IRG1 and iNOS act redundantly with other interferon gamma-induced factors to restrict intracellular replication ofLegionella pneumophila

Abstract

18Interferon gamma (IFNγ) restricts the intracellular replication of many pathogens, but 19how IFNγ confers cell-intrinsic pathogen resistance remains unclear. For example, 20 intracellular replication of the bacterial pathogen Legionella pneumophila in 21 macrophages is potently curtailed by IFNγ, but consistent with prior results, no 22Importance 41 Legionella pneumophila is one example among many species of pathogenic bacteria 42 that replicate within mammalian macrophages during infection. The immune signaling 43 factor interferon gamma (IFNγ) blocks L. pneumophila replication in macrophages and 44 is an essential component of the immune response to L. pneumophila and other 45 intracellular pathogens. However, to date, no study has determined the exact molecular 46 factors induced by IFNγ that are required for its activity. We generated macrophages 47 lacking different combinations of IFNγ-induced genes in an attempt to find a genetic 48 background in which there is a complete loss of IFNγ-mediated restriction of L. 49 pneumophila. We successfully identified six genes that comprise the totality of the IFNγ-50 dependent restriction of L. pneumophila replication in macrophages. Our results clarify 51 the molecular basis underlying the potent effects of IFNγ and highlight how redundancy 52 downstream of IFNγ is key to prevent exploitation of the macrophage niche by 53 pathogens. 54 IFNγ that can restrict L. pneumophila in the absence of iNOS. 93 Previous work has attempted to address the possibility of redundancy in the 94 IFNγ-dependent immune response to L. pneumophila. Pilla et al generated quadruple 95 knockout (QKO) mice deficient in Nos2, Cybb (cytochrome b(558) subunit beta, 96 encoding NADPH oxidase 2 aka NOX2), Irgm1 (immunity-related GTPase family M 97 member 1), and Irgm3 (immunity-related GTPase family M member 3), all induced by 98 IFNγ (20). NOX2 partners with phagosomal oxidase components to generate reactive 99 oxygen species, which, like NO, can cause direct toxicity to phagocytized pathogens in 100 6 neutrophils and macrophages (22, 23). IRGM1 and IRGM3 are antimicrobial GTPases 101 that may participate in the disruption of membrane-bound, pathogen-containing 102 compartments within phagocytes (20, 24). Remarkably, Pilla et al observed that 103 macrophages derived from QKO mice retained potent restriction of L. pneumophila 104 replication when stimulated with IFNγ, and further implicated the bacterial 105 lipopolysaccharide detector caspase 11 (CASP11), which when activated can trigger 106 host macrophage pyroptosis, in some of the residual IFNγ-dependent restriction of L. 107 pneumophila replication in macrophages (20). 108 Recently, Naujoks et al implicated immune responsive gene 1 (IRG1, encoded by 109 the gene Acod1) in the IFNγ-dependent immune response to L. pneumophila, 110demonstrating that driving Acod1 expression in macrophages was sufficient to suppress 111 L. pneumophila replication (21). However, the study did not address whether 112 macrophages deficient in IRG1 were impaired in t...

Coenzyme A governs proinflammatory macrophage metabolism

“…This diverts host metabolism towards aerobic glycolysis (49), indicative of tolerance. IFN potently restricts L. pneumophila intracellular replication in a manner that depends in part on host induction of Nos2 and Irg1 (52). Nos2 and Irg1 were induced in uninfected BMDMs by CoA alone, and induction was further enhanced with CoA/LPS cotreatment (Fig.…”

IRG1 controls host responses to restrict Mycobacterium tuberculosis infection

“…The mammalian catalytic enzyme IRG1 and its generated metabolite itaconate are only induced during infection and/or inflammation (Basler et al 2006) and were previously described for their antimicrobial activities (McKinney et al 2000, Michelucci et al 2013, Naujoks et al 2016, Nair et al 2018, Price et al 2019. In this study, we addressed the role of IRG1 in immunometabolic host responses during Mtb infection and were able to demonstrate that IRG1 is essential for the outcome of immunopathology, both in vitro and in vivo.…”

“…by inhibiting succinate dehydrogenase (Lampropoulou et al 2016), regulating Nrf2 activity (Mills et al 2018) and modulating electrophilic stress responses (Bambouskova et al 2018). In turn, those activities are able to influence hostpathogen interactions, as it was shown in macrophages during Legionella pneumophila infection (Naujoks et al 2016;Price et al 2019). More recently, Nair et al showed that IRG1-deficient mice are highly susceptible to Mtb infection, while no aberrant phenotypes were found during influenza A virus or Listeria monocytogenes infection (Nair et al 2018).…”