Tractional force generation by porcine Müller cells: paracrine stimulation by retinal pigment epithelium.

PURPOSE To examine the ability of retinal pigment epithelial (RPE) cells to modulate Müller cell extracellular matrix contraction through secreted promoters. METHODS Freshly isolated RPE cells were maintained in continuous culture until the morphologic and immunocytochemical changes associated with myofibroblastic dedifferentiation were complete. Secretory products collected from these cells during extended incubations in serum-free medium and at different stages of dedifferentiation were examined for the ability to promote extracellular matrix contraction by Müller cells. The contributions of specific growth factors to RPE-secreted activity were examined with growth factor-neutralizing antibodies. RESULTS Secretory products from RPE cells throughout dedifferentiation contained biologically active quantities of Müller cell contraction promoters. Secretory activity increased during extended incubation in serum-free medium and during myofibroblastic dedifferentiation. Growth factor-specific neutralizing antibodies enabled the determination that insulin-like growth factor- and platelet-derived growth factor-related proteins were the secreted species to which Müller cells responded. Finally, gene expression of insulin-like growth factor 1 and platelet-derived growth factor A chain by porcine RPE cells was confirmed using reverse transcription-polymerase chain reaction. CONCLUSIONS. RPE cells are a viable source of biologically active quantities of two growth factors that stimulate extracellular matrix contraction by Müller cells. This secretory profile persists for extended periods in an otherwise serum-free environment and is enhanced during myofibroblastic dedifferentiation.