血脑屏障转运Aβ异常在糖尿病认知障碍中的作用及机制研究

The mechanism of cognitive dysfunction in diabetes mellitus is still unknown, but it is closely related to the accumulation of β amyloid protein（Aβ）in brain. We put it forward as one hypothesis that the abnormal transport of Aβ across the blood-brain barrier (BBB) is the initiating factor of the cognitive dysfunction in diabetes mellitus because the abnormalities of generation and degradation for Aβ only partly explain the cause of the Aβ accumulation in the brain. Our tentative study showed the abnormal transport of Aβ at the BBB in the streptozocin-induced mice, which is correlated with the Aβ accumulation in the brain. In this study, we will investigate the changes of the RAGE-mediated Aβ influx and LRP1-mediated Aβ efflux across the BBB, the Aβ levels and synaptic plasticity of the hippocampus, and the cognitive dysfunction in type 2 spontaneous diabetic mice, and analyze the correlation of the abnormal transport of Aβ across the BBB with the cognitive dysfunction. The effects of RAGE antagonist, LRP1 activator and hypoglycemic drugs on cognitive dysfunction and the molecular mechanism of the abnormal transport of Aβ across the BBB will also be investigated. Our proposal will reveal that the upregulation of RAGE-mediated Aβ influx or downregulation of LRP1-mediated Aβ efflux across the BBB result in the Aβ accumulation, reduction of synaptic plasticity of the hippocampus and cognitive dysfunction in diabetes mellitus, and what signal pathway regulates transport of Aβ across the BBB, and subsequently confirm the RAGE and LRP1 at the BBB as novel drug targets for prevention and treatment of cognitive dysfunction in diabetes mellitus and lay the foundation for further development of the new drugs.

糖尿病引起的认知障碍机制不明，但与脑内Aβ聚集密切相关。从Aβ生成与降解角度仅能解释部分原因，因此我们提出研究假说：血脑屏障转运Aβ异常是糖尿病认知障碍的始动因素。前期研究发现，链脲霉素诱导的糖尿病小鼠血脑屏障上Aβ转运异常，且与脑内Aβ聚集相关。本研究拟采用自发性2型糖尿病小鼠，以血脑屏障上Aβ内向转运体RAGE和外向转运体LRP1为核心，研究血脑屏障上RAGE和LRP1转运Aβ变化规律及其与海马Aβ水平、突触可塑性和认知障碍的相关性；观察RAGE拮抗剂、LRP1激活剂及降糖药的调控作用；探讨RAGE和LRP1转运Aβ异常的分子机制。从而明确糖尿病血脑屏障上RAGE内向转运Aβ上调、LRP1外向转运Aβ下调导致海马Aβ聚集、突触可塑性下降，造成认知障碍；揭示调节RAGE和LRP1转运Aβ的信号通路；确认RAGE和LRP1是调控糖尿病认知障碍的分子靶标，为研究抗糖尿病认知障碍新药奠定基础。

糖尿病认知障碍是当前全球备受关注的重大公共卫生问题，其发病机制不明。揭示糖尿病认知障碍发生机制、确认其调控分子靶标、寻找有效防治药物已成为国内外研究热点。本项目采用2型糖尿病模型db/db小鼠，研究3、6、9及12周小鼠血脑屏障RAGE与LRP1表达及其转运Aβ功能、海马Aβ水平、海马神经元凋亡与突触可塑性以及动物认知功能，并进行相关性分析；研究RAGE抑制剂、LRP1激活剂以及抗糖尿病药物胰岛素、二甲双胍、格列本脲对糖尿病小鼠血脑屏障RAGE与LRP1转运Aβ、海马Aβ水平、海马神经元凋亡、突触可塑性以及认知功能的影响；研究血脑屏障RAGE与LRP1转运Aβ异常的分子机制。研究结果显示：糖尿病小鼠血脑屏障RAGE表达及其内向转运Aβ功能随病程延长逐渐上调，而LRP1表达及其外向转运Aβ功能随病程延长逐渐下调，海马Aβ水平逐渐增多，突触可塑性和认知功能渐进性下降。RAGE内向转运Aβ上调和LRP1外向转运Aβ下调与记忆损害具有显著相关性。PPARγ激动剂、胰岛素、二甲双胍、格列本脲均能降低血脑屏障RAGE表达及其内向转运Aβ、上调LRP1表达及其外向转运Aβ，降低海马Aβ水平，增强突触可塑性，改善认知功能。RAGE抑制剂能改善糖尿病小鼠认知障碍、下调血脑屏障RAGE表达及内向转运Aβ，但对LRP1表达及其外向转运Aβ无明显影响。体外研究发现，AGEs通过RAGE-NF κB-PPARγ信号通路上调RAGE表达及其内向转运Aβ、下调LRP1表达及其外向转运Aβ，PPARγ激动剂对AGEs诱导Aβ转运具有双向调控作用。综上所述，本项目研究表明，血脑屏障两个转运体RAGE和LRP1转运Aβ异常参与糖尿病认知障碍的发生和发展，PPARγ激动剂、RAGE抑制剂、胰岛素、二甲双胍、格列本脲可通过纠正RAGE或LRP1异常转运Aβ而改善糖尿病认知障碍。本研究诠释了糖尿病认知障碍发生的新机制，发现了降血糖药物的新药理作用，为进一步研究开发防治糖尿病认知障碍药物奠定基础。