title: Mitochondrial superoxide production and nuclear factor erythroid 2-related factor 2 activation in p75 neurotrophin receptor-induced motor neuron apoptosis.
abstract: Nerve growth factor (NGF) can induce apoptosis by signaling through the p75 neurotrophin receptor (p75(NTR)) in several nerve cell populations. Cultured embryonic motor neurons expressing p75(NTR) are not vulnerable to NGF unless they are exposed to an exogenous flux of nitric oxide (*NO). In the present study, we show that p75(NTR)-mediated apoptosis in motor neurons involved neutral sphingomyelinase activation, increased mitochondrial superoxide production, and cytochrome c release to the cytosol. The mitochondria-targeted antioxidants mitoQ and mitoCP prevented neuronal loss, further evidencing the role of mitochondria in NGF-induced apoptosis. In motor neurons overexpressing the amyotrophic lateral sclerosis (ALS)-linked superoxide dismutase 1(G93A) (SOD1(G93A)) mutation, NGF induced apoptosis even in the absence of an external source of *NO. The increased susceptibility of SOD1(G93A) motor neurons to NGF was associated to decreased nuclear factor erythroid 2-related factor 2 (Nrf2) expression and downregulation of the enzymes involved in glutathione biosynthesis. In agreement, depletion of glutathione in nontransgenic motor neurons reproduced the effect of SOD1(G93A) expression, increasing their sensitivity to NGF. In contrast, rising antioxidant defenses by Nrf2 activation prevented NGF-induced apoptosis. Together, our data indicate that p75(NTR)-mediated motor neuron apoptosis involves ceramide-dependent increased mitochondrial superoxide production. This apoptotic pathway is facilitated by the expression of ALS-linked SOD1 mutations and critically modulated by Nrf2 activity.
authors.affiliation: Departamento de Neurobiología Celular y Molecular, Instituto de Investigaciones Biológicas Clemente Estable, Montevideo 11600, Uruguay.
authors.forename: Mariana
authors.initials: M
authors.lastname: Pehar
authors.forename: Marcelo R
authors.initials: MR
authors.lastname: Vargas
authors.forename: Kristine M
authors.initials: KM
authors.lastname: Robinson
authors.forename: Patricia
authors.initials: P
authors.lastname: Cassina
authors.forename: Pablo J
authors.initials: PJ
authors.lastname: Díaz-Amarilla
authors.forename: Tory M
authors.initials: TM
authors.lastname: Hagen
authors.forename: Rafael
authors.initials: R
authors.lastname: Radi
authors.forename: Luis
authors.initials: L
authors.lastname: Barbeito
authors.forename: Joseph S
authors.initials: JS
authors.lastname: Beckman
mesh_terms: D000818:Animals; D030801:Animals, Genetically Modified; D017209:Apoptosis / Q000187:drug effects / Q000502:physiology*; D002478:Cells, Cultured; D045304:Cytochromes c / Q000378:metabolism; D004622:Embryo, Mammalian; D004789:Enzyme Activation / Q000187:drug effects; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005786:Gene Expression Regulation / Q000187:drug effects / Q000502:physiology; D008928:Mitochondria / Q000187:drug effects / Q000378:metabolism*; D009046:Motor Neurons / Q000187:drug effects / Q000502:physiology*; D051267:NF-E2-Related Factor 2 / Q000378:metabolism*; D020932:Nerve Growth Factor / Q000494:pharmacology; D020030:Nitric Oxide Donors / Q000494:pharmacology; D009603:Nitroso Compounds / Q000494:pharmacology; D020319:Oligodeoxyribonucleotides, Antisense / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D017382:Reactive Oxygen Species / Q000378:metabolism; D020800:Receptor, Nerve Growth Factor / Q000378:metabolism*; D013108:Sphingomyelin Phosphodiesterase / Q000378:metabolism; D013116:Spinal Cord / Q000166:cytology*; D013482:Superoxide Dismutase / Q000235:genetics / Q000494:pharmacology
chemical_list: D004791:Enzyme Inhibitors; D051267:NF-E2-Related Factor 2; C495637:Nfe2l2 protein, rat; D020030:Nitric Oxide Donors; D009603:Nitroso Compounds; D020319:Oligodeoxyribonucleotides, Antisense; D017382:Reactive Oxygen Species; D020800:Receptor, Nerve Growth Factor; C094210:2,2'-(hydroxynitrosohydrazono)bis-ethanamine; D045304:Cytochromes c; D020932:Nerve Growth Factor; C109415:SOD1 G93A protein; D013482:Superoxide Dismutase; D013108:Sphingomyelin Phosphodiesterase