核糖体参与调控的内质网未折叠蛋白反应在线虫固有免疫应答过程中的作用及机制研究

The nematode Caenorhabditis elegans has been widely used to study the virulence of human opportunistic pathogens Pseudomonas aeruginosa as well as the host innate immune response. Endoplasmic Reticulum-dependent regulation of protein homeostasis contributes greatly to the host immune response. Using high-throughput genomic reverse genetic screening, 346 genes were identified as novel regulators of C. elegans innate immunity against P. aeruginosa, and 24 of them encodes the ribosome proteins. Inhibition of ribosome proteins lead to up-regulated expression of antimicrobial genes and prolonged survival time upon P. aeruginosa infection. Meanwhile, when infected by P. aeruginosa, C. elegans invoke the ER unfolding protein response to maintain protein homeostasis. Inhibition of a dominant ER UPR regulator IRE-1 greatly attenuated the prolonged survival of ribosome proteins-lacking worms, suggesting that the ribosome proteins may regulates the host innate immunity by mediating the ER UPR. Our further study tries to find out the abnormalities in different processes of protein metabolism including translation in ribosome, translocation to ER membrane, folding and degradation during P. aeruginosa infection, and tries to characterize the cellular function and the molecular mechanism of ribosome protein in regulation of ER dependent protein homeostasis. Our research will give a good diagram how ribosomes and endoplasmic reticulum contribute the proteostasis and host innate immunity.

利用模式生物秀丽隐杆线虫构建铜绿假单胞杆菌感染模型，被广泛应用于铜绿假单胞杆菌致病机理以及宿主固有免疫应答机制的研究。内质网依赖的蛋白质稳态平衡的调节是宿主固有免疫应答的重要组成部分。我们通过大规模反式遗传学筛选发现：（1）24个核糖体结构蛋白的缺失，会显著上升抗菌基因的表达，并延长线虫在铜绿假单胞杆菌感染条件下的存活时间；（2）铜绿假单胞杆菌感染引发宿主细胞内质网未折叠蛋白反应；（3）抑制内质网未折叠蛋白反应可以显著降低核糖体结构蛋白缺失线虫株在铜绿假单胞杆菌感染条件下的存活率。以上结果提示，核糖体蛋白可能通过调节内质网蛋白稳态平衡，进而调节宿主固有免疫应答过程。本项目拟进一步从病原微生物水平、分子细胞水平、动物感染模型等不同层次，研究铜绿假单胞杆菌感染引发的宿主蛋白翻译、折叠、转运、降解等过程中的异常，进而明确核糖体蛋白在这一些过程中所发挥的调控作用，以及对宿主固有免疫应答的调节机制。

利用模式生物秀丽隐杆线虫构建铜绿假单胞杆菌感染模型，被广泛应用于铜绿假单胞杆菌致病机理以及宿主固有免疫应答机制的研究。内质网稳态平衡的调节是宿主固有免疫应答的重要组成部分,我们通过全基因组反式遗传学筛选发现24个核糖体基因参与调节线虫固有免疫。沉默这些基因会显著延长线虫在铜绿假单胞杆菌感染条件下的存活时间并减少线虫体内荷菌量；铜绿假单胞杆菌感染诱导核糖体基因的高表达并促进多聚核糖体的组装，引起线虫总体蛋白翻译速率的增加。过多新合成蛋白来不及正常折叠而形成聚集体从而破坏内质网稳态，使得内质网处于应激状态进而导致线虫在感染状态下存活时间变短。抑制核糖体的生成可以减少非折叠蛋白聚集体的形成并缓解感染导致的内质网应激状态。我们的结果表明核糖体通过引起内质网应激从而负调线虫固有免疫应答反应。