ObjectiveTo explore the effect and mechanism of netrin-1 on blood-retinal barrier permeability in diabetes mellitus (DM) rats. MethodsEighty Sprague-Dawley rats were randomly divided into the normal control group, DM+balanced salt solution (BSS) group, DM+netrin-1 low dose group and DM+netrin-1 high dose group, with 20 rats in each group. DM rats were induced by intraperitoneal injection of streptozocin (STZ). These rats were feed with high sugar and fat for 3 months after STZ injection. All rats were sacrificed at 1 month after intravitreal injection. Retinal vascular permeability was measured by Evans blue. The expression level of occludin was determined by immunohistochemistry. Hematoxylin-eosin (HE) staining of retina was used to observe the pathological change of DM and the level of occludin mRNA was analyzed by real-time fluorescence quantitative reverse transcription polymerase chain reaction (RT-PCR). Five rats of each group. ResultsHE staining of retina showed that the degree of edema and vascularization in DM+netrin-1 high dose group was better than DM+BSS group. Staining of occludin in retina was limited to nerve fiber layer, ganglion cells, inner plexiform layer and inner nuclear layer in normal rats, but in DM+BSS group, the color of staining positive of occludin was lighter and more reduced. However, DM+ netrin-1 group occludin staining was deepen and enlarged. The result of RT-PCR showed that the expression of occludin mRNA in other three groups was less than normal control group (P < 0.05). The significant difference during DM+BSS group, low dose group and DM+netrin-1 high dose group (F=177.13, P=0.00), and the more concentrate of netrin-1 the higher expression of occluding. Compared the DM+netrin-1 low dose group with DM+BSS group, there was significant difference expression of occludin (t=-13.98, P=0.00). There was significant difference between the DM+netrin-1 high dose group and normal control group (t=12.87, P=0.00). There was statistically significant difference in DM+BSS group, DM+netrin-1 low dose group and DM+netrin-1 high dose group (F=179.69, P=0.00). Compared the two group of different concentration netrin-1, the quantification of vascular permeability in DM+netrin-1 high dose group reduced more (t=12.73, P=0.00). ConclusionsNetrin-1 can protect the blood-retinal barrier in DM rats. Netrin-1 may decrease BRB leakage in DM rats by protecting the expression of occludin.