Metabolic Impairment Induces Oxidative Stress, Compromises Inflammatory Responses, and Inactivates a Key Mitochondrial Enzyme in Microglia

• Published in: Journal of neurochemistry Vol. 72; no. 5; pp. 1948 - 1958
• Main Authors: Park, Larry C. H., Zhang, Hui, Sheu, Kwan‐Fu Rex, Calingasan, Noel Y., Kristal, Bruce S., Gordon Lindsay, J., Gibson, Gary E.
• Format: Journal Article
• Language: English
• Published: Oxford, UK Blackwell Publishing Ltd 01-05-1999; Blackwell
• Subjects: Animals; Azide; Azides - pharmacology; Biological and medical sciences; Cell Survival - drug effects; Cells, Cultured; Degenerative and inherited degenerative diseases of the nervous system. Leukodystrophies. Prion diseases; Enzyme Activation - physiology; Glutamate Dehydrogenase - metabolism; Inflammation - physiopathology; Ketoglutarate Dehydrogenase Complex - metabolism; Lipopolysaccharides - pharmacology; Medical sciences; Metabolic impairment; Mice; Mice, Inbred C57BL; Microglia - metabolism; Microglia - physiology; Mitochondria - enzymology; Mitochondrial complex IV; Neurology; Nitrates - pharmacology; Nitric oxide; Nitric Oxide - antagonists & inhibitors; Nitric Oxide - biosynthesis; Nitric Oxide - pharmacology; Oxidative Stress - physiology; Oxidoreductases - metabolism; Oxygen Consumption - drug effects; Peroxynitrite; Reactive oxygen species; Reactive Oxygen Species - metabolism; Tyrosine - analogs & derivatives; Tyrosine - metabolism; α‐Ketoglutarate dehydrogenase complex; Oxidative stress; Mitochondria; Oxygen; Metabolic disorder; Cell line; Neuroglia; Nitric oxide; Degenerative disease; In vitro; Free radical; Microglia
• ISSN: 0022-3042; 1471-4159
• DOI: 10.1046/j.1471-4159.1999.0721948.x

: Microglial activation, oxidative stress, and dysfunctions in mitochondria, including the reduction of cytochrome oxidase activity, have been implicated in neurodegeneration. The current experiments tested the effects of reducing cytochrome oxidase activity on the ability of microglia to respond to inflammatory insults. Inhibition of cytochrome oxidase by azide reduced oxygen consumption and increased reactive oxygen species (ROS) production but did not affect cell viability. Azide also attenuated microglial activation, as measured by nitric oxide (NO*) production in response to lipopolysaccharide (LPS). It is surprising that the inhibition of cytochrome oxidase also diminished the activity of the α‐ketoglutarate dehydrogenase complex (KGDHC), a Krebs cycle enzyme. This reduction was exaggerated when the azide‐treated microglia were also treated with LPS. The combination of the azide‐stimulated ROS and LPS‐induced NO* would likely cause peroxynitrite formation in microglia. Thus, the possibility that KGDHC was inactivated by peroxynitrite was tested. Peroxynitrite inhibited the activity of isolated KGDHC, nitrated tyrosine residues of all three KGDHC subunits, and reduced immunoreactivity to antibodies against two KGDHC components. Thus, our data suggest that inhibition of the mitochondrial respiratory chain diminishes aerobic energy metabolism, interferes with microglial inflammatory responses, and compromises mitochondrial function, including KGDHC activity, which is vulnerable to NO* and peroxynitrite that result from microglial activation. Thus, activation of metabolically compromised microglia can further diminish their oxidative capacity, creating a deleterious spiral that may contribute to neurodegeneration.