INTRACELLULAR O GLCNAC AND GLUCOTOXICITY

细胞内 O GLNAC 和葡萄糖毒性

• 批准号: 2760300
• 负责人: Jeffrey E Kudlow
• 金额: $ 22.21万
• 依托单位: UNIVERSITY OF ALABAMA AT BIRMINGHAM
• 依托单位国家: 美国
• 财政年份: 1998
• 资助国家: 美国
• 起止时间: 1998-09-30 至 2001-09-29
• 项目状态: 已结题
• 来源: https://reporter.nih.gov/project-details/2760300
• 关键词: N acetylglucosamine; acyltransferase; alloxan; animal tissue; cytotoxicity; gene expression; genetically modified animals; glucosamine; glucose metabolism; glycosylation; histopathology; hyperglycemia; immunocytochemistry; in situ hybridization; laboratory mouse; laboratory rat; noninsulin dependent diabetes mellitus; northern blottings; pancreatic islet function; pancreatic islets; posttranslational modifications

Clinical studies and studies on isolated islets or Beta cell lines have indicated that chronic exposure of the Beta cell to supraphysiological levels of glucose results in impaired Beta cell function, an important component in the pathogenesis of type 2 diabetes. How glucose exerts this toxicity upon the Beta cell remains unclear. We propose that the glucose metabolite, glucosamine plays a role in Beta cell function and this glucose toxicity. We came to this hypothesis as a result of our observations on the mechanism of toxicity of the Beta cell- specific toxin, streptozotocin (STZ). STZ is chemically analogous to N- acetylglucosamine (GlcNAc). Furthermore, we found that the Beta cell contains approximately 100-fold more of the mRNA encoding the enzyme o- GlcNAc transferase (OGT). This enzyme modifies nuclear and cytoskeletal proteins by linking the monosaccharide GlcNAc to serine or threonine residues in the protein. The resulting O-GlcNAc modification appears to modify the activity of transcription factors. We found that STZ blocks the activity of an enzyme that removes o-GlcNAc from proteins. Treatment of rats with STZ results in the accumulation of the O-GlcNAc modification specifically in the pancreatic Beta cells, hours before Beta cell death. Because the Beta cells are so richly endowed with OGT, these cells may be the most susceptible to an accumulation of O-GlcNAc on intracellular proteins. We have also shown in other cell types, that nuclear O-GlcNAc is sensitive to ambient glucose concentrations. If this is also true in the Beta cell, then hyperglycemia and STZ may both increase Beta cell O-GlcNAc content, thereby leading to a common mechanism of Beta cell toxicity. The experiments proposed in this grant are designed to determine if hyperglycemia indeed result in increased Beta cell O-GlcNAc. We will also create transgenic mouse models in which glucosamine synthesis from glucose is either augmented or decreased. We will determine the effect of these alterations in glucosamine metabolism on Beta cell function. We have also found that cAMP-dependent protein kinase inhibits the enzyme responsible for glucosamine synthesis. We propose to study the mechanism by which glucosamine synthesis is inhibited. Together, these studies will establish the role of glucosamine in glucose toxicity on the Beta cell and a means of controlling glucose metabolism to glucosamine.

关于分离胰岛或β细胞系的临床研究和研究具有 表明β细胞长期暴露于超生理学 葡萄糖水平会导致β细胞功能受损，这是一个重要的 2型糖尿病发病机理中的成分。 葡萄糖如何施加 对β细胞的这种毒性尚不清楚。 我们建议 葡萄糖代谢产物，葡萄糖胺在β细胞功能和 这种葡萄糖毒性。 由于我们的结果，我们提出了这一假设 观察β细胞特异性毒性机制 毒素，链蛋白酶（STZ）。 STZ在化学上类似于N- 乙酰葡萄糖（GLCNAC）。 此外，我们发现Beta细胞 包含编码酶O-的mRNA大约100倍 GlcNAC转移酶（OGT）。 这种酶修饰核和细胞骨架 通过将单糖GlcNAC与丝氨酸或苏氨酸联系起来，蛋白质 蛋白质中的残留物。 出现了由此产生的O-GLCNAC修饰 修改转录因子的活性。 我们发现STZ 阻断从蛋白质中去除O-GLCNAC的酶的活性。 用STZ治疗大鼠会导致O-GLCNAC的积累 在胰腺β细胞中特别修改，几小时 Beta细胞死亡。 因为Beta细胞是如此丰富的OGT，所以 这些细胞可能最容易受到O-GlCNAC的积累 在细胞内蛋白上。 我们还显示了其他细胞类型， 该核O-GLCNAC对环境葡萄糖浓度敏感。 如果在Beta细胞中也是如此，则高血糖和STZ可能 两者都会增加β细胞O-GLCNAC含量，从而导致常见 β细胞毒性的机理。 提出的实验 授予旨在确定高血糖是否确实导致 β细胞O-GLCNAC增加。 我们还将创建转基因鼠标 从葡萄糖合成葡萄糖的模型要么增强 或减少。 我们将确定这些改变的影响 葡萄糖胺代谢对β细胞功能。 我们还发现 cAMP依赖性蛋白激酶抑制了负责的酶 葡萄糖胺的合成。我们建议研究的机制 葡萄糖合成受到抑制。 这些研究将在一起 确定葡糖胺在葡萄糖毒性中的作用在β细胞上 以及控制葡萄糖代谢葡萄糖的手段。