Heparanase activity in cultured endothelial cells

Targeting the "sweet spot" in septic shock - A perspective on the endothelial glycocalyx regulating proteins Heparanase-1 and -2

Sepsis is a life-threatening syndrome caused by a pathological host response to an infection that eventually, if uncontrolled, leads to septic shock and ultimately, death. In sepsis, a massive aggregation of pathogen-associated molecular patterns (PAMPs) and damage-associated molecular patterns (DAMPs) cause a cytokine storm. The endothelial glycocalyx (eGC) is a gel like layer on the luminal side of the endothelium that consists of proteoglycans, glycosaminoglycans (GAG) and plasma proteins. It is synthesized by endothelial cells and plays an active role in the regulation of inflammation, permeability, and coagulation. In sepsis, early and profound injury of the eGC is observed and circulating eGC components correlate directly with clinical severity and outcome. The activity of the heparan sulfate (HS) specific glucuronidase Heparanase-1 (Hpa-1) is elevated in sepsis, resulting in shedding of heparan sulfate (HS), a main GAG of the eGC. HS induces endothelial barrier breakdown and accelerates systemic inflammation. Lipopolysaccharide (LPS), a PAMP mainly found on the surface of gram-negative bacteria, activates TLR-4, which results in cytokine production and further activation of Hpa-1. Hpa-1 shed HS fragments act as DAMPs themselves, leading to a vicious cycle of inflammation and end-organ dysfunction such as septic cardiomyopathy and encephalopathy. Recently, Hpa-1's natural antagonist, Heparanase-2 (Hpa-2) has been identified. It has no intrinsic enzymatic activity but instead acts by reducing inflammation. Hpa-2 levels are reduced in septic mice and patients, leading to an acquired imbalance of Hpa-1 and Hpa-2 paving the road towards a therapeutic intervention. Recently, the synthetic antimicrobial peptide 19-2.5 was described as a promising therapy protecting the eGC by inhibition of Hpa-1 activity and HS shed fragments in animal studies. However, a recombinant Hpa-2 therapy does not exist to the present time. Therapeutic plasma exchange (TPE), a modality already tested in clinical practice, effectively removes injurious mediators, e.g., Hpa-1, while replacing depleted protective molecules, e.g., Hpa-2. In critically ill patients with septic shock, TPE restores the physiological Hpa-1/Hpa-2 ratio and attenuates eGC breakdown. TPE results in a significant improvement in hemodynamic instability including reduced vasopressor requirement. Although promising, further studies are needed to determine the therapeutic impact of TPE in septic shock.

Heparanase and the hallmarks of cancer

Heparanase is the only mammalian enzyme that cleaves heparan sulphate, an important component of the extracellular matrix. This leads to the remodelling of the extracellular matrix, whilst liberating growth factors and cytokines bound to heparan sulphate. This in turn promotes both physiological and pathological processes such as angiogenesis, immune cell migration, inflammation, wound healing and metastasis. Furthermore, heparanase exhibits non-enzymatic actions in cell signalling and in regulating gene expression. Cancer is underpinned by key characteristic features that promote malignant growth and disease progression, collectively termed the 'hallmarks of cancer'. Essentially, all cancers examined to date have been reported to overexpress heparanase, leading to enhanced tumour growth and metastasis with concomitant poor patient survival. With its multiple roles within the tumour microenvironment, heparanase has been demonstrated to regulate each of these hallmark features, in turn highlighting the need for heparanase-targeted therapies. However, recent discoveries which demonstrated that heparanase can also regulate vital anti-tumour mechanisms have cast doubt on this approach. This review will explore the myriad ways by which heparanase functions as a key regulator of the hallmarks of cancer and will highlight its role as a major component within the tumour microenvironment. The dual role of heparanase within the tumour microenvironment, however, emphasises the need for further investigation into defining its precise mechanism of action in different cancer settings.

