title: Key Markers of mTORC1-Dependent and mTORC1-Independent Signaling Pathways Regulating Protein Synthesis in Rat Soleus Muscle During Early Stages of Hindlimb Unloading.
abstract: OBJECTIVE
  The purpose of the study was to assess the amount of rRNA and phosphorylation status of the key markers of mTORC1-dependent (70s6k, 4E-BP1) and mTORC1-independent (GSK-3β, AMPK) signaling pathways controlling protein synthesis in rat soleus during early stages of mechanical unloading (hindlimb suspension (HS) for 1-, 3- and 7 days).
  
  
  METHODS
  The content of the key signaling molecules of various anabolic signaling pathways was determined by Western-blotting. The amount of 28S rRNA was evaluated by RT-PCR. The rate of protein synthesis was assessed using in-vivo SUnSET technique.
  
  
  RESULTS
  HS for 3 and 7 days induced a significant (p<0.05) decrease in the rate of global protein synthesis in soleus muscle in comparison with control. HS within 24 hours resulted in a significant (p<0.05) decrease in p-4E-BP1 content, p-AMPK content and increase in p-p70s6k content in rat soleus muscle. Following three days of HS the content of p-AKT was decreased (p<0.05). After 7 days of HS the phosphorylation level of AKT and GSK-3beta was significantly reduced (p<0.05) compared to control. We also observed a significant decrease in the amount of 28S rRNA in rat soleus following 1, 3 and 7 days of HS.
  
  
  CONCLUSIONS
  Taken together, the results of our study suggest that a decline in the global rate of protein synthesis in rat soleus during early stages of simulated microgravity is associated with impaired ribosome biogenesis as well as reduced activity of mTORC1-independent signaling pathways.
authors.affiliation: Myology Laboratory, Institute of Bio-medical Problems RAS, Moscow, Russian Federation.
authors.forename: Timur
authors.initials: T
authors.lastname: Mirzoev
authors.forename: Sergey
authors.initials: S
authors.lastname: Tyganov
authors.forename: Natalia
authors.initials: N
authors.lastname: Vilchinskaya
authors.forename: Yulia
authors.initials: Y
authors.lastname: Lomonosova
authors.forename: Boris
authors.initials: B
authors.lastname: Shenkman
mesh_terms: D055372:AMP-Activated Protein Kinases / Q000235:genetics / Q000378:metabolism; D000818:Animals; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism; D005786:Gene Expression Regulation; D000071679:Glycogen Synthase Kinase 3 beta / Q000235:genetics / Q000378:metabolism; D019417:Hindlimb Suspension; D047908:Intracellular Signaling Peptides and Proteins; D008297:Male; D000076222:Mechanistic Target of Rapamycin Complex 1; D046912:Multiprotein Complexes / Q000235:genetics* / Q000378:metabolism; D018482:Muscle, Skeletal / Q000378:metabolism*; D010750:Phosphoproteins / Q000235:genetics / Q000378:metabolism; D010766:Phosphorylation; D051057:Proto-Oncogene Proteins c-akt / Q000235:genetics / Q000378:metabolism; D012339:RNA, Ribosomal, 28S / Q000235:genetics* / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D038762:Ribosomal Protein S6 Kinases, 70-kDa / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction / Q000235:genetics*; D058570:TOR Serine-Threonine Kinases / Q000235:genetics* / Q000378:metabolism; D013997:Time Factors
chemical_list: D002352:Carrier Proteins; C499526:Eif4ebp1 protein, rat; D047908:Intracellular Signaling Peptides and Proteins; D046912:Multiprotein Complexes; D010750:Phosphoproteins; D012339:RNA, Ribosomal, 28S; D000071679:Glycogen Synthase Kinase 3 beta; D000076222:Mechanistic Target of Rapamycin Complex 1; D051057:Proto-Oncogene Proteins c-akt; D038762:Ribosomal Protein S6 Kinases, 70-kDa; D058570:TOR Serine-Threonine Kinases; D055372:AMP-Activated Protein Kinases