Defining the role of KCNN1 in atrial arrhythmias

房颤(房颤)是最常见的心律失常形式，影响多达2%的人口和 估计个人终生风险为25%-30%。房颤与生活质量的显著下降有关 并增加发病率和死亡率。一线治疗，如β受体阻滞剂和钙通道阻滞剂 有助于控制心率以减轻症状，但不能预防房颤。因此，心房的发现- 治疗房颤的具体靶点势在必行。最近，小电导钙激活的钾(SK)通道有 考虑到它们在心室中有限的功能作用，它们被认为是心房特异性抗心律失常的靶点。 来自健康心脏的心肌细胞。所有三种SK通道亚型(SK1-3)都在心房和 脑室。然而，SK2和SK3的治疗潜力仍然存在很大争议，因为两者都失去了- 这些通道的功能增强与不同基因小鼠房性心律失常的增加有关 模型和全球气候变化网络的关联性研究。此外，最近的报道显示，SK电流在心室 来自患病或应激的心脏的心肌细胞，显示在减少对钙的依赖方面起到保护作用 引发心律失常的事件。重要的是，我们之前公布的数据显示，SK1没有明显的作用 (KCNN1)在心室保护中，不同于SK2和SK3。基于这一知识，以及SK1是 只有在心房和心室中高表达2-5倍的异构体，我们推测SK1可能是一个真正的心房- 特定的抗心律失常靶点，不同于SK2和SK3。因此，这项提案的主要目标是建立 SK1在正常心房肌细胞和房颤心脏AM中的作用异常高的活性 肌浆网(SR)钙释放通道复合体，兰诺定受体(RyR2)被认为是基础 心律失常触发房颤。因此，为了测试SK1的抗心律失常电位，我们将使用成熟的小鼠 钙调门蛋白(CASQ2)敲除RyR2复杂功能获得模型，这是一种SR蛋白， 确定控制RyR2活性和SR Ca~(2+)存储容量。要探索的功能后果 ，我们建议产生新的心脏特异的SK1过表达和 KO小鼠品系。重要的是，SK1除了在线粒体内膜上表达外，还可能在线粒体内膜上表达 肌膜。我们推测，促进肌膜SK1通道功能可能会显著降低细胞外信号转导。 心律失常的早期和延迟后除极(分别为EADS和DADS) L型钙通道和Na+/钙离子交换器的作用力，从而降低触发活动。我们假设MITO-SK1 通道激活可通过减少过量的钙离子依赖的DADS和EADS进一步减弱促心律失常 产生破坏性的活性氧，从而改善受干扰的RyR2复合体介导的肌浆网钙离子 在患病的AM中释放。我们预计我们的工作将证实SK1是一种新的心房特异性抗心律失常靶点。

Atrial fibrillation (AF) is the most prevalent form of cardiac arrhythmia affecting up to 2% of population and with an estimated individual lifetime risk of 25%-30%. AF is associated with a significant reduction in quality of life and increased morbidity and mortality. Frontline therapies such as beta blockers and Ca2+ channels blockers help control cardiac rhythm to reduce the symptoms, but do not prevent AF. Therefore the discovery of atria- specific targets to treat AF is imperative. Recently, small conductance Ca2+ activated K+ (SK) channels have emerged as a plausible atria-specific anti-arrhythmic target, given their limited functional roles in ventricular cardiomyocytes from healthy hearts. All three SK channels isoforms (SK1-3) are expressed both in atria and ventricles. However, the therapeutic potential of SK2 and SK3 remains highly controversial, given both loss- and gain-of-function of these channels were linked to increased atrial arrhythmogenesis in various genetic mouse models and in GWAS association studies. Furthermore, recent reports demonstrated SK current in ventricular myocytes from diseased or stressed hearts, revealed to play a protective role in reducing Ca2+-dependent arrhythmia-triggering events. Importantly, our previously published data showed no discernible role of SK1 (KCNN1) in ventricular protection, unlike SK2 and SK3. Based on this knowledge, and the fact that SK1 is the only isoform with 2-5 fold higher expression in atria vs ventricles, we posit that SK1 can be a bona fide atria- specific antiarrhythmic target, unlike SK2 and SK3. Accordingly, the major goal of this proposal is to establish the roles of SK1 in normal atrial myocytes (AMs) and AMs from the hearts with AF. Abnormally high activity of sarcoplasmic reticulum (SR) Ca2+ release channel complex, the ryanodine receptor (RyR2), is thought to underlie arrhythmia trigger for AF. Therefore, to test SK1 antiarrhythmic potential, we will use the well-established mouse model of RyR2 complex gain-of function caused by calsequestrin (CASQ2) knockout, a SR protein that determines controls RyR2 activity and SR Ca2+ storage capacity. To explore the functional consequences of gain- and loss-of-SK1 channel function, we propose to generate new cardiac-specific SK1 overexpression and KO mouse lines. Importantly, SK1 might be expressed in the mitochondrial inner membrane in addition to the sarcolemma. We hypothesize that facilitating sarcolemmal SK1 channel function may substantially diminish pro- arrhythmic early and delayed afterdepolarizations (EADs and DADs respectively) by countering the depolarizing force of L-type Ca2+ channels and Na+/Ca2+ exchanger, thus reducing triggered activity. We posit that mito-SK1 channel activation can further attenuate pro-arrhythmic Ca2+-dependent DADs and EADs by reducing excessive production of damaging reactive oxygen species, thereby improving disturbed RyR2 complex-mediated SR Ca2+ release in diseased AMs. We anticipate our work will validate SK1 as a novel atria-specific antiarrhythmic target.