scholarly journals An increase in essential amino acid availability upregulates amino acid transporter expression in human skeletal muscle

2010 ◽  
Vol 298 (5) ◽  
pp. E1011-E1018 ◽  
Author(s):  
Micah J. Drummond ◽  
Erin L. Glynn ◽  
Christopher S. Fry ◽  
Kyle L. Timmerman ◽  
Elena Volpi ◽  
...  
Keyword(s):  
Skeletal Muscle ◽  
Protein Synthesis ◽  
Amino Acid ◽  
Protein Expression ◽  
Human Skeletal Muscle ◽  
Amino Acid Transporter ◽  
Dependent Manner ◽  
Mtorc1 Signaling ◽  
Acid Transporter ◽  
Transporter Expression

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.

scholarly journals Skeletal muscle amino acid transporter expression is increased in young and older adults following resistance exercise

2011 ◽  
Vol 111 (1) ◽  
pp. 135-142 ◽  
Author(s):  
Micah J. Drummond ◽  
Christopher S. Fry ◽  
Erin L. Glynn ◽  
Kyle L. Timmerman ◽  
Jared M. Dickinson ◽  
...  
Keyword(s):  
Older Adults ◽  
Amino Acid ◽  
Resistance Exercise ◽  
Amino Acid Transporter ◽  
Initiation Factor ◽  
Amino Acid Transporters ◽  
Α Subunit ◽  
Mtorc1 Signaling ◽  
Acid Transporter ◽  
Transporter Expression

Amino acid transporters and mammalian target of rapamycin complex 1 (mTORC1) signaling are important contributors to muscle protein anabolism. Aging is associated with reduced mTORC1 signaling following resistance exercise, but the role of amino acid transporters is unknown. Young ( n = 13; 28 ± 2 yr) and older ( n = 13; 68 ± 2 yr) subjects performed a bout of resistance exercise. Skeletal muscle biopsies ( vastus lateralis) were obtained at basal and 3, 6, and 24 h postexercise and were analyzed for amino acid transporter mRNA and protein expression and regulators of amino acid transporter transcription utilizing real-time PCR and Western blotting. We found that basal amino acid transporter expression was similar in young and older adults ( P > 0.05). Exercise increased L-type amino acid transporter 1/solute-linked carrier (SLC) 7A5, CD98/SLC3A2, sodium-coupled neutral amino acid transporter 2/SLC38A2, proton-assisted amino acid transporter 1/SLC36A1, and cationic amino acid transporter 1/SLC7A1 mRNA expression in both young and older adults ( P < 0.05). L-type amino acid transporter 1 and CD98 protein increased only in younger adults ( P < 0.05). eukaryotic initiation factor 2 α-subunit (S52) increased similarly in young and older adults postexercise ( P < 0.05). Ribosomal protein S6 (S240/244) and activating transcription factor 4 nuclear protein expression tended to be higher in the young, while nuclear signal transducer and activator of transcription 3 (STAT3) (Y705) was higher in the older subjects postexercise ( P < 0.05). These results suggest that the rapid upregulation of amino acid transporter expression following resistance exercise may be regulated differently between the age groups, but involves a combination of mTORC1, activating transcription factor 4, eukaryotic initiation factor 2 α-subunit, and STAT3. We propose an increase in amino acid transporter expression may contribute to enhanced amino acid sensitivity following exercise in young and older adults. In older adults, the increased nuclear STAT3 phosphorylation may be indicative of an exercise-induced stress response, perhaps to export amino acids from muscle cells.

scholarly journals Characterisation of L-Type Amino Acid Transporter 1 (LAT1) Expression in Human Skeletal Muscle by Immunofluorescent Microscopy

