Determining the Role of Junctophilin-2 in Cardiac Disease

描述(申请人提供)：肥厚型心肌病(HCM)是最常见的遗传性心脏病，以左室壁增厚、收缩功能障碍和潜在的致命心律失常为特征。大量证据表明，兴奋收缩偶联(ECC)的缺陷与心肌病和心律失常的发病机制有关。膜连接是细胞膜上L型钙通道的重要亚细胞结构，它与肌浆网上的兰尼定受体(RyR2)进行通讯，启动细胞收缩。对JMCs内适当的亚细胞靶向钙通道的蛋白知之甚少，但JPH2(JPH2)已被确定为关键候选蛋白。在人类中，JPH2的错义突变导致了HCM，尽管其分子机制仍未解决。我们最近已经证明JPH2也与JMC中的RyR2通道结合并调节，但参与这些相互作用的确切蛋白质结构域仍不清楚。此外，据报道，在肥厚性心肌病患者和心力衰竭的动物模型中，JPH2的表达减少，但尚不清楚JPH2的缺失是否与心力衰竭时的收缩能力受损和/或心律失常直接相关。我们已经建立了几个与HCM相关的JPH2突变或心脏JPH2表达水平升高/降低的小鼠模型。该项目的长期目标是确定JPH2及其相关分子调节正常心脏JMC完整性和EC偶联的分子机制，以及JPH2功能异常如何导致肥厚性心肌梗死、心力衰竭和心律失常。我们的总体假设是，在正常心脏中，JPH2对于JMC的完整性和其中的钙通道的调节是必需的，而由于下调或突变导致的JPH2功能丧失会导致心肌病、心力衰竭和心律失常。为了验证这一假设，我们建议：在目标1中，确定JPH2在JMC内组织关键的钙处理蛋白中的作用。-在目标2中，揭示遗传JPH2变异导致HCM的机制。-在目标3中，确定JPH2下调是否是心力衰竭中TTS/JMCs丢失的原因。

DESCRIPTION (provided by applicant): Hypertrophic cardiomyopathy (HCM) is the most-common inherited form of heart disease, characterized by thickening of the left ventricular wall, contractile dysfunction, and potentially fatal arrhythmias. There is extensive evidence that defects in excitation-contraction coupling (ECC) contribute to the pathogenesis of both cardiomyopathy and arrhythmias. Specialized membrane junctions known as 'junctional membrane complexes' (JMC) are important subcellular structures in L-type Ca channels (LTCC) on the plasmalemma communicate with ryanodine receptors (RyR2) on the sarcoplasmic reticulum (SR) to initiate contraction. Little is known about the proteins that govern proper subcellular targeting of Ca channels within JMCs, but junctophilin-2 (JPH2) has been identified as a key candidate. In humans, missense mutations in JPH2 cause HCM, although the molecular mechanisms remain unresolved. We have recently demonstrated that JPH2 also binds to and modulates RyR2 channels in the JMC, but the exact protein domains involved in these interactions are still unknown. Moreover, reduced expression of JPH2 has been reported in patients with HCM and animal models of heart failure, but it is unclear whether loss of JPH2 is directly linked to impaired contractility and/or arrhythmias in failing hearts. We have generated several mouse models with HCM-linked JPH2 mutations or with increased/decreased JPH2 expression levels in the heart. The long-term goal of this project is to define the molecular mechanisms by which JPH2 and associated molecules regulate JMC integrity and EC coupling in normal hearts, and how aberrant JPH2 function causes HCM, heart failure, and arrhythmias. Our overall hypothesis is that in normal hearts JPH2 is required for JMC integrity and the regulation of Ca channels therein, whereas loss of JPH2 function due to downregulation or mutation causes cardiomyopathy, heart failure and arrhythmias. To test this hypothesis, we propose to: In Aim 1, determine the role of JPH2 in organizing key Ca handling proteins within the JMC. - In Aim 2, unravel the mechanisms by which genetic JPH2 variants cause HCM. - In Aim 3, determine if JPH2 downregulation is the cause of loss of TTs/JMCs in heart failure.