Lead Exposure and Beta-Amyloid Transport by Brain Barriers

摘要： β-淀粉样蛋白（Aβ）在脑细胞外实质和液体中的积聚是导致阿尔茨海默病（AD）病因学中神经元细胞损伤的淀粉样蛋白级联反应中的关键事件。血液和脑间质液之间的血脑屏障（BBB）和血液和脑脊液（CSF）之间的血-CSF屏障（BCB）在维持脑细胞外环境中A B的稳态中起重要作用。由于脑屏障系统是铅毒性的已知靶点，因此铅对脑屏障的毒性很可能影响脑屏障系统中调节A B转运和代谢的关键过程。因此，在本研究中要测试的中心假设是，暴露于Pb损害脑屏障系统，这损害清除率并最终增加BBB和BCB处的A B的泄漏，促进A B和Pb离子之间的物理化学反应，最终导致大脑和血管中淀粉样蛋白斑块的形成增加。为了验证这一假设，我们设计了三组具体目标。在目标1中，我们将使用最先进的动态对比增强计算机断层扫描（DCE-CT）来定量过表达A B并在脑中具有可检测的淀粉样蛋白斑块的Tg-APP小鼠以及WT小鼠中铅暴露前后的真实的脑局部血流量、血容量和BBB渗透性。我们还将以剂量-时间依赖性方式表征铅暴露导致的原纤维A B沉积物从脑毛细血管向脑实质的转移。我们将重点关注两种转运蛋白，LRP-1和LRP-1，在血脑屏障与铅处理的表达。目标2中的实验将重点关注两个A B的作用， 转运蛋白，即，脂蛋白受体蛋白-1（LRP 1）和晚期糖基化终产物（AGEs）介导A B 主要通过BCB的运输，以及Pb暴露如何影响A-B穿过BCB的运输方向。最后，在目标3中，我们将使用同步加速器X射线荧光（XRF）成像技术结合免疫组织化学来共定位Pb与淀粉样聚集体，并使用K X射线荧光（KXRF）技术量化骨中的真实的时间Pb浓度（PbBn），并建立不同剂量和时间Pb暴露后PbBn与脑和血管中淀粉样聚集体之间的关联。这些研究将建立一个新的概念，即脑屏障在调节铅诱导的脑A B寡聚体和斑块以及血管中起关键作用。我们还将建立铅暴露和脑屏障对AB通量的渗透性变化之间的关系，并提供线索，慢性铅暴露和脑血管渗透性的变化是否有助于AD的发病机制和发展。该研究将有助于为AD的诊断、治疗和预防提供新的策略。 PHS 398/2590（版本06/09）第1页续格式页

Abstract:   Accumulation of beta‐amyloid (Aβ) in brain extracellular parenchyma and fluid is the key event in the amyloid cascade leading to neuronal cell damage in the etiology of Alzheimer's disease (AD). The blood‐brain barrier (BBB) between the blood and brain interstitial fluid and the blood-CSF barrier (BCB) between the blood and cerebrospinal fluid (CSF) play an important role in maintaining the homeostasis of AΒ in brain extracellular milieu. Since the brain barrier systems are the known targets of Pb toxicity, it is quite possible that Pb toxicity on brain barriers may affect the critical processes in brain barrier systems that regulate AΒ transport and metabolism. Thus, the central hypothesis to be tested in this study is that exposure to Pb damages the brain barrier systems, which compromises the clearance and eventually increases the leakage of AΒ at the BBB and BCB, facilitates the physiochemical reactions between AΒ and Pb ions, ultimately leading to an increased formation of amyloid plaques in both brains and blood vessels. To test this hypothesis, we have designed three sets of specific aims. In aim 1, we will use the state‐of‐the‐art dynamic contrast‐ enhanced computed tomography (DCE‐CT) to quantify the real‐time brain regional blood flow, blood volume, and BBB permeability before and after Pb exposure in Tg‐APP mice which overexpress AΒ and have the detectable amyloid plaques in brain as well as WT mice. We will also characterize the shift of fibril AΒ deposits from the brain's capillary vessels to its parenchyma as a result of Pb exposure in a dose‐time dependent fashion. We will focus on expressions of two transporters, RAGE and LRP‐1, in the BBB treated with Pb. The experiments in Aim 2 will focus on the role of two AΒ transporters, i.e., lipoprotein receptor protein‐1 (LRP1) and advanced glycation end products (RAGE) in mediating AΒ transport by mainly the BCB, and how Pb exposure may affect the direction of AΒ transport across the BCB. Finally, in Aim 3, we will use synchrotron X‐ray fluorescence (XRF) imaging technique coupled with immunohistochemistry to co‐ localize Pb with amyloidal aggregates and K X‐ray fluorescence (KXRF) technique quantify real‐time Pb concentrations in bone (PbBn) and to establish the association between PbBn and amyloid aggregation in brain and blood vessels after Pb exposure at different doses and time. These studies will establish a novel concept that the brain barriers play a key role in regulating Pb‐induced brain AΒ oligomers and plaques as well as in blood vessels. We will also establish the relationship between Pb exposure and permeability changes of brain barriers to AΒ fluxes and provide clues as to whether chronic Pb exposure and changes in cerebral vascular permeability contribute to AD pathogenesis and development. The research will help develop the novel strategies for diagnosis, treatment and prevention of AD.    PHS 398/2590 (Rev. 06/09) Page 1 Continuation Format Page