Characterization of M-CSF and its receptor in microphthalmic mice
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1Department of Pediatrics, Medical University of South Carolina, Charleston.
Abstract:
The macrophage colony-stimulating factor (M-CSF) gene expression in osteopetrotic mice (op/op) is defective due to a point-mutation in the M-CSF gene [1]. However, almost all osteopetrotic patients have been shown to have a normal or elevated circulating level of bioactive M-CSF [2]. To investigate the action of the M-CSF in mi/mi mice (microphthalmic; another osteopetrotic mouse mutant), M-CSF levels and its receptors were studied. We found that serum levels of M-CSF in mi/mi mice were not significantly different from normal control mice. The M-CSF receptor binding affinity of spleen-adherent cells was similar to that of control mice. In spleen cells from mi/mi mice, the receptor binding sites per cell (normalized to total spleen cells, M-CSF receptor positive cells, or M-CSF receptor RNA positive cells) were present in a greater number than in spleen cells from phenotypically normal siblings. Northern blot analysis showed that there is no significant difference in transcripts of the M-CSF receptor (c-fms) in the mi/mi and phenotypically normal mice. Unlike the op/op mutant, M-CSF levels, as well as the affinity and number of M-CSF receptors, do not explain the defect in osteoclastic function in the mi/mi mutation.
Insights
Osteopetrotic mi/mi mice show normal macrophage colony-stimulating factor (M-CSF) levels and receptor affinity. However, increased M-CSF receptor numbers do not explain their osteoclast dysfunction.
Area of Science:
- Cell Biology
- Genetics
- Immunology
Background:
- Osteopetrosis is a genetic disorder characterized by impaired osteoclast function.
- Macrophage colony-stimulating factor (M-CSF) is crucial for osteoclast development.
- The op/op mouse model exhibits M-CSF gene defects, but human patients often have normal M-CSF levels.
Purpose of the Study:
- To investigate the role of M-CSF and its receptors in the mi/mi mouse model of osteopetrosis.
- To determine if M-CSF levels or receptor characteristics explain the osteoclast defect in mi/mi mice.
Main Methods:
- Quantification of serum M-CSF levels in mi/mi and control mice.
- Assessment of M-CSF receptor binding affinity and number on spleen cells.
- Analysis of M-CSF receptor (c-fms) gene expression using Northern blot.
Main Results:
- Serum M-CSF levels were comparable between mi/mi mice and normal siblings.
- M-CSF receptor binding affinity was similar in both groups.
- Spleen cells from mi/mi mice displayed a higher number of M-CSF receptor binding sites per cell.
- M-CSF receptor (c-fms) transcript levels were not significantly different.
Conclusions:
- Unlike the op/op model, M-CSF levels and receptor characteristics do not fully explain the osteoclast dysfunction in mi/mi mice.
- The underlying cause of osteoclast defect in mi/mi mice remains to be elucidated, suggesting other pathways may be involved.