Plasma transglutaminase factor XIII induces microvessel ingrowth into biodegradable hydroxyapatite implants in rats

Advances of Blood Coagulation Factor XIII in Bone Healing

The biologic process of bone healing is complicated, involving a variety of cells, cytokines, and growth factors. As a result of bone damage, the activation of a clotting cascade leads to hematoma with a high osteogenic potential in the initial stages of healing. A major factor involved in this course of events is clotting factor XIII (FXIII), which can regulate bone defect repair in different ways during various stages of healing. Autografts and allografts often have defects in clinical practice, making the development of advanced materials that support bone regeneration a critical requirement. Few studies, however, have examined the promotion of bone healing by FXIII in combination with biomaterials, in particular, its effect on blood coagulation and osteogenesis. Therefore, we mainly summarized the role of FXIII in promoting bone regeneration by regulating the extracellular matrix and type I collagen, bone-related cells, angiogenesis, and platelets, and described the research progress of FXIII = related biomaterials on osteogenesis. This review provides a reference for investigators to explore the mechanism by which FXIII promotes bone healing and the combination of FXIII with biomaterials to achieve targeted bone tissue repair.

Vascularization Strategies in the Prevention of Nonunion Formation

Delayed healing and nonunion formation are major challenges in orthopedic surgery, which require the development of novel treatment strategies. Vascularization is considered one of the major prerequisites for successful bone healing, providing an adequate nutrient supply and allowing the infiltration of progenitor cells to the fracture site. Hence, during the last decade, a considerable number of studies have focused on the evaluation of vascularization strategies to prevent or to treat nonunion formation. These involve (1) biophysical applications, (2) systemic pharmacological interventions, and (3) tissue engineering, including sophisticated scaffold materials, local growth factor delivery systems, cell-based techniques, and surgical vascularization approaches. Accumulating evidence indicates that in nonunions, these strategies are indeed capable of improving the process of bone healing. The major challenge for the future will now be the translation of these strategies into clinical practice to make them accessible for the majority of patients. If this succeeds, these vascularization strategies may markedly reduce the incidence of nonunion formation. Impact statement Delayed healing and nonunion formation are a major clinical problem in orthopedic surgery. This review provides an overview of vascularization strategies for the prevention and treatment of nonunions. The successful translation of these strategies in clinical practice is of major importance to achieve adequate bone healing.

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.

Prevascularization of a gas-foaming macroporous calcium phosphate cement scaffold via coculture of human umbilical vein endothelial cells and osteoblasts

The lack of a vasculature in tissue-engineered constructs is currently a major challenge in tissue regeneration. There has been no report of prevascularization of macroporous calcium phosphate cement (CPC) via coculture of endothelial cells and osteoblasts. The objectives of this study were to (1) investigate coculture of human umbilical vein endothelial cells (HUVEC) and human osteoblasts (HOB) on macroporous CPC for the first time; and (2) develop a new microvasculature-CPC construct with angiogenic and osteogenic potential. A gas-foaming method was used to create macropores in CPC. HUVEC and HOB were seeded with a ratio of HUVEC:HOB=4:1, at 1.5×10(5) cells/scaffold. The constructs were cultured for up to 42 days. CPC with a porosity of 83% had a flexural strength (mean±SD; n=6) of 2.6±0.2 MPa, and an elastic modulus of 340±30 MPa, approaching the reported values for cancellous bone. Reverse transcription-polymerase chain reaction showed that HUVEC+HOB coculture on CPC had much higher vascular endothelial growth factor (VEGF) and collagen I expressions than monoculture (p<0.05). Osteogenic markers alkaline phosphatase, osteocalcin (OC), and runt-related transcription factor 2 (Runx2) were also highly elevated. Immunostaining of PECAM1 (CD31) showed abundant microcapillary-like structures on CPC in coculture at 42 days, as HUVEC self-assembled into extensive branches and net-like structures. However, no microcapillary was found on CPC in monoculture. In immunohistochemical staining, the neo-vessels were strongly positive for PECAM1, the von Willebrand factor, and collagen I. Scanning electron microscopy revealed microcapillary-like structures mingling with mineral nodules on CPC. Cell-synthesized minerals increased by an order of magnitude from 4 to 42 days. In conclusion, gas-foaming macroporous CPC was fabricated and HUVEC+HOB coculture was performed for prevascularization, yielding microcapillary-like structures on CPC for the first time. The novel macroporous CPC-microvasculature construct is promising for a wide range of orthopedic applications with enhanced angiogenic and osteogenic capabilities.

