title: Redundancy and interaction of thrombin- and collagen-mediated platelet activation in tail bleeding and carotid thrombosis in mice.
abstract: OBJECTIVE
  Current antiplatelet strategies to prevent myocardial infarction and stroke are limited by bleeding risk. A better understanding of the roles of distinct platelet-activating pathways is needed. We determined whether platelet activation by 2 key primary activators, thrombin and collagen, plays distinct, redundant, or interacting roles in tail bleeding and carotid thrombosis in mice.
  
  
  RESULTS
  Platelets from mice deficient for the thrombin receptor protease-activated receptor-4 (Par4) and the collagen receptor glycoprotein VI protein (GPVI) lack responses to thrombin and collagen, respectively. We examined tail bleeding and FeCl3-induced carotid artery occlusion in mice lacking Par4, GPVI, or both. We also examined a series of Par mutants with increasing impairment of thrombin signaling in platelets. Ablation of thrombin signaling alone by Par4 deficiency increased blood loss in the tail bleeding assay and impaired occlusive thrombus formation in the carotid occlusion assay. GPVI deficiency alone had no effect. Superimposing GPVI deficiency on Par4 deficiency markedly increased effect size in both assays. In contrast to complete ablation of thrombin signaling, 9- and 19-fold increases in EC50 for thrombin-induced platelet activation had only modest effects.
  
  
  CONCLUSIONS
  The observation that loss of Par4 uncovered large effects of GPVI deficiency implies that Par4 and GPVI made independent, partially redundant contributions to occlusive thrombus formation in the carotid and to hemostatic clot formation in the tail under the experimental conditions examined. At face value, these results suggest that thrombin- and collagen-induced platelet activation can play partially redundant roles, despite important differences in how these agonists are made available to platelets.
authors.affiliation: From the Cardiovascular Research Institute, University of California, San Francisco (Y.S.B.-S., I.C., D.P., D.D., C.C., S.R.C.); and Department of Physiology & Biophysics, University of Arkansas for Medical Sciences, Little Rock (J.W.).
authors.forename: Yamini S
authors.initials: YS
authors.lastname: Bynagari-Settipalli
authors.affiliation: From the Cardiovascular Research Institute, University of California, San Francisco (Y.S.B.-S., I.C., D.P., D.D., C.C., S.R.C.); and Department of Physiology & Biophysics, University of Arkansas for Medical Sciences, Little Rock (J.W.).
authors.forename: Ivo
authors.initials: I
authors.lastname: Cornelissen
authors.affiliation: From the Cardiovascular Research Institute, University of California, San Francisco (Y.S.B.-S., I.C., D.P., D.D., C.C., S.R.C.); and Department of Physiology & Biophysics, University of Arkansas for Medical Sciences, Little Rock (J.W.).
authors.forename: Daniel
authors.initials: D
authors.lastname: Palmer
authors.affiliation: From the Cardiovascular Research Institute, University of California, San Francisco (Y.S.B.-S., I.C., D.P., D.D., C.C., S.R.C.); and Department of Physiology & Biophysics, University of Arkansas for Medical Sciences, Little Rock (J.W.).
authors.forename: Daniel
authors.initials: D
authors.lastname: Duong
authors.affiliation: From the Cardiovascular Research Institute, University of California, San Francisco (Y.S.B.-S., I.C., D.P., D.D., C.C., S.R.C.); and Department of Physiology & Biophysics, University of Arkansas for Medical Sciences, Little Rock (J.W.).
authors.forename: Cherry
authors.initials: C
authors.lastname: Concengco
authors.affiliation: From the Cardiovascular Research Institute, University of California, San Francisco (Y.S.B.-S., I.C., D.P., D.D., C.C., S.R.C.); and Department of Physiology & Biophysics, University of Arkansas for Medical Sciences, Little Rock (J.W.).
authors.forename: Jerry
authors.initials: J
authors.lastname: Ware
authors.affiliation: From the Cardiovascular Research Institute, University of California, San Francisco (Y.S.B.-S., I.C., D.P., D.D., C.C., S.R.C.); and Department of Physiology & Biophysics, University of Arkansas for Medical Sciences, Little Rock (J.W.). shaun.coughlin@ucsf.edu.
authors.forename: Shaun R
authors.initials: SR
authors.lastname: Coughlin
mesh_terms: D000818:Animals; D001792:Blood Platelets / Q000378:metabolism; D002341:Carotid Artery Thrombosis / Q000097:blood* / Q000209:etiology; D003094:Collagen / Q000097:blood*; D006470:Hemorrhage / Q000097:blood* / Q000209:etiology; D006487:Hemostasis; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D015539:Platelet Activation / Q000502:physiology*; D010980:Platelet Membrane Glycoproteins / Q000172:deficiency / Q000235:genetics; D044462:Receptors, Proteinase-Activated / Q000097:blood / Q000172:deficiency / Q000235:genetics; D018179:Receptors, Thrombin / Q000097:blood / Q000172:deficiency / Q000235:genetics; D013623:Tail; D013917:Thrombin / Q000378:metabolism*
chemical_list: D010980:Platelet Membrane Glycoproteins; D044462:Receptors, Proteinase-Activated; D018179:Receptors, Thrombin; C098341:platelet membrane glycoprotein VI; C481941:protease-activated receptor 3, mouse; D003094:Collagen; D013917:Thrombin; C112908:protease-activated receptor 4
keywords: collagen; glycoprotein VI; hemostasis; mouse assays; platelets; protease-activated receptor-3; protease-activated receptor-4; thrombin; thrombosis