Abstract：
Alzheimer\'s Disease (AD) is a neurodegenerative disease characterized by profound memory impairments, synaptic loss, neuroinflammation, and hallmark pathological markers. High-fat diet (HFD) consumption increases the risk of developing AD even after controlling for metabolic syndrome, pointing to a role of the diet itself in increasing risk. In AD, the complement system, an arm of the immune system which normally tags redundant or damaged synapses for pruning, becomes pathologically overactivated leading to tagging of healthy synapses. While the unhealthy diet to AD link is strong, the underlying mechanisms are not well understood in part due to confounding variables associated with long-term HFD which can independently influence the brain. Therefore, we experimented with a short-term diet regimen to isolate the diet\'s impact on brain function without causing obesity. This project investigated the effect of short-term HFD on 1) memory, 2) neuroinflammation including complement, 3) AD pathology markers, 4) synaptic markers, and 5) in vitro microglial synaptic phagocytosis in the 3xTg-AD mouse model. Following the consumption of either standard chow or HFD, 3xTg-AD and non-Tg mice were tested for memory impairments. In a separate cohort of mice, levels of hippocampal inflammatory markers, complement proteins, AD pathology markers, and synaptic markers were measured. For the last set of experiments, BV2 microglial phagocytosis of synapses was evaluated. Synaptoneurosomes isolated from the hippocampus of 3xTg-AD mice fed chow or HFD were incubated with equal numbers of BV2 microglia. The number of BV2 microglia that phagocytosed synaptoneurosomes was tracked over time with a live-cell imaging assay. Finally, we incubated BV2 microglia with a complement receptor inhibitor (NIF) and repeated the assay. Behavioral analysis showed 3xTg-AD mice had significantly impaired long-term contextual and cued fear memory compared to non-Tg mice that was further impaired by HFD. HFD significantly increased inflammatory markers and complement expression while decreasing synaptic marker expression only in 3xTg-AD mice, without altering AD pathology markers. Synaptoneurosomes from HFD-fed 3xTg-AD mice were phagocytosed at a significantly higher rate than those from chow-fed mice, suggesting the synapses were altered by HFD. The complement receptor inhibitor blocked this effect in a dose-dependent manner, demonstrating the HFD-mediated increase in phagocytosis was complement dependent. This study indicates HFD consumption increases neuroinflammation and over-activates the complement cascade in 3xTg-AD mice, resulting in poorer memory. The in vitro data point to complement as a potential mechanistic culprit and therapeutic target underlying HFD\'s influence in increasing cognitive vulnerability to AD.
摘要：
阿尔茨海默病（AD）是一种神经退行性疾病，其特征是严重的记忆障碍，突触损失,神经炎症，和标志病理标记。即使在控制代谢综合征后，高脂饮食（HFD）摄入也会增加患AD的风险。指出饮食本身在增加风险中的作用。在AD中,补充系统，免疫系统的手臂，通常标记多余或受损的突触以进行修剪，在病理上变得过度激活，导致健康突触的标记。虽然不健康的饮食与AD的联系很强，潜在的机制尚未得到很好的理解,部分原因是与长期HFD相关的混杂变量可以独立影响大脑.因此,我们试验了短期饮食方案，以分离饮食对大脑功能的影响，而不引起肥胖。该项目研究了短期HFD对1)记忆的影响，2）神经炎症，包括补体，3)AD病理标记物,4）突触标记，5)3xTg-AD小鼠模型中的体外小胶质细胞突触吞噬作用。在消耗标准食物或HFD之后，测试3xTg-AD和非Tg小鼠的记忆损伤。在一个单独的小鼠队列中，海马炎症标志物的水平，补体蛋白，AD病理标记物,并测量了突触标记。在最后一组实验中,评估了突触的BV2小胶质细胞吞噬作用。将从喂食食物或HFD的3xTg-AD小鼠的海马中分离的突触神经体与相等数量的BV2小胶质细胞一起孵育。用活细胞成像测定随时间追踪吞噬突触神经体的BV2小胶质细胞的数量。最后,我们将BV2小胶质细胞与补体受体抑制剂(NIF)孵育,并重复试验.行为分析显示3xTg-AD小鼠与进一步被HFD损害的非Tg小鼠相比具有显著损害的长期背景和提示的恐惧记忆。HFD仅在3xTg-AD小鼠中显著增加炎性标志物和补体表达,同时降低突触标志物表达,而不改变AD病理学标志物。HFD喂养的3xTg-AD小鼠的突触神经体的吞噬率明显高于饮食喂养的小鼠，提示HFD改变了突触。补体受体抑制剂以剂量依赖的方式阻断了这种作用，证明HFD介导的吞噬作用增加是补体依赖性的。这项研究表明，在3xTg-AD小鼠中，HFD消耗会增加神经炎症并过度激活补体级联，导致记忆力下降。体外数据表明，补体是HFD影响增加对AD的认知脆弱性的潜在机制罪魁祸首和治疗靶标。