The Good and Bad Sides of Heparanase-1 and Heparanase-2

In this chapter, we will emphasize the importance of heparan sulfate proteoglycans (HSPG) in controlling various physiological and pathological molecular mechanisms and discuss how the heparanase enzyme can modulate the effects triggered by HSPG. Additionally, we will also navigate about the existing knowledge of the possible role of heparanase-2 in biological events. Heparan sulfate is widely distributed and evolutionarily conserved, evidencing its vital importance in cell development and functions such as cell proliferation, migration, adhesion, differentiation, and angiogenesis. During remodeling of the extracellular matrix, the breakdown of heparan sulfate by heparanase results in the release of molecules containing anchored glycosaminoglycan chains of great interest in heparanase-mediated cell signaling pathways in various physiological states, tumor development, inflammation, and other diseases. Taken together, it appears that heparanase plays a key role in the maintenance of the pathology of cancer and inflammatory diseases and is a potential target for anti-cancer therapies. Therefore, heparanase inhibitors are currently being examined in clinical trials as novel cancer therapeutics. Heparanase-2 has no enzymatic activity, displays higher affinity for heparan sulfate and the coding region alignment shows 40% identity with the heparanase gene. Heparanase-2 plays an important role in embryogenic development however its mode of action and biological function remain to be elucidated. Heparanase-2 functions as an inhibitor of the heparanase-1 enzyme and also inhibits neovascularization mediated by VEGF. The HPSE2 gene is repressed by the Polycomb complex, together suggesting a role as a tumor suppressor.

Heparanase-2 protects from LPS-mediated endothelial injury by inhibiting TLR4 signalling

The endothelial glycocalyx and its regulated shedding are important to vascular health. Endo-β-D-glucuronidase heparanase-1 (HPSE1) is the only enzyme that can shed heparan sulfate. However, the mechanisms are not well understood. We show that HPSE1 activity aggravated Toll-like receptor 4 (TLR4)-mediated response of endothelial cells to LPS. On the contrary, overexpression of its endogenous inhibitor, heparanase-2 (HPSE2) was protective. The microfluidic chip flow model confirmed that HPSE2 prevented heparan sulfate shedding by HPSE1. Furthermore, heparan sulfate did not interfere with cluster of differentiation-14 (CD14)-dependent LPS binding, but instead reduced the presentation of the LPS to TLR4. HPSE2 reduced LPS-mediated TLR4 activation, subsequent cell signalling, and cytokine expression. HPSE2-overexpressing endothelial cells remained protected against LPS-mediated loss of cell-cell contacts. In vivo, expression of HPSE2 in plasma and kidney medullary capillaries was decreased in mouse sepsis model. We next applied purified HPSE2 in mice and observed decreases in TNFα and IL-6 plasma concentrations after intravenous LPS injections. Our data demonstrate the important role of heparan sulfate and the glycocalyx in endothelial cell activation and suggest a protective role of HPSE2 in microvascular inflammation. HPSE2 offers new options for protection against HPSE1-mediated endothelial damage and preventing microvascular disease.

Heparan sulfate is a plasma biomarker of acute cellular allograft rejection

Despite advances in management of immunosuppression, graft rejection remains a significant clinical problem in solid organ transplantation. Non-invasive biomarkers of graft rejection can facilitate earlier diagnosis and treatment of acute rejection. The purpose of this study was to investigate the potential role of heparan sulfate as a novel biomarker for acute cellular rejection. Heparan sulfate is released from the extracellular matrix during T-cell infiltration of graft tissue via the action of the enzyme heparanase. In a murine heart transplant model, serum heparan sulfate is significantly elevated during rejection of cardiac allografts. Moreover, expression of the enzyme heparanase is significantly increased in activated T-cells. In human studies, plasma heparan sulfate is significantly elevated in kidney transplant recipients with biopsy-proven acute cellular rejection compared to healthy controls, recipients with stable graft function, and recipients without acute cellular rejection on biopsy. Taken together, these findings support further investigation of heparan sulfate as a novel biomarker of acute cellular rejection in solid organ transplantation.

Heparanase: Potential roles in multiple sclerosis

Heparanase is a heparan sulfate degrading enzyme that cleaves heparan sulfate (HS) chains present on HS proteoglycans (HSPGs), and has been well characterized for its roles in tumor metastasis and inflammation. However, heparanase is emerging as a contributing factor in the genesis and severity of a variety of neurodegenerative diseases and conditions. This is in part due to the wide variety of HSPGs on which the presence or absence of HS moieties dictates protein function. This includes growth factors, chemokines, cytokines, as well as components of the extracellular matrix (ECM) which in turn regulate leukocyte infiltration into the CNS. Roles for heparanase in stroke, Alzheimer's disease, and glioma growth have been described; roles for heparanase in other disease such as multiple sclerosis (MS) are less well established. However, given its known roles in inflammation and leukocyte infiltration, it is likely that heparanase also contributes to MS pathology. In this review, we will briefly summarize what is known about heparanase roles in the CNS, and speculate as to its potential role in regulating disease progression in MS and its animal model EAE (experimental autoimmune encephalitis), which may justify testing of heparanase inhibitors for MS treatment.

