title: Activated platelets present high mobility group box 1 to neutrophils, inducing autophagy and promoting the extrusion of neutrophil extracellular traps.
abstract: BACKGROUND
  Increasing evidence implicates both platelets and neutrophils in the formation, stabilization, and growth of peripheral and coronary thrombi. Neutrophil extracellular traps (NETs) play a key role. The early events in the deregulated cross-talk between platelets and neutrophils are poorly characterized.
  
  
  OBJECTIVE
  To identify at the molecular level the mechanism through which platelets induce the generation of NETs in sterile conditions.
  
  
  METHODS
  The presence of NETs was determined in 26 thrombi from patients with acute myocardial infarction by immunohistochemistry and immunofluorescence and markers of NETs assessed in the plasma. In vitro NET generation was studied in static and in physiological flow conditions.
  
  
  RESULTS
  Coronary thrombi mainly consist of activated platelets, neutrophils, and NETs in close proximity of platelets. Activated platelets commit neutrophils to NET generation. The event abates in the presence of competitive antagonists of the high mobility group box 1 (HMGB1) protein. Hmgb1(-/-) platelets fail to elicit NETs, whereas the HMGB1 alone commits neutrophils to NET generation. Integrity of the HMGB1 receptor, Receptor for Advanced Glycation End products (RAGE), is required for NET formation, as assessed using pharmacologic and genetic tools. Exposure to HMGB1 prevents depletion of mitochondrial potential, induces autophagosome formation, and prolongs neutrophil survival. These metabolic effects are caused by the activation of autophagy. Blockade of the autophagic flux reverts platelet HMGB1-elicited NET generation.
  
  
  CONCLUSIONS
  Activated platelets present HMGB1 to neutrophils and commit them to autophagy and NET generation. This chain of events may be responsible for some types of thromboinflammatory lesions and indicates novel paths for molecular intervention.
authors.affiliation: Division of Regenerative Medicine, Gene Therapy and Stem Cells, Department of Medicine, San Raffaele Scientific Institute and Vita Salute San Raffaele University, Milan, Italy.
authors.forename: N
authors.initials: N
authors.lastname: Maugeri
authors.forename: L
authors.initials: L
authors.lastname: Campana
authors.forename: M
authors.initials: M
authors.lastname: Gavina
authors.forename: C
authors.initials: C
authors.lastname: Covino
authors.forename: M
authors.initials: M
authors.lastname: De Metrio
authors.forename: C
authors.initials: C
authors.lastname: Panciroli
authors.forename: L
authors.initials: L
authors.lastname: Maiuri
authors.forename: A
authors.initials: A
authors.lastname: Maseri
authors.forename: A
authors.initials: A
authors.lastname: D'Angelo
authors.forename: M E
authors.initials: ME
authors.lastname: Bianchi
authors.forename: P
authors.initials: P
authors.lastname: Rovere-Querini
authors.forename: A A
authors.initials: AA
authors.lastname: Manfredi
mesh_terms: D000328:Adult; D000368:Aged; D000818:Animals; D000911:Antibodies, Monoclonal / Q000737:chemistry; D001343:Autophagy; D001792:Blood Platelets / Q000166:cytology; D001854:Bone Marrow Cells / Q000166:cytology; D016022:Case-Control Studies; D065206:Extracellular Traps / Q000378:metabolism*; D024243:HMGB1 Protein / Q000235:genetics*; D006801:Humans; D007113:Immunity, Innate; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D008875:Middle Aged; D008928:Mitochondria / Q000473:pathology; D009504:Neutrophils / Q000166:cytology*; D015539:Platelet Activation; D017382:Reactive Oxygen Species / Q000378:metabolism; D013927:Thrombosis / Q000097:blood / Q000473:pathology
chemical_list: D000911:Antibodies, Monoclonal; D024243:HMGB1 Protein; C585491:HMGB1 protein, human; D017382:Reactive Oxygen Species
keywords: HMGB1; autophagy; innate immunity; neutrophils; platelets; thrombosis