Beclin1 and autophagie in Alzheimers disease

阿尔茨海默病（AD）是最常见的神经退行性疾病，其特征是细胞外淀粉样斑块（由淀粉样β (Abeta)肽组成）、神经原纤维缠结、神经炎症和神经变性。淀粉样蛋白级联假说认为，β蛋白在脑实质中的沉积是阿尔茨海默病发展的关键步骤之一。小胶质细胞是中枢神经系统的常驻免疫细胞，它参与了AD的两个方面：分别是吞噬作用清除细胞外β的失败和细胞因子的产生和释放。除了在阿尔茨海默病晚期已被证实的神经炎症增强外，最近的数据表明炎症在阿尔茨海默病的发展中也起着作用。参与神经炎症和Abeta清除的一个候选过程是自噬。随着年龄的增长，自噬的效率似乎有所下降。此外，自噬是巨噬细胞炎症反应的调节机制。Beclin1是自噬的关键蛋白，也被证明参与受体循环和体外吞噬的逆转录物募集。基于这些数据，我们推测Beclin1是小胶质细胞中的关键分子，通过自噬和吞噬作用影响神经炎症和β沉积。这一假设将通过采用两种不同的方法来分析体内小胶质Beclin1缺失的影响：诱导性和构成性Beclin1缺失。在诱导模型中，Beclin1在不同时间点被耗尽，将靶向髓系细胞的诱导通量系统与已建立的AD小鼠模型APPPS1+/-交叉，以确定小胶质Beclin1在体内完全丧失后对自噬和吞噬（aim 1）、炎症（aim 2）和Abeta沉积（aim 3）的小胶质特异性影响。作为额外的系统，以查明髓细胞驱动的影响，诱导通量系统将被用来实现一般损失的Beclin1。接下来，我们将使用具有Beclin1一般组成型杂合缺失的小鼠，将其交叉到APPPS1小鼠中，以模拟人类AD患者小胶质细胞的情况。我们将再次研究体内Beclin1水平降低对自噬和吞噬作用（目的1）、炎症（目的2）和β斑块沉积（目的3）的发生或进展的影响。通过使用这两个小鼠系统，本项目不仅可以阐明Beclin1在体内小胶质细胞自噬和吞噬中的作用，而且也非常适合阐明AD和Abeta沉积中小胶质炎症的因果关系和时间关系。

Alzheimers disease (AD) is the most common neurodegenerative disorder, hallmarked by extracellular amyloid plaques (composed of amyloid-beta (Abeta) peptide), neurofibrillary tangles, neuroinflammation and neurodegeneration. The amyloid cascade hypothesis states that deposition of Abeta in the brain parenchyma is one of the crucial steps in the development of AD. Microglia, the resident immune cells of the central nervous system are involved in two aspects of AD: the removal respectively the failure of removal of extracellular Abeta by phagocytosis and the production and release of cytokines. Next to the well-established enhanced neuroinflammation in the late stages of AD, recent data suggests a role for inflammation in the development of AD as well. A candidate process involved in both neuroinflammation and removal of Abeta is autophagy. The efficiency of autophagy seems to decline during aging. In addition, autophagy is a regulatory mechanism for the inflammatory response in macrophages. Beclin1, a crucial protein for autophagy, was also shown to be involved in receptor recycling and retromer recruitment for phagocytosis in vitro. Based on these data we postulate that Beclin1 is a key molecule in microglia, influencing neuroinflammation and Abeta deposition via autophagy and phagocytosis. This hypothesis will be tested by analyzing the impact of microglial Beclin1 loss in vivo employing two different approaches: inducible and constitutive loss of Beclin1.For the inducible model Beclin1 will be depleted at different time points with an inducible flox system targeting myeloid cells crossed to the established AD mouse model APPPS1+/- to determine the microglia-specific impact on autophagy and phagocytosis (aim 1), inflammation (aim 2) and Abeta deposition (aim 3) after complete loss of microglial Beclin1 in vivo. As additional system to pinpoint myeloid-driven effects an inducible flox system will be used to achieve a general loss of Beclin1.Next to that we will employ mice with a general constitutive heterozygous deletion of Beclin1 that will be crossed to APPPS1 mice, to mimic the situation in microglia from human AD patients. Again the effect of diminished Beclin1 levels in vivo on autophagy and phagocytosis (aim 1), inflammation (aim 2) and onset or progression of Abeta plaque deposition (aim 3) will be investigated.By using these two mouse systems this project will not only clarify the role of Beclin1 in microglial autophagy and phagocytosis in vivo but it is also very well suited to elucidate the causal and temporal relationship of microglial inflammation in AD and Abeta deposition.