title: Oligopeptides stimulate glucagon-like peptide-1 secretion in mice through proton-coupled uptake and the calcium-sensing receptor.
abstract: OBJECTIVE
  Ingested protein is a well-recognised stimulus for glucagon-like peptide-1 (GLP-1) release from intestinal L cells. This study aimed to characterise the molecular mechanisms employed by L cells to detect oligopeptides.
  
  
  METHODS
  GLP-1 secretion from murine primary colonic cultures and Ca(2+) dynamics in L cells were monitored in response to peptones and dipeptides. L cells were identified and purified based on their cell-specific expression of the fluorescent protein Venus, using GLU-Venus transgenic mice. Pharmacological tools and knockout mice were used to characterise candidate sensory pathways identified by expression analysis.
  
  
  RESULTS
  GLP-1 secretion was triggered by peptones and di-/tripeptides, including the non-metabolisable glycine-sarcosine (Gly-Sar). Two sensory mechanisms involving peptide transporter-1 (PEPT1) and the calcium-sensing receptor (CaSR) were distinguishable. Responses to Gly-Sar (10 mmol/l) were abolished in the absence of extracellular Ca(2+) or by the L-type calcium-channel blocker nifedipine (10 μmol/l) and were PEPT1-dependent, as demonstrated by their sensitivity to pH and 4-aminomethylbenzoic acid and the finding of impaired responses in tissue from Pept1 (also known as Slc15a1) knockout mice. Peptone (5 mg/ml)-stimulated Ca(2+) responses were insensitive to nifedipine but were blocked by antagonists of CaSR. Peptone-stimulated GLP-1 secretion was not impaired in mice lacking the putative peptide-responsive receptor lysophosphatidic acid receptor 5 (LPAR5; also known as GPR92/93).
  
  
  CONCLUSIONS
  Oligopeptides stimulate GLP-1 secretion through PEPT1-dependent electrogenic uptake and activation of CaSR. Both pathways are highly expressed in native L cells, and likely contribute to the ability of ingested protein to elevate plasma GLP-1 levels. Targeting nutrient-sensing pathways in L cells could be used to mobilise endogenous GLP-1 stores in humans, and could mimic some of the metabolic benefits of bariatric surgery.
authors.affiliation: Cambridge Institute for Medical Research, Wellcome Trust/MRC Building, Addenbrooke's Hospital, Box 139, Hills Road, Cambridge, CB2 0XY, UK.
authors.forename: Eleftheria
authors.initials: E
authors.lastname: Diakogiannaki
authors.forename: Ramona
authors.initials: R
authors.lastname: Pais
authors.forename: Gwen
authors.initials: G
authors.lastname: Tolhurst
authors.forename: Helen E
authors.initials: HE
authors.lastname: Parker
authors.forename: James
authors.initials: J
authors.lastname: Horscroft
authors.forename: Beate
authors.initials: B
authors.lastname: Rauscher
authors.forename: Tamara
authors.initials: T
authors.lastname: Zietek
authors.forename: Hannelore
authors.initials: H
authors.lastname: Daniel
authors.forename: Fiona M
authors.initials: FM
authors.lastname: Gribble
authors.forename: Frank
authors.initials: F
authors.lastname: Reimann
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism*; D020746:Calcium Channels, L-Type / Q000378:metabolism*; D002460:Cell Line; D000242:Cyclic AMP / Q000378:metabolism; D019858:Enteroendocrine Cells / Q000378:metabolism*; D052216:Glucagon-Like Peptide 1 / Q000378:metabolism*; D051379:Mice; D018345:Mice, Knockout; D008822:Mice, Transgenic; D009842:Oligopeptides / Q000378:metabolism*; D010461:Peptones / Q000378:metabolism; D011236:Prediabetic State / Q000378:metabolism*; D011522:Protons; D044169:Receptors, Calcium-Sensing / Q000378:metabolism*; D018027:Receptors, Glucagon / Q000378:metabolism; D015398:Signal Transduction
chemical_list: D020746:Calcium Channels, L-Type; D009842:Oligopeptides; D010461:Peptones; D011522:Protons; D044169:Receptors, Calcium-Sensing; D018027:Receptors, Glucagon; D052216:Glucagon-Like Peptide 1; D000242:Cyclic AMP; D002118:Calcium
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