Use of Multiphoton Intravital Imaging and a Multiscale Computational Model of Thrombus Development to Study the Role of FVII in Thrombogenesis

Using 2-photon intravital microscopy we have generated high resolution, near real-time 3-dimensional images of a developing thrombus. Following Titanium - Sapphire laser-induced injuries in mouse mesenteric vessels, the developing thrombus was monitored by collecting stacks of confocal images through the developing thrombus. Data were collected in 3 channels for fluorescently labeled platelets, fibrinogen and 70,000 MW dextran. By including fluorescently labeled dextran in the blood we were able to monitor flow (plasma) and not labeled cells (leukocytes and erythrocytes) forming black silhouettes in the plasma. Since each 3-D reconstruction involves a series of scans, we were able to generate approximately 2–3 reconstructions per minute. Thus, the system sacrifices temporal resolution for high resolution structural information revealing the changing, heterogeneous sub-domain structure of the developing thrombus. The imaging system has been used to study the consequences of FVII-deficiency. Following injury, of the luminal surface of the vessel, a thin layer of platelets and fibrin accumulated at the injury site. Unlike injuries in wild-type mice where the thrombus continues to grow, the injuries in FVII deficient mice failed to grow as a result of frequent embolization from the developing structure. Interestingly, in a model of ferric chloride induced injury of the carotid artery, thrombi in FVII deficient mice form large structures capable of reducing flow although, unlike wild type mice, the FVII deficient animals fail to form stable occlusive clots. In parallel with the modified experimental vascular injury model, we have begun development of a computational model of thrombus development. The modeling framework consists of a stochastic and discrete Cellular Potts Model (CPM) to describe platelet and cellular interactions and continuous submodels to describe hydrodynamic and biochemical reactions. Our multiscale model includes the vessel wall, platelets (in resting and activated states), blood cells, coagulation reactions, fibrin formation, and hydrodynamic parameters as components. By comparing the in vivo experimental results with those of simulations varying the concentration of FVII we are able to refine and validate the computational model of thrombogenesis.