Junctophilin-2调控窦房结细胞内钙信号及起搏机制研究

Cardiac rhythm is controlled by the spontaneous electrical activity of the sinoatrial node (SAN), and SAN dysfunction is one of the major causes of human cardiovascular disease. A key unanswered question is the origin of SAN cell spontaneous diastolic depolarization. Classic studies have suggested a preeminent role for sarcolemmal voltage-gated ion channels for depolarization (“membrane or voltage clock”). More recently, multiple groups have implicated a critical role for intracellular Ca2+ in SAN automaticity (“Ca2+ clock”). The emerging realization that cellular Ca2+ homeostasis is fundamental to SAN function raises basic questions about molecular and cellular mechanisms for controlling SR Ca2+ release in SAN cells. However, the mechanism of how SR Ca2+ release is controlled in SAN cells remains unclear. Our exciting preliminary data showed that JP2, the only junctophilin family member found in the heart that mediates the junctional coupling between plasma membrane and intracellular sarcoplasmic reticulum (SR), plays a critical role and contributes to heart rate regulation. In the proposed studies, we will utilize cardiac specific transgenic mice with either JP2 overexpression or knockdown, in combination with high resolution confocal microscopy, patch-clamp electrophysiology and electron microscopy, to investigate the essential role of JP2 in SAN intracellular calcium regulation and ultrastructure of SAN cells. This project will elucidate the fundamental role of JP2-mediated plasma membrane / SR coupling in regulating intracellular Ca2+ of SAN cells and heart rate control.

正常心脏节律受窦房结自发性电活动控制。窦房结细胞舒张期自动去极启动动作电位，驱动节律性心跳。既往研究提出“膜钟或电压钟学说”，认为窦房结起搏机制依赖于细胞膜电压门控离子通道的周期性激活与失活。近年来又提出“钙钟学说”，认为窦房结细胞内肌浆网自发性钙释放是窦性心律运转机制。课题组前期研究发现，Junctophilin-2 （JP2）作为心肌细胞膜和肌浆网间迄今唯一的结构偶联分子，具有明显的调节心脏节律作用。本研究将利用实验室已有的心脏特异性JP2超表达或敲除的转基因小鼠，结合高分辨率激光共聚焦显微镜钙成像和心肌电生理技术，观察JP2对窦房结细胞内钙调控作用，并应用透射电子显微镜技术，观察窦房结细胞超微结构。本研究将阐明JP2介导的膜-肌浆网偶联机制在窦房结细胞内钙调控和心率调节中的作用，有助于加深对窦房结胞内钙调控及心脏起搏机制的全面认识。