Roles of Prostanoids in the Regulation of Platelet Function

Special Article - Platelets

Thromb Haemost Res. 2018; 2(2): 1014.

Roles of Prostanoids in the Regulation of Platelet Function

Kashiwagi H¹*, Yuhki K¹, Imamichi Y¹, Kojima F², Kumei S¹, Narumiya S³ and Ushikubi F¹

¹Department of Pharmacology, Asahikawa Medical University, Japan

²Department of Pharmacology, Kitasato University, Japan

³Department of Drug Discovery Medicine, Kyoto University, Japan

*Corresponding author: Kashiwagi H, Department of Pharmacology, Asahikawa Medical University, Midorigaoka-Higashi 2-1-1-1, Asahikawa, Japan

Received: September 25, 2018; Accepted: October 24, 2018; Published: October 31, 2018

Abstract

Prostanoids consisting of Prostaglandins (PGs) and Thromboxane (TX) exert a wide range of actions in the body through their respective receptors. Regulation of platelet function is one of the actions of prostanoids. Platelets participate critically in the pathogenesis of thrombotic diseases. Activated platelets aggregate and release various bioactive substances. Aggregation is the most notable criterion for evaluation of platelet activation. In this article, the effects of PGD2, PGE1, PGE2, PGI2 and TXA2 on platelet aggregation are reviewed.

Keywords: Prostaglandin; Thromboxane; Platelet Aggregation; Hemostasis; Thrombosis

Abbreviations

ADP: Adenosine Diphosphate; cAMP: Cyclic Adenosine Monophosphate; CRTH2: Chemoattractant Receptor-Homologous Molecule Expressed on Th2 Cells; DP: Prostaglandin D2 Receptor; EP: Prostaglandin E2 Receptor; FP: Prostaglandin F2a receptor; IP: Prostaglandin I2 Receptor; PG: Prostaglandin; PLC: Phospholipase C; TP: Thromboxane A2 receptor; TX: Thromboxane

Introduction

Platelets are involved not only in hemostasis but also in pathological thrombus formation. Activated platelets achieve their roles by both aggregating and releasing various bioactive substances such as growth factors, lysophospholipids and chemokines [1-3]. Accordingly, platelets play a critical role in several pathological conditions such as atherosclerosis, cerebral thrombosis and myocardial infarction [4-6].

Prostanoids consisting of Prostaglandins (PGs) and Thromboxane (TX) are lipid mediators that bind to cognate receptors named DP, EP, FP, IP and TP that are specific for PGD2, PGE2, PGF2a, PGI2 (prostacyclin) and TXA2, respectively [7]. There are four subtypes of EP: EP1, EP2, EP3 and EP4 [8-11]. In these four subtypes, EP3 is unique and has several isoforms derived from alternative splicing [12,13]. In addition to these eight types and subtypes of prostanoid receptors, a novel PGD2 receptor that has been isolated from type 2 T helper cells and named CRTH2 (DP2) has no significant sequence homology of amino acids with DP (DP1) and other prostanoid receptors [14].

Prostanoids exert a variety of actions in various tissues and cells [15] via their respective receptors. Regulation of platelet function is one of the most well-known actions of prostanoids [16,17].

Expression of prostanoid receptors in platelets

Several prostanoid receptors have been reported to be expressed in platelets. EP2, EP3, EP4EP4, IP and TP were shown to be expressed in murine platelets [18], and human platelets were shown to express DP1 along with EP2, EP3, EP4, IP and TP [19,20].

Stimulatory effect of TXA2 on platelet aggregation

TXA2 is well known as a potent stimulator of platelets [4]. TP couples to Gq and activates phospholipase C (PLC), leading to elevation of intracellular Ca2+ concentrations. In human and rabbit platelets, a stable TXA2 mimetic induced platelet aggregation and release of granule contents from platelets [21]. Platelets express TP constitutively and produce TXA2 when activated with collagen, Adenosine Diphosphate (ADP), epinephrine, thrombin and TXA2.

Therefore, TXA2 plays an important role in the regulation of platelet function, working as a positive feedback regulator. In mice lacking TP, bleeding time was significantly prolonged compared with that in wild-type mice [22], suggesting that TXA2 plays an important role in hemostasis.

