Aconitate decarboxylase 1 mediates acute airway inflammatory response to environmental exposures

Background: Environmental lipopolysaccharide (LPS) and microbial component-enriched organic dusts cause significant lung diseases. These environmental exposures induce the recruitment and activation of distinct lung monocyte/macrophage subpopulations involved in disease pathogenesis. Given monocyte/macrophage activation is tightly linked to metabolism, the objective of these studies was to determine the role of the immunometabolic regulator, aconitate decarboxylase 1 (ACOD1), in environmental exposure-induced lung inflammation. Methods: Wild-type (WT) mice were intratracheally instilled (I.T.) with 10 ug LPS or saline. Whole lungs were profiled using bulk RNA sequencing or sorted to isolate monocyte/macrophage subpopulations. Sorted subpopulations were then characterized transcriptomically using a NanoString innate immunity multiplex array 48 hours post-exposure. Next, WT and Acod1-/- mice were instilled with LPS, 25% organic dust extract (ODE), or saline with serum, bronchoalveolar lavage fluid (BALF), and lung tissues collected. BALF metabolites of the tricarboxylic acid (TCA) cycle were quantified by mass-spectrometry. Cytokines/chemokines and tissue remodeling mediators were quantitated by ELISA. Lung immune cells were characterized by flow cytometry. Whole body plethysmography was performed 3 hours post-LPS with WT and Acod1-/- mice. Results: By bulk sequencing, Acod1 was one of the most significantly upregulated genes following LPS (vs. saline) exposure of murine whole lungs. Transcriptomic profiling of sorted lung monocyte/macrophage subpopulations corroborated Acod1 significance. Acod1-/- mice treated with LPS (vs. WT) demonstrated decreased BALF levels of itaconate, TCA cycle reprogramming, decreased BALF neutrophils, increased lung CD4+ T cells, decreased BALF and lung levels of TNF-a, and decreased BALF CXCL1. In comparison, Acod1-/- mice treated with ODE (vs. WT) demonstrated decreased serum pentraxin-2, BALF levels of itaconate, lung total cell, neutrophil, monocyte, and B cell infiltrates with decreased BALF levels of TNF-a, IL-6, and decreased lung CXCL1. Mediators of tissue remodeling (TIMP1, MMP8, MMP9) were also decreased in the LPS-exposed Acod1-/- mice, with MMP-9 also decreased in the ODE-exposed Acod1-/- mice. Lung function assessments demonstrated a blunted response to LPS-induced airway hyper-responsiveness in Acod1-/- mice. Conclusion: Acod1 is robustly upregulated in the lungs following LPS-exposure and encodes a key immunometabolic regulator. ACOD1 mediates the pro-inflammatory response to acute inhaled, environmental LPS and organic dust exposure-induced lung inflammation.