High-Mobility Group Box-1 Modulates the Expression of Inflammatory and Angiogenic Signaling Pathways in Diabetic Retina

PURPOSE: The expression of high-mobility group box-1 (HMGB1) is upregulated in epiretinal membranes and vitreous fluid from patients with proliferative diabetic retinopathy and in the diabetic retina. HMGB1 mediates inflammation, breakdown of the blood-retinal barrier and apoptosis in the diabetic retina. Here, we investigated inflammatory and angiogenic signaling pathways activated by HMGB1 in diabetic retina. METHODS: Human retinal microvascular endothelial cells (HRMEC) and retinas from 1-month diabetic rats and normal rats intravitreally injected with HMGB1 were studied using RT-PCR, Western blot analysis and co-immunoprecipitation. We also studied the effect of the HMGB1 inhibitor glycyrrhizin on diabetes-induced biochemical changes in the retina. RESULTS: Diabetes and intravitreal injection of HMGB1 in normal rats induced significant upregulation of the mRNA levels of the chemokine stromal cell-derived factor-1 (SDF-1/CXCL12) receptor CXCR4 and protein levels of hypoxia-inducible factor-1α, early growth response-1, tyrosine kinase 2 and the CXCL12/CXCR4 chemokine axis. Constant glycyrrhizin intake from onset of diabetes did not affect the metabolic status of the diabetic rats, but it restored these increased mediators to control values. Stimulation of HRMEC with HMGB1 and intraviteral injection of HMGB1 significantly increased the expression of vascular endothelial growth factor (VEGF) and VEGF receptor-2. Co-immunoprecipitation studies showed that diabetes increased the interaction between CXCL12 and CXCR4 and between HMGB1 and receptor for advanced glycation end products (RAGE), but not between HMGB1 and the CXCL12/CXCR4 chemokine axis. CONCLUSIONS: Our findings suggest that HMGB1 activates inflammatory and angiogenic signaling pathways in diabetic retina mediated by RAGE.