Increased O-GlcNAcylation of NF-kappa B Enhances Retinal Ganglion Cell Death in Streptozotocin-induced Diabetic Retinopathy

Abstract

Purpose: Hyperglycemia results in increased flux through the hexoxamine biosynthetic pathway. We examined whether hyperglycemia increases O-GlcNAcylation in the diabetic retina and whether elevated O-GlcNAcylation of nuclear factor (NF)-kappa B increases apoptosis of retinal ganglion cells (RGCs) in diabetic retinopathy (DR). Materials and methods: Diabetes was induced in C57BL/6 mice by five consecutive intraperitoneal injections of 55 mg/kg streptozotocin. All mice were killed 2 months after injections and expression levels of O-GlcNAcylated proteins, O-linked N-acetylglucosamine transferase (OGT), beta-D-N-acetylglucosaminidase and NF-kappa B, and the extent of RGC death were examined. Immunoprecipitations were performed to investigate whether O-GlcNAcylation of NF-kappa B led to its activation and RGC death in DR. Results: The expression levels of O-GlcNAcylated proteins and OGT were markedly higher in diabetic retinas than in control retinas. OGT colocalized with NeuN, a RGC-specific marker, and terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling-positive cells in the ganglion cell layer of diabetic retinas. The p65 subunit of NF-kappa B was O-GlcNAcylated and the level of O-GlcNAcylated p65 was higher in diabetic retinas than in control retinas. Conclusion: The present data suggest that hyperglycemia increases O-GlcNAcylation in DR and that O-GlcNAcylation of the p65 subunit of NF-kappa B is involved in hyperglycemia-induced NF-kappa B activation and RGC death in DR.