Effect of pigment epithelium-derived factor on glutamate uptake in retinal Muller cells under high-glucose conditions

A predominant function of Müller cells is to regulate glutamate levels, but it is compromised in diabetic retinopathy (DR). The present study was performed to determine the role of pigment epithelium-derived factor (PEDF) in glutamate uptake in retinal Müller cells in high-glucose conditions.

The levels of Kir4.1, PEDF, and GLAST in retinal Müller cells in high-glucose conditions were analyzed by Western blot analysis and real-time RT-PCR, and a glutamate uptake assay was undertaken to investigate the activity of GLAST. Intracellular reactive oxygen species (ROS) generation was measured, and a glutathione peroxidase (GPx) activity assay was performed to determine oxidative stress in the presence of high glucose. After being treated with PEDF in high-glucose conditions, these proteins (Kir4.1 and GLAST) and their mRNAs, glutamate uptake activity, and oxidative stress in Müller cells were investigated. A PEDF siRNA method was used to confirm the effect of PEDF on glutamate uptake activity in Müller cells.

In high-glucose conditions, glutamate uptake and Kir4.1, PEDF, and GLAST expression in Müller cells decreased significantly. Simultaneously, ROS generation increased, and GPx activity decreased. PEDF treatment inhibited the high-glucose-induced decreases in glutamate uptake and in Kir4.1 and GLAST expression and ameliorated oxidative stress. Moreover, downregulation of PEDF expression by siRNA in Müller cells resulted in decreases in glutamate uptake, Kir4.1 and GLAST expression, and induced oxidative stress.

These findings suggest that PEDF acts as an antioxidative agent against the decrease in Kir4.1 and GLAST expression and compromise of glutamate uptake activity in retinal Müller cells in diabetic conditions.