect and without serious complications. It indicates that stem cells treatment is a valid method for refractory nerve system diseases.

Clinical and Imaging Features of Multiple System Atrophy: Challenges for an Early and Clinically Definitive Diagnosis

Multiple system atrophy (MSA) is an adult-onset, progressive neurodegenerative disorder. Patients with MSA show various phenotypes during the course of their illness, including parkinsonism, cerebellar ataxia, autonomic failure, and pyramidal signs. Patients with MSA sometimes present with isolated autonomic failure or motor symptoms/ signs. The median duration from onset to the concomitant appearance of motor and autonomic symptoms is approximately 2 years but can range up to 14 years. As the presence of both motor and autonomic symptoms is essential for the current diagnostic criteria, early diagnosis is difficult when patients present with isolated autonomic failure or motor symptoms/signs. In contrast, patients with MSA may show severe autonomic failure and die before the presentation of motor symptoms/signs, which are currently required for the diagnosis of MSA. Recent studies have also revealed that patients with MSA may show nonsupporting features of MSA such as dementia, hallucinations, and vertical gaze palsy. To establish early diagnostic criteria and clinically definitive categorization for the successful development of disease-modifying therapy or symptomatic interventions for MSA, research should focus on the isolated phase and atypical symptoms to develop specific clinical, imaging, and fluid biomarkers that satisfy the requirements for objectivity, for semi- or quantitative measurements, and for uncomplicated, worldwide availability. Several novel techniques, such as automated compartmentalization of the brain into multiple parcels for the quantification of gray and white matter volumes on an individual basis and the visualization of α-synuclein and other candidate serum and cerebrospinal fluid biomarkers, may be promising for the early and clinically definitive diagnosis of MSA.

In vitro models of multiple system atrophy from primary cells to induced pluripotent stem cells

Multiple system atrophy (MSA) is a rare neurodegenerative disease with a fatal outcome. Nowadays, only symptomatic treatment is available for MSA patients. The hallmarks of the disease are glial cytoplasmic inclusions (GCIs), proteinaceous aggregates mainly composed of alpha‐synuclein, which accumulate in oligodendrocytes. However, despite the extensive research efforts, little is known about the pathogenesis of MSA. Early myelin dysfunction and alpha‐synuclein deposition are thought to play a major role, but the origin of the aggregates and the causes of misfolding are obscure. One of the reasons for this is the lack of a reliable model of the disease. Recently, the development of induced pluripotent stem cell (iPSC) technology opened up the possibility of elucidating disease mechanisms in neurodegenerative diseases including MSA. Patient specific iPSC can be differentiated in glia and neurons, the cells involved in MSA, providing a useful human disease model. Here, we firstly review the progress made in MSA modelling with primary cell cultures. Subsequently, we focus on the first iPSC‐based model of MSA, which showed that alpha‐synuclein is expressed in oligodendrocyte progenitors, whereas its production decreases in mature oligodendrocytes. We then highlight the opportunities offered by iPSC in studying disease mechanisms and providing innovative models for testing therapeutic strategies, and we discuss the challenges connected with this technique.

Recent advances in neuropathology, biomarkers and therapeutic approach of multiple system atrophy

Multiple system atrophy (MSA) is a progressive neurodegenerative disorder characterised by a variable combination of autonomic failure, levodopa-unresponsive parkinsonism, cerebellar ataxia and pyramidal symptoms. The pathological hallmark is the oligodendrocytic glial cytoplasmic inclusion (GCI) consisting of α-synuclein; therefore, MSA is included in the category of α-synucleinopathies. MSA has been divided into two clinicopathological subtypes: MSA with predominant parkinsonism and MSA with predominant cerebellar ataxia, which generally correlate with striatonigral degeneration and olivopontocerebellar atrophy, respectively. It is increasingly recognised, however, that clinical and pathological features of MSA are broader than previously considered.In this review, we aim to describe recent advances in neuropathology of MSA from a review of the literature and from information derived from review of nearly 200 definite MSA cases in the Mayo Clinic Brain Bank. In light of these new neuropathological findings, GCIs and neuronal cytoplasmic inclusions play an important role in clinicopathological correlates of MSA. We also focus on clinical diagnostic accuracy and differential diagnosis of MSA as well as candidate biomarkers. We also review some controversial topics in MSA. Cognitive impairment, which has been a non-supporting feature of MSA, is considered from both clinical and pathological perspectives. The cellular origin of α-synuclein in GCI and a 'prion hypothesis' are discussed. Finally, completed and ongoing clinical trials targeting disease modification, including immunotherapy, are summarised.

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.

Multiple System Atrophy: An Oligodendroglioneural Synucleinopathy1

Multiple system atrophy (MSA) is an orphan, fatal, adult-onset neurodegenerative disorder of uncertain etiology that is clinically characterized by various combinations of parkinsonism, cerebellar, autonomic, and motor dysfunction. MSA is an α-synucleinopathy with specific glioneuronal degeneration involving striatonigral, olivopontocerebellar, and autonomic nervous systems but also other parts of the central and peripheral nervous systems. The major clinical variants correlate with the morphologic phenotypes of striatonigral degeneration (MSA-P) and olivopontocerebellar atrophy (MSA-C). While our knowledge of the molecular pathogenesis of this devastating disease is still incomplete, updated consensus criteria and combined fluid and imaging biomarkers have increased its diagnostic accuracy. The neuropathologic hallmark of this unique proteinopathy is the deposition of aberrant α-synuclein in both glia (mainly oligodendroglia) and neurons forming glial and neuronal cytoplasmic inclusions that cause cell dysfunction and demise. In addition, there is widespread demyelination, the pathogenesis of which is not fully understood. The pathogenesis of MSA is characterized by propagation of misfolded α-synuclein from neurons to oligodendroglia and cell-to-cell spreading in a "prion-like" manner, oxidative stress, proteasomal and mitochondrial dysfunction, dysregulation of myelin lipids, decreased neurotrophic factors, neuroinflammation, and energy failure. The combination of these mechanisms finally results in a system-specific pattern of neurodegeneration and a multisystem involvement that are specific for MSA. Despite several pharmacological approaches in MSA models, addressing these pathogenic mechanisms, no effective neuroprotective nor disease-modifying therapeutic strategies are currently available. Multidisciplinary research to elucidate the genetic and molecular background of the deleterious cycle of noxious processes, to develop reliable biomarkers and targets for effective treatment of this hitherto incurable disorder is urgently needed.

