Platelet purinergic receptors

https://doi.org/10.1016/S1471-4892(03)00007-9Get rights and content

Abstract

Activation of P2Y1 and P2Y12 receptors, through secreted ADP that is stimulated by agonists such as thrombin, thromboxane and collagen, is a major mechanism of platelet activation. P2X1 receptors also participate in platelet shape change and potentiation of calcium mobilization. The cloning of the P2Y12 receptor and its subsequent knockout in mice promises further understanding of its downstream signaling events.

Introduction

Purinergic receptors are divided into adenosine receptors (P1) and nucleotide receptors (P2). Receptors for nucleotides are further classified into two main groups: ligand-gated ion channels (P2X) and G-protein-coupled receptors (P2Y). This review focuses on the recent advances in the platelet purinergic receptor field. The historic studies and the pharmacology of these platelet receptors have been dealt with in recent reviews 1., 2., 3..

Upon vascular injury, platelets aggregate at the site of injury to form a hemostatic plug. Abnormal activation of platelets leads to thrombosis, resulting in a greater risk of stroke and myocardial infarction. The importance of ADP in platelet activation was established by the development of bleeding diatheses in patients with deficiencies in either the storage of ADP, the mechanisms of dense-granule secretion, or in the P2Y ADP receptors themselves, as well as by the efficacy of drugs that antagonize or ‘target’ the ADP receptors.

Section snippets

Receptors for nucleotide-induced platelet activation

We have proposed the presence of three distinct P2 receptor subtypes on platelets [4]: the first is coupled to inhibition of adenylyl cyclase through activation of the inhibitory Gαi subunit; the second is coupled to mobilization of calcium from intracellular stores through activation of the stimulatory Gαq subunit, with resultant phospholipase C activation; and the third is an ionotropic P2X1 receptor coupled to rapid calcium influx. Several other studies 5., 6., 7., 8. independently confirmed

Pharmacological profile of P2 receptors in platelets

Several adenosine bisphosphates, namely A3P5PS, A3P5P, A2P5P and MRS 2179, have been developed as selective competitive antagonists of the P2Y1 receptor 17., 18., 19. without any effect on P2Y12 receptors 10., 11., 13.••. Hydrolysis-resistant derivatives of 2-substituted ATP (e.g. AR-C 66096 and AR-C69931MX) have been developed as potent inhibitors of ADP-induced platelet aggregation [20], and have been shown to selectively antagonize the P2Y12 receptor subtype when used at limited

The P2Y1 receptor

The Gαq-coupled P2Y1 receptor was the first to be cloned, and is responsible for inositol trisphosphate formation through activation of phospholipase C, leading to mobilization of calcium and rapid platelet shape change. Downstream of Gαq, the P2Y1 receptor can also activate the small molecular-weight G protein RhoA that ultimately results in a redundant pathway for platelet shape change. Pharmacological data have revealed an essential role for the P2Y1 receptor in ADP-induced platelet

The P2Y12 receptor

The P2Y12 receptor has been the target for antithrombotic thienopyridine compounds such as ticlopidine, clopidogrel [30] and CS747 [31]. Even though these compounds are effective in treating a variety of thrombotic diseases, these drugs have been shown to cause the development of the immune-mediated syndrome thrombotic thrombocytopenic purpura [32]. The P2Y12 receptor was recently cloned by several groups, and P2Y12 receptor knockout mice have been generated [16]. Pharmacological approaches

The P2X1 receptor

P2X1 receptor-mediated short-lived intracellular calcium increases in platelets are sufficient only for the onset of platelet shape change and not for aggregation 43., 44.. P2X1 receptor activation can lead to activation of extracellular signal-regulated kinase 2 with a resultant amplifying effect on platelet dense-granule secretion [45]. Also, costimulation of the P2X1 and P2Y1 receptors on human platelets by α,β-meATP and ADP, respectively, potentiates the extent of calcium release, which is

Role of ADP receptors in shear-induced platelet aggregation

The initial rolling and tethering of a platelet to the vessel wall involves the interaction of the glycoprotein GPIbα with the A1 domain of von Willebrand Factor (vWF). The platelet signaling and molecular interactions that occur after this initial contact have been the focus of intense study, and recently ADP has been identified as playing a significant role in the mechanism of GPIbα-mediated platelet activation.