Inhibitory effect of PGI2 on platelet aggregation

In contrast to TXA2, PGI2 efficiently inhibits platelet aggregation [17]. The inhibitory potency of PGI2 in platelet aggregation is higher than that of the other inhibitory prostanoids, PGD2 and PGE1 [23]. IP couples to Gs and increases intracellular Cyclic Adenosine Monophosphate (cAMP) concentrations, leading to activation of protein kinase A and inhibition of platelet aggregation. Bleeding time in mice lacking IP was not different from that in wild-type mice, but the susceptibility of mice lacking IP to thrombosis was increased, suggesting that PGI2 is vital for the prevention of thrombus formation [24].

Inhibitory effect of PGD2 on platelet aggregation

In addition to PGI2, PGD2 is also known as an inhibitor of platelet aggregation [25]. The inhibitory effect of PGD2 on aggregation is observed in human and rabbit platelets but not in murine platelets due to the presence or absence of DP1 coupling to Gs. In human platelets, the inhibitory potency of PGD2 was two-times higher than that of PGE1 but much less than that of PGI2 [23,25].

Inhibitory effect of PGE1 on platelet aggregation

Previous studies showed that PGE1 stimulates cAMP synthesis and inhibits platelet aggregation [26,27]. In human platelets, PGE1 can bind to IP as well as EPs [28]. The rank order of affinity of PGE1 for murine EPs and IP was EP3> EP4> EP2> EP1, IP [29]. However, the inhibitory effect of PGE1 on human platelet aggregation was blocked by an IP antagonist but not by an EP4 antagonist [30], suggesting that PGE1 inhibits platelet aggregation via IP but not EP4, the role of which will be described below.

Biphasic effect of PGE2 on platelet aggregation

PGE2 has been reported to have a biphasic effect on platelet aggregation; PGE2 potentiates the aggregation at lower concentrations and inhibits it at higher concentrations [31,32]. However, PGE2 alone could not induce platelet aggregation [18]. It has been thought that Gi- and Gq-mediated signaling activates platelets and that Gs- mediated signaling inhibits platelet activation. Accordingly, among the EP subtypes expressed in platelets, EP3 (mainly Gi) is regarded as a stimulatory receptor, whereas EP2 (Gs) and EP4 (Gs) are regarded as inhibitory receptors in aggregation. Furthermore, EP4 signaling has been reported to activate phosphatidylinositol 3-kinase, leading to activation of protein kinase B (Akt) [33].

Potentiating effect of PGE2 at lower concentrations on platelet aggregation: First, the role of EP3 in the regulation of platelet function was examined because the expression level of EP3 mRNA was the highest among EP subtypes in platelets. In murine platelets lacking EP3, the potentiating effect of PGE2 at lower concentrations on platelet aggregation completely disappeared. In platelets prepared from wild-type mice, a specific EP3 agonist enhanced aggregation induced by a TP agonist in a concentration-dependent manner [18]. These results indicate that EP3 is involved in the potentiating effect of PGE2 on platelet aggregation. In agreement with the potentiating effect of PGE2 via EP3, the bleeding time was significantly prolonged and the mortality after induction of arachidonic acid-induced acute thromboembolism was remarkably reduced in mice lacking EP3 compared with those in wild-type mice. Moreover, the formation of thrombi in pulmonary arterioles and alveolar hemorrhage observed after injection of arachidonic acid were alleviated in mice lacking EP3 [18]. Similarly, venous thrombosis induced by periadventitial application of arachidonic acid was almost completely abolished, although the bleeding time was not significantly prolonged in mice lacking EP3 [34]. Furthermore, a previous study showed that atherosclerotic plaque-produced PGE2 activated platelets through EP3 and promoted atherothrombosis when the plaque was mechanically ruptured [35]. These results indicate that PGE2 plays an important role in thromboembolism through activation of platelets via EP3.

Inhibitory effect of PGE2 at higher concentrations on platelet aggregation: It has been suggested that the inhibitory effect of PGE2 on platelet aggregation is mediated by IP [36,37]. In fact, the inhibitory effect of PGE2 was significantly blunted but was not entirely abolished in murine platelets lacking IP [38]. Meanwhile, specific agonists for EP2 or EP4 potently inhibited aggregation of murine and human platelets [38-41]. These results suggest that selective activation of EP2 or EP4 leads to inhibition of platelet aggregation. It is noteworthy that the inhibitory potency of an EP4 agonist was two rank orders higher than that of an EP2 agonist and was as high as that of an IP agonist in human platelets [38].

Table 1: Prostanoid receptor types and subtypes.





