Tryptophan derivatives in EHEC pathogenesis

项目摘要 结肠含有色氨酸衍生物，如吲哚，这是一种微生物来源的信号分子， 主要在胃肠道合成的宿主衍生的血清素神经递质。吲哚也被认为是 被宿主细胞吸收，并有助于加强肠道屏障的完整性，被视为 微生物/宿主相互作用中的有益化学线索。吲哚是由甘露聚糖酶合成的， 由tnaA基因编码。我们已经表明，吲哚的浓度是显着较高的内腔 与结肠组织（其中吲哚是 被肠上皮细胞吸收）。5-羟色胺在肠嗜铬细胞中由这种酶合成 色氨酸羟化酶（TpH 1）。在其合成时，血清素被释放到固有层中并被分泌 进入管腔。肠粘膜中的5-羟色胺信号传导通过由肠粘膜中的细胞清除5-羟色胺而终止。 5-羟色胺选择性再摄取转运蛋白（SERT），由上皮细胞表达。我们发现， 5-羟色胺和吲哚降低肠出血性大肠杆菌毒力基因表达大肠杆菌（EHEC） 和啮齿类柠檬酸杆菌，一种用作EHEC替代动物模型的鼠病原体。我们也 确定这些信号的细菌受体为CpxA。在感知血清素和/或吲哚时，CpxA 主要作为磷酸酶发挥作用，使自身和CpxR去磷酸化，激活其 磷酸化状态通过转录组研究，我们还鉴定了吲哚螯合受体（Isr）， 其在不存在吲哚的情况下直接激活毒力表达。然而，在吲哚的存在下，Isr是 不再能够激活毒力基因的转录。使用TpH 1药理学抑制剂（降低 肠道中5-羟色胺水平）和SERT敲除小鼠（管腔5-羟色胺水平增加），我们发现， 小鼠肠道中较高水平的5-羟色胺降低了C.啮齿动物， 而血清素水平的降低有助于增加发病率。此外，我们综合 改变了小鼠胃肠道中吲哚的浓度。这使我们能够评估自产的作用， 与微生物群产生的吲哚相比，并显示吲哚浓度降低促进细菌 发病机制，而吲哚水平的增加降低了细菌毒力基因的表达， 感染总的来说，5-羟色胺和吲哚都降低了C.啮齿类动物感染。我们 研究表明，吲哚和5-羟色胺神经递质水平的波动会显著影响 疾病预后然而，关于细菌的这种精致的信号调节的几个问题 毒力仍然没有答案。因此，这项赠款的具体目标是：目标1。定义CpxA/CpxR 和Isr血清素/吲哚信号级联。目标2.研究血清素与内源性 和外源吲哚信号转导在哺乳动物感染期间细菌发病机制中的作用。

PROJECT SUMMARY The colon contains tryptophan derivatives such as indole, which is a microbiota-derived signaling molecule, and the host-derived serotonin neurotransmitter that is primarily synthesized in the GI tract. Indole is also known to be absorbed by host cells and helps strengthen the integrity of the intestinal barrier, being regarded as a beneficial chemical cue within microbial/host interactions. Indole is synthesized by tryptophanase, which is encoded by the tnaA gene. We have shown that the concentration of indole is significantly higher in the lumen of the colon (the compartment where the microbiota resides) compared to colonic tissues (where indole is absorbed by intestinal epithelial cells). Serotonin is synthesized in enterochromaffin cells by the enzyme tryptophan hydroxylase (TpH1). Upon its synthesis, serotonin is released into the lamina propria and is secreted into the lumen. Serotonin signaling in the intestinal mucosa is terminated by removal of serotonin by the serotonin selective reuptake transporter (SERT), which is expressed by epithelial cells. We showed that both serotonin and indole converge to decrease virulence gene expression from enterohemorrhagic E. coli (EHEC) and Citrobacter rodentium, a murine pathogen employed as a surrogate animal model for EHEC. We also identified the bacterial receptor for these signals as CpxA. Upon sensing serotonin and/or indole, CpxA functions primarily as a phosphatase, dephosphorylating itself and CpxR, that activates virulence in its phosphorylated state. Through transcriptome studies we also identified the Indole Sequestering Receptor (Isr), which in the absence of indole directly activates virulence expression. However, in the presence of indole, Isr is no longer able to activate transcription of virulence genes. Using TpH1 pharmacological inhibitors (decrease the levels of serotonin in the gut) and SERT knockout mice (have increased levels of luminal serotonin), we showed that the presence of higher levels of serotonin in the intestine of mice decreased virulence in C. rodentium, while decreased levels of serotonin are conducive to increased pathogenesis. Moreover, we synthetically altered the concentration of indole in the GI tract of mice. This allowed us to assess the role of self-produced versus microbiota-produced indole, and show that decreased indole concentrations promote bacterial pathogenesis, while increased levels of indole decreases bacterial virulence gene expression during murine infection. Altogether, both serotonin and indole decrease virulence of C. rodentium during murine infection. Our studies show that fluctuations in the levels of indole and the serotonin neurotransmitter significantly impact disease prognosis. However several questions regarding this exquisite signaling regulation of bacterial virulence remain unanswered. Consequently the specific aims of this grant are: Aim 1. Define the CpxA/CpxR and Isr serotonin/indole signaling cascade. Aim 2. Investigate the intersection of serotonin with endogenous and exogenous indole signaling in bacterial pathogenesis during mammalian infection.