慢性缺氧致大鼠右心室心肌细胞凋亡及其机制研究

目的：通过建立大鼠慢性缺氧心肌肥大模型，探讨慢性缺氧致大鼠心肌细胞凋亡的发生规律及其机制。方法: 将大鼠随机分为慢性缺氧组和正常对照组，每组30只，慢性缺氧组置于氧浓度为(10.0±0.5)％的大型玻璃舱中，分别持续缺氧14、21、28 d,分别于第14、21、28 d处死大鼠，取心脏称重，留右心室，进行形态学观察，分析心肌细胞凋亡形态及计量，检测肌球蛋白β重链(β-MHC)、原癌基因B淋巴细胞瘤-2（bcl-2）、Bad 等mRNA及Bcl-2、Bad蛋白的表达水平。结果: (1)慢性缺氧14、21、28 d组大鼠右心室/（左心室+室间隔）［RV/(LV+S)］、右心室/体重（RV/BW）比值及右心室β-MHC mRNA和蛋白表达均明显高于正常对照组(均Ｐ<0.01)，并且随时间延长而增高(均Ｐ<0.01)。(2) 慢性缺氧心肌细胞凋亡指数14、21、28 d组大鼠均明显高于正常对照组(均Ｐ<0.01)，且随着时间的延长而增加(均Ｐ<0.01)。（3）慢性缺氧14、21、28 d组大鼠右心室bcl-2 mRNA表达和Bcl-2蛋白表达均明显低于正常对照组(均Ｐ<0.05)，缺氧28 d组bcl-2 mRNA表达和Bcl-2蛋白表达较缺氧14 d组显著降低 (均Ｐ<0.05)。慢性缺氧14、21、28 d组大鼠右心室bad mRNA表达和Bad蛋白表达与正常对照组比较无明显改变 (均Ｐ>0.05)。（4）慢性缺氧14、21、28 d组大鼠右心室bcl-2/bad比值均明显低于正常对照组(均Ｐ<0.05)，缺氧28 d组bcl-2/bad比值较缺氧14 d组显著降低 (Ｐ<0.05)。结论: 慢性缺氧可以诱导大鼠右心室心肌细胞凋亡和心肌肥大，且大鼠右心室心肌细胞凋亡和心肌肥大程度随着缺氧时间的延长而增加。慢性缺氧通过抑制大鼠右心室心肌细胞抗凋亡基因bcl-2表达，使bcl-2/bad比值下调，打破原有的平衡，导致心肌细胞凋亡。

Potential mechanism of myocardium apoptosis of right ventricle in rat under chronic hypoxia

AIM:We used an animal model of chronic hypoxia to mimic right ventricular hypertrophy and try to study the potential mechanism of myocardium apoptosis of right heart in rat under chronic hypoxia. METHODS: Rat hypoxia models were established by exposing the rats to normobaric chronic hypoxia (oxygen levels were maintained at 9.5%-10.5%). Sixty rats were separated into two groups: one exposed to hypoxia and the other serving as control. Ten rats, randomly selected from each group were killed at 14, 21, 28 d after hypoxia. The apoptosis was determined. The changes of RV weight to left ventricle and interventricular septum weight ratio［RV/(LV+S)］, the RV weight to body weight ratio (RV/BW) were also observed. The β-MHC, bcl-2 and bad mRNA levels in right ventricle were detected by semi-quantitative RT-PCR assays and expression of β-MHC, Bcl-2 and Bad protein levels were detected by Western blotting.RESULTS: The RV/(LV+S), RV/BW and apoptosis index in chronic hypoxia group were higher than those in normal control group (P<0.01). The results of RT-PCR and Western blotting showed that β-MHC mRNA levels and protein levels in chronic hypoxia group were higher than those in normal control group (P<0.01). The rate of apoptosis, the RV/(LV+S), RV/BW and the expression of β-MHC in hypoxia group all increased with time. The bcl-2 mRNA and Bcl-2 protein expressions in chronic hypoxia group were lower compared with control group at 14, 21 and 28 d (P<0.05). In contrast, no significant change of bad mRNA and Bad protein expressions in chronic hypoxia group were observed compared with control group (P>0.05). Finally, a decreased bcl-2/bad〖STBZ〗 ratio in chronic hypoxia group was found compared with control group (P<0.05). Both the expression of bcl-2 and the bcl-2/bad ratio decreased with time (P<0.05).CONCLUSION:These data demonstrate that chronic hypoxia may induce right ventricular hypertrophy, as well as cardiomyocytes apoptosis. Furthermore, apoptosis in hypertrophic cardiomyocytes induced by hypoxia is mainly due to the inhibition of bcl-2 expression and decrease of bcl-2/bad ratio.