OBJECTIVES: To determine the expression of inducible nitric oxide synthase (iNOS) in human trophoblast and to examine the possible regulation of iNOS gene by cytokines.
MATERIALS AND METHODS: Total RNA was isolated from: 1) homogenized placental tissue; from 2) isolated and purified cytotrophoblast cells; and 3) cytotrophoblast and syncytiotrophoblast cells treated with cytokines in vitro. RNA was reverse transcribed and amplified by polymerase chain reaction, using specific primers for iNOS. Trophoblast cells were treated in vitro by interferon-γ (IFN-γ) in a dose of 10 ng/mL, Interleukin 1β (IL-1β) (4 ng/mL) and leukemia inhibitory factor (LIF) (1 ng/mL). Trophoblasts were also subjected to immunocytochemistry using iNOS-specific antibody to detect iNOS protein expression in these cells.
RESULTS: The expression of iNOS mRNA was found both in placental tissue and isolated cytotrophoblast cells. In culture, the highly differentiated syncytiotrophoblast expressed more mRNA than cytotrophoblast cells. IFN-γ and LIF, but not IL-1β, induced iNOS mRNA expression in trophoblast cells in vitro. The effects of these cytokines on iNOS mRNA were only observed in syncytiotrophoblast cells, but not in cytotrophoblast cells. Immunocytochemical staining confirmed the trophoblast cells as a major source of the iNOS synthase production.
CONCLUSIONS: 1) Human trophoblast cells are able to express the iNOS mRNA, hence suggesting a role for NO in placental growth and function. 2) LIF and IFN-γ, but not IL-1β, induce the iNOS mRNA expression in syncytiotrophoblast cells in vitro, suggesting possible similar regulatory mechanisms in vivo. 3) This study, for the first time, demonstrates the stimulating effect of LIF on iNOS gene expression in human tissue.