[Osteoclastogenesis inhibitory factor (OCIF)/osteoprotegerin (OPG)].

Osteoclastogenesis inhibitory factor (OCIF) was isolated from the conditioned medium of human embryonic lung fibroblasts. OCIF is a novel member of the tumor necrosis factor receptor superfamily and identical with Osteoprotegerin (OPG) discovered by the Amgen researchers. Consequently, through the identification of receptor activator of NF-kappaB ligand (RANKL) as a target molecule of OCIF/OPG, it was demonstrated that RANKL is a crucial factor in the differentiation, maturation, and activation of osteoclasts. Discovery of OCIF/OPG and RANKL has broken new ground in the field of bone physiopathology. Moreover, OCIF/OPG not only contributes to the field of basic science but also is anticipated as a novel therapeutic candidate for the treatment of primary and secondary osteoporosis through a series of pre-clinical and clinical studies. Because OCIF/OPG and RANKL have been proven to be involved in the onset and development of many metabolic bone diseases besides osteoporosis, OCIF/OPG is also expected as a therapeutic candidate for the treatment of such bone diseases.