CILP Inhibits hyaline cartilage fibrosis and chondrocyte ferroptosis via keap1-Nrf2 axis in early osteoarthritis exercise therapy

By analyzing the single-cell RNA-Seq libraries we established of OA joints during exercise therapy, we found cartilage intermediate zone might participate in early OA exercise therapy. Early OA rat model was established by 4-week anterior cruciate ligament transection (ACLT). The radiomics was used to evaluate the relative damaged and undamaged area in OA patients’ cartilage. We overexpressed and knocked down CILP in early OA chondrocyte to explore its potential mechanism. The quantitative proteomics was used to examine the protein profiles of the CILP-treated chondorcyte. The Yeast One-Hybrid Assay, Co-Immunoprecipitation (Co-IP), Nrf2 cytosol-nuclei fractionation and ubiquitination assay were used to investigate the potential mechanism in CILP intervention. Western blot, ROS, JC-1, Ferrous ion, MDA and GSH detection, transmission electron microscopy (TEM) were used to explored the therapeutic effect of CILP on OA. Moderate exercise up-regulates CILP in the articular cartilage intermediate zone. CILP recovers the ratio of type II / I collagen, Sox9, α-SMA expression and competitively bind to Keap1 protein and reduce the stability of Keap1-Nrf2 dimer, thereby reducing the degree of Nrf2 ubiquitination and promoting Nrf2 nuclear translocation. Nrf2 nuclear translocation activated SLC7A11, HO-1, GPX4 and SOD-1 expression, then decreased the MDA contents, but increased GSH content, which ultimately inhibited chondrocytes ferroptosis and promoted hyalinization of fibrocartilage. Exercise induced cartilage intermediate zone and CILP-Keap1-Nrf2 axis inhibits hyaline cartilage fibrosis and chondrocyte ferroptosis to alleviate early osteoarthritis.