Elucidation of diabetes-related genes

Wolfram综合征是一种常染色体隐性遗传病，与糖尿病和视神经萎缩相关，是由编码内质网（ER）膜蛋白的WFS1基因突变引起的。我们在此报道wfs1缺陷小鼠的胰岛表现出pkr样ER激酶磷酸化，伴侣基因表达和活性XBP1蛋白水平的增加，表明ER应激反应增强。我们将wfsl缺陷小鼠与在β-细胞中表达猴病毒40大T抗原的小鼠杂交，建立了wfsl缺陷MIN6克隆β-细胞。这些细胞在内质网应激反应中表现出与WFS1缺陷的胰岛基本相同的变化，这种变化通过重新表达WFS1蛋白或过表达GRP78（内质网应激的主要调节剂）来逆转。相反，在wfs1缺乏的心脏、骨骼肌和棕色脂肪组织中均未观察到这些变化。内质网应激增强导致caspase 3切割增加，BrdU掺入减少，表明突变胰岛细胞凋亡过程加速，细胞周期进程受损。这些变化与wfsl缺陷胰岛和克隆β细胞中p21^<CIP1>的表达增加有关。用内质网应激诱导剂thapsigarin处理胰岛后，p21^<CIP1>的表达增加，而p21^<CIP1>的强制表达减少了MIN6 β-细胞的数量，提示内质网应激诱导的p21^<CIP1>表达的增加参与了突变型胰岛中β-细胞的损失。这些数据表明，wfs1缺乏特异性激活β-细胞内质网应激反应，通过增加凋亡和细胞周期进展受损导致β-细胞损失。

Wolfram syndrome, an autosomal recessive disorder associated with diabetes mellitus and optic atrophy is caused by mutations in the WFS1 gene encoding an endoplasmic reticulum (ER) membrane protein. We herein report that pancreatic islets of wfs1-deficient mice exhibit increases in PKR-like ER kinase phosphorylation, chaperone gene expressions and active XBP1 protein levels, indicating an enhanced ER stress response. We established wfsl-deficient MIN6 clonal β-cells by crossing wfsl-deficient mice with mice expressing simian virus 40 large T antigen in β-cells. These cells show essentially the same alterations in ER stress responses as wfsl-deficient islets, which were reversed by re-expression of WFS1 protein or overexpression of GRP78, a master regulator of ER stress. In contrast, these changes are observed neither in heart, skeletal muscle, nor brown adipose tissues with WFS1-deficiency. The enhanced ER stress results in increased caspase 3 cleavage and reduced BrdU incorporation, indicating accelerated apoptotic processes and impaired cell cycle progression in the mutant islets. These changes are associated with increased expression of p21^<CIP1> in wfsl-deficient islets and clonal β-cells. Treatment of islets with thapsigargin, an ER stress inducer increased p21^<CIP1> expression, and forced expression of p21^<CIP1> reduced MIN6 β-cell numbers, suggesting that the ER stress-induced increase in p21^<CIP1> expression to be involved in β-cell loss in the mutant islets. These data indicate that WFS1-deficiency activates the ER stress response specifically in β-cells, causing β-cell loss through increased apoptosis and impaired cell cycle progression.