Co-ordinated expression of MMP-2 and its putative activator, MT1-MMP, in human placentation

The spatial expression of mRNA for matrix metalloproteinase 2 (MMP-2), its putative activator, the membrane-type 1 matrix metalloproteinase (MT1-MMP), and the MMP-2 substrate type IV collagen was investigated in human placentas of both normal and tubal ectopic pregnancies and in cyclic endometrium using in-situ hybridization. Cytokeratin staining applied to adjacent sections was used to identify epithelial and trophoblast cells. In both normal and tubal pregnancies MT1-MMP, MMP-2 and type IV collagen mRNA were highly expressed and co-localized in the extravillous cytotrophoblasts of anchoring villi, in cytotrophoblasts that had penetrated into the placental bed and in cytotrophoblastic cell islands. In addition, the decidual cells of normal pregnancies in some areas co-expressed MT1-MMP and MMP-2 mRNA, with moderate signals for both components. Fibroblast-like stromal cells in tubal pregnancies were positive for MMP-2 mRNA but generally negative for MT1-MMP mRNA. The consistent co-localization of MT1-MMP with MMP-2 and type IV collagen in the same subset of cytotrophoblasts strongly suggests that all three components co-operate in the tightly regulated fetal invasion process. The co-expression of MT1-MMP and MMP-2 mRNA in some of the decidual cells indicates that these cells are also actively involved in the placentation process.