Regulation of Chromatin Signaling in Heart Failure by BET Bromodomain Proteins

 描述(由申请人提供)：尽管目前的护理标准，心力衰竭(HF)的诊断与较低的生活质量和接近50%的5年死亡率有关。鉴于这种迫切的未得到满足的需求，阐明与心力衰竭发病机制有关的新机制有望为这种流行和致命的疾病找到新的治疗方法。这一应用的PI首次阐明了一个保守的乙酰赖氨酸“阅读器”蛋白家族(BET溴域)在病理性心肌肥厚和心衰的转录控制中的关键作用。重要的是，这些研究利用了JQ1，一种一流的BET溴域的特定小分子抑制剂。这一多PI应用试图垂直推进我们对异常染色质依赖信号转导(通过BET家族成员BRD4)如何驱动病理性心脏重构的理解。我们的长期目标是开发BET溴域抑制作为一种新的治疗策略。令人振奋的初步研究表明，BRD4在体外介导心肌细胞(CM)肥大，JQ1抑制BET有效地抑制压力超负荷介导的小鼠心肌肥厚的发展。从机制上讲，我们证明了BRD4在成年小鼠心脏中占据了活性增强子，将PTEF-b活性招募到转录起始位置，并触发RNA聚合酶II的暂停释放，以激活对HF发病至关重要的基因。有趣的是，我们证明了病理性应激导致CMS中BRD4蛋白的特异性积累，而不增加Brd4的mRNA。最后，我们证明了I类HDAC，通常是促肥大的，是BRD4蛋白积累所特需的。基于这一原理，这一提议将检验中心假设，即BRD4作为病理性心脏重构的节点转录调节因子，可以在体内进行药理学靶向。在强大的初步数据指导下，这一假说将通过追求三个强有力的特定目标来检验：(1)阐明BET抑制在临床相关心力衰竭模型和生理性心脏可塑性过程中的作用；(2)剖析BRD4在心脏应激期间驱动动态增强子重构、染色质依赖的信号转导和选择性基因控制的转录机制；(3)确定HDAC与BET蛋白相互作用以整合上游信号与心脏促肥大基因表达的机制。这项拟议的研究具有重要意义，因为它试图开发药理BET溴域抑制作为治疗心力衰竭的新策略，因此解决了一个巨大的未得到满足的临床需求。我们的方案具有很高的创新性，因为我们通过一种前所未有的方法成功地对病理性心肌转录和重塑进行了药物治疗。鉴于我们财团的协同专业知识，我们预计，我们高度合作的团队的持续贡献将为心血管疾病的新型“表观遗传疗法”的开发铺平道路。

 DESCRIPTION (provided by applicant): Despite current standard of care, a diagnosis of heart failure (HF) is associated with poor quality-of-life and a 5-year mortality approaching 50%. In light of this urgent unmet need, the elucidation of novel mechanisms involved in HF pathogenesis holds promise for identifying new therapies for this prevalent and deadly disease. The PIs of this application were the first to illustrate a crucial role for a conserved family of acetyl-lysine "reader" proteins (BET bromodomains) in the transcriptional control of pathological cardiac hypertrophy and HF. Importantly, these studies leveraged the use of JQ1, a first-in-class, specific small molecule inhibitor of BET bromodomains. This multi-PI application seeks to vertically advance our understanding of how aberrant chromatin dependent signal transduction (via the BET family member BRD4) drives pathologic cardiac remodeling. Our long-term objective is to develop BET bromodomain inhibition as a novel therapeutic strategy in HF. Exciting preliminary studies demonstrate that BRD4 mediates cardiomyocyte (CM) hypertrophy in vitro and that BET inhibition with JQ1 potently suppresses the development of pressure-overload mediated cardiac hypertrophy in mice. Mechanistically, we demonstrate that BRD4 occupies active enhancers in the adult mouse heart, recruits PTEF-b activity to transcriptional start sites, and triggers pause-release of RNA Polymerase II to activate genes critical for HF pathogenesis. Intriguingly, we demonstrate that pathologic stress leads to specific accumulation of BRD4 protein in CMs without any increase in Brd4 mRNA. Finally, we demonstrate that class I HDACs, which are generally pro-hypertrophic, are specifically required for BRD4 protein accumulation. Based on this rationale, this proposal will test the central hypothesis that BRD4 functions as a nodal transcriptional regulator of pathological cardiac remodeling that can be pharmacologically targeted in vivo. Guided by strong preliminary data, this hypothesis will be tested by pursuing three robust specific aims: (1) Elucidate the effects of BET inhibition in clinically relevant models of HF and during physiological cardiac plasticity; (2) Dissect the transcriptional mechanisms by which BRD4 drives dynamic enhancer remodeling, chromatin-dependent signal transduction, and selective gene control during cardiac stress; (3) Define the mechanisms by which HDACs crosstalk with BET proteins to integrate upstream signals with pro-hypertrophic gene expression in the heart. The proposed research is significant because it seeks to develop pharmacologic BET bromodomain inhibition as a novel therapeutic strategy in HF, and therefore addresses an enormous unmet clinical need. Our proposal is highly innovative because we successfully "drug" pathologic myocardial transcription and remodeling via an unprecedented approach. Given the synergistic expertise of our consortium, we envision that sustained contributions from our highly-collaborative group will pave the way for the development of novel "epigenetic therapies" for cardiovascular disease.