Biphasic Effect of Prostaglandin E2 on Osteoclast Formation in Spleen Cell Cultures: Role of the EP2 Receptor

Abstract

Abstract 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. Introduction: 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. Materials and 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.