- Email: [email protected]
Hemostasis: Old System, New Players, New Directions
Thrombosis Research 133 (2014) S1–S2
Contents lists available at ScienceDirect
Thrombosis Research journal homepage: www.elsevier.com/locate/thromres
Regular Article
Hemostasis: Old System, New Players, New Directions Maureane Hoffman a,⁎, Rafal Pawlinski b,⁎⁎ a b
Duke University Durham Veterans Affairs Medical Centers Durham, NC, USA Division of Hematology/Oncology Department of Medicine, University of North Carolina at Chapel Hill, Chapel Hill, NC
a r t i c l e
i n f o
a b s t r a c t Initiation of clotting cascade by tissue factor (TF): Factor VII (FVII) complex is essential for hemostasis however pathologic expression of TF leads to thrombosis. In contrast, the contact pathway factor XII, and to the smaller extent FXI are dispensable for normal hemostasis but still contribute to pathologic thrombosis. New data suggest that not only platelets but also leukocytes and red blood cells can actively participate to thrombosis. Growing evidence demonstrates that coagulation proteases not only regulate hemostasis and thrombosis but also contribute to the many cellular responses via activation of protease activated receptors (PARs). The reviews in this supplement summarize the latest findings related to TF and coagulation proteases, including novel models of hemostasis and thrombosis, new insights into mechanism of thrombosis and trauma induced coagulopathy, interplay between coagulation and innate immune system and pathophysiology of contact activation pathway. Published by Elsevier Ltd.
Models of Hemostasis and Thrombosis
Coagulation, PARs and Viral Infections
The first section in these proceedings is about models of hemostasis and thrombosis. A model is a representation containing the essential structure of some object or event in the real world. These representations take two major forms: 1) Physical – a model system that can be explored experimentally; and 2) Symbolic – a descriptive or conceptual construct to aid in understanding. A good model should be simple enough to improve clarity, but complicated enough to reflect the realities of the system. Thus, the choice or design of a model is absolutely critical to getting results that reveal something meaningful about the real world. The opening session of the symposium will highlight several very different ways to approach modeling hemostasis and related phenomena, from whole animal models (Monroe and Bergmeier) to mathematical/ computer simulations (Leiderman and Brummel-Ziedins). Every model has strengths and weaknesses. The goal of this session is to show how very different models can all provide high quality mechanistic data. However, it is critical that the type of model selected be well suited to the question being investigated, and the relevance of the results obtained must be checked by comparison with clinical reality.
Similar to bacterial infection, the coagulation system is also activated during viral infection. Initially, activation of the coagulation cascade in response to viral infection could be a part of the host defense system to attenuate the spread of the viruses. However, excessive clotting can also have deleterious effects and lead to increased inflammation, disseminated intravascular coagulation and subsequent hemorrhage. Tissue factor (TF) appears to be the major activator of the coagulation cascade during viral infection. In the first review Pryzdial and colleagues summarize their data demonstrating that herpes simplex virus types 1 (HSV1) utilizes host cell-derived TF, incorporated into the viral envelope, to generate and amplify clotting factor Xa and thrombin. The authors also found that coagulation proteases activated on the HSV1 envelope participate in the virus replication mechanism by enhancing the susceptibility of cells to infection. The role of protease activated receptor (PARs) in this process is also discussed. In the next review, Mackman and Antoniak discuss the contribution of coagulation proteases and PARs to the host response during single stranded RNA virus infection, including coxsackievirus B3-induced myocarditis and H1N1 influenza A infection. Based on their own results and data from other groups, the authors proposed the model in which activation of PAR-1 and PAR-2 regulates the innate immune responses mediated by Toll like receptors (TLR), particularly TLR3 and TLR4. The final review by Funderburg and Lederman highlights the growing problem of thrombotic complications, observed in patients infected with human immunodeficiency virus (HIV) compared to uninfected controls. While antiretroviral therapy has improved dramatically the diseasefree survival in HIV infection, recent data show that HIV-infected patients are at increased risk of developing venous thromboembolism
⁎ Correspondence to: M. Hoffman, Pathology & Laboratory Medicine Svc, (113) Durham VA Medical Center, 508 Fulton St, Durham, NC 27705. Tel.: +1 919 286 6925; fax: +1 919 286 6818. ⁎⁎ Correspondence to: R. Pawlinski, Division of Hematology/Oncology, Department of Medicine, University of North Carolina, 320A Mary Ellen Jones Bldg, 98 Manning Drive Chapel Hill, NC 27599. Tel: +1 919 843 8387; fax: +1 919 843 4896. E-mail addresses: [email protected] (M. Hoffman), [email protected] (R. Pawlinski).
http://dx.doi.org/10.1016/j.thromres.2014.03.001 0049-3848/Published by Elsevier Ltd.
