Plasma Transglutaminase Research Articles

The role of factor XIII in patient blood management.

Factor XIII (FXIII), a plasma transglutaminase, is a coagulation factor that plays a crucial role in blood clotting and patient blood management. The studies have demonstrated that FXIII targets a wide range of additional substrates that have an important role in hemostasis, especially in posttraumatic patients, patients undergoing surgery or obstetrics, being involved in wound healing and tissue repair. Morover, FXIII deficiency has also been described and an extensive research has shown that FXIII deficiency is a rare coagulopathy that leads to longer bleeding time, perioperative and postoperative complications and slower wound healing. Present article aims to overview the diverse functions of FXIII and to highlight its role in patient blood management.

Antibodies against non-catalytic B subunit of factor XIII inhibit activation of factor XIII and fibrin crosslinking.

Coagulation factor XIII (FXIII) is a proenzyme of plasma transglutaminase. It comprises two catalytic A subunits (FXIII-A) and two carrier B subunits (FXIII-B). We previously reported that alloantibodies against FXIII-B could promote FXIII clearance in a patient with congenital FXIII-B deficiency who had received infusions of plasma-derived human FXIII (A2B2 heterotetramer). We aimed to investigate whether anti-FXIII-B antibodies affect the catalytic function of FXIII. FXIII activation and fibrin crosslinking were examined in the presence of patient plasma, isolated patient IgG, or rat anti-FXIII-B monoclonal antibodies. Alloantibody levels were increased by repeated infusions of plasma-derived A2B2 heterotetramer, which enhanced binding to the functionally important FXIII-B Sushi domains. The patient plasma strongly inhibited cleavage of the FXIII-A activation peptide, amine incorporation, and fibrin crosslinking in normal plasma. Further, anti-FXIII-B alloantibodies blocked the formation of the complex of FXIII-B with FXIII-A, and fibrinogen. Rat monoclonal antibodies against the 10th Sushi domain of FXIII-B inhibited the incorporation of FXIII-B to fibrin, FXIII activation (i.e., cleavage of FXIII-A activation peptide), and ultimately fibrin crosslinking in normal plasma, independent of their effect on heterotetramer assembly with FXIII-A. Alloantibody binding to the A2B2 heterotetramer blocked the access of thrombin to the FXIII-A cleavage site, as indicated by the reaction of the alloantibodies to the A2B2 heterotetramer and FXIII-B, but not to FXIII-A. Anti-FXIII-B antibodies binding to the A2B2 heterotetramer and FXIII-B inhibited FXIII activation and its crosslinking function despite being directed against its non-catalytic subunit (FXIII-B).

Feasibility of an automated coagulation factor XIIIa test using its isopeptidase activity

Plasma transglutaminase FXIII provides mechanical and biochemical stability to blood clots. Congenital or acquired deficiency may be associated with bleeding diathesis and requires therefore careful monitoring. The precise automated measurement of a large number of plasma samples can provide new insights regarding the clinical relevance of certain FXIII levels. There is still the unmet diagnostic need for a reliable high-throughput method. Here we report the development and feasibility study of a promising prototype, adapting the precise FXIIIa isopeptidase assay principle on the optimized automated Ceveron s100 platform.

Factor XIII topology: organization of B subunits and changes with activation studied with single‐molecule atomic force microscopy

