Retinal vein occlusion induced by laser treatment in mice. Mus musculus

Purpose: Several animal models are available for investigating retinal vein occlusion (RVO). Laser-induced RVO has been studied in pigs, rabbits, and rats. Mice have been rarely used despite the huge number of available mutants, ease of handling and cost effectiveness. The aim of this study was to find out if the RVO mouse model is useful for investigating effects of hypoxia. Methods: C57Bl/6J mice were injected with eosin Y for photo-sensitization. Subsequently, large retinal veins were laser-treated in one eye to induce vascular occlusion. Contralateral control eyes received non-occlusive laser treatment of the retina sparing large vessels. The animals were followed for up to eight days and assessed by fundoscopy, angiography, hypoxyprobe staining, histopathology and gene expression analysis by qPCR and RNA sequencing. Another group of mice was left untreated and studied at a single time point to determine baseline characteristics. Results: In the RVO group, half of the retinal veins stayed occluded for three days, and one third did so for the whole test period of 8 days. Hypoxia was observed in all RVO eyes for up to 5 days with a maximum around days 2-3. Large retinal edematous areas were present in all laser-treated eyes irrespective of vascular occlusion status. Accordingly, expression of genes associated with inflammation or cell damage was highly up-regulated in both groups as compared to untreated eyes while expression of genes associated with angiogenesis or hypoxia did not change much. Conclusion: In the laser-induced RVO mouse model, general tissue damage and inflammation responses predominate and obscure specific hypoxia- or angiogenesis-related changes. A non-occlusive control laser treatment is essential to allow for proper data interpretation. Overall design: Six retinas from 6 mice were combined to one sample. Three replicate retinal tissue samples were obtained in each treatment group (laser treatment of all veins (RVO) or equivalent laser treatment between large vessels (Control)) two days after laser treatment. Three equivalent samples were obtained from untreated mice.