Papp-Lantos inclusions and the pathogenesis of multiple system atrophy: an update

Computer-Based Evaluation of α-Synuclein Pathology in Multiple System Atrophy as a Novel Tool to Recognize Disease Subtypes

Multiple system atrophy (MSA) is a neurodegenerative disorder with variable disease course and distinct constellations of clinical (cerebellar [MSA-C] or parkinsonism [MSA-P]) and pathological phenotypes, suggestive of distinct α-synuclein (αSyn) strains. Neuropathologically, MSA is characterized by the accumulation of αSyn in oligodendrocytic glial cytoplasmic inclusions (GCI). Using a novel computer-based method, this study quantified the size of GCIs, density of all αSyn pathology, density of only the GCIs, and number of GCIs in MSA cases (n = 20). The putamen and cerebellar white matter were immunostained with the disease-associated 5G4 anti-αSyn antibody. Following digital scanning and image processing, total 5G4-immunoreactive pathology (ie, neuronal, neuritic, and glial) and GCIs were optically dissected for inclusion size and density measurement and then evaluated applying a novel computer-based method using ImageJ. GCI size varied between cases and brain regions (P < .0001), and heterogeneity in the density of all αSyn pathology including the density and number of GCIs were observed between regions and across cases, where MSA-C cases had a significantly higher density of all αSyn pathology in the cerebellar white matter (P = .049). Some region-specific morphologic variables inversely correlated with the age of onset and death, suggestive of an underlying aging-related cellular mechanism. Unsupervised K-means cluster analysis classified MSA cases into 3 distinct groups based on region-specific morphologic variables. In conclusion, we developed a novel computer-based method that is easily accessible, providing a first step to developing artificial intelligence-based evaluation strategies for large scale comparative studies. Our observations on the variability of morphologic variables between brain regions and cases highlight (1) the importance of computer-based approaches to detect features not considered in the routine diagnostic practice, and (2) novel aspects for the identification of previously unrecognized MSA subtypes that do not necessarily reflect the current clinical classification of MSA-C or MSA-P.

Association of Parkinson's disease to Parkinson's plus syndromes, Lewy body dementia, and Alzheimer's dementia

Background

Parkinson's disease (PD) is a condition that affects movement and is usually seen in those over the age of 50. It is caused by the death of dopaminergic neurons, particularly in the substantia nigra. PD has shifted from being perceived as an uncommon condition to a significant neurological illness, mostly due to the increasing number of elderly individuals and the impact of environmental factors. Parkinson's plus syndromes, such as progressive supranuclear palsy (PSP), multiple system atrophy (MSA), corticobasal degeneration (CBD), and vascular Parkinsonism (VaP), provide difficulties in distinguishing them clinically from PD since they have similar characteristics.

Methodology

A thorough examination was performed utilizing the PubMed, Medline, Scopus, and Web of Science databases. The search utilized specific keywords like "Parkinson's disease," "Parkinson's plus syndrome," "Lewy body dementia," "Alzheimer's dementia," "progressive supranuclear palsy," and "multiple system atrophy." The selection criteria were aimed at English-language literature, with a particular focus on examining the connection between PD and associated disorders or dementias.

Results and Discussion

Parkinson's plus syndromes, such as PSP, MSA, CBD, and VaP, exhibit unique clinical characteristics, imaging results, and diverse reactions to levodopa. This makes it difficult to distinguish them from PD. LBD is characterized by Lewy bodies containing α-synuclein, which leads to both motor and cognitive deficits. PD and Alzheimer's disease (AD) exhibit a complex interaction, including common pathogenic processes, genetic predispositions, and clinical characteristics of dementia.

Conclusion

The interrelatedness of PD, Parkinson's plus syndromes, LBD, and AD highlights the significance of comprehending shared disease-causing processes. Aberrant protein clumping, impaired functioning of mitochondria, increased oxidative stress, and inflammation in the brain are common factors which can be addressed for specific treatments. More research is essential for understanding complicated connections and developing effective therapies for these sophisticated neurological illnesses.

From Synaptic Physiology to Synaptic Pathology: The Enigma of α-Synuclein

Alpha-synuclein (α-syn) has gained significant attention due to its involvement in neurodegenerative diseases, particularly Parkinson's disease. However, its normal function in the human brain is equally fascinating. The α-syn protein is highly dynamic and can adapt to various conformational stages, which differ in their interaction with synaptic elements, their propensity to drive pathological aggregation, and their toxicity. This review will delve into the multifaceted role of α-syn in different types of synapses, shedding light on contributions to neurotransmission and overall brain function. We describe the physiological role of α-syn at central synapses, including the bidirectional interaction between α-syn and neurotransmitter systems.

A Novel Brain PET Radiotracer for Imaging Alpha Synuclein Fibrils in Multiple System Atrophy

Abnormal α-synuclein (α-syn) aggregation characterizes α-synucleinopathies, including Parkinson's disease (PD) and multiple system atrophy (MSA). However, no suitable positron emission tomography (PET) radiotracer for imaging α-syn in PD and MSA exists currently. Our structure-activity relationship studies identified 4-methoxy-N-(4-(3-(pyridin-2-yl)-3,8-diazabicyclo[3.2.1]octan-8-yl)phenyl)benzamide (4i) as a PET radiotracer candidate for imaging α-syn. In vitro assays revealed high binding of 4i to recombinant α-syn fibrils (inhibition constant (Ki) = 6.1 nM) and low affinity for amyloid beta (Aβ) fibrils in Alzheimer's disease (AD) homogenates. However, [3H]4i also exhibited high specific binding to AD, progressive supranuclear palsy, and corticobasal degeneration tissues as well as PD and MSA tissues, suggesting notable affinity to tau. Nevertheless, the specific binding to pathologic α-syn aggregates in MSA post-mortem brain tissues was significantly higher than in PD tissues. This finding demonstrated the potential use of [11C]4i as a PET tracer for imaging α-syn in MSA patients. Nonhuman primate PET studies confirmed good brain uptake and rapid washout for [11C]4i.

Mutant α-synuclein propagates via the lymphatic system of the brain in the monomeric state

Prion-like protein propagation is considered a common pathogenic mechanism in neurodegenerative diseases. Here we investigate the in vivo propagation pattern and aggregation state of mutant α-synuclein by injecting adeno-associated viral (AAV)-α-synuclein-A53T-EGFP into the mouse olfactory cortex. Comparison of aggregation states in various brain regions at multiple time points after injection using western blot analyses shows that the monomeric state of the mutant/misfolded protein propagates to remote brain regions by 2 weeks and that the propagated proteins aggregate in situ after being incorporated into neurons. Moreover, injection of Alexa 488-labeled α-synuclein-A53T confirms the monomeric propagation at 2 weeks. Super-resolution microscopy shows that both α-synuclein-A53T proteins propagate via the lymphatic system, penetrate perineuronal nets, and reach the surface of neurons. Electron microscopy shows that the propagated mutant/misfolded monomer forms fibrils characteristic of Parkinson's disease after its incorporation into neurons. These findings suggest a mode of propagation different from that of aggregate-dependent propagation.

microRNA and circRNA in Parkinson's Disease and atypical parkinsonian syndromes

Multiple System Atrophy (MSA) and Progressive Supranuclear Palsy (PSP) are atypical parkinsonian syndromes (APS) with various clinical phenotypes and considerable clinical overlap with idiopathic Parkinson's disease (iPD). This disease heterogeneity makes ante-mortem diagnosis extremely challenging with up to 24% of patients misdiagnosed. Because diagnosis is predominantly clinical, there is great interest in identifying biomarkers for early diagnosis and differentiation of the different types of parkinsonism. Compared to protein biomarkers, microRNAs (miRNAs) and circularRNAs (circRNAs) are stable tissue-specific molecules that can be accurately measured by reverse transcription-quantitative polymerase chain reaction (RT-qPCR). This chapter critically reviews miRNAs and circRNAs as diagnostic biomarkers and therapeutics to differentiate atypical parkinsonian disorders and their role in disease pathogenesis.

