Objectives To examine the effect of interleukin-17 (IL-17) on rheumatoid arthritis (RA) synoviocyte migration and invasiveness.

Methods IL-17A and tumour necrosis factor α (TNFα)-induced messenger RNA expression in RA synoviocytes was analysed using Affymetrix U133A microarrays. The capacity of IL-17 alone or in combination with TNFα to induce synoviocyte migration and invasion was tested using Boyden and transwell Matrigel invasion chambers. A functional DNA binding assay was used to evaluate the regulation of the key hypoxia-related gene hypoxia-inducible factor 1 (HIF-1α) expression and activation. The role of metalloproteinase 2 (MMP2) in IL-17-induced invasiveness was assessed using small interfering RNA. Hypoxia pathway gene expression was measured in the blood of RA patients and healthy volunteers using Affymetrix microarrays.

Results Among the genes induced by IL-17A in RA synoviocytes, a molecular pattern of inflammation hypoxia-related genes, including CXC chemokine receptor 4 (CXCR4) and MMP2 was identified. Using immunofluorescence microscopy, the expression of CXCR4 was confirmed on synoviocytes. IL-17A and TNFα induced synoviocyte migration and invasion through a CXCR4-dependent mechanism with a synergistic effect. Their combination activated HIF-1α through the nuclear factor κB pathway. IL-17 enhanced invasion through MMP2 induction as demonstrated using siRNA. Finally, hypoxia genes were overexpressed in the blood of RA patients.

Conclusion IL-17A, specifically when combined with TNFα may contribute to the progression of RA, notably through their effect on synoviocyte aggressiveness. Part of this effect results from activation of the CXCR4/stromal cell-derived factor 1 and hypoxia-mediated pathways.