GROWTH-FACTORS MODULATE CLONAL GROWTH AND DIFFERENTIATION OF CULTUREDRABBIT LIMBAL AND CORNEAL EPITHELIUM

Purpose. To compare the extent of modulation by various growth factors on clonal growth and differentiation between corneal and stem cell-co ntaining limbal epithelium. Methods. A reported serum-free clonal grow th assay was used. The mitogenic response was measured by colony formi ng efficiency, colony size, and bromodeoxyuridine labelling index; the differentiation was assessed by AE-5 monoclonal antibody staining. Re sults. As compared to controls in an insulin-containing basic medium, the addition of epidermal growth factor, acidic fibroblast growth fact or, basic fibroblast growth factor, and a high dose of nerve growth fa ctor was mitogenic for both epithelia. Cholera toxin was also mitogeni c, but platelet-derived growth factor might not have, and insulin-like growth factor type I lacked an additive mitogenic effect with insulin . The mitogenic effect of epidermal growth factor differed from the ot hers in its dose-dependent down-regulation and in having more migrator y cells in epidermal growth factor-stimulated colonies. In contrast to these mitogens, transforming growth factor-beta 1 exhibited a clear i nhibitory effect in the controls as well as in epidermal growth factor - or fibroblast growth factor-stimulated cultures. Transforming growth factor-beta I's inhibitory effect was correlated with strong AE-5 sta ining, whereas the mitogenic effect of epidermal growth factors, fibro blast growth factors or nerve growth factors was correlated with the p resence of negative AE-5 colonies. Conclusion. There exist potential d ynamic interactions among various growth-modifying cytokines in contro lling epithelial growth and differentiation. The lack of specific acti vation of limbal stem cells in this culture assay also suggests that o ther unidentified factor(s) might be regulating stem cell functions.