Sustained beta1-adrenergic stimulation modulates cardiac contractility by Ca2+/calmodulin kinase signaling pathway.

Wang Wang,Shiqiang Wang,Michael T Crow,Heping Cheng,Rui-Ping Xiao,Weizhong Zhu,Dongmei Yang

doi:10.1161/01.res.0000145361.50017.aa

Wang Wang, Shiqiang Wang + Show 5 more

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https://doi.org/10.1161/01.res.0000145361.50017.aa

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Abstract

A tenet of beta1-adrenergic receptor (beta1AR) signaling is that stimulation of the receptor activates the adenylate cyclase-cAMP-protein kinase A (PKA) pathway, resulting in positive inotropic and relaxant effects in the heart. However, recent studies have suggested the involvement of Ca2+/calmodulin-dependent protein kinase II (CaMKII) in beta1AR-stimulated cardiac apoptosis. In this study, we determined roles of CaMKII and PKA in sustained versus short-term beta1AR modulation of excitation-contraction (E-C) coupling in cardiac myocytes. Short-term (10-minute) and sustained (24-hour) beta1AR stimulation with norepinephrine similarly enhanced cell contraction and Ca2+ transients, in contrast to anticipated receptor desensitization. More importantly, the sustained responses were largely PKA-independent, and were sensitive to specific CaMKII inhibitors or adenoviral expression of a dominant-negative CaMKII mutant. Biochemical assays revealed that a progressive and persistent CaMKII activation was associated with a rapid desensitization of the cAMP/PKA signaling. Concomitantly, phosphorylation of phospholamban, an SR Ca2+ cycling regulatory protein, was shifted from its PKA site (16Ser) to CaMKII site (17Thr). Thus, beta1AR stimulation activates dual signaling pathways mediated by cAMP/PKA and CaMKII, the former undergoing desensitization and the latter exhibiting sensitization. This finding may bear important etiological and therapeutical ramifications in understanding beta1AR signaling in chronic heart failure.

Highlights

A tenet of ␤1-adrenergic receptor (␤1AR) signaling is that stimulation of the receptor activates the adenylate cyclase-cAMP-protein kinase A (PKA) pathway, resulting in positive inotropic and relaxant effects in the heart
We have systematically examined the signaling mechanisms underlying cardiac contractile modulation by short-term and sustained ␤1AR stimulation (24 hours), using myocyte culture combined with genetic manipulation, confocal imaging, and biochemical measurements
In contrast to the anticipated receptor desensitization,[5,6,7,27] we demonstrated that shortterm and sustained ␤1AR stimulation enhance Ca2ϩ transients and contraction and accelerate relaxation (Figures 1 and 3)

Summary

Introduction

A tenet of ␤1-adrenergic receptor (␤1AR) signaling is that stimulation of the receptor activates the adenylate cyclase-cAMP-protein kinase A (PKA) pathway, resulting in positive inotropic and relaxant effects in the heart. A s a prototypical member of G protein– coupled receptor (GPCR) superfamily, ␤-adrenergic receptor (␤AR) plays a central role in sympathetic regulation of cardiac function.[1,2] Stimulation of ␤AR by catecholamines induces robust chronotropic, inotropic, and relaxant effects via the Gs-adenylate cyclase-cAMP-protein kinase A (PKA) pathway.[3,4] This signaling pathway is thought to be responsible for other functions of ␤AR, such as regulation of metabolism, gene expression, cell growth, and apoptosis.[2] sustained ␤AR activation under pathological conditions such as hypertension and congestive heart failure will result in downregulation and desensitization of ␤AR attributable to the negative feedback of this pathway.[5,6,7]. Its regulator, phospholamban (PLB), ryanodine receptor (RyR) Ca2ϩ release channels, and sarcolemmal L-type Ca2ϩ channels (LCC).[18,19,20,21,22] the involvement of CaMKII in ␤1AR modulation of myocardial contractility remains obscure

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