Aggregation of α-syn in dopaminergic human cell lines infected with recombinant human α-syn short amyloid fibrils and sub-passaged over five passages (p5). (A) Western blot of different assemblies formed in vitro. (B) Western blot of cell lysates (SH: SH-SY5Y cells; SH-OE SH-SY5Y overexpressing human α-syn); Ctrl: non-treated cells. SFp5: α-syn short amyloid fibril-infected cells at fifth passage. HMW: High molecular weight aggregates. (C) Western blot analysis of aggregated SH-OE cell lysates treated with α-syn short amyloid fibrils, and non-treated (Ctrl); Total: total cell lysates. Sequential extraction of α-syn aggregates in 1% Triton X-100 lysis buffer (S-TX), followed by 2% SDS lysis buffer (S). (P): a pellet fraction after the pellet was treated with 2% SDS. Anti-human α-syn (C-20)-R antibody was used (Additional file 6: Table S2).