痢疾杆菌毒力蛋白OspG抑制宿主免疫应答分子机制的研究

In recent years, bacterial and amoebic dysentery Shigella has taken the fourth incidence of infectious diseases in China. Shigella spp. are human-adaptor pathogens that are capable of injecting multiple virulence proteins into the intestinal epithelial cell by type III secretion systems, causing a series of inflammatory reactions and lead to massive necrosis of the intestinal tissue. The virulence protein OspG could inhibit the immune response of the host cell and play a key role in Shigella infection. We found that the virulence protein OspG specifically binds to a histone deacetylase complex member-SAP18 protein, and inhibits the host histone acetylation levels during the early infection. The ospG mutant strain leads to the induction of a stronger inflammatory response upon infection than the wild-type strain. This project will focus on the mechanisms of OspG regulates the host immune response underlying gene transcription level by combining methods in molecular biology, cell biology and epigenetics. Demonstrate the Shigella effector modulates host inflammatory responses by targeting epigenetic modifications. Exploring the bacteria how to avoid the host’s immune defenses and effectively colonize on intestinal tissue is crucial to elucidate the mechanism of Shigella infection, will also provides an important basis for new drug design and developing effective preventive vaccines.

细菌性痢疾近年来一直居于我国传染病发病率第四位，其病原菌痢疾杆菌利用三型分泌系统将多种毒力蛋白释放至人体肠道的上皮细胞中，引起一系列炎症反应并导致肠道组织的大面积坏死。其中毒力蛋白OspG在痢疾杆菌的侵染中起关键作用，它能抑制宿主细胞的免疫应答反应。我们发现在痢疾杆菌侵染初期，OspG能抑制宿主细胞中组蛋白的乙酰化水平，并特异性结合组蛋白去乙酰化酶复合物中的成员SAP18蛋白。本项目将结合分子生物学、细胞生物学和表观遗传学方法，对痢疾杆菌和突变菌株感染肠上皮细胞后的转录组进行比较分析，重点研究OspG靶向组蛋白去乙酰化酶复合物的作用方式，揭示OspG通过改变组蛋白的修饰状态，从而调控宿主中免疫应答相关基因转录水平的机制。探讨细菌如何避开宿主的免疫防御，有效地寄生于肠道组织的新策略，对阐明痢疾杆菌的感染机理具有重要意义，也将为开发和研制新型药物和有效的痢疾预防性疫苗提供重要基础。

痢疾杆菌入侵宿主后，通过三型分泌系统产生的效应因子改变机体的天然保护机制，破坏宿主先天免疫系统，利于其在宿主中寄生、增殖并引起严重的肠道损伤，引起细菌性痢疾的发生。OspG蛋白是痢疾杆菌三型分泌系统中一个重要的效应分子，能够强烈抑制宿主细胞免疫应答反应，在细菌感染和致病过程中起关键作用。本项目综合运用细胞生物学、生物化学和微生物等研究方法，通过鉴定效应蛋白OspG的生化活性和宿主中的靶蛋白，阐明OspG蛋白调控宿主免疫反应的分子机制，取得如下结果：（1）与野生型痢疾杆菌相比，ospG基因敲除的痢疾杆菌感染宿主细胞后，在感染早期和感染晚期，宿主细胞组蛋白H3发生大量的乙酰化修饰。（2）在肠上皮细胞感染实验中，与野生型痢疾杆菌相比，ospG基因敲除的痢疾杆菌能够显著提高宿主细胞mapk8、mapk43等免疫相关基因的表达。（3）通过免疫共沉淀、pull-down、酵母双杂交等实验，验证效应蛋白OspG与组蛋白去乙酰化酶复合物在体外和体内的相互作用。本研究对阐明痢疾杆菌侵染过程中效应因子对宿主的调控作用具有理论意义，将为新一代抗菌药物的研发提供线索。