Oxidative stress induces an interactive decline in Wnt and Nrf2 signaling in degenerating retinal pigment epithelium.

Aims: Cells have evolved a highly sophisticated web of cytoprotective systems to neutralize unwanted oxidative stress, but are challenged by unique modern day stresses such as cigarette smoking and ingestion of a high-fat diet (HFD). Age-related disease, such as age-related macular degeneration (AMD), the most common cause of blindness among the elderly in Western societies, develops in part, when oxidative stress overwhelms cytoprotective systems to injure tissue. Since most studies focus on the protection by a single protective system, the aim of this study was to investigate the impact of more than one cytoprotective system against oxidative stress. Results: Wingless (Wnt) and nuclear factor-erythroid 2-related factor 2 (Nrf2), two fundamental signaling systems that are vital to cell survival, decline after mice are exposed to chronic cigarette smoke and HFD, two established AMD risk factors, in a bidirectional feedback loop through phosphorylated glycogen synthase kinase 3 beta. Decreased Wnt and Nrf2 signaling leads to retinal pigment epithelial dysfunction and apoptosis, and a phenotype that is strikingly similar to geographic atrophy (GA), an advanced form of AMD with no effective treatment. Innovation: This study is the first to show that chronic oxidative stress from common modern day environmental exposures reduces two fundamental and vital cytoprotective networks in a bidirectional feedback loop, and their decline leads to advanced disease phenotype. Conclusion: Our data offer new insights into how combined modern oxidative stresses of cigarette smoking and HFD contribute to GA through an interactive decline in Wnt and Nrf2 signaling.