Detection of pathogen infection by monitoring host cell membrane dynamics

项目摘要 病原菌的先天识别包括感知潜在有害物质的物理存在， 微生物和伴随感染的宿主生理的扰动。通过监测 病原体对宿主的感染而不是对感染微生物本身的监视免疫 使宿主能够在感染过程中直接针对真正的病原体进行免疫防御， 肠道细菌。监视免疫的概念首先在植物和线虫中被描述 C.线虫，随后，一些具体的例子已经在哺乳动物中进行了表征。但据 病原体诱导的宿主生理变化如何激活免疫防御尚不清楚。 在这里，我们提出了一个新的假设，先天免疫感应，源于监督的概念 免疫力这一建议的中心假设是，病原体感染引起的流动性的变化， 肠质膜，其被宿主感知以诱导先天性免疫防御。我们特别 提出病原体感染改变了血浆磷脂区室中的脂肪酸去饱和 膜，这降低了它们的流动性，并导致细胞内免疫信号级联的激活。 通过对C. elegans，我们做了几个 观察提供了这个想法的基本原理：（i）膜流动性动态监测激活 先天免疫防御脂肪酸生物合成和去饱和的转录调节因子的破坏 降低膜流动性并以重现肠道感染的方式引起免疫激活 细菌病原体。(ii)p38 PMK-1先天免疫途径是线虫的宿主防御途径， 在C.具有膜流动性病理的线虫突变体。(iii)病原体感染迅速耗尽 宿主脂肪酸并抑制合成单不饱和脂肪酸的基因的转录。 重要的是，我们发现病原体感染也会破坏肠上皮细胞血浆的流动性 膜。(iv)最后，细胞膜流动性是抵抗病原体所必需的。C.线虫突变体， 膜流动性的缺陷对病原体感染是高度敏感的， 动力学补充了这种突变表型。 在这个建议中，我们将表征宿主监测肠细胞质膜流动性作为一种新的 激活先天免疫的机制（目的1）。我们还将定义病原体引起的变化， 降低质膜流动性的膜组成（目的2），并确定p38的机制 细菌感染期间PMK-1途径活化（目的3）。拟议的研究将确定一项总体战略 由C。elegans检测病原体引起的干扰宿主生理，揭示基本 深入了解了一种以前未被认识的、进化上古老的免疫激活策略。

PROJECT SUMMARY Innate recognition of pathogenic bacteria involves sensing both the physical presence of potentially harmful microbes and the perturbations of host physiology that accompany infection. By monitoring for the effects of pathogen infection on the host rather than for the infectious microorganism itself, surveillance immunity enables the host to direct immune defenses towards bona fide pathogens during an infection and not harmless commensal bacteria. The concept of surveillance immunity was first described in plants and in the nematode C. elegans, and subsequently, a few specific examples have been characterized in mammals. However, it is unknown how pathogen-induced changes in host physiology activate immune defenses. Here, we advance a new hypothesis of innate immune sensing that stems from the concept of surveillance immunity. The central hypothesis of this proposal is that pathogen infection causes a change in the fluidity of intestinal plasma membranes, which is sensed by the host to induce innate immune defenses. Specifically, we propose that pathogen infection alters fatty acid desaturation in the phospholipid compartment of plasma membranes, which reduces their fluidity and leads to activation of intracellular immune signaling cascades. Through genetic studies of host-pathogen interactions in the nematode C. elegans, we made several observations that provide the rationale for this idea: (i) Membrane fluidity dynamics are monitored to activate innate immune defenses. Disruption of a transcriptional regulator of fatty acid biogenesis and desaturation decreases membrane fluidity and causes immune activation in a manner that recapitulates intestinal infection by bacterial pathogens. (ii) The p38 PMK-1 innate immune pathway, a host defense pathway of nematodes, is activated in C. elegans mutants that have membrane fluidity pathology. (iii) Pathogen infection rapidly depletes host fatty acids and suppresses the transcription of genes that synthesize monounsaturated fatty acids. Importantly, we found that pathogen infection also disrupts the fluidity of intestinal epithelial cell plasma membranes. (iv) Finally, cell membrane fluidity is required for pathogen resistance. C. elegans mutants with defects in membrane fluidity are hypersusceptible to pathogen infection, and restoration of membrane fluidity dynamics complements this mutant phenotype. In this proposal, we will characterize host surveillance of intestinal cell plasma membrane fluidity as a novel mechanism to activate innate immunity (Aim 1). We will also define the pathogen-induced changes in membrane composition that decrease plasma membrane fluidity (Aim 2) and determine the mechanism of p38 PMK-1 pathway activation during bacterial infection (Aim 3). The proposed study will define a general strategy employed by C. elegans to detect pathogen-induced disturbances in host physiology, revealing fundamental insights into a previously unrecognized, evolutionarily ancient strategy of immune activation.