Mechanisms Involved in 3′,5′-Cyclic Adenosine Monophosphate-Mediated Inhibition of the Ubiquitin-Proteasome System in Skeletal Muscle

• Published in: Endocrinology (Philadelphia) Vol. 150; no. 12; pp. 5395 - 5404
• Main Authors: Gonçalves, Dawit A. P, Lira, Eduardo C, Baviera, Amanda M, Cao, Peirang, Zanon, Neusa M, Arany, Zoltan, Bedard, Nathalie, Tanksale, Preeti, Wing, Simon S, Lecker, Stewart H, Kettelhut, Isis C, Navegantes, Luiz C. C
• Format: Journal Article
• Language: English
• Published: United States Endocrine Society 01.12.2009; Oxford University Press
• Subjects: 1-Methyl-3-isobutylxanthine - pharmacology; Adenosine monophosphate; Adrenergic beta-2 Receptor Agonists; Agonists; AKT protein; Animals; Atrophy; Biodegradation; Blotting, Western; Catecholamines; Cell Line; Clenbuterol; Clenbuterol - pharmacology; Cyclic AMP; Cyclic AMP - metabolism; Dexamethasone; Dexamethasone - pharmacology; Dietary restrictions; Forkhead Box Protein O3; Forkhead Transcription Factors - metabolism; FOXO3 protein; Gene expression; In Vitro Techniques; Inactivation; Male; Mice; Mice, Inbred C57BL; Mice, Knockout; mRNA; Muscle Proteins - genetics; Muscle Proteins - metabolism; Muscle, Skeletal - cytology; Muscle, Skeletal - drug effects; Muscle, Skeletal - metabolism; Muscles; Musculoskeletal system; Myotubes; Peroxisome Proliferator-Activated Receptor Gamma Coactivator 1-alpha; Peroxisome proliferator-activated receptors; Phosphodiesterase inhibitors; Phosphodiesterase Inhibitors - pharmacology; Phosphorylation; Phosphorylation - drug effects; Proteasome Endopeptidase Complex - genetics; Proteasome Endopeptidase Complex - metabolism; Proteasomes; Proteins; Proto-Oncogene Proteins c-akt - metabolism; Rats; Rats, Wistar; Receptors (physiology); Receptors, Adrenergic, beta-2 - genetics; Receptors, Adrenergic, beta-2 - metabolism; Reverse Transcriptase Polymerase Chain Reaction; Skeletal muscle; SKP Cullin F-Box Protein Ligases - genetics; SKP Cullin F-Box Protein Ligases - metabolism; Trans-Activators - genetics; Trans-Activators - metabolism; Transcription Factors; Tripartite Motif Proteins; Ubiquitin - genetics; Ubiquitin - metabolism; Ubiquitin-protein ligase; Ubiquitin-Protein Ligases - genetics; Ubiquitin-Protein Ligases - metabolism
• DOI: 10.1210/en.2009-0428
• ISSN: 0013-7227

Although it is well known that catecholamines inhibit skeletal muscle protein degradation, the molecular underlying mechanism remains unclear. This study was undertaken to investigate the role of β2-adrenoceptors (AR) and cAMP in regulating the ubiquitin-proteasome system (UPS) in skeletal muscle. We report that increased levels of cAMP in isolated muscles, promoted by the cAMP phosphodiesterase inhibitor isobutylmethylxanthine was accompanied by decreased activity of the UPS, levels of ubiquitin-protein conjugates, and expression of atrogin-1, a key ubiquitin-protein ligase involved in muscle atrophy. In cultured myotubes, atrogin-1 induction after dexamethasone treatment was completely prevented by isobutylmethylxanthine. Furthermore, administration of clenbuterol, a selective β2-agonist, to mice increased muscle cAMP levels and suppressed the fasting-induced expression of atrogin-1 and MuRF-1, atrogin-1 mRNA being much more responsive to clenbuterol. Moreover, clenbuterol increased the phosphorylation of muscle Akt and Foxo3a in fasted rats. Similar responses were observed in muscles exposed to dibutyryl-cAMP. The stimulatory effect of clenbuterol on cAMP and Akt was abolished in muscles from β2-AR knockout mice. The suppressive effect of β2-agonist on atrogin-1 was not mediated by PGC-1α (peroxisome proliferator-activated receptor-γ coactivator 1α known to be induced by β2-agonists and previously shown to inhibit atrogin-1 expression), because food-deprived PGC-1α knockout mice were still sensitive to clenbuterol. These findings suggest that the cAMP increase induced by stimulation of β2-AR in skeletal muscles from fasted mice is possibly the mechanism by which catecholamines suppress atrogin-1 and the UPS, this effect being mediated via phosphorylation of Akt and thus inactivation of Foxo3. The cAMP increase induced by stimulation of β2-adrenoceptors is possibly the mechanism by which clenbuterol, via Akt/Foxo3 signaling, attenuate the fasting-induced muscle atrophy.