Cell shape, intracellular pH, and fibroblast growth factor responsiveness during transdifferentiation of retinal pigment epithelium into neuroepithelium in vitro

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Abstract
In this report we show that some retinal pigment epithelial (RPE) cells, with no expression of neural cell adhesion molecule (N-CAM) [Formula: see text], spontaneously lose pigment and start to express N-CAM in culture. Chick RPE cells normally do not express N-CAM, while the protein is present in chick neural retina. Thus some of the RPE cells in culture started to transdifferentiate into a neuroepithelium[Formula: see text]. We have measured intracellular pH (pHi) in the RPE cultures and followed its changes in response to basic fibroblast growth factor (bFGF). The depigmented cells protrude above the RPE cell sheet and have a lower resting pHi (≈7.05) than the pigmented RPE cells (≈7.15). The majority of cells with low resting pHi express N-CAM. The difference in the resting pHi between [Formula: see text]and [Formula: see text] cells is not due to the N-CAM expression by [Formula: see text] cells, as their pHi is the same as the pHi of freshly plated single "round" [Formula: see text] cells that have not spread yet. [Formula: see text] cells respond to bFGF with a quick and sustained pHi rise. In contrast, neither the cuboidal [Formula: see text] cells in a colony centre nor single round [Formula: see text] cells respond to bFGF with cytoplasmic alkalinization. RPE cells do not proliferate in response to bFGF, while NE cells respond to bFGF with a stimulation of growth. We conclude that bFGF acts not on the fully differentiated [Formula: see text], but only on those cells which have already started to transdifferentiate and changed their shape and (or) adhesive status. bFGF provides [Formula: see text] cells that transdifferentiated from [Formula: see text] cells with a signal necessary to transdifferentiate and (or) histodifferentiate further.Key words: retinal pigment epithelium, retina, transdifferentiation, intracellular pH, basic fibroblast growth factor.

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