Whey protein intake after resistance exercise activates mTOR signaling in a dose-dependent manner in human skeletal muscle
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Protein ingestion after resistance exercise increases muscle protein synthesis (MPS) in a dose-dependent manner. However, the molecular mechanism(s) for the dose-dependency of MPS remains unclear. This study aimed to determine the dose response of mammalian target of rapamycin (mTOR) signaling in muscle with ingestion of protein after resistance exercise.
Fifteen male subjects performed four sets of six unilateral isokinetic concentric knee extensions. Immediately after exercise, eight subjects consumed water only. The other seven subjects, in a randomized-order crossover design, took either a 10 [3.6 g essential amino acids (EAA)] or 20 g (7.1 g EAA) solution of whey protein. Muscle biopsies from the vastus lateralis muscle were taken 30 min before and 1 h after resistance exercise. Phosphorylation of Akt (Ser473), mTOR (Ser2448), 4E-BP1 (Thr37/46), and S6K1 (Thr389) was measured by western blotting.
Concentric knee extension exercise alone did not increase phosphorylation of Akt and mTOR 1 h after exercise, but ingesting protein after exercise significantly increased the phosphorylation of Akt and mTOR in a dose-dependent manner (P < 0.05). 4E-BP1 phosphorylation significantly decreased after resistance exercise (P < 0.05), but subjects who took 10 or 20 g of protein after exercise showed increased 4E-BP1 from post-exercise dephosphorylation (P < 0.05). S6K1 phosphorylation significantly increased after resistance exercise (P < 0.05), and 20 g of protein further increased S6K1 phosphorylation compared with ingestion of 10 g (P < 0.05).
These findings suggest that whey protein intake after resistance exercise activates mTOR signaling in a dose-dependent manner in untrained men.
KeywordsMammalian target of rapamycin Whey hydrolysate Concentric contraction Muscle protein synthesis
Protein kinase B
Essential amino acids
Eukaryotic initiation factor
Mammalian target of rapamycin
Myosin heavy chain
Muscle protein breakdown
Muscle protein synthesis
Ribosomal protein S6 kinase 1
This study was supported by the MEXT-Supported Program for the Juntendo University, and a Grant-in Aid for Scientific Research B (No. 21300238 to HN, and No. 24700703 to RK) from the Ministry of Education, Culture, Sports, Science, and Technology of Japan. We thank the research subjects for their invaluable contribution to this study.
Conflict of interest
The authors declare that they have no conflicts of interest.
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