Menaquinone-7 preserves Prg4⁺ chondrocytes from iron-driven damage in aging associated osteoarthritis by targeting...

Aging-associated knee osteoarthritis (KOA) is a degenerative joint disease with limited disease-modifying treatment options. Increasing evidence suggests that iron accumulation in aging joints drives oxidative stress and lipid peroxidation, potentially contributing to cartilage degeneration through ferroptosis. However, the cellular targets and molecular mechanisms underlying iron-driven ferroptotic injury in articular cartilage remain largely unclear.

This study aimed to investigate whether menaquinone-7 (MK-7) acts as a mechanism-based intervention targeting GPR68 to protect Prg4⁺ chondrocytes from iron-driven ferroptosis and to define the underlying signaling mechanisms in aging-associated KOA.

Clinical cartilage and synovial samples were analyzed to characterize iron accumulation and redox alterations in aging-associated KOA. Synovial metabolomic profiling was performed to identify changes in iron-related metabolic pathways. To investigate the underlying mechanisms, in vivo and ex vivo osteoarthritis models, including murine and equine systems, were established to examine ferroptosis-related changes in Prg4⁺ chondrocytes using histological, biochemical, and imaging-based analyses. GPR68 knockout mice were employed to determine the role of GPR68 in mediating iron-driven ferroptosis. Subsequently, in vitro experiments were conducted to evaluate the effects of MK-7 on iron-induced ferroptosis in chondrocytes. Molecular docking, surface plasmon resonance (SPR), and cellular thermal shift assay (CETSA) were used to assess the interaction between MK-7 and GPR68. Downstream signaling analyses were performed to elucidate the involvement of the GPR68/MAPK/GPX4 axis.

Clinical analyses and synovial metabolomic profiling revealed that aging-associated osteoarthritic joints exhibited marked iron accumulation accompanied by depletion of vitamin K2-related metabolites, suggesting profound redox remodeling in the joint microenvironment. Iron overload was preferentially associated with ferroptosis-like injury in Prg4⁺ superficial chondrocytes, characterized by enhanced lipid peroxidation, impaired GPX4-dependent antioxidant defense, and early extracellular matrix (ECM) damage. Mechanistically, iron overload selectively activated GPR68 and triggered a pathological MAPK/GPX4 feed-forward loop that amplified ferroptotic vulnerability in Prg4⁺ chondrocytes. Genetic ablation of GPR68 attenuated iron-driven ferroptotic injury and alleviated cartilage degeneration, confirming its critical role in this process. Among vitamin K2 isoforms, MK-7 directly bound to GPR68, restored GPX4-dependent redox homeostasis, and suppressed MAPK hyperactivation under iron overload. In vivo and ex vivo murine and equine models further demonstrated that intra-articular MK-7 administration reduced chondrocyte ferroptosis, preserved ECM integrity, and attenuated osteoarthritic progression.

This study identifies iron-driven ferroptotic stress in Prg4⁺ superficial chondrocytes as a key pathological feature of aging-associated osteoarthritis. We demonstrate that GPR68 functions as a critical sensor linking iron-induced microenvironmental alterations to MAPK activation and GPX4-dependent redox imbalance, thereby promoting ferroptosis-associated cartilage degeneration. Importantly, we further show that MK-7 directly targets GPR68 to restore redox homeostasis, suppress ferroptotic injury, and preserve cartilage integrity in both in vivo and ex vivo models. These findings not only provide mechanistic insights into the role of iron-driven ferroptosis in osteoarthritis progression but also highlight MK-7 as a promising mechanism-based therapeutic candidate for disease modification in aging-associated KOA.