SAT004 A Novel Therapeutic Target Of Mitochondrial Protein To Prevent Steroid-induced Muscle Atrophy Through Regulation Of Proteolysis And Myogenesis

Disclosure: M. Kim: None. I.S. Sinam: None. S. Kim: None. Z. Siddique: None. S. Kwon: None. J. Jeon: None. I. Lee: None. Objectives: Muscle atrophy, defined as a progressive loss of muscle mass and function induced by various etiology. Steroids is well-known muscle atrophy-inducible drug by enhancing of muscle catabolism and proteolysis. Pyruvate dehydrogenase kinase (PDK), a mitochondrial protein that inhibits the pyruvate dehydrogenase complex, is highly upregulated in metabolic diseases, especially pathologic muscle conditions associated with enhanced muscle proteolysis and aberrant myogenesis. Here, we investigated the role of PDK on proteolysis and myogenesis in steroid-induced muscle atrophy. Methods & Materials: Human skeletal (gluteus-maximus) muscles obtained from patients who underwent hip replacement surgery according to steroid administration were used for evaluated at the molecular level by expression of key genes and proteins involved in myogenesis. Steroid-induced muscle atrophy models were developed administered with glucocorticoid (GC) 25 mg/kg, intraperitoneally, for 10 days. Muscle dysfunction was studied in vivo in wild-type and PDK4 knockout mice treated with GC. We used C2C12 myotubes treated with GC for 24 h for in vitro study. Results: The expression of PDK4, as well as muscle-specific E3 ligases: muscle RING finger 1(MuRF1) and muscle atrophy F box (MAFbx), are significantly increased in skeletal muscle of steroid-user. In mouse model of steroid-induced muscle atrophy, expression of PDK4 and MAFbx are also upregulated, whereas knockdown of PDK4 reduces MAFbx expression and ameliorated steroid-induced muscle atrophy; increased muscle strength and muscle fibers. In C2C12 myotubes, knockdown of PDK4 was also associated with reduction of myogenin induction and MAFbx expression. To find out the mechanism, we used coimmunoprecipitation and liquid chromatography-mass spectrometry analysis and found that myogenin is novel substrate of PDK4. Mechanistically, this result suggests that PDK4 promotes MAFbx recruitment to catalyze muscle atrophy-induced MYOG ubiquitination and degradation. Conclusion: Taken together, the results suggest that PDK4-dependent activation of the ubiquitin degradation pathway appears to underly the promotion of muscle atrophy by directly targeting the muscle-specific MAFbx. Therefore, the inhibition of PDK4 represents as a novel therapeutic target to alleviate steroid-induced muscle atrophy. Presentation: Saturday, June 17, 2023