A selective EP4 receptor antagonist abrogates the stimulation of osteoblast recruitment from bone marrow stromal cells by prostaglandin E2 in vivo and in vitro

Recent evidence indicates that systemic administration of PGE(2) increases bone formation and bone mass via activation of the EP4 receptor. Previously, we demonstrated that osteoblastic recruitment from rat bone marrow stromal cells (BMSC) is a major mechanism for the anabolic effect of PGE(2). In this study, we used a selective EP4 antagonist to test if the stimulation of osteoblast differentiation from rat BMSC in vitro and in vivo involves the EP4 receptor. In vitro, PGE(2) (100 nM) increased nodule formation and alkaline phosphatase (ALP) activity in cultures of rat BMSC 1.5- to 2-fold. These effects were abolished by the EP4 antagonist at 10(-6) M but not 10(-9) M. Furthermore, PGE(2) increased the number of surviving adherent BMSC by similar to225% and the EP4 antagonist prevented this effect as well. The antagonist had no effect on basal levels of nodule formation and adherent cell number. In vivo, daily systemic administration of PGE(2) at 6 mg/kg for 2 weeks increased cancellous bone area (by similar to50%) and increased nodule formation (measured as mineralized area) in ex vivo stromal cultures by similar to50%. Pre-administration of the EP4 antagonist at 10 mg/kg abrogated both the increase in bone mass as well as the increase in nodule formation. These data indicate that PGE(2) Stimulates osteoblastic commitment of BMSC via activation of the EP4 receptor. (C) 2003 Elsevier Inc. All rights reserved.