A functional role for alpha-synuclein in neuroimmune responses

Alpha-synuclein is a neuronal protein with unclear function but is associated with the pathogenesis of Parkinson's disease and other synucleinopathies. In this review, we discuss the emerging functional role of alpha-synuclein in support of the unique immune responses in the nervous system. Recent data now show that alpha-synuclein functions to support interferon signaling within neurons and is released from neurons to support chemoattraction and activation of local glial cells and infiltrating immune cells. Inflammatory activation and interferon signaling also induce post-translational modifications of alpha-synuclein that are commonly associated with Parkinson's disease pathogenesis. Taken together, emerging data implicate complex interactions between alpha-synuclein and host immune responses that may contribute to the pathogenesis of Parkinson's disease. Additional study of the function of alpha-synuclein in the brain's immune response may provide disease-modifying therapeutic targets for Parkinson's disease in the future.

Serotonin in synucleinopathies

Dysfunction of the serotonergic system represents an important feature in synucleinopathies like Parkinson disease (PD), dementia with Lewy bodies (DLB) and Multiple system atrophy (MSA). Serotonergic fibers from the raphe nuclei (RN) extend broadly throughout the central nervous system, innervating several brain areas affected in synucleinopathies. Alterations of the serotonergic system are associated with non-motor symptoms or motor complications in PD as well as with autonomic features of MSA. Postmortem studies, data from transgenic animal models and imaging techniques greatly contributed to the understanding of this serotonergic pathophysiology in the past, even leading to preclinical and clinical candidate drug tests targeting different parts of the serotonergic system. In this article, we review most recent work extending the knowledge of the serotonergic system and highlighting its relevance for the pathophysiology of synucleinopathies.

A Mouse Model of Multiple System Atrophy: Bench to Bedside

Multiple system atrophy (MSA) is a rare neurodegenerative disorder with unclear etiology, currently difficult and delayed diagnosis, and rapid progression, leading to disability and lethality within 6 to 9 years after symptom onset. The neuropathology of MSA classifies the disease in the group of a-synucleinopathies together with Parkinson's disease and other Lewy body disorders, but features specific oligodendroglial inclusions, which are pathognomonic for MSA. MSA has no efficient therapy to date. Development of experimental models is crucial to elucidate the disease mechanisms in progression and to provide a tool for preclinical screening of putative therapies for MSA. In vitro and in vivo models, based on selective neurotoxicity, a-synuclein oligodendroglial overexpression, and strain-specific propagation of a-synuclein fibrils, have been developed, reflecting various facets of MSA pathology. Over the years, the continuous exchange from bench to bedside and backward has been crucial for the advancing of MSA modelling, elucidating MSA pathogenic pathways, and understanding the existing translational gap to successful clinical trials in MSA. The review discusses specifically advantages and limitations of the PLP-a-syn mouse model of MSA, which recapitulates motor and non-motor features of the human disease with underlying striatonigral degeneration, degeneration of autonomic centers, and sensitized olivopontocerebellar system, strikingly mirroring human MSA pathology.

Development of an α-synuclein fibril and oligomer specific tracer for diagnosis of Parkinson's disease, dementia with Lewy bodies and multiple system atrophy

The development of specific disease-associated PET tracers is one of the major challenges, the realization of which in neurodegenerative diseases would enable not only the efficiency of diagnosis but also support the development of disease-modifying therapeutics. Parkinson's disease (PD) is the most common neurodegenerative movement disorder and is characterized by neuronal fibrillary inclusions composed of aggregated α-synuclein (α-syn). However, these deposits are not only found in PD, but also in other related diseases such as multiple system atrophy (MSA) and dementia with Lewy bodies (DLB), which are grouped under the term synucleinopathies. In this study, we used NGS-guided phage display selection to identify short peptides that bind aggregated α-syn. By surface plasmon resonance (SPR)-based affinity screening, we identified the peptide SVLfib-5 that recognizes aggregated α-syn with high complex stability and sequence specificity. Further analysis SPR showed that SVLfib-5 is not only specific for aggregated α-syn, but in particular recognizes fibrillary and oligomeric structures. Moreover, fluorescence microscopy of human brain tissue sections from PD, MSA, and DLB patients with SVLfib-5 allowed specific recognition of α-syn and a clear discrimination between diseased and non-diseased samples. These findings provide the basis for the further development of an α-syn PET tracer for early diagnosis and monitoring of disease progression and therapy progress.

Common Variants Near ZIC1 and ZIC4 in Autopsy-Confirmed Multiple System Atrophy

BACKGROUND

Multiple System Atrophy is a rare neurodegenerative disease with alpha-synuclein aggregation in glial cytoplasmic inclusions and either predominant olivopontocerebellar atrophy or striatonigral degeneration, leading to dysautonomia, parkinsonism, and cerebellar ataxia. One prior genome-wide association study in mainly clinically diagnosed patients with Multiple System Atrophy failed to identify genetic variants predisposing for the disease.

OBJECTIVE

Since the clinical diagnosis of Multiple System Atrophy yields a high rate of misdiagnosis when compared to the neuropathological gold standard, we studied only autopsy-confirmed cases.

METHODS

We studied common genetic variations in Multiple System Atrophy cases (N = 731) and controls (N = 2898).

RESULTS

The most strongly disease-associated markers were rs16859966 on chromosome 3, rs7013955 on chromosome 8, and rs116607983 on chromosome 4 with P-values below 5 × 10-6 , all of which were supported by at least one additional genotyped and several imputed single nucleotide polymorphisms. The genes closest to the chromosome 3 locus are ZIC1 and ZIC4 encoding the zinc finger proteins of cerebellum 1 and 4 (ZIC1 and ZIC4).

INTERPRETATION

Since mutations of ZIC1 and ZIC4 and paraneoplastic autoantibodies directed against ZIC4 are associated with severe cerebellar dysfunction, we conducted immunohistochemical analyses in brain tissue of the frontal cortex and the cerebellum from 24 Multiple System Atrophy patients. Strong immunohistochemical expression of ZIC4 was detected in a subset of neurons of the dentate nucleus in all healthy controls and in patients with striatonigral degeneration, whereas ZIC4-immunoreactive neurons were significantly reduced inpatients with olivopontocerebellar atrophy. These findings point to a potential ZIC4-mediated vulnerability of neurons in Multiple System Atrophy. © 2022 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

Multiple system atrophy prions transmit neurological disease to mice expressing wild-type human α-synuclein

In multiple system atrophy (MSA), the protein α-synuclein misfolds into a prion conformation that self-templates and causes progressive neurodegeneration. While many point mutations in the α-synuclein gene, SNCA, have been identified as the cause of heritable Parkinson's disease (PD), none have been identified as causing MSA. To examine whether MSA prions can transmit disease to mice expressing wild-type (WT) human α-synuclein, we inoculated transgenic (Tg) mice denoted TgM20+/- with brain homogenates prepared from six different deceased MSA patients. All six samples transmitted CNS disease to the mice, with an average incubation period of ~ 280 days. Interestingly, TgM20+/- female mice developed disease > 60 days earlier than their male counterparts. Brains from terminal mice contained phosphorylated α-synuclein throughout the hindbrain, consistent with the distribution of α-synuclein inclusions in MSA patients. In addition, using our α-syn-YFP cell lines, we detected α-synuclein prions in brain homogenates prepared from terminal mice that retained MSA strain properties. To our knowledge, the studies described here are the first to show that MSA prions transmit neurological disease to mice expressing WT SNCA and that the rate of transmission is sex dependent. By comparison, TgM20+/- mice inoculated with WT preformed fibrils (PFFs) developed severe neurological disease in ~ 210 days and exhibited robust α-synuclein neuropathology in both limbic regions and the hindbrain. Brain homogenates from these animals exhibited biological activities that are distinct from those found in MSA-inoculated mice when tested in the α-syn-YFP cell lines. Differences between brains from MSA-inoculated and WT PFF-inoculated mice potentially argue that α-synuclein prions from MSA patients are distinct from the PFF inocula and that PFFs do not replicate MSA strain biology.

