Osteoprotegerin produced by osteoblasts is an important regulator in osteoclast development and function

• Published in: Endocrinology (Philadelphia) Vol. 141; no. 9; pp. 3478 - 3484
• Main Authors: Udagawa, N, Takahashi, N, Yasuda, H, Mizuno, A, Itoh, K, Ueno, Y, Shinki, T, Gillespie, M T, Martin, T J, Higashio, K, Suda, T
• Format: Journal Article
• Language: English
• Published: United States 01.09.2000
• Subjects: Animals; Bone Development - physiology; Bone Resorption - pathology; Carrier Proteins - metabolism; Coculture Techniques; Glycoproteins - biosynthesis; Glycoproteins - genetics; Glycoproteins - physiology; Membrane Glycoproteins - metabolism; Mice; Mice, Inbred C57BL; Mice, Knockout; NF-kappa B - metabolism; Organ Culture Techniques; Osteoblasts - metabolism; Osteoclasts - physiology; Osteoprotegerin; RANK Ligand; Receptor Activator of Nuclear Factor-kappa B; Receptors, Cytoplasmic and Nuclear; Receptors, Tumor Necrosis Factor - biosynthesis; Receptors, Tumor Necrosis Factor - genetics; Receptors, Tumor Necrosis Factor - physiology; Reverse Transcriptase Polymerase Chain Reaction; RNA, Messenger - biosynthesis; RNA, Messenger - genetics
• DOI: 10.1210/endo.141.9.7634
• ISSN: 0013-7227

Osteoprotegerin (OPG), a soluble decoy receptor for receptor activator of nuclear factor-kappaB ligand (RANKL)/osteoclast differentiation factor, inhibits both differentiation and function of osteoclasts. We previously reported that OPG-deficient mice exhibited severe osteoporosis caused by enhanced osteoclastic bone resorption. In the present study, potential roles of OPG in osteoclast differentiation were examined using a mouse coculture system of calvarial osteoblasts and bone marrow cells prepared from OPG-deficient mice. In the absence of bone-resorbing factors, no osteoclasts were formed in cocultures of wild-type (+/+) or heterozygous (+/-) mouse-derived osteoblasts with bone marrow cells prepared from homozygous (-/-) mice. In contrast, homozygous (-/-) mouse-derived osteoblasts strongly supported osteoclast formation in the cocultures with homozygous (-/-) bone marrow cells, even in the absence of bone-resorbing factors. Addition of OPG to the cocultures with osteoblasts and bone marrow cells derived from homozygous (-/-) mice completely inhibited spontaneously occurring osteoclast formation. Adding 1alpha,25-dihydroxyvitamin D3 [1alpha,25(OH)2D3] to these cocultures significantly enhanced osteoclast differentiation. In addition, bone-resorbing activity in organ cultures of fetal long bones derived from homozygous (-/-) mice was markedly increased, irrespective of the presence and absence of bone-resorbing factors, in comparison with that from wild-type (+/+) mice. Osteoblasts prepared from homozygous (-/-), heterozygous (+/-), and wild-type (+/+) mice constitutively expressed similar levels of RANKL messenger RNA, which were equally increased by the treatment with 1alpha,25(OH)2D3. When homozygous (-/-) mouse-derived osteoblasts and hemopoietic cells were cocultured, but direct contact between them was prevented, no osteoclasts were formed, even in the presence of 1alpha,25(OH)2D3 and macrophage colony-stimulating factor. These findings suggest that OPG produced by osteoblasts/stromal cells is a physiologically important regulator in osteoclast differentiation and function and that RANKL expressed by osteoblasts functions as a membrane-associated form.