Molecules in blastocyst implantation. Role of matrix metalloproteinases, cytokines and growth factors.

Initiation of implantation is due not to passive growth pressure but to an active biochemical process that requires a blastocyst to interact with a carefully prepared endometrium. This versatile and dynamic process requires a variety of different molecules secreted by human trophoblast as well as endometrial cells that play a unique role. Several molecules have been shown to regulate, by an autocrine and paracrine manner, the cross-talk between the implanting blastocyst and the endometrial epithelium. Particularly, the molecular dialogue involves either cell-to-cell or cell-to-extracellular matrix interactions, mediated by matrix metalloproteinases, cytokines and growth factors. The present overview of the literature reports on the most significant molecules involved in the implantation process and describes the mechanisms of interaction and control. Since impaired blastocyst implantation is a significant cause of natural and in vitro fertilization pregnancy failure, a better understanding of the aforementioned molecular dynamics would be useful in improving the chance of viable pregnancy.