Disease-, region- and cell type specific diversity of α-synuclein carboxy terminal truncations in synucleinopathies

Abstract

Synucleinopathies, including Parkinson’s disease (PD), Lewy body dementia (LBD), Alzheimer’s disease with amygdala restricted Lewy bodies (AD/ALB), and multiple system atrophy (MSA) comprise a spectrum of neurodegenerative disorders characterized by the presence of distinct pathological α-synuclein (αSyn) inclusions. Experimental and pathological studies support the notion that αSyn aggregates contribute to cellular demise and dysfunction with disease progression associated with a prion-like spread of αSyn aggregates via conformational templating. The initiating event(s) and factors that contribute to diverse forms of synucleinopathies remain poorly understood. A major post-translational modification of αSyn associated with pathological inclusions is a diverse array of specific truncations within the carboxy terminal region. While these modifications have been shown experimentally to induce and promote αSyn aggregation, little is known about their disease-, region- and cell type specific distribution. To this end, we generated a series of monoclonal antibodies specific to neo-epitopes in αSyn truncated after residues 103, 115, 119, 122, 125, and 129. Immunocytochemical investigations using these new tools revealed striking differences in the αSyn truncation pattern between different synucleinopathies, brain regions and specific cellular populations. In LBD, neuronal inclusions in the substantia nigra and amygdala were positive for αSyn cleaved after residues 103, 119, 122, and 125, but not 115. In contrast, in the same patients' brain αSyn cleaved at residue 115, as well as 103, 119 and 122 were abundant in the dorsal motor nucleus of the vagus. In patients with AD/ALB, these modifications were only weakly or not detected in amygdala αSyn inclusions. αSyn truncated at residues 103, 115, 119, and 125 was readily present in MSA glial cytoplasmic inclusions, but 122 cleaved αSyn was only weakly or not present. Conversely, MSA neuronal pathology in the pontine nuclei was strongly reactive to the αSyn x-122 neo-epitope but did not display any reactivity for αSyn 103 cleavage. These studies demonstrate significant disease-, region- and cell type specific differences in carboxy terminal αSyn processing associated with pathological inclusions that likely contributes to their distinct strain-like prion properties and promotes the diversity displayed in the degrees of these insidious diseases.

Is Multiple System Atrophy a Prion-like Disorder?

“…It is preferentially propagated in oligodendrocytes despite their lower αSyn expression levels due to a favorable cleavage environment that produces the more potent strains. Aberrant protease activities in MSA could exacerbate this process, but this should be confirmed by future experiments [41]. Both soluble and insoluble fractions of MSA extracts have robust seeding activity, while only the insoluble fraction of PD extracts displayed seeding activity.…”

“…Carboxy truncations of αSyn promote both its aggregation and toxicity [61]. Specific carboxy truncated forms of αSyn have been detected by immunostaining with antibodies that specifically react with their precise forms showing their specific distribution [41]. In DLB, neuronal inclusions in the SN and amygdala were positive for αSyn cleaved after residues 103, 119, 122, and 125, whereas in MSA GCIs αSyn truncated at residues 103, 115, 119, and 125 were present.…”

“…Converging evidence suggests a "prion-like" spreading of misfolded αSyn "strains" as a pathogenic key event [14][15][16][17][18][19][20][21][22][23][24][25], while others suggested that MSA is a prion disease [26][27][28][29]. The prion hypothesis of human synucleinopathies and the question of whether αSyn is a prion or prion-like are a matter of continuous discussion [15,[30][31][32][33][34][35][36][37][38][39][40][41][42]. In both PD and MSA, the debate for and against considering them as prion diseases simply from a prionoid perspective-is ongoing [22,[43][44][45][46][47].…”

Pathological Relevance of Post-translationally Modified Alpha-Synuclein (pSer87, pSer129, nTyr39) in Idiopathic Parkinson’s Disease and Multiple System Atrophy

“…Clearly, larger case-cohort studies are warranted including validation and quantification using other techniques such as specific ELISAs. A recent study has elegantly demonstrated diversity of -synuclein C-terminal truncations in discriminating different synucleinopathies [40]. By continuing to interrogate human post-mortem tissue pathology using novel -synuclein antibodies, our understanding of disease pathogenesis will increase profoundly and may also pose as a basis of both biomarker (prognostic and diagnostic) and therapeutic discoveries.…”

Pathological relevance of post-translationally modified alpha-synuclein (pSer87, pSer129, nTyr39) in idiopathic Parkinson’s disease and Multiple System Atrophy

“…Clearly, larger case-cohort studies are warranted including validation and quantification using other techniques such as specific ELISAs. A recent study has elegantly demonstrated diversity of a-synuclein C-terminal truncations in discriminating different synucleinopathies [40]. By continuing to interrogate human post-mortem tissue pathology using novel a-synuclein antibodies, our understanding of disease pathogenesis will increase profoundly and may also pose as a basis of both biomarker (prognostic and diagnostic) and therapeutic discoveries.…”