da Silva Xavier Gabriela, Loder Merewyn K, McDonald Angela, Tarasov Andrei I, Carzaniga Raffaella, Kronenberger Katrin, Barg Sebastian, Rutter Guy A
Section of Cell Biology, Division of Medicine, Faculty of Medicine, Imperial College, London, UK.
Diabetes. 2009 Apr;58(4):894-905. doi: 10.2337/db08-1187. Epub 2009 Jan 23.
Polymorphisms in the human TCF7L2 gene are associated with reduced insulin secretion and an increased risk of type 2 diabetes. However, the mechanisms by which TCF7L2 affect insulin secretion are still unclear. We define the effects of TCF7L2 expression level on mature beta-cell function and suggest a potential mechanism for its actions.
TCF7L2 expression in rodent islets and beta-cell lines was altered using RNAi or adenoviral transduction. Beta-cell gene profiles were measured by quantitative real-time PCR and the effects on intracellular signaling and exocytosis by live cell imaging, electron microscopy, and patch clamp electrophysiology.
Reducing TCF7L2 expression levels by RNAi decreased glucose- but not KCl-induced insulin secretion. The glucose-induced increments in both ATP/ADP ratio and cytosolic free Ca2+ concentration ([Ca2+]i) were increased compared with controls. Overexpression of TCF7L2 exerted minor inhibitory effects on glucose-regulated changes in [Ca2+]i and insulin release. Gene expression profiling in TCF7L2-silenced cells revealed increased levels of mRNA encoding syntaxin 1A but decreased Munc18-1 and ZnT8 mRNA. Whereas the number of morphologically docked vesicles was unchanged by TCF7L2 suppression, secretory granule movement increased and capacitance changes decreased, indicative of defective vesicle fusion.
TCF7L2 is involved in maintaining expression of beta-cell genes regulating secretory granule fusion. Defective insulin exocytosis may thus underlie increased diabetes incidence in carriers of the at-risk TCF7L2 alleles.
人类TCF7L2基因的多态性与胰岛素分泌减少及2型糖尿病风险增加有关。然而，TCF7L2影响胰岛素分泌的机制仍不清楚。我们确定了TCF7L2表达水平对成熟β细胞功能的影响，并提出了其作用的潜在机制。
使用RNA干扰或腺病毒转导改变啮齿动物胰岛和β细胞系中TCF7L2的表达。通过定量实时PCR测量β细胞基因谱，并通过活细胞成像、电子显微镜和膜片钳电生理学研究对细胞内信号传导和胞吐作用的影响。
RNA干扰降低TCF7L2表达水平可减少葡萄糖诱导而非氯化钾诱导的胰岛素分泌。与对照组相比，葡萄糖诱导的ATP/ADP比值和胞质游离钙离子浓度（[Ca2+]i）升高。TCF7L2的过表达对[Ca2+]i和胰岛素释放的葡萄糖调节变化产生轻微抑制作用。TCF7L2沉默细胞中的基因表达谱显示，编码突触融合蛋白1A的mRNA水平升高，但Munc18-1和锌转运体8（ZnT8）mRNA水平降低。虽然TCF7L2抑制对形态学上对接的囊泡数量没有影响，但分泌颗粒运动增加而电容变化减少，表明囊泡融合存在缺陷。
TCF7L2参与维持调节分泌颗粒融合的β细胞基因的表达。因此，胰岛素胞吐缺陷可能是携带风险TCF7L2等位基因者糖尿病发病率增加的基础。
