Increased metallothionein in light damaged mouse retinas and in human AMD retinas

Abstract

Abstract: : Purpose: Oxidative stress plays a role in human age–related macular degeneration (AMD) and in the light damage model of retinal degeneration. Metallothionein (MT), an antioxidant, has been reported to protect retinal pigment epithelial cells against apoptosis and oxidative stress. The purpose of this study was to determine whether MT levels increase in the mouse retina in response to photo–oxidation and to compare MT levels in human retinas from donors with and without AMD. Methods: Balb/c mice were exposed to cool white fluorescent light (10,000lux) for seven hours. In three independent experiments, at several intervals after the light injury, retinal MTs were studied at the protein level by immunohistochemistry (IHC) and Western analysis, and at the mRNA level by quantitative PCR with isoform–specific primers. IHC was performed on sections from 8 normal human and 11 AMD retinas. Results: Western analysis and IHC indicated an increase in MT protein in the mouse retina following light damage. MT localized to the retinal pigment epithelium and several layers of neural retina. Quantitative PCR identified the expression of MT I–III isoforms, not the MT IV isoform in the mouse retina, and, following light damage, showed increased expression of retinal MT–I and MT–II mRNAs by 8 and 22 fold, respectively. IHC showed increased levels of metallothionein in photoreceptors in human AMD retinas in areas of partial photoreceptor and RPE atrophy. Conclusions: Increased expression of the antioxidant MT in the light damaged mouse suggests that upregulation of MT is an important retinal response to acute photo–oxidative stress. Photoreceptors in retinas from patients with AMD may upregulate MT to combat chronic oxidative stress.

Keywords: antioxidants • oxidation/oxidative or free radical damage • photoreceptors