SKP2‐mediated ubiquitination and degradation of KLF11 promotes osteoarthritis via modulation of JMJD3/NOTCH1 pathway

Osteoarthritis (OA) is the main cause of cartilage damage and disability. This study explored the biological function of S‐phase kinase‐associated protein 2 (SKP2) and Kruppel‐like factor 11 (KLF11) in OA progression and its underlying mechanisms. C28/I2 chondrocytes were stimulated with IL‐1β to mimic OA in vitro. We found that SKP2, Jumonji domain‐containing protein D3 (JMJD3), and Notch receptor 1 (NOTCH1) were upregulated, while KLF11 was downregulated in IL‐1β‐stimulated chondrocytes. SKP2/JMJD3 silencing or KLF11 overexpression repressed apoptosis and extracellular matrix (ECM) degradation in chondrocytes. Mechanistically, SKP2 triggered the ubiquitination and degradation of KLF11 to transcriptionally activate JMJD3, which resulted in activation of NOTCH1 through inhibiting H3K27me3. What's more, the in vivo study found that KLF11 overexpression delayed OA development in rats via restraining apoptosis and maintaining the balance of ECM metabolism. Taken together, ubiquitination and degradation of KLF11 regulated by SKP2 contributed to OA progression by activation of JMJD3/NOTCH1 pathway. Our findings provide promising therapeutic targets for OA. The mechanism of KLF11 on osteoarthritis. SKP2 degraded KLF11 through ubiquitination, and the decreased KLF11 promoted transcriptional activation of JMJD3 and expression of NOTCH1, thus promoting chondrocyte injury in osteoarthritis.