Calsequestrin in Ventricular Arrhythmia and Sudden Death

摘要 心脏钙调蛋白(CASQ2)及其结合蛋白连接素和三聚氰胺-1(TRDN)是细胞外信号转导的关键调节因子。 肌浆网(SR)钙的储存和释放。在人类中，CASQ2突变会导致 儿茶酚胺能多形性室性心动过速(CPVT)和心脏性猝死。在上一次 在资助期内，我们已经培育并研究了Casq2缺失(Casq2-/-)小鼠，以确定其机制 由此CASQ2突变导致电生理不稳定性。我们发现，尽管缺乏Casq2蛋白， 这些小鼠维持着接近正常的SR钙储存、钙释放和收缩功能，这可能是由于 SR体积扩大，Casq2结合蛋白Triadin-1和Junctin急剧减少。案例2-/- 小鼠表现出CPVT表型，即儿茶酚胺引起多形性室性心动过速 输液或锻炼。我们目前的概念是，钙的丢失释放了难治性和过早的SR 在高SR钙负荷条件下释放，导致延迟后除极，触发心搏和 多形性室性心动过速。然而，如果触发起源于心室肌细胞或来自 传导系统的特殊细胞--浦肯野细胞--尚未分解。来自RyR2的实验数据 突变小鼠模型和理论考虑倾向于浦肯野网络。此外，生化方面， 电子显微镜和共聚焦研究表明，Casq2只存在于小鼠的终池中。 与RyR2钙释放通道密切接触的结合性SR。因此，我们假设简化后的 在心室肌细胞和/或浦肯野细胞中存在靠近RyR2的Casq2是一种基本缺陷 这会导致SR钙过早释放，并增加心律失常的易感性。这适用于 遗传性综合征(例如，Casq2连锁的CPVT；AIMS 1+2)和潜在的获得性心脏病，原因是 向RyR2贩运和/或在RyR2附近保留Casq2的缺陷(目标3)。 目的1.验证Casq2基因修复可挽救Casq2-/-小鼠CPVT表型的假说。 目的2.检验浦肯野细胞中Casq2缺失是必要和充分的假设 引起CPVT 目的3.验证心肌RyR2钙释放通道附近Casq2减少的假说 心肌梗死后的生存

ABSTRACT Cardiac calsequestrin (CASQ2), and its binding partners junctin and triadin-1 (TRDN), are key regulators of sarcoplasmic reticulum (SR) Ca storage and release. In humans, CASQ2 mutations cause the syndrome of catecholaminergic polymorphic ventricular tachycardia (CPVT) and sudden cardiac death. During the previous funding period, we have generated and studied Casq2 null (Casq2-/-) mice to determine the mechanisms whereby CASQ2 mutations cause electrophysiological instability. We found that despite a lack of Casq2 protein, these mice maintain near normal SR Ca storage, Ca release and contractile function, likely as a result of an expansion of SR volume and drastic reductions in the Casq2 binding proteins triadin-1 and junctin. Casq2-/- mice exhibit the CPVT phenotype, i.e. they develop polymorphic ventricular tachycardia with catecholamine infusion or exercise. Our current concept is that the loss of Ca release refractoriness and premature SR Ca release under conditions of high SR Ca load, results in delayed after-depolarizations, triggered beats and polymorphic ventricular tachycardia. However, if the trigger originates from ventricular myocytes or from specialized cells of the conduction system, the Purkinje cells, is unresolved. Experimental data from a RyR2 mutant mouse model and theoretical considerations favor the Purkinje network. Furthermore, biochemical, electron microscopy and confocal studies show that Casq2 is only found in the terminal cisternae of the junctional SR in close contact with RyR2 Ca release channels. Thus, we hypothesize that the reduced presence of Casq2 near the RyR2 in ventricular myocytes and/or Purkinje cells is a fundamental defect that causes premature SR Ca release and increases arrhythmia susceptibility. This is applicable to inherited syndromes (e.g., Casq2-linked CPVT; Aims 1+2) and potentially acquired heart disease due to defects in the trafficking to and/or retention of Casq2 near the RyR2 (Aim 3). Aim 1. To test the hypothesis that restoration of Casq2 rescues the CPVT phenotype of Casq2-/- mice. Aim 2. To test the hypothesis that loss of Casq2 in Purkinje cells is both necessary and sufficient to cause CPVT Aim 3. To test the hypothesis that Casq2 is reduced near RyR2 Ca release channels in cardiac muscle surviving after myocardial infarction