Both hypoxia and interleukin-17A (IL-17A) promote the migration and invasion of fibroblast-like synoviocytes (FLSs), which are critical for the pathogenesis of rheumatoid arthritis (RA). However, the biochemical pathways regulating IL-17A combined with hypoxia are not well defined. In this study, we found that co-stimulating RA-FLSs with IL-17A and hypoxia did not appear to promote the epithelial-mesenchymal transition (EMT), but did increase cell motility. We further showed that a proinvasive effect of IL-17A on FLSs under hypoxia might be through upregulation of matrix metalloproteinase 2 (MMP2) and MMP9. Moreover, IL-17A-induced expression of MMP2 and MMP9 under hypoxia was accompanied by increased activation of nuclear factor-κB (NF-κB)/hypoxia-inducible factor-1α (HIF-1α). Knockdown or inhibition of HIF-1α and NF-κB by small interfering RNA or specific small molecule inhibitors blocked IL-17A-mediated and hypoxia-mediated MMP2 and MMP9 expression, cell migration, and invasion. In addition, the inhibition of NF-κB led to a marked decrease in the expression of HIF-1α, which indicated that IL-17A activated HIF-1α via the NF-κB pathway in hypoxia. Taken together, our observations suggest a synergetic effect of IL-17A and hypoxia that might contribute to the migration and invasion of RA-FLSs by upregulating the expression of MMP2 and MMP9 by activation of the NF-κB/HIF-1α pathway.
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