Shaun Coughlin, MD, PhD

Professor & Director
Cardiovascular Research Institute
+1 415 502-8667

The lab currently focuses on two general areas:

1) Mechanisms and Roles of Protease Signaling.

a) Structural basis PAR function. To determine how thrombin and related proteases regulate the behavior of platelets and other cells, our laboratory discovered and characterized a family of protease-activated G protein-coupled receptors (PARs). Mutational and biochemical studies suggest that PARs are activated by an elegant proteolytic mechanism. Thrombin cleaves the N-terminal exodomain of PAR1 to create a new N-terminus that then serves as a tethered peptide agonist, binding intramolecularly to the receptor's heptahelical bundle to effect transmembrane movement and G protein activation. To test and refine this model, an crystal structure of on-state PAR1 that reveals how the tethered ligand docks and triggers transmembrane signaling is needed. In collaboration with Brian Kobilka's laboratory, we recently described an off-state structure of PAR1 in complex with its antagonist vorapaxar. This structure explained the effectively irreversible action of vorapaxar and suggested a novel of drug entry into the receptor as well as a possible contribution of entry kinetics to drug specificity – areas of current inquiry. Efforts to solve a structure of on-state PAR1 in complex with its tethered ligand and the G proteins to which it couples – Gi, Gq and G12 ­– are ongoing. In addition to revealing the details of tethered ligand docking and transmembrane signaling, these structures will reveal how a single GPCR can couple to distinct G proteins – perhaps providing structural insight into the mechanism of biased agonism.

b) Physiology. In the adult, PARs link tissue injury to cellular responses that regulate blood clotting, inflammation, pain sensation, and perhaps cytoprotection and repair. Characterization of roles of PARs in platelet activation led to the development of vorapaxar, which was recently approved for secondary prevention of heart attacks and stroke in selected at-risk patients. Current work in this area focuses on better defining the roles and interactions of coagulation factors, PARs and other regulators of hemostasis and thrombosis in mouse and zebrafish models. Related work seeks to develop a clinical probe IgG to define the role of a novel antithrombotic target in humans.

c) Embryonic Development. In the mouse embryo, PAR function in endothelial cells contributes to blood vessel development and integrity. Work to define the role of endothelial PARs in this context in mouse and zebrafish models is ongoing. In addition to revealing novel biology, results may help illuminate the mechanisms underlying increased bleeding in vorapaxar-treated humans.

d) Epithelial Biology. Recent work in the lab suggests that local membrane-tethered proteases may regulate epithelial structure and function in part via PAR2, which is co-expressed with these proteases in virtually all epithelia. Current work utilizes cell culture, zebrafish and mouse models to identify the molecular and cellular mechanisms underlying these phenomena, which regulate normal epithelial barrier function and epithelial neoplasia.

2) Other signaling mechanisms in cardiovascular homeostasis and development.

We found that the bioactive lipid sphingosine-1-phosphate (S1P) in the plasma compartment is important for maintaining normal endothelial barrier function and vascular integrity in the adult mouse; current work seeks to determine whether plasma S1P acts directly on its receptor S1P1 on endothelial cells to mediate this effect and, if so, whether such signaling plays a tonic maintenance function and/or triggers a dynamic response to vascular leak.

Using cardiomyocyte-specific knockout of S1P1 in mice, we unexpectedly found that signaling via this receptor in the cardiomyocyte is necessary for normal heart development in the embryo. Preliminary work in mice in which S1P1 was deleted after birth suggests that this receptor may also be necessary for normal response to stress in the adult. Ongoing work will define the mechanisms involved. Other studies are utilizing zebrafish to examine the regulatory mechanisms governing cardiac trabeculation and related processes.

Primary Thematic Area: 
Vascular & Cardiac Biology
Secondary Thematic Area: 
Tissue / Organ Biology & Endocrinology
Research Summary: 
Regulatory mechanisms in cardiovascular biology and disease
Publications: 

The lung is a site of platelet biogenesis and a reservoir for haematopoietic progenitors.

Nature

Lefrançais E, Ortiz-Muñoz G, Caudrillier A, Mallavia B, Liu F, Sayah DM, Thornton EE, Headley MB, David T, Coughlin SR, Krummel MF, Leavitt AD, Passegué E, Looney MR

Platelet and Erythrocyte Sources of S1P Are Redundant for Vascular Development and Homeostasis, but Both Rendered Essential After Plasma S1P Depletion in Anaphylactic Shock.

Circulation research

Gazit SL, Mariko B, Thérond P, Decouture B, Xiong Y, Couty L, Bonnin P, Baudrie V, Le Gall SM, Dizier B, Zoghdani N, Ransinan J, Hamilton JR, Gaussem P, Tharaux PL, Chun J, Coughlin SR, Bachelot-Loza C, Hla T, Ho-Tin-Noé B, Camerer E

Factor XIa-specific IgG and a reversal agent to probe factor XI function in thrombosis and hemostasis.

Science translational medicine

David T, Kim YC, Ely LK, Rondon I, Gao H, O'Brien P, Bolt MW, Coyle AJ, Garcia JL, Flounders EA, Mikita T, Coughlin SR

Rational Design of a GFP-Based Fluorogenic Caspase Reporter for Imaging Apoptosis In Vivo.

Cell chemical biology

To TL, Schepis A, Ruiz-González R, Zhang Q, Yu D, Dong Z, Coughlin SR, Shu X

Sphingosine 1-phosphate receptor-1 in cardiomyocytes is required for normal cardiac development.

Developmental biology

Clay H, Wilsbacher LD, Wilson SJ, Duong DN, McDonald M, Lam I, Park KE, Chun J, Coughlin SR