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Abstract
The System L1-type amino acid transporter mediates transport of large neutral amino acids (LNAA) in many mammalian cell-types. LNAA such as leucine are required for full activation of the mTOR-S6K signalling pathway promoting protein synthesis and cell growth. The SLC7A5 (LAT1) catalytic subunit of high-affinity System L1 functions as a glycoprotein-associated heterodimer with the multifunctional protein SLC3A2 (CD98). We generated a floxed Slc7a5 mouse strain which, when crossed with mice expressing Cre driven by a global promoter, produced Slc7a5 heterozygous knockout (Slc7a5+/-) animals with no overt phenotype, although homozygous global knockout of Slc7a5 was embryonically lethal. Muscle-specific (MCK Cre-mediated) Slc7a5 knockout (MS-Slc7a5-KO) mice were used to study the role of intracellular LNAA delivery by the SLC7A5 transporter for mTOR-S6K pathway activation in skeletal muscle. Activation of muscle mTOR-S6K (Thr389 phosphorylation) in vivo by intraperitoneal leucine injection was blunted in homozygous MS-Slc7a5-KO mice relative to wild-type animals. Dietary intake and growth rate were similar for MS-Slc7a5-KO mice and wild-type littermates fed for 10 weeks (to age 120 days) with diets containing 10%, 20% or 30% of protein. In MS-Slc7a5-KO mice, Leu and Ile concentrations in gastrocnemius muscle were reduced by ∼40% as dietary protein content was reduced from 30 to 10%. These changes were associated with >50% decrease in S6K Thr389 phosphorylation in muscles from MS-Slc7a5-KO mice, indicating reduced mTOR-S6K pathway activation, despite no significant differences in lean tissue mass between groups on the same diet. MS-Slc7a5-KO mice on 30% protein diet exhibited mild insulin resistance (e.g. reduced glucose clearance, larger gonadal adipose depots) relative to control animals. Thus, SLC7A5 modulates LNAA-dependent muscle mTOR-S6K signalling in mice, although it appears non-essential (or is sufficiently compensated by e.g. SLC7A8 (LAT2)) for maintenance of normal muscle mass.
Original language | English |
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Article number | e89547 |
Number of pages | 14 |
Journal | PLoS ONE |
Volume | 9 |
Issue number | 2 |
DOIs | |
Publication status | Published - 26 Feb 2014 |
Keywords
- Animals
- Blotting, Western
- Cells, Cultured
- Dietary Proteins
- Glucose Tolerance Test
- Insulin
- Insulin Resistance
- Integrases
- Large Neutral Amino Acid-Transporter 1
- Leucine
- Mice
- Mice, Knockout
- Mice, Transgenic
- Muscle, Skeletal
- Phosphorylation
- RNA, Messenger
- Real-Time Polymerase Chain Reaction
- Reverse Transcriptase Polymerase Chain Reaction
- Ribosomal Protein S6 Kinases, 70-kDa
- Signal Transduction
- TOR Serine-Threonine Kinases
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- 1 Finished
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Non-Genomic Mechanisms Stabilizing the Abundance of SNAT2, a Nutrient Transceptor Protein, in Response to Diverse Catabotic Signals
Hundal, H. (Investigator) & Taylor, P. (Investigator)
3/10/11 → 2/07/15
Project: Research