FBXW7 promotes osteoarthritis injury by regulating SLC7A11 ubiquitination degradation and chondrocyte ferroptosis

F-box and WD repeat domain-containing 7 (FBXW7), a ubiquitinating enzyme, has been verified as a key factor linking to the mechanical overloading and chondrocyte senescence in the pathology of osteoarthritis (OA). Given the lack of deeply mechanism research on the regulation of OA by FBXW7, elucidation of the action mechanism of FBXW7 in OA could provide theoretical basis for the treatment of OA. OA model was established by injuring the anterior cruciate ligament (ACL). Ferrostatin-1 (Fer-1) was applied for analysis of Ferroptosis. After overexpressed or silence of FBXW7, cell viability and Apoptosis were determined via CCK-8 and TUNEL staining. The intracellular Fe^{2 +} , GSH concentration, ROS levels and mitochondrial membrane potential were assessed by iron determination kit, ELISA, C11-BODIPY/DCFH-DA and JC-1 staining methods. Western blot and RT-qPCR were carried out for determination of ferroptosis-correlated factors (SLC7A11 and GPX4) and ECM-related factors (Collagen II (Col II) and ADAMTS5). The interaction between SLC7A11 protein and FBXW7 was detected by immunofluorescence (IF) and immunoprecipitation (IP). Up-regulation of FBXW7, and down-regulation of SLC7A11 and GPX4 were observed in OA groups, compared to that in Control group. Moreover, FBXW7 overexpression significantly hindered cell viability, injured cell morphology, promoted Apoptosis and reduced Col II protein level, while Fer-1 treatment blocked the function of FBXW7 overexpression in OA injury. Additionally, silence of FBXW7 showcased the opposite results, meanwhile decreased Fe²⁺ level, increased GSH release, reduced ROS content, raised mitochondrial membrane potential and elevated SLC7A11 and GPX4 in OA chondrocytes. Furthermore, SLC7A11 and FBXW7 were co-localized in chondrocytes and exhibited protein interaction. The ubiquitination degradation of SLC7A11 was accelerated by FBXW7 in chondrocytes, which was intercepted by MG132 treatment. In vivo experimental results further uncovered the alleviated functions of FBXW7 knockdown in Ferroptosis and cartilage damage in OA model. The finding demonstrated that FBXW7 aggravated OA injury and Ferroptosis, which might be linked to the ubiquitination degradation of SLC7A11.

FBXW7; Ferroptosis; Ferrostatin-1; Osteoarthritis; SLC7A11 ubiquitination.