The neuropathology of multiple system atrophy and its therapeutic implications

Multiple system atrophy (MSA) is a fatal neurodegenerative disorder characterized by the abnormal accumulation of toxic forms of the synaptic protein alpha-synuclein (α-syn) within oligodendrocytes and neurons. The presence of α-syn within oligodendrocytes in the form of glial cytoplasmic inclusions is the diagnostic hallmark of MSA. However, it has been postulated that α-syn is produced in neurons and propagates to oligodendrocytes, where unknown mechanisms lead to its accumulation. The presence of α-syn within neurons in MSA has not been so extensively studied, but it may shed light into neuropathological mechanisms leading to oligodendroglial accumulation. Here we summarize the principal neuropathological events of MSA, and discuss how a deeper knowledge of these mechanisms may help develop effective therapies targeting α-syn accumulation and spreading.

Insulin resistance and exendin-4 treatment for multiple system atrophy

See Stayte and Vissel (doi:10.1093/awx064) for a scientific commentary on this article. Multiple system atrophy is a fatal sporadic adult-onset neurodegenerative disorder with no symptomatic or disease-modifying treatment available. The cytopathological hallmark of multiple system atrophy is the accumulation of α-synuclein aggregates in oligodendrocytes, forming glial cytoplasmic inclusions. Impaired insulin/insulin-like growth factor-1 signalling (IGF-1) and insulin resistance (i.e. decreased insulin/IGF-1) have been reported in other neurodegenerative disorders such as Alzheimer's disease. Increasing evidence also suggests impaired insulin/IGF-1 signalling in multiple system atrophy, as corroborated by increased insulin and IGF-1 plasma concentrations in multiple system atrophy patients and reduced IGF-1 brain levels in a transgenic mouse model of multiple system atrophy. We here tested the hypothesis that multiple system atrophy is associated with brain insulin resistance and showed increased expression of the key downstream messenger insulin receptor substrate-1 phosphorylated at serine residue 312 in neurons and oligodendrocytes in the putamen of patients with multiple system atrophy. Furthermore, the expression of insulin receptor substrate 1 (IRS-1) phosphorylated at serine residue 312 was more apparent in inclusion bearing oligodendrocytes in the putamen. By contrast, it was not different between both groups in the temporal cortex, a less vulnerable structure compared to the putamen. These findings suggest that insulin resistance may occur in multiple system atrophy in regions where the neurodegenerative process is most severe and point to a possible relation between α-synuclein aggregates and insulin resistance. We also observed insulin resistance in the striatum of transgenic multiple system atrophy mice and further demonstrate that the glucagon-like peptide-1 analogue exendin-4, a well-tolerated and Federal Drug Agency-approved antidiabetic drug, has positive effects on insulin resistance and monomeric α-synuclein load in the striatum, as well as survival of nigral dopamine neurons. Additionally, plasma levels of exosomal neural-derived IRS-1 phosphorylated at serine residue 307 (corresponding to serine residue 312 in humans) negatively correlated with survival of nigral dopamine neurons in multiple system atrophy mice treated with exendin-4. This finding suggests the potential for developing this peripheral biomarker candidate as an objective outcome measure of target engagement for clinical trials with glucagon-like peptide-1 analogues in multiple system atrophy. In conclusion, our observation of brain insulin resistance in multiple system atrophy patients and transgenic mice together with the beneficial effects of the glucagon-like peptide-1 agonist exendin-4 in transgenic mice paves the way for translating this innovative treatment into a clinical trial.

Translational therapies for multiple system atrophy: Bottlenecks and future directions

Over the last decade a prominent amount of studies in preclinical transgenic models of multiple system atrophy (MSA) has been performed. These studies have helped understand mechanisms downstream to the α-synuclein oligodendroglial accumulation relevant to human MSA. However, the successful translation of the preclinical outcomes into a clinical trial has failed. Looking back, we can now identify possible confounders for the failure. Biomarkers of disease progression are mostly missing. Early diagnosis and initiation of therapeutic clinical trials is limited. The need of both proof-of-concept as well as clinically relevant preclinical study designs with clinically relevant timing and preclinical readouts is identified as a must in our translational efforts for MSA to date. Finally, improved clinical study designs with improved enrollment criteria, and measurement outcomes are warranted on the way to finding the successful therapeutic approach for MSA. This review provides an overview of experimental studies and clinical trials for MSA and the lessons learned over the last decade towards the identification of the cure for MSA.

Key themes and future prospects in translational multiple system atrophy research

Multiple system atrophy (MSA) is a rapidly progressive neurodegenerative disorder with a highly variable clinical presentation. Unfortunately, there exists no effective therapy that can improve the course of the disease and symptomatic treatment options remain limited. Although significant progress in research has improved our understanding of MSA, knowledge gaps still remain. Thus, a global network focusing on different research areas is required to face this fatal disease.

Multiple System Atrophy - State of the Art

Multiple system atrophy (MSA) is a rare and fatal neurodegenerative disorder that is characterized by a variable combination of parkinsonism, cerebellar impairment, and autonomic dysfunction. Some symptomatic treatments are available while neuroprotection or disease-modification remain unmet treatment needs. The pathologic hallmark is the accumulation of aggregated alpha-synuclein (α-syn) in oligodendrocytes forming glial cytoplasmic inclusions, which qualifies MSA as synucleinopathy together with Parkinson's disease and dementia with Lewy bodies. Despite progress in our understanding of the pathogenesis of MSA, the origin of α-syn aggregates in oligodendrocytes is still a matter of an ongoing debate. We critically review here studies published in the field over the past 5 years dealing with pathogenesis, genetics, clinical signs, biomarker for improving diagnostic accuracy, and treatment development.

Higher levels of myelin phospholipids in brains of neuronal α-Synuclein transgenic mice precede myelin loss

α-Synuclein is a protein involved in the pathogenesis of synucleinopathies, including Parkinson’s disease (PD), dementia with Lewy bodies (DLB) and multiple system atrophy (MSA). We investigated the role of neuronal α-Syn in myelin composition and abnormalities. The phospholipid content of purified myelin was determined by ³¹P NMR in two mouse lines modeling PD, PrP-A53T α-Syn and Thy-1 wt-α-Syn. Significantly higher levels of phospholipids were detected in myelin purified from brains of these α-Syn transgenic mouse models than in control mice. Nevertheless, myelin ultrastructure appeared intact. To further investigate the effect of α-Syn on myelin abnormalities, we systematically analyzed the striatum, a brain region associated with neurodegeneration in PD. An age and disease-dependent loss of myelin basic protein (MBP) signal was detected by immunohistochemistry in striatal striosomes (patches). The age-dependent loss of MBP signal was associated with lower P25α levels in oligodendrocytes. In addition, we found that α-Syn inhibited oligodendrocyte maturation and the formation of membranous sheets in vitro. Based on these results we concluded that neuronal α-Syn is involved in the regulation and/or maintenance of myelin phospholipid. However, axonal hypomyelination in the PD models is evident only in progressive stages of the disease and associated with α-Syn toxicity.

