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重塑的关键过程。在哺乳动物转录组中，由于选择性RNA剪接，很大一部分基因产生不止一种转录物。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，在患病心脏中，可选择的RNA剪接的全局模式适应胎儿样的特征，包括转录因子Mef2家族所有成员Mef2a、Mef2c和Mef2d的高度保守的互斥剪接。我们进一步发现Fox1是一种肌肉富集的反式作用RNA剪接因子，它调节心脏中特定的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。Fox1在小鼠和人类衰竭心脏中的表达减少。斑马鱼Fox1的失活会导致发育缺陷和心功能障碍。最值得注意的是，恢复小鼠Fox1表达可显著减轻压力过载引起的心脏肥厚和功能障碍。因此，选择性RNA剪接是一个高度调控的过程，对心脏转录组编程有重要贡献。它在心脏发育和发病机制中具有重要的作用，但以前未被重视。这些令人兴奋的新发现支持了我们目前的假设，即Fox1-MEF2是心脏转录网络中一个新的调控回路，在心力衰竭中起关键作用。在本文中，我们将在多个模型系统的分子和功能水平上探索这一新的假设，以充分建立Fox-1介导的RNA剪接调节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中完成：确定Fox-1对心肌细胞转录组复杂性的具体贡献；目的2：研究Mef2a剪接变异在心脏中的分子基础和功能影响；目的3：建立Fox-1-Mef2回路在心肌肥厚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，并为治疗开发提供有希望的新靶点。

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.