Host innate immune mechanisms control temporal expression of flagellin by pathogenic Salmonella

项目摘要 炎症体是一种多蛋白复合体，它能感知微生物的感染，并通过诱导caspase- 1-介导的炎性细胞死亡形式，称为下垂。炎症性小体被认为与 检测和清除各种细菌病原体，但对是否存在活性知之甚少 寄主感知机制与病原菌刺激配体表达之间的串扰。我们 他们发现，炎症小体的激活调节了沙门氏菌对NLRC4配体鞭毛蛋白的表达。一个 NLRC4介导的巨噬细胞焦虑症释放的宿主脂刺激通过增加鞭毛蛋白的表达 胞外细菌在内化时增强下垂，建立一个正反馈循环， 加强沙门氏菌的检测和清除。随着感染的进展，一种天然的I型干扰素依赖性 宿主负反馈反应关闭NLRC4和溶血磷脂生物合成的表达 IPLA2酶降至低于基线水平，将沙门氏菌转化为巨噬细胞内鞭毛蛋白低的表型。 基于这些发现，我们假设沙门氏菌已经进化到同时激活NLRC4和脂质 最初增加胞外鞭毛蛋白的产生，从而促进病原体的全身传播 冒着NLRC4介导的清除的风险，然后利用NLRC4和脂质产生减少的优势 (一种宿主策略，可能旨在限制过度的NLRC4介导的免疫病理)下调鞭毛蛋白 在巨噬细胞内。在这项提案中，我们将研究宿主细胞固有的固有调节 涉及I型干扰素信号、NLRC4和iPLA2活性的调节沙门氏菌时间开关的电路 巨噬细胞内从高鞭毛到低鞭毛的表型。我们会在以下地点进行调查： 具体目标如下：1)确定巨噬细胞焦虑症如何促进鞭毛蛋白产量的早期增加 通过细胞外沙门氏菌；2)剖析天然的I型干扰素依赖宿主的负反馈 建立NLRC4低和iPLA2低的胞内环境的反应，促使沙门氏菌切换 到巨噬细胞内鞭毛蛋白含量低的表型。我们的调查将确定时间和双相 病原体来源的炎症体配体在炎症小体激活过程中的调节作用 宿主-病原菌相互作用的新模式，揭示了沙门氏菌利用宿主形成的机制 巨噬细胞内鞭毛蛋白下调和免疫逃逸。这些研究也将有更广泛的 理解宿主先天免疫如何有助于调节微生物效应物的意义 影响感染的发展和解决。

Project Summary Inflammasomes are multiprotein complexes that sense microbial infections and respond by inducing a caspase- 1-mediated form of inflammatory cell death called pyroptosis. Inflammasomes have been implicated in the detection and clearance of a variety of bacterial pathogens, but little is known about whether there is active cross-talk between the host sensing mechanism and the expression of stimulatory ligands by the pathogen. We have found that inflammasome activation regulates expression of the NLRC4 ligand, flagellin, by Salmonella. A host lipid stimulus released upon NLRC4-mediated macrophage pyroptosis increases expression of flagellin by extracellular bacteria that enhances pyroptosis upon internalization, establishing a positive feedback loop that potentiates Salmonella detection and clearance. As infection progresses, a natural type I interferon-dependent host negative feedback response shuts down expression of NLRC4 and the lysophospholipid biosynthetic enzyme iPLA2 to sub-baseline levels, switching Salmonella to a flagellin-low phenotype inside macrophages. Based on these findings we hypothesize that Salmonella has evolved to co-opt NLRC4 activation and lipid production to initially enhance production of extracellular flagellin that promotes systemic spread of the pathogen at the risk of NLRC4-mediated clearance, and later on take advantage of decreased NLRC4 and lipid production (a host strategy likely aimed at limiting excessive NLRC4-mediated immunopathology) to downregulate flagellin intracellularly within macrophages. In this proposal we will investigate the host cell-intrinsic innate regulatory circuit involving type I IFN signaling, NLRC4 and iPLA2 activity that regulates the temporal switch of Salmonella from a flagellin-high to a flagellin-low phenotype inside macrophages. We will conduct these investigations in the following specific aims: 1) To identify how macrophage pyroptosis promotes early increase in flagellin production by extracellular Salmonella; 2) To dissect the natural type I interferon-dependent host negative feedback response that establishes a NLRC4-low and iPLA2-low intracellular environment prompting Salmonella to switch to a flagellin-low phenotype inside macrophages. Our investigations will identify the temporal and biphasic regulation of a pathogen-derived inflammasome ligand by the very process of inflammasome activation as a novel mode of host-pathogen cross-talk and reveal a host mechanism that Salmonella takes advantage of for flagellin downregulation and immune escape within macrophages. These studies will also have broader implications for understanding how host innate immunity contributes to modulation of microbial effectors impacting the development and resolution of infections.