ACUTE LUNG INJURY FIBROBLAST MIGRATION AND INVASION OF A FIBRIN MATRIX IS MEDIATED BY CD44

Fibrosis results when myofibroblasts invade the wound fibrin provision al matrix. Extracellular matrix receptors on the cell. surface mediate cell adhesion, migration, and invasion. Recent work with transformed cells indicates that these cells use the cell surface matrix receptor CD44 for migration and invasion. In this study, we examine whether lun g fibroblasts, isolated from patients dying with acute alveolar fibros is, use CD44 to invade a fibrin matrix. Consistent with a role for CD4 4 in mediating fibroblast invasion and subsequent tissue fibrosis, imm unohistochemical analysis of lung tissue from patients who died from a cute alveolar fibrosis after lung injury reveals CD44-expressing mesen chymal cells throughout newly formed fibrotic tissue. PCR, Western, an d immunoprecipitation analysis demonstrate that the 85-kD CD44 isoform is expressed by acute lung injury fibroblasts. Consistent with a role in mediating matrix adhesion and migration ultrastructurally, CD44 wa s found uniformly over the cell surface and was found densely labeling filopodia and lamellipodia, highly motile structures involved in cell migration. To determine if lung injury fibroblasts use CD44 to invade fibrin, a fibrin gel model of fibrosis was used. By blocking the func tion of CD44 with monoclonal antibodies, fibroblast invasion into a fi brin matrix was inhibited. To examine the mechanism by which CD44 medi ates fibroblast invasion, the role of CD44 in fibroblast migration and adhesion was evaluated. Anti-CD44 antibody blocked fibroblast migrati on on the provisional matrix proteins fibronectin, fibrinogen, and hya luronic acid. Additionally, fibroblast CD44 mediated adhesion to the p rovisional matrix proteins fibronectin, fibrin, and hyaluronic acid, b ut not to laminin, a component of the basement membrane. These finding s support the hypothesis that fibroblast CD44 functions as an adhesion receptor for provisional matrix proteins and is capable of mediating fibroblast migration and invasion of the wound provisional matrix resu lting in the formation of fibrotic tissue.