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Regulation of Leucine‐induced mTORC1 Activation in Skeletal Muscle of Neonatal Pigs
Author(s) -
Suryawan Agus,
Nguyen Hanh V,
Parada Rosemarie D,
Davis Teresa A
Publication year - 2017
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.31.1_supplement.652.8
Subject(s) - leucine , mtorc1 , amino acid , biochemistry , microbiology and biotechnology , biology , chemistry , signal transduction , pi3k/akt/mtor pathway
Background Leucine acts as anabolic agent that stimulates protein synthesis in skeletal muscle via activation of mammalian/mechanistic target of rapamycin complex 1 (mTORC1). Studies using cell cultures have proposed several models of the leucine‐induced activation of mTORC1 that involve Sestrin2, leucyl‐tRNA synthetase (LRS), and SH3 domain binding protein 4 (SH3BP4). In the first model, Sestrin2 (a GATOR2‐interacting protein) is a leucine sensor upstream of mTORC1. Lack of leucine causes Sestrin2 to interact with GATOR2, leading to inhibition of mTORC1. Under leucine‐rich condition, the binding of leucine to Sestrin2 disturbs the Sestrin2‐GATOR2 complex resulting in the activation of mTORC1. In a second proposed model, LRS acts as a leucine sensor that positively regulates mTORC1. In this model, there are two proposed pathways involving RagD and Vps34. In the first pathway, leucine binding to LRS stimulates LRS‐RagD interaction, which then promotes activation of mTORC1. In the second pathway, Vps34 mediates amino acid signaling to mTORC1. Leucine‐induced LRS‐Vps34 interaction is necessary for Vps34 activation towards Phospholipase D 1 (PLD1). PLD1 is essential for mTORC1 activation. In the third model, the binding of SH3BP4 to RagB acts as a potent inhibitor of amino acid‐induced activation of mTORC1. Leucine obstructs the interaction of SH3BP4 with RagB, allowing RagB to become fully active and participate in mTORC1 activation. Objective We aimed to determine whether these components participate in the leucine‐induced stimulation of mTORC1 in skeletal muscle in vivo . Methods Fasted 5‐d‐old piglets were gavage fed every 4 hours either: 1) low protein diet (LP), 2) LP supplemented with Leu (LP+Leu), or 3) high protein diet (HP). Diets were isocaloric and lactose was equal. At 25 h, piglets were injected with L[4‐ 3 H] phenylalanine to measure fractional protein synthesis rates and killed 30 min later. Leucine action toward mTORC1 signaling was determined by measuring mTORC1 activation (mTORC1‐associated mTOR Ser‐2481 autophosphorylation) and the protein‐protein interactions among purported regulatory components of mTORC1 (Sestrin2‐Mios [GATOR2], RagA‐mTOR, RagC‐mTOR, RagB‐SH3BP4, RagD‐LRS, and Vps34‐LRS). Results Muscle protein synthesis and mTORC1 activation were higher in the LP+Leu and the HP groups than the LP group. The abundance of the Sestrin2‐GATOR2 complex was lower, and RagA‐mTOR and RagC‐mTOR complexes were greater in the LP+Leu and the HP groups than the LP group. RagB‐SH3BP4, RagD‐LRS, and Vps34‐LRS abundances did not differ among groups. Conclusion Sestrin2 and the Rag proteins, but not LRS and SH3BP4, are crucial for the leucine‐induced activation of mTORC1 in skeletal muscle of neonatal pigs. Support or Funding Information NIH AR444474, NIH HD085573, NIH HD072891, USDA NIFA 2013‐67015‐20438, and USDA/ARS 6250‐51000‐055.