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      Immune evasion and provocation by Mycobacterium tuberculosis

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          Abstract

          Mycobacterium tuberculosis, the causative agent of tuberculosis, has infected humans for millennia. M. tuberculosis is well adapted to establish infection, persist in the face of the host immune response and be transmitted to uninfected individuals. Its ability to complete this infection cycle depends on it both evading and taking advantage of host immune responses. The outcome of M. tuberculosis infection is often a state of equilibrium characterized by immunological control and bacterial persistence. Recent data have highlighted the diverse cell populations that respond to M. tuberculosis infection and the dynamic changes in the cellular and intracellular niches of M. tuberculosis during the course of infection. M. tuberculosis possesses an arsenal of protein and lipid effectors that influence macrophage functions and inflammatory responses; however, our understanding of the role that specific bacterial virulence factors play in the context of diverse cellular reservoirs and distinct infection stages is limited. In this Review, we discuss immune evasion and provocation by M. tuberculosis during its infection cycle and describe how a more detailed molecular understanding is crucial to enable the development of novel host-directed therapies, disease biomarkers and effective vaccines.

          Abstract

          In this Review, Chandra, Grigsby and Philips discuss how Mycobacterium tuberculosis evades immune-mediated clearance while capitalizing on the host inflammatory response at different phases of its life cycle. They focus on recent studies, highlight gaps in knowledge and consider how our current understanding will inform new therapies, vaccines and diagnostics.

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          Most cited references202

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          Succinate is an inflammatory signal that induces IL-1β through HIF-1α.

          Macrophages activated by the Gram-negative bacterial product lipopolysaccharide switch their core metabolism from oxidative phosphorylation to glycolysis. Here we show that inhibition of glycolysis with 2-deoxyglucose suppresses lipopolysaccharide-induced interleukin-1β but not tumour-necrosis factor-α in mouse macrophages. A comprehensive metabolic map of lipopolysaccharide-activated macrophages shows upregulation of glycolytic and downregulation of mitochondrial genes, which correlates directly with the expression profiles of altered metabolites. Lipopolysaccharide strongly increases the levels of the tricarboxylic-acid cycle intermediate succinate. Glutamine-dependent anerplerosis is the principal source of succinate, although the 'GABA (γ-aminobutyric acid) shunt' pathway also has a role. Lipopolysaccharide-induced succinate stabilizes hypoxia-inducible factor-1α, an effect that is inhibited by 2-deoxyglucose, with interleukin-1β as an important target. Lipopolysaccharide also increases succinylation of several proteins. We therefore identify succinate as a metabolite in innate immune signalling, which enhances interleukin-1β production during inflammation.
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            Succinate Dehydrogenase Supports Metabolic Repurposing of Mitochondria to Drive Inflammatory Macrophages.

            Activated macrophages undergo metabolic reprogramming, which drives their pro-inflammatory phenotype, but the mechanistic basis for this remains obscure. Here, we demonstrate that upon lipopolysaccharide (LPS) stimulation, macrophages shift from producing ATP by oxidative phosphorylation to glycolysis while also increasing succinate levels. We show that increased mitochondrial oxidation of succinate via succinate dehydrogenase (SDH) and an elevation of mitochondrial membrane potential combine to drive mitochondrial reactive oxygen species (ROS) production. RNA sequencing reveals that this combination induces a pro-inflammatory gene expression profile, while an inhibitor of succinate oxidation, dimethyl malonate (DMM), promotes an anti-inflammatory outcome. Blocking ROS production with rotenone by uncoupling mitochondria or by expressing the alternative oxidase (AOX) inhibits this inflammatory phenotype, with AOX protecting mice from LPS lethality. The metabolic alterations that occur upon activation of macrophages therefore repurpose mitochondria from ATP synthesis to ROS production in order to promote a pro-inflammatory state.
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              mTOR- and HIF-1α-mediated aerobic glycolysis as metabolic basis for trained immunity.

              Epigenetic reprogramming of myeloid cells, also known as trained immunity, confers nonspecific protection from secondary infections. Using histone modification profiles of human monocytes trained with the Candida albicans cell wall constituent β-glucan, together with a genome-wide transcriptome, we identified the induced expression of genes involved in glucose metabolism. Trained monocytes display high glucose consumption, high lactate production, and a high ratio of nicotinamide adenine dinucleotide (NAD(+)) to its reduced form (NADH), reflecting a shift in metabolism with an increase in glycolysis dependent on the activation of mammalian target of rapamycin (mTOR) through a dectin-1-Akt-HIF-1α (hypoxia-inducible factor-1α) pathway. Inhibition of Akt, mTOR, or HIF-1α blocked monocyte induction of trained immunity, whereas the adenosine monophosphate-activated protein kinase activator metformin inhibited the innate immune response to fungal infection. Mice with a myeloid cell-specific defect in HIF-1α were unable to mount trained immunity against bacterial sepsis. Our results indicate that induction of aerobic glycolysis through an Akt-mTOR-HIF-1α pathway represents the metabolic basis of trained immunity. Copyright © 2014, American Association for the Advancement of Science.

                Author and article information

                Contributors
                philips.j.a@wustl.edu
                Journal
                Nat Rev Microbiol
                Nat Rev Microbiol
                Nature Reviews. Microbiology
                Nature Publishing Group UK (London )
                1740-1526
                1740-1534
                25 July 2022
                : 1-17
                Affiliations
                [1 ]GRID grid.4367.6, ISNI 0000 0001 2355 7002, Division of Infectious Diseases, Department of Medicine, , Washington University School of Medicine, ; St Louis, MO USA
                [2 ]GRID grid.4367.6, ISNI 0000 0001 2355 7002, Department of Molecular Microbiology, , Washington University School of Medicine, ; St Louis, MO USA
                Author information
                http://orcid.org/0000-0001-6301-7617
                http://orcid.org/0000-0003-4701-7355
                http://orcid.org/0000-0002-9476-0240
                Article
                763
                10.1038/s41579-022-00763-4
                9310001
                35879556
                a2242794-c4fe-4434-9fb7-63f530a2e5cc
                © Springer Nature Limited 2022

                This article is made available via the PMC Open Access Subset for unrestricted research re-use and secondary analysis in any form or by any means with acknowledgement of the original source. These permissions are granted for the duration of the World Health Organization (WHO) declaration of COVID-19 as a global pandemic.

                History
                : 20 June 2022
                Categories
                Review Article

                pathogens,immunology,cellular microbiology
                pathogens, immunology, cellular microbiology

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