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

Abstract

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 PKCbeta; inhibitor ruboxistaurin (LY333531). In endothelial cell culture, overexpression of PKCbeta;1 and -beta;2, but not PKCalpha;, -delta;, or -zeta;, decreased insulin-stimulated Akt phosphorylation and eNOS expression. Overexpression of PKCbeta;1 and -beta;2, but not PKCalpha; or -delta;, also decreased Akt phosphorylation stimulated by vascular endothelial growth factor (VEGF). In microvessels isolated from transgenic mice overexpressing PKCbeta;2 only in vascular cells, Akt phosphorylation stimulated by insulin was decreased compared with wild-type mice. Thus, activation of PKCbeta; in endothelial cells and vascular tissue inhibits Akt activation by insulin and VEGF, inhibits Akt-dependent eNOS regulation by insulin, and causes endothelial dysfunction in obesity-associated insulin resistance. © 2006 by the American Diabetes Association.