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Platelet tissue factor: To be or not to be
Thrombosis Research 132 (2013) 3–5
Contents lists available at SciVerse ScienceDirect
Thrombosis Research journal homepage: www.elsevier.com/locate/thromres
Editorial
Platelet tissue factor: To be or not to be
Tissue factor (TF) is the receptor for factor VII/VIIa and functions as the primary activator of blood coagulation. In 1989 Tom Drake and colleagues [1] characterized TF expression in human tissues and found that it was present at high levels on adventitial fibroblast surrounding blood vessels and on epithelial cells at body surfaces. It was proposed that TF formed a “hemostatic envelope” around blood vessels that rapidly activated blood coagulation after vessel injury. Due to its high procoagulant activity it was thought that no TF was present in blood. However, this view changed in 1999 with a publication reporting the presence of so-called “blood-borne” TF [2]. This study showed that native human blood rapidly formed a TF-dependent thrombus on collagen-coated glass slides. Blood-borne TF was proposed to be “involved in thrombus propagation at the site of vascular injury” [2]. However, the authors qualified their results by saying that “this finding suggests that the TF originated in the blood (although leeching from the arterial segment could not be excluded)”. Indeed, it is difficult to determine if the traces of TF present in a blood sample originated from the blood itself or from the vessel wall. Importantly, the level of TF in the vessel wall vastly exceeds that found in blood. Not surprisingly there has been much debate about whether or not TF is present in blood. Mann and colleagues [3] were the first to dispute the idea that there was active TF present in whole human blood. They later reported that whole human blood containing the contact pathway inhibitor corn trypsin inhibitor did not contain physiologically active TF and that as little as 20 fM of TF induced clot formation [4]. We found that the recalcification time of citrated human whole blood was not prolonged by an inhibitory anti-TF antibody [5]. However, these studies do not exclude the possibility that human blood contains low levels of encrypted or inactive TF that can be activated at sites of vessel injury. Low levels of TF present in blood would be expected to bind factor VII/VIIa and this complex would be inhibited by tissue factor pathway inhibitor (TFPI) thus preventing inadvertent activation of clotting. This “blood-borne” TF may be derived from transiently activated monocytes or from damaged vessels and tissues. Interestingly, the “idling” of the clotting cascade in healthy people is dependent on the extrinsic pathway of coagulation (TF/factor VIIa) and not on the intrinsic pathway of coagulation indicating that there is some active TF exposed to blood in healthy people [6]. We found very low levels of TF activity in small membrane vesicles called microparticles (MPs) that were isolated from the blood of healthy people [7]. Removal of TFPI during the isolation of the MPs may be required for detection of this MP TF activity. In addition, human blood was reported to contain monocyte-derived, TF+ MPs [8]. A small subset of monocytes (~1.5%) has been shown to express TF [9] and these may contribute to the pool of TF+ MPs in the blood. In a mouse model of laser injury of small cremaster arterioles using healthy mice we found that hematopoietic cell-derived TF + MPs contribute to thrombosis [10]. Furthermore, it has been shown that binding of monocyte-derived TF+ MPs to the injured vessel was mediated by 0049-3848/$ – see front matter © 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.thromres.2013.05.009
