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Polymorphisms in the IRGM gene are associated with susceptibility to tuberculosis in humans. A murine ortholog of Irgm, Irgm1, is also essential for controlling Mycobacterium tuberculosis (Mtb) infection in mice. Multiple processes have been associated with IRGM1 activity that could impact the host response to Mtb infection, including roles in autophagy-mediated pathogen clearance and expansion of activated T cells. However, what IRGM1-mediated pathway is necessary to control Mtb infection in vivo and the mechanistic basis for this control remains unknown. We dissected the contribution of IRGM1 to immune control of Mtb pathogenesis in vivo and found that Irgm1 deletion leads to higher levels of IRGM3-dependent type I interferon signaling. The increased type I interferon signaling precludes T cell expansion during Mtb infection. The absence of Mtb-specific T cell expansion in Irgm1 -/- mice results in uncontrolled Mtb infection in neutrophils and alveolar macrophages, which directly contributes to susceptibility to infection. Together, our studies reveal that IRGM1 is required to promote T cell-mediated control of Mtb infection in neutrophils, which is essential for the survival of Mtb-infected mice. These studies also uncover new ways type I interferon signaling can impact T H 1 immune responses., Competing Interests: Declaration of Competing Interest The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: Christina Stallings reports financial support was provided by National Institute of Health. Michael McNehlan reports financial support was provided by National Institute of Health. Rachel Kinsella reports financial support was provided by Potts Memorial Foundation. Christina Stallings reports financial support was provided by Burroughs Wellcome Fund. If there are other authors, they declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 The Authors. Published by Elsevier Inc. All rights reserved.)

Although autophagy sequesters Mycobacterium tuberculosis (Mtb) in in vitro cultured macrophages, loss of autophagy in macrophages in vivo does not result in susceptibility to a standard low-dose Mtb infection until late during infection, leaving open questions regarding the protective role of autophagy during Mtb infection. Here we report that loss of autophagy in lung macrophages and dendritic cells results in acute susceptibility of mice to high-dose Mtb infection, a model mimicking active tuberculosis. Rather than observing a role for autophagy in controlling Mtb replication in macrophages, we find that autophagy suppresses macrophage responses to Mtb that otherwise result in accumulation of myeloid-derived suppressor cells and subsequent defects in T cell responses. Our finding that the pathogen-plus-susceptibility gene interaction is dependent on dose has important implications both for understanding how Mtb infections in humans lead to a spectrum of outcomes and for the potential use of autophagy modulators in clinical medicine., (© 2024. The Author(s), under exclusive licence to Springer Nature Limited.)

The rise in multidrug resistant tuberculosis cases underscores the urgent need to develop new treatment strategies for tuberculosis. Herein, we report the discovery and synthesis of a new series of compounds containing a 3-thio-1,2,4-triazole moiety that show inhibition of Mycobacterium tuberculosis ( Mtb ) growth and survival. Structure-activity relationship studies led us to identify several potent analogs displaying low micromolar to nanomolar inhibitory activity, specifically against Mtb . The potent analogs demonstrated no cytotoxicity in mammalian cells at over 100 times the effective concentration required in Mtb and were bactericidal against Mtb during infection of macrophages. In the exploratory ADME investigations, we observed suboptimal ADME characteristics, which prompted us to identify potential metabolic liabilities for further optimization. Our preliminary investigations into the mechanism of action suggest that this series is not engaging the promiscuous targets that arise from many phenotypic screens. We selected for resistant mutants with the nanomolar potent nitro-containing compound 20 and identified resistant isolates with mutations in genes required for coenzyme F 420 biosynthesis and the nitroreductase Ddn. This suggests that the aromatic nitro-1,2,4-triazolyl pyridines are activated by F 420 -dependent Ddn activity, similar to the nitro-containing TB drug pretomanid. We were able to circumvent the requirement for F 420 -dependent Ddn activity using compounds that contained non-nitro groups, identifying a key feature to be modified to avoid this predominant resistance mechanism. These studies provide the foundation for the development of a new class of 1,2,4-triazole compounds for the treatment of tuberculosis.

The immune response to Mycobacterium tuberculosis infection determines tuberculosis disease outcomes, yet we have an incomplete understanding of what immune factors contribute to a protective immune response. Neutrophilic inflammation has been associated with poor disease prognosis in humans and in animal models during M. tuberculosis infection and, therefore, must be tightly regulated. ATG5 is an essential autophagy protein that is required in innate immune cells to control neutrophil-dominated inflammation and promote survival during M. tuberculosis infection; however, the mechanistic basis for how ATG5 regulates neutrophil recruitment is unknown. To interrogate what innate immune cells require ATG5 to control neutrophil recruitment during M. tuberculosis infection, we used different mouse strains that conditionally delete Atg5 in specific cell types. We found that ATG5 is required in CD11c+ cells (lung macrophages and dendritic cells) to control the production of proinflammatory cytokines and chemokines during M. tuberculosis infection, which would otherwise promote neutrophil recruitment. This role for ATG5 is autophagy dependent, but independent of mitophagy, LC3-associated phagocytosis, and inflammasome activation, which are the most well-characterized ways that autophagy proteins regulate inflammation. In addition to the increased proinflammatory cytokine production from macrophages during M. tuberculosis infection, loss of ATG5 in innate immune cells also results in an early induction of TH17 responses. Despite prior published in vitro cell culture experiments supporting a role for autophagy in controlling M. tuberculosis replication in macrophages, the effects of autophagy on inflammatory responses occur without changes in M. tuberculosis burden in macrophages. These findings reveal new roles for autophagy proteins in lung resident macrophages and dendritic cells that are required to suppress inflammatory responses that are associated with poor control of M. tuberculosis infection., Competing Interests: The authors have declared that no competing interest exist., (Copyright: © 2023 Kinsella et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.)

Neutrophils are the most abundant cell type in the airways of tuberculosis patients. Mycobacterium tuberculosis (Mtb) infection induces the release of neutrophil extracellular traps (NETs); however, the molecular regulation and impact of NET release on Mtb pathogenesis are unknown. We find that during Mtb infection in neutrophils, PAD4 citrullinates histones to decondense chromatin that gets released as NETs in a manner that can maintain neutrophil viability and promote Mtb replication. Type I interferon promotes the formation of chromatin-containing vesicles that allow NET release without compromising plasma membrane integrity. Analysis of nonhuman primate granulomas supports a model where neutrophils are exposed to type I interferon from macrophages as they migrate into the granuloma, thereby enabling the release of NETs associated with necrosis and caseation. Our data reveal NET release as a promising target to inhibit Mtb pathogenesis. [Display omitted] • Mtb -induced NET release is PAD4 and type I IFN dependent • Type I IFN promotes NET release without compromising plasma membrane integrity • NET release by neutrophils promotes Mtb replication • NET release in granulomas is associated with necrosis and caseation in NHPs Sur Chowdhury et al. report that Mycobacterium tuberculosis (Mtb) infection results in the release of neutrophil extracellular traps (NETs) that promote Mtb replication and associate with tissue damage. Blocking NET release results in better control of Mtb replication, revealing a strategy for treating these deadly infections. [ABSTRACT FROM AUTHOR]