Prostaglandin E2 induced the differentiation of osteoclasts in mouse osteoblast-depleted bone marrow cells

Abstract

Prostaglandin (PG) E₂ is a known bone absorbing agent that acts on osteoblasts to facilitate osteoclastogenesis by increasing the secretion of RANKL. In the present study, we investigated the direct action of PGE₂ on osteoclastic progenitors that differentiate into TRAP-positive multinucleated cells. The hematopoietic stem cell obtained from murine bone marrow was purified by a Sephadex G-10 column, and cultured in the presence of CSF-1 and RANKL to facilitate cell differentiation. The introduction of low-density PGE₂ into the culture resulted in a drastic increase of TRAP-positive multinucleated cells, whereas the addition of high-density PGE₂ had the opposite effect. PCR analysis revealed increased level of EP3 mRNA in undifferentiated cells and reduced level after the development of osteoclast; EP1, EP2 and EP4 were constitutively expressed throughout the differentiation. Investigation of intracellular signaling verified that low-density PGE₂ suppressed PKA activity in undifferentiated cells, suggesting that PGE₂ acts on the osteoclastic cell lineage to facilitate cell differentiation by suppressing PKA in the presence of RANKL.