Regulation of Osteoclast and T Cell Differentiation By DC-STAMP and TRAF3

Yahui Grace Chiu¹, Jinbo Li², Dongge Li¹, Brendan Boyce² and Christopher T. Ritchlin³, ¹Allergy, Immunology and Rheumatology, University of Rochester, Rochester, NY, ²Pathology, University of Rochester, Rochester, NY, ³Allergy Immunology & Rheumatology, University of Rochester Medical Center, Rochester, NY

Meeting: 2014 ACR/ARHP Annual Meeting

Keywords: bone biology, osteoclastogenesis, osteoclasts and osteoporosis, T cells

Session Information

Title: Biology and Pathology of Bone and Joint: Osteoclasts, Osteoblasts and Bone Remodeling

Session Type: Abstract Submissions (ACR)

Background/Purpose

DC-STAMP (Dendritic Cell-Specific Transmembrane Protein) is a 7-pass transmembrane protein essential for cell-to-cell fusion during OC differentiation. We have previously shown that DC-STAMP is a specific cell surface marker of OC precursors (OCP) and the frequency of DC-STAMP⁺cells is elevated in patients with psoriatic arthritis (PsA). Intriguingly, we found that the level of TNF receptor-associated factor 3 (TRAF3) was also significantly elevated in the OCPs of PsA patients. In addition, osteoporosis can be prevented in mice by reducing osteoclastogenesis through inhibition of TRAF3 degradation by chloroquine. Although both DC-STAMP and TRAF3 play critical roles in OC formation, it is unknown if there is an interplay between these two molecules during osteoclastogenesis. Herein, to investigate a possible mutual regulation between them, we quantified and monitored these two proteins in DC-STAMP knock-out (KO) mice and TRAF3 conditional KO (cKO) mice.

Methods

We analyzed the expression of DC-STAMP and TRAF3 in the spleen, thymus, lymph nodes, bone marrow and skeleton by flow cytometry and Western blotting in the TRAF3 KO and DC-STAMP KO mouse strains. We also examined the effects of chloroquine on the expression of DC-STAMP and TRAF3. The TRAF3 cKO mouse line was established by conditional deletion of TRAF3 in OC lineage cells by crossing Traf3^fl/fland CatK-Cre.

Results

In DC-STAMP KO mice, TRAF3⁺ T cells were identified in the bone marrow, bone, spleen, lymph nodes, but not in the thymus. We showed that the DC-STAMP deficiency blocked the differentiation of TRAF3⁺CD8⁺T cells in thymus, and TRAF3 protein was not present in the thymus by Western blot analysis. In contrast, the expression level of DC-STAMP and DC-STAMP+ cell frequency was unchanged in the TRAF3 cKO mice. Chloroquine treatment increased the expression levels of extracellular DC-STAMP and intracellular TRAF3 and prevented osteoclast formation in human PBMC cell cultures.

Conclusion

The expression of DC-STAMP is normal in the TRAF3 cKO mouse cells, whereas TRAF3 expression was dramatically decreased in the thymus of DC-STAMP KO mice. Our results suggest that (1) DC-STAMP is critical for the regulation of T cell differentiation in the thymus; (2) DC-STAMP and TRAF3 are both required for osteoclastogenesis; (3) chloroquine exerts its negative osteoclastogenic effect by inhibiting the degradation of both TRAF3 and DC-STAMP. Thus, understanding the molecular events that regulate the synthesis and degradation of DC-STAMP and TRAF3 may reveal novel therapeutic targets in metabolic and inflammatory bone diseases.

Disclosure:

Y. G. Chiu,
None;

J. Li,
None;

D. Li,
None;

B. Boyce,
None;

C. T. Ritchlin,

Eli Lilly and Company,

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