Single‐chain factor XII exhibits activity when complexed to polyphosphate

Engel, Ruchira; Brain, Chelsea; Paget, Jane; Lionikiene, Ausra S.; Mutch, Nicola J.

doi:10.1111/jth.12663

Cited by 47 publications

(57 citation statements)

References 57 publications

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“…Because polyP is a known activator of FXII, 20,21,35 we examined its capacity to both stimulate FXII activation and subsequently stimulate its plasminogen activator function. CLTs were significantly longer with FXII (.300 minutes) compared with aFXIIa (238 6 58 minutes) and, similarly, rates of plasmin generation were significantly lower with FXII compared with aFXIIa, presumably reflecting the time for transition of zymogen to protease.…”

Section: Results Afxiia Plasminogen Activator Activity Is Enhanced Bymentioning

confidence: 99%

“…We observed binding of polyP to FXII(a) and plasminogen, indicating that the cofactor function of this polymer is potentially mediated via a template mechanism on direct conversion of plasminogen to plasmin (Figure 7). PolyP also stimulates autoactivation of FXII to aFXIIa 35 and, indeed, affords some protection against autodegradation. This could be relevant in terms of time frame, Interaction of aFXII(a), plasminogen, polyp, and fibrin.…”

Section: Discussionmentioning

confidence: 99%

“…35 Briefly, aFXIIa (50 nM) and S2302 (0.25 mM), with or without polyP 70 (70 mM), were added to microtiter plates and the absorbance was read at 405 nm for 4 hours, with addition of 5 mL (5 mM) S2302 or 5 mL (50 nM) protein at the 2-hour midpoint.…”

Section: Fxiia Activity Assaymentioning

confidence: 99%

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Polyphosphate colocalizes with factor XII on platelet-bound fibrin and augments its plasminogen activator activity

Mitchell

Lionikiene

Georgiev

et al. 2016

Blood

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Key Points• PolyP significantly augments the plasminogen activator capacity of FXIIa.• Platelet-bound fibrin acts as a reservoir for plasminogen, FXII(a), and polyP.Activated factor XII (FXIIa) has plasminogen activator capacity but its relative contribution to fibrinolysis is considered marginal compared with urokinase and tissue plasminogen activator. Polyphosphate (polyP) is released from activated platelets and mediates FXII activation. Here, we investigate the contribution of polyP to the plasminogen activator function of aFXIIa. We show that both polyP 70 , of the chain length found in platelets (60-100 mer), and platelet-derived polyP significantly augment the plasminogen activation capacity of aFXIIa. PolyP 70 stimulated the autoactivation of FXII and subsequent plasminogen activation, indicating that once activated, aFXIIa remains bound to polyP 70 . Indeed, complex formation between polyP 70 and aFXIIa provides protection against autodegradation. Plasminogen activation by bFXIIa was minimal and not enhanced by polyP 70 , highlighting the importance of the anion binding site. PolyP 70 did not modulate plasmin activity but stimulated activation of Glu and Lys forms of plasminogen by aFXIIa. Accordingly, polyP 70 was found to bind to FXII, aFXIIa, and plasminogen, but not bFXIIa. Fibrin and polyP 70 acted synergistically to enhance aFXIIa-mediated plasminogen activation. The plasminogen activator activity of the aFXIIa-polyP 70 complex was modulated by C1 inhibitor and histidine-rich glycoprotein, but not plasminogen activator inhibitors 1 and 2. Platelet polyP and FXII were found to colocalize on the activated platelet membrane in a fibrin-dependent manner and decorated fibrin strands extending from platelet aggregates. We show that in the presence of platelet polyP and the downstream substrate fibrin, aFXIIa is a highly efficient and favorable plasminogen activator. Our data are the first to document a profibrinolytic function of platelet polyP. (Blood. 2016;128(24):2834-2845

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Section: Results Afxiia Plasminogen Activator Activity Is Enhanced Bymentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

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Polyphosphate colocalizes with factor XII on platelet-bound fibrin and augments its plasminogen activator activity

Mitchell

Lionikiene

Georgiev

et al. 2016

Blood

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“…The effect of polyP on thrombin generation has downstream repercussions in terms of fibrinolysis, where it augments activation of the fibrinolytic modulator, thrombin activatable fibrinolysis inhibitor (TAFI). PolyP also binds to a number of the haemostatic proteins including thrombin [11], kallikrein [12], FXI [10] and FXII [7,13]. It also associates with fibrinogen [14] which, once cleaved by thrombin to fibrin, provides the main scaffold of the forming clot.…”

