Aryl hydrocarbon receptor senses bacterial pigmented virulence factors and orchestrates anti-bacterial defenses (part 2)

The aryl hydrocarbon receptor (AhR) is a highly conserved ligand-dependent transcription factor that senses environmental toxins and endogenous ligands, thereby inducing detoxifying enzymes and modulating immune cell differentiation and responses. We hypothesized that AhR not only evolved to sense pollutants from the environment, but also insults of microbial origin. We demonstrate that bacterial pigmented virulence factors, namely the phenazines pyocyanin and 1-hydroxyphenazine from Pseudomonas aeruginosa and the naphthoquinone phthiocol from Mycobacterium tuberculosis, are ligands of AhR. AhR activation leads to degradation of these virulence factors and regulated cytokine and chemokine production. The relevance of AhR to host defense is underlined by heightened susceptibility of AhR-deficient mice, both to P. aeruginosa and M. tuberculosis. Our data demonstrate that AhR senses distinct bacterial virulence factors and controls anti-bacterial responses. We provide evidence for a previously unidentified role for AhR as an intracellular pattern recognition receptor, and identify bacterial pigmented virulence factors as a new class of pathogen-associated molecular patterns. Microarray experiments were performed as dual-color hybridizations. To compensate for dye-specific effects, a dye-reversal color-swap was applied. Quality control and quantification of total RNA amount was assessed using an Agilent 2100 Bioanalyzer (Agilent Technologies) and a NanoDrop 1000 spectrophotometer (Kisker).

芳香烃受体（aryl hydrocarbon receptor, AhR）是一类高度保守的配体依赖性转录因子，可感知环境毒素与内源性配体，进而诱导解毒酶表达，并调控免疫细胞分化与免疫应答。我们提出假说：AhR的演化不仅为感知环境污染物，亦能识别微生物来源的损伤信号。本研究证实，细菌色素型毒力因子——即铜绿假单胞菌（Pseudomonas aeruginosa）产生的吩嗪类毒素绿脓菌素与1-羟基吩嗪，以及结核分枝杆菌（Mycobacterium tuberculosis）产生的萘醌类毒素结核萘醌（phthiocol）——均为AhR的配体。AhR激活可促使这些毒力因子降解，并调控细胞因子与趋化因子的产生。AhR缺陷型小鼠对铜绿假单胞菌与结核分枝杆菌的易感性均显著升高，这进一步凸显了AhR在宿主防御中的核心作用。本研究数据表明，AhR可感知不同种类的细菌毒力因子，并调控抗菌免疫应答。我们的研究证实了AhR此前未被发现的功能——作为一类细胞内模式识别受体（intracellular pattern recognition receptor），并将细菌色素型毒力因子鉴定为一类新型的病原相关分子模式（pathogen-associated molecular patterns）。微阵列实验采用双色杂交法开展。为补偿染料特异性带来的实验偏差，我们采用了染料逆转（色交换）的实验设计。总RNA的质量控制与定量检测通过安捷伦2100生物分析仪（Agilent 2100 Bioanalyzer，安捷伦科技公司）与NanoDrop 1000分光光度计（Kisker）完成。