Role of heparan sulfate proteoglycans in the uptake and degradation of tissue factor pathway inhibitor-coagulation factor Xa complexes

The Glycosaminoglycan Side Chains and Modular Core Proteins of Heparan Sulphate Proteoglycans and the Varied Ways They Provide Tissue Protection by Regulating Physiological Processes and Cellular Behaviour

This review examines the roles of HS-proteoglycans (HS-PGs) in general, and, in particular, perlecan and syndecan as representative examples and their interactive ligands, which regulate physiological processes and cellular behavior in health and disease. HS-PGs are essential for the functional properties of tissues both in development and in the extracellular matrix (ECM) remodeling that occurs in response to trauma or disease. HS-PGs interact with a biodiverse range of chemokines, chemokine receptors, protease inhibitors, and growth factors in immune regulation, inflammation, ECM stabilization, and tissue protection. Some cell regulatory proteoglycan receptors are dually modified hybrid HS/CS proteoglycans (betaglycan, CD47). Neurexins provide synaptic stabilization, plasticity, and specificity of interaction, promoting neurotransduction, neurogenesis, and differentiation. Ternary complexes of glypican-1 and Robbo-Slit neuroregulatory proteins direct axonogenesis and neural network formation. Specific neurexin-neuroligin complexes stabilize synaptic interactions and neural activity. Disruption in these interactions leads to neurological deficits in disorders of functional cognitive decline. Interactions with HS-PGs also promote or inhibit tumor development. Thus, HS-PGs have complex and diverse regulatory roles in the physiological processes that regulate cellular behavior and the functional properties of normal and pathological tissues. Specialized HS-PGs, such as the neurexins, pikachurin, and Eyes-shut, provide synaptic stabilization and specificity of neural transduction and also stabilize the axenome primary cilium of phototoreceptors and ribbon synapse interactions with bipolar neurons of retinal neural networks, which are essential in ocular vision. Pikachurin and Eyes-Shut interactions with an α-dystroglycan stabilize the photoreceptor synapse. Novel regulatory roles for HS-PGs controlling cell behavior and tissue function are expected to continue to be uncovered in this fascinating class of proteoglycan.

The Tissue Factor Pathway in Cancer: Overview and Role of Heparan Sulfate Proteoglycans

Historically, the only focus on tissue factor (TF) in clinical pathophysiology has been on its function as the initiation of the extrinsic coagulation cascade. This obsolete vessel-wall TF dogma is now being challenged by the findings that TF circulates throughout the body as a soluble form, a cell-associated protein, and a binding microparticle. Furthermore, it has been observed that TF is expressed by various cell types, including T-lymphocytes and platelets, and that certain pathological situations, such as chronic and acute inflammatory states, and cancer, may increase its expression and activity. Transmembrane G protein-coupled protease-activated receptors can be proteolytically cleaved by the TF:FVIIa complex that develops when TF binds to Factor VII (PARs). The TF:FVIIa complex can activate integrins, receptor tyrosine kinases (RTKs), and PARs in addition to PARs. Cancer cells use these signaling pathways to promote cell division, angiogenesis, metastasis, and the maintenance of cancer stem-like cells. Proteoglycans play a crucial role in the biochemical and mechanical properties of the cellular extracellular matrix, where they control cellular behavior via interacting with transmembrane receptors. For TFPI.fXa complexes, heparan sulfate proteoglycans (HSPGs) may serve as the primary receptor for uptake and degradation. The regulation of TF expression, TF signaling mechanisms, their pathogenic effects, and their therapeutic targeting in cancer are all covered in detail here.

Alterations in heparan sulfate proteoglycan synthesis and sulfation and the impact on vascular endothelial function

The glycocalyx attached to the apical surface of vascular endothelial cells is a rich network of proteoglycans, glycosaminoglycans, and glycoproteins with instrumental roles in vascular homeostasis. Given their molecular complexity and ability to interact with the intra- and extracellular environment, heparan sulfate proteoglycans uniquely contribute to the glycocalyx's role in regulating endothelial permeability, mechanosignaling, and ligand recognition by cognate cell surface receptors. Much attention has recently been devoted to the enzymatic shedding of heparan sulfate proteoglycans from the endothelial glycocalyx and its impact on vascular function. However, other molecular modifications to heparan sulfate proteoglycans are possible and may have equal or complementary clinical significance. In this narrative review, we focus on putative mechanisms driving non-proteolytic changes in heparan sulfate proteoglycan expression and alterations in the sulfation of heparan sulfate side chains within the endothelial glycocalyx. We then discuss how these specific changes to the endothelial glycocalyx impact endothelial cell function and highlight therapeutic strategies to target or potentially reverse these pathologic changes.

Endothelial Glycocalyx Degradation in Critical Illness and Injury

The endothelial glycocalyx is a gel-like layer on the luminal side of blood vessels that is composed of glycosaminoglycans and the proteins that tether them to the plasma membrane. Interest in its properties and function has grown, particularly in the last decade, as its importance to endothelial barrier function has come to light. Endothelial glycocalyx studies have revealed that many critical illnesses result in its degradation or removal, contributing to endothelial dysfunction and barrier break-down. Loss of the endothelial glycocalyx facilitates the direct access of immune cells and deleterious agents (e.g., proteases and reactive oxygen species) to the endothelium, that can then further endothelial cell injury and dysfunction leading to complications such as edema, and thrombosis. Here, we briefly describe the endothelial glycocalyx and the primary components thought to be directly responsible for its degradation. We review recent literature relevant to glycocalyx damage in several critical illnesses (sepsis, COVID-19, trauma and diabetes) that share inflammation as a common denominator with actions by several common agents (hyaluronidases, proteases, reactive oxygen species, etc.). Finally, we briefly cover strategies and therapies that show promise in protecting or helping to rebuild the endothelial glycocalyx such as steroids, protease inhibitors, anticoagulants and resuscitation strategies.

N-trimethyl chitosan coated nano-complexes enhance the oral bioavailability and chemotherapeutic effects of gemcitabine

N-trimethyl chitosan (TMC) is a multifunctional polymer that can be used in various nanoparticle forms in the pharmaceutical, nutraceutical and biomedical fields. In this study, TMC was used as a mucoadhesive adjuvant to enhance the oral bioavailability and hence antitumour effects of gemcitabine formulated into nanocomplexes composed of poly(lactic-co-glycolic acid) nanoparticles (PLGA NPs) conjugated with d-α-tocopheryl polyethylene glycol 1000 succinate (TPGS). A central composite design was applied to achieve the optimal formulation. Cellular uptake and drug transportation studies revealed the nanocomplexes permeate over the intestinal cells via adsorptive-mediated and caveolae-mediated endocytosis. Pharmacokinetic studies demonstrated the oral drug bioavailability of the nanocomplexes was increased 5.1-fold compared with drug solution. In pharmacodynamic studies, the formulation reduced tumour size 3.1-fold compared with the drug solution. The data demonstrates that TMC modified nanocomplexes can enhance gemcitabine oral bioavailability and promote the anticancer efficacy.

