Tumour necrosis factor-alpha induces cyclo-oxygenase-2 gene expression in first trimester trophoblasts: suppression...

Tumour necrosis factor-alpha (TNF-alpha) is a pleiotropic cytokine which stimulates the synthesis and release of prostaglandins (PGs) in several in vitro and in vivo models of preterm labour. While TNF-alpha simulated PG production has been described in decidual, amnion and myometrial cells, to date no studies have focused on the role of TNF-alpha in the stimulation of arachidonic acid metabolism in placental trophoblast cells. Cyclo-oxygenase-2 (COX-2) is the rate-limiting enzyme in PG biosynthesis and is expressed de novo during cellular activation by cytokines. To test whether TNF-alpha alters expression of COX-2, trophoblasts from first trimester chorionic vili were cultured as a continuous cell line and treated with TNF-alpha alone or with TNF-alpha and dexamethasone (Dex). Total RNA and protein were extracted from the trophoblasts and subjected to Northern and immunoblot analysis, respectively. Northern blots were hybridized with a 32P-labelled probe encoding the COX-2 cDNA and immunoblots were incubated with anti-COX-2 antibodies. There was a time- and dose-dependent increase in COX-2 mRNA and protein expression in cells stimulated with TNF-alpha. The effect of TNF-alpha on COX-2 mRNA and protein expression was inhibited by dexamethasone (Dex). To examine the production of PGE2 and PGF(2 alpha), specific RIAs were performed on culture media from similarly stimulated cells. PG accumulation after TNF-alpha stimulation occurred in a time- and dose-dependent fashion with a similar inhibition of PG accumulation after Dex exposure. To be certain that TNF-alpha stimulated PGE2 production was, indeed, a result of COX-2 induction, RIAs were carried out with the COX-2-selective inhibitor NS-398. Cells stimulated with the NS-398 after TNF-alpha exposure demonstrated suppression of TNF-alpha-stimulated PGE2 formation. The results suggest that TNF-alpha elicits part of its pathophysiologic effects in preterm labour via alterations in COX-2 gene expression within the placental microenvironment.