The etiology of chagasic heart disease is multifactorial resulting from compromised microcirculation and the direct invasion of the myocardium by, T. cruzi; both of which may lead to an inflammatory response. In recent years we delineated some of the factors associated with the pathogenesis of T. cruzi-induced heart disease. We have demonstrated that T. cruzi causes expression of iNOS, TNF-alpha and lL-1beta in the myocardium and that infection of cultured cardiac myocytes causes an increase in NO and a decrease in beat rate. Therefore, on the basis of these in vitro and in vivo observations we hypothesize that infection induces the expression of myocardial cytokines and iNOS and contributes to myocardial dysfunction. The hypothesis to be tested in this proposal is that following infection with T cruzi, the host responds by the activation of nuclear factors and cytokines resulting in upregulation of the inflammatory process and induction of iNOS causing a sustained release of toxic concentrations of NO which profoundly alters myocardial function. T. cruzi infection of endothelial cells and cardiac myocytes leads to expression of vascular adhesion molecules and iNOS by activation of IkappaB-alpha (NF-kappaB). We plan to study the mechanism whereby T. cruzi activates this pathway and the specificity of NF-kappaB activation in the transcription of those cytokines that upregulate the inflammatory response and iNOS expression. We hypothesize that the expression of iNOS and the increased synthesis of NO resulting from the activation of NF-kappaB causes cardiac myocyte dysfunction and cell death. Accordingly, using an in vitro model we will examine the influence of T. cruzi infection on cardiac myocytes. Upregulatory vs downregulatory cytokines will be studied and the influence of iNOS expression on cardiac myocyte contractility and cell death will be determined. In addition, we will employ in vitro co- culture techniques to test the hypothesis that T. cruzi infection of macrophages, vascular smooth muscle or endothelial cells results in NO- mediated altered contractility in adjacent cardiac myocytes cells. We will examine the kinetics of myocardial cytokines expression in T. cruzi-infected mice. We believe that expression of myocardial cytokines results in cardiac dysfunction which will be assessed by the administration of specific antibodies and the utilization of cytokine knock out mice. We will examine the kinetics of myocardial iNOS expression in T. cruzi-infected mice and the significance of iNOS in influencing myocardial function in acute and chronic infection will be assessed by utilizing verapamil, inhibitors of NOS, and the iNOS-/- (KO) mouse model. The consequences of myocardial cytokine and iNOS expression on """"""""down-stream"""""""" events will be determined by pathological, biochemical and functional studies (ECG, gated MRI).
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