TITLE:
Consecutive-Day Intake of Whey Protein Upregulates mTOR mRNA and Protein Expression in Resting Skeletal Muscle of Mice
AUTHORS:
Hajime Sasaki
KEYWORDS:
Whey Protein Intake, Resting Skeletal Muscle, Enhancement, Protein Synthesis, mTOR Pathway
JOURNAL NAME:
Food and Nutrition Sciences,
Vol.10 No.9,
September
3,
2019
ABSTRACT: Background: Although the effect of whey protein intake on protein metabolism in exercise-loaded
skeletal muscle has been well documented, little has been reported on its
effect on resting muscle. The effects of whey protein intake on protein metabolism
in resting mouse skeletal muscle were investigated. Methods: Mice were
fed AIN-93G composed of either casein or whey protein as the protein source for
3 or 7 consecutive days. The gastrocnemius muscle was excised, and the
expression levels of the regulatory factor, mTOR, and its subunits, Raptor and
Rictor, were measured by real-time PCR. The protein expression levels of mTOR
and its phosphorylated form were measured by immunofluorescent western
blotting. The effects of whey protein were compared to those of the case in
control. Results: mTOR expression increased in the gastrocnemius muscle
of mice fed whey protein for 7 consecutive days. The expression of Raptor
significantly increased, whereas that of Rictor did not change, suggesting a
dominant formation of mTORC1 relating to the upregulation of protein synthesis.
The protein levels of mTOR and its phosphorylated form significantly increased
in mice fed whey protein, indicating enhanced protein synthesis. Increased mTOR
expression was not seen in the gastrocnemius muscle of mice fed whey protein
for 3 consecutive days. Conclusions: These results indicate that the
intake of whey protein for 7 consecutive days, but not 3 days, upregulates the
mRNA and protein expression of mTOR in the resting gastrocnemius muscle of
mice, suggesting its ability to enhance protein synthesis. Consecutive-day
intake of whey protein may induce constitutive alteration of the skeletal
muscle, including continuous upregulation of muscle protein synthesis.