β-adrenergic receptor regulation of pigment epithelial-derived factor expression in rat retina

In the present study, we have examined a potential mechanism by which sympathetic nerves regulate PEDF and whether its down regulation may be responsible for increased capillary density observed after sympathectomy. Six weeks post-sympathectomy, eyes were removed from female Sprague-Dawley rats for Western blot analysis, RNA isolation, real-time PCR, and immunohistochemistry for measurement of PEDF expression. The contralateral or left eye was used as an intra-animal control. In addition, retinal pigment epithelial cells were grown in culture and treated with norepinephrine and propranolol. An ELISA assay was used to determine the amount of PEDF secreted into the RPE media. Quantitative results of Western blot analysis and real-time PCR confirm that both steady-state gene expression and protein levels of PEDF are significantly decreased in the sympathectomized retina (P < 0.05) when compared to the contralateral retina. Qualitative results of immunohistochemistry verify that PEDF is located predominantly in the RPE cell layer of the retina, and levels are decreased in the sympathectomized retina. ELISA results illustrate that norepinephrine significantly increases PEDF secretion by RPE cells and propranolol slightly decreases PEDF secretion into RPE cell medium. In conclusion, down regulation of PEDF may contribute to the increased capillary density of the outer plexiform layer in the retina noted after sympathectomy. Furthermore, expression of PEDF was significantly increased after treatment of norepinephrine in RPE medium demonstrating a role of β-adrenergic regulation of PEDF. Since sympathetic nerves are damaged in diabetes and PEDF appears to be regulated by β-adrenergic receptors, these results suggest a role for sympathetic nerves in diabetic retinopathy. This knowledge, in turn, may be used for future treatment and prevention of diabetic retinopathy and other ocular diseases.