Stochastic Misfolding Drives the Emergence of Distinct α-Synuclein Strains

The existence of α-synuclein conformational strains provides a potential explanation for the clinical and pathological differences among synucleinopathies such as Parkinson’s disease and multiple system atrophy. However, how distinct α-synuclein strains are formed in vivo remains unknown. Here, we examined whether unique strains of self-propagating α-synuclein aggregates can arise within a consistent molecular environment. Unexpectedly, we observed conformational heterogeneity between individual preparations of α-synuclein pre-formed fibrils (PFFs) generated by polymerizing recombinant wild-type or A53T-mutant human α-synuclein under identical conditions. Moreover, we found that α-synuclein aggregates formed spontaneously in the brains of a transgenic synucleinopathy mouse model were conformationally diverse, leading to the identification of three distinct disease subtypes. Propagation of putative PFF- and brain-derived α-synuclein strains in mice initiated several distinct synucleinopathies, characterized by differences in disease onset times, cerebral α-synuclein deposition patterns, and the conformational attributes of α-synuclein aggregates. The conformational diversity of α-synuclein aggregates across PFF preparations and between the brains of individual transgenic mice demonstrates that α-synuclein can spontaneously form multiple self-propagating strains within an identical environment both in vitro and in vivo . This suggests that stochastic misfolding into distinct aggregate structures drives the emergence of α-synuclein strains and implies that the intrinsic variability of common synucleinopathy research tools must be considered when designing and interpreting experiments.