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Kelly Donovan, Oleg Alekseev, Jane Azizkhan-Clifford; Role of Sp1 transcription factor in the pathogenesis of diabetic retinopathy. Invest. Ophthalmol. Vis. Sci. 2013;54(15):5605. doi: https://doi.org/.
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Proangiogenic factors VEGF-A (vascular endothelial growth factor A) and Cyr61 (cysteine-rich angiogenic inducer 61) contribute to neovascularization in diabetic retinopathy. The promoters of these genes are responsive to the transcription factor Sp1 (specificity protein 1). This study investigated the effects of hyperglycemia on Sp1-mediated expression of VEGF-A and Cyr61 in the retinal endothelium and pigment epithelium. Characterization of Sp1’s participation in the pathogenesis of this disease will promote identification of novel therapeutic targets.
Hyperglycemia-exposed ARPE-19 (human retinal pigment epithelial cells) and TR-iBRB (rat retinal microendothelial cells) were assayed for levels of VEGF-A and Cyr61 by RT-qPCR,Western blot, and tubule formation. VEGF-A and Cyr61 levels were measured in cells depleted of Sp1 by shRNA. Chromatin immunoprecipitation was used to assess levels of Sp1 bound to the VEGF-A and Cyr61 promoter. VEGF-A promoter driving the luciferase gene was used to directly measure changes in Sp1’s transcriptional activity in response to hyperglycemia.
Hyperglycemic treatment resulted in increased VEGF-A and Cyr61transcript and protein expression in ARPE-19 and TR-iBRB cells. Sp1 depletion significantly abrogated these glucose-induced changes in both cell types, while minimally affecting basal expression. ChIP analysis showed that glucose raised the amount of promoter-bound Sp1 for both genes. Knock down of Sp1 reduced VEGF-A promoter activity in cells treated with high glucose.
VEGF-A and Cyr61 are upregulated in ARPE-19 and TR-iBRB with hyperglycemia. An increased amount of Sp1 was bound to these genes’ promoters with high glucose treatment, and depletion of Sp1 significantly reduced their aberrant expression. Sp1 may significantly participate in the pathogenesis of diabetic retinopathy through expression of these proangiogenic genes.
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