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Updated: Aug 10, 2026
Skeletal Phenotype Analysis of a Conditional Stat3 Deletion Mouse Model
Published on: July 3, 2020
Linkage of M-CSF signaling to Mitf, TFE3, and the osteoclast defect in Mitf(mi/mi) mice
K N Weilbaecher1, G Motyckova, W E Huber
1Department of Adult Oncology, Dana-Farber Cancer Institute, Boston, MA 02115, USA.
Abstract:
Osteoclasts are multinucleated hematopoietic cells essential for bone resorption. Macrophage colony-stimulating factor (M-CSF) is critical for osteoclast development and function, although its nuclear targets in osteoclasts are largely unknown. Mitf and TFE3 are two closely related helix-loop-helix (HLH) transcription factors previously implicated in osteoclast development and function. We demonstrate that cultured Mitf(mi/mi) osteoclasts are immature, mononuclear, express low levels of TRAP, and fail to mature upon M-CSF stimulation. In addition, M-CSF induces phosphorylation of Mitf and TFE3 via a conserved MAPK consensus site, thereby triggering their recruitment of the coactivator p300. Furthermore, an unphosphorylatable mutant at the MAPK consensus serine is specifically deficient in formation of multinucleated osteoclasts, mimicking the defect in Mitf(mi/mi) mice. These results identify a signaling pathway that appears to coordinate cytokine signaling with the expression of genes vital to osteoclast development.
Insights
Macrophage colony-stimulating factor (M-CSF) signaling activates transcription factors Mitf and TFE3, crucial for osteoclast maturation and bone resorption. This pathway coordinates cytokine signals with essential gene expression for osteoclast development.
Area of Science:
- Cell Biology
- Hematopoiesis
- Bone Biology
Background:
- Osteoclasts are critical for bone remodeling.
- Macrophage colony-stimulating factor (M-CSF) is vital for osteoclast development and function.
- Nuclear targets of M-CSF in osteoclasts remain largely uncharacterized.
Purpose of the Study:
- To investigate the role of transcription factors Mitf and TFE3 in M-CSF-mediated osteoclastogenesis.
- To identify the signaling pathway linking M-CSF to osteoclast nuclear gene expression.
Main Methods:
- Analysis of Mitf(mi/mi) osteoclasts.
- M-CSF stimulation assays.
- Phosphorylation site mutagenesis of Mitf and TFE3.
- Co-immunoprecipitation with p300.
Main Results:
- Mitf(mi/mi) osteoclasts exhibit immature, mononuclear phenotypes with reduced TRAP expression.
- M-CSF induces phosphorylation of Mitf and TFE3 at a conserved MAPK site.
- Phosphorylation is essential for Mitf/TFE3 recruitment of p300 and multinucleated osteoclast formation.
- An unphosphorylatable mutant mimics the osteoclast defects seen in Mitf(mi/mi) mice.
Conclusions:
- A novel signaling pathway links M-CSF to osteoclast development via Mitf/TFE3 phosphorylation.
- Mitf and TFE3 are key nuclear targets of M-CSF signaling in osteoclasts.
- This pathway is essential for coordinating cytokine signaling with gene expression vital for osteoclast maturation.
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