Multiple system atrophy: insights into a rare and debilitating movement disorder

Multiple system atrophy (MSA) is a devastating and fatal neurodegenerative disorder. The clinical presentation of this disease is highly variable, with parkinsonism, cerebellar ataxia and autonomic failure being the most common - and often debilitating - symptoms. These symptoms progress rapidly, and patients die from MSA-related complications after 9 years of symptom duration on average. Unfortunately, the course of the disease cannot be improved by drug or surgical treatment. In addition, symptomatic treatment options are currently limited, and therapeutic benefits are often only transient. Thus, further interventional studies of candidate disease-modifying and symptomatic therapies are essential to improve patient care. In the past 15 years, the understanding of MSA-specific requirements in trial methodology has improved, resulting in a substantial increase in high-quality interventional studies. In this Review, we discuss MSA risk factors, clinical presentation and neuropathology, and we provide a hypothesis on key pathophysiological events, a summary of recent randomized controlled trials, and an overview of ongoing international collaborations.

Role of the microtubule-associated TPPP/p25 in Parkinson's and related diseases and its therapeutic potential

INTRODUCTION

The discovery and development of therapeutic strategies for the treatments of Parkinson's disease (PD) and other synucleinopathies are limited by a lack of understanding of the pathomechanisms and their connection with different diseases such as cancers. Areas covered: The hallmarks of these diseases are frequently multifunctional disordered proteins displaying moonlighting and/or chameleon features, which are challenging drug targets. A representative of these proteins is the disordered Tubulin Polymerization Promoting Protein (TPPP/p25) expressed specifically in oligodendrocytes (OLGs) in normal brain. Its non-physiological level is tightly related to the etiology of PD and Multiple System Atrophy (TPPP/p25 enrichment in inclusions of neurons and OLGs, respectively), multiple sclerosis (TPPP/p25-positive OLG destruction), as well as glioma (loss of TPPP/p25 expression). The established anti-proliferative potency of TPPP/p25 may raise its influence in cancer development. The recognition that whereas too much TPPP/p25 could kill neurons in PD, but its loss keeps cells alive in cancer could contribute to our understanding of the interrelationship of 'TPPP/p25 diseases'. Expert commentary: The knowledge accumulated so far underlines the key roles of the multifunctional TPPP/p25 in both physiological and diverse pathological processes, consequently its validation as drug target sorely needs a new innovative strategy that is briefly reviewed here.

Review: Multiple system atrophy: emerging targets for interventional therapies

Multiple system atrophy (MSA) is a fatal orphan neurodegenerative disorder that manifests with rapidly progressive autonomic and motor dysfunction. The disease is characterized by the accumulation of α-synuclein fibrils in oligodendrocytes that form glial cytoplasmic inclusions, a neuropathological hallmark and central player in the pathogenesis of MSA. Here, we summarize the current knowledge on the etiopathogenesis and neuropathology of MSA. We discuss the role of α-synuclein pathology, microglial activation, oligodendroglial dysfunction and putative cell death mechanisms as candidate therapeutic targets in MSA.

Anti-MAG autoantibodies are increased in Parkinson's disease but not in atypical parkinsonism

There is emerging evidence that glial cells are involved in the neuropathological process in Parkinson's disease (PD) in addition to degeneration of neuronal structures. Recently, we confirmed the presence of an adaptive immune response against different glial-derived antigens in PD, with a possible role of anti-MAG, anti-MBP and anti-PLP antibodies in the disease progression. The aim of the present study was to assess humoral response against myelin-associated glycoprotein (MAG) in patients with parkinsonism (both idiopathic and atypical) to check whether these antibodies could serve as biomarkers of PD, its severity and progression. Anti-MAG autoantibodies were measured by an ELISA system in 99 PD patients, 33 atypical parkinsonism patients, and 36 control subjects. In PD patients, anti-MAG IgM autoantibodies were significantly higher in comparison to healthy control subjects (p = 0.038). IgM anti-MAG autoantibodies titers were also significantly higher in the whole group of patients with parkinsonism (either idiopathic or atypical) in comparison to healthy control subjects (1.88 ± 0.84 vs 1.70 ± 1.19, p = 0.017). This difference was mainly driven by the PD group, as the atypical parkinsonism group did not differ significantly from the control group in anti-MAG antibody levels (p = 0.51). A negative correlation between anti-MAG levels and disease duration was found in PD patients. Our study provides evidence for an increased production of autoantibodies against a protein of glial origin in PD. The negative correlation between anti-MAG antibodies and disease duration may suggest possible involvement of the immune system in disease progression. Increasing evidence that glia are involved in the neurodegenerative process to a greater extent than previously thought may turn out be useful in the search for biomarkers of the neurodegenerative process in PD.

Progression of alpha-synuclein pathology in multiple system atrophy of the cerebellar type

AIMS

The aim of this study was to identify early foci of α-synuclein (α-syn pathology) accumulation, subsequent progression and neurodegeneration in multiple system atrophy of the cerebellar type (MSA-C).

METHODS

We analysed 70-μm-thick sections of 10 cases with MSA-C and 24 normal controls.

RESULTS

MSA-C cases with the lowest burden of pathology showed α-syn glial cytoplasmic inclusions (GCIs) in the cerebellum as well as in medullary and pontine cerebellar projections. Cerebellar pathology was highly selective and severely involved subcortical white matter, whereas deep white matter and granular layer were only mildly affected and the molecular layer was spared. Loss of Purkinje cells increased with disease duration and was associated with neuronal and axonal abnormalities. Neocortex, basal ganglia and spinal cord became consecutively involved with the increasing burden of α-syn pathology, followed by hippocampus, amygdala, and, finally, the visual cortex. GCIs were associated with myelinated axons, and the severity of GCIs correlated with demyelination.

CONCLUSIONS

Our findings indicate that cerebellar subcortical white matter and cerebellar brainstem projections are likely the earliest foci of α-syn pathology in MSA-C, followed by involvement of more widespread regions of the central nervous system and neurodegeneration with disease progression.