The glycocalyx: a central regulator of vascular function

The endothelial glycocalyx is a specialized extracellular matrix that covers the apical side of vascular endothelial cells, projecting into the lumen of blood vessels. The composition of the glycocalyx has been studied in great detail, and it is known to be composed of a mixture of proteoglycans, glycosaminoglycans, and glycoproteins. Although this structure was once believed to be a passive physical barrier, it is now recognized as a multifunctional and dynamic structure that participates in many vascular processes, including but not limited to vascular permeability, inflammation, thrombosis, mechanotransduction, and cytokine signaling. Because of its participation in many physiological and pathophysiological states, comprehensive knowledge of the glycocalyx will aid future vascular biologists in their research. With that in mind, this review discusses the biochemical structure of the glycocalyx and its function in many vascular physiological processes. We also briefly review a more recent discovery in glycocalyx biology, the placental glycocalyx.

Vascular endothelial injury exacerbates coronavirus disease 2019: The role of endothelial glycocalyx protection

The potential for a rapid increase in severity is among the most frightening aspects of severe acute respiratory syndrome coronavirus 2 infection. Evidence increasingly suggests that the symptoms of coronavirus disease‐2019 (COVID‐19)‐related acute respiratory distress syndrome (ARDS) differ from those of classic ARDS. Recently, the severity of COVID‐19 has been attributed to a systemic, thrombotic, and inflammatory disease that damages not only the lungs but also multiple organs, including the heart, brain, toes, and liver. This systemic form of COVID‐19 may be due to inflammation and vascular endothelial cell injury. The vascular endothelial glycocalyx comprises glycoproteins and plays an important role in systemic capillary homeostasis maintenance. The glycocalyx covers the entire vascular endothelium, and its thickness varies among organs. The endothelial glycocalyx is very thin in the pulmonary capillaries, where it is affected by gaseous exchange with the alveoli and the low intravascular pressure in the pulmonary circulation. Despite the clearly important roles of the glycocalyx in vascular endothelial injury, thrombosis, vasculitis, and inflammation, the link between this structure and vascular endothelial cell dysfunction in COVID‐19 remains unclear. In this prospective review, we summarize the importance of the glycocalyx and its potential as a therapeutic target in cases of systemic COVID‐19.

A C-terminal peptide of TFPI-1 facilitates cytosolic delivery of nucleic acid cargo into mammalian cells

Efficient intracellular nucleic acid delivery into mammalian cells remains a long-standing challenge owing to poor cell permeability and uptake of naked nucleic acids across the cell membrane and limited cargo stability. Conventional delivery methods have several drawbacks, such as cytotoxicity, limited cell-type applicability, low efficiency, hindrances that limit the potential of oligonucleotide delivery in functional genomics, therapeutics and diverse research applications. Thus, new approaches that are robust, safe, effective and valid across multiple cell types are much needed. Here, we demonstrate that GGL27, a TFPI-1-derived novel cationic host defence peptide, facilitates the delivery of nucleic acid cargo into the cytosol of a range of mammalian cells. The GGL27 peptide is non-cytotoxic and is internalized in a broad range of mammalian cell-types, including transformed cell lines and primary cells. GGL27 spontaneously forms complexes with nucleic acids of variable sizes, protects them from nuclease degradation, and delivers cargo effectively. Together, our observations demonstrate the versatile cell-penetrating property of GGL27, providing an excellent template for developing a simple, non-toxic peptide-based cytosolic delivery tool for wide use in biomedical research.

Mass Spectrometry Reveals a Multifaceted Role of Glycosaminoglycan Chains in Factor Xa Inactivation by Antithrombin

Factor Xa (fXa) inhibition by antithrombin (AT) enabled by heparin or heparan sulfate is critical for controlling blood coagulation. AT activation by heparin has been investigated extensively, while interaction of heparin with trapped AT/fXa intermediates has received relatively little attention. We use native electrospray ionization mass spectrometry to study the role of heparin chains of varying length [hexa-, octa-, deca-, and eicosasaccharides (dp6, dp8, dp10, and dp20, respectively)] in AT/fXa complex assembly. Despite being critical promoters of AT/Xa binding, shorter heparin chains are excluded from the final products (trapped intermediates). However, replacement of short heparin segments with dp20 gives rise to a prominent ionic signal of ternary complexes. These species are also observed when the trapped intermediate is initially prepared in the presence of a short oligoheparin (dp6), followed by addition of a longer heparin chain (dp20), indicating that binding of heparin to AT/fXa complexes takes place after the inhibition event. The importance of the heparin chain length for its ability to associate with the trapped intermediate suggests that the binding likely occurs in a bidentate fashion (where two distinct segments of oligoheparin make contacts with the protein components, while the part of the chain separating these two segments is extended into solution to minimize electrostatic repulsion). This model is corroborated by both molecular dynamics simulations with an explicit solvent and ion mobility measurements in the gas phase. The observed post-inhibition binding of heparin to the trapped AT/fXa intermediates hints at the likely role played by heparan sulfate in their catabolism.

N-trimethyl chitosan nanoparticles and CSKSSDYQC peptide: N-trimethyl chitosan conjugates enhance the oral bioavailability of gemcitabine to treat breast cancer

Gemcitabine is a nucleoside analogue effective against a number of cancers. However, the full potential of this drug has not been realised, in part due to low oral bioavailability and frequent dosing requirements. This study reports the synthesis, in-vitro, ex-vivo and in-vivo evaluation of trimethyl chitosan (TMC) - CSKSSDYQC (CSK) peptide conjugates capable of enhancing the oral bioavailability of gemcitabine due to the ability to target intestinal goblet cells and promote intestinal cellular uptake. TMC was synthesized by a novel two-step methylation method to improve quanternization and yield. The CSK-TMC conjugates were prepared by ionic gelation to achieve particles sized at 173.6 ± 6.8 nm, zeta potential of +18.5 ± 0.2 mV and entrapment efficiency of 66.4 ± 0.1%, capable of sustained drug release. By encapsulating gemcitabine into CSK-TMC conjugates, an increased amount of drug permeated through porcine intestinal epithelial membranes compared with the unconjugated TMC nanoparticles (NPs). The rate of cellular uptake of drug loaded conjugates into HT29-MTX-E12 intestinal goblet cells, was time- and concentration-dependant. The conjugates underwent active transport associated with adsorptive mediated, clathrin and caveolae mediated endocytosis. In cellular transport studies, drug loaded conjugates had greater drug transport capability compared with drug solution and TMC NPs over the co-cultured Caco-2/HT29-MTX-E12 cell monolayer. The drug loaded conjugates exhibited electrostatic interaction with the intestinal epithelial cells. Both P-glycoprotein (P-gp) and multiple resistance protein-2 (MRP2) efflux affected the cellular transport of the conjugates. Importantly, during the pharmacokinetic studies, the orally administrated drug loaded into TMC NPs showed an improved oral bioavailability of 54.0%, compared with gemcitabine solution of 9.9%. Notable, the CSK-TMC conjugates further improved oral bioavailability to 60.1% and reduced the tumour growth rate in a BALB/c nude mouse model, with a 5.1-fold and 3.3-fold reduction compare with the non-treated group and gemcitabine solution group. Furthermore, no major evidence of toxicity was discernible on histologic studies of selected organs. In conclusion, the presented CSK-TMC conjugates and TMC nanoparticles both significantly improve the oral bioavailability of gemcitabine and have the potential for the treatment of breast cancer.

