Astrocyte-Derived Nitric Oxide Causes Both Reversible and Irreversible Damage to the Neuronal Mitochondrial Respiratory Chain

Authors

  • Victoria C Stewart,

  • Martyn A Sharpe,

  • John B Clark,

  • Simon J R Heales


  • Abbreviations used : FBS, fetal bovine serum ; IFN, interferon ; iNOS, nitric oxide synthase of the inducible type ; LDH, lactate dehydrogenase ; LPS, lipopolysaccharide ; MEM, minimal essential medium ; MS, multiple sclerosis ; l-NAME, N-nitro-l-arginine methyl ester ; NO, nitric oxide ; NOS, nitric oxide synthase ; ONOO-, peroxynitrite ; PTFE, polytetrafluoroethane ; TBE, trypan blue exclusion.

Address correspondence and reprint requests to Dr. V. C. Stewart at Department of Neurochemistry, Institute of Neurology, University College London, Queen Square, London WC1N 3BG, U.K. E-mail : V. Stewart@ion.ucl.ac.uk

Abstract

Cytokine-stimulated astrocytes produce nitric oxide (NO), which, along with its metabolite peroxynitrite (ONOO-), can inhibit components of the mitochondrial respiratory chain. We used astrocytes as a source of NO/ONOO- and monitored the effects on neurons in coculture. We previously demonstrated that astrocytic NO/ONOO- causes significant damage to the activities of complexes II/III and IV of neighbouring neurons after a 24-h coculture. Under these conditions, no neuronal death was observed. Using polytetrafluoroethane filters, which are permeable to gases such as NO but impermeable to NO derivatives, we have now demonstrated that astrocyte-derived NO is responsible for the damage observed in our coculture system. Expanding on these observations, we have now shown that 24 h after removal of NO-producing astrocytes, neurons exhibit complete recovery of complex II/III and IV activities. Furthermore, extending the period of exposure of neurons to NO-producing astrocytes does not cause further damage to the neuronal mitochondrial respiratory chain. However, whereas the activity of complex II/III recovers with time, the damage to complex IV caused by a 48-h coculture with NO-producing astrocytes is irreversible. Therefore, it appears that neurons can recover from short-term damage to mitochondrial complex II/III and IV, whereas exposure to astrocytic-derived NO for longer periods causes permanent damage to neuronal complex IV.

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