Determining the Role of Junctophilin-2 in Cardiac Disease

描述（由申请人提供）：肥厚型心肌病（HCM）是最常见的遗传性心脏病，其特征为左心室壁增厚、收缩功能障碍和潜在的致命性心律失常。有大量证据表明，兴奋-收缩偶联（ECC）的缺陷有助于心肌病和心律失常的发病机制。被称为“连接膜复合物”（JMC）的特化膜连接是质膜上的L型Ca通道（LTCC）中的重要亚细胞结构，其与肌浆网（SR）上的兰尼碱受体（RyR 2）通信以启动收缩。关于JMCs内钙通道的适当亚细胞靶向蛋白质知之甚少，但嗜连接蛋白-2（JPH 2）已被确定为关键候选者。在人类中，JPH 2的错义突变导致HCM，尽管分子机制尚未解决。我们最近已经证明，JPH 2也结合和调节RyR 2通道在JMC，但确切的蛋白质结构域参与这些相互作用仍然是未知的。此外，在HCM患者和心力衰竭动物模型中已经报道了JPH 2的表达减少，但尚不清楚JPH 2的丧失是否与心力衰竭中的收缩力受损和/或心律失常直接相关。我们已经产生了几个小鼠模型与HCM连接的JPH 2突变或增加/减少JPH 2的表达水平在心脏。该项目的长期目标是确定JPH 2和相关分子调节正常心脏中JMC完整性和EC偶联的分子机制，以及JPH 2功能异常如何导致HCM，心力衰竭和心律失常。我们的总体假设是，在正常心脏中，JPH 2是JMC完整性和其中Ca通道调节所必需的，而由于下调或突变导致的JPH 2功能丧失导致心肌病、心力衰竭和心律失常。为了验证这一假设，我们提出：在目的1，确定JPH 2在组织关键的钙处理蛋白的JMC内的作用。- 在目标2中，阐明遗传JPH 2变体导致HCM的机制。- 在目标3中，确定JPH 2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.