EXPRESSION OF ENDOTHELIAL (TYPE-III) NITRIC-OXIDE SYNTHASE IN CYTOTROPHOBLASTIC CELL-LINES - REGULATION BY HYPOXIA AND INFLAMMATORY CYTOKINES

Expression of endothelial nitric oxide synthase (eNOS) has been locali zed to the villous syncytiotrophoblasts suggesting that NO release fro m these cells could prevent platelet adhesion and aggregation in the i ntervillous space. Hypoxia- or inflammation dependent changes in the r elease of this vasoactive substance may result in thrombus formation a nd altered vascular resistance which occur in the placental bed of pre -eclamptic patients. To evaluate the influence of low-oxygen tension a nd inflammation on eNOS production in the trophoblast steady-state eNO S mRNA and protein levels were investigated in cytotrophoblastic BeWo and Jeg-3 cells cultured at 3.5 per cent oxygen and/or in the presence of the pro-infammatory cytokines IL-1 and TNF-a. By RT-PCR and immuno cytochemistry we demonstrate that BeWo cells produce eNOS mRNA and pro tein while eNOS polypeptide was undetectable in JEG-3 cells. In BeWo c ells addition of both cytokines decreases eNOS mRNA and protein abunda ncies within 24 h of incubation while each substance alone had no effe ct. Compared to controls, the amount of eNOS transcripts was found to be elevated at low-oxygen tension, however, eNOS protein was downregul ated after 24 h in the hypoxic environment, as shown by immunocytochem istry and Western blot analysis. Forskolin and methotrexate, which ind uce biochemical differentiation/growth arrest in choriocarcinoma cells , stimulate eNOS mRNA and protein synthesis, but cannot overcome the d ecline of eNOS polypeptide levels during hypoxic incubation. It is spe culated that acute hypoxia and inflammation impair eNOS/NO production of the trophoblast in vivo, which might contribute to pathological con ditions of gestational diseases. (C) 1998 W. B. Saunders Company Ltd.