| Diabetic retinopathy is the most common complication of diabetes resulting in blindness.The study about pathogenesis has become the hot topic.The abnormal increased angiogenesis promoters is thought as the major cause of diabetic retinopathy,vascular endothelial growth factor(VEGF) is an important factor involved.In the recent years,it has been found that hypoxia-inducible factor-1(HIF-1) was a key point in the modulating vascular endothelial growth factor signal transduction pathway under hypoxic condition.However,whether these factors also have expression in the early diabetic retinopathy is ready for further study.ObjectivesThe purpose of this study was to detect the spatiotemporal expression of HIF-1αand VEGF in retinas of streptozocin(STZ) induced diabetic rats.To approach the mechanism of nonproliferative diabetic microangiopathy was also concerned.Methods130 SD rats were randomly divided into two groups:control group(C) and diabetes group(DM).70 rats were received vena caudal injection of STZ as diabetes group,and the rest were taken as controls.The rats were euthanized and eyes were enucleated for paraffin section with HE staining,examining the lens and retina espectively at 2,4,6,8,10,12 weeks after STZ injection.After peeling off retina of rats with careful manipulation under the microscope,RT-PCR and immunofluorescence were taken to detect the expression of HIF-1αand VEGF in retina respectively at 2,4,6,8,10,12 weeks after STZ injection.ResultsSTZ induced diabetic rats had lasting and stable hyperglycaemia,displaying with the obvious signs of "polydipsia,polyphagia,hyperdiuresis and loss of weight". There was significant difference of weight and plasma glucose of rats between the two groups at different time points(P＜0.05).The epithelial cells of lens are in regular arrangement in control groups.There was no sign of morphologic alteration at 4 weeks after STZ injection and mild signs of cataract at 8 weeks after STZ injection.All lens of diabetes eyes were detected to cataract alteration at 12 weeks after STZ injection.There was no significant sign of morphologic alteration of retina in control groups. The retinal structure of diabetic rats is similar as control eyes at 2 to 6 weeks after STZ injection by HE staining.There was hypocellularity of the nuclear layer in diabetes group at 8 weeks after STZ injection and there were signs of thinness, dissolution and cells loss in the retinas of diabetic rats at 12 weeks after STZ injection.HIF-1αmRNA were expressed in normal retina and began to increase at 2 weeks after STZ injection(P＜0.05).The longer duration of the disease,the more expression of HIF-1αmRNA.The expression at 10 weeks after STZ injection began to decrease(P＜0.05).The expression of HIF-1αat 12 weeks after STZ injection was lower than at 10 weeks after STZ injection(P＜0.05).The expression of HIF-1αprotein in retina was found in control group.It mainly localized in the ganglion cell layer,outer plexiform layer.HIF-1αprotein began to increase at 2 weeks after STZ injection.It mainly localized in the ganglion cell layer,inner plexiform layer,inner nuclear layer,outer plexiform layer.The longer duration of the disease,the more expression of HIF-1αprotein(P＜0.05).The expression of HIF-1αprotein reached peak at 10 weeks and decreased after 12 weeks after STZ injection(P＜0.05).VEGF mRNA were also expressed in retinas of normal rats,the expression began to increase at 2 weeks after STZ injection(P＜0.05).The longer duration of the disease,the more expression of VEGF.The expression at 12 weeks after STZ injection is 4 fold compared with control animals(P＜0.05).The expression of VEGF protein in retinas was found in control group.It mainly localized in the ganglion cell layer,inner plexiform layer,inner nuclear layer,outer plexiform layer,outer nulear layer.VEGF protein began to increase at 2 weeks after STZ injection.The longer duration of the disease,the more expression of VEGF protein(P＜0.05).Conclusions(1) STZ induced diabetic rat is a reliable animal model which can be used to imitate human nonproliferation diabetic retinopathy.(2) The expression of HIF-1αand VEGF can be detected on retina of early diabetic rats. (3) The protein expression trend of HIF-1αand VEGF is similar as the expression of mRNA.It was showed that hypoxia played an important role in DR.(4) HIF-1αmay regulated the expression of VEGF by combinating with hypoxia response element of VEGF on the retina of early diabetic rats.Further study is needed.
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