Restoration of Mesenchymal RPE by Transcription Factor-Mediated Reprogramming.

Purpose: Transforming growth factor β-mediated epithelial-to-mesenchymal transition (EMT) is a major component of the wound healing response and a negative determinant of retinal pigment epithelium (RPE) differentiation. We have shown previously that inhibition of TGFβ signaling restored the capacity of mesenchymal RPE to differentiate; however, the potential lessens with extensive passaging. We investigated TGFβ-independent mechanisms that regulate RPE differentiation following repetitive passaging.

Methods: Retinal pigment epithelium-EMT was induced by repetitive passaging of fetal RPE at subconfluence. Suppression of EMT was achieved by the addition of A-83-01, a TGFβ receptor kinase inhibitor. Transcriptomic analysis was used to identify potential TGFβ independent processes that prevent differentiation after extensive passage. Downregulated transcription factors were identified and transduced into highly passaged RPE to restore cell differentiation. Restoration was evaluated according to morphology, expression of RPE/mesenchymal markers, transcriptomic analysis, cell doubling time, and senescence-associated β-galactosidase (SA-β-gal) activity.

Results: A-83-01-treated RPE failed to differentiate after 7 passages (P7). This failure was concomitant with downregulation of RPE genes, misregulation of cell cycle genes, a decline in proliferative potential, and cell senescence. Exogenous expression of MYCN and OTX2 in conjunction with A-83-01 restored P7-RPE differentiation to a status similar to minimally passaged RPE. Moreover, the treatment allowed cells to maintain their differentiation capacity after extended passaging.

Conclusions: Retinal pigment epithelium subjected to chronic wound stimulus undergoes TGFβ-mediated EMT, loss of expression of signature RPE genes, and senescence. Targeting these aspects with a TGFβ receptor kinase inhibitor, a RPE transcription factor, and a cell cycle regulator restores the capacity of highly passaged RPE cells to regenerate and differentiate.