Parkinson's disease (PD) and multiple system atrophy (MSA) are neurodegenerative diseases characterized by intracellular accumulation of alpha-synuclein (⍺-Syn) aggregates. It is hypothesized that ⍺-Syn propagates through the nervous system, resulting in cellular dysfunction and neurodegeneration. Despite the common presence of ⍺-Syn aggregates, PD and MSA present distinct clinical symptoms and neuropathology.

Structurally distinct polymorphs of ⍺-Syn aggregates, or strains, have been demonstrated in PD and MSA, supporting a hypothesis of strain-specific diseases. These structural differences in ⍺-Syn strains are hypothesized to dictate pathological spreading and cellular impact. In this study, we aim to explore a potential role of the MSA-associated oligodendroglia protein, p25⍺, in ⍺-Syn strain formation and to investigate patient-derived ⍺-Syn aggregates from both PD and MSA.

Using a substoichiometric amount of p25⍺, we generated an ⍺-Syn/p25⍺ fibril strain, and from the cerebrospinal fluid (CSF) of a small cohort (n=4) of PD and MSA patients, we generate disease-specific fibrils. Using an array of biophysical and biochemical techniques, we examined the structural differences and detergent stability in these ⍺-Syn strains. Furthermore, we probed functional differences between the strains using cell models such as an ⍺-Syn overexpressing oligodendroglia cell model and induced pluripotent stem cell-derived neurons.

We demonstrate that ⍺-Syn/p25⍺ fibrils are structurally distinct from de-novo generated fibrils, resulting in increased cellular seeding and morphologically distinct inclusions. Furthermore, PD and MSA-derived aggregate strains display disease-specific structural differences. We observed a differential cellular seeding propensity of patient-derived PD and MSA strains, potentially resulting from variations in cellular internalization. Additionally, our results reveal a cell-type specific difference in inclusion formation between patient-derived PD and MSA strains. Investigating the stability of the fibrils, we demonstrate a strain-specific differential stability in the common detergent sarkosyl, that may have implications for our interpretation of the strains we are able to isolate and characterize from biological sources.

Overall, this study enhances our understanding of ⍺-Syn aggregate strains and supports a hypothesis of a differential functional impact of structurally distinct strains in synucleinopathies.