TY - JOUR
T1 - An increase in essential amino acid availability upregulates amino acid transporter expression in human skeletal muscle
AU - Drummond, Micah J.
AU - Glynn, Erin L.
AU - Fry, Christopher S.
AU - Timmerman, Kyle L.
AU - Volpi, Elena
AU - Rasmussen, Blake B.
PY - 2010/5
Y1 - 2010/5
N2 - Essential amino acids (EAA) stimulate skeletal muscle mammalian target of rapamycin complex 1 (mTORC1) signaling and protein synthesis. It has recently been reported that an increase in amino acid (AA) transporter expression during anabolic conditions is rapamycin-sensitive. The purpose of this study was to determine whether an increase in EAA availability increases AA transporter expression in human skeletal muscle. Muscle biopsies were obtained from the vastus lateralis of seven young adult subjects (3 male, 4 female) before and 1-3 h after EAA ingestion (10 g). Blood and muscle samples were analyzed for leucine kinetics using stable isotopic techniques. Quantitative RT-PCR, and immunoblotting were used to determine the mRNA and protein expression, respectively, of AA transporters and members of the general AA control pathway [general control nonrepressed (GCN2), activating transcription factor (ATF4), and eukaryotic initiation factor (eIF2) α-subunit (Ser52)]. EAA ingestion increased blood leucine concentration, delivery of leucine to muscle, transport of leucine from blood into muscle, intracellular muscle leucine concentration, ribosomal protein S6 (Ser240/244) phosphorylation, and muscle protein synthesis. This was followed with increased L-type AA transporter (LAT1), CD98, sodium-coupled neutral AA transporter (SNAT2), and proton-coupled amino acid transporter (PAT1) mRNA expression at 1 h (P < 0.05) and modest increases in LAT1 protein expression (3 h post-EAA) and SNAT2 protein expression (2 and 3 h post-EAA, P < 0.05). Although there were no changes in GCN2 expression and eIF2α phosphorylation, ATF4 protein expression reached significance by 2 h post-EAA (P < 0.05). We conclude that an increase in EAA availability upregulates human skeletal muscle AA transporter expression, perhaps in an mTORC1-dependent manner, which may be an adaptive response necessary for improved AA intracellular delivery.
AB - Essential amino acids (EAA) stimulate skeletal muscle mammalian target of rapamycin complex 1 (mTORC1) signaling and protein synthesis. It has recently been reported that an increase in amino acid (AA) transporter expression during anabolic conditions is rapamycin-sensitive. The purpose of this study was to determine whether an increase in EAA availability increases AA transporter expression in human skeletal muscle. Muscle biopsies were obtained from the vastus lateralis of seven young adult subjects (3 male, 4 female) before and 1-3 h after EAA ingestion (10 g). Blood and muscle samples were analyzed for leucine kinetics using stable isotopic techniques. Quantitative RT-PCR, and immunoblotting were used to determine the mRNA and protein expression, respectively, of AA transporters and members of the general AA control pathway [general control nonrepressed (GCN2), activating transcription factor (ATF4), and eukaryotic initiation factor (eIF2) α-subunit (Ser52)]. EAA ingestion increased blood leucine concentration, delivery of leucine to muscle, transport of leucine from blood into muscle, intracellular muscle leucine concentration, ribosomal protein S6 (Ser240/244) phosphorylation, and muscle protein synthesis. This was followed with increased L-type AA transporter (LAT1), CD98, sodium-coupled neutral AA transporter (SNAT2), and proton-coupled amino acid transporter (PAT1) mRNA expression at 1 h (P < 0.05) and modest increases in LAT1 protein expression (3 h post-EAA) and SNAT2 protein expression (2 and 3 h post-EAA, P < 0.05). Although there were no changes in GCN2 expression and eIF2α phosphorylation, ATF4 protein expression reached significance by 2 h post-EAA (P < 0.05). We conclude that an increase in EAA availability upregulates human skeletal muscle AA transporter expression, perhaps in an mTORC1-dependent manner, which may be an adaptive response necessary for improved AA intracellular delivery.
KW - L-type amino acid transporter type 1
KW - Mammalian target of rapamycin
KW - Nutrient signaling
KW - Protein metabolism
KW - Sodium-coupled neutral amino acid transporter type 2
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U2 - 10.1152/ajpendo.00690.2009
DO - 10.1152/ajpendo.00690.2009
M3 - Article
C2 - 20304764
AN - SCOPUS:77950839133
SN - 0193-1849
VL - 298
SP - E1011-E1018
JO - American Journal of Physiology - Endocrinology and Metabolism
JF - American Journal of Physiology - Endocrinology and Metabolism
IS - 5
ER -