Histone deacetylases in pathogenesis of heart failure

描述（由申请人提供）：本提案的长期目标是研究ii类组蛋白去乙酰化酶（hdac）在心力衰竭发病机制中的作用。ii类hdac在心肌细胞中大量表达。它们与心肌生成因子形成Ca2+敏感复合物并调节其转录活性。最近，我们发现血清反应因子（SRF）是HDAC4的一个功能性相互作用靶点。在肌细胞中，HDAC4与SRF结合，导致SRF-HDAC4复合物的核定位和SRF介导的基因转录抑制。这种关联被细胞肥大的诱导以及Ca2+/CaMK信号的直接激活所破坏，导致HDAC4输出到细胞质和SRF转录活性的重新激活。我们认为，在细胞质中，HDAC4使微管蛋白和cofilin去乙酰化，从而导致细胞-细胞骨架网络密度的改变。这些事件促进了肥大早期肌细胞结构和功能的变化，如蛋白质合成增强，胎儿基因程序的诱导和细胞骨架的稳定。此外，在衰竭心脏的终末期，SRF的剪接异构体（srfd4,5）被合成，它作为SRF介导的基因调控的显性阴性异构体。基于这些结果，我们假设从SRF-HDAC复合体中以Ca2+敏感的方式释放ii类hdac，导致早期肥厚反应，然后由于srfd4,5异构体的合成而进展为扩张和衰竭。我们将在以下几个方面验证这一假设：(1)确定不同失代偿水平的兔心脏中srf - hdac关联相关蛋白的表达和细胞分布。(2)探讨hdac在改变细胞骨架密度中的作用。(3)评价hdac抑制剂在肥大心肌细胞中的作用。(4)研究体内hdac抑制剂对衰竭心脏左室收缩动力学和生化特征的影响。hdac抑制剂被认为是抑制细胞生长的治疗药物。它们已经在临床试验中用于治疗肿瘤和癫痫。这一建议的结果将确立hdac在心力衰竭发病机制中的作用。这将为心力衰竭的发病机制提供新的见解，反过来可能有助于在未来为心力衰竭的管理设计新的治疗策略。

DESCRIPTION (provided by applicant): The long-term goal of this proposal is to investigate the role of class-II histone deacetylases (HDACs) in the pathogenesis of heart failure. Class-II HDACs are abundantly expressed in cardiac myocytes. They form Ca2+ sensitive complexes with cardiac myogenic factors and regulate their transcrptional activity. Recently, we have shown that serum response factor (SRF) is a functional interacting target of HDAC4. In myocytes HDAC4 binds to SRF leading to nuclear localization of the SRF-HDAC4 complex and repression of SRFmediated gene transcription. This association is disrupted by induction of cell-hypertrophy as well as by direct activation of Ca2+/CaMK signaling, resulting in export of HDAC4 to cytoplasm and reactivation of SRF transcription activity. We believe that in the cytoplasm HDAC4 deacetylates tubulin and cofilin, an event which consequently leads to altered cell-cytoskeleton network density. These events promote changes in myocytes structure and function seen in the early stages of hypertrophy, e.g. enhanced protein synthesis, induction of fetal-gene program and stabilization of cytoskeleton. In addition, in the end-stage of failing hearts a spliced isoform of SRF (SRFD4,5) is synthesized, which acts as a dominant negative isoform for SRF-mediated gene regulation. Based on these results, we hypothesize that the release of class-II HDACs from the SRF-HDAC complex, in a Ca2+-sensitive manner, leads to an early hypertrophic response, which then progresses to dilatation and failure due to synthesis of the SRFD4,5 isoform. We will test this hypothesis in the following specific aims: (1) Determine expression and cellular distribution of proteins related to SRF-HDACs association in rabbit hearts with different levels of decompensation. (2) Examine the role HDACs in altering the cell-cytoskeleton density. (3) Evaluate the role of HDAC-inhibitors in hypertrophied cardiac myocytes. (4) Examine the effect of HDAC-inhibitors in in vivo on the LV systolic dynamics and biochemical profile of the failing heart. HDAC-inhibitors are recognized as therapeutic agents to arrest cell growth. They are already in clinical trials to manage tumors and seizures. Results obtained from this proposal should establish the role of HDACs in the pathogenesis of heart failure. This would then provide new insights into pathogenesis of heart failure and in turn might well help devise novel therapeutic strategies for managment of heart failure in the future.