DERMAL FIBROBLASTS ACTIVATE KERATINOCYTE OUTGROWTH ON COLLAGEN GELS

The effects of dermal fibroblasts on keratinocyte outgrowth on collage n substrata was studied using an in vitro keratinocyte-collagen gel co mposite model. Skin fibroblasts were seeded inside collagen gels, whic h remained attached to the cell culture plastic substratum. Fibroblast s incorporated in collagen gels were either kept viable throughout the study, or were lysed hypotonically with water at different time inter vals (2 hours and 5 days). Results show that very little keratinocyte outgrowth occurred on either plain collagen gels or gels that had prev iously contained viable fibroblasts for 2 hours. A 3- to 4-fold increa se in keratinocyte outgrowth occurred on collagen gels that had previo usly contained viable fibroblasts for 5 days. A striking increase (20- fold) in keratinocyte outgrowth was observed on collagen gels that con tain viable fibroblasts. The effect of fibroblast diffusible factors o n keratinocyte outgrowth was further studied with a co-culture system using Millicell inserts. It was found that the co-culture of fibroblas ts with the composite enhanced keratinocyte outgrowth on collagen gels that had previously contained viable fibroblasts for 5 days. Among al l, however, the keratinocyte outgrowth was far better on gels containi ng viable fibroblasts. Addition of keratinocyte growth factor or its n eutralizing antibody did not affect keratinocyte outgrowth. These resu lts suggest that dermal fibroblasts can activate keratinocyte outgrowt h on collagen matrices through some diffusible factors other than kera tinocyte growth factor, and epithelial-mesenchymal interactions exert some special effects on keratinocyte outgrowth on collagen gels.