Investigation of the host transcriptional response to intracellular bacterial infection using Dictyostelium discoideum as a host model

Jonas Kjellin,Fredrik Söderbom,Maria Pränting,Roshan Vaid,Frauke Bach,Zhiru Li,Monica Hagedorn,Manfred Grabherr,Bart Edelbroek,Ralph R Isberg,Marc P Hoeppner

doi:10.1186/s12864-019-6269-x

Abstract

BackgroundDuring infection by intracellular pathogens, a highly complex interplay occurs between the infected cell trying to degrade the invader and the pathogen which actively manipulates the host cell to enable survival and proliferation. Many intracellular pathogens pose important threats to human health and major efforts have been undertaken to better understand the host-pathogen interactions that eventually determine the outcome of the infection. Over the last decades, the unicellular eukaryote Dictyostelium discoideum has become an established infection model, serving as a surrogate macrophage that can be infected with a wide range of intracellular pathogens. In this study, we use high-throughput RNA-sequencing to analyze the transcriptional response of D. discoideum when infected with Mycobacterium marinum and Legionella pneumophila. The results were compared to available data from human macrophages.ResultsThe majority of the transcriptional regulation triggered by the two pathogens was found to be unique for each bacterial challenge. Hallmark transcriptional signatures were identified for each infection, e.g. induction of endosomal sorting complexes required for transport (ESCRT) and autophagy genes in response to M. marinum and inhibition of genes associated with the translation machinery and energy metabolism in response to L. pneumophila. However, a common response to the pathogenic bacteria was also identified, which was not induced by non-pathogenic food bacteria. Finally, comparison with available data sets of regulation in human monocyte derived macrophages shows that the elicited response in D. discoideum is in many aspects similar to what has been observed in human immune cells in response to Mycobacterium tuberculosis and L. pneumophila.ConclusionsOur study presents high-throughput characterization of D. discoideum transcriptional response to intracellular pathogens using RNA-seq. We demonstrate that the transcriptional response is in essence distinct to each pathogen and that in many cases, the corresponding regulation is recapitulated in human macrophages after infection by mycobacteria and L. pneumophila. This indicates that host-pathogen interactions are evolutionary conserved, derived from the early interactions between free-living phagocytic cells and bacteria. Taken together, our results strengthen the use of D. discoideum as a general infection model.

Highlights

During infection by intracellular pathogens, a highly complex interplay occurs between the infected cell trying to degrade the invader and the pathogen which actively manipulates the host cell to enable survival and proliferation
High-throughput sequencing of D. discoideum cells infected with M. marinum and L. pneumophila In order to characterize the early transcriptional regulation of host genes after infection by M. marinum and L. pneumophila respectively, we performed highthroughput sequencing of poly(A) enriched RNA from infected and non-infected cells
To obtain RNA for transcriptional studies of M. marinum infected D. discoideum, we used a high multiplicity of infection (MOI of 200) in order to acquire a strong and synchronized transcriptional signature of infected cells already 2.5 h post infection

Summary

Introduction

During infection by intracellular pathogens, a highly complex interplay occurs between the infected cell trying to degrade the invader and the pathogen which actively manipulates the host cell to enable survival and proliferation. The infected host turns on defense mechanisms to clear the infection This leads to a series of complex and dynamic host-pathogen interactions that eventually will determine the outcome of the infection. The processes used by the bacteria to establish an infection in D. discoideum, are in many aspects very similar to the infectious route in mammalian macrophages [1]. For these reasons, D. discoideum has over the past decades emerged as a valuable model system to study the basic interactions between a host cell and a wide range of intracellular pathogens, e.g. Legionella pneumophila, different mycobacterial species, and Francisella noatunensis (reviewed in [2,3,4])

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