Yefimova M G, Jeanny J C, Guillonneau X, Keller N, Nguyen-Legros J, Sergeant C, Guillou F, Courtois Y
Sechenov Institute of Evolutionary Physiology and Biochemistry, Russian Academy of Sciences, St. Petersburg.
Invest Ophthalmol Vis Sci. 2000 Jul;41(8):2343-51.
The retina and other tissues need iron to survive. However, the normal iron metabolism in rodent retinas had not been characterized. This study was intended to investigate iron and iron homeostasis protein (ferritin, transferrin [Tf] and transferrin receptor [Tf-R]) distribution in 20- to 55-day-old rat retinas.
Iron was revealed on retinal sections directly by proton-induced x-ray emission (PIXE) and indirectly by electron microscopy (EM). Ferritin, Tf, and Tf-R proteins were localized by immunohistochemistry. Transferrin expression was localized by in situ hybridization (ISH). Transferrin and ferritin proteins and mRNA were analyzed by Western blot analysis and reverse transcription-polymerase chain reaction (RT-PCR), respectively.
Iron is widely and unevenly distributed throughout the adult rat retina. The highest concentration was observed by PIXE in the choroid and the retinal pigmented epithelial cell (RPE) layer, and in inner segments of photoreceptors (IS). Outer segments of photoreceptors (OS) also contain iron. EM studies suggested the presence of iron inclusions inside the photoreceptor discs. Choroid, RPE, and IS showed a strong immunoreactivity for ferritin. Transferrin accumulated mainly in the IS and OS areas and in RPE cells but can also be detected slightly in retinal capillaries. Western blot analysis for Tf and ferritin confirmed their presence in the adult neural retina. By RT-PCR, H- and L-chains of ferritin and Tf mRNAs were expressed in neural retina, but the main sites of Tf synthesis observed by ISH were the RPE and choroid cell layers. Tf-R immunoreactivity was detected in the ganglion cell layer, inner nuclear layer, outer plexiform layer, IS, RPE, and choroid. These results were similar for all stages studied.
For the first time, the present study characterized both iron and iron homeostasis proteins in rodent retinas. In the outer retina, iron and ferritin shared the same distribution patterns. In contrast, Tf, mainly synthesized by RPE cells and detected in OS and IS areas, probably helps to transport iron to photoreceptors through their Tf-R. This is a likely pathway for filling iron needs in the outer retina.
视网膜和其他组织需要铁来维持生存。然而，啮齿动物视网膜中的正常铁代谢尚未得到表征。本研究旨在调查20至55日龄大鼠视网膜中铁和铁稳态蛋白（铁蛋白、转铁蛋白[Tf]和转铁蛋白受体[Tf-R]）的分布。
通过质子诱导X射线发射（PIXE）直接在视网膜切片上显示铁，并通过电子显微镜（EM）间接显示。通过免疫组织化学对铁蛋白、Tf和Tf-R蛋白进行定位。通过原位杂交（ISH）对转铁蛋白表达进行定位。分别通过蛋白质印迹分析和逆转录-聚合酶链反应（RT-PCR）分析转铁蛋白和铁蛋白的蛋白质及mRNA。
铁在成年大鼠视网膜中广泛且不均匀地分布。通过PIXE观察到脉络膜和视网膜色素上皮细胞（RPE）层以及光感受器内段（IS）中的铁浓度最高。光感受器外段（OS）也含有铁。EM研究表明在光感受器盘内存在铁包涵体。脉络膜、RPE和IS对铁蛋白显示出强烈免疫反应性。转铁蛋白主要积聚在IS和OS区域以及RPE细胞中，但在视网膜毛细血管中也可轻微检测到。对Tf和铁蛋白的蛋白质印迹分析证实了它们在成年神经视网膜中的存在。通过RT-PCR，铁蛋白的H链和L链以及Tf mRNA在神经视网膜中表达，但ISH观察到的Tf合成主要部位是RPE和脉络膜细胞层。在神经节细胞层、内核层、外网状层、IS、RPE和脉络膜中检测到Tf-R免疫反应性。在所有研究阶段，这些结果都是相似的。
本研究首次对啮齿动物视网膜中的铁和铁稳态蛋白进行了表征。在外视网膜中，铁和铁蛋白具有相同的分布模式。相比之下，主要由RPE细胞合成并在OS和IS区域检测到的Tf，可能通过其Tf-R帮助将铁转运至光感受器。这可能是满足外视网膜铁需求的一条途径。