Essentials Factor XIII is a heterotetramer with 2 catalytic A subunits and 2 non-catalytic B subunits. Structure of active and inactive factor XIII was studied with atomic force microscopy. Inactive factor XIII is made of an A2 globule and 2 flexible B subunits extending from it. Activated factor XIII separates into a B2 homodimer and 2 monomeric active A subunits. SUMMARY: Background Factor XIII (FXIII) is a precursor of the blood plasma transglutaminase (FXIIIa) that is generated by thrombin and Ca2+ and covalently crosslinks fibrin to strengthen blood clots. Inactive plasma FXIII is a heterotetramer with two catalytic A subunits and two non-catalytic B subunits. Inactive A subunits have been characterized crystallographically, whereas the atomic structure of the entire FXIII and B subunits is unknown and the oligomerization state of activated A subunits remains controversial. Objectives Our goal was to characterize the (sub)molecular structure of inactive FXIII and changes upon activation. Methods Plasma FXIII, non-activated or activated with thrombin and Ca2+ , was studied by single-molecule atomic force microscopy. Additionally, recombinant separate A and B subunits were visualized and compared with their conformations and dimensions in FXIII and FXIIIa. Results and Conclusions We showed that heterotetrameric FXIII forms a globule composed of two catalytic A subunits with two flexible strands comprising individual non-catalytic B subunits that protrude on one side of the globule. Each strand corresponds to seven to eight out of 10 tandem repeats building each B subunit, called sushi domains. The remainder were not seen, presumably because they were tightly bound to the globular A2 dimer. Some FXIII molecules had one or no visible strands, suggesting dissociation of the B subunits from the globular core. After activation of FXIII with thrombin and Ca2+ , B subunits dissociated and formed B2 homodimers, whereas the activated globular A subunits dissociated into monomers. These results characterize the molecular organization of FXIII and changes with activation.

841: Elevated plasma transglutaminase activity is an early biomarker of gestational hypertension or preeclampsia and correlates to its severity

841: Elevated plasma transglutaminase activity is an early biomarker of gestational hypertension or preeclampsia and correlates to its severity

Elevated Transglutaminase Activity Triggers Angiotensin Receptor Activating Autoantibody Production and Pathophysiology of Preeclampsia.

BackgroundPreeclampsia (PE) is a life‐threatening hypertensive disorder of pregnancy associated with autoantibodies, termed AT 1‐AA, that activate the AT 1 angiotensin receptor. Although the pathogenic nature of these autoantibodies has been extensively studied, little is known about the molecular cause of their generation.Methods and ResultsHere we show that tissue transglutaminase (TG2), an enzyme that conducts posttranslational modification of target proteins, directly modified the 7‐amino acid (7‐aa) epitope peptide that localizes to the second extracellular loop of the AT 1 receptor. These findings led us to further discover that plasma transglutaminase activity was induced and contributed to the production of AT 1‐AA and disease development in an experimental model of PE induced by injection of LIGHT, a tumor necrosis factor superfamily member. Key features of PE were regenerated by adoptive transfer of purified IgG from LIGHT‐injected pregnant mice and blocked by the 7‐amino acid epitope peptide. Translating our mouse research to humans, we found that plasma transglutaminase activity was significantly elevated in PE patients and was positively correlated with AT 1‐AA levels and PE features.ConclusionsOverall, we provide compelling mouse and human evidence that elevated transglutaminase underlies AT 1‐AA production in PE and highlight novel pathogenic biomarkers and innovative therapeutic possibilities for the disease.

Coagulation factor XIII: a multifunctional transglutaminase with clinical potential in a range of conditions.

Coagulation factor XIII (FXIII), a plasma transglutaminase, is best known as the final enzyme in the coagulation cascade, where it is responsible for cross-linking of fibrin. However, a growing body of evidence has demonstrated that FXIII targets a wide range of additional substrates that have important roles in health and disease. These include antifibrinolytic proteins, with cross-linking of α2-antiplasmin to fibrin, and potentially fibrinogen, being the principal mechanism(s) whereby plasmin-mediated clot degradation is minimised. FXIII also acts on endothelial cell VEGFR-2 and αvβ3 integrin, which ultimately leads to downregulation of the antiangiogenic protein thrombospondin-1, promoting angiogenesis and neovascularisation. Under infectious disease conditions, FXIII cross-links bacterial surface proteins to fibrinogen, resulting in immobilisation and killing, while during wound healing, FXIII induces cross-linking of the provisional matrix. The latter process has been shown to influence the interaction of leukocytes with the provisional extracellular matrix and promote wound healing. Through these actions, there are good rationales for evaluating the therapeutic potential of FXIII in diseases in which tissue repair is dysregulated or perturbed, including systemic sclerosis (scleroderma), invasive bacterial infections, and tissue repair, for instance healing of venous leg ulcers or myocardial injuries. Adequate levels of FXIII are also required in patients undergoing surgery to prevent or treat perioperative bleeding, and its augmentation in patients with/at risk for perioperative bleeding may also have potential clinical benefit. While there are preclinical and/or clinical data to support the use of FXIII in a range of settings, further clinical evaluation in these underexplored applications is warranted.

