Elsevier

Molecular Metabolism

Volume 6, Issue 3, March 2017, Pages 245-255
Molecular Metabolism

Original Article
Enteroendocrine-derived glucagon-like peptide-2 controls intestinal amino acid transport

https://doi.org/10.1016/j.molmet.2017.01.005Get rights and content
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Highlights

  • GLP-2 promotes intestinal amino acid absorption in vivo.

  • Intestinal amino acid absorption is reduced in Glp2r−/− mice.

  • GLP-2 stimulates amino acid transport independently of blood flow.

  • GLP-2, but not GLP-1, activates the mTORC1 signaling pathway.

  • Amino acid transport by GLP-2 requires the enteric nervous system and mTORC1.

Abstract

Objective

Glucagon-like peptide-2 (GLP-2) is co-secreted with GLP-1 from gut endocrine cells, and both peptides act as growth factors to expand the surface area of the mucosal epithelium. Notably, GLP-2 also enhances glucose and lipid transport in enterocytes; however, its actions on control of amino acid (AA) transport remain unclear. Here we examined the mechanisms linking gain and loss of GLP-2 receptor (GLP-2R) signaling to control of intestinal amino acid absorption in mice.

Methods

Absorption, transport, and clearance of essential AAs, specifically lysine, were measured in vivo by Liquid Chromatography triple quadrupole Mass Spectrometry (LC-MS/MS) and ex vivo with Ussing chambers using intestinal preparations from Glp2r+/+ and Glp2r/ mice. Immunoblotting determined jejunal levels of protein components of signaling pathways (PI3K-AKT, and mTORC1-pS6-p4E-BP1) following administration of GLP-2, protein gavage, and rapamycin to fasted Glp2r+/+ and Glp2r/ mice. Expression of AA transporters from full thickness jejunum and 4F2hc from brush border membrane vesicles (BBMVs) was measured by real-time PCR and immunoblotting, respectively.

Results

Acute administration of GLP-2 increased basal AA absorption in vivo and augmented basal lysine transport ex vivo. GLP-2-stimulated lysine transport was attenuated by co-incubation with wortmannin, rapamycin, or tetrodotoxin ex vivo. Phosphorylation of mTORC1 effector proteins S6 and 4E-BP1 was significantly increased in wild-type mice in response to GLP-2 alone, or when co-administered with protein gavage, and abolished following oral gavage of rapamycin. In contrast, activation of GLP-1R signaling did not enhance S6 phosphorylation. Disruption of GLP-2 action in Glp2r−/− mice reduced lysine transport ex vivo and attenuated the phosphorylation of S6 and 4E-BP1 in response to oral protein. Moreover, the expression of cationic AA transporter slc7a9 in response to refeeding, and the abundance of 4F2hc in BBMVs following protein gavage, was significantly attenuated in Glp2r−/− mice.

Conclusions

These findings reveal an important role for GLP-2R signaling in the physiological and pharmacological control of enteral amino acid sensing and assimilation, defining an enteroendocrine cell-enterocyte axis for optimal energy absorption.

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Keywords

GLP-2
GLP-1
Amino acid absorption
Rapamycin
Gut peptides

Abbreviations

mTORC1
mechanistic target of rapamycin complex 1
4E-BP1
eukaryotic translation initiation factor 4E (eIF4e)-binding protein 1
GLP-1
Glucagon-like peptide-1
AA
amino acid
LC-MS/MS
liquid chromatography triple quadrupole mass spectrometry
GLP-2R
GLP-2 receptor
S6K1
70 kDa ribosomal protein S6 kinase 1
GLP-2
glucagon-like peptide-2
EECs
enteroendocrine cells
PGDP
proglucagon-derived peptides
EAA
essential amino acid
BBMV
brush border membrane vesicles
ENS
enteric nervous system

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