title: Neuroprotection by hypoxic preconditioning involves oxidative stress-mediated expression of hypoxia-inducible factor and erythropoietin.
abstract: OBJECTIVE
  Hypoxic preconditioning is an endogenous protection against subsequent lethal hypoxia, but the mechanism involved is not understood. Hypoxia is followed by reactive oxygen species (ROS) production and induces hypoxia-inducible factor (HIF) and its downstream factor erythropoietin (Epo), which is associated with neuroprotection. We hypothesized that these endogenous processes may contribute to hypoxic preconditioning.
  
  
  METHODS
  We used a mouse neuronal culture model, with 2 hours of hypoxia as preconditioning followed by 15 hours of hypoxic insult, and examined the expression of HIF-1alpha, Epo, and their downstream proteins by Western blotting. Copper/zinc-superoxide dismutase (SOD1) transgenic (Tg) mice were used to detect the effect of ROS. Cell survival and apoptosis were detected by mitogen-activated protein 2 quantification, apoptotic-related DNA fragmentation, and caspase-3 fragmentation. Antisense Epo was used to block endogenously produced Epo.
  
  
  RESULTS
  Hypoxic preconditioning was protective in wild-type (Wt) neurons but not in neurons obtained from SOD1 Tg mice. In Wt neurons, HIF-1alpha and Epo expression showed a greater increase after hypoxia compared with Tg neurons and reached a higher level with preconditioned hypoxia, followed by pJak2, pStat5, and nuclear factor kappaB (NF-kappaB) expression. Antisense Epo decreased these downstream proteins and the neuroprotection of hypoxic preconditioning.
  
  
  CONCLUSIONS
  Hypoxic preconditioning induces ROS, which may downregulate the threshold for production of HIF-1alpha and Epo expression during subsequent lethal hypoxia, thus exerting neuroprotection through the Jak2-Stat5 and NF-kappaB pathways.
authors.affiliation: Department of Neurosurgery, Stanford University School of Medicine, Stanford, California 94305-5487, USA.
authors.forename: Jing
authors.initials: J
authors.lastname: Liu
authors.forename: Purnima
authors.initials: P
authors.lastname: Narasimhan
authors.forename: Fengshan
authors.initials: F
authors.lastname: Yu
authors.forename: Pak H
authors.initials: PH
authors.lastname: Chan
mesh_terms: D000818:Animals; D017209:Apoptosis; D015153:Blotting, Western; D053148:Caspase 3; D020169:Caspases / Q000378:metabolism; D002470:Cell Survival; D002478:Cells, Cultured; D053938:DNA Fragmentation; D004921:Erythropoietin / Q000494:pharmacology*; D006579:Heterozygote; D000860:Hypoxia / Q000378:metabolism; D051793:Hypoxia-Inducible Factor 1 / Q000378:metabolism; D019194:Ischemic Preconditioning; D053614:Janus Kinase 2; D051379:Mice; D008822:Mice, Transgenic; D019950:Mitogen-Activated Protein Kinase 1 / Q000378:metabolism; D016328:NF-kappa B / Q000378:metabolism; D009474:Neurons / Q000378:metabolism; D018696:Neuroprotective Agents / Q000494:pharmacology; D016376:Oligonucleotides, Antisense / Q000494:pharmacology; D018384:Oxidative Stress; D011505:Protein-Tyrosine Kinases / Q000378:metabolism; D011518:Proto-Oncogene Proteins / Q000378:metabolism; D017382:Reactive Oxygen Species; D011994:Recombinant Proteins; D020133:Reverse Transcriptase Polymerase Chain Reaction; D050799:STAT5 Transcription Factor / Q000378:metabolism; D013482:Superoxide Dismutase / Q000235:genetics / Q000378:metabolism / Q000502:physiology
chemical_list: D051793:Hypoxia-Inducible Factor 1; D016328:NF-kappa B; D018696:Neuroprotective Agents; D016376:Oligonucleotides, Antisense; D011518:Proto-Oncogene Proteins; D017382:Reactive Oxygen Species; D011994:Recombinant Proteins; D050799:STAT5 Transcription Factor; D004921:Erythropoietin; D013482:Superoxide Dismutase; D011505:Protein-Tyrosine Kinases; C507926:Jak2 protein, mouse; D053614:Janus Kinase 2; D019950:Mitogen-Activated Protein Kinase 1; C505409:Casp3 protein, mouse; D053148:Caspase 3; D020169:Caspases