Nitric oxide from inflammatory-activated glia synergizes with hypoxia to induce neuronal death.
Inflammatory-activated glia are seen in numerous central nervous system (CNS) pathologies and can kill nearby neurons through the release of cytotoxic mediators. Glia, when activated, can express the inducible isoform of nitric oxide synthase (iNOS) producing high levels of nitric oxide (NO), which can kill neurons in certain conditions. We show, however, that inflammatory activation of glia in a mature culture of cerebellar granule neurons and glia causes little or no neuronal death under normal (21%) oxygen conditions. Similarly, hypoxia (2% oxygen) or low levels of an NO donor (100 microM DETA/NO) caused little or no neuronal death in nonactivated cultures. If inflammatory activation of glia or addition of NO donor was combined with hypoxia, however, extensive neuronal death occurred. Death in both cases was prevented by the N-methyl-D-aspartate (NMDA) receptor blocker MK-801, implying that death was mediated by the glutamate receptor. Low levels of NO were found to increase the apparent K(M) of cellular oxygen consumption for oxygen, probably due to NO-induced inhibition of mitochondrial respiration, in competition with oxygen, at cytochrome oxidase. Necrotic death, induced by hypoxia plus DETA/NO, was increased further by deoxyglucose, an inhibitor of glycolysis, suggesting that necrosis was mediated by energy depletion. Hypoxia was found to be a potent stimulator of microglia proliferation, but this proliferation was not significant in inflammatory-activated cultures. These results suggest that low levels of NO can induce neuronal death under hypoxic conditions, mediated by glutamate after NO inhibition of respiration in competition with oxygen. Brain inflammation can thus sensitize to hypoxia-induced death, which may be important in pathologies such as stroke, neurodegeneration, and brain aging.
Mander
Palwinder
P
Department of Biochemistry, University of Cambridge, Tennis Court Road, Cambridge CB2 1QW, United Kingdom.
Borutaite
Vilma
V
Moncada
Salvador
S
Brown
Guy C
GC
D000578:Amidines / Q000494:pharmacology; D000704:Analysis of Variance; D000818:Animals; D000831:Animals, Newborn; D001253:Astrocytes / Q000201:enzymology*; D001596:Benzylamines / Q000494:pharmacology; D016923:Cell Death / Q000502:physiology; D049109:Cell Proliferation / Q000187:drug effects; D002470:Cell Survival / Q000187:drug effects; D002478:Cells, Cultured; D002531:Cerebellum / Q000166:cytology*; D018920:Coculture Techniques / Q000379:methods; D003847:Deoxyglucose / Q000494:pharmacology; D016291:Dizocilpine Maleate / Q000494:pharmacology; D004357:Drug Synergism; D004791:Enzyme Inhibitors / Q000494:pharmacology; D018691:Excitatory Amino Acid Antagonists / Q000494:pharmacology; D000860:Hypoxia / Q000201:enzymology*; D007249:Inflammation / Q000139:chemically induced / Q000201:enzymology*; D007371:Interferon-gamma / Q000494:pharmacology; D008070:Lipopolysaccharides / Q000633:toxicity; D009474:Neurons / Q000502:physiology*; D009569:Nitric Oxide / Q000378:metabolism*; D019001:Nitric Oxide Synthase / Q000378:metabolism; D052247:Nitric Oxide Synthase Type II; D010101:Oxygen Consumption / Q000187:drug effects; D051381:Rats; D014226:Triazenes / Q000494:pharmacology
C105351:1-hydroxy-2-oxo-3,3-bis(2-aminoethyl)-1-triazene; D000578:Amidines; D001596:Benzylamines; D004791:Enzyme Inhibitors; D018691:Excitatory Amino Acid Antagonists; D008070:Lipopolysaccharides; C104820:N-(3-(aminomethyl)benzyl)acetamidine; D014226:Triazenes; D009569:Nitric Oxide; D016291:Dizocilpine Maleate; D007371:Interferon-gamma; D003847:Deoxyglucose; D019001:Nitric Oxide Synthase; D052247:Nitric Oxide Synthase Type II; C496318:Nos2 protein, rat