S2
M. Hoffman, R. Pawlinski / Thrombosis Research 133 (2014) S1–S2
and myocardial infarction. The possible contribution of the chronic immune activation and inflammation to the activation of coagulation in HIV infected patients is discussed. In summary, further studies are needed to analyze the role of the coagulation system and PARs in different viral infections. TIC Versus DIC: Similar but not the Same This session focuses on two types of complex coagulopathy, the acute trauma induced coagulopathy (TIC) and disseminated intravascular coagulopathy (DIC) associated with sepsis. In the first review Mitch Cohen highlights the unique coagulopathy that has recently been described in patients who have suffered trauma and shock. Dilutional coagulopathy and DIC can also result from trauma, but the acute TIC has unique mechanistic features involving the activation of Protein C. The coagulopathy in sepsis is intimately intertwined with the inflammatory response. The article by Lupu et al highlights the interactions of complement and coagulation systems in this setting in a baboon model. Complement and coagulation are activated by bacterial products as part of the host response to infection. However, systems that are protective in the initial stages of infection are important mechanisms of tissue injury and dysfunction in the later stages of the process. The review by Hartmut Weiler discusses the roles of Protein C in modulating experimental autoimmune encephalitis, diabetes and sepsis. This includes the role of aPC-resistant FV in modulating the outcome of sepsis. The Protein C system plays an important role in the host response in trauma, sepsis and inflammatory/immune disorders. While aPC has important cytoprotective effects, it can also be a twoedged sword. The challenge is to find ways to prevent the harmful effects of host responses without impairing their critical protective effects during the initial defensive response. Mechanism of Thrombosis Thrombotic disorders, including venous thromboembolism and arterial thrombosis, are the most frequent cause of mortality worldwide. Venous thrombosis results from blood stasis in the absence of endothelial injury whereas arterial thrombosis is mostly trigger by the rupture of atherosclerotic plaques. Both processes require activation of platelets and the formation of fibrin. However, recent data suggest that innate immune cells (monocytes and neutrophils) and red blood cells actively participate in both arterial and venous thrombosis. Thrombosis not only affects large vessels, but also occurs in the microvasculature. In first review, Engelmann and Massberg summarize their work on microvascular thrombosis. They propose that microvascular thrombosis is part of the immune defense system that contributes to recognition, containment and destruction of pathogens. This so called “immunothrombosis’ is supported by immune cells and by specific thrombosis-related molecules including TF and factor XII. However, if uncontrolled, immunothrombosis can trigger and contribute to venous and arterial thrombosis. Second review by Wolberg and colleagues focuses on the mechanism of deep vein thrombosis with the emphasis on the interactions between red blood cells and fibrinogen. The comprehensive review of the literature is followed by the description of the recent data from the Wolberg lab demonstrating that fibrin(ogen)-mediated transport of factor XIII(a) to the clot is necessary for red blood cells retention in thrombi. This intriguing observation has a high potential therapeutic value for reducing deep vein thrombosis and its consequences.
