探讨FXR通过TRPA1介导胃旁路手术增进胰岛素1相分泌的机制

The hallmark of type 2 diabetes mellitus is loss of 1st phase of glucose-stimulated insulin secretion. It has been found that Roux-en-Y gastric bypass (RYGB) signifcantly potentiates 1st phase of insulin secretion. However, the mechanisms underlying remain largely unknown. It is known that FXR (farsenoid-X receptor) is reponsible for the improved glycemic control by RYGB. TRPA1 (transient receptor potential ankyrin 1) is non-selective cation channel and the major TRP channel in pancreatic β-cells. Stimulation of TRPA1 channel leads to membrane depolarization and insulin secretion. Our data show that TRPA1 channel is implicated in glucose-stimulated electrical firing and insulin secretion. TRPA1 expression is decreased in pancreatic β-cells of diabetic GK rats. By contrast, TRPA1 is essentially increased after RYGB operation, accompanied by increased FXR level. Moreover, we have found that FXR binds to TRPA1 promoter directly; thus stimulation of FXR increases TRPA1 expression. Therefore we would use molecular biological and electrophyisological approaches in this study to explore①if FXR and TRPA1 are involved in RYGB-enhanced 1st of insulin secretion;②how does FXR epigenetically regulate TRPA1 expression;③if TRPA1 is implicated in stimulus-secretion coupling and acidification of insulin-containing granules,which results in enlarged 1st phase of insulin secretion. These results will shed light on revealing the cellular mechanisms underlying RYGB-potentiated β-cell function.

2型糖尿病重要特征之一是葡萄糖诱导的胰岛素1相分泌缺失，胃旁路术（RYGB）恢复糖尿病胰岛素的1相分泌但机制不清楚。研究发现胃旁路手术对机体代谢的调节作用由胆汁酸受体FXR介导。我们的前期工作显示胃旁路手术提高胰岛FXR的表达，而FXR通过结合TRPA1启动子增高β细胞TRPA1的表达。TRPA1是β细胞表达的主要的非选择性阳离子通道，我们进一步发现TRPA1激动剂增进葡萄糖诱导的胰岛素1相分泌；而其抑制剂抑制葡萄糖诱导的β细胞兴奋和胰岛素分泌,同时也抑制RYGB的降糖效应。以此为基础，我们将采用分子生物学、电生理等方法探讨①FXR和TRPA1是否参与胃旁路术增进胰岛素1相分泌；②FXR如何调节TRPA1的表达；③TRPA1通过何种机制兴奋β细胞、增进胰岛素1相分泌。研究结果将为揭示胃旁路术促进糖尿病胰岛β细胞功能，恢复胰岛素1相分泌的机理提供新理论。

本课题完成项目申报书的研究内容，利用TRPA1基因敲出小鼠等模型，我们证实TRPA1参与葡萄糖刺激的β细胞的去极化和胰岛素1相分泌，是刺激-分泌偶联机制的重要环节；胃旁路手术的糖尿病大鼠模型、FXR基因敲出小鼠我们首次报道TRPA1是胆汁酸核受体FXR调节的靶基因，激活FXR表观遗传增进TRPA1启动子的乙酰化水平，增进TRPA1的表达。胃旁路手术通过胆汁酸- FXR-TPRA1轴恢复糖尿病胰岛β细胞葡萄糖的反应能力，从而改善糖尿病胰岛β细胞胰岛素 1 相分泌。除完成该项目申报书的研究内容外，我们还发现胃旁路手术通过FXR-GLP1R轴 , FXR-ADCY8轴增进糖尿病胰岛B细胞GLP-1的敏感性，也参与胃旁路手术增进胰岛B细胞功能机制。我们进一步发现B细胞GLP-1信号增强导致B细胞数量增多，其作用主要通过通过抑制转录调节因子menin促进胰岛B细胞的增值；此外，抑制menin也通过表观遗传促进胰岛前体细胞的分化，增进胰岛B细胞数量。在Molecular Metabolism，Diabetes，JCB等专业学术期刊发表论文5篇。