Developing an "aging" model using iPSC-derived RPE cells

National Eye Institute

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Abstract

Age-related macular degeneration (AMD) is the leading cause of blindness among the elderly in the developed world. Dysfunction of the retinal pigment epithelium (RPE) is thought to initiate early AMD, while RPE degeneration drives progression to geographic atrophy, an advanced stage of AMD characterized by photoreceptor cell death and irreversible vision loss. The RPE is a post-mitotic monolayer situated between photoreceptors and the choroid, where it maintains homeostasis of both tissues. With aging, RPE cells lose the ability to fully perform these functions, disrupting retinal–choroidal homeostasis and likely triggering AMD onset. To investigate the mechanisms of RPE aging, we developed an in vitro iPSC-derived RPE aging model. Skin fibroblasts from both healthy individuals and AMD patients were reprogrammed into iPSCs using Yamanaka factors, fully characterized, and differentiated into RPE cells using a developmentally guided protocol. After eight weeks of culture on semi-permeable membranes, the iPSC-derived RPE formed functionally mature, polarized monolayers. These RPE monolayers were then stressed with complement-competent human serum and assessed for key RPE functions, including barrier integrity, phagocytosis of photoreceptor outer segments, and junctional stability. Under stress, RPE cells exhibited features of cellular aging and AMD-like pathology, including reduced phagocytic activity, decreased transepithelial resistance, APOE deposition, intracellular protein aggregates, epithelial phenotype loss, and lipid metabolism defects. We are currently investigating the intracellular signaling pathways that drive these changes. We have extended this model to monogenic retinal diseases, such as Stargardt disease, and observed similar complement-mediated effects. This RPE-aging model therefore provides a powerful system to (1) uncover mechanisms of RPE dysfunction and atrophy, (2) dissect the contribution of AMD-associated genetic risk alleles to disease initiation and progression, and (3) identify potential therapeutic interventions for both AMD and inherited retinal degenerations. We recently reported lipidomic changes in Stargardt RPE and photoreceptors and have now expanded these studies to AMD patients carrying various genetic risk alleles, further strengthening the relevance of this model.