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Colony-stimulating factor-1 injections improve but do not cure skeletal sclerosis in osteopetrotic (op) mice
K T Sundquist1, M G Cecchini, S C Marks
1Department of Cell Biology, University of Massachusetts Medical School, Worcester 01655, USA.
Abstract:
The osteopetrotic (op) mutation in mice is characterized by general skeletal sclerosis; reduced numbers of osteoclasts, macrophages, and monocytes; and failure to be cured by bone marrow transplantation. This mutation has been shown to result from an absence of colony-stimulating factor-1 (CSF-1) and reported to be cured by treatment with CSF-1. Contrary to previous reports, we have noted persistent metaphyseal sclerosis in op mice treated with CSF-1 at doses above physiological concentrations of circulating CSF-1. We pursued this observation by quantitating osteoclasts and macrophages in the first 500 microns (area A) and the subsequent 1000 microns (area B) in the proximal tibial metaphysis using tartrate-resistant acid phosphatase and F4/80 as cell markers. In untreated normal mice, osteoclasts and macrophages were found in areas A (9.1 and 13.8 cells/1000 microns2) and B (4.1 and 9.4 cells/1000 microns2), respectively. In untreated mutants, osteoclasts and macrophages as percentages of normal were, respectively, 0% and 2% (area A) and 30% and 13% (area B). After CSF-1 treatment (0.15, 0.3, 0.5, and 1.0 x 10(6) U/day) for 28 days, marrow cavity size and numbers of osteoclasts and macrophages increased significantly in area B. However, area A remained sclerotic, with few macrophages (3% to 20%), and although osteoclast numbers were normal, their distribution was not, being absent in subepiphyseal sites. High CSF-1 gene expression occurs at bone modeling sites, co-localizes with osteoblasts, and temporally correlates with their differentiation.(ABSTRACT TRUNCATED AT 250 WORDS)
Insights
Osteopetrotic (op) mice treated with colony-stimulating factor-1 (CSF-1) showed persistent bone sclerosis despite increased osteoclast and macrophage numbers. High-dose CSF-1 did not fully restore normal cell distribution in op mice.
Area of Science:
- Skeletal biology
- Cellular and molecular biology
- Hematopoiesis
Background:
- Osteopetrosis (op) in mice causes skeletal sclerosis due to defects in osteoclast and macrophage development.
- Colony-stimulating factor-1 (CSF-1) is crucial for osteoclast and macrophage production.
- Previous studies suggested CSF-1 treatment could cure the op mutation.
Purpose of the Study:
- To investigate the persistent metaphyseal sclerosis in op mice treated with CSF-1.
- To quantify osteoclasts and macrophages in specific regions of the proximal tibial metaphysis after CSF-1 treatment.
- To analyze the distribution and differentiation of these cells in response to varying CSF-1 doses.
Main Methods:
- Quantification of osteoclasts and macrophages using tartrate-resistant acid phosphatase and F4/80 markers.
- Analysis of cell populations in two distinct regions (Area A and Area B) of the proximal tibial metaphysis.
- Treatment of op mice with varying doses of CSF-1 for 28 days.
Main Results:
- CSF-1 treatment increased marrow cavity size and cell numbers in Area B but not Area A.
- Area A remained sclerotic with significantly reduced macrophage presence (3-20%).
- While osteoclast numbers normalized in Area A, their subepiphyseal distribution was abnormal.
Conclusions:
- High-dose CSF-1 treatment does not fully resolve metaphyseal sclerosis in op mice.
- Abnormal osteoclast distribution and persistent macrophage deficiency in specific bone regions indicate incomplete therapeutic efficacy.
- CSF-1 gene expression at bone modeling sites suggests a complex interplay with osteoblasts during bone development.