title: Endotoxin enhances microvascular thrombosis in mouse cremaster venules via a TLR4-dependent, neutrophil-independent mechanism.
abstract: Endotoxemia promotes adhesive interactions between platelets and microvascular endothelium in vivo. We sought to determine whether endotoxin (lipopolysaccharide, LPS) modified platelet thrombus formation in mouse cremaster venules and whether Toll-like receptor 4 (TLR4) and neutrophils were involved in the response. Intravital videomicroscopy was performed in the cremaster microcirculation of pentobarbital-anesthetized mice; venular platelet thrombi were induced with a light/dye endothelial injury model. C57BL/6 mice treated with Escherichia coli endotoxin had enhanced rates of venular platelet thrombus formation: the time to microvessel occlusion was reduced by approximately 50% (P < 0.005) compared with saline-treated animals. Enhanced microvascular thrombosis was evident as early as 2 h after LPS administration. LPS had no effect on thrombosis in either of two mouse strains with altered TLR4 signaling (C57BL/10ScNJ or C3H/HeJ), whereas it enhanced thrombosis in the control strains (C57BL/10J and C3H/HeN). LPS also enhanced platelet adhesion to endothelium in the absence of light/dye injury. Platelet adhesion, but not enhanced thrombosis, was inhibited by depletion of circulating neutrophils. LPS failed to enhance platelet aggregation ex vivo and did not influence platelet P-selectin expression, a marker of platelet activation. These findings support the notion that endotoxemia promotes platelet thrombus formation independent of neutrophils and without enhancement of platelet aggregation, via a TLR4-dependent mechanism.
authors.affiliation: Medical Care Line, Michael E. DeBakey Veterans Affairs Medical Center, Baylor College of Medicine, Houston, TX 77030, USA. rrumbaut@bcm.tmc.edu
authors.forename: Rolando E
authors.initials: RE
authors.lastname: Rumbaut
authors.forename: Ricardo V
authors.initials: RV
authors.lastname: Bellera
authors.forename: Jaspreet K
authors.initials: JK
authors.lastname: Randhawa
authors.forename: Corie N
authors.initials: CN
authors.lastname: Shrimpton
authors.forename: Swapan K
authors.initials: SK
authors.lastname: Dasgupta
authors.forename: Jing-Fei
authors.initials: JF
authors.lastname: Dong
authors.forename: Alan R
authors.initials: AR
authors.lastname: Burns
mesh_terms: D000818:Animals; D004731:Endotoxins / Q000506:poisoning*; D008070:Lipopolysaccharides / Q000506:poisoning; D051379:Mice; D008810:Mice, Inbred C57BL; D008833:Microcirculation / Q000187:drug effects / Q000276:immunology; D018482:Muscle, Skeletal / Q000098:blood supply* / Q000187:drug effects / Q000276:immunology; D018375:Neutrophil Activation / Q000187:drug effects / Q000276:immunology*; D009504:Neutrophils / Q000187:drug effects / Q000276:immunology*; D051197:Toll-Like Receptor 4 / Q000378:metabolism*; D020246:Venous Thrombosis / Q000139:chemically induced / Q000276:immunology*; D014699:Venules / Q000187:drug effects / Q000276:immunology*
chemical_list: D004731:Endotoxins; D008070:Lipopolysaccharides; C493487:Tlr4 protein, mouse; D051197:Toll-Like Receptor 4; C044101:endotoxin, Escherichia coli