APP Metabolism in Transgenic Down Syndrome Mouse Models

描述（由申请人提供）：大脑中β -淀粉样斑块中小A β肽的积累是阿尔茨海默病（AD）的不变特征，阿尔茨海默病是影响600多万美国人的最常见的神经退行性疾病。β是通过淀粉样前体蛋白（APP）的蛋白水解加工而产生的淀粉样前体蛋白。患有唐氏综合症（DS； 21三体）的人不可避免地会在四、五岁时出现AD病理，包括β -淀粉样斑块。App基因位于人类第21号染色体上，一般认为这一额外的App基因拷贝是导致DS个体AD的机制。使用人类DS的小鼠模型，如Ts65Dn小鼠（小鼠16号染色体的一个片段与人类21号染色体的DS关键区域同源），将在完整的中枢神经系统中检测APP的代谢和Abeta的产生。将确定Ts65Dn小鼠APP代谢物水平作为衰老的功能，并检测Ts65Dn小鼠体内APP和APP代谢物（分泌性APP片段、c端APP片段、Abeta）周转率的变化（Aim 1）。Ts65Dn小鼠在AD和DS以及年龄依赖性基底前脑胆碱能神经元变性中也表现出选择性的胞吞异常。鉴于先前已经证明APP蛋白水解加工可以发生在早期核内体中，Ts65Dn模型中神经元内吞作用改变与APP代谢之间的联系将通过免疫定位技术和亚细胞分离来检验（Aim 2）。通过被动接种抗小鼠Abeta单克隆抗体（Aim 3），降低中枢神经系统中的Abeta水平，从而在该模型中建立神经退行性变与Abeta水平/APP代谢不良之间的联系，从而验证Ts65Dn小鼠APP代谢不良与神经退行性变机制相关的假设。这些研究将描述体内脑APP代谢的特征，并在DS模型中验证APP代谢不良是基底前脑胆碱能神经变性的原因。这些发现将对AD在退行性椎体滑移中的发病机制具有重要意义，并可能提示AD神经退行性变的共同模式。

DESCRIPTION (provided by applicant): Accumulation of the small A beta peptide in the brain in beta-amyloid plaques is an invariant feature of Alzheimer's disease (AD), the most common type of neurodegeneration affecting over six million Americans. Abeta is derived from the amyloid precursor protein by proteolytic processing of the amyloid precursor protein (APP). Individuals with Down syndrome (DS; trisomy 21) inevitably develop AD pathology, including beta-amyloid plaques, in their fourth or fifth decade of life. The App gene is located on human chromosome 21, and it is generally thought that this additional gene copy of App mechanistically leads to AD in DS individuals. Using mouse models of human DS such as the Ts65Dn mouse, which is trisomic for a segment of murine chromosome 16 orthologous to the DS critical region of human chromosome 21, the metabolism of APP and the production of Abeta will be examined in the intact CNS. APP metabolite levels will be determined as a function of aging in the Ts65Dn mouse, and alterations in the rate of APP and APP metabolite (secretory APP fragments, C-terminal APP fragments, Abeta) turnover in vivo in the Ts65Dn mouse will be examined (Aim 1). The Ts65Dn mouse also shows abnormalities in endocytosis seen selectively in AD and DS and age-dependent basal forebrain cholinergic neuron degeneration. Given that it has been previously shown that APP proteolytic processing can occur in early endosomes, the link between neuronal endocytosis alterations in the Ts65Dn model and APP metabolism will be examined using immunolocalization techniques as well as subcellular fractionation (Aim 2). The hypothesis that APP mismetabolism in the Ts65Dn mouse is mechanistically linked to neurodegeneration will be tested by reducing Abeta levels in the CNS using passive vaccination with an anti-murine Abeta monoclonal antibody (Aim 3), thereby establishing a connection between neurodegeneration and Abeta levels/APP mismetabolism in this model. These studies will characterize in vivo brain APP metabolism and test the idea that APP mismetabolism is a cause of basal forebrain cholinergic neurodegeneration in a DS model. These findings will have important implication for the mechanisms of AD pathogenesis in DS and may suggest common modalities of neurodegeneration with AD.