Disruption of iron homeostasis by HERC2-FTL axis leads to chondrocyte loss and exacerbates osteoarthritis.

Osteoarthritis (OA) is a common degenerative joint disease marked by cartilage degradation, inflammation, and subchondral bone remodeling. Ferroptosis, an iron-dependent form of programmed cell death, has recently emerged as a key contributor to OA progression. However, its upstream regulatory mechanisms remain unclear. HERC2, a HECT-domain E3 ubiquitin ligase, is known to regulate iron metabolism, but its role in OA has not been investigated. ATDC5 chondrocytes were treated with IL-1β or Erastin. The effects of HERC2 knockdown or overexpression on ferroptosis, autophagy, oxidative stress, and cartilage matrix proteins were evaluated. Proteins identified from HERC2 immunoprecipitation-mass spectrometry were cross-referenced with UbiBrowser-predicted substrates, and PPI networks were constructed using STRING and Cytoscape. HERC2-FTL interaction was validated via co-immunoprecipitation and ubiquitination assays. To identify therapeutic compounds, molecular docking was performed between HERC2and ferroptosis-related compounds from PubChem using AutoDock Vina. Proanthocyanidins (PAC) emerged as a top candidate and was validated in vitro. In vivo, HERC2-deficient mice underwent DMM surgery to induce OA. HERC2 was upregulated in OA and promoted ferroptosis by ubiquitinating and degrading ferritin light chain (FTL), resulting in iron accumulation, autophagy activation, and cartilage matrix loss. In vitro, treatment with the ferroptosis inhibitor Liproxstatin-1 or the HERC2-targeting compound PAC restored redox homeostasis, reduced lipid peroxidation, and improved chondrocyte viability under inflammatory and ferroptosis stress. In vivo, HERC2 deficiency alleviated OA severity, preserved cartilage and subchondral bone integrity, and improved joint function. HERC2 promotes OA progression by activating autophagy-dependent ferroptosis via FTL degradation. Targeting this pathway using ferroptosis inhibitors or HERC2-binding compounds like PAC may offer a promising disease-modifying approach for OA treatment.