factor-dependent and –independent activities of FVIIa. The contact factors, FXII, high molecular weight kininogen (HMK), prekallikrein (PK) and FXI have been of lesser interest. This has primarily been because patients deficient in FXII, HMK or PK do not have a clinical bleeding tendency. However, interest in the contact factors has surged in recent years following publication of articles that link activation of the contact factors to thrombosis in mouse models. This raises the possibility that inhibition of the contact factors could reduce thrombosis without leading to serious bleeding complications. The review by David Gailani discusses the unique structural features of FXI, and how they relate to its biochemical activities. Alvin Schmaier discusses the interactions of the contact pathway with other physiologically and pathologically important pathways, such as the kallikrein/kinin and renin/angiotensin systems. He points out that, while mouse knockouts of proteins related to the contact pathway are protected from arterial thrombosis, the effects of these deficiencies are not necessarily mediated through reduced activation of the coagulation system. The article by Andras Gruber discusses the role of FXII in thrombosis in animal models, and its potential (though as yet unproven) role in human thrombosis. Activation of Coagulation in Disease The final section in this series contains three reviews focusing on the mechanism of activation of coagulation in various pathological conditions. Sickle cell disease is the hematologic disorder associated with chronic activation of coagulation. The possible mechanisms leading to hypercoagulable state in sickle cell patients may include increased TF expression, increased platelet activation, increased number of procoagulant microparticles or decreased levels of natural anticoagulant proteins. In the first review Key and colleagues describe the development of new assay designed to measure thrombin generation in the whole blood and their attempt to answer the question whether the increase in coagulation activation observed in SCD is initiated primarily through the extrinsic or intrinsic pathway with red cells and their shed MPs playing a key role in the latter. The second review by Spronk and colleagues elegantly summarizes the proposed mechanisms that may be responsible for the conversion of cryptic TF to its active form and discuss the role of TF and phosphatidylserine in coagulation. They conclude that TF is the main physiological initiator of coagulation, whereas phosphatidylserine brings components of the coagulation cascade together, thereby increasing the enzymatic rate of substrate conversion. Finally, several recent studies demonstrate that activation of coagulation is associated with liver toxicity. Kopec and Luyendyk described their recent study on the role of TF in activation of coagulation in acute and chronic liver diseases. Despite the very low level of TF expression by hepatocytes, this cellular source of TF plays a significant role in the activation of coagulation after liver damage. The authors summarize the regulation of hepatocyte TF expression and the contribution of coagulation proteases to the progression of liver disease. Conclusion The reviews in this supplement highlight the involvement of coagulation proteins in diseases and processes that are not traditionally thought of as being related to coagulation. The work presented at this symposium truly explores many new horizons in the field of “coagulation” research. Conflict of Interest Statement
Intrinsic Pathway The authors state that they have no conflict of interest. A discussion of the “contact pathway” is new territory for this symposium. Historically this meeting has focused on tissue factor and tissue
Contents lists available at ScienceDirect
Thrombosis Research journal homepage: www.elsevier.com/locate/thromres
Regular Article
Hemostasis: Old System, New Players, New Directions Maureane Hoffman a,⁎, Rafal Pawlinski b,⁎⁎ a b
Duke University Durham Veterans Affairs Medical Centers Durham, NC, USA Division of Hematology/Oncology Department of Medicine, University of North Carolina at Chapel Hill, Chapel Hill, NC
a r t i c l e
i n f o
a b s t r a c t Initiation of clotting cascade by tissue factor (TF): Factor VII (FVII) complex is essential for hemostasis however pathologic expression of TF leads to thrombosis. In contrast, the contact pathway factor XII, and to the smaller extent FXI are dispensable for normal hemostasis but still contribute to pathologic thrombosis. New data suggest that not only platelets but also leukocytes and red blood cells can actively participate to thrombosis. Growing evidence demonstrates that coagulation proteases not only regulate hemostasis and thrombosis but also contribute to the many cellular responses via activation of protease activated receptors (PARs). The reviews in this supplement summarize the latest findings related to TF and coagulation proteases, including novel models of hemostasis and thrombosis, new insights into mechanism of thrombosis and trauma induced coagulopathy, interplay between coagulation and innate immune system and pathophysiology of contact activation pathway. Published by Elsevier Ltd.
Models of Hemostasis and Thrombosis
Coagulation, PARs and Viral Infections
The first section in these proceedings is about models of hemostasis and thrombosis. A model is a representation containing the essential structure of some object or event in the real world. These representations take two major forms: 1) Physical – a model system that can be explored experimentally; and 2) Symbolic – a descriptive or conceptual construct to aid in understanding. A good model should be simple enough to improve clarity, but complicated enough to reflect the realities of the system. Thus, the choice or design of a model is absolutely critical to getting results that reveal something meaningful about the real world. The opening session of the symposium will highlight several very different ways to approach modeling hemostasis and related phenomena, from whole animal models (Monroe and Bergmeier) to mathematical/ computer simulations (Leiderman and Brummel-Ziedins). Every model has strengths and weaknesses. The goal of this session is to show how very different models can all provide high quality mechanistic data. However, it is critical that the type of model selected be well suited to the question being investigated, and the relevance of the results obtained must be checked by comparison with clinical reality.
