Prostaglandin E2 stimulates osteoclast formation via endogenous IL-1 beta expressed through protein kinase A

The present study was conducted to determine whether endogenous IL-1 is involved as a potent mediator of PGE2-stimulated osteoclast formation in 1 alpha,25-dihydroxyvitamin D3 (1 alpha,25-(OH)2D3)-primed calvarial cells from mouse embryos. PGE2 induced IL-1 beta gene expression in the primed calvarial cells. IL-1 beta gene expression was also induced in a dose-dependent manner by forskolin and dibutyryl cAMP. PGE2-induced IL-1 beta gene expression was markedly inhibited by H-89, a potent inhibitor of protein kinase A. On the other hand, osteoclast formation in 1 alpha,25-(OH)2D3-primed calvarial cells was also stimulated by forskolin and dibutyryl cAMP, and their stimulatory effects were dose dependent. H-89 also inhibited PGE2-stimulated osteoclast formation. The presence of the IL-1 beta gene product in the conditioned medium of 1 alpha,25-(OH)2D3-primed calvarial cells treated with PGE2 was proved by the results of an immunoprecipitation assay using anti-mouse IL-1 beta Ab. The addition of anti-mouse IL-1 beta Ab to 1 alpha,25-(OH)2D3 primed calvarial cell cultures markedly inhibited PGE2-stimulated osteoclast formation. The stimulatory effect of conditioned medium of primed calvarial cells treated with PGE2 on osteoclast formation was also inhibited by anti-IL-1 beta Ab pretreatment. Furthermore, we found that endogenous IL-6 is partially involved in PGE2-stimulated osteoclast formation.