Biphasic influence of PGE2 on the resorption activity of osteoclast-like cells derived from human peripheral blood monocytes and mouse RAW264.7 cells

• PGE2 is an important pro-inflammatory mediator regulating osteoclast function.
• The effect of PGE2 on TRAP and resorptive activity of osteoclastic cells was studied.
• PGE2 inhibited the differentiation of human and mouse osteoclast precursor cells.
• PGE2 had no influence on already differentiated human and mouse osteoclasts.
• Downregulation of PGE2 receptors enables osteoclasts function during inflammation.

Osteoclasts are large bone-resorbing cells of hematopoietic origin. Their main function is to dissolve the inorganic component hydroxyapatite and to degrade the organic bone matrix. Prostaglandin E2 (PGE2) indirectly affects osteoclasts by stimulating osteoblasts to release factors that influence osteoclast activity. The direct effect of PGE2 on osteoclasts is still controversial. To study the influence of PGE2 on osteoclast activity, human peripheral blood monocytes (hPBMC) and mouse RAW264.7 cells were cultured on osteoblast-derived extracellular matrix. hPBMC and RAW264.7 cells were differentiated by the addition of macrophage colony-stimulation factor and receptor activator of NFκB ligand and treated with PGE2 before and after differentiation induction. The pit area, an indicator of resorption activity, and the activity of tartrate-resistant acid phosphatase were dose-dependently inhibited when PGE2 was present ab initio, whereas the resorption activity remained unchanged when the cells were exposed to PGE2 from day 4 of culture. These results lead to the conclusion that PGE2 treatment inhibits only the differentiation of precursor osteoclasts whereas differentiated osteoclasts are not affected.