Pathogenic Mutations Differentially Regulate Cell-to-Cell Transmission of α-Synuclein

Recent studies suggest that the cell-to-cell spread of pathological alpha-synuclein (alpha-syn) plays important roles in the development of Parkinson's disease (PD). PD patients who carry alpha-syn gene mutations often have an earlier onset and more severe clinical symptoms and pathology than sporadic PD cases who carry the wild-type (WT) alpha-syn gene. However, the molecular mechanism by which alpha-syn gene mutations promote PD remains unclear. Here, we hypothesized that pathogenic mutations facilitate the intercellular transfer and cytotoxicity of alpha-syn, favoring an early disease onset and faster progression. We investigated the effects of eight known pathogenic mutations in human alpha-syn (A18T, A29S, A30P, E46K, H50Q, G51D, A53E, and A53T) on its pathological transmission in terms of secretion, aggregation, intracellular level, cytotoxicity, seeding, and induction of neuroinflammation in SH-SY5Y neuroblastoma cells, cultured rat neurons, and microglia, and the rat substantia nigra pars compacta. We found that 2 of the 8 mutations (H50Q and A53T) significantly increased alpha-syn secretion while 6 mutations (A18T, A29S, A30P, G51D, A53E, and E46K) tended to enhance it.In vitro alpha-syn aggregation experiments showed that H50Q promoted while G51D delayed aggregation most strongly. Interestingly, 3 mutations (E46K, H50Q, and G51D) greatly increased the intracellular alpha-syn level when cultured cells were treated with preformed alpha-syn fibrils (PFFs) compared with the WT, while the other 5 had no effect. We also demonstrated that H50Q, G51D, and A53T PFFs, but not E46K PFFs, efficiently seededin vivoand acutely induced neuroinflammation in rat substantia nigra pars compacta. Our data indicate that pathogenic mutations augment the prion-like spread of alpha-syn at different steps and blockade of this pathogenic propagation may serve as a promising therapeutic intervention for PD.