Several forms of retinal degenerative diseases including age-related macular degeneration (AMD) are associated with functional defects in the RPE. Previous work suggests that replacing diseased RPE with healthy RPE may provide visual benefits for affected individuals. Based on this hypothesis, we seek to develop an autologous cell-based therapy for AMD patients using RPE differentiated from patients iPS cells. In order to achieve clinical-grade manufacturing of iPS cell derived RPE cells, one needs to develop a differentiation protocol that is robust and reproducible under well-defined GMP conditions. To achieve this goal, we generated a reporter iPS cell line that expresses RFP under the control of a constitutive promoter and GFP under the control of an RPE-specific enhancer of the gene TYROSINASE. GFP expression in this line coincides with the induction of RPE phenotype. Using GFP as a marker of RPE differentiation, we are optimizing and improving RPE differentiation efficiency from iPS cells. Based on published and our previous work on RPE differentiation in animal models, we are manipulating activities of IGF, FGF, WNT, and NODAL pathways to improve RPE differentiation efficiency. Our results suggest that manipulation of these developmental pathways leads to a physiological co-expression of RPE inducing transcription factors MITF and PAX6, and a strong increase in GFP expressing cells. Committed RPE cells are cultured on semi-permeable transwell membranes for maturation. Functional maturation of these cells is assessed by the expression of fetal/adult-specific markers and by the electrical and physiological properties of RPE monolayers. Our results show that, in 6-8 weeks, RPE cells form electrically intact monolayers that are able to perform several RPE functions. These functionally authenticated RPE cells are tested on bio-degradable scaffolds for their ability to form confluent, polarized, functional monolayers of RPE tissue. Currently, these RPE tissues are being authenticated in vitro and are being tested in animal models to check for safety and efficacy. When completed, this project will provide a protocol that is ready for clinical-grade manufacturing of RPE tissue from patient specific iPS cells. These RPE tissues will provide potential therapeutics for AMD patients.
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