抑制Ras法尼基化改善阿尔兹海默病认知功能的分子机制研究

Alzheimer’s disease (AD), the most common form of dementia, is characterized by progressive loss of neurons and decline in memory and cognition. The main hallmarks of AD are the accumulation of beta-amyloid (amyloid plaques) outside neurons and the deposits of tau protein (neurofibrillary tangles) inside neurons. There is no effective therapeutics for the treatment of AD up to now. Our previous studies showed that reducing the farnesylation substrate of Ras, named isoprenoid farnesyl-pyrophosphate (FPP), improves the cognitive function in mouse model of AD associated with memory impairment. The current project will examine the effects and underlying mechanisms of farnesyltransferase inhibitor (FTI) lonafarnib and the farnesyl thiosalicylic acid (FTS) on memory function of AD mice. The present study will investigate: (1) whether inhibited Ras farnesylation can upregulate α7nAChR (function, expression, structure-activity and trafficking) to resist the neurotoxicity of Aβ; (2) whether inhibited Ras farnesylation can increase α7nAChR-related PI3K-Akt pathway leading to LTP enhancement and spatial cognitive potentiation; (3) whether inhibited Ras farnesylation through increasing phosphorylation of Akt and expression of BDNF can reduce the death of neuronal cells in a α7nAChR-dependent manner. In this way, we can get the underlying mechanisms of inhibited Ras on cognitive impairment of Alzheimer's disease (AD), The successful accomplishment of this project will provide evidence for the development of novel therapeutics for the treatment of AD by targeting Ras farnesylation.

阿尔兹海默病（AD）是以进行性认知障碍为主要临床表现的神经退行性疾病，其主要病理特征是β-淀粉肽（Aβ）沉积和神经元纤维缠结。目前仍缺乏有效的防治措施。我们前期研究结果表明，减少小G蛋白Ras法尼基化底物焦磷酸法尼酯（FPP）产生可有效拮抗Aβ诱导的认知功能障碍。在此基础上，本课题以法尼基转移酶抑制剂（FTI）洛那法尼和膜结合抑制剂法尼基硫代水杨酸（FTS）作为工具药物靶向抑制Ras法尼基化，探讨抑制Ras法尼基化是否通过（1）上调α7胆碱能受体（功能、表达、构效和膜分布）以拮抗Aβ神经毒作用；（2）激活α7胆碱能受体介导的PI3K-Akt信号通路而增强AD脑突触可塑性；（3）活化α7胆碱能受体增强Akt磷酸化水平及BDNF水平进而保护AD脑海马神经再生。明确抑制Ras法尼基化改善AD认知障碍的神经保护作用及其分子机制，为靶向Ras法尼基化开发新的AD防治药物提供科学依据。

阿尔兹海默症（Alzheimer’s disease，AD），是以进行性认知障碍为主要临床表现的神经退行性疾病。Ras蛋白是小G蛋白超家族的一种，法尼基化是小G蛋白Ras翻译后修饰的第一步。AD早期患者脑内Ras水平（包括细胞膜上活化的和细胞质内的）已有明显增强。我们的前期研究发现，他汀类药物通过减少Ras活化物FPP的产生可增强正常成年小鼠的认知功能。海马α7胆碱能受体（nicotinic acetylcholine receptor α7-subunit，α7nAChR）对记忆形成有重要作用。Aβ (β-淀粉样蛋白，β-amyloid peptides) 通过与α7nAChR结合，抑制α7nAChR电流，减弱海马突触传递、突触可塑性及学习记忆能力。α7nAChR活化与其表达、构效及由胞内向细胞膜的迁移水平密切相关。AD脑的关键性改变是神经元棘密度显著减少而引起的突触功能失活。H-Ras信号通路与突触可塑性和记忆形成密切相关。因此，我们推测抑制Ras法尼基化改善AD的认知功能可能与其神经保护作用，即对突触功能、神经再生及相关受体的改善作用有关。本研究首次创新性地提出并证实，Ras靶向抑制剂Lonafarnib可抑制CHRNΑ7启动子DNA甲基化，增加α7nAChR的总表达，并且增加CaMKII通路介导的α7nAChR的膜转运，进而上调海马CA1锥体细胞中α7nAChR活性；通过对α7nAChR的上调作用，Lonafarnib通过H-Ras-α7nachr依赖的CaMKⅡ-CREB通路上调BDNF含量，拯救受损的树突棘、树突形态和突触蛋白(Syn和PSD95)，改善Aβ1-42小鼠的突触传递和可塑性，挽救其突触损失，进而改善AD模型鼠的认知功能。为抑制Ras抗痴呆作用的细胞基础提供新的理论依据，为研发高效更具靶向性的抗痴呆药物提供新靶标和新策略。