Similar to bacterial infection, the coagulation system is also activated during viral infection. Initially, activation of the coagulation cascade in response to viral infection could be a part of the host defense system to attenuate the spread of the viruses. However, excessive clotting can also have deleterious effects and lead to increased inflammation, disseminated intravascular coagulation and subsequent hemorrhage. Tissue factor (TF) appears to be the major activator of the coagulation cascade during viral infection. In the first review Pryzdial and colleagues summarize their data demonstrating that herpes simplex virus types 1 (HSV1) utilizes host cell-derived TF, incorporated into the viral envelope, to generate and amplify clotting factor Xa and thrombin. The authors also found that coagulation proteases activated on the HSV1 envelope participate in the virus replication mechanism by enhancing the susceptibility of cells to infection. The role of protease activated receptor (PARs) in this process is also discussed. In the next review, Mackman and Antoniak discuss the contribution of coagulation proteases and PARs to the host response during single stranded RNA virus infection, including coxsackievirus B3-induced myocarditis and H1N1 influenza A infection. Based on their own results and data from other groups, the authors proposed the model in which activation of PAR-1 and PAR-2 regulates the innate immune responses mediated by Toll like receptors (TLR), particularly TLR3 and TLR4. The final review by Funderburg and Lederman highlights the growing problem of thrombotic complications, observed in patients infected with human immunodeficiency virus (HIV) compared to uninfected controls. While antiretroviral therapy has improved dramatically the diseasefree survival in HIV infection, recent data show that HIV-infected patients are at increased risk of developing venous thromboembolism
⁎ Correspondence to: M. Hoffman, Pathology & Laboratory Medicine Svc, (113) Durham VA Medical Center, 508 Fulton St, Durham, NC 27705. Tel.: +1 919 286 6925; fax: +1 919 286 6818. ⁎⁎ Correspondence to: R. Pawlinski, Division of Hematology/Oncology, Department of Medicine, University of North Carolina, 320A Mary Ellen Jones Bldg, 98 Manning Drive Chapel Hill, NC 27599. Tel: +1 919 843 8387; fax: +1 919 843 4896. E-mail addresses: [email protected] (M. Hoffman), [email protected] (R. Pawlinski).
http://dx.doi.org/10.1016/j.thromres.2014.03.001 0049-3848/Published by Elsevier Ltd.
S2
M. Hoffman, R. Pawlinski / Thrombosis Research 133 (2014) S1–S2
and myocardial infarction. The possible contribution of the chronic immune activation and inflammation to the activation of coagulation in HIV infected patients is discussed. In summary, further studies are needed to analyze the role of the coagulation system and PARs in different viral infections. TIC Versus DIC: Similar but not the Same This session focuses on two types of complex coagulopathy, the acute trauma induced coagulopathy (TIC) and disseminated intravascular coagulopathy (DIC) associated with sepsis. In the first review Mitch Cohen highlights the unique coagulopathy that has recently been described in patients who have suffered trauma and shock. Dilutional coagulopathy and DIC can also result from trauma, but the acute TIC has unique mechanistic features involving the activation of Protein C. The coagulopathy in sepsis is intimately intertwined with the inflammatory response. The article by Lupu et al highlights the interactions of complement and coagulation systems in this setting in a baboon model. Complement and coagulation are activated by bacterial products as part of the host response to infection. However, systems that are protective in the initial stages of infection are important mechanisms of tissue injury and dysfunction in the later stages of the process. The review by Hartmut Weiler discusses the roles of Protein C in modulating experimental autoimmune encephalitis, diabetes and sepsis. This includes the role of aPC-resistant FV in modulating the outcome of sepsis. The Protein C system plays an important role in the host response in trauma, sepsis and inflammatory/immune disorders. While aPC has important cytoprotective effects, it can also be a twoedged sword. The challenge is to find ways to prevent the harmful effects of host responses without impairing their critical protective effects during the initial defensive response. Mechanism of Thrombosis Thrombotic disorders, including venous thromboembolism and arterial thrombosis, are the most frequent cause of mortality worldwide. Venous thrombosis results from blood stasis in the absence of endothelial injury whereas arterial thrombosis is mostly trigger by the rupture of atherosclerotic plaques. Both processes require activation of platelets and the formation of fibrin. However, recent data suggest that innate immune cells (monocytes and neutrophils) and red blood cells