The Non-catalytic B Subunit of Coagulation Factor XIII Accelerates Fibrin Cross-linking

Covalent cross-linking of fibrin chains is required for stable blood clot formation, which is catalyzed by coagulation factor XIII (FXIII), a proenzyme of plasma transglutaminase consisting of catalytic A (FXIII-A) and non-catalytic B subunits (FXIII-B). Herein, we demonstrate that FXIII-B accelerates fibrin cross-linking. Depletion of FXIII-B from normal plasma supplemented with a physiological level of recombinant FXIII-A resulted in delayed fibrin cross-linking, reduced incorporation of FXIII-A into fibrin clots, and impaired activation peptide cleavage by thrombin; the addition of recombinant FXIII-B restored normal fibrin cross-linking, FXIII-A incorporation into fibrin clots, and activation peptide cleavage by thrombin. Immunoprecipitation with an anti-fibrinogen antibody revealed an interaction between the FXIII heterotetramer and fibrinogen mediated by FXIII-B and not FXIII-A. FXIII-B probably binds the γ-chain of fibrinogen with its D-domain, which is near the fibrin polymerization pockets, and dissociates from fibrin during or after cross-linking between γ-chains. Thus, FXIII-B plays important roles in the formation of a ternary complex between proenzyme FXIII, prosubstrate fibrinogen, and activator thrombin. Accordingly, congenital or acquired FXIII-B deficiency may result in increased bleeding tendency through impaired fibrin stabilization due to decreased FXIII-A activation by thrombin and secondary FXIII-A deficiency arising from enhanced circulatory clearance.

Recombinant factor XIII (rFXIII): a novel treatment of congenital factor XIII deficiency

Factor XIII (FXIII) is composed of two catalytic A subunits and two carrier B subunits. Following activation by thrombin FXIII becomes plasma transglutaminase, which cross-links the γ-glutamyl-e-lysine residues of fibrin chains stabilizing fibrin clot. Congenital deficiency of factor XIII results in a severe life-long hemorrhagic disorder, abnormal wound healing in about 30% of patients and recurrent abortions. Most of the FXIII deficiency patients have mutations in the F13A gene. Only few mutations in F13B gene have been published. Plasma-derived concentrate of factor XIII used to be the treatment of choice. Recently, recombinant FXIII concentrate has been developed and tested in multinational clinical studies. This new product appears to be safe and appropriate for life-long prophylactic treatment of patients with FXIII A deficiency.

Down-regulation of Fas-mediated apoptosis by plasma transglutaminase factor XIII that catalyzes fetal-specific cross-link of the Fas molecule

The Fas antigen, also designated as APO-1 or CD95, is a member of the tumor necrosis factor receptor superfamily and can mediate apoptotic cell death in various cells. We report here that blood coagulation factor XIII (plasma transglutaminase, fibrin stabilizing factor) inhibits apoptosis induced by a cytotoxic anti-Fas monoclonal antibody in Jurkat cells. When cells were treated with the antibody in fetal calf serum-containing media, higher-molecular-weight (180K) polypeptides containing Fas molecule were detected by immunoblotting. Under conditions where the transglutaminase activity was eliminated or suppressed, the cross-link of Fas was not observed, and concurrently cell death was hastened. Moreover, an antibody against factor XIII strongly accelerated the Fas-mediated apoptosis. Furthermore, addition of partially purified factor XIII neutralized the apoptosis-promoting effect of anti-factor XIII antibody, indicating that this enzyme is involved in cross-link of Fas and down-regulates Fas-mediated apoptotic cell death. Significantly, the cross-link of Fas was seen only in fetal calf serum but not in newly-born calf serum, 1-year-old calf serum or adult bovine serum. These data suggest that plasma transglutaminase factor XIII may play a key role in fetal development of vertebrates via cross-link of Fas antigen.

