Epigenetic Control of Smooth Muscle Cell Lineage and Phenotypic Switching

描述（由申请人提供）：已知平滑肌细胞（SMC）分化状态的控制改变或“表型转换”在许多主要人类疾病（包括动脉粥样硬化、哮喘和血管成形术后再狭窄）的发生和/或进展中起关键作用。然而，控制SMC表型转换的机制知之甚少。这个建议的重点是确定组蛋白模式的染色质，在高等真核细胞的表观遗传控制，调节SMC分化的发展和疾病的机制。具有重要意义的是，在目前的资助期内，我们完成了一系列开创性的研究，表明胚胎干细胞（ESC）的SMC的发展与SMC标记基因位点的组蛋白修饰的独特模式的收购有关，这些标记基因位点将其与非SMC区分开来，并使这些位点允许转录激活。相比之下，SMC响应血管损伤或PDGF BB治疗的表型转换与许多SMC选择性组蛋白修饰的丧失以及与转录沉默/染色质浓缩相关的组蛋白变化的获得有关。然而，在SMC标记基因位点的H3 K4去甲基化，一个组蛋白的变化，出现在SMC从ESC的发展过程中，是完全不变的SMC表型转换检查的所有模型中，这表明它可能是相对“固定”，并在可逆的表型转换过程中保存SMC的“谱系记忆”。两者合计，结果表明，有一个独特的模式，区分SMC和非SMC的组蛋白修饰，这些SMC和基因位点特异性表观遗传修饰可能发挥关键作用，在调节SMC分化标记基因表达的发展和疾病。该项目的重点是测试的假设，即SMC从胚胎干细胞的发展与收购的SMC标记（和监管）基因位点的组蛋白修饰的独特模式，这些组蛋白修饰发挥关键作用，在确定这些基因位点的转录激活的许可，以及在可逆的表型转换过程中提供“SMC谱系记忆”。我们将通过解决以下两个具体目标来解决这个假设。目的1是确定SMC选择性/特异性染色质修饰调节SMC分化标志物和调控基因表达的机制。这将包括直接测试特定组蛋白修饰在SMC谱系/分化控制中的作用以及这些组蛋白修饰如何在发育过程中获得的第一批研究。目的2是确定表观遗传修饰在介导血管SMC可逆表型转换中的作用，以响应体内血管损伤或用PDGF BB治疗培养的SMC。研究将确定控制SMC分化的基本机制，并可能导致用于治疗SMC表型转换起主要作用的疾病的新疗法。

DESCRIPTION (provided by applicant): Altered control of the differentiated state of the smooth muscle cell (SMC) or "phenotypic switching" is known to play a critical role in the development and/or progression of a number of major human diseases including atherosclerosis, asthma, and post-angioplasty restenosis. However, the mechanisms that control SMC phenotypic switching are poorly understood. The focus of this proposal is to determine mechanisms by which histone patterning of chromatin, a key epigenetic control in higher eukaryotic cells, regulates SMC differentiation in development and disease. Of major significance, during the current funding period, we completed a series of pioneering studies showing that development of SMC from embryonic stem cells (ESC) is associated with acquisition of a unique pattern of histone modifications at SMC marker gene loci that distinguish them from non-SMC, and make these loci permissive for transcriptional activation. In contrast, phenotypic switching of SMC in response to vascular injury, or PDGF BB treatment, was associated with loss of many of these SMC-selective histone modifications, as well as acquisition of histone changes associated with transcriptional silencing/chromatin condensation. However, H3K4 demethylation at SMC marker gene loci, a histone change that appears during development of SMC from ESC, was completely unchanged in all models of SMC phenotypic switching examined, suggesting that it may be relatively "fixed", and serve to preserve SMC "lineage memory" during reversible phenotypic switching. Taken together, results indicate that there is a distinct pattern of histone modifications that distinguishes SMC from non-SMC, and that these SMC- and gene locus-specific epigenetic modifications are likely to play a key role in regulating SMC differentiation marker gene expression in development and disease. The focus of this project is to test the hypothesis that development of SMC from embryonic stem cells is associated with acquisition of a unique pattern of histone modifications at SMC marker (and regulatory) gene loci and that these histone modifications play a key role in determining the permissiveness of these gene loci for transcriptional activation as well as in providing "SMC lineage memory" during reversible phenotypic switching. We will address this hypothesis by addressing the following two specific aims. Aim 1 is to determine mechanisms by which SMC selective/specific chromatin modifications regulate expression of SMC differentiation marker and regulatory genes during development of SMC lineages from multipotential stem cells. This will include the first studies to directly test the role of specific histone modifications in control of SMC lineage/differentiation, and how these histone modifications are acquired during development. Aim 2 is to define the role of epigenetic modifications in mediating reversible phenotypic switching of vascular SMC in response to vascular injury in vivo or treatment of cultured SMC with PDGF BB. Studies will define fundamental mechanisms that control differentiation of SMC, and are likely to lead to novel therapies for treatment of diseases in which SMC phenotypic switching plays a major role.