α-Synuclein-induced myelination deficit defines a novel interventional target for multiple system atrophy

Multiple system atrophy (MSA) is a rare atypical parkinsonian disorder characterized by a rapidly progressing clinical course and at present without any efficient therapy. Neuropathologically, myelin loss and neurodegeneration are associated with α-synuclein accumulation in oligodendrocytes, but underlying pathomechanisms are poorly understood. Here, we analyzed the impact of oligodendrocytic α-synuclein on the formation of myelin sheaths to define a potential interventional target for MSA. Post-mortem analyses of MSA patients and controls were performed to quantify myelin and oligodendrocyte numbers. As pre-clinical models, we used transgenic MSA mice, a myelinating stem cell-derived oligodendrocyte-neuron co-culture, and primary oligodendrocytes to determine functional consequences of oligodendrocytic α-synuclein overexpression on myelination. We detected myelin loss accompanied by preserved or even increased numbers of oligodendrocytes in post-mortem MSA brains or transgenic mouse forebrains, respectively, indicating an oligodendrocytic dysfunction in myelin formation. Corroborating this observation, overexpression of α-synuclein in primary and stem cell-derived oligodendrocytes severely impaired myelin formation, defining a novel α-synuclein-linked pathomechanism in MSA. We used the pro-myelinating activity of the muscarinic acetylcholine receptor antagonist benztropine to analyze the reversibility of the myelination deficit. Transcriptome profiling of primary pre-myelinating oligodendrocytes demonstrated that benztropine readjusts myelination-related processes such as cholesterol and membrane biogenesis, being compromised by oligodendrocytic α-synuclein. Additionally, benztropine restored the α-synuclein-induced myelination deficit of stem cell-derived oligodendrocytes. Strikingly, benztropine also ameliorated the myelin deficit in transgenic MSA mice, resulting in a prevention of neuronal cell loss. In conclusion, this study defines the α-synuclein-induced myelination deficit as a novel and crucial pathomechanism in MSA. Importantly, the reversible nature of this oligodendrocytic dysfunction opens a novel avenue for an intervention in MSA.

Multiple system atrophy: pathogenic mechanisms and biomarkers

Multiple system atrophy (MSA) is a unique proteinopathy that differs from other α-synucleinopathies since the pathological process resulting from accumulation of aberrant α-synuclein (αSyn) involves the oligodendroglia rather than neurons, although both pathologies affect multiple parts of the brain, spinal cord, autonomic and peripheral nervous system. Both the etiology and pathogenesis of MSA are unknown, although animal models have provided insight into the basic molecular changes of this disorder. Accumulation of aberrant αSyn in oligodendroglial cells and preceded by relocation of p25α protein from myelin to oligodendroglia results in the formation of insoluble glial cytoplasmic inclusions that cause cell dysfunction and demise. These changes are associated with proteasomal, mitochondrial and lipid transport dysfunction, oxidative stress, reduced trophic transport, neuroinflammation and other noxious factors. Their complex interaction induces dysfunction of the oligodendroglial-myelin-axon-neuron complex, resulting in the system-specific pattern of neurodegeneration characterizing MSA as a synucleinopathy with oligodendroglio-neuronopathy. Propagation of modified toxic αSyn species from neurons to oligodendroglia by "prion-like" transfer and its spreading associated with neuronal pathways result in a multi-system involvement. No reliable biomarkers are currently available for the clinical diagnosis and prognosis of MSA. Multidisciplinary research to elucidate the genetic and molecular background of the deleterious cycle of noxious processes, to develop reliable diagnostic biomarkers and to deliver targets for effective treatment of this hitherto incurable disorder is urgently needed.

Changes in the miRNA-mRNA Regulatory Network Precede Motor Symptoms in a Mouse Model of Multiple System Atrophy: Clinical Implications

Multiple system atrophy (MSA) is a fatal rapidly progressive α-synucleinopathy, characterized by α-synuclein accumulation in oligodendrocytes. It is accepted that the pathological α-synuclein accumulation in the brain of MSA patients plays a leading role in the disease process, but little is known about the events in the early stages of the disease. In this study we aimed to define potential roles of the miRNA-mRNA regulatory network in the early pre-motor stages of the disease, i.e., downstream of α-synuclein accumulation in oligodendroglia, as assessed in a transgenic mouse model of MSA. We investigated the expression patterns of miRNAs and their mRNA targets in substantia nigra (SN) and striatum, two brain regions that undergo neurodegeneration at a later stage in the MSA model, by microarray and RNA-seq analysis, respectively. Analysis was performed at a time point when α-synuclein accumulation was already present in oligodendrocytes at neuropathological examination, but no neuronal loss nor deficits of motor function had yet occurred. Our data provide a first evidence for the leading role of gene dysregulation associated with deficits in immune and inflammatory responses in the very early, non-symptomatic disease stages of MSA. While dysfunctional homeostasis and oxidative stress were prominent in SN in the early stages of MSA, in striatum differential gene expression in the non-symptomatic phase was linked to oligodendroglial dysfunction, disturbed protein handling, lipid metabolism, transmembrane transport and altered cell death control, respectively. A large number of putative miRNA-mRNAs interaction partners were identified in relation to the control of these processes in the MSA model. Our results support the role of early changes in the miRNA-mRNA regulatory network in the pathogenesis of MSA preceding the clinical onset of the disease. The findings thus contribute to understanding the disease process and are likely to pave the way towards identifying disease biomarkers for early diagnosis of MSA.

Animal modeling an oligodendrogliopathy--multiple system atrophy

Multiple system atrophy (MSA) is a rare, yet rapidly-progressive neurodegenerative disease that presents clinically with autonomic failure in combination with parkinsonism or cerebellar ataxia. The definitive neuropathology differentiating MSA from Lewy body diseases is the presence of α-synuclein aggregates in oligodendrocytes (called glial cytoplasmic inclusion or GCI) rather than the fibrillar aggregates in neurons (called Lewy bodies). This makes the pathological pathway(s) in MSA unique in that oligodendrocytes are involved rather than predominantly neurons, as is most other neurodegenerative disorders. MSA is therefore regarded as an oligodendrogliopathy. The etiology of MSA is unknown. No definitive risk factors have been identified, although α-synuclein and other genes have been variably linked to MSA risk. Utilization of postmortem brain tissues has greatly advanced our understanding of GCI pathology and the subsequent neurodegeneration. However, extrapolating the early pathogenesis of MSA from such resource has been difficult and limiting. In recent years, cell and animal models developed for MSA have been instrumental in delineating unique MSA pathological pathways, as well as aiding in clinical phenotyping. The purpose of this review is to bring together and discuss various animal models that have been developed for MSA and how they have advanced our understanding of MSA pathogenesis, particularly the dynamics of α-synuclein aggregation. This review will also discuss how animal models have been used to explore potential therapeutic avenues for MSA, and future directions of MSA modeling.