Alpha-Synuclein Strain Variability in Body-First and Brain-First Synucleinopathies

Pathogenic alpha-synuclein (asyn) aggregates are a defining feature of neurodegenerative synucleinopathies, which include Parkinson's disease, Lewy body dementia, pure autonomic failure and multiple system atrophy. Early accurate differentiation between these synucleinopathies is challenging due to the highly heterogeneous clinical profile at early prodromal disease stages. Therefore, diagnosis is often made in late disease stages when a patient presents with a broad range of motor and non-motor symptoms easing the differentiation. Increasing data suggest the clinical heterogeneity seen in patients is explained by the presence of distinct asyn strains, which exhibit variable morphologies and pathological functions. Recently, asyn seed amplification assays (PMCA and RT-QuIC) and conformation-specific ligand assays have made promising progress in differentiating between synucleinopathies in prodromal and advanced disease stages. Importantly, the cellular environment is known to impact strain morphology. And, asyn aggregate pathology can propagate trans-synaptically along the brain-body axis, affecting multiple organs and propagating through multiple cell types. Here, we present our hypothesis that the changing cellular environments, an asyn seed may encounter during its brain-to-body or body-to-brain propagation, may influence the structure and thereby the function of the aggregate strains developing within the different cells. Additionally, we aim to review strain characteristics of the different synucleinopathies in clinical and preclinical studies. Future preclinical animal models of synucleinopathies should investigate if asyn strain morphology is altered during brain-to-body and body-to-brain spreading using these seeding amplification and conformation-specific assays. Such findings would greatly deepen our understanding of synucleinopathies and the potential link between strain and phenotypic variability, which may enable specific diagnosis of different synucleinopathies in the prodromal phase, creating a large therapeutic window with potential future applications in clinical trials and personalized therapeutics.

Passive Immunization in Alpha-Synuclein Preclinical Animal Models

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

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

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

Novel Therapies for Parkinsonian Syndromes-Recent Progress and Future Perspectives

Background: Atypical parkinsonian syndromes are rare, fatal neurodegenerative diseases associated with abnormal protein accumulation in the brain. Examples of these syndromes include progressive supranuclear palsy, multiple system atrophy, and corticobasal degeneration. A common clinical feature in parkinsonism is a limited improvement with levodopa. So far, there are no disease-modifying treatments to address these conditions, and therapy is only limited to the alleviation of symptoms. Diagnosis is devastating for patients, as prognosis is extremely poor, and the disease tends to progress rapidly. Currently, potential causes and neuropathological mechanisms involved in these diseases are being widely investigated. Objectives: The goal of this review is to summarize recent advances and gather emerging disease-modifying therapies that could slow the progression of atypical parkinsonian syndromes. Methods: PubMed and Google Scholar databases were searched regarding novel perspectives for atypical parkinsonism treatment. The following medical subject headings were used: "atypical parkinsonian syndromes-therapy," "treatment of atypical parkinsonian syndromes," "atypical parkinsonian syndromes-clinical trial," "therapy of tauopathy," "alpha-synucleinopathy treatment," "PSP therapy/treatment," "CBD therapy/treatment," "MSA therapy/treatment," and "atypical parkinsonian syndromes-disease modifying." All search results were manually reviewed prior to inclusion in this review. Results: Neuroinflammation, mitochondrial dysfunction, microglia activation, proteasomal impairment, and oxidative stress play a role in the neurodegenerative process. Ongoing studies and clinical trials target these components in order to suppress toxic protein accumulation. Various approaches such as stem cell therapy, anti-aggregation/anti-phosphorylation agent administration, or usage of active and passive immunization appear to have promising results. Conclusion: Presently, disease-modifying strategies for atypical parkinsonian syndromes are being actively explored, with encouraging preliminary results. This leads to an assumption that developing accurate, safe, and progression-halting treatment is not far off. Nevertheless, the further investigation remains necessary.

MOBP and HIP1 in multiple system atrophy: New α-synuclein partners in glial cytoplasmic inclusions implicated in the disease pathogenesis

AIMS

Multiple system atrophy (MSA) is a fatal neurodegenerative disease. Similar to Parkinson's disease (PD), MSA is an α-synucleinopathy, and its pathological hallmark consists of glial cytoplasmic inclusions (GCIs) containing α-synuclein (SNCA) in oligodendrocytes. We previously identified consistent changes in myelin-associated oligodendrocyte basic protein (MOBP) and huntingtin interacting protein 1 (HIP1) DNA methylation status in MSA. We hypothesized that if differential DNA methylation at these loci is mechanistically relevant for MSA, it should have downstream consequences on gene regulation.

METHODS

We investigated the relationship between MOBP and HIP1 DNA methylation and mRNA levels in cerebellar white matter from MSA and healthy controls. Additionally, we analysed protein expression using western blotting, immunohistochemistry and proximity ligation assays.

RESULTS

We found decreased MOBP mRNA levels significantly correlated with increased DNA methylation in MSA. For HIP1, we found a distinct relationship between DNA methylation and gene expression levels in MSA compared to healthy controls, suggesting this locus may be subjected to epigenetic remodelling in MSA. Although soluble protein levels for MOBP and HIP1 in cerebellar white matter were not significantly different between MSA cases and controls, we found striking differences between MSA and other neurodegenerative diseases, including PD and Huntington's disease. We also found that MOBP and HIP1 are mislocalized into the GCIs in MSA, where they appear to interact with SNCA.

CONCLUSIONS

This study supports a role for DNA methylation in downregulation of MOBP mRNA in MSA. Most importantly, the identification of MOBP and HIP1 as new constituents of GCIs emphasizes the relevance of these two loci to the pathogenesis of MSA.

Roles for α-Synuclein in Gene Expression

α-Synuclein (α-Syn) is a small cytosolic protein associated with a range of cellular compartments, including synaptic vesicles, the nucleus, mitochondria, endoplasmic reticulum, Golgi apparatus, and lysosomes. In addition to its physiological role in regulating presynaptic function, the protein plays a central role in both sporadic and familial Parkinson’s disease (PD) via a gain-of-function mechanism. Because of this, several recent strategies propose to decrease α-Syn levels in PD patients. While these therapies may offer breakthroughs in PD management, the normal functions of α-Syn and potential side effects of its depletion require careful evaluation. Here, we review recent evidence on physiological and pathological roles of α-Syn in regulating activity-dependent signal transduction and gene expression pathways that play fundamental role in synaptic plasticity.

Sodium, Potassium, Calcium, and Magnesium in the Scalp Hair and Blood Samples Related to the Clinical Stages of the Parkinson's Disease

Neurodegeneration disorders are complex and multifaceted, leading to many chronic diseases, like Parkinson's disease (PD). Electrolytes imbalance has a significant role in the pathophysiology of neurological disorders, which might serve as a bio-indicator of these problems. In the present study, the disturbances of the electrolytes, calcium (Ca), magnesium (Mg), sodium (Na), and potassium (K), concentrations, and their correlation with biochemical parameters of PD patients at three different age groups (15 to 75 years) and stages were studied. The all resulted data of PD patients was compared with non-diseased/referents (PD) of same age groups. The biological samples (scalp hair, serum and plasma) were collected from Parkinson's disease (PD) patients, diagnosed at three stages, early (15 to 30 years), mild (30 to 60 years) and severe (61 to 75 years). The electrolyte concentrations were measured after acid digested biological samples using flame atomic absorption spectrometry. The precision of the digestion method was verified by matrices matched certified reference materials. The resulted data indicated that the contents of Ca and Mg were found to be higher in scalp hair samples of PD patients at early to severe stages as compared with those results obtained from referents. The concentrations of Na and K were found to be lower for all PD patients groups as compared with referents; however, the difference was not significant (p < 0.05). Electrolytes levels in blood serum and plasma were found to be lower in all patients than healthy groups (p < 0.01). These results suggest a disturbance in the electrolytes homeostasis during the different clinical stages of PD, whereas the higher disturbance was observed in patients at severe stage (61 to 75 years).

