Accumulating evidence strongly implicates iron in the pathogenesis of aging and disease. Iron levels have been found to increase with age in both the human and mouse retinas. We and others have shown that retinal diseases such as age-related macular degeneration and diabetic retinopathy are associated with disrupted iron homeostasis, resulting in retinal iron accumulation. In addition, hereditary disorders due to mutation in one of the iron regulatory genes lead to age dependent retinal iron overload and degeneration. However, our knowledge on whether iron toxicity contributes to the retinopathy is limited. Recently, we reported that iron accumulation is associated with the upregulation of retinal and renal renin–angiotensin system (RAS). Evidences indicate that multiple genes/components of the RAS are targets of Wnt/β-catenin signaling. Interestingly, aberrant activation of Wnt/β-catenin signaling is observed in several degenerative diseases. In the present study, we explored whether iron accumulation regulates canonical Wnt signaling in the retina. We found that in vitro and in vivo iron treatment resulted in the upregulation of Wnt/β-catenin signaling and its downstream target genes including renin–angiotensin system in the retina. We confirmed further that iron activates canonical Wnt signaling in the retina using TOPFlash T-cell factor/lymphoid enhancer factor promoter assay and Axin2-LacZ reporter mouse. The presence of an iron chelator or an antioxidant reversed the iron-mediated upregulation of Wnt/β-catenin signaling in retinal pigment epithelial (RPE) cells. In addition, treatment of RPE cells with peroxisome proliferator-activated receptor (PPAR) α-agonist fenofibrate prevented iron-induced activation of oxidative stress and Wnt/β-catenin signaling by chelating the iron. The role of fenofibrate, an FDA-approved drug for hyperlipidemia, as an iron chelator has potentially significant therapeutic impact on iron associated degenerative diseases.

越来越多的证据表明铁与衰老和疾病的发病机制有关。已发现人类和小鼠视网膜中的铁含量随着年龄的增长而增加。我们和其他人已经表明，年龄相关性黄斑变性和糖尿病性视网膜病变等视网膜疾病与铁稳​​态紊乱有关，导致视网膜铁积累。此外，由于铁调节基因之一的突变导致的遗传性疾病导致年龄依赖性视网膜铁过载和退化。然而，我们关于铁毒性是否会导致视网膜病变的知识有限。最近，我们报道铁积累与视网膜和肾肾素-血管紧张素系统（RAS）的上调有关。有证据表明，RAS 的多个基因/成分是 Wnt/β-catenin 信号传导的目标。有趣的是，在几种退行性疾病中观察到 Wnt/β-catenin 信号的异常激活。在本研究中，我们探讨了铁积累是否调节视网膜中的典型 Wnt 信号。我们发现体外和体内铁处理导致 Wnt/β-catenin 信号及其下游靶基因（包括视网膜中的肾素-血管紧张素系统）上调。我们使用 TOPFlash T 细胞因子/淋巴增强因子启动子试验和 Axin2-LacZ 报告小鼠进一步证实，铁激活了视网膜中的经典 Wnt 信号传导。铁螯合剂或抗氧化剂的存在逆转了视网膜色素上皮 (RPE) 细胞中铁介导的 Wnt/β-连环蛋白信号传导的上调。此外，用过氧化物酶体增殖物激活受体 (PPAR) α-激动剂非诺贝特处理 RPE 细胞，通过螯合铁来防止铁诱导的氧化应激激活和 Wnt/β-连环蛋白信号传导。非诺贝特（一种 FDA 批准的高脂血症药物）作为铁螯合剂的作用对铁相关的退行性疾病具有潜在的显着治疗影响。