Expression patterns of iron regulatory proteins after intense light exposure in a cone-dominated retina.

Iron is implicated in ocular diseases such as in age-related macular degeneration. Light is also considered as a pathological factor in this disease. Earlier, two studies reported the influence of constant light environment on the pattern of expressions of iron-handling proteins. Here, we aimed to see the influence of light in 12-h light-12-h dark (12L:12D) cycles on the expression of iron-handling proteins in chick retina. Chicks were exposed to 400 lx (control) and 5000 lx (experimental) light at 12L:12D cycles and sacrificed at variable timepoints. Retinal ferrous ion (Fe) level, ultrastructural changes, lipid peroxidation level, immunolocalization and expression patterns of iron-handling proteins were analysed after light exposure. Both total Fe level (p = 0.0004) and lipid peroxidation (p = 0.002) significantly increased at 12-, 48- and 168-h timepoint (for Fe) and 48- and 168-h timepoint (for lipid peroxidation), and there were degenerative retinal changes after 168 h of light exposure. Intense light exposure led to an increase in the levels of transferrin and transferrin receptor-1 (at 168-h) and ferroportin-1, whereas the levels of ferritins, hephaestin, (at 24-, 48- and 168-h timepoint) and ceruloplasmin (at 168-h timepoint) were decreased. These changes in iron-handling proteins after light exposure are likely due to a disturbance in the iron storage pool evident from decreased ferritin levels, which would result in increased intracellular Fe levels. To counteract this, Fe is released into the extracellular space, an observation supported by increased expression of ferroportin-1. Ceruloplasmin was able to convert Fe into Fe until 48 h of light exposure, but its decreased expression with time (at 168-h timepoint) resulted in increased extracellular Fe that might have caused oxidative stress and retinal cell damage.