Developmental Programming of Ischemic-Sensitive Phenotype in the Heart

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DESCRIPTION (provided by applicant): Heart disease is the leading cause of death in the United States, with ischemic heart disease a major cause of morbidity and mortality. Yet the molecular mechanisms remain largely elusive. In addition to other risk factors, large epidemiological and animal studies have shown a clear association of fetal stress during the development with increased risk of ischemic heart disease in adulthood. Glucocorticoids play a center role in the response to stress. Our recent studies demonstrated that maternal/fetal hypoxia resulted in a decrease in glucocorticoid receptor (GR) mRNA and protein abundance in fetal hearts that persisted in adult offspring, suggesting in utero epigenetic programming of GR gene repression in the developing heart. The pathophysiological significance of decreased GR expression levels in the heart is highlighted by the findings that demonstrate cardioprotective effects of glucocorticoids in the acute setting of myocardial ischemia and reperfusion injury both in humans and in animals. Our preliminary studies suggested that hypoxia increased GR gene promoter methylation in fetal hearts. DNA methylation is a chief mechanism in epigenetic modification of gene expression patterns. Although methylation of the GR promoter has been reported to occur as function of physiological regulation of the hypothalamic- pituitary-adrenal axis, little is known about the epigenetic regulation of GR gene expression patterns in the developing heart and its functional consequences. The proposed studies will address these major gaps in our knowledge and test the hypothesis that epigenetic repression of glucocorticoid receptor gene in the developing heart results in developmental programming of ischemic-sensitive phenotype in the heart. Three specific aims are proposed to determine whether: 1) maternal/fetal hypoxia during gestation increases the promoter methylation resulting in GR gene repression in the developing heart, 2) hypoxia has direct causal effects leading to heightened GR promoter methylation and gene repression, and 3) hypoxia-mediated GR gene repression in the developing heart contributes to developmental programming of ischemic-sensitive phenotype in the heart. The overall impact of the proposed studies is that the findings will not only significantly advance our knowledge of molecular mechanisms underlying fetal stress-induced programming of ischemic-sensitive phenotype in the heart and hence improve our understanding of pathophysiology of ischemic heart disease, but they will also provide important original insights into epigenetic mechanisms regulating GR gene expression patterns in a broad field of developmental programming of health and disease, given that glucocorticoids play a common and center role in the stress response.