The sudden formation of a blood clot in a coronary or cerebral artery is the most common cause of death in the United States. A major goal of our research has been to understand the molecular events that regulate clot formation and dissolution, in order to derive better treatment and prevention strategies. Our research focuses on the molecular interactions that regulate the plasminogen-plasmin enzyme system. This dissolves blood clots and we hypothesize that its function is modulated by protein-protein interactions with plasminogen activators (such as tissue plasminogen activator and streptokinase), inhibitors (such as alpha2-antiplasmin) and the fibrin crosslinking enzyme, factor XIIIa. Using molecular biologic techniques we have identified structural features of streptokinase which are responsible for its activity as an indirect plasminogen activator. We have also modified these structural features to enhance the potency and fibrin selectivity of streptokinase as a therapeutic agent. We have generated monoclonal antibodies that act as highly specific inhibitors of both alpha-2-antiplasmina and factor XIII. One of these, an inhibitor of blood coagulation factor XIII, completely prevents fibrin cross linking in clots which causes these clots to "spontaneously dissolve." Studies with an a2-antiplasmin inhibitor show that it markedly and synergistically accelerates clot lysis by plasminogen activators in vitro. In vivo this antiplasmin inhibitor also induces "spontaneous" clot lysis and markedly improves the dissolution of blood clots which go to the lungs (pulmonary thromboemboli). Our long term goal is to evaluate these type of agents in the prevention and treatment of thrombotic disease in humans.
Recurrent episodes of platelet thrombosis in the wall of the artery (mural thrombosis) markedly accelerate the atherosclerotic process causing progressive occlusion of the arteries. These processes of thrombosis and vascular remodelling are mediated in large part by the highly regulated secretion of effector molecules (agonists, coagulation enzymes, adhesion molecules, growth factors, etc.) from platelet intracellular granules, a process that remains poorly understood. We have cloned and identified novel platelet homologues of proteins involved in triggered secretion in neurons. We are using these interacting molecules to study the molecular regulation of granule docking and fusion in platelet secretion.