RGS Protein Function in Cardiac Physiology

描述（由申请人提供）：人类心脏肥大通常与预后不良相关。在培养的大鼠心肌细胞中，配体如苯肾上腺素、内皮素-1、血管紧张素II和前列腺素F2 α促进肥大反应。有证据表明，这些配体对培养细胞的作用类似于人类的心脏肥大。引起培养的心肌细胞肥大的大多数激动剂通过异源三聚体G蛋白发出信号。G蛋白信号调节蛋白（Regulator of G protein signaling，RGS）是一种G蛋白三聚体活化蛋白（GT3 activating proteins，GAP），可使异源三聚体G蛋白亚基失活。本研究的主要目的是探讨RGS蛋白在心脏肥大生长过程中的生理作用。中心假设是RGS蛋白决定心肌细胞对细胞外刺激的反应性，并且RGS基因表达增加作为限制G蛋白介导的信号转导的适应性机制。在最初的资助期间，我们证明了RGS蛋白存在于心脏中，RGS3和RGS4基因表达对外部刺激有反应，小鼠中RGS4的心脏特异性过表达阻断了压力超负荷和运动诱导的心脏肥大，并且RGS4是体内心脏中Gq的GAP。尽管有这些发现，RGS蛋白在心脏病中的作用仍存在许多问题。在该项目的下一阶段，我们建议通过在培养细胞中使用"敲低"策略来研究RGS2、RGS3和RGS4在心肌细胞肥大中的特定作用。其次，我们研究了RGS4在压力超负荷和运动诱导的心脏肥大中的具体作用，通过使用具有全身和心脏特异性靶向破坏该基因的小鼠。第三，我们研究了RGS3在压力超负荷和运动诱导的心脏肥大中的具体作用，通过使用全身靶向破坏该基因的小鼠。这些实验将有助于确定RGS蛋白在心肌肥厚和收缩功能障碍的发病机制中的作用，并可能为开发新的治疗药物提供重要信息。

DESCRIPTION (provided by applicant): Cardiac hypertrophy in humans is frequently associated with a poor prognosis. In cultured rat cardiac myocytes, ligands such as phenylephrine, endothelin-1, angiotensin II, and prostaglandin F2alpha promote a hypertrophic response. There is evidence that the action of these ligands on cultured cells mimics cardiac hypertrophy in humans. Most agonists that cause cultured cardiomyocytes to hypertrophy signal via heterotrimeric G proteins. Regulator of G protein signaling (RGS) proteins are GTPase activating proteins (GAPs) that deactivate asubunits of heterotrimeric G proteins. The main aim of this proposal is to investigate the physiologic role of RGS proteins in the regulation of cardiac hypertrophic growth program. The central hypothesis is that RGS proteins determine the responsiveness of cardiac myocytes to extracellular stimuli, and that RGS gene expression is increased as an adaptive mechanism to limit Gprotein- mediated signal transduction. In the original funding period, we demonstrated that RGS proteins are present in heart, that RGS3 and RGS4 gene expression is responsive to external stimuli, that cardiacspecific overexpression of RGS4 in mice blocks pressure overload- and exercise-induced cardiac hypertrophy, and that RGS4 is a GAP for Gq in the in vivo heart. Despite these findings, many questions remain about the role of RGS proteins in heart disease. In the next phase of this project, we propose to investigate the specific role of RGS2, RGS3, and RGS4, in cardiac myocyte hypertrophy by use of a "knock-down" strategy in cultured cells. Second, we investigate the specific role of RGS4 in pressure overload- and exercise-induced cardiac hypertrophy by use of mice with both whole-body and cardiacspecific targeted disruption of this gene. Third, we investigate the specific role of RGS3 in pressure overload- and exercise-induced cardiac hypertrophy by use of mice with whole-body targeted disruption of this gene. These experiments will help define the role of RGS proteins in the pathogenesis of cardiac hypertrophy and contractile dysfunction and may provide important information for the development of novel therapeutic agents.