Increased c-fos mRNA Expression By Human Fibroblasts Contracting Stressed Collagen Matrices

Abstract

We studied early changes in gene expression during fibroblast contraction of stressed collagen matrices. The level of c-fos mRNA increased dramatically and peaked 50 to 60 min after matrix contraction was initiated. This response did not require serum and could not be accounted for simply by disruption of the actin cytoskeleton. Increased c-fos mRNA levels required Ca 2؉ influx but not the cyclic AMP or extracellular signal-regulated kinase (ERK 1/2) signaling pathways, both of which are activated when fibroblasts contract stressed collagen matrices. The levels of two other immediate-early genes, fosb and c-jun, also increased transiently after fibroblast contraction, whereas the levels of fra-1, fra-2, c-myc, and the transcription factor NF-B remained the same, indicating that fibroblast contraction caused changes in a selective group of genes. The increase in c-fos mRNA during contraction of stressed collagen matrices may reflect a unique role for c-fos in mechanoregulated events at the end of wound repair.Mechanical force influences cell function in animal and plant tissues (6,11,30,67). For instance, increased mechanical load, such as fluid flow over endothelial cells or tension applied to muscle cells, has been shown to result in cell proliferation or hypertrophy (15, 64). During wound repair, mechanical force within the wound tissue pulls the wound edges closer together, which in pathological cases results in scarring and loss of function (29, 52). Wound contraction is believed to be mediated by fibroblasts as they go through a cycle of migration, proliferation, contraction, and regression (13,40).Fibroblasts cultured in collagen matrices have been used as an in vitro model for wound contraction (3,20). In this model, cells reorganize the extracellular matrix through migratory and contractile activities (3, 25), resulting in formation of a dense, tissue-like structure. The fibroblast phenotype that develops during collagen matrix reorganization differs dramatically depending upon whether collagen matrices are floating in medium or attached to a rigid support. After reorganization of attached matrices, the cells resemble proliferating fibroblasts of wound tissue under mechanical stress and are characterized by polarized morphology, prominent stress fibers, and fibronexus junctions (23,37,45,62). Cells in attached collagen matrices exert force on the matrix similar to that observed in contracting skin wounds (12, 34). After reorganization of floating matrices, on the other hand, cells resemble nondividing fibroblasts of resting dermis or scar tissue in a state of mechanical equilibrium and are characterized by isometric (stellate) cell morphology and cytoskeletal meshwork (3, 4).We have combined the attached and floating models to study the regulatory events associated with the transition of fibroblasts from mechanically stressed to mechanically equilibrated conditions (stress-relaxation) such as occurs by the end of wound repair. Initially, fibroblasts are cultured in attached collagen matrices until mechan...

Distinct pathways in the over-expression of matrix metalloproteinases in human fibroblasts by relaxation of mechanical tension

“…The participation of AP-1 site(s) in the over-expression of MMP-1, -3, -9 and -13, induced by CD and in RCG, needs further investigation. Its (their) activity is, however, suggested by the induction of c-Fos and c-Jun by the abrupt release of stress in retracting collagen gels (Rosenfeldt et al, 1998) and the induction of c-Fos by CD in HeLa and WI-38 cells (Zambetti et al, 1991).…”

Collagen matrix as a tool in studying fibroblastic cell behavior

“…95 The release of stressed matrix is followed by a burst of c-fos expression and ERK 1/2 kinase activation. 96 Cell survival, collagen synthesis and degradation are regulated by integrins. Antibodies to a2b1 integrins prevent the contraction and reduce apoptosis.…”

Defective Myofibroblast Formation from Mesenchymal Stem Cells in the Aging Murine Heart

“…22 Contraction was initiated by releasing the attached gels using a spatula. Gels were incubated for 24 hours in DMEM with or without 10 ng/mL TGF-␤1.…”