Since activated JNK is one of the mediators of ER stress‐induced apoptosis (Szegezdi et al, 2006), we also determined the levels of markers of ER stress, XBP1, and ATF6α and the extent of eIF2α phosphorylation, in SOD1G93A NSC34 cells. The levels of these ER stress markers in the SOD mutant cells, which were higher than in WT cells, were significantly reduced following P110 treatment, thus indicating a functional connection between Drp1 hyperactivation and ER stress (Figs 2F and EV3C). Other ER stress markers, GRP78 and CHOP, increased by serum starvation in G93A expressing in motor neuron‐like cells as compared to the WT (Fig EV3C), were significantly normalized by P110 treatment (Fig EV3C).