Molecular Basis of Myocardin Function in the Heart

描述(由申请人提供)：转录共激活子扩展基因组中编码的信息，以适应环境扰动和压力。Myocardin是一种非常有效的转录因子，仅在心脏和平滑肌细胞(SMC)中表达。我们在小鼠身上使用转基因和基因打靶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)myocardin在心肌细胞和SMC中以精确的发育调控模式表达，ii)myocardin在胚胎干细胞中的强制表达激活了与肥大基因计划相关的心脏受限基因，iii)myocardin和MRTF-A激活了重叠但不同的几组基因，最重要的是iv)心脏特异的有条件去除myocardin基因的小鼠表现出肥厚性心肌病。总之，这些研究提出了将在拟议的研究中检验的中心假设：Myocardin作为心肌细胞生长和应激适应的中枢调节因子，通过两种前馈机制发挥作用，包括激活与胎儿/肥大基因计划相关的基因，以及调节细胞增殖的反馈机制。这项建议的总体目标是阐明肌钙蛋白在心脏中的作用，特别是确定其在心脏的心肌细胞分化和适应中的功能。其具体目标是：1)心脏中肌钙蛋白依赖和MEF2依赖的转录和形态发生程序，2)区分心肌钙蛋白、MRTF-A和MRTF-B在心脏中的活性和特异性的机制，以及3)调节成人心脏中肌钙蛋白依赖的转录激活和对肥大刺激的反应的分子机制。所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，这些研究将为调控心肌细胞分化和心脏形态发育的转录程序提供新的见解。这些研究还为调节心脏对应激适应的分子机制和心肌病的发病机制提供了见解。公共卫生相关性：这项应用将研究转录辅助激活因子Myocardin如何调节心脏的分化状态和心脏对血流动力学应激的反应能力。我们已经培育出心脏受限的Myocardin基因消融的转基因小鼠。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，以及它们在成年心脏受到压力时重新编程基因表达的作用。这些研究将对心脏发育以及心力衰竭和心肌病的潜在原因提供新的理解。

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.