Activation of collagen gene expression in keloids: co-localization of type I and VI collagen and transforming growth factor-beta 1 mRNA

Untreated, clinically active keloids were examined as model system to study the spatial expression of extracellular matrix and transforming growth factor-beta 1 (TGF-beta 1) genes in fibrotic skin diseases. In situ hybridizations localized active expression of type I and VI collagen genes to the areas containing an abundance of fibroblasts and apparently representing the expanding border of the lesions. Within this zone, microvascular endothelial cells also expressed the type I collagen genes, as evaluated by simultaneous use of in situ hybridization for collagen gene expression and immunolocalization for factor VIII-related antigen, a marker for endothelial cell differentiation. Slot-blot hybridizations of RNA isolated from this zone suggested that the expression of type I and IV collagen genes was selectively enhanced, as compared to type III collagen gene expression. TGF-beta 1 protein and mRNA were also detected in areas active in type I and type VI collagen gene expression, indicating that TGF-beta 1 gene is transcribed and the corresponding protein is deposited in areas of elevated collagen gene expression, including microvascular endothelial cells. We conclude that the initial step in the development of fibrotic reaction in keloids involves the expression of the TGF-beta 1 gene by the neovascular endothelial cells, thus activating the adjacent fibroblasts to express markedly elevated levels of TGF-beta 1, as well as type I and VI collagen genes.