Mechanism of Extracellular Aggregate-induced Alpha-synuclein Transmission

Abstract

Deposition of alpha-synuclein (αSyn) aggregates is a pathological feature of Parkinsons disease. Cell-to-cell transmission of αSyn aggregates was suggested as the underlying mechanism of the progression of Parkinsons disease. According to the prion-like spreading hypothesis, aggregate transmission increases dependently on the template seeding mechanism. αSyn aggregates work like infectious prion, amplifying protein aggregation and accumulation. However, this still remains unclear. V40G variant of αSyn has seeding blocking property

thereby elucidation of template seeding hypothesis becomes possible. Here, αSyn aggregate transmission rate was observed using Bimolecular Fluorescence Complementation (BiFC) system to verify whether this seeding ability plays a major role in αSyn aggregate propagation. Aggregate transmission level was increased in the V40G aggregate treated condition even the V40G aggregate has no seeding activity. Therefore, αSyn aggregate transmission might involve the mechanism other than the direct template seeding. To elucidate the mechanism of transmission, I assessed the endo-lysosomal degradation rate using fluorescein-conjugated dextran. When the cells were exposed to the extracellular αSyn, the endo-lysosomal degradation rate was decreased, while the lysosomal integrity and function were unaffected. RNA sequencing analysis revealed that the pathways related to the transcriptional regulation, cytoskeleton organization, immune response, and mitochondria were changed by extracellular αSyn aggregates. Altogether, this study suggests that the templated seeding mechanism is not the main principle of αSyn aggregate propagation and that the mechanism is related with the changes in the trafficking through the endo-lysosomal pathway.