TFEB调控的溶酶体降解途径在ALA改善AD相关病变中的作用及机制研究

Alzheimer's disease (AD) is a chronic progressive neurodegenerative disease. Due to the complex molecular pathologies, current treatment for this disease is little effective. Recent studies have shown that autophagy-lysosomal degradation pathway is involved in the degradation of Aβ and hyperphosphorylated tau, two key proteins responsible for the formation of senile plaque and neurofibrillary tangles, the characteristic pathologies of AD. In the early stage of AD development, autophagy is induced but lysosomal degradation activity is compromised, resulting in Aβ and hyperphosphorylated tau accumulation, finally triggering AD. We recently uncovered that, the plant-derived omega-3 polyunsaturated fatty acid, alpha-linolenic acid (ALA), has the effect of antagonizing AD, and the neuroprotective properties of ALA are closely related to the regulation of lysosomes. Moreover, functional activity of lysosomal degradation pathway is directly dependent on the regulation of transcription factor EB (TFEB). Therefore, we hypothesized that ALA may play a neuroprotective role by activating TFEB-mediated lysosomal degradation activity, and then enhancing the lysosomal degradation of Aβ and hyperphosphorylated tau, inhibiting characteristic pathologies formation of AD in the early stage. To investigate the role and mechanism of lysosomal degradation pathway in the ameliorative effects of ALA on characteristic pathologies formation of AD, the current project will use senescence accelerated mouse prone 8 (SAMP8) mouse as AD animal model, and focus on the interaction between lysosomal degradation pathway and the early formation of Aβ deposition and tau hyperphosphorylation. In vivo and in vitro studies will be applied to explore the role of TFEB-mediated lysosomal degradation pathway in the protective effects of ALA on AD-related pathologies and its underlying mechanisms. This project will provide new insight into the early and nutritional prevention and control for AD.

阿尔茨海默病（AD）是一种慢性进行性发展的神经退行性疾病，尚缺乏特异性防治方法。前期研究表明，自噬—溶酶体系统参与AD特征性病变（老年斑和神经原纤维缠结）关键蛋白Aβ和p-Tau的清除。在AD病变早期自噬被激活但溶酶体降解功能出现障碍，导致Aβ和p-Tau蓄积，最终促发AD。我们近期发现ω-3多不饱和脂肪酸α-亚麻酸（ALA）能够拮抗AD，且文献提示其神经保护作用与调节溶酶体有关，而溶酶体活性受转录因子EB（TFEB）直接调控。据此我们推测ALA可能通过TFEB调节溶酶体活性，增强溶酶体对Aβ和p-Tau的清除，进而改善AD相关病变。本项目拟以快速老化小鼠SAMP8作为AD模型，以溶酶体降解途径与AD特征性病变形成早期的相互作用为切入点，采用体内动物和体外细胞试验相结合的方法，探讨TFEB调控的溶酶体降解途径在ALA改善AD相关病变中的作用及分子机制，为AD的早期预防和营养防治提供新思路。

阿尔茨海默病（AD）已成为严重的社会公共卫生问题，因其病因和机制不明尚缺乏特异性防治方法。本项目通过构建自然衰老的动物模型及PBDE-47染毒神经细胞模型，探讨TFEB调控的自噬溶酶体降解途径在α-亚麻酸（ALA）改善AD相关病变中的作用及分子机制。在体内研究中，通过ALA干预自然衰老的动物模型12个月，我们发现长期ALA干预能明显改善衰老大鼠的空间学习记忆能力，调节脑皮质和海马脂肪酸含量，明显减少脑实质和脑血管Aβ聚集引起的淀粉样蛋白沉积，并在一定程度上缓解脑内Tau蛋白过度磷酸化，提示膳食ALA干预能改善自然衰老导致的AD样病变。在体外研究中，我们选用日常生活中常见的一种阻燃剂，新型持久性有机污染物2, 2', 4, 4'-四溴联苯醚（PBDE-47），探讨其对AD发生的影响及TFEB调控的自噬溶酶体降解途径在其中的作用。用不同浓度PBDE-47对PC12神经细胞进行染毒，发现PBDE-47可引起神经细胞发生AD的两大特征病理改变：Tau过度磷酸化和Aβ蓄积；进一步机制研究发现，PBDE-47可通过抑制自噬生成并同时抑制自噬降解两个环节损伤神经细胞自噬；通过损伤神经细胞溶酶体的生物合成和功能，阻碍了自噬体与溶酶体的融合，从而阻断了自噬溶酶体对Aβ相关蛋白APP、β-CTF、α-CTF和Aβ42的降解；值得注意的是，过表达自噬相关基因7（ATG7）增强自噬无法逆转PBDE-47诱导的自噬和溶酶体损伤，但过表达组织蛋白酶D（Cathepsin B）、过表达调控自噬溶酶体合成的转录因子TFEB和沉默ATG7可显著改善PBDE-47诱导的自噬和溶酶体损伤状况，并减轻Aβ病理改变。有趣的是，这些有益作用均可被溶酶体抑制剂氯喹（CQ）所阻断。提示TFEB在PBDE-47致自噬溶酶体通路损伤引起AD病变的过程中发挥重要的调控作用。本研究以易获取的植物源性ALA为研究对象，从膳食营养干预角度探讨其对AD样病变的防治作用，既为阐明散发性AD环境病因和发病机制提供了新思路，也为ALA的开发利用提供了新方向。