Abstract
Listeria monocytogenes is a Gram-positive facultative intracellular pathogen, causing serious illness in immunocompromised individuals and pregnant women. Upon detection by macrophages, which are key players of the innate immune response against infection, L. monocytogenes induces specific host cell responses which need to be tightly controlled at transcriptional and post-transcriptional levels. Here, we ask whether and how host miRNAs, which represent an important mechanism of post-transcriptional regulation in a wide array of biological processes, are altered by a model pathogen upon live infection of murine bone marrow derived macrophages. We first report that L. monocytogenes subverts the host genome-wide miRNA profile of macrophages in vitro. Specifically, we show that miR-155, miR-146a, miR-125a-3p/5p and miR-149 were amongst the most significantly regulated miRNAs in infected macrophages. Strikingly, these miRNAs were highly upregulated upon infection with the Listeriolysin-deficient L. monocytogenes mutant Δhly, that cannot escape from the phagosome thus representing a vacuolar-contained infection. The vacuolar miRNA response was significantly reduced in macrophages deficient for MyD88. In addition, miR-146a and miR-125a-3p/5p were regulated at transcriptional levels upon infection, and miR-125a-3p/5p were found to be TLR2 responsive. Furthermore, miR-155 transactivation in infection was regulated by NF-κB p65, while miR-146a and miR-125a-3p/5p expression was unaffected in p65-deficient primary macrophages upon L. monocytogenes infection. Our results demonstrate that L. monocytogenes promotes significant changes in the miRNA expression profile in macrophages, and reveal a vacuolar-dependent miRNA signature, listeriolysin-independent and MyD88-dependent. These miRNAs are predicted to target immune genes and are therefore most likely involved in regulation of the macrophage innate immune response against infection at post-transcriptional levels.
Highlights
Listeria monocytogenes is a Gram positive facultative intracellular bacterium that has been used as a model pathogen to study hostpathogen interactions [1]
Signalling via the so-called vacuolar/Toll-like receptor (TLR) - and the cytosolic/nuclear oligomerisation domain (NOD)-like receptor (NLR) - dependent pathways lead to mitogen-activated protein kinase (MAPK), nuclear factor kappa B (NF-kB) and Interferon Regulatory Factor-3 (IRF3) activation [5]
Using the Applied Biosystems (ABI) RQ Manager 1.2 and DataAssist v2.0 software for analyses, we comprehensively identified 385 miRNAs that were expressed in our samples, of which 13 were significantly ($1.5 fold, P value#0.05) up-regulated at 6 h post-infection
Summary
Listeria monocytogenes is a Gram positive facultative intracellular bacterium that has been used as a model pathogen to study hostpathogen interactions [1]. This opportunistic food-borne pathogen causes serious illness to immunocompromised individuals, pregnant women and the developing foetus [2]. To establish an infection in a host organism, the bacterium must first overcome the barriers of the innate immune system. Macrophages are professional phagocytes which provide a first line of innate immune defence against invading pathogens. Detection of L. monocytogenes by macrophages at the cell surface, within phagosomes or the cytosol triggers distinct host cell transcriptional responses via pattern recognition receptors (PRR) [3,4]. Numerous proinflammatory mediators and other molecules are expressed that further instruct elicitation of antigen-specific acquired immunity and clearance of infection
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