Molecular Basis of Myocardin Function in the Heart

描述（由申请人提供）：转录共激活因子扩展基因组内编码的适应环境扰动和压力所需的信息。肌心素是一种非常有效的转录只表达在心脏和平滑肌细胞（SMC）。我们已经在小鼠中使用转基因和基因靶向策略来阐明调节心脏和血管发育的分子机制。初步研究表明：i）心肌素在心肌细胞和SMC中以精确的发育调节模式表达，ii）心肌素在胚胎干细胞中的强制表达激活与肥大基因程序相关的心脏限制性基因，iii）心肌素和MRTF-A激活重叠但不同的基因组，最重要的是iv）具有心肌素基因的心脏特异性条件性消融的小鼠表现出肥大性心肌病。这些研究共同提出了将在拟议的研究中检查的中心假设：myocardin通过前馈机制（包括与胎儿/肥大基因程序相关的基因激活）和调节细胞增殖的反馈机制作为心肌细胞生长和适应应激的中心调节因子发挥作用。该提案的总体目标是阐明心肌素在心脏中的作用，特别关注定义其在心肌细胞分化和心脏适应中的功能。具体目的是表征：1）心脏中由心肌素调节的SRF和MEF 2依赖性转录和形态发生程序，2）区分心肌素、MRTF-A和MRTF-B在心脏中的活性和特异性的机制，以及3）调节成人心脏中心肌素依赖性转录激活和对肥大刺激反应的分子机制。部署的实验策略强调在基因工程小鼠中翻译和验证分子和细胞数据。在基础水平上，这些研究将为调节心肌细胞分化和心脏形态发生发育的转录程序提供新的见解。这些研究也提供了对调节心脏适应压力的分子机制和心肌病发病机制的见解。公共卫生相关性：本申请将研究如何转录辅激活因子，心肌，调节心脏的分化状态和心脏的能力，以应对血流动力学的压力。我们已经产生了基因改变的小鼠与心脏限制性消融心肌素基因。对这些小鼠的分析将使我们能够确定myocardin是否控制心肌细胞的早期分化，以及当成年心脏受到压力时，它们在重新编程基因表达中的作用。这些研究将为心脏发育以及心力衰竭和心肌病的根本原因提供新的认识。

DESCRIPTION (provided by applicant): Transcriptional co-activators expand information encoded within the genome required for adaptation to environmental perturbation and stress. Myocardin is a remarkably potent transcriptional expressed exclusively in the heart and smooth muscle cells (SMCs). We have used transgenic and gene targeting strategies in mice to elucidate the molecular mechanisms that regulate heart and vascular development. Preliminary studies reveal that: i) myocardin is expressed in a precise developmentally regulated pattern in cardiomyocytes and SMCs, ii) forced expression of myocardin in embryonic stem cells activates cardiac-restricted genes associated with the hypertrophic gene program, iii) myocardin and MRTF-A activate overlapping, but distinct, sets of genes and most importantly iv) mice harboring a cardiac-specific conditional ablation of the myocardin gene exhibit hypertrophic cardiomyopathy. Together these studies suggest the central hypothesis that will be examined in the proposed studies: myocardin functions as a central regulator of cardiomyocyte growth and adaptation to stress via both feed-forward mechanisms, including activation of genes associated with the fetal /hypertrophic gene program, and feedback mechanisms regulating cell proliferation. The overall goal of this proposal is to elucidate the role of myocardin in the heart with particular focus on defining its function in cardiac myocyte differentiation and adaptation of the heart. The specific aims are to characterize: 1) the SRF- and MEF2-dependent transcriptional and morphogenetic programs regulated by myocardin in the heart, 2) mechanisms that distinguish activity and specificity of myocardin, MRTF-A and MRTF-B in the heart, and 3) molecular mechanisms modulating myocardin-dependent transcriptional activation in the adult heart and response to hypertrophic stimuli. The experimental strategy deployed emphasizes the translation and validation of molecular and cellular data in genetically engineered mice. At a basic level these studies will provide new insights into the transcriptional programs regulating cardiac myocyte differentiation and morphogenetic development of the heart. These studies also provide insights into the molecular mechanisms regulating adaptation of the heart to stress and the pathogenesis of cardiomyopathy. PUBLIC HEALTH RELEVANCE: This application will investigate how the transcriptional coactivator, Myocardin, regulates the differentiated state of the heart and the capacity of the heart to respond to hemodynamic stress. We have generated genetically altered mice with cardiac-restricted ablation of the Myocardin gene. Analysis of these mice will permit us to determine if myocardin controls the early differentiation of cardiac myocytes, as well as their role in re-programming gene expression in the adult heart when it is subjected to stress. These studies will provide new understanding into cardiac development as well as the underlying causes of heart failure and cardiomyopathy.