Combining ASCL1 and NEUROD1 reprograms human RPE into neurons of distinct lineages

There are currently few promising approaches for treatment of photoreceptor pathologies: for example, gene therapy to augment or replace mutated genes, has proven successful in preclinical studies, and some of these therapies are moving towards the clinic. Another approach aims to unlock the inherent stem-cell potential of non-neuronal retinal cells to regenerate neurons in situ. This line of research is based on the discovery that some vertebrates can restore even severely damaged retina from RPE with all the necessary cell types to regain full functionality. In this study we first established a robust in vitro culture system based on isolated fetal human RPE. We then employed a barcode-multiplexed, single cell RNAseq based screen to find factors that would reprogram human RPE into a photoreceptor-like state. With this approach we were able to identify NEUROD1 as a complimentary factor to ASCL1. Their combined overexpression together with a treatment with bFGF and Activin A inhibitor produced RPE-derived neuronal cells with expression patterns characteristic of different lineages.