MOLECULAR PATHOGENESIS OF CARDIAC DYSFUNCTION

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The goal of this proposal is to determine the molecular mechanisms of cardiac dysfunction that occurs during septic shock and following thermal trauma. Previous work has demonstrated that cardiac dysfunction is mediated by the cytokine tumor necrosis factor-alpha (TNF), which is produced locally in the myocardium by cardiac myocytes. This proposal utilizes novel molecular and genetic strategies to investigate the mechanisms of TNF's detrimental effects and to develop therapeutic approaches for TNF-related cardiac contributions. First, we will study transgenic mice in which TNF is constitutively expressed only by cardiac myocytes. These mice develop profound cardiac dysfunction, cardiomyopathy, myocarditis, and cardiac failure which mimics cardiac contractile dysfunction in humans. By breeding these transgenic animals to mice which have undergone targeted disruption of iNOS (inducible nitric oxide synthase), IRAK (IL-1 receptor associated kinase), and ICAM-1 / P-selectin, as well as by pharmacological inhibition of specific pathways, we will quantitatively determine the involvement of iNOS, IL-1, and transmigrated leukocytes in the pathogenesis of myocardial failure. Cardiac phenotype will be characterized primarily by in vitro Langendorff perfusion of isolated mouse hearts; confirmatory longitudinal analysis of function will be accomplished in vivo by ECG-gated MRI imaging. Physiologic findings will be correlated with survival, post-mortem histology, and the pattern of cardiac gene expression. Next, we will optimize the transgenic animal model by developing a binary transgene system which is cardiac specific, and regulatable by dietary tetracycline. Through this system, we will determine if the effects of TNF are related to dose and duration of expression. We will describe the cascade of secondary cytokines induced by TNF. We will also determine whether low-level, transient expression of TNF may be evolutionary adaptive, and serve a protective role against subsequent cardiac insults. By understanding the molecular mechanisms by which TNF impedes myocardial performance, it will be possible to develop specific, targeted therapeutic strategies for the treatment of sepsis, burn trauma, and other TNF-related cardiac conditions such as cardiomyopathy, myocarditis, and ischemic heart disease.