Ulinastatin attenuates pulmonary endothelial glycocalyx damage and inhibits endothelial heparanase activity in LPS-induced ARDS

Acute respiratory distress syndrome (ARDS) is a syndrome of acute respiratory failure characterized by major pathologic mechanisms of increased microvascular permeability and inflammation. The glycocalyx lines on the endothelial surface, which determines the vascular permeability, and heparanase play pivotal roles in the degradation of heparan sulfate (HS). HS is the major component of the glycocalyx. The aim of this study is to examine the effects of Ulinastatin (UTI) on vascular permeability and pulmonary endothelial glycocalyx dysfunction induced by lipopolysaccharide (LPS). In our study, C57BL/6 mice and human umbilical vein endothelial cells were stimulated with LPS to induce injury models. After 6 h of LPS stimulation, pulmonary pathological changes, pulmonary edema, and vascular permeability were notably attenuated by UTI. UTI inhibited LPS-induced endothelial glycocalyx destruction and significantly decreased the production of HS as determined by ELISA and immunofluorescence. UTI also reduced the active form of heparanase (50 kDa) expression and heparanase activity. Moreover, lysosome pH was investigated because heparanase (65 kDa) can be reduced easily in its active form at 50 kDa in a low pH environment within lysosome. Results showed that UTI could inhibit LPS-induced pH elevation in lysosome. In conclusion, UTI protects pulmonary endothelial glycocalyx integrity and inhibits heparanase activity during LPS-induced ARDS.

Atrasentan Reduces Albuminuria by Restoring the Glomerular Endothelial Glycocalyx Barrier in Diabetic Nephropathy

Atrasentan, a selective endothelin A receptor antagonist, has been shown to reduce albuminuria in type 2 diabetes. We previously showed that the structural integrity of a glomerular endothelial glycocalyx is required to prevent albuminuria. Therefore we tested the potential of atrasentan to stabilize the endothelial glycocalyx in diabetic apolipoprotein E (apoE)-deficient mice in relation to its antialbuminuric effects. Treatment with atrasentan (7.5 mg/kg/day) for 4 weeks reduced urinary albumin-to-creatinine ratios by 26.0 ± 6.5% (P < 0.01) in apoE knockout (KO) mice with streptozotocin-induced diabetes consuming an atherogenic diet, without changes in gross glomerular morphology, systemic blood pressure, and blood glucose concentration. Endothelial cationic ferritin surface coverage, investigated using large-scale digital transmission electron microscopy, revealed that atrasentan treatment increases glycocalyx coverage in diabetic apoE KO mice from 40.7 ± 3.2% to 81.0 ± 12.5% (P < 0.05). This restoration is accompanied by increased renal nitric oxide concentrations, reduced expression of glomerular heparanase, and a marked shift in the balance of M1 and M2 glomerular macrophages. In vitro experiments with endothelial cells exposed to laminar flow and cocultured with pericytes confirmed that atrasentan reduced endothelial heparanase expression and increased glycocalyx thickness in the presence of a diabetic milieu. Together these data point toward a role for the restoration of endothelial function and tissue homeostasis through the antialbuminuric effects of atrasentan, and they provide a mechanistic explanation for the clinical observations of reduced albuminuria with atrasentan in diabetic nephropathy.

Mice deficient in heparanase exhibit impaired dendritic cell migration and reduced airway inflammation

Heparanase is a β-d-endoglucuronidase that cleaves heparan sulphate, a key component of the ECM and basement membrane. The remodelling of the ECM by heparanase has been proposed to regulate both normal physiological and pathological processes, including wound healing, inflammation, tumour angiogenesis and cell migration. Heparanase is also known to exhibit non-enzymatic functions by regulating cell adhesion, cell signalling and differentiation. In this study, constitutive heparanase-deficient (Hpse(-/-) ) mice were generated on a C57BL/6 background using the Cre/loxP recombination system, with a complete lack of heparanase mRNA, protein and activity. Although heparanase has been implicated in embryogenesis and development, Hpse(-/-) mice are anatomically normal and fertile. Interestingly, consistent with the suggested function of heparanase in cell migration, the trafficking of dendritic cells from the skin to the draining lymph nodes was markedly reduced in Hpse(-/-) mice. Furthermore, the ability of Hpse(-/-) mice to generate an allergic inflammatory response in the airways, a process that requires dendritic cell migration, was also impaired. These findings establish an important role for heparanase in immunity and identify the enzyme as a potential target for regulation of an immune response.

