Biphasic effect of prostaglandin E2 on osteoclast formation in spleen cell cultures: role of the EP2 receptor.
We examined the effect of PGE2 on OC formation from spleen cells treated with M-CSF and RANKL. PGE2 decreased OC number at 5-6 days of culture and increased OC number, size, and resorptive activity at 7-8 days. A selective EP2 receptor agonist mimicked these effects. Deletion of the EP2 receptor or depletion of T-cells abrogated the increase in OC number.


BACKGROUND
Prostaglandin E2 (PGE2) has been reported to increase osteoclast (OC) number in spleen cells cultured with RANKL and macrophage-colony-stimulating factor (M-CSF). In this study, we examined the time course of PGE2 effects on spleen cells cultured with RANKL and M-CSF. We then investigated which PGE receptors and cell types were involved in these effects.


METHODS
Spleen cells were cultured from wildtype C57BL/6 mice and EP2 or EP4 receptor-deficient (-/-) and wildtype (+/+) mice on a mixed genetic background. Spleen cells were cultured with M-CSF and RANKL for 5-9 days with or without PGE2 or selective agonists for the four PGE2 receptors (EP1A, EP2A, EP3A, or EP4A). Some cultures were performed using T-cell-depleted spleen cells. OC number and size were quantitated. OC apoptosis and pit formation were measured at 7 or 8 days.


RESULTS
PGE2 decreased the number of OCs formed in the presence of RANKL and M-CSF at 5-6 days of culture and increased OC number at 8-9 days compared with cultures without PGE2. PGE2 also increased OC size at 7 and 8 days, decreased apoptosis of OC at 7 days, and increased pit formation at 8 days. EP1A or EP4A had no effect on OC. EP3A decreased OC number. EP2A mimicked effect of PGE2. EP2(-/-) spleen cells showed no increase in OC number in response to PGE2, whereas deletion of EP4 had no effect. Depletion of T-cells abrogated the late increase of OC number.


CONCLUSIONS
We conclude that PGE2 has an initial inhibitory effect on OC formation in spleen cell cultures, possibly mediated by both EP2 and EP3 receptors, and a later stimulatory effect, mediated by the EP2 receptor, possibly acting on T-cells.
Ono
Katsuhiro
K
Department of Medicine, University of Connecticut Health Center, Farmington, Connecticut 06030, USA.
Kaneko
Hironori
H
Choudhary
Shilpa
S
Pilbeam
Carol C
CC
Lorenzo
Joseph A
JA
Akatsu
Takuhiko
T
Kugai
Nobuo
N
Raisz
Lawrence G
LG
D000818:Animals; D001862:Bone Resorption; D002352:Carrier Proteins / Q000494:pharmacology; D002452:Cell Count; D002454:Cell Differentiation / Q000187:drug effects; D002478:Cells, Cultured; D015232:Dinoprostone / Q000494:pharmacology*; D005260:Female; D008212:Lymphocyte Depletion; D016173:Macrophage Colony-Stimulating Factor / Q000494:pharmacology; D008562:Membrane Glycoproteins / Q000494:pharmacology; D051379:Mice; D008817:Mice, Mutant Strains; D010010:Osteoclasts / Q000166:cytology* / Q000187:drug effects; D053245:RANK Ligand; D053246:Receptor Activator of Nuclear Factor-kappa B; D018078:Receptors, Prostaglandin E / Q000819:agonists / Q000502:physiology*; D058307:Receptors, Prostaglandin E, EP2 Subtype; D058308:Receptors, Prostaglandin E, EP3 Subtype; D013154:Spleen / Q000166:cytology* / Q000187:drug effects; D013601:T-Lymphocytes / Q000502:physiology
D002352:Carrier Proteins; D008562:Membrane Glycoproteins; C545645:Ptger2 protein, mouse; C545648:Ptger3 protein, mouse; D053245:RANK Ligand; D053246:Receptor Activator of Nuclear Factor-kappa B; D018078:Receptors, Prostaglandin E; D058307:Receptors, Prostaglandin E, EP2 Subtype; D058308:Receptors, Prostaglandin E, EP3 Subtype; C505687:Tnfrsf11a protein, mouse; C505689:Tnfsf11 protein, mouse; D016173:Macrophage Colony-Stimulating Factor; D015232:Dinoprostone