Models of Multiple System Atrophy

Chapter 19 - Etiology, Pathology, and Pathogenesis

Recent post-mortem studies reported 22-37% of patients with multiple system atrophy can develop cognitive impairment. With the aim of identifying associations between cognitive impairment including memory impairment and α-synuclein pathology, 148 consecutive patients with pathologically proven multiple system atrophy were reviewed. Among them, 118 (79.7%) were reported to have had normal cognition in life, whereas the remaining 30 (20.3%) developed cognitive impairment. Twelve of them had pure frontal-subcortical dysfunction, defined as the presence of executive dysfunction, impaired processing speed, personality change, disinhibition or stereotypy; six had pure memory impairment; and 12 had both types of impairment. Semi-quantitative analysis of neuronal cytoplasmic inclusions in the hippocampus and parahippocampus revealed a disease duration-related increase in neuronal cytoplasmic inclusions in the dentate gyrus and cornu ammonis regions 1 and 2 of patients with normal cognition. In contrast, such a correlation with disease duration was not found in patients with cognitive impairment. Compared to the patients with normal cognition, patients with memory impairment (pure memory impairment: n = 6; memory impairment + frontal-subcortical dysfunction: n = 12) had more neuronal cytoplasmic inclusions in the dentate gyrus, cornu ammonis regions 1-4 and entorhinal cortex. In the multiple system atrophy mixed pathological subgroup, which equally affects the striatonigral and olivopontocerebellar systems, patients with the same combination of memory impairment developed more neuronal inclusions in the dentate gyrus, cornu ammonis regions 1, 2 and 4, and the subiculum compared to patients with normal cognition. Using patients with normal cognition (n = 18), frontal-subcortical dysfunction (n = 12) and memory impairment + frontal-subcortical dysfunction (n = 18), we further investigated whether neuronal or glial cytoplasmic inclusions in the prefrontal, temporal and cingulate cortices or the underlying white matter might affect cognitive impairment in patients with multiple system atrophy. We also examined topographic correlates of frontal-subcortical dysfunction with other clinical symptoms. Although no differences in neuronal or glial cytoplasmic inclusions were identified between the groups in the regions examined, frontal release signs were found more commonly when patients developed frontal-subcortical dysfunction, indicating the involvement of the frontal-subcortical circuit in the pathogenesis of frontal-subcortical dysfunction. Here, investigating cognitive impairment in the largest number of pathologically proven multiple system atrophy cases described to date, we provide evidence that neuronal cytoplasmic inclusion burden in the hippocampus and parahippocampus is associated with the occurrence of memory impairment in multiple system atrophy. Further investigation is necessary to identify the underlying pathological basis of frontal-subcortical dysfunction in multiple system atrophy.

Certain genetic defects in LRRK2 and parkin are pathogenic for Parkinson's disease (PD) and both proteins deposit in the characteristic Lewy bodies. LRRK2 is thought to be involved in the early initiation of Lewy bodies. The involvement of LRRK2 and parkin in the similar cellular deposition of fibrillar alpha-synuclein in glial cytoplasmic inclusions (GCI) in multiple system atrophy (MSA) has not yet been assessed. To determine whether LRRK2 and parkin may be similarly associated with the abnormal deposition of alpha-synuclein in MSA GCI, paraffin-embedded sections from the basal ganglia of 12 patients with MSA, 4 with PD and 4 controls were immunostained for LRRK2, parkin, alpha-synuclein and oligodendroglial proteins using triple labelling procedures. The severity of neuronal loss was graded and the proportion of abnormally enlarged oligodendroglia containing different combinations of proteins assessed in 80-100 cells per case. Parkin immunoreactivity was observed in only a small proportion of GCI. In contrast, LRRK2 was found in most of the enlarged oligodendroglia in MSA and colocalised with the majority of alpha-synuclein-immunopositive GCI. Degrading myelin sheaths containing LRRK2-immunoreactivity were also observed, showing an association with one of the earliest oligodendroglial abnormalities observed in MSA. The proportion of LRRK2-immunopositive GCI was negatively associated with an increase in neuronal loss and alpha-synuclein-immunopositive dystrophic axons. Our results indicate that an increase in LRRK2 expression occurs early in association with myelin degradation and GCI formation, and that a reduction in LRRK2 expression in oligodendroglia is associated with increased neuronal loss in MSA.

