Heart disease is the leading cause of death in the USA. ?-adrenergic receptor (?-AR) stimulation is the primary mechanism to increase cardiac contractility. However chronic sympathetic stimulation, as occurs in heart failure (HF), results in receptor desensitization and reduced contractility. ?-AR stimulation signals through PKA-dependent phosphorylation in part by PKA binding to A-kinase anchoring proteins (AKAPs) to influence Ca2+ homeostasis. AKAPs are targeted to specific intracellular locations resulting in localization of PKA with its substrates. Thus agents that modify PKA signaling would be expected to mediate an enhanced inotropic response. Based on observations in myocytes that (a) adenoviral (Ad) mediated Ht31 expression, a competing regulatory PKA subunit (Rll) binding peptide, disrupted PKA anchoring to AKAPs which increased the contractile response to ?-AR stimulation and this (b) surprisingly occurred in the absence of increased Ca2+ transients. We are eager to test the central hypothesis of this project that disruption of PKA binding to AKAPs in hearts in vivo, enhances the contractile response to ?-AR stimulation in normal hearts and rescues the impaired contractile response a model of HF. I propose that this increased inotropic response is mediated in part by increasing myofilament Ca2+ sensitivity. Our goal is to understand AKAP function and the signal transduction of this multi-component regulator of PKA signaling in health and in cardiovascular disease. By using Ad-mediated Ht31 peptide expression via in vivo gene transfer of rat hearts to disrupt PKA/AKAP interactions, we will evaluate whether cardiac contractility and myocardial remodeling are increased in both normal and failing rat hearts (Aim 1);and whether the events mediating altered contractility results from decreased PKA-dependent phosphorylation leading to increased myofilament Ca2+ sensitivity (Aim 2). By using gravin (AKAP12) knockout mice to specifically target and disrupt PKA localization to the ?2- AR, we will determine whether cardiac function in vivo, is increased by blocking AKAP12 regulated receptor desensitization, similar to that observed with ?ARKct's ability to restore cardiac function in HF (Aim 3);and whether increased cardiac function following ?-AR stimulation is mediated by increased ?2-AR dependent mediated signaling, using hearts and myocytes from these mice (Aim 4). Achievement of our aims, should not only improve our understanding of the function and signal transduction for this central regulator of PKA signaling, but may potentially represent a novel therapeutic target for inotropic therapy for patients with HF.
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