Differential production of superoxide by neuronal mitochondria.
BACKGROUND
Mitochondrial DNA (mtDNA) mutations, which are present in all mitochondria-containing cells, paradoxically cause tissue-specific disease. For example, Leber's hereditary optic neuropathy (LHON) results from one of three point mutations mtDNA coding for complex I components, but is only manifested in retinal ganglion cells (RGCs), a central neuron contained within the retina. Given that RGCs use superoxide for intracellular signaling after axotomy, and that LHON mutations increase superoxide levels in non-RGC transmitochondrial cybrids, we hypothesized that RGCs regulate superoxide levels differently than other neuronal cells. To study this, we compared superoxide production and mitochondrial electron transport chain (METC) components in isolated RGC mitochondria to mitochondria isolated from cerebral cortex and neuroblastoma SK-N-AS cells.


RESULTS
In the presence of the complex I substrate glutamate/malate or the complex II substrate succinate, the rate of superoxide production in RGC-5 cells was significantly lower than cerebral or neuroblastoma cells. Cerebral but not RGC-5 or neuroblastoma cells increased superoxide production in response to the complex I inhibitor rotenone, while neuroblastoma but not cerebral or RGC-5 cells dramatically decreased superoxide production in response to the complex III inhibitor antimycin A. Immunoblotting and real-time quantitative PCR of METC components demonstrated different patterns of expression among the three different sources of neuronal mitochondria.


CONCLUSIONS
RGC-5 mitochondria produce superoxide at significantly lower rates than cerebral and neuroblastoma mitochondria, most likely as a result of differential expression of complex I components. Diversity in METC component expression and function could explain tissue specificity in diseases associated with inherited mtDNA abnormalities.
Hoegger
Mark J
MJ
Department of Ophthalmology and Visual Sciences, University of Wisconsin Medical School, Madison, USA. markhoegger@gmail.com
Lieven
Christopher J
CJ
Levin
Leonard A
LA
D000818:Animals; D002460:Cell Line; D042967:Electron Transport Complex I / Q000187:drug effects / Q000235:genetics / Q000378:metabolism; D014450:Electron Transport Complex III / Q000187:drug effects / Q000235:genetics / Q000378:metabolism; D004734:Energy Metabolism / Q000187:drug effects / Q000235:genetics; D018698:Glutamic Acid / Q000378:metabolism; D020271:Heredodegenerative Disorders, Nervous System / Q000235:genetics / Q000378:metabolism*; D008928:Mitochondria / Q000235:genetics / Q000378:metabolism*; D009474:Neurons / Q000378:metabolism*; D029242:Optic Atrophy, Hereditary, Leber / Q000235:genetics / Q000378:metabolism*; D018384:Oxidative Stress / Q000235:genetics*; D051381:Rats; D020318:Rats, Long-Evans; D012165:Retinal Ganglion Cells / Q000378:metabolism; D019802:Succinic Acid / Q000378:metabolism; D013481:Superoxides / Q000378:metabolism*; D014475:Uncoupling Agents / Q000494:pharmacology
D014475:Uncoupling Agents; D013481:Superoxides; D018698:Glutamic Acid; D019802:Succinic Acid; D042967:Electron Transport Complex I; D014450:Electron Transport Complex III