Temporal stimulation of corneal fibroblast wound healing activity by differentiating epithelium in vitro.

PURPOSE To determine whether differentiating corneal epithelium can temporally stimulate fibroblast activity. METHODS Corneal epithelial cells were cultured to confluence and then stimulated to mature into multilayered epithelia with addition of serum-containing medium. Differentiation was assessed morphologically and immunocytochemically using a monoclonal antibody to cytokeratin 3. At intervals after onset of differentiation serum-free conditioned medium was collected up to 28 days. Preliminary experiments deduced the optimum concentration of conditioned medium to be used for assessing fibroblast activity. Conditioned medium (25% vol/vol) was added to donor-matched corneal fibroblasts in migration chambers, WST-1 reagent proliferation assays, and fibroblast-populated collagen gel contraction assays. Platelet-derived growth factor (PGDF)-AB and interleukin (IL)-1beta in conditioned media were quantified by enzyme-linked immunosorbent assay (ELISA). Fibroblast migration and collagen contraction assays were performed with concentrations of PDGF-AB. RESULTS Conditioned medium collected from differentiating epithelium stimulated fibroblast migration and collagen gel contraction, with activity peaks occurring with medium collected on day 14 (P < 0.05). No significant difference was detected between fibroblast growth rates in each of the conditioned media. Levels of PDGF-AB increased during epithelial culture up to 22 days (up to approximately 360 pg/ml) with a subsequent decrease by 28 days. IL-1beta inversely correlated with fibroblast activity induced by conditioned medium, with a trough in concentration (2 pg/ml) occurring at 14 days. Both fibroblast migration and collagen contraction were stimulated in a dose-dependent manner by PDGF-AB. CONCLUSIONS Corneal epithelium is capable of temporally stimulating fibroblast wound-healing characteristics during its differentiation. One of the growth factors potentially involved in this epithelial-stromal interaction is PDGF. This work demonstrated that developing epithelium (possibly similar to repairing epithelium in vivo) regulated fibroblast behavior and may indicate a mechanism of fibroblast recruitment to a wound after epithelial closure.