Platelet-Derived Toll-Like Receptor 4 (Tlr-4) Is Sufficient to Promote Microvascular Thrombosis in Endotoxemia

Ryan J Stark,Rolando E Rumbaut,Niloufar Aghakasiri,Markus M Heimesaat

doi:10.1371/journal.pone.0041254

Ryan J Stark, Rolando E Rumbaut + Show 2 more

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https://doi.org/10.1371/journal.pone.0041254

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Abstract

Endotoxin (lipopolysaccharide, LPS) produced by gram-negative bacteria initiates a host of pro-inflammatory effects through Toll-like receptor 4 (TLR-4). We reported previously that LPS enhances microvascular thrombosis in cremaster venules of wild-type mice, but had no effect in mice deficient in TLR-4. Since TLR-4 is expressed on various cell types, the cellular origin of TLR-4 responsible for the LPS-enhanced thrombosis remains undetermined. Platelets are known to express functional TLR-4. Platelet-derived TLR-4 has been suggested to mediate various inflammatory responses in endotoxemia, including production of tumor necrosis factor alpha (TNF-α) and interleukin-1 beta (IL-1β), two cytokines reported to enhance microvascular thrombosis. We determined whether platelet-derived TLR-4 was sufficient to mediate the enhanced thrombosis induced by endotoxin and whether these responses were accompanied by systemic increases in TNF-α and IL-1β. We isolated platelets from wild-type mice and transfused them into either of two strains of TLR-4-deficient mice (C57BL/10ScN and B6.B10ScN-TLR-4lps-del/Jth). The mice were then injected with LPS or saline, and the kinetics of thrombosis were studied 4 hours later. Transfusion of wild-type platelets restored responsiveness to LPS in TLR-4-deficient mice with regards to microvascular thrombosis but not to plasma levels of TNF-α or IL-1β. The accelerated rates of microvascular thrombosis induced by platelet transfusions were specific to TLR-4, since isolation and transfusion of platelets derived from TLR-4-deficient donors did not restore responsiveness to LPS. These studies demonstrate that platelet-derived TLR-4 is sufficient to promote microvascular thrombosis in endotoxemia, independent of systemic increases in TNF-α or IL-1β.

Highlights

Sepsis, defined as a systemic inflammatory response secondary to an infection, is a leading cause of mortality in populations worldwide [1]
Following transfusion of platelets from wild-type donor mice (C57BL/10) into Toll-like receptor 4 (TLR-4)-deficient mice, exposure to LPS enhanced the kinetics of microvascular thrombosis relative to saline (Figure 1A); both times to onset of thrombosis and flow cessation were significantly lower in LPS-treated mice, by approximately 40% (p,0.05)
To exclude the possibility that the enhancement of thrombosis was a result of platelet activation during isolation and transfusion of platelets, we performed a control experiment by transfusing platelets derived from TLR4-deficient donor mice into Toll-like receptor (TLR)-4-deficient recipient mice

Summary

Introduction

Sepsis, defined as a systemic inflammatory response secondary to an infection, is a leading cause of mortality in populations worldwide [1]. One consequence of this syndrome is a systemic alteration in coagulation, called disseminated intravascular coagulation, which is associated with multi-organ system dysfunction and higher mortality [2,3]. While there has been evidence to support a functional role of TLR-4 on both platelets [10] and endothelial cells [11], there is increasing evidence supporting the role of platelets serving as an important link between the innate immune system and thrombosis

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