Supplementary Videos
Parkinson’s disease (PD) and multiple system atrophy (MSA) are α-synucleinopathies that are currently differentiated by clinical manifestations. However, their distinct α-synuclein (α-Syn) pathologies and potential proteoforms may be exploited for accurate ante-mortem biomarker development. To distinguish these diseases through their underlying α-Syn pathology, particularly early on when clinical features are often ambiguous, it is paramount to have an informed understanding of disease-specific proteoform pathologies. This will also have ramifications for using biomarker assays preclinically.
We recently identified a broader diversity of α-Syn aggregates in clinical PD (npj Parkinson’s disease (2024)10:1), prompting this comparative study of the same epitope-specific immunoreactivities for α-Syn inclusion pathologies in MSA. Whether there is a broader diversity of MSA pathology, or if there are similarities with the novel α-Syn pathologies now identified in PD, needs to be determined. Here, we utilised an α-Syn antibody cocktail – that collectively detects each of the three structural domains of α-Syn – to compare the epitope-specific aggregation of α-Syn across multiple brain regions prone to α-Syn accumulation in PD and MSA. This multiplex approach identifies aggregates with different α-Syn proteoforms within the same tissue section.
We demonstrate that N-terminus and C-terminus antibodies detect significantly more α-Syn pathology in MSA compared to phosphorylated (pS129) α-Syn antibodies, which are classically used to detect α-Syn. Importantly, C-terminus immunolabelling detected a significantly higher percentage of α-Syn pathology in MSA compared to PD; meanwhile, N-terminus immunolabelling consistently detected the highest percentage of α-Syn in affected regions of both diseases, which could be of biological significance. We confirm oligodendroglial involvement distinguishes MSA from PD, as expected, and in contrast to PD, no substantial astrocytic or microglial α-Syn accumulation in MSA occurs. These data confirm glial-specific changes between these diseases, even when immunolabelling the N-terminus epitope. In addition to previously detected neuronal inclusions, PD neurons contain more N-terminus α-Syn, while MSA neurons contain all epitopes except pS129 α-Syn. This explains why identification of neuronal MSA pathologies is currently lacking and challenges the standard reliance on pS129 antibodies for diagnosing α-synucleinopathies.
These findings underscore the necessity of utilising a diverse selection of α-Syn antibodies, especially those targeting the N-terminus, to ensure capture of the entire spectrum of α-Syn proteoforms in α-synucleinopathies. Our data provide novel insights toward the biological differentiation of these α-synucleinopathies and pave the way for more refined ante-mortem diagnostic methods to facilitate the early identification and intervention of these neurodegenerative diseases.