Abstract 275: Tissue Transglutaminase Stabilizes Placental AT1 Receptor and Contributes to Pathophysiology in Preeclampsia

Preeclampsia (PE) is a serious hypertensive disease of pregnancy associated with the presence of the major angiotensin receptor AT1-agnostic autoantibodies (AT1-AAs) that cause the defining PE features when introduced into pregnant mice. To understand AT1-AA-mediated receptor activation in PE, we explored the role of tissue transglutaminases (TG2), the most ubiquitous member of a group of enzymes modifying proteins by catalyzing the formation of ε-(γ-glutamyl)-lysine isopeptide bonds. TG2, a versatile protein that can also function as a G protein, is enriched in the syncytiotrophoblasts of placenta, the key organ in PE pathogenesis. Western blot analysis and IHC-IF double staining initially revealed that TG2 and transglutaminase (TG)-mediated isopeptide modification levels are increased approximately 2X in PE vs normotensive (NT) placental tissue (n=4 or 5, p<0.05). Next, we identified a similar increase in PE plasma TG activity (NT=3.1±0.5, mild PE=5.4±0.6, severe PE=9.1±0.7milliunit/ml, n=26-29, p<0.01), and the increased plasma TG activity is positively correlated with the key disease features including blood pressure and proteinuria (r 2 >0.5, p<0.01). We also found a higher level of AT1 receptor with isopeptide modification in PE placentas by immunoprecipitation and IF colocalization. A pathogenic role for TG2 in PE is suggested by in vivo experiments in which TG inhibitor cystamine, or siRNA-mediated TG2 knockdown, significantly attenuated AT1-AA-induced PE features in pregnant mice including hypertension (PE=160±6 vs PE+cystamine=133±3mmHg, p<0.01, n=6; PE+control siRNA=161±3 vs PE+ TG2 siRNA=137±7mmHg, p<0.05, n=5-6), proteinuria (PE=133±21 vs PE+cystamine=58±12ng albumin/mg creatine, p<0.01, n=6; PE+control siRNA=102±51 vs PE+ TG2 siRNA=26±6ng albumin/mg creatine, p<0.05, n=4), and placental isopeptide modification. In trophoblasts, AT1-AA stimulation enhanced the interaction between AT1 receptor and TG2, and resulted in increased AT1 receptor stabilization via isopeptide modification, which is further confirmed by mutagenesis studies. Taken together, our results not only identify a pathogenic role of TG2 in PE, but also shed light on a previously unrecognized mechanism of TG2-mediated GPCR stabilization.

Mechanisms of fibrin polymerization and clinical implications

AbstractResearch on all stages of fibrin polymerization, using a variety of approaches including naturally occurring and recombinant variants of fibrinogen, x-ray crystallography, electron and light microscopy, and other biophysical approaches, has revealed aspects of the molecular mechanisms involved. The ordered sequence of fibrinopeptide release is essential for the knob-hole interactions that initiate oligomer formation and the subsequent formation of 2-stranded protofibrils. Calcium ions bound both strongly and weakly to fibrin(ogen) have been localized, and some aspects of their roles are beginning to be discovered. Much less is known about the mechanisms of the lateral aggregation of protofibrils and the subsequent branching to yield a 3-dimensional network, although the αC region and B:b knob-hole binding seem to enhance lateral aggregation. Much information now exists about variations in clot structure and properties because of genetic and acquired molecular variants, environmental factors, effects of various intravascular and extravascular cells, hydrodynamic flow, and some functional consequences. The mechanical and chemical stability of clots and thrombi are affected by both the structure of the fibrin network and cross-linking by plasma transglutaminase. There are important clinical consequences to all of these new findings that are relevant for the pathogenesis of diseases, prophylaxis, diagnosis, and treatment.

