Hierarchies in the binding of human factor XIII, factor XIIIa, and endothelial cell transglutaminase to human plasma fibrinogen, fibrin, and fibronectin

Transglutaminase 2 Facilitates Murine Wound Healing in a Strain-Dependent Manner

Transglutaminase 2 (TG2) plays a role in cellular processes that are relevant to wound healing, but to date no studies of wound healing in TG2 knockout mice have been reported. Here, using 129T2/SvEmsJ (129)- or C57BL/6 (B6)-backcrossed TG2 knockout mice, we show that TG2 facilitates murine wound healing in a strain-dependent manner. Early healing of in vivo cutaneous wounds and closure of in vitro scratch wounds in murine embryonic fibroblast (MEF) monolayers were delayed in 129, but not B6, TG2 knockouts, relative to their wild-type counterparts, with wound closure in 129 being faster than in B6 wild-types. A single dose of exogenous recombinant wild-type TG2 to 129 TG2-/- mice or MEFs immediately post-wounding accelerated wound closure. Neutrophil and monocyte recruitment to 129 cutaneous wounds was not affected by Tgm2 deletion up to 5 days post-wounding. Tgm2 mRNA and TG2 protein abundance were higher in 129 than in B6 wild-types and increased in abundance following cutaneous and scratch wounding. Tgm1 and factor XIIA (F13A) mRNA abundance increased post-wounding, but there was no compensation by TG family members in TG2-/- relative to TG2+/+ mice in either strain before or after wounding. 129 TG2+/+ MEF adhesion was greater and spreading was faster than that of B6 TG2+/+ MEFs, and was dependent on syndecan binding in the presence, but not absence, of RGD inhibition of integrin binding. Adhesion and spreading of 129, but not B6, TG2-/- MEFs was impaired relative to their wild-type counterparts and was accelerated by exogenous addition or transfection of TG2 protein or cDNA, respectively, and was independent of the transamidase or GTP-binding activity of TG2. Rho-family GTPase activation, central to cytoskeletal organization, was altered in 129 TG2-/- MEFs, with delayed RhoA and earlier Rac1 activation than in TG2+/+ MEFs. These findings indicate that the rate of wound healing is different between 129 and B6 mouse strains, correlating with TG2 abundance, and although not essential for wound healing, TG2 facilitates integrin- and syndecan-mediated RhoA- and Rac1-activation in fibroblasts to promote efficient wound contraction.

Methylsulfonylmethane increases osteogenesis and regulates the mineralization of the matrix by transglutaminase 2 in SHED cells

Methylsulfonylmethane (MSM) is a naturally occurring, sulfate-containing, organic compound. It has been shown to stimulate the differentiation of mesenchymal stem cells into osteoblast-like cells and bone formation. In this study, we investigated whether MSM influences the differentiation of stem cells from human exfoliated deciduous teeth (SHED) into osteoblast-like cells and their osteogenic potential. Here, we report that MSM induced osteogenic differentiation through the expression of osteogenic markers such as osterix, osteopontin, and RUNX2, at both mRNA and protein levels in SHED cells. An increase in the activity of alkaline phosphatase and mineralization confirmed the osteogenic potential of MSM. These MSM-induced effects were observed in cells grown in basal medium but not osteogenic medium. MSM induced transglutaminase-2 (TG2), which may be responsible for the cross-linking of extracellular matrix proteins (collagen or osteopontin), and the mineralization process. Inhibition of TG2 ensued a significant decrease in the differentiation of SHED cells and cross-linking of matrix proteins. A comparison of mineralization with the use of mineralized and demineralized bone particles in the presence of MSM revealed that mineralization is higher with mineralized bone particles than with demineralized bone particles. In conclusion, these results indicated that MSM could promote differentiation and osteogenic potential of SHED cells. This osteogenic property is more in the presence of mineralized bone particles. TG2 is a likely cue in the regulation of differentiation and mineral deposition of SHED cells in response to MSM.