New developments in the area of factor XIII

Coagulation factor (F)XIII is best known for its role in fibrin stabilization and cross-linking of antifibrinolytic proteins to the fibrin clot. From patients with congenital FXIII deficiency, it is known that FXIII also has important functions in wound healing and maintaining pregnancy. Over the last decade more and more research groups with different backgrounds have studied FXIII and have unveiled putative novel functions for FXIII. FXIII, with its unique role as a transglutaminase among the other serine protease coagulation factors, is now recognized as a multifunctional protein involved in regulatory mechanisms and construction and repair processes beyond hemostasis with possible implications in many areas of medicine. The aim of this review was to give an overview of exciting novel findings and to highlight the remarkable diversity of functions attributed to FXIII. Of course, more research into the underlying mechanisms and (patho-)physiological relevance of the many described functions of FXIII is needed. It will be exciting to observe future developments in this area and to see if and how these interesting findings may be translated into clinical practice in the future.

Factor XIII: a coagulation factor with multiple plasmatic and cellular functions

Factor XIII (FXIII) is unique among clotting factors for a number of reasons: 1) it is a protransglutaminase, which becomes activated in the last stage of coagulation; 2) it works on an insoluble substrate; 3) its potentially active subunit is also present in the cytoplasm of platelets, monocytes, monocyte-derived macrophages, dendritic cells, chondrocytes, osteoblasts, and osteocytes; and 4) in addition to its contribution to hemostasis, it has multiple extra- and intracellular functions. This review gives a general overview on the structure and activation of FXIII as well as on the biochemical function and downregulation of activated FXIII with emphasis on new developments in the last decade. New aspects of the traditional functions of FXIII, stabilization of fibrin clot, and protection of fibrin against fibrinolysis are summarized. The role of FXIII in maintaining pregnancy, its contribution to the wound healing process, and its proangiogenic function are reviewed in details. Special attention is given to new, less explored, but promising fields of FXIII research that include inhibition of vascular permeability, cardioprotection, and its role in cartilage and bone development. FXIII is also considered as an intracellular enzyme; a separate section is devoted to its intracellular activation, intracellular action, and involvement in platelet, monocyte/macrophage, and dendritic cell functions.

Transglutaminases and disease: lessons from genetically engineered mouse models and inherited disorders

The human transglutaminase (TG) family consists of a structural protein, protein 4.2, that lacks catalytic activity, and eight zymogens/enzymes, designated factor XIII-A (FXIII-A) and TG1-7, that catalyze three types of posttranslational modification reactions: transamidation, esterification, and hydrolysis. These reactions are essential for biological processes such as blood coagulation, skin barrier formation, and extracellular matrix assembly but can also contribute to the pathophysiology of various inflammatory, autoimmune, and degenerative conditions. Some members of the TG family, for example, TG2, can participate in biological processes through actions unrelated to transamidase catalytic activity. We present here a comprehensive review of recent insights into the physiology and pathophysiology of TG family members that have come from studies of genetically engineered mouse models and/or inherited disorders. The review focuses on FXIII-A, TG1, TG2, TG5, and protein 4.2, as mice deficient in TG3, TG4, TG6, or TG7 have not yet been reported, nor have mutations in these proteins been linked to human disease.

Improved tissue-engineered bone regeneration by endothelial cell mediated vascularization

Natural bone growth greatly depends on the precedent vascular network that supplies oxygen and essential nutrients and removes metabolites. Likewise, it is crucial for tissue-engineered bone to establish a vascular network that temporally precedes new bone formation, and spatially originates from within the graft. In order to recapitulate physiological skeletal development, we have developed a complex bone graft to repair rat bone defects. We have demonstrated that endothelial cells and osteoblasts (identified by cell morphology, quantification of specific marker antigens, calcium deposition and capillary-like growth) were able to differentiate and expand from donor rat bone marrow mononuclear cell populations. The biocompatibilities of poly-epsilon-caprolactone (PCL)-hydroxyapatite (HA) composites used for graft fabrication were evaluated at different component ratios to identify the optimal and support of cellular viability and functions for endothelial cells and osteoblasts. Using point-injection and low-pressure techniques, seeded endothelial cells and osteoblasts were able to assemble into microvascular networks and form bony matrix in grafts. The exogenous origination of these cells and their contribution to the vascularization and osteogenesis was confirmed using sex-mismatch implantation and Y chromosome tracking. By pre-seeding with endothelial cells, the resulting vascularization was able to promote osteogenesis, prevent ischemic necrosis and improve the mechanical properties in engineered bone tissue. Taken together, the results indicated that the integration of complex cell populations with composite scaffold materials provided an effective technique to improve osteogenesis in engineered bone graft. These findings suggest that hybrid grafts have great potential for clinical use to treat large bone defects.

