The anabolic effect of PGE(2) in rat bone marrow cultures is mediated via the EP4 receptor subtype

Prostaglandin E-2 (PGE(2)) is an anabolic agent in vivo that stimulates bon e formation by recruiting osteoblasts from bone marrow precursors. To under stand which of the known PGE(2) receptors (EP1-4) is involved in this proce ss, we tested the effect of PGE(2) and various EP agonists and/or antagonis ts on osteoblastic differentiation in cultures of bone marrow cells by coun ting bone nodules and measuring alkaline phosphatase activity. PGE(2) incre ased both parameters, peaking at 100 nM, an effect that was mimicked by for skolin and was abolished by 2',3'-dideoxyadenosine (an adenylate cyclase in hibitor) and was thus cAMP dependent, pointing to the involvement of EP2 or EP4. Consistently, 17-phenyl-omega-trinor PGE(2) (EP1 agonist) and sulpros tone (EP3/ EP1 agonist) lacked any anabolic activity. Furthermore, butapros t (EP2 agonist) was inactive, 11-deoxy-PGE(1) (EP4/EP2 agonist) was as effe ctive as PGE(2), and the PGE(2) effect was abolished dose dependently by th e selective EP4 antagonist AH-23848B, suggesting the involvement of EP4. We also found that PGE(2) increased nodule formation and AP activity when add ed for the initial attachment period of 24 h only. Thus this study shows th at PGE(2) stimulates osteoblastic differentiation in bone marrow cultures, probably by activating the EP4 receptor, and that this effect may involve r ecruitment of noncommitted (nonadherent) osteogenic precursors, in agreemen t with its suggested mode of operation in vivo.