ROLE OF IGF-I IN PREVENTING CARDIOMYOCYTE APOPTOSIS

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The primary purpose of this Mentored Clinical Scientist Development Award is to prepare the applicant for a career as an independent investigator in cardiac research. To build on his previous training in biochemistry an experience in studying inflammatory mediators, the applicant proposes to acquire additional skills in molecular biology and somatic gene transfer in the context of the current proposed study. Cardiomyocyte apoptosis has been documented in many clinically important conditions including ischemic heart disease and heart failure. Insulin-like growth factor-I (IGF-I) has beneficial effects on both cardiomyocyte function and survival. However, the intracellular mechanisms controlling cardiomyocyte apoptosis and the antiapoptotic effect of IGF-I in cardiac ischemia-reperfusion injury remain largely unexplored. Binding of IGF-I to its receptor (IGF-IR) initiates two intracellular signaling pathways: 1) phosphorylation of insulin receptor substrate (IRS)-I with activation of phosphatidylinositol (PI) 3-kinase and subsequent activation of Akt, a serine-threonine kinase, and 2) the Ras/MAP (mitogen-activated protein) kinase pathway. In many systems, activation of PI 3-kinase is critical for the anti-apoptotic effect of IGF-I. This proposal is based on four hypotheses: 1) that cardiac apoptosis plays an important role in ischemia-reperfusion (IR)-induced cardiac injury; 2) that cardiac apoptosis induced by IR is mediated through specific intracellular signaling pathways involving caspases; and 3) that through somatic gene transfer. IGF-I can be overexpressed locally in myocardium at high level and function as a "paracrine" mediator protecting the surrounding cardiomyocytes against IR injury, and 4) that the beneficial effects of IGF-I in IR-induced injury are mediated through activation of PI-3 kinase and Akt with subsequent inhibition of caspase- dependent apoptosis. To test these hypotheses we will use adenoviral vectors to express human IGF-I, CrmA, and Akt. In Specific Aim 1, we will develop and characterize the necessary vectors. In Specific Aim 2, we will explore the molecular mechanisms of the anti-apoptotic effect of IGF-I by examining the functional consequences of viral expression of human IGF-I, alone and in combination with other constructs, on cardiomyocyte apoptosis and functions. In Specific Aim 3, we will study the protective effect of viral expression of IGF-I in vivo and explore the underlying mechanisms in cardiac apoptosis in the rat model of IR- induced injury. Understanding the role of specific intracellular molecules such as caspases in the molecular pathogenesis of cardiac injury and defining the underlying mechanisms involved in the beneficial effect of IGF-I through somatic gene transfer may provide novel therapeutic approaches for the management of many clinically important disorders.