Hyperglycemia inhibits vascular smooth muscle cell apoptosis through a protein kinase C-dependent pathway

We hypothesized that the pathogenesis of diabetic vasculopathy involves the abnormal regulation of vascular smooth muscle cell (VSMC) apoptosis. In nondiabetic mice, a reduction in carotid artery blood flow resulted in. a significant loss of medial VSMCs via apoptosis (normal flow 84+/-1 viable VSMCs, reduced flow 70+/-5 viable VSMCs; n=12, P<0.01). In contrast, flow-induced VSMC apoptosis was markedly attenuated in streptozotocin-induced diabetic mice (normal flow 85+/-2 viable VSMC, reduced flow 82+/-4 viable VSMC; n=13, NS). In accord with our in vivo findings, the exposure of cultured rat and human VSMCs to high glucose (17.5 mmol/L) significantly attenuated the induction of apoptosis in response to serum withdrawal (rat VSMCs in normal [5.5 mmol/L] glucose 28+/-1%, high D-glucose 19+/-2%; P<0.0001). High glucose also inhibited apoptosis induced by Fas ligand (100 ng/ml)(normal 23+/-2%, high D-glucose 13+/-2%; P<0.006). Supplementation with the nonmetabolized enantiomer L-glucose had no effect. We confirmed reports that high glucose activates protein kinase C (PKC) and demonstrated that PKC-blockade with long-term phorbol ester treatment or calphostin C prevented the antiapoptotic effect (P<0.001). Moreover, the upregulation of either PKC alpha or PKC beta II expression was sufficient to inhibit serum withdrawal-induced apoptosis (control 25+/-2%, PKC alpha 11+/-2%, PKC beta II 8+/-2%; P<0.0001), whereas the upregulation of PKC delta had no significant effect. Taken together, these findings demonstrate that hyperglycemia inhibits VSMC apoptosis via a PKC-dependent pathway.