Background:

Dr. Bouchard received her Ph.D. in the Cell & Molecular Biology Program at the University of Vermont in 1996. Her dissertation research focused on the regulation of procoagulant enzyme complex assembly and function on cells. During a Postdoctoral Fellowship with Barbara Furie, Ph.D. at Harvard Medical School, she continued with her research interests in coagulation studying the vitamin K-dependent gamma-glutamyl carboxylase, the enzyme responsible for catalyzing an important post-translational modification of the blood clotting proteins. In 2000, she returned to UVM and is now a Research Assistant Professor of Biochemistry.

Research Interests:

Coagulation Biology & Disease
Cell & Molecular Biology

Project Description:

Platelet- and plasma-derived factor Va serve essential roles in thrombin generation catalyzed by the prothrombinase complex assembled on activated platelets.  Several observations indicate that the platelet-derived cofactor is more important in maintaining normal hemostasis, and is physically and structurally  distinct from its plasma counterpart.  Despite these differences, it has been demonstrated unequivocally that the entire platelet-derived factor Va pool originates via endocytosis of the procofactor, factor V, from plasma by megakaryocytes, the platelet precursor cells.  Factor V endocytosis by megakaryocytes is specific, clathrin-dependent, and appears to be mediated by a two receptor system.  In this model, factor V initially binds to a specific factor V receptor expressed only on megakaryocytes able to endocytose factor V.  This binding event facilitates an interaction between a second factor V molecule and LDL receptor-related protein-1 (LRP-1), an endocytic receptor, which subsequently mediates the endocytosis of bound factor V.  These combined observations represent a unique role for LRP-1 in endocytosis of a coagulation protein not destined for lysosomal degradation.  Rather, subsequent to its endocytosis, factor V is functionally modified, trafficked to, and stored in alpha-granules.

The overall goal of our laboratory is to identify and characterize the proteins that form the megakaryocyte two receptor system involved in the binding and endocytosis of plasma-derived factor V.

Some specific projects include:  (1) Identification of the specific, factor V receptor expressed on human megakaryocytes; (2) Determination of the fates of the factor V receptor and LRP-1 subsequent to factor V endocytosis, and during megakaryocyte development and platelet formation; (3) Identification of the minimum factor V amino acid sequence(s) involved in its interactions witht he factor V receptor, as well as LRP-1 expressed on megakaryocytes; and (4) Definition of the intracellular signaling events that regulate factor V binding and endocytosis by megakaryocytes.  In collaboration with Dr. Benjamin Surratt (Department of Medicine), we are also assessing the cellular mechanisms that regulate endocytosis of factor V by mouse megakaryocytes to identify an appropriate animal model to test our hypotheses.

Our laboratory is also involved in large population-based studies of thrombophilic and hemophilic individuals.  These studies, being performed in collaboration with Dr. Kathleen Brummel-Ziedins, use a flow cytometry-based assay of prothrombinase complex assembly on activated platelets in whole blood developed by our laboratory to predict an individual's propensity to bleed or clot.