title: Rapid generation of mitochondrial superoxide induces mitochondrion-dependent but caspase-independent cell death in hippocampal neuronal cells that morphologically resembles necroptosis.
abstract: Studies in recent years have revealed that excess mitochondrial superoxide production is an important etiological factor in neurodegenerative diseases, resulting from oxidative modifications of cellular lipids, proteins, and nucleic acids. Hence, it is important to understand the mechanism by which mitochondrial oxidative stress causes neuronal death. In this study, the immortalized mouse hippocampal neuronal cells (HT22) in culture were used as a model and they were exposed to menadione (also known as vitamin K(3)) to increase intracellular superoxide production. We found that menadione causes preferential accumulation of superoxide in the mitochondria of these cells, along with the rapid development of mitochondrial dysfunction and cellular ATP depletion. Neuronal death induced by menadione is independent of the activation of the MAPK signaling pathways and caspases. The lack of caspase activation is due to the rapid depletion of cellular ATP. It was observed that two ATP-independent mitochondrial nucleases, namely, AIF and Endo G, are released following menadione exposure. Silencing of their expression using specific siRNAs results in transient suppression (for ~12h) of mitochondrial superoxide-induced neuronal death. While suppression of the mitochondrial superoxide dismutase expression markedly sensitizes neuronal cells to mitochondrial superoxide-induced cytotoxicity, its over-expression confers strong protection. Collectively, these findings showed that many of the observed features associated with mitochondrial superoxide-induced cell death, including caspase independency, rapid depletion of ATP level, mitochondrial release of AIF and Endo G, and mitochondrial swelling, are distinctly different from those of apoptosis; instead they resemble some of the known features of necroptosis.
authors.affiliation: Department of Pharmacology, Toxicology and Therapeutics, School of Medicine, University of Kansas Medical Center, Kansas City, KS 66160, USA.
authors.forename: Masayuki
authors.initials: M
authors.lastname: Fukui
authors.forename: Hye Joung
authors.initials: HJ
authors.lastname: Choi
authors.forename: Bao Ting
authors.initials: BT
authors.lastname: Zhu
mesh_terms: D000818:Animals; D051033:Apoptosis Inducing Factor / Q000378:metabolism; D016923:Cell Death / Q000187:drug effects / Q000502:physiology; D002460:Cell Line; D004706:Endodeoxyribonucleases / Q000378:metabolism; D006624:Hippocampus / Q000187:drug effects / Q000378:metabolism* / Q000473:pathology; D051379:Mice; D046529:Microscopy, Electron, Transmission; D008928:Mitochondria / Q000187:drug effects / Q000378:metabolism* / Q000648:ultrastructure; D019636:Neurodegenerative Diseases / Q000378:metabolism* / Q000473:pathology; D009474:Neurons / Q000187:drug effects / Q000378:metabolism* / Q000473:pathology; D018384:Oxidative Stress / Q000187:drug effects / Q000502:physiology*; D013482:Superoxide Dismutase / Q000378:metabolism; D000072105:Superoxide Dismutase-1; D013481:Superoxides / Q000378:metabolism*; D024483:Vitamin K 3 / Q000494:pharmacology*; D000099156:Superoxide Dismutase 2
chemical_list: D051033:Apoptosis Inducing Factor; D004706:Endodeoxyribonucleases; D013482:Superoxide Dismutase; D000072105:Superoxide Dismutase-1; D013481:Superoxides; D024483:Vitamin K 3; D000099156:Superoxide Dismutase 2; C000606291:Sod1 protein, mouse; C052391:endonuclease G