Kurita Yayoi, Ohki Tsuyoshi, Soejima Eri, Yuan Xiaohong, Kakino Satomi, Wada Nobuhiko, Hashinaga Toshihiko, Nakayama Hitomi, Tani Junichi, Tajiri Yuji, Hiromatsu Yuji, Yamada Kentaro, Nomura Masatoshi
Division of Endocrinology and Metabolism, Department of Internal Medicine, Kurume University School of Medicine.
Diabetes Center of Asakura Medical Association Hospital.
Kurume Med J. 2019 May 16;65(2):55-62. doi: 10.2739/kurumemedj.MS652008. Epub 2019 Mar 11.
Aims/Introduction: Several lines of evidence suggest that dysregulation of the WNT signaling pathway is involved in the pathogenesis of type 2 diabetes. This study was performed to elucidate the effects of a high-fat/high-sucrose (HF/HS) diet on pancreatic islet functions in relation to modulation of WNT ligand expression in β-cells.
Mice were fed either standard mouse chow or a HF/HS diet from 8 weeks of age. At 20 weeks of age, intraperitoneal glucose tolerance tests were performed in both groups of mice, followed by euthanasia and isolation of pancreatic islets. WNT-related gene expression in islets and MIN6 cells was measured by quantitative real-time RT-PCR. To explore the direct effects of WNT signals on pancreatic β-cells, MIN6 cells were exposed to recombinant mouse WNT4 protein (rmWNT4) for 48 h, and glucose-induced insulin secretion was measured. Furthermore, Wnt4 siRNAs were transfected into MIN6 cells, and cell viability and insulin secretion were measured in control and Wnt4 siRNA-transfected MIN6 cells.
Mice fed the HF/HS diet were heavier and their plasma glucose and insulin levels were higher compared with mice fed standard chow. Wnt4, Wnt5b, Ror1, and Ror2 expression was upregulated, while Fzd4, Fzd5, Fzd6, Lrp5, and Lrp6 expression was downregulated in the islets of mice fed the HF/HS diet. Wnt4 was the most abundantly expressed WNT ligand in β-cells, and its expression was increased by the HF/HS diet. Although exposure to recombinant mouse WNT4 protein for 48 h did not alter glucose-induced insulin secretion, it was significantly reduced by knockdown of Wnt4 in MIN6 cells.
We demonstrated that the HF/HS diet-induced increase of WNT4 signaling in β-cells is involved in augmentation of glucose-induced insulin secretion and impaired β-cell proliferation. These results strongly indicate an essential role of WNT4 in the regulation of β-cell functions in mouse pancreatic islets.
目的/引言：多项证据表明，WNT信号通路失调参与2型糖尿病的发病机制。本研究旨在阐明高脂/高糖（HF/HS）饮食对胰岛功能的影响，以及与β细胞中WNT配体表达调节的关系。
小鼠从8周龄开始喂食标准小鼠饲料或HF/HS饮食。在20周龄时，对两组小鼠进行腹腔葡萄糖耐量试验，随后实施安乐死并分离胰岛。通过定量实时RT-PCR检测胰岛和MIN6细胞中WNT相关基因的表达。为探究WNT信号对胰腺β细胞的直接作用，将MIN6细胞暴露于重组小鼠WNT4蛋白（rmWNT4）48小时，并检测葡萄糖诱导的胰岛素分泌。此外，将Wnt4 siRNAs转染到MIN6细胞中，并检测对照和Wnt4 siRNA转染的MIN6细胞的细胞活力和胰岛素分泌。
与喂食标准饲料的小鼠相比，喂食HF/HS饮食的小鼠体重更重，其血浆葡萄糖和胰岛素水平更高。在喂食HF/HS饮食的小鼠胰岛中，Wnt4、Wnt5b、Ror1和Ror2的表达上调，而Fzd4、Fzd5、Fzd6、Lrp5和Lrp6的表达下调。Wnt4是β细胞中表达最丰富的WNT配体，其表达因HF/HS饮食而增加。虽然暴露于重组小鼠WNT4蛋白48小时不会改变葡萄糖诱导的胰岛素分泌，但在MIN6细胞中敲低Wnt4可使其显著降低。
我们证明，HF/HS饮食诱导的β细胞中WNT4信号增加参与了葡萄糖诱导的胰岛素分泌增强和β细胞增殖受损。这些结果强烈表明WNT4在调节小鼠胰腺胰岛β细胞功能中起重要作用。
