钙激活中性蛋白酶在脓毒症小鼠心肌半胱氨酸蛋白酶-3活化中的作用及其机制

Association between myocardial calpain activation and apoptosis in lipopolysaccharide-induced septic mouse model

目的 探讨钙激活中性蛋白酶（calpain）在脓毒症小鼠心肌半胱氨酸蛋白酶-3（caspase-3）活化中的作用及其机制.方法 （1）体内实验：腹腔注射脂多糖（LPS,4 mg/kg）建立脓毒症小鼠模型.Western blot检测心肌组织中calpain、caspase-3活性和calpain-1、calpain-2、calpain特异性抑制蛋白calpastatin水平以及凋亡相关蛋白Bcl-2、Bid水平及剪切片段,TUNEL法检测心肌细胞凋亡情况,Langendorff灌注装置评价小鼠心脏的收缩和舒张功能.（2）体外实验：成年大鼠心肌细胞给予LPS（1μg/ml）处理4 h,或同时予以calpain抑制剂calpain inhibitor-Ⅲ（10 μmol/L）干预后,检测心肌细胞calpain和caspase-3活性,Bcl-2、Bid蛋白水平以及心肌细胞凋亡情况.结果 （1）体内实验：在脓毒症小鼠心肌组织中,calpain活性增高2.7倍,caspase-3活性增高1.8倍,给予calpain-inhibitor-Ⅲ或PD150606,均可抑制caspase-3活性的增高.脓毒症小鼠心肌组织calpain-1、calpain-2、calpastatin以及Bcl-2、Bid蛋白水平未见改变,亦未检测到Bcl-2、Bid剪切片段.Calpain inhibitor-Ⅲ则可使脓毒症小鼠心室最快压力上升速率和心室最快压力下降速率分别增加34.5%和34.6%,从而改善脓毒症小鼠心功能障碍.（2）体外实验：LPS可诱导成年大鼠心肌细胞calpain和caspase-3活性增高,给予calpain inhibitor-Ⅲ则可抑制caspase-3活性的增高,心肌细胞Bcl-2、Bid蛋白水平未见改变.体内外实验均未发现LPS可诱导心肌细胞凋亡的增加.结论 脓毒症小鼠心肌calpain活性增高,可活化心肌caspase-3,但未导致心肌细胞凋亡,其机制与凋亡蛋白Bcl-2和Bid无关.

Objective In septic mice, myocardial calpain was activated and induced caspase-3 activation, the association between calpain activation and apoptosis was explored in this experiment. Methods In in vivo model, adult C57 mice were injected with lipopolysaccharide （LPS, 4rg/kg, i. p. ） to induce sepsis. Myocardial calpain and caspase-3 activities, protein levels of calpain-1,calpain-2, calpastatin, Bcl-2 and Bid were detected by Western blot analysis and myocardial apoptosis was detected by TUNEL, myocardiac function was evaluated by Langendorff system. In in vitro model, adult rat cardiomyocytes were incubated with LPS （1μg/ml） or co-incubated with calpain inhibitor-Ⅲ （10μmol/L）, calpain activity, caspase-3 activity, protein levels of Bcl-2 and Bid, and cardiomyocyte apoptosis were detected. Results In septic mice, myocardial calpain and caspase-3 activity were increased up to 2. 7-and 1.8-folds, respectively. Both calpain inhibitor-Ⅲ and PD150606 significantly attenuated the increase of caspase-3 activity. Myocardial protein levels of calpain-1, calpain-2, calpastatin, Bcl-2 and Bid were similar between control and septic mice, and no cleavage of both Bcl-2 and Bid was found in septic mice. Calpain inhibitor-Ⅲ significantly improved myocardial function in septic mice. In in vitro model, calpain and caspase-3 activities were increased after 4 h LPS treatment, co-treatment with calpain inhibitor-Ⅲ prevented caspase-3 activity increase, protein Bcl-2 and Bid were similar between normal cardiomyocytes and LPS-treated cardiomyocytes. Cardiomyocyte apoptosis was similar in in vivo and in vitro septic models. Conclusion Myocardial calpain activity is increased in LPS induced septic mice, subsequent caspase-3 activation may contribute to myocardial dysfunction in septic mice without aggravating myocardial apoptosis and Bcl-2 and Bid are not involved on calpain induced caspase-3 activation in our model.