外周源性Abeta在阿尔茨海默病发生中的作用和机制研究

It is believed that amyloid β protein (Aβ) deposits in the brain of patients with Alzheimer’s disease (AD) originate from the brain itself. However, Aβ is also generated by peripheral tissues and cells, such as skeletal muscles, skin, bone and platelets. Whether peripheral Aβ contributes to brain AD-type pathologies remains largely unknown. In our preliminary experiment, using a model of parabiosis between wild type (Wt) mice and APPswe/PS1dE9 transgenic AD mice, we observed the formation of cerebral amyloid angiopathy and Aβ plaques in the wild type mice after a 12-month period of parabiosis, which were similar to those in the brains of control AD mice. Theirfore, we speculate that peripheral Aβ can enter the brain, form AD-type pathologies and cause cognitive impairment. In this project, the entry dynamics and mechanism of peripheral Aβ into brain will be investigated; Moreover, using a model of parabiosis between Wt mice and AD mice, we intend to explore the role of peripheral Aβ in inducing AD-type pathologies and cognitive impairment; In addition, we will investigate the preventive and therapeutic effect of inhibiting the entry of peripheral Aβ into brain on AD process using RAGE inhibitors or RAGE gene deletion method. The completion of this project will provide novel insight into AD pathogenesis from a systemic view, and support the development of therapies for AD by targeting Aβ metabolism in both the brain and the periphery.

传统观点认为AD患者脑内沉积的Aβ来自于脑内产生的Aβ（中枢源性），外周组织如骨骼肌、皮肤和血小板等均产生Aβ（外源性），但外周源性Aβ在AD发生中的作用尚不清楚。我们前期发现，系统疾病和外周脏器功能与Aβ代谢或AD风险密切相关，并将野生型小鼠和APP/PS1小鼠并联后发现，源于APP/PS1小鼠的Aβ可通过血液进入野生型小鼠脑内，并形成典型的淀粉样脑血管病（CAA）和Aβ斑块。基于这些发现，我们提出：外周源性Aβ可通过血脑屏障进入脑内，沉积形成Aβ斑块，并诱发AD相关病理和认知障碍，参与AD的发生。为此，本项目拟首先探讨外周源性Aβ进入脑内的动力学及机制；进一步通过并联模型，阐明外周源性Aβ进入小鼠脑内形成AD相关病理和对认知损害的影响，并揭示相关机制；最后探讨抑制外周源性Aβ进入脑内对AD的干预作用。本项目对于从系统角度来揭示AD发病机制、寻找AD防治新途径具有重要意义。

本项目首先探讨了外周源性Aβ是否可进入脑组织，将荧光标记Aβ通过尾静脉注射进入野生型小鼠体内，2小时后，通过双光子显微镜观察到脑组织中该荧光标记蛋白的存在；应用微透析技术在尾静脉注射Aβ后的野生型小鼠脑内进行动态微量生化取样，检测到脑组织间液Aβ水平先升高后降低。为明确外周源性Aβ进入脑内后是否可形成AD相关病理改变，进一步通过手术将野生型小鼠和APP/PS1转基因AD小鼠并联，使两只动物的外周循环系统合成一体，使其血液能够交换，为野生型小鼠施加外周血液Aβ干预，发现在并联12个月后，由APP/PS1小鼠进入野生型小鼠血液的Aβ，可进入其脑内沉积形成老年斑等AD特征性病理改变，诱发tau蛋白过度磷酸化、神经变性、神经炎症。进一步发现，与AD小鼠并联的野生型小鼠海马CA1区神经元的LTP明显受损，提示突触可塑性降低，表明其学习和记忆功能受损。血细胞产生的Aβ是外周Aβ主要来源，为了探讨外周血细胞产生的Aβ在AD发生中的作用，我们建立小鼠骨髓移植模型，发现将AD小鼠骨髓移植至Wt小鼠，产生的外周Aβ可以进入Wt小鼠脑内，并导致AD相关病理和行为缺陷。而将Wt小鼠骨髓移植到AD小鼠重建其外周血液系统，降低血细胞来源Aβ水平，发现可减轻AD相关病理和行为缺陷，进一步验证血细胞来源Aβ在AD发病中的重要作用，抑制外周Aβ产生可能是AD的潜在干预策略。这项研究发现了外周源性Aβ在AD发生中的病理作用，从全新角度揭示了AD发生发展的外周新机制，提示AD可能不仅仅是大脑本身的疾病，为从系统的角度来理解AD的发病机制和防治策略提供思路。