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Published on: February 28, 2017
Transforming growth factor beta affects osteoclast differentiation via direct and indirect actions
1Department of Medicine, St. Vincent's Institute of Medical Research and The University of Melbourne, Fitzroy, Victoria, Australia.
Summary
Transforming growth factor beta (TGF-beta) has dual effects on bone cells. It inhibits osteoclast formation by reducing osteoblast RANKL production but promotes it by acting directly on precursors.
Area of Science:
- Bone Biology
- Cell Signaling
- Osteoclastogenesis
Background:
- Transforming growth factor beta (TGF-beta) plays a complex role in bone remodeling.
- Osteoclast formation is regulated by osteoblasts via RANKL and OPG, and by TNF-alpha.
- TGF-beta's multifaceted effects suggest multiple underlying mechanisms.
Purpose of the Study:
- To investigate the distinct mechanisms by which TGF-beta influences osteoclast formation.
- To differentiate TGF-beta's effects in osteoblast-dependent and -independent systems.
Main Methods:
- Coculture systems involving hematopoietic cells and osteoblasts (OBs).
- Use of OPG null (opg-/-) mice models.
- Stimulation with recombinant RANKL and TNF-alpha.
- Measurement of RANKL messenger RNA (mRNA) expression in OBs.
Main Results:
- TGF-beta inhibited osteoclast formation in OB/hematopoietic cell cocultures, primarily by decreasing OB RANKL mRNA expression.
- Exogenous RANKL partially rescued osteoclastogenesis in TGF-beta-treated, OPG-deficient cocultures.
- In the absence of OBs, TGF-beta significantly enhanced osteoclast formation stimulated by RANKL or TNF-alpha, suggesting direct action on precursors.
Conclusions:
- TGF-beta's inhibitory effect on osteoclastogenesis is mainly mediated by suppressing osteoblast RANKL production.
- TGF-beta can also potently promote osteoclast formation through a RANKL-independent pathway, likely acting on osteoclast precursors.
- These dual actions highlight TGF-beta's critical role in regulating physiological and pathological osteolysis.
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