Novel Regulatory Circuit in Cardiac Hypertrophy Via RNA Splicing

描述(申请人提供)：转录组重编程是心脏病理性重构的关键过程。在哺乳动物转录组中，由于选择性的RNA剪接，很大一部分基因产生不止一个转录物种类。然而，选择性RNA剪接对总转录组复杂性的贡献及其在心力衰竭中的调节机制仍然知之甚少，研究不足。基于RNA测序和广泛的验证研究，我们发现全球替代RNA剪接模式适合疾病心脏中的胎儿样轮廓，包括转录因子Mef2家族的所有成员Mef2a、MEF2c和Mef2d的高度保守的互斥剪接。我们进一步发现，Fox1是一种富含肌肉的反式作用RNA剪接因子，它调节心脏中的这种特定的Mef2剪接事件，产生具有不同转录活性和不同功能影响的剪接变体。在老鼠和人类衰竭的心脏中，Fox1的表达减弱。斑马鱼中Fox1的失活会导致发育缺陷和心脏功能障碍。最值得注意的是，在小鼠体内恢复Fox1的表达显著减轻了压力超负荷引起的心肌肥大和功能障碍。因此，选择性RNA剪接是一个高度调控的过程，对心脏的转录组编程有重要贡献。它对心脏发育和发病机制有重要的影响，但以前没有得到充分认识。这些令人兴奋的新发现导致了我们目前的假设，即Fox1-MEF2是心脏转录网络中的一个新的调节电路，在心力衰竭中起着关键作用。在这个方案中，我们将在分子和功能水平上在多个模型系统中阐述这一新的假说，以充分确立Fox-1介导的RNA剪接调控在心力衰竭中的潜在机制和功能重要性。更具体地说，我们计划在目标1：确定Fox-1对心肌细胞转录组复杂性的具体贡献；在目标2：研究Mef2a剪接变异体在心脏中的分子基础和功能影响；在目标3：建立Fox-1-Mef2电路在心肌肥大和心力衰竭中的功能影响。这些研究将为心脏转录组在正常发育和疾病中的调控提供令人兴奋的新见解，并有望成为治疗开发的新靶点。

DESCRIPTION (provided by applicant): Transcriptome reprogramming is a key process of pathological remodeling in heart. In mammalian transcriptome, a significant portion of the genes produce more than one transcript species due to alternative RNA splicing. However, the contribution of alternative RNA splicing to total transcriptome complexity and its regulatory mechanism in heart failure is still poorly understood and understudied. Based on RNA sequencing and extensive validation studies, we have discovered that global pattern of alternative RNA splicing adapts a fetal-like profile in diseased hearts, including a highly conserved mutually exclusive splicing for all members of the transcriptional factor Mef2 family, Mef2a, Mef2c and Mef2d. We further find that Fox1 is a muscle enriched trans-acting RNA splicing factor that regulates this specific Mef2 splicing event in heart, producing splicing variants with distinct transcriptional activities and different functional impact in heart. Fox1 expression is diminished in mouse and human failing hearts. Inactivation of Fox1 in zebrafish causes developmental defects and cardiac dysfunction. Most remarkably, restoring Fox1 expression in mice significantly attenuates cardiac hypertrophy and dysfunction induced by pressure-overload. Therefore, alternative RNA splicing is a highly regulated process that significantly contributes to the transcriptome programming in heart. It has an important and previously underappreciated impact on cardiac development and pathogenesis. These exciting new findings lead to our current hypothesis that Fox1-MEF2 is a novel regulatory circuit in cardiac transcriptional network with a pivotal role in heart failure. In this proposal, we will expore this novel hypothesis at molecular and functional levels in multiple model systems in order to fully establish the underling mechanism and the functional importance of Fox-1 mediated RNA splicing regulation in heart failure. More specifically, we plan to accomplish in Aim 1: to determine the specific contribution of Fox-1 to transcriptome complexity in cardiomyocytes; in Aim 2: to investigate the molecular basis and functional impact of Mef2a splicing variants in heart; in Aim 3: to establish the functional impact of Fox-1-Mef2 circuit in cardiac hypertrophy and heart failure. These studies will provide exciting new insights to cardiac transcriptome regulation in normal development and diseases, and promising new targets for therapeutic development.