The role of Salmonella protease PgtE in evading host immune responses

项目摘要 细菌感染仍然是全球发病率和死亡率的主要原因，也是一个严重的健康问题 由于抗生素耐药性增加和疫苗有限。非伤寒沙门氏菌（NTS）血清型，如 肠道沙门氏菌血清型鼠伤寒（STm）是炎症性腹泻的主要原因， 健康个体，导致通常局限于肠道的感染。在免疫功能低下的 对于个体、儿童和老年人，STm可引起需要抗生素治疗的潜在致命菌血症。 先天性宿主防御，防止细菌从胃肠道传播到胃肠道， 血液中的抗微生物肽、补体系统蛋白和吞噬细胞，包括 巨噬细胞和嗜中性粒细胞。STm的致病菌株可以破坏吞噬溶酶体而存活 细胞内的巨噬细胞，因此自噬系统出现作为一个关键步骤，杀死细胞内 STm。PgtE是一种STm外膜蛋白酶，先前已描述其切割超过12种哺乳动物的蛋白酶。 蛋白质底物，包括补体蛋白C3，但这些活性仅在 具有有缺陷的外膜的无毒突变株。近年来，一个新出现的分支， 侵袭性STm是撒哈拉以南非洲菌血症流行病的原因，有几项研究表明 提示PgtE表达增加是重要的毒力机制， 仍然未知。我们的初步研究表明，PgtE在感染过程中起着重要作用， 初始粘膜定殖和在系统阶段与毒性STm。我们的核心假设是， STm已被吞噬，STm利用PgtE保护破坏的外膜免受抗菌剂的侵害。 肽，补体和自噬杀伤，从而促进其在宿主中的存活。在目标1中，我将确定 PgtE在STm被吞噬后使STm逃避IL-22介导的肠上皮防御中的作用 管腔。在目标2中，我将确定PgtE如何破坏补体成分C3信号传导和巨噬细胞 自噬性杀伤这项工作将为病原体如何利用蛋白酶逃避免疫提供一个框架 具有潜在的新型治疗靶点的系统。

Project Summary Bacterial infections remain a leading cause of morbidity and mortality worldwide and a critical health issue due to increasing antibiotic resistance and limited vaccines. Non-typhoidal Salmonella (NTS) serovars such as Salmonella enterica serovar Typhimurium (STm) are a leading cause of inflammatory diarrhea in otherwise healthy individuals, causing infections that are usually localized to the gut. Among immunocompromised individuals, children, and elderly, STm can cause a potentially lethal bacteremia that requires antibiotic treatment. Pivotal to innate host defense in preventing the spread of bacteria from the gastrointestinal tract to the bloodstream are antimicrobial peptides, complement system proteins, and phagocytic cells including macrophages and neutrophils. Pathogenic strains of STm can subvert the phagolysosome to survive intracellularly in macrophages, whereupon the autophagy system emerges as a critical step for killing intracellular STm. PgtE, a STm outer membrane protease, has been previously described to cleave over a dozen mammalian protein substrates in vitro, including complement protein C3, but these activities have only been observed with avirulent mutant strains possessing a defective outer membrane. In recent years, a newly emergent clade of invasive STm has been responsible for an epidemic of bacteremia in sub-Saharan Africa, with several studies suggesting an increased expression of PgtE as an important virulence mechanism although the mechanism remains unknown. Our preliminary studies suggest that PgtE plays an important role during infection in both the initial mucosal colonization and in the systemic phase with a virulent STm. Our central hypothesis is that after STm has been phagocytosed, STm utilizes PgtE to protect the disrupted outer membrane from antimicrobial peptides, complement, and autophagy killing, thereby promoting its survival in the host. In Aim 1, I will determine the role of PgtE in enabling STm to evade IL-22-mediated gut epithelial defenses after STm is phagocytosed in the lumen. In Aim 2, I will determine how PgtE subverts complement component C3 signaling and macrophage autophagic killing. This work will provide a framework on how pathogens utilize proteases to evade the immune system with potential novel therapeutic targets.