Regulation of osteoclast precursors in inflammatory bone loss.

Osteoclasts are multinucleated cells that form in response to M-CSF and RANKL (receptor activator for NF kappaB ligand) from osteoclast precursors (OCPs), which are generated in the bone marrow. The role of osteoclast and anti-osteoclast therapy in the treatment of various bone loss disorders has been extensively studied, but the regulation of OCPs has not been addressed until recently. A critical difference between OCPs and mature osteoclasts is that OCPs circulate in the bloodstream and home to inflammatory sites, which usually have no osteoclast formation. Thus, the regulation of OCP mobilization among bone marrow, blood and inflamed sites may be an important factor in the pathogenesis of inflammatory bone disorders, and represents a new therapeutic strategy.