  

    
Prostanoid

    
Type

    
Subtype

    
G-protein

    
Main signal

  

  

    
PGD2

    
DP (DP1)

    
 

    
Gs

    
cAMP ?

  

  

    
CRTH2 (DP2)

    
 

    
Gi

    
cAMP ?

  

  

    
PGE2

    
EP

    
EP1

    
Gq

    
PLC ?

  

  

    
EP2

    
Gs

    
cAMP ?

  

  

    
EP3

    
Gi

    
cAMP ?

  

  

    
EP4

    
Gs

    
cAMP ?

  

  

    
PGF2a

    
FP

    
 

    
Gq

    
PLC ?

  

  

    
PGI2

    
IP

    
 

    
Gs

    
cAMP ?

  

  

    
TXA2

    
TP

    
 

    
Gq

    
PLC ?

  










Table 1: Prostanoid receptor types and subtypes.

Figure 1: Effects of prostanoids on platelet aggregation. Prostanoids play a role in the regulation of platelet aggregation via respective receptors. EP3 and TP are stimulatory receptors, whereas DP1, EP2, EP4 and IP are inhibitory receptors in aggregation.

    

    
    

    

    Figure 1:  Effects of prostanoids on platelet aggregation.
Prostanoids play a role in the regulation of platelet aggregation via respective
receptors. EP3 and TP are stimulatory receptors, whereas DP1, EP2, EP4 and
IP are inhibitory receptors in aggregation.

Conclusion

Anti-platelet agents having various mechanisms of action have been developed and used to prevent the recurrence of thrombotic diseases such as cerebral thrombosis and myocardial infarction, which have been major causes of death in developed countries [42,43]. The targets of these agents including aspirin, prasugrel and cilostazol are cyclooxygenase, ADP receptor P2Y12 and phosphodiesterase, respectively. Although an IP agonist (PGI2 or PGE1 analogue) and a TX synthase inhibitor have been used for anti-platelet therapy, there are still no anti-platelet agents targeting EPs. Previous studies showed roles of EP3 in thromboembolism [18,34,35] and higher inhibitory potency of an EP4 agonist in platelet aggregation [38], suggesting a potential of EP3 antagonists and EP4 agonists as novel anti-platelet agents [41,44,45].

