Change search
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
The role of platelet thrombin receptors PAR1 and PAR4 in health and disease
Linköping University, Department of Clinical and Experimental Medicine, Clinical Chemistry. Linköping University, Faculty of Health Sciences.
2011 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Blood cells are continuously flowing in our systems maintaining haemostasis in the arteries and veins. If a vessel is damaged, the smallest cell fragments in the blood (platelets) are directed to cover the wound and plug the leakage to prevent blood loss. Most of the time platelets stop the blood leak without any difficulties. During other, pathological, circumstances, platelets continue to form a thrombus, preventing the blood flow and may cause myocardial infarction or stroke.

Thrombin is the most potent platelet agonist and is a product created in the coagulation cascade. This thesis is focused on the interactions between the two platelet thrombin receptors; protease activated receptors 1 (PAR1) and PAR4 in vitro. We have investigated potential differences between these receptors in several situations associated with cardiovascular disease.

First we studied interactions between PAR1 and PAR4 and the oral pathogen Porphyromonas gingivalis (which secretes enzymes, gingipains, with properties similar to thrombin). Here we showed that P. gingivalis is signaling mainly, but not exclusively, via PAR4. Our second study showed that the cross-talk between the stress hormone epinephrine and thrombin occur exclusively through PAR4 if the key-substance ATP is present and cyclooxygenase-1 inhibited by aspirin. The third study investigated platelet secretion, with focus on the protein plasminogen activator inhibitor 1(PAI-1), an inhibitor of the fibrinolytic process responsible for dissolving a formed clot. Here we showed that PAI-1 secretion and synthesis was more sensitive to stimulation through PAR1 than PAR4. Finally this thesis describes differences between PAR1 and PAR4 in cell-signaling pathways regulating the stability of a platelet aggregate, where PAR4 seems to be of importance to create stable platelet aggregates and that this stability is dependent on ADP activation via P2Y12 and cell signaling via PI3-kinase.

Until now, PAR1 has been considered to be the most important thrombin receptor, due to its high affinity for thrombin. However, there must be a reason why platelets express two different thrombin receptors. This thesis highlights several situations where PAR4 plays a complementary and important role in platelet signaling and haemostasis.

In conclusion, this thesis suggests that PAR4 plays a major role in calcium signaling and the induction of sustained aggregation, while PAR1 shows a more prominent role in platelet secretion and synthesis. This thesis also reveals new interactions between platelet thrombin receptors and the ADP-, ATP- and epinephrine receptors. The results described in this thesis contribute to an increased knowledge of the platelet thrombin receptors and their interplay in situations such as infection, stress, fibrinolysis, and platelet aggregation.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press , 2011. , 63 p.
Series
Linköping University Medical Dissertations, ISSN 0345-0082 ; 1261
National Category
Medical and Health Sciences
Identifiers
URN: urn:nbn:se:liu:diva-71395ISBN: 978-91-7393-067-3 (print)OAI: oai:DiVA.org:liu-71395DiVA: diva2:448091
Public defence
2011-11-04, Berzeliussalen, Hälsouniversitetet, Campus US, Linköpings universitet, Linköping, 13:00 (English)
Opponent
Supervisors
Available from: 2011-10-14 Created: 2011-10-14 Last updated: 2011-11-28Bibliographically approved
List of papers
1. The periodontal pathogen Porphyromonas gingivalis sensitises human blood platelets to epinephrine
Open this publication in new window or tab >>The periodontal pathogen Porphyromonas gingivalis sensitises human blood platelets to epinephrine
2008 (English)In: Platelets, ISSN 1369-1635, Vol. 19, no 5, 352-358 p.Article in journal (Refereed) Published
Abstract [en]

Recent studies indicate connections between periodontitis and atherothrombosis, and the periodontal pathogen Porphyromonas gingivalis has been found within atherosclerotic lesions. P. gingivalis-derived proteases, designated gingipains activate human platelets, probably through a "thrombin-like" activity on protease-activated receptors (PARs). However, the potential interplay between P. gingivalis and other physiological platelet activators has not been investigated. The aim of this study was to elucidate consequences and mechanisms in the interaction between P. gingivalis and the stress hormone epinephrine. By measuring changes in light transmission through platelet suspensions, we found that P. gingivalis provoked aggregation, whereas epinephrine alone never had any effect. Intriguingly, pre-treatment of platelets with a low, sub-threshold number of P. gingivalis (i.e. a density that did not directly provoke platelet aggregation) resulted in a marked aggregation response when epinephrine was added. This synergistic action was not inhibited by the cyclooxygenas inhibitor aspirin. Furthermore, fura-2-measurements revealed that epinephrine caused an intracellular Ca(2+) mobilization in P. gingivalis pre-treated platelets, whereas epinephrine alone had no effect. Inhibition of the arg-specific gingipains, but not the lys-specific gingipains, abolished the aggregation and the Ca(2+) response provoked by epinephrine. Similar results were achieved by separate blockage of platelet alpha(2)-adrenergic receptors and PARs. In conclusion, the present study shows that a sub-threshold number of P. gingivalis sensitizes platelets to epinephrine. We suggest that P. gingivalis-derived arg-specific gingipains activates a small number of PARs on the surface of the platelets. This leads to an unexpected Ca(2+) mobilization and a marked aggregation response when epinephrine subsequently binds to the alpha(2)-adrenergic receptor. The present results are consistent with a direct connection between periodontitis and stress, and describe a novel mechanism that may contribute to pathological platelet activation.