The value of neurofilament light chain (NfL) levels as a biomarker for the diagnosis and differential diagnosis in patients with Parkinson's disease (PD) and atypical parkinsonian syndromes (APS) remains controversial. Furthermore, few studies have directly compared NfL levels among specific APS categories. This study aimed to compare cerebrospinal fluid (CSF) and blood NfL levels among PD, APS, other PD-related disorders, and controls, as well as rank NfL levels across these groups. PubMed, Embase, Web of Science, and the Cochrane Library were searched from the inception up to November 1st, 2024, to identify eligible studies reporting CSF or blood NfL concentrations in PD, PD dementia (PDD), multiple system atrophy (MSA), progressive supranuclear palsy (PSP), dementia with Lewy bodies (DLB), corticobasal syndrome (CBS), vascular parkinsonism (VP), essential tremor (ET), idiopathic rapid eye movement sleep behavior disorder (iRBD), and controls. The Bayesian approach was utilized to estimate the standardized mean difference (SMD) and the associated 95% credible intervals (CrIs) of NfL levels. The surface under the cumulative ranking curve (SUCRA) was employed to evaluate the ranking probabilities of NfL levels. Subgroup analysis and meta-regression were conducted to explore the sources of heterogeneity. The present network meta-analysis (NMA) included 78 studies with 13,120 participants (4050 controls, 5021 PD, 191 PDD, 1173 MSA, 887 PSP, 1254 DLB, 319 CBS, 160 ET, 65 iRBD, and 0 VP). Of these, the NMA of CSF NfL included 34 studies with 6,013 participants, while the NMA of blood NfL included 49 studies with 7,787 participants. Both CSF and blood NfL levels were significantly elevated in patients with PD and APS compared to controls. Compared to PD patients, CSF NfL levels were significantly elevated in MSA (SMD 1.85; 95% CrI 1.55-2.15), CBS (1.42; 1.08-1.75), PSP (1.35; 1.06-1.64), and DLB 0.52; 0.20-0.85) patients. Similarly, blood NfL levels were significantly higher in patients with MSA (1.36; 1.02-1.71), PDD (1.19; 0.65-1.72), PSP (1.15; 0.77-1.54), CBS (0.92; 0.11-1.72), and DLB (0.63; 0.14-1.12) compared to PD. Among APS, CSF NfL levels in MSA patients were significantly higher than those in PSP, DLB, and CBS patients, while blood NfL levels in MSA patients were significantly higher only compared to DLB. In both CSF and blood NfL, MSA patients exhibited the highest probability of ranking first for NfL level elevations (CSF: SUCRA = 0.998; blood: SUCRA = 0.925). Age significantly influenced the SMD of the comparison between MSA and PD in CSF NfL (β = -0.15; p = 0.016). CSF and blood NfL levels in PD and APS are higher than those in controls, and all APS categories show higher levels than PD, suggesting that NfL levels may serve as a potential biomarker for the differential diagnosis between PD and APS. However, caution is warranted when using NfL as a diagnostic biomarker for PD. Significant differences in NfL levels are also observed between certain APS categories. Patients with MSA exhibit the highest NfL levels among PD and related disorders.

Multiple system atrophy is characterized pathologically by the accumulation of alpha-synuclein (aSyn) into glial cytoplasmic inclusions (GCIs). The mechanism underlying the formation of GCIs is not well understood.In this study, correlative light and electron microscopy was employed to investigate aSyn pathology in the substantia nigra and putamen of post-mortem multiple system atrophy brain donors.Three distinct types of aSyn immuno-positive inclusions were identified in oligodendrocytes, neurons and dark cells presumed to be dark microglia. Oligodendrocytes contained fibrillar GCIs that were consistently enriched with lysosomes and peroxisomes, supporting the involvement of the autophagy pathway in aSyn aggregation in multiple system atrophy. Neuronal cytoplasmic inclusions exhibited ultrastructural heterogeneity resembling both fibrillar and membranous inclusions, linking multiple systems atrophy and Parkinson’s disease. The novel aSyn pathology identified in the dark cells, displayed GCI-like fibrils or non-GCI-like ultrastructures suggesting various stages of aSyn accumulation in these cells.The observation of GCI-like fibrils within dark cells suggests these cells may be an important contributor to the origin or spread of pathological aSyn in multiple system atrophy. Our results suggest a complex interplay between multiple cell types that may underlie the formation of aSyn pathology in multiple system atrophy brain and highlight the need for further investigation into cell-specific disease pathologies in multiple system atrophy.

