Résumé
The conversion of skeletal muscle into meat, i.e. maturation, is a complex process where muscle undergoes different biochemical and physiological changes. In agronomic field, the study of these events is of particular interest, in order to improve the quality of meat.It is well established that the proteolytic events generated by the enzymes such as cathepsins, calpains and ubiquitine proteasome system are involved in skeletal muscle maturation. Recent data suggest that other mechanisms, such as apoptosis and autophagy, may also contribute to the post-mortem maturation. However, their intervention is not clearly described. We designed a pilot study using mice to evaluate the proteolytic mechanisms within a 48h post-mortem time frame and their interaction with myostatin, a negative regulator of skeletal muscle mass. We measured the proteolysis of myofibrillar proteins (filamin, desmin, troponin T), as well as the activation and the expression of proteins involved in autophagic pathways. Our data showed a significant progressive degradation of myofibrillar proteins over the 48h PM period. Moreover, it was more pronounced in the muscle of Mstn KO mice. AMPK activation was attenuated in Mstn KO mice and was associated to a lower activation of the protein kinase ULK (inducer of autophagy) which suggests a reduced autophagy in Mstn KO mice. Using colchicine (an inhibitor of autophagy), we showed in Mstn KO muscle a reduced basal autophagic flux that remained low within the postmortem time frame. In conclusion, our results showed a difference in the proteolytic profile between the two genotypes during the post-mortem maturation of skeletal muscle. The absence of myostatin promotes a faster degradation of myofibrillar proteins associated to a reduced level of autophagy. The mechanisms responsible for this difference between the two genotypes remain to be elucidated.