Neurons and Glia Interplay in α-Synucleinopathies

Accumulation of the neuronal presynaptic protein alpha-synuclein within proteinaceous inclusions represents the key histophathological hallmark of a spectrum of neurodegenerative disorders, referred to by the umbrella term a-synucleinopathies. Even though alpha-synuclein is expressed predominantly in neurons, pathological aggregates of the protein are also found in the glial cells of the brain. In Parkinson's disease and dementia with Lewy bodies, alpha-synuclein accumulates mainly in neurons forming the Lewy bodies and Lewy neurites, whereas in multiple system atrophy, the protein aggregates mostly in the glial cytoplasmic inclusions within oligodendrocytes. In addition, astrogliosis and microgliosis are found in the synucleinopathy brains, whereas both astrocytes and microglia internalize alpha-synuclein and contribute to the spread of pathology. The mechanisms underlying the pathological accumulation of alpha-synuclein in glial cells that under physiological conditions express low to non-detectable levels of the protein are an area of intense research. Undoubtedly, the presence of aggregated alpha-synuclein can disrupt glial function in general and can contribute to neurodegeneration through numerous pathways. Herein, we summarize the current knowledge on the role of alpha-synuclein in both neurons and glia, highlighting the contribution of the neuron-glia connectome in the disease initiation and progression, which may represent potential therapeutic target for a-synucleinopathies.

Human alpha-synuclein overexpressing MBP29 mice mimic functional and structural hallmarks of the cerebellar subtype of multiple system atrophy

Multiple system atrophy (MSA) is a rare, but fatal atypical parkinsonian disorder. The prototypical pathological hallmark are oligodendroglial cytoplasmic inclusions (GCIs) containing alpha-synuclein (α-syn). Currently, two MSA phenotypes are classified: the parkinsonian (MSA-P) and the cerebellar subtype (MSA-C), clinically characterized by predominant parkinsonism or cerebellar ataxia, respectively. Previous studies have shown that the transgenic MSA mouse model overexpressing human α-syn controlled by the oligodendroglial myelin basic protein (MBP) promoter (MBP29-hα-syn mice) mirrors crucial characteristics of the MSA-P subtype. However, it remains elusive, whether this model recapitulates important features of the MSA-C-related phenotype. First, we examined MSA-C-associated cerebellar pathology using human post-mortem tissue of MSA-C patients and controls. We observed the prototypical GCI pathology and a preserved number of oligodendrocytes in the cerebellar white matter (cbw) accompanied by severe myelin deficit, microgliosis, and a profound loss of Purkinje cells. Secondly, we phenotypically characterized MBP29-hα-syn mice using a dual approach: structural analysis of the hindbrain and functional assessment of gait. Matching the neuropathological features of MSA-C, GCI pathology within the cbw of MBP29-hα-syn mice was accompanied by a severe myelin deficit despite an increased number of oligodendrocytes and a high number of myeloid cells even at an early disease stage. Intriguingly, MBP29-hα-syn mice developed a significant loss of Purkinje cells at a more advanced disease stage. Catwalk XT gait analysis revealed decreased walking speed, increased stride length and width between hind paws. In addition, less dual diagonal support was observed toward more dual lateral and three paw support. Taken together, this wide-based and unsteady gait reflects cerebellar ataxia presumably linked to the cerebellar pathology in MBP29-hα-syn mice. In conclusion, the present study strongly supports the notion that the MBP29-hα-syn mouse model mimics important characteristics of the MSA-C subtype providing a powerful preclinical tool for evaluating future interventional strategies.

Mechanisms of Neurodegeneration in Various Forms of Parkinsonism-Similarities and Differences

Parkinson’s disease (PD), dementia with Lewy body (DLB), progressive supranuclear palsy (PSP), corticobasal degeneration (CBD) and multiple system atrophy (MSA) belong to a group of neurodegenerative diseases called parkinsonian syndromes. They share several clinical, neuropathological and genetic features. Neurodegenerative diseases are characterized by the progressive dysfunction of specific populations of neurons, determining clinical presentation. Neuronal loss is associated with extra- and intracellular accumulation of misfolded proteins. The parkinsonian diseases affect distinct areas of the brain. PD and MSA belong to a group of synucleinopathies that are characterized by the presence of fibrillary aggregates of α-synuclein protein in the cytoplasm of selected populations of neurons and glial cells. PSP is a tauopathy associated with the pathological aggregation of the microtubule associated tau protein. Although PD is common in the world’s aging population and has been extensively studied, the exact mechanisms of the neurodegeneration are still not fully understood. Growing evidence indicates that parkinsonian disorders to some extent share a genetic background, with two key components identified so far: the microtubule associated tau protein gene (MAPT) and the α-synuclein gene (SNCA). The main pathways of parkinsonian neurodegeneration described in the literature are the protein and mitochondrial pathways. The factors that lead to neurodegeneration are primarily environmental toxins, inflammatory factors, oxidative stress and traumatic brain injury.

Reduced oligodendrocyte exosome secretion in multiple system atrophy involves SNARE dysfunction

Transportation of key proteins via extracellular vesicles has been recently implicated in various neurodegenerative disorders, including Parkinson's disease, as a new mechanism of disease spreading and a new source of biomarkers. Extracellular vesicles likely to be derived from the brain can be isolated from peripheral blood and have been reported to contain higher levels of α-synuclein (α-syn) in Parkinson's disease patients. However, very little is known about extracellular vesicles in multiple system atrophy, a disease that, like Parkinson's disease, involves pathological α-syn aggregation, though the process is centred around oligodendrocytes in multiple system atrophy. In this study, a novel immunocapture technology was developed to isolate blood CNPase-positive, oligodendrocyte-derived enriched microvesicles (OEMVs), followed by fluorescent nanoparticle tracking analysis and assessment of α-syn levels contained within the OEMVs. The results demonstrated that the concentrations of OEMVs were significantly lower in multiple system atrophy patients, compared to Parkinson's disease patients and healthy control subjects. It is also noted that the population of OEMVs involved was mainly in the size range closer to that of exosomes, and that the average α-syn concentrations (per vesicle) contained in these OEMVs were not significantly different among the three groups. The phenomenon of reduced OEMVs was again observed in a transgenic mouse model of multiple system atrophy and in primary oligodendrocyte cultures, and the mechanism involved was likely related, at least in part, to an α-syn-mediated interference in the interaction between syntaxin 4 and VAMP2, leading to the dysfunction of the SNARE complex. These results suggest that reduced OEMVs could be an important mechanism related to pathological α-syn aggregation in oligodendrocytes, and the OEMVs found in peripheral blood could be further explored for their potential as multiple system atrophy biomarkers.

Assessment of the Retina of Plp-α-Syn Mice as a Model for Studying Synuclein-Dependent Diseases

Purpose

Synucleinopathies such as multiple system atrophy (MSA) and Parkinson's disease are associated with a variety of visual symptoms. Functional and morphological retinal aberrations are therefore supposed to be valuable biomarkers for these neurodegenerative diseases. This study examined the retinal morphology and functionality resulting from human α-synuclein (α-Syn) overexpression in the transgenic Plp-α-Syn mouse model.

