Thrombin Inhibits the Migration of Human Liver Myofibroblasts

Scarring of the cornea, the transparent tissue at the front of the eyeball, is an important cause of visual impairment. A major chemokine upregulated in tear fluid after corneal injury is platelet‐derived growth factor (PDGF), which induces the stromal cells of the cornea (keratocytes) to assume a fibroblastic phenotype. We have investigated the role of PDGF in matrix contraction by human corneal fibroblasts (HCF) using the standard three‐dimensional (3D) fibroblast‐populated collagen matrix model (FPCM).
When stimulated with PDGF, HCF in monolayer (2D) display circular ruffles (CR) on their dorsal surface. Using immunolabeling, we found that CR contain proteins of the Arp2/3 complex, which is required for the assembly of filamentous actin during protrusive activity. This PDGF‐mediated ruffling ability is altered by antibodies or blocking peptides that specifically interfere with the Arp2/3‐mediated pathway of actin polymerization, as well as by the myosin light chain kinase inhibitor, ML9. Preincubation with anti‐PDGF‐BB antibody or with the tyrosine kinase inhibitor, AG1295, also inhibits CR. While PDGF efficiently stimulates HCF‐mediated cell protrusive activity and macroscopic collagen gel contraction in the 3D model, this effect is directly inhibited by all the substances which inhibit CR in 2D, demonstrating a direct involvement of the PDGF‐mediated CR pathway in tissue contraction. Thus, 3D PDGF‐induced matrix contraction by HCF involves the same players as CR, a phenomenon observed in 2D cell cultures: PDGF‐BB receptor, receptor tyrosine kinase, the machinery for filamentous actin assembly (Arp 2/3 complex, Scar and Wasp proteins), and myosin. The functional role of circular ruffling or its equivalent in three‐dimensional fibroblast‐populated collagen matrices seems to be a rapid reorganization of the actin cytoskeleton in preparation for cell‐matrix interaction.