ChREBP Isoforms in Pancreatic Beta Cells

胰腺 β 细胞中的 ChREBP 亚型

• 批准号: 9914106
• 负责人: DONALD K. SCOTT
• 金额: $ 41.19万
• 依托单位: ICAHN SCHOOL OF MEDICINE AT MOUNT SINAI
• 依托单位国家: 美国
• 财政年份: 2017
• 资助国家: 美国
• 起止时间: 2017-04-18 至 2021-03-31
• 项目状态: 已结题
• 来源: https://reporter.nih.gov/project-details/9914106
• 关键词: Adenoviruses; Adipose tissue; Alternative Splicing; Apoptosis; Beta Cell; Binding; Binding Proteins; Carbohydrates; Cell Death; Cell Nucleus; Cell Proliferation; Cell physiology; Data; Diabetes Mellitus; Gene Expression; Genes; Genetic Transcription; Glucose; Goals; Human; Hyperglycemia; In Vitro; Insulin-Dependent Diabetes Mellitus; Islet Cell; Islets of Langerhans Transplantation; Lead; Length; Liver; LoxP-flanked allele; Mediator of activation protein; Molecular; Mus; Non-Insulin-Dependent Diabetes Mellitus; Nuclear; Nuclear Export; Outcome; Pathway interactions; Physiological; Protein Isoforms; Research Personnel; Response Elements; Rodent; SCID Mice; Signal Transduction; Streptozocin; Structure of beta Cell of islet; System; Testing; Therapeutic; Toxic effect; Transplantation; Viral; blood glucose regulation; diabetic; gain of function; gene product; glucose metabolism; improved; in vivo; insulin sensitivity; islet; lipid biosynthesis; loss of function; novel; overexpression; promoter; tool

Expansion of functional pancreatic beta cell mass is a major therapeutic goal for both Type 1 and Type 2 diabetes. Glucose is a key physiological driver of adaptive beta cell mass expansion, promoting beta cell proliferation both in vitro and in vivo. We have been studying mechanisms of glucose-regulated gene expression for nearly two decades. In 2012 we found that carbohydrate response element binding protein (ChREBP; Mlxipl) is required for glucose-stimulated beta cell proliferation in both rodent and human beta cells. That same year, our co-investigator (Dr. Mark Herman) discovered that ChREBP exists as 2 major isoforms. ChREBPα is the full-length form that is mostly cytoplasmic and repressed in low glucose. ChREBPβ is a product of alternative splicing, with the nuclear export signals and the low glucose inhibitory domain removed. Consequently, ChREBPβ is mostly nuclear, and is constitutively and potently active. ChREBPβ transcription is induced by a powerful carbohydrate response element after activation of the glucose-responsive ChREBPα, creating a vigorous feed-forward loop (Fig. 1). Remarkably, in every system studied in detail, the induction of ChREBPβ is the molecular engine that drives the major physiological effects of ChREBP. In adipose tissue or liver, induction of ChREBPβ increases de novo lipogenesis and either increases or decreases insulin sensitivity, respectively.. In beta cells, we recently showed that the exponential induction of ChREBPβ - from a nearly undetectable level to amounts comparable to ChREBPα - is required for glucose-stimulated proliferation. Strikingly, however, overexpression of ChREBPβ in beta cells, as may happen with prolonged hyperglycemia or by ectopic viral expression, results in beta cell apoptosis. In stark contrast, overexpression of ChREBPα amplifies glucose-stimulated beta cell proliferation without cell death. Our overarching hypothesis is that the ratio of ChREBPα to ChREBPβ abundance is critically important for beta cell function, both for beta cell mass expansion and, when dysregulated, as a mediator of glucose toxicity. We will test our hypothesis by performing the following Specific Aims: (1) Determine the effects of increasing or decreasing the abundance of ChREBPβ specifically in beta cells on beta cell mass and glucose homeostasis; (2) Determine if exogenous expression of ChREBPα or ChREBPβ in human islets improves or worsens islet transplantation outcomes; and (3) Determine how the ratio of ChREBPα to ChREBPβ controls the fate of beta cells. This application uses novel tools that will provide an essential mechanistic understanding of transcriptional glucose sensing that will inform therapies to expand and protect beta cell mass.

扩大功能性胰岛β细胞团是1型和2型糖尿病的主要治疗目标。葡萄糖是适应性胰岛细胞大量扩增的关键生理驱动力，在体外和体内都能促进胰岛细胞的增殖。近二十年来，我们一直在研究葡萄糖调节基因表达的机制。2012年，我们发现糖反应元件结合蛋白(ChREBP；MLXIPL)是葡萄糖刺激的啮齿动物和人类β细胞增殖所必需的。同年，我们的合作者(Mark Herman博士)发现ChREBP以两种主要亚型存在。ChREBPα是一种全长形式，主要存在于细胞质中，在低糖中被抑制。ChREBPβ是选择性剪接的产物，去除了核输出信号和低糖抑制结构域。因此，ChREBPβ主要是核的，并且具有结构性和潜在的活性。ChREBPβ转录是由一个强大的碳水化合物反应元件诱导的，在激活葡萄糖响应的ChREBPα后，创建了一个强大的前馈环(图1)。值得注意的是，在每个详细研究的系统中，ChREBPβ的诱导是驱动ChREBP主要生理效应的分子引擎。在脂肪组织或肝脏中，诱导ChREBPβ增加新生脂肪生成，或增加或降低胰岛素敏感性。在β细胞中，我们最近发现，ChREBPβ的指数诱导--从几乎检测不到的水平到与ChREBPα相当的数量--是葡萄糖刺激的增殖所必需的。然而，引人注目的是，在贝塔细胞中过表达ChREBPβ，就像长期高血糖或异位病毒表达可能发生的那样，导致贝塔细胞凋亡。与之形成鲜明对比的是，过度表达ChREBPα可以增强葡萄糖刺激的β细胞增殖，而不会导致细胞死亡。我们的主要假设是，ChREBPα和ChREBPβ丰度的比率对于β细胞功能至关重要，无论是对于β细胞质量的扩张，还是当调控失调时，作为葡萄糖毒性的中介。我们将通过以下方式验证我们的假设 执行以下具体目标：(1)确定增加或减少丰度的影响 目的：(1)确定在胰岛细胞中特异性表达ChREBPβ对胰岛细胞质量和葡萄糖动态平衡的影响；(2)确定外源ChREBPα或ChREBPβ在人胰岛中的表达是改善还是恶化胰岛移植的结果；以及(3)确定ChREBPα和ChREBPβ的比例如何控制β细胞的命运。这项应用使用了新的工具，将提供对转录葡萄糖感应的基本机械理解，这将为扩大和保护β细胞团的治疗提供信息。