Activation of vascular protein kinase C-β inhibits Akt-dependent endothelial nitric oxide synthase function in obesity-associated insulin resistance

Activation of protein kinase C (PKC) in vascular tissue is associated with endothelial dysfunction and insulin resistance. However, the effect of vascular PKC activation on insulin-stimulated endothelial nitric oxide (NO) synthase (eNOS) regulation has not been characterized in obesity-associated insulin resistance. Diacylglycerol (DAG) concentration and PKC activity were increased in the aorta of Zucker fatty compared with Zucker lean rats. Insulin-stimulated increases in Akt phosphorylation and cGMP concentration (a measure of NO bioavailability) after euglycemic-hyperinsulinemic clamp were blunted in the aorta of fatty compared with lean rats but were partly normalized after 2 weeks of treatment with the PKC beta inhibitor ruboxistaurin (LY333531). In endothelial cell culture, overexpression of PKC beta 1 and -beta 2, but not PKC alpha, -delta, or -zeta, decreased insulin-stimulated Akt phosphorylation and eNOS expression. Overexpression of PKC beta 1 and -beta 2, but not PKC alpha or -delta, also decreased Akt phosphorylation stimulated by vascular endothelial growth factor (VEGF). In microvessels isolated from transgenic mice overexpressing PKC beta 2 only in vascular cells, Akt phosphorylation stimulated by insulin was decreased compared with wild-type mice. Thus, activation of PKC beta in endothelial cells and vascular tissue inhibits Akt activation by insulin and VEGF, inhibits Nkt-dependent eNOS regulation by insulin, and causes endothelial dysfunction in obesity-associated insulin resistance.