Plasmic degradation of fibrin rapidly decreases platelet adhesion and
spreading
M Hamaguchi, LA Bunce, LA Sporn and CW Francis
Department of Medicine, University of Rochester School of Medicine and
Dentistry, NY.
Plasmin cleaves fibrin at or near sites involved in platelet recognition
and may modulate platelet adhesion and spreading. Using an in vitro system,
we have characterized the effects of limited plasmic degradation of
polymerized fibrin on platelet adhesion and spreading. As shown by scanning
electron microscopy, exposure to plasmin changed the tight fibrillar fibrin
surface to a less dense structure with irregular and broken fibers. There
was a gradient of proteolytic degradation through the fibrin clot as shown
by sodium dodecyl sulfate polyacrylamide gel electrophoresis with the most
extensive degradation at the surface. Plasmic degradation resulted in a
rapid and progressive decrease in platelet adhesion. Plasmin exposure for 5
minutes resulted in only 6% solubilization of the fibrin but a 56% decrease
in platelet adhesion. After 30 minutes of plasmin exposure, spreading of
adherent platelets on fibrin also decreased sharply to a minimum of 35% of
baseline. Inhibition experiments with specific monoclonal antibodies
(MoAbs) indicated that platelet adhesion to undergraded fibrin involved
residues within the sequence 566 through 580 of the alpha chain (including
the RGDS site), the carboxyl terminal dodecapeptide of the gamma chain, and
the amino terminus of the beta chain. MoAb 7E3, reactive with alpha IIb
beta 3, inhibited platelet adhesion to fibrinogen by 90% +/- 5%, and to
desA fibrin, prepared with Reptilase (American Diagnostica, Greenwich, CT),
by 94% +/- 6%, whereas inhibition of adhesion to undegraded desAB fibrin
was significantly less (48% +/- 8%, P < .01). The addition of 7E3 to
MoAb T2G1, reactive with beta 15-21, significantly increased inhibition to
desAB fibrin to 69% +/- 6% (P < .025), suggesting that the newly exposed
amino terminus of the beta chain contributes to platelet adhesion. The
results show that plasmin exposure of fibrin markedly decreases platelet
adhesion and spreading, suggesting that plasmin degradation may play a role
in modulating cellular responses to fibrin.
Volume 84,
Issue 4,
pp. 1143-1150,
08/15/1994
Copyright © 1994 by The American Society of Hematology
