[The regulation of endometrial and trophoblastic metalloproteinases during blastocyst implantation]

The trophoblastic cells of the blastocyst and of the placenta express an invasive phenotype. These cells produce and secrete metalloproteinases which are capable of digesting the extracellular matrix and invade it. The different endometrial cells produce the same enzymes and favour thus the implantation process. Among the numerous endometrial factors that control trophoblastic invasion, the components of the extracellular matrix such as laminin and fibronectin, play an important role. These glycoproteins, control the proteolytic activity of the invading cells by binding to their receptors (integrins) expressed on the cell membrane. When these receptors are distributed in a non polarised way they don't bind their ligands and the cells secrete proteases and invade the endometrium. Conversely, when the receptors are clustered, they bind to their ligands and the cell's invasive behaviour and protease secretion is inhibited. The endometrial extracellular matrix is thus a potent regulator of trophoblast invasion.