Background/Purpose: DC-STAMP is a transmembrane protein involved in the fusion of mononuclear osteoclasts and essential for the formation of fully functional multinucleated osteoclasts (OCs). Recently we found impaired accumulation of macrophages in the inflamed synovium, and a correlation between reduced bone resorption and the area occupied by TRAP⁺OCs in bones of DCSTAMP^+/+TNF Tg mice.  Interestingly, serum concentration of murine TNF and MCP-1, a macrophage attracting chemokine, was lower in DCS-STAMP^-/-TNF Tg mice than TNF Tg mice. These results suggested that impaired bone erosion in DC-STAMP^-/-TNF Tg mice may result from defective attraction of immune cells to the joints. Thus, we examined both the mechanism and type of cells involved in the progression of TNF-driven inflammatory arthritis in the presence or absence of DCSTAMP.

Methods: C57BL/6 mice were irradiated and reconstituted with 1X10⁷CD45.2⁺TNF Tg and 1X10⁷CD45.1⁺DCSTAMP^-/-bone marrow cells. Six weeks after bone marrow transfer, mice were i.p injected, at days 0 and 3, with 150 ml of serum from NOD.KRN mice. CD45.2⁺and CD45.1⁺cells were enumerated by flow cytometry or immunofluorescence. To elucidate whether DCSTAMP on stromal cells participates in bone resorption, we generated reciprocal chimeric mice, using WT, DCSTAMP^-/-, TNF Tg, DCSTAMP^-/-TNF Tg mice as recipients or donors of BM cells, and measured bone density by mCT scan. Migration of bone marrow cells isolated from WT, DCSTAMP^-/-, TNF Tg and DCSTAMP^-/- TNF Tg mice was tested by chemotaxis assays using conditioned media from stromal cells activated with TNF. mRNA expression of inflammatory cytokines by macrophages activated with IL-4 or LPS/IFNgwas quantitated with qPCR.

Results: Enumeration of congenic cells by flow cytometry in 50:50 bone marrow chimeras showedthat 77% ±1.5 and 70% ±1 of CD45.1⁺DC-STAMP^-/-cells accumulated in popliteallymph nodes and spleen, respectively; but they were absent in the inflamed synovium. In contrast, CD45.2⁺ TNF-producing cells were significantly increased in the synovium of mice with acute arthritis. Moreover, polarized macrophages of DC-STAMP^-/-and DC-STAMP^-/- TNF Tg mice had a significantly lower expression of TNF (p = 0.004), IL1b (p = 0.02) and iNOS (p = 0.001) and higher IL10 expression (p = 0.04). We also found that bone volume in mice expressing DC-STAMP on the stromal or hematopoietic cells increased 2-fold in femur (p = 0.05) and 2.5-fold in tibia (p=0.04), compared with mice expressing TNF in both stromal and hematopoietic cells.  Interestingly, DCSTAMP^-/-stromal cells activated with mouse or human TNF had lower expression of MCP1 (p = 0.002), CX3CL1 (p = 0.001), IL-1b (p = 0.03) and MMP9 than WT stromal cells. In vitro chemotaxis assay using supernatant collected from WT stromal cells showed a 28-fold decrease in migration of monocytes from DCSTAMP^-/-(p = 0.02) and DCSTAMP^-/-  TNF mice (p = 0.01). These monocytes also had 4-fold decrease (p = 0.01) in the migration towards supernatant from DC-STAMP^-/-stromal cells.

Conclusion: Our data reveal an unexpected role for stromal cell-derived DC-STAMP in the modulation of migration and pathogenic polarization of monocytes into inflamed arthritic joints.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/stromal-cell-derived-dcstamp-coordinates-cell-migration-and-osteoclast-activation-in-tnf-driven-murine-arthritis/