Protein aggregation and calcium dysregulation are hallmarks of familial Parkinson's disease in midbrain dopaminergic neurons.

Mutations in the SNCA gene cause autosomal dominant Parkinson's disease (PD), with loss of dopaminergic neurons in the substantia nigra, and aggregation of α-synuclein. The sequence of molecular events that proceed from an SNCA mutation during development, to end-stage pathology is unknown. Utilising human-induced pluripotent stem cells (hiPSCs), we resolved the temporal sequence of SNCA-induced pathophysiological events in order to discover early, and likely causative, events. Our small molecule-based protocol generates highly enriched midbrain dopaminergic (mDA) neurons: molecular identity was confirmed using single-cell RNA sequencing and proteomics, and functional identity was established through dopamine synthesis, and measures of electrophysiological activity. At the earliest stage of differentiation, prior to maturation to mDA neurons, we demonstrate the formation of small ß-sheet-rich oligomeric aggregates, in SNCA-mutant cultures. Aggregation persists and progresses, ultimately resulting in the accumulation of phosphorylated α-synuclein aggregates. Impaired intracellular calcium signalling, increased basal calcium, and impairments in mitochondrial calcium handling occurred early at day 34-41 post differentiation. Once midbrain identity fully developed, at day 48-62 post differentiation, SNCA-mutant neurons exhibited mitochondrial dysfunction, oxidative stress, lysosomal swelling and increased autophagy. Ultimately these multiple cellular stresses lead to abnormal excitability, altered neuronal activity, and cell death. Our differentiation paradigm generates an efficient model for studying disease mechanisms in PD and highlights that protein misfolding to generate intraneuronal oligomers is one of the earliest critical events driving disease in human neurons, rather than a late-stage hallmark of the disease.

Pathological structural conversion of α-synuclein at the mitochondria induces neuronal toxicity.

Aggregation of alpha-synuclein (α-Syn) drives Parkinson's disease (PD), although the initial stages of self-assembly and structural conversion have not been directly observed inside neurons. In this study, we tracked the intracellular conformational states of α-Syn using a single-molecule Förster resonance energy transfer (smFRET) biosensor, and we show here that α-Syn converts from a monomeric state into two distinct oligomeric states in neurons in a concentration-dependent and sequence-specific manner. Three-dimensional FRET-correlative light and electron microscopy (FRET-CLEM) revealed that intracellular seeding events occur preferentially on membrane surfaces, especially at mitochondrial membranes. The mitochondrial lipid cardiolipin triggers rapid oligomerization of A53T α-Syn, and cardiolipin is sequestered within aggregating lipid-protein complexes. Mitochondrial aggregates impair complex I activity and increase mitochondrial reactive oxygen species (ROS) generation, which accelerates the oligomerization of A53T α-Syn and causes permeabilization of mitochondrial membranes and cell death. These processes were also observed in induced pluripotent stem cell (iPSC)-derived neurons harboring A53T mutations from patients with PD. Our study highlights a mechanism of de novo α-Syn oligomerization at mitochondrial membranes and subsequent neuronal toxicity.

Investigating ELOVL7 coding variants in multiple system atrophy.

Multiple system atrophy (MSA) is a rare sporadic, progressive parkinsonism characterised by autonomic dysfunction. A recent genome-wide association study reported an association at the Elongation of Very Long Fatty Acids Protein 7 (ELOVL7) locus with MSA risk. In the current study four independent and unrelated cohorts were assessed, consisting of pathologically confirmed MSA cases, Parkinson's disease (PD) cases, and two unrelated, healthy control groups. All exons of ELOVL7 were sequenced in pathologically confirmed MSA cases; data for PPMI samples and Biobank controls was extracted from whole genome sequence. Coding variants in ELOVL7 were extremely rare, and we observed no significant association of ELOVL7 coding variants with risk of MSA.

Frequency of spinocerebellar ataxia mutations in patients with multiple system atrophy.

