Trophoblast differentiation is a complex process involving interactions of cytotrophoblastic cells with their evolutive milieu. During pregnancy, the feto-placental unit produces large amounts of steroids. Progesterone and oestradiol are increasingly produced when the syncytiotrophoblast is highly differentiated. Furthermore, receptors to these hormones are expressed by the trophoblast. This led us to test the hypothesis that steroid production could affect the morphological and functional differentiation of the trophoblast during gestation. The fusion of cytotrophoblastic cells into syncytiotrophoblast was assessed using fluorescence recovery after photobleaching for gap junctional communication analysis (gap-FRAP), desmoplakin immunostaining and connexin 43 expression. In parallel, functional differentiation was assessed by beta-human chorionic gonadotrophin (betahCG) production and human chorionic somatomammotropin (hCS) expression analysis. The presence of oestradiol, 1 microm, increased the percentage of coupled cells (3. 8-fold), connexin 43 expression and stimulated the syncytium formation. In parallel, oestradiol (1, 3 and 5 microm) induced a significant increase in the daily hCG production. The steroid action was specific, as the stimulatory effects were inhibited by tamoxifen. Oestradiol also stimulated hCS expression (51 per cent compared to control after 3 days). As trophoblastic differentiation is specifically stimulated by hCG, oestradiol could act via the stimulation of hCG production or via a direct action. In the presence of an efficient concentration of hCG antibody, oestradiol still stimulated hCS expression, suggesting a self-sufficient effect of the steroid. Physiological concentrations of progesterone were ineffective in modulating trophoblast differentiation. In conclusion, oestradiol could be implicated in the maturation and aging of the trophoblast.
Copyright 1999 Harcourt Publishers Ltd.