Fibrinogen and Fibrin are Anti-Adhesive for Keratinocytes: A Mechanism for Fibrin Eschar Slough During Wound Repair

During cutaneous wound repair the epidermis avoids the fibrin-rich clot; rather it migrates down the collagen-rich dermal wound margin and over fibronectin-rich granulation tissue. The mechanism(s) underlying keratinocyte movement in this precise pathway has not been previously addressed. Here we demonstrate that cultured human keratinocytes do not express functional fibrinogen/fibrin receptors, specifically αvβ3. Biologic modifiers known to induce integrin expression or activation did not induce adhesion to fibrin, fibrinogen, or its fragments. Epidermal explant outgrowth and single epidermal cell migration failed to occur on either fibrin or fibrinogen. Surprisingly, fibrin and fibrinogen mixed at physiologic molar ratios with fibronectin abrogated keratinocyte attachment to fibronectin. Keratinocytes transduced with the β3 integrin subunit cDNA, expressed αvβ3 on their surface and attached to and spread on fibrinogen and fibrin. β-gal cDNA-transduced keratinocytes did not demonstrate this activity. Furthermore, β3 cDNA-transduced keratinocyte adhesion to fibrin was inhibited by LM609 monoclonal antibody to αvβ3 in a concentration-dependent fashion. From these data, we conclude that normal human keratinocytes cannot interact with fibrinogen and its derivatives due to the lack of αvβ3. Thus, fibrinogen and fibrin are authentic anti-adhesive for keratinocytes. This may be a fundamental reason why the migrating epidermis dissects the fibrin eschar from wounds.