Transfusion Medicine Reviews 28 (2014) 56–60
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Platelet Receptor Expression and Shedding: Glycoprotein Ib-IX-V and Glycoprotein VI Elizabeth E. Gardiner, Robert K. Andrews ⁎ Australian Centre for Blood Diseases, Monash University, Melbourne, Australia
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Available online 12 March 2014 Keywords: Platelets Hemostasis Thrombosis Glycoprotein Ib Glycoprotein VI
a b s t r a c t Quantity, quality, and lifespan are 3 important factors in the physiology, pathology, and transfusion of human blood platelets. The aim of this review is to discuss the proteolytic regulation of key platelet-specific receptors, glycoprotein(GP)Ib and GPVI, involved in the function of platelets in hemostasis and thrombosis, and nonimmune or immune thrombocytopenia. The scope of the review encompasses the basic science of platelet receptor shedding, practical aspects related to laboratory analysis of platelet receptor expression/shedding, and clinical implications of using the proteolytic fragments as platelet-specific biomarkers in vivo in terms of platelet function and clearance. These topics can be relevant to platelet transfusion regarding both changes in platelet receptor expression occurring ex vivo during platelet storage and/or clinical use of platelets for transfusion. In this regard, quantitative analysis of platelet receptor profiles on blood samples from individuals could ultimately enable stratification of bleeding risk, discrimination between causes of thrombocytopenia due to impaired production vs enhanced clearance, and monitoring of response to treatment prior to change in platelet count. © 2014 Elsevier Inc. All rights reserved.
Contents Production of Circulating Platelets . . . . . . . . . . . . Platelet Receptors GPIb-IX-V and GPVI . . . . . . . . . . Ectodomain Shedding of GPIbα and GPVI . . . . . . . . Analysis of Platelet GPIbα and GPVI Expression/Shedding . Clinical Implications of Platelet Receptor Shedding . . . . Platelet Lifespan and Clearance: Low-temperature Exposure Conclusions . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . .
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A recent report of a case of the congenital platelet defect, BernardSoulier syndrome (“Image in Hematology” [1]) showed a blood smear and described misdiagnosis of the patient as acute immune thrombocytopenia (ITP) resulting in ineffective steroid treatment and splenectomy. Bernard-Soulier syndrome is characterized by low platelet count, larger-than-normal platelets (macrothrombocytopenia), and increased bleeding risk, and it involves defective expression and function of the platelet glycoprotein (GP)Ib-IX-V complex [2–4]. Sources of support: National Health and Medical Research Council of Australia, National Heart Foundation of Australia, Monash University, Alfred Hospital. Conflict of interest: All authors have no conflict of interest to disclose. ⁎ Corresponding author. Robert K. Andrews, PhD, Australian Centre for Blood Diseases, Monash University, Alfred Medical Research and Education Precinct (AMREP), Commercial Road, Melbourne, Australia. E-mail address: [email protected] (R.K. Andrews). 0887-7963/$ – see front matter © 2014 Elsevier Inc. All rights reserved. http://dx.doi.org/10.1016/j.tmrv.2014.03.001
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Misdiagnosis of (macro)thrombocytopenia [1–5] and problems with diagnosis and monitoring treatment of immune or nonimmune thrombocytopenia more widely highlight the lack of broadly available platelet-based assays that quantify the hemostatic quality of platelets, or that can be used at low platelet count or with platelets of abnormal size. Platelet count is the most common clinical measurement but does not necessarily predict bleeding risk and does not distinguish between thrombocytopenia due to decreased platelet production from megakaryocytes in the bone marrow or increased platelet clearance, for example, due to antiplatelet autoantibodies. As a consequence, patients may be subjected to unnecessary platelet transfusions or, if autoimmune thrombocytopenia is misdiagnosed, treatment with steroids or immunosuppressants [1,5]. For ITP, time for response to for first-, second-, or third-line treatment may take several weeks or longer [6,7]. Increased understanding of platelet receptor expression and function could
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provide new ways of improving diagnosis of platelet defects, analyzing platelet quality and functionality at normal or low platelet count, and evaluating bleeding or thrombotic risk and monitoring treatment. Production of Circulating Platelets Platelets play a central role in normal hemostasis as well as in cardiovascular disease and inflammation, in the regulation of coagulation, and in tumor metastasis [8–12]. Blood cells are derived from megakaryocyte precursor cells in the bone marrow under the control of growth factors such as thrombopoietin produced by the liver and kidneys. Mature megakaryocytes transform into proplatelets (elongated branched tubular structures containing cytoplasm) with new anucleate platelets forming at the tips. Diseases or drug treatments that impair platelet production result in low platelet count (thrombocytopenia), bleeding, and/or defects in platelet function. Platelets normally number between 100 and 400×10 9/L in blood. Once released into the bloodstream, platelets circulate with an average lifespan of 7 to 10 days until cleared by hemostatic consumption or cleared by the reticuloendothelial system, processes that may be mediated in part by platelet surface receptors [13–15]. Platelet Receptors GPIb-IX-V and GPVI Newly formed young platelets are larger and express higher levels of GPIbα, which decreases as platelets age (see below). For the purpose of quantitative platelet analysis, GPIbα of the GPIb-IX-V complex and GPVI, are of particular interest because these receptors are essentially platelet specific, are critical for initiation of thrombus formation at arterial shear rates, and are implicated in wider platelet functions beyond hemostasis and thrombosis, as well as platelet aging and clearance. Glycoprotein Ibα is a member of the leucine-rich repeat (LRR) protein family and is a type I transmembrane receptor containing an extracellular ligand-binding domain featuring the LRR domains, a sialomucin domain, a transmembrane domain, and an intracellular domain. Glycoprotein Ibα is disulphide linked to GPIbβ and noncovalently linked to GPIX and GPV, all members of the LRR family. There are multiple ligands for GPIbα Fig. (A), including its main adhesive ligand; von Willebrand factor (VWF); coagulation factors XII, XI, and thrombin; P-selectin expressed on activated endothelial cells or platelets; and the leukocyte integrin, αMβ2. There are also multiple intracellular binding partners for GPIb-IX-V, including calmodulin that binds GPIbβ and GPV and regulates stable surface expression of the complex, 14-3-3ζ that binds phosphorylated sequences within GPIbα and GPIbβ, the p85 subunit of phosphatidylinositol 3-kinase (p85/p110) that regulates signal transduction, and filamin-A that binds GPIbα and links the complex to the actin-containing cytoskeleton—these interactions enable this receptor complex to finely regulate platelet adhesion, activation, shape change and thrombus formation, interactions with endothelial cells and leukocytes, and platelet survival and clearance (reviewed in Refs. [16–20]). Glycoprotein V is a receptor with a role in regulating platelet-collagen interactions [21], is a substrate for active thrombin, and is also shed by either metalloproteinase- or thrombindependent pathways [22–26] (Fig.; see below). Glycoprotein VI is a member of the immunoglobulin (Ig)-like superfamily, a type I transmembrane receptor with 2 extracellular Ig domains, a mucin-like domain, a transmembrane, and an intracellular sequence (reviewed in Refs. [27–29]; Fig. (A). Glycoprotein VI forms a noncovalent complex with GPIbα on resting or activated platelets [30] and signals via associated Src/Syk kinase pathways. Critical in GPVImediated signaling is the coassociated FcR γ-chain (FcRγ), which contains an immunoreceptor tyrosine-based activation motif (ITAM) [21–23] within its cytoplasmic domain. Other ITAM-based immunoreceptors expressed on human platelets are CLEC-2 [27,31] and FcγRIIa Fig. (A), with FcγRIIa playing a key role in platelet activation in response to antiplatelet (auto)antibodies. Dual proteolytic inactiva-
Fig 1. In response to vascular damage or antiplatelet antibodies in autoimmune disease, engagement of platelet receptors GP Ib-IX-V, GPVI, and/or FcγRIIa leads to platelet adhesion and activation (A) as well as irreversible proteolysis (B) generating soluble fragments as potential biomarkers and resulting in loss of adhesive function and clearance associated with platelet aging and thrombocytopenia (C). See the text for details.
tion pathways for GPVI (ectodomain shedding) and FcγRIIa (intracellular de-ITAM-ization) have been described [32] and imply that GPVI shedding is a consequence of FcγRIIa engagement by antiplatelet antibodies (see below). Downstream of GPIbα and GPVI, common early activation pathways initiate secondary responses to Gprotein–coupled receptors for soluble agonists including thrombin, ADP, and thromboxane A2, leading to activation of the plateletspecific integrin, αIIbβ3, which binds VWF and fibrinogen, thereby mediating platelet aggregation and thrombus formation ([16,17,33], and references therein).
