RHOA KINASES IN CARDIAC HYPERTROPHY

由血流动力学超负荷和/或结构性心脏病引发的心肌肥厚的机制仍不完全清楚。阐明心肌细胞如何将机械应激相关信号从膜转导到核转录，将有助于我们理解心肌肥厚的临床问题。RhoA是一种小分子GTP结合蛋白，是调控多种细胞功能的分子开关，是肥大信号的潜在介导者。我们假设RhoA在将拉伸依赖信号与体内心脏基因表达的诱导联系起来的诱导级联中起关键转导作用。此外，我们认为Ser/Thr激酶P160是介导RhoA肥大效应的主要信号分子，最近被发现是Rho1A的下游效应因子。我们的初步结果表明，RhoA和p160ROCK与β1整合素及其黏附依赖作用一起，是一条新的信号通路，通过p160ROCK依赖于SRF的磷酸化激活心肌细胞中依赖于SRF的基因，如骨骼α-肌动蛋白。我们还观察到，在超负荷的心脏中，p160ROCK mRNA的转录水平明显被诱导，这表明该分子在心肌肥厚的发展中起着重要的作用。我们的结果提示，160ROCK对SRF的磷酸化可能是心肌肥厚过程中激活胎儿心脏基因表达的关键步骤。该建议的具体目的是：1)确定RhoA、p160ROCK和SRF在介导拉伸诱导的心肌细胞肥大反应中的作用；2)确定RhoA信号通路是否通过160ROCK对SRF的磷酸化来调节依赖SRF的肥大基因的表达；3)在转基因小鼠模型中确定RhoA和p160ROCK在介导压力超负荷诱导的心肌肥大反应中的作用。总的目标是确定RhoA、β1整合素、p160ROCK和SRF是否是一个潜在的重要的新信号通路的主要介体，该信号通路有助于在牵张诱导的心肌肥厚中重新编程心肌细胞基因表达。

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.