Immune-Responsive Gene 1 expression in myeloid cells prevents neutrophil mediated immunopathology during Mycobacterium tuberculosis infection [macrophage]

Immune-Responsive Gene 1 (Irg1) is a mitochondrial enzyme that produces itaconate under inflammatory conditions principally in cells of myeloid lineage. Cell culture studies suggest that itaconate regulates inflammation through inhibitory effects on cytokine and reactive oxygen species production. To evaluate the functions of Irg1 in vivo, we challenged wild-type (WT) and Irg1-/- mice with Mycobacterium tuberculosis (Mtb) and monitored disease progression. Irg1-/- but not WT mice succumbed rapidly to Mtb, and mortality was associated with increased infection, inflammation, and pathology. Infection of LysM-Cre Irg1fl/fl, MPR8-Cre Irg1fl/fl, and CD11c-Cre Irg1fl/fl conditional knockout mice along with neutrophil depletion experiments revealed a role for Irg1 in alveolar macrophages and LysM+ myeloid cells in preventing neutrophil-mediated immunopathology and disease. RNA-seq analyses suggest that Irg1 and its production of itaconate temper Mtb-induced inflammatory responses in myeloid cells at the transcriptional level. Thus, Irg1 modulates inflammation to curtail Mtb-induced lung disease. Overall design: Macrophages were obtained by culturing bone marrow cells in RPMI-1640 (Invitrogen) supplemented with 10% heat inactivated fetal bovine serum, 2 mM L-glutamine, 1% non-essential amino acids, 100 U penicillin per mL, 100 µg streptomycin per mL, and 22 ng M-CSF (Peprotech) per ml for 6 days at 37°C, 5% CO2. Fresh media was added on day 3 of culture. After 6 days of culture, non-adherent cells were discarded. Adherent macrophages were switched into antibiotic-free media and seeded at 105 cells per well and 9 x 105 cells per well in tissue culture-treated 96 and 6 well plates respectively. In some cases, macrophages were treated with 0.25 mM itaconic acid (Sigma) for 12 h prior to inoculation with Mtb. Mtb was grown to mid-log phase, washed with PBS, sonicated to disperse clumps, and resuspended in antibiotic-free macrophage culture media. Macrophage cultures were inoculated by adding Mtb-containing media at a multiplicity of infection (MOI) of 1 and centrifuging for 10 min at 200 x g. Cells were washed twice with PBS to remove unbound Mtb, fresh culture media was added, and cells were incubated at 37°C, 5% CO2. In some cases culture media was supplemented with 0.25 mM itaconic acid.

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Nair S, Huynh JP, Lampropoulou V, Loginicheva E, Esaulova E, Gounder AP, Boon ACM, Schwarzkopf EA, Bradstreet TR, Edelson BT, Artyomov MN, Stallings CL, Diamond MS