Repeated brief episodes of ischemia and reperfusion render the myocardium more resistant against subsequent sustained ischemia and reperfusion, a phenomenon called ischemic preconditioning (PC). The protective effect of ischemic preconditioning is transient, subsiding within 2-3 hours of its induction. However, the cardioprotective effect of PC reappears 24 hours following the stimulus. A similar delayed protection is observed following whole body heat shock (HS). Although the clinical potential of delayed protection is more attractive than classical PC because of its long duration, little work has been performed to determine the mechanisms involved in mediating its effect. Accordingly, the overall goal of this proposal is to understand the cellular and molecular mechanisms involved in delayed myocardial protection. The first hypothesis is that delayed cardio-protection induced in vivo by PC or HS is mediated by activation of protein kinase C, induction of nitric oxide synthase and opening of ATP-sensitive potassium channels (KATP channels). The investigators will determine the role of protein kinase C activation in induction of nitric oxide and opening of KATP channel in delayed preconditioning in vivo. The second hypothesis is that PC and HS induce delayed cardiac protection by upregulation of novel antioxidant Bcl-2 and repression of apoptosis (programmed cell death). The investigators will demonstrate if PC and HS express Bcl-2 and inhibit apoptosis following ischemia/reperfusion. They will also show if the protection rendered by Bcl-2 is in part due to its antioxidant effect on cardiac myocytes. The third hypothesis is that delayed myocardial protection can be simulated by direct in vivo overexpression of protective proteins such as Bcl-2, HSP 72 and MnSOD which are known to be upregulated following preconditioning. The investigators will overexpress HSP-72, MnSOD and Bcl-2 by direct injection of adenovirus constructs into the intact myocardium and determine their effects on ischemia protection, repression of apoptosis and opening of KATP channel. They will use state-of-the-art techniques, including adenovirus mediated gene transfer, in vivo myocardial ischemia/reperfusion and preconditioning, retrovirus-mediated stable transfection of Bcl-2 in embryonic myogenic cells and cell culture methods to answer these questions. The mechanism underlying the delayed protection may provide a better insight into the nature of myocardial adaptation to ischemia and open new therapeutic avenues capable of modifying the outcome following myocardial ischemic episodes.
Showing the most recent 10 out of 78 publications
