Resting and load-induced levels of myogenic gene transcripts differ between older adults with demonstrable sarcopenia and young men and women

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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 × gender × 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 × gender × load interaction was found for MyoD (P < 0.05). An age × load interaction for type 1 IGF receptor (P < 0.05) was driven by a small increase in O (16%, P < 0.05). A gender × 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.