Wound contraction can substantially reduce the amount of new tissue needed to reestablish organ integrity after tissue loss. Fibroblasts, rich in
F-actin bundles, generate the force of
wound contraction.
Fibronectin-containing microfibrils link fibroblasts to each other and to
collagen bundles and thereby provide transduction cables across the
wound for contraction. The temporal relationships of
F-actin bundle formation,
collagen and
fibronectin matrix assembly, and
fibronectin receptor expression to
wound contraction have not been determined. To establish these relationships, we used a cutaneous gaping
wound model in outbred Yorkshire pigs. Granulation tissue filled approximately 80% of the
wound space by day 5 after injury while
wound contraction was first apparent at day 10. Neither actin bundles nor
fibronectin receptors were observed in 5-d
wound fibroblasts. Although
fibronectin fibrils were assembled on the surfaces of 5-d fibroblasts, few fibrils coursed between cells. Day-7 fibroblasts stained strongly for nonmuscle-type
F-actin bundles consistent with a contractile fibroblast phenotype. These cells expressed
fibronectin receptors, were embedded in a
fibronectin matrix that appeared to connect fibroblasts to the matrix and to each other, and were coaligned across the
wound. Transmission EM confirmed the presence of microfilament bundles, cell-cell and cell-matrix linkages at day 7. Fibroblast coalignment, matrix interconnections, and actin bundles became more pronounced at days 10 and 14 coinciding with tissue contraction. These findings demonstrate that granulation tissue formation,
F-actin bundle and
fibronectin receptor expression in
wound fibroblasts, and fibroblast-matrix linkage precede
wound contraction.