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Retinal neuroprotection by hypoxic preconditioning is independent of hypoxia-inducible factor-1α expression in photoreceptors

Authors

  • Markus Thiersch,

    1. Department of Ophthalmology, Laboratory of Retinal Cell Biology, Center for Integrative Human Physiology and Neuroscience Center Zurich, University of Zurich, Frauenklinikstrasse 24, CH-8091 Zurich, Switzerland
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  • Christina Lange,

    1. Department of Ophthalmology, Laboratory of Retinal Cell Biology, Center for Integrative Human Physiology and Neuroscience Center Zurich, University of Zurich, Frauenklinikstrasse 24, CH-8091 Zurich, Switzerland
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  • Sandrine Joly,

    1. Department of Ophthalmology, Laboratory of Retinal Cell Biology, Center for Integrative Human Physiology and Neuroscience Center Zurich, University of Zurich, Frauenklinikstrasse 24, CH-8091 Zurich, Switzerland
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  • Severin Heynen,

    1. Department of Ophthalmology, Laboratory of Retinal Cell Biology, Center for Integrative Human Physiology and Neuroscience Center Zurich, University of Zurich, Frauenklinikstrasse 24, CH-8091 Zurich, Switzerland
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  • Yun Zheng Le,

    1. Health Sciences Center, University of Oklahoma, Oklahoma City, OK, USA
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  • Marijana Samardzija,

    1. Department of Ophthalmology, Laboratory of Retinal Cell Biology, Center for Integrative Human Physiology and Neuroscience Center Zurich, University of Zurich, Frauenklinikstrasse 24, CH-8091 Zurich, Switzerland
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  • Christian Grimm

    1. Department of Ophthalmology, Laboratory of Retinal Cell Biology, Center for Integrative Human Physiology and Neuroscience Center Zurich, University of Zurich, Frauenklinikstrasse 24, CH-8091 Zurich, Switzerland
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Dr C. Grimm, as above.
E-mail: cgrimm@opht.uzh.ch.

Abstract

Hypoxic preconditioning stabilizes hypoxia-inducible factor (HIF) 1α in the retina and protects photoreceptors against light-induced cell death. HIF-1α 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-1α is essential to protect photoreceptors by hypoxic preconditioning, we knocked down expression of HIF-1α specifically in photoreceptor cells, using the cyclization recombinase (Cre)–lox system. The Cre-mediated knockdown caused a 20-fold reduced expression of Hif-1α 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-1α protein levels. Accordingly, HIF-1 target gene expression after hypoxia was significantly diminished. Retinas of Hif-1α 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-1α in photoreceptor cells. Hypoxia-mediated stabilization of HIF-2α and phosphorylation of signal transducer and activator of transcription 3 (STAT 3) were not affected in the retinas of Hif-1α 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.

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