Microdomain regulation of Ca2+ release in cardiac physiology and disease

 描述(申请人提供)：由心律失常引起的猝死是心脏疾病最常见的后果，通常是由异常冲动形成的结果。这种被触发的活动与肌浆网(SR)的异常钙释放有关，是儿茶酚胺能多形性室性心动过速(CPVT)的标志。Ryanodine受体(RyR2)或Calequestrin(Casq2)是SR内主要的钙结合蛋白，CPVT相关突变使RyR2泄漏，并使这些患者容易发生心律失常。房颤是CPVT的另一个常见表现，表明CPVT中的钙离子处理不当并不是孤立于脑室的。尽管CPVT对钙通道阻滞剂和/或β-受体阻滞剂有很高的反应，但难治性病例往往需要以钠通道抑制剂为基础的治疗。然而，钠内流与CPVT心律失常前的钙处理障碍之间的关系仍然知之甚少。申请人开发了一种实验系统，使用各种CPVT小鼠模型，将细胞水平上的钙处理信息与组织中的电生理表型相结合。申请人计划调查钠通道亚群(神经性钠通道；nNav)通过微域Na/Ca~(2+)信号参与致心律失常的钙异常释放的假说。具体地说，该提案将在指导阶段(K99)解决以下目标：1)阐明亚域特异性Na/Ca~(2+)信号对钙依赖型房性和室性心律失常发生中异常钙释放的分子和亚细胞影响。在这里，我们将验证亚域特异性Na/Ca~(2+)信号参与致心律失常的异常钙释放的假说，同时试图确定局部Na/Ca~(2+)亚域信号的分子决定因素。2)明确Na/Ca~(2+)信号在组织范围内异常钙释放同步化中的作用。这些翻译研究将验证一种假设，即亚域特异的Na/Ca~(2+)信号促进心肌与异常Ca~(2+)释放的同步化，并促进随后在完整的心室组织中的异位活动。3)验证的适用性 Na/Ca~(2+)信号传导到体内环境。在独立期(R00)，该方案将：1)研究亚域特异性Na/Ca~(2+)信号在房性心律失常发生中的作用。2)研究心房异常钙释放同步化过程中亚区特异性Na/Ca~(2+)信号的区域异质性。3)验证Na/Ca~(2+)信号在房性心律失常环境中的治疗潜力并翻译 获得性钙介导的心律失常动物模型的适用性。在细胞和组织水平上获得的机制和药理学见解将提供一种基于机制的治疗方法，将在体内进行测试。此外，这些研究将确定这种致心律失常的机制(S)是否适用于临床相关的钙介导的心律失常模型。这项研究的长期目标是更好地了解钙介导的心律失常发生的细胞和分子机制。

 DESCRIPTION (provided by applicant): Project Summary Sudden death resulting from cardiac arrhythmias is the most common consequence of cardiac disease and is oftena result of abnormal impulse formation. Such triggered activity are associated with abnormal Ca2+ release from the sarcoplasmic reticulum (SR) and are a hallmark of catecholaminergic polymorphic ventricular tachycardia (CPVT). CPVT-associated mutations in the ryanodine receptors (RyR2) or calsequestrin (Casq2), the major intra-SR Ca2+ binding protein render the RyR2 leaky and predispose these patients to arrhythmias. Atrial fibrillation is an another common finding in CPVT, indicating that Ca2+ mishandling in CPVT is not isolated to the ventricles. Despite high response of CPVT to Ca2+ channel- and/or beta-blockers, refractory cases often require Na+ channel inhibitor based therapy. However, the relationship between Na+ influx and disturbances in Ca2+ handling immediately preceding arrhythmias in CPVT remains poorly understood. The applicant has developed an experimental system using various murine models of CPVT that integrates information of Ca2+ handling at the cellular level with the electrophysiologic phenotype in tissue. The applicant plans to investigate the hypothesis that subpopulation of Na+ channels (neuronal Na+ channels; nNav) contribute to arrhythmogenic aberrant Ca2+ release through the microdomain Na+/Ca2+ signaling. Specifically the proposal will address the following aims during the mentored phase (K99): 1) Elucidate the molecular and subcellular consequences of subdomain-specific Na+/Ca2+ signaling on aberrant Ca2+ release in the genesis of Ca2+ -dependent atrial and ventricular arrhythmias. Here we will test the hypothesis that subdomain-specific Na+/Ca2+ signaling contributes to arrhythmogenic aberrant Ca2+ release while attempting to identify the molecular determinants of local Na+/Ca2+ subdomain signaling. 2) Define the role of Na+/Ca2+ signaling in tissue wide aberrant Ca2+ release synchronization. These translational studies will test the hypothesis that subdomain-specific Na+/Ca2+ signaling facilitates myocardial synchronization of aberrant Ca2+ release and promotes subsequent ectopic activity in intact ventricular tissue. 3) Validate the applicability of Na+/Ca2+ signaling to in vivo settings. During the independent phase (R00) the proposal will: 1) Investigate the role of subdomain-specific Na+/Ca2+ signaling on aberrant Ca2+ release in the genesis of atrial arrhythmias. 2) Examine the regional heterogeneities of the subdomain-specific Na+/Ca2+ signaling in atrial aberrant Ca2+ release synchronization. 3) Validate the therapeutic potential of perturbation of Na+/Ca2+ signaling in settings of atrial arrhythmias and translate the applicability to animal models of acquired Ca2+-mediated arrhythmias. The mechanistic and pharmacological insights gained on the cellular as well as on tissue levels will offer a mechanism-based therapeutic approach that will be tested in vivo. Furthermore, these studies will determine whether such arrhythmogenic mechanism(s) is/are applicable to a clinically-relevant model of Ca2+-mediated arrhythmias. A long term goal of this study is to better understand the cellular and molecular mechanisms of Ca2+-mediated arrhythmogenesis.