Selective Inhibition of Protein Kinase Cβ 2 Prevents Acute Effects of High Glucose on Vascular Cell Adhesion Molecule-1 Expression in Human Endothelial Cells

Abstract

Background— Enhanced expression of adhesion molecules by the endothelium may account for vascular damage in diabetics and nondiabetic patients who develop stress hyperglycemia during acute myocardial infarction. We analyzed the phosphorylation of protein kinase Cβ 2 (PKCβ 2 ) at serine/threonine residues, which may contribute to the endothelial dysfunction during acute hyperglycemia. Furthermore, this study was designed to investigate whether selective blockade of this regulatory mechanism may prevent the development of endothelial hyperadhesiveness. Methods and Results— Incubation of the human aortic endothelial cells with high glucose (22.2 mmol/L) resulted in significant increase of vascular cell adhesion molecule (VCAM)-1 protein expression (172±15% versus control; P <0.01). Phorbol 12-myristate 13-acetate, a potent activator of PKC, mimicked the effect of high glucose on VCAM-1 expression. High glucose led to a rapid increase (181±22% versus control; P <0.01) of membrane-bound PKCβ, reflecting activation of this enzyme. The nonselective inhibitor of PKCβ 1 and PKCβ 2 isoforms LY379196, as well as CGP53353, a highly selective inhibitor of PKCβ 2 , prevented in a dose-dependent manner upregulation of VCAM-1. Incubation with high glucose was associated with increased PKCβ 2 phosphorylation at the Ser-660 residue, and both LY379196 and CGP53353 prevented this event. Exposure of the cells to high glucose also reduced the protein level of the inhibitory subunit of nuclear factor-κB, IκBα, leading to its enhanced binding activity. Selective inhibition of PKCβ abolished IκBα degradation. Conclusions— Our findings demonstrate for the first time that phosphorylation of Ser-660 represents a selective regulatory mechanism for glucose-induced upregulation of VCAM-1. Therefore, PKCβ 2 -selective inhibitors may be promising drugs for treatment of endothelial dysfunction during acute hyperglycemia and possibly in diabetes.