Quercetin activates autophagy suppresses apoptosis, inflammation and cartilage matrix degradation in LPS-induced chondrocytes through targeting AMPK/mTOR/ULK1 signaling pathway

Abstract Background: Osteoarthritis (OA) is a chronic joint disease characterised by degeneration of articular cartilage, massive apoptosis of chondrocytes and changes in subchondral bone. Quercetin (QUE), a naturally occurring flavonoid, has shown potent anti-inflammatory effects; however, its effects and underlying mechanisms on OA have seldom been systematically illuminated. In this study, we explored the protective effects of QUE on repairing OA-induced chondrocytes injuries and its possible mechanisms.Methods: Human articular chondrocytes were isolated and cultured, and then induced by lipopolysaccharide (LPS). Chondrocytes were assigned into Control group (normal complete culture medium), LPS induction group (Model group), QUE+LPS induction group (QUE group), 3-MA+LPS induction group (3-MA group), 3-MA+QUE+LPS induction group (3-MA+QUE group), compound C (Com C) +LPS induction group (Com C group) and Com C+QUE+LPS induction group (Com C +QUE group). The optimal intervention concentration of LPS and QUE were selected by the Cell Cycle Kit‑8 assay (CCK‑8), osteoarthritis and inflammatory factors relevant to osteoarthritis, interleukin‑1β (LI-1β) and tumor necrosis factor‑α(TNF-α), were tested by enzyme‑linked immunosorbent assay (ELISA). Quantitative real-time polymerase chain reaction (qRT-PCR) was performed to detect mRNA expressions of autophagy-related genes (LC3 Ⅱ and P62). Western blotting and Immunofluorescence staining were utilized to detect expressions of cartilage matrix degradation, apoptosis and autophagy-related proteins and of relevant proteins in the AMPK/mTOR/ULK1 signaling pathway. Cell cycle and apoptosis were detected by flow cytometry. Transmission electron microscope (TEM) images were used to detect autophagosomes, and Lyso-Tracker Red was applied to measure lysosomal activity.Results: In current study, we demonstrated that QUE can activate autophagy in LPS-induced chondrocytes. And, QUE can suppress apoptosis, inflammation and cartilage matrix degradation in LPS-induced chondrocytes by autophagy-based. Furthermore, these results demonstrated that QUE activates autophagy can suppress apoptosis, inflammation and cartilage matrix degradation in LPS-induced chondrocytes through targeting AMPK/mTOR/ULK1 signaling pathway.Conclusions: QUE activates autophagy alleviated LPS-induced chondrocytes injuries through targeting AMPK/mTOR/ULK1 signaling pathway.