Sterling Jacob, Guttha Samyuktha, Song Ying, Song Delu, Hadziahmetovic Majda, Dunaief Joshua L
F.M. Kirby Center for Molecular Ophthalmology, Scheie Eye Institute, Perelman School of Medicine at the University of Pennsylvania, 305 Stellar-Chance Laboratory, 422 Curie Blvd, Philadelphia, PA 19104, USA.
Exp Eye Res. 2017 Feb;155:15-23. doi: 10.1016/j.exer.2016.12.008. Epub 2017 Jan 3.
Intracellular retinal iron accumulation has been implicated in the pathogenesis of age-related macular degeneration (AMD), the leading cause of irreversible blindness among individuals over the age of 50. Ceruloplasmin/hephaestin double knockout mice (Cp/Heph DKO) and hepcidin knockout mice (Hepc KO) accumulate retinal iron and model some features of AMD. Two canonical pathways govern cellular iron import - transferrin-bound iron import and non-transferrin bound iron import. In Cp/Heph DKO and Hepc KO iron-loaded retinas, transferrin-bound iron import is downregulated. Despite this effort to reduce cellular iron burden, iron continues to accumulate in these retinas in an age-dependent manner. Quantitative RT-PCR and Western analysis were used to quantify the expression of three ferrous iron importers, Dmt1, Zip8, and Zip14, in wild-type (Wt), Cp/Heph DKO, and Hepc KO retinas. Zip8 and Zip14 protein levels were analyzed using Western analysis in mice injected intravitreally with either apo- or holo-transferrin to elucidate one possible mechanism of Zip14 regulation in the retina. Both zip8 and zip14 were expressed in the mouse retina. Paradoxically, protein levels of non-transferrin bound iron importers were upregulated in both Cp/Heph DKO and Hepc KO retinas. Intravitreal holo-transferrin injection decreased Zip 14 protein levels. These data indicate that Zip8 and Zip14 may take up increasing amounts of non-transferrin bound iron in these two mouse models of retinal iron accumulation. Their upregulation in these already iron-loaded retinas suggests a vicious cycle leading to toxicity.
细胞内视网膜铁蓄积与年龄相关性黄斑变性（AMD）的发病机制有关，AMD是50岁以上人群不可逆失明的主要原因。铜蓝蛋白/亚铁氧化酶双敲除小鼠（Cp/Heph DKO）和铁调素敲除小鼠（Hepc KO）会蓄积视网膜铁，并呈现出AMD的一些特征。有两条经典途径调控细胞铁的摄入——转铁蛋白结合铁的摄入和非转铁蛋白结合铁的摄入。在Cp/Heph DKO和Hepc KO铁过载的视网膜中，转铁蛋白结合铁的摄入下调。尽管有减少细胞铁负荷的这种作用，但铁仍以年龄依赖性方式在这些视网膜中持续蓄积。采用定量逆转录聚合酶链反应（RT-PCR）和蛋白质免疫印迹分析来量化野生型（Wt）、Cp/Heph DKO和Hepc KO视网膜中三种亚铁离子转运体Dmt1、Zip8和Zip14的表达。通过蛋白质免疫印迹分析对玻璃体内注射脱铁转铁蛋白或全铁转铁蛋白的小鼠的Zip8和Zip14蛋白水平进行分析，以阐明视网膜中Zip14调控的一种可能机制。Zip8和Zip14均在小鼠视网膜中表达。矛盾的是，非转铁蛋白结合铁转运体的蛋白水平在Cp/Heph DKO和Hepc KO视网膜中均上调。玻璃体内注射全铁转铁蛋白会降低Zip14蛋白水平。这些数据表明，在这两种视网膜铁蓄积的小鼠模型中，Zip8和Zip14可能摄取越来越多的非转铁蛋白结合铁。它们在这些已经铁过载的视网膜中的上调提示存在导致毒性的恶性循环。
