Insulin resistance, cardiovascular stiffening and cardiovascular disease

Abstract

The cardiometabolic syndrome (CMS) and obesity are typically characterized by a state of metabolic insulin resistance. As global and US rates of obesity increase there is an acceleration of the incidence and prevalence of insulin resistance along with associated cardiovascular disease (CVD). Under physiological conditions insulin regulates glucose homeostasis by enhancing glucose disposal in insulin sensitive tissues while also regulating delivery of nutrients through its vasodilation actions on small feed arteries. Specifically, insulin-mediated production of nitric oxide from the vascular endothelium leads to increased blood flow enhancing disposal of glucose. Typically, insulin resistance is considered as a decrease in sensitivity or responsiveness to the metabolic actions of insulin including insulin-mediated glucose disposal. However, a decreased sensitivity to the normal vascular actions of insulin, especially diminished nitric oxide production, plays an additional important role in the development of CVD in states of insulin resistance. One mechanism by which insulin resistance and attendant hyperinsulinemia promote CVD is via increases in vascular stiffness. Although obesity and insulin resistance are known to be associated with substantial increases in the prevalence of vascular fibrosis and stiffness the mechanisms and mediators that underlie vascular stiffening in insulin resistant states are complex and have only recently begun to be addressed. Current evidence supports the role of increased plasma levels of aldosterone and insulin and attendant reductions in bioavailable nitric oxide in the pathogenesis of impaired vascular relaxation and vascular stiffness in the CMS and obesity. Aldosterone and insulin both increase the activity of serum and glucocorticoid kinase 1 (SGK-1) which in turn is a major regulator of vascular and renal sodium (Na+) channel activity.The importance of SGK-1 in the pathogenesis of the CMS is highlighted by observations that gain of function mutations in SGK-1 in humans promotes hypertension, insulin resistance and obesity. In endothelial cells, an increase in Na+ flux contributes to remodeling of the cytoskeleton, reduced NO bioavailability and vascular stiffening. Thus, endothelial SGK-1 may represent a point of convergence for insulin and aldosterone signaling in arterial stiffness associated with obesity and the CMS. This review examines our contemporary understanding of the link between insulin resistance and increased vascular stiffness with emphasis placed on a role for enhanced SGK-1 signaling as a key node in this pathological process.