背景:脱氧核糖核酸酶2(DNaseII)在清除细胞质双链DNA(dsDNA)中起关键作用。DNA酶II的缺乏导致DNA在细胞质中的积累。神经元中的持续dsDNA是衰老和神经退行性疾病(包括阿尔茨海默病(AD))的早期病理标志。然而,目前尚不清楚DNaseII和神经元细胞质dsDNA如何影响神经发病机制。Tau过度磷酸化是AD发病的关键因素。DNaseII和神经元细胞质dsDNA对神经元tau过度磷酸化的影响仍未阐明。
方法:用免疫组织化学和免疫标记法检测不同年龄WT和Tau-P301S小鼠的神经元DNaseII和dsDNA水平,用ELISA法测定AD患者血浆中DNaseⅡ的水平。为了研究DNaseII对tau蛋白病变的影响,磷酸化tau的水平,磷酸激酶,磷酸酶突触蛋白,神经元DNaseII缺陷型WT小鼠脑中的神经胶质增生和促炎细胞因子,通过免疫标记评估神经元DNaseII缺陷型Tau-P301S小鼠和神经元DNaseII过表达的Tau-P301S小鼠,免疫印迹或ELISA。使用莫里斯水迷宫测试确定认知表现,Y-迷宫测试,新颖的物体识别测试和开放现场测试。
结果:AD患者的大脑和血浆中DNaseII的水平显着降低。DNaseII还在WT和Tau-P301S小鼠的神经元中年龄依赖性地降低,随着dsDNA在细胞质中积累的增加。神经元DNA酶II缺乏诱导的DNA积累通过上调细胞周期蛋白依赖性样激酶5(CDK5)和钙/钙调蛋白激活的蛋白激酶II(CaMKII)和下调磷酸酶蛋白磷酸酶2A(PP2A)来驱动tau磷酸化。此外,DNaseII敲低诱导并显著加剧神经元丢失,WT和Tau-P301S小鼠的神经炎症和认知缺陷,分别,而神经元DNaseII的过表达显示出治疗益处。
结论:DNaseII缺乏和细胞质dsDNA积累可以启动tau磷酸化,提示DNaseII是tau相关疾病的潜在治疗靶点。
BACKGROUND: Deoxyribonuclease 2 (DNase II) plays a key role in clearing cytoplasmic double-stranded DNA (dsDNA). Deficiency of DNase II leads to DNA accumulation in the cytoplasm. Persistent dsDNA in neurons is an early pathological hallmark of senescence and neurodegenerative diseases including Alzheimer\'s disease (AD). However, it is not clear how DNase II and neuronal cytoplasmic dsDNA influence neuropathogenesis. Tau hyperphosphorylation is a key factor for the pathogenesis of AD. The effect of DNase II and neuronal cytoplasmic dsDNA on neuronal tau hyperphosphorylation remains unclarified.
METHODS: The levels of neuronal DNase II and dsDNA in WT and Tau-P301S mice of different ages were measured by immunohistochemistry and immunolabeling, and the levels of DNase II in the plasma of AD patients were measured by ELISA. To investigate the impact of DNase II on
tauopathy, the levels of phosphorylated tau, phosphokinase, phosphatase, synaptic proteins, gliosis and proinflammatory cytokines in the brains of neuronal DNase II-deficient WT mice, neuronal DNase II-deficient Tau-P301S mice and neuronal DNase II-overexpressing Tau-P301S mice were evaluated by immunolabeling, immunoblotting or ELISA. Cognitive performance was determined using the Morris water maze test, Y-maze test, novel object recognition test and open field test.
RESULTS: The levels of DNase II were significantly decreased in the brains and the plasma of AD patients. DNase II also decreased age-dependently in the neurons of WT and Tau-P301S mice, along with increased dsDNA accumulation in the cytoplasm. The DNA accumulation induced by neuronal DNase II deficiency drove tau phosphorylation by upregulating cyclin-dependent-like kinase-5 (CDK5) and calcium/calmodulin activated protein kinase II (CaMKII) and downregulating phosphatase protein phosphatase 2A (PP2A). Moreover, DNase II knockdown induced and significantly exacerbated neuron loss, neuroinflammation and cognitive deficits in WT and Tau-P301S mice, respectively, while overexpression of neuronal DNase II exhibited therapeutic benefits.
CONCLUSIONS: DNase II deficiency and cytoplasmic dsDNA accumulation can initiate tau phosphorylation, suggesting DNase II as a potential therapeutic target for tau-associated disorders.