title: Clenbuterol suppresses proteasomal and lysosomal proteolysis and atrophy-related genes in denervated rat soleus muscles independently of Akt.
abstract: Although it is well known that administration of the selective β(2)-adrenergic agonist clenbuterol (CB) protects muscle following denervation (DEN), the underlying molecular mechanism remains unclear. We report that in vivo treatment with CB (3 mg/kg sc) for 3 days induces antiproteolytic effects in normal and denervated rat soleus muscle via distinct mechanisms. In normal soleus muscle, CB treatment stimulates protein synthesis, inhibits Ca(2+)-dependent proteolysis, and increases the levels of calpastatin protein. On the other hand, the administration of CB to DEN rats ameliorates the loss of muscle mass, enhances the rate of protein synthesis, attenuates hyperactivation of proteasomal and lysosomal proteolysis, and suppresses the transcription of the lysosomal protease cathepsin L and of atrogin-1/MAFbx and MuRF1, two ubiquitin (Ub) ligases involved in muscle atrophy. These effects were not associated with alterations in either IGF-I content or Akt phosphorylation levels. In isolated muscles, CB (10(-6) M) treatment significantly attenuated DEN-induced overall proteolysis and upregulation in the mRNA levels of the Ub ligases. Similar responses were observed in denervated muscles exposed to 6-BNZ-cAMP (500 μM), a PKA activator. The in vitro addition of triciribine (10 μM), a selective Akt inhibitor, did not block the inhibitory effects of CB on proteolysis and Ub ligase mRNA levels. These data indicate that short-term treatment with CB mitigates DEN-induced atrophy of the soleus muscle through the stimulation of protein synthesis, downregulation of cathepsin L and Ub ligases, and consequent inhibition of lysosomal and proteasomal activities and that these effects are independent of Akt and possibly mediated by the cAMP/PKA signaling pathway.
authors.affiliation: Dept. of Physiology, School of Medicine, Ribeirão Preto University of São Paulo, Ribeirão Preto, SP, Brazil.
authors.forename: Dawit A P
authors.initials: DA
authors.lastname: Gonçalves
authors.forename: Wilian A
authors.initials: WA
authors.lastname: Silveira
authors.forename: Eduardo C
authors.initials: EC
authors.lastname: Lira
authors.forename: Flávia A
authors.initials: FA
authors.lastname: Graça
authors.forename: Silvia
authors.initials: S
authors.lastname: Paula-Gomes
authors.forename: Neusa M
authors.initials: NM
authors.lastname: Zanon
authors.forename: Isis C
authors.initials: IC
authors.lastname: Kettelhut
authors.forename: Luiz C C
authors.initials: LC
authors.lastname: Navegantes
mesh_terms: D000318:Adrenergic beta-Agonists / Q000494:pharmacology / Q000627:therapeutic use*; D000818:Animals; D056668:Cathepsin L / Q000378:metabolism; D002976:Clenbuterol / Q000494:pharmacology / Q000627:therapeutic use*; D017868:Cyclic AMP-Dependent Protein Kinases / Q000737:chemistry; D020536:Enzyme Activators / Q000494:pharmacology; D015971:Gene Expression Regulation, Enzymologic / Q000187:drug effects; D066298:In Vitro Techniques; D008247:Lysosomes / Q000187:drug effects* / Q000201:enzymology; D008297:Male; D009121:Muscle Denervation / Q000009:adverse effects; D009124:Muscle Proteins / Q000235:genetics / Q000378:metabolism; D018482:Muscle, Skeletal / Q000187:drug effects* / Q000294:innervation / Q000378:metabolism / Q000473:pathology; D009133:Muscular Atrophy / Q000201:enzymology / Q000378:metabolism / Q000517:prevention & control; D011480:Protease Inhibitors / Q000494:pharmacology*; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism; D061988:Proteasome Inhibitors; D014176:Protein Biosynthesis / Q000187:drug effects; D059748:Proteolysis / Q000187:drug effects; D051057:Proto-Oncogene Proteins c-akt / Q000037:antagonists & inhibitors / Q000378:metabolism; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D044843:SKP Cullin F-Box Protein Ligases / Q000235:genetics / Q000378:metabolism; D000070584:Tripartite Motif Proteins; D044767:Ubiquitin-Protein Ligases / Q000235:genetics / Q000378:metabolism
chemical_list: D000318:Adrenergic beta-Agonists; D020536:Enzyme Activators; D009124:Muscle Proteins; D011480:Protease Inhibitors; D061988:Proteasome Inhibitors; D012333:RNA, Messenger; D000070584:Tripartite Motif Proteins; C486692:Fbxo32 protein, rat; D044843:SKP Cullin F-Box Protein Ligases; C499086:Trim63 protein, rat; D044767:Ubiquitin-Protein Ligases; D051057:Proto-Oncogene Proteins c-akt; D017868:Cyclic AMP-Dependent Protein Kinases; D056668:Cathepsin L; C534280:Ctsl protein, rat; D046988:Proteasome Endopeptidase Complex; D002976:Clenbuterol