title: Human neutrophil alpha-defensins induce formation of fibrinogen and thrombospondin-1 amyloid-like structures and activate platelets via glycoprotein IIb/IIIa.
abstract: BACKGROUND
  Human neutrophil α-defensins (HNPs) are important constituents of the innate immune system. Beyond their antimicrobial properties, HNPs also have pro-inflammatory features. While HNPs in plasma from healthy individuals are barely detectable, their level is strongly elevated in septic plasma and plasma from patients with acute coronary syndromes.
  
  
  OBJECTIVE
  As thrombosis and inflammation are intertwined processes and activation of human polymorphonuclear leukocytes (PMNL) and subsequent degranulation is associated with full activation of surrounding platelets, we studied the effect of HNPs on platelet function.
  
  
  METHODS
  The effect of HNPs on platelet activation parameters and apoptosis was investigated via aggregometry, flow cytometry, confocal microscopy and the ELISA technique.
  
  
  RESULTS
  It was found that HNPs activate platelets in pathophysiologically relevant doses, inducing fibrinogen and thrombospondin-1 binding, aggregation, granule secretion, sCD40L shedding, and procoagulant activity. HNPs bound directly to the platelet membrane, induced membrane pore formation, microparticle formation, mitochondrial membrane depolarization and caspase-3-activity. Confocal microscopy revealed the HNP-induced formation of polymeric fibrinogen and thrombospondin-1 amyloid-like structures, which bound microorganisms. Platelets adhered to these structures and formed aggregates. Blocking of glycoprotein IIb/IIIa (GPIIb/IIIa) markedly inhibited HNP-induced platelet activation. In addition, heparin, heparinoid, serpins and α(2)-macroglobulin, which all bind to HNPs, blocked HNP-1-induced platelet activation in contrast to direct thrombin inhibitors such as hirudin.
  
  
  CONCLUSIONS
  HNPs activate platelets and induce platelet apoptosis by formation of amyloid-like proteins. As these structures entrapped bacteria and fungi, they might reflect an additional function of HNPs in host defense. The described mechanism links again thrombosis and infection.
authors.affiliation: Department of Anaesthesiology and Intensive Care, Experimental and Clinical Haemostasis, University of Muenster, Muenster, Germany.
authors.forename: M
authors.initials: M
authors.lastname: Horn
authors.forename: A
authors.initials: A
authors.lastname: Bertling
authors.forename: M F
authors.initials: MF
authors.lastname: Brodde
authors.forename: A
authors.initials: A
authors.lastname: Müller
authors.forename: J
authors.initials: J
authors.lastname: Roth
authors.forename: H
authors.initials: H
authors.lastname: Van Aken
authors.forename: K
authors.initials: K
authors.lastname: Jurk
authors.forename: C
authors.initials: C
authors.lastname: Heilmann
authors.forename: G
authors.initials: G
authors.lastname: Peters
authors.forename: B E
authors.initials: BE
authors.lastname: Kehrel
mesh_terms: D000682:Amyloid / Q000378:metabolism*; D000991:Antithrombins / Q000494:pharmacology; D017209:Apoptosis; D001792:Blood Platelets / Q000187:drug effects / Q000276:immunology / Q000378:metabolism* / Q000473:pathology; D053148:Caspase 3 / Q000378:metabolism; D015550:Cell Degranulation; D004797:Enzyme-Linked Immunosorbent Assay; D005340:Fibrinogen / Q000378:metabolism*; D005434:Flow Cytometry; D006801:Humans; D007249:Inflammation / Q000097:blood / Q000276:immunology; D039421:Integrin alpha2 / Q000378:metabolism*; D039661:Integrin beta3 / Q000378:metabolism*; D053078:Membrane Potential, Mitochondrial; D018613:Microscopy, Confocal; D018375:Neutrophil Activation; D009504:Neutrophils / Q000276:immunology / Q000378:metabolism*; D010973:Platelet Adhesiveness; D010974:Platelet Aggregation; D010975:Platelet Aggregation Inhibitors / Q000494:pharmacology; D010979:Platelet Function Tests; D019039:Platelet Glycoprotein GPIIb-IIIa Complex / Q000037:antagonists & inhibitors / Q000378:metabolism*; D015843:Serpins / Q000494:pharmacology; D013927:Thrombosis / Q000097:blood / Q000276:immunology; D019700:Thrombospondin 1 / Q000378:metabolism*; D013997:Time Factors; D023084:alpha-Defensins / Q000378:metabolism*
chemical_list: D000682:Amyloid; D000991:Antithrombins; C056564:ITGA2B protein, human; C061248:ITGB3 protein, human; D039421:Integrin alpha2; D039661:Integrin beta3; D010975:Platelet Aggregation Inhibitors; D019039:Platelet Glycoprotein GPIIb-IIIa Complex; D015843:Serpins; D019700:Thrombospondin 1; D023084:alpha-Defensins; C406413:human neutrophil peptide 1; D005340:Fibrinogen; C505407:CASP3 protein, human; D053148:Caspase 3