[Effects of Phenylalanine on Glucose Uptake in Mouse Myoblast Cell Line C2C12 and Its Relationship with mTOR-p70S6K Pathway].

OBJECTIVE: To investigate the influence of phenylalanine(Phe) on glucose uptake in mouse myoblast cell line C2C12 and to explore its relationship with mTOR-p70S6K pathway.

METHODS: C2C12 cells were cultured to promote formation of multinucleated myotubes in vitro. The cells were deprived and incubated with Phe at different concentrations (1.25,2.5,5,10,20 mmol/L).Krebs-Ringer buffer (KRB) was used as control.The 2-NBDG was used to measure glucose uptake of C2C12.The expression of mTOR,p70S6K,IRS-1,and Akt protein were evaluated by Western blot.

RESULTS: Compared with KBP treatment,glucose uptake of the cells incubated with 5 mmol/L leucine (Leu) was decreased by 30% ( P =0.001), while a 40% increase was detected in the cells incubated with 5 mmol/L Phe ( P <0.01).The promotion of glucose uptake was Phe concentration-dependent.Phe stimulation had no effect on the phosphorylation of mTOR at Ser2448. Phosphorylation of p70S6K at Thr389 was inhibited in the cells incubated with Phe at concentration higher than 1.25 mmol/L, but the difference was not significant ( P =0.815). Leu stimulated but Phe over 1.25 mmol/L inhibited phosphorylation of IRS-1 at Ser636/639, although the difference was not significant ( P =0.381).Neither Leu nor Phe affected the expression of phospho-Akt (Ser473) significantly.

CONCLUSION: Phenylalanine inhibits phosphorylation of IRS-1 at Ser636/639 possibly through inhibiting the activation of p70S6K.The effect of Phe on mTOR-p70S6K pathway is Akt-independent.