Realization of Mechanical Signal during Gravitational Unloading: a Respone of mTORC1 Targets to Eccentric Contractions
The aim of the study was to assess the response of key mTORC1 substrates to a bout of contractile stimuli at different times of functional unloading. Functional unloading of hindlimb muscles was carried out by the method of «antiorthostatic suspension». 28 Wistar rats were divided into four groups: control, hindlimb suspension for 1, 3 and 7-days. After hindlimb suspension, isolated soleus muscles of rats were subjected to a bout of ex vivo eccentric contractions. Using western blotting, we determined the content of phosphorylated forms of p70S6K and 4E-BP1. We discovered that an eccentric load resulted in a significant increase in p70S6K phosphorylation and reduced 4E-BP1 phosphorylation both in control and HS rats, but in the HS rats these changes were less pronounced. We can conclude that a bout of eccentric contractions during functional unloading causes a weaker activation of Akt-mTORC1-p70S6K pathway in isolated rat soleus muscle compared to control. This may indicate that it is important to maintain muscle tone for better muscle mechanical signal perception and subsequent activation of anabolic signaling pathways.