Molecular and morphological evidence for cadaver vitreous-stimulated transformation of differentiation-competent retinal pigment epithelial cells into neuron-like cells.

Retinal pigment epithelia (RPE) and retinal neurons (RN) arise from the same underlying precursor cell population. It is worthwhile to explore the transdifferentiation potential of RPE cells, given the benefits that could accrue from turning RPE into neural retina containing all its normal cellular subpopulations. Factors such as retinoic acid (RA, acting as an inducer of transdifferentiation) and epidermal growth factor (EGF) and basic fibroblast growth factor (bFGF) (E+F, acting as stem cell maintenance and predifferentiating factors) have been known to stimulate the conversion of RPE into observably neuron-like cells. However, since such treatment does not actually transform RPE into neurons, there is a need to rationally explore the efficacy of other factors as well. In this paper, we have compared the effects of RA, a known transdifferentiating factor in optical and other tissues, with the effects of cadaver vitreous on D407 RPE cells, using a combination of light microscopy, immunofluorescent microimaging and flow cytometry. We show that cadaver-derived vitreous (CV) is comparable to, or better than, RA as a transdifferentiation factor in an EGF + bFGF maintenance background. The vitreous humor could thus be an important stimulator of the differentiation of dedifferentiated RPE cells into neurons. This finding assumes significance in light of the fact that vitreous humor is a factor naturally present in the environment of the developing retina.