Leucine supplementation after mechanical stimulation activates protein synthesis via L‐type amino acid transporter 1 in vitro

• Published in: Journal of cellular biochemistry Vol. 119; no. 2; pp. 2094 - 2101
• Main Authors: Nakai, Naoya, Kawano, Fuminori, Murakami, Taro, Nakata, Ken, Higashida, Kazuhiko
• Format: Journal Article
• Language: English
• Published: United States Wiley Subscription Services, Inc 01.02.2018
• Subjects: Acids; Amino Acid Transport System y+ - metabolism; Amino acids; Animals; Chain branching; Chains; Crosstalk; Dietary supplements; Gene Expression Regulation - drug effects; In Vitro Techniques; Kinases; Leucine; Leucine - pharmacology; Mechanical stimuli; Mice; mtor; Muscle Fibers, Skeletal - cytology; Muscle Fibers, Skeletal - drug effects; Muscle Fibers, Skeletal - metabolism; Muscles; Myotubes; Nutrition; p70 S6 kinase; Phosphorylation; Phosphorylation - drug effects; Protein biosynthesis; Protein Biosynthesis - drug effects; Protein synthesis; Proteins; Rapamycin; Ribosomal Protein S6 Kinases, 70-kDa - metabolism; Signal transduction; Signaling; siRNA; Skeletal muscle; Stimulation; Stress, Mechanical; Stretching; Synergistic effect; TOR protein; TOR Serine-Threonine Kinases - metabolism; Translation initiation; Up-Regulation; leucine; mechanical stimuli; mtor; protein synthesis; p70 S6 kinase
• ISSN: 0730-2312; 1097-4644
• DOI: 10.1002/jcb.26371

Branched‐chain amino acid supplements consumed following exercise are widely used to increase muscle mass. Although both exercise (ie, mechanical stimulation) and branched‐chain amino acid leucine supplementation have been reported to stimulate muscle protein synthesis by activating the mammalian target of rapamycin (mTOR) signaling pathway independently, the mechanisms underlying their synergistic effects are largely unknown. Utilizing cultured differentiated C2C12 myotubes, we established a combination treatment model in which the cells were subjected to cyclic uniaxial mechanical stretching (4 h, 15%, 1 Hz) followed by stimulation with 2 mM leucine for 45 min. Phosphorylation of p70 S6 kinase (p70S6K), an mTOR‐regulated marker of protein translation initiation, was significantly increased following mechanical stretching alone but returned to the baseline after 4 h. Leucine supplementation further increased p70S6K phosphorylation, with a greater increase observed in the stretched cells than in the non‐stretched cells. Notably, the expression of L‐type amino acid transporter 1 (LAT1), a stimulator of the mTOR pathway, was also increased by mechanical stretching, and siRNA‐mediated knockdown partially attenuated leucine‐induced p70S6K phosphorylation. These results suggest that mechanical stretching promotes LAT1 expression and, consequently, amino acid uptake, leading to enhanced leucine‐induced activation of protein synthesis. LAT1 has been demonstrated to be a point of crosstalk between exercise‐ and nutrition‐induced skeletal muscle growth. The results in the present study suggest that mechanical stretching promotes LAT1 expression and, consequently, amino acid uptake, leading to enhanced leucine‐induced activation of protein synthesis. LAT1 has been demonstrated to be a point of crosstalk between exercise‐ and nutrition‐induced skeletal muscle growth.