PURPOSE The avascular cornea, trabecular meshwork (TM), and lens obtain iron, an essential biometal, from the aqueous humor (AH). The mechanism by which this exchange is regulated, however, is unclear. Recently we reported that non-pigmented ciliary epithelial cells express ferroportin (Fpn) (Ashok, 2018b), an iron export protein modulated by hepcidin, the master regulator of iron homeostasis secreted mainly by the liver. Here, we explored whether ciliary epithelial and other cells in the anterior segment synthesize hepcidin, suggesting local regulation of iron exchange at this site. METHODS Human and bovine eyes were dissected to isolate the ciliary body (CB), corneal endothelial (CE), TM, lens epithelial (LE), and outer epithelial cell layer of the iris. Total mRNA and protein lysates were processed to evaluate the synthesis and expression of hepcidin, the iron regulatory peptide hormone, Fpn, the only known iron export protein, ceruloplasmin (Cp), a ferroxidase necessary for iron export, transferrin receptor (TfR), a major iron uptake protein, and ferritin, a major iron storage protein. A combination of techniques including reverse transcription polymerase chain reaction (RT-PCR) of total mRNA, Western blotting of protein lysates, and immunofluorescence of fixed tissue sections were used to accomplish these goals. RESULTS RT-PCR of isolated tissue samples revealed hepcidin-specific mRNA in the CB, TM, CE, and LE of the bovine eye. Western blotting of protein lysates from these tissues showed reactivity for hepcidin, Fpn, ferritin, and TfR. Western blotting and immunohistochemistry of similar tissues isolated from cadaveric human eyes showed expression of hepcidin, Fpn, and Cp in these samples. Notably, Fpn and Cp were expressed on the basolateral membrane of non-pigmented ciliary epithelial cells, facing the AH. CONCLUSIONS Synthesis and expression of hepcidin and Fpn in the ciliary epithelium suggests local regulation of iron transport from choroidal plexus in the ciliary body to the AH across the blood-aqueous barrier. Expression of hepcidin and Fpn in CE, TM, and LE cells indicates additional regulation of iron exchange between the AH and cornea, TM, and lens, suggesting autonomous regulation of iron homeostasis in the anterior segment. Physiological and pathological implications of these observations are discussed.

中文翻译：

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眼前段铁调素的局部合成：具有生理和病理意义的新观察。

目的 无血管角膜、小梁网 (TM) 和晶状体从房水 (AH) 中获取铁（一种必需的生物金属）。然而，这种交易所的监管机制尚不清楚。最近我们报道，非色素性睫状上皮细胞表达铁转运蛋白（Fpn）（Ashok，2018b），这是一种由铁调素调节的铁输出蛋白，铁调素是主要由肝脏分泌的铁稳态的主要调节剂。在这里，我们探讨了眼前段的睫状上皮和其他细胞是否合成铁调素，这表明该部位铁交换的局部调节。方法 解剖人和牛眼，分离睫状体（CB）、角膜内皮（CE）、TM、晶状体上皮（LE）和虹膜外上皮细胞层。对总 mRNA 和蛋白裂解物进行处理，以评估铁调素（铁调节肽激素）、Fpn（唯一已知的铁输出蛋白）、铜蓝蛋白 (Cp)（铁输出所需的亚铁氧化酶）、转铁蛋白受体 (TfR)、铁调素 (铁调节肽激素) 的合成和表达。主要的铁吸收蛋白和铁蛋白，一种主要的铁储存蛋白。结合使用总 mRNA 的逆转录聚合酶链式反应 (RT-PCR)、蛋白质裂解物的蛋白质印迹和固定组织切片的免疫荧光等技术来实现这些目标。结果 分离组织样本的 RT-PCR 显示牛眼 CB、TM、CE 和 LE 中存在铁调素特异性 mRNA。这些组织的蛋白质裂解物的蛋白质印迹显示对铁调素、Fpn、铁蛋白和 TfR 具有反应性。从人眼尸体中分离出的类似组织的蛋白质印迹和免疫组织化学显示，这些样本中表达了铁调素、Fpn 和 Cp。值得注意的是，Fpn 和 Cp 在面向 AH 的非色素性睫状上皮细胞的基底外侧膜上表达。结论 睫状体上皮中铁调素和 Fpn 的合成和表达表明，铁从睫状体脉络丛穿过血水屏障到 AH 的运输受到局部调节。CE、TM 和 LE 细胞中铁调素和 Fpn 的表达表明 AH 与角膜、TM 和晶状体之间铁交换的额外调节，表明眼前节铁稳态的自主调节。讨论了这些观察结果的生理学和病理学意义。