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Cutting edge: Stat6-dependent substrate depletion regulates nitric oxide production
1Department of Infectious Diseases, Howard Hughes Medical Institute, St. Jude Children's Research Hospital, Memphis, TN 38105, USA.
Abstract:
The cytokines IL-4 and IL-13 inhibit the production of NO from activated macrophages through an unresolved molecular mechanism. We show here that IL-4 and IL-13 regulate NO production through depletion of arginine, the substrate of inducible NO synthase (iNOS). Inhibition of NO production from murine macrophages stimulated with LPS and IFN-gamma by IL-4 or IL-13 was dependent on Stat6, cell density in the cultures, and pretreatment for at least 6 h. IL-4/IL-13 did not interfere with the expression or activity of iNOS but up-regulated arginase I (the liver isoform of arginase) in a Stat6-dependent manner. Addition of exogenous arginine completely restored NO production in IL-4-treated macrophages. Furthermore, impaired killing of the intracellular pathogen Toxoplasma gondii in IL-4-treated macrophages was overcome by supplementing L-arginine. The simple system of regulated substrate competition between arginase and iNOS has implications for understanding the physiological regulation of NO production.
Insights
Interleukin-4 (IL-4) and Interleukin-13 (IL-13) reduce nitric oxide (NO) production by depleting arginine, essential for inducible NO synthase (iNOS). Restoring arginine levels reverses this inhibition and improves pathogen killing in macrophages.
Area of Science:
- Immunology
- Molecular Biology
- Cellular Physiology
Background:
- Interleukin-4 (IL-4) and Interleukin-13 (IL-13) are known to inhibit nitric oxide (NO) production in activated macrophages.
- The precise molecular mechanism underlying this inhibition has remained unclear.
- Nitric oxide is crucial for macrophage-mediated immune responses.
Purpose of the Study:
- To elucidate the molecular mechanism by which IL-4 and IL-13 inhibit NO production in activated macrophages.
- To investigate the role of arginine availability and arginase activity in this regulatory pathway.
Main Methods:
- Murine macrophages were stimulated with lipopolysaccharide (LPS) and interferon-gamma (IFN-γ).
- The effects of IL-4 and IL-13 on NO production, inducible NO synthase (iNOS) expression and activity, and arginase I expression were assessed.
- Experiments involved varying cell density, pretreatment times, and L-arginine supplementation.
Main Results:
- IL-4 and IL-13 inhibited NO production in a Stat6-dependent manner, requiring specific cell density and pretreatment duration.
- This inhibition was mediated by the upregulation of arginase I, which depletes arginine, the substrate for iNOS.
- iNOS expression and activity remained unaffected; addition of exogenous arginine fully restored NO production and enhanced killing of Toxoplasma gondii.
Conclusions:
- IL-4 and IL-13 inhibit macrophage NO production by inducing arginase I, leading to arginine depletion and substrate competition with iNOS.
- This mechanism highlights the critical role of substrate availability in regulating NO synthesis.
- Understanding this pathway has implications for modulating macrophage function in infectious and inflammatory diseases.