[SIGNALING PATHWAYS REGULATING PROTEIN SYNTHESIS IN RAT SOLEUS MUSCLE DURING EARLY STAGES OF HINDLIMB UNLOADING].

The impact of mechanical unloading (hindlimb suspension for 1-, 3- and 7 days) on the protein synthesis intensity and as well as intracellular signaling pathways controlling mRNA translation was investigated. The content of the key signaling molecules of the various anabolic signaling pathways was determined by Western-blotting. The rate of protein synthesis was assessed using in vivo SUnSET technique. Hindlimb suspension (HS) within 24 hours resulted in a significant (p < 0.05) decrease in p-4E-BP 1 content and increase in p-p70s6k content in soleus muscle. Follo- wing three days of HS the content of p-AKT and p-90RSK1 was decreased (p <0.05). After 7 days of HS phosphorylation level of AKT and GSK-3beta was significantly reduced (p < 0.05) compared to the control group. We also observed a significant decrease in the amount of 28S rRNA in soleus following 3 and 7 days of HS. The rate of protein synthesis after 3 and 7 days of HS was decreased (p < 0.05) in comparison with the basal level. Our data suggest that the decrease in the protein synthesis rate in rat soleus during early stages of simulated microgravity could be associated with the impaired ribosome biogenesis as well as reduced activity of the mTORC1-independent signaling pathways.