Stimulation of DNA synthesis in human and bovine RPE by peptide growth factors: The response to TNF-α and EGF is dependent upon culture density

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Abstract
A range of concentrations of several peptide mitogens was tested for growth activity on bovine and human RPE cells under serum free conditions by analysis of 3H-thymidine incorporation within the first 24 hrs of exposure to the agents. For cultures which were subconfluent or in early confluence, TNF-a, a product of activated macrophages, was the most effective mitogen; little or no growth stimulation was observed for PDGF, EGF, NGF, IGF-1, IL-1B, bFGF or TGF-β1. For TNF-a and EGF the growth response was analyzed in cultures of varying density. TNF-a was more active in sparse RPE cultures whereas EGF stimulation was greater in dense cultures. The response to growth factors was similar in RPE cells from the two species sources, but the apparent magnitude of the response was greater for bovine cells because the growth rate in serum free medium, which was used as the basal reference, was lower for bovine RPE. It is concluded that culture conditions, especially the timing of the assay and the level of confluence of the cells, affect the detection of a growth response to peptide mitogens. Although several of the agents which were tested did not stimulate DNA synthesis in RPE in this study, they may nonetheless promote growth when assayed in combination with other agents or they may affect other biological functions of RPE cells.