Microglial gene signature reveals loss of homeostatic microglia associated with neurodegeneration of Alzheimer's disease. Microglial gene signature reveals loss of homeostatic microglia associated with neurodegeneration of Alzheimer's disease

Microglia-mediated neuroinflammation has been implicated in the pathogenesis of Alzheimer's disease (AD). Although microglia in aging and neurodegenerative disease model mice show a loss of homeostatic phenotype and activation of disease-associated microglia (DAM), a correlation between those phenotypes and the degree of neuronal cell loss has not been clarified. In this study, we performed RNA sequencing of microglia isolated from three representative neurodegenerative mouse models, AppNL-G-F/NL-G-F with amyloid pathology, rTg4510 with tauopathy, and SOD1G93A with motor neuron disease by magnetic activated cell sorting. In parallel, gene expression patterns of the human precuneus with early Alzheimer's change (n=11) and control brain (n=14) were also analyzed by RNA sequencing. We found that a substantial reduction of homeostatic microglial genes in rTg4510 and SOD1G93A microglia, whereas DAM genes were uniformly upregulated in all mouse models. The reduction of homeostatic microglial genes was correlated with the degree of neuronal cell loss. In human precuneus with early AD pathology, reduced expression of genes related to microglia- and oligodendrocyte-specific markers was observed, although the expression of DAM genes was not upregulated. Our results implicate a loss of homeostatic microglial function in the progression of AD and other neurodegenerative diseases. Moreover, analyses of human precuneus also suggest loss of microglia and oligodendrocyte functions induced by early amyloid pathology in human. Overall design: We analyzed gene expression in microglia isolated by magnetic-activated cell sorting (MACS) from cerebral cortex of AppNL-G-F/NL-G-F and rTg4510 mice or lumbar spinal cord of SOD1G93A mice.

小胶质细胞（microglia）介导的神经炎症已被证实参与阿尔茨海默病（Alzheimer's disease, AD）的发病机制。尽管衰老及神经退行性疾病模型小鼠的小胶质细胞呈现稳态表型丢失与疾病相关小胶质细胞（disease-associated microglia, DAM）激活的特征，但上述表型与神经元丢失程度之间的关联尚未阐明。
本研究通过磁激活细胞分选（magnetic activated cell sorting, MACS）技术，从三种代表性神经退行性疾病小鼠模型中分离小胶质细胞并进行RNA测序（RNA sequencing）：分别为携带淀粉样蛋白病理的AppNL-G-F/NL-G-F小鼠、表现tau蛋白病的rTg4510小鼠，以及携带运动神经元病表型的SOD1G93A小鼠。与此同时，本研究还通过RNA测序分析了11例存在早期阿尔茨海默病改变的人类楔前叶组织与14例对照脑组织的基因表达模式。
研究发现，rTg4510与SOD1G93A小鼠的小胶质细胞中，稳态小胶质细胞相关基因显著下调，而所有小鼠模型的疾病相关小胶质细胞相关基因均呈现一致的上调趋势。稳态小胶质细胞相关基因的下调程度与神经元丢失程度呈显著正相关。在存在早期AD病理的人类楔前叶组织中，尽管疾病相关小胶质细胞相关基因的表达未出现上调，但小胶质细胞与少突胶质细胞（oligodendrocyte）特异性标志物相关基因的表达均显著降低。
本研究结果提示，稳态小胶质细胞功能的丢失参与了阿尔茨海默病及其他神经退行性疾病的病情进展。此外，对人类楔前叶的分析还表明，早期淀粉样蛋白病理可诱导人类小胶质细胞与少突胶质细胞的功能受损。
【实验设计概述】本研究通过磁激活细胞分选（MACS）分离小胶质细胞，对AppNL-G-F/NL-G-F与rTg4510小鼠的大脑皮层、以及SOD1G93A小鼠的腰脊髓组织进行基因表达分析。