细菌类硫氧还蛋白调控MAPK信号通路及鱼类抗感染机制的研究

The mitogen-activated protein kinase (MAPK) signaling pathway activation plays critical role in regulating inflammatory responses. However, many pathogens have evolved divers strategies to inhibit MAPK and regulate host immune responses, which are often associated with increased virulence. Edwardsiella picisida is an important fish pathogen. To better understand the virulence of E. picisida during infection, in our previous work, we compared the transcriptome between in vitro-cultured and in vivo-infected bacteria, and revealed that ETAE_2186, trxlp, encoding a thioredoxin-like protein was significantly induced, and the Trxlp was proved to play an essential role in inhibiting ERK- and p38-MAPK signaling pathways, however, how Trxlp mediates MAPK inhibition in vivo and its roles in regulating fish immunologic defense are not well defined. In this work, using zebrafish larvae as the infection model, we plan to investigate the regulation of fish MAPK pathways by E. picisida virulence factor-Trxlp in vivo and further evaluate the effect of Trxlp-regulated MAPK signaling cascades on bacterial infection in vivo. Then, we will try to examine how Trxlp-regulated MAPK signaling cascades affect inflammatory cytokines-mediated and immune cells-mediated host anti-infection defense mechanism, which controls systemic infection of E. picisida in vivo. This work will give insights into how E. picisida escape fish host innate immunologic defenses, and also provide a platform to study the interaction of fish bacteria with fish host in vivo.

MAPK信号通路介导的炎症反应在宿主免疫防御中发挥了重要作用。同时，细菌通过毒力因子靶向MAPK信号以操控宿主免疫防御是病原实现系统性感染的重要机制。杀鱼爱德华氏菌是重要的鱼类病原，前期研究发现了一个新的细菌毒力因子-类硫氧还蛋白，其能够抑制ERK-和p38-MAPK信号通路，但该抑制信号如何调控鱼类的抗感染过程是一个有待研究的关键科学问题。我们推测类硫氧还蛋白抑制MAPK信号通路，可能影响了炎症因子的表达及免疫细胞的活化和招募，从而促进细菌的系统性感染。本项目将斑马鱼作为研究水产养殖病原和鱼类互作机制的模式动物，阐明类硫氧还蛋白在活体水平上对鱼类ERK-和p38-MAPK信号通路的抑制效应及其对增强细菌系统性感染的影响，进一步解析类硫氧还蛋白抑制MAPK信号通路对宿主抗感染机制的调控作用。本研究的成功实施将为深入理解杀鱼爱德华氏菌调控鱼类炎症信号通路、逃避宿主免疫杀伤机制奠定基础。

MAPK信号通路接到的炎症反应在宿主免疫防御中发挥了重要作用。同时，细菌通过独立音字靶向MAPK信号以操控宿主免疫防御是病原实现系统性感染的重要机制。本项目基于杀鱼爱德华氏菌效应物高通量筛选平台，鉴定了一个新的类硫氧还蛋白效应分子，采用晶体结构解析发现该蛋白具有保守的-WCxxC-基序特点，当其被转运到宿主细胞质后，通过模拟内源性硫氧还蛋白，靶向凋亡信号调节激酶 (ASK1) N端的特异性空间结合位点，阻断ASK1的磷酸化，抑制其下游Erk/p38-MAPK信号的级联磷酸化响应过程。基于上述结果，课题组建立了杀鱼爱德华氏菌显微注射感染斑马鱼幼鱼活体模型，进一步阐明了ASK1-MAPK信号通路的激活是控制细菌感染的关键信号之一。该研究成果首次发现了硫氧还蛋白作为效应分子在细菌感染过程中扮演角色，为深入解析病原-宿主互作分子机制提供了新思路。依托本项目的实施，在PLoS Pathogens等杂志发表论文4篇，培养研究生4人。

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