非共生发光杆菌毒力基因簇激活NF-kB和MAPK信号通路促进细菌对巨噬细胞的侵染

Photorhabdus virulence cassette promotes bacterial invasion into macrophages by activating NF-kB and MAPK signaling pathway

摘要:

发光杆菌是一种来自肠杆菌科的革兰氏阴性细菌，一般情况下与昆虫或线虫共生。除了作为昆虫病原体的角色，一种名为非共生发光杆菌 (Photorhabdus asymbiotica，Pa) 的物种在世界各地能引起人体组织的感染。然而，这种跨界感染的分子机制目前尚未有深入研究。本论文通过探究非共生发光杆菌毒力装置 (PVC) 对于真核细胞的影响，对其感染机制进行阐释。首先，RNA测序和qPCR等研究数据表明，在PVC处理的哺乳动物巨噬细胞中，NF-kB和MAPK通路被强烈激活。进而本研究在细胞水平通过Western blotting等方法对PVC处理引起的MAPK信号通路激活的现象进行多重验证。NF-kB活性的检测以及p65蛋白核移位的实验结果证实了巨噬细胞经PVC处理后产生的NF-kB活化作用。此外，PVC处理早期也能促进巨噬细胞对细菌的吞噬作用，而细胞骨架聚合抑制剂能抑制这种吞噬作用。结果表明，PVC通过激活NF-kB和MAPK信号通路参与细菌对巨噬细胞的侵染作用，这将为分析Pa在人类感染中的致病性提供新的思路。

Abstract:

Photorhabdus is a Gram-negative bacterium from the family Enterobacteriaceae that lives in a symbiotic association with nematode or insects. In addition to the role of being insect pathogens, one species called Photorhabdus asymbiotica (Pa) causes human infection around the world. Nevertheless, how does this transkingdom infection occur remains elusive. Here we focus on one pathogenic determinant called Photorhabdus virulence cassette (PVC) that is founded in the Pa genome and many other pathogens. The RNA-seq and qPCR data showed that the NF-kB and MAPK pathways were drastically activated in the PVC-treated mammalian macrophages. Western blotting assays using samples treated with various inhibitors of the affected pathways confirmed the results we have observed for MAPK pathway previously. p65 translocation assays validated the NF-kB activation in the macrophages after PVC treatment. Moreover, the bacterial phagocytosis by macrophage was also promoted by PVC at the early stage, and this phagocytosis was inhibited by cytoskeleton inhibitors. Thus, the results indicated that PVC is involved in the bacterial invasion by activating NF-kB and MAPK signaling pathway, providing a new perspective for analyzing the pathogenicity of Pa in human infections.