Department of Neurology, Emory University, Atlanta, GA, USA.
Xiangya Hospital, Central South University, Changsha, Hunan Province, China.
Glia. 2019 Oct;67(10):1958-1975. doi: 10.1002/glia.23678. Epub 2019 Jul 13.
Microglia transform from homeostatic to disease-associated-microglia (DAM) profiles in neurodegeneration. Within DAM, we recently identified distinct pro-inflammatory and anti-inflammatory sub-profiles although transcriptional regulators of homeostatic and distinct DAM profiles remain unclear. Informed by these studies, we nominated CEBPα, IRF1, and LXRβ as likely regulators of homeostatic, pro-inflammatory and anti-inflammatory DAM states and performed in-vitro siRNA studies in primary microglia to identify roles of each transcriptional factor (TF) in regulating microglial activation, using an integrated transcriptomics, bioinformatics and experimental validation approach. Efficient (>70%) silencing of TFs in microglia revealed reciprocal regulation between each TF specifically following pro-inflammatory activation. Neuroinflammatory transcriptomic profiling of microglia coupled with qPCR validation revealed distinct gene clusters with unique patterns of regulation by each TF, which were independent of LPS stimulation. While all three TFs (especially IRF1 and LXRβ) positively regulated core DAM genes (Apoe, Axl, Clec7a, Tyrobp, and Trem2) as well as homeostatic and pro-inflammatory DAM genes, LPS, and IFNγ increased pro-inflammatory DAM but suppressed homeostatic and anti-inflammatory DAM gene expression via an Erk1/2-dependent signaling pathway. IRF1 and LXRβ silencing suppressed microglial phagocytic activity for polystyrene microspheres as well as fAβ42 while IRF1 silencing strongly suppressed production of pro-inflammatory cytokines in response to LPS. Our studies reveal complex transcriptional regulation of homeostatic and DAM profiles whereby IRF1, LXRβ, and CEBPα positively regulate both pro- and anti-inflammatory DAM genes while activating stimuli independently augment pro-inflammatory DAM responses and suppress homeostatic and anti-inflammatory responses via Erk signaling. This framework can guide development of therapeutic immuno-modulatory strategies for neurodegeneration.
小胶质细胞在神经退行性变中从稳态向疾病相关小胶质细胞 (DAM) 表型转变。在 DAM 中，我们最近虽然确定了不同的促炎和抗炎亚表型，但稳态和不同 DAM 表型的转录调节剂仍不清楚。受这些研究的启发，我们提名 CEBPα、IRF1 和 LXRβ 作为稳态、促炎和抗炎 DAM 状态的可能调节剂，并在原代小胶质细胞中进行体外 siRNA 研究，以确定每个转录因子 (TF) 在调节小胶质细胞激活中的作用，采用综合转录组学、生物信息学和实验验证方法。TF 在小胶质细胞中的高效 (>70%)沉默揭示了每个 TF 之间的相互调节，特别是在促炎激活后。小胶质细胞的神经炎症转录组谱与 qPCR 验证相结合，揭示了每个 TF 独特调节的独特基因簇，这些基因簇独立于 LPS 刺激。虽然所有三个 TF（尤其是 IRF1 和 LXRβ）都正向调节核心 DAM 基因（Apoe、Axl、Clec7a、Tyrobp 和 Trem2）以及稳态和促炎 DAM 基因，但 LPS 和 IFNγ 增加了促炎 DAM 基因，但通过 Erk1/2 依赖性信号通路抑制了稳态和抗炎 DAM 基因的表达。IRF1 和 LXRβ 的沉默抑制了小胶质细胞对聚苯乙烯微球和 fAβ42 的吞噬活性，而 IRF1 的沉默强烈抑制了 LPS 反应中小胶质细胞促炎细胞因子的产生。我们的研究揭示了稳态和 DAM 谱的复杂转录调节，其中 IRF1、LXRβ 和 CEBPα 正向调节促炎和抗炎 DAM 基因，而激活刺激则独立地增强促炎 DAM 反应，并通过 Erk 信号抑制稳态和抗炎反应。该框架可以为神经退行性变的治疗性免疫调节策略提供指导。