Multiple system atrophy (MSA) is a neurodegenerative disorder characterized by parkinsonism, cerebellar dysfunction, and autonomic failure. Key pathological features of MSA include the formation of glial cytoplasmic inclusions (GCIs) in oligodendrocytes (OLs), myelin loss, and neuroinflammation. Although both inflammation and myelination are known to be critical in MSA, the roles of myelin proteins and their relationship with inflammation have often been overlooked. In this study, we injected AAV-Olig001 vectors carrying either human SNCA (AAV-hSNCA) or eGFP (AAV-eGFP) into the striatum of TgM83 transgenic mice, which express the A53T mutant form of human alpha-synuclein (αSyn), as well as into wild-type (WT) mice. We then assessed myelin protein expression and inflammatory responses. TgM83 mice injected with AAV-hSNCA exhibited demyelination, increased activation of microglia and astrocytes, and altered cytokine and chemokine profiles (including IL-1α, IL-10, IL-12(p40), CCL2, CCL3, CCL4, and CCL5), compared to both WT mice and TgM83 mice injected with AAV-eGFP. Interestingly, myelin basic protein (MBP) levels were significantly elevated around the injection site in TgM83 mice injected with AAV-hSNCA. Notably, we observed a positive correlation between MBP expression and inflammatory markers, as indicated by Iba1 and GFAP staining. These findings suggest that hSNCA overexpression is associated with increased MBP levels and enhanced inflammatory responses, implicating that MBP and myelination processes may play previously underappreciated roles in the pathogenesis of MSA.

Glial cytoplasmic inclusions (GCIs) characteristically occur in the oligodendrocytes of patients with multiple system atrophy (MSA). Cyclin-dependent kinase 5 (Cdk5) regulates cytoskeletal dynamism through phosphorylation of cytoskeletal proteins such as neurofilament proteins, tau and microtubule-associated protein 2. We examined the immunohistochemical localization of p39, a Cdk5 activator, in human brain specimens obtained post mortem from controls and patients with MSA. Among control specimens, p39 immunoreactivity was found in some neuronal somata and axons. Similar immunoreactivity was detected in MSA neuronal cell bodies and axons, but a number of inclusions were heavily labeled. These results suggest that p39 and Cdk5 are up-regulated in oligodendrocytes and may be involved in the formation of GCIs through phosphorylation of cytoskeletal proteins in oligodendrocytes in MSA.

Multiple system atrophy (MSA) is a sporadic neurodegenerative disease clinically marked by autonomic failure and variable degrees of parkinsonism and cerebellar ataxias. The average age of onset is in the sixth decade of life with a five-year survival, although fulminant and more benign courses have been described (1). The pathologic hallmark of MSA is abundant α-synuclein-positive protein aggregates within oligodendrocytes (glial cytoplasmic inclusions, GCI) and neurons (neuronal cytoplasmic inclusions, NCI, and neuronal nuclear inclusions, NNI). The density of GCIs has been correlated with disease duration and severity of neuronal loss (2). Here, we present an unusual case of MSA clinically characterized by rapid decline followed by a 20-year disease duration in a severely affected state. At autopsy, the brain showed severe gliosis and neuronal loss in a pattern characteristic of MSA. Additionally, there were atypical Pick body-like and ring-shaped α-synuclein inclusions, most prominent in limbic regions, consistent with a recently described subtype of MSA designated "atypical MSA" (3). Four different α-synuclein antibodies highlighted only scant α-synuclein-positive pathology; however, Gallyas and Campbell-Switzer silver stains identified additional GCIs most prominent in subcortical white matter. Interestingly, many of the α-synuclein-positive limbic inclusions were Gallyas-negative, while many of the Gallyas-positive inclusions were α-synuclein-negative (4). This observation of markedly disparate α-synuclein immunohistochemical versus Gallyas reactivity of MSA inclusions is unusual and could support the possibility that MSA inclusions have variable compositions, something which has been recently suggested (5).

