Syringic acid promotes cartilage extracellular matrix generation and attenuates osteoarthritic cartilage degradation by activating TGF-β/Smad and inhibiting NF-κB signaling pathway

Osteoarthritis (OA) is a common chronic degenerative disease which is characterized by the disruption of articular cartilage. Syringic acid (SA) is a phenolic compound with anti-inflammatory, antioxidant, and other effects including promoting osteogenesis. However, the effect of SA on OA has not yet been reported. Therefore, the purpose of our study was to investigate the effect and mechanism of SA on OA in a mouse model of medial meniscal destabilization. The expressions of genes were evaluated by qPCR or western blot or immunofluorescence. RNA-seq analysis was performed to examine gene transcription alterations in chondrocytes treated with SA. The effect of SA on OA was evaluated using destabilization of the medial meniscus model of mice. We found that SA had no obvious toxic effect on chondrocytes, while promoting the expressions of chondrogenesis-related marker genes. The results of RNA-seq analysis showed that extracellular matrix–receptor interaction and transforming growth factor-β (TGF-β) signaling pathways were enriched among the up-regulated genes by SA. Mechanistically, we demonstrated that SA transcriptionally activated Smad3. In addition, we found that SA inhibited the overproduction of lipopolysaccharide-induced inflammation-related cytokines including tumor necrosis factor-α and interleukin-1β, as well as matrix metalloproteinase 3 and matrix metalloproteinase 13. The cell apoptosis and nuclear factor-kappa B (NF-κB) signaling were also inhibited by SA treatment. Most importantly, SA attenuated cartilage degradation in a mouse OA model. Taken together, our study demonstrated that SA could alleviate cartilage degradation in OA by activating the TGF-β/Smad and inhibiting NF-κB signaling pathway.