POTENTIAL ROLE OF PHOSPHORYLATION OF p70~S6K IN DIFFERENT EXTENTS OF MUSCLE ATROPHY ACCORDING TO TYPE OF SKELETAL MUSCLE DURING ANKLE IMMOBILIZATION IN RAT

摘要

Akt and p70 ribosomal S6 kinase (p70~s6k) play a critical role in regulation of skeletal muscle mass in response to a variety of mechanical stimuli. However, the regulation of these molecules under decreased muscle usage has rarely been investigated according to skeletal muscle types that affect the rate of disuse muscle atrophy. This study was conducted in rats to elucidate the responses of Akt and p70~s6k phosphorylation to ankle immobilization in different types of plantar flexors and its association with the muscle atrophy rate in the muscles. The results revealed that the rate of muscle atrophy in response to ten days of ankle immobilization was significantly less in the plantaris (PL) and gastrocnemius, which could not be completely immobilized with the ankle fixation, than in the soleus (SOL) (P<0.05). In accordance with these findings, the decrease in phosphorylation of p70~s6k (T389) that was observed in SOL (P<0.001) was not observed in PL, and its level even increased in fast-twitch white gastrocnemius (WG) (P<0.05). However, phosphorylation of Akt (S473) was lower in all three muscles in response to immobilization treatment. The Akt-independent phosphorylations of p70~s6k in PL and WG were further confirmed by the decreased phosphorylation of Akt (T308) and GSK3alpha. These results suggest that the skeletal muscle type-specific different rates of muscle atrophy that occur during ankle immobilization may be mediated by p70~s6k, which responds differently in the distinct types of skeletal muscle.