Glycoconjugates and related molecules in human vascular endothelial cells

Vascular endothelial cells (ECs) form the inner lining of blood vessels. They are critically involved in many physiological functions, including control of vasomotor tone, blood cell trafficking, hemostatic balance, permeability, proliferation, survival, and immunity. It is considered that impairment of EC functions leads to the development of vascular diseases. The carbohydrate antigens carried by glycoconjugates (e.g., glycoproteins, glycosphingolipids, and proteoglycans) mainly present on the cell surface serve not only as marker molecules but also as functional molecules. Recent studies have revealed that the carbohydrate composition of the EC surface is critical for these cells to perform their physiological functions. In this paper, we consider the expression and functional roles of endogenous glycoconjugates and related molecules (galectins and glycan-degrading enzymes) in human ECs.

Radiation therapy causes loss of dermal lymphatic vessels and interferes with lymphatic function by TGF-beta1-mediated tissue fibrosis

Although radiation therapy is a major risk factor for the development of lymphedema following lymphadenectomy, the mechanisms responsible for this effect remain unknown. The purpose of this study was therefore to determine the effects of radiation on lymphatic endothelial cells (LECs) and lymphatic function. The tails of wild-type or acid sphingomyelinase (ASM)-deficient mice were treated with 0, 15, or 30 Gy of radiation and then analyzed for LEC apoptosis and lymphatic function at various time points. To analyze the effects of radiation fibrosis on lymphatic function, we determined the effects of transforming growth factor (TGF)-beta1 blockade after radiation in vivo. Finally, we determined the effects of radiation and exogenous TGF-beta1 on LECs in vitro. Radiation caused mild edema that resolved after 12-24 wk. Interestingly, despite resolution of tail edema, irradiated animals displayed persistent lymphatic dysfunction. Radiation caused loss of capillary lymphatics and was associated with a dose-dependent increase in LEC apoptosis. ASM-/- mice had significantly less LEC apoptosis; however, this finding did not translate to improved lymphatic function at later time points. Short-term blockade of TGF-beta1 function after radiation markedly decreased tissue fibrosis and significantly improved lymphatic function but did not alter LEC apoptosis. Radiation therapy decreases lymphatic reserve by causing depletion of lymphatic vessels and LECs as well as promoting soft tissue fibrosis. Short-term inhibition of TGF-beta1 activity following radiation improves lymphatic function and is associated with decreased soft tissue fibrosis. ASM deficiency confers LEC protection from radiation-induced apoptosis but does not prevent lymphatic dysfunction.

Heparanase alters arterial structure, mechanics, and repair following endovascular stenting in mice

Heparan sulfate proteoglycans (HSPGs) are potent regulators of vascular remodeling and repair. Heparanase is the major enzyme capable of degrading heparan sulfate in mammalian cells. Here we examined the role of heparanase in controlling arterial structure, mechanics, and remodeling. In vitro studies supported that heparanase expression in endothelial cells serves as a negative regulator of endothelial inhibition of vascular smooth muscle cell (vSMC) proliferation. Arterial structure and remodeling to injury were also modified by heparanase expression. Transgenic mice overexpressing heparanase had increased arterial thickness, cellular density, and mechanical compliance. Endovascular stenting studies in Zucker rats demonstrated increased heparanase expression in the neointima of obese, hyperlipidemic rats in comparison to lean rats. The extent of heparanase expression within the neointima strongly correlated with the neointimal thickness following injury. To test the effects of heparanase overexpression on arterial repair, we developed a novel murine model of stent injury using small diameter self-expanding stents. Using this model, we found that increased neointimal formation and macrophage recruitment occurs in transgenic mice overexpressing heparanase. Taken together, these results support a role for heparanase in the regulation of arterial structure, mechanics, and repair.

