title: Resting and load-induced levels of myogenic gene transcripts differ between older adults with demonstrable sarcopenia and young men and women.
abstract: Regenerative capacity appears to be impaired in sarcopenic muscle. As local growth factors and myogenic regulatory factors (MRFs) modulate repair/regeneration responses after overload, we hypothesized that resistance loading (RL)-induced expression of MRFs and muscle IGF-I-related genes would be blunted in older (O) males (M) and females (F) with demonstrable sarcopenia vs. young (Y) adults. Y (20-35 yr, 10 YF, 10 YM) and O (60-75 yr, 9 OF, 9 OM) underwent vastus lateralis biopsy before and 24 h after knee extensor RL. Sarcopenia was assessed by cross-sectional area of type I, IIa, and IIx myofibers. Transcript levels were assessed by relative RT-PCR and analyzed by age x gender x load repeated-measures ANOVA. O were sarcopenic based on type II atrophy with smaller type IIa (P < 0.05) and IIx (P < 0.001) myofibers. Within-gender cross-sectional area differences were more marked in F (OF < YF: IIa 21%, IIx 42%). Load effects (P < 0.05) were seen for four of seven mRNAs as IGF-IEa (34%), myogenin (53%), and MyoD (20%) increased, and myf-6 declined 10%. Increased IGF-IEa was driven by O (48%) and/or M (43%). An age x gender x load interaction was found for MyoD (P < 0.05). An age x load interaction for type 1 IGF receptor (P < 0.05) was driven by a small increase in O (16%, P < 0.05). A gender x load interaction (P < 0.05) was noted for IGF binding protein-4. Age effects (P < 0.05) resulted from higher MyoD (54%), myf-5 (21%), and IGF binding protein-4 (17%) in O and were primarily localized to F at baseline (OF > YF; MyoD 94%, myf-5 47%, P < 0.05). We conclude that RL acutely increases mRNA expression of IGF-IEa and myogenin, which may promote growth/regeneration in both Y and O. Higher resting levels of MRFs in OF vs. YF suggest elevated basal regenerative activity in sarcopenic muscle of OF.
authors.affiliation: Dept. of Physiology, Univeristy of Alabama, Birmingham, AL, USA.
authors.forename: Jeong-su
authors.initials: JS
authors.lastname: Kim
authors.forename: David J
authors.initials: DJ
authors.lastname: Kosek
authors.forename: John K
authors.initials: JK
authors.lastname: Petrella
authors.forename: James M
authors.initials: JM
authors.lastname: Cross
authors.forename: Marcas M
authors.initials: MM
authors.lastname: Bamman
mesh_terms: D000328:Adult; D000367:Age Factors; D000368:Aged; D000375:Aging; D005260:Female; D005786:Gene Expression Regulation; D006133:Growth Substances / Q000378:metabolism; D006801:Humans; D008297:Male; D008875:Middle Aged; D009124:Muscle Proteins / Q000378:metabolism*; D018482:Muscle, Skeletal / Q000503:physiopathology*; D009133:Muscular Atrophy / Q000503:physiopathology*; D018006:Myogenic Regulatory Factors / Q000378:metabolism; D005082:Physical Exertion; D012146:Rest; D012737:Sex Factors
chemical_list: D006133:Growth Substances; D009124:Muscle Proteins; D018006:Myogenic Regulatory Factors