Leviev Heart Center, Sheba Medical Center, Tel Hashomer and Sackler School of, Medicine, Tel Aviv University, Tel Aviv, Israel.
Biochem Pharmacol. 2013 Dec 1;86(11):1576-83. doi: 10.1016/j.bcp.2013.09.012. Epub 2013 Sep 23.
Humans and genetically engineered mice with recessively inherited CPVT develop arrhythmia which may arise due to malfunction or degradation of calsequestrin (CASQ2). We investigated the relation between protein level and arrhythmia severity in CASQ2(D307H/D307H) (D307H), compared to CASQ2(Δ/Δ) (KO) and wild type (WT) mice. CASQ2 expression and Ca²⁺ transients were recorded in cardiomyocytes from neonatal or adult mice. Arrhythmia was studied in vivo using heart rhythm telemetry at rest, exercise and after epinephrine injection. CASQ2 protein was absent in KO heart. Neonatal D307H and WT hearts expressed significantly less CASQ2 protein than the level found in the adult WT. Adult D307H expressed only 20% of CASQ2 protein found in WT. Spontaneous Ca²⁺ release was more prevalent in neonatal KO cardiomyocytes (89%) compared to 33-36% of either WT or D307H, respectively, p<0.001. Adult cardiomyocytes from both mutant mice had more Ca²⁺ abnormalities compared to control (KO: 82%, D307H 63%, WT 12%, p<0.01). Calcium oscillations were most common in KO cardiomyocytes. We then treated mice with bortezomib to inhibit CASQ2(D307H) degradation. Bortezomib increased CASQ2 expression in D307H hearts by ∼50% (p<0.05). Bortezomib-treated D307H mice had lower CPVT prevalence and less premature ventricular beats during peak exercise. No benefit against arrhythmia was observed in bortezomib treated KO mice. These results indicate that the mutant CASQ2(D307H) protein retains some of its physiological function. Its expression decreases with age and is inversely related to arrhythmia severity. Preventing the degradation of mutant protein should be explored as a possible therapeutic strategy in appropriate CPVT2 patients.
患有隐性遗传 CPVT 的人类和基因工程小鼠会出现心律失常，这可能是由于 calsequestrin (CASQ2) 的功能障碍或降解引起的。我们研究了 CASQ2(D307H/D307H) (D307H) 与 CASQ2(Δ/Δ) (KO) 和野生型 (WT) 小鼠之间的蛋白水平与心律失常严重程度的关系。我们记录了来自新生或成年小鼠心肌细胞中的 CASQ2 表达和 Ca²⁺ 瞬变。通过在休息、运动和肾上腺素注射后使用心脏节律遥测进行体内心律失常研究。KO 心脏中不存在 CASQ2 蛋白。新生 D307H 和 WT 心脏中的 CASQ2 蛋白表达水平明显低于成年 WT 心脏中的水平。成年 D307H 仅表达 WT 心脏中 CASQ2 蛋白的 20%。与 WT 或 D307H 相比，新生 KO 心肌细胞中的自发性 Ca²⁺ 释放更为普遍（分别为 89%、33-36%，p<0.001）。与对照（KO：82%、D307H：63%、WT：12%，p<0.01）相比，来自两种突变小鼠的成年心肌细胞的 Ca²⁺ 异常更为常见。钙振荡在 KO 心肌细胞中最为常见。然后，我们用硼替佐米治疗小鼠以抑制 CASQ2(D307H) 降解。硼替佐米使 D307H 心脏中的 CASQ2 表达增加了约 50%（p<0.05）。用硼替佐米治疗的 D307H 小鼠在运动高峰时 CPVT 的发生率较低，室性早搏较少。在用硼替佐米治疗的 KO 小鼠中，没有观察到对心律失常的益处。这些结果表明，突变的 CASQ2(D307H) 蛋白保留了一些其生理功能。其表达随年龄而降低，与心律失常严重程度呈负相关。防止突变蛋白的降解应作为一种潜在的治疗策略，在适当的 CPVT2 患者中进行探索。
