Abnormal Hyperphosphorylation of Tau

描述(申请人提供)：这项建议的总体目标是了解异常过度磷酸化的tau蛋白的神经纤维变性的分子机制，并在此基础上确定阿尔茨海默病(AD)、唐氏综合症和其他以这种脑损伤为特征的tauopathy的特定治疗靶点。调节tau磷酸化的蛋白磷酸酶(PP)-2A的活性又受其抑制剂I2PP2A的部分调节。在AD脑内的大部分神经元中，I2PP2A从其最初定位于胞核向胞浆移位。由于PP-2A和tau定位于细胞质，I2PP2A在AD脑内的胞浆定位增加解释了PP-2A的抑制、tau的过度磷酸化和神经原纤维缠结的形成。我们建议：(1)研究I2PP2A在正常神经元中核与胞浆定位的分子机制。将确定介导I2PP2A进出细胞核的运输因子(核粘附素)，以及与这些因子相互作用的I2PP2A结构域；(2)阐明改良神经元I2PP2A在阿尔茨海默病中定位的原因(S)。我们将研究发生在AD大脑中的I2PP2A裂解对I2PP2A与运输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脑中定位的影响，以及I2PP2A磷酸化的作用；(3)在诱导表达系统的控制下，建立表达N端半I2PP2A(观察到AD大脑神经元的细胞质中)或该蛋白的对照变体的转基因小鼠。这些转基因对PP-2A活性、PP-2A调节的tau酶活性和tau异常过度磷酸化的影响，以及对神经变性和认知功能损害的影响，将被研究。这些研究将有助于阐明神经纤维变性的机制，并确定一个或多个治疗靶点。这些研究还将导致产生一种细胞和动物模型，该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.