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Toll-like receptor 2 stimulation of platelets is mediated by purinergic P2X1-dependent Ca2+ mobilisation, cyclooxygenase and purinergic P2Y1 and P2Y12 receptor activation
Linköping University, Department of Medical and Health Sciences, Division of Cardiovascular Medicine. Linköping University, Faculty of Health Sciences.
Linköping University, Department of Medical and Health Sciences, Pharmacology. Linköping University, Faculty of Health Sciences.
Linköping University, Department of Medical and Health Sciences, Pharmacology. Linköping University, Faculty of Health Sciences.
Linköping University, Department of Clinical and Experimental Medicine, Medical Microbiology. Linköping University, Faculty of Health Sciences.
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2010 (English)In: Thrombosis and Haemostasis, ISSN 0340-6245, Vol. 103, no 2, 398-407 p.Article in journal (Refereed) Published
Abstract [en]

Toll-like receptor 2 (TLR2), which recognise and respond to conserved microbial pathogen-associated molecular patterns, is expressed on the platelet surface. Furthermore, it has recently been shown that the TLR2/1 agonist Pam(3)CSK(4) stimulates platelet activation. The aim of the present study was to clarify important signalling events in Pam(3)CSK(4)-induced platelet aggregation and secretion. Platelet interaction with Pam(3)CSK(4) and the TLR2/6 agonist MALP-2 was studied by analysing aggregation, ATP-secretion, [Ca2+](i) mobilisation and thromboxane B2 (TxB(2)) production. The results show that Pam(3)CSK(4) but not MALP-2 induces [Ca2+](i) increase, TxB(2) production, dense granule secretion and platelet aggregation. Preincubation of platelets with MALP-2 inhibited the Pam(3)CSK(4)-induced responses. The ATP-secretion and aggregation in Pam(3)CSK(4)-stimulated platelets was impeded by the purinergic P2X(1) inhibitor MRS 2159, the purinergic P2Y(1) and P2Y(12) antagonists MRS 2179 and cangrelor, the phospholipase C inhibitor U73122, the calcium chelator BAPT-AM and aspirin. The calcium mobilisation was lowered by MRS 2159, aspirin and U73122 whereas the TxB(2) production was antagonised by MRS 2159, aspirin and BAPT-AM. When investigating the involvement of the myeloid differentiation factor-88 (MyD88) -dependent pathway, we found that platelets express MyD88 and interleukin 1 receptor-associated kinase (IRAK-1), which are proteins important in TLR signalling. However, Pam(3)CSK(4) did not stimulate a rapid (within 10 minutes) phosphorylation of IRAK-1 in platelets. In conclusion, the results show that Pam(3)CSK(4)-induced platelet aggregation and secretion depends on a P2X(1)-mediated Ca2+ mobilisation, production of TxA(2) and ADP receptor activation. The findings in this study further support a role for platelets in sensing bacterial components.

Place, publisher, year, edition, pages
2010. Vol. 103, no 2, 398-407 p.
Keyword [en]
Infection, purinergic P2X(1) receptor, atherosclerosis, MALP-2, Pam(3)CSK(4), platelet, MyD88, IRAK-1
National Category
Medical and Health Sciences
Identifiers
URN: urn:nbn:se:liu:diva-54249DOI: 10.1160/TH09-07-0442ISI: 000274734100022OAI: oai:DiVA.org:liu-54249DiVA: diva2:302302
Available from: 2010-03-05 Created: 2010-03-05 Last updated: 2017-12-12Bibliographically approved
In thesis
1. Platelets in inflammation: Role of complement protein C1q, C-reactive proteinand toll-like receptors
Open this publication in new window or tab >>Platelets in inflammation: Role of complement protein C1q, C-reactive proteinand toll-like receptors
2010 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Platelets are proven essential in haemostasis, however, they are now also increasingly recognized as cells with important immunomodulatory properties, e.g. through interaction with leukocytes and several species of bacteria and by release inflammatory mediators upon activation. Moreover, platelets express receptors involved in immunity and inflammation such as Fcγ‐receptor IIa, complement protein C1q‐receptors (gC1qR, cC1qR, CD93 and α2β1) and toll‐like receptors (TLR‐1, ‐2, ‐4, ‐6 and ‐9). C1q, C‐reactive protein (CRP) and TLRs are all pattern recognition molecules able to recognize non‐self structures and initiate an immune response. Uncontrolled or misdirected activation of platelets and the immune response is involved in the onset and progress of several conditions with an inflammatory component, such as coronary artery disease and autoimmune diseases.

Hence, the aims of the present thesis were to investigate the effects and q mechanisms of C1and CRP on platelet activation, and to clarify the intracellular signaling events provoked by TLR‐2 stimulation of platelets. Platelet interaction with immune complexes is poorly understood, however by utilizing well‐characterized model surfaces with adsorbed IgG and microscopy, we show that both C1q and CRP are able to inhibit FcγR‐mediated platelet adhesion and spreading. Using isolated platelets in suspension and flow cytometry, we also found that C1q triggers a rapid, moderate and transient up‐regulation of P‐selectin that is sensitive to blockade of gC1qR and protein kinase C (PKC), but not blockade of α2β1. Additionally, subsequent platelet activation by collagen or collagen‐related peptide (GPVI specific) is inhibited by C1q, suggesting a role for GPVI in C1q‐mediated regulation of collagen‐induced platelet activation. Whole blood studies revealed that C1q inhibits total cell aggregation, formation of platelet‐leukocyte aggregates, and potentiates the production of reactive oxygen species (ROS), all in a platelet‐dependent manner. Furthermore, using the TLR‐2/1 agonist Pam3CSK4 we found that TLR‐2/1‐activation of platelets is mediated via a P2X1‐dependent increase in intracellular free Ca2+, P2Y1 and P2Y12 –receptor ligation, and activation of cyclooxygenase. We also found that platelets express IRAK‐1, however, without being rapidly phosphorylated upon Pam3CSK4 stimulation and thus probably not involved in the early aggregation/secretion response. Furthermore, TLR‐2/6 stimulation does not lead to platelet activation but instead inhibits TLR‐2/1‐provoked activation. Taken together, these findings further strengthen the role of platelets as key players in inflammatory processes.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2010. 80 p.
Series
Linköping University Medical Dissertations, ISSN 0345-0082 ; 1176
National Category
Medical and Health Sciences
Identifiers
urn:nbn:se:liu:diva-54667 (URN)978-91-7393-418-3 (ISBN)
Public defence
2010-04-16, Berzeliussalen, Campus US, Linköpings universitet, Linköping, 09:00 (English)
Opponent
Supervisors
Available from: 2010-03-30 Created: 2010-03-30 Last updated: 2015-06-29Bibliographically approved

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Kälvegren, HannaSkoglund, CarolineLerm, MariaGrenegård, MagnusBengtsson, Torbjörn

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