Expression and localization of matrix metalloproteinases (MT1-MMP, MMP-2) and tissue inhibitor of metalloproteinase-2 (TIMP-2) during synepitheliochorial placentation of goats (Capra hircus)

Abstract

Matrix metalloproteinases (MMPs) and tissue inhibitor of metalloproteinases (TIMPs) play key roles during the placentation of highly invasive haemochorial type. Our knowledge is yet scanty, however, regarding the roles played by MMPs and TIMPs in the placentation of non-invasive synepitheliochorial type. In the present study, expression patterns of MT1-MMP, MMP-2 and TIMP-2 mRNAs as well as the encoded proteins in the endometrium and the placenta were examined on Days 35, 75, and 100 of pregnancy, representing roughly the 1st, 2nd and 3rd trimesters of caprine gestation, by means of quantitative RT-PCR analysis, in situ hybridization, immunoblotting, gelatin zymography and immunohistochemistry. In the endometrium and the intercotyledonal trophoblast, the expression levels of the 3 genes remained relatively uniform throughout the period of gestation examined. Curiously, however, in the placentomes, the relative expression levels of MT1-MMP mRNA increased linearly from Day 35 to Day 100, while those of MMP-2 and TIMP-2 were clearly down-regulated in Day 100 placentae. The expression levels of MT1-MMP and TIMP-2 proteins in placentomes were well correlated with those of the respective mRNAs. In the case of MMP-2, the total amount of MMP-2 protein (the combined values of the latent, the intermediate and the active forms) decreased slightly, while the levels of the active form increased markedly from Day 35 to Day 100. Immunohistochemical analysis of the placentome revealed that MT1-MMP and TIMP-2 proteins were co-localized in the binucleate trophoblast cells; expression of these 2 proteins was not detected in the uninuclear principal trophoblast cells. MMP-2 expression was detected both in the binucleate and in the uninuclear principal cells of the trophoblast and in the endometrial stromal cells of the uterine septum, regardless of the stages of gestation examined. The co-localization of MT1-MMP, MMP-2 and TIMP-2 in binucleate trophoblast cells, the cotyledonal trophoblast cells and the subsyncytial stromal cells is likely to reflect the functional coordination of the 3 proteins in these cells during trophoblastic invasion and the placental tissue remodeling in the placentome.