Background Tie2 is a tyrosine kinase receptor that has an essential role in blood vessel remodeling and angiogenesis, through its activation by its ligands angiopoietin (Ang)-1 and Ang-2. Tie2 and its ligands are expressed in RA synovial tissue, and we have reported that Ang-1 signaling to Tie2 promotes disease persistence and progression in early RA. Furthermore, we have found recently that Tie2 is mainly expressed and activated in RA synovial macrophages, that Ang-2 plays a crucial role in murine arthritis, and that Tie2 signaling promotes the inflammatory activation of monocyte-derived macrophages (MDM). However, the effect of Tie2 signaling on macrophages from arthritis patients has not been assessed yet.
Objectives The aim of this study was to examine how complex differentiation stimuli present in the RA and PsA synovial microenvironment might regulate Tie2 expression and signaling on macrophages, as well as the role of Tie2 signaling in macrophages from RA and PsA patients.
Methods Human peripheral blood mononuclear cells (PBMCs) were isolated from blood buffy coats (HD) and from RA and PsA patients. Monocytes were differentiated into macrophages in the presence the pro-inflammatory cyokine interferon- gamma (IFN-γ), the anti-inflammatory cytokine interleukin-10 (IL-10), or in the presence of RA or PsA patient synovial fluid (SF). At day 6, Tie-2 expression was analyzed by flow cytometry and quantitative PCR. At day 7, differentiated macrophages were stimulated with TNF in the presence or absence of Ang-1 or Ang-2 and macrophage gene expression of inflammatory mediators and angiogenic factors was analyzed by quantitative PCR.
Results Tie2 protein and mRNA expression was observed in HD macrophages differentiated in RA and PsA SF and expression levels where similar to those found in IL-10 and IFN-γ -differentiated HD macrophages. Gene expression analysis of angiogenic factors demonstrated distinct expression profiles under each polarization condition, although unsupervised clustergram analysis demonstrated a high relationship between IL-10, RA SF and PsA SF -differentiated HD macrophages. TNF stimulation of RA SF and PsA SF –differentiated HD macrophages, enhanced expression of the pro-inflammatory cytokines IL-6, IL-8 and TNF and the chemokines CCL-3, CXCL-2, 3, 5, 6 10 and 11, and Ang-1 and Ang-2 stimulation significantly enhanced TNF-driven expression of IL-6, IL-8, CCL-3, CXCL-2, 3, and 6. In RA and PsA patient macrophages differentiated in IL-10 and IFN-γ, Ang-1 and Ang-2 stimulation significantly synergized with TNF to enhance the expression of IL-6, IL-12B, IL-8, CCL-3 and CXCL-6.
Conclusions Our results demonstrate that Tie2 is functionally expressed by both RA and PsA macrophages. In both RA and PsA SF -differentiated HD macrophages, and IL-10 and IFN-γ -differentiated RA and PsA patient macrophages, Ang-1 and Ang-2 stimulation enhances TNF induced pro-inflammatory cytokine and chemokine expression. These results suggest that Tie2 signaling, in combination with TNF, induces a pro-inflammatory and pro-angiogenic profile in arthritic macrophages, and provides a molecular basis for the role of Tie2 signaling in promoting and perpetuating disease in RA and PsA.
Disclosure of Interest : None declared