Induction of osteoclast differentiation by Runx2 through receptor activator of nuclear factor-kappa B ligand (RANKL) and osteoprotegerin regulation and partial rescue of osteoclastogenesis in Runx2-/- mice by RANKL transgene.
Receptor activator of nuclear factor-kappaB ligand (RANKL), osteoprotegerin (OPG), and macrophage-colony stimulating factor play essential roles in the regulation of osteoclastogenesis. Runx2-deficient (Runx2-/-) mice showed a complete lack of bone formation because of maturational arrest of osteoblasts and disturbed chondrocyte maturation. Further, osteoclasts were absent in these mice, in which OPG and macrophage-colony stimulating factor were normally expressed, but RANKL expression was severely diminished. We investigated the function of Runx2 in osteoclast differentiation. A Runx2-/- calvaria-derived cell line (CA120-4), which expressed OPG strongly but RANKL barely, severely suppressed osteoclast differentiation from normal bone marrow cells in co-cultures. Adenoviral introduction of Runx2 into CA120-4 cells induced RANKL expression, suppressed OPG expression, and restored osteoclast differentiation from normal bone marrow cells, whereas the addition of OPG abolished the osteoclast differentiation induced by Runx2. Addition of soluble RANKL (sRANKL) also restored osteoclast differentiation in co-cultures. Forced expression of sRANKL in Runx2-/- livers increased the number and size of osteoclast-like cells around calcified cartilage, although vascular invasion into the cartilage was superficial because of incomplete osteoclast differentiation. These findings indicate that Runx2 promotes osteoclast differentiation by inducing RANKL and inhibiting OPG. As the introduction of sRANKL was insufficient for osteoclast differentiation in Runx2-/- mice, however, our findings also suggest that additional factor(s) or matrix protein(s), which are induced in terminally differentiated chondrocytes or osteoblasts by Runx2, are required for osteoclastogenesis in early skeletal development.
Enomoto
Hirayuki
H
Department of Molecular Medicine, Osaka University Graduate School of Medicine, Suita, Osaka 565-0871, Japan.
Shiojiri
Satoko
S
Hoshi
Kazuto
K
Furuichi
Tatsuya
T
Fukuyama
Ryo
R
Yoshida
Carolina A
CA
Kanatani
Naoko
N
Nakamura
Reiko
R
Mizuno
Atsuko
A
Zanma
Akira
A
Yano
Kazuki
K
Yasuda
Hisataka
H
Higashio
Kanji
K
Takada
Kenji
K
Komori
Toshihisa
T
D000818:Animals; D002352:Carrier Proteins / Q000096:biosynthesis / Q000235:genetics / Q000494:pharmacology*; D002454:Cell Differentiation; D002460:Cell Line; D050659:Core Binding Factor Alpha 1 Subunit; D005786:Gene Expression Regulation; D006023:Glycoproteins / Q000037:antagonists & inhibitors* / Q000378:metabolism; D008562:Membrane Glycoproteins / Q000096:biosynthesis / Q000235:genetics / Q000494:pharmacology*; D051379:Mice; D018345:Mice, Knockout; D009363:Neoplasm Proteins; D010010:Osteoclasts / Q000166:cytology*; D053244:Osteoprotegerin; D053245:RANK Ligand; D053246:Receptor Activator of Nuclear Factor-kappa B; D018160:Receptors, Cytoplasmic and Nuclear / Q000037:antagonists & inhibitors* / Q000378:metabolism; D018124:Receptors, Tumor Necrosis Factor; D015398:Signal Transduction; D014157:Transcription Factors / Q000235:genetics / Q000502:physiology*; D019076:Transgenes
D002352:Carrier Proteins; D050659:Core Binding Factor Alpha 1 Subunit; D006023:Glycoproteins; D008562:Membrane Glycoproteins; D009363:Neoplasm Proteins; D053244:Osteoprotegerin; D053245:RANK Ligand; 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; D014157:Transcription Factors