组蛋白去乙酰化酶2磷酸化微管相关蛋白tau负向调控学习记忆

Learning and memory is the main clinical character in Alzheimer’s disease(AD), and therapeutic drugs like nerve growth factors and acetylcholine enhancers can never reverse its pathological progress. Thus, to clarify its etiology is necessary. Transgenic mice models and brain slices of patients died from AD both show that there are hypoacetylated histone and abnormally elevated HDAC2 in AD early stages(Braak and Braak stage I-II, BB I-II). BB is determined by the location and numbers of NFTs(Neurofibrillary tangles), which is mainly composed of hyperphosphorylated tau. What’s the relationship between elevated HDAC2 in BB early stages and the BB determiner hyperphosphorylated tau? Our preliminary data shows that elevated HDAC2 can induce tau to be hyperphosphorylated significantly. Since hyperphosphorylated tau itself can induce AD-like neurodegeneration, so we propose that HDAC2 impairs learning and memory via hyperphosphorylated tau. Reports have shown that the mechanism of HDAC2 negatively regulate learning and memory is that HDAC2 should directly bind to the promoter or coding region of learning and memory related genes then inhibit the transcription of them. Unlike the reported ones, our project on the other side shows a thoroughly new mechanism of HDAC2 in memory impairments, that is without the directly binding to memeory related genes, HDAC2 can also impair learning and memory via hyperphosphorylated tau. Hippocampal stereoinjection, immunoprecipitation and confocal imaging are all employed in this project to utterly classify this new finding.

学习记忆障碍是阿尔茨海默病（AD）最显著的临床症状，神经生长因子类和提高乙酰胆碱的药物虽能缓解症状却完全无法逆转AD致死性的病理进程。因此，明确AD的发病原因十分必要。AD病人死后脑内和转基因小鼠模型发现组蛋白乙酰化水平显著降低和组蛋白去乙酰化酶2（HDAC2）的异常增高。那在AD病理早期便异常增高并导致记忆永久性损伤的HDAC2和AD病理分期指标过度磷酸化的tau蛋白之间有什么样的联系呢？申请者前期工作显示HDAC2水平上调后tau蛋白磷酸化水平显著升高，而过度磷酸化的tau本身便能导致AD样病变。由此我们推测不需要HDAC2本身结合到靶基因上抑制学习记忆相关基因转录，HDAC2便可通过使tau蛋白发生过度磷酸化而导致神经退行性变，这是HDAC2负性调控学习记忆的新机制。本项目将采用海马立体定位注射、免疫共沉淀、激光共聚焦扫描成像等技术全面阐述HDAC2在学习记忆中的负向调控作用新机制。

阿尔茨海默病（Alzheimer’s disease, AD）是一种进行性发展的神经系统退行性疾病。约90%以上的病人为散发性。表观遗传在此过程中起着重要作用。本项目中申请者发现组蛋白去乙酰化酶2（HDAC2）在3xTg-AD转基因小鼠（一种公认的AD转基因小鼠模型）中含量显著上升，并能使AD的病理分期指标微管相关蛋白tau发生过度磷酸化，且导致突起损伤及树突棘成熟障碍从而导致学习记忆受损。那么，HDAC2这个去乙酰化的酶为何会导致tau蛋白发生磷酸化，而非乙酰化反应呢？生物信息学手段及实验证实能量代谢相关激酶AMPK执行了这一作用。申请者研究结果显示AMPK的含量跟活性受到miR101b的调控。那在胞核内高表达的HDAC2是如何调控胞浆内下游miR101b的水平的呢？同样，生物信息学手段及实验证实核内发挥作用的miR101b的转录因子HNF-4A受到HDAC2去乙酰化调控作用于miR101b的前体上，从而调控了miR101b的含量。这样通过环环相扣，逐步递进，我们阐明了在AD里起着“坏作用”的去乙酰化酶HDAC2的分子机理。这是继2009及2012年麻省理工学院的蔡立惠教授发表在Nature文章的进一步延伸，即：不需要HDAC2本身的直接结合，而是通过去乙酰化作用调控miR101b的转录因子HNF-4A的水平进而调控miR101b的下游分子AMPK，最终使微管相关蛋白tau过度磷酸化，最后通过过度磷酸化的tau 引起的突起及树突棘损伤导致学习记忆障碍。这为HDAC2成为AD治疗的有效靶点提供了新的有力的实验依据。这也是在人脑内异常上升的HDAC2导致AD病理分期指标过度磷酸化的tau的直接报道。