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

Nobuyuki Udagawa, Naoyuki Takahashi, Hisataka Yasuda, Atsuko Mizuno, Kanami Itoh, Yutaka Ueno, Toshimasa Shinki, Matthew T. Gillespie, T. John Martin, Kanji Higashio, Tatsuo Suda

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278 Citations (Scopus)

Abstract

Osteoprotegerin (OPG), a soluble decoy receptor for receptor activator of nuclear factor-κB 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 boneresorbing factors. Addition of OPG to the cocultures with osteoblasts and bone marrow cells derived from homozygous (-/-) mice completely inhibited spontaneously occurring osteoclast formation. Adding 1α,25-dihydroxyvitamin D3 [1α,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 1α,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 1α,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.

Original languageEnglish
Pages (from-to)3478-3484
Number of pages7
JournalEndocrinology
Volume141
Issue number9
DOIs
Publication statusPublished - 1 Jan 2000
Externally publishedYes

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