Dermal fibroblasts activate keratinocyte outgrowth on collagen gels

The effects of dermal fibroblasts on keratinocyte outgrowth on collagen substrata was studied using an in vitro keratinocyte-collagen gel composite model. Skin fibroblasts were seeded inside collagen gels, which remained attached to the cell culture plastic substratum. Fibroblasts incorporated in collagen gels were either kept viable throughout the study, or were lysed hypotonically with water at different time intervals (2 hours and 5 days). Results show that very little keratinocyte outgrowth occurred on either plain collagen gels or gels that had previously contained viable fibroblasts for 2 hours. A 3- to 4-fold increase in keratinocyte outgrowth occurred on collagen gels that had previously contained viable fibroblasts for 5 days. A striking increase (20-fold) in keratinocyte outgrowth was observed on collagen gels that contain viable fibroblasts. The effect of fibroblast diffusible factors on keratinocyte outgrowth was further studied with a co-culture system using Millicell inserts. It was found that the co-culture of fibroblasts with the composite enhanced keratinocyte outgrowth on collagen gels that had previously contained viable fibroblasts for 5 days. Among all, however, the keratinocyte outgrowth was far better on gels containing viable fibroblasts. Addition of keratinocyte growth factor or its neutralizing antibody did not affect keratinocyte outgrowth. These results suggest that dermal fibroblasts can activate keratinocyte outgrowth on collagen matrices through some diffusible factors other than keratinocyte growth factor, and epithelial-mesenchymal interactions exert some special effects on keratinocyte outgrowth on collagen gels.