Place, publisher, year, edition, pages
Taylor & Francis, 2008
Keyword
Atherosclerosis, growth factors, infection, inflammation, lipoproteins
National Category
Medical and Health Sciences
Identifiers
urn:nbn:se:liu:diva-20725 (URN)10.1080/09537100802056102 (DOI)18791941 (PubMedID)
Available from: 2009-09-18 Created: 2009-09-18 Last updated: 2011-10-14
2. The ATP-gated P2X1 receptor plays a pivotal role in activation of aspirin-treated platelets by thrombin and epinephrine
Open this publication in new window or tab >>The ATP-gated P2X1 receptor plays a pivotal role in activation of aspirin-treated platelets by thrombin and epinephrine
Show others...
2008 (English)In: Journal of Biological Chemistry, ISSN 0021-9258, E-ISSN 1083-351X, Vol. 283, no 27, 18493-18504 p.Article in journal (Refereed) Published
Abstract [en]

Human platelets express protease-activated receptor 1 (PAR1) and PAR4 but limited data indicate for differences in signal transduction. We studied the involvement of PAR1 and PAR4 in the cross-talk between thrombin and epinephrine. The results show that epinephrine acted via alpha(2A)-adrenergic receptors to provoke aggregation, secretion, and Ca(2+) mobilization in aspirin-treated platelets pre-stimulated with subthreshold concentrations of thrombin. Incubating platelets with antibodies against PAR4 or the PAR4-specific inhibitor pepducin P4pal-i1 abolished the aggregation. Furthermore, platelets pre-exposed to the PAR4-activating peptide AYPGKF, but not to the PAR1-activating peptide SFLLRN, were aggregated by epinephrine, whereas both AYPGKF and SFLLRN synergized with epinephrine in the absence of aspirin. The roles of released ATP and ADP were elucidated by using antagonists of the purinergic receptors P2X(1), P2Y(1), and P2Y(12) (i.e. NF449, MRS2159, MRS2179, and cangrelor). Intriguingly, ATP, but not ADP, was required for the epinephrine/thrombin-induced aggregation. In Western blot analysis, a low concentration of AYPGKF, but not SFLLRN, stimulated phosphorylation of Akt on serine 473. Moreover, the phosphatidyl inositide 3-kinase inhibitor LY294002 antagonized the effect of epinephrine combined with thrombin or AYPGKF. Thus, in aspirin-treated platelets, PAR4, but not PAR1, interacts synergistically with alpha(2A)-adrenergic receptors, and the PI3-kinase/Akt pathway is involved in this cross-talk. Furthermore, in PAR4-pretreated platelets, epinephrine caused dense granule secretion, and subsequent signaling from the ATP-gated P2X(1)-receptor and the alpha(2A)-adrenergic receptor induced aggregation. These results suggest a new mechanism that has ATP as a key element and circumvents the action of aspirin on epinephrine-facilitated PAR4-mediated platelet activation.

National Category
Medical and Health Sciences
Identifiers
urn:nbn:se:liu:diva-20726 (URN)10.1074/jbc.M800358200 (DOI)18480058 (PubMedID)
Available from: 2009-09-18 Created: 2009-09-18 Last updated: 2017-12-13Bibliographically approved
3. The role of thrombin receptors PAR1 and PAR4 for PAI-1 storage, synthesis and secretion by human platelets
Open this publication in new window or tab >>The role of thrombin receptors PAR1 and PAR4 for PAI-1 storage, synthesis and secretion by human platelets
Show others...
2012 (English)In: Thrombosis Research, ISSN 0049-3848, E-ISSN 1879-2472, Vol. 129, no 4, E51-E58 p.Article in journal (Refereed) Published
Abstract [en]

INTRODUCTION:

Arterial thrombi contain more platelets than venous thrombi and are more resistant to fibrinolysis. This resistance could partly be due to plasminogen activator inhibitor 1 (PAI-1) secreted by platelets. The aim of this study was to elucidate differences between thrombin receptors protease-activated receptor (PAR) 1 and 4 and platelet storage, secretion and synthesis of platelet PAI-1, as compared to other platelet α-granule proteins such as VEGF and endostatin.

