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T. Zhou, K. Zhou, G. Gao, J. Ma; Lipid Peroxidation Products--A New Activator of the Canonical Wnt Pathway. Invest. Ophthalmol. Vis. Sci. 2010;51(13):5961.
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We have shown previously that the Wnt signaling pathway plays pathogenic roles in diabetic retinopathy and age-related macular degeneration. The purpose of this study is to investigate the causative role of oxidative stress in the canonical Wnt pathway activation.
Cultured ARPE19 cells derived from human RPE and bovine retinal capillary endothelial cells (BRCEC) were treated with a lipid peroxidation product, 4-hydroxynonenal (HNE) and an antioxidant, N-Acetyl-Cysteine (NAC). The activation of the canonical Wnt pathway was measured by TOPFLASH assay, an activity assay for luciferase reporter driven by a promoter with TCF/β-catenin-binding sites and by Western blot analysis of Wnt pathway components and target genes. In vivo, rats with streptozotocin-induced diabetes were treated by NAC in drinking water for 8 weeks. Levels of Wnt pathway components and target genes in the eyecups were measured by Western blot analysis. Oxidative stress in the retina was evaluated by immunostaining of 3-nitrotyrosine, a marker of oxidative stress.
Levels of phosphorylated and total LRP6, a co-receptor of Wnts and totoal β-catenin, a Wnt effector, were significantly increased by HNE. Similarly, TOPFLASH activity and expression of connected tissue growth factor (CTGF), a Wnt target gene, were also up-regulated by HNE. NAC blocked the Wnt activation induced by HNE, suggesting the Wnt pathway activation was induced by oxidative stress. In diabetic rats, HNE and 3-nitrotyrosine immunosignal were more intensive the retina, compared to that of non-diabetic rats, suggesting an increase in oxidative stress. Retinal levels of total LRP6, β-catenin and CTGF were significantly increased in diabetic rats and reduced by the NAC treatment.
Lipid peroxidation products activated the canonical Wnt pathway through oxidative stress, which plays an important role in the development of retinal diseases.
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