Erythropoietin Protects Retinal Cells in Diabetic Rats Through Upregulating ZnT8 via Activating ERK Pathway and Inhibiting HIF-1α Expression

Abstract

PURPOSE: Zinc transporter 8 (ZnT8) was downregulated in hypoxic retina, which could be rescued by hypoxia-inducible factor-1α (HIF-1α) inhibition. Erythropoietin (EPO) protects retinal cells in diabetic rats through inhibiting HIF-1α as one of its mechanisms. We hence tried to explore the effect of EPO in regulating ZnT8 and protecting retinal cells in diabetic rats and possible mechanisms. METHODS: Diabetes was induced in Sprague-Dawley rats. Intravitreal injection of EPO was performed 1 month after diabetes onset. The CoCl2-treated rat Müller cell line (rMC-1) was cotreated with EPO, soluble EPO receptor (sEPOR), digoxin, or U0126. Cell viability, cell death, and intracellular zinc level were examined. The expression of ZnT8, HIF-1α, AKT, and ERK was studied. RESULTS: In diabetic rat retinas, EPO significantly decreased HIF-1α expression and increased ZnT8 expression. In CoCl2-treated rMC-1 cells, EPO increased cell viability and decreased intracellular zinc. Erythropoietin or digoxin could activate ERK pathway, downregulate HIF-1α, and upregulate ZnT8. The effect of EPO was abolished by sEPOR and U0126. Transient knockdown of ZnT8 increased intracellular zinc level, but not to a degree that would decrease cell viability or cause cell death. CONCLUSIONS: In diabetic retinas, EPO maintains zinc homeostasis through activating the ERK pathway and downregulating HIF-1α, and thus upregulating ZnT8 expression. This work proposed a possible new protective mechanism for EPO in, and indicated a potential target for, the treatment of diabetic retinopathy.