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Ectodomain Shedding of GPIbα and GPVI Given the functional importance of GPIbα/GPVI and their potential as platelet-specific biomarkers, understanding mechanisms regulating expression and function of these receptors is critical. One key mechanism involves ectodomain proteolysis as depicted in Fig., where intact receptors (panel A) undergo proteolysis leading to generation of soluble ectodomain fragments and rapid, irreversible depletion of the surface receptor (panels B and C; reviewed in Ref. [34]). Importantly, proteolytic inactivation of these receptors on human platelets involves distinct mechanisms, with respect to the sheddases involved and the pathophysiological triggers which induce shedding. On human platelets, GPVI is predominantly shed by the metalloproteinase, ADAM10, whereas ADAM17 plays a major role in shedding of GPIbα. This is based on experimental studies using recombinant forms of the sheddases and synthetic peptides spanning the cleavage region, expression of human GPVI on cell lines where specific residues adjacent to the cleavage site were mutated [26], and inhibition of GPVI shedding by the ADAM10selective inhibitor, GI254023 [35,36]. A predominant role for ADAM17 in GPIbα shedding in vitro and in vivo has also been shown in mouse and human platelets [37], whereas ADAM10 as well as other metalloproteinase(s) may play a role in GPVI shedding in mice because platelettargeted loss of ADAM10 activity only partially attenuates shedding in this system [38]. In addition to thrombin, both ADAM10 and ADAM17 participate in shedding of GPV from activated platelets [25,26] Fig. (B). Analysis of Platelet GPIbα and GPVI Expression/Shedding Receptor shedding can be analyzed experimentally by analysis of untreated platelets or platelet samples treated with agents to induce shedding, and detecting loss of intact receptor and formation of 1 or both proteolytic fragments, that is, the shed ectodomain in supernatant and/or the membrane-associated remnant. With washed platelets, analysis may involve Western blot with antibodies N- or C-terminal of the cleavage site to detect intact receptor and/or proteolytic fragments. With washed platelets, platelet-rich plasma, or whole blood, flow cytometry with anti-GPIbα or anti-GPVI ectodomain antibodies can detect time-dependent loss of intact receptor, and immune-type enzyme-linked immunosorbent assay or bead-based assays can detect sGPIbα ectodomain (termed glycocalicin) or sGPVI in cell-free supernatant or platelet-free plasma [26,39–52]. For clinical studies, measuring glycocalicin or sGPVI in plasma is also feasible using available assays that have suitable sensitivity, linearity over a practical range, and lower detection limits compatible with levels found in healthy human plasma or elevated levels in disease [44–52]. Measuring sGPVI requires fresh or frozen platelet-free plasma, but not serum due to coagulation-induced shedding [35,44]. There is a major difference between levels of glycocalicin (~1000–3000 ng/mL glycocalicin [51]) compared with sGPVI (~10–20 ng/mL or less) in healthy human plasma [44–46]), taking into account differences in molecular weight and approximate copy number per platelet (glycocalicin, ~130 kd and ~30 000 copies of GPIbα/platelet cf. sGPVI, ~55 kd and ~6000 copies GPVI/platelet) [41]. This platelet GPVI copy number may be an underestimate; ~10 000 has been determined from biophysical approaches [53]. The glycocalicin index (the plasma glycocalicin level corrected for platelet count) has been evaluated as a surrogate marker of peripheral platelet turnover [52]. Compared with GPIbα, which is constitutively shed, GPVI is also stable on normal platelets, with essentially no membrane-associated fragment detectable by Western blot [26,54]. This implies that changes in plasma levels over basal levels may be more sensitive for evaluating shedding events involving platelet GPVI compared with GPIbα. Triggers of GPVI shedding from human platelets include the following: the major physiological ligand, collagen, and other nonphysiological GPVI ligands; coagulation resulting in activation of clotting factor Xa, which leads to activation of ADAM10-dependent shedding; autoantibodies that either bind GPVI directly or bind other
platelet surface antigens and act via FcγRIIa; exposure of platelets to elevated shear stress, which potently induces GPVI shedding independent of intracellular signals, platelet activation or aggregation; and a range of artificial agents previously shown to activate ADAM family sheddases on other cells, such as the protein kinase C– activator phorbol myristate acetate, the thiol-modifying agent Nethylmaleimide, calmodulin antagonists, or the mitochondrial poison, carbonyl cyanide M-chlorophenylhydrazone ([39–42], and references therein). Shedding of GPIbα mediated by ADAM17 is not known to be induced by GPVI ligands but is triggered by elevated shear stress (VWF dependent), and phorbol myristate acetate, N-ethylmaleimide, calmodulin antagonists, or carbonyl cyanide M-chlorophenylhydrazone, as well as by the agonist serotonin, or exposure of platelets to oxidative stress or diesel exhaust particles [26,37,54–58]. Aspirin also activates ADAM17-mediated shedding events on platelets, which may limit platelet reactivity in addition to aspirin's known role as an inhibitor of platelet activation [59]. Under conditions of shear stress, shedding of GPVI independent of known GPVI ligands, platelet activation, or VWF-dependent aggregation implies an effect of shear on activation of the sheddase or altered membrane properties facilitating ADAM10-mediated cleavage of GPVI. In this regard, cholesterol depletion or cholesterol-altering statins affect membrane fluidity and ADAM10 activity toward substrates on other types of cells [60,61]. Finally, not only do GPVI ligands induce shedding of GPVI and release of sGPVI, but they also cause simultaneous calpain-mediated intracellular proteolysis of FcγRIIa Fig. (B) [32]. Conversely, antiplatelet IgG that engages FcγRIIa also induces ADAM10-mediated shedding of GPVI and release of sGPVI, inhibitable by a function blocking anti-FcγRIIa antibody, IV.3 [32,54]. Both GPVI/FcRγ and FcγRIIa are ITAM-bearing receptors [27,31], and inhibition of Src/Syk signaling pathways effectively block proteolysis of both GPVI and FcγRIIa on human platelets [32]. Clinical Implications of Platelet Receptor Shedding The relationship between platelet reactivity and surface density of primary platelet receptors suggests that controlled shedding could limit platelet reactivity under prothrombotic conditions or regulate transition from resting circulating platelets to adherent activated platelets in a stable thrombus in response to prothrombotic stimuli. Experimental findings imply that GPIbα or GPVI shedding in vivo could result from multiple potential causes, including vascular damage exposing VWF/collagen, pathological shear stress due to stenosis, disorders leading to platelet hyperreactivity such as metabolic disorders or infection, coagulopathy, or autoimmune disease associated with antiplatelet autoantibodies. Alterations in plasma sGPVI have been reported in ischemic stroke [62–64], coronary disease [36,45,65–67], disseminated intravascular coagulation [35], lupus nephritis [68], thrombotic microangiopathy [46], and ITP [54,69]. Plasma sGPVI is decreased compared with control in Alzheimer disease, consistent with decreased activity of platelet ADAM10 [70]. Glycocalicin (glycocalicin index) has been evaluated together with immature platelet fraction in ITP [52,71,72]. Glycoprotein V shedding from activated platelets due to active thrombin or ADAM10/ADAM17 sheddases has also been measured using sGPV enzyme-linked immunosorbent assay in experimental thrombosis models [23], as a platelet activation marker in the context of platelet transfusion [22,24], and in atherothrombotic or other disorders associated with platelet hyperreactivity [73–76]. Platelet Lifespan and Clearance: Low-temperature Exposure and Transfusion A major limitation on the shelf-life of platelets stored for blood transfusion is that platelets exposed to lower temperature for as little as 1 hour may be rapidly cleared from the circulation after transfusion
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[77]. Mechanisms underlying this clearance are linked to changes of platelet GPIbα and enhanced GPIbα-mediated interactions with phagocytic cells in the liver via αMβ2 or other receptors. Glycoprotein Ibα clustering, shedding, and changes in glycosylation/sialic acid have been investigated as important regulators of exacerbated clearance of cooled platelets [14,15,77,78]. Lower temperatures (b15°C) change platelet shape and actin filament-cytoskeletal arrangements, and also increase intracellular Ca 2+, although selectively blocking these events does not prevent posttransfusion clearance [77]. However, rapid clearance was overcome in αMβ2-deficient mice, and proteolysis of GPIbα from mouse platelets prior to transfusion had a similar protective effect, although interestingly, cold treatment did not adversely affect VWF binding to GPIbα. Although GPIbα and αMβ2 are implicated in the mechanism of platelet clearance after low-temperature exposure, there is also an important role for changes in glycosylation and sialic acid on platelets/ GPIbα. First, αMβ2 recognizes N-linked glycan structures on GPIbα; blocking this interaction on cooled platelets also prevents rapid clearance [79]. Second, upon rewarming, refrigerated platelets secrete sialidase(s), which remove sialic acid from glycosylation sites on GPIbα and other receptors [15]. This enhances ADAM17-mediated shedding of GPIbα (and GPV) and coincides with increased susceptibility for clearance. Third, prolonged low-temperature exposure increases both the density and the amount of galactose residues on platelets [14]. As a consequence, in addition to αMβ2-mediated clearance after shorter-term exposure, Ashwell-Morell receptors on hepatocytes become proportionately more important for platelet clearance after longer-term chilling [14,78]. By a similar mechanism, AshwellMorell receptor that recognizes galactose and N-acetylgalactosamine on de-sialylated GPs is implicated in thrombocytopenia associated with the action of desialylating Streptococcal neuraminidases in sepsis, which likely influences onset/progression of disseminated intravascular coagulation [80,81]. Platelet receptor expression influenced by clustering and shedding of GPIbα is a clearly major factor in regulating platelet function and determining platelet survival and lifespan and clearance [14,15,77,78,82,83]. Normal circulating human platelets contain a proportion of proteolyzed GPIbα, which is constitutively shed, but no detectable proteolytic remnant fragment of GPVI [26,54], consistent with a link between loss of GPIbα/GPVI expression and clearance from the circulation. Like cooled platelets, apoptotic platelets from mice deficient in the prosurvival protein Bcl-xL, or platelets that have been experimentally damaged or aged, also shed GPIbα [37,84–87]. The association of the regulatory protein, 14-3-3ζ, with the cytoplasmic domain of GPIbα is a critical regulator of apoptosis, because sequestration by GPIbα can prevent 14-3-3ζ binding to death regulators, as well as through regulating GPIbα-dependent ligand binding or signaling [18–20,88,89]. ADAM17-mediated shedding of GPIbα in stored platelets is dependent on p38 mitogen-activated protein kinase, and inhibition of this pathway during storage may improve posttransfusion recovery [85]. Finally, clustering and/or shedding of GPIbα could also regulate clearance by controlling the spatial density of the receptor and interaction with αMβ2-bearing phagocytes. Recent experimental studies uniquely demonstrate an optimal spatial density requirement for neutrophil αMβ2-GPIbα interaction [90], which could imply enhanced clearance at an optimal surface density as GPIbα expression is decreased. Conclusions Studies described above involving analysis of expression and function of platelet receptors GPIb-IX-V and GPVI could ultimately play a role in the diagnosis of platelet defects, analyzing platelet quality at normal or low platelet count, and/or evaluating bleeding or thrombotic risk and monitoring treatment. To maximize benefits from clinical application of these measurements, further research is
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required to correlate quantitative changes in levels of these markers with clinical outcomes in prospective studies and determine whether these changes predict response to treatment prior to changes in platelet count.
