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Toll-like receptor 9 ligand blocks osteoclast differentiation through induction of phosphatase.
- Source :
-
Journal of bone and mineral research : the official journal of the American Society for Bone and Mineral Research [J Bone Miner Res] 2007 Aug; Vol. 22 (8), pp. 1301-10. - Publication Year :
- 2007
-
Abstract
- Unlabelled: CpG-ODN, in addition to stimulation of osteoclastogenic signals in early osteoclast precursors, also induces phosphatase, shifting the pattern of ERK phosphorylation from sustained to transient. This shift results in the degradation of c-fos, an essential molecule for osteoclast differentiation. Therefore, CpG-ODN blocks osteoclast differentiation.<br />Introduction: Activation of either Toll-like receptor 9 (TLR9) or RANK induces similar responses in osteoclast precursors. Paradoxically, activation of TLR9 results in inhibition of RANKL-induced osteoclastogenesis.<br />Materials and Methods: We used bone marrow-derived osteoclast precursors. Analyses of signaling molecules phosphorylation were performed using Western blotting. Different levels of gene expression analyses were performed using RT-PCR, Northern, and run-on analyses (for RNA), and EMSA, Western, and pulse-chase experiments (for protein). Phosphatase activity was measured spectrophotometrically.<br />Results: We found that RANKL and TLR9 ligand, oligodeoxynucleotides containing unmethylated CpG dinucleotides (CpG-ODN), induce sustained and transient extracellular signal-regulated kinase (ERK) phosphorylation, respectively. Furthermore, together they induce a transient phosphorylation of ERK. The duration of ERK phosphorylation is a key factor in determining induction of c-fos, a protein critical for osteoclastogenesis. Indeed, we found that CpG-ODN does not induce c-fos and inhibits its induction by RANKL by enhancing c-fos mRNA and protein degradation. Our observation that CpG-ODN, but not RANKL, induces the expression of the phosphatase PP2A suggests that CpG-ODN exerts its inhibitory activity by induction of ERK dephosphorylation. Moreover, together with the phosphatase inhibitor okadaic acid, CpG-ODN induces sustained ERK phosphorylation and c-fos expression.<br />Conclusions: Our findings suggest that the increased rate of c-fos degradation by the TLR9 ligand mediates the inhibition of RANKL-induced osteoclast differentiation. The TLR9 ligand, through induction of dephosphorylation, prevents the sustained ERK phosphorylation needed for maintaining high c-fos levels that are essential for osteoclast differentiation.
- Subjects :
- Animals
Enzyme Induction
Extracellular Signal-Regulated MAP Kinases metabolism
Ligands
Male
Mice
Mice, Inbred BALB C
NF-kappa B metabolism
Oligodeoxyribonucleotides pharmacology
Osteoclasts drug effects
Phosphoric Monoester Hydrolases genetics
Phosphorylation
Proto-Oncogene Proteins c-fos genetics
Proto-Oncogene Proteins c-fos metabolism
RANK Ligand antagonists & inhibitors
RANK Ligand pharmacology
Cell Differentiation
Osteoclasts cytology
Osteoclasts metabolism
Phosphoric Monoester Hydrolases metabolism
RANK Ligand metabolism
Toll-Like Receptor 9 metabolism
Subjects
Details
- Language :
- English
- ISSN :
- 0884-0431
- Volume :
- 22
- Issue :
- 8
- Database :
- MEDLINE
- Journal :
- Journal of bone and mineral research : the official journal of the American Society for Bone and Mineral Research
- Publication Type :
- Academic Journal
- Accession number :
- 17488193
- Full Text :
- https://doi.org/10.1359/jbmr.070501