Song Lei, Alcalai Ronny, Arad Michael, Wolf Cordula M, Toka Okan, Conner David A, Berul Charles I, Eldar Michael, Seidman Christine E, Seidman J G
Department of Genetics, Harvard Medical School, Boston, MA 02115, USA.
J Clin Invest. 2007 Jul;117(7):1814-23. doi: 10.1172/JCI31080.
Catecholamine-induced polymorphic ventricular tachycardia (CPVT) is a familial disorder caused by cardiac ryanodine receptor type 2 (RyR2) or calsequestrin 2 (CASQ2) gene mutations. To define how CASQ2 mutations cause CPVT, we produced and studied mice carrying a human D307H missense mutation (CASQ(307/307)) or a CASQ2-null mutation (CASQ(DeltaE9/DeltaE9)). Both CASQ2 mutations caused identical consequences. Young mutant mice had structurally normal hearts but stress-induced ventricular arrhythmias; aging produced cardiac hypertrophy and reduced contractile function. Mutant myocytes had reduced CASQ2 and increased calreticulin and RyR2 (with normal phosphorylated proportions) but unchanged calstabin levels, as well as reduced total sarcoplasmic reticulum (SR) Ca(2+), prolonged Ca(2+) release, and delayed Ca(2+) reuptake. Stress further diminished Ca(2+) transients, elevated cytosolic Ca(2+), and triggered frequent, spontaneous SR Ca(2+) release. Treatment with Mg(2+), a RyR2 inhibitor, normalized myocyte Ca(2+) cycling and decreased CPVT in mutant mice, indicating RyR2 dysfunction was critical to mutant CASQ2 pathophysiology. We conclude that CPVT-causing CASQ2 missense mutations function as null alleles. In the absence of CASQ2, calreticulin, a fetal Ca(2+)-binding protein normally downregulated at birth, remains a prominent SR component. Adaptive changes to CASQ2 deficiency (increased posttranscriptional expression of calreticulin and RyR2) maintained electrical-mechanical coupling, but increased RyR2 leakiness, a paradoxical response further exacerbated by stress. The central role of RyR2 dysfunction in CASQ2 deficiency unifies the pathophysiologic mechanism underlying CPVT due to RyR2 or CASQ2 mutations and suggests a therapeutic approach for these inherited cardiac arrhythmias.
儿茶酚胺诱导的多形性室性心动过速（CPVT）是一种由心脏2型兰尼碱受体（RyR2）或肌集钙蛋白2（CASQ2）基因突变引起的家族性疾病。为了明确CASQ2突变如何导致CPVT，我们培育并研究了携带人类D307H错义突变（CASQ(307/307)）或CASQ2基因敲除突变（CASQ(DeltaE9/DeltaE9)）的小鼠。两种CASQ2突变产生了相同的结果。年轻的突变小鼠心脏结构正常，但应激可诱发室性心律失常；随着年龄增长，出现心脏肥大且收缩功能降低。突变心肌细胞中CASQ2减少，钙网蛋白和RyR2增加（磷酸化比例正常），但钙稳蛋白水平不变，同时肌浆网（SR）总Ca(2+)减少，Ca(2+)释放延长，Ca(2+)再摄取延迟。应激进一步减少Ca(2+)瞬变，升高胞质Ca(2+)，并触发频繁的、自发的SR Ca(2+)释放。用RyR2抑制剂Mg(2+)治疗可使突变小鼠心肌细胞Ca(2+)循环正常化，并减少CPVT，这表明RyR2功能障碍对突变CASQ2的病理生理学至关重要。我们得出结论，导致CPVT的CASQ2错义突变起无效等位基因的作用。在缺乏CASQ2的情况下，钙网蛋白（一种通常在出生时下调的胎儿Ca(2+)结合蛋白）仍是SR的主要成分。对CASQ2缺乏的适应性变化（钙网蛋白和RyR2转录后表达增加）维持了电 - 机械偶联，但增加了RyR2的渗漏，这种矛盾的反应在应激时进一步加剧。RyR2功能障碍在CASQ2缺乏中的核心作用统一了由RyR2或CASQ2突变引起的CPVT的病理生理机制，并提示了针对这些遗传性心律失常的治疗方法。
