Abstract
Purpose :
Progressive loss of retinal endothelial cells is a central event in the pathogenesis of diabetic retinopathy. Activation of the unfolded protein response (UPR) in response to cell stress has been shown to critically regulate retinal inflammation and vascular leakage at early stages of the disease. In current study, we investigate the role of X-box binding protein 1 (XBP1), a major transcription factor of the UPR, in endothelial cell survival and retinal vascular degeneration in relation to aging and diabetes.
Methods :
Primary human retinal endothelial cells (HRECs) and mouse brain endothelial cells (BMECs) isolated from endothelial cell (EC)-specific XBP1 knockout (XBP1EC-/-) mice were used for in vitro study. ER stress, mitochondrial damage, ROS generation, anti-oxidant gene expression, glutathione peroxidase (Gpx) activity, and apoptosis were assessed in cells overexpressing or lacking active XBP1. In vivo, retinal vascular pathologies were evaluated in aged (15 month-old) and streptozotocin-induced diabetic XBP1EC-/- and control mice.
Results :
In HRECs blockade of XBP1 activation by pharmacological inhibitor exacerbated ER stress- or high glucose- induced apoptosis. In BMECs conditional deletion of XBP1 gene resulted in impaired cell proliferation and migration, and amplifed apoptosis under high glucose condition. Coincidently, XBP1-negative BMECs manifested reduced mitochondrial membrane potential, increased superoxide generation and lipid peroxidation, decreased Gpx gene expression and activity, and reduced level of glutathione. These changes were significantly reversed by treatment with adenovirus expressing active XBP1. In vivo, aged and diabetic XBP1EC-/- mice showed increased acellular capillary formation, reduced EC number, and less vascular density compared to the corresponding wildtype controls.
Conclusions :
These findings suggest an essential role of XBP1 in retinal endothelial cell survival through coordinating the ER and mitochondrial responses to cell stress. Therefore, enhancing the function of XBP1 and its downstream anti-apoptotic pathways may provide novel therapeutic approaches to prevention of vascular damage in diabetic retinopathy and age-related retinal diseases.
This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.