title: Enteroendocrine-derived glucagon-like peptide-2 controls intestinal amino acid transport.
abstract: 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.
  
  
  
  Absorption, transport, and clearance of essential AAs, specifically lysine, were measuredin vivoby Liquid Chromatography triple quadrupole Mass Spectrometry (LC-MS/MS) andex vivowith Ussing chambers using intestinal preparations fromGlp2r+/+andGlp2r-/-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 fastedGlp2r+/+andGlp2r-/-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.
  
  
  
  Acute administration of GLP-2 increased basal AA absorptionin vivoand augmented basal lysine transportex vivo. GLP-2-stimulated lysine transport was attenuated by co-incubation with wortmannin, rapamycin, or tetrodotoxinex 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 inGlp2r-/-mice reduced lysine transportex vivoand attenuated the phosphorylation of S6 and 4E-BP1 in response to oral protein. Moreover, the expression of cationic AA transporterslc7a9in response to refeeding, and the abundance of 4F2hc in BBMVs following protein gavage, was significantly attenuated inGlp2r-/-mice.
  
  
  
  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.
authors.affiliation: Department of Medicine, University of Toronto, Canada; Lunenfeld-Tanenbaum Research Institute, Mt. Sinai Hospital, Toronto, ON M5G 1X5, Canada.
authors.forename: Jennifer
authors.initials: J
authors.lastname: Lee
authors.affiliation: Department of Medicine, University of Toronto, Canada; Lunenfeld-Tanenbaum Research Institute, Mt. Sinai Hospital, Toronto, ON M5G 1X5, Canada.
authors.forename: Jacqueline
authors.initials: J
authors.lastname: Koehler
authors.affiliation: Department of Medicine, University of Toronto, Canada; Lunenfeld-Tanenbaum Research Institute, Mt. Sinai Hospital, Toronto, ON M5G 1X5, Canada.
authors.forename: Bernardo
authors.initials: B
authors.lastname: Yusta
authors.affiliation: Department of Medicine, University of Toronto, Canada; Lunenfeld-Tanenbaum Research Institute, Mt. Sinai Hospital, Toronto, ON M5G 1X5, Canada.
authors.forename: Jasmine
authors.initials: J
authors.lastname: Bahrami
authors.affiliation: Department of Medicine, University of Toronto, Canada; Lunenfeld-Tanenbaum Research Institute, Mt. Sinai Hospital, Toronto, ON M5G 1X5, Canada.
authors.forename: Dianne
authors.initials: D
authors.lastname: Matthews
authors.affiliation: Department of Medicine, University of Toronto, Canada; Lunenfeld-Tanenbaum Research Institute, Mt. Sinai Hospital, Toronto, ON M5G 1X5, Canada.
authors.forename: Mahroukh
authors.initials: M
authors.lastname: Rafii
authors.affiliation: Department of Medicine, University of Toronto, Canada; Lunenfeld-Tanenbaum Research Institute, Mt. Sinai Hospital, Toronto, ON M5G 1X5, Canada.
authors.forename: Paul B
authors.initials: PB
authors.lastname: Pencharz
authors.affiliation: Department of Medicine, University of Toronto, Canada; Lunenfeld-Tanenbaum Research Institute, Mt. Sinai Hospital, Toronto, ON M5G 1X5, Canada. Electronic address: drucker@lunenfeld.ca.
authors.forename: Daniel J
authors.initials: DJ
authors.lastname: Drucker
mesh_terms: D026905:Amino Acid Transport Systems / Q000378:metabolism*; D000596:Amino Acids / Q000378:metabolism; D000818:Animals; D019858:Enteroendocrine Cells / Q000378:metabolism; D052216:Glucagon-Like Peptide 1 / Q000378:metabolism / Q000502:physiology; D053767:Glucagon-Like Peptide 2 / Q000378:metabolism* / Q000502:physiology; D000067758:Glucagon-Like Peptide-2 Receptor / Q000378:metabolism; D005947:Glucose / Q000378:metabolism; D007408:Intestinal Absorption / Q000187:drug effects*; D007413:Intestinal Mucosa / Q000378:metabolism; D007421:Intestine, Small / Q000378:metabolism; D007583:Jejunum / Q000378:metabolism; D051379:Mice; D008810:Mice, Inbred C57BL; D010455:Peptides / Q000378:metabolism; D018027:Receptors, Glucagon / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects
chemical_list: D026905:Amino Acid Transport Systems; D000596:Amino Acids; D053767:Glucagon-Like Peptide 2; D000067758:Glucagon-Like Peptide-2 Receptor; D010455:Peptides; D018027:Receptors, Glucagon; D052216:Glucagon-Like Peptide 1; D005947:Glucose
keywords: 4E-BP1, eukaryotic translation initiation factor 4E (eIF4e)-binding protein 1; AA, amino acid; Amino acid absorption; BBMV, brush border membrane vesicles; EAA, essential amino acid; EECs, enteroendocrine cells; ENS, enteric nervous system; GLP-1; GLP-1, Glucagon-like peptide-1; GLP-2; GLP-2, glucagon-like peptide-2; GLP-2R, GLP-2 receptor; Gut peptides; LC-MS/MS, liquid chromatography triple quadrupole mass spectrometry; PGDP, proglucagon-derived peptides; Rapamycin; S6K1, 70 kDa ribosomal protein S6 kinase 1; mTORC1, mechanistic target of rapamycin complex 1