The heart has the highest concentration of mitochondrial oxidative phosphorylation (OXPHOS) enzymes of any organ in the body. It has been proposed that in many forms of heart failure, the myocardial cells enter a chronic energy deficient state which ultimately leads to dysfunction and death. The cardiac myocytes respond to this low energy state, by induction of a number of fetal contractile and energy system isoforms which presumably are more optimal for reduced mitochondrial energy production. We have cloned and sequenced the human mitochondrial ATP synthase beta subunit (ATPsyn beta) and heart-skeletal muscle adenine nucleotide translocator (ANT1) genes. Both are expressed at very high levels in heart and skeletal muscle, but in other tissues ATPsyn beta is expressed at low levels and the ANT1 is replaced by two other isoforms, ANT2 and ANT3. With these genes we will explore the energy deficiency hypothesis of heart failure by: (1) defining the molecular basis for the high ex- pression of OXPHOS genes in heart and muscle, (2) determining the changes that occur in OXPHOS gene expression in the failing heart and (3) demonstrating that direct genetic and biochemical inhibition of heart OXPHOS can cause cardiomyopathy. To define the molecular basis of heart-muscle expression of OXPHOS genes, we have prepared promoter-reporter gene constructs for both genes and have identified a shared heart-muscle control element, the OXBOX. Other muscle-specific elements are being mapped and the associated trans-acting factors sought. To identify energetic changes associated with failing hearts, we will examine the expression of these genes in both spontaneous and hereditary forms of heart disease for alteration in ANT isoform expression, changes in mRNA levels and variation in implicated transcription factors. To demonstrate that OXPHOS defects can cause heart failure, we will screen idiopathic cardiomyopathy hearts for possible mtDNA deletions, and determine if the ANT autoantibodies which are associated with myocarditis and dilated cardiomyopathy are specific for ANT1 and capable of perturbing cardiac myocyte energy metabolism and of inducing cardiomyopathy.
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