Comprehensive Diabetes Center, Department of Medicine, Division of Endocrinology, Diabetes and Metabolism, University of Alabama at Birmingham, Birmingham, AL 35294, USA.
Comprehensive Diabetes Center, Department of Medicine, Division of Endocrinology, Diabetes and Metabolism, University of Alabama at Birmingham, Birmingham, AL 35294, USA.
Mol Metab. 2016 Sep 30;5(12):1208-1215. doi: 10.1016/j.molmet.2016.09.010. eCollection 2016 Dec.
Carbohydrate-response element-binding protein (ChREBP) is the major transcription factor conferring glucose-induced gene expression in pancreatic islets, liver and adipose tissue. Recently, a novel ChREBP isoform, ChREBP-β, was identified in adipose tissue and found to be also expressed in islets and involved in glucose-induced beta cell proliferation. However, the physiological function of this less abundant β-isoform in the islet, and in diabetes, is largely unknown. The aims of the present study, therefore, were to determine how diabetes affects ChREBP-β and elucidate its physiological role in pancreatic beta cells.
Non-obese diabetic and obese, diabetic ob/ob mice were used as models of T1D and T2D and human islets and the rat INS-1 beta cell line were exposed to low/high glucose and used for ChREBP isoform-specific gain-and-loss-of-function experiments. Changes in ChREBP-β and ChREBP-α were assessed by qRT-PCR, immunoblotting, promoter luciferase, and chromatin immunoprecipitation studies.
Expression of the ChREBP-β isoform was highly induced in diabetes and by glucose, whereas ChREBP-α was downregulated. Interestingly, ChREBP-β gain-of-function experiments further revealed that it was ChREBP-β that downregulated ChREBP-α through a negative feedback loop. On the other hand, ChREBP-β knockdown led to unabated ChREBP-α activity and glucose-induced expression of target genes, suggesting that one of the physiological roles of this novel β-isoform is to help keep glucose-induced and ChREBP-α-mediated gene expression under control.
We have identified a previously unappreciated negative feedback loop by which glucose-induced ChREBP-β downregulates ChREBP-α-signaling providing new insight into the physiological role of islet ChREBP-β and into the regulation of glucose-induced gene expression.
碳水化合物反应元件结合蛋白（ChREBP）是赋予胰岛、肝脏和脂肪组织葡萄糖诱导基因表达的主要转录因子。最近，在脂肪组织中发现了一种新型 ChREBP 同工型 ChREBP-β，并且发现其也在胰岛中表达，并参与葡萄糖诱导的β细胞增殖。然而，这种在胰岛中含量较少的β-同工型在糖尿病中的生理功能在很大程度上尚不清楚。因此，本研究的目的是确定糖尿病如何影响 ChREBP-β，并阐明其在胰腺β细胞中的生理作用。
使用非肥胖型糖尿病（NOD）和肥胖型、糖尿病 ob/ob 小鼠作为 1 型糖尿病（T1D）和 2 型糖尿病（T2D）模型，以及人胰岛和大鼠 INS-1β细胞系，暴露于低/高葡萄糖，并进行 ChREBP 同工型特异性增益和功能丧失实验。通过 qRT-PCR、免疫印迹、启动子荧光素酶和染色质免疫沉淀研究评估 ChREBP-β 和 ChREBP-α 的变化。
ChREBP-β 同工型的表达在糖尿病和葡萄糖作用下高度诱导，而 ChREBP-α 则下调。有趣的是，ChREBP-β 功能获得实验进一步表明，正是 ChREBP-β 通过负反馈回路下调 ChREBP-α。另一方面，ChREBP-β 敲低导致 ChREBP-α 活性和葡萄糖诱导的靶基因表达不受抑制，这表明这种新型β-同工型的生理作用之一是帮助控制葡萄糖诱导的和 ChREBP-α 介导的基因表达。
我们已经确定了一个以前未被认识的负反馈回路，即葡萄糖诱导的 ChREBP-β 下调 ChREBP-α 信号，为胰岛 ChREBP-β 的生理作用以及葡萄糖诱导的基因表达的调节提供了新的见解。