Patients dosed with ticlopidine for seven days before experimentation showed no

Conclusions

Only now are the molecular mechanisms of ADP-induced platelet activation becoming clear. The resolution of the concept of a single P2T receptor into three components (i.e. the P2Y1, P2Y12 and P2X1 receptors) and their interactivity helped to explain the intracellular and physiological effects of ADP on platelets (Figure 1). The interaction of signaling events downstream of the P2Y1 and P2Y12 receptors is a novel mechanism of physiological response, and could be a general mechanism of αIIbβ3

Update

Radiolabeled antagonists of the P2Y1 receptor have been developed for further characterization of this receptor [54]. Most recently, the blockade of P2Y1 receptors on platelets under high shear stress conditions on immobilized vWF resulted in a decrease of platelet recruitment and intracellular calcium mobilization [55]. In addition, recent evidence with P2Y12 receptor knockout mice shows that delayed thrombus formation and increased embolization occurs under flow conditions in the P2Y12 null

References and recommended reading

Papers of particular interest, published within the annual period of review, have been highlighted as:

  • of special interest

  • ••

    of outstanding interest

Acknowledgements

This work was supported by research grants HL60683, HL64943 and HL63933 from the National Heart Lung and Blood Institute, National Institutes of Health. This work was performed during the tenure of an Established Investigator award in Thrombosis from American Heart Association and Genentech.

References (56)

  • T.M. Quinton et al.

    Glycoprotein VI-mediated platelet fibrinogen receptor activation occurs through calcium-sensitive and PKC-sensitive pathways without a requirement for secreted ADP

    Blood

    (2002)
  • J. Yang et al.

    Signaling through Gi family members in platelets. Redundancy and specificity in the regulation of adenylyl cyclase and other effectors

    J. Biol. Chem.

    (2002)
  • C. Dangelmaier et al.

    Potentiation of thromboxane A2-induced platelet secretion by Gi signaling through the phosphoinositide-3 kinase pathway

    Thromb. Haemost.

    (2001)
  • G. Kauffenstein et al.

    The P2Y(12) receptor induces platelet aggregation through weak activation of the alpha(IIb)beta(3) integrin — a phosphoinositide 3-kinase-dependent mechanism

    FEBS Lett.

    (2001)
  • M.G. Rolf et al.

    Platelet shape change evoked by selective activation of P2X1 purinoceptors with alpha, beta-methylene ATP

    Thromb. Haemost.

    (2001)
  • K. Mulryan et al.

    Reduced vas deferens contraction and male infertility in mice lacking P2X1 receptors

    Nature

    (2000)
  • S. Goto et al.

    Functional significance of adenosine 5′-diphosphate receptor (P2Y(12)) in platelet activation initiated by binding of von Willebrand factor to platelet GP Ibalpha induced by conditions of high shear rate

    Circulation

    (2002)
  • J.A. Remijn et al.

    Role of ADP receptor P2Y(12) in platelet adhesion and thrombus formation in flowing blood

    Arterioscler. Thromb. Vasc. Biol.

    (2002)
  • D.C.B. Mills

    ADP receptor in platelets

    Thromb. Haemost.

    (1996)
  • C. Gachet et al.

    Purinergic receptors on blood platelets

    Platelets

    (1996)
  • M.S. Fagura et al.

    P2y(1)-receptors in human platelets which are pharmacologically distinct from P2y(ADP)-receptors

    Br. J. Pharmacol.

    (1998)
  • H.-M. Jantzen et al.

    Evidence for two distinct G-protein-coupled ADP receptors mediating platelet activation

    Thromb. Haemost.

    (1999)
  • J. Takasaki et al.

    Molecular cloning of the platelet P2T(AC) ADP receptor: pharmacological comparison with another ADP receptor, the P2Y(1) receptor

    Mol. Pharmacol.

    (2001)
  • J. Hollopeter et al.

    Identification of the platelet ADP receptor targeted by antithrombotic drugs

    Nature

    (2001)
  • J.E. Fabre et al.

    Decreased platelet aggregation, increased bleeding time and resistance to thromboembolism in P2Y1-deficient mice

    Nat. Med.

    (1999)
  • C. Leon et al.

    Defective platelet aggregation and increased resistance to thrombosis in purinergic P2Y(1) receptor-null mice

    J. Clin. Invest.

    (1999)
  • C.J. Foster et al.

    Molecular identification and characterization of the platelet ADP receptor targeted by thienopyridine antithrombotic drugs

    J. Clin. Invest.

    (2001)
  • J.L. Boyer et al.

    Identification of competitive antagonists of the P2y(1) receptor

    Mol. Pharmacol.

    (1996)
  • Cited by (136)

    • Antiplatelet agents for the treatment of adults with COVID-19

      2023, Cochrane Database of Systematic Reviews
    View all citing articles on Scopus
    View full text