Determining the Role of Junctophilin-2 in Cardiac Disease

描述（由申请人提供）：肥厚性心肌病（HCM）是最常见的遗传性心脏病，其特征是左心室壁增厚、收缩功能障碍和潜在致命的心律失常。有大量证据表明，兴奋-收缩耦合（ECC）缺陷参与心肌病和心律失常的发病机制。被称为“连接膜复合物”（JMC）的特殊膜连接是质膜上l型Ca通道（LTCC）中重要的亚细胞结构，它与肌浆网（SR）上的ryanodine受体（RyR2）通信以启动收缩。在jmc中，控制Ca通道亚细胞靶向的蛋白知之甚少，但结膜亲蛋白-2 （JPH2）已被确定为一个关键的候选蛋白。在人类中，JPH2的错义突变引起HCM，尽管分子机制尚不清楚。我们最近已经证明JPH2也结合并调节JMC中的RyR2通道，但参与这些相互作用的确切蛋白质结构域仍然未知。此外，在HCM患者和心力衰竭动物模型中也有JPH2表达降低的报道，但尚不清楚JPH2的缺失是否与心力衰竭患者的收缩力受损和/或心律失常直接相关。我们已经建立了几种具有hcm相关的JPH2突变或心脏中JPH2表达水平增加/减少的小鼠模型。该项目的长期目标是明确JPH2及其相关分子在正常心脏中调控JMC完整性和EC耦合的分子机制，以及异常的JPH2功能如何导致HCM、心力衰竭和心律失常。我们的总体假设是，在正常心脏中，JPH2是JMC完整性和Ca通道调节所必需的，而由于JPH2下调或突变导致的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，我们提出：在目标1中，确定JPH2在组织JMC内关键钙处理蛋白中的作用。在Aim 2中，揭示遗传JPH2变异导致HCM的机制。-在Aim 3中，确定JPH2下调是否是心力衰竭中tt / jmc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.