Signaling mechanisms in cardiovascular biology and disease, thrombin signaling
My laboratory seeks to define signaling mechanisms that govern cardiovascular biology and disease, with a focus on G protein-coupled receptors (GPCRs). We discovered and characterized protease-activated receptors (PARs), a family of GPCRs that permit thrombin and related proteases to regulate the behavior of platelets and other cells. Together with the coagulation cascade, these receptors link tissue injury to cellular responses that regulate blood clotting, inflammation, pain sensation, and perhaps cytoprotection and repair. PARs are necessary for platelet activation by thrombin, and a PAR1 antagonist was recently shown to prevent myocardial infarction and ischemic stroke in patients with known atherothrombotic disease, albeit at the cost of increased bleeding. Current work focuses on better defining the roles and interactions of coagulation factors, PARs and other regulators of hemostasis and thrombosis in mouse and zebrafish models. Additionally, in collaboration with Brian Kobilka, we seek to solve crystal structures of PAR1 off and on states to more fully understand PAR pharmacology and the “tethered ligand” activation mechanism we postulated for these receptors.
PARs also contribute to embryonic development. PAR function in endothelial cells is necessary for normal hemostasis, blood vessel remodeling and/or integrity in midgestation mouse embryos. PAR signaling in surface ectoderm appears to be necessary for neural tube closure; recent findings suggest involvement of local membrane-tethered proteases that regulate epithelial structure and function in part via PARs. Current work utilizes zebrafish and mouse models to identify the molecular and cellular mechanisms underlying these phenomena.
The role of sphingosine-1-phosphate (S1P) signaling via S1P1 and related GPCRs in regulation of vascular permeability is another focus. We found that S1P in the plasma compartment is important for normal vascular permeability/integrity in the adult mouse; current work seeks to determine whether S1P’s acting directly on endothelial cell S1P1 mediates this effect and, if so, whether such signaling plays a tonic maintenance function and/or triggers a dynamic response to vascular leak. A second area of focus reflects an unexpected finding made in S1P1 morphant zebrafish embryos generated to better define the roles of S1P1 in the vasculature: S1P1 is necessary for normal sarcomere formation in the developing zebrafish heart. Ongoing work focuses on defining the mechanisms involved and determining whether this system also functions in mammals.