Interactive protein network of FXIII-A1 in lipid rafts of activated and non-activated platelets

Lipid-rafts are defined as membrane microdomains enriched in cholesterol and glycosphingolipids within platelet plasma membrane. Lipid raft-mediated clot retraction requires factor XIII and other interacting proteins. The aim of this study was to investigate the proteins that interact with factor XIII in raft and non-raft domains of activated and non-activated platelet plasma membrane. By lipidomics analysis, we identified cholesterol- and sphingomyelin-enriched areas as lipid rafts. Platelets were activated by thrombin. Proteomics analysis provided an overview of the pathways in which proteins of rafts and non-rafts participated in the interaction network of FXIII-A1, a catalytic subunit of FXIII. "Platelet activation" was the principal pathway among KEGG pathways for proteins of rafts, both before and after activation. Network analysis showed four types of interactions (activation, binding, reaction, and catalysis) in raft and non-raft domains in interactive network of FXIII-A1. FXIII-A1 interactions with other proteins in raft domains and their role in homeostasis highlight the specialization of the raft domain in clot retraction via the Factor XIII protein network.

Characterization of the transglutaminase gene family in zebrafish and in vivo analysis of transglutaminase-dependent bone mineralization

We have characterized the protein cross-linking enzyme transglutaminase (TGs) genes in zebrafish, Danio rerio, based on the analysis of their genomic organization and phylogenetics. Thirteen zebrafish TG genes (zTGs) have been identified, of which 11 show high homology to only 3 mammalian enzymes: TG1, TG2 and FXIIIa. No zebrafish homologues were identified for mammalian TGs 3-7. Real-time PCR analysis demonstrated distinct temporal expression profiles for zTGs in larvae and adult fish. Analysis by in situ hybridization revealed restricted expression of zTG2b and zFXIIIa in skeletal elements, resembling expression of their mammalian homologues in osteo-chondrogenic cells. Mammalian TG2 and FXIIIa have been implicated in promoting osteoblast differentiation and bone mineralization in vitro, however, mouse models lacking either gene have no skeletal phenotype likely due to a compensation effect. We show in this study that mineralization of the newly formed vertebrae is significantly reduced in fish grown for 5 days in the presence of TG inhibitor KCC-009 added at 3-5 days post fertilization. This treatment reduces average vertebrae mineralization by 30%, with complete inhibition in some fish, and no effect on the overall growth and vertebrae number. This is the first in vivo demonstration of the crucial requirement for the TG-catalyzed cross-linking activity in bone mineralization.

Thrombomodulin-dependent effect of factor VLeiden mutation on factor XIII activation

INTRODUCTION

Factor V Leiden mutation (FV(Leiden)) is associated with impaired down-regulation of activated FV procoagulant activity and loss of FV anticoagulant function that result in an increased risk of venous thromboembolism. As the downstream effects of FV(Leiden) on clot formation and fibrinolyis have only partially been revealed, we investigated its effect on the activation of factor XIII (FXIII) and the cross-linking of fibrin.

METHODS

In the plasma samples of fifteen healthy individuals with known FV genotypes coagulation was initiated by recombinant human tissue factor and phospholipids with or without recombinant human thrombomodulin (rhTM). FV deficient plasma supplemented with purified wild type FV or FV(Leiden) were also investigated. Clots were recovered and analyzed by SDS-PAGE and quantitative densitometric evaluation of Western blots.

RESULTS

rhTM considerably delayed the activation of FXIII in the plasma from FV wild type individuals. This effect of rhTM was significantly impaired in the plasma from FV(Leiden) carriers. The results were confirmed in experiments with FV deficient plasma supplemented by FV prepared from wild type individuals or FV(Leiden) homozygotes. Fibrin γ-chain dimerization was also considerably delayed by rhTM in plasma samples from individuals without Leiden mutation, but not in plasma samples from FV(Leiden) heterozygotes or homozygotes. The difference between heterozygotes and homozygotes was not statistically significant.

CONCLUSION

The highly diminished delaying effect of TM on FXIII activation and on the cross-linking of fibrin in FV(Leiden) carriers might represent a novel mechanism contributing to the increased thrombosis risk of these individuals.

