Division of Endocrinology, Diabetes, and Metabolism and the Department of Medicine, University of Vermont, Burlington, Vermont, USA.
Diabetes. 2010 Jun;59(6):1445-50. doi: 10.2337/db09-1655. Epub 2010 Mar 23.
We previously showed that peroxisome proliferator-activated receptor (PPAR)-gamma in beta-cells regulates pdx-1 transcription through a functional PPAR response element (PPRE). Gene Bank blast for a homologous nucleotide sequence revealed the same PPRE within the rat glucose-dependent insulinotropic polypeptide receptor (GIP-R) promoter sequence. We investigated the role of PPARgamma in GIP-R transcription.
Chromatin immunoprecipitation assay, siRNA, and luciferase gene transcription assay in INS-1 cells were performed. Islet GIP-R expression and immunohistochemistry studies were performed in pancreas-specific PPARgamma knockout mice (PANC PPARgamma(-/-)), normoglycemic 60% pancreatectomy rats (Px), normoglycemic and hyperglycemic Zucker fatty (ZF) rats, and mouse islets incubated with troglitazone.
In vitro studies of INS-1 cells confirmed that PPAR-gamma binds to the putative PPRE sequence and regulates GIP-R transcription. In vivo verification was shown by a 70% reduction in GIP-R protein expression in islets from PANC PPARgamma(-/-) mice and a twofold increase in islets of 14-day post-60% Px Sprague-Dawley rats that hyperexpress beta-cell PPARgamma. Thiazolidinedione activation (72 h) of this pathway in normal mouse islets caused a threefold increase of GIP-R protein and a doubling of insulin secretion to 16.7 mmol/l glucose/10 nmol/l GIP. Islets from obese normoglycemic ZF rats had twofold increased PPARgamma and GIP-R protein levels versus lean rats, with both lowered by two-thirds in ZF rats made hyperglycemic by 60% Px.
Our studies have shown physiologic and pharmacologic regulation of GIP-R expression in beta-cells by PPARgamma signaling. Also disruption of this signaling pathway may account for the lowered beta-cell GIP-R expression and resulting GIP resistance in type 2 diabetes.
我们之前已经证明，β细胞中的过氧化物酶体增殖物激活受体（PPAR）-γ通过功能性 PPAR 反应元件（PPRE）调节 PDX-1 转录。基因库同源核苷酸序列的比对揭示了大鼠葡萄糖依赖性胰岛素释放肽受体（GIP-R）启动子序列中存在相同的 PPRE。我们研究了 PPARγ在 GIP-R 转录中的作用。
在 INS-1 细胞中进行染色质免疫沉淀测定、siRNA 和荧光素酶基因转录测定。在胰腺特异性 PPARγ敲除小鼠（PANC PPARγ（-/-））、正常血糖 60%胰腺切除术大鼠（Px）、正常血糖和高血糖 Zucker 肥胖（ZF）大鼠以及用曲格列酮孵育的小鼠胰岛中进行胰岛 GIP-R 表达和免疫组织化学研究。
体外研究证实，PPAR-γ与假定的 PPRE 序列结合并调节 GIP-R 转录。体内验证是通过 PANC PPARγ（-/-）小鼠胰岛中 GIP-R 蛋白表达减少 70%和 14 天 60% Px Sprague-Dawley 大鼠胰岛中β细胞 PPARγ过度表达导致 GIP-R 增加两倍来显示的。该途径的噻唑烷二酮激活（72 小时）导致正常小鼠胰岛中 GIP-R 蛋白增加三倍，胰岛素分泌增加至 16.7mmol/l 葡萄糖/10nmol/l GIP。与瘦鼠相比，肥胖正常血糖 ZF 大鼠的胰岛中 PPARγ和 GIP-R 蛋白水平增加了两倍，而通过 60% Px 使 ZF 大鼠高血糖，两者降低了三分之二。
我们的研究表明，PPARγ信号对β细胞中 GIP-R 表达具有生理和药理学调节作用。此外，该信号通路的破坏也可能导致 2 型糖尿病中β细胞 GIP-R 表达降低和 GIP 抵抗。
