title: Formation of platelet strings and microthrombi in the presence of ADAMTS-13 inhibitor does not require P-selectin or beta3 integrin.
abstract: BACKGROUND
  Ultra-large von Willebrand factor (ULVWF) and the receptor P-selectin are released from endothelial Weibel-Palade bodies during injury or inflammation. VWF mediates platelet adhesion and P-selectin promotes leukocyte rolling. ADAMTS-13 limits the duration of platelet adhesion by cleaving the ULVWF. In the absence of ADAMTS-13, long VWF filaments decorated with platelets form. Recent in vitro studies suggested that P-selectin might anchor these platelet strings to endothelium, but whether the same mechanism exists in vivo remains to be elucidated.
  
  
  METHODS
  We address the role of P-selectin and beta(3) integrin in platelet string formation in vivo using intravital microscopy by infusing inhibitory ADAMTS-13 antibody in P-selectin-/- and beta(3)-deficient mice and activating the endothelium by injecting histamine.
  
  
  RESULTS
  We show that inhibition of ADAMTS-13 combined with endothelial activation leads to similar extents of platelet string formation in wild-type, P-selectin- and integrin beta(3)-deficient mice. Further, in venules the platelet strings can coalesce into VWF-platelet aggregates. This process utilizes neither the platelet beta(3) integrin nor P-selectin. We also show in vitro that platelets can act as a bridge between the VWF fibers and that VWF can self-associate even in areas devoid of platelets.
  
  
  CONCLUSIONS
  The formation or retention of the platelet strings does not require P-selectin or the endothelial VWF receptor alpha(v)beta(3). Furthermore, in the presence of low ADAMTS-13 activity, VWF-dependent and alpha(IIb)beta(3)-independent platelet clustering occurs in veins, as has been shown at high arterial shear rates. Our study further supports the importance of regulation of VWF multimer size upon secretion from Weibel-Palade bodies.
authors.affiliation: CBR Institute for Biomedical Research and Department of Pathology, Harvard Medical School, Boston, MA 02115, USA.
authors.forename: A K
authors.initials: AK
authors.lastname: Chauhan
authors.forename: T
authors.initials: T
authors.lastname: Goerge
authors.forename: S W
authors.initials: SW
authors.lastname: Schneider
authors.forename: D D
authors.initials: DD
authors.lastname: Wagner
mesh_terms: D000071120:ADAMTS13 Protein; D000818:Animals; D000906:Antibodies / Q000494:pharmacology; D001792:Blood Platelets / Q000378:metabolism*; D002478:Cells, Cultured; D004730:Endothelium, Vascular / Q000187:drug effects / Q000378:metabolism; D006632:Histamine / Q000494:pharmacology; D039661:Integrin beta3 / Q000235:genetics / Q000378:metabolism*; D008666:Metalloendopeptidases / Q000037:antagonists & inhibitors / Q000276:immunology / Q000378:metabolism*; D051379:Mice; D008807:Mice, Inbred BALB C; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D018715:Microscopy, Video; D019007:P-Selectin / Q000235:genetics / Q000378:metabolism*; D010973:Platelet Adhesiveness; D010974:Platelet Aggregation; D013314:Stress, Mechanical; D013927:Thrombosis / Q000097:blood / Q000378:metabolism*; D014699:Venules / Q000378:metabolism; D014841:von Willebrand Factor / Q000378:metabolism*
chemical_list: D000906:Antibodies; D039661:Integrin beta3; D019007:P-Selectin; D014841:von Willebrand Factor; D006632:Histamine; C502939:ADAMTS13 protein, mouse; D008666:Metalloendopeptidases; D000071120:ADAMTS13 Protein