Age-related macular degeneration (AMD) is the leading cause of blindness in elderly population in the developed world. Dysfunction of retinal pigment epithelium (RPE) likely triggers early AMD stages, whereas RPE degeneration leads to an advanced AMD stage geographic atrophy, eventually leading to photoreceptor cell death and vision loss. RPE is a post mitotic monolayer located between photoreceptors and the choroid and maintains the homeostasis of these two tissues. With aging, RPE cells are unable to perform some of their functions affecting homeostasis in the photoreceptors and the choroid, likely triggering the early stages of AMD. In order to understand the factors and processes causing RPE aging, we developed an in vitro aging model using induced pluripotent stem cell (iPSC)-derived RPE cells. Fibroblast derived from both healthy and AMD patients skin biopsies were reprogrammed to pluripotent state using the Yamanaka factors. Fully-characterized iPSCs were differentiated to RPE using a developmentally guided differentiation protocol. iPSC-derived RPE were cultured on semi-permeable membranes for 8 weeks to obtain a functionally mature and polarized monolayer tissue. iPSC-derived RPE monolayer was stressed with complement competent human serum. Stressed cells were checked for RPE specific functions like measurement of electric intactness, ability to digest photoreceptors outer segments, and the junctional integrity. Complement competent human serum stressed RPE exhibited several features of aged cells and displayed AMD-like disease processes including reduced ability to digest photoreceptor outer segments, decreased trans epithelial resistance, and increased APOE deposition, intracellular basal protein aggregates, loss of epithelial phenotype, lipid metabolism defect. Complement competent human serum also increased IL-6 secretion, and caspase-1 activation in iPSC- derived RPE cells. We are determining intracellular signaling pathways that determine these changes in RPE cells. We propose that this cell culture model of RPE-aging provides a basis to discover mechanism of disease-related RPE dysfunction and atrophy, a tool to identify the role of AMD genetics in disease initiation and progression, and to discover potential therapeutic interventions for AMD.
