Novel Tau-mediated Neurodegeneration Mechanisms

在该项目的第一个资助期(2000-2004年)进行的实验首次证明老年斑与阿尔茨海默病(AD)细胞模型系统中的tau病理之间存在直接联系(Rapoport等人，2002年)。这项研究表明，在预聚集的β淀粉样蛋白(Aβ)存在下，表达人tau的神经元退化，而在Aβ处理的tau缺失的神经元中没有检测到退化的迹象(Rapoport等人，2002年)。在第二个资助期(2005-2009年)获得的数据表明，Calain介导的tau裂解导致17 kDa片段的产生是神经元退化的重要步骤(Park和Ferreira 2005，Park等人，2007年)。最近，我们获得的初步证据表明，这种tau神经毒性片段的水平可能不仅在AD患者中升高，而且在其他tau病中也是如此。然而，这种tau片段诱导神经毒性的机制仍然知之甚少。我们推测，17 kDa tau片段的产生是导致不同tau病神经元变性的一种保守机制。 为了验证这一假设，我们将确定：1)从AD和其他tauopathy患者获得的大脑样本中是否存在17 kDa tau片段；以及2)我们将生成一个过度表达这种有毒片段的转基因动物模型。这一动物模型可以为未来研究该片段对原位发育的中枢神经元的神经毒性作用提供必要的工具。这些实验将通过多种技术的组合进行，包括：Western印迹分析、免疫细胞化学、Calain活性分析、实时RT-PCR和同源重组技术。所获得的数据可以为AD和其他疾病的诊断、预防以及最终的治疗提供有用的信息。

The experiments performed during the first funded period of this project (2000-2004) led to the first evidence of a direct link between senile plaques and tau pathology in an Alzheimer’s disease (AD) cell model system (Rapoport et al., 2002). This study showed that neurons expressing human tau degenerated in the presence of preaggregated beta amyloid (Aβ), while no signs of degeneration were detected in Aβ-treated tau-depleted neurons (Rapoport et al., 2002). Data obtained during the second funded period (2005-2009) have identified calpain-mediated tau cleavage leading to the generation of a 17 kDa fragment as an important step in neuronal degeneration (Park and Ferreira 2005, Park et al., 2007). More recently, we have obtained preliminary evidence suggesting that the levels of this tau neurotoxic fragment might be elevated not only in AD but also in other tauopathies. However, the mechanisms by which this tau fragment could induce neurotoxicity remain poorly understood. We speculate that the generation of a 17 kDa tau fragment is a conserved mechanism leading to neuronal degeneration in different tauopathies. To test this hypothesis, we will determine: 1) the presence of the 17 kDa tau fragment in brain samples obtained from AD and other tauopathies patients; and 2) we will generate a transgenic animal model in which this toxic fragment is over expressed. This animal model could provide an essential tool for future studies on the neurotoxic effects of this fragment in central neurons that develop in situ. These experiments will be performed by means of a combination of techniques including: Western blot analysis, immunocytochemistry, calpain activity assays, real-time RT-PCR, and homologous recombination techniques. The data obtained could provide useful for the diagnosis, prevention, and eventually the treatment of AD and other tauopathies.