Effect of exercise on protein turnover in muscles of lean and obese mice

The effect of work-induced hypertrophy on skeletal muscle protein metabolism was studied in lean mice and in mice rendered obese with goldthioglucose. After tenotomy of the gastrocnemius muscle, the adaptative growth of soleus muscle was less pronounced in obese than in lean mice. Protein turnover was studied in the isolated soleus muscle 4 days after the operation. Tyrosine incorporation in total proteins and tyrosine release in the incubation medium (indices of protein synthesis and degradation) were increased by 3- and 2-fold in overloaded (i.e. work-induced hypertrophied) muscles of lean and obese mice, respectively, compared to the control muscles isolated from the non-operated leg. The qualitative modifications in the pattern of proteins synthetized from 35S-methionine were identical in both groups of mice. This increase in protein turnover in overloaded muscles results from an increased rate of polypeptide chain initiation (3-fold in lean mice, 2.2-fold in obese mice) without any modification of peptide chain elongation rates. Work-induced hypertrophy was also able to reverse the defect in amino acid uptake which is present in soleus muscles of GTG-obese mice. These results suggest that the work-induced increase of skeletal muscle protein turnover is diminished in obese mice.