Endosome Dysfunction in Alzheimer's Disease

20年前，我们发现rab 5阳性核内体异常是一种标志性的病理学， 阿尔茨海默病（Alzheimer's disease，AD）是迄今为止最早出现的AD特异性神经元病变， 知道的遗传学数据已经独立地集中于内吞作用作为AD的主要早期靶点。我们有 显示核内体异常的发展需要Rab 5的病理性过度激活， 早期内体上的调节性GT3，以触发显著上调的内吞作用和异常的内体 融合、运输和细胞信号传导导致胆碱能神经变性。Rab 5过度激活导致 通过AD和Down中APP-β CTF（APP的β-切割C-末端片段）的内体水平升高 综合征（DS），由于额外的APP拷贝导致AD的原因。APP-β CTF直接结合并募集APPL 1， 信号传导效应物，其异常稳定rab 5的活化（GTP负载）状态，触发内体 功能障碍rab 5过度激活的致病重要性被我们的新的表型所强调。 神经元rab 5过度激活的转基因小鼠模型，其发展AD相关的内体功能障碍 以及逆向转运、营养因子信号传导、突触可塑性、认知和神经元存活中的AD样缺陷， 所有这些都反映了rab 5在神经元中的许多已知作用的受损。我们认为早期内体功能障碍 是引发晚发性AD β-淀粉样蛋白生成的前期病理学的关键部分， 在此基础上，rab 5过度激活通过多种途径进一步驱动AD的发展。我们进一步建议， 其他增加AD风险的遗传因素，包括ApoE和GWAS鉴定的在内吞作用中起作用的基因 通过rab 5失调或加剧rab 5对内体动力学和细胞影响而增加疾病风险 发信号。为了验证这些概念，我们将定义在哺乳动物中调节rab 5活性的多种途径/因子。 神经元（Aim 1a），并通过rab 5和其他因素控制启动AD相关的内体功能障碍 AD和DS的细胞和小鼠模型中的内体再循环和成熟（目的1b）。我们将定义 选择性rab 5过度激活对体内脑功能的影响，并验证其预测的疾病- 在AD的hAPP（wt）小鼠模型中的加速作用（目的2）。令人兴奋的临床相关性，我们将验证， 在目前的临床试验中，我们已经证明， 在低纳摩尔浓度下逆转DS患者细胞中的rab 5活化和内体功能障碍（目的3）。 APPL 1和APPL 2在直接连接APP-β CTF与rab 5超激活中的关键作用将被探索 并且还在我们的过表达APPL 1或缺乏APPL 1和/或APPL 2的小鼠中得到验证， 与AD模型交叉（目标4）。我们将检验GWAS AD风险基因在以下假设： 内吞作用部分地通过加剧rab 5驱动的内体功能障碍而带来风险（目的5）。这些都是新奇的 与AD的分子起源高度相关的AD病理生物学的未探索领域。我们的最终 目的是鉴定和验证针对这种最早的AD病理学的创新疗法。

Two decades ago, we identified abnormalities of rab5-positive endosomes as a signature pathology of Alzheimer’s disease (AD), which is considered the earliest appearing neuronal pathology specific to AD yet known. Genetic data have independently converged on endocytosis as a prime early target in AD. We have shown that development of endosome anomalies requires pathological hyper-activation of rab5, the master regulatory GTPase on early endosomes, to trigger markedly upregulated endocytosis and aberrant endosomal fusion, trafficking, and cell signaling leading to cholinergic neurodegeneration. Rab5 over-activation is caused by elevated endosomal levels of APP-ßCTF (ß-cleaved C-terminal fragment of APP) in AD and in Down Syndrome (DS), a cause of AD due to an extra APP copy. APP-ßCTF directly binds and recruits APPL1, a signaling effector, which aberrantly stabilizes the activated (GTP-loaded) state of rab5, triggering endosomal dysfunction. The pathogenic importance of rab5 over-activation is underscored by the phenotype of our new transgenic mouse model of neuronal rab5 over-activation, which develops AD-related endosome dysfunction and AD-like deficits in retrograde transport, trophin signaling, synaptic plasticity, cognition, and neuron survival, all reflecting impairment of rab5’s many known roles in neurons. We propose that early endosome dysfunction is a key part of the antecedent pathobiology initiating ß-amyloidogenesis in late-onset AD and that its underlying basis, rab5 hyper-activation, further drives AD development through multiple pathways. We further propose that other genetic influences increasing AD risk, including ApoE and GWAS-identified genes with roles in endocytosis increase disease risk by dysregulating rab5 or exacerbating rab5’s impact on endosome dynamics and cell signaling. To validate these concepts, we will define the multiple pathways/factors that regulate rab5 activity in neurons (Aim1a) and that initiate AD-related endosome dysfunction via rab5 and additional factors controlling endosomal recycling and maturation in cell and mouse models of AD and DS (Aim 1b). We will define the consequences of selective rab5 over-activation on brain function in vivo and validate its predicted disease- accelerating effects in an hAPP(wt) mouse model of AD(Aim 2). Of exciting clinical relevance, we will validate in vivo the predicted actions on endocytosis of an AD therapeutic in current clinical trials, which we have shown to reverse rab5 activation and endosome dysfunction in DS patient cells at low nanomolar concentrations (Aim 3). The crucial roles of APPL1 and APPL2 in directly linking APP- ßCTF to rab5 hyper-activation will be explored and also validated in our mice that over-express APPL1 or lack APPL1 and/or APPL2 and also in these mice crossed to AD models (Aim 4). We will test the hypothesis that GWAS AD risk genes with suspected roles in endocytosis confer risk in part by exacerbating rab5-driven endosome dysfunction (Aim 5). These are all novel unexplored areas of AD pathobiology that are highly relevant to the molecular origin(s) of AD. Our ultimate objectives are identifying and validating innovative therapeutics that target this earliest AD pathobiology.