Interaction of a blood coagulation factor on electrically polarized hydroxyapatite surfaces

Although the polarization treatment of hydroxyapatite (HA) remarkably enhances the osteoconductivity, the mechanisms have not yet been completely understood. The interaction of proteins in blood and tissue fluids with biomaterials are reportedly triggers for later cellular responses and played a major role in osteoconductive processes. Considering this, we disclosed the interaction of polarized HA surface with a coagulation factor, fibrin stabilizing factor XIII (FXIII). The HA activated FXIII even in Ca2+ free buffer, based on the SDS-PAGE detections of alpha-polymer and gamma-dimer bands assigned to stabilized fibrin. The Ca2+ ions, possibly released from the HA surfaces, were examined whether they initiate the activation of the FXIII. It was experimentally proved by ICP analysis that the induced large negative charges on the electrically polarized HA significantly increased the released Ca2+ concentration for the short pre-incubation time of 3 min. The more Ca2+ ions released from the negatively charged HA (N-HA) surfaces were more effective in the activation of the FXIII, resulting in the rapider disappearance of the gamma-chain bands in fibrin. The slightly lower Ca2+ concentration in the positively charged HA, compared to the nonpolarized HA activated the FXIII at an almost equal rate. The accelerated activation contributed to the stabilization of fibrin scaffold. Therefore, the polarity difference of the induced charges of the polarized HA surface altered the rate of the FXIII activation. The early stage interaction of the HA surfaces with blood proteins was considered to be an essential process of the accelerated new bone formation near implanted N-HA surface.

Effect of FXIII on Monocyte and Fibroblast Function

Factor XIII is a plasma transglutaminase that participates in the final stage of the coagulation cascade. Thrombin-activated FXIII (FXIIIa) catalyzes the formation of covalent crosslinks between gamma-glutamyl and epsilon-lysyl residues on fibrin molecules to yield the mature clot. In addition to its role in hemostasis, FXIIIa was previously shown by us to stimulate endothelial cells to exhibit pro-angiogenic activity. In this work, we studied the effect of FXIIIa on other cells that participate in angiogenesis and tissue repair, such as monocytes and fibroblasts. FXIIIa significantly enhanced migration and proliferation, and inhibited apoptosis of monocytes and fibroblasts. Similar to our previous observations with endothelial cells, the stimulating effect of FXIIIa on monocytes and fibroblasts was elicited via its binding to alpha (v)beta (3) integrin leading to cJun upregulation and TSP-1 downregulation. Since monocytes and fibroblasts are essential components of the tissue repair process, the results of this study, together with the proangiogenic activity of FXIIIa, further substantiate a significant role of FXIII in tissue repair.

Roles of transglutaminases in cardiac and vascular diseases

All transglutaminases share the common enzymatic activity of transamidation, or the cross-linking of glutamine and lysine residues to form N epsilon (gamma-glutamyl) lysyl isopeptide bonds. The plasma proenzyme factor XIII is responsible for stabilizing the fibrin clot against physical and fibrinolytic disruption. Another member of the transglutaminase family, tissue transglutaminase or TG2 is abundantly expressed in cardiomyocytes, vascular cells and macrophages. The transglutaminases have a variety of functions independent of their transamidating activity. For example, TG2 binds and hydrolyzes GTP, thereby fostering signal transduction by several G protein coupled receptors. Accumulating evidence points to novel roles for factor XIII and TG2 in cardiovascular biology including: (a) modulating platelet activity, (b) regulating glucose control, (c) contributing to the development of hypertension, (d) influencing the progression of atherosclerosis, (e) regulating vascular permeability and angiogenesis (f) and contributing to myocardial signaling, contractile activity and ischemia/reperfusion injury. In this review, we summarize the cardiovascular biology of two members of the family of transglutaminases, Factor XIII and TG2.