Relationships of Coagulation Factor XIII Activity with Cell-Type and Stage of Non-Small Cell Lung Cancer

PurposeFactor XIII (FXIII), a thrombin-activated plasma transglutaminase zymogen, is involved in cancer development and progression through a triggered coagulation pathway. The aim of this study was to examine whether FXIII activity levels differed in non-small cell lung cancer (NSCLC) patients according to histological types and TNM stage when compared with healthy subjects.Materials and MethodsTwenty-eight NSCLC patients and 28 normal controls who had been individually age-, gender-, body mass index-, smoking status-, and smoking amount-matched were enrolled: 13 adenocarcinomas, 11 squamous cell carcinomas, and four undifferentiated NSCLCs; four stage I, two stage II, 12 stage III, and 10 stage IV NSCLCs. FXIII activity was measured using fluorescence-based protein arrays.ResultsThe median FXIII activity level of the NSCLC group [24.2 Loewy U/mL, interquartile range (IQR) 14.9-40.4 Loewy U/mL] was significantly higher than that of the healthy group (17.5 Loewy U/mL, IQR 12.6-26.4 Loewy U/mL) (p=0.01). There were no differences in FXIII activity between adenocarcinoma (median 18.6 Loewy U/mL) and squamous cell carcinoma (median 28.7 Loewy U/mL). NSCLC stage significantly influenced FXIII activity (p=0.02). The FXIII activity of patients with stage III NSCLC (median 27.3 Loewy U/mL, IQR 19.3-40.5 Loewy U/mL) was significantly higher than those of patients with stage I or II (median 14.0 Loewy U/mL, IQR 13.1-23.1 Loewy U/mL, p=0.04). FXIII activity was negatively correlated with aPTT in NSCLC patients (r=-0.38, p=0.04).ConclusionPatients with advanced-stage NSCLC exhibited higher coagulation FXIII activity than healthy controls and early-stage NSCLC patients.

Abstract 9453: Dual Probe Hybrid Molecular PET/MR Imaging of Post-infarct Myocardial Inflammation and Healing

Background: Myocardial infarction elicits a strong inflammatory response, with profound recruitment of innate immune cells. The magnitude of inflammation influences infarct size and severity of post-MI ventricular dysfunction. Inflammatory monocytes and macrophages produce substantial amounts of myeloperoxidase (MPO), which leads to oxidative stress. In addition, plasma transglutaminase factor XIII (FXIII) plays a key role in wound healing, via its contribution to extracellular matrix organization. Thus, we hypothesize that targeted molecular imaging of FXIII and MPO activity using a hybrid PET/ MRI approach will enable simultaneous in vivo assessment of infarct healing and post-infarct inflammation. Methods and Results: To assess in vivo FXIII activity, we developed a fluorine-18 labeled affinity peptide (18F-FXIII), with a blood half-life of 13.3 min, using a facile ‘click-chemistry’ approach. FXIII recognizes the PET probe as a substrate and cross-links it to extracellular matrix proteins, leading to local entrapment within the healing infarct. 18F-FXIII and gadolinium-based activatable sensor of MPO activity (MPO-Gd) were injected in C57BL/6 mice on day 4 after permanent coronary ligation. PET/MR imaging was performed and fusion was facilitated using external fiducial markers. 18F-FXIII uptake in the heart was significantly higher in animals with MI as compared to controls, as measured by scintillation counting (percent injected dose per gram tissue 0.29±0.01 vs 0.17± 0.03, p<0.03). On autoradiography, 18F-FXIII uptake correlated well with infarct area on TTC staining. PET/MR imaging allowed for simultaneous in vivo assessment of MPO and FXIII activity (Figure). Conclusion: Dual probe hybrid PET/MR imaging with 18F-FXIII and MPO-Gd allows non-invasive assessment of post-infarct myocardial inflammation and infarct healing.