References [1] Moiz B, Rashid A. BSS misdiagnosed as ITP. Blood 2013;122(10):1693. [2] Bernard J, Soulier J-P. Sur une nouvelle variété de dystrophie thrombocytairehémorragipare congénitale. Sem Hop 1948;24:3217–23. [3] López JA, Andrews RK, Afshar-Kharghan V, Berndt MC. Bernard-Soulier syndrome. Blood 1998;91:4397–418. [4] Berndt MC, Andrews RK. Bernard-Soulier syndrome: an update. Sem Thromb Haemost 2013;39(6):656–62. [5] Althaus K, Greinacher A. MYH-9 related platelet disorders: strategies for management and diagnosis. Transfus Med Hemother 2010;3(5):260–7. [6] Lakshmanan S, Cuker A. Contemporary management of primary immune thrombocytopenia in adults. J Thromb Haemost 2012;10(10):1988–98. [7] Rodrigo C, Gooneratne L. Dapsone for primary immune thrombocytopenia in adults and children: an evidence-based review. J Thromb Haemost 2013; 11(11):1946–53. [8] Ombrello C, Block R, Morrell C. Our expanding view of platelet functions and its clinical implications. J Cardiovasc Transl Res 2010;3(5):538–46. [9] Riedl J, Pabinger I, Ay C. Platelets in cancer and thrombosis. Hamostaseologie 2014;34(1):54–62. [10] Versteeg HH, Heemskerk JW, Levi M, Reitsma PH. New fundamentals in hemostasis. Physiol Rev 2013;93(1):327–58. [11] Zhang W, Huang W, Jing F. Contribution of blood platelets to vascular pathology in Alzheimer's disease. J Blood Med 2013;4:141–7. [12] Andrews RK, Berndt MC, Elalamy I. Platelets: from function to dysfunction in essential thrombocythaemia. Eur Haematol Oncol 2011;7(2):125–31. [13] Dowling MR, Josefsson EC, Henley KJ, Hodgkin PD, Kile BT. Platelet senescence is regulated by an internal timer, not damage inflicted by hits. Blood 2010; 116(10):1776–8. [14] Rumjantseva V, Grewal PK, Wandall HH, Josefsson EC, Sørensen AL, Larson G, et al. Dual roles for hepatic lectin receptors in the clearance of chilled platelets. Nat Med 2009;15(11):1273–80. [15] Jansen AJG, Josefsson EC, Rumjantseva V, Liu QP, Falet H, Bergmeier W, et al. Desialylation accelerates platelet clearance after refrigeration and initiates GPIbα metalloproteinase-mediated cleavage in mice. Blood 2012;119(5):1263–73. [16] Andrews RK, Berndt MC. Platelet physiology and thrombosis. Thromb Res 2004;114:447–53. [17] Andrews RK, Berndt MC. The glycoprotein Ib-IX-V complex. In: Michelson A, editor. Platelets, 3rd ed.San Diego: Academic Press; 2012. p. 195–211. [18] Andrews RK, Du X, Berndt MC. The 14-3-3ζ–GPIb-IX-V complex as an antiplatelet target. Drug News Perspect 2007;20:285–92. [19] Mu F-T, Andrews RK, Arthur JF, Munday AM, Cranmer SL, Jackson SP, et al. A functional 14-3-3ζ–independent association of PI3-kinase with glycoprotein Ibα, the major ligand-binding subunit of the platelet glycoprotein Ib-IX-V complex. Blood 2008;111:4580–7. [20] Mu F-T, Cranmer SL, Andrews RK, Berndt MC. Functional association of PI3-kinase with platelet glycoprotein Ibα, the major ligand-binding subunit of the glycoprotein Ib-IX-V complex. J Thromb Haemost 2010;8:324–30. [21] Moog S, Mangin P, Lenain N, Strassel C, Ravanat C, Schuhler S, et al. Platelet glycoprotein V binds to collagen and participates in platelet adhesion and aggregation. Blood 2001;98(4):1038–46. [22] Azorsa DO, Moog S, Ravanat C, Schuhler S, Folléa G, Cazenave JP, et al. Measurement of GPV released by activated platelets using a sensitive immunocapture ELISA—its use to follow platelet storage in transfusion. Thromb Haemost 1999;81(1):131–8. [23] Ravanat C, Freund M, Mangin P, Azorsa DO, Schwartz C, Moog S, et al. GPV is a marker of in vivo platelet activation—study in a rat thrombosis model. Thromb Haemost 2000;83(2):327–33. [24] Javela K, Eronen J, Sarna S, Kekomäki R. Soluble glycoprotein V as a quality marker of platelet concentrates stressed by transportation. Transfusion 2005;45(9):1504–11. [25] Rabie T, Strehl A, Ludwig A, Nieswandt B. Evidence for a role of ADAM17 (TACE) in the regulation of platelet glycoprotein V. J Biol Chem 2005;280(15):14462–8. [26] Gardiner EE, Karunakaran D, Shen Y, Andrews RK, Berndt MC. Controlled shedding of platelet glycoprotein (GP)VI and GPIb-IX-V by ADAM family metalloproteinases. J Thromb Haemost 2007;5:1530–7. [27] Ozaki Y, Suzuki-Inoue K, Inoue O. Platelet receptors activated via mulitmerization: glycoprotein VI, GPIb-IX-V, and CLEC-2. J Thromb Haemost 2013;11(Suppl. 1):330–9. [28] Zahid M, Mangin P, Loyau S, Hechler B, Billiald P, Gachet C, et al. The future of glycoprotein VI as an antithrombotic target. J Thromb Haemost 2012;10(12):2418–27. [29] Dütting S, Bender M, Nieswandt B. Platelet GPVI: a target for antithrombotic therapy?! Trends Pharmacol Sci 2012;33(11):583–90. [30] Arthur JF, Matzaris M, Gardiner EE, Taylor SG, Wijeyewickrema LC, Ozaki Y, et al. Glycoprotein (GP)VI is associated with GPIb-IX-V on the membrane of resting and activated platelets. Thromb Haemost 2005;93:716–23. [31] Bergmeier W, Stefanini L. Platelet ITAM signaling. Curr Opin Hematol 2013;20(5):445–50.
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[32] Gardiner EE, Karunakaran D, Arthur JF, Mu F-T, Powell MS, Baker RI, et al. Dual ITAM-mediated proteolytic pathways for irreversible inactivation of platelet receptors: De-ITAM-ising FcγRIIa. Blood 2008;111:165–74. [33] Gardiner EE, Arthur JF, Shen Y, Karunakaran D, Moore LA, Am Esch II Jr Schulte, et al. GPIbα-selective activation of platelets induces platelet signalling events comparable to GPVI activation events. Platelets 2010;21:244–52. [34] Andrews RK, Karunakaran D, Gardiner EE, Berndt MC. Platelet receptor shedding: a mechanism for downregulating platelet reactivity. Arterioscler Thromb Vasc Biol 2007;27:1511–20. [35] Al-Tamimi M, Grigoriadis G, Tran H, Paul E, Servadei P, Berndt MC, et al. Coagulation-induced shedding of platelet glycoprotein VI mediated by Factor Xa. Blood 2011;117(14):3912–20. [36] Al-Tamimi M, Tan CW, Qiao J, Pennings GJ, Javadzadegan A, Yong ASC, et al. Pathological shear triggers shedding of vascular receptors: a novel mechanism for downregulation of platelet glycoprotein (GP)VI in stenosed coronary vessels. Blood 2012;119(18):4311–20. [37] Bergmeier W, Piffath CL, Cheng G, Dole VS, Zhang Y, von Andrian UH, et al. Tumor necrosis factor-α–converting enzyme (ADAM17) mediates GPIbα shedding from platelets in vitro and in vivo. Circ Res 2004;95(7):677–83. [38] Bender M, Hofmann S, Stegner D, Chalaris A, Bösl M, Braun A, et al. Differentially regulated GPVI ectodomain shedding by multiple platelet-expressed proteinases. Blood 2010;116(17):3347–55. [39] Al Tamimi M, Arthur JF, Gardiner EE, Andrews RK. Focusing on plasma GPVI. Thromb Haemost 2012;107(4):648–55. [40] Gardiner EE, Andrews RK. Plasma sGPVI: changing levels in human disease. Thromb Res 2014;133(3):306–7. [41] Qiao J, Shen Y, Gardiner EE, Andrews RK. Proteolysis of platelet receptors in humans and other species. Biol Chem 2010;391:893–900. [42] Bigalke B, Elvers M, Schönberger T, Gawaz M. Platelet and soluble glycoprotein VI —novel applications in diagnosis and therapy. Curr Drug Targets 2011;12(12): 1821–30. [43] Brill A, Chauhan AK, Canault M, Walsh MT, Bergmeier W, Wagner DD. Oxidative stress activates ADAM17/TACE and induces its target receptor shedding in platelets in a p38-dependent fashion. Cardiovasc Res 2009;84(1):137–44. [44] Al-Tamimi M, Mu FT, Moroi M, Gardiner EE, Berndt MC, Andrews RK. Measuring soluble platelet glycoprotein VI in human plasma by ELISA. Platelets 2009;20:143–9. [45] Bigalke B, Pötz O, Kremmer E, Geisler T, Seizer P, Puntmann VO, et al. Sandwich immunoassay for soluble glycoprotein VI in patients with symptomatic coronary artery disease. Clin Chem 2011;57(6):898–904. [46] Yamashita Y, Naitoh K, Wada H, Ikejiri M, Mastumoto T, Ohishi K, et al. Elevated plasma levels of soluble platelet glycoprotein VI (GPVI) in patients with thrombotic microangiopathy. Thromb Res 2014;133(3):440–4. [47] Qiao J, Schoenwaelder SM, Mason K, Tran H, Davis AK, Jackson SP, et al. Low adhesion receptor levels on circulating platelets in patients with lymphoproliferative diseases prior to receiving Navitoclax (ABT-263). Blood 2013;121(8): 1479–81. [48] Kunishima S, Hayashi K, Kobayashi S, Naoe T, Ohno R. New enzyme-linked immunosorbent assay for glycocalicin in plasma. Clin Chem 1991;37(2):169–72. [49] Bessos H, Murphy WG. A new competitive binding enzyme-linked immunosorbent assay for glycocalicin in plasma and platelet concentrate supernatants. Thromb Res 1990;59(3):497–507. [50] Adelman B, Michelson AD, Loscalzo J, Greenberg J, Handin RI. Plasmin effect on platelet glycoprotein Ib–von Willebrand factor interactions. Blood 1985;65(1):32–40. [51] Coller BS, Kalomiris E, Steinberg M, Scudder LE. Evidence that glycocalicin circulates in normal plasma. J Clin Invest 1984;73:794–9. [52] Steinberg MH, Kelton JG, Coller BS. Plasma glycocalicin. An aid in the classification of thrombocytopenic disorders. N Engl J Med 1987;317(17):1037–42. [53] Burkhart JM, Vaudel M, Gambaryan S, Radau S, Walter U, Martens L, et al. The first comprehensive and quantitative analysis of human platelet protein composition allows the comparative analysis of structural and functional pathways. Blood 2012;120(15):e73–82. [54] Gardiner EE, Al-Tamimi M, Mu FT, Karunakaran D, Thom JY, Moroi M, et al. Compromised ITAM-based platelet receptor function in a patient with immune thrombocytopenic purpura. J Thromb Haemost 2008;6(7):1175–82. [55] Duerschmied D, Canault M, Lievens D, Brill A, Cifuni SM, Bader M, et al. Serotonin stimulates platelet receptor shedding by tumor necrosis factor-α–converting enzyme (ADAM17). J Thromb Haemost 2009;7(7):1163–71. [56] Mo X, Nguyen NX, Mu FT, Yang W, Luo SZ, Fan H, et al. Transmembrane and transsubunit regulation of ectodomain shedding of platelet glycoprotein Ibα. J Biol Chem 2010;285(42):32096–104 [15]. [57] Cheng H, Yan R, Li S, Yuan Y, Liu J, Ruan C, et al. Shear-induced interaction of platelets with von Willebrand factor results in glycoprotein Ibα shedding. Am J Physiol Heart Circ Physiol 2009;297(6):H2128–35. [58] Forestier M, Al-Tamimi M, Gardiner EE, Hermann C, Meyer SC, Beer JH. Diesel exhaust particles impair platelet response to collagen and are associated with GPIbα shedding. Toxicol In Vitro 2012;26(6):930–8. [59] Aktas B, Pozgajova M, Bergmeier W, Sunnarborg S, Offermanns S, Lee D, et al. Aspirin induces platelet receptor shedding via ADAM17 (TACE). J Biol Chem 2005;280(48):39716–22. [60] Kojro E, Gimpl G, Lammich S, Marz W, Fahrenholz F. Low cholesterol stimulates the nonamyloidogenic pathway by its effect on the α-secretase ADAM 10. Proc Natl Acad Sci U S A 2001;98(10):5815–20. [61] Murai T, Maruyama Y, Mio K, Nishiyama H, Suga M, Sato C. Low cholesterol triggers membrane microdomain-dependent CD44 shedding and suppresses tumor cell migration. J Biol Chem 2011;286(3):1999–2007.
