State Key Laboratory of Freshwater Ecology and Biotechnology, Institute of Hydrobiology, Chinese Academy of Sciences, Wuhan, China.
University of Chinese Academy of Sciences, Beijing, China.
Cell Microbiol. 2020 Jul;22(7):e13193. doi: 10.1111/cmi.13193. Epub 2020 Mar 5.
The type III secretion system effector EseJ plays a regulatory role inside bacteria. It suppresses the adherence of Edwardsiella piscicida (E. piscicida) to host epithelial cells by down regulating type 1 fimbriae. In this study, we observed that more macrophages infected with ΔeseJ strain of E. piscicida detached as compared with those infected with the wild-type (WT) strain. Terminal deoxynucleotidyl transferase dUTP nick-end labelling (TUNEL) staining and cleaved caspase-3 examination revealed that the detachment is due to increased apoptosis, suggesting that EseJ suppresses macrophage apoptosis. However, apoptosis inhibition by EseJ is not relative to a type III secretion system (T3SS) and is not related to EseJ's translocation. Since EseJ negatively regulates type 1 fimbriae, murine J774A.1 cells were infected with ΔeseJΔfimA or ΔeseJΔfimH strains. It was demonstrated that ΔeseJ stimulates macrophage apoptosis through type 1 fimbriae. Moreover, we found that infecting J774A.1 cells with the ΔeseJ strain increased levels of cleaved caspase-8, caspase-9, and caspase-3, demonstrating that EseJ inhibits apoptosis through either an extrinsic or a combination of extrinsic and intrinsic pathways. Pre-treatment of macrophages with caspase-8 inhibitor prior to infection with the ΔeseJ strain decreased the levels of cleaved caspase-8, caspase-9, and caspase-3, indicating that the ΔeseJ strain stimulates apoptosis, mainly through an extrinsic pathway by up regulating type 1 fimbriae. Zebrafish larvae or blue gourami fish infected with the ΔeseJ strain consistently exhibited higher apoptosis than those infected with the E. piscicida WT strain or ΔeseJΔfimA strain. Taken together, we revealed that the T3SS protein EseJ of E. piscicida inhibits host apoptosis, mainly through an extrinsic pathway by down regulating type 1 fimbriae.
III 型分泌系统效应蛋白 EseJ 在细菌内部发挥调节作用。它通过下调 I 型菌毛来抑制爱德华氏菌（E. piscicida）黏附宿主上皮细胞。在本研究中，我们观察到与野生型（WT）菌株相比，更多感染ΔeseJ 株的巨噬细胞脱落。末端脱氧核苷酸转移酶 dUTP 缺口末端标记（TUNEL）染色和裂解的 caspase-3 检测表明，这种脱落是由于细胞凋亡增加所致，提示 EseJ 抑制巨噬细胞凋亡。然而，EseJ 对凋亡的抑制作用与 III 型分泌系统（T3SS）无关，也与 EseJ 的易位无关。由于 EseJ 负调控 I 型菌毛，我们用ΔeseJΔfimA 或ΔeseJΔfimH 株感染 J774A.1 细胞。结果表明，ΔeseJ 通过 I 型菌毛刺激巨噬细胞凋亡。此外，我们发现感染 J774A.1 细胞的ΔeseJ 株增加了裂解的 caspase-8、caspase-9 和 caspase-3 的水平，表明 EseJ 通过外源性或外源性和内源性途径的组合抑制凋亡。感染ΔeseJ 株前用 caspase-8 抑制剂预处理巨噬细胞可降低裂解的 caspase-8、caspase-9 和 caspase-3 的水平，表明ΔeseJ 株通过上调 I 型菌毛刺激凋亡，主要通过外源性途径。感染ΔeseJ 株的斑马鱼幼虫或蓝孔雀鱼的凋亡水平明显高于感染 E. piscicida WT 株或ΔeseJΔfimA 株的鱼。综上所述，我们揭示了 E. piscicida 的 T3SS 蛋白 EseJ 抑制宿主凋亡，主要通过下调 I 型菌毛通过外源性途径。