Diffusion tensor imaging in the characterization of multiple system atrophy

PURPOSE

Multiple system atrophy (MSA) is a rare neurodegenerative disease that remains poorly understood, and the diagnosis of MSA continues to be challenging. We endeavored to improve the diagnostic process and understanding of in vivo characteristics of MSA by diffusion tensor imaging (DTI).

MATERIALS AND METHODS

Twenty MSA subjects, ten parkinsonian dominant (MSA-P), ten cerebellar dominant (MSA-C), and 20 healthy volunteer subjects were recruited. Fractional anisotropy, mean diffusivity, radial diffusivity, and axial diffusivity maps were processed using tract-based spatial statistics. Diffusion data were additionally evaluated in the basal ganglia. A support vector machine was used to assess diagnostic utility, leave-one-out cross-validation in the evaluation of classification schemes, and receiver operating characteristic analyses to determine cutoff values.

RESULTS

We detected widespread changes in the brain white matter of MSA subjects; however, no group-wise differences were found between MSA-C and MSA-P subgroups. Altered DTI metrics in the putamen and middle cerebellar peduncles were associated with a positive parkinsonian and cerebellar phenotype, respectively. Concerning clinical applicability, we achieved high classification performance on mean diffusivity data in the combined bilateral putamen and middle cerebellar peduncle (accuracy 90.3%±9%, sensitivity 86.5%±11%, and specificity 99.3%±4%).

CONCLUSION

DTI in the middle cerebellar peduncle and putamen may be used in the diagnosis of MSA with a high degree of accuracy.

Genetics Underlying Atypical Parkinsonism and Related Neurodegenerative Disorders

Atypical parkinsonism syndromes, such as dementia with Lewy bodies, multiple system atrophy, progressive supranuclear palsy and corticobasal degeneration, are neurodegenerative diseases with complex clinical and pathological features. Heterogeneity in clinical presentations, possible secondary determinants as well as mimic syndromes pose a major challenge to accurately diagnose patients suffering from these devastating conditions. Over the last two decades, significant advancements in genomic technologies have provided us with increasing insights into the molecular pathogenesis of atypical parkinsonism and their intriguing relationships to related neurodegenerative diseases, fueling new hopes to incorporate molecular knowledge into our diagnostic, prognostic and therapeutic approaches towards managing these conditions. In this review article, we summarize the current understanding of genetic mechanisms implicated in atypical parkinsonism syndromes. We further highlight mimic syndromes relevant to differential considerations and possible future directions.

Spread of pathology in amyotrophic lateral sclerosis: assessment of phosphorylated TDP-43 along axonal pathways

Introduction

The progression of amyotrophic lateral sclerosis (ALS) through the brain has recently been staged using independent neuropathological and neuroimaging modalities. The two schemes tie into the concept of pathological spread through corticofugal axonal transmission that stems from observation of oligodendrocyte pTDP-43 aggregates along with neuronal inclusions. Here, we aimed to assess evidence of transmission along axonal pathways by looking for pTDP-43 oligodendrocyte pathology in involved white matter tracts, and to present a first validation of the neuropathological staging scheme.

pTDP-43 immunohistochemistry was performed in select white matter tracts and grey matter regions from the staging scheme in postmortem-confirmed ALS cases (N = 34). Double-labelling immunofluorescence was performed to confirm co-localisation of pTDP-43 immunoreactivity to oligodendrocytes.

Results

While pTDP-43 immunoreactive oligodendrocytes were frequent in the white matter under the motor and sensory cortices, similar assessment of the white matter along the corticospinal tract and in the corpus callosum and cingulum bundle of the same cases revealed no pTDP-43 pathology, questioning the involvement of oligodendrocytes in pathological propagation. The assessment of Betz cell loss revealed that the lack of deep white matter pTDP-43 oligodendrocyte pathology was not due to an absence of motor axons. Assessment of the propagation of pathology to different grey matter regions validated that all cases could be allocated to one of four neuropathological stages, although Stage 4 cases were found to differ significantly in age of onset (~10 years older) and disease duration (shorter duration than Stage 3 and similar to Stage 2).

Conclusions

Four stages of ALS neuropathology can be consistently identified, although evidence of sequential clinical progression requires further assessment. As limited pTDP-43 oligodendrocyte pathology in deep corticospinal and other white matter tracts from the motor cortex was observed, the propagation of pathology between neurons may not involve oligodendrocytes and the interpretation of the changes observed on neuroimaging should be modified accordingly.

Electronic supplementary material

The online version of this article (doi:10.1186/s40478-015-0226-y) contains supplementary material, which is available to authorized users.

Failure of Neuroprotection Despite Microglial Suppression by Delayed-Start Myeloperoxidase Inhibition in a Model of Advanced Multiple System Atrophy: Clinical Implications

Multiple system atrophy (MSA) is a rapidly progressive neurodegenerative disease. Post-mortem hallmarks of MSA neuropathology include oligodendroglial α-synuclein (αSYN) inclusions, striatonigral degeneration, olivopontocerebellar atrophy, and increased microglial activation that accompanies the wide spread neurodegeneration. Recently, we demonstrated upregulation of myeloperoxidase (MPO) in activated microglia and provided evidence for the role of microglial MPO in the mediation of MSA-like neurodegeneration (Stefanova et al. Neurotox Res 21:393–404, 2015). The aim of the current study was to assess the therapeutic potency of MPO inhibition (MPOi) in a model of advanced MSA. We replicated the advanced pathology of MSA by intoxicating transgenic PLP-α-synuclein transgenic mice with 3-nitropropionic acid (3NP). After onset of the full-blown pathology, MSA mice received either MPOi or vehicle over 3 weeks. Motor phenotype and neuropathology were analyzed to assess the therapeutic efficacy of MPOi compared to vehicle treatment in MSA mice. MPOi therapy initiated after the onset of severe MSA-like neuropathology in mice failed to attenuate motor impairments and neuronal loss within the striatum, substantia nigra pars compacta, inferior olives, pontine nuclei, and cerebellar cortex. However, we observed a significant reduction of microglial activation in degenerating brain areas. Further, nitrated αSYN accumulation was reduced in the striatonigral region. In summary, delayed-start MPOi treatment reduced microglial activation and levels of nitrated αSYN in a mouse model of advanced MSA. These effects failed to impact on motor impairments and neuronal loss in contrast to previously reported disease modifying efficacy of early-start therapy with MPOi in MSA.

