Myosin Heavy Chain Plasticity in Aging Skeletal Muscle with Aerobic Exercise Training

Abstract

PURPOSE: To comprehensively assess myosin heavy chain (MHC) plasticity in aging skeletal muscle in response to aerobic exercise training. METHODS: Muscle biopsy samples were obtained from the vastus lateralis of eight older women (70±2y) before and after 12-wks of cycle ergometer training. MHC composition was measured at the mRNA level via qPCR and at the protein level in muscle homogenates and individual myofibers using SDS-PAGE. RESULTS: At the mRNA level, aerobic training reduced (p<0.05) MHC IIx and tended to elevate (p=0.10) MHC I mRNA expression. The homogenate proportion of MHC I protein increased (54±4 to 61±2%, p<0.05) and MHC IIx protein decreased (8±1 to 4±1%, p<0.05) after training while the MHC IIa proportion was unaltered. Single myofiber analysis demonstrated a robust elevation (42±4 to 52±3%, p<0.05) in the percentage of MHC I fibers with a reciprocal decrease (48±3 to 38±4% p<0.05) in the percentage of MHC IIa fibers after training. CONCLUSION: These results document a reduction in the relative amount of fast MHC isoforms (MHC IIa or IIx) with a concomitant increase in slow MHC I isoforms independent of the method employed. The shift to an oxidative myosin heavy chain phenotype indicates that aerobic exercise training augments skeletal muscle health of older women and may serve as a countermeasure to age-related skeletal muscle atrophy. Supported by NIH AG032127