Multiple system atrophy (MSA) is a horrible and unrelenting neurodegenerative disorder with an uncertain etiology and pathophysiology. MSA is a unique proteinopathy in which alpha-synuclein (α-syn) accumulates preferentially in oligodendroglia rather than neurons. Glial cytoplasmic inclusions (GCIs) of α-syn are thought to elicit changes in oligodendrocyte function, such as reduced neurotrophic support and demyelination, leading to neurodegeneration. To date, only a murine model using one of three promoters exist to study this disease. We sought to develop novel rat and nonhuman primate (NHP) models of MSA by overexpressing α-syn in oligodendroglia using a novel oligotrophic adeno-associated virus (AAV) vector, Olig001. To establish tropism, rats received intrastriatal injections of Olig001 expressing GFP. Histological analysis showed widespread expression of GFP throughout the striatum and corpus callosum with >95% of GFP+ cells co-localizing with oligodendroglia and little to no expression in neurons or astrocytes. We next tested the efficacy of this vector in rhesus macaques with intrastriatal injections of Olig001 expressing GFP. As in rats, we observed a large number of GFP+ cells in gray matter and white matter tracts of the striatum and the corpus callosum, with 90–94% of GFP+ cells co-localizing with an oligodendroglial marker. To evaluate the potential of our vector to elicit MSA-like pathology in NHPs, we injected rhesus macaques intrastriatally with Olig001 expressing the α-syn transgene. Histological analysis 3-months after injection demonstrated widespread α-syn expression throughout the striatum as determined by LB509 and phosphorylated serine-129 α-syn immunoreactivity, all of which displayed as tropism similar to that seen with GFP. As in MSA, Olig001-α-syn GCIs in our model were resistant to proteinase K digestion and caused microglial activation. Critically, demyelination was observed in the white matter tracts of the corpus callosum and striatum of Olig001-α-syn but not Olig001-GFP injected animals, similar to the human disease. These data support the concept that this vector can provide novel rodent and nonhuman primate models of MSA.

