Host pathogen signaling in the intestine

描述（由申请人提供）：致命的胃肠道病原体肠出血性大肠杆菌（EHEC） O157:H7利用感知宿主的应激激素肾上腺素（epi）和去甲肾上腺素（NE）来激活其毒力特征。应激反应对生物体的生理和生存有着深远的影响，也被细菌感知为衡量宿主代谢和免疫状态的一种手段。在哺乳动物中，这些激素通过肾上腺素能受体g偶联蛋白受体（gpcr）感知。然而，细菌通过组氨酸感应激酶（HKs）感知这些激素，HKs与反应调节蛋白（RR）协同作用，构成一个双组分系统。当HK感应到它的信号时，它在一个组氨酸残基中自磷酸化，然后将这个磷酸转移到它同源的RR中的一个天冬氨酸残基中。大多数RRs是转录因子，在磷酸化后被激活。我们首次报道了EHEC的两种肾上腺素能受体：HKs QseC和QseE， QseE在该信号级联中位于QseC的下游（考虑到QseE的转录是通过QseC激活的）。QseC同源物至少存在于25种重要的人类和植物病原体中，而QseE的分布仅限于肠道细菌。在体外和体内的幼兔感染模型中，已显示出肠出血性大肠杆菌qseC和qseE突变体的毒力减弱。然而，由于缺乏小鼠模型来研究肠出血性大肠杆菌在胃肠道中的发病机制，因此通过该信号系统研究肠出血性大肠杆菌与宿主之间的真正相互作用一直具有挑战性。因此，许多研究人员利用天然小鼠病原体啮齿柠檬酸杆菌作为小鼠肠出血性大肠杆菌胃肠道发病机制的替代模型。所有已知的肠出血性大肠杆菌毒力基因都已在体内通过啮齿c小鼠感染得到验证。啮齿鼠模型的利用利用了宿主和病原体强大的遗传可追溯性，揭示了宿主识别和感染的机制。我们已经证明，epi和NE激活了啮齿c中所有毒力基因的表达，与我们在肠出血性大肠杆菌中观察到的情况相似（初步结果）。C. rodentium qseC和qseE突变体在体外和体内（小鼠感染）的毒力也被减弱（初步研究），使其成为一种遗传上可处理的模型，用于解剖宿主化学信号在发病过程中的贡献。因此，本应用的具体目的是：表征宿主Epi/NE激素在小鼠感染期间对啮齿c发病机制的贡献。

DESCRIPTION (provided by applicant): The deadly gastrointestinal pathogen enterohemorrhagic E. coli (EHEC) O157:H7 exploits sensing the host's stress hormones epinephrine (epi) and norepinephrine (NE) to activate its virulence traits. Stress responses have a profound effect in an organism's physiology and survival, and are also sensed by bacteria as a means to gauge the metabolic and immune state of the host. These hormones in mammals are sensed by adrenergic receptors that are G-coupled protein receptors (GPCRs). Bacteria, however, sense these hormones through histidine sensor kinases (HKs), which act in concert with a response regulator (RR) protein constituting a two-component system. Upon sensing its signal, the HK autophosphorylates in a histidine residue, and then transfers this phosphate to an aspartate residue in its cognate RR. The majority of the RRs are transcription factors, which are activated upon phosphorylation. We have first reported EHEC's two adrenergic receptors: the HKs QseC and QseE with QseE being downstream of QseC in this signaling cascade (given that transcription of qseE is activated through QseC). QseC homologues are present in at least 25 important human and plant pathogens, while the distribution of QseE is limited to enteric bacteria. EHEC qseC and qseE mutants have been shown to be attenuated for virulence in vitro and in vivo using an infant rabbit model of infection However, the study of the true interplay between EHEC and the host through this signaling system has been challenging due to the lack of murine models to study EHEC pathogenesis in the GI tract. Hence, many investigators utilize the natural mouse pathogen Citrobacter rodentium as a surrogate model for EHEC GI pathogenesis in mice. All of the known virulence genes of EHEC have been validated in vivo using C. rodentium murine infections. The utilization of the C. rodentium model capitalizes in merging the powerful genetically tractability of host and pathogen to unravel the mechanisms involved in host recognition and infection. We have shown that epi and NE activate expression of all virulence genes in C. rodentium, in a similar scenario to what we have observed with EHEC (Preliminary results). C. rodentium qseC and qseE mutants are also attenuated for virulence in vitro and in vivo (murine infection) (Preliminary studies), making this a genetically tractable model to dissect the contribution of host chemical signals during pathogenesis. In accordance, the Specific Aim of this application is: Characterize the contribution of the host Epi/NE hormones to C. rodentium pathogenesis during murine infection. PUBLIC HEALTH RELEVANCE: Several human deadly pathogens tightly regulate expression of their virulence traits; when these pathogens infect a suitable host, many chemical signals are sensed so they can gage the host and site of infection, and subsequently activate expression of their virulence genes. Some of these signals are the host stress hormones epinephrine and norepinephrine to activate their virulence genes. In this grant we will study how Citrobacter rodentium (a mouse pathogen used as a model for E. coli O157:H7) sense and respond to these hormones in vitro and during animal infection.