The effect of light exposure at night on retinal neovascularization in a mouse model of oxygen-induced retinopathy

Background Oxygen-induced retinal neovascularization is the main pathological basis for many retinal vascular diseases.Research showed that light exposure at night can suppress retinal neovascularization in oxygen-induced retinopathy(OIR),but there were few reports discussing its effect on ROP.Objective This study aimed to observe the effect of light exposure at night on retinal neovascularization in an OIR mouse model.Methods Sixty-four newborn C57 BL/6J mice were randomly divided into four groups,with 16 mice for each group.OIR models were established by rearing the newborn C57BL/6J mice with their mothers in a(75±2)％ oxygen environment from postnatal day 7(P7)to Pl2,and then transferred to room air.In the OIR model group,the environmental illumination level was the same as the normal control group,and the model mice were exposed to 100 lx light at night in the OIR+ light exposure group.In the simple light exposure group,normal mice were reared in room air and were exposed to light at night from P12 to P17.All the mice were sacrificed on P17,and retinal flat mounts were prepared to assess the oxygen-induced changes of retinal vessels using the adenosine diphosphatase(ADPase)histochemical technique.The amount of proliferative neovascularization was quantified by counting the number of endotheliocyte nuclei in new vessels extending from the retinal inner limiting membrane into the vitreous in ocular cross-sections.The expression of the vascular endothelial growth factor(VEGF)protein was detected by immunohistochemistry.Real-time PCR analysis was performed to examine the expression of VEGF mRNA.The rearing and usage of the animals complied with the Statement of ARVO.Results Less free-vascular areas and new blood vessels were seen in the OIR+light exposure group compared with the OIR model group.On day 17 of the mouse life,the number of the endotheliocyte nuclei in new vessels extending from retinal inner limiting membrane were 0.97±0.83,1.00±0.72,38.57±5.01 and 16.92±3.39 in the normal group,simple light exposure group,OIR model group and OIR+light exposure group,respectively,showing significant differences among them(F =78.767,P =0.000).The number of nuclei in the OIR+light exposure group were less than that of the OIR model group(t=20.446,P＜0.01).Immunochemistry showed that the expression of VEGF in retina was weaker in the OIR+light exposure group than the OIR model group.The relative expression values of VEGF mRNA were 1.00±0.00,0.94±0.07,2.08±0.50 and 1.43±0.21 in the normal group,simple light exposure group,OIR model group and OIR+light exposure group,respectively,showing a significant difference (F=11.268,P =0.003),where the VEGF mRNA level in the OIR+light exposure group was lower than that of the OIR model group(t =20.163,P＜0.05).Conclusions Light exposure at night can weaken retinal neovascularization in OIR mice Key words: Oxygen-induced retinopathy; Retinal neovascularization; Light exposure