Toward a Mechanism-Based Approach to Treating Atrial Fibrillation

描述（由申请人提供）：虽然房颤（AF）是最常见的心律失常，需要抗心律失常药物治疗，但个体患者的反应是高度可变的，因为房颤的复发频率很高。药物治疗的有限成功部分归因于未能针对潜在机制进行靶向治疗。本小组和其他研究人员最近在小鼠模型中进行的实验工作表明，通过2型ryanodine受体（RyR2） Ca释放通道的Ca泄漏是触发阵发性房颤的一个重要机制。虽然AF患者心房组织中有Ca泄漏的记录，但与人类房颤的因果关系仍存在争议。因此，本文提出将验证我们的总体假设，即泄漏的RyR2通道会导致AF风险，可以在人类中进行靶向治疗。我们已发表的和初步的数据表明，普罗帕酮的r -对映体是临床批准的抗心律失常药物中最有效的RyR2 Ca释放抑制剂。r -普罗帕酮在钙sequestrin无效小鼠（Casq2-/-）中抑制ca触发的局灶性房颤显著有效，而s -普罗帕酮在很大程度上缺乏RyR2阻断特性，其效果明显较差。由于R-和s -普罗帕酮是同等效力的钠通道阻滞剂，而且临床上使用外消旋普罗帕酮，因此这两种普罗帕酮对映体可以作为确定RyR2通道泄漏对人类房颤风险贡献的工具，使我们能够将小鼠的研究结果转化为患者。在人类中，靠近配对样同源结构域转录因子2 （PITX2）的常见AF相关4q25单核苷酸多态性（snp）是目前AF风险最强的遗传标记。虽然snp的功能影响仍有争议，但我们发表的数据显示，携带4q25风险等位基因的个体对IC类药物氟氯胺和普罗帕酮的反应更好，这两种药物也能抑制RyR2通道。相比之下，缺乏RyR2阻断特性的III类药物在4q25携带者中效果较差。这些结果提出了一种令人兴奋的可能性，即4q25风险等位基因是AF患者RyR2通道泄漏的标记。因此，Aim 1将确定Ca泄漏是否有助于诱导AF的多种小鼠模型中的潜在促心律失常机制。Pitx2单倍不足小鼠（Pitx2+/-），携带人类心房钠通道（Scn5a-D1275N）心房利钠肽（muta - nppa）和引起心房肥厚和纤维化的肌钙蛋白T （TnT-F110I）突变的小鼠。目的2将验证潜在的电生理机制预测小鼠对药物治疗反应的假设。Aim 3的临床试验将测试小鼠房颤模型的结果是否能预测阵发性房颤患者抗心律失常药物的疗效，以及4q25风险等位基因是否能识别将受益于RyR2通道阻断的房颤患者。完成这些目标可以证明小鼠心房颤动研究可应用于人类的概念，并且在临床EP实验室进行心房颤动消融时的药物测试可能有助于个体化心房颤动药物治疗。

DESCRIPTION (provided by applicant): Although atrial fibrillation (AF) is the most prevalent cardiac arrhythmia requiring antiarrhythmic drug therapy, response in an individual patient is highly variable with frequent AF recurrence. The limited success of drug therapy has been attributed in part to failure to target therapy to underlying mechanisms. Recent experimental work from our group and others in mouse models suggests that Ca leak via type 2 ryanodine receptor (RyR2) Ca release channels is one important mechanism responsible for triggering paroxysmal AF. While Ca leak has been documented in atrial tissue from AF patients, the causal relationship to human AF remains controversial. Hence, proposed here will test our overarching hypothesis that leaky RyR2 channels confer AF risk that can be targeted therapeutically in humans. Our published and preliminary data demonstrate that the R-enantiomer of propafenone is the most potent inhibitor of RyR2 Ca release among clinically approved antiarrhythmic drugs. R-propafenone was strikingly effective in suppressing Ca-triggered focal AF in calsequestrin null mice (Casq2-/-), whereas S-propafenone that largely lacks RyR2 blocking properties was significantly less effective. Since R- and S-propafenone are equipotent Na channel blockers and racemic propafenone is used clinically, the two propafenone enantiomers can be used as tools to determine the contribution of leaky RyR2 channels to AF risk in humans, enabling us to translate findings from mice to patients. In humans, common AF-associated 4q25 single nucleotide polymorphisms (SNPs) near the paired-like homeodomain transcription factor 2 (PITX2) are currently the strongest genetic markers of AF risk. While the functional effects of the SNPs remain controversial, our published data show that individuals carrying 4q25 risk alleles respond better to Class IC drugs flecainide and propafenone, both of which also inhibit RyR2 channels. In contrast, Class III drugs that lack RyR2 blocking properties were less effective in 4q25 carriers. These results raise the exciting possibility to be tested below that 4q25 risk alleles are markers for leaky RyR2 channels in humans with AF. Hence, Aim 1 will determine whether Ca leak contributes to the underlying pro-arrhythmic mechanism in diverse mouse models with inducible AF: Pitx2 haploinsufficient mice (Pitx2+/-), mice carrying human AF mutations in the cardiac Na channel (Scn5a-D1275N) in the atrial natriuretic peptide (mut-NPPA), and in troponin T that causes atrial hypertrophy and fibrosis (TnT-F110I). Aim 2 will test the hypothesis that the underlying electrophysiological mechanisms predict response to drug therapy in mice. The clinical trial in Aim 3 will test whether results from murine AF models predict antiarrhythmic drug efficacy in humans with paroxysmal AF, and whether the 4q25 risk alleles can identify AF patients who will benefit from RyR2 channel block. Accomplishing the aims could provide proof of concept that mouse AF research is translatable to humans, and that drug testing at the time of AF ablation in the clinical EP lab may help individualize AF drug therapy.