七叶甙抑制少突胶质细胞凋亡降低白质脱髓鞘改善AD早期认知功能的作用机制

Alzheimer's disease (AD), also known as senile dementia, is the primary predisposing factor for all functional cognitive disorders. Currently, there are at least 5 million patients with AD in China. AD has exerted a tremendous pressure on China’s national health care system. The pathogenesis of AD is complex and has not been fully established yet. Huge investments have been made in the development of drugs against the main pathological changes in AD with very few rewards; drugs currently available for its treatment can only moderately delay the progression of the disease. Hence, researchers have moved their attention to the early stage of AD, i.e. the stage with mild cognitive impairment. The focus of AD research has also been switched to prevention and early active intervention..With a view to developing new means for the prevention and treatment of early AD, we have referred to a Traditional Chinese medicine (TCM) extract, esculetin (Esc). Having anti-inflammatory, anti-tumorous and anti-apoptotic activities, Esc can ameliorate Parkinson's disease, strokes, depression and other nervous system disorders. However, no Esc-based interventional therapy for AD has been reported. In our previous studies, it was found that Esc can improve the spatial memory ability of early transgenic AD mice. Therefore, we propose a new assumption that Esc can improve the cognitive function in the early stage of AD. Like other researchers, we believe that white matter demyelination is present in the early stage of AD prior to the occurrence of typical symptoms and pathological changes. In our previous studies on multiple sclerosis, it was found that Esc could reduce demyelination of corpus callosum in animal models with the disease. Therefore, we propose a new assumption that Esc improves the cognitive function by inhibiting white matter demyelination in early AD. We will innovatively investigate how Esc inhibits oligodendrocyte apoptosis and reduces demyelination of myelinated fibers in the white matter in early AD by suppressing oxidative stress and activating the JAK2/STAT signaling system to ultimately improve the cognitive function in early AD and delay the progression of AD..The transgenic AD animal model APP/PS1/TAU was adopted in this project to conduct behavioral tests such as Morris water maze and novel object recognition in AD mice after Esc intervention. Then systematically, accurately and objectively quantitative study of myelinated myelin sheath in the white matter of AD mice using stereological three-dimensional quantitative methods to observe whether Esc can reduce white matter demyelination in early AD. Immunohistochemistry and optical fractionation were combined to conduct the accurate quantitative analysis of white matter oligodendrocytes in AD mice. Molecular biological methods were used to detect oxidative stress system, JAK2/STAT3 signaling system and apoptosis signal in the white matter, thus to observe whether Esc can inhibit oxidative stress and activate JAK2/STAT3 in early AD, thereby inhibiting the apoptosis of white matter oligodendrocytes..Through the final implementation of this study, we will verify that Esc improves the cognitive function in early AD and delays the progression of AD, reveal that Esc improves the cognitive function in early AD by inhibiting white matter demyelination and elucidate how Esc suppresses oxidative stress and oligodendrocyte apoptosis to inhibit white matter demyelination and improve the cognitive function. The study results have identified a new target for the early prevention and treatment of AD, i.e. the oligodendrocyte-medullary sheath system, broadened the scope of nervous system disorders that can be treated by Esc, a TCM extract, and established the structural and molecular basis of Esc for improving the learning and memory ability in early AD, providing theoretical and practical guidance for applying TCM for the prevention and treatment of AD.

阿尔茨海默病（AD）干预手段有限，早期干预成为重点。研究表明AD早期即存在大脑白质少突胶质细胞损伤及脱髓鞘。因此在前期发现七叶甙（Esc）可改善AD早期认知功能，抑制胼胝体脱髓鞘及心肌细胞凋亡的基础上，提出Esc通过抑制氧化应激及激动JAK2/STAT3减少少突胶质细胞凋亡降低白质脱髓鞘改善AD早期认知的新设想。采用APP/PS1/TAU3xTgAD鼠，体视学方法定量大脑白质内有髓神经纤维及髓鞘，光学分合法研究其内少突胶质细胞，结合行为学测试，明确Esc在AD早期减少大脑白质少突胶质细胞凋亡，从而抑制白质脱髓鞘，改善认知；运用分子生物学方法检测氧化应激体系、JAK2/STAT3信号系统及内源性细胞凋亡通路，明确Esc通过抑制氧化应激，激动JAK2/STAT3信号系统，减少少突胶质细胞凋亡。最终从理论上阐明Esc抑制少突胶质细胞凋亡，减少白质脱髓鞘改善认知的机制，为传统中药防治AD提供指导。

阿尔茨海默病（AD）是所有认知功能障碍性疾病的首要发病因素，其发病机制复杂，治疗效果有限。AD早期即轻度认知功能障碍期被认为是可能干预的最佳时期。为寻找防治早期AD的新手段，我们把目光投向了中药。七叶甙（Esc）可改善帕金森病、中风、抑郁等神经系统相关疾病。然而，尚未见到Esc干预治疗AD的报道。本研究采用2-3月龄APP/PS1/TAU转基因AD鼠，连续4个月腹腔注射Esc（50mg/kg）。通过水迷宫与旷场实验，我们研究发现：Esc能够有效延缓AD早期认知功能下降，并提高动物的活跃度；通过体视学与电子显微镜技术相结合，我们研究发现：Esc药物干预组AD鼠大脑白质有髓神经纤维的总长度及体积较对照组高，Esc能够有效保护AD早期大脑白质结构完整；通过光学分合法，我们研究发现：Esc能够有效减少AD早期白质内成熟少突胶质细胞的丢失。以上研究结果为早期防治AD、改善认知提供了一个新的手段—Esc，也明确了早期防治AD的新靶点—少突胶质细胞-髓鞘系统。.Esc具有抗炎、止痛、抗肿瘤、抗氧化等作用。通过分子生物学研究，我们发现：信号传导与转录激活因子3（STAT3）活化抑制蛋白（PIAS3）在AD患者的脑脊液中含量较正常人群明显下降；PIAS3蛋白在体外培养细胞中的表达随着Aβ蛋白作用浓度及作用时间的增加而显著下降；PIAS3通过抑制STAT3磷酸化，提高Nestin/Nrf-2/HO-1表达，改善Aβ蛋白导致的细胞死亡。而Esc能够提高AD大脑白质内PIAS3的表达，抑制STAT3磷酸化，抑制白质内细胞凋亡。因此，PIAS3可能作为AD的早期诊断标志物，同时从PIAS3/STAT3通路认识了Esc改善AD早期认知障碍的机制。Esc是陕西特色中药秦皮的提取物，本研究结果为日后Esc用于AD早期防治提供了理论依据和实验资料，拓宽了中药防治AD的应用前景，为减轻AD医疗负担提供了指导。