Section: Platelets and Polypmentioning

confidence: 97%

“…A major obstacle in defining the physiological role of this pathway has been the lack of an appropriate biological surface capable of initiating contact activation. However, in the past decade, our work [7,8,13] and work by others [28][29][30] have identified natural surfaces, such as RNA [28], misfolded proteins [29], collagen [30] and, relevant to this review, polyP [7,8,13], that all fuel FXII activation.…”

Section: Polyp-mediated Effects On the Contact Pathwaymentioning

confidence: 99%

Polyphosphate as a haemostatic modulator

Mutch

2016

Biochemical Society Transactions

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Platelets are small anuclear cells that play a central role in haemostasis. Platelets become activated in response to various stimuli triggering release of their granular contents into the surrounding milieu. One of these types of granules, termed dense granules, have been found to contain polyphosphate (polyP) in addition to other inorganic biomolecules, such as serotonin, ADP, ATP, PPi. Individuals deficient in dense granules exhibit bleeding tendencies, emphasizing their importance in haemostasis. Platelet polyP is of a relatively defined size, approximately 60-100 phosphate monomers in length. These linear polymers act at various points in the coagulation and fibrinolytic systems thereby modulating the haemostatic response. Due to its highly anionic nature, polyP lends itself to being a natural activator of the contact system. The contact system functions in multiple pathways including coagulation, fibrinolysis, inflammation and complement. Activation of the contact system accelerates thrombin generation, the terminal enzyme in the coagulation cascade. PolyP also modulates factors further downstream in the coagulation cascade to augment thrombin generation. The net effect is increased fibrin formation and platelet activation resulting in faster clot formation. PolyP is incorporated into the forming clot thereby modifying the structure of the resulting fibrin network and its susceptibility to degradation by certain plasminogen activators. In conclusion, release of platelet polyP at the site of injury may facilitate clot formation and augment clot stability thereby promoting wound healing.

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Polyphosphate in thrombosis, hemostasis, and inflammation

Baker

Smith

Morrissey

2019

Research and Practice in Thrombosis and Haemostasis

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This illustrated review focuses on polyphosphate as a potent modulator of the plasma clotting cascade, with possible roles in hemostasis, thrombosis, and inflammation. Polyphosphates are highly anionic, linear polymers of inorganic phosphates that are widespread throughout biology. Infectious microorganisms accumulate polyphosphates with widely varying polymer lengths (from a few phosphates to over a thousand phosphates long), while activated human platelets secrete polyphosphate with a very narrow size distribution (about 60‐100 phosphates long). Work from our lab and others has shown that long‐chain polyphosphate is a potent trigger of clotting via the contact pathway, while polyphosphate of the size secreted by platelets accelerates factor V activation, blocks the anticoagulant activity of tissue factor pathway inhibitor, promotes factor XI activation by thrombin, and makes fibrin fibrils thicker and more resistant to fibrinolysis. Polyphosphate also modulates inflammation by triggering bradykinin release, inhibiting the complement system, and modulating endothelial function. Polyphosphate and nucleic acids have similar physical properties and both will trigger the contact pathway—although polyphosphate is orders of magnitude more procoagulant than either DNA or RNA. Important caveats in these studies include observations that nucleic acids and polyphosphate may co‐purify, and that these preparations can be contaminated with highly procoagulant microparticles if silica‐based purification methods are employed. Polyphosphate has received attention as a possible therapeutic, with some recent studies exploring the use of polyphosphate in a variety of formulations to control bleeding. Other studies are investigating treatments that block polyphosphate function as novel antithrombotics with the possibility of reduced bleeding side effects.

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Single‐chain factor XII exhibits activity when complexed to polyphosphate

Abstract: Autoactivation of FXII by polyP, of the size found in platelets, proceeds via an active single-chain intermediate. scFXII-polyP70 shows activity towards physiological substrates, and may represent the primary event in initiating contact activation in vivo.

Cited by 47 publications

References 57 publications

Polyphosphate colocalizes with factor XII on platelet-bound fibrin and augments its plasminogen activator activity

Polyphosphate colocalizes with factor XII on platelet-bound fibrin and augments its plasminogen activator activity

Polyphosphate as a haemostatic modulator

Polyphosphate in thrombosis, hemostasis, and inflammation

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