Activins and related proteins in the establishment of pregnancy.

Activin A and related proteins (inhibins, follistatin [FS], follistatin-related gene [FLRG], endometrial bleeding associated factors [ebaf]) are involved in the complex mechanisms allowing the establishment and the maintenance of pregnancy. As a consequence of ovarian progesterone stimuli, activin A is expressed and secreted by the stromal endometrial cells, which locally induces the decidualization process, a prerequisite for implantation. Moreover, activin A does influence the implantation phase, also enhancing cytotrophoblast differentiation, indirectly, by increasing the expression of other molecules involved in embryo implantation, such as matrix metalloproteinases (MMPs) and leukemia inhibitory factor (LIF). The local derangement of activin A pathway in some pregnancy disorders (incomplete and complete miscarriages, recurrent abortion, and ectopic pregnancy [EP]) further sustains the hypothesis that activin A and its related proteins play a relevant role in the establishment of pregnancy.