Matrix Metalloproteinases and Their Endogenous Inhibitors During the Implantation Period in the Rat Uterus

Rats were studied to determine if matrix metalloproteinases (MMPs) and tissue inhibitors of MMPs (TIMPs) were detectable in developing embryonic and uterine tissues during the implantation period; that is, Days 6-8 of pregnancy. Tissue extracts were studied by zymography, reverse zymography and Western blotting. Immunohistochemistry procedures using antibodies against MMPs and TIMPs were applied to tissue sections that passed through implantation sites. The MMP inhibitor, doxycycline, was injected intraluminally into uterine horns of pseudopregnant animals. MMP-2 and -9, and TIMP-2 were detected in gelatin and reverse zymographs, respectively, from extracts of implantation sites on each day studied. Western blots defined bands corresponding to MMP-1, but casein zymographs did not consistently show evidence of extractable MMP-1 or -3. In tissue sections the primary decidual tissue area stained consistently for TIMP-2 and on Days 7 and 8 this area also had positive staining for MMP-1 in close proximity to the implanting embryo. On Day 8 positive staining in the outer stromal tissue was detected using an antibody against MMP-9, and another MMP (possibly MMP-3) was localized exclusively in ectoplacental cone/trophoblastic cells. Intraluminal injection of doxycycline did not significantly prevent the growth of the uterine horns following surgical induction of pseudopregnancy on Day 5. The strong localization of TIMP-2 in the primary decidual tissue is similar to that reported previously for TIMP-3, indicating that these inhibitors have a role in decidualization, including the regulation of trophoblastic invasion.