Low calcium environment effects osteoprotegerin ligand/osteoclast differentiation factor

In coculture with osteoblastic cell line MC3T3-E1 (El) and mouse bone marro w cells, we reported that numbers of osteoclasts rose significantly on expo sure to a low-calcium environment. Here we examined how osteoblasts influen ce osteoclastogenesis under a low-calcium environment. Comparing low extrac ellular calcium with a regular calcium environment, osteoprotegerin ligand (OPGL)/osteoclast differentiation factor (ODF) mRNA expression show more in crease in the culture of low-calcium environment than in that of a regular calcium environment. Calcium-sensing receptor (CaSR), which was supposed as one of the mechanisms of recognizing extracellular calcium, existed on the surface of El cells. When El cells stimulated with agonists of CaSR, gadol inium, and neomycin, OPGL/ODF mRNA expression decreased. Moreover, these ag onists reduced osteoclast formation in coculture. Taken together, it is pos sible that osteoblasts may recognize extracellular calcium via CaSR and reg ulate osteoclastogenesis. (C) 2000 Academic Press.