the interaction of P-selectin glycoprotein ligand 1 on the MPs with P-selectin on activated endothelial cells or activated platelets [8]. These studies support the notion that blood contains very low levels of TF that can be activated at sites of vessel injury. However, in a mouse carotid artery thrombosis model that is associated with loss of the endothelium thrombosis is driven by vessel wall TF and not “blood-borne” TF [11]. Monocytes stimulated with bacterial lipopolysaccharide express TF and are often used as a positive control in studies on TF. However, whether or not activated platelets synthesize TF is highly controversial. We have divided platelet TF expression into 3 groups: quiescent platelets, rapidly activated platelets and long-term activated platelets (Fig. 1). Studies by two independent groups reported that quiescent platelets contain TF mRNA, TF antigen and TF activity [12–14]. In contrast, the current study by Osterud and Olsen [15] concludes that “human platelets do not express TF”. This is in agreement with work from Mann and Butenas [4,16,17]. One study found very low levels of TF in the open cannicular system of resting platelets [18]. However, only a small subset of platelets contained TF and it is unclear if this low level of TF would be sufficient to increase the procoagulant activity of platelets. We carefully isolated platelets from human blood in the presence of platelet inhibitors and found no TF mRNA expression [19]. However, prolonged stimulation of the platelets with various agonists induced splicing of TF pre-mRNA to mature TF mRNA [19] (Fig. 1). Splicing of TF pre-mRNA to mature TF mRNA was also observed in sepsis patients and in patients with type 2 diabetes [20,21]. This suggests that the early studies reporting the presence of TF mRNA in quiescent platelets likely analyzed platelets that were activated during isolation. Therefore, quiescent platelets contain TF pre-mRNA but do not contain TF mRNA or TF protein (Fig. 1). The key question is do platelets synthesize TF. We and others have reported that activated platelets express TF protein and activity [14,19,22]. In contrast to these studies, Osterud and Olsen [15] and others [16,17] failed to detect any TF protein or TF activity on activated platelets. How can we explain these differences? Our studies clearly show that activated platelets contain TF mRNA and that platelets have the machinery to translate mRNA into protein as shown by their ability to synthesize IL-1β. However, this does not mean that TF mRNA is translated into TF protein in platelets. The most likely explanation for the different results is related to technical issues in the measurement of TF. These can be divided into methods used to detect TF protein and TF activity. A variety of anti-TF antibodies have been used to detect TF protein on platelets by flow cytometry and in platelet lysates by Western blotting and ELISA. In general, the specificity and sensitivity of the immunological detection of an antigen depend not only on accessibility of the exposed epitope but also on the antibodies and assay protocols. We and others have questioned the specificity of some of these anti-TF antibodies particularly the ones used for commercial ELISAs
4
Editorial
TF PS PSGL-1
Monocyte-derived MP
TF
P-selectin
PS PS
Thrombosis
TF pre-mRNA
5’
3’
Fast (~5 min)
Quiescent Platelet
5’
3’
Activated Platelet Slow (~30 min) TF mRNA
5’ 5’
3’ 3’
Fig. 1. Platelet TF. Quiescent platelets contain TF pre-mRNA but no TF and phosphatidlyserine (PS) is present on the inner leaflet of the plasma membrane. TF present on rapidly activated platelets is likely derived from the binding of monocyte-derived TF+ MPs via an interaction between PSGL-1 and P-selectin. Platelet activation will also expose PS on the outer leaflet of the plasma membrane where it will enhance TF activity. TF present on platelets likely contributes to thrombosis in different diseases. Platelets activated with various agonists will splice TF pre-mRNA into mature mRNA but it is unclear at the point if this mRNA is translated into TF protein.
