cAMP REDUCES THE ATROPHY-RELATED UBIQUITIN LIGASE ATROGIN-1 IN SKELETAL MUSCLES FROM NORMAL RATS.

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Lira, EC (1); Gonçalves, DAP (1); Zanon, NM (1); Baviera, AM (1); Bedard, N (2); Wing, S S (2); Kettelhut, ÍC (1); Navegantes, LCC(1).

(1)Departments of Physiology, Biochemistry and Immunology, School of Medicine of Ribeirão Preto, University of São Paulo, Brazil.

 Aim:This study was undertaken to investigate the role of beta-2 adrenoceptors and cAMP in regulating the Ubiquitin-proteasome system (UPS)  in skeletal muscles from normal rats.Methods and results:The activity of UPS and the Akt/FoxO signaling pathway were measured in skeletal muscle from rats treated with clenbuterol (3 mg/kg wt; sc), a selective beta-2 adrenergic agonist, for 3 days. In extensor digital longus (EDL) muscle, clenbuterol increased by 30% muscle weight, reduced by 45% the UPS activity and increased by 30% the phosphorylation of Akt and FoxO3. The addition of isobutylmethylxanthine (IBMX; 10^-3M), a cAMP phosphodiesterase inhibitor, to the incubation medium increased cAMP levels (4-fold) and decreased by 50% the UPS activity in isolated soleus and EDL muscles from normal rats. IBMX in vitro also reduced the levels of ubiquitin-protein conjugated and the mRNA levels of the atrogin-1/MAFbx (50%) and the E₂-14KDa ubiquitin conjugating enzyme (30%) transcripts in muscles from normal rats. Ubiquitin and MuRF1 mRNA were not altered by IBMX in vitro. Conclusions: These data suggest that stimulation of beta-2 adrenoceptors, through the activation of cAMP and Akt signaling pathways, inhibit ubiquitin-proteasome proteolysis by increasing FoxO3 phosphorylation and suppressing atrogin-1 mRNA expression in skeletal muscle from normal rats.Financial support: CNPq, FAPESP.