Potential regulation of human muscle plasticity by MLC2 post-translational modifications during bed rest and countermeasures

This study investigated the effects of a 60-day bed rest with or without countermeasures on muscular phenotype and post-translational modifications of the regulatory Myosin Light Chain 2 (MLC2) protein. Soleus biopsies were obtained from female subjects before and after bed rest. Control subjects were assigned only to bed rest (BR), BR + Ex subjects were submitted to combined aerobic and resistive exercises, and BR + Nut to nutritional leucine and valine diet. We determined Myosin Heavy Chains (MHC) and MLC2 composition of muscles using 1D SDS–PAGE. MLC2 phosphorylation was measured on 2D gels and O-N-Acetyl Glucosaminylation (O-GlcNAc) level of MLC2 was determined. Our results showed a slow-to-fast shift of MHC and MLC2 isoforms in BR and BR + Nut while BR + Ex combinations prevented these phenotype changes. After BR, the MLC2 phosphorylation state was increased while the global MLC2 glycosylation level was decreased. Exercises prevented the variations of phosphorylation and glycosylation observed after BR whereas nutrition had no effects. These results suggested an interplay between phosphorylation and glycosylation of MLC2, which might be involved in the development of muscle atrophy and associated changes. These findings of differential responses to exercises and nutrition protocols were discussed with implications for future prescription models to preserve muscle against long-term unloading.