Hypoxia-Inducible-Factor 1 Ablation in a Model of Retinal Neuroprotection by Hypoxic Preconditioning

Abstract

Purpose: : Hypoxic preconditioning is an established method to protect mice from various degenerative stimuli. In our model of light induced retinal degeneration it completely protects photoreceptors from cell death. During hypoxic preconditioning, transcription factor hypoxia-inducible-factor 1 (HIF-1) is stabilized in the retina and regulates the differential expression of a large number of genes. Here we analyze whether photoreceptors require intrinsic HIF-1 to prevent cell death after hypoxic preconditioning.

Methods: : Therefore, we used the cre-lox system to conditionally ablate HIF-1 in photoreceptor cells. The knock out efficiency of tamoxifen inducible PrpCre mice and of OpnCre mice was determined by real time PCR and western blot of total retinal RNA or proteins, respectively. Hypoxic preconditioning was for 6 h at 6% O2. Mice were exposed to 13‘000 lux of light for 2 h. Cell death was quantified by measurement of nucleosomal release and by morphological analyzes.

Results: : Total retinal HIF-1 RNA was reduced by about 70 % in TAM treated PrpCre mice and by about 45% in OpnCre mice. After hypoxic exposure, HIF-1 protein levels were reduced accordingly and expression of HIF1- target genes was less induced in knockout mice. Expression of other genes regulated by hypoxia was not affected by the knockout. Both knockout strains were resistant to light induced retinal degeneration. HIF-1 was also not required in photoreceptors to adapt to short time hypoxia.

Keywords: hypoxia • neuroprotection • transcription factors