Multi-omic analysis reveals nitric oxide dependent remodeling in classically activated macrophages and identifies negative regulation mediated by AKR1A1.

Nitric oxide (NO•) is an important signaling molecule in many biological processes, including immune response. During response to classical activation stimuli lipopolysaccharide (LPS) and interferon-γ (IFNγ), macrophages generate NO• via inducible nitric oxide synthase (iNOS). To comprehensively define the effects of NO•, we applied a multi-omic strategy integrating proteomics and transcriptomics to profile murine macrophages across conditions with or without LPS/IFNγ-activation, with or without iNOS expression or exogenous NO• donor treatment. The results revealed NO• has broad, yet selected and controlled, regulatory effects, playing a key role in coordinating the systematic remodeling during macrophage classical activation. Among the proteins that are most suppressed in a NO•-dependent manner, electron transport chain (ETC) is the most enriched. NO• drives complex-specific remodeling of ETC, causing selected downregulation of complex I, II, and IV, through a different combination of transcriptional and post-transcriptional mechanisms for each complex. Functionally, we found NO• is required, but not sufficient, for the strong suppression of cellular respiration upon macrophage activation. Among the most consistently upregulated proteins are many enzymes involved in redox defense. AKR1A1 was identified as a top hit. We found Akr1a1 induction requires both NO• and LPS/IFNγ stimulation. The S-nitroso-CoA reductase activity of AKR1A1 mitigates NO•-driven inhibition of pyruvate dehydrogenase complex by limiting the inhibitory modifications targeting its lipoyl cofactor. Knocking out Akr1a1 causes accelerated remodeling of TCA cycle, dysregulated immunoregulatory metabolite level, and altered functional gene expression and cytokine production at later stage of immune response. Thus, the NO•-dependent upregulation of AKR1A1 forms a negative regulatory loop to fine-tune NO•-mediated metabolic and functional remodeling during immune response. Together, this work provided a systems-level map of NO•-dependent regulation, revealed the crosstalk between NO• and immune signaling, and demonstrated mechanisms providing redox adaptation and precise control of NO•'s effects.