HMGB1引起心肌细胞肌浆网钙漏流的作用和机制及其在缺血-再灌注心脏损伤中的作用

Recent studies have reported that cardiac ischemia-reperfusion (I/R) injury enhances sarcoplasmic reticulum (SR) Ca2+ leak by reducing the stability of cardiac ryanodine receptor (RyR2) at diastole. The enhancement of Ca2+ leak results in severe cardiac dysfunction by inducing reduction of cardiac contractility and myocardial injury. However, the mechanisms underlying the I/R injury-induced cardiac SR Ca2+ leak are largely unknown. Recently, we examined the effect of high mobility group box1 (HMGB1), an inflammatory factor which plays an important role in cardiac I/R injury,on the occurrence of Ca2+ sparks which reflect RyR activities in cardiomyocytes. Our preliminary data demonstrated that HMGB1 increased the frequency of Ca2+ sparks, indicating that HMGB1 enhances SR Ca2+ leak. In this project, we will elucidate the mechanism underlying HMGB1 enhancing SR Ca2+ leak. We will test the hypothesized mechanism, that is HMGB1 activates receptors of advanced glycation end product (RAGE) and/or toll-like receptor 4 (TLR4) - reactive oxygen species (ROS) signaling pathway(s). Increased intracellular ROS increases oxidative stress and oxidative modification of RyR2, which induces conformational change of RyR2 and dissociation of FKBP12.6 from RyR2, resulting in hyperactive RyR2 and SR Ca2+ leak. Furthermore, we will investigate the role of HMGB1 in the pathogenesis of SR Ca2+ leak in cardiac I/R injury. Meanwhile, we will study the involvement of HMGB1 in the pathogenesis of cardiac arrhythmia, reduction of cardiac contractility and myocardial injury, the major detrimental outcomes of SR Ca2+ leak in cardiac I/R injury. Through these efforts, we hope to enrich our understanding of the mechanisms of cardiac I/R injury and shed new lights on the treatment of cardiac I/R injury.

心脏缺血-再灌注(I/R)损伤降低心肌细胞舒张期肌浆网(SR)钙释放通道－ryanodine receptor(RyR2)稳定性，造成SR钙漏流，通过引起心肌收缩力减弱、心肌损伤等导致心脏功能严重损害。我们前期工作发现，在I/R损伤中起重要作用的炎症因子高迁移率族蛋白B1(HMGB1)增加心肌细胞SR钙漏流。本研究拟采用共聚焦显微钙成像技术、分子生物学、在体复制I/R模型、膜片钳和心电功能检测等技术开展以下研究：1.阐明HMGB1引起SR钙漏流的机制，是否激活糖基化终产物受体(RAGE)和/或Toll样受体(TLR4)-氧自由基信号通路，通过增强RyR2氧化应激降低RyR2稳定性，导致SR钙漏流。2.查明HMGB1在I/R损伤所引起的SR钙漏流中的作用，以及HMGB1在I/R损伤引起的心律失常、心肌收缩力减弱和细胞损伤中的作用。进一步阐明I/R心脏损伤的机制，为临床治疗提供新思路.

心脏缺血-再灌注(I/R)损伤增强心肌细胞舒张期肌浆网(SR)钙释放通道－ryanodine receptor (RyR2)活性，造成SR钙漏流，通过引起心律失常、心肌收缩力减弱、心肌损伤等导致心脏功能严重损害。但I/R 引起心肌细胞SR 钙漏流的研机制尚不清楚。. 在I/R损伤中起重要作用的炎症因子高迁移率族蛋白B1(HMGB1)可以呈浓度依赖性增加钙火花发放频率，引起心肌细胞SR钙漏流，进而减小动作电位诱发的收缩期钙瞬变以及心肌细胞缩短幅度，减弱心肌收缩力，造成I/R心肌损伤。. 通过应用TLR4受体的阻滞剂TAK-242及RNA干扰降低TLR4表达，可以显著抑制HMGB1引起的高频钙火花发放。应用抗氧化剂MnTBAP亦可以抑制HMGB1引起的高频钙火花发放。进一步应用TLR4阻滞剂TAK-242同样可以抑制HMGB1引起的ROS生成和RyR2氧化修饰。因此，TLR4 - ROS 信号通路在HMGB1 引起的SR 钙漏流中的发挥着重要的作用。. 复制心脏I/R模型，I/R小鼠心肌细胞钙火花发放频率异常增加，钙漏流增强，钙信号调控紊乱。给予抑制肌浆网钙漏流的药物JTV-519进行在体治疗，可以显著抑制心肌细胞钙火花异常发放，显著增强模型小鼠的心肌收缩力和恢复心功能。利用TLR4-/-小鼠复制心脏I/R模型，亦显著抑制I/R 引起心肌细胞SR 钙漏流，进一步明确了HMGB1通过TLR4 - ROS 信号通路在I/R 损伤SR 钙漏流发生和心功能损害中的作用。. 综上所述，本项目揭示了I/R 心脏损伤中的重要炎症因子——HMGB1，通过引起心肌细胞钙火花异常发放、SR 钙漏流而造成心脏损伤，这在I/R 心脏损伤发病机制的理论研究上具有创新性。阐明HMGB1 造成心脏损伤的机制，可以针对性地抑制其损害作用，保留其促进梗死心脏再生修复的有益作用，对临床I/R 心脏损伤的治疗提供新的靶点和思路。因此，本研究具有重要的基础理论价值和临床治疗意义。