Methods

Immunohistochemistry on retinal sections and whole-mounts was performed on 8- to 11-week-old and 12-month-old Plp-α-Syn mice and C57BL/6N controls. Quantitative RT-PCR experiments were performed to study the expression of endogenous and human α-Syn and tyrosine hydroxylase (TH). We confirmed the presence of human α-Syn in the retina in western blot analyses. Multi-electrode array (MEA) analyses from light-stimulated whole-mounted retinas were used to investigate their functionality.

Results

Biochemical and immunohistochemical analyses showed human α-Syn in the retina of Plp-α-Syn mice. We found distinct staining in different retinal cell layers, most abundantly in rod bipolar cells of the peripheral retina. In the periphery, we also observed a trend toward a decline in the number of retinal ganglion cells. The number of TH+ neurons was unaffected in this human α-Syn overexpression model. MEA recordings showed that Plp-α-Syn retinas were functional but exhibited mild alterations in dim light conditions.

Conclusions

Together, these findings implicate an impairment of retinal neurons in the Plp-α-Syn mouse. The phenotype partly relates to retinal deficits reported in MSA patients. We further propose the suitability of the Plp-α-Syn retina as a biological model to study synuclein-mediated mechanisms.

Current Management and Emerging Therapies in Multiple System Atrophy

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

Histone Deacetylase 6 and the Disease Mechanisms of α-Synucleinopathies

The abnormal accumulation of α-Synuclein (α-Syn) is a prominent pathological feature in a group of diseases called α-Synucleinopathies, such as Parkinson’s disease, dementia with Lewy bodies (DLB), and multiple system atrophy (MSA). The formation of Lewy bodies (LBs) and glial cytoplasmic inclusions (GCIs) in neurons and oligodendrocytes, respectively, is highly investigated. However, the molecular mechanisms behind α-Syn improper folding and aggregation remain unclear. Histone deacetylase 6 (HDAC6) is a Class II deacetylase, containing two active catalytic domains and a ubiquitin-binding domain. The properties of HDAC6 and its exclusive cytoplasmic localization allow HDAC6 to modulate the microtubule dynamics, acting as a specific α-tubulin deacetylase. Also, HDAC6 can bind ubiquitinated proteins, facilitating the formation of the aggresome, a cellular defense mechanism to cope with higher levels of misfolded proteins. Several studies report that the aggresome shares similarities in size and composition with LBs and GCIs. HDAC6 is found to co-localize with α-Syn in neurons and in oligodendrocytes, together with other aggresome-related proteins. The involvement of HDAC6 in several neurodegenerative diseases is already under discussion, however, the results obtained by modulating HDAC6 activity are not entirely conclusive. The main goal of this review is to summarize and critically discuss previous in vitro and in vivo data regarding the specific role of HDAC6 in the context of α-Syn accumulation and protein aggregation in α-Synucleinopathies.

Overexpression of α-Synuclein Reorganises Growth Factor Profile of Human Astrocytes

Misfolding and accumulation of aberrant α-synuclein in the brain is associated with the distinct class of neurodegenerative diseases known as α-synucleinopathies, which include Parkinson's disease, dementia with Lewy bodies and multiple system atrophy. Pathological changes in astrocytes contribute to all neurological disorders, and astrocytes are reported to possess α-synuclein inclusions in the context of α-synucleinopathies. Astrocytes are known to express and secrete numerous growth factors, which are fundamental for neuroprotection, synaptic connectivity and brain metabolism; changes in growth factor secretion may contribute to pathobiology of neurological disorders. Here we analysed the effect of α-synuclein overexpression in cultured human astrocytes on growth factor expression and release. For this purpose, the intracellular and secreted levels of 33 growth factors (GFs) and 8 growth factor receptors (GFRs) were analysed in cultured human astrocytes by chemiluminescence-based western/dot blot. Overexpression of human α-synuclein in cultured foetal human astrocytes significantly changes the profile of GF production and secretion. We found that human astrocytes express and secrete FGF2, FGF6, EGF, IGF1, AREG, IGFBP2, IGFBP4, VEGFD, PDGFs, KITLG, PGF, TGFB3 and NTF4. Overexpression of human α-synuclein significantly modified the profile of GF production and secretion, with particularly strong changes in EGF, PDGF, VEGF and their receptors as well as in IGF-related proteins. Bioinformatics analysis revealed possible interactions between α-synuclein and EGFR and GDNF, as well as with three GF receptors, EGFR, CSF1R and PDGFRB.

An update on MSA: premotor and non-motor features open a window of opportunities for early diagnosis and intervention

In this review, we describe the wide clinical spectrum of features that can be seen in multiple system atrophy (MSA) with a focus on the premotor phase and the non-motor symptoms providing an up-to-date overview of the current understanding in this fast-growing field. First, we highlight the non-motor features at disease onset when MSA can be indistinguishable from pure autonomic failure or other chronic neurodegenerative conditions. We describe the progression of clinical features to aid the diagnosis of MSA early in the disease course. We go on to describe the levels of diagnostic certainty and we discuss MSA subtypes that do not fit into the current diagnostic criteria, highlighting the complexity of the disease as well as the need for revised diagnostic tools. Second, we describe the pathology, clinical description, and investigations of cardiovascular autonomic failure, urogenital and sexual dysfunction, orthostatic hypotension, and respiratory and REM-sleep behavior disorders, which may precede the motor presentation by months or years. Their presence at presentation, even in the absence of ataxia and parkinsonism, should be regarded as highly suggestive of the premotor phase of MSA. Finally, we discuss how the recognition of the broader spectrum of clinical features of MSA and especially the non-motor features at disease onset represent a window of opportunity for disease-modifying interventions.

Fluid Biomarkers for Synaptic Dysfunction and Loss

Synapses are the site for brain communication where information is transmitted between neurons and stored for memory formation. Synaptic degeneration is a global and early pathogenic event in neurodegenerative disorders with reduced levels of pre- and postsynaptic proteins being recognized as a core feature of Alzheimer's disease (AD) pathophysiology. Together with AD, other neurodegenerative and neurodevelopmental disorders show altered synaptic homeostasis as an important pathogenic event, and due to that, they are commonly referred to as synaptopathies. The exact mechanisms of synapse dysfunction in the different diseases are not well understood and their study would help understanding the pathogenic role of synaptic degeneration, as well as differences and commonalities among them and highlight candidate synaptic biomarkers for specific disorders. The assessment of synaptic proteins in cerebrospinal fluid (CSF), which can reflect synaptic dysfunction in patients with cognitive disorders, is a keen area of interest. Substantial research efforts are now directed toward the investigation of CSF synaptic pathology to improve the diagnosis of neurodegenerative disorders at an early stage as well as to monitor clinical progression. In this review, we will first summarize the pathological events that lead to synapse loss and then discuss the available data on established (eg, neurogranin, SNAP-25, synaptotagmin-1, GAP-43, and α-syn) and emerging (eg, synaptic vesicle glycoprotein 2A and neuronal pentraxins) CSF biomarkers for synapse dysfunction, while highlighting possible utilities, disease specificity, and technical challenges for their detection.

Neuroinflammation is associated with infiltration of T cells in Lewy body disease and α-synuclein transgenic models

BACKGROUND

α-Synuclein (α-syn) is a pre-synaptic protein which progressively accumulates in neuronal and non-neuronal cells in neurodegenerative diseases such as Parkinson's disease (PD), dementia with Lewy bodies (DLB), and multiple system atrophy. Recent evidence suggests that aberrant immune activation may be involved in neurodegeneration in PD/DLB. While previous studies have often focused on the microglial responses, less is known about the role of the peripheral immune system in these disorders.

METHODS

To understand the involvement of the peripheral immune system in PD/DLB, we evaluated T cell populations in the brains of α-syn transgenic (tg) mice (e.g., Thy1 promoter line 61) and DLB patients.

