title: Disassociation between the effects of amino acids and insulin on signaling, ubiquitin ligases, and protein turnover in human muscle.
abstract: We determined the effects of intravenous infusion of amino acids (AA) at serum insulin of 5, 30, 72, and 167 mU/l on anabolic signaling, expression of ubiquitin-proteasome components, and protein turnover in muscles of healthy young men. Tripling AA availability at 5 mU/l insulin doubled incorporation of [1-(13)C]leucine [i.e., muscle protein synthesis (MPS), P < 0.01] without affecting the rate of leg protein breakdown (LPB; appearance of d(5)-phenylalanine). While keeping AA availability constant, increasing insulin to 30 mU/l halved LPB (P < 0.05) without further inhibition at higher doses, whereas rates of MPS were identical to that at 5 mU/l insulin. The phosphorylation of PKB Ser(473) and p70(S6k) Thr(389) increased concomitantly with insulin, but whereas raising insulin to 30 mU/l increased the phosphorylation of mTOR Ser(2448), 4E-BP1 Thr(37/46), or GSK3beta Ser(9) and decreased that of eEF2 Thr(56), higher insulin doses to 72 and 167 mU/l did not augment these latter responses. MAFbx and proteasome C2 subunit proteins declined as insulin increased, with MuRF-1 expression largely unchanged. Thus increasing AA and insulin availability causes changes in anabolic signaling and amounts of enzymes of the ubiquitin-proteasome pathway, which cannot be easily reconciled with observed effects on MPS or LPB.
authors.affiliation: Centre for Integrated Systems Biology and Medicine, Univ. of Nottingham, Queen's Medical Centre, Nottingham NG7 2UH, UK. paul.greenhaff@nottingham.ac.uk
authors.forename: P L
authors.initials: PL
authors.lastname: Greenhaff
authors.forename: L G
authors.initials: LG
authors.lastname: Karagounis
authors.forename: N
authors.initials: N
authors.lastname: Peirce
authors.forename: E J
authors.initials: EJ
authors.lastname: Simpson
authors.forename: M
authors.initials: M
authors.lastname: Hazell
authors.forename: R
authors.initials: R
authors.lastname: Layfield
authors.forename: H
authors.initials: H
authors.lastname: Wackerhage
authors.forename: K
authors.initials: K
authors.lastname: Smith
authors.forename: P
authors.initials: P
authors.lastname: Atherton
authors.forename: A
authors.initials: A
authors.lastname: Selby
authors.forename: M J
authors.initials: MJ
authors.lastname: Rennie
mesh_terms: D000328:Adult; D000596:Amino Acids / Q000494:pharmacology*; D001786:Blood Glucose / Q000378:metabolism; D015153:Blotting, Western; D004305:Dose-Response Relationship, Drug; D015870:Gene Expression / Q000187:drug effects; D006801:Humans; D007004:Hypoglycemic Agents / Q000494:pharmacology*; D007328:Insulin / Q000097:blood / Q000494:pharmacology*; D008297:Male; D009124:Muscle Proteins / Q000378:metabolism*; D018482:Muscle, Skeletal / Q000187:drug effects* / Q000378:metabolism*; D010766:Phosphorylation; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism; D011494:Protein Kinases / Q000378:metabolism; D012313:RNA / Q000096:biosynthesis; D012333:RNA, Messenger / Q000096:biosynthesis / Q000235:genetics; D012039:Regional Blood Flow / Q000502:physiology; D020133:Reverse Transcriptase Polymerase Chain Reaction; D038762:Ribosomal Protein S6 Kinases, 70-kDa / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects*; D058570:TOR Serine-Threonine Kinases; D043743:Ubiquitin-Protein Ligase Complexes / Q000378:metabolism*
chemical_list: D000596:Amino Acids; D001786:Blood Glucose; D007004:Hypoglycemic Agents; D007328:Insulin; D009124:Muscle Proteins; D012333:RNA, Messenger; D012313:RNA; D043743:Ubiquitin-Protein Ligase Complexes; D011494:Protein Kinases; C546842:MTOR protein, human; D038762:Ribosomal Protein S6 Kinases, 70-kDa; D058570:TOR Serine-Threonine Kinases; D046988:Proteasome Endopeptidase Complex