[62] Bigalke B, Stellos K, Geisler T, Kremmer E, Seizer P, May AE, et al. Expression of platelet glycoprotein VI is associated with transient ischemic attack and stroke. Eur J Neurol 2010;17(1):111–7. [63] Al-Tamimi M, Gardiner EE, Thom JY, Shen Y, Cooper MN, Hankey GJ, et al. Soluble glycoprotein VI is raised in the plasma of patients with acute ischemic stroke. Stroke 2011;42(2):498–500. [64] Wurster T, Poetz O, Stellos K, Kremmer E, Melms A, Schuster A, et al. Plasma levels of soluble glycoprotein VI (sGPVI) are associated with ischemic stroke. Platelets 2013;24(7):560–5. [65] Bigalke B, Stellos K, Geisler T, Lindemann S, May AE, Gawaz M. Glycoprotein VI as a prognostic biomarker for cardiovascular death in patients with symptomatic coronary artery disease. Clin Res Cardiol 2010;99(4):227–33. [66] Bigalke B, Stellos K, Weig HJ, Geisler T, Seizer P, Kremmer E, et al. Regulation of platelet glycoprotein VI (GPVI) surface expression and of soluble GPVI in patients with atrial fibrillation (AF) and acute coronary syndrome (ACS). Basic Res Cardiol 2009;104(3):352–7. [67] Pennings GJ, Yong ASC, Wong C, Al-Tamimi M, Gardiner EE, Andrews RK, et al. Circulating levels of soluble EMMPRIN (CD147) correlate with levels of soluble glycoprotein VI in human plasma. Platelets 2013. http://dx.doi.org/10.3109/ 09537104.2013.852660 [in press]. [68] Nurden P, Tandon N, Takizawa H, Couzi L, Morel D, Fiore M, et al. An acquired inhibitor to the GPVI platelet collagen receptor in a patient with lupus nephritis. J Thromb Haemost 2009;7(9):1541–9. [69] Gardiner EE, Thom JY, Al-Tamimi M, Hughes A, Berndt MC, Andrews RK, et al. Restored platelet function after romiplostim treatment in a patient with immune thrombocytopenic purpura. Br J Haematol 2010;149(4):625–8. [70] Laske C, Leyhe T, Stransky E, Eschweiler GW, Bueltmann A, Langer H, et al. Association of platelet-derived soluble glycoprotein VI in plasma with Alzheimer's disease. J Psychiatr Res 2008;42(9):746–51. [71] Barsam SJ, Psaila B, Forestier M, Page LK, Sloane PA, Geyer JT, et al. Platelet production and platelet destruction: assessing mechanisms of treatment effect in immune thrombocytopenia (ITP). Blood 2011;117(21):5723–32. [72] Psaila B, Bussel JB, Linden MD, Babula B, Li Y, Barnard MR, et al. In vivo effects of eltrombopag on platelet function in immune thrombocytopenia: no evidence of platelet activation. Blood 2012;119(17):4066–72. [73] Blann AD, Lanza F, Galajda P, Gurney D, Moog S, Cazenave JP, et al. Increased platelet glycoprotein V levels in patients with coronary and peripheral atherosclerosis—the influence of aspirin and cigarette smoking. Thromb Haemost 2001;86(3):777–83. [74] Morel O, Hugel B, Jesel L, Lanza F, Douchet MP, Zupan M, et al. Sustained elevated amounts of circulating procoagulant membrane microparticles and soluble GPV after acute myocardial infarction in diabetes mellitus. Thromb Haemost 2004;91(2):345–53. [75] Acar K, Sucak A, Beyazit Y, Genc G, Haznedaroglu IC, Aksu S, et al. Lack of platelet activation reflected by circulating soluble glycoprotein V in pre-eclampsia. J Int Med Res 2007;35(5):704–8. [76] Falcinelli E, Francisci D, Belfiori B, Petito E, Guglielmini G, Malincarne L, et al. In vivo platelet activation and platelet hyperreactivity in abacavir-treated HIVinfected patients. Thromb Haemost 2013;110(2):349–57. [77] Hoffmeister KM, Felbinger TW, Falet H, Denis CV, Bergmeier W, Mayadas TN, et al. The clearance mechanism of chilled blood platelets. Cell 2003;112(1):87–97. [78] Rumjantseva V, Hoffmeister KM. Novel and unexpected clearance mechanisms for cold platelets. Transfus Apher Sci 2010;42(1):63–70. [79] Hoffmeister KM, Josefsson EC, Isaac NA, Clausen H, Hartwig JH, Stossel TP. Glycosylation restores survival of chilled blood platelets. Science 2003;301 (5639):1531–4. [80] Grewal PK. The Ashwell-Morell receptor. Methods Enzymol 2010;479:223–41. [81] Grewal PK, Uchiyama S, Ditto D, Varki N, Le DT, Nizet V, et al. The Ashwell receptor mitigates the lethal coagulopathy of sepsis. Nat Med 2008;14(6):648–55. [82] Fox JE. Shedding of adhesion receptors from the surface of activated platelets. Blood Coagul Fibrinolysis 1994;5(2):291–304. [83] Bergmeier W, Burger PC, Piffath CL, Hoffmeister KM, Hartwid JH, Nieswandt B, et al. Metalloproteinase inhibitors improve the recovery and hemostatic function of in vitro–aged or -injured mouse platelets. Blood 2003;102(12):4229–35. [84] Josefsson EC, James C, Henley KJ, Debrincat MA, Rogers KL, Dowling MR, et al. Megakaryocytes possess a functional intrinsic apoptosis pathway that must be restrained to survive and produce platelets. J Exp Med 2011;208(10):2017–31. [85] Canault M, Duerschmied D, Brill A, Stefanini L, Schatzberg D, Cifuni SM, et al. p38 mitogen–activated protein kinase activation during platelet storage: consequences for platelet recovery and hemostatic function in vivo. Blood 2010;115(9):1835–42. [86] van der Wal DE, Du VX, Lo KS, Rasmussen JT, Verhoef S, Akkerman JW. Platelet apoptosis by cold-induced glycoprotein Ibα clustering. J Thromb Haemost 2010;8(11):2554–62. [87] Gitz E, Koekman CA, van den Heuvel DJ, Deckmyn H, Akkerman JW, Gerritsen HC, et al. Improved platelet survival after cold storage by prevention of glycoprotein Ibα clustering in lipid rafts. Haematologica 2012;97(12):1873–81. [88] Yuan Y, Zhang W, Yan R, Liao Y, Zhao L, Ruan C, et al. Identification of a novel 14-33ζ binding site within the cytoplasmic domain of platelet glycoprotein Ibα that plays a key role in regulating the von Willebrand factor binding function of glycoprotein Ib-IX. Circ Res 2009;105(12):1177–85. [89] van der Wal DE, Gitz E, Du VX, Lo KS, Koekman CA, Versteeg S, et al. Arachidonic acid depletion extends survival of cold-stored platelets by interfering with the [glycoprotein Ibα–14-3-3ζ] association. Haematologica 2012;97(10):1514–22. [90] Kruss S, Erpenbeck L, Amschler K, Mundinger TA, Helms H-J, Friede T, et al. Adhesion maturation of neutrophils on nanoscopically presented platelet receptor GPIbα. ACS Nano 2013;7(11):9984–96.
