Function of ceramide in neurodegenerative disease

 描述（由申请人提供）：阿尔茨海默病（AD）的特征为进行性神经变性和Aβ肽、淀粉样蛋白斑块和神经元tau蛋白缠结的积聚。目前预防Aβ形成或分泌的策略并不成功。在增强Aβ摄取和清除的同时防止Aβ积聚是将Aβ肽的影响降至最低的替代方法。阻止Aβ积聚和改善清除的新药开发进展的一个关键障碍是缺乏对Aβ淀粉样蛋白斑块如何成核和增殖而不是Aβ如何被神经胶质细胞摄取和清除的透彻理解。我们的目标是中断淀粉样斑块的成核和传播，以提高Aβ清除率，延迟AD的发作并减少AD的神经退行性变。我们的中心假设是，星形胶质细胞分泌的富含神经酰胺的外泌体与Aβ形成复合物（Aβ/Exos），作为“种子”催化神经毒性斑块的成核和增殖，而不是促进小胶质细胞的Aβ转运和清除。神经酰胺水平升高可增强Aβ/Exos的分泌、聚集和神经毒性，特别是中性鞘磷脂酶2（nSMase 2），这是一种在被Aβ激活时产生神经酰胺的酶。药物（例如，nSMase 2抑制剂）诱导的神经酰胺减少将阻止Aβ/Exo积聚/扩散并保护神经元，这是AD的新治疗选择。我们的目标是：1）检测控制外泌体分泌的关键调节因子及其与Aβ的关联; 2）检测Aβ/Exos诱导斑块形成、tau蛋白过度磷酸化和神经元细胞死亡的新分子机制; 3）检测体外和体内预防外泌体分泌、Aβ/Exo诱导的斑块形成、tau蛋白过度磷酸化和神经元细胞死亡的药物;以及4）测试AD模型小鼠和AD患者的血清和脑脊液中的Aβ/Exos是否可以用作监测斑块和缠结积聚以及治疗成功的新诊断工具。我们的预期结果包括1）确定诱导与Aβ、斑块成核和增殖、tau过度磷酸化和神经元细胞死亡相关的外泌体组成; 2）鉴定预防Aβ/Exo诱导的斑块形成、tau过度磷酸化和神经元细胞死亡的神经酰胺调节药物;和3）定义血清中Aβ/Exos的水平，其指示AD的严重程度和治疗的成功。该项目对公共卫生的影响将包括开发新策略和治疗所需的知识，这些策略和治疗可以延迟和减少AD进行性神经退行性变的发生。我们将测试神经酰胺促进Aβ42缔合和聚集的机制（目的1），Aβ42/Exos如何诱导斑块形成和神经变性（目的2），以及哪种治疗可预防外泌体诱导的淀粉样蛋白聚集、斑块形成和AD病理学（目的3）。

 DESCRIPTION (provided by applicant): Alzheimer's disease (AD) is characterized by progressive neurodegeneration and build-up of Aβ peptides, amyloid plaques, and neurofibrillary tau tangles. Current strategies to prevent Aβ formation or secretion are not successful. Preventing Aβ build-up while enhancing Aβ uptake and clearance is an alternative approach to minimize the effect of Aβ peptides. A critical barrier to progress in the development of novel drugs that prevent Aβ build-up and improve clearance is the lack of a thorough understanding of how Aβ amyloid plaques are nucleated and proliferate instead of Aβ being taken up and cleared by glial cells. Our goal is to interrupt amyloid plaque nucleation and propagation to enhance Aβ clearance and delay the onset and reduce neurodegeneration in AD. Our central hypothesis is that ceramide-enriched exosomes secreted by astrocytes form complexes with Aβ (Aβ/Exos) that function as "seeds" to catalyze nucleation and propagation of neurotoxic plaques instead of facilitating Aβ transport and clearance by microglia. Secretion, aggregation, and neurotoxicity of Aβ/Exos is enhanced by elevation of ceramide levels, in particular by neutral sphingomyelinase 2 (nSMase2), an enzyme generating ceramide when activated by Aβ. Drug (e.g., nSMase2 inhibitor)-induced reduction of ceramide will prevent Aβ/Exo build-up/spreading and protect neurons, which is a novel treatment option for AD. Our objectives are to 1) test key regulatory factors that control secretion of exosomes and their association with Aβ; 2) test a novel molecular mechanism by which Aβ/Exos induce plaque formation, tau hyperphosphorylation, and neuronal cell death; 3) test pharmacological drugs that prevent exosome secretion, Aβ/Exo-induced plaque formation, tau hyperphosphorylation, and neuronal cell death in vitro and in vivo; and 4) test if Aβ/Exos in serum and cerebrospinal fluid from AD model mice and AD patients can be used as a novel diagnostic tool for monitoring plaque and tangle build-up, and treatment success. Our expected outcomes include 1) determining an exosome composition that induces association with Aβ, plaque nucleation and propagation, tau hyperphosphorylation, and neuronal cell death; 2) identifying ceramide- modulating drugs that prevent Aβ/Exo-induced plaque formation, tau hyperphosphorylation, and neuronal cell death; and 3) defining a level of Aβ/Exos in serum that indicates severity of AD and success of treatment. The impact of this project on public health will include knowledge needed for the development of new strategies and treatments that could delay and reduce the onset of progressive neurodegeneration in AD. We will test by which mechanism ceramide promotes association and aggregation of Aβ42 (Aim 1), how Aβ42/Exos induce plaque formation and neurodegeneration (Aim 2), and which treatment prevents exosome-induced amyloid aggregation, plaque formation, and AD pathology (Aim 3).