Suppression of atrogin-1 and MuRF1 prevents dexamethasone-induced atrophy of cultured myotubes

• Published in: Metabolism, clinical and experimental clinical and experimental, 2013-10, Vol.62 (10), p.1495-1502
• Main Authors: Castillero, Estibaliz, Alamdari, Nima, Lecker, Stewart H, Hasselgren, Per-Olof
• Format: Article
• Language: English
• Subjects: Animals; Biological and medical sciences; Cells, Cultured; Dexamethasone - pharmacology; Endocrinology & Metabolism; Feeding. Feeding behavior; Fundamental and applied biological sciences. Psychology; Glucocorticoids; Glucocorticoids - pharmacology; Muscle Cells - drug effects; Muscle Cells - metabolism; Muscle Cells - pathology; Muscle Fibers, Skeletal - drug effects; Muscle Fibers, Skeletal - metabolism; Muscle Fibers, Skeletal - pathology; Muscle Proteins - genetics; Muscle Proteins - metabolism; Muscle wasting; Muscle, Skeletal - drug effects; Muscle, Skeletal - metabolism; Muscle, Skeletal - pathology; Muscular Atrophy - chemically induced; Muscular Atrophy - genetics; Muscular Atrophy - metabolism; Muscular Atrophy - pathology; Protein Biosynthesis - drug effects; Protein Biosynthesis - genetics; Protein synthesis; Proteolysis; Proteolysis - drug effects; Rats; RNA, Messenger - genetics; SKP Cullin F-Box Protein Ligases - genetics; SKP Cullin F-Box Protein Ligases - metabolism; Tripartite Motif Proteins; Ubiquitin - genetics; Ubiquitin - metabolism; Ubiquitin ligases; Ubiquitin-Protein Ligases - genetics; Ubiquitin-Protein Ligases - metabolism; Vertebrates: anatomy and physiology, studies on body, several organs or systems
• ISSN: 0026-0495; 1532-8600
• DOI: 10.1016/j.metabol.2013.05.018

Abstract Objective The mechanistic role of the ubiquitin ligases atrogin-1 and MuRF1 in glucocorticoid-induced muscle wasting is not fully understood. Here, we tested the hypothesis that glucocorticoid-induced muscle atrophy is at least in part linked to atrogin-1 and MuRF1 expression and that the ubiquitin ligases are regulated by compensatory mechanisms. Methods The expression of atrogin-1 and MuRF1 was suppressed individually or in combination in cultured L6 myotubes by using siRNA technique. Myotubes were treated with dexamethasone followed by determination of mRNA and protein levels for atrogin-1 and MuRF1, protein synthesis and degradation rates, and myotube morphology. Results Suppression of atrogin-1 resulted in increased expression of MuRF1 and vice versa, suggesting that the ubiquitin ligases are regulated by compensatory mechanisms. Simultaneous suppression of atrogin-1 and MuRF1 resulted in myotube hypertrophy, mainly reflecting stimulated protein synthesis, and prevented dexamethasone-induced myotube atrophy, mainly reflecting inhibited protein degradation. Conclusions The results provide evidence for a link between upregulated atrogin-1 and MuRF1 expression and glucocorticoid-induced muscle atrophy. The study also suggests that atrogin-1 and MuRF1 levels are regulated by compensatory mechanisms and that inhibition of both ubiquitin ligases may be needed to prevent glucocorticoid-induced muscle proteolysis and atrophy.