Objective: To examine the impact of multiple system atrophy (MSA) brain-derived alpha synuclein (αSyn) with diverse seeding activities in an inoculation-based animal model.

Background: We have observed extensive heterogeneity in the seeding activity of αSyn in Lewy body disorders [1] and have observed up to ten-fold differences in seeding activity among MSA patient brains [2]. This molecular diversity surpasses the present clinical and neuropathological phenotyping of synucleinopathies and might underlie the extensive clinical heterogeneity within these diseases. To explore the potential contribution of differences in αSyn seeding activity to disease heterogeneity, we have employed an inoculation-based synucleinopathy model. We hypothesise that αSyn extracted from human MSA brains with differing seeding activity will confer distinct characteristics in an inoculation-based model of synucleinopathy.

Method: Hemizygous transgenic M83 mice (N=12/group) were inoculated with brain extracts (1% w/v) from MSA patients characterised as high seeders (HS), low seeders (LS) or healthy controls [2]. Mice underwent open field testing monthly and were sacrificed at 152 days post-inoculation. Brains were subject to immunohistochemistry for hyperphosphorylated αSyn (EP1536Y) as well as an αSyn seeding amplification assay (αSyn-SAA) where 5µg of PBS-soluble protein from inoculated M83 mouse brains was used to seed human K23Q/A53T αSyn.

Results: Commencing 30 days post-inoculation, HS-inoculated mice consistently exhibited a trend of reduced locomotor activity compared to LS- and control-inoculated mice (p<0.05). Brains from HS (8/12) and LS (9/12) inoculated mice exhibited widespread hyperphosphorylated αSyn, which was absent in control-inoculated mice. By SAA, samples from HS-inoculated mice produced significantly higher maximum Thioflavin T signal (p=0.03) compared to those from LS-inoculated mice.

Conclusion: Our data support that αSyn gain-of-function (seeding ability) contributes to disease pathogenesis. Moreover, HS and LS phenotypes are conserved upon propagation in an animal model, suggesting that heterogeneity in self-propagating αSyn aggregate species may contribute to disease heterogeneity in MSA. What factors determine the seeding capacity of αSyn from a given patient brain remain to be identified, but ultimately our work may advocate for tailored therapeutic approaches targeting a spectrum of αSyn seeds in MSA.

References: 1. Martinez-Valbuena I, Swinkin E, Santamaria E, Fernandez-Irigoyen J, Sackmann V, Kim A, et al. α-Synuclein molecular behavior and nigral proteomic profiling distinguish subtypes of Lewy body disorders. Acta Neuropathol [Internet]. 2022; Available from: https://link.springer.com/10.1007/s00401-022-02453-0
2. Martinez-Valbuena I, Visanji NP, Kim A, Lau HHC, So RWL, Alshimemeri S, et al. Alpha-synuclein seeding shows a wide heterogeneity in multiple system atrophy. Transl Neurodegener. 2022;11.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/alpha-synuclein-seeding-activity-drives-disease-heterogeneity-in-an-animal-model-of-multiple-system-atrophy/