免疫治疗阻断tau朊样传播及其分子机制研究

Alzheimer’s disease (AD), a neurodegenerative disorder with no cure so far and the most common cause of dementia, has been emerging as one of the most challenging health problems and a huge socioeconomic burden as the Chinese population ages. As evidence shows the correlation between severity of dementia and extent of tau pathology load in the brain, tau has been selected to target for therapeutic intervention. Recent studies have shown that passive immunization with antibodies targeting tau may reduce tau pathology load and improve cognition in transgenic mouse models of AD. The therapeutic benefits of tau antibodies was thought to attribute to removal of pathological tau and inhibition of the induction of templated misfolding of normal tau by pathogenic tau which has been taken up in healthy neurons, possibly by antibody-mediated degradation of exogenous pathogenic tau within recipient neurons. However, the mechanism proposed above leaves unresolved the question why treatment with tau antibody reduces the levels of not only total tau but soluble tau as well. Given that direct reduction of tau protein expression by antisense oligonucleotides mitigates and even reverses pathological tau in vivo and inhibits tau seeding in vitro, we hypothesize that the major contribution of tau antibodies to block tau pathology propagation is to facilitate the degradation of, instead of exogenous tau aggregates, endogenous tau and thus reduce total tau level. To test this hypothesis, we propose in the present application to first screen panels of antibodies targeting either total or phosphorylated tau for inhibition of tau seeding in HEK293 cells expressing full-length, P301L mutated human 0N4R tau which is C-terminally tagged with venus, and to verify, with 1-3 of the antibodies showing highest efficacy in vitro, the inhibition of tau spread in vivo, and then to study the molecular mechanisms underlying the inhibitory effect of tau antibodies on prion-like spread of tau. The mechanistic study will be carried out by using molecular biology techniques in vitro in cell models, emphasizing on identification of the pathway by which endogenous tau is degraded and reduced. The completion of the proposed study will shed light on novel mechanisms of tau immunization, and help develop therapeutic strategy for the treatment of AD and related neurodegenerative disorders.

阿尔茨海默病(AD)是影响我国人口健康的突出问题，尚无有效防治手段。tau在AD致病中起重要作用，病理性tau呈朊样传播。近年研究显示用tau抗体进行免疫治疗可减轻AD动物模型自发性tau病理并改善记忆，但机制不明，文献推测可能是抗体介导外源致病性tau降解而阻断其向正常神经元的朊样传播。我们预实验显示抗体43D能阻断体内tau朊样传播，并且发现tau病理发生有赖于一定tau水平，而直接降低tau表达可抑制tau病理，因此我们提出抗体治疗主要降低细胞内源性tau的假设。本项目拟首先利用tau朊样传播细胞模型，体外筛选对tau传播有明确阻断作用的tau抗体，进行动物体内验证，然后利用体外细胞模型，通过分析细胞tau变化和抑制胞膜Fc受体、敲除胞内Fc受体TRIM21、抑制蛋白酶体及自噬等，验证上述假设，探讨免疫治疗阻断tau朊样传播的分子机制，为tau病理相关神经退行性疾病治疗提供实验基础。

随着我国人口老龄化程度不断加重，阿尔茨海默病（AD）已然成为影响我国人口健康的突出问题。AD作为一种最常引起认知功能减退（或痴呆）的渐进性中枢神经系统退行性疾病，目前尚无有效治疗手段。现有药物主要对晚期患者进行对症治疗，既不能治愈疾病，也不能改变疾病进程。目前已知微管相关蛋白tau的病理改变在神经细胞退行性变中起重要作用并与临床症状呈正相关，且在阿尔茨海默病患脑内的异常tau呈朊样传播。本项目研究发现，静脉注射针对tau蛋白分子上特定区域的小鼠源性单克隆抗体，可在一定程度上阻断病理性tau蛋白在模型小鼠脑内的朊样传播，从而起到减缓脑内tau病理进展的作用。免疫治疗手段阻断tau朊样传播涉及多环节作用机制，包括小胶质细胞吞噬清除抗原抗体复合物和神经元内降解清除病理性tau等。项目研究提示采用tau蛋白抗体治疗可能起到抑制或延缓AD疾病进展的治疗作用。后续转化医学研究将着眼于将该小鼠源性单克隆抗体人源化，即通过基因工程等手段将本质上属于小鼠免疫球蛋白的该抗体转化为人免疫球蛋白，同时保持其抗原决定簇和免疫反应性，从而保持其被动免疫治疗作用。