Department of Molecular Biology, Center of Basic Research, Biomedical Research Foundation, Academy of Athens, Soranou Efessiou 4, 115 27, Athens, Greece.
Department of Cardiovascular Sciences, KU Leuven, Leuven, Belgium.
Cardiovasc Res. 2017 Sep 1;113(11):1403-1417. doi: 10.1093/cvr/cvx113.
The histidine-rich calcium-binding protein (HRC) Ser96Ala variant has previously been identified as a potential biomarker for ventricular arrhythmias and sudden cardiac death in patients with idiopathic dilated cardiomyopathy. Herein, the role of this variant in cardiac pathophysiology is delineated through a novel mouse model, carrying the human mutation in the homologous mouse position.
The mouse HRC serine 81, homologous to human HRC serine 96, was mutated to alanine, using knock-in gene targeting. The HRC-Ser81Ala mice presented increased mortality in the absence of structural or histological abnormalities, indicating that early death may be arrhythmia-related. Indeed, under stress-but not baseline-conditions, the HRC-Ser81Ala mice developed ventricular arrhythmias, whilst at the cardiomyocyte level they exhibited increased occurrence of triggered activity. Cardiac contraction was decreased in vivo, ex vivo, and in vitro. Additionally, Ca2+ transients and SR Ca2+ load were both reduced suggesting that cytosolic Ca2+ overload is not the underlying proarrhythmic mechanism. Interestingly, total SR Ca2+ leak was increased in HRC-Ser81Ala cardiomyocytes, without an increase in Ca2+ spark and wave frequency. However, Ca2+ wave propagation was significantly slower and the duration of the associated Na/Ca exchange current was increased. Moreover, action potential duration was also increased. Notably, Ca2+/Calmodulin kinase II (CaMKII) phosphorylation of the ryanodine receptor was increased, whilst KN-93, an inhibitor of CaMKII, reduced the occurrence of arrhythmias.
The homologous mutation Ser81Ala in HRC in mice, corresponding to Ser96Ala in humans, is associated with sudden death and depressed cardiac function. Ventricular arrhythmias are related to abnormal Ca2+ cycling across the SR. The data further support a role for CaMKII with the perspective to treat arrhythmias through CaMKII inhibition.
先前已发现富含组氨酸的钙结合蛋白（HRC）Ser96Ala 变体是特发性扩张型心肌病患者室性心律失常和心源性猝死的潜在生物标志物。在此，通过携带同源小鼠位置人类突变的新型小鼠模型来阐明该变体在心脏病理生理学中的作用。
使用基因敲入靶向方法，将小鼠 HRC 丝氨酸 81（与人 HRC 丝氨酸 96 同源）突变为丙氨酸。HRC-Ser81Ala 小鼠在没有结构或组织学异常的情况下死亡率增加，表明早期死亡可能与心律失常有关。事实上，在应激而非基线条件下，HRC-Ser81Ala 小鼠发生室性心律失常，而在心肌细胞水平上，它们表现出触发活动的发生率增加。体内、体外和体外，心脏收缩均降低。此外，Ca2+ 瞬变和 SR Ca2+ 负荷均降低，表明细胞浆 Ca2+ 超载不是潜在的致心律失常机制。有趣的是，HRC-Ser81Ala 心肌细胞中的总 SR Ca2+ 泄漏增加，而 Ca2+ 火花和波频率没有增加。然而，Ca2+ 波传播明显减慢，相关的 Na/Ca 交换电流持续时间增加。此外，动作电位持续时间也增加。值得注意的是，ryanodine 受体的 Ca2+/钙调蛋白激酶 II（CaMKII）磷酸化增加，而 CaMKII 抑制剂 KN-93 可降低心律失常的发生。
在小鼠的 HRC 中，对应于人类的 Ser81Ala 同源突变与突然死亡和心脏功能降低有关。室性心律失常与 SR 中异常的 Ca2+ 循环有关。该数据进一步支持 CaMKII 的作用，并有望通过 CaMKII 抑制来治疗心律失常。
