Mechanisms of Chorioamnionitis-associated Preterm Birth: Interleukin 1 β inhibits Progesterone Receptor Expression in Decidual Cells

In chorioamnionitis (CAM), a major cause of preterm birth (PTB), maternal-fetal inflammatory responses in the decidua and amnio-chorion cause the release of cytokines that elicit cervical ripening, fetal membrane rupture and myometrial activation. We posited that this inflammatory milieu can trigger PTB via inhibited progesterone receptor (PR) expression and increased decidual prostaglandin (PG) production. We found significantly lower decidual cell PR levels in CAM-complicated PTB using immunohistochemistry. Decidual cells (DCs) treated with IL-1β displayed decreased PR expression and significantly increased PGE2 and PGF2α production and COX2 expression. While addition of PGF2α to DC cultures was also found to suppress PR expression, the COX inhibitor, indomethacin, did not reverse IL-1β suppression of PR expression in DC cultures. Although IL-1β treatment activated NF-B, ERK1/2 and p38 MAPK signaling cascades in DCs, only inhibition of ERK1/2 MAPK signaling completely reversed IL-1β suppressed PR levels. These findings suggest that CAM-associated PTB is induced at least in part by IL-1β-mediated functional progesterone withdrawal. Total RNA (n=3) obtained from cultured TDCs incubated 6h with estradiol or estradio + medroxyprogesterone acetate with or without 1 ng/ml IL-1β for 6h.