Synucleinopathies are neurodegenerative diseases pathologically characterized by aggregates of α-synuclein protein in selectively vulnerable neurons and/or glia.1 These include neuronal Lewy bodies (LB) and Lewy neurites in Parkinson's disease (PD), dementia with LB, and PD dementia, and predominantly oligodendroglial cytoplasmic inclusions in multiple system atrophy (MSA).1 Isolated rapid eye movement sleep behavior disorder (iRBD) and pure autonomic failure (PAF) are often underpinned by α-synuclein pathology, sometimes revealing themselves as prodromal stages of the aforementioned disorders in retrospect.2, 3 The self-propagation of misfolded proteins assembling into seeds that induce normal-like proteins to misshape and aggregate was first recognized as mechanism of neurotoxicity in prion diseases. Increasing evidence supports the prion-like behavior of other proteins in neurodegeneration, including amyloid-β, tau, and α-synuclein.4 Therefore, detecting protein aggregates in easily accessible biospecimens represents a promising diagnostic avenue,5 especially in synucleinopathies, which can be difficult to clinically differentiate in early stages and lack specific positron emission tomography radiotracers. Moreover, because the prion-like process may precede their clinical onset by years or decades, iRBD and PAF are potential targets for an early biochemical diagnosis of synucleinopathies.2, 3, 5 Real-time quaking-induced conversion (RT-QuIC) is a high-sensitive amplification assay to detect the seeding activity of protein aggregates in biospecimens at the expense of a substrate (ie, the recombinant protein) under shaking conditions, which is monitored by thioflavin T fluorescence. RT-QuIC was first validated in sporadic Creutzfeldt-Jacob disease and is now included in its diagnostic criteria.6 Recently, it has also been explored in synucleinopathies.7 Following an established protocol,8 Rossi and colleagues9 performed cerebrospinal fluid α-synuclein RT-QuIC in a large cohort of (1) neuropathologically verified cases of LB-positive and LB-negative dementia, atypical parkinsonism, and LB-negative controls and (2) clinically diagnosed cases of PD, atypical parkinsonism, dementia, iRBD, and PAF. The assay accurately detected α-synuclein seeding activity across LB-related synucleinopathies (ie, PD, dementia with LB, iRBD, and PAF), with an overall sensitivity of 95.3% (100% in definite dementia with LB and iRBD) and an overall specificity of 98% against cases lacking LB on neuropathology.9 Intriguingly, negative RT-QuIC results were found in almost all MSA cases, 1 iRBD case with subsequent phenoconversion to MSA, and 1 PAF case showing normal adrenergic cardiac innervation on iodine-123 meta-iodobenzylguanidine single photon emission computed tomography, as observed in MSA.9 Finally, quantification of α-synuclein seeding activity through fluorescence analysis did not discriminate among LB-related clinical syndromes.9 Besides supporting the prion-like nature of LB-related synucleinopathies, this study demonstrates that α-synuclein RT-QuIC provides an accurate and reliable biomarker for these disorders in the largest cohort hitherto investigated.9 It also proves that RT-QuIC detects α-synuclein seeding activity in prodromal syndromes, allowing early diagnosis of synucleinopathy and identification of candidates for disease-modifying trials.9 Interpretation of negative assay results in most MSA cases is arguable. Although it might confirm that MSA and LB-related syndromes are associated with different conformational α-synuclein strains,10 further research needs to clarify whether different RT-QuIC set-ups may detect α-synuclein seeding activity in MSA, thus differentiating synucleinopathies. In conclusion, these findings endorse the inclusion of an RT-QuIC-based biomarker in diagnostic criteria for LB-related synucleinopathies and promote studies to test the α-synuclein RT-QuIC analysis of other biospecimens and its potential as a progression/prognostic tool. (1) Research Project: A. Conception, B. Organization, C. Execution; (2) Data Analysis: A. Design, B. Execution, C. Review and Critique; (3) Manuscript Preparation: A. Writing of the First Draft, B. Review and Critique. F.M.: 1A, 2A, 2B, 3A M.T.: 2C, 3B K.P.B.: 1A, 2C, 3B We confirm that we have read the Journal's position on issues involved in ethical publication and affirm that this work is consistent with those guidelines. The authors confirm that the approval of an institutional review board was not required for this work. The authors confirm that no patient consent was required for this work. No specific funding was received for this work. The authors declare that there are no conflicts of interest relevant to this work. F.M. is supported by the European Academy of Neurology Research Fellowship 2020. M.T. reports no disclosures. K.P.B. has received grant support from Welcome/Medical Research Council, National Institute for Health Research, Parkinsons's UK, and EU Horizon 2020. He receives royalties from publication of the Oxford Specialist Handbook Parkinson's Disease and Other Movement Disorders (Oxford University Press, 2008), Marsden's Book of Movement Disorders (Oxford University Press, 2012), and Case Studies in Movement Disorders–Common and Uncommon Presentations (Cambridge University Press, 2017). He has received honoraria/personal compensation for participating as consultant/scientific board member from Ipsen, Allergan, and Merz and honoraria for speaking at meetings and from Allergan, Ipsen, Merz, Sun Pharma, Teva, UCB Pharmaceuticals, and the American Academy of Neurology, and the International Parkinson's Disease and Movement Disorders Society.

A mouse model of adult-onset multiple system atrophy

Chapter 3 Multiple System Atrophy

The progression of cognitive decline is heterogeneous in the three most common idiopathic parkinsonian diseases: Parkinson disease, multiple system atrophy and progressive supranuclear palsy. The causes for this heterogeneity are not fully understood, and there are no validated biomarkers that can accurately identify patients who will develop dementia and when. In this population-based, prospective study, comprehensive neuropsychological testing was performed repeatedly in new-onset, idiopathic parkinsonism. Dementia was diagnosed until 10 years and participants (N = 210) were deeply phenotyped by multimodal clinical, biochemical, genetic and brain imaging measures. At baseline, before the start of dopaminergic treatment, mild cognitive impairment was prevalent in 43.4% of the patients with Parkinson disease, 23.1% of the patients with multiple system atrophy and 77.8% of the patients with progressive supranuclear palsy. Longitudinally, all three diseases had a higher incidence of cognitive decline compared with healthy controls, but the types and severity of cognitive dysfunctions differed. In Parkinson disease, psychomotor speed and attention showed signs of improvement after dopaminergic treatment, while no such improvement was seen in other diseases. The 10-year cumulative probability of dementia was 54% in Parkinson disease and 71% in progressive supranuclear palsy, while there were no cases of dementia in multiple system atrophy. An easy-to-use, multivariable model that predicts the risk of dementia in Parkinson disease within 10 years with high accuracy (area under the curve: 0.86, P < 0.001) was developed. The optimized model adds CSF biomarkers to four easily measurable clinical features at baseline (mild cognitive impairment, olfactory function, motor disease severity and age). The model demonstrates a highly variable but predictable risk of dementia in Parkinson disease, e.g. a 9% risk within 10 years in a patient with normal cognition and CSF amyloid-β42 in the highest tertile, compared with an 85% risk in a patient with mild cognitive impairment and CSF amyloid-β42 in the lowest tertile. Only small or no associations with cognitive decline were found for factors that could be easily modifiable (such as thyroid dysfunction). Risk factors for cognitive decline in multiple system atrophy and progressive supranuclear palsy included signs of systemic inflammation and eye movement abnormalities. The predictive model has high accuracy in Parkinson disease and might be used for the selection of patients into clinical trials or as an aid to improve the prevention of dementia.

