ApoE and LRP1 in brain insulin signaling and glucose metabolism (Competitive Renewal)

 描述(由申请人提供)：apoE4是阿尔茨海默病(AD)最强的遗传风险因素；然而，apoE4如何使人们患上AD的风险仍不清楚。临床研究表明，APOE4携带者，无论是健康的成年人还是痴呆症患者，大脑葡萄糖代谢较低，神经炎症增加，这些情况在糖尿病患者中也很常见。有趣的是，糖尿病和胰岛素信号受损与AD的发病机制有关。支持这一点的是，最近在AD患者中使用胰岛素鼻内喷雾进行的临床试验在防止认知能力下降方面取得了积极的结果，这导致了一项新的国家计划，即第二阶段/第三阶段试验。因此，迫切需要了解临床前模型中脑胰岛素信号和葡萄糖代谢的功能和调节。在上一个供资周期和本项目的初步阶段， 我们发现apoE及其主要受体LRP1调节脑内脂肪和葡萄糖的代谢。具体地说，使用体内微透析技术，我们发现APOE4靶向替换(TR)小鼠和LRP1神经元基因敲除小鼠的大脑葡萄糖代谢受到损害。我们还发现LRP1与胰岛素受体(IR)相互作用，并以依赖于葡萄糖转运蛋白4(GLUT4)功能的方式调节胰岛素信号和葡萄糖代谢。APOE4组小鼠的胰岛素信号转导受损和慢性神经炎症因淀粉样变性(A？)病理或神经元LRP1缺失而进一步加重。因此，我们这次更新项目的目标是研究apoE4与促炎细胞因子和Aü协同作用以损害神经元胰岛素信号和葡萄糖代谢的分子和细胞机制，并测试APOE4-tr小鼠胰岛素信号的恢复是否可以挽救APOE4相关的AD表型。我们假设apoE4以一种依赖于apoE受体LRP1和葡萄糖转运体功能的方式损害神经元的胰岛素信号和葡萄糖代谢，神经炎症和A？我们提出了三个具体目标来检验我们的假设。在目标1中，我们计划剖析apoE4在体外、在体APOE-tr小鼠和人脑中损害神经元胰岛素信号和葡萄糖代谢的机制。在目标2中，我们将研究促炎细胞因子和Aü如何与apoE4在减少神经元胰岛素信号和葡萄糖代谢方面协同作用。在目标3中，我们计划测试脑内注射胰岛素或胰岛素增敏药物二甲双胍，或恢复apoE4表达和脂肪是否可以拯救受损的葡萄糖代谢，减少apoE4相关的神经炎症，并改善突触功能和认知。这些研究不仅将探讨APOE4携带者和AD患者胰岛素信号和葡萄糖代谢受损的潜在机制，还将测试针对胰岛素和载脂蛋白E途径的治疗潜力。

 DESCRIPTION (provided by applicant): APOE4 is the strongest genetic risk factor for Alzheimer's disease (AD); however, how apoE4 predisposes people for the risk for AD is still not clear. Clinical studies have shown that APOE4 carriers, both as healthy adults or with dementia, have lower cerebral glucose metabolism and increased neuroinflammation, conditions that are also common in individuals with diabetes. Interestingly, diabetes and impaired insulin signaling are linked to the pathogenesis of AD. Supporting these, a recent clinical trial with insulin intranasal spray in AD patients has yielded positive results in preventing cognitive decline and this has led to a new national plan for a Phase II/III trial. Thus, there is an urgent need to understand the function and regulation of brain insulin signaling and glucose metabolism in preclinical models. In the previous funding cycle and during the preliminary stage of this project, we found that apoE and its major receptor LRP1 regulate the metabolism of both lipid and glucose in the brain. Specifically, using in vivo microdialysis techniques, we found that brain glucose metabolism is impaired in APOE4-targeted replacement (TR) mice and in Lrp1 neuronal knockout mice. We also found that LRP1 interacts with insulin receptor (IR) and regulates insulin signaling and glucose metabolism in a manner that depends on the function of glucose transporter 4 (GLUT4). Impaired insulin signaling and chronic neuroinflammation were further exacerbated in the APOE4 mice by either amyloid-ß (Aß) pathology or a loss of neuronal LRP1. Thus, our goal for this renewal project is to study the molecular and cellular mechanisms by which apoE4 synergizes with pro-inflammatory cytokines and Aß to impair neuronal insulin signaling and glucose metabolism and test whether a restoration of insulin signaling in APOE4-TR mice allows a rescue of APOE4-related AD phenotypes. We hypothesize that apoE4 impairs neuronal insulin signaling and glucose metabolism in a manner that depends on the functions of apoE receptor LRP1 and glucose transporters, and that neuroinflammation and Aß further exacerbate these events in aging and AD. We propose three Specific Aims to test our hypothesis. In Aim 1, we plan to dissect the mechanisms by which apoE4 impairs neuronal insulin signaling and glucose metabolism in vitro in neurons, in vivo in APOE-TR mice, and in human brains. In Aim 2, we will examine how pro-inflammatory cytokines and Aß synergize with apoE4 in reducing neuronal insulin signaling and glucose metabolism. In Aim 3, we plan to test whether brain administration of insulin or insulin-sensitizing drug metformin, or a restoration of apoE4 expression and lipidation rescues impaired glucose metabolism, reduces apoE4-associated neuroinflammation, and improve synaptic functions and cognition. These studies will not only address the underlying mechanisms of impaired insulin signaling and glucose metabolism in APOE4 carriers and AD patients but will also test therapeutic potentials targeting insulin and apoE pathways.