RESULTS

Immunohistochemical analysis showed perivascular and parenchymal infiltration by CD3+/CD4+ helper T cells, but not cytotoxic T cells (CD3+/CD8+) or B cells (CD20+), in the neocortex, hippocampus, and striatum of α-syn tg mice. CD3+ cells were found in close proximity to the processes of activated astroglia, particularly in areas of the brain with significant astrogliosis, microgliosis, and expression of pro-inflammatory cytokines. In addition, a subset of CD3+ cells co-expressed interferon γ. Flow cytometric analysis of immune cells in the brains of α-syn tg mice revealed that CD1d-tet+ T cells were also increased in the brains of α-syn tg mice suggestive of natural killer T cells. In post-mortem DLB brains, we similarly detected increased numbers of infiltrating CD3+/CD4+ T cells in close proximity with blood vessels.

CONCLUSION

These results suggest that infiltrating adaptive immune cells play an important role in neuroinflammation and neurodegeneration in synucleinopathies and that modulating peripheral T cells may be a viable therapeutic strategy for PD/DLB.

No genetic evidence for the involvement of GGC repeat expansions of the NOTCH2NLC gene in Chinese patients with multiple system atrophy

Recent studies have identified an expanded GGC repeat in the 5' untranslated region of the NOTCH2NLC gene as a possible pathogenic genetic cause of neuronal intranuclear inclusion disease. Converging evidence verifying the presence of the same GGC repeat expansion in patients with Alzheimer's disease, Parkinson's disease, and other neurodegenerative diseases has also received increased attention. Inspired by some of the clinical similarities between neuronal intranuclear inclusion disease and multiple system atrophy (MSA), we used repeat-primed PCR to explore the occurrence of GGC repeats in 328 patients with MSA in mainland China. Our result failed to detect any GGC repeat expansion in these patients with MSA, indicating that the NOTCH2NLC gene may not be involved in the pathogenesis of MSA.

Current Symptomatic and Disease-Modifying Treatments in Multiple System Atrophy

Multiple system atrophy (MSA) is a rare, severe, and rapidly progressive neurodegenerative disorder categorized as an atypical parkinsonian syndrome. With a mean life expectancy of 6-9 years after diagnosis, MSA is clinically characterized by parkinsonism, cerebellar ataxia, autonomic failure, and poor l-Dopa responsiveness. Aside from limited symptomatic treatment, there is currently no disease-modifying therapy available. Consequently, distinct pharmacological targets have been explored and investigated in clinical studies based on MSA-related symptoms and pathomechanisms. Parkinsonism, cerebellar ataxia, and autonomic failure are the most important symptoms targeted by symptomatic treatments in current clinical trials. The most prominent pathological hallmark is oligodendroglial cytoplasmic inclusions containing alpha-synuclein, thus classifying MSA as synucleinopathy. Additionally, myelin and neuronal loss accompanied by micro- and astrogliosis are further distinctive features of MSA-related neuropathology present in numerous brain regions. Besides summarizing current symptomatic treatment strategies in MSA, this review critically reflects upon potential cellular targets and disease-modifying approaches for MSA such as (I) targeting α-syn pathology, (II) intervening neuroinflammation, and (III) neuronal loss. Although these single compound trials are aiming to interfere with distinct pathogenetic steps in MSA, a combined approach may be necessary to slow down the rapid progression of the oligodendroglial associated synucleinopathy.

Models of multiple system atrophy

Multiple system atrophy (MSA) is a neurodegenerative disease with diverse clinical manifestations, including parkinsonism, cerebellar syndrome, and autonomic failure. Pathologically, MSA is characterized by glial cytoplasmic inclusions in oligodendrocytes, which contain fibrillary forms of α-synuclein. MSA is categorized as one of the α-synucleinopathy, and α-synuclein aggregation is thought to be the culprit of the disease pathogenesis. Studies on MSA pathogenesis are scarce relative to studies on the pathogenesis of other synucleinopathies, such as Parkinson’s disease and dementia with Lewy bodies. However, recent developments in cellular and animal models of MSA, especially α-synuclein transgenic models, have driven advancements in research on this disease. Here, we review the currently available models of MSA, which include toxicant-induced animal models, α-synuclein-overexpressing cellular models, and mouse models that express α-synuclein specifically in oligodendrocytes through cell type-specific promoters. We will also discuss the results of studies in recently developed transmission mouse models, into which MSA brain extracts were intracerebrally injected. By reviewing the findings obtained from these model systems, we will discuss what we have learned about the disease and describe the strengths and limitations of the models, thereby ultimately providing direction for the design of better models and future research.

A review of the models available for studying multiple system atrophy (MSA), a Parkinson’s-like disease, may help identify new treatment options. MSA is difficult to diagnose and unresponsive to drugs. Similar to Parkinson’s disease, it involves accumulation of protein aggregates in brain and spinal cord cells, but the causes are poorly understood. He-Jin Lee at Konkuk University, and Seung-Jae Lee at Seoul National University College of Medicine in South Korea and coworkers have reviewed the models available to study the disease, including toxin-induced and transgenic animal models, and recent evidence that transferring the protein aggregates into cells causes MSA symptoms. Each model mimics some aspects of the disease, but none captures the full range of symptoms. This review helps highlight research pathways that may illuminate treatments for this complex and debilitating adult-onset disease.

MicroRNAs Dysregulation and Metabolism in Multiple System Atrophy

Multiple system atrophy (MSA) is an adult onset, fatal disease, characterized by an accumulation of alpha-synuclein (α-syn) in oligodendroglial cells. MicroRNAs (miRNAs) are small non-coding RNAs involved in post-translational regulation and several biological processes. Disruption of miRNA-related pathways in the central nervous system (CNS) plays an important role in the pathogenesis of neurodegenerative diseases, including MSA. While the exact mechanisms underlying miRNAs in the pathogenesis of MSA remain unclear, it is known that miRNAs can repress the translation of messenger RNAs (mRNAs) that regulate the following pathogenesis associated with MSA: autophagy, neuroinflammation, α-syn accumulation, synaptic transmission, oxidative stress, and apoptosis. In this review, the metabolism of miRNAs and their functional roles in the pathogenesis of MSA are discussed, thereby highlighting miRNAs as potential new biomarkers for the diagnosis of MSA and in increasing our understanding of the disease process.

Depopulation of dense α-synuclein aggregates is associated with rescue of dopamine neuron dysfunction and death in a new Parkinson's disease model

Parkinson’s disease (PD) is characterized by the presence of α-synuclein aggregates known as Lewy bodies and Lewy neurites, whose formation is linked to disease development. The causal relation between α-synuclein aggregates and PD is not well understood. We generated a new transgenic mouse line (MI2) expressing human, aggregation-prone truncated 1–120 α-synuclein under the control of the tyrosine hydroxylase promoter. MI2 mice exhibit progressive aggregation of α-synuclein in dopaminergic neurons of the substantia nigra pars compacta and their striatal terminals. This is associated with a progressive reduction of striatal dopamine release, reduced striatal innervation and significant nigral dopaminergic nerve cell death starting from 6 and 12 months of age, respectively. In the MI2 mice, alterations in gait impairment can be detected by the DigiGait test from 9 months of age, while gross motor deficit was detected by rotarod test at 20 months of age when 50% of dopaminergic neurons in the substantia nigra pars compacta are lost. These changes were associated with an increase in the number and density of 20–500 nm α-synuclein species as shown by dSTORM. Treatment with the oligomer modulator anle138b, from 9 to 12 months of age, restored striatal dopamine release, prevented dopaminergic cell death and gait impairment. These effects were associated with a reduction of the inner density of large α-synuclein aggregates and an increase in dispersed small α-synuclein species as revealed by dSTORM. The MI2 mouse model recapitulates the progressive dopaminergic deficit observed in PD, showing that early synaptic dysfunction is associated to fine behavioral motor alterations, precedes dopaminergic axonal loss and neuronal death that become associated with a more consistent motor deficit upon reaching a certain threshold. Our data also provide new mechanistic insight for the effect of anle138b’s function in vivo supporting that targeting α-synuclein aggregation is a promising therapeutic approach for PD.

