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Transforming growth factor-beta stimulates the production of osteoprotegerin/osteoclastogenesis inhibitory factor by
1Department of Geriatric Research, National Institute for Longevity Sciences, Obu, Aichi 474-8522, Japan.
Abstract:
Osteoprotegerin (OPG)/osteoclastogenesis inhibitory factor (OCIF) is a recently identified cytokine that belongs to the tumor necrosis factor receptor superfamily and regulates bone mass by inhibiting osteoclastic bone resorption. The present study was undertaken to determine whether OPG/OCIF is produced in bone microenvironment and how the expression is regulated. A transcript for OPG/OCIF at 3.1 kilobases was detected in bone marrow stromal cells (ST2 and MC3T3-G2/PA6) as well as in osteoblastic cells (MC3T3-E1). Transforming growth factor-beta1 (TGF-beta1) markedly increased the steady-state level of OPG/OCIF mRNA in a dose-dependent manner, while TGF-beta1 suppressed the mRNA expression of tumor necrosis factor-related activation-induced cytokine (TRANCE)/receptor activator of NF-kappaB ligand (RANKL), a positive regulator of osteoclastogenesis to which OPG/OCIF binds. The effect of TGF-beta1 on the expression of OPG/OCIF mRNA was transient, with a peak level at 3-6 h. The up-regulation of OPG/OCIF mRNA by TGF-beta1 in ST2 cells did not require de novo protein synthesis and involved both a transcriptional and a post-transcriptional mechanism. Western blot analysis and an enzyme-linked immunosorbent assay revealed that TGF-beta1 significantly increased the secretion of OPG/OCIF protein by ST2 cells at 6-24 h. In murine bone marrow cultures, TGF-beta1 markedly inhibited the formation of tartrate-resistant acid phosphatase-positive multinucleated osteoclast-like cells in the presence of 1,25-dihydroxyvitamin D3, whose effect was significantly reversed by a neutralizing antibody against OPG/OCIF. These results suggest that TGF-beta1 negatively regulates osteoclastogenesis, at least in part, through the induction of OPG/OCIF by bone marrow stromal cells and that the balance between OPG/OCIF and TRANCE/RANKL in local environment may be an important determinant of osteoclastic bone resorption.
Insights
Transforming growth factor-beta1 (TGF-beta1) upregulates osteoprotegerin (OPG) production in bone cells, inhibiting osteoclast formation. This suggests TGF-beta1 negatively regulates bone resorption by increasing OPG levels.
Area of Science:
- Bone biology and endocrinology
- Cellular and molecular mechanisms of bone remodeling
- Cytokine signaling in skeletal homeostasis
Background:
- Osteoprotegerin (OPG) is a key cytokine regulating bone mass by inhibiting osteoclast activity.
- The bone microenvironment's role in OPG production and its regulation is not fully understood.
- Understanding OPG regulation is crucial for addressing bone diseases characterized by resorption imbalances.
Purpose of the Study:
- To investigate the production of OPG/osteoclastogenesis inhibitory factor (OCIF) within the bone microenvironment.
- To elucidate the regulatory mechanisms controlling OPG/OCIF expression.
- To determine the role of transforming growth factor-beta1 (TGF-beta1) in OPG/OCIF regulation and its impact on osteoclastogenesis.
Main Methods:
- Detection of OPG/OCIF mRNA in bone marrow stromal and osteoblastic cells.
- Dose- and time-dependent analysis of TGF-beta1 effects on OPG/OCIF mRNA and protein expression.
- Investigation of TGF-beta1's impact on TRANCE/RANKL mRNA levels.
- Western blot and ELISA for OPG/OCIF protein secretion analysis.
- Murine bone marrow cultures to assess the functional role of OPG/OCIF in osteoclast formation.
Main Results:
- OPG/OCIF transcripts were detected in bone marrow stromal cells (ST2, MC3T3-G2/PA6) and osteoblastic cells (MC3T3-E1).
- TGF-beta1 significantly increased OPG/OCIF mRNA and protein levels in a dose-dependent and transient manner.
- TGF-beta1 suppressed TRANCE/RANKL mRNA expression, a key regulator of osteoclastogenesis.
- TGF-beta1 inhibited osteoclast-like cell formation, an effect reversed by an OPG/OCIF neutralizing antibody.
Conclusions:
- TGF-beta1 induces OPG/OCIF production in bone marrow stromal cells, contributing to the negative regulation of osteoclastogenesis.
- The interplay between OPG/OCIF and TRANCE/RANKL in the local bone environment is a critical determinant of osteoclastic bone resorption.
- These findings highlight a novel mechanism by which TGF-beta1 influences skeletal homeostasis.