Quantitative magnetic resonance characterization of the effect of physical training on skeletal muscle of the Ts65Dn mice, a model of Down syndrome

Down syndrome (DS) is characterized by muscle hypotonia and low muscle strength associated with motor dysfunction. Elucidation of the determinants of muscle weakness in DS would be relevant for therapeutic approaches aimed at treating/mitigating a physical disability with a strong impact on the quality of life in persons with DS. The Ts65Dn mice is a recognized mouse model of DS, with trisomic mice presenting gross motor and muscle phenotypes. The aim of this work was to assess the effect of physical exercise, a well-known tool to improve skeletal muscle condition, in the hindlimbs of trisomic and euploid male mice using quantitative magnetic resonance imaging (MRI). Magnetic resonance spectroscopy (MRS) metabolomics and histological fiber typing were used to further characterize the post-exercise muscle. Quantitative MRI showed not significantly different amounts of skeletal muscle in proximal hindlimbs in trisomic and euploid mice both at baseline and after physical exercise (P>0.05). Similar results were obtained for hindlimbs subfascia adipose tissue, and subcutaneous adipose tissue (P>0.05). MRS showed lower amounts of exercise-related metabolites (valine, isoleucine, leucine) in euploid vs. trisomic mice after exercise (P <=.0.05). The percentage of slow-twitch fibers was similar in the two genotypes (P>0.05). We conclude that in DS adapted physical exercise (one month of training) does not induce quantitative changes in skeletal muscle or fiber type composition therein; however, the metabolic response of skeletal muscle to exercise may be affected by trisomy. These findings prompt further research investigating the role of physical exercise as a cue to clarify the mechanisms of the muscular deficit found in DS.