Forkhead box O3 attenuates osteoarthritis by suppressing ferroptosis through inactivation of NF-κB/MAPK signaling.

Background: Ferroptosis is a nonapoptotic cell death process that is characterized by lipid peroxidation and intracellular iron accumulation. As osteoarthritis (OA) progresses, inflammation or iron overload induces ferroptosis of chondrocytes. However, the genes that play a vital role in this process are still poorly studied. Methods: Ferroptosis was elicited in the ATDC5 chondrocyte cell line and primary chondrocytes by administration of the proinflammatory cytokines, interleukin (IL)-1β and tumor necrosis factor (TNF)-α, which play key roles in OA. The effect of FOXO3 expression on apoptosis, extracellular matrix (ECM) metabolism, and ferroptosis in ATDC5 cells and primary chondrocytes was verified by western blot, Immunohistochemistry (IMHC), immunofluorescence (IF) and measuring Malondialdehyde (MDA) and Glutathione (GSH) levels. The signal cascades that modulated FOXO3-mediated ferroptosis were identified by using chemical agonists/antagonists and lentivirus. In vivo experiments were performed following destabilization of medial meniscus surgery on 8-week-old C57BL/6 mice and included micro-computed tomography measurements. Results: In vitro administration of IL-1β and TNF-α, to ATDC5 cells or primary chondrocytes induced ferroptosis. In addition, the ferroptosis agonist, erastin, and the ferroptosis inhibitor, ferrostatin-1, downregulated or upregulated the protein expression of forkhead box O3 (FOXO3), respectively. This, suggested, for the first time, that FOXO3 may regulate ferroptosis in articular cartilage. Our results further suggested that FOXO3 regulated ECM metabolism via the ferroptosis mechanism in ATDC5 cells and primary chondrocytes. Moreover, a role for the NF-κB/mitogen-activated protein kinase (MAPK) signaling cascade in regulating FOXO3 and ferroptosis was demonstrated. In vivo experiments confirmed the rescue effect of intra-articular injection of a FOXO3-overexpressing lentivirus against erastin-aggravated OA. Conclusions: The results of our study show that the activation of ferroptosis promotes chondrocyte death and disrupts the ECM both in vivo and in vitro. In addition, FOXO3 can reduce OA progression by inhibiting ferroptosis through the NF-κB/MAPK signaling pathway. The Translational potential of this article: This study highlights the important role of chondrocyte ferroptosis regulated by FOXO3 through the NF-κB/MAPK signaling in the progression of OA. The inhibition of chondrocyte ferroptosis by activating FOXO3 is expected to be a new target for the treatment of OA.