High-throughput methods for measuring heparanase activity and screening potential antimetastatic and anti-inflammatory agents

Heparanase plays an important role in the degradation of the extracellular matrix. It is implicated in inflammation, tumor angiogenesis and metastasis. We have developed two high-throughput methods for measuring heparanase activity and screening potential inhibitors. The first method involves coating fibroblast growth factor (FGF) on microtiter plates and capturing fluorescein isothiocyanate (FITC)-labeled heparin sulfate (HS), which is used as a substrate for heparanase digestion. Labeled HS fragments are released into the medium and quantitated by fluorescence intensity measurement. We have implemented this assay method into a Zeiss uHTS system and screened compound libraries for heparanase inhibitors. The second method involves labeling HS with biotin followed by FITC to generate a dual-labeled HS. The labeled material is bound to streptavidin-coated plates and used as a substrate for heparanase digestion. Both methods are sensitive and easily applicable to robotic systems. In addition, we have labeled both HS and biotin-HS with Eu-chelate, a fluorophore that exhibits long decay fluorescence. Assays using Eu-labeled HS and Eu-labeled biotin-HS have been developed and show higher sensitivity than those using FITC-labeled material. Furthermore, assays using Eu-chelate HS (or biotin-HS) should eliminate the interference of fluorescence compounds.

Early growth response gene 1 (EGR1) regulates heparanase gene transcription in tumor cells

Heparanase is an endoglycosidase that degrades heparan sulfate chains of heparan sulfate proteoglycans, a key component of extracellular matrix and basement membranes. Studies using heparanase inhibitors and gene silencing have provided evidence to support an important role for heparanase in tumor metastasis and angiogenesis. The expression of heparanase is normally very tightly controlled, however, it is commonly deregulated in tumor cells, which express elevated heparanase activity that correlates with high levels of heparanase mRNA. We recently identified the transcription factor early growth response gene 1, EGR1, as a key regulator of inducible heparanase transcription in T cells. In this study using chromatin immunoprecipitation, we demonstrate for the first time that EGR1 binds to the heparanase gene promoter in vivo. The important question of the role of EGR1 in regulating heparanase transcription in tumor cells was then assessed. Studies were carried out in four epithelial tumor lines of different tissue origin. Functional dissection of the heparanase promoter identified a 280-bp region that was critical for transcription of the heparanase gene. Transactivation studies using an EGR1 expression vector co-transfected with a reporter construct containing the 280-bp region showed EGR1-activated heparanase promoter activity in a dose-dependent manner in prostate or breast adenocarcinoma and colon carcinoma cell lines. In contrast, overexpression of EGR1 resulted in a dose-dependent repression of promoter activity in melanoma cells. Using site-directed mutagenesis the 280-bp region was found to contain two functional EGR1 sites and electrophoretic mobility shift assays showed binding of EGR1 to both of these sites upon activation of tumor cells. Furthermore, the heparanase promoter region containing the EGR1 sites was also inducible in tumor cells and induction corresponded to HPSE expression levels. These studies show that EGR1 regulates heparanase transcription in tumor cells and importantly, can have a repressive or activating role depending on the tumor type.

Multiple fragments related to angiostatin and endostatin in fluid from venous leg ulcers

To investigate whether compromised angiogenesis could contribute to the impaired healing of venous leg ulcers, we have analyzed fluids from venous leg ulcers for the presence of the angiogenesis inhibitors angiostatin and endostatin. Multiple fragments related to angiostatin were detected by Western blot analysis. One angiostatin fragment was identified by mass spectrometry as plasminogen kringle domains 1-3 containing amino acids 82-343 of plasminogen, and a fraction containing this fragment inhibited tubule formation of human umbilical vein endothelial cells in a Matrigel assay. The leg ulcer fluids also contained endogenous endostatin (20 kDa) as well as higher molecular weight endostatin-related proteins. The concentrations of endostatin in the wound fluids, which ranged from 12.8 to 65.5 ng/ml, were higher than the concentration in human serum (7.7 ng/ml). Most of the endostatin in leg ulcer fluid appeared to be bound to the proteoglycan glypican-1. These data suggest that anti-angiogenic activity is present at the site of venous leg ulcers, and at least in the case of angiostatin, is biologically active.

