Salmonella small RNA fragment Sal-1 facilitates bacterial survival in infected cells via suppressing iNOS induction in a microRNA manner

Chihao Zhao,Fenyong Liu,Tianfu Zhang,Chen-Yu Zhang,Zhen Zhou,Ke Zen,Hongwei Gu

doi:10.1038/s41598-017-17205-4

Chihao Zhao, Fenyong Liu + Show 5 more

Open Access

https://doi.org/10.1038/s41598-017-17205-4

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Abstract

Salmonella can hijack host atypical miRNA processing machinery to cleave its small non-coding RNA into a ~22-nt RNA fragment, Sal-1, which facilitates Salmonella survival in the infected host. The mechanism through which Sal-1 promotes Salmonella survival, however, remains unknown. In the present study, we reported that Sal-1 targets cellular inducible nitric oxide synthase (iNOS) in a miRNA manner, leading to attenuation of host cell iNOS/NO-mediated anti-microbial capacity. First, depletion of Sal-1 in Salmonella-infected epithelial cells significantly increased the iNOS level but not the levels of various inflammatory cytokines. Bioinformatics analysis and mutagenesis strategies were consistent with the identification of mRNA of iNOS as a target of Sal-1 in both human and mice. Second, western blot and immunohistochemical analysis confirmed that Sal-1 suppressed iNOS expression in vitro and in vivo, thus reducing the production of NO. Finally, Sal-1 facilitating Salmonella survival through suppressing iNOS induction was confirmed in mouse model by expressing mutated iNOS that is not targeted by Sal-1 in mice colon. In conclusion, our study provides new insight into the pathogenic mechanism of intracellular bacteria to modulate host innate immune response.

Highlights

As a leading cause of food-borne illness worldwide[1], Salmonella have developed different mechanisms to survive in host cells[2,3,4]
When Salmonella-infected cells were treated with anti-Sal-1 antagomir, the mRNA levels of most inflammatory cytokines were not altered, whereas the level of inducible nitric oxide synthase (iNOS) mRNA was further increased compared to Salmonella-infected cells treated with control oligonucleotide (NTC) (Fig. 1a)
As iNOS and its associated nitric oxide (NO) production serves as a critical anti-microbial mechanism[13,14,19,20], attenuating NO production in the infected cells may serve as a mechanism by which Sal-1 facilitates bacterial intracellular survival

Summary

Introduction

As a leading cause of food-borne illness worldwide[1], Salmonella have developed different mechanisms to survive in host cells[2,3,4]. Generation of high level of inflammatory cytokines serves as another strategy of cell anti-bacteria, for example, Ye et al showed that interleukin-17 (IL-17) secreted by CD4+ T cells could augment host defense against bacterial pneumonia[16], Godinez et al reported that intestinal T cells amplifies innate immune responses by producing cytokines that regulate innate immune functions during Salmonella infection[14]. It remains unknown whether the reduction of iNOS/NO or inflammatory cytokine production serves as a mechanism underlying the facilitation of Sal-1 on Salmonella intracellular survival. By suppressing NO production, Salmonella are able to survive in host epithelial cells

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Results

Conclusion