Abstract
Purpose: :
It has been reported that retinal blood flow decreases early in the streptozotocin (STZ)-induced mouse and rat model of diabetes. It has also been reported that capillary density decreases early in diabetic rats. We hypothesized that these changes in capillary density and retinal blood flow lead to an increase in retinal hypoxia resulting to an up-regulation of the transcription factor Hypoxia Inducible Factor-1 (HIF-1).
Methods: :
Male C57BL/6J mice and male Wistar rats were injected with STZ, 180 mg/kg and 60 mg/kg respectively. Age-matched control mice and rats were injected with vehicle alone. After four weeks of hyperglycemia, mice and rats were sacrificed. Eyes were enucleated and placed in phosphate buffered 4% paraformaldehyde for 2.5 hours followed by overnight cryoprotection in 20% sucrose solution. Retinal cross-sections were cut at 10 µm thickness. Retinal cross-sections were labeled with rabbit anti-HIF-1 primary antibody and goat anti-rabbit conjugated to FITC for the secondary antibody. Immunofluorescent images were quantitatively analyzed to determine changes in fluorescence. The inner retinal layers (ganglion cell layer, inner plexiform layer, inner nuclear layer, and outer plexiform layer) and the outer retinal layers (outer nuclear layer and photoreceptor layer) were analyzed in the peripheral retina and central retina.
Results: :
No diabetes-induced changes in HIF-1 were detected in any retinal layer of mice. Moreover, the only change detected in diabetic rats was in the central region of the outer retinal layers, and instead of being an increase, the change was a small diabetes-induced decrease (p<0.05).
Keywords: diabetic retinopathy • hypoxia • immunohistochemistry