Oligodendroglia and Myelin in Neurodegenerative Diseases: More Than Just Bystanders?

Oligodendrocytes, the myelinating cells of the central nervous system, mediate rapid action potential conduction and provide trophic support for axonal as well as neuronal maintenance. Their progenitor cell population is widely distributed in the adult brain and represents a permanent cellular reservoir for oligodendrocyte replacement and myelin plasticity. The recognition of oligodendrocytes, their progeny, and myelin as contributing factors for the pathogenesis and the progression of neurodegenerative disease has recently evolved shaping our understanding of these disorders. In the present review, we aim to highlight studies on oligodendrocytes and their progenitors in neurodegenerative diseases. We dissect oligodendroglial biology and illustrate evolutionary aspects in regard to their importance for neuronal functionality and maintenance of neuronal circuitries. After covering recent studies on oligodendroglia in different neurodegenerative diseases mainly in view of their function as myelinating cells, we focus on the alpha-synucleinopathy multiple system atrophy, a prototypical disorder with a well-defined oligodendroglial pathology.

Glia and alpha-synuclein in neurodegeneration: A complex interaction

α-Synucleinopathies (ASP) comprise adult-onset, progressive neurodegenerative disorders such as Parkinson's disease (PD), dementia with Lewy bodies (DLB) and multiple system atrophy (MSA) that are characterized by α-synuclein (AS) aggregates in neurons or glia. PD and DLB feature neuronal AS-positive inclusions termed Lewy bodies (LB) whereas glial cytoplasmic inclusions (GCIs, Papp-Lantos bodies) are recognized as the defining hallmark of MSA. Furthermore, AS-positive cytoplasmic aggregates may also be seen in astroglial cells of PD/DLB and MSA brains. The glial AS-inclusions appear to trigger reduced trophic support resulting in neuronal loss. Moreover, microgliosis and astrogliosis can be found throughout the neurodegenerative brain and both are key players in the initiation and progression of ASP. In this review, we will highlight AS-dependent alterations of glial function and their impact on neuronal vulnerability thereby providing a detailed summary on the multifaceted role of glia in ASP.

Multiple system atrophy: the application of genetics in understanding etiology

Classically defined phenotypically by a triad of cerebellar ataxia, parkinsonism, and autonomic dysfunction in conjunction with pyramidal signs, multiple system atrophy (MSA) is a rare and progressive neurodegenerative disease affecting an estimated 3-4 per every 100,000 individuals among adults 50-99 years of age. With a pathological hallmark of alpha-synuclein-immunoreactive glial cytoplasmic inclusions (GCIs; Papp-Lantos inclusions), MSA patients exhibit marked neurodegenerative changes in the striatonigral and/or olivopontocerebellar structures of the brain. As a member of the alpha-synucleinopathy family, which is defined by its well-demarcated alpha-synuclein-immunoreactive inclusions and aggregation, MSA's clinical presentation exhibits several overlapping features with other members including Parkinson's disease (PD) and dementia with Lewy bodies (DLB). Given the extensive fund of knowledge regarding the genetic etiology of PD revealed within the past several years, a genetic investigation of MSA is warranted. While a current genome-wide association study is underway for MSA to further clarify the role of associated genetic loci and single-nucleotide polymorphisms, several cases have presented solid preliminary evidence of a genetic etiology. Naturally, genes and variants manifesting known associations with PD (and other phenotypically similar neurodegenerative disorders), including SNCA and MAPT, have been comprehensively investigated in MSA patient cohorts. More recently variants in COQ2 have been linked to MSA in the Japanese population although this finding awaits replication. Nonetheless, significant positive associations with subsequent independent replication studies have been scarce. With very limited information regarding genetic mutations or alterations in gene dosage as a cause of MSA, the search for novel risk genes, which may be in the form of common variants or rare variants, is the logical nexus for MSA research. We believe that the application of next generation genetic methods to MSA will provide valuable insight into the underlying causes of this disease, and will be central to the identification of etiologic-based therapies.

Exploring myelin dysfunction in multiple system atrophy

Multiple system atrophy (MSA) is a rare, yet fatal neurodegenerative disease that presents clinically with autonomic failure in combination with parkinsonism or cerebellar ataxia. MSA impacts on the autonomic nervous system affecting blood pressure, heart rate and bladder function, and the motor system affecting balance and muscle movement. The cause of MSA is unknown, no definitive risk factors have been identified, and there is no cure or effective treatment. The definitive pathology of MSA is the presence of α-synuclein aggregates in the brain and therefore MSA is classified as an α-synucleinopathy, together with Parkinson's disease and dementia with Lewy bodies. Although the molecular mechanisms of misfolding, fibrillation and aggregation of α-synuclein partly overlap with other α-synucleinopathies, the pathological pathway of MSA is unique in that the principal site for α-synuclein deposition is in the oligodendrocytes rather than the neurons. The sequence of pathological events of MSA is now recognized as abnormal protein redistributions in oligodendrocytes first, followed by myelin dysfunction and then neurodegeneration. Oligodendrocytes are responsible for the production and maintenance of myelin, the specialized lipid membrane that encases the axons of all neurons in the brain. Myelin is composed of lipids and two prominent proteins, myelin basic protein and proteolipid protein. In vitro studies suggest that aberration in protein distribution and lipid transport may lead to myelin dysfunction in MSA. The purpose of this perspective is to bring together available evidence to explore the potential role of α-synuclein, myelin protein dysfunction, lipid dyshomeostasis and ABCA8 in MSA pathogenesis.

Multiple system atrophy: genetic or epigenetic?

Multiple system atrophy (MSA) is a rare, late-onset and fatal neurodegenerative disease including multisystem neurodegeneration and the formation of α-synuclein containing oligodendroglial cytoplasmic inclusions (GCIs), which present the hallmark of the disease. MSA is considered to be a sporadic disease; however certain genetic aspects have been studied during the last years in order to shed light on the largely unknown etiology and pathogenesis of the disease. Epidemiological studies focused on the possible impact of environmental factors on MSA disease development. This article gives an overview on the findings from genetic and epigenetic studies on MSA and discusses the role of genetic or epigenetic factors in disease pathogenesis.

