title: Platelet secretion of CXCL4 is Rac1-dependent and regulates neutrophil infiltration and tissue damage in septic lung damage.
abstract: OBJECTIVE
  Platelets are potent regulators of neutrophil accumulation in septic lung damage. We hypothesized that platelet-derived CXCL4 might support pulmonary neutrophilia in a murine model of abdominal sepsis.
  
  
  METHODS
  Polymicrobial sepsis was triggered by coecal ligation and puncture (CLP) in C57BL/6 mice. Platelet secretion of CXCL4 was studied by using confocal microscopy. Plasma and lung levels of CXCL4, CXCL1 and CXCL2 were determined by elisa. Flow cytometry was used to examine surface expression of Mac-1 on neutrophils.
  
  
  RESULTS
  CLP increased CXCL4 levels in plasma, and platelet depletion reduced plasma levels of CXCL4 in septic animals. Rac1 inhibitor NSC23766 decreased the CLP-enhanced CXCL4 in plasma by 77%. NSC23766 also abolished PAR4 agonist-induced secretion of CXCL4 from isolated platelets. Inhibition of CXCL4 reduced CLP-evoked neutrophil recruitment, oedema formation and tissue damage in the lung. However, immunoneutralization of CXCL4 had no effect on CLP-induced expression of Mac-1 on neutrophils. Targeting CXCL4 attenuated plasma and lung levels of CXCL1 and CXCL2 in septic mice. CXCL4 had no effect on neutrophil chemotaxis in vitro, indicating it has an indirect effect on pulmonary neutrophilia. Intratracheal CXCL4 enhanced infiltration of neutrophils and formation of CXCL2 in the lung. CXCR2 antagonist SB225002 markedly reduced CXCL4-provoked neutrophil accumulation in the lung. CXCL4 caused secretion of CXCL2 from isolated alveolar macrophages.
  
  
  CONCLUSIONS
  Rac1 controls platelet secretion of CXCL4 and CXCL4 is a potent stimulator of neutrophil accumulation in septic lungs via generation of CXCL2 in alveolar macrophages. Platelet-derived CXCL4 plays an important role in lung inflammation and tissue damage in polymicrobial sepsis.
authors.affiliation: Department of Clinical Sciences, Malmö, Section for Surgery, Lund University, Malmö, Sweden.
authors.forename: Rundk
authors.initials: R
authors.lastname: Hwaiz
authors.affiliation: Department of Clinical Sciences, Malmö, Section for Surgery, Lund University, Malmö, Sweden.
authors.forename: Milladur
authors.initials: M
authors.lastname: Rahman
authors.affiliation: Islet Pathophysiology, Lund University, Malmö, Sweden.
authors.forename: Enming
authors.initials: E
authors.lastname: Zhang
authors.affiliation: Department of Clinical Sciences, Malmö, Section for Surgery, Lund University, Malmö, Sweden.
authors.forename: Henrik
authors.initials: H
authors.lastname: Thorlacius
mesh_terms: D000818:Animals; D001792:Blood Platelets / Q000378:metabolism*; D001992:Bronchoalveolar Lavage Fluid / Q000166:cytology; D054360:Chemokine CXCL1 / Q000097:blood / Q000378:metabolism; D054426:Chemokine CXCL2 / Q000097:blood / Q000378:metabolism; D008168:Lung / Q000378:metabolism* / Q000473:pathology; D016676:Macrophages, Alveolar / Q000378:metabolism; D008297:Male; D008810:Mice, Inbred C57BL; D009479:Neuropeptides / Q000097:blood / Q000378:metabolism*; D020556:Neutrophil Infiltration; D010978:Platelet Factor 4 / Q000097:blood / Q000378:metabolism*; D018805:Sepsis / Q000378:metabolism* / Q000473:pathology; D020830:rac1 GTP-Binding Protein / Q000097:blood / Q000378:metabolism*
chemical_list: D054360:Chemokine CXCL1; D054426:Chemokine CXCL2; C475895:Cxcl1 protein, mouse; C404915:Cxcl2 protein, mouse; D009479:Neuropeptides; C484602:Rac1 protein, mouse; D010978:Platelet Factor 4; D020830:rac1 GTP-Binding Protein