Fig. 7.

Inhibition of mTOR reduces the increase in expression of nuclear p21^Cip1/WAF1 in cardiomyocytes induced by H₂O₂ and promotes apoptosis. (A) Cardiomyocytes were unstimulated (Control) or exposed to 0.2 mM H₂O₂ (2 h) in the presence of 1 μM KU63794, 10 μM Rapamycin or vehicle only. (B and C) Nuclear or cytosolic samples were immunoblotted with antibodies to p21^Cip1/WAF1, [(A) and (B)] or cleaved caspase 3 [(A) and (C)]. Data are means ± SEM (n = 3 independent myocyte preparations); *p < .05, **p < .01, ***p < .001 relative to vehicle control; #p < .05 relative to H₂O₂ (one-way ANOVA with Tukey post-test). (D) Schematic for regulation of signalling and gene expression under conditions of redox stress vs signalling. In conditions of low H₂O₂, immediate early genes (IEGs) are upregulated and mTOR is activated to promote protein synthesis, leading to production of antioxidant enzymes and cytoprotective proteins such as p21^Cip1/WAF1 to alleviate the stress of increased oxidative burden. Under conditions of high H₂O₂, ATP levels fall dramatically causing activation of AMPK with phosphorylation of Raptor, inhibition of mTORC1 and decreased protein synthesis. Cells are unable to synthesise cytoprotective proteins such as p21^Cip1/WAF1 and undergo apoptosis.