The Role of Interleukin-18 in Myocardial Hypertrophy and Failure

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DESCRIPTION (provided by applicant): Myocardial hypertrophy and its transition to failure remains a significant cause of morbidity and mortality. Sustained production of inflammatory cytokines is a hallmark of all phases of this transition. In particular, interleukin (IL)-18 is upregulated in heart failure, which directly correlates with the severity of myocardial damage and dysfunction, and poor clinical outcome in heart failure. Our preliminary studies demonstrate that IL-18 induces cardiomyocyte hypertrophy and fibroblast migration and proliferation in vitro, suggesting potential pro-hypertrophic and pro-fibrotic roles for IL-18 in vivo. Our studies in wild-type mice show that pressure overload induced by transverse aortic constriction (TAC) leads to left ventricular hypertrophy (LVH) and increased IL-18 expression. Remarkably, this hypertrophy can be significantly reduced by IL-18 neutralizing antibodies. IL-18 knockout mice develop significantly less LVH in response to TAC; conversely, cardiac-specific overexpression of IL-18 induces LVH and heart failure in the absence of TAC. Rabbit models also exhibit LVH and increased IL-18 expression in response to TAC. Furthermore, our preliminary human studies clearly demonstrate the prognostic power of systemic IL-18 levels to predict cardiac failure. Thus, our central HYPOTHESIS is that IL-18 is a key mediator of LVH and failure that results in pathological remodeling through the induction of hypertrophy-associated kinases, fetal genes, growth factors, and matrix metalloproteinases. To address this HYPOTHESIS, we will investigate IL-18-dependent signaling in cardiomyocytes in vitro (Specific Aim 1), the molecular mechanisms involved in IL-18-mediated cardiac fibroblast migration and proliferation in vitro (Specific Aim 2), and the causal role of IL-18 in LVH, fibrosis and failure in vivo, using cardiac-restricted IL-18KO and cardiac-specific IL-18 transgenic mice (Specific Aim 3). Results obtained in mice will be validated in a rabbit model of pressure-overload hypertrophy and failure. Systemic IL-18 levels will be measured and correlated with the relative severity of cardiac hypertrophy and failure in humans. Collectively, these proposed studies will establish IL-18 as a potentially use therapeutic target to attenuate the progression of LVH to cardiac failure.