RESUMEN
BACKGROUND: Human placentation is mediated by fetal trophoblastic cells that invade the maternal uterine endometrium. Trophoblast invasion requires a precisely regulated secretion of specific proteolytic enzymes able to degrade the endometrial basement membrane and extracellular matrix. EXPERIMENTAL DESIGN: Several studies have documented the key roles of matrix metalloproteinases and their tissue inhibitors in the invasion of various matrices by cultured trophoblasts. In vitro studies suggest that placentation could result from a balance between the secretion of these enzymes by trophoblast cells and their inhibition by the natural tissue inhibitors (TIMPs) produced by maternal decidual cells. The precise localization and levels of expression of these proteins that account for and control invasion during human placentation in vivo however, have not been described. We have evaluated, in vivo, by immunohistochemistry, Northern blot analysis and in situ hybridization, the expression of two metalloproteinases (gelatinases A and B) and their two tissue inhibitors (TIMPs 1 and 2) in placental villi and placental beds of first and third trimesters of normal pregnancy. RESULTS: Human first trimester intermediate trophoblast produced both gelatinases A and B; these two gelatinases were respectively less and no more detected at term in these cells. We found that both TIMP1 and 2 were also expressed in maternal decidual cells with a dramatic increase of TIMP1 at the term of pregnancy. In floating villi, gelatinase A and TIMP1 were localized in the stromal compartment, whereas gelatinase B and TIMP2 were codistributed in trophoblast cells. CONCLUSIONS: The gelatinases A and B and their tissue inhibitors are thus expressed by specific cells in early and late placental beds and villi. This pattern of expression varies during pregnancy. Therefore, our morphologic study supports biologic findings suggesting that these proteins may participate in placentation.