The effect of hydroxyapatite nanocrystals on microvascular endothelial cell viability and functions

To favor bone reconstitution with biomaterials endothelial cells should maintain proper functions to drive angiogenesis. To this aim nanocrystals of hydroxyapatite (HA) have been synthesized and characterized on endothelial cells. Microvascular endothelial cells have been exposed to stoichiometric HA nanocrystals. Cell morphology and organization of cytoskeletal proteins have been monitored by SEM analysis and immunofluorescence. Biochemical markers of physiological and pathological responses of endothelial cells, endothelial constitutive nitric oxide synthase, and cycloxygenase-2 (ecNOS and COX-2, respectively) have been measured by immunofluorescence. Crystallized HA sustained endothelial survival without any cytotoxic effect. At the observation with SEM, endothelial cell morphology was maintained in the presence of HA. The localization and organization of beta-actin documented the formation of stress fibers, indicating an activation of endothelial cells induced by HA nanocrystals. Immunohistochemistry for biochemical key signaling pathways in endothelium demonstrated that nanocrystals of HA maintained the expression of ecNOS and did not increase COX-2 expression. In conclusion, the present findings indicate that HA nanocrystals exhibit high biocompatibility for microvascular endothelium. In the presence of HA nanocrystals endothelial cells maintain biochemical markers of healthy endothelium. They do not acquire a proinflammatory or thrombogenic phenotype, but express markers of functioning endothelium that might contribute to angiogenesis.

The use of a bioresorbable nano-crystalline hydroxyapatite paste in acetabular bone impaction grafting

Calcium phosphates such as TCP-HA granules are considered promising bone graft substitutes. In the future, they may completely replace allograft bone for impaction grafting procedures. Mechanically, acetabular reconstructions with TCP-HA granules show high stability, however this is partly caused by excessive cement penetration, which is unfavourable from a biological perspective. It has been hypothesised that mixtures of morselised cancellous bone grafts (MCB) and/or TCP-HA granules with a nano-crystalline hydroxyapatite paste (Ostim) may reduce cement penetration while maintaining adequate implant stability and biocompatibility of the graft mixture. To investigate this hypothesis, destructive lever-out tests and in vivo animal test were performed with various combinations of materials. Mechanically, the addition of 10% Ostim to mixtures of MCB and/or TCP-HA granules reduced cement penetration and resulted in a mechanical stability comparable to pure allograft (the current gold standard). Biologically, the application of Ostim with MCB or TCP-HA granules did not hamper the biocompatibility of the materials. Ostim was mostly osseous-integrated with MCB or TCP-HA granules after 8 weeks. Also, non-osseous-integrated Ostim remnants were observed. In tartrate resistant acid phosphatase stained sections, these few non-osseous integrated Ostim remnants were actively being resorbed by osteoclasts. In conclusion, Ostim HA-paste could be a valuable addition when TCP-HA ceramic granules are being used for acetabular bone impaction grafting procedures.

Factor XIII (FXIII) and angiogenesis

Factor XIII is a plasma transglutaminase that participates in the final stage of the coagulation cascade. Thrombin-activated FXIII (FXIIIa) catalyzes the formation of covalent cross-links between gamma-glutamyl and epsilon-lysyl residues on adjacent fibrin chains in polymerized fibrin to yield the mature clot. In addition to its role in hemostasis, FXIII is known to participate in wound healing and embryo implantation, which are processes involving angiogenesis. In this review, we discuss the role of FXIII in angiogenesis and the molecular mechanisms underlying its proangiogenic effects. The FXIII role in tissue repair and remodeling may at least in part be attributed to its pro-angiogenic activity.

The effect of the addition of a polyglutamate motif to RGD on peptide tethering to hydroxyapatite and the promotion of mesenchymal stem cell adhesion

Mimicking endogenous bone-binding proteins, RGD peptides have been synthesized with polyacidic amino acid domains in order to ionically tether the peptides to bone-like synthetic biomaterials, including hydroxyapatite (HA). However, a direct comparison of unmodified RGD with polyacidic-conjugated RGD has not been performed, and thus a benefit for the acidic domain has not been established. We evaluated the peptide/HA bond of RGD peptides with and without an attached polyglutamate sequence (E(7)), as well as examined mesenchymal stem cell (MSC) adhesion and morphology as they were affected by the conjugated peptide. We found that significantly more E(7)RGD was bound to HA than RGD at all coating concentrations tested, and moreover, more E(7)RGD was retained on the HA surface even after extended washing in serum-free media. Consistent with in vitro results, higher levels of E(7)RGD than RGD remained on HA that had been implanted in vivo for 24 h, indicating that the polyacidic domain improved peptide-binding efficiency. At several peptide concentrations, E(7)RGD increased cell adhesion compared to RGD surfaces, establishing a biological benefit for the E(7) modification. In addition, HA pre-coated sequentially with low-density E(7)RGD (1-10 microg/ml) and serum (FBS) stimulated cell adhesion and spreading, compared to either coating alone, suggesting that an ionic linkage allows for the potential adsorption of serum proteins to unoccupied sites, which may be important for bone formation in vivo. Collectively, these results suggest that tethering peptides to HA via a polyglutamate domain is an effective method for improving the peptide/HA bond, as well as for enhancing MSC adhesion.