title: Age-associated decrease in contraction-induced activation of downstream targets of Akt/mTor signaling in skeletal muscle.
abstract: In this study, we investigated the effect of age on the association of eukaryotic initiation factor 4E (eIF4E) with eukaryotic initiation factor 4G (eIF4G), as well as the activity of its binding protein (4E-BP1) and the activity of glycogen synthase kinase-3 (GSK-3) after a single bout of rat hindlimb muscle contractile activity elicited by high-frequency electrical stimulation (HFES) of the sciatic nerve. Tibialis anterior (TA) and plantaris (Pla) muscles from adult (Y; 6 mo old) and aged (O; 30 mo old) Fischer 344 x Brown Norway rats were collected immediately or 6 h after HFES. eIF4E-eIF4G association was elevated at 6 h of recovery in TA (1.9 +/- 0.2-fold, P < 0.05) and immediately and 6 h after exercise in Pla (2.1 +/- 0.3- and 2.1 +/- 0.7-fold, P < 0.05) in Y rats. No significant increase was observed in O rats. An increase in 4E-BP1 phosphorylation was observed only 6 h after HFES in TA (5.0 +/- 2.0-fold, P < 0.05) in Y rats. Phosphorylation of GSK-3alpha was increased immediately and 6 h after contraction in TA (1.6 +/- 0.3- and 4.1 +/- 0.8-fold, P < 0.05) and Pla (1.7 +/- 0.2- and 2.1 +/- 0.4-fold, P < 0.05) in Y rats and remained unaffected in O rats. Phosphorylation of GSK-3beta was observed only immediately after HFES in TA (1.5 +/- 0.2-fold, P < 0.05) in Y rats. Overall, eIF4E-eIF4G association and phosphorylation of 4E-BP1 and GSK-3 are increased after HFES in adult, but not in aged, animals. These observations suggest that the anabolic response to muscle stimulation is attenuated with aging and may contribute to the limited capacity of hypertrophy in aged animals.
authors.affiliation: Nutrition, Exercise Physiology, and Sarcopenia Laboratory, Jean Mayer USDA Human Nutrition Research Center on Aging, Tufts University, 711 Washington St., Boston, MA 02111, USA.
authors.forename: Katsuhiko
authors.initials: K
authors.lastname: Funai
authors.forename: Jascha D
authors.initials: JD
authors.lastname: Parkington
authors.forename: Silvia
authors.initials: S
authors.lastname: Carambula
authors.forename: Roger A
authors.initials: RA
authors.lastname: Fielding
mesh_terms: D000375:Aging; D000818:Animals; D002352:Carrier Proteins / Q000378:metabolism; D039561:Eukaryotic Initiation Factor-4E / Q000378:metabolism; D039603:Eukaryotic Initiation Factor-4G / Q000378:metabolism; D038362:Glycogen Synthase Kinase 3 / Q000378:metabolism; D000071679:Glycogen Synthase Kinase 3 beta; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins; D008297:Male; D009119:Muscle Contraction / Q000502:physiology*; D018482:Muscle, Skeletal / Q000033:anatomy & histology / Q000502:physiology*; D009929:Organ Size; D010750:Phosphoproteins / Q000378:metabolism; D010766:Phosphorylation; D011494:Protein Kinases / Q000378:metabolism; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism*; D051381:Rats; D011916:Rats, Inbred F344; D015398:Signal Transduction; D058570:TOR Serine-Threonine Kinases
chemical_list: D002352:Carrier Proteins; C499526:Eif4ebp1 protein, rat; D039561:Eukaryotic Initiation Factor-4E; D039603:Eukaryotic Initiation Factor-4G; D047908:Intracellular Signaling Peptides and Proteins; D010750:Phosphoproteins; D011494:Protein Kinases; C546842:MTOR protein, human; C546845:mTOR protein, rat; C000605506:GSK3B protein, human; D000071679:Glycogen Synthase Kinase 3 beta; C000605508:Gsk3b protein, rat; D051057:Proto-Oncogene Proteins c-akt; D058570:TOR Serine-Threonine Kinases; D038362:Glycogen Synthase Kinase 3; C448021:glycogen synthase kinase 3 alpha