Exploring the Molecular Physiology of Atrial Fibrillation

心房纤颤（AF）是最常见的心律失常，并且占相当大的发病率和死亡率。 mortality.尽管经过几十年的研究，目前的治疗方法仍然只是部分有效，或者在这种情况下， 消融、侵入性、昂贵且对某些患者无效。开发新型、有效和安全的治疗方法 由于缺乏反映人类房颤的动物模型，当一些大型动物 尽管这些模型表现出人类AF的各个方面，但在人类中难以测试和开发用于AF的新型小分子疗法。 这些昂贵而有限的模型。理想情况下，忠实地模仿人类AF的小动物模型将是 这是一个非常宝贵的工具，既可以理解AF的分子生理学，也可以潜在地识别和 测试新的小分子疗法。事实上，小鼠模型在开发 癌症、糖尿病和肥胖症的新疗法。缺乏AF的小鼠模型是一个障碍， 对这一重大疾病的研究。为了解决这一空白，我们创建了强力霉素诱导的转基因（TG）小鼠 具有人SCN 5A中局部麻醉剂结合位点突变（F1759 A），心脏NaV 1.5通道 基因偶然的是，这些小鼠表现出适度的心房增大和纤维化，线粒体形态异常， 频繁、持续的自发性AF发作和非持续性多形性室性心动过速， 在没有强力霉素的情况下早在5周龄时就观察到。持续性和自发性心房颤动 心律失常是一种不寻常的，如果不是唯一的表型在小鼠，使初步探索的机制，房颤 使用体内（遥测）、离体（光学电压映射）和体外（细胞电生理学）技术。 我们现在建议使用这种小鼠模型来更全面地表征 胚胎发生，探索改变的Ca 2+稳态是否有助于胚胎的发生和维持。 AF，以及靶向改变Ca 2+稳态是否可以有效治疗AF。 目的1：研究细胞内Ca 2+增加细胞内Ca 2+浓度的下游机制。 我们将使用遗传学和药理学方法测试Na+-Ca 2+抑制剂是否 钙离子交换蛋白（NCX）和钙调蛋白依赖性激酶（CaMKII）可抑制体内和螺旋型房颤 离体波/转子。目的2：检测持续性Na+电流增加、“渗漏”RyR 2、 我们将使用药理学和遗传学方法来抑制RyR 2泄漏， 它是否在AF中起作用以及它是否可能成为新的治疗靶点。目标3：检验因果关系 由于持续性Na+电流增加和RyR 2通道渗漏导致线粒体功能障碍， AF的易感性。所提出的研究可以确定功能失调的Na+通道之间的重要联系， AF中SR Ca 2+释放异常、AF中Ca 2+依赖性信号传导缺陷、线粒体功能障碍和 我们的研究旨在提供严格和可靠的假设检验， 对AF分子基础的新认识，并为新的，基于机制的， 有效和安全的治疗。

Atrial fibrillation (AF) is the most common cardiac arrhythmia and accounts for substantial morbidity and mortality. Despite decades of research current treatments remain only partially effective, or in the case of ablation, invasive, costly and not effective in some patients. Development of novel, effective and safe therapy for AF has been hampered by the lack of animal models that reflect AF in humans. While some large animal models exhibit aspects of human AF it is difficult to test and develop novel small molecule therapies for AF in these costly and limited models. Ideally, a small animal model that faithfully phenocopies human AF would be an invaluable tool for both understanding the molecular physiology of AF and potentially for identifying and testing novel small molecule therapeutics. Indeed, murine models have proved invaluable in the development of novel therapeutics for cancer, diabetes and obesity. The lack of a mouse model for AF is a barrier to research in this important disease. To address this gap we created doxycycline-inducible transgenic (TG) mice with a mutation (F1759A) of the local anesthetic binding site in human SCN5A, the cardiac NaV1.5 channel gene. Fortuitously these mice exhibit modest atrial enlargement and fibrosis, mitochondrial dysmorphology, frequent, sustained episodes of spontaneous AF, and non-sustained polymorphic ventricular tachycardia, observed as early as 5 weeks of age in the absence of doxycycline. The sustained and spontaneous atrial arrhythmias, an unusual if not unique phenotype in mice, enabled initial explorations of mechanisms of AF using in vivo (telemetry), ex vivo (optical voltage mapping), and in vitro (cellular electrophysiology) techniques. We now propose to use this mouse model to more fully characterize the molecular mechanisms of arrhythmogenesis, to explore whether altered Ca2+ homeostasis contributes to the genesis and maintenance of AF, and whether targeting altered Ca2+ homeostasis could be an effective treatment of AF. Three Aims are proposed: Aim 1: To examine the downstream mechanisms by which increased cytosolic Ca2+ increases the propensity of AF. We will test using genetic and pharmacological approaches whether inhibitors of Na+-Ca2+ exchanger (NCX) and Ca2+-calmodulin dependent kinase (CaMKII) can inhibit AF in vivo and and spiral waves/rotors ex vivo. Aim 2: To test the causal link between increased persistent Na+ current, “leaky” RyR2, and the susceptibility for AF. We will use pharmacological and genetic approaches to inhibit RyR2 leak to see whether it plays a role in AF and whether it may be a novel therapeutic target. Aim 3: To test the causal link between mitochondrial dysfunction due to increased persistent Na+ current and leaky RyR2 channels, and the susceptibility for AF. The proposed studies may identify important links between dysfunctional Na+ channels, abnormal SR Ca2+ release in AF, defective Ca2+-dependent signaling in AF, mitochondrial dysfunction and oxidative overload in AF. Our studies are designed to provide rigorous and robust hypothesis-testing to open new understandings of the molecular bases of AF and to pave the way towards novel, mechanism-based, effective and safe treatments.