Narirutin mitigates osteoarthritis by targeting USP15 to promote KEAP1 degradation and suppress chondrocyte ferroptosis.

BACKGROUND: Osteoarthritis (OA) is a prevalent degenerative joint disease characterized by progressive cartilage degeneration and joint dysfunction, for which effective therapeutic options remain limited. Increasing evidence suggests that ferroptosis, an iron-dependent form of regulated cell death driven by lipid peroxidation, contributes to chondrocyte injury and extracellular matrix (ECM) degradation during OA progression. PURPOSE: This study aimed to investigate the protective effects of narirutin on OA and to elucidate its underlying mechanisms in regulating ferroptosis and ECM homeostasis in chondrocytes. METHODS: Primary chondrocytes were treated with interleukin-1β (IL-1β) to establish an in vitro OA model, and a destabilization of the medial meniscus (DMM) mouse model was used in vivo. Ferroptosis was assessed by Western blotting, BODIPY 581/591 C11, FerroOrange probe, DCFH-DA staining, and immunohistochemistry. ECM degradation was evaluated by Western blotting, Alcian blue staining, immunofluorescence, Safranin O staining, and immunohistochemistry. Mechanistically, molecular docking, cellular thermal shift assay, and ubiquitination assays were performed to identify the molecular target of narirutin. RESULTS: Narirutin significantly attenuated IL-1β-induced chondrocyte ferroptosis and ECM degradation. Mechanistically, narirutin targeted ubiquitin-specific protease 15 (USP15) and reduced its protein abundance, thereby inhibiting USP15-mediated deubiquitination of Kelch-like ECH-associated protein 1 (KEAP1). This promoted K48-linked ubiquitination and proteasomal degradation of KEAP1, leading to activation of the Nrf2 antioxidant pathway. Consequently, Nrf2 activation reduced lipid peroxidation, suppressed both ferroptosis and ECM degradation in chondrocytes. In vivo, narirutin alleviated cartilage destruction in the DMM mouse model. CONCLUSION: Narirutin protects against OA progression by suppressing chondrocyte ferroptosis and ECM degradation via the USP15/KEAP1/Nrf2 signaling axis, suggesting its potential as a therapeutic candidate for OA treatment.