MATERIALS AND METHODS:

Human isolated platelets were incubated with thrombin (0.5U/ml), PAR1-activating peptide (AP) (0.4-30μM) or PAR4-AP (1.5-300μM) for up to 24hours. ELISA, western blot and fluorescence microscopy were used to measure secretion, contents and localization of PAI-1, VEGF and endostatin.

RESULTS:

Our results show that PAI-1 and VEGF might be co-localized and that endostatin does not co-localize with either PAI-1 or VEGF. PAI-1 and VEGF show a similar secretion pattern, being more sensitive to low grade PAR1 activation, but secretion was also observed with higher concentrations of PAR4-APs. PAI-1 is secreted in an active form. PAI-1 mRNA was found in platelets, and elevated levels of PAI-1 were detected after 24hours incubation of platelets.

CONCLUSIONS:

PAI-1 and VEGF, but not endostatin, might be stored in the same α-granule in human platelets. PAI-1 and VEGF also show a similar secretion pattern, being more sensitive to PAR1 than to PAR4 activation, but the secretion is not exclusively selective. Our results also show that platelet PAI-1 is increased if incubated for 24hours, both with addition of PAR1-activating peptide and without activation, which could indicate de novo synthesis.

Place, publisher, year, edition, pages
Elsevier, 2012
National Category
Medical and Health Sciences
Identifiers
urn:nbn:se:liu:diva-71393 (URN)10.1016/j.thromres.2011.12.021 (DOI)000301587400010 ()
Note

funding agencies|Swedish Research Council| K2010-65X-15060-07-3 |strategic research area Cardiovascular Inflammation Research Center (CIRC)||County Council of Ostergotland||University of Linkoping||

Available from: 2011-10-14 Created: 2011-10-14 Last updated: 2017-12-08Bibliographically approved
4. Release of ADP or PAR4 Activation is Required to Sustain Thrombin-induced Platelet Aggregation
Open this publication in new window or tab >>Release of ADP or PAR4 Activation is Required to Sustain Thrombin-induced Platelet Aggregation
Show others...
(English)Manuscript (preprint) (Other academic)
Abstract [en]

Thrombin activates human platelets through cleavage of two G-protein-coupled proteaseactivatedreceptors (PARs) denoted PAR1 and PAR4. The aim of this study was to investigatedifferences in PAR1 and PAR4 signaling regarding formation and stability of plateletaggregates. We show that weak PAR1-mediated aggregation is reversible, whereas PAR4-mediated aggregation, weak or strong, is always sustained. PAR1-induced plateletaggregation is decreased and more reversible in the presence of the P2Y12 antagonistcangrelor. However, the effects by cangrelor can be concentration-dependently reversed byconcomitant PAR4 activation in a PI3-kinase-dependent manner. In contrast; in PAR4-APstimulated platelets, aggregation is reduced by cangrelor or inhibition of PI3-kinase byLY294002 but remains irreversible. However, a combined inhibition of PI3-K and P2Y12results in reduced and reversible aggregation. In the light of recently published data on PAR1desensitization, we suggest that the physiological role of the differences between PAR1 andPAR4 activation on aggregate and clot stability could be to fine-tune the response tothrombin. A repeated or continuous very low thrombin generation will desensitize PAR1 andeven if small platelet aggregates are formed they will dissolve, preventing inappropriatethrombus formation. At higher concentrations of thrombin, PAR4 will become activatedabrogating desensitization of PAR1 and enforcing stability of platelet aggregates.

National Category
Medical and Health Sciences
Identifiers
urn:nbn:se:liu:diva-71394 (URN)
Available from: 2011-10-14 Created: 2011-10-14 Last updated: 2015-03-13Bibliographically approved

Open Access in DiVA

The role of platelet thrombin receptors PAR1 and PAR4 in health and disease(1163 kB)1502 downloads
File information
File name FULLTEXT01.pdfFile size 1163 kBChecksum SHA-512
c4912146fa7a9eb330497e94ce0b44ae6372c65f2805da74bea03d66edd71ad65caa5ea0bb029f932579d85681a8afdd73f5fcf94c2c3f8537639a26891810e2
Type fulltextMimetype application/pdf
omslag(315 kB)28 downloads
File information
File name COVER01.pdfFile size 315 kBChecksum SHA-512
4d05cffb952ecee309ab1ea4796608676000bc14e42be23946f25a0df52ff9f7c7b3f86089e4767730c6bc2e5264fff19314dc94ec995a385fd09ab0c2c2cda9
Type coverMimetype application/pdf

Search in DiVA

By author/editor
Nylander, Martina
By organisation
Clinical ChemistryFaculty of Health Sciences
Medical and Health Sciences

Search outside of DiVA

GoogleGoogle Scholar
Total: 1502 downloads
The number of downloads is the sum of all downloads of full texts. It may include eg previous versions that are now no longer available

isbn
urn-nbn

Altmetric score

isbn
urn-nbn
Total: 621 hits
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf