Hydrogen peroxide and extracellular signal-related kinase 1/2 pathway regulate ferritin levels in retinal pigmented and lens epithelial cells

PURPOSE Iron plays a central role in the oxidative stress caused by hydrogen peroxide. The ubiquitous iron storage protein, ferritin, safely sequesters iron, reducing its ability to cause oxidative damage. Oxidative stress can activate mitogen-activated protein (MAP) kinase pathways with many downstream effects. The purpose of this study was to determine the effects of hydrogen peroxide on MAP kinase pathways (extracellular signal-related kinase [ERK]1/2, c-Jun N-terminal kinase [JNK], and p38) and ferritin levels in canine lens and retinal epithelial cells (lens epithelial cells [LECs] and retinal pigmented epithelial [RPE] cells). METHODS Primary cultures of canine LECs and RPE cells were used in these studies. Hydrogen peroxide was delivered either by a single 250 μM bolus or 0.25 mU/ml glucose oxidase (GO). Immunoblotting was used to determine the activation of the MAP kinase pathways. Ferritin was detected with enzyme immunosorbent assay. RESULTS Baseline activation of ERK1/2 in the untreated RPE cells and LECs was decreased by treatment with U-0126. Bolus hydrogen peroxide greatly increased ERK1/2 activation that had been blocked by U-0126, whereas GO had no significant effect on ERK1/2 phosphorylation. Hydrogen peroxide, either bolus or constant low levels, increased ferritin levels in the LECs and RPE cells. Surprisingly, U-0126 not only did not inhibit the effect of hydrogen peroxide on the ferritin levels but also increased the ferritin levels in both cell types. Neither bolus nor chronic hydrogen peroxide exposure activated the JNK or p38 pathway. Additionally, neither JNK nor p38 inhibitors had any effect on the ferritin concentrations in the LECs or RPE cells. CONCLUSIONS Although U-0126 inhibited the hydrogen peroxide-induced increase in ERK1/2 phosphorylation, U-0126's lack of inhibition of the peroxide-induced increase in intracellular ferritin levels indicates that this pathway is not involved in ferritin induction by hydrogen peroxide. This is the first study to demonstrate that hydrogen peroxide and an inhibitor of ERK1/2 activation can increase the levels of the iron storage protein, ferritin. Since ferritin can shield cells from iron-catalyzed damage, this downstream effect likely plays a protective role, which, in the case of the ERK1/2 inhibitor, U-0126, demonstrates a potential therapeutic target.