Nutrients ◽  
2017 ◽  
Vol 10 (1) ◽  
pp. 23 ◽  
Author(s):  
Nathan Hodson ◽  
Thomas Brown ◽  
Sophie Joanisse ◽  
Nick Aguirre ◽  
Daniel West ◽  
...  
Keyword(s):  
Skeletal Muscle ◽  
Amino Acid ◽  
Human Skeletal Muscle ◽  
Amino Acid Transporter ◽  
Immunofluorescent Microscopy ◽  
Acid Transporter

scholarly journals Bed rest impairs skeletal muscle amino acid transporter expression, mTORC1 signaling, and protein synthesis in response to essential amino acids in older adults

2012 ◽  
Vol 302 (9) ◽  
pp. E1113-E1122 ◽  
Author(s):  
Micah J. Drummond ◽  
Jared M. Dickinson ◽  
Christopher S. Fry ◽  
Dillon K. Walker ◽  
David M. Gundermann ◽  
...  
Keyword(s):  
Older Adults ◽  
Amino Acid ◽  
Protein Content ◽  
Bed Rest ◽  
Essential Amino Acids ◽  
Amino Acid Transporter ◽  
Transporter Protein ◽  
Mtorc1 Signaling ◽  
Acid Transporter ◽  
Transporter Expression

Skeletal muscle atrophy during bed rest is attributed, at least in part, to slower basal muscle protein synthesis (MPS). Essential amino acids (EAA) stimulate mammalian target of rapamycin (mTORC1) signaling, amino acid transporter expression, and MPS and are necessary for muscle mass maintenance, but there are no data on the effect of inactivity on this anabolic mechanism. We hypothesized that bed rest decreases muscle mass in older adults by blunting the EAA stimulation of MPS through reduced mTORC1 signaling and amino acid transporter expression in older adults. Six healthy older adults (67 ± 2 yr) participated in a 7-day bed rest study. We used stable isotope tracers, Western blotting, and real-time qPCR to determine the effect of bed rest on MPS, muscle mTORC1 signaling, and amino acid transporter expression and content in the postabsorptive state and after acute EAA ingestion. Bed rest decreased leg lean mass by ∼4% ( P < 0.05) and increased postabsorptive mTOR protein ( P < 0.05) levels while postabsorptive MPS was unchanged ( P > 0.05). Before bed rest acute EAA ingestion increased MPS, mTOR (Ser2448), S6 kinase 1 (Thr389, Thr421/Ser424), and ribosomal protein S6 (Ser240/244) phosphorylation, activating transcription factor 4, L-type amino acid transporter 1 and sodium-coupled amino acid transporter 2 protein content ( P < 0.05). However, bed rest blunted the EAA-induced increase in MPS, mTORC1 signaling, and amino acid transporter protein content. We conclude that bed rest in older adults significantly attenuated the EAA-induced increase in MPS with a mechanism involving reduced mTORC1 signaling and amino acid transporter protein content. Together, our data suggest that a blunted EAA stimulation of MPS may contribute to muscle loss with inactivity in older persons.

scholarly journals Effect of the lysosomotropic agent chloroquine on mTORC1 activation and protein synthesis in human skeletal muscle

2021 ◽  
Vol 18 (1) ◽  
Author(s):  
Michael S. Borack ◽  
Jared M. Dickinson ◽  
Christopher S. Fry ◽  
Paul T. Reidy ◽  
Melissa M. Markofski ◽  
...  
Keyword(s):  
Skeletal Muscle ◽  
Protein Synthesis ◽  
Amino Acid ◽  
Human Skeletal Muscle ◽  
Muscle Protein ◽  
C2c12 Cells ◽  
Mtorc1 Signaling ◽  
Lysosomotropic Agent ◽  
Amino Acid Sensing

