Aspirin induces increased expression of both prostaglandin H synthase-1 and prostaglandin H synthase-2 in cultured human placental trophoblast

OBJECTIVE: We tested the hypothesis that aspirin affects trophoblast like other epithelial cells do, by inhibiting prostanoid production, inducing prostaglandin H synthase-2 expression, and enhancing secretion of 15- hydroxyeicosatetraenoic acid. STUDY DESIGN: Cytotrophoblast from placentas (n = 15) of uncomplicated singleton pregnancies were cultured in medium 199 for 4 to 72 hours in the presence or absence of aspirin. RESULTS: Aspirin (10^{- 4} M) inhibited (p < 0.01) average trophoblast prostaglandin E₂ release by 60% and thromboxane B₂ by 86%. Western immunoblotting showed the prostaglandin H synthase-1 was constitutively expressed in cytotrophoblast, and aspirin treatment caused a twofold increase in prostaglandin H synthase- 1 expression. Prostaglandin H synthase-2 was also constitutively expressed in untreated cytotrophoblast but at lower levels than prostaglandin H synthase- 1. Aspirin enhanced prostaglandin H synthase-2 expression in trophoblast cultures, but prostaglandin H synthase-2 contributed a range of only 10% to 33% (n = 4) of the total cellular prostaglandin H synthase protein pool even after aspirin induction. The increased prostaglandin H synthase expression depended on both transcription and translation because actinomycin D and cycloheximide each inhibited the increased prostaglandin H synthase protein expression after aspirin treatment. The aspirin induction of prostaglandin H synthase was accompanied by decreased release of 15-hydroxyeicosatetraenoic acid. CONCLUSIONS: Trophoblast differs from other cells studied because aspirin enhances expression of both prostaglandin H synthase-1 and prostaglandin H synthase-2 isozymes while decreasing, instead of increasing, the secretion of 15-hydroxyeicosatetraenoic acid. The aspirin effects on prostaglandin H synthase synthesis and 15-hydroxyeicosatetraenoic acid release in trophoblast suggest that the mechanisms of action for aspirin in the prophylaxis of preeclampsia may be more diverse than simply altering platelet thromboxane production.