电压门控钠通道β1及β1b亚基在心脏电生理中的作用

Cardiac sodium channelopathies are important reasons responsible for lethal cardiac arrhythmia. It is composed of one αsubunit and two β subunits. Mutations in gene SCN1B has been associated with human cardiac arrhythmia such as atrial fibrillation, cardiac conduction defects, long QT syndrome and Brugada syndrome. SCN1B encodes two splice varients, β1 and β1b. We found that β1 and β1b can differentially modulate sodium current and channel biophysical properties. Since mutations either affect β1 or β1b could lead to arrhythmia, we proposed that β1 and β1b play different electrophysiological roles in the heart. We will study the cardiac phenotype in genetically manipulated mouse model, in which β1 or β1b was reintroduced in Scn1b null mice via bacterial artificial chromosome. This study will not only promote our understanding of electrophysiological role of β1 and β1b in the heart, but also be a critical step in the development of risk stratification and therapeutic strategies to the cardiac sodium channelopathy.

心脏电压门控钠通道突变是导致致死性恶性心律失常的重要原因，钠通道由一个α及两个β亚基构成。SCN1B基因突变已被发现与多种心律失常如房颤，心脏传导系统疾病，长QT间期综合征以及Brugada综合征相关。SCN1B基因编码钠通道β1及β1b两个亚基，互为剪切变体。我们在体外细胞系中观测到β1及β1b均可调控钠电流，通道生物物理特性，但作用方式不同。结合临床中发现β1、β1b突变均可导致心律失常。我们提出β1和β1b在心脏电生理中均有重要作用，且作用不同的假设。拟通过细菌人工染色体（BAC）在Scn1b敲除鼠（β1及β1b双缺失）中重新导入β1或β1b来研究单个剪切变体在心脏中的作用。通过对单纯缺失β1或β1b模型表型的研究，有助于我们理解SCN1B突变所致心律失常的机制。以期将来为心脏钠离子通道并的治疗、风险分层及预后判断提供依据。

在本研究中，我们探索了心脏钠通道scn1b的两个剪切变体beta1和beta1在心脏电生理中的作用。通过构建Kv4.3稳定转染的体外细胞株，转入beta1和beta1b，发现两剪切变体具有相反的效应：beta1b使Kv4.3电流密度增大，细胞膜上的表达增多，而转染了beta1后Kv4.3电流密度降低，上膜减少。同时，免疫荧光显示beta1b能够滞留在细胞膜上，且与Kv4.3存在共定位。另外，我们构建了SCN1B心脏特异性敲除小鼠，发现其表现出明显的QRS波增宽，提示潜在的室性心律失常。通过AAV9分别将beta1和beta1b分别导回敲除鼠中，能够实现在体内验证两个剪切变体对Kv4.3的作用并探索其他的电生理表型，我们的研究为今后理解scn1b对心律失常的作用提供重要参考。