KCNJ2-Induced Arrhythmia Mechanisms in CPVT and Heart Failure.

心律失常性心脏性猝死(SCD)是美国主要的死亡原因，可由以下因素引起 遗传性心律失常综合征或获得性心脏病(如心脏)中的离子电流异常 失败了。本课题主要研究心脏内向整流电流(Ik1)对肾上腺素能依赖性的影响。 遗传性和获得性室性心律失常。IK1维持静息膜电位，参与第三相 复极，并在心力衰竭时重塑。KCNJ2编码离子通道Kir2.1，它形成了 人心室中IK1的主要蛋白孔亚基。存在功能丧失的KCNJ2突变 有两种临床表型，Adersen-Tawil综合征(ATS)，由三组室性心律失常组成， 畸形特征和周期性瘫痪，或儿茶酚胺能多形性室性心动过速 (CPVT)，表现为肾上腺素能依赖性室性心律失常，包括多形性室性心律失常 心动过速(PMVT)和双向室速(BiVT)缺乏非心源性ATS特征。CPVT一直是 归因于与钙处理基因突变相关的异常钙处理及其特征 CPVT，BiVT的心律失常是由钙超载引起的。与其他CPVT目标不同，Kir2.1不直接 参与钙动态平衡，但钙通过特异性地阻断向外的Kir2.1电流来调节Kir2.1。 -肾上腺素能刺激激活蛋白激酶A，使kir2.1与随后的 增加向外基尔2.1的电流。导致CPVT突变的Kir2.1是如何对PKA没有反应的 未知，特别是因为已知的CPVT突变不是磷酸化位点。我们的中心假设是 在-肾上腺素能刺激下，引起慢性静脉曲张的Kir2.1突变通道的外向电流损失是由于 缺乏PKA反应和对钙拮抗剂的敏感性增加，从而减少外向电流，从而 复极驱动导致膜电位不稳定，有利于延迟后除极(DAD) 触发了活动。此外，收缩性心力衰竭时IK1降低被认为是室性心衰的一个关键特征。 心律失常和SCD。我们假设，在-肾上腺素能刺激过程中，Ik1主要降低 以类似于CPVT导致KCNJ2突变的方式升高钙。在这项研究中，我们将解决这些问题 问题：使用各种细胞模型和转基因小鼠模型来确定生物物理 KCNJ2基因突变的性质、钙敏感性、磷酸化状态及心律失常机制 CPVT或ATS表型，并将其与心力衰竭模型进行比较。我们的创新方法将 包括高清晰度质谱学、光学测绘和钙成像。这样做的结果是 研究将使我们能够阐明-肾上腺素能依赖的IK1丢失导致 CPVT和心力衰竭的室性心律失常，并与ATS的心律失常机制进行比较。 阐明-肾上腺素能应激下IK1功能障碍和钙调节的细微差别将导致更多 SCD的循证治疗方法和预防。

Arrhythmic sudden cardiac death (SCD) is a leading cause of death in the United States and can be caused by ionic current abnormalities occurring in genetic arrhythmia syndromes or acquired heart disease such as heart failure. This project focuses on the impact of cardiac inward rectifier current (IK1) on -adrenergic-dependent genetic and acquired ventricular arrhythmias. IK1 maintains resting membrane potential, contributes to phase 3 repolarization, and is remodeled in heart failure. KCNJ2 encodes the ion channel Kir2.1 that forms the dominant protein pore subunit for IK1 in the human cardiac ventricle. Loss of function KCNJ2 mutations present with two clinical phenotypes, Adersen-Tawil Syndrome (ATS), composed of a triad of ventricular arrhythmias, dysmorphic features and periodic paralysis, or Catecholaminergic Polymorphic Ventricular Tachycardia (CPVT), which presents with adrenergic-dependent ventricular arrhythmias including polymorphic ventricular tachycardia (PMVT) and bidirectional VT (BiVT) with a lack non-cardiac ATS features. CPVT has been attributed to abnormal calcium (Ca2+) handling related to mutations in Ca2+ handling genes and the signature arrhythmia for CPVT, BiVT, is caused by Ca2+ overload. Unlike the other CPVT targets, Kir2.1 does not directly participate in Ca2+ homeostasis, yet Ca2+ modulates Kir2.1 by specifically blocking the outward Kir2.1 current. -adrenergic stimulation activates protein-kinase A (PKA), which phosphorylates Kir2.1 with subsequent increase in outward Kir2.1 current. How Kir2.1 with CPVT-causing mutations fail to respond to PKA is unknown, particularly since the known CPVT mutations are not phosphorylation sites. Our central hypothesis is that under -adrenergic stimulation, CPVT-causing Kir2.1 mutant channels have loss of outward current due to both lack of a PKA response and increased sensitivity to Ca2+ block, reducing outward current and thus repolarization drive causing membrane potential instability, favoring delayed after-depolarizations (DADs) triggered activity. Additionally, decreased IK1 in systolic heart failure is thought to be a key feature in ventricular arrhythmias and SCD. We hypothesize that IK1 is decreased predominately during -adrenergic stimulation due to elevated Ca2+ in a manner similar to CPVT-causing KCNJ2 mutations. In this study, we will address these questions using a variety of cellular models and transgenic mouse models to determine the biophysical properties, Ca2+ sensitivity, phosphorylation state and arrhythmia mechanism of KCNJ2 mutations associated with a CPVT or an ATS phenotype and compare that to a heart failure model. Our innovative methods will include high-definition mass spectrometry, optical mapping and calcium imaging. The outcomes of this research will allow us to elucidate the mechanism by which -adrenergic-dependent loss of IK1 can result in ventricular arrhythmia in CPVT and heart failure and compare that to an ATS arrhythmia mechanism. Elucidating the nuances of IK1 dysfunction and Ca2+ handling under -adrenergic stress will lead to more evidence-based treatment approaches and prevention of SCD.