PURPOSE: Investigate single nucleotide variants and short tandem repeats in 39 genes related to spinocerebellar ataxia in clinical and pathologically defined cohorts of multiple system atrophy. METHODS: Exome sequencing was conducted in 28 clinical multiple system atrophy patients to identify single nucleotide variants in spinocerebellar ataxia-related genes. Novel variants were validated in two independent disease cohorts: 86 clinically diagnosed multiple system atrophy patients and 166 pathological multiple system atrophy cases. Expanded repeat alleles in spinocerebellar ataxia genes were evaluated in 36 clinically diagnosed multiple system atrophy patients, and CAG/CAA repeats in TATA-Box Binding Protein (TBP, causative of SCA17) were screened in 216 clinical and pathological multiple system atrophy patients and 346 controls. RESULTS: No known pathogenic spinocerebellar ataxia single nucleotide variants or pathogenic range expanded repeat alleles of ATXN1, ATXN2, ATXN3, CACNA1A, AXTN7, ATXN8OS, ATXN10, PPP2R2B, and TBP were detected in any clinical multiple system atrophy patients. However, four novel variants were identified in four spinocerebellar ataxia-related genes across three multiple system atrophy patients. Additionally, four multiple system atrophy patients (1.6%) and one control (0.3%) carried an intermediate length 41 TBP CAG/CAA repeat allele (OR = 4.11, P = 0.21). There was a significant association between the occurrence of a repeat length of longer alleles (> 38 repeats) and an increased risk of multiple system atrophy (OR = 1.64, P = 0.03). CONCLUSION: Occurrence of TBP CAG/CAA repeat length of longer alleles (> 38 repeats) is significantly associated with increased multiple system atrophy risk. This discovery warrants further investigation and supports a possible genetic overlap of multiple system atrophy with SCA17.

GBA variation and susceptibility to multiple system atrophy.

INTRODUCTION: Genetic variants in the glucocerebrosidase (GBA) gene have been previously associated with susceptibility to synucleinopathies. The risk is well-established in Lewy body disease but is not as confirmed for multiple system atrophy (MSA). We aim to evaluate associations between exonic variants in GBA and risk of neuropathologically-confirmed multiple system atrophy (MSA). METHODS: Sanger gene sequencing of GBA was performed on 167 pathologically confirmed MSA patients collected at Mayo Clinic Florida Brain Bank, and data were extracted from whole-genome sequencing of 834 clinical controls. Common GBA variants were assessed for association with MSA. Rare GBA variants (and also all GBA variants) were collapsed together and evaluated for association with MSA risk using a gene-burden test. RESULTS: A total of 17 exonic GBA variants were observed, including a novel p.Q112X variant that is likely pathogenic in a patient with mixed parkinsonism-cerebellar subtype MSA. The more common p.N409S and p.L483P variants that recessively cause Gaucher's disease (GD), and are associated with risk of Lewy body disease, were not observed. When collapsing across all GBA variants, the presence of any GBA variant was significantly more frequent in MSA patients than in controls (OR = 1.90, P = 0.031). However, this association was driven by p.T408M, which had a significantly higher frequency in MSA patients compared to controls (OR = 4.21, P = 0.002). There was no significant association with risk of MSA for the p.E365K variant (OR = 0.79, P = 0.72). CONCLUSIONS: Other than the specific GBA p.T408M variant, coding GBA variants are not associated with risk of MSA.

Spinocerebellar ataxia type 6 family with phenotypic overlap with Multiple System Atrophy.

AIM OF THE STUDY: Multiple system atrophy (MSA) and spinocerebellar ataxia (SCA) share similar symptomatology. We describe a rare occurrence of familial MSA that proved to be SCA6 upon genetic analysis. MATERIALS AND METHODS: Eighty MSA patients were enrolled in our study; blood samples were collected and genetic screening of the familial case for known SCA loci was performed. RESULTS: A 68-year-old woman presented with recurrent and severe episodes of light-headedness, imbalance, frequent falls, neck and lower back stiffness, subjective arm and leg weakness, and numbness and tingling in both feet. One year later, her condition had declined; she experienced more falls, worsening instability, again more generalised but still subjective weakness, impaired fine motor movements, slurred speech, difficulty swallowing, episodes of choking, bladder incontinence, and constipation. Clinical suspicion included parkinsonism, MSA, and SCA. The patient was enrolled in our MSA study and was found to have 22 and 12 CAG repeats in CACNA1A. The other 79 clinical MSA patients were negative for SCA6 screening. CONCLUSIONS AND CLINICAL IMPLICATIONS: While MSA and SCA may have similar presentations during early disease stages, the presence of both conditions on the list of differential diagnoses can be a diagnostic dilemma. Further analysis will aid in developing a biomarker to distinguish between the two conditions and guide proper management.

