Lead Exposure and Beta-Amyloid Transport by Brain Barriers

摘要：中国--中国 在阿尔茨海默病(AD)的病因学中，β-淀粉样蛋白(A-β)在脑细胞外实质和液体中的积聚是淀粉样蛋白级联反应导致神经细胞损伤的关键事件。血与脑组织液之间的血脑屏障和血与脑脊液之间的血脑屏障在维持脑细胞外环境中AΒ的动态平衡方面起着重要作用。由于脑屏障系统是铅毒性的已知靶点，脑屏障上的铅毒性很可能影响脑屏障系统中调节A-Β转运和代谢的关键过程。因此，本研究要检验的中心假设是，铅暴露损害了脑屏障系统，损害了清除，最终增加了血脑屏障和血脑屏障AΒ的渗漏，促进了AΒ与铅离子之间的物理化学反应，最终导致脑和血管中淀粉样斑块的形成增加。为了验证这一假设，我们设计了三套具体的目标。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)来实时量化铅暴露前后TG-APP小鼠大脑区域的血流量、血容量和血脑屏障通透性，这些小鼠在大脑中过表达AΒ并在大脑中有可检测到的淀粉样斑块。我们还将以剂量-时间依赖的方式表征由于铅暴露而导致的原纤维AΒ沉积从大脑的毛细血管到脑实质的转移。我们将重点研究两种转运蛋白RAGE和LRP-1在铅处理的血脑屏障中的表达。AIM 2的实验将集中于两个AΒ转运体，即脂蛋白受体蛋白1(LRP1)和晚期糖基化终末产物(RAGE)在主要通过血脑屏障介导AΒ转运中的作用，以及铅暴露如何影响AΒ跨血脑屏障转运的方向。最后，在目标3中，我们将使用同步辐射X射线荧光(XRF)成像技术和免疫组织化学相结合的方法对铅与淀粉样聚集体进行共定位，并使用KXRF技术实时定量骨中铅浓度(PbBn)，建立不同剂量和时间铅暴露后脑组织和血管中铅与淀粉样聚集性之间的联系。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AΒ寡聚体和斑块以及血管中发挥关键作用。我们还将建立铅暴露与脑屏障A-Β通透性变化之间的关系，为慢性铅暴露和脑血管通透性变化是否参与AD的发生发展提供线索。这项研究将有助于开发AD的诊断、治疗和预防的新策略。 这是一个很大的问题。 PHS 398/2590(06/09版)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