Multiple system atrophy (MSA) is a devastating neurodegenerative disease characterized by the clinical triad of parkinsonism, cerebellar ataxia and autonomic failure, impacting on striatonigral, olivopontocerebellar and autonomic systems. At early stage of the disease, the clinical symptoms of MSA can overlap with those of Parkinson’s disease (PD). The key pathological hallmark of MSA is the presence of glial cytoplasmic inclusions (GCI) in oligodendrocytes. GCI comprise insoluble proteinaceous filaments composed chiefly of α-synuclein aggregates, and therefore MSA is regarded as an α-synucleinopathy along with PD and dementia with Lewy bodies. The etiology of MSA is unknown, and the pathogenesis of MSA is still largely speculative. Much data suggests that MSA is a sporadic disease, although some emerging evidence suggests rare genetic variants increase susceptibility. Currently, there is no general consensus on the susceptibility genes as there have been differences due to geographical distribution or ethnicity. Furthermore, many of the reported studies have been conducted on patients that were only clinically diagnosed without pathological verification. The purpose of this review is to bring together available evidence to cross-examine the susceptibility genes and genetic pathomechanisms implicated in MSA. We explore the possible involvement of the SNCA, COQ2, MAPT, GBA1, LRRK2 and C9orf72 genes in MSA pathogenesis, highlight the under-explored areas of MSA genetics, and discuss future directions of research in MSA.

Multiple system atrophy (MSA) is characterized by glial cytoplasmic inclusions (GCIs) containing aggregated α-synuclein (α-syn) in oligodendrocytes. The origin of α-syn accumulation in GCIs is unclear, in particular whether abnormal α-syn aggregates result from the abnormal elevation of endogenous α-syn expression in MSA or ingested from the neuronal source. Tubulin polymerization promoting protein (TPPP) has been reported to play a crucial role in developing GCI pathology. Here, the total cell body, nucleus, and cytoplasmic area density of SNCA and TPPP transcripts in neurons and oligodendrocytes with and without various α-syn pathologies in the pontine base in autopsy cases of MSA (n = 4) and controls (n = 2) were evaluated using RNAscope with immunofluorescence. Single-nucleus RNA-sequencing data for TPPP was evaluated using control frontal cortex (n = 3). SNCA and TPPP transcripts were present in the nucleus and cytoplasm of oligodendrocytes in both controls and diseased, with higher area density in GCIs and glial nuclear inclusions in MSA. Area densities of SNCA and TPPP transcripts were lower in neurons showing cytoplasmic inclusions in MSA. Indeed, TPPP transcripts were unexpectedly found in neurons, while the anti-TPPP antibody failed to detect immunoreactivity. Single-nucleus RNA-sequencing revealed significant TPPP transcript expression predominantly in oligodendrocytes, but also in excitatory and inhibitory neurons. This study addressed the unclear origin of accumulated α-syn in GCIs, proposing that the elevation of SNCA transcripts may supply templates for misfolded α-syn. In addition, the parallel behavior of TPPP and SNCA transcripts in GCI development highlights their potential synergistic contribution to inclusion formation. In conclusion, this study advances our understanding of MSA pathogenesis, offers insights into the dynamics of SNCA and TPPP transcripts in inclusion formation, and proposes regulating their transcripts for future molecular therapy to MSA.