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Updated: Jan 24, 2026

Isolation, Purification, and Differentiation of Osteoclast Precursors from Rat Bone Marrow
Published on: May 19, 2019
TNFα blockade mediates bone protection in antigen-induced arthritis by reducing osteoclast precursor supply
Stephanie Uster1, Fernanda Matos Coelho2, Daniel Aeberli3
1Department of Rheumatology, Immunology & Allergology, University Hospital, Bern, Switzerland; Theodor Kocher Institute, University of Bern, Bern, Switzerland; Graduate School for Cellular and Biomedical Sciences, University of Bern, Bern, Switzerland.
Abstract:
Bone protective effects of TNFα inhibition in rheumatoid arthritis are thought to be mediated by inhibiting synovial osteoclast differentiation and activity. However, it has not been addressed, if TNFα inhibitors alter the pool of peripheral osteoclast precursor cells (OPCs). Here, we blocked TNFα function in C57BL/6 mice with antigen induced arthritis (AIA) using the soluble TNFα receptor etanercept. Synovial bone lesions and osteoclasts were markedly reduced upon Etanercept in the early chronic phase of AIA. Unexpectedly this was not associated with a reduced recruitment of circulating OPCs to the arthritic joint nor to reduced synovial inflammation. In contrast we found that OPC numbers in bone marrow and blood were significantly reduced. Overall our study suggests that arrest of osteoclast mediated bone lesions upon inhibition of TNFα is, at least initially, based on reduced OPC availability in the periphery, and not on OPC recruitment or local anti-inflammatory effects in the arthritic joint.
Insights
Tumor necrosis factor-alpha (TNFα) inhibitors reduce bone damage in rheumatoid arthritis by decreasing osteoclast precursor cells (OPCs) in the blood and bone marrow, not by affecting their joint recruitment.
Area of Science:
- Immunology
- Rheumatology
- Cell Biology
Background:
- Rheumatoid arthritis (RA) involves bone erosion driven by osteoclasts.
- Tumor necrosis factor-alpha (TNFα) inhibitors are effective RA treatments, believed to work by reducing osteoclast activity in joints.
- The impact of TNFα inhibitors on the overall pool of osteoclast precursor cells (OPCs) remains unclear.
Purpose of the Study:
- To investigate whether TNFα inhibition affects the number of peripheral osteoclast precursor cells (OPCs).
- To determine the mechanism by which TNFα inhibition protects bone in antigen-induced arthritis (AIA).
Main Methods:
- Mice with antigen-induced arthritis (AIA) were treated with etanercept, a TNFα inhibitor.
- Osteoclast numbers, synovial inflammation, and OPC recruitment to the joint were assessed.
- OPC populations in bone marrow and peripheral blood were quantified.
Main Results:
- Etanercept treatment significantly reduced synovial bone lesions and osteoclasts in AIA mice.
- Contrary to expectations, OPC recruitment to the arthritic joint and synovial inflammation were not reduced.
- A significant decrease in OPC numbers was observed in the bone marrow and blood of etanercept-treated mice.
Conclusions:
- TNFα inhibition protects against bone loss in early chronic AIA primarily by reducing the availability of peripheral osteoclast precursor cells (OPCs).
- The protective effect is not mediated by reduced OPC recruitment to the joint or local anti-inflammatory actions within the synovium.
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