Interactions between factor XIII and the αC region of fibrinogen

Fibrinogen αC residues 242-424 have been shown to have a major regulatory role in the activation of factor XIII-A2B2 (FXIII-A2B2); however, the interactions underpinning this enhancing effect have not been determined. Here, we have characterized the binding of recombinant (r)FXIII-A subunit and FXIII-A2B2 with fibrin(ogen) and fibrin αC residues 233-425. Using recombinant truncations of the fibrin αC region 233-425 and surface plasmon resonance, we found that activated rFXIII-A bound αC 233-425 (Kd of 2.35 ± 0.09μM) which was further localized to αC 389-403. Site-directed mutagenesis of this region highlighted Glu396 as a key residue for binding of activated rFXIII-A. The interaction was specific for activated rFXIII-A and depended on the calcium-induced conformational change known to occur in rFXIII-A during activation. Furthermore, nonactivated FXIII-A2B2, thrombin-cleaved FXIII-A2B2, and activated FXIII-A2B2 each bound fibrin(ogen) and specifically αC region 371-425 with high affinity (Kd < 35nM and Kd < 31nM, respectively), showing for the first time the potential involvement of the αC region in binding to FXIII-A2B2. These results suggest that in addition to fibrinogen γ′ chain binding, the fibrin αC region also provides a platform for the binding of FXIII-A2B2 and FXIII-A subunit.

Plasma membrane factor XIIIA transglutaminase activity regulates osteoblast matrix secretion and deposition by affecting microtubule dynamics

Transglutaminase activity, arising potentially from transglutaminase 2 (TG2) and Factor XIIIA (FXIIIA), has been linked to osteoblast differentiation where it is required for type I collagen and fibronectin matrix deposition. In this study we have used an irreversible TG-inhibitor to ‘block –and-track’ enzyme(s) targeted during osteoblast differentiation. We show that the irreversible TG-inhibitor is highly potent in inhibiting osteoblast differentiation and mineralization and reduces secretion of both fibronectin and type I collagen and their release from the cell surface. Tracking of the dansyl probe by Western blotting and immunofluorescence microscopy demonstrated that the inhibitor targets plasma membrane-associated FXIIIA. TG2 appears not to contribute to crosslinking activity on the osteoblast surface. Inhibition of FXIIIA with NC9 resulted in defective secretory vesicle delivery to the plasma membrane which was attributable to a disorganized microtubule network and decreased microtubule association with the plasma membrane. NC9 inhibition of FXIIIA resulted in destabilization of microtubules as assessed by cellular Glu-tubulin levels. Furthermore, NC9 blocked modification of Glu-tubulin into 150 kDa high-molecular weight Glu-tubulin form which was specifically localized to the plasma membrane. FXIIIA enzyme and its crosslinking activity were colocalized with plasma membrane-associated tubulin, and thus, it appears that FXIIIA crosslinking activity is directed towards stabilizing the interaction of microtubules with the plasma membrane. Our work provides the first mechanistic cues as to how transglutaminase activity could affect protein secretion and matrix deposition in osteoblasts and suggests a novel function for plasma membrane FXIIIA in microtubule dynamics.

Transglutaminase-mediated oligomerization promotes osteoblast adhesive properties of osteopontin and bone sialoprotein

Tissue transglutaminase (TG2) is a widely distributed, protein-crosslinking enzyme having a prominent role in cell adhesion as a β1 integrin co-receptor for fibronectin. In bone and teeth, its substrates include the matricellular proteins osteopontin (OPN) and bone sialoprotein (BSP). The aim of this study was to examine effects of TG2-mediated crosslinking and oligomerization of OPN and BSP on osteoblast cell adhesion. We show that surfaces coated with oligomerized OPN and BSP promote MC3T3-E1/C4 osteoblastic cell adhesion significantly better than surfaces coated with the monomeric form of the proteins. Both OPN and BSP oligomer-adherent cells showed more cytoplasmic extensions than those cells grown on the monomer-coated surfaces indicative of increased cell connectivity. Our study suggests a role for TG2 in promoting the cell adhesion function of two matricellular substrate proteins prominent in bone, tooth cementum and certain tumors.

Identification of two GTP-independent alternatively spliced forms of tissue transglutaminase in human leukocytes, vascular smooth muscle, and endothelial cells