Contents lists available at ScienceDirect
Transfusion Medicine Reviews journal homepage: www.tmreviews.com
Platelet Receptor Expression and Shedding: Glycoprotein Ib-IX-V and Glycoprotein VI Elizabeth E. Gardiner, Robert K. Andrews ⁎ Australian Centre for Blood Diseases, Monash University, Melbourne, Australia
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Available online 12 March 2014 Keywords: Platelets Hemostasis Thrombosis Glycoprotein Ib Glycoprotein VI
a b s t r a c t Quantity, quality, and lifespan are 3 important factors in the physiology, pathology, and transfusion of human blood platelets. The aim of this review is to discuss the proteolytic regulation of key platelet-specific receptors, glycoprotein(GP)Ib and GPVI, involved in the function of platelets in hemostasis and thrombosis, and nonimmune or immune thrombocytopenia. The scope of the review encompasses the basic science of platelet receptor shedding, practical aspects related to laboratory analysis of platelet receptor expression/shedding, and clinical implications of using the proteolytic fragments as platelet-specific biomarkers in vivo in terms of platelet function and clearance. These topics can be relevant to platelet transfusion regarding both changes in platelet receptor expression occurring ex vivo during platelet storage and/or clinical use of platelets for transfusion. In this regard, quantitative analysis of platelet receptor profiles on blood samples from individuals could ultimately enable stratification of bleeding risk, discrimination between causes of thrombocytopenia due to impaired production vs enhanced clearance, and monitoring of response to treatment prior to change in platelet count. © 2014 Elsevier Inc. All rights reserved.
Contents Production of Circulating Platelets . . . . . . . . . . . . Platelet Receptors GPIb-IX-V and GPVI . . . . . . . . . . Ectodomain Shedding of GPIbα and GPVI . . . . . . . . Analysis of Platelet GPIbα and GPVI Expression/Shedding . Clinical Implications of Platelet Receptor Shedding . . . . Platelet Lifespan and Clearance: Low-temperature Exposure Conclusions . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . .
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A recent report of a case of the congenital platelet defect, BernardSoulier syndrome (“Image in Hematology” [1]) showed a blood smear and described misdiagnosis of the patient as acute immune thrombocytopenia (ITP) resulting in ineffective steroid treatment and splenectomy. Bernard-Soulier syndrome is characterized by low platelet count, larger-than-normal platelets (macrothrombocytopenia), and increased bleeding risk, and it involves defective expression and function of the platelet glycoprotein (GP)Ib-IX-V complex [2–4]. Sources of support: National Health and Medical Research Council of Australia, National Heart Foundation of Australia, Monash University, Alfred Hospital. Conflict of interest: All authors have no conflict of interest to disclose. ⁎ Corresponding author. Robert K. Andrews, PhD, Australian Centre for Blood Diseases, Monash University, Alfred Medical Research and Education Precinct (AMREP), Commercial Road, Melbourne, Australia. E-mail address: [email protected] (R.K. Andrews). 0887-7963/$ – see front matter © 2014 Elsevier Inc. All rights reserved. http://dx.doi.org/10.1016/j.tmrv.2014.03.001
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Misdiagnosis of (macro)thrombocytopenia [1–5] and problems with diagnosis and monitoring treatment of immune or nonimmune thrombocytopenia more widely highlight the lack of broadly available platelet-based assays that quantify the hemostatic quality of platelets, or that can be used at low platelet count or with platelets of abnormal size. Platelet count is the most common clinical measurement but does not necessarily predict bleeding risk and does not distinguish between thrombocytopenia due to decreased platelet production from megakaryocytes in the bone marrow or increased platelet clearance, for example, due to antiplatelet autoantibodies. As a consequence, patients may be subjected to unnecessary platelet transfusions or, if autoimmune thrombocytopenia is misdiagnosed, treatment with steroids or immunosuppressants [1,5]. For ITP, time for response to for first-, second-, or third-line treatment may take several weeks or longer [6,7]. Increased understanding of platelet receptor expression and function could
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provide new ways of improving diagnosis of platelet defects, analyzing platelet quality and functionality at normal or low platelet count, and evaluating bleeding or thrombotic risk and monitoring treatment. Production of Circulating Platelets Platelets play a central role in normal hemostasis as well as in cardiovascular disease and inflammation, in the regulation of coagulation, and in tumor metastasis [8–12]. Blood cells are derived from megakaryocyte precursor cells in the bone marrow under the control of growth factors such as thrombopoietin produced by the liver and kidneys. Mature megakaryocytes transform into proplatelets (elongated branched tubular structures containing cytoplasm) with new anucleate platelets forming at the tips. Diseases or drug treatments that impair platelet production result in low platelet count (thrombocytopenia), bleeding, and/or defects in platelet function. Platelets normally number between 100 and 400×10 9/L in blood. Once released into the bloodstream, platelets circulate with an average lifespan of 7 to 10 days until cleared by hemostatic consumption or cleared by the reticuloendothelial system, processes that may be mediated in part by platelet surface receptors [13–15]. Platelet Receptors GPIb-IX-V and GPVI Newly formed young platelets are larger and express higher levels of GPIbα, which decreases as platelets age (see below). For the purpose of quantitative platelet analysis, GPIbα of the GPIb-IX-V complex and GPVI, are of particular interest because these receptors are essentially platelet specific, are critical for initiation of thrombus formation at arterial shear rates, and are implicated in wider platelet functions beyond hemostasis and thrombosis, as well as platelet aging and clearance. Glycoprotein Ibα is a member of the leucine-rich repeat (LRR) protein family and is a type I transmembrane receptor containing an extracellular ligand-binding domain featuring the LRR domains, a sialomucin domain, a transmembrane domain, and an intracellular domain. Glycoprotein Ibα is disulphide linked to GPIbβ and noncovalently linked to GPIX and GPV, all members of the LRR family. There are multiple ligands for GPIbα Fig. (A), including its main adhesive ligand; von Willebrand factor (VWF); coagulation factors XII, XI, and thrombin; P-selectin expressed on activated endothelial cells or platelets; and the leukocyte integrin, αMβ2. There are also multiple intracellular binding partners for GPIb-IX-V, including calmodulin that binds GPIbβ and GPV and regulates stable surface expression of the complex, 14-3-3ζ that binds phosphorylated sequences within GPIbα and GPIbβ, the p85 subunit of phosphatidylinositol 3-kinase (p85/p110) that regulates signal transduction, and filamin-A that binds GPIbα and links the complex to the actin-containing cytoskeleton—these interactions enable this receptor complex to finely regulate platelet adhesion, activation, shape change and thrombus formation, interactions with endothelial cells and leukocytes, and platelet survival and clearance (reviewed in Refs. [16–20]). Glycoprotein V is a receptor with a role in regulating platelet-collagen interactions [21], is a substrate for active thrombin, and is also shed by either metalloproteinase- or thrombindependent pathways [22–26] (Fig.; see below). Glycoprotein VI is a member of the immunoglobulin (Ig)-like superfamily, a type I transmembrane receptor with 2 extracellular Ig domains, a mucin-like domain, a transmembrane, and an intracellular sequence (reviewed in Refs. [27–29]; Fig. (A). Glycoprotein VI forms a noncovalent complex with GPIbα on resting or activated platelets [30] and signals via associated Src/Syk kinase pathways. Critical in GPVImediated signaling is the coassociated FcR γ-chain (FcRγ), which contains an immunoreceptor tyrosine-based activation motif (ITAM) [21–23] within its cytoplasmic domain. Other ITAM-based immunoreceptors expressed on human platelets are CLEC-2 [27,31] and FcγRIIa Fig. (A), with FcγRIIa playing a key role in platelet activation in response to antiplatelet (auto)antibodies. Dual proteolytic inactiva-
Fig 1. In response to vascular damage or antiplatelet antibodies in autoimmune disease, engagement of platelet receptors GP Ib-IX-V, GPVI, and/or FcγRIIa leads to platelet adhesion and activation (A) as well as irreversible proteolysis (B) generating soluble fragments as potential biomarkers and resulting in loss of adhesive function and clearance associated with platelet aging and thrombocytopenia (C). See the text for details.
tion pathways for GPVI (ectodomain shedding) and FcγRIIa (intracellular de-ITAM-ization) have been described [32] and imply that GPVI shedding is a consequence of FcγRIIa engagement by antiplatelet antibodies (see below). Downstream of GPIbα and GPVI, common early activation pathways initiate secondary responses to Gprotein–coupled receptors for soluble agonists including thrombin, ADP, and thromboxane A2, leading to activation of the plateletspecific integrin, αIIbβ3, which binds VWF and fibrinogen, thereby mediating platelet aggregation and thrombus formation ([16,17,33], and references therein).
