三氧化二砷对小鼠卵母细胞线粒体DNA氧化损伤作用及其机制

Oxidative damage to mitochondrial DNA induced by arsenic trioxide in mouse oocytes in vitro and in vivo

目的研究三氧化二砷(As2O3)对小鼠卵母细胞线粒体DNA(mt DNA)的氧化损伤作用及其作用机制。方法 1体外实验挤压正常小鼠卵巢获取卵母细胞,培养成熟后,分为As2O31和2μmol·L-1单独处理组、N-乙酰半胱氨酸(NAC)5 mmol·L-1处理组、2,2,6,6-四甲基哌啶-1-氧基(Tempo)1 mmol·L-1处理组、As2O31或2μmol·L-1+NAC 5 mmol·L-1共处理组、As2O31或2μmol·L-1+Tempo 1 mmol·L-1共处理组,培养20 h后,收集成熟卵母细胞进行后续实验指标测定。2体内实验雌性昆明小鼠ip给药,分为As2O31和2 mg·kg-1染毒组、As2O31或2 mg·kg-1+NAC 200 mg·kg-1组,每日1次,连续60 d,椎脱臼处死取卵母细胞。2′,7′-二氯荧光黄双乙酸盐荧光染色检测细胞内活性氧(ROS)水平;8-羟基脱氧鸟苷酶(8-OHd G)联免疫反应检测提取mt DNA中8-OHd G含量;Western蛋白印迹法检测DNA聚合酶γ(Polγ)和线粒体转录因子A(mt TFA)的蛋白表达;β-半乳糖苷酶(β-Gal)报告基因检测试剂盒检测溶酶体活力。结果 1体外实验As2O3单独处理组小鼠卵母细胞中ROS和8-OHd G含量升高,Polγ和mt TFA蛋白表达水平降低(P<0.05);而As2O3与NAC或Tempo共处理组卵母细胞中ROS含量减少,8-OHd G水平降低,Polγ和mt TFA蛋白表达水平显著上调(P<0.05)。2体内实验As2O3单独处理组小鼠卵母细胞中ROS和8-OHd G含量升高,Polγ和mt TFA蛋白表达水平降低(P<0.05);As2O3与NAC共处理组小鼠卵母细胞中ROS含量减少,8-OHd G水平降低,Polγ和mt TFA蛋白表达水平提高(P<0.05)。As2O3单独处理组体外培养的卵母细胞,β-Gal活力显著提高(P<0.05),而As2O3与NAC或Tempo共处理组β-Gal活力显著下降(P<0.05)。体内实验各处理组β-Gal活力无显著差异。结论砷暴露可诱导小鼠卵母细胞大量生成ROS,抑制线粒体基因组修复与复制相关因子Polγ及mt TFA的表达,同时改变溶酶体活力,最终诱发mt DNA氧化损伤。

OBJECTIVE To investigate the arsenic trioxide（As2O3）-induced oxidative damage to mitochondrial DNA（mt DNA） in mouse oocytes and possible mechanisms. METHODS 1 For in vitro assay,the mouse oocytes were denuded from ovaries of normal mice and incubated in medium for 20 h in different treatment groups：control,As2O31 and 2 μmol · L- 1,N- acetylcysteine（NAC）5 mmol·L- 1, 2,2,6,6-tetramethyl-1-piperidinyloxy（Tempo）1 mmol·L- 1,As2O3（1 and 2 μmol·L- 1）＋NAC 5 mmol·L- 1,As2O3（1 and 2 μmol·L- 1）＋Tempo 1 mmol·L- 1. 2 For in vivo assay,mice were subjected to ip injection with physiological saline（normal control）,As2O31 and 2 mg·kg- 1,or As2O3（1 and 2 mg·kg- 1）＋NAC 200 mg·kg- 1, respectively. After 60 d,all the mice were sacrificed and their ovaries were quickly excised. Intracellular reactive oxygen species（ROS） levels were determined by 2′,7′- dichlorofluorescein- diacetate（DCFH- DA）. The oxidative damage to mt DNA was induced using enzyme-linked immunosorbent assay（ELISA）for 8-hydroxy-2′-deoxyguanosine（8-OHd G）. The expression of DNA polymerase γ（Pol γ）and mitochondrial transcription factor A（mt TFA）was detected by Western blotting and the vitality of lysosomes was monitored by β-galactosidase（β-Gal）Assay Kit.RESULTS 1 In vitro experiments,As2O3 elevated 8-OHd G levels of mt DNA in mouse oocytes accompanied by increased levels of ROS（P〈0.05）,but co- treatment with NAC or Tempo significantly reduced ROS and 8- OHd G levels（P〈0.05）. Meanwhile, the expression levels of Pol γ and mt TFA were down-regulated by As2O3（P〈0.05）,but were markedly elevated by the addition of NAC or Tempo（P〈0.05）. 2 In vivo assay,As2O3 elevated ROS as well as 8- OHd G levels of mt DNA in mouse oocytes,while the expression levels of Pol γ and mt TFA were down-regulated by As2O3（P〈0.05）. Co-treatment with NAC significantly reduced ROS and 8-OHd G levels,but markedly elevated Pol γ and mt TFA levels（P〈0.05）. Besides,a notable increase in β-Gal activity was shown in As2O3-treated mouse oocytes in vitro（P〈0.05）,while antioxidants efficiently reduced the activity（P〈0.05）.However,no significant changes were observed in the in vivo study. CONCLUSION The oxidative damage to mt DNA induced by As2O3 in mouse oocytes may be mediated by ROS and associated with down- regulation of protein levels of Pol γ and mt TFA as well as increment of lysosomal activity.