The physiological metabolite ?-ketoglutarate ameliorates osteoarthritis by regulating mitophagy and oxidative stress

Osteoarthritis (OA) is an age-related metabolic disease. Low-grade inflammation and oxidative stress are the last common pathway of OA. alpha-ketoglutarate (alpha-KG) is an essential physiological metabolite from the mitochondrial tricarboxylic acid (TCA) cycle, with multiple functions, including anti-inflammation and antioxidation, and exhibits decreased serum levels with age. Herein, we aimed to investigate the effect and mechanism of alpha-KG on OA. We first quantified the alpha-KG levels in human cartilage tissue and osteoarthritic chondrocytes induced by IL-1 beta. Besides, IL-1 beta-induced osteoarthritic chondrocytes were treated with different concentrations of alpha-KG. Chondrocyte proliferation and apoptosis, synthesis and degradation of extracellular matrix, and inflammation mediators were analyzed. RNA sequencing was used to explore the mechanism of alpha-KG, and mitophagy and oxidative stress levels were further detected. These results were verified in an anterior cruciate ligament tran-section (ACLT) induced age-related OA rat model. We found that alpha-KG content decreased by 31.32% in damaged medial cartilage than in normal lateral cartilage and by 36.85% in IL-1 beta-induced human osteoarthritic chon-drocytes compared to control. alpha-KG supplementation reversed IL-1 beta-induced chondrocyte proliferation inhibition and apoptosis, increased the transcriptomic and proteinic expression of ACAN and COL2A1 in vivo and in vitro, but inhibited the expression of MMP13, ADAMTS5, IL-6, and TNF-alpha. In mechanism, alpha-KG promoted mitophagy and inhibited ROS generation, and these effects could be prevented by Mdivi-1 (a mitophagy inhibitor). Overall, alpha-KG content decreased in human OA cartilage and IL-1 beta-induced osteoarthritic chondrocytes. Moreover, alpha-KG supplementation could alleviate osteoarthritic phenotype by regulating mitophagy and oxidative stress, sug-gesting its potential as a therapeutic target to ameliorate OA.