This proposal is focused on the molecular and cellular basis of congestive heart failure (CHF), particularly forms which are not due to causes such as valvular disease or myocardial infarction. Despite new approaches to treating CHF, the five-year mortality remains >50%, and the underlying mechanisms responsible for the syndrome, the causes of its progression, and a basis for developing new therapeutic agents are not well understood. Beta-adrenergic receptors (betaAR) play a major role in modulating cardiac inotropic and chronotropic responses to catecholamines, and a cardinal feature of CHF is depressed cardiac responsiveness to catecholamines, pointing towards dysfunctional cardiac Beta1AR or Beta2AR. This has been confirmed in specimens from cardiac biopsies or transplanted hearts using traditional pharmacologic approaches. However, the mechanisms responsible for this BetaAR dysfunction are not known. We have recently found naturally occurring mutations (polymorphisms) of the BetaARs, some of which impart distinct differences in agonist or antagonist binding affinities, coupling to G-proteins, activation of adenylyl cyclase, or agonist-mediated regulation, as compared to the """"""""wild type"""""""" receptor. This suggests a novel concept concerning the role of polymorphic forms of adrenergic receptors in cardiovascular disease. The long-term goals of this proposal are centered around determining whether Beta1AR or Beta2AR genetic variants play roles in the pathophysiology or clinical course of CHF.
For specific aim 1, a group of normal subjects and patients with early or late CHF will undergo analysis for Beta1AR and Beta2AR gene defects and then will be clinically followed for the duration of the five year period. This will allow us to determine whether mutations of these genes play a major role in the pathogenesis of heart failure or influence its clinical course.
For specific aim 2, receptor polymorphisms will be mimicked by site-directed mutagenesis, cloned into mammalian expression vectors, expressed in cells and the specific signal transduction defect, if any, imposed by these polymorphisms determined.
For specific aim 3, in order to correlate BetaAR gene defects with in vivo cardiac BetaAR function, CHF patients with selected BetaAR gene defects will be studied hemodynamically to determine the functional responsiveness of cardiac BetaAR to infused dobutamine.
In specific aim 4, the presence of genetic variants of the Beta1AR or Beta2AR in patients with CHF will be correlated with receptor expression and function in tissue obtained from left endomyocardial biopsies. The results of these endeavors may provide for new insights into the molecular basis of dysfunctional BetaAR in CHF and provide for novel therapeutic approaches.
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