Chronic photo-oxidative stress and subsequent MCP-1 activation as causative factors for age-related macular degeneration

Age-related macular degeneration (AMD) is the leading cause of blindness among the elderly in developed countries. Although pathogenic factors, such as oxidative stress, inflammation and genetics are thought to contribute to the development of AMD, little is known about the relationships and priorities between these factors. Here, we show that chronic photo-oxidative stress is an environmental factor involved in AMD pathogenesis. We first demonstrated that exposure to light induced phospholipid oxidation in the mouse retina, which was more prominent in aged animals. The induced oxidized phospholipids led to an increase in the expression of monocyte chemoattractant protein-1, which then resulted in macrophage accumulation, an inflammatory process. Antioxidant treatment prevented light-induced phospholipid oxidation and the subsequent increase of monocyte chemoattractant protein-1 (also known as C-C motif chemokine 2; CCL2), which are the beginnings of the light-induced changes. Subretinal application of oxidized phospholipids induced choroidal neovascularization, a characteristic feature of wet-type AMD, which was inhibited by blocking monocyte chemoattractant protein-1. These findings strongly suggest that a sequential cascade from photic stress to inflammatory processes through phospholipid oxidation has an important role in AMD pathogenesis. Finally, we succeeded in mimicking human AMD in mice with low-level, long-term photic stress, in which characteristic pathological changes, including choroidal neovascularization formation, were observed. Therefore, we propose a consecutive pathogenic pathway involving photic stress, oxidation of phospholipids and chronic inflammation, leading to angiogenesis. These findings add to the current understanding of AMD pathology and suggest protection from oxidative stress or suppression of the subsequent inflammation as new potential therapeutic targets for AMD.