Differential effect of sepsis on ability of leucine and IGF-I to stimulate muscle translation initiation.
Polymicrobial sepsis impairs skeletal muscle protein synthesis, which results from impairment in translation initiation under basal conditions. The purpose of the present study was to test the hypothesis that sepsis also impairs the anabolic response to amino acids, specifically leucine (Leu). Sepsis was induced by cecal ligation and puncture, and 24 h later, Leu or saline (Sal) was orally administered to septic and time-matched nonseptic rats. The gastrocnemius was removed 20 min later for assessment of protein synthesis and signaling components important in peptide-chain initiation. Oral Leu increased muscle protein synthesis in nonseptic rats. Leu was unable to increase protein synthesis in muscle from septic rats, and synthetic rates remained below those observed in nonseptic + Sal rats. In nonseptic + Leu rats, phosphorylation of eukaryotic initiation factor (eIF)4E-binding protein 1 (4E-BP1) in muscle was markedly increased compared with values from time-matched Sal-treated nonseptic rats. This change was associated with redistribution of eIF4E from the inactive eIF4E.4E-BP1 to the active eIF4E.eIF4G complex. In septic rats, Leu-induced phosphorylation of 4E-BP1 and changes in eIF4E distribution were completely abrogated. Sepsis also antagonized the Leu-induced increase in phosphorylation of S6 kinase 1 and ribosomal protein S6. Sepsis attenuated Leu-induced phosphorylation of mammalian target of rapamycin and eIF4G. The ability of sepsis to inhibit anabolic effects of Leu could not be attributed to differences in plasma concentrations of insulin, insulin-like growth factor I, or Leu between groups. In contrast, the ability of exogenous insulin-like growth factor I to stimulate the same signaling components pertaining to translation initiation was not impaired by sepsis. Hence, sepsis produces a relatively specific Leu resistance in skeletal muscle that impairs the ability of this amino acid to stimulate translation initiation and protein synthesis.
Lang
Charles H
CH
Department of Cellular and Molecular Physiology, H166, Pennsylvania State University College of Medicine, 500 University Dr., Hershey 17033, USA. clang@psu.edu
Frost
Robert A
RA
D000818:Animals; D015153:Blotting, Western; D002352:Carrier Proteins; D007328:Insulin / Q000097:blood; D007334:Insulin-Like Growth Factor I / Q000378:metabolism / Q000494:pharmacology*; D047908:Intracellular Signaling Peptides and Proteins; D007930:Leucine / Q000097:blood / Q000494:pharmacology*; D008297:Male; D009124:Muscle Proteins / Q000096:biosynthesis; D018482:Muscle, Skeletal / Q000187:drug effects / Q000378:metabolism*; D010442:Peptide Chain Initiation, Translational / Q000187:drug effects; D010750:Phosphoproteins; D010766:Phosphorylation; D011233:Precipitin Tests; D014176:Protein Biosynthesis / Q000187:drug effects*; D011494:Protein Kinases / Q000378:metabolism; D012333:RNA, Messenger / Q000096:biosynthesis; D051381:Rats; D017207:Rats, Sprague-Dawley; D038762:Ribosomal Protein S6 Kinases, 70-kDa / Q000378:metabolism; D018805:Sepsis / Q000503:physiopathology*; D015398:Signal Transduction / Q000187:drug effects; D013268:Stimulation, Chemical; D058570:TOR Serine-Threonine Kinases
D002352:Carrier Proteins; C499526:Eif4ebp1 protein, rat; D007328:Insulin; D047908:Intracellular Signaling Peptides and Proteins; D009124:Muscle Proteins; D010750:Phosphoproteins; D012333:RNA, Messenger; D007334:Insulin-Like Growth Factor I; D011494:Protein Kinases; C546845:mTOR protein, rat; D038762:Ribosomal Protein S6 Kinases, 70-kDa; D058570:TOR Serine-Threonine Kinases; C448959:ribosomal protein S6 kinase, 70kD, polypeptide 2; D007930:Leucine