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Nitric oxide production and neurotoxicity mediated by activated microglia from human versus mouse brain
P K Peterson1, S Hu, W R Anderson
1Dept. of Medicine, Hennepin County Medical Center, Minneapolis, MN 55415.
Abstract:
Recent studies indicate that human macrophages lack a high-output inducible nitric oxide synthase (NOS) antimicrobial system. In the present study, microglial cells derived from fetal human versus neonatal mouse brain were compared in a coculture assay of human and murine neuronal cell injury. Neurotoxicity (reflected by lactate dehydrogenase release and impaired neuronal uptake of [3H] gamma-amino butyric acid) and nitric oxide (NO) production (assessed by measurement of nitrite) were observed only in cocultures containing interferon (IFN)-gamma-lipopolysaccharide (LPS)-stimulated murine microglia. Cultures of purified human fetal microglia, however, did produce low levels of NO upon stimulation with IFN-gamma-LPS. These findings support the proposal that human macrophages have an inefficient IFN-gamma-inducible NOS and suggest that in tissues, such as brain, this deficiency could be advantageous for neighboring cells.
Insights
Human microglia show limited nitric oxide (NO) production, unlike mouse microglia. This inefficient inducible nitric oxide synthase (iNOS) system in human brain cells may protect surrounding neural tissue.
Area of Science:
- Neuroscience
- Immunology
- Cell Biology
Background:
- Human macrophages and microglia are reported to have a deficient inducible nitric oxide synthase (iNOS) antimicrobial system.
- Microglia are the primary immune cells of the central nervous system.
Purpose of the Study:
- To compare the nitric oxide (NO) production and neurotoxic potential of human fetal microglia versus neonatal mouse microglia.
- To investigate the functional consequences of human microglia's iNOS system in a neuroinflammatory context.
Main Methods:
- Coculture assay of human and murine neuronal cells with stimulated microglia.
- Measurement of neurotoxicity via lactate dehydrogenase release and [3H] gamma-amino butyric acid uptake.
- Assessment of nitric oxide (NO) production by measuring nitrite levels.
Main Results:
- Murine microglia, when stimulated with interferon-gamma (IFN-γ) and lipopolysaccharide (LPS), induced significant neurotoxicity and NO production in cocultured neurons.
- Human fetal microglia produced only low levels of NO in response to IFN-γ-LPS stimulation.
- Human microglia cocultures did not exhibit significant neurotoxicity under the same stimulation conditions.
Conclusions:
- Human microglia possess an inefficient IFN-γ-inducible NOS system compared to murine microglia.
- This deficiency in NO production by human microglia may serve a protective role for adjacent neuronal cells in the brain.
- The findings support the hypothesis of an inefficient iNOS system in human macrophages and microglia.