[23–25]. However, for the detection of TF in or on platelets most of the groups have used well characterized anti-human TF mAbs that were evaluated in a CD142 workshop [26]. Therefore, some of the variable results reported with these antibodies may not be due to the antibodies themselves but rather due to the assay conditions. With regard to the very low concentration of TF reported to be expressed by platelets, artifacts created by the immunological methods cannot be excluded. TF activity is typically detected in a two-stage assay that involves addition of factor VIIa and factor X to the sample and then measurement of the levels of factor Xa generated. One concern is that the supraphysiologic concentration of factor VIIa used in the assay can convert factor X to factor Xa in a TF-independent manner under some conditions. However, this potential artifact is excluded in the majority of studies because assays were performed in the presence and absence of inhibitory anti-TF antibodies to distinguish TF-dependent from TF-independent factor Xa activity. Another important factor is how the platelet sample is prepared? TF activity has been measured in whole platelets, platelet lysates and platelet membranes. We reported that membranes isolated from activated platelets contained TF activity [19], although no TF activity was detected in platelet lysates (H. Schwertz and A. Weyrich, unpublished data). In contrast, Osterud and Olsen [15] failed to detect any TF activity in whole platelets. One possibility is that TF on platelets is inhibited by TFPI but addition of an ant-TFPI antibody did not reveal any TF activity [15]. At present, it appears that there is no compelling data to support the idea that platelets synthesize TF. Numerous studies have shown that rapidly activated platelets can bind monocyte-derived TF + MPs [8,27–29]. Zillmann and colleagues [30] reported that a 5 minute stimulation of human blood with collagen shortened the clotting time in a TF-dependent manner. It was proposed that TF present on platelets was inhibited by TFPI and that neutrophils were required to inactive TFPI [18,30]. An alternative explanation for these results is that the collagen activated platelets rapidly bind TF+ MPs present in the blood that is then activated on the surface of the platelets. Indeed, collagen stimulation of isolated platelets did not increase TF activity. Studies have shown significantly higher amounts of
TF+ platelets in patients with sepsis and acute coronary syndromes compared with healthy controls [20,31]. This platelet associated TF is likely to be due to the binding of monocyte-derived TF+ MPs rather than de novo synthesis by the platelets themselves (Fig. 1). These studies suggest that platelets loaded with TF likely contribute to the formation of pathologic thrombi (Fig. 1). Acknowledgements We would like to acknowledge Dr. Raj Kasthuri (University of North Carolina at Chapel Hill), Dr. Alisa Wolberg (University of North Carolina at Chapel Hill) and Dr. Andy Weyrich (University of Utah) for helpful discussions and Julia Geddings (University of North Carolina at Chapel Hill) for help in preparing the editorial. References [1] Drake TA, Morrissey JH, Edgington TS. Selective cellular expression of tissue factor in human tissues. Implications for disorders of hemostasis and thrombosis. Am J Pathol 1989;134:1087–97. [2] Giesen PL, Rauch U, Bohrmann B, Kling D, Roque M, Fallon JT, et al. Blood-borne tissue factor: another view of thrombosis. Proc Natl Acad Sci U S A 1999;96: 2311–5. [3] Butenas S, Mann KG. Active tissue factor in blood? Nat Med 2004;10:1155–6 [author reply 6]. [4] Butenas S, Bouchard BA, Brummel-Ziedins KE, Parhami-Seren B, Mann KG. Tissue factor activity in whole blood. Blood 2005;105:2764–70 [Epub 004 Dec 16]. [5] Santucci RA, Erlich J, Labriola J, Wilson M, Kao KJ, Kickler TS, et al. Measurement of tissue factor activity in whole blood. Thromb Haemost 2000;83:445–54. [6] Mackman N. The role of tissue factor and factor VIIa in hemostasis. Anesth Analg 2009;108:1447–52. [7] Khorana AA, Francis CW, Menzies KE, Wang JG, Hyrien O, Hathcock J, et al. Plasma tissue factor may be predictive of venous thromboembolism in pancreatic cancer. J Thromb Haemost 2008;6:1983–5. [8] Falati S, Liu Q, Gross P, Merrill-Skoloff G, Chou J, Vandendries E, et al. Accumulation of tissue factor into developing thrombi in vivo is dependent upon microparticle P-selectin glycoprotein ligand 1 and platelet P-selectin. J Exp Med 2003;197: 1585–98. [9] Egorina EM, Sovershaev MA, Bjorkoy G, Gruber FX, Olsen JO, Parhami-Seren B, et al. Intracellular and surface distribution of monocyte tissue factor: application to intersubject variability. Arterioscler Thromb Vasc Biol 2005;25:1493–8 [Epub 2005 Apr 28].
