Platelet surface-associated activation and secretion-mediated inhibition of coagulation factor XII

PLoS One. 2015 Feb 17;10(2):e0116665. doi: 10.1371/journal.pone.0116665. eCollection 2015.


Coagulation factor XII (fXII) is important for arterial thrombosis, but its physiological activation mechanisms are unclear. In this study, we elucidated the role of platelets and platelet-derived material in fXII activation. FXII activation was only observed upon potent platelet stimulation (with thrombin, collagen-related peptide, or calcium ionophore, but not ADP) accompanied by phosphatidylserine exposure and was localised to the platelet surface. Platelets from three patients with grey platelet syndrome did not activate fXII, which suggests that platelet-associated fXII-activating material might be released from α-granules. FXII was preferentially bound by phosphotidylserine-positive platelets and annexin V abrogated platelet-dependent fXII activation; however, artificial phosphotidylserine/phosphatidylcholine microvesicles did not support fXII activation under the conditions herein. Confocal microscopy using DAPI as a poly-phosphate marker did not reveal poly-phosphates associated with an activated platelet surface. Experimental data for fXII activation indicates an auto-inhibition mechanism (ki/ka = 180 molecules/platelet). Unlike surface-associated fXII activation, platelet secretion inhibited activated fXII (fXIIa), particularly due to a released C1-inhibitor. Platelet surface-associated fXIIa formation triggered contact pathway-dependent clotting in recalcified plasma. Computer modelling suggests that fXIIa inactivation was greatly decreased in thrombi under high blood flow due to inhibitor washout. Combined, the surface-associated fXII activation and its inhibition in solution herein may be regarded as a flow-sensitive regulator that can shift the balance between surface-associated clotting and plasma-dependent inhibition, which may explain the role of fXII at high shear and why fXII is important for thrombosis but negligible in haemostasis.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adult
  • Aged
  • Aged, 80 and over
  • Blood Coagulation / drug effects
  • Blood Coagulation Factor Inhibitors / metabolism*
  • Blood Coagulation Factor Inhibitors / pharmacology
  • Blood Platelets / metabolism*
  • Cell Membrane / metabolism*
  • Cell-Derived Microparticles / metabolism
  • Complement C1 Inactivator Proteins / metabolism
  • Complement C1 Inactivator Proteins / pharmacology
  • Enzyme Activation / drug effects
  • Factor XII / agonists*
  • Factor XII / antagonists & inhibitors*
  • Factor XII / chemistry
  • Factor XII / metabolism
  • Family
  • Female
  • Gray Platelet Syndrome / blood
  • Gray Platelet Syndrome / metabolism
  • Humans
  • Male
  • Models, Biological
  • Protein Binding
  • Secretory Vesicles / metabolism


  • Blood Coagulation Factor Inhibitors
  • Complement C1 Inactivator Proteins
  • Factor XII

Grants and funding

This study was supported by the Russian Science Foundation grant 14-14-00195 (http://xn--m1afn.xn--p1ai/) (MAP). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.