Related Experiment Video
Updated: Apr 15, 2026
Investigation of Macrophage Polarization Using Bone Marrow Derived Macrophages
Published on: June 23, 2013
Myeloid cell-derived inducible nitric oxide synthase suppresses M1 macrophage polarization
Geming Lu1, Ruihua Zhang1, Shuo Geng2
1Department of Medicine, Immunology Institute, Icahn School of Medicine at Mount Sinai, New York, New York 10029, USA.
Abstract:
Here we show that iNOS-deficient mice display enhanced classically activated M1 macrophage polarization without major effects on alternatively activated M2 macrophages. eNOS and nNOS mutant mice show comparable M1 macrophage polarization compared with wild-type control mice. Addition of N6-(1-iminoethyl)-L-lysine dihydrochloride, an iNOS inhibitor, significantly enhances M1 macrophage polarization while S-nitroso-N-acetylpenicillamine, a NO donor, suppresses M1 macrophage polarization. NO derived from iNOS mediates nitration of tyrosine residues in IRF5 protein, leading to the suppression of IRF5-targeted M1 macrophage signature gene activation. Computational analyses corroborate a circuit that fine-tunes the expression of IL-12 by iNOS in macrophages, potentially enabling versatile responses based on changing microenvironments. Finally, studies of an experimental model of endotoxin shock show that iNOS deficiency results in more severe inflammation with an enhanced M1 macrophage activation phenotype. These results suggest that NO derived from iNOS in activated macrophages suppresses M1 macrophage polarization.
Insights
Nitric oxide (NO) from inducible nitric oxide synthase (iNOS) suppresses M1 macrophage polarization. iNOS deficiency enhances M1 macrophage activation, worsening endotoxin shock inflammation.
Area of Science:
- Immunology
- Cell Biology
- Molecular Biology
Background:
- Macrophages play critical roles in immune responses, with distinct polarization states like M1 (pro-inflammatory) and M2 (anti-inflammatory).
- Nitric oxide (NO) is a signaling molecule implicated in various cellular processes, including immune cell function.
Purpose of the Study:
- To investigate the role of nitric oxide synthase (NOS) isoforms, particularly inducible NOS (iNOS), in regulating macrophage polarization.
- To elucidate the molecular mechanisms by which iNOS influences M1 macrophage activation.
Main Methods:
- Utilized iNOS-deficient mice and pharmacological inhibitors/donors of iNOS.
- Assessed macrophage polarization (M1/M2 markers) and key transcription factors.
- Studied endotoxin shock models to evaluate in vivo consequences.
Main Results:
- iNOS deficiency enhanced M1 macrophage polarization, while eNOS and nNOS mutants showed no significant difference.
- iNOS inhibition promoted M1 polarization; NO donors suppressed it.
- NO from iNOS mediates tyrosine nitration of IRF5, inhibiting M1 gene activation.
- iNOS deficiency exacerbated endotoxin shock with increased M1 activation.
Conclusions:
- Inducible nitric oxide synthase (iNOS)-derived NO suppresses M1 macrophage polarization.
- This regulatory pathway fine-tunes inflammatory responses and macrophage phenotypes.