Complement-coagulation crosstalk on cellular and artificial surfaces

The humoral serine proteases of the complement system and the coagulation system play central roles during the events of an inflammatory response. While the complement system confers immunoprotective and -regulatory functions, the coagulation cascade is responsible to ensure hemostatic maintenance. Although these two systems individually unfold during inflammation, several studies have reported on the "crosstalk" between components of the complement and the coagulation system in the fluid phase. However, both cascades are usually initiated on or in close proximity to foreign or activated surfaces, and there is increasing evidence for interacting complement and coagulation proteins on various superficial areas on endothelium, circulating entities like platelets, leukocytes, microparticles and pathogens, and even on artificial surfaces. This review aims at summarizing these interactions to complete the picture.

The emerging role of coagulation proteases in kidney disease

A role of coagulation proteases in kidney disease beyond their function in normal haemostasis and thrombosis has long been suspected, and studies performed in the past 15 years have provided novel insights into the mechanisms involved. The expression of protease-activated receptors (PARs) in renal cells provides a molecular link between coagulation proteases and renal cell function and revitalizes research evaluating the role of haemostasis regulators in renal disease. Renal cell-specific expression and activity of coagulation proteases, their regulators and their receptors are dynamically altered during disease processes. Furthermore, renal inflammation and tissue remodelling are not only associated, but are causally linked with altered coagulation activation and protease-dependent signalling. Intriguingly, coagulation proteases signal through more than one receptor or induce formation of receptor complexes in a cell-specific manner, emphasizing context specificity. Understanding these cell-specific signalosomes and their regulation in kidney disease is crucial to unravelling the pathophysiological relevance of coagulation regulators in renal disease. In addition, the clinical availability of small molecule targeted anticoagulants as well as the development of PAR antagonists increases the need for in-depth knowledge of the mechanisms through which coagulation proteases might regulate renal physiology.

Selective disruption of heparin and antithrombin-mediated regulation of human factor IX

BACKGROUND

Interaction with antithrombin and heparin regulates distribution, activity, and clearance of factor IXa (FIXa). Hemophilia B prophylaxis targets plasma FIX levels > 1% but neglects extravascular FIX, which colocalizes with antithrombin-heparan sulfate.

OBJECTIVE

Combined mutagenesis of FIX was undertaken to selectively disrupt heparin- and antithrombin-mediated regulation of the protease.

METHODS

Human FIX alanine substitutions in the heparin (K126A and K132A) and antithrombin (R150A) exosites were characterized with regard to coagulant activity, plasma thrombin generation, antithrombin inhibition, and plasma half-life.

RESULTS

Single or combined (K126A/R150A or K132A/R150A) exosite mutations variably reduced coagulant activity relative to wild-type (WT) for FIX (27-91%) and FIXa (25-91%). Double mutation in the heparin exosite (K126A/K132A and K126A/K132A/R150A) markedly reduced coagulant activity (7-21%) and plasma TG. In contrast to coagulant activity, FIX K126A (1.8-fold), R150 (1.6-fold), and K132A/R150A (1.3-fold) supported increased tissue factor-initiated plasma TG, while FIX K132A and K126A/R150A were similar to WT. FIXa K126A/R150A and K132A/R150A (1.5-fold) demonstrated significantly increased FIXa-initiated TG, while FIXa K132A, R150A, and K126A (0.8-0.9-fold) were similar to WT. Dual mutations in the heparin exosite or combined mutations in both exosites synergistically reduced the inhibition rate for antithrombin-heparin. The half-life of FIXa WT in FIX-deficient plasma was remarkably lengthy (40.9 ±1.4 min) and further prolonged for FIXa R150A, K126A/R150A, and K132A/R150A (> 2 h).

CONCLUSION

Selective disruption of exosite-mediated regulation by heparin and antithrombin can be achieved with preserved or enhanced thrombin generation capacity. These proteins should demonstrate enhanced therapeutic efficacy for hemophilia B.

Syndecan-3 and TFPI colocalize on the surface of endothelial-, smooth muscle-, and cancer cells

Background

Tissue factor (TF) pathway inhibitor (TFPI) exists in two isoforms; TFPIα and TFPIβ. Both isoforms are cell surface attached mainly through glycosylphosphatidylinositol (GPI) anchors. TFPIα has also been proposed to bind other surface molecules, like glycosaminoglycans (GAGs). Cell surface TFPIβ has been shown to exert higher anticoagulant activity than TFPIα, suggesting alternative functions for TFPIα. Further characterization and search for novel TFPI binding partners is crucial to completely understand the biological functions of cell associated TFPI.

Methods and Results

Potential association of TFPI to heparan sulphate (HS) proteoglycans in the syndecan family were evaluated by knock down studies and flow cytometry analysis. Cell surface colocalization was assessed by confocal microscopy, and native PAGE or immunoprecipitation followed by Western blotting was used to test for protein interaction. Heparanase was used to enzymatically degrade cell surface HS GAGs. Anticoagulant potential was evaluated using a factor Xa (FXa) activity assay. Knock down of syndecan-3 in endothelial,- smooth muscle- and breast cancer cells reduced the TFPI surface levels by 20-50%, and an association of TFPIα to syndecan-3 on the cell surface was demonstrated. Western blotting indicated that TFPIα was found in complex with syndecan-3. The TFPI bound to syndecan-3 did not inhibit the FXa generation. Removal of HS GAGs did not release TFPI antigen from the cells.

Conclusions

We demonstrated an association between TFPIα and syndecan-3 in vascular cells and in cancer cells, which did not appear to depend on HS GAGs. No anticoagulant activity was detected for the TFPI associated with syndecan-3, which may indicate coagulation independent functions for this cell associated TFPI pool. This will, however, require further investigation.

