The long-term goal is to understand why hearts of elderly humans and animal models are more prone to irreversible damage from ischemia-reperfusion (I/R). I/R generates reactive oxygen species (ROS) that modify thiol groups on proteins, leading to mixed disulfides between glutathione (GSH) and protein-SH (protein-SSG). Our previous studies characterized glutaredoxin (GRx) as the enzyme that specifically catalyzes protein-SH/-SSG exchange in cells. Using an established animal model of aging, Fischer 344 rats, our preliminary studies revealed that GRx activity in cytosol and mitochondria was decreased in heart cells from elderly rats compared to young adults. The operating hypothesis is that such age-dependent changes in glutaredoxin activity perturb the thiol-disulfide steady-state and corresponding activity of specific proteins that are intermediates in redox signaling pathways that determine whether a cell survives an oxidative insult or commits to apoptosis. Thus, cardiomyocytes of the elderly are more susceptible to oxidant-induced apoptosis. Accordingly, this project focuses on GRx and its regulation of the S-glutathionylation status of apoptotic signaling proteins. Mechanisms of change in cytosolic and mitochondrial GRx activities will be studied as a function of age and ischemia-reperfusion. The protein-SH/-SSG status and activities of apoptotic signaling intermediates in cardiomyocytes of young adult and elderly rat hearts will be studied in relationship to GRx activity. Results will be correlated with the content and distribution of GRx in natural cardiomyocytes and in cardiomyocytes in which the content and/or form of GRx have been manipulated by adenoviral gene transfer in vitro and in vivo. These studies will enhance our general understanding of the role of glutaredoxin in apoptotic regulation. Moreover they will address potential mechanisms for age-dependent predisposition of hearts to irreversible injury and provide insights for novel therapeutic interventions.