Host pathogen signaling in the intestine

描述(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利用感应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深远的影响，细菌也可以感觉到应激反应，作为衡量宿主新陈代谢和免疫状态的一种手段。哺乳动物体内的这些激素是由肾上腺素能受体感知的，肾上腺素能受体是G偶联蛋白受体(GPCRs)。然而，细菌通过组氨酸传感器蛋白(HKS)感知这些激素，组氨酸传感器蛋白与反应调节蛋白(RR)共同作用，构成一个双组分系统。当感应到它的信号时，HK自动磷酸化一个组氨酸残基，然后将这个磷酸转移到其同源RR中的天冬氨酸残基。大多数转录因子是转录因子，在磷酸化后被激活。我们首次报道了EHEC的两个肾上腺素能受体：HKS QSec和QseE，其中QseE位于QSec下游(鉴于qseE的转录是通过QSec激活的)。QSec同源物存在于至少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。EHEC的qsec和qseE突变体在体外和体内的幼兔感染模型中都被证明是毒力减弱的，然而，由于缺乏小鼠模型来研究EHEC在胃肠道的致病机制，通过这个信号系统研究EHEC与宿主之间的真正相互作用一直是具有挑战性的。因此，许多研究人员利用自然的小鼠病原体轮状柠檬酸杆菌作为EHEC GI在小鼠中致病的替代模型。所有已知的EHEC毒力基因都已在体内用轮状芽胞杆菌感染小鼠进行了验证。利用轮状念珠菌模型融合了宿主和病原体强大的遗传易感性，以揭示宿主识别和感染的机制。我们已经证明了EPI和NE激活了轮状芽胞杆菌中所有毒力基因的表达，这与我们在EHEC中观察到的情况类似(初步结果)。轮状念珠菌qsec和qseE突变体在体外和体内(小鼠感染)的毒力也会减弱(初步研究)，这使得这是一个分析宿主化学信号在致病过程中贡献的遗传易处理的模型。因此，本应用的具体目的是：确定宿主EPi/NE激素在小鼠感染轮状芽胞杆菌致病中的作用。 与公共卫生相关：几种人类致命病原体严格控制其毒力特征的表达；当这些病原体感染合适的宿主时，许多化学信号被感知，因此它们可以测量感染的宿主和部位，随后激活其毒力基因的表达。其中一些信号是宿主应激激素肾上腺素和去甲肾上腺素激活它们的毒力基因。在这项资助中，我们将研究轮状柠檬酸杆菌(一种用作O157：H7大肠杆菌模型的小鼠病原体)在体外和动物感染期间如何感知和响应这些激素。

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.