Tissue transglutaminase (tTG) is a multifunctional enzyme with transglutaminase crosslinking (TGase), GTP binding, and hydrolysis activities that play a role in many different disorders. We identified, characterized, and investigated the function and stability of two alternatively spliced forms of tTG using biochemical, cellular, and molecular biological approaches. Using a human aortic vascular smooth muscle cells (VSMC) cDNA library, we identified two cDNAs encoding C-terminal truncated forms, tTG(V1) and tTG(V2). tTG(V1,2) mRNAs were synthesized by a rare splicing event using alternate splice sites within exons 12 and 13 of the tTG gene, respectively. Quantitative PCR and immunoblotting demonstrated that there was unique expression and localization of tTG(V1,2) compared with tTG in human umbilical vein endothelial cells (HUVECs), VSMC, and leukocytes. The loss of C-terminal 52 amino acid residues (AAs) in tTG(V1,2) altered GTP binding, enhanced GTP hydrolysis, rendered the variants insensitive to GTP inhibition, and resulted in <10% residual Ca(+2)-dependent TGase activity. Transfection in HEK293 demonstrated a 28- and 5-fold reduction in the expression of tTG(V1) and tTG(V2), respectively, demonstrating that the C-terminal GTP-binding domain is important in stabilizing and promoting the half-life of tTG. The altered affinity for GTP allowed tTG(V1,2) to exhibit enhanced TGase activity when there is a transient increase in Ca(+2) levels. The abundance of tTG(V1,2) and its distinct intracellular expression patterns in human vascular cells and leukocytes indicate these isoforms likely have unique physiological functions.

Facilitated wound healing by activation of the Transglutaminase 1 gene

Transglutaminase 1 (TGase 1) is a Ca(2+)-dependent enzyme which catalyzes epsilon-(gamma-glutamyl)lysine cross-linking of substrate proteins such as involucrin and loricrin to generate the cornified envelope at the cell periphery of the stratum corneum. We have shown that disruption of the TGase 1 gene in mice results in neonatal lethality, absence of the cornified envelope, and impaired skin barrier function. Based on the importance of TGase 1 in epidermal morphogenesis, we have now assessed its role in wound healing. In neonatal mouse skin, TGase 1 mRNA as well as keratin 6alpha was induced in the epidermis at the wound edges as early as 2 hours after injury and that expression continued in the migrating epidermis until completion of re-epithelialization. The TGase 1 enzyme co-localized on the plasma membrane of migrating keratinocytes with involucrin, but not with loricrin, which suggests the premature assembly of the cornified envelope. Similar injuries to TGase 1 knockout mouse skins grafted on athymic nude mice showed substantial delays in wound healing concomitant with sustained K6alpha mRNA induction. From these results, we suggest that activation of the TGase 1gene is essential for facilitated repair of skin injury.

Tissue transglutaminase is expressed, active, and directly involved in rat dermal wound healing and angiogenesis

Tissue transglutaminase (TG) is an enzyme that stabilizes the structure of tissues by covalently ligating extracellular matrix molecules. Expression and localization of TG are not well established during wound healing. We performed punch biopsy wounds on anesthetized rats and monitored the wound healing process by histological and immunohistochemical methods. The TG antigen and activity are expressed at sites of neovascularization in the provisional fibrin matrix within 24 h of wounding. Endothelial cells, macrophages, and skeletal muscle cells expressed TG throughout the healing process. The TG antigen within the wound was active in vivo based on the detection of isopeptide bonds. The TG antigen increased four- to fivefold by day 3 postwounding and was proteolytically degraded. TG expression occurred in association with TGF-beta, TNF-alpha, IL-6, and VEGF production in the wound. Recombinant TG increased vessel length density (a measure of angiogenesis) when applied topically in rat dorsal skin flap window chambers. We have established that TG is an important tissue stabilizing enzyme that is active during wound healing and can function to promote angiogenesis.

Plasma transglutaminase in hypertrophic chondrocytes: expression and cell-specific intracellular activation produce cell death and externalization

We previously used subtractive hybridization to isolate cDNAs for genes upregulated in chick hypertrophic chondrocytes (Nurminskaya, M. , and T.F. Linsenmayer. 1996. Dev. Dyn. 206:260-271). Certain of these showed homology with the "A" subunit of human plasma transglutaminase (factor XIIIA), a member of a family of enzymes that cross-link a variety of intracellular and matrix molecules. We now have isolated a full-length cDNA for this molecule, and confirmed that it is avian factor XIIIA. Northern and enzymatic analyses confirm that the molecule is upregulated in hypertrophic chondrocytes (as much as eightfold). The enzymatic analyses also show that appreciable transglutaminase activity in the hypertrophic zone becomes externalized into the extracellular matrix. This externalization most likely is effected by cell death and subsequent lysis-effected by the transglutaminase itself. When hypertrophic chondrocytes are transfected with a cDNA construct encoding the zymogen of factor XIIIA, the cells convert the translated protein to a lower molecular weight form, and they initiate cell death, become permeable to macromolecules and eventually undergo lysis. Non-hypertrophic cells transfected with the same construct do not show these degenerative changes. These results suggest that hypertrophic chondrocytes have a novel, tissue-specific cascade of mechanisms that upregulate the synthesis of plasma transglutaminase and activate its zymogen. This produces autocatalytic cell death, externalization of the enzyme, and presumably cross-linking of components within the hypertrophic matrix. These changes may in turn regulate the removal and/or calcification of this hypertrophic matrix, which are its ultimate fates.

