Mycobacterium tuberculosis H37Ra-infected macrophages response to T0901317

Host macrophage transcriptional responses to intracellular pathogens remain poorly characterized. We screened transcriptional enhancers engaged in response to M. tuberculosis (Mtb) infection by ChIPseq analysis of histone H3 lysine 4 monomethylation (H3K4me1). De novo monomethylation during infection was associated with genes implicated in host defense and apoptosis. These regions were enriched for binding sites for ETS transcription factor family members and response elements for nuclear receptors, including liver X receptors (LXRs) and peroxisomal proliferator activated receptors (PPARs), many of which were encompassed by transposable elements. LXRa expression was strongly induced by infection, whereas that of PPARs was unaffected. LXR DNA binding and NCoR corepressor recruitment increased proportionately in infected cells but coactivator association was unchanged, consistent with a lack of induction of endogenous agonists. However, treatment of infected cells with LXR agonist T0901317 strongly increased coactivator recruitment and induced a gene expression program characterized by enhanced innate immune signaling and lipid metabolism. Remarkably, T0901317 treatment selectively induced apoptosis in infected macrophages, and was accompanied by Mtb death, reducing mycobacterial burden 18-fold relative to vehicle 5d after infection. These studies define macrophage transcriptional responses to Mtb infection, and suggest that tissue-specific LXRa agonists may be efficacious in clinical management of tuberculosis. THP-1 cells infected with H37Ra for 24h in the absence or presence of 20nM T0901317

宿主巨噬细胞对胞内病原体的转录应答目前仍未得到充分阐释。本研究通过对组蛋白H3赖氨酸4单甲基化（histone H3 lysine 4 monomethylation, H3K4me1）进行染色质免疫沉淀测序（ChIP-seq）分析，筛选了参与结核分枝杆菌（M. tuberculosis, Mtb）感染应答的转录增强子。感染过程中发生的从头单甲基化修饰与宿主防御及细胞凋亡相关基因密切相关。这些区域富集有ETS转录因子家族（ETS transcription factor family）成员的结合位点，以及包括肝X受体（liver X receptors, LXRs）和过氧化物酶体增殖物激活受体（peroxisomal proliferator activated receptors, PPARs）在内的核受体应答元件，其中多数区域被转座元件所覆盖。感染可强力诱导LXRα的表达，而PPARs的表达水平无明显变化。感染细胞中，LXR的DNA结合能力及核受体辅阻遏物（nuclear receptor corepressor, NCoR）的招募水平均呈比例升高，但辅激活因子的结合情况未发生改变，这与内源性激动剂未被诱导的现象一致。不过，用LXR激动剂T0901317处理感染细胞后，辅激活因子的招募水平显著升高，并诱导出以先天免疫信号通路活化与脂质代谢增强为特征的基因表达程序。值得注意的是，T0901317处理可选择性诱导感染巨噬细胞发生凋亡，同时伴随结核分枝杆菌的死亡：感染后5天，分枝杆菌载量较溶剂对照组降低了18倍。本研究阐明了巨噬细胞对结核分枝杆菌感染的转录应答机制，并提示组织特异性LXRα激动剂或许可用于结核病的临床治疗。实验所用细胞为经20nM T0901317处理或未处理、感染H37Ra菌株24小时的THP-1细胞。