Immunolocalization and regulation of iron handling proteinsferritin and ferroportin in the retina

[摘要] Purpose: CNS iron accumulation is associated with severalneurodegenerative diseases, including age-related macular degeneration.Intracellular overload of free iron is prevented, in part, by the ironexport protein, ferroportin, and the iron storage protein, ferritin. Thepurpose of this study was to assess retinal localization and regulationof ferroportin and ferritin.Methods: Normal murine retinas were analyzed by immunohistochemistryto localize ferroportin, cytosolic ferritin, and mitochondrial ferritin,with double-labeling using cell-specific markers to identify cell types.Retinas deficient in the ferroxidases, ceruloplasmin and hephaestin,accumulate iron in their retinas and RPE, while retinas deficient iniron regulatory proteins (IRPs) lack the ability to regulate severalproteins involved in iron metabolism; retinas from these knockout micealong with their age matched wild type littermates were also examined tostudy regulation of ferritin and ferroportin. To enable visualization oflabel in the retinal pigment epithelial cells, sections from pigmentedmice were bleached with H2O2 prior to IHC, a novel use ofthis technique for study of the RPE.Results: In normal retinas, cytosolic ferritins were foundpredominantly in rod bipolar cells and photoreceptors. Ferroportin wasfound in RPE and Müller cells. Iron accumulation in mice deficient inceruloplasmin and hephaestin was associated with upregulation offerritin and ferroportin. Mice deficient in IRPs showed upregulation offerritin and ferroportin, likely because of their inability to represstranslation.Conclusions: Normal retinas contain ferritin and ferroportin, whoselevels are regulated by iron-responsive, iron regulatory proteins.Ferroportin colocalizes with ceruloplasmin and hephaestin to RPE andMüller cells, supporting a potential cooperation between theseferroxidases and the iron exporter. Cytosolic ferritin accumulates inrod bipolar synaptic terminals, suggesting that ferritin may be involvedin axonal iron transport. Mitochondrial ferritin increases with ironaccumulation, suggesting a role in iron storage.

[学科分类] 生物化学/生物物理