Adrenal GRKs and Adrenergic Signaling in Heart Failure

Thomas Jefferson University, Philadelphia PA

Investigators

Linked publications & trials

Abstract

DESCRIPTION (provided by applicant): Heart failure (HF) represents a significant health problem and one of its salient features is elevated Sympathetic Nervous System (SNS) activity and outflow, reflected by enhanced levels of circulating catecholamines in HF subjects, a significant aggravating factor for the disease. Epinephrine secretion from the adrenal medulla, along with Central norepinephrine release, represent the major catecholamines for SNS outflow and regulate a variety of key physiological events including the chronotropy and inotropy of the heart. Various G protein-coupled receptors (GPCRs) have been shown to regulate adrenal catecholamine release, some enhancing it (e.g. p-adrenergic receptors (pARs), while others inhibit it, most importantly a2ARs. Regulation of these receptors in the adrenal medulla and, specifically in chromaffin cells remains largely unknown, especially in HF. GPCR kinases (GRKs) play a prominent role in GPCR regulation in the heart during HF but their role in adrenal AR regulation is also un-studied. Since SNS activity is elevated in HF, increased adrenal catecholamine secretion would be expected to down-regulate GPCRs in the adrenal gland such as inhibitory a2ARs via the actions of GRKs. Thus, research focusing on GRK-mediated regulation of receptors that control adrenal secretion could reveal important mechanisms of enhanced catecholamine release and SNS activity in HF, and consequently produce novel therapeutic targets and molecular, diagnostic biomarkers of SNS activity in HF. Indeed, novel preliminary data from us show enhanced expression and activity of GRK2 in adrenal glands of multiple models of HF resulting in significant <x2AR dysregulation. In this proposal, we will test our Central Hypothesis that GRK levels and activity in the adrenal gland are altered in HF, which results in significant dysregulation of AR signaling, including uncoupling and receptor down-regulation leading to increased catecholamine secretion in HF contributing significantly to the pathology. Further, adrenal GRKs, in particular GRK2, appear to play a critical role in the regulation of circulating catecholamine levels in HF making them a novel therapeutic target. Our Specific Aims are: (1) To characterize the state of adrenergic signaling and GRK-mediated regulation in the release of catecholamines from the adrenal gland and chromaffin cells in HF;(2) To utilize AR knockout mouse models to determine the mechanistic role of altered adrenergic signaling in adrenal function and catecholamine release in HF;(3) To determine the requirement and mechanistic role of GRK2 in altered adrenergic signaling and function in the adrenal gland during HF using conditional GRK2 knockout mice;(4) To test gene therapy approaches to lower GRK2 activity in the adrenal gland of HF animals to determine if this will restore adrenal cell function and SNS outflow and improve cardiac function in the failing heart.