Heparan sulfate proteoglycans mediate factor XIIa binding to the cell surface

Hageman factor (FXIIa) initiates the intrinsic coagulation pathway and triggers the kallikrein-kinin and the complement systems. In addition, it functions as a growth factor by expressing promitogenic activities toward several cell types. FXIIa binds to the cell surface via a number of structurally unrelated surface receptors; however, the underlying mechanisms are not yet fully understood. Here, we demonstrate that FXIIa utilizes cell membrane-bound glycosaminoglycans to interact with the cell surface of human lung fibroblasts (HLF). The combination of enzymatic, inhibitory, and overexpression approaches identified a heparan sulfate (HS) component of proteoglycans as an important determinant of the FXIIa binding capacity of HLF. Moreover, cell-free assays and competition experiments revealed preferential binding of FXIIa to HS and heparin over dextran sulfate, dermatan sulfate, and chondroitin sulfate A and C. Finally, we demonstrate that fibroblasts isolated from the lungs of the patients suffering from idiopathic pulmonary fibrosis (IPF) exhibit enhanced FXIIa binding capacity. Increased sulfation of HS resulting from elevated HS 6-O-sulfotransferase-1 expression in IPF HLF accounted, in part, for this phenomenon. Application of RNA interference technology and inhibitors of intracellular sulfation revealed the cooperative action of cell surface-associated HS and urokinase-type plasminogen activator receptor in the accumulation of FXIIa on the cell surface of IPF HLF. Moreover, FXIIa stimulated IPF HLF migration, which was abrogated by pretreatment of cells with heparinase I. Collectively, our study uncovers a novel role of HS-type glycosaminoglycans in a local accumulation of FXIIa on the cell membrane. The enhanced association of FXIIa with IPF HLF suggests its contribution to fibrogenesis.

Heparanase-A Link between Coagulation, Angiogenesis, and Cancer

Heparanase that was cloned from and is abundant in the placenta is implicated in cell invasion, tumor metastasis, and angiogenesis. Recently we have demonstrated that heparanase may also affect the hemostatic system in a non-enzymatic manner. Heparanase was shown to up-regulate tissue factor (TF) expression and interact with tissue factor pathway inhibitor (TFPI) on the cell surface, leading to dissociation of TFPI from the cell membrane of endothelial and tumor cells, resulting in increased cell surface coagulation activity. More recently, we have shown that heparanase directly enhances TF activity, resulting in increased factor Xa production and activation of the coagulation system. Data indicate increased levels and possible involvement of heparanase in vascular complications in pregnancy. Taking into account the prometastatic and proangiogenic functions of heparanase, overexpression in human malignancies, and abundance in platelets and placenta, its involvement in the coagulation machinery is an intriguing novel arena for further research.

Heparanase procoagulant effects and inhibition by heparins

Heparanase is an endo-beta-D-glucuronidase capable of cleaving heparan sulfate (HS) side chains of heparan sulfate proteoglycans (HSPG) on cell surfaces and the extracellular matrix, activity that is strongly implicated in tumor metastasis and angiogenesis. Evidence was provided that heparanase over-expression in cancer cells results in a marked increase in tissue factor (TF) levels. Likewise, TF was induced by exogenous addition of recombinant heparanase to tumor cells and primary endothelial cells, induction that was mediated by p38 phosphorylation and correlated with enhanced procoagulant activity. TF induction was further confirmed in heparanase over-expressing transgenic mice and correlated with heparanase expression levels in leukemia patients. Heparanase was also found to be involved in the regulation of tissue factor pathway inhibitor (TFPI). A physical interaction between heparanase and TFPI was demonstrated, suggesting a mechanism by which secreted heparanase interacts with TFPI on the cell surface, leading to dissociation of TFPI from the cell membrane and increased coagulation activity, thus further supporting the local pro-thrombotic function of heparanase. Data indicate a possible involvement of heparanase in early miscarriages and point to a regulatory effect on TFPI and TFPI-2 in trophoblasts. As heparins are strong inhibitor of heparanase, in view of the effect of heparanase on TF, the role of heparins anticoagulant-activity may potentially be expanded. Taking into account the pro-metastatic and pro-angiogenic functions of heparanase, its over-expression in human malignancies and abundance in platelets, its involvement in the coagulation machinery is an intriguing novel arena for further research.

Heparanase coagulation and cancer progression

Heparanase is an endo-beta-D-glucuronidase capable of cleaving heparan sulphate (HS) side chains of heparan sulphate proteoglycans on cell surfaces and the extracellular matrix; activity that is strongly implicated in tumour metastasis and angiogenesis. It has been shown that heparanase overexpression in human leukaemia, glioma and breast carcinoma cells results in a marked increase in tissue factor (TF) levels. In addition, TF was induced by exogenous addition of recombinant heparanase to tumour cells and primary endothelial cells; induction that was mediated by p38 phosphorylation and correlated with enhanced procoagulant activity. TF induction was further confirmed in transgenic mice overexpressing heparanase, and correlated with heparanase expression levels in leukaemia patients. Heparanase was also found to be involved in the regulation of tissue factor pathway inhibitor (TFPI). It has been shown that heparanase overexpression or exogenous addition induces a two- to three-fold increase in TFPI expression. Similarly, heparanase stimulated accumulation of TFPI in the cell culture medium. However, extracellular accumulation exceeded the observed increase in TFPI at the protein level, and appeared to be independent of HS and heparanase enzymatic activity. Instead, a physical interaction between heparanase and TFPI was demonstrated, suggesting a mechanism by which secreted heparanase interacts with TFPI on the cell surface, leading to dissociation of TFPI from the cell membrane and increased coagulation activity, thus further supporting the local prothrombotic function of heparanase. As heparins are strong inhibitors of heparanase, in view of the effect of heparanase on the TF/TFPI pathway, the role of anticoagulant activity of heparin may potentially be expanded. Taking into account the prometastatic and pro-angiogenic functions of heparanase, its overexpression in human malignancies and abundance in platelets, its involvement in the coagulation machinery is an intriguing novel arena for further research.

Host defense peptides in wound healing

Host defense peptides are effector molecules of the innate immune system. They show broad antimicrobial action against gram-positive and -negative bacteria, and they likely play a key role in activating and mediating the innate as well as adaptive immune response in infection and inflammation. These features make them of high interest for wound healing research. Non-healing and infected wounds are a major problem in patient care and health care spending. Increasing infection rates, growing bacterial resistance to common antibiotics, and the lack of effective therapeutic options for the treatment of problematic wounds emphasize the need for new approaches in therapy and pathophysiologic understanding. This review focuses on the current knowledge of host defense peptides affecting wound healing and infection. We discuss the current data and highlight the potential future developments in this field of research.

The endothelial glycocalyx: composition, functions, and visualization

This review aims at presenting state-of-the-art knowledge on the composition and functions of the endothelial glycocalyx. The endothelial glycocalyx is a network of membrane-bound proteoglycans and glycoproteins, covering the endothelium luminally. Both endothelium- and plasma-derived soluble molecules integrate into this mesh. Over the past decade, insight has been gained into the role of the glycocalyx in vascular physiology and pathology, including mechanotransduction, hemostasis, signaling, and blood cell–vessel wall interactions. The contribution of the glycocalyx to diabetes, ischemia/reperfusion, and atherosclerosis is also reviewed. Experimental data from the micro- and macrocirculation alludes at a vasculoprotective role for the glycocalyx. Assessing this possible role of the endothelial glycocalyx requires reliable visualization of this delicate layer, which is a great challenge. An overview is given of the various ways in which the endothelial glycocalyx has been visualized up to now, including first data from two-photon microscopic imaging.