Abstract Background Previous work in HEK-293 cells demonstrated the importance of amino acid-induced mTORC1 translocation to the lysosomal surface for stimulating mTORC1 kinase activity and protein synthesis. This study tested the conservation of this amino acid sensing mechanism in human skeletal muscle by treating subjects with chloroquine—a lysosomotropic agent that induces in vitro and in vivo lysosome dysfunction. Methods mTORC1 signaling and muscle protein synthesis (MPS) were determined in vivo in a randomized controlled trial of 14 subjects (10 M, 4 F; 26 ± 4 year) that ingested 10 g of essential amino acids (EAA) after receiving 750 mg of chloroquine (CHQ, n = 7) or serving as controls (CON, n = 7; no chloroquine). Additionally, differentiated C2C12 cells were used to assess mTORC1 signaling and myotube protein synthesis (MyPS) in the presence and absence of leucine and the lysosomotropic agent chloroquine. Results mTORC1, S6K1, 4E-BP1 and rpS6 phosphorylation increased in both CON and CHQ 1 h post EAA ingestion (P < 0.05). MPS increased similarly in both groups (CON, P = 0.06; CHQ, P < 0.05). In contrast, in C2C12 cells, 1 mM leucine increased mTORC1 and S6K1 phosphorylation (P < 0.05), which was inhibited by 2 mg/ml chloroquine. Chloroquine (2 mg/ml) was sufficient to disrupt mTORC1 signaling, and MyPS. Conclusions Chloroquine did not inhibit amino acid-induced activation of mTORC1 signaling and skeletal MPS in humans as it does in C2C12 muscle cells. Therefore, different in vivo experimental approaches are required for confirming the precise role of the lysosome and amino acid sensing in human skeletal muscle. Trial registration NCT00891696. Registered 29 April 2009.

scholarly journals Prognostic significance of amino-acid transporter expression (LAT1, ASCT2, and xCT) in surgically resected tongue cancer

2014 ◽  
Vol 110 (10) ◽  
pp. 2506-2513 ◽  
Author(s):  
M Toyoda ◽  
K Kaira ◽  
Y Ohshima ◽  
N S Ishioka ◽  
M Shino ◽  
...  
Keyword(s):  
Amino Acid ◽  
Tongue Cancer ◽  
Prognostic Significance ◽  
Amino Acid Transporter ◽  
Acid Transporter ◽  
Transporter Expression

scholarly journals Downregulation of Placental Amino Acid Transporter Expression and mTORC1 Signaling Activity Contributes to Fetal Growth Retardation in Diabetic Rats

2020 ◽  
Vol 21 (5) ◽  
pp. 1849
Author(s):  
Jie Xu ◽  
Jiao Wang ◽  
Yang Cao ◽  
Xiaotong Jia ◽  
Yujia Huang ◽  
...  
Keyword(s):  
Amino Acid ◽  
Rat Model ◽  
Amino Acid Transporter ◽  
Amino Acid Transporters ◽  
Amino Acid Transport System ◽  
Intrauterine Growth ◽  
System L ◽  
Acid Transporter ◽  
Transporter Expression

Alterations in placental transport may contribute to abnormal fetal intrauterine growth in pregnancies complicated by diabetes, but it is not clear whether the placental amino acid transport system is altered in diabetic pregnancies. We therefore studied the changes in the expressions of placental amino acid transporters in a rat model of diabetes induced by streptozotocin, and tested the effects of hyperglycemia on trophoblast amino acid transporter in vitro. Our results showed that the expressions for key isoforms of system L amino acid transporters were significantly reduced in the placentas of streptozotocin-induced diabetic pregnant rats, which was associated with the decreased birthweight in the rats. A decreased placental efficiency and decreased placental mammalian target of rapamycin (mTOR) complex 1 (mTORC1) activity were also found in the rat model. In addition, hyperglycemia in vitro could inhibit amino acid transporter expression and mTORC1 activity in human trophoblast. Inhibition of mTORC1 activity led to reduced amino acid transporter expression in placental trophoblast. We concluded that reduced placental mTORC1 activity during pregnancy resulted in decreased placental amino acid transporter expression and, subsequently, contributed to fetal intrauterine growth restriction in pregnancies complicated with diabetes.

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