CHRONIC ANTAGONISM OF NUCLEAR FACTOR-KAPPA-B ACTIVITY IN CYTOTROPHOBLASTS BY DEXAMETHASONE - A POTENTIAL MECHANISM FOR ANTIINFLAMMATORY ACTION OF GLUCOCORTICOIDS IN HUMAN PLACENTA

Circulating glucocorticoids are present in increasing quantities as hu man gestation progresses, peaking during labor whether it occurs befor e or at term. Although the precise role of glucocorticoids in pregnanc y is not well defined, it is clear that glucocorticoids suppress infla mmation in many cell types by antagonizing the acute stimulatory actio ns of members of the Rel/nuclear factor-kappa B (NF-kappa B) family on cytokine gene expression. In the present study we tested the hypothes is that during pregnancy, glucocorticoids chronically suppress inflamm ation in the human placenta. Cytotrophoblasts obtained from human term placentas were maintained for 48 h in culture medium supplemented wit h 10% charcoal-stripped calf serum with and without 100 nmol/L dexamet hasone (DEX). Enzyme-linked immunosorbent assay studies revealed that cytotrophoblasts constitutively express interleukin-8 (IL-8), a known mediator of placental inflammation, between 24-96 h of culture. A 48-h treatment of cytotrophoblasts with 100 nmol/L DEX significantly reduc ed the production of IL-8 to 24 +/- 1% of control levels (P < 0.01). D EX and cortisol mediated a dose-dependent inhibition of IL-8 expressio n, with ED50 values of 5 and 50 nmol/L, respectively. DEX treatment al so significantly reduced levels of IL-6 and tumor necrosis factor-alph a in culture medium, suggesting that glucocorticoids coordinately redu ce cytokine levels in cytotrophoblasts. As cytokine expression is regu lated by NF-kappa B and activator protein-1 (AP-1) transcription facto rs, electrophoretic mobility shift assays (n = 4) were used to determi ne whether DEX treatment altered the binding of nuclear proteins from cytotrophoblasts to labeled oligonucleotides corresponding to the kapp a B and AP-I response elements. We observed that a 48-h treatment of c ytotrophoblasts with 100 nmol/L DEX markedly reduced binding of nuclea r extracts from cytotrophoblasts to the kappa B response element. DEX treatment promoted a relatively smaller reduction of binding to the AP -1 response element. Northern blotting experiments revealed that DEX t reatment did not alter the level of I kappa B, p50, or p65 messenger r ibonucleic acid, suggesting that the antiinflammatory action of glucoc orticoid in cytotrophoblasts did not directly involve alterations in t he level of NF-kappa B proteins. Our results demonstrate a novel chron ic suppressive action of glucocorticoid on cytokine production and nuc lear binding of NF-kappa B and AP-1 proteins in cytotrophoblasts, prov iding a potential mechanism through which glucocorticoids may suppress inflammation at maternal-fetal interfaces across gestation.