title: Partially Defective Store Operated Calcium Entry and Hem(ITAM) Signaling in Platelets of Serotonin Transporter Deficient Mice.
abstract: BACKGROUND
  Serotonin (5-hydroxytryptamin, 5-HT) is an indolamine platelet agonist, biochemically derived from tryptophan. 5-HT is secreted from the enterochromaffin cells into the gastrointestinal tract and blood. Blood 5-HT has been proposed to regulate hemostasis by acting as a vasoconstrictor and by triggering platelet signaling through 5-HT receptor 2A (5HTR2A). Although platelets do not synthetize 5-HT, they take 5-HT up from the blood and store it in their dense granules which are secreted upon platelet activation.
  
  
  OBJECTIVE
  To identify the molecular composite of the 5-HT uptake system in platelets and elucidate the role of platelet released 5-HT in thrombosis and ischemic stroke.
  
  
  METHODS
  5-HT transporter knockout mice (5Htt-/-) were analyzed in different in vitro and in vivo assays and in a model of ischemic stroke.
  
  
  RESULTS
  In 5Htt-/- platelets, 5-HT uptake from the blood was completely abolished and agonist-induced Ca2+ influx through store operated Ca2+ entry (SOCE), integrin activation, degranulation and aggregation responses to glycoprotein VI (GPVI) and C-type lectin-like receptor 2 (CLEC-2) were reduced. These observed in vitro defects in 5Htt-/- platelets could be normalized by the addition of exogenous 5-HT. Moreover, reduced 5-HT levels in the plasma, an increased bleeding time and the formation of unstable thrombi were observed ex vivo under flow and in vivo in the abdominal aorta and carotid artery of 5Htt-/- mice. Surprisingly, in the transient middle cerebral artery occlusion (tMCAO) model of ischemic stroke 5Htt-/- mice showed nearly normal infarct volume and the neurological outcome was comparable to control mice.
  
  
  CONCLUSIONS
  Although secreted platelet 5-HT does not appear to play a crucial role in the development of reperfusion injury after stroke, it is essential to amplify the second phase of platelet activation through SOCE and plays an important role in thrombus stabilization.
authors.affiliation: Institute of Experimental Biomedicine, University Hospital of Würzburg, Würzburg, Germany.
authors.forename: Karen
authors.initials: K
authors.lastname: Wolf
authors.affiliation: Institute of Experimental Biomedicine, University Hospital of Würzburg, Würzburg, Germany.
authors.forename: Attila
authors.initials: A
authors.lastname: Braun
authors.affiliation: Institute of Experimental Biomedicine, University Hospital of Würzburg, Würzburg, Germany.
authors.forename: Elizabeth J
authors.initials: EJ
authors.lastname: Haining
authors.affiliation: Department of Psychiatry, Taipei Tzu Chi Hospital, Buddhist Tzu Chi Medical Foundation, Taipei, Taiwan.
authors.forename: Yu-Lun
authors.initials: YL
authors.lastname: Tseng
authors.affiliation: Department of Neurology, University Hospital of Würzburg, Würzburg, Germany.
authors.forename: Peter
authors.initials: P
authors.lastname: Kraft
authors.affiliation: Department of Neurology, University Hospital of Würzburg, Würzburg, Germany.
authors.forename: Michael K
authors.initials: MK
authors.lastname: Schuhmann
authors.affiliation: Institute of Experimental Biomedicine, University Hospital of Würzburg, Würzburg, Germany.
authors.forename: Sanjeev K
authors.initials: SK
authors.lastname: Gotru
authors.affiliation: Institute of Experimental Biomedicine, University Hospital of Würzburg, Würzburg, Germany.
authors.forename: Wenchun
authors.initials: W
authors.lastname: Chen
authors.affiliation: Department of Medical Clinic and Policlinic II, Hepatology, University Hospital of Würzburg, Würzburg, Germany.
authors.forename: Heike M
authors.initials: HM
authors.lastname: Hermanns
authors.affiliation: Department of Neurology, University Hospital of Würzburg, Würzburg, Germany.
authors.forename: Guido
authors.initials: G
authors.lastname: Stoll
authors.affiliation: Department of Molecular Psychiatry, University Hospital of Würzburg, Würzburg, Germany.
authors.forename: Klaus-Peter
authors.initials: KP
authors.lastname: Lesch
authors.affiliation: Institute of Experimental Biomedicine, University Hospital of Würzburg, Würzburg, Germany.|Rudolf Virchow Center, University of Würzburg, Würzburg, Germany.
authors.forename: Bernhard
authors.initials: B
authors.lastname: Nieswandt
mesh_terms: D000818:Animals; D001792:Blood Platelets / Q000378:metabolism / Q000502:physiology*; D002118:Calcium / Q000378:metabolism*; D004195:Disease Models, Animal; D005340:Fibrinogen / Q000502:physiology; D006487:Hemostasis / Q000502:physiology; D006897:Hydroxyindoleacetic Acid / Q000652:urine; D008550:Melatonin / Q000097:blood; D051379:Mice; D018345:Mice, Knockout; D010744:Phosphoric Monoester Hydrolases / Q000378:metabolism; D012701:Serotonin / Q000378:metabolism*; D050486:Serotonin Plasma Membrane Transport Proteins / Q000172:deficiency / Q000502:physiology*; D015398:Signal Transduction / Q000502:physiology*; D020521:Stroke / Q000503:physiopathology; D013927:Thrombosis / Q000503:physiopathology
chemical_list: D050486:Serotonin Plasma Membrane Transport Proteins; D012701:Serotonin; D006897:Hydroxyindoleacetic Acid; D005340:Fibrinogen; D010744:Phosphoric Monoester Hydrolases; C021822:myo-inositol-1 (or 4)-monophosphatase; D008550:Melatonin; D002118:Calcium