From The Dorothy M. Davis Heart & Lung Research Institute (M.A.M., J.C., S.C.L., H.M., I.P., S.A.S., P.J.W., S.D.U., J.S., T.J.H., P.J.M. ), Departments of Internal Medicine (S.A.S., P.J.M.), and Physiology and Cell Biology (M.A.M., J.C., S.C.L., H.M., I.P., S.A.S., P.J.W., P.J.M.), The Ohio State University Wexner Medical Center, Columbus; Department of Biomedical Engineering, The Ohio State University College of Engineering, Columbus (S.D.U., J.S., T.J.H.); and Howard Hughes Medical Institute, Department of Biochemistry, Duke University Medical Center, Durham, NC (V.B.).
Circ Res. 2014 Nov 7;115(11):929-38. doi: 10.1161/CIRCRESAHA.115.305154. Epub 2014 Sep 19.
Nav1.5 (SCN5A) is the primary cardiac voltage-gated Nav channel. Nav1.5 is critical for cardiac excitability and conduction, and human SCN5A mutations cause sinus node dysfunction, atrial fibrillation, conductional abnormalities, and ventricular arrhythmias. Further, defects in Nav1.5 regulation are linked with malignant arrhythmias associated with human heart failure. Consequently, therapies to target select Nav1.5 properties have remained at the forefront of cardiovascular medicine. However, despite years of investigation, the fundamental pathways governing Nav1.5 membrane targeting, assembly, and regulation are still largely undefined.
Define the in vivo mechanisms underlying Nav1.5 membrane regulation.
Here, we define the molecular basis of an Nav channel regulatory platform in heart. Using new cardiac-selective ankyrin-G(-/-) mice (conditional knock-out mouse), we report that ankyrin-G targets Nav1.5 and its regulatory protein calcium/calmodulin-dependent kinase II to the intercalated disc. Mechanistically, βIV-spectrin is requisite for ankyrin-dependent targeting of calcium/calmodulin-dependent kinase II-δ; however, βIV-spectrin is not essential for ankyrin-G expression. Ankyrin-G conditional knock-out mouse myocytes display decreased Nav1.5 expression/membrane localization and reduced INa associated with pronounced bradycardia, conduction abnormalities, and ventricular arrhythmia in response to Nav channel antagonists. Moreover, we report that ankyrin-G links Nav channels with broader intercalated disc signaling/structural nodes, as ankyrin-G loss results in reorganization of plakophilin-2 and lethal arrhythmias in response to β-adrenergic stimulation.
Our findings provide the first in vivo data for the molecular pathway required for intercalated disc Nav1.5 targeting/regulation in heart. Further, these new data identify the basis of an in vivo cellular platform critical for membrane recruitment and regulation of Nav1.5.
Nav1.5（SCN5A）是主要的心脏电压门控 Nav 通道。Nav1.5 对心脏兴奋性和传导至关重要，人类 SCN5A 突变导致窦房结功能障碍、心房颤动、传导异常和室性心律失常。此外，Nav1.5 调节缺陷与与人类心力衰竭相关的恶性心律失常有关。因此，针对特定 Nav1.5 特性的治疗方法一直是心血管医学的前沿。然而，尽管经过多年的研究，Nav1.5 膜靶向、组装和调节的基本途径在很大程度上仍未得到定义。
定义 Nav1.5 膜调节的体内机制。
在这里，我们定义了心脏中 Nav 通道调节平台的分子基础。使用新的心脏选择性锚蛋白-G（-/-）（条件敲除小鼠），我们报告锚蛋白-G 将 Nav1.5 和其调节蛋白钙/钙调蛋白依赖性激酶 II 靶向到闰盘。在机制上，βIV- spectrin 是锚蛋白依赖性靶向钙/钙调蛋白依赖性激酶 II-δ所必需的；然而，βIV- spectrin 对于锚蛋白-G 的表达不是必需的。锚蛋白-G 条件敲除小鼠心肌细胞显示 Nav1.5 表达/膜定位减少和 INa 降低，与 Nav 通道拮抗剂引起的明显心动过缓、传导异常和室性心律失常相关。此外，我们报告锚蛋白-G 将 Nav 通道与更广泛的闰盘信号/结构节点连接起来，因为锚蛋白-G 缺失会导致斑联蛋白-2 重组，并对β-肾上腺素刺激产生致命性心律失常。
我们的研究结果提供了心脏中闰盘 Nav1.5 靶向/调节所需的分子途径的第一个体内数据。此外，这些新数据确定了体内细胞平台的基础，该平台对于 Nav1.5 的膜募集和调节至关重要。
