High extracellular calcium affects osteoclastogenesis in mouse bone marrow cell culture

The effects of high extracellular calcium (high Ca) in the local microenvironment on osteoclasts, osteoclast progenitors and stromal cells are not fully understood. We examined high Ca effect on osteoclastogenesis in mouse bone marrow cell culture. Mouse bone marrow cells were cultured for up to 6 days in the medium supplemented with 1, 25(OH)2 vitamin D3 (D3). High Ca treatment at the early stage of culture (the initial 24 hours) reduced the number of tartrate resistant acid phosphatase-positive multinuclear cells (TRAP(+)MNCs). This treatment slightly up-regulated the mRNA expressions of receptor activator of NF-(B ligand (RANKL), RANK and osteoprotegerin (OPG). This inhibitory effect on the formation of TRAP(+)MNCs was recovered by RANKL. In contrast, high Ca treatment at the later stage of osteoclastogenesis (the last 2 days of culture) stimulated the formation of TRAP(+)MNCs, increased RANKL and RANK mRNA expressions and decreased OPG mRNA. High Ca at neither the early nor the later stage of culture affected the total number of adherent cells and the mRNA expression of alkaline phosphatase and osteopontin. In conclusion, high Ca affects osteoclastogenesis in a manner depending on the stage of osteoclastogenesis, which is partly mediated via the RANKL-RANK-OPG regulatory system.