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Ectodomain Shedding of GPIbα and GPVI Given the functional importance of GPIbα/GPVI and their potential as platelet-specific biomarkers, understanding mechanisms regulating expression and function of these receptors is critical. One key mechanism involves ectodomain proteolysis as depicted in Fig., where intact receptors (panel A) undergo proteolysis leading to generation of soluble ectodomain fragments and rapid, irreversible depletion of the surface receptor (panels B and C; reviewed in Ref. [34]). Importantly, proteolytic inactivation of these receptors on human platelets involves distinct mechanisms, with respect to the sheddases involved and the pathophysiological triggers which induce shedding. On human platelets, GPVI is predominantly shed by the metalloproteinase, ADAM10, whereas ADAM17 plays a major role in shedding of GPIbα. This is based on experimental studies using recombinant forms of the sheddases and synthetic peptides spanning the cleavage region, expression of human GPVI on cell lines where specific residues adjacent to the cleavage site were mutated [26], and inhibition of GPVI shedding by the ADAM10selective inhibitor, GI254023 [35,36]. A predominant role for ADAM17 in GPIbα shedding in vitro and in vivo has also been shown in mouse and human platelets [37], whereas ADAM10 as well as other metalloproteinase(s) may play a role in GPVI shedding in mice because platelettargeted loss of ADAM10 activity only partially attenuates shedding in this system [38]. In addition to thrombin, both ADAM10 and ADAM17 participate in shedding of GPV from activated platelets [25,26] Fig. (B). Analysis of Platelet GPIbα and GPVI Expression/Shedding Receptor shedding can be analyzed experimentally by analysis of untreated platelets or platelet samples treated with agents to induce shedding, and detecting loss of intact receptor and formation of 1 or both proteolytic fragments, that is, the shed ectodomain in supernatant and/or the membrane-associated remnant. With washed platelets, analysis may involve Western blot with antibodies N- or C-terminal of the cleavage site to detect intact receptor and/or proteolytic fragments. With washed platelets, platelet-rich plasma, or whole blood, flow cytometry with anti-GPIbα or anti-GPVI ectodomain antibodies can detect time-dependent loss of intact receptor, and immune-type enzyme-linked immunosorbent assay or bead-based assays can detect sGPIbα ectodomain (termed glycocalicin) or sGPVI in cell-free supernatant or platelet-free plasma [26,39–52]. For clinical studies, measuring glycocalicin or sGPVI in plasma is also feasible using available assays that have suitable sensitivity, linearity over a practical range, and lower detection limits compatible with levels found in healthy human plasma or elevated levels in disease [44–52]. Measuring sGPVI requires fresh or frozen platelet-free plasma, but not serum due to coagulation-induced shedding [35,44]. There is a major difference between levels of glycocalicin (~1000–3000 ng/mL glycocalicin [51]) compared with sGPVI (~10–20 ng/mL or less) in healthy human plasma [44–46]), taking into account differences in molecular weight and approximate copy number per platelet (glycocalicin, ~130 kd and ~30 000 copies of GPIbα/platelet cf. sGPVI, ~55 kd and ~6000 copies GPVI/platelet) [41]. This platelet GPVI copy number may be an underestimate; ~10 000 has been determined from biophysical approaches [53]. The glycocalicin index (the plasma glycocalicin level corrected for platelet count) has been evaluated as a surrogate marker of peripheral platelet turnover [52]. Compared with GPIbα, which is constitutively shed, GPVI is also stable on normal platelets, with essentially no membrane-associated fragment detectable by Western blot [26,54]. This implies that changes in plasma levels over basal levels may be more sensitive for evaluating shedding events involving platelet GPVI compared with GPIbα. Triggers of GPVI shedding from human platelets include the following: the major physiological ligand, collagen, and other nonphysiological GPVI ligands; coagulation resulting in activation of clotting factor Xa, which leads to activation of ADAM10-dependent shedding; autoantibodies that either bind GPVI directly or bind other
platelet surface antigens and act via FcγRIIa; exposure of platelets to elevated shear stress, which potently induces GPVI shedding independent of intracellular signals, platelet activation or aggregation; and a range of artificial agents previously shown to activate ADAM family sheddases on other cells, such as the protein kinase C– activator phorbol myristate acetate, the thiol-modifying agent Nethylmaleimide, calmodulin antagonists, or the mitochondrial poison, carbonyl cyanide M-chlorophenylhydrazone ([39–42], and references therein). Shedding of GPIbα mediated by ADAM17 is not known to be induced by GPVI ligands but is triggered by elevated shear stress (VWF dependent), and phorbol myristate acetate, N-ethylmaleimide, calmodulin antagonists, or carbonyl cyanide M-chlorophenylhydrazone, as well as by the agonist serotonin, or exposure of platelets to oxidative stress or diesel exhaust particles [26,37,54–58]. Aspirin also activates ADAM17-mediated shedding events on platelets, which may limit platelet reactivity in addition to aspirin's known role as an inhibitor of platelet activation [59]. Under conditions of shear stress, shedding of GPVI independent of known GPVI ligands, platelet activation, or VWF-dependent aggregation implies an effect of shear on activation of the sheddase or altered membrane properties facilitating ADAM10-mediated cleavage of GPVI. In this regard, cholesterol depletion or cholesterol-altering statins affect membrane fluidity and ADAM10 activity toward substrates on other types of cells [60,61]. Finally, not only do GPVI ligands induce shedding of GPVI and release of sGPVI, but they also cause simultaneous calpain-mediated intracellular proteolysis of FcγRIIa Fig. (B) [32]. Conversely, antiplatelet IgG that engages FcγRIIa also induces ADAM10-mediated shedding of GPVI and release of sGPVI, inhibitable by a function blocking anti-FcγRIIa antibody, IV.3 [32,54]. Both GPVI/FcRγ and FcγRIIa are ITAM-bearing receptors [27,31], and inhibition of Src/Syk signaling pathways effectively block proteolysis of both GPVI and FcγRIIa on human platelets [32]. Clinical Implications of Platelet Receptor Shedding The relationship between platelet reactivity and surface density of primary platelet receptors suggests that controlled shedding could limit platelet reactivity under prothrombotic conditions or regulate transition from resting circulating platelets to adherent activated platelets in a stable thrombus in response to prothrombotic stimuli. Experimental findings imply that GPIbα or GPVI shedding in vivo could result from multiple potential causes, including vascular damage exposing VWF/collagen, pathological shear stress due to stenosis, disorders leading to platelet hyperreactivity such as metabolic disorders or infection, coagulopathy, or autoimmune disease associated with antiplatelet autoantibodies. Alterations in plasma sGPVI have been reported in ischemic stroke [62–64], coronary disease [36,45,65–67], disseminated intravascular coagulation [35], lupus nephritis [68], thrombotic microangiopathy [46], and ITP [54,69]. Plasma sGPVI is decreased compared with control in Alzheimer disease, consistent with decreased activity of platelet ADAM10 [70]. Glycocalicin (glycocalicin index) has been evaluated together with immature platelet fraction in ITP [52,71,72]. Glycoprotein V shedding from activated platelets due to active thrombin or ADAM10/ADAM17 sheddases has also been measured using sGPV enzyme-linked immunosorbent assay in experimental thrombosis models [23], as a platelet activation marker in the context of platelet transfusion [22,24], and in atherothrombotic or other disorders associated with platelet hyperreactivity [73–76]. Platelet Lifespan and Clearance: Low-temperature Exposure and Transfusion A major limitation on the shelf-life of platelets stored for blood transfusion is that platelets exposed to lower temperature for as little as 1 hour may be rapidly cleared from the circulation after transfusion
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[77]. Mechanisms underlying this clearance are linked to changes of platelet GPIbα and enhanced GPIbα-mediated interactions with phagocytic cells in the liver via αMβ2 or other receptors. Glycoprotein Ibα clustering, shedding, and changes in glycosylation/sialic acid have been investigated as important regulators of exacerbated clearance of cooled platelets [14,15,77,78]. Lower temperatures (b15°C) change platelet shape and actin filament-cytoskeletal arrangements, and also increase intracellular Ca 2+, although selectively blocking these events does not prevent posttransfusion clearance [77]. However, rapid clearance was overcome in αMβ2-deficient mice, and proteolysis of GPIbα from mouse platelets prior to transfusion had a similar protective effect, although interestingly, cold treatment did not adversely affect VWF binding to GPIbα. Although GPIbα and αMβ2 are implicated in the mechanism of platelet clearance after low-temperature exposure, there is also an important role for changes in glycosylation and sialic acid on platelets/ GPIbα. First, αMβ2 recognizes N-linked glycan structures on GPIbα; blocking this interaction on cooled platelets also prevents rapid clearance [79]. Second, upon rewarming, refrigerated platelets secrete sialidase(s), which remove sialic acid from glycosylation sites on GPIbα and other receptors [15]. This enhances ADAM17-mediated shedding of GPIbα (and GPV) and coincides with increased susceptibility for clearance. Third, prolonged low-temperature exposure increases both the density and the amount of galactose residues on platelets [14]. As a consequence, in addition to αMβ2-mediated clearance after shorter-term exposure, Ashwell-Morell receptors on hepatocytes become proportionately more important for platelet clearance after longer-term chilling [14,78]. By a similar mechanism, AshwellMorell receptor that recognizes galactose and N-acetylgalactosamine on de-sialylated GPs is implicated in thrombocytopenia associated with the action of desialylating Streptococcal neuraminidases in sepsis, which likely influences onset/progression of disseminated intravascular coagulation [80,81]. Platelet receptor expression influenced by clustering and shedding of GPIbα is a clearly major factor in regulating platelet function and determining platelet survival and lifespan and clearance [14,15,77,78,82,83]. Normal circulating human platelets contain a proportion of proteolyzed GPIbα, which is constitutively shed, but no detectable proteolytic remnant fragment of GPVI [26,54], consistent with a link between loss of GPIbα/GPVI expression and clearance from the circulation. Like cooled platelets, apoptotic platelets from mice deficient in the prosurvival protein Bcl-xL, or platelets that have been experimentally damaged or aged, also shed GPIbα [37,84–87]. The association of the regulatory protein, 14-3-3ζ, with the cytoplasmic domain of GPIbα is a critical regulator of apoptosis, because sequestration by GPIbα can prevent 14-3-3ζ binding to death regulators, as well as through regulating GPIbα-dependent ligand binding or signaling [18–20,88,89]. ADAM17-mediated shedding of GPIbα in stored platelets is dependent on p38 mitogen-activated protein kinase, and inhibition of this pathway during storage may improve posttransfusion recovery [85]. Finally, clustering and/or shedding of GPIbα could also regulate clearance by controlling the spatial density of the receptor and interaction with αMβ2-bearing phagocytes. Recent experimental studies uniquely demonstrate an optimal spatial density requirement for neutrophil αMβ2-GPIbα interaction [90], which could imply enhanced clearance at an optimal surface density as GPIbα expression is decreased. Conclusions Studies described above involving analysis of expression and function of platelet receptors GPIb-IX-V and GPVI could ultimately play a role in the diagnosis of platelet defects, analyzing platelet quality at normal or low platelet count, and/or evaluating bleeding or thrombotic risk and monitoring treatment. To maximize benefits from clinical application of these measurements, further research is
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required to correlate quantitative changes in levels of these markers with clinical outcomes in prospective studies and determine whether these changes predict response to treatment prior to changes in platelet count.
