Suppression of GRK2 expression reduces endothelial dysfunction by restoring glucose homeostasis.

Despite the associations between diabetic complications and vascular endothelial dysfunction, a direct therapeutic method targeting endothelial dysfunction remains poorly characterized. We have previously shown that chemical inhibition of G-protein-coupled receptor kinase 2 (GRK2) slightly enhances insulin sensitivity and reduces endothelial dysfunction in type 2 diabetic mice. In this study, we identified GRK2 as a novel therapeutic target of diabetic endothelial dysfunction and investigated the effect on diabetic endothelial dysfunction through the systemic administration of GRK2 siRNA using a hydrodynamic-based procedure, resulting in suppression of increased GRK2 protein levels in the liver. Suppressed GRK2 levels in the liver markedly improved glucose homeostasis, as well as improved the impaired endothelial Akt/eNOS-dependent signal activation (insulin-stimulated phosphorylation of Akt and eNOS) and vascular responses (clonidine-induced and insulin-induced endothelial-dependent relaxation response and phenylephrine-induced contractile response) in type 2 diabetic aortas. Interestingly, insulin-stimulated Akt/eNOS signaling was increased only by normalizing the glucose concentration in human umbilical vein endothelial cells (HUVECs) with GRK2 overexpression, suggesting of an important role of hepatic GRK2. Our results clarified the relationship among hepatic GRK2, glucose homeostasis, and vascular endothelial function. Liver-targeting GRK2 siRNA delivery represents a novel therapeutic tool to restore glucose homeostasis and reduce endothelial dysfunction.