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Published on: November 21, 2011
Interaction between Mitochondrial Reactive Oxygen Species, Heme Oxygenase, and Nitric Oxide Synthase Stimulates
Andrea Müllebner1,2, Gabriel G Dorighello3, Andrey V Kozlov2
1Institute for Medical Biochemistry, University of Veterinary Medicine Vienna, Vienna, Austria.
Background:
Macrophages are cells of the innate immune system that populate every organ. They are required not only for defense against invading pathogens and tissue repair but also for maintenance of tissue homeostasis and iron homeostasis.
Aim:
The aim of this study is to understand whether heme oxygenase (HO) and nitric oxide synthase (NOS) contribute to the regulation of nicotinamide adenine dinucleotide phosphate oxidase (NOX) activity and phagocytosis, two key components of macrophage function.
Methods:
This study was carried out using resting J774A.1 macrophages treated with hemin or vehicle. Activity of NOS, HO, or NOX was inhibited using specific inhibitors. Reactive oxygen species (ROS) formation was determined by Amplex® red assay, and phagocytosis was measured using fluorescein isothiocyanate-labeled bacteria. In addition, we analyzed the fate of the intracellular heme by using electron spin resonance.
Results:
We show that both enzymes NOS and HO are essential for phagocytic activity of macrophages. NOS does not directly affect phagocytosis, but stimulates NOX activity via nitric oxide-triggered ROS production of mitochondria. Treatment of macrophages with hemin results in intracellular accumulation of ferrous heme and an inhibition of phagocytosis. In contrast to NOS, HO products, including carbon monoxide, neither clearly affect NOX activity nor clearly affect phagocytosis, but phagocytosis is accelerated by HO-mediated degradation of heme.
Conclusion:
Both enzymes contribute to the bactericidal activity of macrophages independently, by controlling different pathways.
Insights
Heme oxygenase (HO) and nitric oxide synthase (NOS) are crucial for macrophage phagocytosis. While NOS stimulates nicotinamide adenine dinucleotide phosphate oxidase (NOX) activity, HO accelerates phagocytosis by degrading heme, independently enhancing bacterial killing.
Area of Science:
- Immunology
- Cell Biology
- Biochemistry
Background:
- Macrophages are vital innate immune cells involved in pathogen defense, tissue repair, and homeostasis.
- Iron homeostasis is a critical function regulated by macrophages.
Purpose of the Study:
- To investigate the roles of heme oxygenase (HO) and nitric oxide synthase (NOS) in regulating nicotinamide adenine dinucleotide phosphate oxidase (NOX) activity and phagocytosis in macrophages.
- To elucidate the mechanisms by which HO and NOS influence key macrophage functions.
Main Methods:
- Utilized J774A.1 macrophage cell line treated with hemin or vehicle.
- Employed specific inhibitors for NOS, HO, and NOX to assess enzyme activity.
- Quantified reactive oxygen species (ROS) production and phagocytosis using biochemical assays and fluorescently labeled bacteria.
- Analyzed intracellular heme fate using electron spin resonance.
Main Results:
- Both NOS and HO are essential for macrophage phagocytic activity.
- NOS enhances NOX activity indirectly through nitric oxide-mediated mitochondrial ROS production.
- Hemin treatment leads to intracellular heme accumulation and inhibits phagocytosis.
- HO-mediated heme degradation accelerates phagocytosis, while HO products have minimal direct impact on NOX or phagocytosis.
Conclusions:
- NOS and HO independently contribute to the bactericidal capacity of macrophages.
- These enzymes regulate distinct pathways critical for macrophage immune function.
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