Partially Differentiated Neuroretinal Cells Promote Maturation of the Retinal Pigment Epithelium.

Purpose: Many studies have demonstrated the ability of the retinal pigment epithelium (RPE) to foster the maturation of the developing retina. Few studies have examined the reciprocal effects of developing retina on the RPE. Methods: RPE isolated from human fetal RPE or differentiated from human stem cells was cultured on Transwell filter inserts. Retinal progenitor cells (RPCs) were differentiated from human stem cells and cultured on a planar scaffold composed of gelatin, chondroitin sulfate, hyaluronic acid, and laminin-521. Cultures were analyzed by quantitative RT-PCR, immunofluorescence, immunoblotting, and transepithelial electrical resistance (TER). Results: RPCs initially differentiated into several retina-like cell types that segregated from one another and formed loosely organized layers or zones. With time, the presumptive photoreceptor and ganglion cell layers persisted, but the intervening zone became dominated by cells that expressed glial markers with no evidence of bipolar cells or interneurons. Co-culture of this underdeveloped retinoid with the RPE resulted in a thickened layer of recoverin-positive cells but did not prevent the loss of interneuron markers in the intervening zone. Although photoreceptor inner and outer segments were not observed, immunoblots revealed that co-culture increased expression of rhodopsin and red/green opsin. Co-culture of the RPE with this underdeveloped retinal culture increased the TER of the RPE and the expression of RPE signature genes. Conclusions: These studies indicated that an immature neurosensory retina can foster maturation of the RPE; however, the ability of RPE alone to foster maturation of the neurosensory retina is limited.