Robust induction of retinal pigment epithelium cells from human induced pluripotent stem cells by inhibiting FGF/MAPK signaling.

Functional decline and loss of the retinal pigment epithelium (RPE) cause retinal diseases. Clinical studies using human embryonic stem cell (hESC)- or induced pluripotent stem cell (hiPSC)-derived RPE cells have shown the safety and potential efficacy of hESC/iPSC-RPE cell transplantation. However, the production of RPE cells remains somewhat problematic. hESCs/iPSCs co-cultured with mouse feeder cells carry the risk of xeno-transmitted infections and immune reactions. Moreover, increasing the rate of cell division to ensure the quantity and purity of cells with low differentiation efficiency elevates the risk of gene mutations and chromosomal abnormalities. Here, we show that the transient inhibition of the FGF/MAPK signaling pathway during the hiPSC maintenance period markedly promotes RPE differentiation efficiency under feeder-free culture conditions. Blockage of FGF/MAPK signal induces neural differentiation and generates RPE cells without subsequent inhibition of Wnt and Nodal signals, which is known to be effective for retinal specification. We also found that additional inhibition of the PKC or BMP signaling pathway together with FGF/MAPK signal inhibition further elevates RPE differentiation efficiency. Our study will be helpful for producing clinical-grade RPE cells and will facilitate the development of therapies using hESC/hiPSC-RPE cells.