RHOA KINASES IN CARDIAC HYPERTROPHY

由血流动力学超载和/或结构性心脏病引发的心脏肥大的机制尚不完全清楚。描述心肌细胞如何将机械应力相关的信号从膜传递到核转录将极大地有助于我们理解心脏肥厚的临床问题。RhoA是一种小分子量GTP结合蛋白，作为控制各种细胞功能的分子开关，是肥厚信号的潜在介质。我们假设RhoA在连接拉伸依赖信号与体内心脏基因表达诱导的诱导级联反应中起关键换能器的作用。此外，我们提出Ser/Thr激酶P160rock是Rho1A的下游效应因子，是介导RhoA肥厚效应的主要信号分子。我们的初步结果表明，RhoA和p160ROCK，连同β 1整合素及其粘附依赖作用，作为一种新的信号通路，通过p160ROCK依赖的SRF磷酸化，激活心肌细胞中心肌富集血清反应因子（SRF）依赖基因，如骨骼α -肌动蛋白。我们还观察到p160ROCK mRNA转录本的水平在负荷过重的心脏中被显著诱导，这表明该分子在心脏肥厚的发生中起着重要作用。我们的研究结果表明，160ROCK对SRF的磷酸化可能是心肌肥厚期间胎儿心脏基因表达激活的关键步骤。本研究的具体目的是：1)确定RhoA、p160ROCK和SRF在介导拉伸诱导的心肌细胞肥厚反应中的作用；2)确定RhoA信号通路是否通过160ROCK磷酸化SRF调控SRF依赖性肥大基因的表达；3)确定RhoA和p160ROCK在基因操纵小鼠模型中介导压力过载诱导的心脏肥厚反应中的作用。总体目标是确定RhoA、β 1整合素、p160ROCK和SRF是否是拉伸性心肌肥大中心肌细胞基因表达重编程的潜在重要新信号通路的主要介质。

The mechanisms directing cardiac hypertrophy, triggered by hemodynamic overload and/or structural heart disease, are still not completely understood. Delineating how cardiac myocytes transduce mechanical stress related signaling from the membrane to nuclear transcription will greatly contribute to our understanding of the clinical problems of cardiac hypertrophy. RhoA, a small molecular weight GTP- binding protein, acts as a molecular switch that controls various cell functions, and is a potential mediator of hypertrophic signals. We hypothesize that RhoA functions as a key transducer in the induction cascade that links stretch dependent signaling to the induction of cardiac gene expression in vivo. In addition, we propose that the Ser/Thr kinase P160rock, recently identified as a downstream effector of Rho1A, is the primary signaling molecule mediating hypertrophic effects of RhoA. Our preliminary results indicate that RhoA and p160ROCK, together with beta1 integrin and its adhesion dependent actions, serve as a novel signal pathway in activating the cardiac enriched serum response factor (SRF) dependent genes in cardiomyocytes, such as skeletal alpha-actin, through the p160ROCK dependent phosphorylation of SRF. We have also observed that the level of p160ROCK mRNA transcripts is markedly induced in the overloaded heart, suggesting an important role for this molecule in the development of cardiac hypertrophy. Our results suggest that phosphorylation of SRF by 160ROCK might be a critical step for the activation of fetal cardiac gene expression during cardiac hypertrophy. The Specific Aims of this proposal are: 1) to determine the role of RhoA, p160ROCK and SRF in mediating hypertrophic responses induced by stretch in cultured cardiomyocytes; 2) to determine if the RhoA signaling pathways regulates SRF-dependent hypertrophic gene expression via phosphorylation of SRF by 160ROCK; 3) to determine the role of RhoA and p160ROCK in mediating cardiac hypertrophic responses induced by pressure overload in genetically manipulated mouse models. The overall objective is to determine if RhoA, beta1 integrin, p160ROCK and SRF are primary mediators of a potentially important novel signal pathway that contributes to reprogramming of cardiomyocyte gene expression in stretch induced cardiac hypertrophy.