A Comparative Analysis of Edwardsiella tarda-Induced Transcriptome Profiles in RAW264.7 Cells Reveals New Insights into the Strategy of Bacterial Immune Evasion.

Huili Li,Boguang Sun,Li Sun,Shuai Jiang,Xianhui Ning

doi:10.3390/ijms20225724

Abstract

Edwardsiella tarda is a Gram-negative bacterial pathogen with a broad host range, including fish, reptiles, and mammals. One prominent virulence feature of E. tarda is its ability to survive and replicate in host phagocytes, but the relevant molecular mechanism is largely unknown. In this study, we examined the transcriptome profiles of RAW264.7 cells, a murine macrophage cell line, infected with live E. tarda or stimulated with dead E. tarda for 4 h and 8 h. Eighteen libraries were constructed, and an average of 69 million clean reads per library were obtained, with ~81.63% of the reads being successfully mapped to the reference genome. In total, 208 and 232 differentially expressed genes (DEGs) were identified between live and dead E. tarda-treated cells at 4 h and 8 h post-infection, respectively. The DEGs were markedly enriched in the Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways associated with immunity. Live E. tarda differed strikingly from dead E. tarda in the regulation of immune related genes. Compared with dead E. tarda-treated cells, live E. tarda-treated cells exhibited marked and significant suppression in the induction of a large amount of immune genes, including RIG-I-like receptors, cytokines, and interferon-related genes. Furthermore, some of the immune genes highly regulated by live E. tarda formed complicated interaction networks with each other. Together, the results of this study revealed a transcriptome profile specifically induced by the active virulence elements of live E. tarda during the infection process, thus adding new insights into the intracellular infection mechanism of E. tarda. This study also provided a valuable set of target genes for further study of the immune evasion strategy of E. tarda.

Highlights

Edwardsiella tarda is a Gram-negative bacteria and a pathogen with a broad range of hosts, including fish, birds, reptiles, and mammals [1,2]
The results showed that in RAW264.7 cells infected with live E. tarda, the intracellular numbers markedly increased with time from 0 to 8 h (Figure 1)
We observed that following incubation of E. tarda with RAW264.7 cells, the number of intracellular bacteria increased with time, indicating an ability of E. tarda to evade the Survival in host phagocytic cells is the most important virulence characteristic of intracellular bacteria [22]

Summary

Introduction

Edwardsiella tarda is a Gram-negative bacteria and a pathogen with a broad range of hosts, including fish, birds, reptiles, and mammals [1,2]. Unlike most bacterial pathogens of aquaculture source, E. tarda exhibits a strong capacity to circumvent the antibacterial immune reactions of the host, which enables the bacteria to disseminate in host tissues and cause systemic infection. Accumulating evidence has indicated that E. tarda is able to survive and replicate in host serum and phagocytes, the latter including macrophages [8,9,10,11,12]. Macrophages, as well as other types of phagocytes, remove pathogens via various means, notably lysosome-dependent bacterial destruction by acidic enzymes, production of reactive oxygen species (ROS) and reactive nitrogen, and secretion of antimicrobial factors that promote other immune cells to clear the pathogens [14,15,16]. The molecular mechanism of E. tarda infection in phagocytes still remains to be investigated

Methods

Results

Conclusion