Endothelial cell protection in xenotransplantation: looking after a key player in rejection

The endothelium, as an organ at the interface between the intra- and extravascular space, actively participates in maintaining an anti-inflammatory and anti-coagulant environment under physiological conditions. Severe humoral as well as cellular rejection responses, which accompany cross-species transplantation of vascularized organs as well as ischemia/reperfusion injury, primarily target the endothelium and disrupt this delicate balance. Activation of pro-inflammatory and pro-coagulant pathways often lead to irreversible injury not only of the endothelial layer but also of the entire graft, with ensuing rejection. This review focuses on strategies targeted at protecting the endothelium from such damaging effects, ranging from genetic manipulation of the donor organ to soluble, as well as membrane-targeted, protective strategies.

Antimicrobial peptides

Antimicrobial peptides (AMPs) are small molecular weight proteins with broad spectrum antimicrobial activity against bacteria, viruses, and fungi. These evolutionarily conserved peptides are usually positively charged and have both a hydrophobic and hydrophilic side that enables the molecule to be soluble in aqueous environments yet also enter lipid-rich membranes. Once in a target microbial membrane, the peptide kills target cells through diverse mechanisms. Cathelicidins and defensins are major groups of epidermal AMPs. Decreased levels of these peptides have been noted for patients with atopic dermatitis and Kostmann's syndrome, a congenital neutropenia. In addition to important antimicrobial properties, growing evidence indicates that AMPs alter the host immune response through receptor-dependent interactions. AMPs have been shown to be important in such diverse functions as angiogenesis, wound healing, and chemotaxis. As our knowledge of AMP biology expands, the precise role and relevance of these peptides will be better elucidated.

Vascular endothelial tissue factor pathway inhibitor kinetics in culture following exposure to DX-9065a--a selective and direct factor Xa inhibitor

BACKGROUND

Tissue factor (TF), a membrane-bound glycoprotein that initiates blood coagulation by allosteric activation of factor (f) VII, is regulated predominantly by tissue factor pathway inhibitor (TFPI). Because vascular endothelial cells synthesize and constitutively secrete TFPI and fXa may directly influence its cellular clearance, we sought to determine the effects of DX-9065a, a direct and selective fXa inhibitor, on TFPI kinetics in culture.

METHODS/RESULTS

Human umbilical vein endothelial cells were grown to confluence and incubated with unfractionated heparin (1.0 U/mL), enoxaparin (1.5 U/mL), or DX-9065a at low (10 ng/ml), moderate (30 ng/ml), or high (90 ng/ml) concentrations. Compared to control, increases in TFPI were seen with both unfractionated heparin (182% higher, p < 0.001) and enoxaparin (194% higher, p < 0.001). Low concentration DX-9065a did not increase TFPI levels above control (0.8% higher, p = 0.91). In contrast, moderate and high concentrations produced 124% higher (p < 0.001) and 198% higher (p < 0.001) TFPI concentrations than control, respectively.

CONCLUSIONS

DX-9065a increases vascular endothelial cell TFPI concentrations in human tissue culture. Although the mechanism has yet to be established, decreased fXa availability may limit fXa-TFPI complex formation and its subsequent cellular uptake. Whether increased surface TFPI contributes to the overall anticoagulant profile of DX-9065a will require further investigation.

Locally targeted cytoprotection with dextran sulfate attenuates experimental porcine myocardial ischaemia/reperfusion injury

AIMS

Intravascular inflammatory events during ischaemia/reperfusion injury following coronary angioplasty alter and denudate the endothelium of its natural anticoagulant heparan sulfate proteoglycan (HSPG) layer, contributing to myocardial tissue damage. We propose that locally targeted cytoprotection of ischaemic myocardium with the glycosaminoglycan analogue dextran sulfate (DXS, MW 5000) may protect damaged tissue from reperfusion injury by functional restoration of HSPG.

METHODS AND RESULTS

In a closed chest porcine model of acute myocardial ischaemia/reperfusion injury (60 min ischaemia, 120 min reperfusion), DXS was administered intracoronarily into the area at risk 5 min prior to reperfusion. Despite similar areas at risk in both groups (39+/-8% and 42+/-9% of left ventricular mass), DXS significantly decreased myocardial infarct size from 61+/-12% of the area at risk for vehicle controls to 39+/-14%. Cardioprotection correlated with reduced cardiac enzyme release creatine kinase (CK-MB, troponin-I). DXS abrogated myocardial complement deposition and substantially decreased vascular expression of pro-coagulant tissue factor in ischaemic myocardium. DXS binding, detected using fluorescein-labelled agent, localized to ischaemically damaged blood vessels/myocardium and correlated with reduced vascular staining of HSPG.

CONCLUSION

The significant cardioprotection obtained through targeted cytoprotection of ischaemic tissue prior to reperfusion in this model of acute myocardial infarction suggests a possible role for the local modulation of vascular inflammation by glycosaminoglycan analogues as a novel therapy to reduce reperfusion injury.

Regulation of tissue factor-induced signaling by endogenous and recombinant tissue factor pathway inhibitor 1

Tissue factor (TF) triggers upstream coagulation signaling via the activation of protease-activated receptors (PARs) of relevance for inflammation and angiogenesis. TF pathway inhibitor 1 (TFPI-1) is the physiologic inhibitor of TF-initiated coagulation, but its role in regulating TF signaling is poorly understood. Here, we demonstrate that endogenous, endothelial cell-expressed TFPI-1 controls TF-mediated signaling through PARs. In endothelial cells transduced with TF to mimic exacerbated TF expression in vascular cells, TF-VIIa-Xa ternary complex-dependent activation of PAR1 remained intact when TF-mediated Xa generation was blocked with 2.5 to 5 nM recombinant TFPI-1 (rTFPI-1). Concordantly, inhibition of signaling in PAR1-expressing Chinese hamster ovary (CHO) cells required about 30-fold higher rTFPI-1 concentrations than necessary for anticoagulation. Studies with proteoglycan-deficient CHO cells document a crucial role of accessory receptors in supporting the anticoagulant and antisignaling activities of rTFPI-1. Coexpression of PAR2 with TF enhanced rTFPI-mediated inhibition of TF-VIIa-Xa-mediated PAR1 signaling, suggesting an unexpected role of PAR2 in the inhibitory control of TF signaling. These experiments are of potential significance for the limited therapeutic benefit of rTFPI-1 in systemic inflammation and recommend caution in using anticoagulant potency as a measure to predict how efficacious TF-directed inhibitors block cell signaling during initiation of coagulation.

