Metabolic Research Laboratories and MRC Metabolic Diseases Unit, WT-MRC Institute of Metabolic Science, Addenbrooke's Hospital, University of Cambridge, Cambridge, CB2 0QQ, UK.
Diabetologia. 2017 Dec;60(12):2475-2485. doi: 10.1007/s00125-017-4420-2. Epub 2017 Sep 2.
AIMS/HYPOTHESIS: Lipids are a potent stimulus for the secretion of glucagon-like peptide (GLP)-1 and glucose-dependent insulinotropic peptide (GIP). Traditionally, this effect was thought to involve the sensing of lipid digestion products by free fatty acid receptor 1 (FFA1) and G-protein coupled receptor 119 (GPR119) on the apical surface of enteroendocrine cells. However, recent evidence suggests that lipids may in fact be sensed basolaterally, and that fatty acid absorption and chylomicron synthesis may be a prerequisite for their stimulatory effect on gut peptide release. Therefore, we investigated the effect of chylomicrons on GLP-1 and GIP secretion in vitro.
The effect of chylomicrons on incretin secretion was investigated using GLUTag cells and duodenal cultures of both murine and human origin. The role of lipoprotein lipase (LPL) and FFA1 in GLUTag cells was assessed by pharmacological inhibition and small (short) interfering RNA (siRNA)-mediated knockdown. The effect of chylomicrons on intracellular calcium concentration ([Ca]) was determined by imaging GLUTag cells loaded with Fura-2. In the primary setting, the contributions of FFA1 and GPR119 were investigated using L cell-specific Gpr119 knockout cultures treated with the FFA1 antagonist GW1100.
Chylomicrons stimulated GLP-1 release from GLUTag cells, and both GLP-1 and GIP secretion from human and murine duodenal cultures. Chylomicron-triggered GLP-1 secretion from GLUTag cells was largely abolished following lipase inhibition with orlistat or siRNA-mediated knockdown of Lpl. In GLUTag cells, both GW1100 and siRNA-mediated Ffar1 knockdown reduced GLP-1 secretion in response to chylomicrons, and, consistent with FFA1 G-coupling, chylomicrons triggered an increase in [Ca]. However, LPL and FFA1 inhibition had no significant effect on chylomicron-mediated incretin secretion in murine cultures. Furthermore, the loss of GPR119 had no impact on GLP-1 secretion in response to chylomicrons, even in the presence of GW1100.
CONCLUSIONS/INTERPRETATION: Chylomicrons stimulate incretin hormone secretion from GLUTag cells as well as from human and murine duodenal cultures. In GLUTag cells, the molecular pathway was found to involve LPL-mediated lipolysis, leading to the release of lipid species that activated FFA1 and elevated intracellular calcium.
目的/假设：脂质是胰高血糖素样肽（GLP-1）和葡萄糖依赖性胰岛素释放肽（GIP）分泌的有效刺激物。传统上，这种作用被认为涉及游离脂肪酸受体 1（FFA1）和 G 蛋白偶联受体 119（GPR119）在肠内分泌细胞顶表面对脂质消化产物的感知。然而，最近的证据表明，脂质实际上可能在基底外侧被感知，脂肪酸吸收和乳糜微粒合成可能是其对肠道肽释放刺激作用的前提。因此，我们研究了乳糜微粒对体外 GLP-1 和 GIP 分泌的影响。
使用 GLUTag 细胞和源自鼠和人的十二指肠培养物研究了乳糜微粒对肠促胰岛素分泌的影响。通过药理学抑制和小（短）干扰 RNA（siRNA）介导的敲低评估了脂蛋白脂肪酶（LPL）和 FFA1 在 GLUTag 细胞中的作用。通过用 Fura-2 负载的 GLUTag 细胞成像来确定乳糜微粒对细胞内钙浓度([Ca])的影响。在初步设置中，使用 L 细胞特异性 Gpr119 敲除培养物，并用 FFA1 拮抗剂 GW1100 处理，研究了 FFA1 和 GPR119 的作用。
乳糜微粒刺激 GLUTag 细胞释放 GLP-1，并且刺激人源和鼠源十二指肠培养物释放 GLP-1 和 GIP。用奥利司他或 Lpl 的 siRNA 介导的敲低抑制脂肪酶后，乳糜微粒触发的 GLUTag 细胞 GLP-1 分泌大大减少。在 GLUTag 细胞中，GW1100 和 siRNA 介导的 Ffar1 敲低均降低了乳糜微粒引起的 GLP-1 分泌，并且与 FFA1 G 偶联一致，乳糜微粒引发了 [Ca]的增加。然而，LPL 和 FFA1 抑制对鼠源培养物中乳糜微粒介导的肠促胰岛素分泌没有显著影响。此外，即使存在 GW1100，GPR119 的缺失也没有对乳糜微粒引起的 GLP-1 分泌产生影响。
结论/解释：乳糜微粒刺激 GLUTag 细胞以及人源和鼠源十二指肠培养物中肠促胰岛素激素的分泌。在 GLUTag 细胞中，该分子途径被发现涉及 LPL 介导的脂肪分解，导致释放激活 FFA1 并升高细胞内钙的脂质种类。
