The retinal degenerative diseases, which together constitute a leading cause of hereditary blindness worldwide, are largely untreatable. Development of reliable methods to culture complex retinal tissues from human pluripotent stem cells (hPSCs) could offer a means to study human retinal development, provide a platform to investigate the mechanisms of retinal degeneration and screen for neuroprotective compounds, and provide the basis for cell-based therapeutic strategies. In this study, we describe an in vitro method by which hPSCs can be differentiated into 3D retinas with at least some important features reminiscent of a mature retina, including exuberant outgrowth of outer segment-like structures and synaptic ribbons, photoreceptor neurotransmitter expression, and membrane conductances and synaptic vesicle release properties consistent with possible photoreceptor synaptic function. The advanced outer segment-like structures reported here support the notion that 3D retina cups could serve as a model for studying mature photoreceptor development and allow for more robust modeling of retinal degenerative disease in vitro.

Age-related macular degeneration (AMD) is associated with dysfunction and death of retinal pigment epithelial (RPE) cells. Cell-based approaches using RPE-like cells derived from human pluripotent stem cells (hPSCs) are being developed for AMD treatment. However, most efficient RPE differentiation protocols rely on complex, stepwise treatments and addition of growth factors, whereas small-moleculeonly approaches developed to date display reduced yields. To identify new compounds that promote RPE differentiation, we developed and performed a high-throughput quantitative PCR screen complemented by a novel orthogonal human induced pluripotent stem cell (hiPSC)-based RPE reporter assay. Chetomin, an inhibitor of hypoxiainducible factors, was found to strongly increase RPE differentiation; combination with nicotinamide resulted in conversion of over onehalf of the differentiating cells into RPE. Single passage of the whole culture yielded a highly pure hPSC-RPE cell population that displayed many of the morphological, molecular, and functional characteristics of native RPE.retinal pigment epithelium | pluripotent stem cells | high-throughput screening | differentiation | age-related macular degeneration A ge-related macular degeneration (AMD) is the leading cause of irreversible vision loss and blindness among the elderly in industrialized countries. Dysfunction of the retinal pigment epithelium (RPE) is an early event associated with AMD. The RPE, a monolayer of pigmented cells directly abutting the photoreceptor cell layer, plays many important roles in vision and in maintaining the health and integrity of the retina (1). As the RPE deteriorates, there is progressive degeneration of photoreceptor cells.Successful antiangiogenesis treatments have been developed for the neovascular, or "wet," form of AMD. However, there are no Food and Drug Administration-approved treatment options available for the majority of AMD patients, who suffer from the more common nonneovascular, or "dry," form of the disease. In the past few years, however, transplantation of human pluripotent stem cellderived RPE (hPSC-RPE) has emerged as a promising new therapy for dry AMD. A Phase I clinical trial of human embryonic stem (hES)-derived RPE cells recently reported some preliminary encouraging results (2). Additionally, a Phase I trial that will use RPE cells generated from human induced pluripotent stem cells (hiPSCs) reprogrammed from the patients' own skin cells recently injected their first patient (3).If the promise of hiPSC-based approaches for AMD is to be translated into the clinic, each patient would require individualized generation of RPE cells from his or her stem cells, thereby necessitating the development of simple, efficient, safe, and affordable protocols for RPE generation. Although highly efficient protocols have been established, they rely upon mixtures of growth factors (4-6) with the use of complex biologics derived from animal cells or bacteria, presenting potential clinical challenges. As an alternative approach, use...

Age-related macular degeneration (AMD), the leading cause of irreversible vision loss and blindness among the elderly in industrialized countries, is associated with the dysfunction and death of the retinal pigment epithelial (RPE) cells. As a result, there has been significant interest in developing RPE culture systems both to study AMD disease mechanisms and to provide substrate for possible cell-based therapies. Because of their indefinite self-renewal, human pluripotent stem cells (hPSCs) have the potential to provide an unlimited supply of RPE-like cells. However, most protocols developed to date for deriving RPE cells from hPSCs involve time-and labor-consuming manual steps, which hinder their use in biomedical applications requiring large amounts of differentiated cells. Here, we describe a simple and scalable protocol for the generation of RPE cells from hPSCs that is less labor-intensive. After amplification by clonal propagation using a myosin inhibitor, differentiation was induced in monolayers of hPSCs, and the resulting RPE cells were purified by two rounds of whole-dish single-cell passage. This approach yields highly pure populations of functional hPSC-derived RPE cells that display many characteristics of native RPE cells, including proper pigmentation and morphology, cell typespecific marker expression, polarized membrane and vascular endothelial growth factor secretion, and phagocytic activity. This work represents a step toward mass production of RPE cells from hPSCs. STEM CELLS TRANSLATIONAL MEDICINE 2013;2:341-354