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Guo-Tong Xu, Daohuan Kang, Jingfa Zhang, Lixia Lu, Haibin Tian, Weiye Li, Guoxu Xu; EPO maintains zinc homeostasis by upregulation of zinc transporter 8 (ZnT8) in diabetic rats. Invest. Ophthalmol. Vis. Sci. 2015;56(7 ):5193.
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© ARVO (1962-2015); The Authors (2016-present)
Zinc ion is an essential cofactor for normal cell function, the zinc transporters play a crucial role in zinc homeostasis. This study is to explore the regulation of erythropoietin (EPO) on zinc transporter 8 (ZnT8) in diabetic rats
Diabetes was induced by intraperitoneal injection of streptozotocin in Sprague-Dawley rats. Four days after intravitreal injection of EPO, the retinas were harvested for detection. The rat Muller cell line (rMC-1) was treated by cobalt chloride (CoCl2) with or without EPO. The changes of HIF-1α, VEGF, ZnT8, phosphor-ERK and ERK were detected with real-time PCR, Western blot and immunofluorescence.
In 4-week diabetic rat retinas, the expression of HIF-1α was up-regulated, while ZnT8 was down-regulated; intravitreal injection of EPO could down-regulate HIF-1α and up-regulated ZnT8 expressions. Retinal HIF-1α was increased at both transcriptional (increased by 23%) and translational (1.7-fold) levels, which were down-regulated by16% (mRNA) and 71% (protein), respectively, by EPO. For ZnT8, the mRNA level and total protein were decreased by 32% (n=5, p=0.002) and 30% (n=5, p=0.0014), separately, in diabetic rat retinas, which were increased by 23% (n=5, p=0.02) and 29% (n=6, p=0.025), separately, by EPO. Membrane protein of ZnT8 protein was significantly decreased by 62% in diabetic rat retinas and was increased by EPO (63%, n=3, p=0.025). The changes of HIF-1α and ZnT8, as well as EPO’s effect on them, were confirmed in CoCl2-treated rMC-1 cells. In CoCl2-treated rMC-1 cells, the ratio of pERK/ERK was decreased by about 40%, and EPO could increase this ratio to normal level. This effect was abolished with ERK inhibitor U0126. The immunofluorescence result showed that rMC-1 expressed ZnT8 both in cytoplasm and cell membrane.
The present data indicated that intravitreal injection of EPO could increase ZnT8 expression in diabetic rat retina possible through its regulation of ERK and HIF-1α pathway.
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