Heparanase protein and gene expression in bladder cancer

PURPOSE

We determined the association of heparanase protein and messenger (m)RNA expression with bladder cancer invasion and metastasis.

MATERIALS AND METHODS

The expression of heparanase protein and mRNA was assessed by immunohistochemical staining and in situ hybridization, respectively, in 67 bladder cancer specimens resected at various stages of disease. To our knowledge this is the first systematic study of heparanase protein and mRNA expression in human bladder cancer.

RESULTS

The expression of heparanase protein in muscular invasive bladder cancer was significantly higher than in superficial cancer (68% versus 19%, p = 0.0001). It was higher in the primary tumor of patients with lymph node metastatic cancer than those with nonmetastatic cancer (80% versus 37%, p = 0.0006). In high grade disease it was significantly higher than in low grade disease (79% versus 29%, p = 0.0001). The expression of heparanase mRNA was also significantly higher in stage pT3 or greater than in stage pT2 or less bladder cancer (96% versus 33%, p = 0.0003). In metastatic N+ cases it was significantly higher than in nonmetastatic bladder cancer (93% versus 46%, p = 0.0037). The heparanase gene and protein showed similar patterns of expression in bladder cancer.

CONCLUSIONS

Our study implies that the expression of heparanase protein and mRNA is associated with bladder cancer invasion and metastasis, and heparanase may have a role in disease progression.

Cloning and expression profiling of Hpa2, a novel mammalian heparanase family member

Heparan sulfate proteoglycans are important constituents of the extracellular matrix and basement membrane. Cleavage of heparan sulfate by heparanase, an endoglycosidase, is implicated in the extravasation of leukocytes and metastatic tumour cells, identifying this enzyme(s) as a target for anti-inflammatory and anti-metastatic therapies. The cloning of a cDNA encoding human heparanase (Hpa1) was reported recently, together with evidence indicating that the hpa1 gene is unique and unlikely to belong to a family of related genes. Here we report the cloning of a cDNA encoding a novel human protein, HPA2, with significant homology to Hpa1. Alternative splicing of the hpa2 transcript yields three different mRNAs, encoding putative proteins of 480, 534, and 592 amino acids. Sequence analyses predict that all three Hpa2 proteins are intracellular, membrane-bound enzymes. Hpa2 also shows a markedly different mRNA distribution to Hpa1 in both normal and cancer tissues. The difference in expression profiles and predicted cellular locations suggests that Hpa2 and Hpa1 proteins have distinct biological functions.

Angiogenesis in inflammatory joint disease: a target for therapeutic intervention

The evidence reviewed here clearly supports the concept that pathological angiogenesis is an important component in inflammatory joint erosion. Of the primary angiogenic factors, VEGF-A is clearly a key participant in this mechanism and a range of anti-VEGF strategies is being developed to neutralize its biological function [54,55]. Currently available drugs are also being screened for VEGF antagonistic effects. In a study of the effects of existing disease-modifying anti-rheumatic drugs on cultured synovial cells, bucillamine and dexamethasone showed significant inhibition of VEGF production [56]. In addition, COX-1 and COX-2 non-steroidal anti-inflammatory drugs have been shown to inhibit angiogenesis by blocking VEGF-induced signal transduction [57]. Modulation of the immune network in RA using TNF-α antagonists is producing promising results, but as outlined in this review, this treatment on its own is unlikely to control joint angiogenesis. It is possible that combination therapy, e.g. TNF-α antagonist and a VEGF signal transduction inhibitor, will be more effective by using antagonists that block different but key control points in the disease pathology.

A novel role for nitric oxide in the endogenous degradation of heparan sulfate during recycling of glypican-1 in vascular endothelial cells

We show here that the endothelial cell-line ECV 304 expresses the heparan sulfate proteoglycan glypican-1. The predominant cellular glycoform carries truncated side-chains and is accompanied by heparan sulfate oligosaccharides. Treatment with brefeldin A results in accumulation of a glypican proteoglycan with full-size side-chains while the oligosaccharides disappear. During chase the glypican proteoglycan is converted to partially degraded heparan sulfate chains and chain-truncated proteoglycan, both of which can be captured by treatment with suramin. The heparan sulfate chains in the intact proteoglycan can be depolymerized by nitrite-dependent cleavage at internally located N-unsubstituted glucosamine moieties. Inhibition of NO-synthase or nitrite-deprivation prevents regeneration of intact proteoglycan from truncated precursors as well as formation of oligosaccharides. In nitrite-deprived cells, formation of glypican proteoglycan is restored when NO-donor is supplied. We propose that, in recycling glypican-1, heparan sulfate chains are cleaved at or near glucosamines with unsubstituted amino groups. NO-derived nitrite is then required for the removal of short, nonreducing terminal saccharides containing these N-unsubstituted glucosamine residues from the core protein stubs, facilitating re-synthesis of heparan sulfate chains.

