The influence of sublethal blue light exposure on human RPE cells

Purpose: To evaluate the in vitro response of retinal pigment epithelial (RPE) cells to a nonlethal dose of blue light. Methods: The human RPE cell line ARPE-19 was irradiated with blue light (405 nm) at an output power of 1 mW/cm(2) or 0.3 mW/cm(2). The following parameters were studied: metabolic activity; apoptosis; reactive oxygen species (ROS) production; mitochondrial membrane potential (MMP); ultrastructural changes of mitochondria; production of advanced glycation endproducts (AGEs); and stress-related cellular proteins. Results: Nonlethal doses of blue light irradiation significantly reduced ARPE-19 metabolic activity and MMP while increasing intracellular ROS levels and expression of stress-related proteins heme oxygenase-1 (HO-1), osteopontin, heat shock protein 27 (Hsp-27), manganese superoxide dismutase (SOD-Mn), and cathepsin D. Blue light irradiation also induced ultrastructural conformation changes in mitochondria, resulting in the appearance of giant mitochondria after 72 h. We further found enhanced formation of AGEs, particularly N-epsilon-(carboxymethyl) lysine (CML) modifications, and a delay in the cell cycle. Conclusions: ARPE-19 cells avoid cell death and recover from blue light irradiation by activating a host of defense mechanisms while simultaneously triggering cellular stress responses that may be involved in RPE disease development. Continuous light exposure can therefore detrimentally affect metabolically stressed RPE cells. This may have implications for pathogenesis of age-related macular degeneration.