actively participate in both arterial and venous thrombosis. Thrombosis not only affects large vessels, but also occurs in the microvasculature. In first review, Engelmann and Massberg summarize their work on microvascular thrombosis. They propose that microvascular thrombosis is part of the immune defense system that contributes to recognition, containment and destruction of pathogens. This so called “immunothrombosis’ is supported by immune cells and by specific thrombosis-related molecules including TF and factor XII. However, if uncontrolled, immunothrombosis can trigger and contribute to venous and arterial thrombosis. Second review by Wolberg and colleagues focuses on the mechanism of deep vein thrombosis with the emphasis on the interactions between red blood cells and fibrinogen. The comprehensive review of the literature is followed by the description of the recent data from the Wolberg lab demonstrating that fibrin(ogen)-mediated transport of factor XIII(a) to the clot is necessary for red blood cells retention in thrombi. This intriguing observation has a high potential therapeutic value for reducing deep vein thrombosis and its consequences.
factor-dependent and –independent activities of FVIIa. The contact factors, FXII, high molecular weight kininogen (HMK), prekallikrein (PK) and FXI have been of lesser interest. This has primarily been because patients deficient in FXII, HMK or PK do not have a clinical bleeding tendency. However, interest in the contact factors has surged in recent years following publication of articles that link activation of the contact factors to thrombosis in mouse models. This raises the possibility that inhibition of the contact factors could reduce thrombosis without leading to serious bleeding complications. The review by David Gailani discusses the unique structural features of FXI, and how they relate to its biochemical activities. Alvin Schmaier discusses the interactions of the contact pathway with other physiologically and pathologically important pathways, such as the kallikrein/kinin and renin/angiotensin systems. He points out that, while mouse knockouts of proteins related to the contact pathway are protected from arterial thrombosis, the effects of these deficiencies are not necessarily mediated through reduced activation of the coagulation system. The article by Andras Gruber discusses the role of FXII in thrombosis in animal models, and its potential (though as yet unproven) role in human thrombosis. Activation of Coagulation in Disease The final section in this series contains three reviews focusing on the mechanism of activation of coagulation in various pathological conditions. Sickle cell disease is the hematologic disorder associated with chronic activation of coagulation. The possible mechanisms leading to hypercoagulable state in sickle cell patients may include increased TF expression, increased platelet activation, increased number of procoagulant microparticles or decreased levels of natural anticoagulant proteins. In the first review Key and colleagues describe the development of new assay designed to measure thrombin generation in the whole blood and their attempt to answer the question whether the increase in coagulation activation observed in SCD is initiated primarily through the extrinsic or intrinsic pathway with red cells and their shed MPs playing a key role in the latter. The second review by Spronk and colleagues elegantly summarizes the proposed mechanisms that may be responsible for the conversion of cryptic TF to its active form and discuss the role of TF and phosphatidylserine in coagulation. They conclude that TF is the main physiological initiator of coagulation, whereas phosphatidylserine brings components of the coagulation cascade together, thereby increasing the enzymatic rate of substrate conversion. Finally, several recent studies demonstrate that activation of coagulation is associated with liver toxicity. Kopec and Luyendyk described their recent study on the role of TF in activation of coagulation in acute and chronic liver diseases. Despite the very low level of TF expression by hepatocytes, this cellular source of TF plays a significant role in the activation of coagulation after liver damage. The authors summarize the regulation of hepatocyte TF expression and the contribution of coagulation proteases to the progression of liver disease. Conclusion The reviews in this supplement highlight the involvement of coagulation proteins in diseases and processes that are not traditionally thought of as being related to coagulation. The work presented at this symposium truly explores many new horizons in the field of “coagulation” research. Conflict of Interest Statement
Intrinsic Pathway The authors state that they have no conflict of interest. A discussion of the “contact pathway” is new territory for this symposium. Historically this meeting has focused on tissue factor and tissue