Influence of apoE on LRP1 function and Beta-Amyloid Transport Across the BBB

apoE 对 LRP1 功能和跨 BBB 的 β-淀粉样蛋白转运的影响

• 批准号: 8893856
• 负责人: Corbin Bachmeier
• 金额: $ 30.46万
• 依托单位: ROSKAMP INSTITUTE, INC.
• 依托单位国家: 美国
• 财政年份: 2012
• 资助国家: 美国
• 起止时间: 2012-08-01 至 2016-05-31
• 项目状态: 已结题
• 来源: https://reporter.nih.gov/project-details/8893856
• 关键词: Affect; Alleles; Alzheimer' s Disease; Amyloid Protein AA; Amyloid beta-Protein; Apolipoprotein E; Attenuated; Binding; Blood; Blood - brain barrier anatomy; Brain; Cause of Death; Cell Culture Techniques; Clinical Trials; Data; Deposition; Disease; Drainage procedure; Excision; Genotype; Impaired cognition; Investigation; LDL-Receptor Related Protein 1; Late Onset Alzheimer Disease; Ligands; Lipoprotein Receptor; Mediating; Modality; Nerve Degeneration; Pathogenesis; Pathway interactions; Patients; Process; Production; Protein Isoforms; Proteins; Reporting; Role; Testing; Time; Transgenic Animals; Transgenic Mice; United States; Work; apolipoprotein E-3; apolipoprotein E-4; drug discovery; genetic risk factor; improved; in vitro Model; in vivo; neurofibrillary tangle formation; neurotoxic; novel; prevent; response; trafficking; transcytosis; treatment strategy

DESCRIPTION (provided by applicant): Alzheimer's disease (AD) is the sixth leading cause of death in the United States and is characterized by the formation of neurofibrillary tangles and the deposition of beta-amyloid (A�) proteins in the brain. A� accumulation in the brain is a key factor in AD pathogenesis and is a predictor of cognitive impairment. A� reducing strategies in AD have primarily targeted A� production mechanisms which, to this point, have been largely unsuccessful in clinical trials. Evidence now suggests that the excessive accumulation of A� in the AD brain is not due to aberrant A� production, but the result of impaired A� removal from the brain. Thus, targeting clearance-related pathways may prove most effective in attenuating A� accumulation in the AD brain. The blood-brain barrier (BBB) transporter primarily responsible for the brain elimination of A� is the low density lipoprotein receptor-related protein 1 (LRP1). One of the ligands with which LRP1 interacts is apolipoprotein E (apoE) and possession of the E4 allele represents the strongest genetic risk factor for AD. However, the role of apoE in the exchange of A� across the BBB is not clearly defined. Several studies in cell culture have shown a stimulation of A� internalization in the presence apoE, while others have reported apoE is disruptive to A� clearance across the BBB. In our preliminary studies we sought to clarify the role of apoE in the BBB clearance of A�. Our studies and the work of others indicate that when apoE is bound to A�, the transport of A� across the BBB is dramatically attenuated. However, for the first time, we demonstrate that unbound apoE in the brain can facilitate A� BBB clearance in an isoform-specific manner (apoE3 >> apoE4). At the BBB level, few studies have investigated the influence of apoE isoforms on LRP1 function, in particular LRP1 shedding (i.e., formation soluble LRP1, which is nonfunctional and does not transcytose A�). In apoE4 transgenic mice and AD patients carrying the E4 allele, we observe elevated LRP1 shedding in the brain compared to apoE3 genotypes. When combined with our in vivo A� BBB transit data, our preliminary studies demonstrate an inverse relationship between LRP1 shedding and A� transport across the BBB, one that is apoE genotype-specific. We hypothesize that apoE4 is less efficient than other apoE isoforms in preventing LRP shedding, which leads to reduced A� clearance across the BBB. Our preliminary findings also show that modulation of LRP1 internalization leads to enhanced LRP1 shedding and reduced A� transport across an in vitro model of the BBB. Since LRP1 internalization and transcytosis are essential steps in eliminating A� from the brain, we will examine the effect of apoE isoforms on LRP1-mediated internalization and subcellular trafficking of A� in the BBB. Overall, the current proposal will investigate severa potential mechanisms to elucidate the apoE- dependant differences we observe in LRP1 shedding and A� transit across the BBB. These studies will improve our understanding of the relationship between apoE and LRP1 in AD and may provide new treatment modalities for this disease.

描述（由申请人提供）：阿尔茨海默氏病（AD）是美国第六大死亡原因，其特征在于神经元缠结的形成和β-淀粉样蛋白（A β）在大脑中的沉积。A β在大脑中的积累是AD发病机制的关键因素，也是认知障碍的预测因子。AD中的A减少策略主要针对A产生机制，到目前为止，在临床试验中基本上是不成功的。现在有证据表明，AD大脑中A β的过度积累不是由于A β产生异常，而是A β从大脑中清除受损的结果。因此，靶向清除相关的途径可能被证明在减弱AD大脑中的A β积累方面最有效。血脑屏障（BBB）转运蛋白主要负责大脑消除A β是低密度脂蛋白受体相关蛋白1（LRP 1）。与LRP 1相互作用的配体之一是载脂蛋白E（apoE），E4等位基因的拥有代表了AD最强的遗传风险因素。然而，apoE在A β跨血脑屏障交换中的作用尚不清楚。在细胞培养中的几项研究表明，在apoE存在的情况下，A β内化受到刺激，而另一些研究则报道apoE对A β穿过BBB的清除具有破坏性。在我们的初步研究中，我们试图阐明apoE在BBB清除A β中的作用。我们的研究和其他人的工作表明，当apoE与A β结合时，A β穿过BBB的转运显著减弱。然而，我们第一次证明了脑中未结合的apoE可以以亚型特异性的方式促进A-BBB的清除（apoE 3>> apoE 4）。在BBB水平，很少有研究调查了apoE同种型对LRP 1功能的影响，特别是LRP 1脱落（即，形成可溶性LRP 1，它是无功能的，不转胞苷A β）。在apoE4转基因小鼠和携带E4等位基因的AD患者中，我们观察到与apoE3基因型相比，LRP 1在脑中的脱落增加。当结合我们的体内A-BBB转运数据时，我们的初步研究表明LRP 1脱落和A-BBB转运之间存在反比关系，这是apoE基因型特异性的。我们假设apoE4在阻止LRP脱落方面比其他apoE亚型效率低，这导致A β穿过BBB的清除率降低。我们的初步研究结果还表明，LRP 1内化的调节导致增强的LRP 1脱落和减少的A β转运通过体外模型的血脑屏障。由于LRP 1内化和转胞吞作用是从大脑中消除A β的重要步骤，因此我们将研究apoE亚型对LRP 1介导的A β在BBB中的内化和亚细胞运输的影响。总的来说，目前的建议将调查几个潜在的机制，以阐明我们观察到的LRP 1脱落和A β通过BBB的apoE依赖性差异。这些研究将提高我们对AD中apoE和LRP 1之间关系的理解，并可能为这种疾病提供新的治疗模式。