ASK1 induces retinal microvascular endothelial cell apoptosis through ER stress-associated pathway

Diabetic retinopathy (DR) is a major microvascular complication in patients with diabetes mellitus; it can cause a variety of eye problems in a high percentage of diabetic patients. The purpose of this study was to determine the role of apoptosis signal-regulating kinase 1 (ASK1) in the regulation of the endoplasmic reticulum (ER) stress-associated apoptosis pathway in microvascular endothelial cells. For in vivo studies, a streptozotocin (STZ)-induced diabetes model was used to assess apoptosis in retinal tissues. Apoptotic cell death was determined by TUNEL assay. For in vitro studies, a high glucose (HG)-induced retinal microvascular endothelial cell injury model was generated to evaluate apoptosis. Apoptotic rates were measured by flow cytometry and apoptosis-related proteins were detected by western blotting. We found that retinal microvascular endothelial cell apoptosis was increased in both animal and cell models. HG-induced apoptosis primarily occurred in an ER stress-dependent manner. HG-induced apoptosis was alleviated by inhibiting ASK1 with shRNA or a specific inhibitor, NQDI-1. TUNEL and western blot assays showed that ASK1 promoted the expression of ER stress-related proteins that are the master regulators of DR. Our study suggests that ASK1 functions as a promoter of DR through the ER stress-induced apoptosis pathway, and it may be a therapeutic target for DR.