Elucidating the mechanism of wound contraction: Rapid versus sustained myosin ATPase activity in attached‐delayed‐released compared with free‐floating fibroblast‐populated collagen lattices

Abstract

Wound contraction closes open wounds by the generation of contractile forces within granulation tissue. We investigated the mechanism of wound contraction using the in vitro fibroblast-populated collagen lattice (FPCL) contraction model. The contraction of the free-floating (FF)-FPCL is through rapid myosin ATPase activity, while the contraction of the attached-delayed-released (ADR)-FPCL is through sustained myosin ATPase activity. All FPCLs were cast identically and the contraction of FF-FPCLs was recorded daily for 4 days and the contraction of ADR-FPCLs was recorded 1 hour after release on day 4. At day, 4 cell numbers were determined and cells undergoing apoptosis were identified and counted. Differences in sustained and rapid myosin ATPase activity were shown by added inosine triphosphate-induced cell contraction in permeabilized fibroblast monolayer preparations. At 2 days, the FF-FPCLs were mostly contracted, while an ADR-FPCL completed contraction 1 hour after release at day 4. Contracted myofibroblasts, identified by alpha-smooth muscle actin-stained stress fibers, were identified in contracted ADR-FPCL, whereas elongated fibroblasts were identified in contracted FF-FPCLs. Vanadate inhibited both inosine triphosphate-induced cell contraction and ADR-FPCL contraction, but neither inhibited ATP-induced cell contraction or FF-FPCL contraction. Genistein inhibited FF-FPCL contraction, but not ADR-FPCL contraction. Advancing tyrosine phosphorylation in fibroblasts promotes rapid myosin ATPase activity, while advancing tyrosine dephosphorylation in myofibroblasts promotes sustained myosin ATPase. The ADR-FPCL had a reduced cell count and a greater proportion of cells had entered apoptosis compared with FF-FPCL. These experiments show that FF-FPCL contraction is through elongated fibroblasts and rapid myosin ATPase, requiring tyrosine phosphorylation. In contrast, the mechanism for ADR-FPCL contraction is through cell contraction by sustained myosin ATPase, involving tyrosine dephosphorylation.