哺乳期双酚A暴露致小鼠睾丸生精细胞减数分裂阻滞的机制研究

Mechanism of meiotic arrest of spermatogenic cells in testis of mice exposed to bisphenol A during lactation

[背景]双酚A(BPA)作为环境内分泌干扰物的一种,能够干扰生精细胞减数分裂进程,进而影响睾丸发育和精子发生,但其影响生精细胞减数分裂的机制仍不清楚。[目的]探讨哺乳期小鼠BPA暴露对睾丸内调控生精细胞减数分裂和细胞周期相关因子表达的影响。[方法]新生ICR雄性仔鼠随机分为3组:对照组(玉米油)、BPA低剂量组(0.1 mg·kg^(-1))、BPA高剂量组(5 mg·kg^(-1)),每组10只。仔鼠于出生后第1天(PND1)开始每天颈背部皮下注射药物持续到PND21断奶。PND22颈椎脱臼处死小鼠后记录小鼠体重,剥取睾丸并称取睾丸重量。流式细胞术DNA倍体分析法检测哺乳期BPA暴露对睾丸生精细胞DNA含量的影响。Western blotting检测睾丸中细胞周期相关蛋白Cdc25A、Cdc25C、Wee1、p-Tyr15 Cdc2、CDK1表达量的变化情况,RT-PCR检测睾丸中细胞周期相关基因Cdc25A、Cdc25C、Wee1、CDK1mRNA水平的变化。[结果]BPA低、高剂量组小鼠体重、睾丸重量及睾丸系数与对照组的差异无统计学意义(均P>0.05)。流式细胞术分析结果显示:低、高剂量组二倍体细胞所占比例分别为(25.05±1.62)%、(25.25±6.67)%,较对照组[(49.33±6.91)%]减少(均P<0.01);低、高剂量组四倍体细胞所占比例分别为(45.89±1.95)%、(51.11±8.89)%,较对照组[(24.72±6.44)%]增多(均P<0.01);低、高剂量组间单倍体细胞和S期细胞所占比例与对照组相比,差异无统计学意义(均P>0.05)。Western blotting结果显示:与对照组相比,BPA高、低剂量染毒组睾丸组织Cdc25A、Cdc25C、Wee1、p-Tyr15 Cdc2蛋白表达水平均降低(均P<0.05);CDK1蛋白表达无明显变化(P>0.05)。RT-PCR结果显示:与对照组相比,BPA染毒组睾丸组织Cdc25A、Cdc25C、Wee1、CDK1的mRNA表达水平差异均无统计学意义(均P>0.05)。[结论]哺乳期BPA暴露能够改变小鼠睾丸内生精细胞的周期分布。BPA可能通过下调细胞周期调控因子Cdc25A、Cdc25C、Wee1的翻译水平使初级精母细胞减数分裂发生阻滞,从而干扰了生精细胞分化进程。

[Background]Bisphenol A(BPA),one of the endocrine disrupting chemicals,can interfere with the meiosis of spermatogenic cells and affect testicular development and spermatogenesis.However,the mechanism of this effect is still unclear.[Objective]This experiment examines the effects of exposure to BPA on the regulation of spermatogenic cell meiosis and cell cycle-related factor expression in the testis of lactating mice.[Methods]Newborn ICR male offspring mice were randomly divided into three groups,with 10 mice in each group:a control group(corn oil),a low-dose BPA group(0.1 mg·kg^(-1)),and a highdose BPA group(5 mg·kg^(-1)).The newborn mice were injected subcutaneously with BPA or corn oil daily from postnatal day 1(PND1)to PND21.They were euthanized by cervical dislocation on PND22.The body weight was recorded and the testes were removed and weighed.Flow cytometry DNA ploidy analysis was used to detect the effects of lactational exposure to BPA on the DNA content of testicular spermatogenic cells.Western blotting was used to measure the expressions of cell cycle-related proteins(Cdc25 A,Cdc25 C,Wee1,p-Tyr15 Cdc2,and CDK1)in testis.RT-PCR was used to determine the expressions of cell cycle-related genes(Cdc25 A,Cdc25 C,Wee1,and CDK1 m RNA)in testis.[Results]Compared with the control group,there were no significant differences in body weight,testis weight,and testis coefficient of the low-dose and high-dose BPA groups(all P>0.05).The flow cytometry results showed that the proportions of diploid cells in the lowand high-dose groups were(25.05±1.62)%and(25.25±6.67)%,respectively,which were less than that in the control group[(49.33±6.91)%](both P<0.01).The proportions of tetraploid cells in the low-and high-dose groups were(45.89±1.95)%and(51.11±8.89)%,respectively,which were more than that in the control group[(24.72±6.44)%](P<0.01).The proportions of haploid cells and S phase cells in the low-and high-dose groups were not different from the proportions of the control group(P>0.05).The Western blotting results showed that compared with the control group,the protein expression levels of Cdc25 A,Cdc25 C,Wee1,and p-Tyr15 Cdc2 in testicular tissues of the two BPA groups decreased(P<0.05),but the expression of CDK1 protein had no significant change(P>0.05).The RT-PCR results showed that compared with the control group,there were no significant differences in the expression levels of Cdc25 A,Cdc25 C,Wee1,and CDK1 m RNA in testicular tissues of the BPA exposed mice(all P>0.05).[Conclusion]Exposure to BPA during lactation can change the cycle proportion of spermatogenic cells in the testis of mice.BPA could arrest the meiosis of primary spermatocytes by down-regulating the translation levels of cell cycle regulators Cdc25 A,Cdc25 C,and Wee1,thereby interfering with the differentiation process of spermatogenic cells.