Nitric oxide orchestrates metabolic rewiring in M1 macrophages by targeting aconitase 2 and pyruvate dehydrogenase

Abstract

Profound metabolic changes are characteristic of macrophages during classical activation and have been implicated in this phenotype. Here we demonstrate that nitric oxide (NO) produced by murine macrophages is responsible for TCA cycle alterations and citrate accumulation associated with polarization. 13 C tracing and mitochondrial respiration experiments map NO-mediated suppression of metabolism to mitochondrial aconitase (ACO2). Moreover, we find that inflammatory macrophages reroute pyruvate away from pyruvate dehydrogenase (PDH) in an NO-dependent and hypoxia-inducible factor 1α (Hif1α)-independent manner, thereby promoting glutamine-based anaplerosis. Ultimately, NO accumulation leads to suppression and loss of mitochondrial electron transport chain (ETC) complexes. Our data reveal that macrophages metabolic rewiring, in vitro and in vivo, is dependent on NO targeting specific pathways, resulting in reduced production of inflammatory mediators. Our findings require modification to current models of macrophage biology and demonstrate that reprogramming of metabolism should be considered a result rather than a mediator of inflammatory polarization.

Resolving Metabolic Heterogeneity in Experimental Models of the Tumor Microenvironment from a Stable Isotope Resolved Metabolomics Perspective

“…Figure 2B shows reduced levels of the 13 C 2 -and 13 C 3 -isotologues of citrate (a), succinate (c), fumarate (d), and Asp (e) in M1-versus M2-and M2+WGP-Mφ, which suggests decreased capacity of the pyruvate dehydrogenase (PDH) and pyruvate carboxylase (PCB)-initiated Krebs cycle, respectively [91]. This is consistent with the compromised Krebs cycle observed in mouse M1-Mφ due to the two breaks at the isocitrate dehydrogenase (IDH) and succinate dehydrogenase (SDH) steps [174][175][176]. We observed succinate buildup and fumarate depletion expected from the SDH break but did not see citrate buildup and αketoglutarate (αKG, b) depletion expected from the IDH block in the Krebs cycle.…”

Amino Assets: How Amino Acids Support Immunity

“…Glutamine anaplerosis to aKG is increased in pro-inflammatory M1-like macrophages, and, due to a break in the TCA cycle, causes a build-up of succinate, which drives IL-1b production. Nitric oxide (NO)-mediated inhibition of pyruvate dehydrogenase and aconitase-2 limits entry of metabolites into the TCA cycle, promoting this glutamine anaplerosis to aKG in inflammatory macrophages (Palmieri et al, 2020). Glutamine is needed to support LPS induction of IL-1 production by macrophages (Wallace and Keast, 1992), though it does not appear to be required for M1-like macrophage development.…”

iNOS Expression by Tumor-Infiltrating Lymphocytes, PD-L1 and Prognosis in Non-Small-Cell Lung Cancer

“…High concentrations, above 500nM, are cytotoxic, promote p53 phosphorylation and have anti-tumor anti-metastatic effects [5,6]. Immune cells producing high amounts of NO, like macrophages or even lymphocytes, have strong anti-tumor activities [7,8]. NO reacts with superoxide to form the cytotoxic molecule peroxynitrite [9], which has a potent antimicrobial and tumoricidal activity.…”