钙释放单位超微重构介导的矛盾性“钙钟”致窦性心动过缓机制研究

Based on the theory“Calcium clock”, enhanced Ca2+ release of Ryanodine receptor (RyR2) function would increase the automaticity of sinoatrial node cell (SANC). Catecholaminergic polymorphic ventricular tachycardia (CPVT) is characterized by the “gain of function” of RyR2, while the patients with CPVT paradoxically manifest sinus bradycardia (SBC). Recently we observed that CPVT mouse CASQ2 R33Q had a resting SBC; in isolated SANC, calcium spark frequency was high, however calcium wave propagation in SANC was always aborted. Previously we demonstrated that calcium release unit (CRU) remodeling was responsible for the aborted calcium wave propagation in isolated R33Q ventricular myocytes, so we proposed that there is a remodeling of CRU in isolated R33Q SANC which hampers the propagation of calcium leak in R33Q SANC, thus impairing the key factor for the automaticity of “Calcium clock”. This project has 2 aims. Aim 1 will verify our hypothesis by multipe state-of-the-art techniques including patch clamp, calcium imaging, super-resolution microscopy at different levels spanning from in vivo whole-animals to cell ultrastructure. Aim 2 will test whether viral gene transfer of CASQ2 wild-type gene can rescue the sinus bradycardia in CPVT mouse CASQ2 R33Q. The proposed work will elucidate a novel mechanism for SBC and identify a promising therapeutic target for SBC.

“钙钟”理论认为RyR2钙漏增加将提高窦房结细胞的自律性。儿茶酚胺敏感性室速（CPVT）患者RyR2钙漏增加，却表现出矛盾性窦性心动过缓（窦缓）。前期工作中课题组证实：CPVT小鼠CASQ2 R33Q心室肌细胞存在钙释放单位超微重构，造成自发性钙波传递障碍；R33Q小鼠存在窦缓，窦房结细胞钙漏增加，且不易形成可扩散的钙波。我们推测R33Q的窦房结细胞可能存在钙释放单位重构，损害其自发性钙波的形成，从而使窦房结细胞触发延迟和自律性下降。本项目立足于前期基础，在R33Q小鼠模型上，首先利用在体和离体电生理检测、钙显像以及超高分辨率显微镜等技术，从整体-细胞-超微结构三个层次，探讨窦房结细胞钙释放单位超微重构致窦缓的机制；后验证以腺相关病毒为载体补充野生型CASQ2的治疗策略能否治疗窦缓。本课题将阐明钙调节紊乱致窦缓的全新机制，是“钙钟”理论的重要补充，将为窦缓的防治提供科学依据。

“钙钟”理论认为RyR2钙漏增加将提高窦房结细胞的自律性。儿茶酚胺敏感性室速（CPVT）患者RyR2钙漏增加，却表现出矛盾性窦性心动过缓（窦缓）。本项目采用在体和离体电生理检测技术明确CPVT转基因CASQ2 R33Q小鼠SANC自律性下降，利用钙显像、膜片钳和电镜检测等技术，从整体-细胞-超微结构三个层次，明确R33Q SANC HCN电流无明显差异，自律性明显降低，自发性钙波发生频率降低，钙火花较小而多，细胞纤维化程度无明显差异，超微结构显示TT周长减少，TT与SR耦联的二联体耦联显著减少，单个耦联子内耦联SR的TT长度占TT周长的百分比均显著降低。利用药物干预（低剂量ISO）后R33Q小鼠心率增加较慢且更易发生心律失常，在细胞水平出现明显钙漏。窦房结细胞CRUs超微重构，小而多的钙火花导致虽然钙漏增加，但钙波扩散减缓，自律性降低，可能是CPVT患者心动过缓的机制。本课题阐述了钙调节紊乱致窦缓的全新机制，是“钙钟”理论的重要补充，将为窦缓的防治提供科学依据。