GENE-EXPRESSION OF NITRIC-OXIDE SYNTHASE IN CULTURED HUMAN TERM PLACENTAL TROPHOBLAST DURING IN-VITRO DIFFERENTIATION

The human placental syncytiotrophoblast is derived from differentiatin g cytotrophoblasts and is in contact with maternal blood. This endothe lial function positions the trophoblast to regulate maternal-fetal exc hange and to influence circulatory dynamics through paracrine interact ions in the placenta. Two isoforms of nitric oxide synthase (NOS) are expressed in placenta, and northern analysis, reverse transcription-po lymerase chain reaction (RT-PCR), and immunocytochemistry were used to correlate expression of the type II, inducible NOS (iNOS) and the typ e III, endothelial NOS (eNOS) with state of differentiation in culture d trophoblast from term placentae. It was also tested whether cytokine s known to induce NOS in other cell systems would induce iNOS in human trophoblast. The mRNA for eNOS was detected by RT-PCR, but not by Nor thern analysis, in cultures grown for 24 h when cytotrophoblasts were dominant. In contrast, eNOS mRNA was abundant in cultures grown for 72 h when syncytiotrophoblast was present. Immunocytochemical staining f or eNOS protein showed specific fluorescence in a few cells in culture s at 24 h, but the vast majority of cells expressed eNOS at 72 h. The iNOS isoform was expressed neither basally in any trophoblast culture nor was this isoform induced in cultures exposed to interleukin-1, tum our necrosis factor-alpha, interferon-gamma and lipopolysaccharide. Th e in vitro pattern of trophoblast eNOS expression models the in vivo p attern of eNOS expression described for villous trophoblast. The resul ts suggest that eNOS plays a role in human trophoblast differentiation and function. (C) 1998 W. B. Saunders Company Ltd.