Endotoxin enhances microvascular thrombosis in mouse cremaster venules via a TLR4-dependent, neutrophil-independent mechanism.
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.
Rumbaut
Rolando E
RE
Medical Care Line, Michael E. DeBakey Veterans Affairs Medical Center, Baylor College of Medicine, Houston, TX 77030, USA. rrumbaut@bcm.tmc.edu
Bellera
Ricardo V
RV
Randhawa
Jaspreet K
JK
Shrimpton
Corie N
CN
Dasgupta
Swapan K
SK
Dong
Jing-Fei
JF
Burns
Alan R
AR
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*
D004731:Endotoxins; D008070:Lipopolysaccharides; C493487:Tlr4 protein, mouse; D051197:Toll-Like Receptor 4; C044101:endotoxin, Escherichia coli