APOE and the PPP: Glucose Metabolism and Oxidative Stress in Alzheimer's Disease

摘要 代谢功能障碍可能导致几种与年龄有关的疾病的发展，包括 阿尔茨海默病(AD)。载脂蛋白E(ApoE)基因编码人类的三种主要亚型 人口：E2、E3和E4。E4是散发性AD最显著的遗传危险因素，而E2是 防护性的。AD患者--以及认知正常的E4患者--的一个未被研究的标志是大脑 葡萄糖代谢不足。E4相关的葡萄糖摄取减少比认知能力早几十年开始 然而，它的发生机制及其与AD风险的相关性仍不清楚。这个 大脑主要代谢葡萄糖，其中很大一部分被分流到戊糖磷酸 神经元和星形胶质细胞中的PPP通路。PPP产生抗氧化剂还原因子，如 NADPH和谷胱甘肽，以及PPP活性降低会增加氧化应激和细胞死亡。有趣的是， 我们新的初步数据描述了一种带有人载脂蛋白E的小鼠模型，该模型概括了E4相关的 葡萄糖代谢减少，也证明多种PPP代谢物减少。因此，中央 该假说认为载脂蛋白E通过异构体特异性影响神经元功能和存活。 葡萄糖代谢的变化。具体地说，我们假设E4与认知障碍有关。 通过代谢重编程减少葡萄糖摄取和通过PPP进行氧化还原管理 是减少的。我们在小鼠身上的初步数据显示，大脑葡萄糖摄取(E2和GT；E3和GT；E4)逐渐减少，以及 体外结果表明，这些差异是由于星形细胞通过GLUT-1摄取的变化所致。因此，在 首先，我们将测试E4通过下调大脑葡萄糖摄取量来降低大脑葡萄糖摄取量的假设 星形细胞葡萄糖转运体GLUT-1结合apoE靶向操纵的闪烁邻近分析 异构体、总蛋白浓度和葡萄糖转运体。要检验E4降低的假设 葡萄糖进入PPP，我们将通过 稳定同位素分解代谢组学(SIRM)提供独特的前体产物“追踪”，并翻译 我们的结果是通过对人脑组织的分析得出的。最后，我们将检验E4会加剧 氧化损伤和细胞死亡是由于PPP介导的氧化应激管理减少所致。这将是 通过PPP酶的药理操作在体外完成，在体内通过评估 脑组织氧化还原蛋白质组学分析对认知功能、AD病理和氧化损伤的影响 用PPP刺激剂治疗的人载脂蛋白E小鼠。如果成功，这项提议将提供新的治疗方法 目标是使高危个体的葡萄糖代谢正常化。通过增加能量来增强大脑代谢 葡萄糖摄取和进入PPP可能在预防或延缓AD的发生方面有很大的影响。

ABSTRACT Metabolic dysfunction may contribute to the development of several age-related diseases, including Alzheimer's disease (AD). The gene Apolipoprotein E (APOE) encodes three major isoforms in the human population: E2, E3, and E4. E4 is the most significant genetic risk factor for sporadic AD, while E2 is protective. An understudied hallmark of AD patients – and of cognitively normal E4 individuals – is cerebral glucose hypometabolism. E4-associated reductions in glucose uptake begin decades prior to cognitive impairment, however the mechanism by which it occurs and its relevance to AD risk remain unknown. The brain predominantly metabolizes glucose, a substantial amount of which is shunted to the pentose phosphate pathway (PPP) in both neurons and astrocytes. The PPP generates antioxidant reducing factors such as NADPH and glutathione, and decreased PPP activity increases oxidative stress and cell death. Interestingly, our novel preliminary data describe a murine model with human apoE that recapitulates an E4-associated decrease in glucose metabolism and also documents decreases in multiple PPP metabolites. Thus, the central hypothesis of this proposal is that APOE influences neuronal function and survival through isoform-specific changes in glucose metabolism. Specifically, we hypothesize that E4 contributes to cognitive impairment through metabolic reprogramming in which glucose uptake is decreased and redox management via the PPP is reduced. Our preliminary data in mice show a stepwise decrease in brain glucose uptake (E2>E3>E4), and in vitro results suggest these differences are due to changes in astrocytic uptake via GLUT-1. Therefore, in the first Aim, we will test the hypothesis that E4 decreases cerebral glucose uptake through downregulation of the astrocytic glucose transporter GLUT-1 using a scintillation proximity assay with targeted manipulation of apoE isoforms, total protein concentrations and glucose transporters. To test the hypothesis that E4 decreases glucose entry into the PPP, we will quantitatively track glucose entry and metabolism in the cell through the unique precursor-product “tracing” afforded by Stable Isotope Resolved Metabolomics (SIRM), and translate our results through analysis of human brain tissue. Finally, we will test the hypothesis that E4 exacerbates oxidative damage and cell death due to a reduction in PPP-mediated management of oxidative stress. This will be accomplished in vitro through pharmacological manipulation of PPP enzymes and in vivo by assessing cognitive function, AD pathology, and oxidative damage using redox proteomics analysis of brain tissue from human apoE mice treated with a PPP stimulant. If successful, this proposal will provide novel therapeutic targets to normalize glucose metabolism in high-risk individuals. Enhancing cerebral metabolism by increasing glucose uptake and entry into the PPP could have great impact in preventing or delaying the onset of AD.