Pigment Epithelium-Derived Factor Regulates Glutamine Synthetase and l-Glutamate/l-Aspartate Transporter in Retinas with Oxygen-induced Retinopathy

Abstract

Purpose: A predominant function of Müller cells is to regulate glutamate levels, but these cells are compromised in oxygen-induced retinopathy. The aim of this study was to investigate the role of pigment epithelium-derived factor (PEDF) in regulating glutamate levels in retina under hypoxia.Materials and methods: One-week-old C57BL/6J mice were exposed to 75% oxygen for 5 days and then kept in room air for another 5 days to establish the oxygen-induced retinopathy (OIR) mouse model. Mice received intravitreous injections of 2 μg PEDF or vehicle on postnatal (P)12 and P14, respectively. Antibody against interleukin-1Beta (IL-1β) (IL-1ab) was used to neutralize the activity of IL-1β, mice received intravitreous injections of 500 ng IL-1ab or vehicle on P12 and P14, respectively, too. At P17, the mice were euthanized and their eyes were enucleated. The expression levels of IL-1β, glutamine synthetase (GS) and l-glutamate/l-aspartate transporter (GLAST) in retinas with different treatments were detected. In addition, wild-type C57BL/6J mice received intravitreous injections of IL-1β or PEDF. After 24 h, the expression of GS and GLAST in the retinas was also detected. Furthermore, high-performance liquid chromatography (HPLC) was performed to determine the glutamate concentrations in retinas with different treatments.Results: The expression of IL-1β and levels of glutamate were increased in retinas with OIR, while the expression of GS and GLAST was decreased. Administration of PEDF ameliorated the characteristic changes in retinas of OIR mice. And neutralization of IL-1β by administration of IL-1ab increased GS and GLAST expression in retinas with OIR. Moreover, the effects of IL-1β on GS and GLAST expression and unbalanced glutamate levels were inhibited after receiving intravitreous injections of PEDF in retinas of normal mice.Conclusions: These results suggested that PEDF might up-regulate GS and GLAST expression and decrease glutamate levels by suppressing the role of IL-1β as an anti-inflammatory factor under hypoxia, and these functions may underlie the neuroprotective effects of PEDF.