17ß-Estradiol Inhibits Retinal Vessel Regression and neovascularization in a Mouse ROP Model by regulating VEGF mRNA Expression

Abstract

Abstract: : Purpose:We previously reported that 17ß-estradiol (E2) increases the expression of VEGFR-2 and VEGF and that it may enhance the proliferation of bovine retinal vascular endothelial cells, while it reduces VEGF under hypoxia, and in a mouse ROP E2 administered during the period of hyperoxia may improve oxygen-induced retinopathy by inhibiting the regression of retinal vessels by high concentration of O₂. In the present study we further investigated how estrogen modulates the expression of VEGF and attenuates mouse ROP. Methods:C57BL/6J mice were exposed to 75% O₂ from postnatal day 7 (P7) to P12, then returned to room air. E2 (1 µg/mouse/day) was administered to mice subcutaneously. The mice were divided into six groups according to the treatment between P7 and P17: room air with vehicle injection (control), room air with E2 injection, hyperoxia with vehicle injection, hyperoxia with E2 administered for 5 days (from P12 to P16), hyperoxia with E2 for 10 days (from P7 to P16) and hyperoxia with E2 for 5 days (from P7 to P11). To study the retinal neovascularization, all retinal vascular cell nuclei anterior to the internal limiting membrane were counted and gene expression of VEGF in the retina was studied by using semi-quantitative PCR. Results:Mice treated with E2 between P12-16 and between P7-16 both developed less extensive extraretinal neovascularization than did oxygen-exposed mice (n=8, P<0.01). Treatment with E2 only during hyperoxia (between P7-11) did not reduce extraretinal neovascularization (n=8). On P12, VEGF gene expression was reduced by 40% in oxygen-exposed mice, while treatment with E2 did not reduce VEGF expression (n=5, P<0.05). On P17, VEGF gene expression was 1.8 times that of the controls in oxygen-exposed mice, and was reduced to 0.9 times in oxygen-exposed mice receiving E2 injection during P12-16 and P7-16 respectively (n=5, P<0.01). Treatment with E2 during P7-11 reduced the expression of VEGF mRNA to 1.1 times, but this effect was not statistically significant (n=5). Conclusion:These results indicated that estrogen administered during the period of hyperoxia restored VEGF mRNA expression back to the control level and also reduced the avascular area, and estrogen administered during relative hypoxia decreased VEGF mRNA expression and also decreased the extraretinal neovascularization.

Keywords: 417 gene/expression • 483 neovascularization • 572 retinopathy of prematurity