KCNJ2-Induced Arrhythmia Mechanisms in CPVT and Heart Failure.

心律失常性心源性猝死（SCD）是美国的主要死因，可由以下原因引起： 在遗传性心律失常综合征或后天性心脏病如心脏 失败本项目主要研究心脏内向整流电流（IK 1）对肾上腺素依赖性心肌细胞凋亡的影响。 遗传性和获得性室性心律失常。IK 1维持静息膜电位，促进3期 复极化，并在心力衰竭中重塑。KCNJ 2编码离子通道Kir2.1，该离子通道Kir2.1形成KCNJ 2。 人心室IK 1的优势蛋白孔亚基。存在KCNJ 2突变的功能丧失 具有两种临床表型，Adersen-Tawil综合征（ATS），由室性心律失常三联征组成， 畸形特征和周期性麻痹，或儿茶酚胺能多形性室性心动过速 （CPVT），表现为肾上腺素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VT（BiVT），缺乏非心脏ATS特征。CPVT一直是 归因于与Ca 2+处理基因突变相关的异常钙（Ca 2+）处理， CPVT，BiVT的心律失常是由Ca 2+过载引起的。与其他CPVT目标不同，Kir2.1不直接 参与Ca ~（2+）稳态，而Ca ~（2+）通过特异性阻断外向Kir2.1电流来调节Kir2.1。 β-肾上腺素能刺激激活蛋白激酶A（PKA），其磷酸化Kir2.1，随后 外向Kir2.1电流增加。Kir2.1与CPVT引起的突变如何不能响应PKA， 未知，特别是因为已知的CPVT突变不是磷酸化位点。我们的核心假设是 在β-肾上腺素能刺激下，引起CPVT的Kir2.1突变体通道由于以下原因而失去外向电流： 缺乏PKA反应和对Ca 2+阻滞的敏感性增加，减少外向电流， 复极化驱动导致膜电位不稳定，有利于延迟后去极化（DAD） 触发活动此外，收缩性心力衰竭中IK 1的降低被认为是心室收缩功能不全的一个关键特征。 心律失常和SCD。我们假设IK 1主要在β-肾上腺素能刺激过程中降低， 以类似于引起CPVT的KCNJ 2突变的方式升高Ca 2+。在这项研究中，我们将解决这些问题。 使用各种细胞模型和转基因小鼠模型来确定生物物理特性的问题 KCNJ 2突变相关的性质、Ca 2+敏感性、磷酸化状态和心律失常机制 与CPVT或ATS表型进行比较，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、光学绘图和钙成像。这个结果 这项研究将使我们能够阐明IK 1的β-肾上腺素能依赖性丧失导致 CPVT和心力衰竭中的室性心律失常，并将其与ATS心律失常机制进行比较。 阐明IK 1功能障碍和β-肾上腺素能应激下Ca 2+处理的细微差别将导致更多的 循证治疗方法和预防SCD。

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.