Objeetive To evaluate the protective effects of decorin on the inner blood-retinal barrier function under high-glucose plus hypoxia conditions,and explore its potential mechanism.Methods The human umbilical vein endothelial cells (HUVEC) were cultured,and the effect of decorin with different concentrations on HUVEC viability was determined by using the cell counting kit-8 assay (CCK-8).At different hours after incubation under high-glucose plus hypoxia conditions (25 mmol · L-1 D-glucose + 100 μmol · L-1 CoCl2),the suppression effects of various concentrations of decorin on the vascular endothelial growth factor (VEGF) expression of HUVEC was detected by enzyme-linked immunosorbent assay (ELISA).HUVEC were divided into normal control group (5.5 mmol · L-1 D-glucose),high-glucose plus hypoxia group (25 mmol · L-1 D-glucose + 100 μmol · L-1 CoCl2),mannitol control group(5.5 mmol· L-1 D-glucose +19.5 mmol · L-1 mannitol) and decorin treatment group (25 mmol · L-1 D-glucose+ 100 μmol · L-1 CoCl2 + 100 nmol · L-1 decorin).HUVEC barrier function was evaluated by detecting transepithelial electrical resistance (TER) and permeability of fluorescein isothiocyanate-dextran (FITC-dextran).The content of tight junction proteins (claudin-5,occludin,and ZO-1) and p38 mitogen-activated protein kinase (MAPK) phosphorylation were examined by Western blotting.Results According to the results of CCK-8,the survival rates of HUVEC in all groups were more than 90％,different concentrations of decorin showed no significant effect on HUVEC survival (all P ＞ 0.05).According to the results of CCK-8 and ELISA,the stimulation of hypoxia for 48 hours and 100 nmol · L-1 decorin was taken as the condition of further experiment.At 14 days,TER of HUVEC reached its peak of (170.67 ±9.07) Ω.TER of high-glucose plus hypoxia group (97.33 ±6.11)Ω was significantly lower than that of decorin treatment group (157.67 ± 11.72)Ω (P ＜0.05).The FITC-dextran permeability of high-glucose plus hypoxia group increased to (2.12 ±0.07) times of normal control group(P ＜0.05).Decorin reversed this effect to (1.16 ± 0.03) times of normal control group (P ＜ 0.05).The expression of claudin-5,occludin and ZO-1 in high-glucose plns hypoxia group were 0.38 ±0.05,0.43 ±0.02,0.25 ± 0.02,compared to the normal control group (0.72 ±0.05,0.90 ±0.01,0.75 ±0.02),there were statistical differences (all P ＜0.05).The expression of claudin-5,occludin and ZO-1 m decorin treatment group were 0.65 ±0.08,0.87 ±0.03,0.60 ±0.01,there were statistical differences compared with high-glucose plns hypoxia group (all P ＜0.05).The ration of p-p38 MAPK/p38 MAPK in high-glucose plus hypoxia group (0.88 ± 0.02) was increased,while the decorin treatment group (0.58 ± 0.04) reached the level of the normal control group (0.56 ±0.02),there was statistical difference compared with high-glucose plns hypoxia group (P ＜0.05).Conclusion Decorin can protect the HUVEC barrier function under high-glucose plus hypoxia conditions and inhibit the activation of p38 MAPK signaling pathway.So it may be used to treat diabetic retinopathy.