Reactive Oxygen Species Regulate Prosurvival ERK1/2 Signaling and bFGF Expression in Gliosis within the Retina

PURPOSE. Gliosis is the response of glial cells within retinal tissue to injury. It can be beneficial in the short term, but if the response is extended it can lead to scar formation, which contributes to blindness. Phosphorylation of extracellular signal regulated kinase 1/2 (ERK1/2) is considered to be a hallmark event of gliosis, but the factors involved throughout its associated signaling pathway remain poorly understood, particularly in the retina. Because reactive oxygen species (ROS) can inhibit phosphatases, thereby altering the phosphorylation of proteins, this study tested the hypothesis that ROS regulate the phosphorylation of ERK1/2 (pERK1/2) in gliosis. METHODS. Increases in pERK1/2 were detected using Western blotting and immunofluorescence in three models of retinal stress, specifically the in vivo light induction, the rd1 disease, and the ex vivo retinal explant models. Explanted murine retinas were used to identify the signaling partners of pERK1/2 via Western blotting, in conjunction with inhibitors. The effect of this pathway on cell death was measured with terminal dUTP nick end labeling. RESULTS. It was demonstrated that several inhibitors of ROS greatly reduce the levels of pERK1/2 in the somata of Muller cells and furthermore decrease two other downstream signaling events: the phosphorylation of STAT3 and the upregulation of basic fibroblast growth factor. Using the specific inhibitor of ERK1/2, UO126, the resultant outcomes of this signaling pathway were determined to contribute significantly to cell survival. CONCLUSIONS. The novel finding of this study that ROS contribute to a prosurvival signaling pathway in retinal Muller cell gliosis indicates that some degree of caution should be used when considering antioxidants as therapeutics. (Invest Ophthalmol Vis Sci. 2012;53:6645-6654) DOI:10.1167/iovs.12-10525