IL-17 and tumour necrosis factor α combination induces a HIF-1α-dependent invasive phenotype in synoviocytes.

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.