TLR2 Plays a Key Role in Platelet Hyperreactivity and Accelerated Thrombosis Associated With Hyperlipidemia

Abstract

Rationale Platelet hyperreactivity, which is common in many pathological conditions, is associated with increased atherothrombotic risk. The mechanisms leading to platelet hyperreactivity are complex and not yet fully understood. Objective Platelet hyperreactivity and accelerated thrombosis, specifically in dyslipidemia, have been mechanistically linked to accumulation in the circulation of a specific group of oxidized phospholipids (oxPCCD36) that are ligands for the platelet pattern-recognition receptor CD36. In the current manuscript, we tested whether the platelet innate immune system contributes to responses to oxPCCD36 and accelerated thrombosis observed in hyperlipidemia. Methods and Results Using in vitro approaches, as well as platelets from mice with genetic deletion of MyD88 or TLRs, we demonstrate that TLR2 and TLR6 are required for the activation of human and murine platelets by oxPCCD36. oxPCCD36 induce formation of CD36/TLR2/TLR6 complex in platelets and activate downstream signaling via TIRAP-MyD88-IRAK1/4-TRAF6, leading to integrin activation via the SFK-Syk-PLCγ2 pathway. Intravital thrombosis studies using ApoE−/− mice with genetic deficiency of TLR2 or TLR6 have demonstrated that oxPCCD36 contribute to accelerated thrombosis specifically in the setting of hyperlipidemia. Conclusions Our studies reveal that TLR2 plays a key role in platelet hyperreactivity and the prothrombotic state in the setting of hyperlipidemia by sensing a wide range of endogenous lipid-peroxidation ligands and activating innate immune signaling cascade in platelets.

Toll-like receptors in immunity and inflammatory diseases: Past, present, and future

“…This is because platelets and TLRs expressed by these cells play a potential role in the process of inflammation, development of neutrophil extracellular traps (NETs) and several inflammatory diseases including atherosclerosis, sepsis [269][270][271][272][273]. For example, both platelet TLR4 and TLR2 are involved in its interaction with neutrophils causing the formation of a heterotypic complex with neutrophils [259,275].…”

“…This Platelet-neutrophil interaction involves P-selectin expressed by platelets and neutrophil PSGL1 (P-Selectin Glycoprotein Ligand 1) or CD162 [252]. During hyperlipidemia activation of platelet TLR2 via oxidized phospholipids [oxPC CD36, oxidized phospholipid bound to CD36 or platelet glycoprotein 4 or fatty acid translocase (FAT)] causes hyperactivation of platelets via activation of TIRAP (Toll-interleukin 1 receptor domain containing adaptor protein)-MyD88-IRAK (interleukin-1 receptor-associated kinase)1/4-TRAF6 (TNF receptor-associated factor 6), causing an activation of integrin through Src family kinase (SFK)-spleen tyrosine kinase (Syk)-PLCγ2 (phospholipase Cγ2) pathway [275]. This hyperactivation of platelets via TLR2 during hyperlipidemia is responsible for the development of thrombosis [275].…”

“…During hyperlipidemia activation of platelet TLR2 via oxidized phospholipids [oxPC CD36, oxidized phospholipid bound to CD36 or platelet glycoprotein 4 or fatty acid translocase (FAT)] causes hyperactivation of platelets via activation of TIRAP (Toll-interleukin 1 receptor domain containing adaptor protein)-MyD88-IRAK (interleukin-1 receptor-associated kinase)1/4-TRAF6 (TNF receptor-associated factor 6), causing an activation of integrin through Src family kinase (SFK)-spleen tyrosine kinase (Syk)-PLCγ2 (phospholipase Cγ2) pathway [275]. This hyperactivation of platelets via TLR2 during hyperlipidemia is responsible for the development of thrombosis [275]. In addition to TLR2, an activation of TLR9 is also involved in the oxidative stress-induced generation of thrombosis via carboxy(alkylpyrrole) protein adducts (CAPs), that act as novel unconventional ligands for TLR9 [276].…”

Coenzyme Q10 Upregulates Platelet cAMP/PKA Pathway and Attenuates Integrin αIIbβ3 Signaling and Thrombus Growth

“…Hyperlipidemia has been shown to promote platelet hyperactivity and increase the risk of myocardial infarction and stroke. [63][64][65] Platelets from patients with hyperlipidemia possess a lower threshold for aggregation and activation, this may be caused by increased circulating oxidized LDL (ox-LDL), and oxidative stress. [64,66] We noticed differing conclusions on whether CoQ10 improves lipid profiles (i.e., lower LDL levels).…”

Contribution of the commensal microbiota to atherosclerosis and arterial thrombosis

“…PRR signalling of platelets (Zhang et al ., ; Biswas et al ., ) and endothelial cells (Ren et al ., ; Jäckel et al ., ) promotes arterial thrombosis in the mouse ferric chloride and the ligation injury model of the carotid artery. Arterial thrombus formation is supported by NOD2, TLR2 and TLR9 in platelets (Panigrahi et al ., ; Zhang et al ., ; Biswas et al ., ) as well as TLR2 and TLR4 in endothelial cells (Ren et al ., ; Jäckel et al ., ). As the gut microbiota is a source of physiologically active PRR agonists in the plasma (Clarke et al ., ; Balmer et al ., ), it is crucial to explore the role of this microbial ecosystem in arterial thrombosis.…”