RGS PROTEIN FUNCTION IN CARDIAC PHYSIOLOGY

出生后的哺乳动物心肌细胞对机械应激、生长因子和激素作用以及代谢异常的反应是放大，但这些细胞无法增殖的原因尚不清楚。人类心肌肥大的临床后果非常显著，包括严重的心律失常、可导致肺水肿和液体超载的舒张性功能障碍以及充血性心力衰竭。细胞内信号转导通路在心肌肥厚的发生发展中起着重要作用。有几条证据支持G蛋白在心肌肥厚发展中的作用。最近发现G蛋白信号转导调节蛋白(RGS)是异源三聚体G蛋白的GTP酶激活蛋白(GAP)。在这个提案中，我们将概述实验，以检验RGS蛋白决定心肌细胞对细胞外刺激的反应性的假设，以及RGS基因的表达可以作为一种适应性机制来限制G蛋白介导的信号转导。我们将研究RGS家族成员在心肌肥厚和充血性心力衰竭动物模型中的表达模式。我们将确定RGS家族成员阻止心肌细胞信号转导和肥大生长的相对能力。我们将在转基因小鼠模型中确定RGS4是否在刺激刺激下抑制心肌肥厚。最后，我们将确定RGS2和RGS4的显性负性突变形式是否促进心肌细胞的信号转导和肥大生长。这些实验将有助于确定RGS蛋白在心肌肥大的病理生理学中的作用，并可能对这种疾病患者和肥厚进展为心力衰竭的患者的未来治疗产生影响。

Postnatal mammalian cardiomyocytes respond to mechanical stress, growth factor and hormonal action, and metabolic abnormalities by enlarging, but these cells are unable to proliferate for reasons that are not understood. The clinical consequences of human cardiac hypertrophy are very significant and include the development of serious cardiac arrhythmias, of diastolic dysfunction that can result in pulmonary edema and fluid overload, and of congestive heart failure. Intracellular signaling cascades play a major role in the development of cardiac hypertrophy. Several lines of evidence support the role of G proteins in the development of cardiac hypertrophy. RGS (regulator of G protein signaling) proteins were recently found to be GTPase activating proteins (GAPs) for heterotrimeric G proteins. In this proposal, we will outline experiments to test the hypothesis that RGS proteins determine the responsiveness of cardiomyocytes to extracellular stimuli, and that RGS gene expression can be increased as an adaptive mechanism to limit G- protein-mediated signal transduction. We will examine the expression pattern of RGS family members in animal models of cardiac hypertrophy and congestive heart failure. We will determine the relative ability of RGS family members to block cardiomyocyte signal transduction and hypertrophic growth. We will determine whether RGS4 inhibits cardiac hypertrophy in a transgenic mouse model in response to provocative stimuli. Finally, we will determine whether dominant negative mutant forms of RGS2 and RGS4 promote cardiomyocyte signal transduction and hypertrophic growth. These experiments will help to establish the role of RGS proteins in the pathophysiology of cardiac hypertrophy and may have an impact on future treatment of patients with this disorder and those in whom hypertrophy has progressed to heart failure.