Clinicopathologic and genetic features of multiple system atrophy with Lewy body disease.

BACKGROUND: Abnormal aggregates of α-synuclein are pathologic hallmarks of multiple system atrophy (MSA) and Lewy body disease (LBD). LBD sometimes coexists with MSA, but the impact of co-pathology, particularly diffuse LBD, on presentation of MSA has not been studied. We aimed to determine the frequency and clinicopathologic features of MSA with LBD (MSA+LBD). METHODS: Using hematoxylin & eosin and α-synuclein-immunostained slides, we assessed the distribution and severity of LBD in 230 autopsy-confirmed MSA patients collected from 1998 to 2018. Alzheimer-type pathology was assessed to assign the likelihood of clinical presentations of dementia with Lewy body (DLB) using the consensus criteria for DLB. We reviewed medical records to characterize clinicopathologic features of MSA+LBD. Genetic risk factors for LBD, including APOE ε4 allele and mutations in GBA, SNCA, LRRK2, and VPS35, were analyzed. RESULTS: LBD was observed in 11 MSA patients (5%); seven were brainstem type, three were transitional type, and one was diffuse type. The latter four had an intermediate or high likelihood of DLB. Three of the four had an antemortem diagnosis of Parkinson's disease with dementia (PDD) or clinically probable DLB. Two patients had neuronal loss in the substantia nigra, but not in striatal or olivocerebellar systems with widespread glial cytoplasmic inclusions, consistent with minimal change MSA. In these cases, LBD was considered the primary pathology, and MSA was considered coincidental. APOE ε4 allele frequency was not different between MSA+LBD and MSA without LBD. Two of nine MSA+LBD patients had a risk variant of GBA (p.T408M and p.E365K). CONCLUSIONS: Although rare, MSA with transitional or diffuse LBD can develop clinical features of PDD or DLB. Minimal change MSA can be interpreted as a coincidental, but distinct, α-synucleinopathy in a subset of patients with diffuse LBD.

Multiple system atrophy and apolipoprotein E.

BACKGROUND: Dysregulation of the specialized lipid metabolism involved in myelin synthesis and maintenance by oligodendrocytes has been associated with the unique neuropathology of MSA. We hypothesized that apolipoprotein E, which is associated with neurodegeneration, may also play a role in the pathogenesis of MSA. OBJECTIVE: This study evaluated genetic associations of Apolipoprotein E alleles with risk of MSA and α-synuclein pathology, and also examined whether apolipoprotein E isoforms differentially affect α-synuclein uptake in a oligodendrocyte cell. METHODS: One hundred sixty-eight pathologically confirmed MSA patients, 89 clinically diagnosed MSA patients, and 1,277 control subjects were genotyped for Apolipoprotein E. Human oligodendrocyte cell lines were incubated with α-synuclein and recombinant human apolipoprotein E, with internalized α-synuclein imaged by confocal microscopy and cells analyzed by flow cytometry. RESULTS: No significant association with risk of MSA or was observed for either Apolipoprotein E ɛ2 or ɛ4. α-Synuclein burden was also not associated with Apolipoprotein E alleles in the pathologically confirmed patients. Interestingly, in our cell assays, apolipoprotein E ɛ4 significantly reduced α-synuclein uptake in the oligodendrocytic cell line. CONCLUSIONS: Despite differential effects of apolipoprotein E isoforms on α-synuclein uptake in a human oligodendrocytic cell, we did not observe a significant association at the Apolipoprotein E locus with risk of MSA or α-synuclein pathology. © 2018 International Parkinson and Movement Disorder Society.