Abstract 1402: Differential Regulation of Caveolin-1/eNOS Association and AMPK Phosphorylation Reduce Nitric Oxide Mediated Glut-4 Translocation in Type-1 Diabetes
Blood glucose homeostasis by insulin involves rapid stimulation of glucose uptake by translocation of glucose transporter Glut-4 from intracellular pool to the caveolar lipid rafts. Impaired Glut-4 translocation generally characterizes diabetes but the role of caveolin-1 & 3 (Cav-1 & 3) in regulation of Glut-4 translocation is not well known. In this study we examined the mechanism of Glut-4 translocation & its regulation by Cav-1 & 3 signaling in the streptozotocin (STZ) induced diabetic myocardium in comparison with non-diabetic control. The rats were divided into 2 groups (n=12): Control (C) & Diabetes Mellitus (DM) (STZ 65mg/Kg b.w, i.p). In vivo left ventricular functions by echocardiography were examined 30 days after intraperitoneal administration of STZ. Decreased ejection fraction (50 vs 68 %) and fractional shortening (27 vs 38 %) was documented in DM as compared to control. Isolated rat hearts subjected to 30min of global ischemia followed by 2hr of reperfusion were used to examine the mechanism involved in Glut-4 translocation. Decreased phosphorylation of AMPK was observed in DM compared to control. Lipid raft fractions isolated on a discontinuous sucrose gradient demonstrated decreased expression of Glut-4, Cav-3 (0.4, 0.6 fold) & increased Cav-1 expression (1.4 fold) in DM compared to the non-diabetic control. In DM significant decrease in phosphorylation of eNOS (1.2 fold)& Akt (1.8fold)was observed as compared to control. Moreover, confocal microscopy demonstrated significant reduction in association of Glut-4 & Cav-3 in DM as compared to control. In contrast, significant association of Cav-1 & eNOS was observed in DM as compared to control. Co-immunoprecipitation demonstrated increased association of cav-1/eNOS & decreased association of cav-3/Glut-4 in DM. In DM significant inhibition of Akt & AMPK phosphorylation was observed which in turn inhibited phosphorylation of eNOS followed by down regulation of NO production which resulted in decreased glucose uptake in diabetic condition. Thus, this study documents a novel mechanism for therapeutic targets in Type-1 diabetes.