Fig. 4.

SYT13 overexpression reduces stress in ALS and SMA motor neuron cultures. a, c Representative images of ALS and e, g SMA iPSC-derived motor neurons show an increase in stress marker staining over time compared to control iPSC-motor neurons (CTR). Cells that express SYT13 had significantly reduced stress marker expression (a, e: BiP red and SMI32 green; c: pEIF2αred and SMI32 green; g: ATF6 red and SMI32 green). In each panel, the inset (rectangle box) shows 1.5x magnification image of stress markers signal (red) of a select region indicated by the arrow (b, d, f, h). The immunoreactivity score of iPSC-derived motor neurons demonstrates that the signal of the specific stress markers was increased in ALS/SMA motor neurons with respect to CTR motor neurons and reduced in SYT13-treated motor neurons with respect to null-treated samples (n = 20/group, BiP ALS: P < 0.001; pEIF2α ALS: P < 0.001; BiP SMA: P < 0.001; ATF6 SMA: P < 0.001, one-way ANOVA). The immunoreactivity score was quantified using ImageJ software. Values are presented as means ± SEM. i Graphic showing the thapsigargin-induced calcium signal measured in C9ORF72, SOD, and SMA motor neurons with or without SYT13. SYT13 treatment restored the altered TG-evoked ER Ca²⁺release. Values are presented as means ± SD from five independent experiments, three samples/group. l Quantification of the area between 50 s (t1) and 150 s (t2), which is representative of the calcium signal measured in C9ORF72, SOD, and SMA motor neurons with or without SYT13