The role of BET proteins in pathological cardiac remodeling

摘要 作为对持续的神经激素/血流动力学应激或损伤的反应，心脏经历了一种病理 重塑过程以心肌细胞肥大和纤维化为典型特征。心脏纤维化， 定义为心脏内过度的细胞外基质沉积，是收缩压和心脏收缩压的主要贡献者 数百万心力衰竭患者的舒张期功能障碍。在受伤后，驻留的静止的成纤维细胞经历 细胞状态转变为高分泌细胞外基质的活化成纤维细胞和肌成纤维细胞 蛋白质，并且可以收缩。纤维性重塑导致左心室僵硬，舒张性受损， 顺应性降低，电导性改变。这推动了疾病的发展和恶化。 病理学。尽管众所周知，心脏纤维化会导致与心脏相关的不良后果 失败后，针对心脏纤维化的有效治疗仍然难以捉摸。BET(溴域)的抑制作用 和超末端结构域)家族具有化学小分子(例如JQ1)的表观遗传阅读器蛋白 已被证明有效地阻断体内心肌肥大、炎症和纤维化，并保存心脏 在心力衰竭啮齿动物模型中的作用。尽管这些抑制剂可以阻断心脏中的所有BET蛋白(BRD2， BRD3，BRD4)，细胞培养实验中单个BET蛋白的基因靶向支持这样的概念 BRD4是主要的BET蛋白，负责激活病理基因表达程序 心肌细胞和心脏成纤维细胞。然而，最近的工作对细胞类型的特定作用有了深入的了解 BRD4在心肌细胞中的表达，揭示了BRD4在维持线粒体动态平衡中的重要作用。 成人心肌细胞BRD4条件性缺失导致进展性心功能障碍 线粒体功能，以及小鼠的最终死亡。综合之前的研究，这表明 小分子BET抑制剂在小鼠心力衰竭模型中的有益作用不太可能是中介的 仅通过抑制心肌细胞中的BRD4。我们假设BRD4在体内的遗传破坏 活化的成纤维细胞将安全地阻止纤维化和多种BET蛋白(即BRD2和BRD3) 介导小分子PAN-BET抑制的有益效果。在目标1中，我们将确定在体内的作用 BRD4在活化的成纤维细胞中的表达，在目标2中，我们将阐明以前未曾探索的个体的作用 BET蛋白通过CHIP-SEQ调控心肌细胞基因表达。这项工作将在 马修·斯特拉顿博士的实验室，他是病理性心脏重构的表观遗传学调节专家，以及 在世界心脏生理学领先者Loren Wold博士的共同监督下。我们的长期目标是 开发安全有效的治疗方法，以改善心脏纤维化和心力衰竭患者的临床结果。

ABSTRACT In response to persistent neurohormonal/hemodynamic stress or injury, the heart undergoes a pathologic remodeling process typically characterized by cardiomyocyte hypertrophy and fibrosis. Cardiac fibrosis, defined as excess extracellular matrix deposition in the heart, is a major contributor to both systolic and diastolic dysfunction for millions of heart failure patients. Upon injury, resident quiescent fibroblasts undergo a cell state transition to become activated fibroblasts and myofibroblasts that hyper-secrete extracellular matrix proteins and can be contractile. Fibrotic remodeling causes stiffening of the left ventricle, impaired relaxation, reduced compliance, and altered electrical conductance. This drives disease progression and worsens pathology. Despite the well-known contribution of cardiac fibrosis to adverse outcomes associated with heart failure, effective therapies targeting fibrosis in the heart remain elusive. Inhibition of the BET (bromodomain and extra-terminal domain) family of epigenetic reader proteins with chemical small molecules (e.g. JQ1) has proven effective at blocking in vivo cardiac hypertrophy, inflammation, and fibrosis and preserving cardiac function in rodent models of heart failure. Though these inhibitors block all BET proteins in the heart (BRD2, BRD3, BRD4), genetic targeting of individual BET proteins in cell culture experiments support the notion that BRD4 is the main BET protein responsible for activation of pathologic gene expression programs in cardiomyocytes and cardiac fibroblasts. However, recent work has given insight on the cell-type specific role of BRD4 in cardiomyocytes, uncovering an essential role for BRD4 in maintaining mitochondrial homeostasis. Conditional deletion of BRD4 in adult cardiomyocytes resulted in progressive cardiac dysfunction, impaired mitochondrial function, and eventual death in mice. Taken together with previous studies, this suggests that the beneficial effects of small molecule BET inhibitors in mouse models of heart failure are unlikely to be mediated exclusively by inhibition of BRD4 in cardiomyocytes. We hypothesize that genetic in vivo disruption of BRD4 in activated fibroblasts will safely block fibrosis and that multiple BET proteins (i.e. also BRD2 and BRD3) mediate the beneficial effects of small-molecule pan-BET inhibition. In Aim 1, we will determine the in vivo role of BRD4 in activated fibroblasts, and in Aim 2 we will elucidate the previously unexplored role of individual BET proteins in cardiac cell gene expression regulation through ChIP-Seq. This work will be carried out in the laboratory of Dr. Matthew Stratton, an expert in epigenetic regulation of pathologic cardiac remodeling, and under the co-supervision of Dr. Loren Wold, a world-leader in cardiac physiology. Our long-term goal is to develop safe and effective therapeutics to improve clinical outcomes for patients with cardiac fibrosis and HF.