Skin-derived α-synuclein strains from PD, DLB, and MSA induce distinct intracellular pathology and neurodegeneration.

α-Synuclein (αSyn) aggregates ("strains") can be detected by seed amplification assays such as real-time quaking-induced conversion from the skin of patients with synucleinopathies including Parkinson's disease (PD), dementia with Lewy bodies (DLB), and multiple system atrophy (MSA). However, whether skin-derived αSyn strains induce disease-specific pathology in a biological system is unknown. We have identified a human glioblastoma cell line U251 that readily forms intracellular αSyn inclusions upon seeding by exogenous αSyn seeds. These intracellular αSyn inclusions are detergent-insoluble and colocalize with phosphorylated-αSyn at serine 129 (p-αSyn), the pathological hallmark of synucleinopathies. We have engineered a Förster resonance energy transfer-based αSyn biosensor in U251 cells to characterize intracellular aggregation of αSyn and morphology of p-αSyn inclusions seeded by real-time quaking-induced conversion-amplified patient skin αSyn strains. The skin-derived αSyn strains from PD, DLB, and MSA patients are capable of inducing intracellular αSyn aggregation characterized by Förster resonance energy transfer-positive inclusions colocalized with p-αSyn. Interestingly, PD skin-amplified strains are more bioactive, which induce a greater pathological burden and a distinct p-αSyn inclusion morphology from DLB skin-amplified strains. Furthermore, the skin-amplified αSyn strains induce neuronal inclusions and trigger degeneration of induced neurons reprogrammed from U251 biosensor cells. Finally, biosensor cell-propagated PD skin αSyn strains induce higher in vitro seeding activity than DLB skin αSyn strains, indicating a strain-specific relationship between intracellular pathological αSyn burden and in vitro seeding activity. In conclusion, αSyn strains derived from PD, DLB, and MSA patient skin are bioactive, pathologically distinct, and trigger neurodegeneration. Our findings emphasize the importance of studying tissue- and strain-specific pathogenesis of synucleinopathies.