Polyphosphate modulates blood coagulation and fibrinolysis

Abstract

Inorganic polyphosphate is an abundant component of acidocalcisomes of bacteria and unicellular eukaryotes. Human platelet dense granules strongly resemble acidocalcisomes, and we recently showed that they contain substantial amounts of polyphosphate, which is secreted upon platelet activation. We now report that polyphosphate is a potent hemostatic regulator, accelerating blood clotting by activating the contact pathway and promoting the activation of factor V, which in turn results in abrogation of the function of the natural anticoagulant protein, tissue factor pathway inhibitor. Polyphosphate was also found to delay clot lysis by enhancing a natural antifibrinolytic agent, thrombin-activatable fibrinolysis inhibitor. Polyphosphate is unstable in blood or plasma, owing to the presence of phosphatases. We propose that polyphosphate released from platelets or microorganisms initially promotes clot formation and stability; subsequent degradation of polyphosphate by blood phosphatases fosters inhibition of clotting and activation of fibrinolysis during wound healing.factor V ͉ platelets ͉ tissue factor pathway inhibitor ͉ acidocalcisomes ͉ dense granules P olyphosphate (polyP) is widely distributed in biology, being found in bacteria, fungi, plants, and animals (1). The biologic functions of polyP have been studied most extensively in prokaryotes and unicellular eukaryotes, in which high levels of polyP accumulate in acidic organelles known as acidocalcisomes. PolyP in these organisms can reach chain lengths of several hundred phosphate units. In unicellular organisms, polyP has been shown to play essential roles in stress responses and virulence (1, 2), although its function in higher eukaryotes, including man, has not been extensively investigated. Recently, we reported that dense granules of human platelets strongly resemble acidocalcisomes and contain millimolar levels of polyP (with chain lengths of Ϸ70-75 phosphate units), making acidocalcisomes the only known class of organelle conserved during evolution from bacteria to humans (3). Human platelets each have three to eight dense granules (also called ␦ granules), a type of secretory granule that contains serotonin, ADP, ATP, and PP i in addition to polyP. Patients with dense granule defects exhibit bleeding diatheses, underscoring the role of these secretory granules in hemostasis (4). Platelets contain Ϸ0.74 nmol polyP per 10 8 platelets, which is secreted after stimulation by platelet agonists such as thrombin (3). Therefore, released polyP could readily attain a concentration of 3 M in whole blood, and this could be far higher in platelet-rich thrombi. (Concentrations of polyP are expressed in this paper as phosphate monomer.)The importance of platelets in hemostasis suggested to us that polyP may play an important role in the blood clotting system. In this study, we found that polyP of the size released from activated platelets has a strongly net procoagulant effect, which is exerted at several levels in the clotting͞fibrinolysis system: PolyP activate...

In situ structural analysis of Golgi intracisternal protein arrays

“…Similar acidocalcisome compartments can be found in other single-celled eukaryotes, including trypanosomes, apicomplexans, and Dictyostelium, as well as evolutionarily distant organisms such as bacteria and humans (53). The mechanisms of polyphosphate traffic and storage may have clinical implications, as platelets release polyphosphate to stimulate blood coagulation (54,55).…”

Myeloma cells contain high levels of inorganic polyphosphate which is associated with nucleolar transcription

“…PolyP polymers of this size are frequently found in mammalian cell signaling, and these molecules have been reported to stimulate mTOR kinase in mammary cancer cells, 39 to interact with fibroblast growth factor, 40 to be released by activated platelets, 6 and to modulate blood coagulation. 7 We have previously described that the addition of millimolar concentrations of extracellular polyP induces apoptosis specifically in MC and plasma cells. 12 However, in the present work, we studied intracellular polyP in MC.…”

“…4 Since our discovery that polyP is abundant and released by activated platelets, 6 there has been increasing interest in this polyanion in hematology. It has been found that released extracellular polyP modulates blood coagulation in vitro 7 and in vivo, 8 increases vascular permeability, 8 enhances fibrin clot structure, 9,10 promotes the inhibitory effect of factor VII activating protease on vascular smooth muscle cell proliferation, 11 and induces apoptosis in plasma cells and MC. 12 In platelets, intracellular polyP is localized principally in dense granules (which are similar to acidocalcisomes), 6 and this characteristic has been used to diagnose d-storage pool diseases.…”

The structure of the FnI-EGF-like tandem domain of coagulation factor XII solved using SIRAS

“…Besides negatively charged artificial surfaces, several 'natural' surfaces have been proposed to activate FXII in vivo, such as amyloid aggregates (Yasuhara et al, 1994;Bergamaschini et al, 1998Bergamaschini et al, , 2001), polyphosphates (Smith et al, 2006;Mü ller et al, 2009), collagen (Meijden et al, 2009) and misfolded proteins (Maas, GoversRiemslag et al, 2008). Remarkably, not all of these surfaces result in activation of both the intrinsic coagulation pathway and the kallikrein-kinin system.…”