Deciphering molecular mechanisms that underlie brain endothelial cell dysfunction with APOE4

摘要 血脑屏障(BBB)在维持大脑完整性方面起着关键作用。BBB可防止不必要的 分子进入大脑，并提供必要的营养和信号分子，以满足高- 神经元的能量需求。特化的脑内皮细胞(BEC)是血脑屏障功能的中枢。 BEC表达紧密连接蛋白，限制细胞旁对血液和BECs因子的通透性 形成一个广泛的网络，每个神经元都由它自己的毛细血管供应。目前的研究表明 BEC功能障碍在衰老中普遍存在，导致更高的渗漏和更低的血管覆盖率。这些 变化可能通过两种方式影响认知：1)对血浆蛋白的较高BEC暴露可导致 直接或通过旁观者效应(例如，神经胶质介导的神经炎症)和；2)下血管 覆盖范围限制了对神经元的必要营养供应。一个重要的问题是范围和潜在的 老年认知功能减退的遗传因素危险因素调节BEC功能的机制(S)。这样的一个 因素是载脂蛋白E基因，因为与载脂蛋白3相比，载脂蛋白4与老年人的认知功能障碍有关 成年人。我们的体内数据支持APOE4与衰老中的BEC功能障碍有关，并且可能 潜在的机制已经显现。血管生成生长因子对控制渗漏和 通过对BEC职能采取行动来维持船只覆盖范围。我们的数据显示了一种机械性的相互作用 存在于APOE和表皮生长因子(EGF)途径之间。具体而言，载脂蛋白(ApoE)E3 由BECs通过apoE受体以自分泌/旁分泌的方式产生信号以增加产量 可改善BEC功能。然而，这一过程被apoE4所破坏。基于这些 数据，我们建议检验这一假设，即apoE4受体信号转导失败导致BEC功能障碍和 EGF可以改善这种功能障碍。我们进一步提出，这一机制有助于促进BEC 阿尔茨海默病(AD)患者观察到的功能障碍。载脂蛋白E4是散发性AD的最大遗传风险， 与载脂蛋白3相比，风险增加高达12倍，大脑中高水平的淀粉样蛋白-β(Aβ)是主要原因 AD的组件。我们的初步数据表明，Aβ会加重与载脂蛋白4相关的BEC功能障碍。因此， 我们的实验将评估载脂蛋白4是否会增加BEC功能障碍，以及β是否会加剧这种功能 体内功能障碍。我们将研究载脂蛋白E受体信号转导失败的可能性。 载脂蛋白E4的功能障碍，这种干扰会因Aβ而加剧。最后，我们将测试外围设备是否 应用EGF可减少BEC和认知功能的缺陷。我们的研究可能与载脂蛋白E4有关 相关BEC功能障碍是导致老年和AD患者认知功能减退的重要途径

ABSTRACT The blood brain barrier (BBB) plays a key role in maintaining brain integrity. The BBB prevents unwanted molecules from entering the brain and supplies essential nutrients and signaling molecules to meet the high- energy demand of neurons. Specialized brain endothelial cells (BECs) are central to the function of the BBB. BECs express tight junction proteins that limit paracellular permeability to factors from the blood and BECs form an extensive network with every neuron supplied by its own capillary. Current research has demonstrated that BEC dysfunction is prevalent in aging leading to both higher leakiness and lower vessel coverage. These changes may affect cognition in two ways: 1) Higher BEC leakiness to plasma proteins can lead to damage of neurons directly or through bystander effects (e.g. glial mediated neuroinflammation) and; 2) Lower vessel coverage limits the supply of essential nutrients to neurons. An important question is the extent and underlying mechanism(s) that genetic factors risk factors for cognitive decline in aging modulate BEC function. One such factor is APOE genotype, as APOE4 is associated with cognitive dysfunction compared to APOE3 in older adults. Our in vivo data supports that APOE4 is associated with BEC dysfunction in aging, and a potential underlying mechanism has emerged. Angiogenic growth factors are important for controlling leakiness and maintaining vessel coverage through actions on BEC function. Our data suggest a mechanistic interaction exists between APOE and epidermal growth factor (EGF) pathways. Specifically, that apolipoprotein (apoE) E3 produced by BECs signals in an autocrine/paracrine-like manner via apoE receptors to increase the production of EGF, resulting in improved BEC function. However, this process is impaired with apoE4. Based on these data, we propose to test the hypothesis that failure in apoE4 receptor signaling leads to BEC dysfunction and that EGF can ameliorate this dysfunction. We further propose that this mechanism contributes to BEC dysfunction observed in Alzheimer's disease (AD) patients. APOE4 is the greatest genetic risk for sporadic AD, increasing risk up to 12-fold compared to APOE3 and high levels of amyloid-β(Aβ) in the brain are a major component of AD. Our preliminary data suggest Aβ exacerbates APOE4 associated BEC dysfunction. Thus, our experiments will evaluate whether APOE4 increases BEC dysfunction and whether Aβ exacerbates this dysfunction in vivo. We will examine the possibility that a failure in apoE receptor signaling underlies BEC dysfunction with apoE4, and that this disruption is exacerbated by Aβ. Finally, we will test whether peripheral administration of EGF reduces deficits in BEC and cognitive function. Our studies would implicate apoE4 associated BEC dysfunction as an important pathway contributing to cognitive decline in both aging and AD