title: Retinal neuroprotection by hypoxic preconditioning is independent of hypoxia-inducible factor-1 alpha expression in photoreceptors.
abstract: Hypoxic preconditioning stabilizes hypoxia-inducible factor (HIF) 1 alpha in the retina and protects photoreceptors against light-induced cell death. HIF-1 alpha is one of the major transcription factors responding to low oxygen tension and can differentially regulate a large number of target genes. To analyse whether photoreceptor-specific expression of HIF-1 alpha is essential to protect photoreceptors by hypoxic preconditioning, we knocked down expression of HIF-1 alpha specifically in photoreceptor cells, using the cyclization recombinase (Cre)-lox system. The Cre-mediated knockdown caused a 20-fold reduced expression of Hif-1 alpha in the photoreceptor cell layer. In the total retina, RNA expression was reduced by 65%, and hypoxic preconditioning led to only a small increase in HIF-1 alpha protein levels. Accordingly, HIF-1 target gene expression after hypoxia was significantly diminished. Retinas of Hif-1 alpha knockdown animals did not show any pathological alterations, and tolerated hypoxic exposure in a comparable way to wild-type retinas. Importantly, the strong neuroprotective effect of hypoxic preconditioning against light-induced photoreceptor degeneration persisted in knockdown mice, suggesting that hypoxia-mediated survival of light exposure does not depend on an autocrine action of HIF-1 alpha in photoreceptor cells. Hypoxia-mediated stabilization of HIF-2 alpha and phosphorylation of signal transducer and activator of transcription 3 (STAT 3) were not affected in the retinas of Hif-1 alpha knockdown mice. Thus, these factors are candidates for regulating the resistance of photoreceptors to light damage after hypoxic preconditioning, along with several potentially neuroprotective genes that were similarly induced in hypoxic knockdown and control mice.
authors.affiliation: Department of Ophthalmology, Laboratory of Retinal Cell Biology, Center for Integrative Human Physiology and Neuroscience Center Zurich, University of Zurich, Zurich, Switzerland.
authors.forename: Markus
authors.initials: M
authors.lastname: Thiersch
authors.forename: Christina
authors.initials: C
authors.lastname: Lange
authors.forename: Sandrine
authors.initials: S
authors.lastname: Joly
authors.forename: Severin
authors.initials: S
authors.lastname: Heynen
authors.forename: Yun Zheng
authors.initials: YZ
authors.lastname: Le
authors.forename: Marijana
authors.initials: M
authors.lastname: Samardzija
authors.forename: Christian
authors.initials: C
authors.lastname: Grimm
mesh_terms: D000818:Animals; D019898:Autocrine Communication / Q000235:genetics / Q000528:radiation effects; D019610:Cytoprotection / Q000502:physiology*; D015536:Down-Regulation / Q000235:genetics; D005786:Gene Expression Regulation / Q000235:genetics / Q000528:radiation effects; D000860:Hypoxia / Q000378:metabolism* / Q000503:physiopathology / Q000628:therapy; D051795:Hypoxia-Inducible Factor 1, alpha Subunit / Q000235:genetics / Q000378:metabolism*; D019194:Ischemic Preconditioning / Q000379:methods*; D008027:Light / Q000009:adverse effects; D051379:Mice; D018345:Mice, Knockout; D008822:Mice, Transgenic; D010775:Photic Stimulation; D020419:Photoreceptor Cells, Vertebrate / Q000378:metabolism* / Q000473:pathology / Q000528:radiation effects; D012333:RNA, Messenger / Q000378:metabolism; D012162:Retinal Degeneration / Q000378:metabolism* / Q000503:physiopathology / Q000628:therapy
chemical_list: C497443:Hif1a protein, mouse; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D012333:RNA, Messenger