Lipopolysaccharide Stimulates Platelet Secretion and Potentiates Platelet Aggregation via TLR4/MyD88 and the cGMP-Dependent Protein Kinase Pathway

Abstract

Bacterial LPS induces rapid thrombocytopenia, hypotension, and sepsis. Although growing evidence suggests that platelet activation plays a critical role in LPS-induced thrombocytopenia and tissue damage, the mechanism of LPS-mediated platelet activation is unclear. In this study, we show that LPS stimulates platelet secretion of dense and α granules as indicated by ATP release and P-selectin expression, and thus enhances platelet activation induced by low concentrations of platelet agonists. Platelets express components of the LPS receptor-signaling complex, including TLR (TLR4), CD14, MD2, and MyD88, and the effect of LPS on platelet activation was abolished by an anti-TLR4-blocking Ab or TLR4 knockout, suggesting that the effect of LPS on platelet aggregation requires the TLR4 pathway. Furthermore, LPS-potentiated thrombin- and collagen-induced platelet aggregation and FeCl3-induced thrombus formation were abolished in MyD88 knockout mice. LPS also induced cGMP elevation and the stimulatory effect of LPS on platelet aggregation was abolished by inhibitors of NO synthase and the cGMP-dependent protein kinase (PKG). LPS-induced cGMP elevation was inhibited by an anti-TLR4 Ab or by TLR4 deficiency, suggesting that activation of the cGMP/protein kinase G pathway by LPS involves the TLR4 pathway. Taken together, our data indicate that LPS stimulates platelet secretion and potentiates platelet aggregation through a TLR4/MyD88- and cGMP/PKG-dependent pathway.

The Toll-like receptor 2/1 (TLR2/1) complex initiates human platelet activation via the src/Syk/LAT/PLCγ2 signalling cascade

“…A broad variety of proteins involved in TLR signalling in nucleated cells has been likewise detected in platelets, including MyD88 and IRAK-1 [12,32]. Whereas it has been shown that human platelet TLR4 signalling engages MyD88 [33], TLR2/1 activation by Pam3CSK4 was reported to not induce IRAK-1 phosphorylation [12]. Although several former studies demonstrated that the bacterial lipopeptide-mimicking TLR2/1-heterodimer agonist Pam3CSK4 concentration-dependently triggers prominent platelet activation and full aggregation [11][12][13], the underlying initial signalling pathway, however, has not been defined in detail so far.…”

Nouvelle Cuisine: Platelets Served with Inflammation

“…The ligands of TLRs have been studied extensively, and they range from secretory components of pathogens to nucleic acids. Many articles reported that TLRs 1-9 are expressed on both human and murine platelets, and some of these are functional, such as TLR4 in the mediation of LPS-induced thrombocytopenia and TNF-a production in vivo (34)(35)(36)(37)(38)(39)(40). Likewise, the previously mentioned platelet-neutrophil interaction leading to NET formation and subsequent trapping of bacteria during sepsis is triggered via platelet TLR4 (6).…”

Annexin A5 Increases Survival in Murine Sepsis Model by Inhibiting HMGB1-Mediated Proinflammation and Coagulation

“…Both LPS (38,39) and HMGB1 (11,12,20) have been suggested to induce coagulation, and each substance is considered as a single factor for aggravating tissue impairment in septic patients other signaling pathway or to interrupt other substances interacting TLR4.…”