The IL-6 Induced Retinal Iron Sequestration Response

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PROJECT SUMMARY Iron plays a critical role in both the healthy and diseased retina. The long term goals of the proposed studies are to understand how inflammation associated with retinal disease promotes iron dysregulation, and discover how to protect against retinal iron toxicity. Iron is necessary in the retina for mitochondrial energy production, membrane synthesis and the visual cycle, but becomes a central producer of oxidative stress when improperly regulated. Iron toxicity is evident in retinal disease as follows: 1) Iron causes rapid retinal degeneration following entry into the eye carried by an intraocular foreign body. 2) Human AMD retinas have more iron than age-matched controls, suggesting that iron overload may play a role in AMD pathogenesis. 3) Consistent with this hypothesis, in the inherited disease aceruloplasminemia, loss of the ferroxidase ceruloplasmin (Cp) results in retinal iron accumulation and early onset macular degeneration. 4) Mice with knockout for Cp and its homolog hephaestin (Heph) have an age-dependent retinal iron overload and degeneration sharing features of AMD, including complement activation and subretinal neovascularization (which causes wet AMD). Recent evidence from non-ocular cells indicates that interleukin 6 (IL-6) can trigger a “cellular iron sequestration response” to prevent microbes from accessing the iron they need for growth and replication. This, combined with the finding of elevated intraocular and serum IL-6 levels in AMD, suggest that IL-6 may promote retinal iron overload in AMD. Experiments proposed herein will utilize human iPSC-RPE cell culture, mouse models, and post mortem human tissue to define the IL-6 retinal iron sequestration response. An inhibitor of the IL-6 trans-signaling pathway will be tested. Following activation or inhibition of IL-6 pathways, changes in the levels of iron and its transporters will be assessed. These changes will be correlated with those in AMD versus normal post mortem retinas. It is expected that these studies will lead to development of novel anti-AMD approaches that diminish inflammation-induced iron accumulation.