Fig. 5: Sulfenic acid-modified SOD1 oligomers induce cytoplasm mislocalization of human TDP-43, the subsequent fibrillization of human TDP-43 and human SOD1 in SH-SY5Y cells

TDP-43 stable cells treated with 5 μM sulfenic acid-modified SOD1 oligomers (+) (a-c, h, k), compared with TDP-43 stable cells treated without SOD1 oligomers (-) (d–g). The merge image (h, j, l, yellow dots) demonstrated co-localization of SOD1 aggregates (red), highlighted by using white arrowheads, with TDP-43 aggregates (green) in cytoplasm of TDP-43 stable cells. TDP-43 stable cells were incubated with 0 or 5 μM sulfenic acid-modified SOD1 oligomers for 3 days at 37 °C, fixed, ruptured, subsequently immunostained by mouse anti-FLAG antibody and IgG conjugated with Alexa Fluo-488 (green); and observed with confocal microscopy (a–f), or subsequently immunostained by mouse anti-FLAG antibody and goat anti-mouse IgG conjugated with Alexa Fluo-488 (green), and subsequently immunostained by rabbit anti-SOD1 antibody and donkey anti-rabbit IgG conjugated with Alexa Fluo-546 (red), and observed with super-resolution fluorescence microscopy (g–l). Nuclei were visualized by DAPI (blue). The enlarged regions (i) and (j–l) show ten-fold enlarged images from (g) and (h), respectively. Aggregates extracted from TDP-43 stable cells incubated with 5 μM sulfenic acid-modified SOD1 oligomers (m) for 3 days at 37 °C were labeled by gold particles. Red arrowheads were used to highlight amyloid fibrils. TDP-43 fibrils were clearly observed by immunogold electron microscopy in such a case. The scale bars represent 10 μm (a–h), 1 μm (i–l), and 20 nm (m), respectively