Understanding the pathogenesis of multiple system atrophy: state of the art and future perspectives

Multiple System Atrophy (MSA) is a severe neurodegenerative disease clinically characterized by parkinsonism, cerebellar ataxia, dysautonomia and other motor and non-motor symptoms.

Although several efforts have been dedicated to understanding the causative mechanisms of the disease, MSA pathogenesis remains widely unknown.

The aim of the present review is to describe the state of the art about MSA pathogenesis, with a particular focus on alpha-synuclein accumulation and mitochondrial dysfunction, and to highlight future possible perspectives in this field.

In particular, this review describes the most widely investigated hypotheses explaining alpha-synuclein accumulation in oligodendrocytes, including SNCA expression, neuron-oligodendrocyte protein transfer, impaired protein degradation and alpha-synuclein spread mechanisms.

Afterwards, several recent achievements in MSA research involving mitochondrial biology are described, including the role of COQ2 mutations, Coenzyme Q10 reduction, respiratory chain dysfunction and altered mitochondrial mass.

Some hints are provided about alternative pathogenic mechanisms, including inflammation and impaired autophagy.

Finally, all these findings are discussed from a comprehensive point of view, putative explanations are provided and new research perspectives are suggested.

Overall, the present review provides a comprehensive and up-to-date overview of the mechanisms underlying MSA pathogenesis.

α-Synuclein and astrocytes: tracing the pathways from homeostasis to neurodegeneration in Lewy body disease

α-Synuclein is a soluble protein that is present in abundance in the brain, though its normal function in the healthy brain is poorly defined. Intraneuronal inclusions of α-synuclein, commonly referred to as Lewy pathology, are pathological hallmarks of a spectrum of neurodegenerative disorders referred to as α-synucleinopathies. Though α-synuclein is expressed predominantly in neurons, α-synuclein aggregates in astrocytes are a common feature in these neurodegenerative diseases. How and why α-synuclein ends up in the astrocytes and the consequences of this dysfunctional proteostasis in immune cells is a major area of research that can have far-reaching implications for future immunobiotherapies in α-synucleinopathies. Accumulation of aggregated α-synuclein can disrupt astrocyte function in general and, more importantly, can contribute to neurodegeneration in α-synucleinopathies through various pathways. Here, we summarize our current knowledge on how astrocytic α-synucleinopathy affects CNS function in health and disease and propose a model of neuroglial connectome altered by α-synuclein proteostasis that might be amenable to immune-based therapies.

Neuropathology and pathogenesis of extrapyramidal movement disorders: a critical update-I. Hypokinetic-rigid movement disorders

Extrapyramidal movement disorders include hypokinetic rigid and hyperkinetic or mixed forms, most of them originating from dysfunction of the basal ganglia (BG) and their information circuits. The functional anatomy of the BG, the cortico-BG-thalamocortical, and BG-cerebellar circuit connections are briefly reviewed. Pathophysiologic classification of extrapyramidal movement disorder mechanisms distinguish (1) parkinsonian syndromes, (2) chorea and related syndromes, (3) dystonias, (4) myoclonic syndromes, (5) ballism, (6) tics, and (7) tremor syndromes. Recent genetic and molecular-biologic classifications distinguish (1) synucleinopathies (Parkinson's disease, dementia with Lewy bodies, Parkinson's disease-dementia, and multiple system atrophy); (2) tauopathies (progressive supranuclear palsy, corticobasal degeneration, FTLD-17; Guamian Parkinson-dementia; Pick's disease, and others); (3) polyglutamine disorders (Huntington's disease and related disorders); (4) pantothenate kinase-associated neurodegeneration; (5) Wilson's disease; and (6) other hereditary neurodegenerations without hitherto detected genetic or specific markers. The diversity of phenotypes is related to the deposition of pathologic proteins in distinct cell populations, causing neurodegeneration due to genetic and environmental factors, but there is frequent overlap between various disorders. Their etiopathogenesis is still poorly understood, but is suggested to result from an interaction between genetic and environmental factors. Multiple etiologies and noxious factors (protein mishandling, mitochondrial dysfunction, oxidative stress, excitotoxicity, energy failure, and chronic neuroinflammation) are more likely than a single factor. Current clinical consensus criteria have increased the diagnostic accuracy of most neurodegenerative movement disorders, but for their definite diagnosis, histopathological confirmation is required. We present a timely overview of the neuropathology and pathogenesis of the major extrapyramidal movement disorders in two parts, the first one dedicated to hypokinetic-rigid forms and the second to hyperkinetic disorders.

Neurodegenerative Diseases and Ageing

This chapter describes the main neuropathological features of the most common age associated neurodegenerative diseases including Alzheimer's disease, Lewy body diseases, vascular dementia and the various types of frontotemporal lobar degeneration. In addition, the more recent concepts of primary age-related tauopathy and ageing-related tau astrogliopathy as well as chronic traumatic encephalopathy are briefly described. One section is dedicated to cerebral multi-morbidity as it is becoming increasingly clear that the old brain is characterised by the presence of multiple pathologies (to varying extent) rather than by one single, disease specific pathology alone. The main aim of this chapter is to inform the reader about the neuropathological basics of age associated neurodegenerative diseases as we feel this is crucial to meaningfully interpret the vast literature that is published in the broad field of dementia research.

Neuroinflammation and Glial Phenotypic Changes in Alpha-Synucleinopathies

The role of neuroinflammation has been increasingly recognized in the field of neurodegenerative diseases. Many studies focusing on the glial cells involved in the inflammatory responses of the brain, namely microglia and astroglia, have over the years pointed out the dynamic and changing behavior of these cells, accompanied by different morphologies and activation forms. This is particularly evident in diseased conditions, where glia react to any shift from homeostasis, acquiring different phenotypes. Particularly for microglia, it has soon become clear that such phenotypes are multiple, as multiple are the functions related to them. Several approaches have over time revealed different facets of microglial phenotypic diversity, and advanced genetic analyses, in recent years, have added new insights into microglial heterogeneity, opening novel scenarios that researchers have just started to explore. Among neurodegenerative diseases, an important section is represented by alpha-synucleinopathies. Here alpha-synuclein accumulates abnormally in the brain and, depending on its pattern of distribution, leads to the development of different clinical conditions. Also for these proteinopathies, neuroinflammation and glial activation have been identified as constant and crucial factors during disease development. In the present review we will address the current literature about glial phenotypic changes with respect to alpha-synucleinopathies, as well as consider the pathophysiological and therapeutic implications of such a dynamic cellular behavior.

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.

L-dopa response pattern in a rat model of mild striatonigral degeneration

Background

Unresponsiveness to dopaminergic therapies is a key feature in the diagnosis of multiple system atrophy (MSA) and a major unmet need in the treatment of MSA patients caused by combined striatonigral degeneration (SND). Transgenic, alpha-synuclein animal models do not recapitulate this lack of levodopa responsiveness. In order to preclinically study interventions including striatal cell grafts, models that feature SND are required. Most of the previous studies focused on extensive nigral and striatal lesions corresponding to advanced MSA-P/SND. The aim of the current study was to replicate mild stage MSA-P/SND with L-dopa failure.

Methods and results

Two different striatal quinolinic acid (QA) lesions following a striatal 6-OHDA lesion replicating mild and severe MSA-P/SND, respectively, were investigated and compared to 6-OHDA lesioned animals. After the initial 6-OHDA lesion there was a significant improvement of motor performance after dopaminergic stimulation in the cylinder and stepping test (p<0.001). Response to L-dopa treatment declined in both MSA-P/SND groups reflecting striatal damage of lateral motor areas in contrast to the 6-OHDA only lesioned animals (p<0.01). The remaining striatal volume correlated strongly with contralateral apomorphine induced rotation behaviour and contralateral paw use during L-dopa treatment in cylinder and stepping test (p<0.001).

