A number of prenatal environmental risk factors have been reported to potentially contribute to SZ,18 and abnormalities in HSF1-HSP70 signaling have been linked to SZ.19,20 Two independent NPC lines from each of four patients with SZ were given sub-threshold environmental challenges of oxidative stress (0.05 mM H2O2) for 3 h. Following treatment, we measured the expression of HSP70 and GAPDH in individual NPCs; all NPC lines showed increased HSP70 expression in response to challenge (Figure 4e). Notably, although average change of HSP70 expression did not differ between control and SZ hiPSC NPCs, cell-to-cell variability in HSP70 expression was significantly larger in SZ hiPSC NPCs following sub-threshold oxidative stress (Figure 4e). We did not observe any difference in cell-to-cell variability in GAPDH measurements, and there was no significant correlation (P=0.22) between the expression levels of GAPDH and HSP70, suggesting that cell-to-cell variability was specific to HSP70 expression. Single-cell equivalents, generated by pooling the lyses of 10 cells and aliquoting 1/10th to use as a single-cell equivalent, showed very small variability (Figure 4e). Stress response, as mediated by HSF1, may be abnormal in a subpopulation of SZ hiPSC NPCs at the single-cell level.