References [1] Moiz B, Rashid A. BSS misdiagnosed as ITP. Blood 2013;122(10):1693. [2] Bernard J, Soulier J-P. Sur une nouvelle variété de dystrophie thrombocytairehémorragipare congénitale. Sem Hop 1948;24:3217–23. [3] López JA, Andrews RK, Afshar-Kharghan V, Berndt MC. Bernard-Soulier syndrome. Blood 1998;91:4397–418. [4] Berndt MC, Andrews RK. Bernard-Soulier syndrome: an update. Sem Thromb Haemost 2013;39(6):656–62. [5] Althaus K, Greinacher A. MYH-9 related platelet disorders: strategies for management and diagnosis. Transfus Med Hemother 2010;3(5):260–7. [6] Lakshmanan S, Cuker A. Contemporary management of primary immune thrombocytopenia in adults. J Thromb Haemost 2012;10(10):1988–98. [7] Rodrigo C, Gooneratne L. Dapsone for primary immune thrombocytopenia in adults and children: an evidence-based review. J Thromb Haemost 2013; 11(11):1946–53. [8] Ombrello C, Block R, Morrell C. Our expanding view of platelet functions and its clinical implications. J Cardiovasc Transl Res 2010;3(5):538–46. [9] Riedl J, Pabinger I, Ay C. Platelets in cancer and thrombosis. Hamostaseologie 2014;34(1):54–62. [10] Versteeg HH, Heemskerk JW, Levi M, Reitsma PH. New fundamentals in hemostasis. Physiol Rev 2013;93(1):327–58. [11] Zhang W, Huang W, Jing F. Contribution of blood platelets to vascular pathology in Alzheimer's disease. J Blood Med 2013;4:141–7. [12] Andrews RK, Berndt MC, Elalamy I. Platelets: from function to dysfunction in essential thrombocythaemia. Eur Haematol Oncol 2011;7(2):125–31. [13] Dowling MR, Josefsson EC, Henley KJ, Hodgkin PD, Kile BT. Platelet senescence is regulated by an internal timer, not damage inflicted by hits. Blood 2010; 116(10):1776–8. [14] Rumjantseva V, Grewal PK, Wandall HH, Josefsson EC, Sørensen AL, Larson G, et al. Dual roles for hepatic lectin receptors in the clearance of chilled platelets. Nat Med 2009;15(11):1273–80. [15] Jansen AJG, Josefsson EC, Rumjantseva V, Liu QP, Falet H, Bergmeier W, et al. Desialylation accelerates platelet clearance after refrigeration and initiates GPIbα metalloproteinase-mediated cleavage in mice. Blood 2012;119(5):1263–73. [16] Andrews RK, Berndt MC. Platelet physiology and thrombosis. Thromb Res 2004;114:447–53. [17] Andrews RK, Berndt MC. The glycoprotein Ib-IX-V complex. In: Michelson A, editor. Platelets, 3rd ed.San Diego: Academic Press; 2012. p. 195–211. [18] Andrews RK, Du X, Berndt MC. The 14-3-3ζ–GPIb-IX-V complex as an antiplatelet target. Drug News Perspect 2007;20:285–92. [19] Mu F-T, Andrews RK, Arthur JF, Munday AM, Cranmer SL, Jackson SP, et al. A functional 14-3-3ζ–independent association of PI3-kinase with glycoprotein Ibα, the major ligand-binding subunit of the platelet glycoprotein Ib-IX-V complex. Blood 2008;111:4580–7. [20] Mu F-T, Cranmer SL, Andrews RK, Berndt MC. Functional association of PI3-kinase with platelet glycoprotein Ibα, the major ligand-binding subunit of the glycoprotein Ib-IX-V complex. J Thromb Haemost 2010;8:324–30. [21] Moog S, Mangin P, Lenain N, Strassel C, Ravanat C, Schuhler S, et al. Platelet glycoprotein V binds to collagen and participates in platelet adhesion and aggregation. Blood 2001;98(4):1038–46. [22] Azorsa DO, Moog S, Ravanat C, Schuhler S, Folléa G, Cazenave JP, et al. Measurement of GPV released by activated platelets using a sensitive immunocapture ELISA—its use to follow platelet storage in transfusion. Thromb Haemost 1999;81(1):131–8. [23] Ravanat C, Freund M, Mangin P, Azorsa DO, Schwartz C, Moog S, et al. GPV is a marker of in vivo platelet activation—study in a rat thrombosis model. Thromb Haemost 2000;83(2):327–33. [24] Javela K, Eronen J, Sarna S, Kekomäki R. Soluble glycoprotein V as a quality marker of platelet concentrates stressed by transportation. Transfusion 2005;45(9):1504–11. [25] Rabie T, Strehl A, Ludwig A, Nieswandt B. Evidence for a role of ADAM17 (TACE) in the regulation of platelet glycoprotein V. J Biol Chem 2005;280(15):14462–8. [26] Gardiner EE, Karunakaran D, Shen Y, Andrews RK, Berndt MC. Controlled shedding of platelet glycoprotein (GP)VI and GPIb-IX-V by ADAM family metalloproteinases. J Thromb Haemost 2007;5:1530–7. [27] Ozaki Y, Suzuki-Inoue K, Inoue O. Platelet receptors activated via mulitmerization: glycoprotein VI, GPIb-IX-V, and CLEC-2. J Thromb Haemost 2013;11(Suppl. 1):330–9. [28] Zahid M, Mangin P, Loyau S, Hechler B, Billiald P, Gachet C, et al. The future of glycoprotein VI as an antithrombotic target. J Thromb Haemost 2012;10(12):2418–27. [29] Dütting S, Bender M, Nieswandt B. Platelet GPVI: a target for antithrombotic therapy?! Trends Pharmacol Sci 2012;33(11):583–90. [30] Arthur JF, Matzaris M, Gardiner EE, Taylor SG, Wijeyewickrema LC, Ozaki Y, et al. Glycoprotein (GP)VI is associated with GPIb-IX-V on the membrane of resting and activated platelets. Thromb Haemost 2005;93:716–23. [31] Bergmeier W, Stefanini L. Platelet ITAM signaling. Curr Opin Hematol 2013;20(5):445–50.
60
E.E. Gardiner, R.K. Andrews / Transfusion Medicine Reviews 28 (2014) 56–60
[32] Gardiner EE, Karunakaran D, Arthur JF, Mu F-T, Powell MS, Baker RI, et al. Dual ITAM-mediated proteolytic pathways for irreversible inactivation of platelet receptors: De-ITAM-ising FcγRIIa. Blood 2008;111:165–74. [33] Gardiner EE, Arthur JF, Shen Y, Karunakaran D, Moore LA, Am Esch II Jr Schulte, et al. GPIbα-selective activation of platelets induces platelet signalling events comparable to GPVI activation events. Platelets 2010;21:244–52. [34] Andrews RK, Karunakaran D, Gardiner EE, Berndt MC. Platelet receptor shedding: a mechanism for downregulating platelet reactivity. Arterioscler Thromb Vasc Biol 2007;27:1511–20. [35] Al-Tamimi M, Grigoriadis G, Tran H, Paul E, Servadei P, Berndt MC, et al. Coagulation-induced shedding of platelet glycoprotein VI mediated by Factor Xa. Blood 2011;117(14):3912–20. [36] Al-Tamimi M, Tan CW, Qiao J, Pennings GJ, Javadzadegan A, Yong ASC, et al. Pathological shear triggers shedding of vascular receptors: a novel mechanism for downregulation of platelet glycoprotein (GP)VI in stenosed coronary vessels. Blood 2012;119(18):4311–20. [37] Bergmeier W, Piffath CL, Cheng G, Dole VS, Zhang Y, von Andrian UH, et al. Tumor necrosis factor-α–converting enzyme (ADAM17) mediates GPIbα shedding from platelets in vitro and in vivo. Circ Res 2004;95(7):677–83. [38] Bender M, Hofmann S, Stegner D, Chalaris A, Bösl M, Braun A, et al. Differentially regulated GPVI ectodomain shedding by multiple platelet-expressed proteinases. Blood 2010;116(17):3347–55. [39] Al Tamimi M, Arthur JF, Gardiner EE, Andrews RK. Focusing on plasma GPVI. Thromb Haemost 2012;107(4):648–55. [40] Gardiner EE, Andrews RK. Plasma sGPVI: changing levels in human disease. Thromb Res 2014;133(3):306–7. [41] Qiao J, Shen Y, Gardiner EE, Andrews RK. Proteolysis of platelet receptors in humans and other species. Biol Chem 2010;391:893–900. [42] Bigalke B, Elvers M, Schönberger T, Gawaz M. Platelet and soluble glycoprotein VI —novel applications in diagnosis and therapy. Curr Drug Targets 2011;12(12): 1821–30. [43] Brill A, Chauhan AK, Canault M, Walsh MT, Bergmeier W, Wagner DD. Oxidative stress activates ADAM17/TACE and induces its target receptor shedding in platelets in a p38-dependent fashion. Cardiovasc Res 2009;84(1):137–44. [44] Al-Tamimi M, Mu FT, Moroi M, Gardiner EE, Berndt MC, Andrews RK. Measuring soluble platelet glycoprotein VI in human plasma by ELISA. Platelets 2009;20:143–9. [45] Bigalke B, Pötz O, Kremmer E, Geisler T, Seizer P, Puntmann VO, et al. Sandwich immunoassay for soluble glycoprotein VI in patients with symptomatic coronary artery disease. Clin Chem 2011;57(6):898–904. [46] Yamashita Y, Naitoh K, Wada H, Ikejiri M, Mastumoto T, Ohishi K, et al. Elevated plasma levels of soluble platelet glycoprotein VI (GPVI) in patients with thrombotic microangiopathy. Thromb Res 2014;133(3):440–4. [47] Qiao J, Schoenwaelder SM, Mason K, Tran H, Davis AK, Jackson SP, et al. Low adhesion receptor levels on circulating platelets in patients with lymphoproliferative diseases prior to receiving Navitoclax (ABT-263). Blood 2013;121(8): 1479–81. [48] Kunishima S, Hayashi K, Kobayashi S, Naoe T, Ohno R. New enzyme-linked immunosorbent assay for glycocalicin in plasma. Clin Chem 1991;37(2):169–72. [49] Bessos H, Murphy WG. A new competitive binding enzyme-linked immunosorbent assay for glycocalicin in plasma and platelet concentrate supernatants. Thromb Res 1990;59(3):497–507. [50] Adelman B, Michelson AD, Loscalzo J, Greenberg J, Handin RI. Plasmin effect on platelet glycoprotein Ib–von Willebrand factor interactions. Blood 1985;65(1):32–40. [51] Coller BS, Kalomiris E, Steinberg M, Scudder LE. Evidence that glycocalicin circulates in normal plasma. J Clin Invest 1984;73:794–9. [52] Steinberg MH, Kelton JG, Coller BS. Plasma glycocalicin. An aid in the classification of thrombocytopenic disorders. N Engl J Med 1987;317(17):1037–42. [53] Burkhart JM, Vaudel M, Gambaryan S, Radau S, Walter U, Martens L, et al. The first comprehensive and quantitative analysis of human platelet protein composition allows the comparative analysis of structural and functional pathways. Blood 2012;120(15):e73–82. [54] Gardiner EE, Al-Tamimi M, Mu FT, Karunakaran D, Thom JY, Moroi M, et al. Compromised ITAM-based platelet receptor function in a patient with immune thrombocytopenic purpura. J Thromb Haemost 2008;6(7):1175–82. [55] Duerschmied D, Canault M, Lievens D, Brill A, Cifuni SM, Bader M, et al. Serotonin stimulates platelet receptor shedding by tumor necrosis factor-α–converting enzyme (ADAM17). J Thromb Haemost 2009;7(7):1163–71. [56] Mo X, Nguyen NX, Mu FT, Yang W, Luo SZ, Fan H, et al. Transmembrane and transsubunit regulation of ectodomain shedding of platelet glycoprotein Ibα. J Biol Chem 2010;285(42):32096–104 [15]. [57] Cheng H, Yan R, Li S, Yuan Y, Liu J, Ruan C, et al. Shear-induced interaction of platelets with von Willebrand factor results in glycoprotein Ibα shedding. Am J Physiol Heart Circ Physiol 2009;297(6):H2128–35. [58] Forestier M, Al-Tamimi M, Gardiner EE, Hermann C, Meyer SC, Beer JH. Diesel exhaust particles impair platelet response to collagen and are associated with GPIbα shedding. Toxicol In Vitro 2012;26(6):930–8. [59] Aktas B, Pozgajova M, Bergmeier W, Sunnarborg S, Offermanns S, Lee D, et al. Aspirin induces platelet receptor shedding via ADAM17 (TACE). J Biol Chem 2005;280(48):39716–22. [60] Kojro E, Gimpl G, Lammich S, Marz W, Fahrenholz F. Low cholesterol stimulates the nonamyloidogenic pathway by its effect on the α-secretase ADAM 10. Proc Natl Acad Sci U S A 2001;98(10):5815–20. [61] Murai T, Maruyama Y, Mio K, Nishiyama H, Suga M, Sato C. Low cholesterol triggers membrane microdomain-dependent CD44 shedding and suppresses tumor cell migration. J Biol Chem 2011;286(3):1999–2007.
