title: Age-related differences in the des IGF-I-mediated activation of Akt-1 and p70 S6K in mouse skeletal muscle.
abstract: The ability of des IGF-I to activate Akt-1 and p70 S6K in skeletal muscle with or without acute endurance exercise was examined in young and old mice. Mice were sacrificed 12 h after a moderate intensity treadmill run following an interperitoneal injection of des-IGF-I or saline. Blood and skeletal muscle were collected and IGF-I receptor, Akt-1 and p70 S6K protein contents and their phosphorylation status were determined. Injection of des IGF-I similarly decreased plasma glucose concentration in both young (P<0.01) and old mice (P<0.01) whereas plasma insulin and total IGF-I levels of young and old mice were not significantly changed by des IGF-I. Total IGF-I receptor protein and IGF-1 receptor phosphorylation were lower in aged mice (P<0.05). Basal phosphorylation of Akt-1 was lower in aged skeletal muscle (P<0.01) and this was not caused by changes in Akt-1 protein. In both young (P<0.01) and aged (P<0.05) mice, des IGF-I significantly increased the phosphorylation of Akt-1 at Ser 473. However, a des IGF-I-mediated increase in the p70 S6K phosphorylation (P<0.01) was only seen in young mice. Prior exercise decreased the total plasma IGF-I level in the presence of des IGF-I in aged mice. Des IGF-I-mediated Akt-1 and p70 S6K phosphorylation was not changed by exercise in either young or old mice. It is concluded that there was an aging-related resistance at the p70 S6K level in mouse skeletal muscle that could not be restored by prior exercise and this resistance is associated with lower IGF-I receptor number and Akt-1 phosphorylation in the aged skeletal muscle.
authors.affiliation: Metabolic Biochemistry Lab, School of Kinesiology, Simon Fraser University, Burnaby, BC, Canada V5A 1S6.
authors.forename: Minghua
authors.initials: M
authors.lastname: Li
authors.forename: Chunmei
authors.initials: C
authors.lastname: Li
authors.forename: Wade S
authors.initials: WS
authors.lastname: Parkhouse
mesh_terms: D000375:Aging / Q000378:metabolism*; D000818:Animals; D001786:Blood Glucose / Q000378:metabolism; D005260:Female; D007334:Insulin-Like Growth Factor I / Q000378:metabolism*; D051379:Mice; D008810:Mice, Inbred C57BL; D018482:Muscle, Skeletal / Q000378:metabolism*; D010766:Phosphorylation; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*; D011518:Proto-Oncogene Proteins; D051057:Proto-Oncogene Proteins c-akt; D017526:Receptor, IGF Type 1 / Q000378:metabolism; D038762:Ribosomal Protein S6 Kinases, 70-kDa / Q000378:metabolism*
chemical_list: D001786:Blood Glucose; D011518:Proto-Oncogene Proteins; D007334:Insulin-Like Growth Factor I; D017526:Receptor, IGF Type 1; D017346:Protein Serine-Threonine Kinases; D051057:Proto-Oncogene Proteins c-akt; D038762:Ribosomal Protein S6 Kinases, 70-kDa