Pigment epithelium-derived factor exerts neuroprotection in oxygen-induced retinopathy by targeting endoplasmic reticulum stress and oxidative stress

Endoplasmic reticulum (ER) stress and oxidative stress have been involved in the occurrence of neuronal apoptosis in ischemic retinopathy. Pigment epitheliu-derived factor (PEDF) is well known for its multifunctional properties, including neuroprotection, anti-inflammation and antioxidant. However, the association between PEDF and ER stress or oxidative stress in ischemic retinopathy remain incompletely understood. In this study, the concentration of the key factor of ER stress C/EBP homologous protein (CHOP) in aqueous humor (AqH) and vitreous samples of proliferative diabetic retinopathy (PDR) patients were measured by ELISA assays. Oxygen-induced retinopathy (OIR) mice model was established and PEDF intravitreal injections were conducted. Primary bone marrow derived macrophages (BMDMs) were isolated and cultured under hypoxic conditions in vitro. Western blotting, real-time RT-PCR, immunofluorescence, transmission electron microscopy (TEM), TUNEL assays were performed to explore roles of PEDF on ER stress and oxidative stress, as well as subsequently neuronal apoptosis under hypoxic conditions in vivo and in vitro. The results revealed that ER stress and oxidative stress were notably activated under hypoxic conditions. We also observed that hypoxia evoked ultrastructural damage of ER and mitochondrion in the retina. However, PEDF significantly prevented ER stress and oxidative stress, as well as the damage of ultrastructure, resulting in diminution of photoreceptor apoptosis in OIR retinas. These results indicate that PEDF may play its neuroprotection role through inhibiting ER stress and oxidative stress in ischemic retinopathy, which is a novel molecular mechanism of PEDF protecting photoreceptors from ischemic damage, thereby suggesting that PEDF is an effective therapeutic agent for the treatment of neuron damage in ischemic retinal diseases.