Adult motor neuron apoptosis is mediated by nitric oxide and Fas death receptor linked by DNA damage and p53 activation.
The mechanisms of injury- and disease-related degeneration of motor neurons (MNs) need clarification. Unilateral avulsion of the sciatic nerve in the mouse induces apoptosis of spinal MNs that is p53 and Bax dependent. We tested the hypothesis that MN apoptosis is Fas death receptor dependent and triggered by nitric oxide (NO)- and superoxide-mediated damage to DNA. MNs in mice lacking functional Fas receptor and Fas ligand were protected from apoptosis. Fas protein levels and cleaved caspase-8 increased in MNs after injury. Fas upregulation was p53 dependent. MNs in mice deficient in neuronal NO synthase (nNOS) and inducible NOS (iNOS) resisted apoptosis. After injury, MNs increased nNOS protein but decreased iNOS protein; however, iNOS contributed more than nNOS to basal and injury-induced levels of NADPH diaphorase activity in MNs. NO and peroxynitrite (ONOO-) fluorescence increased in injured MNs, as did nitrotyrosine staining of MNs. DNA damage, assessed as 8-hydroxy-2-deoxyguanosine and single-stranded DNA, accumulated within injured MNs and was attenuated by nNOS and iNOS deficiency. nNOS deficiency increased DNA repair protein oxoguanine DNA-glycosylase, whereas iNOS deficiency blocked diaphorase activity. MN apoptosis was blocked by the antioxidant Trolox and by overexpression of wild-type human superoxide dismutase-1 (SOD1). In contrast, injured MNs in mice harboring mutant human SOD1 had upregulated Fas and iNOS, escalated DNA damage, and accelerated and increased MN degeneration and underwent necrosis instead of apoptosis. Thus, adult spinal MN apoptosis is mediated by upstream NO and ONOO- genotoxicity and downstream p53 and Fas activation and is shifted to necrosis by mutant SOD1.
Division of Neuropathology, Department of Pathology, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205-2196, USA. martin1@jhmi.edu
Lee J
LJ
Martin
Kevin
K
Chen
Zhiping
Z
Liu
D019943:Amino Acid Substitution; D000690:Amyotrophic Lateral Sclerosis / Q000473:pathology; D000818:Animals; D000870:Anterior Horn Cells / Q000378:metabolism / Q000473:pathology*; D000975:Antioxidants / Q000494:pharmacology / Q000627:therapeutic use; D017209:Apoptosis / Q000502:physiology; D053181:Caspase 8; D020169:Caspases / Q000378:metabolism; D002839:Chromans / Q000494:pharmacology / Q000627:therapeutic use; D004249:DNA Damage; D045647:DNA Glycosylases / Q000096:biosynthesis / Q000235:genetics; D004260:DNA Repair; D004195:Disease Models, Animal; D004790:Enzyme Induction; D053222:Fas Ligand Protein; D006801:Humans; D008297:Male; D008562:Membrane Glycoproteins / Q000172:deficiency / Q000235:genetics / Q000502:physiology; D051379:Mice; D008810:Mice, Inbred C57BL; D008822:Mice, Transgenic; D009252:NADPH Dehydrogenase / Q000378:metabolism; D009336:Necrosis; D009569:Nitric Oxide / Q000502:physiology*; D052248:Nitric Oxide Synthase Type I / Q000096:biosynthesis / Q000235:genetics / Q000502:physiology*; D052247:Nitric Oxide Synthase Type II / Q000172:deficiency / Q000235:genetics / Q000502:physiology*; D052250:Nitric Oxide Synthase Type III; D018384:Oxidative Stress; D030421:Peroxynitrous Acid / Q000378:metabolism; D017354:Point Mutation; D051381:Rats; D017207:Rats, Sprague-Dawley; D011993:Recombinant Fusion Proteins / Q000502:physiology; D012584:Sciatic Nerve / Q000293:injuries* / Q000378:metabolism / Q000473:pathology; D013482:Superoxide Dismutase / Q000172:deficiency / Q000235:genetics / Q000502:physiology*; D000072105:Superoxide Dismutase-1; D013481:Superoxides / Q000378:metabolism; D048069:Tumor Necrosis Factors / Q000172:deficiency / Q000235:genetics / Q000502:physiology; D016159:Tumor Suppressor Protein p53 / Q000172:deficiency / Q000378:metabolism; D019014:fas Receptor / Q000235:genetics / Q000502:physiology*
D000975:Antioxidants; D002839:Chromans; C505661:FASLG protein, human; D053222:Fas Ligand Protein; C505658:Fasl protein, mouse; C505662:Faslg protein, rat; D008562:Membrane Glycoproteins; D011993:Recombinant Fusion Proteins; C000606290:SOD1 protein, human; D048069:Tumor Necrosis Factors; D016159:Tumor Suppressor Protein p53; D019014:fas Receptor; D013481:Superoxides; D030421:Peroxynitrous Acid; D009569:Nitric Oxide; D052248:Nitric Oxide Synthase Type I; D052247:Nitric Oxide Synthase Type II; D052250:Nitric Oxide Synthase Type III; C496321:Nos1 protein, mouse; C496317:Nos2 protein, mouse; C496315:Nos3 protein, mouse; C000606291:Sod1 protein, mouse; C000606292:Sod1 protein, rat; D013482:Superoxide Dismutase; D000072105:Superoxide Dismutase-1; D009252:NADPH Dehydrogenase; D045647:DNA Glycosylases; C485990:Ogg1 protein, mouse; C505530:CASP8 protein, human; C505526:Casp8 protein, mouse; C505528:Casp8 protein, rat; D053181:Caspase 8; D020169:Caspases; C010643:6-hydroxy-2,5,7,8-tetramethylchroman-2-carboxylic acid