Fig. 4

α-Syn PFF exposure to immature OLGs during differentiation-induced abnormal oligodendrogenesis. a Confocal images of oligodendroglial cells on day 4 after differentiation induction showing the colocalization of α-syn immunoreactivity and cleaved caspase-9 expression. The cells were incubated with 1 μM α-syn PFFs for 24 h (day 3–4) before fixation. White arrowheads indicate intracellular inclusions. The regions marked by dotted squares are highlighted in the magnified views. Scale bar = 5 μm. b Scheme showing the experimental protocols of 3 μM α-syn PFF exposure to oligodendroglial cells during two different phases (day 0–1, or day 3–4) of differentiation. c Cell viability analysis (WST assay) of day 8 OLGs, which were obtained through different protocols of α-syn PFF exposure during differentiation (no exposure, exposure on day 0–1, or exposure on days 3–4). N = 5, respectively, independent culture, Kruskal–Wallis, p* < 0.05. d Immunoblot analysis of day 8 OLGs obtained via different protocols of α-syn PFF exposure during differentiation (no exposure, exposure on day 0–1, or exposure on days 3–4), showing the protein expression levels of oligodendroglial cell markers. e, f Quantification of the relative protein expression levels of MBP (e) and BCAS1 (f) in day 8 OLGs obtained using the above-mentioned protocols. The differences between the no exposure group and day 0–1 group in (E) (p = 0.0636) and in (F) (p = 0.1980) were not statistically significant. N = 5, respectively, independent culture, Kruskal–Wallis, p* < 0.05, p** < 0.01. g Graphical representation of in vitro analysis showing two patterns of α-syn PFF-induced maturation inhibition. α-Syn PFF exposure to differentiating OLGs during the BCAS1(+) cell-dominant phase resulted in decreased cell viability (left), while exposure during the OPC-dominant phase resulted in abnormal protein expression levels of OLG markers (right)