Neuromuscular Electrical Stimulation Induces Skeletal Muscle Fiber Remodeling and Specific Gene Expression Profile in Healthy Elderly

Skeletal muscle ageing is strictly related to progressive weakness as results of fiber phenotype modification and their loss. The physiological muscle recruitment to contraction, basically prosecuted under volitional control, can also be engaged by means of neuromuscular electrical stimulation (NMES). Knowing that NMES is effective in improving muscle strength in active healthy elderly, we aimed to investigate which physiological modifications it was able to produce in Vastus lateralis muscle and which pathways were involved. We found that NMES increased the cross sectional area and the isometric strength of type II myofibers in accordance with activated myogenic pathway for shifting glycolytic towards oxidative phenotype of type II fibers, at molecular level and with increase of maximal voluntary contraction at functional level. Using TaqMan low density array on 48 different genes, we found NMES specific gene regulation that highlighted: i- increased protein synthesis with respect to protein degradation; ii- activation of apoptotic pathway involved in the differentiation process; iii- increased regeneration signals; iv- oxidative enzyme regulation. We validated these pathways using confirmatory RT-PCR for genes involved in regeneration process and Myosin isoforms and we investigated the oxidative stress status analyzing superoxide anion levels, the protein expression of two different superoxide dismutase and the activity of both catalase and superoxide anion dismutase, two main antioxidant enzymes. In conclusion, our data demonstrated that NMES is effective on producing physiological adaptation on Vastus Lateralis of active healthy elderly and provided new insights for further researches on elderly who experienced muscle detriment for periodic or permanent immobility.