HYPOXIA IMPAIRS CELL-FUSION AND DIFFERENTIATION PROCESS IN HUMAN CYTOTROPHOBLAST, IN-VITRO

During human pregnancy, the trophoblast develops from differentiation of cytotrophoblast cells into an endocrine active syncytiotrophoblast. In culture, isolated mononuclear cytotrophoblasts aggregate and then fuse to form a syncytium, reproducing the in vivo process. In this stu dy, we examined the effect of low oxygen tension (approximately 9%, hy poxia) compared to standard conditions (approximately 19% oxygen, norm oxia) on these cellular events. Under hypoxia, syncytial formation was less frequently observed, cell staining and electron microscopy revea led that cytotrophoblasts remain aggregated, with a positive prolifera tive cell nuclear antigen (PCNA) immunostaining. Desmoplakin and E-cad herin, both known to disappear with cytotrophoblast fusion, showed per sistent expression in hypoxic cells after 3 days of culture. In contra st, the expression of actin and ezrin, two cytoskeletal proteins, was unchanged, hCG secretion and hPL expression were both decreased in hyp oxic cells, reflecting a reduced syncytial formation. Thus, on day 3, the mean values for hCG secretion were 1,100 +/- 155 and 289 +/- 26 mI U/mL in normoxic and hypoxic conditions, respectively, The reduced cel l fusion process as well as hCG secretion and hPL expression under hyp oxia were reversed by reoxygenation of the cells. We conclude that und er hypoxia, the formation of functional syncytiotrophoblast is impaire d due to a defect in the cytotrophoblast fusion process. This may expl ain the observation of a higher number of cytotrophoblast cells and a reduced syncytial layer in placentas of some pathological pregnancies. (C) 1996 Wiley-Liss, Inc.