Reduced insulin secretion in WFS1-deficient mice may be related to downregulation of Trpm5

Wolfram syndrome, an autosomal recessive disorder characterized by juvenile-onset diabetes mellitus and optic atrophy, is caused by mutations in the WFS1 gene. WFS1 encodes an endoplasmic reticulum resident transmembrane protein. The Wfs1-null mice exhibit progressive insulin deficiency and diabetes. The aim of the present study was to describe the insulin secretion and transcriptome of pancreatic islets in WFS1-deficient mice. WFS1-deficient (Wfs1KO) mice had considerably less pancreatic islets than heterozygous (Wfs1HZ) or wild-type (WT) mice. Wfs1KO pancreatic islets secreted less insulin after stimulation with 2 and 10 mM glucose and with tolbutamide solution compared to WT and Wfs1HZ islets, but not after stimulation with 20 mM glucose. Differences in proinsulin amount were not statistically significant although there was a trend that Wfs1KO had an increased level of proinsulin. After stimulation with 2 mM glucose solution the proinsulin/insulin ratio in Wfs1KO was significantly higher than that of WT and Wfs1HZ. RNA-seq from pancreatic islets found melastatin-related transient receptor potential subfamily member 5 protein gene (Trpm5) to be downregulated in WFS1-deficient mice. Functional annotation of RNA sequencing results showed that WFS1 deficiency influenced significantly the pathways related to tissue morphology, endocrine system development and function, molecular transport network. These findings suggest an interactive role of WFS1 and TRPM5 in insulin secretion. 12 samples: three genotypes, 4 individuals in each genotype沃尔夫勒姆综合征（Wolfram syndrome）是一类以青少年起病糖尿病与视神经萎缩为特征的常染色体隐性遗传病，其致病机制为WFS1基因发生突变。WFS1基因编码一种内质网驻留跨膜蛋白。Wfs1基因敲除（Wfs1-null）小鼠可表现出进行性胰岛素缺乏与糖尿病表型。本研究旨在描述WFS1缺陷小鼠胰岛的胰岛素分泌功能与转录组特征。WFS1缺陷型（Wfs1KO）小鼠的胰岛数量显著少于杂合子型（Wfs1HZ）与野生型（WT）小鼠。相较于WT与Wfs1HZ小鼠的胰岛，Wfs1KO胰岛在经2mM、10mM葡萄糖及甲苯磺丁脲刺激后，胰岛素分泌量显著降低，但经20mM葡萄糖刺激时则无此差异。尽管Wfs1KO小鼠的胰岛素原水平存在升高趋势，但两组间胰岛素原含量的差异未达到统计学显著性水平。经2mM葡萄糖溶液刺激后，Wfs1KO小鼠的胰岛素原/胰岛素比值显著高于WT及Wfs1HZ小鼠。对胰岛进行的RNA测序（RNA-seq）结果显示，瞬时受体电位阳离子通道亚家族M成员5基因（Trpm5）在WFS1缺陷小鼠中表达下调。对RNA测序结果的功能注释分析显示，WFS1缺陷可显著影响与组织形态、内分泌系统发育与功能、分子转运网络相关的通路。上述研究结果提示，WFS1与TRPM5在胰岛素分泌过程中存在相互调控作用。本研究共纳入12个样本，涵盖3种基因型，每种基因型各包含4个个体。