title: Relative contributions of stromal interaction molecule 1 and CalDAG-GEFI to calcium-dependent platelet activation and thrombosis.
abstract: BACKGROUND
  Stromal interaction molecule 1 (STIM1) was recently identified as a critical component of store-operated calcium entry (SOCE) in platelets. We previously reported the Ca(2+) -sensing guanine nucleotide exchange factor CalDAG-GEFI as a critical molecule in Ca(2+) signaling in platelets.
  
  
  OBJECTIVE
  To evaluate the contribution of STIM1/SOCE to Ca(2+) -dependent platelet activation and thrombosis, we here compared the activation responses of platelets lacking STIM1 and platelets lacking CalDAG-GEFI.
  
  
  METHODS
  The murine Stim1 gene was conditionally deleted in the megakaryocyte/platelet lineage. CalDAG-GEFI(-/-) and Stim1(fl/fl) PF4-Cre mice, along with littermate control mice, were used for in vitro and in vivo experiments under flow as well as static conditions.
  
  
  RESULTS
  Integrin α(IIb) β(3) -mediated aggregation was markedly impaired in CalDAG-GEFI-deficient but not STIM1-deficient platelets, under both static and flow conditions. In contrast, deficiency in either STIM1 or CalDAG-GEFI significantly impaired the ability of platelets to express phosphatidylserine on the cell surface. When subjected to a laser injury thrombosis model, mice lacking STIM1 in platelets were characterized by the formation of unstable platelet-rich thrombi and delayed and reduced fibrin generation in injured arterioles. In CalDAG-GEFI(-/-) mice, fibrin generation was also delayed and reduced, but platelet accumulation was almost abolished.
  
  
  CONCLUSIONS
  Our studies suggest that: (i) STIM1/SOCE is critical for the procoagulant activity but not the proadhesive function of platelets; and (ii) at the site of vascular injury, STIM1 and CalDAG-GEFI are critical for the first wave of thrombin generation mediated by procoagulant platelets.
authors.affiliation: Department of Medicine and Cardeza Foundation for Hematologic Research, Thomas Jefferson University, Philadelphia, PA, USA.
authors.forename: F
authors.initials: F
authors.lastname: Ahmad
authors.forename: Y
authors.initials: Y
authors.lastname: Boulaftali
authors.forename: T K
authors.initials: TK
authors.lastname: Greene
authors.forename: T D
authors.initials: TD
authors.lastname: Ouellette
authors.forename: M
authors.initials: M
authors.lastname: Poncz
authors.forename: S
authors.initials: S
authors.lastname: Feske
authors.forename: W
authors.initials: W
authors.lastname: Bergmeier
mesh_terms: D000818:Animals; D015153:Blotting, Western; D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels; D020662:Guanine Nucleotide Exchange Factors / Q000502:physiology*; D008297:Male; D008562:Membrane Glycoproteins / Q000502:physiology*; D051379:Mice; D015539:Platelet Activation; D000071737:Stromal Interaction Molecule 1; D013927:Thrombosis / Q000503:physiopathology*
chemical_list: D015220:Calcium Channels; D020662:Guanine Nucleotide Exchange Factors; D008562:Membrane Glycoproteins; C485927:Rasgrp2 protein, mouse; C100757:Stim1 protein, mouse; D000071737:Stromal Interaction Molecule 1; D002118:Calcium