Expression of Maspin in the Early Pregnant Mouse Endometrium and Its Role during Embryonic Implantation

Maspin (serpin B5), a tumor-suppressing member of the serine protease inhibitor family, participates in cell migration, adhesion, invasion, and apoptosis. These processes are also critical for embryo implantation, but the role of maspin in embryo implantation remains poorly understood. The aim of the present study was to investigate the spatiotemporal expression of maspin in early pregnant mouse endometrium and its role in embryo implantation. Real-time quantitative PCR analysis, immunohistochemistry, and Western blotting were used to detect mRNA and protein expression of maspin in the endometria of nonpregnant and early pregnant (days 0 to 7) mice. On day 3 of pregnancy, mice in the treated group (n = 20) were injected in the left uterine horn with antimaspin polyclonal antibody and in the right horn with purified rabbit IgG; control mice (n = 20) were injected only with purified rabbit IgG in the right uterine horn. Implanted embryos were counted on pregnant day 8. The mRNA and protein expressions of maspin were higher in the endometria of pregnant mice than nonpregnant mice; these levels gradually increased from day 1 of pregnancy, peaked on day 5, and then decreased on days 6 and 7. The mice treated with antimaspin polyclonal antibody group had far fewer implanted embryos than did the control group. Taken together, these results suggest that maspin, a tumor suppressor, may play an important role in embryo implantation.