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Circulation. 2018 Oct 16;138(16):1720-1735. doi: 10.1161/CIRCULATIONAHA.118.034600.

Functional Relevance of the Anaphylatoxin Receptor C3aR for Platelet Function and Arterial Thrombus Formation Marks an Intersection Point Between Innate Immunity and Thrombosis.

Author information

1
Department of Cardiology and Cardiovascular Medicine, University Clinic (R.J.S., H.N., P.M., T.G., O.B., M.G., H.F.L.), Eberhard Karls-University Tübingen, Germany.
2
Section for Cardioimmunology (R.J.S., M.S., F.N.E., H.N., S.E., H.F.L.), Eberhard Karls-University Tübingen, Germany.
3
Department of Pathology and Laboratory Medicine, School of Medicine, University of Pennsylvania, Philadelphia (E.S.R., J.D.L.).
4
Department of Neurology, University of Würzburg, Germany (P.K.).
5
Cardiology and Angiology I, Heart Center Freiburg University and Faculty of Medicine (M.M., D.D.), University of Freiburg, Germany.
6
Institute of Applied Physics (J.R., T.E.S.), Eberhard Karls-University Tübingen, Germany.
7
Proteom Center, Interfaculty Institute for Cell Biology (J.M.), Eberhard Karls-University Tübingen, Germany.
8
Institute of Biochemistry (F.E.), University of Freiburg, Germany.
9
Institute for Biochemistry and Molecular Biology, University of Freiburg, Germany (F.E.).
10
BIOSS, Centre for Biological Signaling Studies, University of Freiburg, Germany (F.E.).
11
Department of Neurology, University of Münster, Germany (S.G.M.).
12
Department of Neurology, University of Essen, Germany (C.K.).

Abstract

BACKGROUND:

Platelets have distinct roles in the vascular system in that they are the major mediator of thrombosis, critical for restoration of tissue integrity, and players in vascular inflammatory conditions. In close spatiotemporal proximity, the complement system acts as the first line of defense against invading microorganisms and is a key mediator of inflammation. Whereas the fluid phase cross-talk between the complement and coagulation systems is well appreciated, the understanding of the pathophysiological implications of such interactions is still scant.

METHODS:

We analyzed coexpression of the anaphylatoxin receptor C3aR with activated glycoprotein IIb/IIIa on platelets of 501 patients with coronary artery disease using flow cytometry; detected C3aR expression in human or murine specimen by polymerase chain reaction, immunofluorescence, Western blotting, or flow cytometry; and examined the importance of platelet C3aR by various in vitro platelet function tests, in vivo bleeding time, and intravital microscopy. The pathophysiological relevance of C3aR was scrutinized with the use of disease models of myocardial infarction and stroke. To approach underlying molecular mechanisms, we identified the platelet small GTPase Rap1b using nanoscale liquid chromatography coupled to tandem mass spectrometry.

RESULTS:

We found a strong positive correlation of platelet complement C3aR expression with activated glycoprotein IIb/IIIa in patients with coronary artery disease and coexpression of C3aR with glycoprotein IIb/IIIa in thrombi obtained from patients with myocardial infarction. Our results demonstrate that the C3a/C3aR axis on platelets regulates distinct steps of thrombus formation such as platelet adhesion, spreading, and Ca2+ influx. Using C3aR-/- mice or C3-/- mice with reinjection of C3a, we uncovered that the complement activation fragment C3a regulates bleeding time after tail injury and thrombosis. Notably, C3aR-/- mice were less prone to experimental stroke and myocardial infarction. Furthermore, reconstitution of C3aR-/- mice with C3aR+/+ platelets and platelet depletion experiments demonstrated that the observed effects on thrombosis, myocardial infarction, and stroke were specifically caused by platelet C3aR. Mechanistically, C3aR-mediated signaling regulates the activation of Rap1b and thereby bleeding arrest after injury and in vivo thrombus formation.

CONCLUSIONS:

Overall, our findings uncover a novel function of the anaphylatoxin C3a for platelet function and thrombus formation, highlighting a detrimental role of imbalanced complement activation in cardiovascular diseases.

KEYWORDS:

anaphylatoxins; blood platelets; complement system proteins; inflammation; myocardial infarction; stroke; thrombosis

PMID:
29802205
PMCID:
PMC6202244
[Available on 2019-10-16]
DOI:
10.1161/CIRCULATIONAHA.118.034600

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