Department of Neurology, Emory University, Atlanta, GA, 30322, USA.
Department of Biochemistry, Emory University, Atlanta, GA, 30322, USA.
Mol Neurodegener. 2018 Jun 28;13(1):34. doi: 10.1186/s13024-018-0266-4.
Microglia are innate immune cells of the brain that perform phagocytic and inflammatory functions in disease conditions. Transcriptomic studies of acutely-isolated microglia have provided novel insights into their molecular and functional diversity in homeostatic and neurodegenerative disease states. State-of-the-art mass spectrometry methods can comprehensively characterize proteomic alterations in microglia in neurodegenerative disorders, potentially providing novel functionally relevant molecular insights that are not provided by transcriptomics. However, comprehensive proteomic profiling of adult primary microglia in neurodegenerative disease conditions has not been performed.
We performed quantitative mass spectrometry based proteomic analyses of purified CD11b acutely-isolated microglia from adult (6 mo) mice in normal, acute neuroinflammatory (LPS-treatment) and chronic neurodegenerative states (5xFAD model of Alzheimer's disease [AD]). Differential expression analyses were performed to characterize specific microglial proteomic changes in 5xFAD mice and identify overlap with LPS-induced pro-inflammatory changes. Our results were also contrasted with existing proteomic data from wild-type mouse microglia and from existing microglial transcriptomic data from wild-type and 5xFAD mice. Neuropathological validation studies of select proteins were performed in human AD and 5xFAD brains.
Of 4133 proteins identified, 187 microglial proteins were differentially expressed in the 5xFAD mouse model of AD pathology, including proteins with previously known (Apoe, Clu and Htra1) as well as previously unreported relevance to AD biology (Cotl1 and Hexb). Proteins upregulated in 5xFAD microglia shared significant overlap with pro-inflammatory changes observed in LPS-treated mice. Several proteins increased in human AD brain were also upregulated by 5xFAD microglia (Aβ peptide, Apoe, Htra1, Cotl1 and Clu). Cotl1 was identified as a novel microglia-specific marker with increased expression and strong association with AD neuropathology. Apoe protein was also detected within plaque-associated microglia in which Apoe and Aβ were highly co-localized, suggesting a role for Apoe in phagocytic clearance of Aβ.
We report a comprehensive proteomic study of adult mouse microglia derived from acute neuroinflammation and AD models, representing a valuable resource to the neuroscience research community. We highlight shared and unique microglial proteomic changes in acute neuroinflammation aging and AD mouse models and identify novel roles for microglial proteins in human neurodegeneration.
小胶质细胞是大脑中的先天免疫细胞，在疾病状态下具有吞噬和炎症功能。急性分离的小胶质细胞的转录组学研究为其在稳态和神经退行性疾病状态下的分子和功能多样性提供了新的见解。最先进的质谱方法可以全面描述神经退行性疾病中小胶质细胞的蛋白质组变化，可能提供转录组学无法提供的新的、功能相关的分子见解。然而，尚未对神经退行性疾病状态下的成年原代小胶质细胞进行全面的蛋白质组学分析。
我们对来自成年（6 个月）正常、急性神经炎症（LPS 处理）和慢性神经退行性疾病（5xFAD 阿尔茨海默病模型）状态下的急性分离 CD11b 小胶质细胞进行了基于定量质谱的蛋白质组学分析。差异表达分析用于表征 5xFAD 小鼠中特定的小胶质细胞蛋白质组变化，并识别与 LPS 诱导的促炎变化的重叠。我们的结果还与野生型小鼠小胶质细胞的现有蛋白质组学数据以及野生型和 5xFAD 小鼠的现有小胶质细胞转录组学数据进行了对比。对选定蛋白的神经病理学验证研究在人类 AD 和 5xFAD 大脑中进行。
在 4133 种鉴定的蛋白质中，187 种小胶质细胞蛋白在 5xFAD 阿尔茨海默病病理模型的 AD 中表达差异，包括具有先前已知（Apoe、Clu 和 Htra1）和先前未报道的与 AD 生物学相关的蛋白（Cotl1 和 Hexb）。在 5xFAD 小胶质细胞中上调的蛋白与 LPS 处理小鼠中观察到的促炎变化有显著重叠。在人类 AD 大脑中增加的几种蛋白质也被 5xFAD 小胶质细胞上调（Aβ 肽、Apoe、Htra1、Cotl1 和 Clu）。Cotl1 被确定为一种新的小胶质细胞特异性标志物，其表达增加且与 AD 神经病理学强烈相关。Apoe 蛋白也在斑块相关小胶质细胞中检测到，其中 Apoe 和 Aβ 高度共定位，表明 Apoe 在 Aβ 的吞噬清除中起作用。
我们报告了一项关于急性神经炎症和 AD 模型中小鼠小胶质细胞的全面蛋白质组学研究，这为神经科学研究社区提供了有价值的资源。我们强调了急性神经炎症、衰老和 AD 小鼠模型中小胶质细胞的共同和独特的蛋白质组学变化，并确定了小胶质细胞蛋白在人类神经退行性变中的新作用。