Editorial [10] Chou J, Mackman N, Merrill-Skoloff G, Pedersen B, Furie BC, Furie B. Hematopoietic cell-derived microparticle tissue factor contributes to fibrin formation during thrombus propagation. Blood 2004;104:3190–7 [Epub 2004 Jul 27]. [11] Day SM, Reeve JL, Pedersen B, Farris DM, Myers DD, Im M, et al. Macrovascular thrombosis is driven by tissue factor derived primarily from the blood vessel wall. Blood 2005;105:192–8. [12] Siddiqui FA, Desai H, Amirkhosravi A, Amaya M, Francis JL. The presence and release of tissue factor from human platelets. Platelets 2002;13:247–53. [13] Camera M, Frigerio M, Toschi V, Brambilla M, Rossi F, Cottell DC, et al. Platelet activation induces cell-surface immunoreactive tissue factor expression, which is modulated differently by antiplatelet drugs. Arterioscler Thromb Vasc Biol 2003;23:1690–6 [Epub 2003 Jul 10]. [14] Camera M, Brambilla M, Toschi V, Tremoli E. Tissue factor expression on platelets is a dynamic event. Blood 2010;116:5076–7. [15] Østerud B, Olsen JH. Human platelets do not express tissue factor. Thromb Res 2013;132:112–5. [16] Bouchard BA, Mann KG, Butenas S. No evidence for tissue factor on platelets. Blood 2010;116:854–5. [17] Bouchard BA, Krudysz-Amblo J, Butenas S. Platelet tissue factor is not expressed transiently after platelet activation. Blood 2012;119:4338–9 [author reply 9-41]. [18] Muller I, Klocke A, Alex M, Kotzsch M, Luther T, Morgenstern E, et al. Intravascular tissue factor initiates coagulation via circulating microvesicles and platelets. FASEB J 2003;17:476–8 [Epub 2003 Jan 2]. [19] Schwertz H, Tolley ND, Foulks JM, Denis MM, Risenmay BW, Buerke M, et al. Signal-dependent splicing of tissue factor pre-mRNA modulates the thrombogenicity of human platelets. J Exp Med 2006;203:2433–40 [Epub 006 Oct 23]. [20] Rondina MT, Schwertz H, Harris ES, Kraemer BF, Campbell RA, Mackman N, et al. The septic milieu triggers expression of spliced tissue factor mRNA in human platelets. J Thromb Haemost 2011;9:748–58. [21] Gerritis AJ, Koekman CA, van Haeften TW, Akkerman JW. Platelet tissue factor synthesis in type 2 diabetes is resistant to inhibition by insulin. Diabetes 2010;59: 1487–95. [22] Panes O, Matus V, Saez CG, Quiroga T, Pereira J, Mezzano D. Human platelets synthesize and express functional tissue factor. Blood 2007;109:5242–50 [Epub 2007 Mar 8]. [23] Parhami-Seren B, Butenas S, Krudysz-Amblo J, Mann KG. Immunologic quantitation of tissue factors. J Thromb Haemost 2006;4:1747–55. [24] Wang JG, Geddings JE, Aleman MM, Cardenas JC, Chantrathammachart P, Williams JC, et al. Tumor-derived tissue factor activates coagulation and enhances thrombosis in a mouse xenograft model of human pancreatic cancer. Blood 2012;119:5543–52 [Epub 2012 Apr 30].
5
[25] Basavaraj MG, Olsen JO, Osterud B, Hansen JB. Differential ability of tissue factor antibody clones on detection of tissue factor in blood cells and microparticles. Thromb Res 2012;130:538–46. [26] Morrissey JH, Agis H, Albrecht S, Dignat-George F, Edgington T, Luther T, et al. CD142 (tissue factor) Workshop Panel report. In: Kishimoto, et al, editor. Leucocyte Typing VI: white cell differentiation antigens. New York: Garland Publishing, Inc.; 1997. p. 742–6. [27] Rauch U, Bonderman D, Bohrmann B, Badimon JJ, Himber J, Riederer MA, et al. Transfer of tissue factor from leukocytes to platelets is mediated by CD15 and tissue factor. Blood 2000;96:170–5. [28] Del Conde I, Shrimpton CN, Thiagarajan P, Lopez JA. Tissue-factor-bearing microvesicles arise from lipid rafts and fuse with activated platelets to initiate coagulation. Blood 2005;106:1604–11 [Epub 2005 Mar 1]. [29] Sovershaev MA, Egorina EM, Osterud B, Hansen JB. Evidence for direct transfer of tissue factor from monocytes to platelets in whole blood. Blood Coagul Fibrinolysis 2012;23:345–50. [30] Zillmann A, Luther T, Muller I, Kotzsch M, Spannagl M, Kauke T, et al. Plateletassociated tissue factor contributes to the collagen-triggered activation of blood coagulation. Biochem Biophys Res Commun 2001;281:603–9. [31] Brambilla M, Camera M, Colnago D, Marenzi G, De Metrio M, Giesen PL, et al. Tissue factor in patients with acute coronary syndromes: expression in platelets, leukocytes, and platelet-leukocyte aggregates. Arterioscler Thromb Vasc Biol 2008;28:947–53.
