Cardiomyocyte bromodomain protein 4 (BRD4) in physiology and disease

项目摘要 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有助于心力衰竭 发病机制此外，表观遗传疗法已经出现在肿瘤学中。工作从 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类组蛋白脱乙酰基酶（乙酰基“橡皮擦”）在压力超负荷应激和 缺血/再灌注损伤。在这份提案中，我们将把重点转向所谓的“读者”， 乙酰化，BRD蛋白，特别是BRD 4。 文献中的先前工作已经证明，BRD蛋白的小分子抑制剂 减弱了病理性心脏重塑，提高了靶向这种生物学的诱人前景 来获得治疗效果这些研究中特定BRD同种型的消耗涉及BRD 4。 重要的是，BRD 4在心脏中编码至少两种同种型（BRD-L和BRD-S）， 选择性外显子使用。长同种型BRD 4-L在BET家族中是独特的，因为它含有 延伸的C末端，其包括P-TEFb相互作用结构域。已知BRD 4调节 超级增强子，即大簇的转录增强子，它们驱动基因的表达， 定义小区标识。事实上，BRD 4-L是超级增强子功能所必需的，其C-末端 域所需的相移发生与超级增强子集群的形成。的 短同种型BRD 4-S缺少该C末端。 除了这些结构上的差异，在肿瘤学和其他领域的背景下， 这些BRD 4同种型具有不同的-实际上是拮抗的-功能，这一事实 使心血管空间中现有数据的解释复杂化。目前， 已知这些BRD 4亚型在心脏中的作用。 我们使用心肌细胞特异性BRD 4基因敲除小鼠的初步数据显示， BRD 4的表达导致心室收缩功能的快速下降和扩张型心肌病。 我们针对特定BRD 4亚型的初步体外研究和体内研究表明， BRD 4-L不是心脏肥大所必需的，相反，肥大反应是 基于BRD 4-S。在这里，我们提出的工作基础上压倒性的假设， BRD 4的特异性同种型在心肌细胞生理学中发挥独特的作用， 病理揭开异构体特异性功能的工作将是迈向精确的重要一步 在疾病治疗中靶向这种生物学。我们已经开发出独特的工具， 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.