Activation of Ca2+/calmodulin (CaM) dependent kinase II (CaMKII) in heart failure (HF) contributes to cardiomyocyte apoptosis, early-after depolarization-induced arrhythmias, and maladaptive remodeling. In heart, most activated CaMKII is associated with the sarcolemma and we have shown that CaMKII is bound to the pore-forming 11C subunit of CaV1.2 (L-type) Ca2+ channels, where it functions as a dedicated integrator of Ca2+ signals. CaMKII also is a CaV1.2 Ca2+ channel-dependent and PKA-independent downstream effector of 2-adrenergic stimulation, thus placing CaMKII at the convergence of the two major signaling pathways affected in HF: hyperadrenergic stimulation and Ca2+ dysregulation. Based upon recent structural information and our new biochemical data, we propose a novel model for the interaction between CaMKII and 11C that offers insight into its function and regulation and provides a basis for understanding how CaMKII activity could be perturbed in HF. The objective of this proposal is to identify and test the molecular details underlying this interaction, and determine how this regulation is altered in HF. We propose three specific aims.
In Aim 1, we will test the hypothesis that CaMKII regulation of, and interaction with, CaV1.2 Ca2+ channels involves mimicry of the CaMKII autoinhibitory peptide (AIP). A variety of complex biochemical and biophysical techniques will be employed to test this novel mimicry model in which we propose that CaMKII interacts with pseudo-AIP domains in the 11C N and/or C termini and that, CaMs or CaM-like Ca2+-binding proteins bound to these 11C domains serve as the Ca2+-sensors that regulate CaMKII and fine-tune the regulation. Building upon those findings, in Aim 2 we will test the hypothesis that CaMKII sits at the convergence of two major signaling pathways perturbed in HF, 2-adrenergic activation and intracellular Ca2+ signaling, by nature of its tethered interaction with CaV1.2 Ca2+ in cardiomyocytes. Using novel strategies to generate functional """"""""knock-ins"""""""" of CaV1.2 subunits in cultured myocytes, we will test the consequences of perturbing the quaternary structure of CaMKII, CaV1.2, CaM and/or other Ca2+-binding proteins upon the bidirectional regulation of CaMKII and CaV1.2 and upon the PKA-dependent 2-adrenergic regulation of CaMKII signaling. These data will then allow us to apply our model in Aim 3 to test the hypothesis that HF perturbs the bidirectional regulation inherent in the CaMKII/CaV1.2 tethered interaction. We will employ several mouse models of HF which result from high """"""""throughput"""""""" through 2-adrenergic signaling pathways. We hypothesize that HF alters the tethering between CaMKII and CaV1.2 Ca2+ channels resulting in mislocalized and dysregulated CaMKII activity, therefore promoting the pathophysiological consequences associated with HF. Not only will this work will lead to a better understanding of cardiac physiology, but it will provide new insights into arrhythmogenesis and impaired cardiac function during HF.
Statement Heart failure affects about 500, 000 Americans annually and is a leading cause of morbidity and mortality. The molecular mechanisms underlying heart failure and the consequences that lead to an increased risk of sudden cardiac death are not well understood. Recently, activation of Ca2+/calmodulin (CaM) dependent kinase II (CaMKII) in heart failure has been shown to contribute to cardiomyocyte apoptosis, early-after depolarization-induced arrhythmias, and maladaptive remodeling, at least in part to an unexpected stimulation by the 2-adrenergic signaling system. We have recently shown that normal CaMKII activity results from tethering of CaMKII to the L-type (CaV1.2) Ca2+ channel. Here we test a novel model for CaMKII tethering to CaV1.2 channels and propose that HF alters this dynamic to lead to abnormal CaMKII activation. ? ? ?
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