Increased Expression of Ceruloplasmin in the Retina following Photic Injury

Abstract

Abstract: : Purpose: Oxidative stress plays a role in the photic injury model of retinal degeneration as well as in age-related macular degeneration. Our previous work using DNA microarray analysis indicated that the antioxidant ceruloplasmin was up-regulated in the retina upon photic injury. The purpose of this study was to further characterize the expression of ceruloplasmin in the retina following light damage. Methods: Light damaged Balb/c mice were tested for retinal ceruloplasmin levels by quantitative PCR, immunohistochemistry, and Western analysis. Retinas from control unexposed mice were compared to those exposed to bright light for seven hours, with analysis at several time points following photic injury. The ceruloplasmin isoforms expressed in the retina were studied using reverse transcription PCR (RT-PCR) with RNA from Sprague Dawley rats. Total RNA isolated from the rat retina, liver and brain was analyzed by RT-PCR with ceruloplasmin primers corresponding to either the GPI-linked or the secreted form. Results: Quantitative PCR confirmed the eight-fold increase of ceruloplasmin detected in the DNA microarray analysis. Ceruloplasmin was detected throughout normal retinas by immunohistochemistry, with a specific increase in Muller cells following photic injury. Western analysis confirmed an increase in ceruloplasmin protein following photic injury. RT-PCR showed that both isoforms of ceruloplasmin were expressed in the retina. Western analysis further revealed eight-fold more ceruloplasmin protein in normal retina than in brain. Conclusions: Ceruloplasmin, a retinal antioxidant, is up-regulated at the mRNA and protein levels upon light damage. The increased protein is primarily in Muller cells. Ceruloplasmin is considerably more abundant in retina than in brain. Both forms of ceruloplasmin, the GPI-linked form and the secreted form, were expressed in the retina. Ceruloplasmin may protect the retina against photo-oxidative stress.

Keywords: antioxidants • Muller cells • radiation damage: light/UV