Nigel Mackman Division of Hematology/Oncology, Department of Medicine, Thrombosis and Hemostasis Program, McAllister Heart Institute, University of North Carolina at Chapel Hill, Chapel Hill, NC, USA Corresponding author. Tel.: +1 919 843 3961; fax: + 1 919 843 4896. E-mail address: [email protected]. Thomas Luther Medizinisches Labor Ostsachsen, D-02526 Bautzen, Germany 5 May 2013
Contents lists available at SciVerse ScienceDirect
Thrombosis Research journal homepage: www.elsevier.com/locate/thromres
Editorial
Platelet tissue factor: To be or not to be
Tissue factor (TF) is the receptor for factor VII/VIIa and functions as the primary activator of blood coagulation. In 1989 Tom Drake and colleagues [1] characterized TF expression in human tissues and found that it was present at high levels on adventitial fibroblast surrounding blood vessels and on epithelial cells at body surfaces. It was proposed that TF formed a “hemostatic envelope” around blood vessels that rapidly activated blood coagulation after vessel injury. Due to its high procoagulant activity it was thought that no TF was present in blood. However, this view changed in 1999 with a publication reporting the presence of so-called “blood-borne” TF [2]. This study showed that native human blood rapidly formed a TF-dependent thrombus on collagen-coated glass slides. Blood-borne TF was proposed to be “involved in thrombus propagation at the site of vascular injury” [2]. However, the authors qualified their results by saying that “this finding suggests that the TF originated in the blood (although leeching from the arterial segment could not be excluded)”. Indeed, it is difficult to determine if the traces of TF present in a blood sample originated from the blood itself or from the vessel wall. Importantly, the level of TF in the vessel wall vastly exceeds that found in blood. Not surprisingly there has been much debate about whether or not TF is present in blood. Mann and colleagues [3] were the first to dispute the idea that there was active TF present in whole human blood. They later reported that whole human blood containing the contact pathway inhibitor corn trypsin inhibitor did not contain physiologically active TF and that as little as 20 fM of TF induced clot formation [4]. We found that the recalcification time of citrated human whole blood was not prolonged by an inhibitory anti-TF antibody [5]. However, these studies do not exclude the possibility that human blood contains low levels of encrypted or inactive TF that can be activated at sites of vessel injury. Low levels of TF present in blood would be expected to bind factor VII/VIIa and this complex would be inhibited by tissue factor pathway inhibitor (TFPI) thus preventing inadvertent activation of clotting. This “blood-borne” TF may be derived from transiently activated monocytes or from damaged vessels and tissues. Interestingly, the “idling” of the clotting cascade in healthy people is dependent on the extrinsic pathway of coagulation (TF/factor VIIa) and not on the intrinsic pathway of coagulation indicating that there is some active TF exposed to blood in healthy people [6]. We found very low levels of TF activity in small membrane vesicles called microparticles (MPs) that were isolated from the blood of healthy people [7]. Removal of TFPI during the isolation of the MPs may be required for detection of this MP TF activity. In addition, human blood was reported to contain monocyte-derived, TF+ MPs [8]. A small subset of monocytes (~1.5%) has been shown to express TF [9] and these may contribute to the pool of TF+ MPs in the blood. In a mouse model of laser injury of small cremaster arterioles using healthy mice we found that hematopoietic cell-derived TF + MPs contribute to thrombosis [10]. Furthermore, it has been shown that binding of monocyte-derived TF+ MPs to the injured vessel was mediated by 0049-3848/$ – see front matter © 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.thromres.2013.05.009
