Increased adrenergic activation provides an important means of increasing cardiac function in the normal heart. However when ventricular function has substantially deteriorated, the effects of sustained adrenergic drive may no longer be desirable. Thus, adrenergic activation serves as an important compensatory mechanism for decreased cardiac function, but ultimately this mechanism exacerbates the problem and may contribute to morbidity and mortality. Our purpose will be to explore the molecular pathogenesis of abnormal adrenergic responsiveness in the hart and in cardiac myocytes during the development of congestive heart failure (CHF). We will use several complementary approaches - assessment of signal transduction mechanisms in an animal model of dilated cardiomyopathy and in isolated myocytes, as well as generation of transgenic mice. We will focus on betaAR signalling and on the molecular mechanism for alterations in signal transduction. We will evaluate the physiological impact of these changes in conscious animals by sequential hemodynamic and ventricular functional assessments. A strength of our laboratories is that we are able to wed physiological and molecular studies of adrenergic function in the heart. Substantial work has been performed regarding changes in beta-adrenergic receptor-mediated signalling in the failing heart, and thus we will focus upon three key areas that have received little attention but that are likely to provide important new mechanistic information; 1) precise assessment of alterations in the quantify and function of the catalytic subunit of adenylyl cyclase (C), and molecular mechanisms for changes in this protein associated with CHF; 2) the molecular pathogenesis and physiological impact of altered levels of beta-adrenergic receptor kinase (betaARK) on adrenergic signalling in the failing heart; and 3) the pathogenesis of decreased cardiac Gsalpha, the alpha subunit of the stimulatory guanine nucleotide regulatory protein, and the role of the intracellular redistribution of cardiac Gsalpha in CHF. We hypothesize that exposure of cardiac myocytes to increased levels of catecholamines in CHF will lead to specific alteration in C, betaARK and Gsalpha. Specific hypotheses regarding each of these are; 1. In CHF the amount and function of one or more isoforms of C, most likely types V and VI, will be decreased. 2. In CHF the amount and function of beta- adrenergic receptor kinase (betaARK) will be increased, thereby promoting the uncoupling of receptors from Gsalpha. 3. In CHF the distribution of Gsalpha will be altered so that less is found in the sarcolemma and a greater portion is found in intracellular compartments, thereby decreasing the likelihood that remaining cell surface receptors activate adenylyl cyclase. Complementary studies on human tissue from failing and control hearts will examine content of the catalytic subunit of adenylyl cyclase, quantity betaARK levels and cellular Gs content and its compartmentation. These investigation should provide new information regarding the molecular pathogenesis for altered myocardial adrenergic signalling in heart failure. Data from these studies, we hope, will provide fundamental information leading to new therapeutic strategies for patients with congestive heart failure.
Showing the most recent 10 out of 74 publications