Epigenetic loss of the familial tumor-suppressor gene exostosin-1 (EXT1) disrupts heparan sulfate synthesis in cancer cells

Germline mutations in the Exostoses-1 gene (EXT1) are found in hereditary multiple exostoses syndrome, which is characterized by the formation of osteochondromas and an increased risk of chondrosarcomas and osteosarcomas. However, despite its putative tumor-suppressor function, little is known of the contribution of EXT1 to human sporadic malignancies. Here, we report that EXT1 function is abrogated in human cancer cells by transcriptional silencing associated with CpG island promoter hypermethylation. We also show that, at the biochemical and cellular levels, the epigenetic inactivation of EXT1, a glycosyltransferase, leads to the loss of heparan sulfate (HS) synthesis. Reduced HS production can be reversed by the use of a DNA demethylating agent. Furthermore, the re-introduction of EXT1 into cancer cell lines displaying methylation-dependent silencing of EXT1 induces tumor-suppressor-like features, e.g. reduced colony formation density and tumor growth in nude mouse xenograft models. Screening a large collection of human cancer cell lines (n=79) and primary tumors (n=454) from different cell types, we found that EXT1 CpG island hypermethylation was common in leukemia, especially acute promyelocytic leukemia and acute lymphoblastic leukemia, and non-melanoma skin cancer. These findings highlight the importance of EXT1 epigenetic inactivation, leading to an abrogation of HS biosynthesis, in the processes of tumor onset and progression.

Effect of bovine lactoferricin on enteropathogenic Yersinia adhesion and invasion in HEp-2 cells

Bovine lactoferricin, a pepsin-generated antimicrobial peptide from bovine lactoferrin active against a wide range of bacteria, was tested for its ability to influence the adhesion and invasion of Yersinia enterocolitica and Yersinia pseudotuberculosis in HEp-2 cells. The addition of non-cytotoxic and non-bactericidal concentrations of lactoferricin to cell monolayers before infection, under different bacterial growth experimental conditions, was ineffective or resulted in about a 10-fold increase in bacterial adhesion, whereas, in bacteria grown in conditions allowing maximal inv gene expression, a 10-fold inhibition of cell invasion by lactoferricin was observed. To confirm that the anti-invasive activity of lactoferricin was exerted against invasin-mediated bacterial entry, experiments were also performed utilizing Escherichia coli strain HB101 (pRI203), harbouring the inv gene from Y. pseudotuberculosis, which allows penetration of mammalian cells. Under these experimental conditions, lactoferricin was able to inhibit bacterial entry into epithelial cells, demonstrating that this peptide acts on inv-mediated Yersinia species invasion. As the inv gene product is the most important virulence factor in enteropathogenic Yersinia, being responsible for bacterial adherence and penetration within epithelial cells of the intestinal lumen and for the subsequent colonization of regional lymph nodes, these data provide additional information on the protective role of lactoferricin against bacterial infection.

The Significance of Circulating Factor IXa in Blood

The presence of activation peptides (AP) of the vitamin K-dependent proteins in the phlebotomy blood of human subjects suggests that active serine proteases may circulate in blood as well. The goal of the current study was to evaluate the influence of trace amounts of key coagulation proteases on tissue factor-independent thrombin generation using three models of coagulation. With procoagulants and select coagulation inhibitors at mean physiological concentrations, concentrations of factor IXa, factor Xa, and thrombin were set either equal to those of their AP or to values that would result based upon the rates of AP/enzyme generation and steady state enzyme inhibition. In the latter case, numerical simulation predicts that sufficient thrombin to produce a solid clot would be generated in approximately 2 min. Empirical data from the synthetic plasma suggest clotting times of 3-5 min, which are similar to that observed in contact pathway-inhibited whole blood (4.3 min) initiated with the same concentrations of factors IXa and Xa and thrombin. Numerical simulations performed with the concentrations of two of the enzymes held constant and one varied suggest that the presence of any pair of enzymes is sufficient to yield rapid clot formation. Modeling of states (numerical simulation and whole blood) where only one circulating protease is present at steady state concentration shows significant thrombin generation only for factor IXa. The addition of factor Xa and thrombin has little effect (if any) on thrombin generation induced by factor IXa alone. These data indicate that 1) concentrations of active coagulation enzymes circulating in vivo are significantly lower than can be predicted from the concentrations of their AP, and 2) expected trace amounts of factor IXa can trigger thrombin generation in the absence of tissue factor.

Heparanase Degrades Syndecan-1 and Perlecan Heparan Sulfate

Heparanase (HPSE-1) is involved in the degradation of both cell-surface and extracellular matrix (ECM) heparan sulfate (HS) in normal and neoplastic tissues. Degradation of heparan sulfate proteoglycans (HSPG) in mammalian cells is dependent upon the enzymatic activity of HPSE-1, an endo-beta-d-glucuronidase, which cleaves HS using a specific endoglycosidic hydrolysis rather than an eliminase type of action. Elevated HPSE-1 levels are associated with metastatic cancers, directly implicating HPSE-1 in tumor progression. The mechanism of HPSE-1 action to promote tumor progression may involve multiple substrates because HS is present on both cell-surface and ECM proteoglycans. However, the specific targets of HPSE-1 action are not known. Of particular interest is the relationship between HPSE-1 and HSPG, known for their involvement in tumor progression. Syndecan-1, an HSPG, is ubiquitously expressed at the cell surface, and its role in cancer progression may depend upon its degradation. Conversely, another HSPG, perlecan, is an important component of basement membranes and ECM, which can promote invasive behavior. Down-regulation of perlecan expression suppresses the invasive behavior of neoplastic cells in vitro and inhibits tumor growth and angiogenesis in vivo. In this work we demonstrate the following. 1) HPSE-1 cleaves HS present on the cell surface of metastatic melanoma cells. 2) HPSE-1 specifically degrades HS chains of purified syndecan-1 or perlecan HS. 3) Syndecan-1 does not directly inhibit HPSE-1 enzymatic activity. 4) The presence of exogenous syndecan-1 inhibits HPSE-1-mediated invasive behavior of melanoma cells by in vitro chemoinvasion assays. 5) Inhibition of HPSE-1-induced invasion requires syndecan-1 HS chains. These results demonstrate that cell-surface syndecan-1 and ECM perlecan are degradative targets of HPSE-1, and syndecan-1 regulates HPSE-1 biological activity. This suggest that expression of syndecan-1 on the melanoma cell surface and its degradation by HPSE-1 are important determinants in the control of tumor cell invasion and metastasis.

Glycosyl phosphatidylinositol anchorage of tissue factor pathway inhibitor

BACKGROUND

The endothelium is a major source of tissue factor pathway inhibitor (TFPI), the endogenous regulator of TF-induced coagulation, and a significant proportion of the expressed TFPI remains associated with the endothelial surface.

METHODS AND RESULTS

Phosphatidylinositol-specific phospholipase C (PI-PLC) treatment reduced TFPI at the surface of cultured endothelial cells by approximately 80%, and at least a portion of the TFPI released by PI-PLC contained an intrinsic glycosylphosphatidylinositol (GPI) anchor that is recognized by anti-crossreactive determinant antibodies. Endothelial cells express both of the alternatively spliced forms of TFPI mRNA at a ratio of TFPIbeta/TFPIalpha mRNA of approximately 0.1 to 0.2. In Chinese hamster ovary (CHO) cells, TFPIalpha is predominantly secreted, whereas TFPIbeta is a GPI-anchored membrane protein. Like TFPIbeta, the small proportion of the TFPIalpha expressed by CHO cells that remains surface associated is also released by PI-PLC treatment, suggesting that it is bound to a separate GPI-anchored protein(s) at the surface of the cells.

