Oligopeptides stimulate glucagon-like peptide-1 secretion in mice through proton-coupled uptake and the calcium-sensing receptor

Abstract

Aims/hypothesisIngested 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.MethodsGLP-1 secretion from murine primary colonic cultures and Ca2+ 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.ResultsGLP-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 Ca2+ 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 Ca2+ 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/interpretationOligopeptides 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.Electronic supplementary materialThe online version of this article (doi:10.1007/s00125-013-3037-3) contains peer-reviewed but unedited supplementary material, which is available to authorised users.

Effect of Roux-en-Y gastric bypass on the distribution and hormone expression of small-intestinal enteroendocrine cells in obese patients with type 2 diabetes

“…This increase in the density of GLP-1-producing cells in the common limb could be linked to an increased flow of nutrients and bile, since both bile [7], fatty acids, carbohydrates [8] and oligopeptides [9] are known secretagogues of GLP-1 and, thus, are potential stimulators of GCG expression. Similarly, our findings are consistent with the increased postprandial plasma levels of GLP-1 found after RYGB [10][11][12][13].…”

Regulation of gut hormone secretion. Studies using isolated perfused intestines

“…However, the molecular mechanisms behind the sensing of and the secretory effects of peptone/amino acids have not been investigated in any detail.Possible mechanisms involve apical amino-acid/sodium cotransport into the cells, with subsequent depolarization and calcium-dependent secretion although metabolism of amino acids may also play a role. Recent single cell studies have suggested that protein-sensing could be linked to the Calcium-sensing receptor (CasR) and the peptide transporter-1 (PEPT1) 11 . However, this might be in addition to the other mechanisms.…”

“…In primary mouse colonic cells, peptone, a meat hydrolysate provided a good stimulus for the incretin hormones 11,63 . Also a number of amino acids have been shown to affect GLP-1 secretion in in vitro studies, including glutamine, alanine, arginine, phenylalanine, asparagine 10,20,43,55,67 .For glutamine, as a consequence, this has been taken into clinical studies as well.In the isolated perfused rat small intestine, peptone was a powerful stimulus of GLP-1 secretion, thusthe effect inculturedcells translated to the cells in situ.…”

Gut chemosensing mechanisms

“…The sensing of these larger protein digestion products has been linked to the activation of MAPKs (52, 53) and the activity of the brush border H + -coupled transporter of dipeptides and tripeptides, peptide transporter 1 (PEPT1) (54,55). Both PEPT1-and CaSR-dependent pathways were recently implicated in the sensing of peptones and dipeptides and tripeptides by primary L cells (56). Another receptor, lysoon plasma incretin levels (33), although small GLP1 responses triggered by oral fructose might be attributable to metabolism (37), as apical fructose uptake is mediated by a non-electrogenic transporter GLUT5.…”

“…In recent years gut microbiota have been increasingly recognized as a fundamental component of host metabolism, and shifts in bacterial populations have been associated with endocrine disorders such as obesity and type 2 diabetes (98-101). Gut microbiota phosphatidic acid receptor 5 (LPAR5, also known as GPR92/93), was reported to mediate peptone-stimulated CCK release in Lpar5-overexpressing STC-1 cells (57), although its expression is not enriched in native I cells (49) or L cells (56). As GLP1 secretion was found not to be impaired in primary colonic cultures from Lpar5 knockout mice (56), further work is required to elucidate what role, if any, LPAR5 plays in intestinal chemosensing.…”