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

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 (Cdc25A, Cdc25C, Wee1, p-Tyr15 Cdc2, and CDK1) in testis. RT-PCR was used to determine the expressions of cell cycle-related genes (Cdc25A, Cdc25C, Wee1, and CDK1 mRNA) 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 Cdc25A, Cdc25C, 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 Cdc25A, Cdc25C, Wee1, and CDK1 mRNA 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 Cdc25A, Cdc25C, and Wee1, thereby interfering with the differentiation process of spermatogenic cells.