Conclusion

Our novel L-dopa response data suggest that L-dopa failure can be induced by restricted lateral striatal lesions combined with dopaminergic denervation. We propose that this sequential striatal double-lesion model replicates a mild stage of MSA-P/SND and is suitable to address neuro-regenerative therapies aimed at restoring dopaminergic responsiveness.

Multiple system atrophy prions retain strain specificity after serial propagation in two different Tg(SNCA*A53T) mouse lines

Previously, we reported that intracranial inoculation of brain homogenate from multiple system atrophy (MSA) patient samples produces neurological disease in the transgenic (Tg) mouse model TgM83+/-, which uses the prion protein promoter to express human α-synuclein harboring the A53T mutation found in familial Parkinson's disease (PD). In our studies, we inoculated MSA and control patient samples into Tg mice constructed using a P1 artificial chromosome to express wild-type (WT), A30P, and A53T human α-synuclein on a mouse α-synuclein knockout background [Tg(SNCA+/+)Nbm, Tg(SNCA*A30P+/+)Nbm, and Tg(SNCA*A53T+/+)Nbm]. In contrast to studies using TgM83+/- mice, motor deficits were not observed by 330-400 days in any of the Tg(SNCA)Nbm mice after inoculation with MSA brain homogenates. However, using a cell-based bioassay to measure α-synuclein prions, we found brain homogenates from Tg(SNCA*A53T+/+)Nbm mice inoculated with MSA patient samples contained α-synuclein prions, whereas control mice did not. Moreover, these α-synuclein aggregates retained the biological and biochemical characteristics of the α-synuclein prions in MSA patient samples. Intriguingly, Tg(SNCA*A53T+/+)Nbm mice developed α-synuclein pathology in neurons and astrocytes throughout the limbic system. This finding is in contrast to MSA-inoculated TgM83+/- mice, which develop exclusively neuronal α-synuclein aggregates in the hindbrain that cause motor deficits with advanced disease. In a crossover experiment, we inoculated TgM83+/- mice with brain homogenate from two MSA patient samples or one control sample first inoculated, or passaged, in Tg(SNCA*A53T+/+)Nbm animals. Additionally, we performed the reverse experiment by inoculating Tg(SNCA*A53T+/+)Nbm mice with brain homogenate from the same two MSA samples and one control sample first passaged in TgM83+/- animals. The TgM83+/- mice inoculated with mouse-passaged MSA developed motor dysfunction and α-synuclein prions, whereas the mouse-passaged control sample had no effect. Similarly, the mouse-passaged MSA samples induced α-synuclein prion formation in Tg(SNCA*A53T+/+)Nbm mice, but the mouse-passaged control sample did not. The confirmed transmission of α-synuclein prions to a second synucleinopathy model and the ability to propagate prions between two distinct mouse lines while retaining strain-specific properties provides compelling evidence that MSA is a prion disease.

Dementia with Lewy bodies: an update and outlook

Dementia with Lewy bodies (DLB) is an age-associated neurodegenerative disorder producing progressive cognitive decline that interferes with normal life and daily activities. Neuropathologically, DLB is characterised by the accumulation of aggregated α-synuclein protein in Lewy bodies and Lewy neurites, similar to Parkinson’s disease (PD). Extrapyramidal motor features characteristic of PD, are common in DLB patients, but are not essential for the clinical diagnosis of DLB. Since many PD patients develop dementia as disease progresses, there has been controversy about the separation of DLB from PD dementia (PDD) and consensus reports have put forward guidelines to assist clinicians in the identification and management of both syndromes. Here, we present basic concepts and definitions, based on our current understanding, that should guide the community to address open questions that will, hopefully, lead us towards improved diagnosis and novel therapeutic strategies for DLB and other synucleinopathies.

Localization of the zinc binding tubulin polymerization promoting protein in the mice and human eye

Tubulin Polymerization Promoting Protein (TPPP/p25) modulates the dynamics and stability of the microtubule network by its bundling and acetylation enhancing activities that can be modulated by the binding of zinc to TPPP/p25. Its expression is essential for the differentiation of oligodendrocytes, the major constituents of the myelin sheath, and has been associated with neuronal inclusions. In this paper, evidence is provided for the expression and localization of TPPP/p25 in the zinc-rich retina and in the oligodendrocytes in the optic nerve. Localization of TPPP/p25 was established by confocal microscopy using calbindin and synaptophysin as markers of specific striations in the inner plexiform layer (IPL) and presynaptic terminals, respectively. Postsynaptic nerve terminals in striations S1, S3 and S5 in the IPL and a subset of amacrine cells show immunopositivity against TPPP/p25 both in mice and human eyes. The co-localization of TPPP/p25 with acetylated tubulin was detected in amacrine cells, oligodendrocyte cell bodies and in synapses in the IPL. Quantitative Western blot revealed that the TPPP/p25 level in the retina was 0.05-0.13 ng/μg protein, comparable to that in the brain. There was a central (from optic nerve head) to peripheral retinal gradient in TPPP/p25 protein levels. Our in vivo studies revealed that the oral zinc supplementation of mice significantly increased TPPP/p25 as well as acetylated tubulin levels in the IPL. These results suggest that TPPP/p25, a microtubule stabilizer can play a role in the organization and reorganization of synaptic connections and visual integration in the eye.

α-Synuclein: Multiple System Atrophy Prions

Multiple system atrophy (MSA) is a rapidly progressive neurodegenerative disease arising from the misfolding and accumulation of the protein α-synuclein in oligodendrocytes, where it forms glial cytoplasmic inclusions (GCIs). Several years of studying synthetic α-synuclein fibrils has provided critical insight into the ability of α-synuclein to template endogenous protein misfolding, giving rise to fibrillar structures capable of propagating from cell to cell. However, more recent studies with MSA-derived α-synuclein aggregates have shown that they have a similar ability to undergo template-directed propagation, like PrP prions. Almost 20 years after α-synuclein was discovered as the primary component of GCIs, α-synuclein aggregates isolated from MSA patient samples were shown to infect cultured mammalian cells and also to transmit neurological disease to transgenic mice. These findings argue that α-synuclein becomes a prion in MSA patients. In this review, we discuss the in vitro and in vivo data supporting the recent classification of MSA as a prion disease.

Advancing Stem Cell Models of Alpha-Synuclein Gene Regulation in Neurodegenerative Disease

Alpha-synuclein (non A4 component of amyloid precursor, SNCA, NM_000345.3) plays a central role in the pathogenesis of Parkinson's disease (PD) and related Lewy body disorders such as Parkinson's disease dementia, Lewy body dementia, and multiple system atrophy. Since its discovery as a disease-causing gene in 1997, alpha-synuclein has been a central point of scientific interest both at the protein and gene level. Mutations, including copy number variants, missense mutations, short structural variants, and single nucleotide polymorphisms, can be causative for PD and affect conformational changes of the protein, can contribute to changes in expression of alpha-synuclein and its isoforms, and can influence regulation of temporal as well as spatial levels of alpha-synuclein in different tissues and cell types. A lot of progress has been made to understand both the physiological transcriptional and epigenetic regulation of the alpha-synuclein gene and whether changes in transcriptional regulation could lead to disease and neurodegeneration in PD and related alpha-synucleinopathies. Although the histopathological changes in these neurodegenerative disorders are similar, the temporal and spatial presentation and progression distinguishes them which could be in part due to changes or disruption of transcriptional regulation of alpha-synuclein. In this review, we describe different genetic alterations that contribute to PD and neurodegenerative conditions and review aspects of transcriptional regulation of the alpha-synuclein gene in the context of the development of PD. New technologies, advanced gene engineering and stem cell modeling, are on the horizon to shed further light on a better understanding of gene regulatory processes and exploit them for therapeutic developments.