Osteoprotegerin produced by osteoblasts is an important regulator in osteoclast development and function.
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.
Udagawa
N
N
Department of Biochemistry, School of Dentistry, Showa University, Tokyo, Japan.
Takahashi
N
N
Yasuda
H
H
Mizuno
A
A
Itoh
K
K
Ueno
Y
Y
Shinki
T
T
Gillespie
M T
MT
Martin
T J
TJ
Higashio
K
K
Suda
T
T
D000818:Animals; D001846:Bone Development / Q000502:physiology*; D001862:Bone Resorption / Q000473:pathology; D002352:Carrier Proteins / Q000378:metabolism; D018920:Coculture Techniques; D006023:Glycoproteins / Q000096:biosynthesis / Q000235:genetics / Q000502:physiology*; D008562:Membrane Glycoproteins / Q000378:metabolism; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D016328:NF-kappa B / Q000378:metabolism; D009924:Organ Culture Techniques; D010006:Osteoblasts / Q000378:metabolism*; D010010:Osteoclasts / Q000502:physiology*; D053244:Osteoprotegerin; D053245:RANK Ligand; D012333:RNA, Messenger / Q000096:biosynthesis / Q000235:genetics; D053246:Receptor Activator of Nuclear Factor-kappa B; D018160:Receptors, Cytoplasmic and Nuclear; D018124:Receptors, Tumor Necrosis Factor / Q000096:biosynthesis / Q000235:genetics / Q000502:physiology*; D020133:Reverse Transcriptase Polymerase Chain Reaction
D002352:Carrier Proteins; D006023:Glycoproteins; D008562:Membrane Glycoproteins; D016328:NF-kappa B; D053244:Osteoprotegerin; D053245:RANK Ligand; D012333:RNA, Messenger; D053246:Receptor Activator of Nuclear Factor-kappa B; D018160:Receptors, Cytoplasmic and Nuclear; D018124:Receptors, Tumor Necrosis Factor; C505687:Tnfrsf11a protein, mouse; C506031:Tnfrsf11b protein, mouse; C505689:Tnfsf11 protein, mouse