Abeta prion spreading: correlation with behavior, prion protein cofactor and effect of somatic mutations in novel animal models

阿尔茨海默病(AD)是最常见的神经退行性疾病，目前尚无根治方法。根据AD发病机制的淀粉样级联假说，APP的异常处理导致Abeta42水平升高及其多聚化是一个重要的触发因素。近年来，越来越多的证据表明，在实验性AD模型中，聚集性Abeta作为一种额外的、加速疾病的机制，可以通过诱导其他尚未处于致病聚集状态的Abeta分子的转化，从而通过普恩样机制复制其病理构象/多聚体，从而在整个大脑中传播。这样的机制也支持体细胞突变假说，即Abeta聚集可能是由少数表达突变APP基因的神经元启动的。到目前为止，用于这些实验的动物模型的缺点是，它们容易发生自发的内源性AD样病理，通过接种只会加速，不会从头产生。在这个项目中，将利用一种用于早期AD的新的动物模型，一种通过二硫键(tgDimer小鼠，Müler-Schiffmann等人，2016，Brain 139：509-25)唯一表达二聚体Abeta的转基因小鼠，它不会自发产生不溶性Abeta斑块或神经病理，但可以被诱导与现有斑块相关联。在这里，通过我们独特的动物模型，我们将回答三个重要的问题，这些问题到目前为止还没有得到回答：1.Aβ蛋白的传播与行为变化有什么关系？2.PrP作为辅助因子在Aβ蛋白传播过程中的行为变化中起什么作用？3.神经元中引起AD的基因的体细胞突变在多大程度上可以触发AD？我们将使用tgDimer小鼠和一种新的品系，其中tgDimer小鼠被交叉进入PrP Ko背景，并将这两个品系培育成GFAP-荧光素酶小鼠，在那里可以通过体内生物发光检测来监测Abeta斑块的传播。将对两个AD菌株和两个合成Abeta菌株进行系统接种，并进行一系列行为测试，包括经典的(例如Morris水迷宫)和使用自动行为分析。为了测试体细胞突变在多大程度上可以触发阿贝塔病毒传播，我们将在宫内将突变的人APP/早老素1电穿孔到tgDimer和APP 23/GFAP-荧光素酶小鼠中，这导致人类突变的APP在有限数量的神经元中表达，可能触发Abeta扩散。在本项目结束时，我们将详细了解Abeta的传播如何与哪些行为变化相关，对PrP在Abeta蛋白传播和行为反应调节中的作用有一个明确的答案，并描绘出体细胞突变在AD发病机制中的作用。这些结果可能为AD急需的治疗研究开辟新的途径。

Alzheimer s disease (AD) is the most prevalent neurodegenerative disease with currently no curative therapy available. According to the amyloid cascade hypothesis of AD pathogenesis, aberrant APP processing leading to increased Abeta 42 levels and its multimerization are an essential trigger. In recent years, evidence has accumulated indicating that as an additional, accelerating disease mechanism in experimental AD models, aggregated Abeta can spread throughout the brain by inducing conversion of other Abeta molecules that are not yet in a pathogenic, aggregated state, thereby replicating its pathological conformer/multimer by a prion-like mechanism. Such a mechanism would also support the somatic mutation hypothesis that states that Abeta aggregation could be started by few neurons expressing mutant APP genes. The shortcoming of animal models used so far for these experiments is that they are prone to spontaneous, endogenous AD-like pathology that by inoculations is only accelerated and not generated de novo. In this project, advantage will be taken of a novel animal model for early AD, a transgenic mouse that expresses exclusively dimeric Abeta crosslinked through a disulfide bridge (tgDimer mouse, Müller-Schiffmann et al., 2016, Brain 139:509-25) that does not develop insoluble Abeta plaques or neuropathology spontaneously, but can be induced to associate to existing plaques. Here, by using our unique animal model, we will answer three questions that are of outstanding importance and have not been answered so far: 1. How does Abeta prion spreading relate to behavioral changes? 2. What role has PrP as a cofactor for the behavioral changes during Abeta spreading or Abeta spreading itself? 3. To what extent can somatic mutations of AD-causing genes in neurons trigger AD? We will use the tgDimer mouse, and a new line where the tgDimer mouse is crossed into the PrP ko background, and breed those two lines into the GFAP-luciferase mouse where Abeta plaque spreading can be monitored through in vivo biolouminescence detection. Systematic inoculations with two AD strains and two synthetic Abeta strains will be perfromed and a battery of behavioral tests, both classical (e.g. Morris water maze) and using automated behavioral analysis. For testing in how far somatic mutations can trigger abeta prion spreading, we will perform in utero electroporation of mutant human APP / presenilin 1 into the tgDimer and APP 23 /GFAP-luciferase mouse which leads to expression of human mutant APP in a limited amount of neurons, potentially triggering Abeta spreading. At the end of this project, we will have detailed knowledge on how Abeta spreading related to which behavioral changes, a definite answer on the role of PrP in Abeta prion spreading and modulation of behavioral response, as well as delineate the role of somatic mutations in the pathogenesis of AD. These results may open new avenues in much-needed therapeutic research in AD.