MST3 kinase phosphorylates TAO1/2 to enable Myosin Va function in promoting spine synapse development

Mammalian Sterile 20 (Ste20)-like kinase 3 (MST3) is a ubiquitously expressed kinase capable of enhancing axon outgrowth. Whether and how MST3 kinase signaling might regulate development of dendritic filopodia and spine synapses is unknown. Through shRNA-mediated depletion of MST3 and kinase-dead MST3 expression in developing hippocampal cultures, we found that MST3 is necessary for proper filopodia, dendritic spine, and excitatory synapse development. Knockdown of MST3 in layer 2/3 pyramidal neurons via in utero electroporation also reduced spine density in vivo. Using chemical genetics, we discovered thirteen candidate MST3 substrates and identified the phosphorylation sites. Among the identified MST3 substrates, TAO kinases regulate dendritic filopodia and spine development, similar to MST3. Furthermore, using stable isotope labeling by amino acids in culture (SILAC), we show that phosphorylated TAO1/2 associates with Myosin Va and is necessary for its dendritic localization, thus revealing a mechanism for excitatory synapse development in the mammalian CNS.

Altered lipid levels provide evidence for myelin dysfunction in multiple system atrophy

Multiple system atrophy (MSA) is a rapidly-progressive neurodegenerative disease characterized by parkinsonism, cerebellar ataxia and autonomic failure. A pathological hallmark of MSA is the presence of α-synuclein deposits in oligodendrocytes, the myelin-producing support cells of the brain. Brain pathology and in vitro studies indicate that myelin instability may be an early event in the pathogenesis of MSA. Lipid is a major constituent (78% w/w) of myelin and has been implicated in myelin dysfunction in MSA. However, changes, if any, in lipid level/distribution in MSA brain are unknown. Here, we undertook a comprehensive analysis of MSA myelin. We quantitatively measured three groups of lipids, sphingomyelin, sulfatide and galactosylceramide, which are all important in myelin integrity and function, in affected (under the motor cortex) and unaffected (under the visual cortex) white matter regions. For all three groups of lipids, most of the species were severely decreased (40-69%) in affected but not unaffected MSA white matter. An analysis of the distribution of lipid species showed no significant shift in fatty acid chain length/content with MSA. The decrease in lipid levels was concomitant with increased α-synuclein expression. These data indicate that the absolute levels, and not distribution, of myelin lipids are altered in MSA, and provide evidence for myelin lipid dysfunction in MSA pathology. We propose that dysregulation of myelin lipids in the course of MSA pathogenesis may trigger myelin instability.

Alpha-synuclein biology in Lewy body diseases

α-Synuclein is an abundantly expressed neuronal protein that is at the center of focus in understanding a group of neurodegenerative disorders called α-synucleinopathies, which are characterized by the presence of aggregated α-synuclein intracellularly. Primary α-synucleinopathies include Parkinson’s disease (PD), dementia with Lewy bodies and multiple system atrophy, with α-synuclein also found secondarily in a number of other diseases, including Alzheimer’s disease. Understanding how α-synuclein aggregates form in these different disorders is important for the understanding of its pathogenesis in Lewy body diseases. PD is the most prevalent of the α-synucleinopathies and much of the initial research on α-synuclein Lewy body pathology was based on PD but is also relevant to Lewy bodies in other diseases (dementia with Lewy bodies and Alzheimer’s disease). Polymorphism and mutation studies of SNCA, the gene that encodes α-synuclein, provide much evidence for a causal link between α-synuclein and PD. Among the primary α-synucleinopathies, multiple system atrophy is unique in that α-synuclein deposition occurs in oligodendrocytes rather than neurons. It is unclear whether α-synuclein originates from oligodendrocytes or whether it is transmitted somehow from neurons. α-Synuclein exists as a natively unfolded monomer in the cytosol, but in the presence of lipid membranes it is thought to undergo a conformational change to a folded α-helical secondary structure that is prone to forming dimers and oligomers. Posttranslational modification of α-synuclein, such as phosphorylation, ubiquitination and nitration, has been widely implicated in α-synuclein aggregation process and neurotoxicity. Recent studies using animal and cell models, as well as autopsy studies of patients with neuron transplants, provided compelling evidence for prion-like propagation of α-synuclein. This observation has implications for therapeutic strategies, and much recent effort is focused on developing antibodies that target extracellular α-synuclein.

An update on the cerebellar subtype of multiple system atrophy

Multiple system atrophy is a rare and fatal neurodegenerative disorder characterized by progressive autonomic failure, ataxia and parkinsonism in any combination. The clinical manifestations reflect central autonomic and striatonigral degeneration as well as olivopontocerebellar atrophy. Glial cytoplasmic inclusions, composed of α-synuclein and other proteins are considered the cellular hallmark lesion. The cerebellar variant of MSA (MSA-C) denotes a distinctive motor subtype characterized by progressive adult onset sporadic gait ataxia, scanning dysarthria, limb ataxia and cerebellar oculomotor dysfunction. In addition, there is autonomic failure and variable degrees of parkinsonism. A range of other disorders may present with MSA-C like features and therefore the differential diagnosis of MSA-C is not always straightforward. Here we review key aspects of MSA-C including pathology, pathogenesis, diagnosis, clinical features and treatment, paying special attention to differential diagnosis in late onset sporadic cerebellar ataxias.

Relocation of p25α/tubulin polymerization promoting protein from the nucleus to the perinuclear cytoplasm in the oligodendroglia of sporadic and COQ2 mutant multiple system atrophy

p25α/tubulin polymerization promoting protein (TPPP) is an oligodendroglial protein that plays crucial roles including myelination, and the stabilization of microtubules. In multiple system atrophy (MSA), TPPP is suggested to relocate from the myelin sheath to the oligodendroglial cell body, before the formation of glial cytoplasmic inclusions (GCIs), the pathologic hallmark of MSA. However, much is left unknown about the re-distribution of TPPP in MSA. We generated new antibodies against the N- and C-terminus of TPPP, and analyzed control and MSA brains, including the brain of a familial MSA patient carrying homozygous mutations in the coenzyme Q2 gene (COQ2). In control brain tissues, TPPP was localized not only in the cytoplasmic component of the oligodendroglia including perinuclear cytoplasm and peripheral processes in the white matter, but also in the nucleus of a fraction (62.4%) of oligodendroglial cells. Immunoelectron microscopic analysis showed TPPP in the nucleus and mitochondrial membrane of normal oligodendroglia, while western blot also supported its nuclear and mitochondrial existence. In MSA, the prevalence of nuclear TPPP was 48.6% in the oligodendroglia lacking GCIs, whereas it was further decreased to 19.6% in the oligodendroglia with phosphorylated α-synuclein (pα-syn)-positive GCIs, both showing a significant decrease compared to controls (62.4%). In contrast, TPPP accumulated in the perinuclear cytoplasm where mitochondrial membrane (TOM20 and cytochrome C) and fission (DRP1) proteins were often immunoreactive. We conclude that in MSA-oligodendroglia, TPPP is reduced, not only in the peripheral cytoplasm, but also in the nucleus and relocated to the perinuclear cytoplasm.