References

  1. Eichholtz T, Jalink K, Fahrenfort I, Moolenaar WH. The bioactive phospholipid lysophosphatidic acid is released from activated platelets. Biochem J. 1993; 291: 677-680.
  2. Grainger DJ, Wakefield L, Bethell HW, Farndale RW, Metcalfe JC. Release and activation of platelet latent TGF-β in blood clots during dissolution with plasmin. Nat Med. 1995; 1: 932-937.
  3. Yatomi Y, Ruan F, Hakomori S, Igarashi Y. Sphingosine-1-phosphate: a platelet-activating sphingolipid released from agonist-stimulated human platelets. Blood. 1995; 86: 193-202.
  4. Ellis EF, Oelz O, Roberts LJ, Payne NA, Sweetman BJ, Nies AS, et al. Coronary arterial smooth muscle contraction by a substance released from platelets: evidence that it is thromboxane A2. Science. (Wash DC) 1976; 193: 1135-1137.
  5. Needleman P, Kulkarni PS, Raz A. Coronary tone modulation: formation and actions of prostaglandins, endoperoxides, and thromboxanes. Science. (Wash DC) 1977; 195: 409-412.
  6. Ross R. Atherosclerosis-an inflammatory disease. N Engl J Med. 1999; 340: 115-126.
  7. Coleman RA, Kennedy I, Humphrey PPA, Bunce K, Lumley P. Prostanoids and their receptors, in Comprehensive Medicinal Chemistry Vol 3: Membranes and receptors. (Emmett JC ed) 1990; 643-714.
  8. Funk CD, Furci L, FitzGerald GA, Grygorczyk R, Rochette C, Bayne MA, et al. Cloning and expression of a cDNA for the human prostaglandin E receptor EP1 J Biol Chem. 1993; 268: 26767-26772.
  9. Regan JW, Bailey TJ, Pepperl DJ, Pierce KL, Bogardus AM, Donello JE, et al. Cloning of a novel human prostaglandin receptor with characteristics of the pharmacologically defined EP2 Mol Pharmacol. 1994; 46: 213-220.
  10. Yang J, Xia M, Goetzl EJ, An S. Cloning and expression of the EP3-subtype of human receptors for prostaglandin E2. BiochemBiophys Res Commun. 1994; 198: 999-1006.
  11. Bastien L, Sawyer N, Grygorczyk R, Metters KM, Adam M.Cloning. Functional expression, and characterization of the human prostaglandin E2 receptor EP2 J Biol Chem. 1994; 269: 11873-11877.
  12. Sugimoto Y, Negishi M, Hayashi Y, Namba T, Honda A, Watabe A, et al. Two isoforms of the EP3 receptor with different carboxyl-terminal domains. Identical ligand binding properties and different coupling properties with Gi J Biol Chem. 1993; 268: 2712-2718.
  13. Irie A, Sugimoto Y, Namba T, Harazono A, Honda A, Watabe A, et al. Third isoform of the prostaglandin-E-receptor EP3 subtype with different C-terminal tail coupling to both stimulation and inhibition of adenylate cyclase. Eur J Biochem. 1993; 217: 313-318.
  14. Hirai H, Tanaka K, Yoshie O, Ogawa K, Kenmotsu K, Takamori Y, et al. Prostaglandin D2 selectively induces chemotaxis in T helper type 2 cells, eosinophils, and basophils via seven-transmembrane receptor CRTH2. J Exp Med. 2001; 193: 255-261.
  15. Narumiya S, Sugimoto Y, Ushikubi F. Prostanoid receptors: structures, properties, and functions. Physiol Rev. 1999; 79: 1193-1226.
  16. Hamberg M, Svensson J, Samuelsson B. Thromboxanes: a new group of biologically active compounds derived from prostaglandin endoperoxides. Proc Natl Acad Sci USA. 1975; 72: 2994-2998.
  17. Moncada S, Gryglewski R, Bunting S, Vane JR. An enzyme isolated from arteries transforms prostaglandin endoperoxides to an unstable substance that inhibits platelet aggregation. Nature (Lond). 1976; 263: 663-665.
  18. Ma H, Hara A, Xiao CY, Okada Y, Takahata O, Nakaya K, et al. Increased bleeding tendency and decreased susceptibility to thromboembolism in mice lacking the prostaglandin E receptor subtype EP3. Circulation. 2001; 104: 1176-1180.
  19. Packham MA, Rand ML, Kinlough-Rathbone RL. Similarities and differences between rabbit and human platelet characteristics and functions. Comp BiochemPhysiol Comp Physiol. 1992; 103: 35-54.
  20. Paul BZ, Ashby B, Sheth SB. Distribution of prostaglandin IP and EP receptor subtypes and isoforms in platelets and human umbilical artery smooth muscle cells. Br J Haematol. 1998; 102: 1204-1211.
  21. Zatta A, Prosdocimi M. Platelet activation induced by a stable analogue of endoperoxides (U46619). Thromb Haemost. 1989; 61: 328-329.
  22. Thomas DW, Mannon RB, Mannon PJ, Latour A, Oliver JA, Hoffman M, et al. Coagulation defects and altered hemodynamic responses in mice lacking receptors for thromboxane A2. J Clin Invest. 1998; 102: 1994-2001.
  23. Whittle BJ, Moncada S, Vane JR. Comparison of the effects of prostacyclin (PGI2), prostaglandin E1 and D2 on platelet aggregation in different species. Prostaglandins. 1978; 16: 373-388.
