N-retinylidene-N-retinylethanolamine degradation in human retinal pigment epithelial cells via memantine- and ifenprodil-mediated autophagy

Abstract

N-methyl-D-aspartate (NMDA) receptors are ionic glutamine receptors involved in brain development and functions such as learning and memory forma-tion. NMDA receptor inhibition is associated with autophagy activation. In this study, we investigated whether the NMDA receptor antagonists, memantine and ifenprodil, induce autophagy in human retinal pigment epithelial cells (ARPE-19) to remove N-retinylidene-N-retinylethanolamine (A2E), an intracellular lipofuscin component. Flu-orometric analysis using labeled A2E (A2E-BDP) and confocal microscopic examina-tion revealed that low concentrations of NMDA receptor antagonists, which did not induce cytotoxicity, significantly reduced A2E accumulation in ARPE-19 cells. In addi-tion, memantine and ifenprodil activated autophagy in ARPE-19 cells as measured by microtubule-associated protein 1A/1B-light chain3-II formation and phosphorylated p62 protein levels. Further, to understand the correlation between memantine-and ifenprodil-mediated A2E degradation and autophagy, autophagy-related 5 (ATG5) was depleted using RNA interference. Memantine and ifenprodil failed to degrade A2E in ARPE-19 cells lacking ATG5. Taken together, our study indicates that the NMDA receptor antagonists, memantine and ifenprodil, can remove A2E accumulated in cells via autophagy activation in ARPE-19 cells.