O-GlcNAcylation of tau: glucose metabolism & neurodegen

描述(申请人提供)：大脑中tau蛋白的异常过度磷酸化和聚集是阿尔茨海默病(AD)神经退行性变的关键。阿尔茨海默病患者大脑葡萄糖摄取/代谢受损，被认为是导致神经退行性变的原因。然而，这种损伤如何导致神经退行性变尚不清楚。这个项目的具体目标是揭示tau O-GlcN酰化[一种独特的O-糖基化类型，通过它将β-N-乙酰氨基葡萄糖(GlcNAc)与蛋白质的丝氨酸或苏氨酸残基连接起来]的性质和功能，并揭示AD脑葡萄糖摄取/代谢受损导致神经退行性变的机制。这项建议的长期目标是了解阿尔茨海默病神经变性的机制，并在此基础上制定预防和治疗该疾病的策略。因此，本研究的具体目标是：(1)定位tau蛋白的O-GlcN酰化位点，并测定其在AD脑内O-GlcN酰化的变化。通过比较AD组和对照组的脑内UDP-GlcNAc水平、O-GlcNAc转移酶和O-GlcNAcase活性，研究tau O-GlcN酰化改变的根本原因。(2)研究在体外和分化的PC12细胞中，tau的O-GlcN酰化和磷酸化的相互作用。通过测定其微管结合和组装活性，以及在tau O-GlcN酰化改变时检测细胞形态和细胞器转运，来研究tau O-GlcN酰化的功能作用。(3)探讨脑葡萄糖摄取/代谢受损参与阿尔茨海默病神经退行性变的分子机制。两种脑葡萄糖摄取/代谢受损的动物模型--禁食小鼠和脑室注射松弛素B后的小鼠--将被用来研究其对tau O-GlcN酰化和磷酸化的影响。O-GlcN酰化在tau过度磷酸化和低葡萄糖摄取/代谢诱导的神经变性中的确切作用也将在小鼠脑中阐明。这些研究将揭示tau O-GlcN酰化的性质和功能作用及其在AD脑中的失调，并揭示AD脑葡萄糖摄取/代谢受损导致神经退行性变的机制。这些研究的完成将为AD的神经退变机制提供新的见解，并有助于开发新的策略来预防和治疗阿尔茨海默病，可能还有其他神经退行性疾病。

DESCRIPTION (provided by applicant): Abnormal hyperphosphorylation and aggregation of tau protein in the brain are critical to neurodegeneration of Alzheimer Disease (AD). Glucose uptake/metabolism is impaired in AD brain, which is believed to cause neurodegeneration. However, how this impairment contributes to neurodegeneration is unknown. The specific goal of this project is to reveal the nature and functional role of tau O-GlcNAcylation [a unique type of O-glycosylation by which beta-N-acetylglucosamine (GlcNAc) is linked to serine or threonine residues of proteins] and to uncover the mechanism by which impaired brain glucose uptake/metabolism of AD contributes to neurodegeneration. The long-term objective of this proposal is to understand the mechanism of neurodegeneration in AD and, based on this knowledge, to develop strategies to prevent and treat the disease. Hence, the Specific Aims are: (1) Map the O-GlcNAcylation sites of tau and determine the change of tau O-GlcNAcylation in AD brain. The underlying cause of the change in tau O-GlcNAcylation will also be studied by comparing brain level of UDP-GlcNAc and activities of O-GlcNAc transferase and O-GlcNAcase between AD and controls. (2) Study the interactions between O-GlcNAcylation and phosphorylation of tau both in vitro and in differentiated PC12 cells. The functional role of tau O-GlcNAcylation will be studied by measuring its microtubule-binding and -assembly activities and examining cell morphology and organelle transport upon alteration of tau O-GlcNAcylation. (3) Investigate the molecular mechanism by which impaired brain glucose uptake/metabolism contributes to neurodegeneration of Alzheimer's disease. Two animal models of impaired brain glucose uptake/metabolism-fasted mice and mice after intracerebroventricular injection of cytochalasin B-will be used to study its effects on tau O-GlcNAcylation and phosphorylation. The exact role of O-GlcNAcylation in tau hyperphosphorylation and neurodegeneration induced by low glucose uptake/metabolism will also be elucidated in the mouse brains. These studies will reveal the nature and functional role of tau O-GlcNAcylation and its dysregulation in AD brain and uncover the mechanism by which impaired brain glucose uptake/metabolism of AD contributes to neurodegeneration. Completion of these studies will provide new insight into the mechanism of neurodegeneration of AD and help develop novel strategies to prevent and treat Alzheimer's disease and probably other neurodegenerative disorders.