Introduction: Tumour Necrosis Factor (TNF) and Interleukin-17A (IL-17A) contribute to the pathogenesis of Rheumatoid Arthritis (RA). The interplay of their signalling leads to remarkable synergistic effects in induction of many inflammatory cytokines and extracellular matrix degrading enzymes in synovial fibroblasts, but the mechanisms of synergy are poorly known. Transcription factor E74-like factor 3 (ELF3) is expressed in inflamed synovial membrane in RA and has been shown to regulate the expression of inflammatory genes in response to IL-1β. The aim of this study was to analyze the possible involvement of ELF3 on the synergistic induction of inflammatory mediators by IL-17A and TNF in synovial fibroblasts.
Methods: Human fibroblasts isolated from synovial membranes were treated with IL-17A and/or TNF and analyzed for ELF3 expression by qRT-PCR and immunofluorescence. The regulation of ELF3 expression and the impact of ELF3 for the signaling mediated by IL-17A and TNF was studied using transient overexpression in HEK293 cells and in synovial fibroblasts, transient knockdown using siRNAs in synovial fibroblasts, signaling inhibitors, ELISA, immunofluorescence and qRT-PCR.
Results: ELF3 was only marginally induced by IL-17A or TNF alone, but the combination of IL-17A and TNF resulted in high and prolonged induction of ELF3. Depletion of ELF3 with siRNA reduced the production of several cytokines, chemokines and matrix metalloproteinases in response to stimulation by IL-17A and TNF. Overexpression of ELF3 in HEK293 cells and in synovial fibroblasts resulted in increased responses to TNF. Induction of ELF3 mRNA expression was mediated by NF-κB pathway but was sensitive to cycloheximide treatment indicating a requirement for de novo protein synthesis.
Conclusions: Transcription factor ELF3 is a key regulator of the signalling mediating the synergy between IL-17A and TNF in the production of inflammatory mediators in synovial fibroblasts.
Disclosure of Interest: None declared