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The periodontal pathogen Porphyromonas gingivalis sensitises human blood platelets to epinephrine
Linköping University, Department of Medicine and Health Sciences, Pharmacology . Linköping University, Faculty of Health Sciences.
Linköping University, Department of Clinical and Experimental Medicine, Clinical Chemistry. Linköping University, Faculty of Health Sciences. Östergötlands Läns Landsting, Centre for Laboratory Medicine, Department of Clinical Chemistry.
Linköping University, Department of Medicine and Health Sciences, Pharmacology . Linköping University, Faculty of Health Sciences.
Linköping University, Department of Medicine and Health Sciences, Pharmacology . Linköping University, Faculty of Health Sciences.
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. Vol. 19, no 5, 352-358 p.
Keyword [en]
Atherosclerosis, growth factors, infection, inflammation, lipoproteins
National Category
Medical and Health Sciences
Identifiers
URN: urn:nbn:se:liu:diva-20725DOI: 10.1080/09537100802056102PubMedID: 18791941OAI: oai:DiVA.org:liu-20725DiVA: diva2:235793
Available from: 2009-09-18 Created: 2009-09-18 Last updated: 2011-10-14
In thesis
1. The thrombin receptors PAR1 and PAR4 and their relative role in platelet activation
Open this publication in new window or tab >>The thrombin receptors PAR1 and PAR4 and their relative role in platelet activation
2009 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

Many blood cell mechanisms in the human body are working all the time to maintain haemostasis in the blood vessels. Once a wound arises platelets are alerted via different substances to cover the wound and prevent loss of blood. Most of the times these mechanisms do stop the blood, and further heal the wound. During other circumstances the platelet-covering continues to form a thrombus, preventing the blood to flow and instead causes myocardial infarction or stroke. There are several risk factors triggering development of circulatory diseases such as obesity, lack of exercise, smoking, infection and stress.

This thesis describes the interaction between the two platelet thrombin receptors PAR1 and PAR4, together with the interaction of the oral pathogen Porphyromonas gingivalis (with thrombin-like gingipains), and the cross talk with the stress hormone epinephrine and its α2A adrenergic receptor. Until now PAR1 is thought to be the most important thrombin receptor due to its high affinity for thrombin. From a phylogenetical and patophysiological point of view there must be a reason why platelets express two different thrombin receptors. Today PAR4 is considered less important, but this thesis implies that PAR4 plays an important role in platelet signaling and haemostasis.

The results show that bacteria pre-stimulated platelets, followed by epinephrine gives a strong and full aggregation and calcium mobilization, in both aspirinated and non-aspirinated human platelets. The amount of bacteria does not itself, or epinephrine alone give aggregation or calcium mobilization. This mechanism is dependent on both Rgp type gingipain released from P. gingivalis, and PARs in an interaction with the α2A adrenergic receptor.

Further, results reveal that PAR4 interacts and cross talks with the platelet α2A-adrenergic receptor in aspirinated platelets. Neither of the two platelet purinergic P2Y-receptors (P2Y12 and P2Y1) contribute to this action, but the purinergic P2X1 does. In aggregation studies a low dose of PAR4 activating peptide (AP), but not PAR1-AP, followed by epinephrine results in a strong aggregation and in a calcium mobilization. ATP secretion measurements did reveal that ATP was released during epinephrine stimulation, which indicate that ATP and P2X1 have a key role in this event. By blocking P2X1 both aggregation and calcium mobilization were abolished, but not by blocking P2Y12 and P2Y1. Inhibition of PI3-kinase, both epinephrine-induced calcium mobilization and aggregation were significant reduced. In non-aspirinated platelets PAR1 synergizes with the α2A adrenergic receptor and P2X1.

In conclusion, this thesis suggests that PAR4 plays an intriguing and important role in platelets with inactived cyclooxygenase 1.  The results described in this thesis contribute to an increased knowledge of the platelet thrombin receptors.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2009. 43 p.
Series
Linköping Studies in Health Sciences. Thesis, ISSN 1100-6013 ; 104
National Category
Pharmacology and Toxicology
Identifiers
urn:nbn:se:liu:diva-19958 (URN)978-91-7393-562-3 (ISBN)
Presentation
2009-09-04, Eken, Hälsouniversitetet, Campus US, Linköpings Universitet, Linköping, 13:00 (Swedish)
Opponent
Supervisors
Available from: 2009-09-18 Created: 2009-08-20 Last updated: 2009-09-18Bibliographically approved
2. The role of platelet thrombin receptors PAR1 and PAR4 in health and disease
Open this publication in new window or tab >>The role of platelet thrombin receptors PAR1 and PAR4 in health and disease
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:nbn:se:liu:diva-71395 (URN)978-91-7393-067-3 (ISBN)
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

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Nylander, MartinaLindahl, Tomas L.Bengtsson, TorbjörnGrenegård, Magnus

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