Tumour necrosis factor-α induces cyclo-oxygenase-2 gene expression in first trimester trophoblasts: suppression by glucocorticoids and NSAIDs

Abstract

Tumour necrosis factor-α (TNF-α) 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-α-stimulated PG production has been described in decidual, amnion and myometrial cells, to date no studies have focused on the role of TNF-α 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-α alters expression of COX-2, trophoblasts from first trimester chorionic villi were cultured as a continuous cell line and treated with TNF-α alone or with TNF-α 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-α. The effect of TNF-α on COX-2 rnRNA and protein expression was inhibited by dexamethasone (Dex). To examine the production of PGE 2 and PGF 2α, specific RIAs were performed on culture media from similarly stimulated cells. PG accumulation after TNF-α-stimulation occurred in a time- and dose-dependent fashion with a similar inhibition of PG accumulation after Dex exposure. To be certain that TNF-α-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-α exposure demonstrated suppression of TNF-α-stimulated PGE 2 formation. The results suggest that TNF-α elicits part of its pathophysiologic effects in preterm labour via alterations in COX-2 gene expression within the placental microenvironment.