| Diabetic retinopathy is the most common complication of diabetes resulting in blindness. The study about pathogenesis and corresponding therapeutic scheme has become the hot topic. The unbalance of angiogenesis promoters and inhibitors is thought as the major cause of proliferative diabetic retinopathy, vascular endothelial growth factor(VEGF) and pigment epithelium-derived factor(PEDF) are two important factors involved. However, whether these factors also have significantroles in the early diabetic retinopathy is ready for further study. Objectives The purpose of this study was to detect the dynamic expression of VEGF andPEDF on retinas of streptozocin (STZ) induced diabetic rats , observe the pathogenic changes of neural retina and blood-retinal barrier. To approach the mechanism of nonproliferative diabetic microangiopathy and retinal neuraldegeneration, and the possible roles of the two factors were also concerned. Methods According to the raising time, 130 SD rats were divided into 8 groups at random,including N0.5, DM0.5, N1, DM1, N3, DM3, N5 and DM5. 90 rats received intravenous injection of STZ as diabetes, and the rest were taken as controls. RT-PCR, Western blot and immunohistochemical staining were taken to detect the expression of VEGF and PEDF. Also TUNEL method, immunohistochemical staining of caspase-3, transmission electron microscopy and Evans blue method were used to locate, qualitate or quantitate the retinal neural degeneration and blood-retinal barrier breakdown.ResultsSTZ induced diabetic rats had lasting and stable hyperglycaemia, displaying with the obvious signs of "polydipsia, polyphagia, hyperdiuresis and loss of weight".VEGF mRNA and protein were expressed on retinas of normal rats, theexpression began to increase in DM0.5 group (P<0.05) . The longer duration of the disease, the more expression of VEGF. The expression in DM5 is 2 fold compared with control animals (P<0.05) .PEDF mRNA were expressed in normal retina and began to decrease in DM1 group(P<0.05 ).The expression was about one half of the normal in DM5(P<0.05 ). PEDF protein had the same tendency with the expression of mRNA.The expression of PEDF in normal groups were about the same, and had no significant difference (P>0.05) .The slight ultrastnictural morphological changes were observed with the transmission electron microscope in inner retinal layers and pigment epithelium of DM1. With progress of the disease, the changes expanded to the full thickness of retina. Apoptosis and necrosis were the two major death styles of neural cells in diabetic retinas. Cells which underwent apoptosis were happened to be in inner retinal layers.Evans blue method showed the vascular leakage in diabetic retinas were more severe than normal controls. From the early beginning of DM0.5 the leakage increased with time (P<0.05) . The leakage in DM5 is about 6 fold compared with control animals (P<0.05) .The structure of inner and outer blood-retinal barrier changed in diabetic rats. The ultrastnictural morphological changes of retinal pigment epithelium and blood capillary were seen in DM1. And the impairment exacerbated with the progression of diabetes.The ultrastnictural changes of choroid took place simultaneously with diabetic retinopathy in diabetic rats.ConclusionsSTZ induced diabetic rat is a simple, easy and reliable animal model. Before the visible diabetic microangiopathy, the blood-retinal barrier of diabetic rats has beendestroyed, showing ultrastructural changes and high permeability of blood vessels. Meanwhile, the retina underwent chronic neural degeneration manifestated by apoptosis and necrosis. The increase of VEGF and reduction of PEDF may play important roles in early diabetic retinopathy and hasten the pathological changes. Besides diabetic retinopathy, attention should also be paid to choroidopathy. |
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