Abstract
Purpose: :
Retinal capillary density and blood flow have been reported to decrease early in the streptozotocin (STZ)-induced rat model of diabetes. We hypothesized that these early changes lead to increased inner retinal hypoxia and subsequent upregulation of the transcription factors hypoxia inducible factor (HIF)-1α and HIF-2α.
Methods: :
Male Wistar rats were injected with STZ (60 mg/kg) or vehicle alone. Rats were hyperglycemic for 3 weeks prior to sacrifice, at which time they were injected with pimonidazole, which forms irreversible adducts in cells with an oxygen tension <10mmHg, allowing measurement of tissue hypoxia. Three hours later, the rats were anesthetized and eyes were enucleated and prepared for frozen retinal cross-sections. Immunostaining was performed with antibodies from rabbits against HIF-1α, HIF-2α, or pimonidazole. A goat anti-rabbit antibody conjugated to FITC was used for the secondary antibody. Fluorescent intensity was quantified in the ganglion cell layer (GCL), inner plexiform layer (IPL), inner nuclear layer (INL), outer plexiform layer (OPL), outer nuclear layer (ONL), and the photoreceptor layer-inner segment (PR-IS) in both the central and peripheral retina.
Results: :
There was an increase in HIF-2α fluorescent intensity in the peripheral retina in the GCL (p<0.001), IPL (p<0.05), and OPL (p<0.05), but there was no change in HIF-1α fluorescent intensity in any layer. Anti-pimonidazole fluorescent intensity was not statistically different between control and diabetic rats; however, there was a trend towards a decrease in fluorescent intensity in all layers of the central retina and in the GCL and IPL of the peripheral retina.
Conclusions: :
Three weeks of diabetes produced a moderate increase in retinal HIF-2α, no change in HIF-1α, and a trend toward decreased hypoxia as measured by pimonidazole.Supported by NIH EY017599 (NRH).
Keywords: diabetic retinopathy • hypoxia • immunohistochemistry