细胞膜通道异常降解在心肌肥厚延迟整流K+电流下调中的作用及激活SGK1对其逆转作用

Electrical remodeling in cardiac hypertrophy and heart failure is characterized by the prolongation of action potential duration, which predisposes individuals to tachycardia arrhythmias. The reduction of outward K+ currents primarily contributes to the delayed repolarisation. The delayed rectifier potassium current IK plays a key role in cardiac repolarisation in big animals including human, which includes rapid (IKr) and slow component (IKs). Human ether-a-go-go-related gene (hERG) encodes the pore forming subunit of the channel underlying IKr and the channel carrying IKs consists of α-subunit encoded by KCNQ1 and β-subunit encoded by KCNE1. Evidence has shown that activation of serum and glucocorticoid inducible kinase isoform SGK1 increase the current and expression level of hERG and KCNQ1 channels on the plasma membrane by inhibiting the degradation of the channels. We and others have recently found that some neurohumoral factors participating in cardiac hypertrophy and heart failure enhance the degradation of hERG and KCNQ1 channels. Therefore, we suppose that the increased degradation of ion channels contributes to the reduction of IK density in cardiac hypertrophy and heart failure. By using electrophysiological and molecular biological technique, we will assess our hypothesis in in vitro human pluripotent stem cell-derived cardiomyocytes and in vivo guinea pig. The study was designed to define the involvement of the degradation of hERG and KCNQ1 channels on the plasma membrane in the development of electrical remodeling under pathological cardiac hypertrophy, and to evaluate the upregulatory effect of the SGK1 activation on hERG and KCNQ1 density at the plasma membrane and thus reverses the electrical remodeling and prevent arrhythmias. The results will gain insight into the molecular mechanisms for the regulation of hERG and KCNQ1 density at the plasma membrane and provide novel evidence for new target for antiarrhythmias.

心肌肥厚、心衰最突出的电重构特征是动作电位复极延迟，易诱发室性快速心律失常。外向K+电流密度减少是复极延迟的重要原因。延迟整流K+电流IK（IKr和IKs）是包括人在内的大动物心室复极的主要电流, IKr通道由hERG基因编码,IKs通道由KCNQ1和KCNE1基因编码。激活血清、糖皮质激素激酶SGK1可抑制hERG和KCNQ1的降解上调细胞膜通道数量。近期发现参与心肌肥厚、心衰的体液因素促进细胞膜上hERG和KCNQ1蛋白的降解。由此我们假设通道降解增加是心肌肥厚病理状态下IK电流密度减小的重要原因。本项目利用电生理、分子生物学技术在人干细胞分化心肌细胞和整体豚鼠心室肥厚模型，拟研究hERG和KCNQ1通道蛋白降解在电重构中的作用、激活SGK1对病理状态下细胞膜IK通道数量的上调作用以及对心肌肥厚心律失常的防治作用。研究将为揭示IK通道转运调控机制、抗心律失常靶点提供新的思路。

病理性心肌肥厚是高血压、心肌缺血、糖尿病心肌病等多种心血管疾病的常见合并症，与心肌肥厚相伴的电生理重构主要表现为心室动作电位复极延迟，使得心律失常、心源性猝死的发生率大大提高，而现有抗心律失常药物大多同时具有潜在的致心律失常风险而使用受限。因此，亟待揭示电重构致心律失常发生的分子机制、寻找新的防治靶点。延迟整流K+电流（IK）是心室动作电位晚期复极的主要电流，包括快激活IKr和慢激活IKs两种成分，已知IK密度减少是心肌肥厚复极延迟的重要原因，但迄今缺乏有效的干预手段。该项目重点研究了泛素中介的膜蛋白降解机制在心肌肥厚IK减少中的作用，探讨了不同的干预手段。主要创新性发现为：（1）病理性心肌肥厚时由泛素中介的细胞膜离子通道降解增加是IKr减小、动作电位时程（APD）延长及因此导致心律失常的重要原因；（2）以SGK1间接抑制泛素连接酶Nedd4-2的方法干预后并不能预防病理性电重构；而心脏特异性过表达无活性Nedd4-2可有效预防IKr减小、APD延长；（3）自行设计的短肽竞争抑制Nedd4-2中介的IKr通道泛素化降解，增加膜通道数量，在整体动物模型和体外内皮素诱导hiPS-CM肥厚模型显示出预防病理性电重构及心律失常的保护效果。上述研究发现为理解心肌病理情况下通道功能改变的机制提供了新的认识，为开发新型抗心律失常药物提供了新靶点，自行设计的选择性Nedd4-2抑制短肽具有新药开发潜力。