TBI-induced exosome release accelerates Alzheimer's disease pathology

阿尔茨海默病（AD）的特征在于Aβ肽的积聚，形成淀粉样斑块和超- tau蛋白的磷酸化形成神经元缠结，这是一种双重蛋白聚集过程， 进行性神经变性和认知能力下降。流行病学研究表明， AD在经历过头部创伤或创伤性脑损伤（TBI）的人中高出4倍， 从战场上回来的退伍军人中很普遍。这种风险增加的原因尚不清楚，也没有战略 预防AD病理学存在。进展的一个关键障碍是缺乏对淀粉样蛋白和 tau蛋白被赋予神经毒性，以及TBI如何诱导或加速这一过程。我们的目标是了解 并防止淀粉样蛋白和tau神经毒性，延迟AD的发作并减少AD的神经变性， 特别是在退伍军人中由TBI诱导或加速时。我们的中心假设是TBI诱导的 剪切力震动并反复弯曲星形胶质细胞中的纤毛，导致钙离子内流， 神经酰胺代谢和富含神经酰胺的外泌体（称为“星形体”）的持续分泌 （即时生效）。Aβ42和tau与神经酰胺结合，将星形体转化为神经毒性β体， 甚至在TBI后数年（延迟效应）。β体还含有前列腺凋亡反应4（PAR-4）， 神经酰胺诱导的细胞凋亡的敏感蛋白。β体被运送到线粒体， 它们增强Aβ42和tau介导的线粒体功能障碍和神经毒性。符合我们 假设，β体在来自AD患者和5xFAD小鼠血清中是可检测的，并诱导线粒体 N2 a细胞和原代培养的神经元中的损伤、半胱天冬酶活化和tau聚集。我们的假设 预测，通过阻断Aβ42和tau蛋白， TBI诱导的钙内流和神经酰胺生成。我们的预期结果包括：1）确定 上调神经酰胺和特定钙通道的酶，其由剪切力激活; 2） 定义星形体中诱导与Aβ42相互作用的神经酰胺组成，tau聚集， 线粒体/神经毒性; 3）确定神经酰胺调节药物和钙通道阻滞剂， 星形体分泌、β体形成、线粒体功能障碍和tau聚集和神经毒性; 和4）定量血清中指示TBI诱导的AD（TBI-AD）的严重性的星形体和β体， 治疗的成功。该项目对保护退伍军人和公共卫生的影响将 包括开发新的治疗策略所需的知识，这些策略可以延迟和/或预防 AD中进行性神经变性的发作，特别是在退伍军人中由轻度TBI诱导时。

Alzheimer's disease (AD) is characterized by build-up of Aβ peptides forming amyloid plaques and hyper- phosphorylation of tau protein forming neurofibrillary tangles, a two-fold protein aggregation process leading to progressive neurodegeneration and cognitive decline. Epidemiological studies show that the risk of developing AD is 4-fold higher in persons who have experienced head trauma or traumatic brain injury (TBI), which is prevalent in Veterans returning from active combat. Reasons for this increased risk are unclear and no strategy to prevent AD pathology exists. A critical barrier to progress is the lack of understanding of how amyloid and tau are rendered neurotoxic, and how TBI may induce or accelerate this process. Our goal is to understand and prevent amyloid and tau neurotoxicity and delay the onset and reduce neurodegeneration in AD, particularly when induced or accelerated by TBI in Veterans. Our central hypothesis is that TBI-induced shear force shakes and repeatedly bends cilia in astrocytes, which leads to calcium influx, reprogramming of ceramide metabolism, and sustained secretion of ceramide-enriched exosomes termed “astrosomes” (immediate effect). Aβ42 and tau associate with ceramide and turn astrosomes into neurotoxic betasomes, even years after TBI (delayed effect). Betasomes also contain prostate apoptosis response 4 (PAR-4), a protein sensitizing neurons to ceramide-induced apoptosis. Betasomes are transported to mitochondria, where they enhance Aβ42 and tau-mediated mitochondrial dysfunction and neurotoxicity. Consistent with our hypothesis, betasomes are detectable in serum from AD patients and 5xFAD mice and induce mitochondrial damage, caspase activation, and tau aggregation in N2a cells and primary cultured neurons. Our hypothesis predicts that astrosome secretion, association with Aβ42 and tau, and neurotoxicity are prevented by blocking TBI-induced calcium influx and ceramide generation. Our expected outcomes include 1) determining enzymes in upregulation of ceramide and specific calcium channels that are activated by shear force; 2) defining a ceramide composition in astrosomes that induces interaction with Aβ42, tau aggregation, and mito/neurotoxicity; 3) identifying ceramide-modulating drugs and calcium channel blockers that prevent astrosome secretion, betasome formation, mitochondrial dysfunction, and tau aggregation and neurotoxicity; and 4) quantifying astrosomes and betasomes in serum that indicate severity of TBI-induced AD (TBI-AD) and success of therapeutic treatment. The impact of this project on protection of Veterans and public health will include knowledge needed for the development of new treatment strategies that could delay and/or prevent the onset of progressive neurodegeneration in AD, in particular when induced by mild TBI in Veterans.