Indwelling catheters and medical implants with FXIIIa inhibitors: A novel approach to the treatment of catheter and medical device-related infections

Central venous catheters (CVCs) are being utilized with increasing frequency in intensive care and general medical wards. In spite of the extensive experience gained in their application, CVCs are related to the long-term risks of catheter sheath formation, infection, and thrombosis (of the catheter or vessel itself) during catheterization. Such CVC-related-complications are associated with increased morbidity, mortality, duration of hospitalization, and medical care cost [1].The present study incorporates a novel group of Factor XIIIa (FXIIIa, plasma transglutaminase) inhibitors into a lubricious silicone elastomer in order to generate an optimized drug delivery system whereby a secondary sustained drug release profile occurs following an initial burst release for catheters and other medical devices. We propose that the incorporation of FXIIIa inhibitors into catheters, stents, and other medical implant devices would reduce the incidence of catheter sheath formation, thrombotic occlusion, and associated staphylococcal infection. This technique could be used as a local delivery system for extended release with an immediate onset of action for other poorly aqueous soluble compounds.

“Activation of tissue tranglutsaminase by removal of carboxyl-terminal peptides”

Tissue transglutaminase (TGC or TG2) functions as transglutaminase (cross-linking), deamidase, kinase, and disulfide isomerase and its activities are implicated in the pathogenesis of several human diseases. Proteolytic activation of zymogens in the transglutaminase family is not unusual. Plasma transglutaminase (FXIIIa), epidermal transglutaminase (TG 3), transglutaminase-5, and microbial transglutaminase (MTG) can be subjected to proteolysis from specific proteases to generate the active functional enzyme. In the present study, calcium or GTP was essential for activation of TGC cross-linking activity by trypsin in membrane fractions from human RBC and was accompanied by the conversion of TGC (80 kDa) to a smaller TG form (55 kDa). While bacterially expressed TGC showed no activity, bacterial expression of C-terminal domain deletion constructs with carboxy-terminal ends ranging from lysine 464 (TG464) to glycine 480 (TG480) produced enzymes that were highly active in cross-linking activity. The product of a construct with a coding region ended at proline 446 (TG446), which interrupted the calcium-binding domain, exhibited weak cross-linking activity. TG480 and TG512 were characterized by about 80% and 10%, respectively, of the cross-linking activities of TG464. This may indicate that the longer the peptide after the calcium binding domain, the less the enzymatic activity expressed, possibly because the folding of such peptide which interfere with the calcium binding site or the catalytic site. Western analysis of MCF7 and T47D human breast cancer cells transfected with TGC showed TGC as a major protein and TG as a minor fragment. Incubation of lysate from transfected cells with serum resulted in the conversion of the TGC to TG, a condition that may be comparable to injury or wounds that lead to rapid enzymatic transamidation activation.

Secretory Leukocyte Protease Inhibitor (SLPI) Is, like Its Homologue Trappin-2 (Pre-Elafin), a Transglutaminase Substrate

Human lungs contain secretory leukocyte protease inhibitor (SLPI), elafin and its biologically active precursor trappin-2 (pre-elafin). These important low-molecular weight inhibitors are involved in controlling the potentially deleterious proteolytic activities of neutrophil serine proteases including elastase, proteinase 3 and cathepsin G. We have shown previously that trappin-2, and to a lesser extent, elafin can be linked covalently to various extracellular matrix proteins by tissue transglutaminases and remain potent protease inhibitors. SLPI is composed of two distinct domains, each of which is about 40% identical to elafin, but it lacks consensus transglutaminase sequence(s), unlike trappin-2 and elafin. We investigated the actions of type 2 tissue transglutaminase and plasma transglutaminase activated factor XIII on SLPI. It was readily covalently bound to fibronectin or elastin by both transglutaminases but did not compete with trappin-2 cross-linking. Cross-linked SLPI still inhibited its target proteases, elastase and cathepsin G. We have also identified the transglutamination sites within SLPI, elafin and trappin-2 by mass spectrometry analysis of tryptic digests of inhibitors cross-linked to mono-dansyl cadaverin or to a fibronectin-derived glutamine-rich peptide. Most of the reactive lysine and glutamine residues in SLPI are located in its first N-terminal elafin-like domain, while in trappin-2, they are located in both the N-terminal cementoin domain and the elafin moiety. We have also demonstrated that the transglutamination substrate status of the cementoin domain of trappin-2 can be transferred from one protein to another, suggesting that it may provide transglutaminase-dependent attachment properties for engineered proteins. We have thus added to the corpus of knowledge on the biology of these potential therapeutic inhibitors of airway proteases.

