Knockout of the murine prostaglandin EP2 receptor impairs osteoclastogenesis in vitro

Prostaglandin E-2 (PGE(2)) stimulates the formation of osteoclastlike tartr ate-resistant acid phosphatase-positive multinucleated cells (TRAP + MNC) i n vitro. This effect likely results from stimulation of adenylyl cyclase, w hich is mediated by two PGE(2) receptors, designated nated EP2 and EP4. We used cells from mice in which the EP2 receptor had been disrupted to test i ts role in the formation of TRAP + MNC. EP2 heterozygous (I)mice in a C57BL /6 x 129/SvEv background were bred to produce homozygous null (EP2 -/-) and wild-type (EP2 +/+) mice. PGE(2), PTH, or 1,25 dihydroxyvitamin D increase d TRAP+ MNC in 7-day cultures of bone marrow cells from EP, +/+ mice. In cu ltures from EP2 -/- animals, responses to PGE(2), PTH, and 1,25 dihydroxyvi tamin D were reduced by 86%, 58%, and 50%, respectively. A selective EP, re ceptor antagonist (EP(4)RA) further inhibited TRAP+ MNC formation in both E P2 +/+ and EP2 -/- cultures. In cocultures of spleen and calvarial osteobla stic cells, the response to PGE(2) or PTH was reduced by 92% or 85% when bo th osteoblastic cells and spleen cells were from EP2 -/- mice, by 88% or 68 % when only osteoblastic cells were from EP2 -/- mice and by 58% or 35% whe n only spleen cells were from EP2 -/- mice. PGE(2) increased receptor activ ator of nuclear factor (NF)-kB ligand (RANKL) messenger RNA expression in o steoblastic and bone marrow cell cultures from EP2 +/+ mice a-fold but had little effect on cells from EP2 -/- mice. Spleen cells cultured with RANKL and macrophage colony stimulating factor produced TRAP + MNC. PGE(2) increa sed the number of TRAP + MNC in spleen cell cultures from EP2 +/+ mice but not in cultures from EP2 -/- mice. EP,RA had no effect on the PGE(2) respon se in spleen cell cultures. PGE(2) decreased the expression of messenger RN A for granulocyte-macrophage colony stimulating factor in spleen cell cultu res from EP2 +/+ mice but had little effect on cells from EP2 -/- mice. The se data demonstrate that the prostaglandin EP2 receptor plays a role in the formation of osteoclast-like cells in vitro. A major defect in EP2 -/- mic e appears to be in the capacity of osteoblastic cells to stimulate osteocla st formation. In addition, there appears to be a defect in the response of cells of the osteoclastic lineage to PGE, in EP2 -/- mice.