Stress-relaxation and contraction of a collagen matrix induces expression of TGF-β and triggers apoptosis in dermal fibroblasts

Abstract

Extracellular matrix serves as a scaffold for cells and can also regulate gene expression and ultimately cell behaviour. In this study, we compared the effects of three forms of type I collagen matrix, which differed only in their mechanical properties, and plastic on the expression of transforming growth factor-beta1 (TGF-beta1), matrix metalloproteinase-1 (collagenase), and type I collagen and on the growth and survival of human dermal fibroblasts. These effects were correlated with alterations in cell morphology and organization of intracellular actin. Cells in detached or stress-relaxed matrices were spherical, lacked stress fibres, and showed increased TGF-beta1 mRNA compared to the cells in anchored collagen matrices or on plastic, which were polygonal or bipolar and formed stress fibres. The levels of TGF-beta measured by bioassay were higher in detached and stress-relaxed collagen matrices, than in anchored collagen matrices. Cells on plastic contained little or no immunoreactive TGF-beta, while most cells in collagen matrices were stained. The levels of collagenase mRNA were significantly higher in all the collagen matrix cultures compared to those on plastic, but there were no statistically significant differences between them. Levels of mRNA for procollagen type I were not significantly affected by culture in the collagen matrices. Apoptotic fibroblasts were detected by the TUNEL assay in detached (5.7%) and to a lesser extent in stress-relaxed (2.2%) matrices, but none were observed in anchored collagen matrices or on plastic. These results show that alterations in the mechanical properties of matrix can induce the expression of TGF-beta and trigger apoptosis in dermal fibroblasts. They further suggest that inability to reorganize this matrix could be responsible for the maintenance of the fibroproliferative phenotype associated with fibroblasts in hypertrophic scarring.