Iron is necessary in the retina for oxidative phosphorylation, membrane biogenesis and many other metabolic processes, but can also produce oxidative stress if improperly regulated, leading to cell death. Iron plays a significant role in retinal degeneration, as follows: 1) Iron toxicity causes retinal degeneration following direct entry of iron into the eye carried by an intraocular foreign body 2) Iron has been implicated in the RCS rats' retinal degeneration, in which the mechanism of iron overload is indirect. 3) Human AMD retinas have more iron than age-matched controls, suggesting that iron overload may play a role in AMD pathogenesis. 4) Inherited defects in iron metabolism result in retinal degeneration in Friedreich's ataxia, pantothenate kinase associated neuropathy, and aceruloplasminemia. The focus of the current proposal is to understand the functions in ocular iron homeostasis of the ferroxidases ceruloplasmin (Cp) and its homologue hephaestin (Heph).
In Aim 1, the retinal localization of Cp and Heph will be assessed.
In Aim 2, an RPE-specific Heph knockout will be generated. This will determine whether RPE Heph expression is necessary for RPE iron homeostasis. It should also provide a mouse model of retinal degeneration that like our Cp-/-Heph-/- mice, has subretinal neovascularization, but unlike Cp-/-Heph-/- mice, has a normal lifespan. In addition it will provide reagents for generating RPE-specific knockouts for the eye research community.
In Aim 3, the retinal degeneration in Cp-/-Heph-/- and Cp-/-RPE-specific Heph-/- mice will be characterized. Both oxidative stress and mechanisms of neovascularization will be studied.
In Aim 4 an RPE in vitro system will be used to determine whether Cp and Heph mediate RPE iron import or export, and assess the polarity of transport. These studies are important because: 1) The mechanism of retinal degeneration in aceruloplasminemia is not known. 2) The retinal functions of Cp and Heph are not known. 3) Our preliminary studies show that Cp-/-Heph-/- mice will provide a model for several features of AMD, including subretinal neovascularization. 4) These mice will provide a model of neurodegeneration caused by age-dependent increases in iron levels, which recent reports suggest may contribute to the pathogenesis of Alzheimer's and Parkinson's diseases and AMD. 5) These mice will provide the opportunity to test iron chelators and antioxidants as potential treatments/preventions for those age-related diseases.
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