Role of transglutaminases in cuff-induced atherosclerotic lesion formation in femoral arteries of ApoE3 Leiden mice

Transglutaminases play an important role in vascular remodeling, calcification, cell adhesion and endothelial barrier function. In this study we investigate the influence of combined inhibition of both tissue-type transglutaminase (TG2) and the plasma transglutaminase FXIIIA on early lesion development. Methods A cuff was placed around the femoral arteries of ApoE3 Leiden mice while fed a Western type diet to induce atherosclerotic lesion development. An osmotic minipump was placed in the intraperitoneal cavity containing an irreversible inhibitor of TG2 and FXIIIA activity ((1,3,4,5-tetramethyl-2-[(2-oxopropyl)thio]imidazolium chloride, Zedira). Atherosclerotic lesion composition was analyzed using immunohistochemistry and RT-PCR. Results Inhibition of transglutaminases did not influence lesion size or geometric remodeling of the vessels. However, systemic transglutaminase inhibition resulted in 41% less macrophage infiltrate in the media of the vessels. Additional in vitro experiments on HL60 cells confirmed a decreased migratory response during transglutaminase inhibition. Conclusion Inhibition of TG2 and FXIIIA during early development of lesions reduced the macrophage content in the media of atherosclerotic vessels, while not affecting lesion size or geometric remodeling.

A Plasma Protein Indistinguishable from Ribosomal Protein S19: Conversion to a Monocyte Chemotactic Factor by a Factor XIIIa-Catalyzed Reaction on Activated Platelet Membrane Phosphatidylserine in Association with Blood Coagulation

A monocyte-chemoattracting factor is generated during blood coagulation and during clotting of platelet-rich plasma. This chemotactic factor attracts monocytes as a ligand of the C5a receptor; however, it inhibits C5a-induced neutrophil chemotaxis as an apparent receptor antagonist. The curious dual function of the serum monocyte chemotactic factor resembles that of the cross-linked homodimer of ribosomal protein S19 (RP S19). Indeed, the inactive precursor of the monocyte chemotactic factor was present in plasma, and the precursor molecule and RP S19, as well as the active form and the RP S19 dimer, were indistinguishable in terms of immunological reactivity and molecular size. Coagulation factor XIIIa, plasma transglutaminase, and membrane phosphatidylserine on the activated platelets were required for conversion of the precursor to the active form. In addition, the precursor molecule in plasma could be replaced by wild-type recombinant RP S19 but not by mutant forms of it. These results indicate that a molecule indistinguishable from RP S19 was present in plasma, and that the RP S19-like molecule was converted to the active form by a transglutaminase-catalyzed reaction on a scaffold that included the phosphatidylserine-exposed platelet membrane.

Impaired clot retraction in factor XIII A subunit–deficient mice

AbstractFactor XIII (FXIII) is a plasma transglutaminase that cross-links fibrin monomers, α2-plasmin inhibitor, and so forth. Congenital FXIII deficiency causes lifelong bleeding symptoms. To understand the molecular pathology of FXIII deficiency in vivo, its knockout mice have been functionally analyzed. Because prolonged bleeding times, a sign of defective/abnormal primary hemostasis, were commonly observed in 2 separate lines of FXIII A subunit (FXIII-A) knockout mice, a possible role or roles of FXIII in platelet-related function was investigated in the present study. Although platelet aggregation induced by adenosine diphosphate or collagen was normal, clot retraction (CR) was lost in the platelet-rich plasma (PRP) of FXIII-A knockout mice. In contrast, there was no CR impairment in the PRP of tissue transglutaminase-knockout mice compared with that of wild-type mice. Furthermore, a transglutaminase inhibitor, cystamine, halted CR in the PRP of wild-type mice. These results indicate that the enzymatic activity of FXIII is necessary for CR, at least in mice.