Protein synthesis, autophagy, and regeneration-related signaling in fast/slow muscles in two mammalian models of disuse
Résumé
Whether regulation of protein synthesis, autophagy, and regeneration are involved in slow/fast muscles in two disuse models (hindlimb unloading Sprague-Dawley rats ( Rattus norvegicus domestica (Berkenhout, 1769))) (HLU) and hibernating ground squirrels ( Spermophilus dauricus Brandt, 1843 (HIB)) is still unclear. Our results showed (1) fiber cross-sectional area was reduced in soleus (SOL) and extensor digitorum longus (EDL) of HLU whereas no change in HIB. The satellite cells/fiber was reduced and myonuclei/fiber was increased in SOL of HLU, while the percentage of satellite cells was significantly reduced in EDL of HIB. (2) Protein levels of phosphorylated- (P-)Akt, mTORC1, P-mTORC1, and P-S6K1 were reduced in SOL of HLU, whereas phosphorylated S6K1 was increased only in EDL of HIB. (3) Myostatin decreased in EDL of HLU but decreased in SOL of HIB. (4) Beclin1 increased in EDL of HLU and in SOL of HIB. (5) The activity of cathepsin L increased in SOL of HIB. (6) Collagen III increased in both SOL and EDL of HLU, but myogenin and collagen III increased in SOL, and collagen III was reduced in EDL of HIB. Taken together, Akt-mTORC1, Beclin1, and myogenin signaling showed muscle-specific responses in slow-twitch versus fast-twitch muscles, which may contribute to disuse atrophy in non-hibernators and anti-atrophy in hibernators.