title: The microRNA miR-181c controls microglia-mediated neuronal apoptosis by suppressing tumor necrosis factor.
abstract: BACKGROUND
  Post-ischemic microglial activation may contribute to neuronal damage through the release of large amounts of pro-inflammatory cytokines and neurotoxic factors. The involvement of microRNAs (miRNAs) in the pathogenesis of disorders related to the brain and central nervous system has been previously studied, but it remains unknown whether the production of pro-inflammatory cytokines is regulated by miRNAs.
  
  
  METHODS
  BV-2 and primary rat microglial cells were activated by exposure to oxygen-glucose deprivation (OGD). Global cerebral ischemia was induced using the four-vessel occlusion (4-VO) model in rats. Induction of pro-inflammatory and neurotoxic factors, such as tumor necrosis factor (TNF)-α, interleukin (IL)-1β, and nitric oxide (NO), were assessed by ELISA, immunofluorescence, and the Griess assay, respectively. The miRNA expression profiles of OGD-activated BV-2 cells were subsequently compared with the profiles of resting cells in a miRNA microarray. BV-2 and primary rat microglial cells were transfected with miR-181c to evaluate its effects on TNF-α production after OGD. In addition, a luciferase reporter assay was conducted to confirm whether TNF-α is a direct target of miR-181c.
  
  
  RESULTS
  OGD induced BV-2 microglial activation in vitro, as indicated by the overproduction of TNF-α, IL-1β, and NO. Global cerebral ischemia/reperfusion injury induced microglial activation and the release of pro-inflammatory cytokines in the hippocampus. OGD also downregulated miR-181c expression and upregulated TNF-α expression. Overproduction of TNF-α after OGD-induced microglial activation provoked neuronal apoptosis, whereas the ectopic expression of miR-181c partially protected neurons from cell death caused by OGD-activated microglia. RNAinterference-mediated knockdown of TNF-α phenocopied the effect of miR-181c-mediated neuronal protection, whereas overexpression of TNF-α blocked the miR-181c-dependent suppression of apoptosis. Further studies showed that miR-181c could directly target the 3'-untranslated region of TNF-α mRNA, suppressing its mRNA and protein expression.
  
  
  CONCLUSIONS
  Our data suggest a potential role for miR-181c in the regulation of TNF-α expression after ischemia/hypoxia and microglia-mediated neuronal injury.
authors.affiliation: Department of Neurology, Huadong Hospital, Fudan University, 221 West Yan An Road, Shanghai, 200040, China.
authors.forename: Li
authors.initials: L
authors.lastname: Zhang
authors.forename: Lian-Yan
authors.initials: LY
authors.lastname: Dong
authors.forename: Ya-Jian
authors.initials: YJ
authors.lastname: Li
authors.forename: Zhen
authors.initials: Z
authors.lastname: Hong
authors.forename: Wen-Shi
authors.initials: WS
authors.lastname: Wei
mesh_terms: D000704:Analysis of Variance; D000818:Animals; D000831:Animals, Newborn; D017209:Apoptosis / Q000187:drug effects / Q000502:physiology*; D002545:Brain Ischemia / Q000378:metabolism / Q000473:pathology*; D039481:CD11b Antigen; D002478:Cells, Cultured; D017077:Culture Media, Conditioned / Q000494:pharmacology; D016207:Cytokines / Q000235:genetics / Q000378:metabolism; D004195:Disease Models, Animal; D020869:Gene Expression Profiling; D005786:Gene Expression Regulation / Q000187:drug effects / Q000502:physiology; D005947:Glucose / Q000172:deficiency; D006624:Hippocampus / Q000166:cytology; D000860:Hypoxia; D035683:MicroRNAs / Q000378:metabolism*; D017628:Microglia / Q000502:physiology*; D009474:Neurons / Q000187:drug effects / Q000502:physiology*; D009569:Nitric Oxide; D052247:Nitric Oxide Synthase Type II / Q000378:metabolism; D020411:Oligonucleotide Array Sequence Analysis; D051381:Rats; D017207:Rats, Sprague-Dawley; D014162:Transfection; D014409:Tumor Necrosis Factor-alpha / Q000378:metabolism*
chemical_list: D039481:CD11b Antigen; D017077:Culture Media, Conditioned; D016207:Cytokines; D035683:MicroRNAs; D014409:Tumor Necrosis Factor-alpha; D009569:Nitric Oxide; D052247:Nitric Oxide Synthase Type II; D005947:Glucose