Vascular insulin resistance is a hallmark of type 2 diabetes (T2D) and dampening of insulin-induced vasodilation is its primary consequence. Notably, in T2D, reduced insulin-stimulated vasodilation and blood flow to tissues such as skeletal muscle significantly limits glucose uptake and contributes to impaired glucose control. A detailed understanding of the precipitating factors and mechanisms underlying the defects in vasodilator actions of insulin is critical for the development of therapeutic strategies aimed at improving glycemic control and protecting against cardiovascular disease. Based on our prior work and most recent and exciting preliminary data, we propose the novel hypothesis that ADAM17-mediated shedding of the insulin receptor alpha (IR?) from endothelial cells impairs insulin-stimulated vasodilation in T2D. We further propose that the increased activity of endothelial ADAM17 is attributed to protein kinase-C (PKC) activation and subsequent externalization of phosphatidylserine (PS) to the outer leaflet of the cell membrane, which serves to guide ADAM17 to its targeted substrates. As exogenous PS is a competitive inhibitor of ADAM17 sheddase activity, we will also determine the efficacy of oral administration of PS for restoring vascular insulin sensitivity in T2D patients. We will test our innovative hypotheses with gain- and loss-of-function genetic-manipulation experiments in human cultured endothelial cells, in isolated resistance arteries harvested from patients undergoing abdominal surgery, and in patients with T2D. Experimental results will determine the role of PS externalization-ADAM17 activation-IR? shedding as a mechanism impairing the vasodilatory actions of insulin in T2D. Specifically, in Aim 1, we will determine the mechanism by which PKC causes the externalization of PS and whether PS externalization is needed for PKC-dependent activation of ADAM17 in endothelial cells. Next, in Aim 2, we will determine the role of ADAM17 activity in IR? shedding and subsequent impairment of insulin-stimulated vasodilation in T2D. Finally, in Aim 3, we will perform a randomized double-blind clinical trial to determine the therapeutic efficacy of oral administration of the competitive inhibitor of ADAM17 sheddase activity, PS, on insulin-stimulated leg blood flow in patients with T2D. Our team is poised to move cardiovascular and diabetes research forward with a project that will exert a sustained, powerful impact across a number of levels of inquiry that are novel conceptually, mechanistically, methodologically, and therapeutically. Indeed, this proposal represents a paradigm shift from our current mechanistic understanding of vascular insulin resistance. Targeting ADAM17 activation holds extraordinary promise for correcting vascular insulin resistance and ultimately preventing/treating T2D-associated metabolic and cardiovascular diseases.
The prevalence of type 2 diabetes (T2D) is increasing by alarming proportions in the US and worldwide. Over the last two decades, the number of new cases of diabetes has almost tripled in the US and current projections estimate that one in three Americans will have diabetes by 2050. This has a tremendous health care significance, as eight out of 10 patients with T2D die from cardiovascular disease. Vascular insulin resistance is an important factor in the pathogenesis of T2D and cardiovascular disease. The proposed study will determine the role that ADAM17 activity has in mediating microvascular insulin resistance in T2D with the goal of elucidating new therapeutic strategies.