Calsequestrin in Ventricular Arrhythmia and Sudden Death

描述（由申请人提供）：Cardiac calsequestrin （CASQ2）及其结合伙伴连接素和triadin-1 （TRDN）是肌浆网（SR） Ca2+储存和释放的关键调节因子。在人类中，CASQ2突变引起儿茶酚胺能多态性室性心动过速综合征和心源性猝死。为了确定CASQ2突变导致电生理不稳定但保持收缩功能的机制，我们产生了CASQ2 null （CASQ2 -/-）小鼠。我们的初步研究表明，尽管缺乏Casq2蛋白，这些小鼠仍保持接近正常的SR Ca2+储存，这可能是由于SR体积的扩大和Casq2结合蛋白triadin-1和连接蛋白的急剧减少。Casq2-/-小鼠通过儿茶酚胺输注或运动产生多形性室性心动过速来表现人类Casq2-相关心律失常。Casq2-/-肌细胞显示过早自发SR Ca2+释放，导致后收缩和触发心跳。值得注意的是，常用的抗抑郁药物在体外破坏Ca2+与CASQ2的结合，也与心源性猝死的发生率增加有关，增加了CASQ2相关的药物性心律失常的可能性，类似于药物相关的长QT综合征。基于这些人类遗传、流行病学和小鼠数据，我们假设Casq2的破坏会导致SR Ca2+释放功能障碍，并导致心律失常易感性和猝死。为了验证我们的中心假设，我们将在Casq2-/-、Casq2+/-、triadin-1 null （Trdn-/-）和选择性杂交动物中检查单细胞、全心和体内电生理、收缩功能、Ca2+稳态、蛋白质表达和SR超微结构。我们的目标是测试Casq2和triadin-1对心律失常易感性的个体贡献，并进一步阐明遗传和可能的药物诱导的Casq2功能障碍导致室性心律失常的分子和细胞机制。这项研究的结果不仅将促进我们对遗传性心律失常综合征病理生理学的理解，而且还有助于揭示数百万患者服用抗抑郁药物导致猝死的机制。

DESCRIPTION (provided by applicant): Cardiac calsequestrin (CASQ2), and its binding partners junctin and triadin-1 (TRDN), are key regulators of sarcoplasmic reticulum (SR) Ca2+ storage and release. In humans, CASQ2 mutations cause a syndrome of catecholaminergic polymorphic ventricular tachycardia and sudden cardiac death. To determine the mechanisms whereby CASQ2 mutations cause electrophysiologic instability but preserve contractile function, we have generated Casq2 null (Casq2-/-) mice. Our preliminary studies demonstrate that despite a lack of Casq2 protein, these mice maintain near normal SR Ca2+ storage, possibly as a result of an expansion of SR volume and drastic reductions in the Casq2 binding proteins triadin-1 and junctin. Casq2-/- mice phenocopy the human CASQ2- linked arrhythmias by developing polymorphic ventricular tachycardia with catecholamine infusion or exercise. Casq2-/- myocytes display premature spontaneous SR Ca2+ releases resulting in after- contractions and triggered beats. Significantly, commonly-used antidepressant drugs, which disrupt Ca2+ binding to CASQ2 in vitro, have also been linked to an increased incidence in sudden cardiac death, raising the possibility of a Casq2-linked form of drug-induced arrhythmias, analogous to the drug-associated long QT syndrome. Based on these human genetic, epidemiological, and mouse data, we hypothesize that disruption of Casq2 causes dysfunctional SR Ca2+ release and contributes to arrhythmia susceptibility and sudden death. To test our central hypothesis, we will examine single cell, whole heart and in vivo electrophysiology, contractile function, Ca2+ homeostasis, protein expression and SR ultrastructure in Casq2-/- , Casq2+/-, triadin-1 null (Trdn-/-) and selectively cross-bred animals. Our goals are to test the individual contribution of Casq2 and triadin-1 to arrhythmia susceptibility and further elucidate the molecular and cellular mechanism(s) that lead to ventricular arrhythmias in response to inherited and possibly drug-induced Casq2 dysfunction. The outcome of this research will not only advance our understanding of the pathophysiology of inherited arrhythmia syndromes, but also help unravel the mechanism(s) responsible for sudden deaths linked to antidepressant medications taken by millions of patients.