Resolvin D1 suppresses inflammation in human fibroblast-like synoviocytes via the p-38, NF-κB, and AKT signaling pathways.

Synovitis represents the initial pathological change in osteoarthritis and contributes to its progression. Resolvin D1 (RV-D1) is a novel and endogenous docosahexaenoic acid-derived lipid mediator, which regulates the duration and magnitude of inflammation by downregulating pro-inflammatory genes and mediators. However, the effects of RV-D1 on synovitis remain unknown. The aim of the present study was to investigate the anti-inflammatory effects of RV-D1 in human fibroblast-like synoviocytes (HFLSs) and the underlying mechanisms. The expression of the HFLS formyl peptide receptor 2 (ALX/FPR) was examined via immunocytochemical analysis. HFLSs were treated with 1 ng/mL recombinant human interleukin-1β (IL-1β) and RV-D1. The gene expression of interleukin-1β (IL1B), matrix metalloproteinase 3 (MMP3), and MMP13 was examined using real-time reverse transcription-polymerase chain reaction after treatment with IL-1β and RV-D1. The effect of RV-D1 on apoptosis was examined based on fluorescence intensity. Phosphorylation of p-38, extracellular signal-regulated kinase, c-Jun N-terminal kinase, nuclear factor kappa B (NF-κB), and AKT was analyzed via western blotting. ALX/FPR staining was observed on the cell surface. RV-D1 significantly suppressed the IL-1β-induced increase in gene and protein expression of IL-1β, MMP-3, and MMP-13. Pretreatment with 100 nM RV-D1 significantly increased the fluorescence intensity compared to that in the non-treatment group. Furthermore, pretreatment with RV-D1 significantly suppressed the phosphorylation of p-38, NF-κB, and AKT. Whereas WRW4, an antagonist of ALX/ FPR2, treatment weakened the effect of RV-D1, resulting in p-38, NF-κB, and AKT phosphorylation and the protein expression of MMP-13 at levels comparable to those in the IL-1β without RV-D1. In conclusion, RV-D1 suppressed IL-1β and MMP expression by inhibiting the phosphorylation of p-38, NF-κB, and AKT in inflammation in HFLSs. RV-D1 can be used to develop treatments for osteoarthritis and other inflammatory disorders.