Alcohol-induced IGF-I resistance is ameliorated in mice deficient for mitochondrial branched-chain aminotransferase.
Acute alcohol intoxication decreases skeletal muscle protein synthesis by impairing mammalian target of rapamycin (mTOR). In 2 studies, we determined whether inhibition of branched-chain amino acid (BCAA) catabolism ameliorates the inhibitory effect of alcohol on muscle protein synthesis by raising the plasma BCAA concentrations and/or by improving the anabolic response to insulin-like growth factor (IGF)-I. In the first study, 4 groups of mice were used: wild-type (WT) and mitochondrial branched-chain aminotransferase (BCATm) knockout (KO) mice orally administered saline or alcohol (5 g/kg, 1 h). Protein synthesis was greater in KO mice compared with WT controls and was associated with greater phosphorylation of eukaryotic initiation factor (eIF)-4E binding protein-1 (4EBP1), eIF4E-eIF4G binding, and 4EBP1-regulatory associated protein of mTOR (raptor) binding, but not mTOR-raptor binding. Alcohol decreased protein synthesis in WT mice, a change associated with less 4EBP1 phosphorylation, eIF4E-eIF4G binding, and raptor-4EBP1 binding, but greater mTOR-raptor complex formation. Comparable alcohol effects on protein synthesis and signal transduction were detected in BCATm KO mice. The second study used the same 4 groups, but all mice were injected with IGF-I (25 microg/mouse, 30 min). Alcohol impaired the ability of IGF-I to increase muscle protein synthesis, 4EBP1 and 70-kilodalton ribosomal protein S6 kinase-1 phosphorylation, eIF4E-eIF4G binding, and 4EBP1-raptor binding in WT mice. However, in alcohol-treated BCATm KO mice, this IGF-I resistance was not manifested. These data suggest that whereas the sustained elevation in plasma BCAA is not sufficient to ameliorate the catabolic effect of acute alcohol intoxication on muscle protein synthesis, it does improve the anabolic effect of IGF-I.
Lang
Charles H
CH
Department of Cellular and Molecular Physiology, Pennsylvania State University College of Medicine, Hershey, PA 17033, USA. clang@psu.edu
Lynch
Christopher J
CJ
Vary
Thomas C
TC
D000435:Alcoholic Intoxication / Q000235:genetics / Q000378:metabolism*; D000597:Amino Acids, Branched-Chain / Q000097:blood / Q000378:metabolism*; D000818:Animals; D000431:Ethanol; D039561:Eukaryotic Initiation Factor-4E / Q000378:metabolism; D039562:Eukaryotic Initiation Factor-4F / Q000378:metabolism*; D039603:Eukaryotic Initiation Factor-4G / Q000378:metabolism; D007334:Insulin-Like Growth Factor I / Q000378:metabolism*; D047908:Intracellular Signaling Peptides and Proteins / Q000378:metabolism*; D051379:Mice; D018345:Mice, Knockout; D008928:Mitochondria / Q000201:enzymology; D009124:Muscle Proteins / Q000096:biosynthesis*; D018482:Muscle, Skeletal / Q000378:metabolism; D009154:Mutation; D010766:Phosphorylation; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*; D038762:Ribosomal Protein S6 Kinases, 70-kDa / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects; D058570:TOR Serine-Threonine Kinases; D000637:Transaminases / Q000172:deficiency* / Q000235:genetics / Q000378:metabolism
D000597:Amino Acids, Branched-Chain; D039561:Eukaryotic Initiation Factor-4E; D039562:Eukaryotic Initiation Factor-4F; D039603:Eukaryotic Initiation Factor-4G; D047908:Intracellular Signaling Peptides and Proteins; D009124:Muscle Proteins; D000431:Ethanol; D007334:Insulin-Like Growth Factor I; D000637:Transaminases; C546843:mTOR protein, mouse; D017346:Protein Serine-Threonine Kinases; D038762:Ribosomal Protein S6 Kinases, 70-kDa; D058570:TOR Serine-Threonine Kinases