title: Platelets from mice lacking the aryl hydrocarbon receptor exhibit defective collagen-dependent signaling.
abstract: BACKGROUND
  We previously identified aryl hydrocarbon receptor (AHR) as a novel regulator of megakaryocytic differentiation and polyploidization and reported that AHR-null mice have approximately 15% fewer platelets than do wild-type mice, yet they exhibit a dramatic, unexplained bleeding phenotype.
  
  
  OBJECTIVE
  The current work tests our hypothesis that AHR-null platelets are functionally deficient, contributing to the previously reported (yet unexplained) bleeding phenotype present in AHR-null mice.
  
  
  METHODS
  AHR-null bone marrow was ex vivo differentiated with thrombopoietin with or without AHR ligands or AHR inhibitors and analyzed for degree of megakaryopoiesis and polyploidization. Platelet function of AHR-null mice was assessed with aggregation and spreading assays. Platelet signaling was examined using Western analysis and Rac activity assays.
  
  
  RESULTS
  AHR ligands differentiate murine bone marrow-derived progenitors into polyploid megakaryocytes in the absence of thrombopoietin, and AHR inhibitors block thrombopoietin-induced megakaryocytic differentiation. Despite their responsiveness toward thrombin, AHR-null platelets demonstrate decreased aggregation and spreading in response to collagen compared with wild-type platelets. AHR-null platelets bind fibrinogen after stimulation with thrombin or AYPGKF and aggregate in response to AYPGKF and adenosine diphosphate. Mechanistically, AHR absence led to down-regulation of Vav1 and Vav3, altered phospholipase Cγ2 phosphorylation, decreased Rac1 activation, and reduced platelet activation in response to collagen.
  
  
  CONCLUSIONS
  These results are consistent with a role for AHR in platelet function, especially as it relates to platelet aggregation and spreading in response to collagen. Our work suggests AHR is a critical component of the physiologic response that platelets undergo in response to collagen and may provide novel treatment options for patients with bleeding disorders.
authors.affiliation: Department of Chemical and Biomolecular Engineering, University of Delaware, Newark, DE, USA.
authors.forename: S
authors.initials: S
authors.lastname: Lindsey
authors.forename: J
authors.initials: J
authors.lastname: Jiang
authors.forename: D
authors.initials: D
authors.lastname: Woulfe
authors.forename: E T
authors.initials: ET
authors.lastname: Papoutsakis
mesh_terms: D000818:Animals; D001792:Blood Platelets / Q000166:cytology*; D001854:Bone Marrow Cells / Q000166:cytology; D002454:Cell Differentiation; D003094:Collagen / Q000737:chemistry*; D005260:Female; D006470:Hemorrhage; D006487:Hemostasis; D008024:Ligands; D008297:Male; D008533:Megakaryocytes / Q000166:cytology; D051379:Mice; D018345:Mice, Knockout; D010641:Phenotype; D015539:Platelet Activation; D010974:Platelet Aggregation; D011003:Ploidies; D018336:Receptors, Aryl Hydrocarbon / Q000235:genetics* / Q000502:physiology; D015398:Signal Transduction; D013234:Stem Cells / Q000166:cytology; D013926:Thrombopoietin
chemical_list: D008024:Ligands; D018336:Receptors, Aryl Hydrocarbon; D003094:Collagen; D013926:Thrombopoietin
keywords: aryl hydrocarbon receptor; blood platelets; cell adhesion; collagen; platelet activation; platelet aggregation