Novel Tau-mediated Neurodegeneration Mechanisms

在该项目的第一个资助期（2000-2004）期间进行的实验导致了阿尔茨海默病（AD）细胞模型系统中老年斑和tau病理学之间直接联系的第一个证据（Rapoport等人，2002年）。该研究显示，表达人tau的神经元在存在预聚集的β淀粉样蛋白（Aβ）的情况下变性，而在Aβ处理的tau耗尽的神经元中未检测到变性的迹象（Rapoport等人，2002年）。在第二个资助期（2005-2009年）期间获得的数据已经鉴定了钙蛋白酶介导的tau切割，导致产生17 kDa片段，作为神经元变性的重要步骤（Park和Ferreira 2005，Park et al.，2007年）。最近，我们已经获得了初步证据，表明这种tau神经毒性片段的水平可能不仅在AD中升高，而且在其他tau蛋白病中也升高。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蛋白病中神经元变性的保守机制。 为了检验这一假设，我们将确定：1）从AD和其他tau蛋白病患者获得的脑样品中17 kDa tau片段的存在;和2）我们将产生其中该毒性片段过表达的转基因动物模型。这种动物模型可以提供一个重要的工具，为未来的研究在中枢神经元，在原位发展的神经毒性作用的片段。这些实验将通过以下技术的组合进行，包括：Western印迹分析、免疫细胞化学、钙蛋白酶活性测定、实时RT-PCR和同源重组技术。所获得的数据可以为AD和其他tau蛋白病的诊断、预防和最终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.