PARTIALLY DEGRADED FIBRIN(OGEN) STIMULATES FIBROBLAST PROLIFERATION IN-VITRO

The conversion by thrombin of soluble plasma fibrinogen to an insolubl e fibrin matrix is central to hemostasis and subsequent wound healing. Fibroblasts adhere to and rapidly grow into fibrin clots, resulting i n collagen deposition and, ultimately, scar formation. Although a numb er of soluble mediators have been implicated in this process, a role f or fibrin(ogen) itself has not been described. The present study furth er investigated the nature of mitogenic activity remaining in solution after in vitro fibrin clot formation. Liquid expressed from a fibrin clot (clot supernatant) elicited a mitogenic response of up to 83 +/- 4.7% above media control. Upon addition of a polyclonal fibrinogen ant ibody, this activity was reduced by 50%. The remaining activity was at tributed to the presence of thrombin and was neutralized by the additi on of a specific thrombin inhibitor. Fibrinogen cleavage products were separated by molecular sieve chromatography and the mitogenic potenti al of each fraction assessed. A peak of activity was observed in fract ions containing proteins with apparent molecular weights of 200 to 300 kD. Enhanced chemiluminescence Western blotting of these fractions es tablished the presence of several fibrin(ogen)-derived protein bands. It is therefore proposed that thrombin cleavage of fibrinogen, in addi tion to producing fibrin, generates high-molecular-weight soluble clea vage products that may play an important role during normal wound heal ing and in the pathogenesis of disease states associated with vascular leakage and fibrosis.