CONCLUSIONS

Both direct (TFPIbeta) and indirect (TFPIalpha) GPI-mediated membrane anchorage is involved in localizing TFPI to the surface of cells.

Heparin-interacting sites of bovine lactoferrin are involved in anti-adenovirus activity

Lactoferrin, a member of the transferrin family of approximately 80 kDa, consists of a single polypeptide chain folded in two symmetric, globular lobes (N- and C-lobes), each able to bind one ferric ion. This glycoprotein, found in physiological fluids of mammals, plays an important role in immune regulation and in defense mechanisms against bacteria, fungi, parasites, and viruses. Although the antiviral activity of lactoferrin is one of the major biological functions of such protein, the mechanism of action is still under debate. We have investigated both the role of tryptic fragments of bovine lactoferrin and the mechanism of lactoferrin antiviral effect toward adenovirus infection in HEp-2 cells. The results obtained demonstrated that the anti-adenovirus activity of lactoferrin is mediated by the N-terminal half of the protein as the N-lobe was able to inhibit adenovirus infection, even if at lower extent than undigested lactoferrin, whereas C-lobe was ineffective. The results also showed that the anti-adenovirus action of lactoferrin and of its N-terminal peptide lactoferricin took place on virus attachment to cell membrane, mainly through competition for common glycosaminoglycan receptors. The data provide evidence that the anti-adenovirus activity of lactoferrin is mediated mainly by the cluster of positive charges at the N-terminus of whole molecule and that the N-terminal peptide lactoferricin alone is sufficient to prevent infection.

Heparanase and tumor invasion patterns in human oral squamous cell carcinoma xenografts

The role of heparanase, an endo-beta-glucuronidase specifically degrading heparan sulfate (HS) glycosaminoglycans, in the mechanism of cancer cell invasion was investigated. Three human oral squamous cell carcinoma (SCC) cell lines (i.e., HSC-2, HSC-3 and LMF4), exhibiting various degrees of invasiveness to their surrounding tissues, were xenografted to the tongue of SCID mice in order to establish experimental cancer foci. Cancer cells and their surrounding tissues were examined for the expression of heparanase mRNA by an in situ hybridization technique, and for various basement membrane (BM)-associated molecules (i.e., perlecan, laminins and type IV collagen) by immunohistochemical procedures. BM structures surrounding cancer tissues were also examined by electron microscopy. Increasing levels of heparanase mRNA expression were observed with the progression of cancer invasiveness, as manifested by the destruction of BM structures. Enhanced heparanase enzyme activities in cancer tissues with more invasive properties were demonstrated by the disappearance of HS glycosaminoglycans in the face of retained HS proteoglycan core proteins. These results demonstrated a positive correlation between the heparanase enzyme activities and the invasiveness of human oral SCC. The roles of heparanase in cancer cell invasion were not precisely clarified by the present morphological study, but the enhanced heparanase activity in an early phase of BM destruction by cancer cells suggested the participation of this enzyme from the early phase of cancer invasion.

The activity of tissue factor pathway inhibitor in experimental models of superantigen-induced shock and polymicrobial intra-abdominal sepsis

OBJECTIVES

To study recombinant human tissue factor pathway inhibitor (rhTFPI) in a superantigen-induced shock model and in a cecal ligation and puncture (CLP) model of peritonitis in mice.

DESIGN

Prospective, randomized, experimental study.

SETTING

An experimental animal research laboratory.

SUBJECTS

Eighty BALB/c mice for the superantigen model, and 56 BALB/c mice for the CLP model.

INTERVENTIONS

In the superantigen-induced shock model, animals received rhTFPI (350 mg/kg) subcutaneously every 12 hrs (n = 30) or saline control (n = 30) for 60 hrs after staphylococcal enterotoxin B (SEB; 10 microg iv) and a sublethal dose of E. coli 0111:B4 lipopolysaccharide (LPS; 75 microg ip). Control groups received SEB alone (n = 10) and LPS alone (n = 10). In the CLP model, rhTFPI or saline was given every 8 hrs for 48 hrs by using a 21-gauge needle (n = 9) or 23-gauge needle (n = 14) for CLP. A sham surgery control group (n = 10) was also included.

MEASUREMENTS AND MAIN RESULTS

There was 0% mortality in the SEB and LPS control groups. The mortality rate was 64% in the saline control group that received both SEB and LPS (19 of 30), whereas the rhTFPI- treated animals had a mortality rate of 20% (6 of 30; p < .01). The rhTFPI-treated group had significantly lower interleukin-6 levels (61.8 +/- 41 pg/mL vs. 285 +/- 63 pg/mL; p < .05) than the control group but no differences in tumor necrosis factor-alpha or interferon-gamma levels. In the CLP experiment, rhTFPI-treated animals did not have any survival advantage over the control group after the large-bore (21-gauge) needle puncture. The rhTFPI group had significantly improved 7-day mortality rate after CLP with the small-bore needle (23-gauge; 21.4% [rhTFPI] vs. 71.4% [control], p < .01). Plasma LPS, interleukin-6, interferon-gamma, and tumor necrosis factor-alpha levels were unchanged by rhTFPI treatment, but significantly reduced LPS (p = .006) and IFNgamma (p = .001) levels were found in the peritoneal fluid.

CONCLUSIONS

Tissue factor pathway inhibitor significantly improves the mortality rate in models of superantigen-induced shock and polymicrobial intra-abdominal infection, supporting its potential use in clinical trials for septic shock.

Disseminated intravascular coagulation and purpura fulminans secondary to infection

Infection is one of the commonest causes of disseminated intravascular coagulation (DIC). DIC is a complex disorder that results from an imbalance of the pro- and anticoagulant regulatory pathways. This chapter will explain the cellular and molecular basis of the disorder and consider the rationale behind current and experimental treatment strategies.

Proteoglycans and pattern formation: sugar biochemistry meets developmental genetics

While it has been long appreciated that sugar-modified proteins coat the cell surface, their functions are poorly understood. Here, I describe recent genetic studies that demonstrate that one class of sugar-modified proteins, cell-surface proteoglycans, play crucial roles in morphogenesis, growth regulation and tumor suppression. Mutations that affect individual proteoglycans or the enzymes required for glycosaminoglycan synthesis regulate Wingless and Decapentaplegic signaling in Drosophila, and body size in mice and humans. Compromising proteoglycan function is also associated with the development of Wilm's tumors and hereditary multiple exostoses. In this review, these biological findings are placed in the context of proteoglycan biochemistry and molecular function.

