MYOCARDIN AND VASCULAR SMOOTH MUSCLE

特定血管内的平滑肌细胞和周细胞的不同模式最终定义和区分了动脉、静脉和毛细血管的功能特性。SMC的表型和模式又是由转录程序决定的，转录程序对发育和环境信号和提示做出反应。我们已经使用转基因和基因打靶策略来阐明调控血管SMC分化的转录程序。我们的团队和其他人最近报道了SAP结构域转录因子myocardin在SMC分化中发挥关键作用。初步研究表明：i)在血管和内脏的SMC中，myocardin以精确的发育调节模式表达，ii)myocardin的强迫表达 在非SMC中激活多个SMC特异性转录调控元件，iii)强制表达myocardin激活未分化胚胎干细胞(ES)中SMC限制性基因，以及iv)在SMC中表达同源负性myocardin突变体蛋白或myocardin siRNA抑制SMC特异性SM22a启动子的活性。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在调节SMC分化和表型的SRF依赖的转录程序中发挥关键作用。本课题的主要任务是阐明肌钙蛋白诱导SMC分化的分子基础。其具体目的是：1)检测肌钙蛋白在SMC胚胎发育过程中的细胞自主功能，以及在维持SMC表型的过程中；2)检测调控SMC分化的依赖于myocardin-SRF的转录程序的活性和特异性的分子机制；3)建立和鉴定含有myocardin基因零突变和条件性突变的小鼠。在基础水平上，这些研究将为调控SMC分化和SMC表型调控的转录程序提供新的见解。因此，这些研究对于了解动脉粥样硬化和其他血管增生性综合征的发病机制是相关的。

The differential patterning of smooth muscle cells (SMCs) and pericytes within specific blood vessels ultimately defines and distinguishes the functional properties of the arteries, veins and capillaries. SMC phenotype and patterning, in turn, are determined via transcriptional programs that respond to developmental and environmental signals and cues. We have used transgenic and gene targeting strategies to elucidate the transcriptional programs that regulate vascular SMC differentiation. Our group and others have reported recently that the SAP domain transcription factor, myocardin, plays a critical role in SMC differentiation. Preliminary studies presented herein demonstrate that: i) myocardin is expressed in a precise developmentally regulated pattern in vascular and visceral SMCs, ii) forced expression of myocardin in non-SMCs activates multiple SMC-specific transcriptional regulatory elements, iii) forced expression of myocardin activates SMC-restricted genes in undifferentiated embryonic stem (ES) cells, and iv) expression of adominant-negative myocardin mutant protein or myocardin siRNA in SMCs represses activity of the SMC-specific SM22alpha-promoter. Together these studies suggest the central hypothesis that will be examined in the proposed studies: myocardin plays a critical role in the SRF-dependent transcriptional program that regulates SMC differentiation and phenotype. The overall goat of this project is to elucidate the molecular basis of myocardin-induced SMC differentiation. The specific aims are to: 1) Examine the cell autonomous functions of myocardin in SMCs during embryonic development, and on maintenance of the SMC phenotype, 2) Examine the molecular mechanisms underlying the activity and specificity of the myocardin-SRF dependent transcriptional program that regulates SMC differentiation, and 3) Generate and characterize mice containing null and conditioned mutations in the myocardin gene. At a basic level these studies will provide new insights into the transcriptional programs regulating SMC differentiation and modulation of SMC phenotype. As such, these studies are relevant to understanding the pathogenesis of atherosclerosis and other vascular proliferative syndromes.