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

Extracellular matrix serves as a scaffold for cells and can also regulate g ene expression and ultimately cell behaviour. In this study, we compared th e 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-beta 1 (TGF-beta 1), matrix metalloproteinase-1 (collagenase) , and type I collagen and on the growth and survival of human dermal fibrob lasts. These effects were correlated with alterations in cell morphology an d organization of intracellular actin. Cells in detached or stress-relaxed matrices were spherical, locked stress fibres, and showed increased TGF-bet a 1 mRNA compared to the cells in anchored collagen matrices or on plastic, which were polygonal or bipolar and formed stress fibres. The levels of TG F-beta measured by bioassay were higher in detached and stress-relaxed coll agen matrices, than in anchored collagen matrices. Cells on plastic contain ed little or no immunoreactive TGF-beta, while most cells in collagen matri ces 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 c ollagen 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 r esults show that alterations in the mechanical properties of matrix can ind uce the expression of TGF-beta and trigger apoptosis in dermal fibroblasts. They further suggest that inability to reorganize this matrix could be res ponsible for the maintenance of the fibroproliferative phenotype associated with fibroblasts in hypertrophic scarring.