GLUT4, the so-called insulin-responsive transporter, is expressed in vascular smooth muscle cells (VSMCs) and participates in basal glucose uptake in VSMCs in an insulin-independent manner. VSMC GLUT4 expression is decreased in many animal models of hypertension, several of which are not associated with generalized insulin resistance. We have found that decreased GLUT4 in VSMCs results in altered vascular contractility and cell signaling. Specifically, in transgenic and knockout animals, reduction of GLUT4 enhances vascular reactivity whereas increased GLUT4 expression prevents hypertension-induced increases in reactivity. Thus, our general hypothesis is that reduction in VSMC GLUT4 expression leads to phenotypic changes in arteries that are characteristic of hypertension. We have found that reduction in GLUT4 expression causes reduced myosin light chain phosphatase activity and that this is likely mediated by Rho kinase. These effects are of potential significance since altered Rho-kinase activity plays a pivotal role in the development of vascular abnormalities in hypertensive animal models and humans. Thus we hypothesize that reduction in VSMC GLUT4 expression leads to enhanced RhoA/Rho-kinase activity which is responsible for phenotypic changes in arteries in hypertension. Our data also suggest that GLUT4 is functionally coupled with certain VSMC agonist receptors such as 5-HT2 receptors. Myosin phosphatase inhibition by 5-HT is augmented by specific blockade of GLUT4-mediated glucose uptake; 5-HT2 receptors and GLUT4 are associated with caveolae and lipid rafts in VSMCs. Thus, we hypothesize that GLUT4 interacts with 5-HT2 receptors or G12/13, GEFs and/or other signaling molecules to reduce 5-HT mediated induction of the RhoA/Rho-kinase pathway. In order to test these hypotheses, we will pursue the following three aims, to: 1. Assess the effects of VSMC-specific modulation of GLUT4 expression on blood pressure and other vascular phenotypes in mice with and without DOCA-salt hypertension. 2. Determine the effects of altered VSMC GLUT4 expression on RhoA/Rho kinase pathway, and alternative pathways that mediate calcium sensitization of arterial VSMCs. 3. Determine how GLUT4-dependent effects on vascular smooth muscle myosin phosphatase are mediated via G-protein coupled receptor (GPCR) signaling pathways. ? LAY SUMMARY: We have found that a protein that transports sugar (glucose) into cells is also involved in preventing abnormalities found in blood vessels from hypertensive animals (and probably humans). We propose studies to determine the mechanisms of these protective effects that could lead to interventions to prevent the vascular damage that occurs in patients with hypertension. ? ? ?
