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Department of Oral Biology, Goldschleger School of Dental Medicine, Tel-Aviv University, Tel-Aviv 69978, Israel
Prostaglandin
E2
(PGE2) is an anabolic agent in
vivo that stimulates bone formation by recruiting osteoblasts from bone
marrow precursors. To understand which of the known
PGE2 receptors
(EP1-4) is involved in this
process, we tested the effect of
PGE2 and various EP agonists
and/or antagonists on osteoblastic differentiation in cultures
of bone marrow cells by counting bone nodules and measuring alkaline
phosphatase activity. PGE2
increased both parameters, peaking at 100 nM, an effect that was
mimicked by forskolin and was abolished by
2',3'-dideoxyadenosine (an adenylate cyclase inhibitor) and
was thus cAMP dependent, pointing to the involvement of
EP2 or
EP4. Consistently,
17-phenyl-
-trinor PGE2
(EP1 agonist) and sulprostone
(EP3/EP1
agonist) lacked any anabolic activity. Furthermore, butaprost
(EP2 agonist) was inactive,
11-deoxy-PGE1 (EP4/EP2
agonist) was as effective as PGE2,
and the PGE2 effect was abolished
dose dependently by the selective
EP4 antagonist AH-23848B,
suggesting the involvement of EP4.
We also found that PGE2 increased
nodule formation and AP activity when added for the initial attachment
period of 24 h only. Thus this study shows that
PGE2 stimulates osteoblastic
differentiation in bone marrow cultures, probably by activating the
EP4 receptor, and that this effect
may involve recruitment of noncommitted (nonadherent) osteogenic precursors, in agreement with its suggested mode of operation in vivo.
prostanoid receptors; osteoblast recruitment; bone nodules
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