Dysregulation of Mitochondrial Iron Regulators as a Basis of Iron-Mediated Retinal Degeneration in Rats.

Iron accumulates with aging. This triggers various pathological changes and diseases. We studied the impact of iron administration on mitochondrial iron metabolism in the retina. Control, four-month-old, male Wistar rats (n = 27) received either sterile distilled water (4MC) or ferrous sulphate (500 mg/kg body weight/week) by gavage until 12 months of age (12ME group). Another group of rats, receiving distilled water, was raised until 12 months and served as age-matched control (12MC). We examined the body weight, liver and retinal iron levels, retinal glutathione levels, histology, TEM, immunohistochemistry, and Western blotting of glutathione peroxidase-4 (a marker of ferroptosis), procaspase-3 and mitochondrial ferritin and frataxin, involved in iron regulation. In 12ME rats, there were elevated iron levels in the liver and retina, and decreased retinal glutathione levels, compared to that in 12MC rats. Prussian blue staining and iron estimation indicated iron accumulation in the liver and retina. There was marked degeneration of the retinal pigment epithelium and photoreceptor cells, resulting in gliosis, as seen by GFAP immunolabeling. Western blotting showed decreased levels of mitochondrial ferritin and frataxin, suggesting iron-induced mitochondrial dysfunction, while a decrease in glutathione levels and glutathione peroxidase-4 expression, and lack of expression of active caspase-3 (a marker of apoptosis) indicated an iron-dependent, non-apoptotic mode of retinal cell death (ferroptosis). Despite the smaller sample size in some assays (histopathology), our data show significant pathological changes of the retina due to iron accumulation at 12-month age of rats, and that dysregulation of the mitochondrial iron homeostasis is a step involved in iron-mediated retinal degeneration with aging.