the interaction of P-selectin glycoprotein ligand 1 on the MPs with P-selectin on activated endothelial cells or activated platelets [8]. These studies support the notion that blood contains very low levels of TF that can be activated at sites of vessel injury. However, in a mouse carotid artery thrombosis model that is associated with loss of the endothelium thrombosis is driven by vessel wall TF and not “blood-borne” TF [11]. Monocytes stimulated with bacterial lipopolysaccharide express TF and are often used as a positive control in studies on TF. However, whether or not activated platelets synthesize TF is highly controversial. We have divided platelet TF expression into 3 groups: quiescent platelets, rapidly activated platelets and long-term activated platelets (Fig. 1). Studies by two independent groups reported that quiescent platelets contain TF mRNA, TF antigen and TF activity [12–14]. In contrast, the current study by Osterud and Olsen [15] concludes that “human platelets do not express TF”. This is in agreement with work from Mann and Butenas [4,16,17]. One study found very low levels of TF in the open cannicular system of resting platelets [18]. However, only a small subset of platelets contained TF and it is unclear if this low level of TF would be sufficient to increase the procoagulant activity of platelets. We carefully isolated platelets from human blood in the presence of platelet inhibitors and found no TF mRNA expression [19]. However, prolonged stimulation of the platelets with various agonists induced splicing of TF pre-mRNA to mature TF mRNA [19] (Fig. 1). Splicing of TF pre-mRNA to mature TF mRNA was also observed in sepsis patients and in patients with type 2 diabetes [20,21]. This suggests that the early studies reporting the presence of TF mRNA in quiescent platelets likely analyzed platelets that were activated during isolation. Therefore, quiescent platelets contain TF pre-mRNA but do not contain TF mRNA or TF protein (Fig. 1). The key question is do platelets synthesize TF. We and others have reported that activated platelets express TF protein and activity [14,19,22]. In contrast to these studies, Osterud and Olsen [15] and others [16,17] failed to detect any TF protein or TF activity on activated platelets. How can we explain these differences? Our studies clearly show that activated platelets contain TF mRNA and that platelets have the machinery to translate mRNA into protein as shown by their ability to synthesize IL-1β. However, this does not mean that TF mRNA is translated into TF protein in platelets. The most likely explanation for the different results is related to technical issues in the measurement of TF. These can be divided into methods used to detect TF protein and TF activity. A variety of anti-TF antibodies have been used to detect TF protein on platelets by flow cytometry and in platelet lysates by Western blotting and ELISA. In general, the specificity and sensitivity of the immunological detection of an antigen depend not only on accessibility of the exposed epitope but also on the antibodies and assay protocols. We and others have questioned the specificity of some of these anti-TF antibodies particularly the ones used for commercial ELISAs
4
Editorial
TF PS PSGL-1
Monocyte-derived MP
TF
P-selectin
PS PS
Thrombosis
TF pre-mRNA
5’
3’
Fast (~5 min)
Quiescent Platelet
5’
3’
Activated Platelet Slow (~30 min) TF mRNA
5’ 5’
3’ 3’
Fig. 1. Platelet TF. Quiescent platelets contain TF pre-mRNA but no TF and phosphatidlyserine (PS) is present on the inner leaflet of the plasma membrane. TF present on rapidly activated platelets is likely derived from the binding of monocyte-derived TF+ MPs via an interaction between PSGL-1 and P-selectin. Platelet activation will also expose PS on the outer leaflet of the plasma membrane where it will enhance TF activity. TF present on platelets likely contributes to thrombosis in different diseases. Platelets activated with various agonists will splice TF pre-mRNA into mature mRNA but it is unclear at the point if this mRNA is translated into TF protein.
