Intact Toll-like receptor 9 signaling in neutrophils modulates normal thrombogenesis in mice.
BACKGROUND
Deletion of Toll-like receptor 9 (Tlr9) signaling, which is important for sterile inflammatory processes, results in impaired resolution of venous thrombosis (VT) in mice. The purpose of this study was to determine if deletion of Tlr9 affected sterile necrosis, apoptosis, and neutrophil extracellular trap (NET) production in VT.


METHODS
Stasis and nonstasis murine models of VT were used in wild-type (WT) and Tlr9-/-mice, with assessment of thrombus size and determination of NETs, necrosis, and apoptosis markers. Anti-polymorphonuclear neutrophil (PMN) and antiplatelet antibody strategies were used to determine the cellular roles and their roles in WT and Tlr9-/-mice.


RESULTS
At 2 days, stasis thrombi in Tlr9-/-mice were 62% larger (n = 6-10), with 1.4-fold increased uric acid levels, 1.7-fold more apoptotic cells, 2-fold increased citrullinated histones, 2-fold increased peptidylarginine deiminase 4 (PAD4), and 1.5-fold increased elastase and a 2.4-fold reduction in tissue factor pathway inhibitor compared with WT mice (all n = 4-7; P < .05). In contrast, the sizes of nonstasis thrombi were not significantly different in Tlr9-/-mice (n = 4-6), and they did not have elevated necrosis or NET markers. Stasis thrombus size was not reduced at the 2-day time point in WT or Tlr9-/-mice that received treatment with deoxyribonuclease I or in PAD4-/-mice, which are incapable of forming NETs. In Tlr9-/-mice undergoing PMN depletion (n = 8-10), stasis thrombus size was reduced 18% and was associated with 29-fold decreased citrullinated histones, 1.3-fold decreased elastase, and 1.5-fold increased tissue factor pathway inhibitor (all n = 6; P < .05). Last, platelet depletion (>90% reduction) did not significantly reduce stasis thrombus size in Tlr9-/-mice.


CONCLUSIONS
These data suggest that the thrombogenic model affects Tlr9 thrombogenic mechanisms and that functional Tlr9 signaling in PMNs, but not in platelets or NETs, is an important mechanism in early stasis experimental venous thrombogenesis.
Department of Vascular Surgery, University of Michigan Medical School, Ann Arbor, Mich.
Osama M
OM
El-Sayed
Department of Vascular Surgery, University of Michigan Medical School, Ann Arbor, Mich.
Nicholas A
NA
Dewyer
Department of Vascular Surgery, University of Michigan Medical School, Ann Arbor, Mich.
Catherine E
CE
Luke
Department of Vascular Surgery, University of Michigan Medical School, Ann Arbor, Mich.
Megan
M
Elfline
Department of Vascular Surgery, University of Michigan Medical School, Ann Arbor, Mich.
Adriana
A
Laser
Department of Pathology, University of Michigan Medical School, Ann Arbor, Mich.
Cory
C
Hogaboam
Department of Pathology, University of Michigan Medical School, Ann Arbor, Mich.
Steven L
SL
Kunkel
Department of Vascular Surgery, University of Michigan Medical School, Ann Arbor, Mich. Electronic address: henke@umich.edu.
Peter K
PK
Henke
D000818:Animals; D017209:Apoptosis; D015415:Biomarkers / Q000097:blood; D001777:Blood Coagulation / Q000187:drug effects; D003850:Deoxyribonuclease I / Q000494:pharmacology; D004195:Disease Models, Animal; D065206:Extracellular Traps / Q000378:metabolism; D005838:Genotype; D006867:Hydrolases / Q000172:deficiency / Q000235:genetics; D008297:Male; D008807:Mice, Inbred BALB C; D018345:Mice, Knockout; D009336:Necrosis; D009504:Neutrophils / Q000187:drug effects / Q000378:metabolism* / Q000473:pathology; D010641:Phenotype; D000080002:Protein-Arginine Deiminase Type 4; D015398:Signal Transduction; D013997:Time Factors; D051217:Toll-Like Receptor 9 / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D020246:Venous Thrombosis / Q000097:blood / Q000235:genetics / Q000378:metabolism* / Q000473:pathology
D015415:Biomarkers; C495370:Tlr9 protein, mouse; D051217:Toll-Like Receptor 9; D006867:Hydrolases; D003850:Deoxyribonuclease I; D000080002:Protein-Arginine Deiminase Type 4; C552151:peptidylarginine deiminase 4, mouse