Intracellular alpha-synuclein affects early maturation of primary oligodendrocyte progenitor cells

Myelin loss is a widespread neuropathological hallmark of the atypical parkinsonian disorder multiple system atrophy (MSA). On a cellular level, MSA is characterized by alpha-synuclein (aSyn)-positive glial cytoplasmic inclusions (GCIs) within mature oligodendrocytes leading to demyelination as well as axonal and neuronal loss. Oligodendrocyte progenitor cells (OPCs) represent a proliferative cell population distributed throughout the adult mammalian central nervous system. During remyelination, OPCs are recruited to sites of demyelination, differentiate, and finally replace dysfunctional mature oligodendrocytes. However, comprehensive studies investigating OPCs and remyelination processes in MSA are lacking. In the present study, we therefore investigate the effect of human aSyn (h-aSyn) on early primary rat OPC maturation. Upon lentiviral transduction, h-aSyn expressing OPCs exhibit fewer and shorter primary processes at the initiation of differentiation. Until day 4 of a 6day differentiation paradigm, h-aSyn expressing OPCs further show a severely delayed maturation evidenced by reduced myelin gene expression and increased levels of the progenitor marker platelet derived growth factor receptor-alpha (PDGFRα). Matching these results, OPCs that take up extracellular recombinant h-aSyn exhibit a similar delayed differentiation. In both experimental setups however, myelin gene expression is restored at day 6 of differentiation paralleled by decreased intracellular h-aSyn levels indicating a reverse correlation of h-aSyn and the differentiation potential of OPCs. Taken together, these findings suggest a tight link between the intracellular level of h-aSyn and maturation capacity of primary OPCs.

Novel therapeutic approaches in multiple system atrophy

Multiple system atrophy (MSA) is a sporadic, adult onset, relentlessly progressive neurodegenerative disease characterized by autonomic abnormalities associated with parkinsonism, cerebellar dysfunction, pyramidal signs, or combinations thereof. Treatments that can halt or reverse the progression of MSA have not yet been identified. MSA is neuropathologically defined by the presence of α-synuclein-containing inclusions, particularly in the cytoplasm of oligodendrocytes (glial cytoplasmic inclusions, GCIs), which are associated with neurodegeneration. The mechanisms by which oligodendrocytic α-synuclein inclusions cause neuronal death in MSA are not completely understood. The MSA neurodegenerative process likely comprises cell-to-cell transmission of α-synuclein in a prion-like manner, α-synuclein aggregation, increased oxidative stress, abnormal expression of tubulin proteins, decreased expression of neurotrophic factors, excitotoxicity and microglial activation, and neuroinflammation. In an attempt to block each of these pathogenic mechanisms, several pharmacologic approaches have been tried and shown to exert neuroprotective effects in transgenic mouse or cellular models of MSA. These include sertraline, paroxetine, and lithium, which hamper arrival of α-synuclein to oligodendroglia; rifampicin, lithium, and non-steroidal anti-inflammatory drugs, which inhibit α-synuclein aggregation in oligodendrocytes; riluzole, rasagiline, fluoxetine and mesenchymal stem cells, which exert neuroprotective actions; and minocycline and intravenous immunoglobulins, which reduce neuroinflammation and microglial activation. These and other potential therapeutic strategies for MSA are summarized in this review.

Towards translational therapies for multiple system atrophy

Multiple system atrophy (MSA) is a fatal adult-onset neurodegenerative disorder of uncertain etiopathogenesis manifesting with autonomic failure, parkinsonism, and ataxia in any combination. The underlying neuropathology affects central autonomic, striatonigral and olivopontocerebellar pathways and it is associated with distinctive glial cytoplasmic inclusions (GCIs, Papp-Lantos bodies) that contain aggregates of α-synuclein. Current treatment options are very limited and mainly focused on symptomatic relief, whereas disease modifying options are lacking. Despite extensive testing, no neuroprotective drug treatment has been identified up to now; however, a neurorestorative approach utilizing autologous mesenchymal stem cells has shown remarkable beneficial effects in the cerebellar variant of MSA. Here, we review the progress made over the last decade in defining pathogenic targets in MSA and summarize insights gained from candidate disease-modifying interventions that have utilized a variety of well-established preclinical MSA models. We also discuss the current limitations that our field faces and suggest solutions for possible approaches in cause-directed therapies of MSA.

Lipid dysfunction and pathogenesis of multiple system atrophy

Multiple system atrophy (MSA) is a progressive neurodegenerative disease characterized by the accumulation of α-synuclein protein in the cytoplasm of oligodendrocytes, the myelin-producing support cells of the central nervous system (CNS). The brain is the most lipid-rich organ in the body and disordered metabolism of various lipid constituents is increasingly recognized as an important factor in the pathogenesis of several neurodegenerative diseases. α-Synuclein is a 17 kDa protein with a close association to lipid membranes and biosynthetic processes in the CNS, yet its precise function is a matter of speculation, particularly in oligodendrocytes. α-Synuclein aggregation in neurons is a well-characterized feature of Parkinson’s disease and dementia with Lewy bodies. Epidemiological evidence and in vitro studies of α-synuclein molecular dynamics suggest that disordered lipid homeostasis may play a role in the pathogenesis of α-synuclein aggregation. However, MSA is distinct from other α-synucleinopathies in a number of respects, not least the disparate cellular focus of α-synuclein pathology. The recent identification of causal mutations and polymorphisms in COQ2, a gene encoding a biosynthetic enzyme for the production of the lipid-soluble electron carrier coenzyme Q₁₀ (ubiquinone), puts membrane transporters as central to MSA pathogenesis, although how such transporters are involved in the early myelin degeneration observed in MSA remains unclear. The purpose of this review is to bring together available evidence to explore the potential role of membrane transporters and lipid dyshomeostasis in the pathogenesis of α-synuclein aggregation in MSA. We hypothesize that dysregulation of the specialized lipid metabolism involved in myelin synthesis and maintenance by oligodendrocytes underlies the unique neuropathology of MSA.