Detection and characterization, using fluoresceincadaverine, of amine acceptor protein substrates accessible to active transglutaminase expressed by rabbit articular chondrocytes

The purpose of this study was to investigate the implication of transglutaminases in the biology of articular chondrocytes. Transglutaminase activity measurements performed on cell lysates showed that a transglutaminase was present in chondrocytes in primary culture and that it was strongly activated by limited proteolysis. In chondrocytes dedifferentiated by subculture or retinoic acid treatment, this transglutaminase appeared to be downregulated, while type II transglutaminase expression was induced. However, protein levels, mRNA steady-state levels or transglutaminase activity in whole-cell lysates do not necessarily reflect the activity present in living cells, as it is strongly regulated. Therefore, Fluoresceincadaverine, a fluorescent polyamine, was used for detecting amine acceptor protein substrates accessible to active transglutaminase in living cells. After incubation of chondrocytes with Fluoresceincadaverine, dedifferentiated cells exhibited an extracellular labelling, while chondrocytes in primary culture did not, unless thrombin was added to the culture medium. In contrast, Fluoresceincadaverine labelling was not detected in the cytosol, although the transglutaminases were also partly cytosolic. By confocal microscopy and Western blot analysis of labelled cells in culture, fibronectin was shown to be the main substrate for both transglutaminases. The transglutaminases present in articular chondrocytes may, therefore, contribute to the organization and the stabilization of their extracellular matrix.

Characterization of the reciprocal binding sites on human alpha-thrombin and factor XIII A-chain

Solution- and solid-phase techniques were used to probe Factor XIII A-chain-alpha-thrombin interactions. Alpha-thrombin activated Factor XIII more efficiently (Km = 0.83 +/- 0.08 x 10(-7) M; V/K = 14.90 +/- 3.20 x 10(-3) min(-1)) than beta-thrombin (Km = 6.14 +/- 1.26 x 10(-7) M; V/K = 3.30 +/- 1.00 x 10(-3) min(-1)) or gamma-thrombin (Km = 6.25 +/- 1.15 x 10(-7) M; V/K = 3.00 +/- 0.80 x 10(-3) min(-1)). Immobilized FPR-alpha-thrombin bound plasma Factor XIII (Kd = 0.17 +/- 0.04 x 10(-7) M) > Factor XIIIa (Kd = 0.69 +/- 0.18 x 10(-7) M) > liver transglutaminase (Kd = 4.73 +/- 1.01 x 10(-7) M) > Factor XIII A-chain (Kd = 49.00 +/- 9.40 x 10(-7) M). FPR-alpha-thrombin and alpha-thrombin also bound immobilized Factor XIII A-chain with affinities inversely related to protease activity: maximal binding at 1.36 x 10(-7) M and 13.6 x 10(-7) M, respectively. Plasma Factor XIII, transglutaminase, and dithiothreitol competitively inhibited Factor XIII A-chain binding to FPR-alpha-thrombin: IC50 = 1.0 x 10(-7) M, 3.0 x 10(-6) M and 1.52 x 10(-4) M, respectively. Transglutaminase also inhibited Factor XIII binding to alpha-thrombin (IC50 = 2.0 x 10(-6) M). Thrombin-binding site was localized to G38-M731 fragment of Factor XIII A-chain, probably within homologous regions (N72-A493) of transglutaminase. R320-E579 of alpha-thrombin was Factor XIII A-chain binding site. Intra-B-chain disulfides in alpha-thrombin were essential for binding but not catalytic H363 or residues R382-N394 and R443-G475. These studies propose a structural basis for Factor XIII activation, provide a regulatory mechanism for Factor XIIIa generation, and could eventually help in the development of new structure-based inhibitors of thrombin and Factor XIIIa.