Abstract 1420: Differential Interaction of p38mapk-alpha and p38 mapk-beta with Caveolin-1 and Caveolin-3 Regulates Cardioprotection by Ischemic Preconditioning
Activation of p38MAP kinase (p38MAPK) appears to be essential for preconditioning (PC); however, its mechanism of action remains controversial. Based on the recent reports that MAPKs can be translocated into caveolins, we hypothesized that caveolins could regulate MAPKs action on PC. Sprague Dawley rats were divided into five groups:
desipramine [a sphingomyelinase inhibitor]+PC,
C2-ceramide( cell permeable analog of ceramide).
The isolated perfused hearts were subjected to 30 min I followed by 2 h R with or without PC achieved by repeated short terms I/R. In desipramine group, the hearts were preperfused for 15 min with desipramine. For ceramide group heart was perfused with C2-ceramide for 15 min before I/R. Cardioprotection was analyzed by monitoring ventricular performance, infarct size and apoptosis. At the end, caveolin fraction was isolated from the hearts and immunoprecipitated with either caveolin 1 or caveolin 3. Western blot analysis was then performed with antibodies against p38MAPKa, p38MAPKb, IkB, Akt and Bcl-2. Our results indicated PC-mediated cardioprotection as evidenced by improved myocardial performance, reduced infarct size and apoptosis, which were blocked with desipramine , indicating the involvement of sphingomyelin breakdown in PC. HPTLC identified I/R-mediated breakdown of sphingomyelin, which was prevented with desipramine. In the PC hearts, there was an increased association of the proapoptotic p38MAPKa with caveolin-1 while there was a reduced association of anti-apoptotic p38MAPKb with caveolin-3 indicating the availability of reduced amount of p38MAPKa and increased amount of p38MAPKb to the PC hearts thereby generating an anti-apoptotic signal, and its reversal with desipramine. The anti-apoptotic signal was further confirmed by increased expression of IKB and Bcl-2 as well as Akt phosphorylation, Interestingly, IkB, Bcl-2 and Akt were not associated with either caveolin-1 or caveolin-3 fractions. The results indicated an unique role of sphingomyelin in the PC hearts involving caveolins, which provided cardioprotection by differentially associating the p38MAPKa and p38MAPKb with the caveolin-1 and caveoli-3, respectively.