Iron-induced oxidative stress can cause or exacerbate retinal degenerative diseases. Retinal iron overload has been reported in several mouse disease models with systemic or neural retina-specific knockout (KO) of homologous ferroxidases ceruloplasmin (Cp) and hephaestin (Heph). Cp and Heph can potentiate ferroportin (Fpn) mediated cellular iron export. Here, we used retina-specific Fpn KO mice to test the hypothesis that retinal iron overload in Cp/Heph DKO mice is caused by impaired iron export from neurons and glia. Surprisingly, there was no indication of retinal iron overload in retina-specific Fpn KO mice: the mRNA levels of transferrin receptor in the retina were not altered at 7-10-months age. Consistent with this, levels and localization of ferritin light chain were unchanged. To "stress the system", we injected iron intraperitoneally into Fpn KO mice with or without Cp KO. Only mice with both retina-specific Fpn KO and Cp KO had modestly elevated retinal iron levels. These results suggest that impaired iron export through Fpn is not sufficient to explain the retinal iron overload in Cp/Heph DKO mice. An increase in the levels of retinal ferrous iron caused by the absence of these ferroxidases, followed by uptake into cells by ferrous iron importers, is most likely necessary.

Department of Ophthalmology The 2nd Hospital of Jilin University No 218 Ziqiang Street Changchun Jilin China

Department of Ophthalmology The 2nd Hospital of Jilin University No 218 Ziqiang Street Changchun Jilin China; 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 USA

Department of Physiology Anatomy and Genetics University of Oxford Oxford United Kingdom

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 USA

Institute of Molecular Genetics Academy of Sciences of the Czech Republic Prague Czech Republic

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Conditional knockout of hephaestin in the neural retina disrupts retinal iron homeostasis