Mechanisms of thrombosis under flow
We examined how neutrophils, platelets and erythrocytes interact with each other under coagulating flow conditions to stimulate and enhance thrombotic processes. Experiments were designed to decouple flow-regulated adhesion events from flow-regulated coagulation biochemistry. Individual surface adherent neutrophils were found to accelerate fibrin deposition by generating and capturing fibrin protofibrils in a CD18-dependent mechanism and generating thrombin and fibrin when the contact pathway is intact through elastase/cathepsin G-mediated pathways. At the same time, neutrophils promoted fibrin production by interacting with platelets and turning them into fully procoagulant structures via released elastase/cathepsin G, even when FXIIa was inhibited by corn trypsin inhibitor. As relative rates of thrombin generation for various coagulation scenarios were measured under static conditions to complement the videomicroscopy-imaged flow assays, purified cathepsin G was found to be a more potent activator of platelet-dependent coagulation than elastase. Platelet activation by cathepsin G was more critical than the role of cathepsin G in cleaving coagulation factors. Individual GPVI activated platelets supported prothrombinase activity in the absence of activated coagulation factors or external tissue factor from plasma through pathways mediated by VIIa and tissue factor. We demonstrated that normal red blood cells can perform active roles in thrombosis by adhering to activated neutrophils, activated platelets and surface-deposited fibrin (polymerized from plasma) at low wall shear rates below 100 s−1 through receptor-mediated adhesion. Adhesion of red cells to activated platelets was partly CD36 and GPIb dependent and sensitive to soluble fibrinogen. The adhesion of normal RBC to activated neutrophils was found to be mediated by Mac-1 and LW (ICAM-4) and was insensitive to physiological levels of fibrinogen. We also demonstrated that linkage of tPA or reteplase to RBC (via biotin-streptavidin crosslinking) preserves the fibrin specificity and the fibrinolytic activity of these plasminogen activators. This research provides fundamental insight relevant to deep vein thrombosis, biomaterial thrombosis and inflammation-coagulation crosstalk. ^
Biology, Cell|Engineering, Biomedical|Engineering, Chemical
Mukul Shri Goel,
"Mechanisms of thrombosis under flow"
(January 1, 2003).
Dissertations available from ProQuest.