A20 inhibits the release of inflammatory cytokines by suppressing the activation of the nuclear factor-kappa B pathway in osteoarthritic fibroblast-like synoviocytes.

A growing number of studies suggest that synovitis plays an important role in the pathogenesis and progression of osteoarthritis (OA). As a negative mediator of the nuclear factor-kappa B (NF-κB) signaling pathway, the zinc finger protein A20 has significant anti-inflammatory properties. In this study, the differential expression of A20 was investigated at the mRNA and protein levels in human normal OA fibroblast-like synoviocytes (FLSs) and normal FLSs pretreated with TNF-α. We then measured the activation of the NF-κB pathway and expression of pro-inflammatory cytokines in the above three groups by western blotting, a human cytokine array and ELISA. We found that TNF-α activated the NF-κB pathway, increased the expression of the pro-inflammatory cytokines IL-6 and IL-8, and A20 expression in human normal FLSs. However, the role of A20 in FLSs was unclear. To clarify this, we investigated the effect of A20 overexpression in human normal FLSs. The results indicate that A20 inhibits the NF-κB signaling pathway activation and OA-associated pro-inflammatory cytokines release. The results of this study indicate that A20 has anti-inflammatory effects in FLSs, which makes it a potential target for OA synovitis treatment.

Dual specificity phosphatase 1 has a protective role in osteoarthritis fibroblast­like synoviocytes via inhibition of the MAPK signaling pathway.

Increasing evidence indicates the important role of inflammation in the pathogenesis and progression of osteoarthritis (OA). Dual specificity phosphatase 1 (DUSP1), a negative regulator of the mitogen­activated protein kinase (MAPK) signaling pathway, has anti­inflammatory properties. In the present study, the expression of DUSP1 was investigated in human OA fibroblast­like synoviocytes (FLSs), human normal FLSs and OA FLSs pretreated with dexamethasone at the mRNA and protein levels. Then, the activation of MAPK pathway proteins and the expression of matrix metalloproteinase­13 (MMP­13) and cyclooxygenase­2 (COX­2) were measured by western blot analysis in the three groups of cells. Dexamethasone induced the expression of DUSP1 and inhibited the activation of the MAPK pathway and reduced the expression of MMP­13 and COX­2 in OA FLSs. However, the role of DUSP1 remained unclear. To clarify this, the effects of overexpression of DUSP1 in OA FLSs were determined using a DUSP1­overexpressing lentivirus. The results demonstrated that overexpression of DUSP1 in OA FLSs inhibited the activation of the MAPK pathway and expression of OA­associated mediators. The findings of the present study indicate that DUSP1 has a protective role in OA FLSs and may be a potential target in the treatment of OA.