叶酸通过miR-339-5p调控Neuronatin表达在阿尔茨海默病中的作用及机制

Alzheimer's disease (AD) is an insidious progressive neurodegenerative disease, characterized by progressive loss of neuron which is associated with cognitive deficits. However, the underlying biochemical mechanisms of AD remain obscure, and we need more effective means of diagnosis and treatment. Our previous research found that the level of miR-339-5p was significantly decreased in AD patients and APP/PS1 transgenic mice. Our preliminary results also show that miR-339-5p can bind to the 3’ untranslated region (UTR) of Neuronatin (Neuronatin, NNAT) mRNA and decreased its transcription. NNAT, a brain specific expression gene, is involved in the regulation of calcium ion channel, and play an important role in the formation and maintenance of the nervous system. NNAT is considered to be associated with memory impairment in Alzheimer's disease. Based on the literature and preliminary results, we hypothesized that, in pathological conditions, inhibition of miR-339-5p may increase the expression of NNAT, resulting in calcium overload in neurons, and then damage the synaptic function, which closely related to the loss of memory. The folic acid may regulate the expression of NNAT to relieve calcium overload in neuron via miR-339-5p. First we will investigate differential expression of plasma miR-339-5p in AD patients. Employing the APP/PS1 transgenic mice to build AD model, we try to explore the role of NNAT in calcium overload and synapsis, to investigate the effect of folic acid on the expression of miR-339-5p and NNAT, and to elucidate the protective function and mechanism of folic acid in AD. This project will provide a basis for the pathogenesis of neuroregeneration, and explore a new strategy for the treatment of AD.

阿尔茨海默病是一种起病隐匿的渐进性中枢神经系统退行性疾病，主要病理改变为神经元进行性丢失。其发病机制尚不明确缺乏有效的诊疗措施。前期研究结果发现AD患者和动物模型中miR-339-5p水平显著降低，miR-339-5p负性调控Neuronatin（Neuronatin, NNAT）的表达。脑内特异性表达的NNAT参与调控钙通道，被认为与记忆障碍有关。我们推测：病理情况下抑制表达的miR-339-5p使NNAT表达升高导致神经元内钙超载，损伤突触功能导致记忆功能缺失；叶酸通过调控miR-339-5p抑制NNAT表达，减少神经元钙超载发挥保护作用。本项目将明确AD患者血浆miR-339-5p的表达差异，采用转基因小鼠模型探索NNAT在神经元损伤中的作用，研究叶酸对miR-339-5p和NNAT表达的影响，阐明叶酸的神经元保护作用及机制。本研究将为AD发病机制提供依据，为AD治疗提供新策略。

阿尔茨海默病（Alzheimer's disease，AD）是一种发生在老年期或老年前期的慢性渐进性中枢神经系统退行性疾病，以不可逆的进行性记忆障碍和认知功能损害为主要临床症状。阿尔茨海默病的病因被认为是多因素、多基因、环境和年老因素共同作用导致的疾。其发病机制尚不明确，缺乏有效的诊疗手段。microRNAs在神经系统中广泛分布、稳定性高，在AD的发病中起着重要的调控作用，可作为理想的早期诊断生物学标记物。microRNA-339-5p（miR-339-5p）在AD患者脑组织中明显降低，其靶基因及在AD发病中的作用值得深入研究。我们的研究结果显示，在轻度认知功能障碍患者（MCI）及AD患者血浆中miR-339-5p的水平明显降低，提示循环的miR-339-5p可作为AD早期诊断的生物学标记物。通过萤光素酶报告基因和WB实验，明确了miR-339-5p通过与大脑发育相关基因（NNAT）的 mRNA 3’非翻译区的结合，抑制其的转录后翻译成Neuronatin。在皮层原代成熟神经元中，Neuronatin存在于神经元细胞膜上，与PSD-95存在共定位，提示其参与突触功能。过表达miR-339-5p能够显著下调Neuronatin的表达水平，改善细胞钙离子转运失衡，减轻细胞内钙超载，减少神经元死亡。在APP/PS1转基因小鼠中，血浆及脑组织中miR-339-5p的水平明显较低，且脑内Neuronatin的水平明显升高，提示了用叶酸调控miR-339-5p可能具有神经保护作用，可能作为AD的一种有效的治疗手段。