CARDIOCYTE RESPONSES TO HYPOXIA

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DESCRIPTION (adapted from the applicant's abstract): The long term goals of this application are to define molecular genetic responses of heart cells to redox stress, analyze DNA regulatory elements that mediate these responses, and define a new approach to express foreign genes in ischemic myocardium. Myocardial ischemia imposes two primary forms of redox stress on cardiac myocytes: 1) a hypoxic component determined by the severity of the ischemia, and 2) hyperoxic stress caused by reoxygenation. Both forms of stress trigger a complex series of reactions. At least two molecular genetic responses to hypoxia can be distinguished: a rapid, immediate early response (minutes to hours) and a late response that occurs over several days. Induction of proto-oncogenes is part of the early response, and induction of glycolytic enzyme genes, skeletal a-actin, and endothelin (ET-1) are examples of late hypoxia response genes. Neither the oxygen sensing mechanism nor the second messengers that relay the redox signals are known. The response to oxidative stress is obligatorily rapid since reactive oxygen intermediates are highly reactive and immediately oxidize cellular proteins and lipids without diffusing far from their sites of generation. Studies are proposed to investigate redox regulation of specific genes in cardiac myocytes and vascular endothelial cells. The impact of severe redox stress on zinc finger transcription factors will be characterized. Molecular analyses of glycolytic enzymes and ET-1 genes are proposed to identify hypoxia responsible elements (HREs) and the proteins that bind them. Finally, studies are proposed to investigate the in vivo expression of reporter genes linked to HREs. DNA will be delivered into the heart by direct injection, the heart will be subjected to ischemia, and the reporter expression will be compared with that from constructs without HREs.