by Jianfeng Xiao, Yanmei Liu, Zhiling Li, Yongcui Zhou, Hong Lin, Xiaoyan Wu, Man Chen, Wanfen Xiao

Cryopreservation of human semen for assisted reproduction is complicated by cryodamage to spermatozoa caused by excessive reactive oxygen species (ROS) generation.

We used exogenous ROS (H₂O₂) to simulate cryopreservation and examined DNA damage repair in embryos fertilized with sperm with H₂O₂-induced DNA damage. Sperm samples were collected from epididymis of adult male KM mice and treated with capacitation medium (containing 0, 0.1, 0.5 and 1 mM H₂O₂) or cryopreservation. The model of DNA-damaged sperm was based on sperm motility, viability and the expression of ?H2AX, the DNA damage-repair marker. We examined fertility rate, development, cell cleavage, and ?H2AX level in embryos fertilized with DNA-damaged sperm. Cryopreservation and 1-mM H₂O₂ treatment produced similar DNA damage. Most of the one- and two-cell embryos fertilized with DNA-damaged sperm showed a delay in cleavage before the blastocyst stage. Immunocytochemistry revealed ?H2AX in the one- and four-cell embryos.

?H2AX may be involved in repair of preimplantation embryos fertilized with oxygen-stressed spermatozoa.