Dietary copper restriction causes cardiac hypertrophy, ultimately leading to heart failure. A proposed mechanism for this cardiomyopathy is the accumulation of reactive oxygen species. Using a cardiac-specific metallothionein (MT)- overexpressing transgenic mouse model, we have observed that elevation of this potent antioxidant in the heart suppresses the progression of heart hypertrophy and likely results in the retarded development of heart failure induced by dietary copper restriction. This observation suggests that oxidative stress may play a crucial role in the pathogenesis of heart failure. We therefore propose to test the hypothesis that oxidative stress triggers the transition from heart hypertrophy to failure induced by copper deficiency. We will use the cardiac-specific MT- overexpressing transgenic mouse model to carry out the following specific aims: (1) To define the role of oxidative stress in the transition from heart hypertrophy to failure, a detailed time- course study of the development of heart failure by dietary copper restriction will be performed. In particular, this study will focus on defining the cause-and-effect relationship between oxidative stress and dynamic changes in cardiomyopathy, cardiac dysfunction and heart failure. (2) To determine cellular events involved in the transition from heart hypertrophy to failure, the significance of cell death in the pathogenesis will be defined by immuno-gold TUNEL and electron microscopy in combination with a novel procedure using cardiac alpha-sarcomeric actin antibody to label necrotic cells. The relative contributions of apoptosis and necrosis to the total cell loss will be analyzed. (3) To investigate signaling pathways leading to myocardial cell death during the transition from heart hypertrophy to failure, oxidative stress-induced mitochondrial cytochrome c release and activation of caspase-9 and -3 will be examined by immunohistochemical method, enzymatic assay and Western blot analysis. The consequence of caspase inhibition will be analyzed in order to dissect major pathways leading to cell death. (4) To examine the role of atrial natriuretic peptide (ANP) and tumor necrosis factor-alpha (TNF-alpha) in the late phase transition from heart hypertrophy to failure, dynamic changes in ANP and TNF-alpha production will be studied. Molecular mechanisms of up-regulation of these cytokines will be analyzed through examining the activation of transcription factors NF-kappaB and AP-1. (5) To explore possible mechanisms by which MT inhibits oxidative stress-mediated myocardial cell death induced by dietary copper deficiency, the effect of MT on oxidative stress- mediated mitochondrial membrane changes that lead to cytochrome c release will be examined. The overall goal of this study is to define the role of oxidative stress in copper deficiency-induced pathogenesis of heart failure. This study will give critical insights into the signaling pathways and molecular mechanisms of failure induced by copper deficiency. Importantly, the data obtained will provide valuable information for novel experimental as well as clinical approaches for possible interventions of the transition from heart hypertrophy to heart failure.
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