Pathobiological Studies of BACE1 and APP in Alzheimer's Diseases

1. BACE 1升高参与阿尔茨海默病三重转基因模型中淀粉样斑块的发展：早发性轴突终末病理的差异性A-β抗体标记 APP和早老素突变导致早发性家族性阿尔茨海默病（FAD）。一些基于FAD的小鼠模型产生淀粉样蛋白斑块，其他则不会。β-淀粉样蛋白（A-β）沉积可以表现为致密和弥漫性斑块;目前还不清楚为什么相同的A-β分子以不同的模式聚集。是否有一个基本的细胞过程控制A-β斑块的发病机制？我们在一些FAD小鼠模型中发现，致密斑块的形成与β-分泌酶（BACE 1）表达增加固有的进行性轴突病理学相关，β-分泌酶1是启动APP淀粉样蛋白形成过程的酶。单克隆A抗体3D 6在斑块发生前观察到明显的轴突末端标记。本研究旨在了解BACE 1和轴突变化相对于弥漫性斑块的发展，并进一步表征新的轴突A抗体免疫反应性（IR），使用三重转基因AD（3xTg-AD）小鼠作为实验模型。老年转基因动物前脑中存在弥漫性斑块，并与BACE 1标记的肿胀/发芽轴突终末增加区域相关。增加BACE 1/3D 6 IR在轴突终末发生在年轻动物斑块发病前。这些轴突元件也被靶向A β结构域的N末端和中部区域以及APP的C末端的其他抗体共同标记，但没有被针对A β C末端和APP N末端的抗体共同标记。结果表明，淀粉样变性轴突病理之前弥漫性斑块形成的3xTg-AD小鼠，和早发性轴突A-β抗体IR在转基因模型的AD可能涉及到一个交叉反应性的推定APP β-羧基末端片段。 2. APP诱导的神经变性的体内嗅觉模型揭示了可逆的细胞自主功能。 APP长期以来一直与阿尔茨海默病（AD）的神经退行性变有关，但相关的细胞死亡一直难以在体内捕获，APP在影响神经元损失中的作用仍不清楚。嗅觉功能障碍是AD的早期症状，嗅上皮中的淀粉样蛋白病理与AD患者的脑病理密切相关。由于嗅感觉神经元（OSNs）不断再生，未成熟和成熟的OSNs共存于同一嗅上皮中，我们试图利用这一独特的系统来研究APP诱导的神经变性。在这里，我们已经开发了一种基于嗅觉的转基因小鼠模型，该模型在成熟或不成熟的OSN中过表达含有家族性AD突变（hAPP）的人源化APP，并且发现尽管不存在细胞外斑块，但在3周龄时检测到惊人数量的凋亡神经元。重要的是，细胞凋亡仅限于过表达hAPP的特定群体，成熟或不成熟的OSN，而不包括那些没有hAPP的OSN。有趣的是，我们观察到这种广泛的神经变性可以通过降低未成熟神经元中的hAPP表达水平来迅速挽救。总之，这些数据表明，单独过表达hAPP可以诱导成熟和未成熟神经元中的细胞自主凋亡，挑战淀粉样蛋白斑块是神经变性所必需的概念。此外，我们表明hAPP诱导的神经变性是可逆的，这表明AD相关的神经损失可能被挽救。因此，我们建议这种独特的体内模型不仅有助于确定AD相关神经退行性变的机制，而且还可以作为测试可能治疗方法的平台。

1. BACE1 elevation is involved in amyloid plaque development in the triple transgenic model of Alzheimers disease: Differential A-beta antibody labeling of early-onset axon terminal pathology. APP and presenilins mutations cause early-onset familial Alzheimers disease (FAD). Some FAD-based mouse models produce amyloid plaques, others dont. Beta-Amyloid (A-beta) deposition can manifest as compact and diffuse plaques; it is unclear why the same A-beta molecules aggregate in different patterns. Is there a basic cellular process governing A-beta plaque pathogenesis? We showed in some FAD mouse models that compact plaque formation is associated with a progressive axonal pathology inherent with increased expression of beta-secretase (BACE1), the enzyme initiating the amyloidogenic processing of APP. A monoclonal A antibody, 3D6, visualized distinct axon terminal labeling before plaque onset. The present study was set to understand BACE1 and axonal changes relative to diffuse plaque development and to further characterize the novel axonal A antibody immunoreactivity (IR), using triple transgenic AD (3xTg-AD) mice as experimental model. Diffuse-like plaques existed in the forebrain in aged transgenics and were regionally associated with increased BACE1 labeled swollen/sprouting axon terminals. Increased BACE1/3D6 IR at axon terminals occurred in young animals before plaque onset. These axonal elements were also co-labeled by other antibodies targeting the N-terminal and mid-region of A-beta domain and the C-terminal of APP, but not co-labeled by antibodies against the A-beta C-terminal and APP N-terminal. The results suggest that amyloidogenic axonal pathology precedes diffuse plaque formation in the 3xTg-AD mice, and that the early-onset axonal A-beta antibody IR in transgenic models of AD might relate to a cross-reactivity of putative APP beta-carboxyl terminal fragments. 2. In vivo Olfactory Model of APP-induced Neurodegeneration Reveals a Reversible Cell-autonomous Function. APP has long been linked to the neurodegeneration of Alzheimers disease (AD), but the associated cell death has been difficult to capture in vivo, and the role of APP in effecting neuron loss is still unclear. Olfactory dysfunction is an early symptom of AD with amyloid pathology in the olfactory epithelium correlating well to the brain pathology of AD patients. As olfactory sensory neurons (OSNs) regenerate continuously with immature and mature OSNs co-existing in the same olfactory epithelium, we sought to utilize this unique system to study APP-induced neurodegeneration. Here we have developed an olfactory-based transgenic mouse model that overexpresses humanized-APP containing familial AD-mutations (hAPP) in either mature or immature OSNs, and found that despite the absence of extracellular plaques a striking number of apoptotic neurons were detected by 3 weeks of age. Importantly, apoptosis was restricted to the specific population overexpressing hAPP, either mature or immature OSNs, sparing those without hAPP. Interestingly, we observed that this widespread neurodegeneration could be rapidly rescued by reducing hAPP expression levels in immature neurons. Together, these data argue that overexpressing hAPP alone could induce cell autonomous apoptosis in both mature and immature neurons, challenging the notion that amyloid plaques are necessary for neurodegeneration. Furthermore, we show that hAPP induced neurodegeneration is reversible, suggesting that AD-related neural loss could potentially be rescued. Thus, we propose that this unique in vivo model will not only help determine the mechanisms underlying AD-related neurodegeneration but also serve as a platform to test possible treatments.