[23–25]. However, for the detection of TF in or on platelets most of the groups have used well characterized anti-human TF mAbs that were evaluated in a CD142 workshop [26]. Therefore, some of the variable results reported with these antibodies may not be due to the antibodies themselves but rather due to the assay conditions. With regard to the very low concentration of TF reported to be expressed by platelets, artifacts created by the immunological methods cannot be excluded. TF activity is typically detected in a two-stage assay that involves addition of factor VIIa and factor X to the sample and then measurement of the levels of factor Xa generated. One concern is that the supraphysiologic concentration of factor VIIa used in the assay can convert factor X to factor Xa in a TF-independent manner under some conditions. However, this potential artifact is excluded in the majority of studies because assays were performed in the presence and absence of inhibitory anti-TF antibodies to distinguish TF-dependent from TF-independent factor Xa activity. Another important factor is how the platelet sample is prepared? TF activity has been measured in whole platelets, platelet lysates and platelet membranes. We reported that membranes isolated from activated platelets contained TF activity [19], although no TF activity was detected in platelet lysates (H. Schwertz and A. Weyrich, unpublished data). In contrast, Osterud and Olsen [15] failed to detect any TF activity in whole platelets. One possibility is that TF on platelets is inhibited by TFPI but addition of an ant-TFPI antibody did not reveal any TF activity [15]. At present, it appears that there is no compelling data to support the idea that platelets synthesize TF. Numerous studies have shown that rapidly activated platelets can bind monocyte-derived TF + MPs [8,27–29]. Zillmann and colleagues [30] reported that a 5 minute stimulation of human blood with collagen shortened the clotting time in a TF-dependent manner. It was proposed that TF present on platelets was inhibited by TFPI and that neutrophils were required to inactive TFPI [18,30]. An alternative explanation for these results is that the collagen activated platelets rapidly bind TF+ MPs present in the blood that is then activated on the surface of the platelets. Indeed, collagen stimulation of isolated platelets did not increase TF activity. Studies have shown significantly higher amounts of
TF+ platelets in patients with sepsis and acute coronary syndromes compared with healthy controls [20,31]. This platelet associated TF is likely to be due to the binding of monocyte-derived TF+ MPs rather than de novo synthesis by the platelets themselves (Fig. 1). These studies suggest that platelets loaded with TF likely contribute to the formation of pathologic thrombi (Fig. 1). Acknowledgements We would like to acknowledge Dr. Raj Kasthuri (University of North Carolina at Chapel Hill), Dr. Alisa Wolberg (University of North Carolina at Chapel Hill) and Dr. Andy Weyrich (University of Utah) for helpful discussions and Julia Geddings (University of North Carolina at Chapel Hill) for help in preparing the editorial. References [1] Drake TA, Morrissey JH, Edgington TS. Selective cellular expression of tissue factor in human tissues. Implications for disorders of hemostasis and thrombosis. Am J Pathol 1989;134:1087–97. [2] Giesen PL, Rauch U, Bohrmann B, Kling D, Roque M, Fallon JT, et al. Blood-borne tissue factor: another view of thrombosis. Proc Natl Acad Sci U S A 1999;96: 2311–5. [3] Butenas S, Mann KG. Active tissue factor in blood? Nat Med 2004;10:1155–6 [author reply 6]. [4] Butenas S, Bouchard BA, Brummel-Ziedins KE, Parhami-Seren B, Mann KG. Tissue factor activity in whole blood. Blood 2005;105:2764–70 [Epub 004 Dec 16]. [5] Santucci RA, Erlich J, Labriola J, Wilson M, Kao KJ, Kickler TS, et al. Measurement of tissue factor activity in whole blood. Thromb Haemost 2000;83:445–54. [6] Mackman N. The role of tissue factor and factor VIIa in hemostasis. Anesth Analg 2009;108:1447–52. [7] Khorana AA, Francis CW, Menzies KE, Wang JG, Hyrien O, Hathcock J, et al. Plasma tissue factor may be predictive of venous thromboembolism in pancreatic cancer. J Thromb Haemost 2008;6:1983–5. [8] Falati S, Liu Q, Gross P, Merrill-Skoloff G, Chou J, Vandendries E, et al. Accumulation of tissue factor into developing thrombi in vivo is dependent upon microparticle P-selectin glycoprotein ligand 1 and platelet P-selectin. J Exp Med 2003;197: 1585–98. [9] Egorina EM, Sovershaev MA, Bjorkoy G, Gruber FX, Olsen JO, Parhami-Seren B, et al. Intracellular and surface distribution of monocyte tissue factor: application to intersubject variability. Arterioscler Thromb Vasc Biol 2005;25:1493–8 [Epub 2005 Apr 28].