Recombinant full-length tissue factor pathway inhibitor fails to bind to the cell surface: implications for catabolism in vitro and in vivo

Tissue factor pathway inhibitor (TFPI) plays a key role in the regulation of tissue factor-initiated blood coagulation secondary to loss of the integrity of the blood vessel wall. TFPI is a naturally occurring Kunitz-type protease inhibitor that inhibits coagulation factor Xa and, in a factor Xa-dependent manner, mediates feedback inhibition of the factor VIIa/tissuefactor catalytic complex. In vivo full-length TFPI is thought to be primarily bound to the vascular endothelium and the high affinity binding requires an intact carboxy terminus. Here we describe a full-length TFPI molecule, expressed in mouse C127 cells (TFPIC127), which exhibits virtually no cellular binding yet contains the intact carboxy terminus. This TFPI (TFPIC127) is neither internalized nor degraded via the TFPI endocytic receptor, LDL-receptor–related protein. Pharmacokinetic studies of TFPIC127 in vivo demonstrate a 10-fold prolongation in the plasma half-life, compared with that of bacterial recombinant TFPI.

Heparan sulfate glycosaminoglycans are involved in adenovirus type 5 and 2-host cell interactions

Gene therapy vectors derived from subgroup C adenoviruses of the serotype 5 (Ad5) and 2 (Ad2) resulted in inefficient infection of well differentiated respiratory cells, both in vitro and in vivo. The level of expression and localization of the primary receptor for Ad5 and Ad2, termed CAR, do not completely explain why the infection efficiency varies greatly in different experimental conditions. The possibility that additional receptors like proteoglycans are involved in the infection of Ad5 and Ad2 was investigated, because several pathogenic microorganisms use heparan sulfate-glycosaminoglycans (HS-GAGs) as coreceptors for multistep attachment to target cells. The HS-GAG analog heparin decreased Ad5- and Ad2-mediated infection and binding starting from the concentration of 0.1 microgram/ml, up to a maximum of 50%. A similar reduction in Ad5 binding and infection was obtained by treatment of cells with heparin lyases I, II, and III but not with chondroitin ABC lyase. The effect of heparin on Ad5 binding has not been observed in surface GAG-defective Raji cells and after treating A549 cells with heparin lyases I, II,and III. The binding of Ad5 was completely abolished when both CAR was blocked with RmcB antibody and HS-GAGs were competitively inhibited by heparin. Parallel experiments demonstrate that HS-GAGs are irrelevant to binding and infection of the subgroup B adenovirus type 3. Collectively, these results demonstrate for the first time that HS-GAGs expressed on the cell surface are involved in the binding of Ad5 and Ad2 to host cells.

Reversible regulation of tissue factor-induced coagulation by glycosyl phosphatidylinositol-anchored tissue factor pathway inhibitor

Endothelial and tumor cells synthesize tissue factor pathway inhibitor (TFPI-1), which regulates tissue factor (TF) function by TF. VIIa. Xa. TFPI-1 quaternary complex formation (where VIIa and Xa are coagulation factors) and by translocation of these complexes into glycosphingolipid-rich microdomains of the cell membrane. Recombinant TFPI-1 added exogenously to cells is targeted to a degradation pathway. This study analyzes whether quaternary complex formation with endogenous TFPI-1 results also in internalization and degradation. We demonstrate that endogenous TFPI-1 and recombinant TFPI-1 differ in their distribution on the cell surface. Recombinant TFPI-1 is found in phospholipid- and glycosphingolipid-rich membrane domains, whereas endogenous TFPI-1 preferentially localizes to glycosphingolipid-rich microdomains. On quaternary complex formation, endogenous TFPI-1 remains protease sensitive and accessible for antibodies on intact cells, demonstrating that it is not appreciably internalized. Rather, regulation of TF by TFPI-1 is restored within 12 hours, consistent with dissociation of quaternary complexes on the cell surface. Endogenous TFPI-1 can be released from the cell surface by phospholipase treatment, indicating that TFPI-1 either is a glycosyl phosphatidylinositol (GPI)-anchored protein or binds to a GPI-linked receptor. We demonstrate that expression of a recombinant GPI-anchored form of TFPI-1 targets TF. VIIa complexes to glycosphingolipid-rich membrane fractions. Thus, GPI anchoring of TFPI-1 is sufficient for regulation of TF. VIIa complex function by a pathway of reversible inhibition rather than internalization and degradation.

Human heparanase. Purification, characterization, cloning, and expression

Heparan sulfate and heparan sulfate proteoglycans are present in the extracellular matrix as well as on the external cell surface. They bind various molecules such as growth factors and cytokines and modulate the biological functions of binding proteins. Heparan sulfate proteoglycans are also important structural components of the basement membrane. Heparanase is an endo-beta-D-glucuronidase capable of cleaving heparan sulfate and has been implicated in inflammation and tumor angiogenesis and metastasis. In this study, we report the purification of a human heparanase from an SV40-transformed embryonic fibroblast cell line WI38/VA13 by four sequential column chromatographies. The activity was measured by high speed gel permeation chromatography of the degradation products of fluorescein isothiocyanate-labeled heparan sulfate. The enzyme was purified to homogeneity, yielding a peptide with an apparent molecular mass of 50 kDa when analyzed by SDS-polyacrylamide gel electrophoresis. Using the amino acid sequences of the N-terminal and internal heparanase peptides, a cDNA coding for human heparanase was cloned. NIH3T3 and COS-7 cells stably transfected with pBK-CMV expression vectors containing the heparanase cDNA showed high heparanase activities. The homology search revealed that no homologous protein had been reported.

A kinetic analysis of the interaction of human recombinant tissue factor pathway inhibitor with factor Xa utilizing and immunoassay and the effect of antithrombin III/heparin on the complex formation

We have recently shown that a complex formation of tissue factor pathway inhibitor (TFPI) and factor Xa (Xa) promotes a clearance of proteoglycans-associated TFPI. In the current studies, the interaction between human recombinant TFPI (h-rTFPI) and Xa were kinetically analyzed by utilizing both a protease inhibitor, p-(amidophenyl) methanesulfonyl fluoride hydrochloride, and a specific enzyme-linked immunosorbent assay for the complex of h-rTFPI with Xa. We further investigated the effect of antithrombin III on the complex formation between h-rTFPI and Xa. We found that the h-rTFPI/Xa complex formed in a time-dependent manner: the second-order rate constant (K1) for the complex formation was calculated to be 0.86x10(6) M(-1)s(-1). The addition of antithrombin III to the h-rTFPI solution modestly reduced the rate of the complex formation between h-rTFPI and Xa. Heparin strikingly enhanced antithrombin III's inhibition of Xa and resulted in complete abrogation of the complex formation between h-rTFPI and Xa in the absence or presence of acidic phospholipids. Furthermore, antithrombin III induced dissociation of the preformed h-rTFPI/Xa complex in the presence of heparin. These results suggest that in the presence of heparin, antithrombin III interferes with the catabolism of TFPI mediated via Xa.