title: Specific inhibition of hypoxia inducible factor 1 exaggerates cell injury induced by in vitro ischemia through deteriorating cellular redox environment.
abstract: Hypoxia inducible factor 1 (HIF-1) has been suggested to play a critical role in the fate of cells exposed to hypoxic stress. However, the mechanism of HIF-1-regulated cell survival is still not fully understood in ischemic conditions. Redox status is critical for decisions of cell survival, death and differentiation. We investigated the effects of inhibiting HIF-1 on cellular redox status in SH-SY5Y cells exposed to hypoxia or oxygen and glucose deprivation (OGD), coupled with cell death analyses. Our results demonstrated that inhibiting HIF-1alpha expression by HIF-1alpha specific small interfering RNA (siRNA) transfection increased reactive oxygen species generation, and transformed the cells to more oxidizing environments (low GSH/GSSG ratio, low NADPH level) under either hypoxic or OGD exposure. Cell death increased dramatically in the siRNA transfected cells, compared to non-transfected cells after hypoxic/OGD exposures. In contrast, increasing HIF-1alpha expression by desferrioxamine, a metal chelator and hydroxylase inhibitor, induced a more reducing environment (high GSH/GSSG ratio, high NADPH level) and reduced cell death. Further studies showed that HIF-1 regulated not only glucose transporter-1 expression, but also the key enzymes of the pentose phosphate pathway such as glucose-6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase. These enzymes are important in maintaining cellular redox homeostasis by generating NADPH, the primary reducing agent in cells. Moreover, catalase significantly decreased cell death in the siRNA-transfected cells induced by hypoxia and OGD. These results suggest that maintenance of cellular redox status by HIF-1 protects cells from hypoxia and ischemia mediated injuries.
authors.affiliation: University of New Mexico Health Sciences Center, Albuquerque, USA.
authors.forename: Shuhong
authors.initials: S
authors.lastname: Guo
authors.forename: Minoru
authors.initials: M
authors.lastname: Miyake
authors.forename: Ke Jian
authors.initials: KJ
authors.lastname: Liu
authors.forename: Honglian
authors.initials: H
authors.lastname: Shi
mesh_terms: D000704:Analysis of Variance; D016923:Cell Death / Q000187:drug effects; D015687:Cell Hypoxia / Q000187:drug effects / Q000502:physiology*; D045744:Cell Line, Tumor; D003676:Deferoxamine / Q000494:pharmacology; D004797:Enzyme-Linked Immunosorbent Assay; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects; D005947:Glucose / Q000172:deficiency; D051272:Glucose Transporter Type 1 / Q000378:metabolism; D005978:Glutathione / Q000378:metabolism; D019803:Glutathione Disulfide / Q000378:metabolism; D006801:Humans; D051793:Hypoxia-Inducible Factor 1 / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D007770:L-Lactate Dehydrogenase / Q000378:metabolism; D009249:NADP / Q000378:metabolism; D009447:Neuroblastoma; D010084:Oxidation-Reduction / Q000187:drug effects; D034741:RNA, Small Interfering / Q000235:genetics / Q000378:metabolism; D017382:Reactive Oxygen Species / Q000378:metabolism; D017262:Siderophores / Q000494:pharmacology; D015533:Transcriptional Activation; D014162:Transfection / Q000379:methods
chemical_list: D051272:Glucose Transporter Type 1; D051793:Hypoxia-Inducible Factor 1; D034741:RNA, Small Interfering; D017382:Reactive Oxygen Species; D017262:Siderophores; D009249:NADP; D007770:L-Lactate Dehydrogenase; D005978:Glutathione; D005947:Glucose; D003676:Deferoxamine; D019803:Glutathione Disulfide