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Macrophage Epithelial Reprogramming Underlies Mycobacterial Granuloma Formation and Promotes Infection

ABSTRACT: Mycobacterium tuberculosis infection in humans triggers formation of granulomas, tightly organized immune cell aggregates that are the central structure of tuberculosis. Infected and uninfected macrophages interdigitate, assuming an altered, flattened appearance. Although pathologists have described these changes for over a century, the molecular and cellular programs underlying this transition are unclear. We find that mycobacterial granuloma formation is accompanied by macrophage induction of canonical epithelial molecules and structures. Using the zebrafish-Mycobacterium marinum model, we identify fundamental macrophage reprogramming events that parallel E-cadherin-dependent mesenchymal-epithelial transitions. Macrophage-specific disruption of E-cadherin function results in disordered granuloma formation, enhanced immune cell access, decreased bacterial burden and increased host survival, suggesting that the granuloma can also serve a bacteria-protective role. In humans, we find that granuloma macrophages are similarly transformed. Long considered largely through the prism of immune signaling pathways, granuloma macrophages are reprogrammed by epithelial modules that alter the trajectory of mycobacterial infection.

ORGANISM(S): Danio rerio

PROVIDER: GSE81913 | GEO | 2016/10/18

REPOSITORIES: GEO

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Project description:Pathogenic mycobacteria have the ability to survive within macrophages and persist inside granulomas composed of host immune cells. The complex host-pathogen interactions that determine the outcome of a mycobacterial infection process result in marked alterations of the host gene expression profile. Here we used the zebrafish model to investigate the specificity of the host response to infections with two mycobacterium strains that give distinct disease outcomes: an acute disease with early lethality or a chronic disease with granuloma formation, caused by Mycobacterium marinum strains Mma 20 and E11, respectively. We performed a microarray study of different stages of disease progression in adult zebrafish and found that the acute and the chronic strains evoked partially overlapping host transcriptome signatures, despite that they induce profoundly different disease phenotypes. Both strains affected many signaling cascades, including Wnt and Tlr pathways. Interestingly, the strongest differences were observed at the initial stage of the disease. The immediate response to the acute strain was characterized by higher expression of genes encoding MHC class I proteins, matrix metalloproteinases, transcription factors, cytokines and other common immune response proteins. In contrast, small GTPase and histone gene groups showed higher expression in response to the chronic strain. We also found that nearly 1,000 mycobacterium-responsive genes overlapped between the expression signatures of infected zebrafish adults and embryos at different stages of granuloma formation. Since adult zebrafish possess an adaptive immune system similar to mammals and zebrafish embryos rely solely on innate immunity, this overlap indicates a major contribution of the innate component of the immune system in the response to mycobacterium infection. Taken together, our comparison of the transcriptome responses involved in acute versus chronic infections and in the embryonic versus adult situation provides important new leads for investigating the mechanism of mycobacterial pathogenesis.

Project description:Phagocytosis requires the activation of a plethora of mechanisms that include the activation of the actin cytoskeleton guided by the Arp2/3 complex. These are promoted by activators such as the Wiskott Aldrich Syndrome Protein (WASP) family members. In order to further understand the molecular mechanisms involved in the early events leading the phagocytosis of the pathogenic Mycobacterium tuberculosis, we set out to examine potential roles of miRNAs in phagocytosis using genome-wide expression profiling to identify miRNAs differentially regulated following mycobacterial infection. One of the miRNAs activated upon infection of mouse macrophages with the non-pathogenic Mycobacterium smegmatis, the widely conserved miR-142-3p, was predicted and confirmed to target the Neural-WASP (N-WASP). Upregulating of miR-142-3p in mouse macrophages inversely correlated with levels of N-WASP, upon infection with live pathogenic and non-pathogenic mycobacteria, suggesting an active role of Mycobacterium tuberculosis on the regulation of phagocytosis, at the post-transcriptional level, in host cells. The reduction of N-WASP correlated with a reduced internalization of bacteria per macrophage, independently of the phagocytosis index. Furthermore, the downregulation of WASP levels accompanied those of N-WASP, at early but not at late time points, suggesting a closely regulatory mechanism among both family members, dependent on the time frame of the phagocytosis. Additionally, upregulating of miR-142-3p promoted the change in the protein levels of another predicted and confirmed target, the Cofilin2 protein, in a phagocytosis-independent fashion. Downregulation experiments promoted aberrant morphologic phenotypes in macrophages, similar to observed by others in PBMCs of humans with Wiskott Aldrich Syndrome, suggesting the strong involvement of miR-142-3p on the regulation of the actin machinery in macrophages. Altogether these results show for the first time that miRNAs are involved in the regulation of actin-mediated phagocytosis of pathogenic bacteria and that these are direct targets of Mycobacterium tuberculosis. Expression analysis of mouse macrophage cell line J774A.1 in response to infection with Mycobacterium smegmatis mc2155 EGFP. Three biological replicates each for uninfected and infected samples.

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Macrophage Epithelial Reprogramming Underlies Mycobacterial Granuloma Formation and Promotes Infection

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