Pax6突变杂合子小鼠糖代谢异常的分子机制  

The molecular mechanism of abnormal glucose metabolism in heterozygous Pax6 mutant mice

作　　者：陈园园[1] 洪天配[1] 文锦华[1] 丁钧[1] 高翔[1] 李凌松[2] 

机构地区：[1]北京大学第三医院内分泌科,北京大学干细胞研究中心,100191 [2]南京大学模式动物研究所

出　　处：《中国糖尿病杂志》2009年第5期335-339,共5页Chinese Journal of Diabetes

基　　金：国家自然科学基金资助项目(30771032,30700879,30871251);北京市自然科学基金资助项目(7062067);国家973计划资助项目(2006CB503900);国家863计划资助项目(2006AA02A112)

摘　　要：目的探讨Pax6突变杂合子小鼠是否存在糖代谢异常,并对其分子机制进行研究。方法采用腹腔注射葡萄糖耐量试验(IPGTT),观察Pax6突变杂合子小鼠血糖和胰岛素原/总胰岛素比值的变化,胰岛素耐量试验(ITT)分析胰岛素敏感性的变化;小鼠离体胰岛采用定量PCR和Western印迹分析检测激素原转化酶1(PC1)表达;小鼠胰岛β细胞系用于染色质免疫共沉淀Ch1P分析以确定PAX6蛋白能否与Pc1基因启动子区域相结合,进而采用荧光素酶报告分析观察Pax6突变对Pc1基因表达的影响。结果与野生型小鼠相比,Pax6突变杂合子小鼠在6月龄时存在明显的负荷后高血糖,胰岛素敏感性未见显著变化,胰岛素原/总胰岛素比值不适当升高早于负荷后高血糖,类似人类Pax6基因突变的无虹膜症患者中糖代谢异常的表型特征。Pax6突变杂合子小鼠胰岛中PC1表达水平显著降低。PAX6蛋白可直接结合到Pc1基因启动子区域,野生型PAX6可上调Pc1表达,而突变型PAX6则无此作用。结论 PAX6通过PC1介导的胰岛素原剪切加工调控葡萄糖代谢,这是PAX6的一种新功能。PC1缺乏引起的胰岛素原剪切加工缺陷是Pax6突变导致葡萄糖代谢异常的最重要分子机制之一。Objective To investigate the phenotype of abnormal glucose metabolism and its molecular mechanism in heterozygous Pax6 mutant mice. Methods Heterozygous Pax6 mutant mice were examined for plasma glucose levels and proinsulin/total insulin ratio after intraperitoneal glucose tolerance test （IPGTT）. Insulin sensitivity was evaluated by insulin tolerance test （ITT）. Islets isolated from the mouse pancreata were used to detect the expression of prohormone convertase 1 （PC1） by semiquantitative PCR and Western blot. In order to determine if PAX6 protein binds to Pcl promoter region in a mouse f-cell line, chromatin immunoprecipitation assay was performed. The effects of Pax6 mutation on the Pcl gene expression were analyzed by luciferase reporter assay. Results The heterozygous Pax6 mutant mice in 6-month-old obviously exhibited post-load hyperglycemia compared with wild-type mice, although insulin sensitivity was unchanged. Their post-load hyperglycemia was preceded by an inappropriately elevated plasma proinsulin/total insulin ratio. These findings resemble the glucose intolerance phenotype in aniridia patients with PAX6 mutation. The levels of PC1 expression were significantly decreased in the islets of the heterozygous mice. The binding of PAX6 protein to the Pcl promoter was shown in the Q-cell line. Wild-type PAX6, but not the mutant form, was found to upregulate the expression of Pcl. Conclusions PAX6 regulates glucose metabolism via proinsulin processing mediated by PC1, which is a novel function for this transcription factor. Defective proinsulin processing secondary to PC1 deficiency is one of the most important molecular mechanisms for abnormal glucose metabolism caused by heterozygous Pax6 mutations.

关 键 词：PAX6 激素原转化酶1 葡萄糖代谢 胰岛素原 

分 类 号：R341[医药卫生—基础医学]