Abnormal Hyperphosphorylation of Tau

描述（由申请人提供）：本提案的总体目标是了解异常高磷酸化tau蛋白的神经原纤维变性的分子机制，并基于此知识，确定阿尔茨海默病（AD），唐氏综合征和其他以该脑病变为特征的tau病的特异性治疗靶点。调节tau蛋白磷酸化的蛋白磷酸酶(PP)-2A的活性反过来部分受其抑制剂I2PP2A的调节。在很大比例的AD脑神经元中，I2PP2A从其最初定位的细胞核转移到细胞质中。由于PP-2A和tau定位于细胞质中，I2PP2A在AD脑中的细胞质定位增加解释了PP-2A、tau过度磷酸化和神经原纤维缠结形成的抑制。我们建议(1)研究正常神经元中I2PP2A的核定位与胞质定位的分子机制。将确定介导I2PP2A进出细胞核的转运因子（核丝蛋白），以及与这些因子相互作用的I2PP2A结构域；(2)阐明阿尔茨海默病中神经元I2PP2A定位改变的原因。我们将研究在AD大脑中发生的I2PP2A断裂对I2PP2A与转运因子相互作用的影响。我们还将研究I2PP2A与其他可溶性和固定蛋白的相互作用对I2PP2A在正常和AD大脑中的定位的影响，以及I2PP2A磷酸化的作用；(3)在诱导表达系统的控制下，产生表达n端一半I2PP2A（在AD脑神经元细胞质中观察到）或该蛋白定位于细胞核的控制变体的转基因小鼠。这些转基因对PP-2A活性、PP-2A调控的tau激酶活性、tau异常过磷酸化以及神经变性和认知障碍的影响将被研究。这些研究将有助于阐明神经原纤维变性的机制，并确定一个或多个治疗靶点。这些研究还将导致产生牛头病变的细胞和动物模型，可用于开发以这种病变为特征的疾病的治疗药物。

DESCRIPTION (provided by applicant): The overall objective of this proposal is to understand the molecular mechanism of neurofibrillary degeneration of abnormally hyperphosphorylated tau protein and, based on this knowledge, identify specific therapeutic targets for Alzheimer disease (AD), Down syndrome and other tauopathies which are characterized by this brain lesion. The activity of protein phosphatase (PP)-2A, which regulates phosphorylation of tau, is in turn regulated partly by its inhibitor I2PP2A. In a large percentage of neurons in AD brain, I2PP2A is translocated from its primary localization in the nucleus to the cytoplasm. As PP-2A and tau are localized in the cytoplasm, the increased cytoplasmic localization of I2PP2A in AD brain explains the inhibition of PP-2A, tau hyperphosphorylation and formation of neurofibrillary tangles. We propose (1) to investigate the molecular mechanism which controls the nuclear vs. cytoplasmic localization of I2PP2A in normal neurons. The transport factors (karyopherins) that mediate the import and export of I2PP2A into and out of the nuclei, and the I2PP2A domains which interact with these factors will be identified; (2) to elucidate the cause(s) of modified neuronal I2PP2A localization in Alzheimer's disease. We will investigate the effect of the cleavage of I2PP2A, which occurs in AD brains, on the I2PP2A interaction with the transport factors. We will also investigate the effects of the interactions of I2PP2A with other soluble and fixed proteins on I2PP2A localization in normal and AD brain, and the role of I2PP2A phosphorylation; (3) to generate transgenic mice which express the N-terminal half I2PP2A (observed in the cytoplasm of neurons in the AD brain) or a control variant of this protein localized in the nuclei, under the control of an inducible expression system. The effect of these transgenes on PP-2A activity, the activities of tau kinases regulated by PP-2A and abnormal hyperphosphorylation of tau, and as well as neurodegeneration and cognitive impairment, will be studied. These studies will lead to the elucidation of the mechanism of neurofibrillary degeneration and to the identification of one or more therapeutic targets. The studies will lead also to the generation of a cellular and an animal model of tauopathies, which can be used for the development of therapeutic drugs for diseases characterized by this lesion.