Abstract 1901: Disorganization of Lipid Rafts Abolished the Ischemic Preconditioning Effect on Regulation of Caveolar-Scaffold Proteins Cav-1, Cav-3, Akt, e-NOS and Glut-4 Following Ischemia-Reperfusion Injury
Ischemia / reperfusion (I/R) injury generated reactive oxygen species enhance myocardial injury, but brief periods of myocardial I followed by R (ischemic preconditioning, IP) induce cardioprotection. Translocation of Glut-4 from the intracellular vesicles to plasma membrane and stimulated glucose uptake during ischemia has been demonstrated. However the role of caveolae, the plasma membrane invaginations needs to be elucidated. In the present study we demonstrate the role of lipid raft scaffold proteins caveolin-1 (cav-1), caveolin-3 (cav-3), Akt, eNOS & Glut-4 in IP mediated cardioprotection. The rats were divided into: Control Sham, I/R, IP + I/R (IP) & IP + Methyl beta-cyclodextrin (regulator for cholesterol mediated caveolae disruption) (IPM). In I/R the hearts were subjected to 30 min of I by Left anterior descending artery ligation (LAD) followed by 3, 48 hr of R. IP was performed by four cycles of 4 min of I & 4 min of R followed by I/R. Increased mRNA expression of Glut-4, cav-3 (2.2, 1.5 fold) & decreased cav-1 (0.5 fold) was observed after 3h of reperfusion in IP compared to other groups. IP demonstrated increased protein expression of Glut-4, cav-3, p-eNOS, p-AKT (1.9, 2, 1.6 and 1.5 fold) and decreased expression of cav-1 (0.6 fold) after 48hr in the isolated caveolin rich lipid raft fractions compared to IR. Significant Glut-4 translocation and cav-3 association was also observed in IP which was disrupted in IPM demonstrating that lipid raft rupture abolished the IP mediated Glut-4 translocation & cav-3 association. These findings clearly documented significant role of lipid raft in the cav-1/cav-3/Akt/eNOS mediated regulation of Glut-4 translocation. Moreover, IP mediated reduction in infarct size & cardiomyocyte apoptosis after 24 hr of reperfusion was abolished in IPM. In conclusion, these findings demonstrate that IP mediates cardioprotection through caveolin-1 down regulation, induced expression of cav-3, p-Akt, p-eNOS and translocation of Glut-4 to the caveolar invaginations, however the disruption of the lipid raft organization by Methyl beta-cyclodextrin abolishes the IP effect which demonstrates that the caveolin-rich lipid rafts and their scaffold proteins plays a critical role in the IP mediated cardioprotection.