title: Role of cytochrome c in α-synuclein radical formation: implications of α-synuclein in neuronal death in Maneb- and paraquat-induced model of Parkinson's disease.
abstract: The pathological features of Parkinson's disease (PD) include an abnormal accumulation of α-synuclein in the surviving dopaminergic neurons. Though PD is multifactorial, several epidemiological reports show an increased incidence of PD with co-exposure to pesticides such as Maneb and paraquat (MP). In pesticide-related PD, mitochondrial dysfunction and α-synuclein oligomers have been strongly implicated, but the link between the two has not yet been understood. Similarly, the biological effects of α-synuclein or its radical chemistry in PD is largely unknown. Mitochondrial dysfunction during PD pathogenesis leads to release of cytochrome c in the cytosol. Once in the cytosol, cytochrome c has one of two fates: It either binds to apaf1 and initiates apoptosis or can act as a peroxidase. We hypothesized that as a peroxidase, cytochrome c leaked out from mitochondria can form radicals on α-synuclein and initiate its oligomerization.
  
  
  
  Samples from controls, and MP co-exposed wild-type and α-synuclein knockout mice were studied using immuno-spin trapping, confocal microscopy, immunohistochemistry, and microarray experiments.
  
  
  
  Experiments with MP co-exposed mice showed cytochrome c release in cytosol and its co-localization with α-synuclein. Subsequently, we used immuno-spin trapping method to detect the formation of α-synuclein radical in samples from an in vitro reaction mixture consisting of cytochrome c, α-synuclein, and hydrogen peroxide. These experiments indicated that cytochrome c plays a role in α-synuclein radical formation and oligomerization. Experiments with MP co-exposed α-synuclein knockout mice, in which cytochrome c-α synuclein co-localization and interaction cannot occur, mice showed diminished protein radical formation and neuronal death, compared to wild-type MP co-exposed mice. Microarray data from MP co-exposed wild-type and α-synuclein knockout mice further showed that the absence of α-synuclein per se or its co-localization with cytochrome c confers protection from MP co-exposure, as several important pathways were unaffected in α-synuclein knockout mice.
  
  
  
  Altogether, these results show that peroxidase activity of cytochrome c contributes to α-synuclein radical formation and oligomerization, and that α-synuclein, through its co-localization with cytochrome c or on its own, affects several biological pathways which contribute to increased neuronal death in an MP-induced model of PD.
authors.affiliation: Free Radical Biology Group, Immunity, Inflammation, and Disease Laboratory, National Institute of Environmental Health Sciences, National Institutes of Health, 111 T.W. Alexander Dr., Research Triangle Park, Durham, NC, 27709, USA. kumara10@niehs.nih.gov.
authors.forename: Ashutosh
authors.initials: A
authors.lastname: Kumar
authors.affiliation: Free Radical Biology Group, Immunity, Inflammation, and Disease Laboratory, National Institute of Environmental Health Sciences, National Institutes of Health, 111 T.W. Alexander Dr., Research Triangle Park, Durham, NC, 27709, USA.
authors.forename: Douglas
authors.initials: D
authors.lastname: Ganini
authors.affiliation: Free Radical Biology Group, Immunity, Inflammation, and Disease Laboratory, National Institute of Environmental Health Sciences, National Institutes of Health, 111 T.W. Alexander Dr., Research Triangle Park, Durham, NC, 27709, USA.
authors.forename: Ronald P
authors.initials: RP
authors.lastname: Mason
mesh_terms: D000818:Animals; D016923:Cell Death; D045304:Cytochromes c / Q000378:metabolism*; D005609:Free Radicals / Q000378:metabolism*; D007150:Immunohistochemistry; D008297:Male; D008344:Maneb / Q000633:toxicity; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D018613:Microscopy, Confocal; D009474:Neurons / Q000378:metabolism / Q000473:pathology*; D020411:Oligonucleotide Array Sequence Analysis; D018384:Oxidative Stress / Q000502:physiology; D010269:Paraquat / Q000633:toxicity; D020734:Parkinsonian Disorders / Q000139:chemically induced / Q000378:metabolism / Q000473:pathology*; D010575:Pesticides / Q000633:toxicity; D051844:alpha-Synuclein / Q000378:metabolism*
chemical_list: D005609:Free Radicals; D010575:Pesticides; D051844:alpha-Synuclein; D008344:Maneb; D045304:Cytochromes c; D010269:Paraquat
keywords: Cytochrome c; Immuno-spin trapping; Parkinson’s disease; Peroxidase; α-synuclein radical