RAGE and Mechanisms of Cardiac Dysfunction

Cardiac injury secondary to ischemiaJreperfusion (I/R) is a major cause of morbidity and mortality, especially in diabetes. Activation of aldose reductase (AR) contributes to myocardial ischemic injury and impaired energy metabolism in the euglycemic and diabetic heart by a number of key mechanisms AR activation disrupts sodium and calcium homeostasis; the resulting increased cytosolic NADH/NAD+ ratio leads to generation of diacylglycerol (DAG) and activation of Protein Kinase (PKC), and generation of 3-deoxyglucosone (3-DG), a key precursor leading to generation of Advanced Glycation Endproducts (AGEs), !igands for Receptor for AGE (RAGE). Molecular pathways mediating the impact of AR include, at least in part, activation of JAK/STAT signaling and AGES. AGEs accumulate in the diabetic heart at an accelerated rate due to increased levels of glucose, and superimposed oxidant and chronic inflammatory stress. In addition, S100/calgranulin polypeptides, a family of proinflammatory molecules, are also are ligands for RAGE and co-localize with AGEs in the vasculature and sites of inflammatory cell infiltration in the diabetic heart. Pharmacological blockade of RAGE in the isolated perfused heart suppressed induction of tumor necrosis factor-alpha and the nitric oxide-cGMP axis in diabetic hearts and improved myocardial function and energy metabolism in diabetic hearts under basal conditions and upon ischemia/reperfusion (I/R). In homozygous RAGE null (0), and transgenic mice expressing a RAGE transgene in which the cytosolic tail was deleted, thereby imbuing a "dominant negative" (DN) effect in endothelial cells (EC) or inflammatory cells, protection from the biochemical and metabolic consequences of I/R was observed. Comp[ared to rats or humans, murine hearts express low levels of AR, and, thus, endogenous generation of 3-DG is relatively low. We hypothesize that accumulation of AGEs (driven to some degree by AR) and S100/calgranulins, and the interaction of these products with RAGE, sets the stage for cardiac dysfunction - a process that is exaggerated in diabetes. To address the role of RAGE in cardiac I/R, we postulated that the introduction of the gene encoding human AR (hAR) at levels corresponding to those seen in human subjects would feasibly recapitulate, in mice, the metabolic and biochemical milieu of human diabetes with respect to the heart. We will test these concepts using novel RAGE- and AR-modified mice in the isolated perfused heart and in cardiac ischemia/reperfusion. This Project will share mouse models and ligand-RAGE reagents with the other two projects and will utilize all three cores of the Program.