[62] Bigalke B, Stellos K, Geisler T, Kremmer E, Seizer P, May AE, et al. Expression of platelet glycoprotein VI is associated with transient ischemic attack and stroke. Eur J Neurol 2010;17(1):111–7. [63] Al-Tamimi M, Gardiner EE, Thom JY, Shen Y, Cooper MN, Hankey GJ, et al. Soluble glycoprotein VI is raised in the plasma of patients with acute ischemic stroke. Stroke 2011;42(2):498–500. [64] Wurster T, Poetz O, Stellos K, Kremmer E, Melms A, Schuster A, et al. Plasma levels of soluble glycoprotein VI (sGPVI) are associated with ischemic stroke. Platelets 2013;24(7):560–5. [65] Bigalke B, Stellos K, Geisler T, Lindemann S, May AE, Gawaz M. Glycoprotein VI as a prognostic biomarker for cardiovascular death in patients with symptomatic coronary artery disease. Clin Res Cardiol 2010;99(4):227–33. [66] Bigalke B, Stellos K, Weig HJ, Geisler T, Seizer P, Kremmer E, et al. Regulation of platelet glycoprotein VI (GPVI) surface expression and of soluble GPVI in patients with atrial fibrillation (AF) and acute coronary syndrome (ACS). Basic Res Cardiol 2009;104(3):352–7. [67] Pennings GJ, Yong ASC, Wong C, Al-Tamimi M, Gardiner EE, Andrews RK, et al. Circulating levels of soluble EMMPRIN (CD147) correlate with levels of soluble glycoprotein VI in human plasma. Platelets 2013. http://dx.doi.org/10.3109/ 09537104.2013.852660 [in press]. [68] Nurden P, Tandon N, Takizawa H, Couzi L, Morel D, Fiore M, et al. An acquired inhibitor to the GPVI platelet collagen receptor in a patient with lupus nephritis. J Thromb Haemost 2009;7(9):1541–9. [69] Gardiner EE, Thom JY, Al-Tamimi M, Hughes A, Berndt MC, Andrews RK, et al. Restored platelet function after romiplostim treatment in a patient with immune thrombocytopenic purpura. Br J Haematol 2010;149(4):625–8. [70] Laske C, Leyhe T, Stransky E, Eschweiler GW, Bueltmann A, Langer H, et al. Association of platelet-derived soluble glycoprotein VI in plasma with Alzheimer's disease. J Psychiatr Res 2008;42(9):746–51. [71] Barsam SJ, Psaila B, Forestier M, Page LK, Sloane PA, Geyer JT, et al. Platelet production and platelet destruction: assessing mechanisms of treatment effect in immune thrombocytopenia (ITP). Blood 2011;117(21):5723–32. [72] Psaila B, Bussel JB, Linden MD, Babula B, Li Y, Barnard MR, et al. In vivo effects of eltrombopag on platelet function in immune thrombocytopenia: no evidence of platelet activation. Blood 2012;119(17):4066–72. [73] Blann AD, Lanza F, Galajda P, Gurney D, Moog S, Cazenave JP, et al. Increased platelet glycoprotein V levels in patients with coronary and peripheral atherosclerosis—the influence of aspirin and cigarette smoking. Thromb Haemost 2001;86(3):777–83. [74] Morel O, Hugel B, Jesel L, Lanza F, Douchet MP, Zupan M, et al. Sustained elevated amounts of circulating procoagulant membrane microparticles and soluble GPV after acute myocardial infarction in diabetes mellitus. Thromb Haemost 2004;91(2):345–53. [75] Acar K, Sucak A, Beyazit Y, Genc G, Haznedaroglu IC, Aksu S, et al. Lack of platelet activation reflected by circulating soluble glycoprotein V in pre-eclampsia. J Int Med Res 2007;35(5):704–8. [76] Falcinelli E, Francisci D, Belfiori B, Petito E, Guglielmini G, Malincarne L, et al. In vivo platelet activation and platelet hyperreactivity in abacavir-treated HIVinfected patients. Thromb Haemost 2013;110(2):349–57. [77] Hoffmeister KM, Felbinger TW, Falet H, Denis CV, Bergmeier W, Mayadas TN, et al. The clearance mechanism of chilled blood platelets. Cell 2003;112(1):87–97. [78] Rumjantseva V, Hoffmeister KM. Novel and unexpected clearance mechanisms for cold platelets. Transfus Apher Sci 2010;42(1):63–70. [79] Hoffmeister KM, Josefsson EC, Isaac NA, Clausen H, Hartwig JH, Stossel TP. Glycosylation restores survival of chilled blood platelets. Science 2003;301 (5639):1531–4. [80] Grewal PK. The Ashwell-Morell receptor. Methods Enzymol 2010;479:223–41. [81] Grewal PK, Uchiyama S, Ditto D, Varki N, Le DT, Nizet V, et al. The Ashwell receptor mitigates the lethal coagulopathy of sepsis. Nat Med 2008;14(6):648–55. [82] Fox JE. Shedding of adhesion receptors from the surface of activated platelets. Blood Coagul Fibrinolysis 1994;5(2):291–304. [83] Bergmeier W, Burger PC, Piffath CL, Hoffmeister KM, Hartwid JH, Nieswandt B, et al. Metalloproteinase inhibitors improve the recovery and hemostatic function of in vitro–aged or -injured mouse platelets. Blood 2003;102(12):4229–35. [84] Josefsson EC, James C, Henley KJ, Debrincat MA, Rogers KL, Dowling MR, et al. Megakaryocytes possess a functional intrinsic apoptosis pathway that must be restrained to survive and produce platelets. J Exp Med 2011;208(10):2017–31. [85] Canault M, Duerschmied D, Brill A, Stefanini L, Schatzberg D, Cifuni SM, et al. p38 mitogen–activated protein kinase activation during platelet storage: consequences for platelet recovery and hemostatic function in vivo. Blood 2010;115(9):1835–42. [86] van der Wal DE, Du VX, Lo KS, Rasmussen JT, Verhoef S, Akkerman JW. Platelet apoptosis by cold-induced glycoprotein Ibα clustering. J Thromb Haemost 2010;8(11):2554–62. [87] Gitz E, Koekman CA, van den Heuvel DJ, Deckmyn H, Akkerman JW, Gerritsen HC, et al. Improved platelet survival after cold storage by prevention of glycoprotein Ibα clustering in lipid rafts. Haematologica 2012;97(12):1873–81. [88] Yuan Y, Zhang W, Yan R, Liao Y, Zhao L, Ruan C, et al. Identification of a novel 14-33ζ binding site within the cytoplasmic domain of platelet glycoprotein Ibα that plays a key role in regulating the von Willebrand factor binding function of glycoprotein Ib-IX. Circ Res 2009;105(12):1177–85. [89] van der Wal DE, Gitz E, Du VX, Lo KS, Koekman CA, Versteeg S, et al. Arachidonic acid depletion extends survival of cold-stored platelets by interfering with the [glycoprotein Ibα–14-3-3ζ] association. Haematologica 2012;97(10):1514–22. [90] Kruss S, Erpenbeck L, Amschler K, Mundinger TA, Helms H-J, Friede T, et al. Adhesion maturation of neutrophils on nanoscopically presented platelet receptor GPIbα. ACS Nano 2013;7(11):9984–96.