  24. Murata T, Ushikubi F, Matsuoka T, Hirata M, Yamasaki A, Sugimoto Y, et al. Altered pain perception and inflammatory response in mice lacking prostacyclin receptor. Nature (Lond). 1997; 388: 678-682.
  25. Smith JB, Silver MJ, Ingerman CM, Kocsis JJ. Prostaglandin D2 inhibits the aggregation of human platelets. Thromb Res. 1974; 5: 291-299.
  26. Emmons PR, Hampton JR, Harrison MJ, Honour AJ, Mitchell JR. Effect of prostaglandin E1 on platelet behaviour in vitro and in vivo. Br Med J. 1967; 2: 468-472.
  27. Marquis NR, Vigdahl RL, Tavormina PA. Platelet aggregation I Regulation by cyclic AMP and prostaglandin E1. BiochemBiophys Res Commun. 1969; 36: 965-972.
  28. Schafer AI, Cooper B, O'Hara D, Handin RI. Identification of platelet receptors for prostaglandin I2 and D2. J Biol Chem. 1979; 254: 2914-2917.
  29. Kiriyama M, Ushikubi F, Kobayashi T, Hirata M, Sugimoto Y, Narumiya S. Ligand binding specificities of the eight types and subtypes of the mouse prostanoid receptors expressed in Chinese hamster ovary cells. Br J Pharmacol. 1997; 122: 217-224.
  30. Iyú D, Jüttner M, Glenn JR, White AE, Johnson AJ, Fox SC, et al. PGE1 and PGE2 modify platelet function through different prostanoid receptors. Prostaglandins Other Lipid Mediat. 2011; 94: 9-16.
  31. Shio H, Ramwell P. Effect of prostaglandin E2 and aspirin on the secondary aggregation of human platelets. Nat New Biol. 1972; 236: 45-46.
  32. McDonald JW, Stuart RK. Interaction of prostaglandins E1 and E2 in regulation of cyclic-AMP and aggregation in human platelets: evidence for a common prostaglandin receptor. J Lab Clin Med. 1974; 84: 111-121.
  33. Fujino H, West KA, Regan JW. Phosphorylation of glycogen synthase kinase-3 and stimulation of T-cell factor signaling following activation of EP2 and EP4 prostanoid receptors by prostaglandin E2. J Biol Chem. 2002; 277: 2614-2619.
  34. Fabre JE, Nguyen M, Athirakul K, Coggins K, McNeish JD, Austin S, et al. Activation of the murine EP3 receptor for PGE2 inhibits cAMP production and promotes platelet aggregation. J Clin Invest. 2001; 107: 603-610.
  35. Gross S, Tilly P, Hentsch D, Vonesch JL, Fabre JE. Vascular wall-produced prostaglandin E2 exacerbates arterial thrombosis and atherothrombosis through platelet EP3 J Exp Med. 2007; 204: 311-320.
  36. Andersen NH, Eggerman TL, Harker LA, Wilson CH, De B. On the multiplicity of platelet prostaglandin receptors. I. Evaluation of competitive antagonism by aggregometry. Prostaglandins. 1980; 19: 711-735.
  37. Tynan SS, Andersen NH, Wills MT, Harker LA, Hanson SR. On the multiplicity of platelet prostaglandin receptors II. The use of N-0164 for distinguishing the loci of action for PGI2, PGD2, PGE2 and hydantoin analogs. Prostaglandins. 1984; 27: 683-696.
  38. Kuriyama S, Kashiwagi H, Yuhki K, Kojima F, Yamada T, Fujino T, et al. Selective activation of the prostaglandin E2 receptor subtype EP2 or EP4 leads to inhibition of platelet aggregation. Thromb Haemost. 2010; 104: 796-803.
  39. Smith JP, Haddad EV, Downey JD, Breyer RM, Boutaud O. PGE2 decreases reactivity of human platelets by activating EP2 and EP4. Thromb Res. 2010; 126: e23-e29.
  40. Iyú D, Glenn JR, White AE, Johnson AJ, Fox SC, Heptinstall S. The role of prostanoid receptors in mediating the effects of PGE2 on human platelet function. Platelets. 2010; 21: 329-342.
  41. Philipose S, Konya V, Sreckovic I, Marsche G, Lippe IT, Peskar BA, et al. The prostaglandin E2 receptor EP4 is expressed by human platelets and potently inhibits platelet aggregation and thrombus formation. Arterioscler Thromb Vasc Biol. 2010; 30: 2416-2423.
  42. Schwartz SM, Heimark RL, Majesky MW. Developmental mechanisms underlying pathology of arteries. Physiol Rev. 1990; 70: 1177-1209.
  43. Ross R. The pathogenesis of atherosclerosis: a perspective for the 1990s. Nature. 1993; 362: 801-809.
  44. Heptinstall S, Espinosa DI, Manolopoulos P, Glenn JR, White AE, Johnson A, et al. DG-041 inhibits the EP3 prostanoid receptor--a new target for inhibition of platelet function in atherothrombotic disease. Platelets. 2008; 19: 605-613.
  45. Singh J, Zeller W, Zhou N, Hategen G, Mishra R, Polozov A, et al. Antagonists of the EP3 receptor for prostaglandin E2 are novel antiplatelet agents that do not prolong bleeding. ACS Chem Biol. 2009; 4: 115-126.

Citation: Kashiwagi H, Yuhki K, Imamichi Y, Kojima F, Kumei S, Narumiya S, et al. Roles of Prostanoids in the Regulation of Platelet Function. Thromb Haemost Res. 2018; 2(2): 1014.