Differences in the mechanism for high- versus moderate-density fibroblast-populated collagen lattice contraction

The free-floating fibroblast-populated collagen lattice (FPCL) model introd uced by Bell contains 0.5 x 10(5) cell/ml and here is defined as a moderate -density FPCL (MD-FPCL). One modification of the model is to increase the c ell density by a factor of 10, where 5 x 10(5) cells/ml defines a high-dens ity FPCL (HD-FPCL). The initial detection of HD-FPCL contraction is 2 h, wh ereas MD-FPCL is later, 6 h. A contracted HD-FPCL has a doughnut-like appea rance, due to the high density of cells accumulating at the periphery. A co ntracted MD-FPCL is a flattened disc. The compacted collagen of MD-FPCL lat tice exhibits a strong birefringence pattern due to organized collagen fibe r bundles. In contracted HD-FPCL, a minimal birefringence develops, indicat ing minimal organization of collagen fiber bundles. MD-FPCL contraction was reduced with less than 10% serum; the disruption of microtubules, uncoupli ng of gap junctions, inhibition of tyrosine kinases, and addition of a bloc king antibody to alpha2 beta1 collagen integrin. Making HD-FPCL with only 1 % serum or including the inhibitory agents had only minimal affect on latti ce contraction. On the other hand, platelet-derived growth factor stimulate d HD-FPCL contraction but had no influence on MD-FPCL contraction. It is su ggested that the mechanism for HD-FPCL contraction is limited to the proces s of cells spreading. HD-FPCL contraction is independent of collagen organi zation, microtubules, gap junctions, alpha2 beta1 integrin, and tyrosine ph osphorylation. MD-FPCL contraction involves collagen organization and is op timized by the involvement of microtubules, gap junctions, alpha2 beta1 int egrin, and tyrosine phosphorylation. When studying cell physiology in a col lagen matrix, cell-density influences need to be considered. J. Cell. Physi ol. 185:432-439, 2000. (C) 2000 Wiley-Liss, Inc.