Cardiomyocyte bromodomain protein 4 (BRD4) in physiology and disease

项目摘要 再加上修饰基因、序列变异、内源性因素和 环境线索，强有力的证据表明表观遗传事件导致心力衰竭 发病机制。此外，表观遗传疗法已经出现在肿瘤学中。工作地点： 我们的实验室和其他实验室已经证明了小分子抑制剂的强大心脏保护作用。 1类组蛋白去乙酰基酶(乙酰基“擦除器”)在压力过载应激和 缺血/再灌注损伤。在这项提案中，我们将把重点放在所谓的 乙酰化，BRD蛋白，特别是BRD4。 先前的文献工作表明，BRD蛋白的一种小分子抑制剂 钝化病理性心脏重塑，增加了针对这一生物学的诱人前景 为了治疗的收获。在这些研究中，特定的BRD亚型缺失与BRD4有关。 重要的是，BRD4在心脏中编码至少两种亚型(Brd-L和Brd-S)，通过 外显子的替代用法。长的异构体BRD4-L在BET家族中是独一无二的，因为它包含 扩展的C末端，包括P-TEFb相互作用结构域。已知BRD4调节 超级增强子，一大簇转录增强子，驱动基因的表达 定义小区身份。的确，BRD4-L是超强启动子功能所必需的，带有C-末端 形成超增强子簇时发生相移所必需的结构域。这个 短的异构体BRD4-S缺少这个C末端。 除了这些结构性差异之外，在肿瘤学和其他领域的背景下，这是显而易见的 这些BRD4亚型具有截然不同的--实际上是拮抗的--功能，这一事实 使心血管领域现有数据的解释复杂化。目前，没有什么是 已知这些BRD4亚型在心脏中的作用。 我们的初步数据显示，使用心肌细胞特异的BRD4基因敲除小鼠，这种丢失 BRD4的存在会导致心脏收缩功能的迅速下降和扩张型心肌病。 我们针对特定BRD4亚型的初步体外研究和体内研究表明 BRD4-L不是心肌肥厚所必需的，相反，肥大反应是 依赖BRD4-S。在这里，我们提出了基于凌驾性假设的工作 BRD4的特定亚型在心肌细胞生理学和生物学中发挥不同的作用 病理学。揭开异构体特定功能的面纱将是迈向精确度的重要一步 在疾病治疗中以这种生物学为目标。我们已经开发了独特的工具来直接 评估这些异构体在体外和体内的作用。

Project Summary Together with the effects of modifier genes, sequence variants, endogenous factors, and environmental cues, strong evidence points to epigenetic events contributing to heart failure pathogenesis. Furthermore, epigenetic therapies have emerged already in oncology. Work from our lab and others has demonstrated robust cardioprotective effects of small molecule inhibitors of class 1 histone deacetylases (acetyl “erasers”) in both pressure-overload stress and ischemia/reperfusion injury. In this proposal, we will turn our focus to the so-called “readers“ of acetylation, the BRD proteins, specifically BRD4. Prior work in the literature has demonstrated that a small molecule inhibitor of BRD proteins blunts pathological cardiac remodeling, raising the tantalizing prospect of targeting this biology for therapeutic gain. Depletion of specific BRD isoforms in those studies implicated BRD4. Importantly, BRD4 encodes at least two isoforms in the heart (BRD-L and BRD-S) via alternative exon usage. The long isoform BRD4-L is unique in the BET family in that it contains an extended C terminus that includes a P-TEFb-interacting domain. BRD4 is known to regulate superenhancers, large clusters of transcriptional enhancers that drive expression of genes that define cell identity. Indeed, BRD4-L is required for super-enhancer function, with the C-terminal domain necessary for the phase-shift occurring with formation of super-enhancer clusters. The short isoform BRD4-S lacks this C terminus. Beyond these structural differences, it is clear in the context of oncology and other domains that these BRD4 isoforms have distinct – indeed antagonistic – functions, a fact which complicates the interpretation of existing data in the cardiovascular space. Presently, nothing is known about the role of these BRD4 isoforms in the heart. Our preliminary data, using a cardiomyocyte-specific BRD4 knockout mouse, show that loss of BRD4 results in a rapid decline in ventricular contractile function and dilated cardiomyopathy. Our preliminary in vitro studies and in vivo studies targeting specific BRD4 isoforms suggests that BRD4-L is not required for cardiac hypertrophy, but rather, the hypertrophic response is dependent on BRD4-S. Here, we propose work based on the over-riding hypothesis that specific isoforms of BRD4 play distinct roles in cardiomyocyte physiology and pathology. Work to unveil isoform-specific functions will be a major step toward precision targeting of this biology in disease therapy. Already, we have developed unique tools to directly assess the roles of these isoforms both in vitro and in vivo.