Diakogiannaki Eleftheria, Pais Ramona, Tolhurst Gwen, Parker Helen E, Horscroft James, Rauscher Beate, Zietek Tamara, Daniel Hannelore, Gribble Fiona M, Reimann Frank
Cambridge Institute for Medical Research, Wellcome Trust/MRC Building, Addenbrooke's Hospital, Box 139, Hills Road, Cambridge, CB2 0XY, UK.
Diabetologia. 2013 Dec;56(12):2688-96. doi: 10.1007/s00125-013-3037-3. Epub 2013 Sep 18.
AIMS/HYPOTHESIS: 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.
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.
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/INTERPRETATION: 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.
目的/假设：摄入的蛋白质是肠L细胞释放胰高血糖素样肽-1（GLP-1）的一种公认刺激物。本研究旨在阐明L细胞检测寡肽所采用的分子机制。
监测来自小鼠原代结肠培养物的GLP-1分泌以及L细胞中Ca(2+)动力学，以响应蛋白胨和二肽。使用GLU-Venus转基因小鼠，基于荧光蛋白金星的细胞特异性表达来鉴定和纯化L细胞。使用药理学工具和基因敲除小鼠来表征通过表达分析鉴定的候选感觉通路。
蛋白胨和二肽/三肽，包括不可代谢的甘氨酸-肌氨酸（Gly-Sar），可触发GLP-1分泌。涉及肽转运体-1（PEPT1）和钙敏感受体（CaSR）的两种感觉机制是可区分的。在无细胞外Ca(2+)或使用L型钙通道阻滞剂硝苯地平（10 μmol/l）时，对Gly-Sar（10 mmol/l）的反应消失，且其依赖于PEPT1，这通过它们对pH和4-氨基甲基苯甲酸的敏感性以及在Pept1（也称为Slc15a1）基因敲除小鼠组织中反应受损得以证明。蛋白胨（5 mg/ml）刺激的Ca(2+)反应对硝苯地平不敏感，但被CaSR拮抗剂阻断。在缺乏假定的肽反应性受体溶血磷脂酸受体5（LPAR5；也称为GPR92/93）的小鼠中，蛋白胨刺激的GLP-1分泌未受损。
结论/解读：寡肽通过依赖于PEPT1的电中性摄取和CaSR的激活来刺激GLP-1分泌。这两种途径在天然L细胞中均高度表达，可能有助于摄入的蛋白质提高血浆GLP-1水平。靶向L细胞中的营养感知途径可用于调动人类内源性GLP-1储备，并可模拟减重手术的一些代谢益处。