Editorial [10] Chou J, Mackman N, Merrill-Skoloff G, Pedersen B, Furie BC, Furie B. Hematopoietic cell-derived microparticle tissue factor contributes to fibrin formation during thrombus propagation. Blood 2004;104:3190–7 [Epub 2004 Jul 27]. [11] Day SM, Reeve JL, Pedersen B, Farris DM, Myers DD, Im M, et al. Macrovascular thrombosis is driven by tissue factor derived primarily from the blood vessel wall. Blood 2005;105:192–8. [12] Siddiqui FA, Desai H, Amirkhosravi A, Amaya M, Francis JL. The presence and release of tissue factor from human platelets. Platelets 2002;13:247–53. [13] Camera M, Frigerio M, Toschi V, Brambilla M, Rossi F, Cottell DC, et al. Platelet activation induces cell-surface immunoreactive tissue factor expression, which is modulated differently by antiplatelet drugs. Arterioscler Thromb Vasc Biol 2003;23:1690–6 [Epub 2003 Jul 10]. [14] Camera M, Brambilla M, Toschi V, Tremoli E. Tissue factor expression on platelets is a dynamic event. Blood 2010;116:5076–7. [15] Østerud B, Olsen JH. Human platelets do not express tissue factor. Thromb Res 2013;132:112–5. [16] Bouchard BA, Mann KG, Butenas S. No evidence for tissue factor on platelets. Blood 2010;116:854–5. [17] Bouchard BA, Krudysz-Amblo J, Butenas S. Platelet tissue factor is not expressed transiently after platelet activation. Blood 2012;119:4338–9 [author reply 9-41]. [18] Muller I, Klocke A, Alex M, Kotzsch M, Luther T, Morgenstern E, et al. Intravascular tissue factor initiates coagulation via circulating microvesicles and platelets. FASEB J 2003;17:476–8 [Epub 2003 Jan 2]. [19] Schwertz H, Tolley ND, Foulks JM, Denis MM, Risenmay BW, Buerke M, et al. Signal-dependent splicing of tissue factor pre-mRNA modulates the thrombogenicity of human platelets. J Exp Med 2006;203:2433–40 [Epub 006 Oct 23]. [20] Rondina MT, Schwertz H, Harris ES, Kraemer BF, Campbell RA, Mackman N, et al. The septic milieu triggers expression of spliced tissue factor mRNA in human platelets. J Thromb Haemost 2011;9:748–58. [21] Gerritis AJ, Koekman CA, van Haeften TW, Akkerman JW. Platelet tissue factor synthesis in type 2 diabetes is resistant to inhibition by insulin. Diabetes 2010;59: 1487–95. [22] Panes O, Matus V, Saez CG, Quiroga T, Pereira J, Mezzano D. Human platelets synthesize and express functional tissue factor. Blood 2007;109:5242–50 [Epub 2007 Mar 8]. [23] Parhami-Seren B, Butenas S, Krudysz-Amblo J, Mann KG. Immunologic quantitation of tissue factors. J Thromb Haemost 2006;4:1747–55. [24] Wang JG, Geddings JE, Aleman MM, Cardenas JC, Chantrathammachart P, Williams JC, et al. Tumor-derived tissue factor activates coagulation and enhances thrombosis in a mouse xenograft model of human pancreatic cancer. Blood 2012;119:5543–52 [Epub 2012 Apr 30].
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Nigel Mackman Division of Hematology/Oncology, Department of Medicine, Thrombosis and Hemostasis Program, McAllister Heart Institute, University of North Carolina at Chapel Hill, Chapel Hill, NC, USA Corresponding author. Tel.: +1 919 843 3961; fax: + 1 919 843 4896. E-mail address: [email protected]. Thomas Luther Medizinisches Labor Ostsachsen, D-02526 Bautzen, Germany 5 May 2013