Spatial Propagation and Localization of Blood Coagulation Are Regulated by Intrinsic and Protein C Pathways, Respectively

Abstract

Blood coagulation in vivo is a spatially nonuniform, multistage process: coagulation factors from plasma bind to tissue factor (TF)-expressing cells, become activated, dissociate, and diffuse into plasma to form enzymatic complexes on the membranes of activated platelets. We studied spatial regulation of coagulation using two approaches: 1), an in vitro experimental model of clot formation in a thin layer of plasma activated by a monolayer of TF-expressing cells; and 2), a computer simulation model. Clotting in factor VIII- and factor XI-deficient plasmas was initiated normally, but further clot elongation was impaired in factor VIII- and, at later stages, in factor XI-deficient plasma. The data indicated that clot elongation was regulated by factor Xa formation by intrinsic tenase, whereas factor IXa was formed by extrinsic tenase on activating cells and diffused into plasma, thus sustaining clot growth. Far from the activating cells, additional factor IXa was produced by factor XIa. Exogenously added TF had no effect on the clot growth rate, suggesting that plasma TF does not contribute significantly to the clot propagation process in a reaction-diffusion system without flow. Addition of thrombomodulin at 3-100 nM caused dose-dependent termination of clot elongation with a final clot size of 2-0.2 mm. These results identify roles of specific coagulation pathways at different stages of spatial clot formation (initiation, elongation, and termination) and provide a possible basis for their therapeutic targeting.

Thrombin generation, fibrin clot formation and hemostasis

“…68 These findings suggest that thrombin generated on the surface of platelets during the propagation phase dictates that rate of fibrin clot formation away from the initiating cells. [67][68][69][70] Fibrin formation during cell-mediated thrombin generation likely includes a complex spatial component as well. It is likely that this physical progression of procoagulant activity from the tissue factor-bearing cell (low levels of thrombin generation) to the activated platelet surface (rapid burst of thrombin generation) induces the formation of a thrombin gradient in space.…”

Spatial Dynamics of Contact-Activated Fibrin Clot Formationin vitroandin silicoin Haemophilia B: Effects of Severity and Ahemphil B Treatment

“…The mathematical model used in this study was a modification of a previously published one [3], which described clotting activated by both extrinsic and intrinsic pathways in homogeneous and spatial-distributed conditions and was verified by extensive comparison of the simulation results with experiments. It consisted (in the homogeneous case) of 27 ordinary differential equations (ODEs)…”

“…Fig. 2B and C demonstrate simulated thrombin and fibrin concentration profiles obtained with the complex mathematical model [3] describing the above mentioned reactions.…”

“…It is shown that clotting under these experimental conditions is sensitive to congenital deficiencies of FVIII, FIX [6,7] and FXI [3,8], that are associated with abnormal clotting commonly referred as haemophilias A, B and C, respectively. Extremely low concentrations of FVIII, FIX and, to a lesser extent, FXI have been shown to disrupt clot propagation in space.…”

“…Experimental investigation was performed in plasma of healthy donors, patients with different FIX clotting activity and patients with severe FIX deficiency ([FIX]<1%) during the infused FIX concentrate clearance and before treatment. For simulations, a detailed quantitative mathematical model of coagulation [3] adapted for the experimental setting was used.…”