Proteolysis activation and proteome alterations in murine skeletal muscle submitted to 1 week of hindlimb suspension.

The aim of this study was to investigate the temporal involvement of different proteolytic systems and muscle proteome changes during experimental disuse atrophy (up to 1 week hindlimb suspension, HS) in murine gastrocnemius muscle. The results showed that proteolysis, cytoprotection mechanisms and signs of cellular infiltration occurred very early. After 1 day of HS, signals of lysosomal activation, rather than programmed cell death (apoptosis), seem to trigger protein breakdown in the whole skeletal muscle. Moreover, the ubiquitin-proteasome pathway remained elevated later whereas all other proteolytic parameters returned to control values when atrophy was fully established. Using proteomics, evidence is provided for metabolic alterations toward glycolysis and for cytoskeleton remodelling suggestive of reduced capacity for force generation. Overall, our data highlight an early and coordinated time-dependent activation of proteolysis, which explains the global proteome alterations observed in gastrocnemius under atrophic conditions.