title: Neuroprotective role of superoxide dismutase 1 in retinal ganglion cells and inner nuclear layer cells against N-methyl-d-aspartate-induced cytotoxicity.
abstract: The N-methyl-d-aspartate (NMDA) receptor-induced apoptosis is implicated in the pathological mechanisms of neural tissues, increasing the release of reactive oxygen species (ROS), resulting in a type of apoptotic cell death called excitotoxicity. Although intrinsic mechanisms to remove ROS, such as antioxidant enzymes, are provided by the tissue, the association between NMDA-induced excitotoxicity and antioxidative enzymes is not well understood. In this study, we focused on superoxide dismutase 1 (SOD1), an antioxidant enzyme, and investigated the role of SOD1 in the NMDA-induced neuronal cell death in the retina. NMDA was intravitreally injected into wild-type (WT) and SOD1 total knock-out (SOD1-deficient) mice. The number of TUNEL-positive cells in the retinal ganglion cell layer (GCL) and inner nuclear layer (INL) counted in the retinal sections and flatmount retinas were significantly higher in the SOD1-deficient mice than the WT mice after NMDA injection. Visual function assessed by dark-adapted electroretinogram (ERG) showed that the amplitudes of a-wave, b-wave, and oscillatory potential 2 were significantly reduced in the NMDA-injected SOD1-deficient mice. The level of ROS in the GCL and INL, measured using dihydroethidium, and the number of positive cells for γ-H2AX, a marker for DNA double strand breaks, and 8-OHdG, a marker for DNA oxidation, in the GCL were significantly increased in the SOD1-deficient mice after NMDA injection. We also measured mRNA and protein levels of SOD1 and SOD2 in the retina of WT mice, to find that mRNA and protein levels of SOD1, but not SOD2, were significantly reduced after NMDA injection. SOD1 deficiency exacerbated NMDA-induced damage to the inner retinal neurons, and NMDA reduced SOD1 levels in the retina of WT mice. Therefore, SOD1 protected retinal neurons against NMDA-induced retinal neurotoxicity, and NMDA-induced SOD1 reduction may be involved in neuronal vulnerability to excitotoxicity.
authors.affiliation: Laboratory of Retinal Cell Biology, Keio University School of Medicine, 35 Shinanomachi, Shinjuku-ku, Tokyo 160-8582, Japan; Department of Ophthalmology, Keio University School of Medicine, 35 Shinanomachi, Shinjuku-ku, Tokyo 160-8582, Japan.
authors.forename: Kenya
authors.initials: K
authors.lastname: Yuki
authors.forename: Tetsu
authors.initials: T
authors.lastname: Yoshida
authors.forename: Seiji
authors.initials: S
authors.lastname: Miyake
authors.forename: Kazuo
authors.initials: K
authors.lastname: Tsubota
authors.forename: Yoko
authors.initials: Y
authors.lastname: Ozawa
mesh_terms: D025042:Amacrine Cells / Q000187:drug effects / Q000201:enzymology* / Q000473:pathology; D000818:Animals; D017209:Apoptosis / Q000187:drug effects; D001224:Aspartic Acid / Q000378:metabolism; D003623:Dark Adaptation; D004596:Electroretinography; D018690:Excitatory Amino Acid Agonists / Q000633:toxicity*; D019084:Fluorescent Antibody Technique, Indirect; D015151:Immunoblotting; D020287:In Situ Nick-End Labeling; D058449:Intravitreal Injections; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D016202:N-Methylaspartate / Q000633:toxicity*; D012333:RNA, Messenger / Q000378:metabolism; D017382:Reactive Oxygen Species / Q000378:metabolism; D060888:Real-Time Polymerase Chain Reaction; D051245:Retinal Bipolar Cells / Q000187:drug effects / Q000201:enzymology* / Q000473:pathology; D012165:Retinal Ganglion Cells / Q000187:drug effects / Q000201:enzymology* / Q000473:pathology; D051248:Retinal Horizontal Cells / Q000187:drug effects / Q000201:enzymology* / Q000473:pathology; D013482:Superoxide Dismutase / Q000502:physiology*; D000072105:Superoxide Dismutase-1
chemical_list: D018690:Excitatory Amino Acid Agonists; D012333:RNA, Messenger; D017382:Reactive Oxygen Species; D001224:Aspartic Acid; D016202:N-Methylaspartate; C000606291:Sod1 protein, mouse; D013482:Superoxide Dismutase; D000072105:Superoxide Dismutase-1
keywords: N-methyl-d-aspartate; electroretinogram; excitotoxicity; reactive oxygen species; retina; superoxide dismutase 1