激活TRPV1促进GLP-1分泌降低血糖的分子机制

Glucagon-like peptide 1 (GLP-1) has the function of promoting glucose-dependent insulin secretion and multiple outside the pancreas functions, and has become a new target of diabetes treatment. Recently it is reported that capsaicin can reduce the weight, produce anti-inflammatory effect and improve endothelial function through activating TRPV1. Furthermore, it can promote insulin secretion, reduce blood glucose and relieve obesity-induced insulin resistance in rats. But whether capsaicin promote gastrointestinal endogenous GLP-1 secretion is still unclear. Our study found that TRPV1 knockout mice has a significant decrease insulin levels and show the impaired glucose tolerance, and capsaicin can promote the release of GLP-1 in intestinal endocrine tumor cells in mice. So, we hypothesis capsaicin can activate TRPV1 to cause calcium signal change in intestinal L cell and activate CaM/cAMP-PKA/Raf-1 / MAPK signaling pathways to promote GLP-1 secretion. To confirm our assumptions, we plan to take the db/db mice and TRPV1 knockout mice as the research models, to discuss the mechanism of TRPV1 promoting GLP-1 secretion from the whole, cellular and molecular levels, provide the theory evidence for clinical diabetes control. As the dietary factors, capsaicin intervention is expected to become a new strategy for diabetes prevention and control.

胰高血糖素样肽-1(GLP-1)具有葡萄糖依赖性的促胰岛素分泌及多重胰腺外作用，已成为糖尿病治疗的新靶点。最近报道辣椒素通过激活TRPV1，能减轻体重、抗炎和改善血管内皮功能等作用，还可促进大鼠胰岛素分泌、降低血糖，减轻肥胖诱导的胰岛素抵抗。但辣椒素是否促进肠道内源性GLP-1分泌尚不清楚。我们研究发现TRPV1基因敲除小鼠胰岛素水平显著下降，糖耐量降低，辣椒素能促进小鼠肠道内分泌肿瘤细胞释放GLP-1。因此，我们设想膳食因子辣椒素干预能激活TRPV1引发肠道L细胞内钙信号改变，激活CaM/cAMP-PKA/Raf-1/MAPK信号通路，促进GLP-1分泌。为证实上述假设，我们拟以db/db小鼠及TRPV1基因敲除小鼠为研究对象，从整体、细胞和分子水平探讨TRPV1促进GLP-1分泌的机制，为临床糖尿病人群防治提供理论依据，膳食因子辣椒素干预有望成为防治糖尿病的新策略。

我们按照课题研究计划，以膳食因子辣椒素激活TRPV1引发肠道L细胞内钙信号改变，促进GLP-1分泌为核心，以db/db小鼠、TRPV1-/-小鼠、原代培养小鼠肠道内分泌肿瘤细胞（STC-1细胞）和WT（C57BL/6J）小鼠回肠为研究对象，从整体、离体水平探讨TRPV1促进GLP-1分泌，发挥降糖作用的机制进行了系列研究。取得的重要研究成果如下：.1、证实了TRPV1和GLP-1在STC-1细胞和WT（C57BL/6J）小鼠回肠均有表达；TRPV1受体激动剂——辣椒素刺激STC-1细胞内GLP-1的释放是剂量依赖性模式，且可被TRPV1特异性阻断剂capsazepine和iRTX阻断，这明确了TRPV1在STC-1细胞及小鼠回肠中对GLP-1分泌的促进作用。.2、阐明了辣椒素干预WT小鼠激活TRPV1刺激GLP-1的分泌，改善葡萄糖耐量，降低24小时动态血糖，TRPV1-/-小鼠上述指标无变化；膳食辣椒素改善db/db小鼠的高血糖状态，减轻体重，改善胰岛素抵抗；无论是急性刺激，还是长期干预，上述作用均存在。提示辣椒素以TRPV1依赖的模式，促进GLP-1的分泌。.3、证实了辣椒素刺激STC-1细胞内GLP-1分泌是通过TRPV1介导的Ca2+浓度的升高所致，且有电压依赖性Ca2+通道参与；分别利用TRPV1通路蛋白阻断剂干预后该效应被显著抑制。提示辣椒素激活CaM，引起cAMP依赖的PKA活化，通过调节Raf-1/MAPK活性，促进GLP-1分泌。.4、揭示了TRPV1的激活是通过增加细胞中的Ca2+含量增加AMPK的磷酸化和SIRT1的活性从而促进GLP-1的合成和分泌的。阻止AMPK磷酸化或者抑制SIRT1的活性能够以TRPV1非依赖的方式阻断capsaicin所造成的GLP-1合成和分泌。从而证实了我们的设想——膳食因子辣椒素干预能激活TRPV1引发肠道L细胞内钙信号改变，激活CaM/cAMP-PKA/Raf-1/MAPK信号通路，促进GLP-1分泌。