Fibroblast contraction occurs on release of tension in attached collagen lattices: Dependency on an organized actin cytoskeleton and serum

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Abstract
The generation of tension in granulation tissue undergoing contraction is believed to be a cell-mediated event. In this study we used attached collagen lattices as a model system for studying the cellular mechanisms of tension generation by fibroblasts in an extracellular matrix. Fibroblasts in attached collagen lattices developed stress fibers, surface associated fibronectin fibrils, and a fibronexus-like transmembrane association interconnecting the two structural components. Release of the attached collagen lattice from its points of attachment resulted in a rapid, symmetrical contraction of the collagen lattice. Rapid contraction occurred within the first 10 minutes after release of the lattice from the substratum, with greater than 70% of the contraction occurring within the first 2 minutes. Rapid contraction resulted in a shortening of the elongate fibroblasts and compaction of the stress fibers with their subsequent disappearance from the cell. Cytochalasin D treatment prior to release disrupted the actin cytoskeleton and completely inhibited rapid contraction. The removal of serum prior to release inhibited rapid contraction, while the re-addition of serum restored rapid contraction. These results demonstrate that fibroblasts can develop tension in an attached collagen lattice and that upon release of tension the fibroblasts undergo contraction resulting in a rapid contraction of the collagen lattice. Fibroblast contraction is dependent upon an organized actin cytoskeleton and is promoted by the presence of serum.