Cloning of mammalian heparanase, an important enzyme in tumor invasion and metastasis

The endoglycosidase heparanase is an important in the degradation of the extracellular matrix by invading cells, notably metastatic tumor cells and migrating leukocytes. Here we report the cDNA sequence of the human platelet enzyme, which encodes a unique protein of 543 amino acids, and the identification of highly homologous sequences in activated mouse T cells and in a highly metastatic rat adenocarcinoma. Furthermore, the expression of heparanase mRNA in rat tumor cells correlates with their metastatic potential. Exhaustive studies have shown only one heparanase sequence, consistent with the idea that this enzyme is the dominant endoglucuronidase in mammalian tissues.

Partial sequence of human platelet heparitinase and evidence of its ability to polymerize

Heparitinase cleaves heparan sulfate, a glycosaminoglycan associated with all nucleated mammalian cells and extracellular matrices. Despite the important physiologic role heparitinase is postulated to play in such processes as tumor metastasis and inflammation, the identity of the enzyme remains a matter of controversy and there is a question of whether heparitinase is CTAP III. We report a 900,000-fold purification of heparitinase from human platelets. A multi-step procedure utilizing chromatography on heparin, DEAE, hydroxyapatite and size exclusion matrices was employed and yielded a single protein as judged by Coomassie staining of protein separated by SDS-PAGE. The purified protein had an apparent molecular mass of 35 kDa by size exclusion chromatography and 55 kDa by SDS-PAGE. During purification, heparitinase activity co-eluted from the hydroxyapatite and size exclusion columns with the 35-55 kDa protein, confirming that the purified protein was indeed heparitinase. The 35-55 kDa protein reacted strongly with concanavalin A, a lectin known to bind to heparitinase, further confirming that the protein was heparitinase. Platelet heparitinase formed dimers and tetramers upon storage in a purified form, possibly accounting for the various molecular weights previously reported for the enzyme. A partial amino acid sequence of the protein revealed that heparitinase has not been previously sequenced.

Regulation of platelet heparanase during inflammation: role of pH and proteinases

Heparan sulfate is rapidly degraded by an endoglycosidase (heparanase) secreted by activated platelets. Since the cleavage and release of heparan sulfate would profoundly alter the local physiology of the endothelium, platelet heparanase activity should be tightly regulated. Consistent with this hypothesis, platelet heparanase was found to degrade endothelial cell heparan sulfate at pH 6.0 but not at pH 7.4, even though 25% of maximum activity was detected at pH 7.4. Loss of heparanase activity occurred rapidly (t1/2 is approximately equal to 20 min) and reversibly at physiologic pH but did not occur at acidic pH (<7.0). Inactivation of heparanase at pH 7.4 did not affect heparin binding and was reversed by 0.5 M NaCl or by heparan sulfate but not by chondroitin sulfate, suggesting inactive heparanase could be tethered on cell surfaces and the function regulated by heparan sulfate. Heparanase was gradually inactivated by trypsin and urokinase (t1/2 = 5 h) but resisted cleavage by leukocyte cathepsin G, leukocyte elastase, plasmin, and thrombin. These findings are consistent with a model in which platelet heparanase is active at the low pH of inflammation but inactive under physiologic conditions preventing inadvertent cleavage of heparan sulfate and loss of physiologic functions of endothelial cells.

Human platelet heparanase: purification, characterization and catalytic activity

Heparan sulphate (HS) is an important component of the extracellular matrix (ECM) and the vasculature basal lamina (BL) which functions as a barrier to the extravasation of metastatic and inflammatory cells. Platelet-tumour cell aggregation at the capillary endothelium results in activation and degranulation of platelets. Cleavage of HS by endoglycosidase or heparanase activity produced in relatively large amounts by the platelets and the invading cells may assist in the disassembly of the ECM and BL, and thereby facilitate cell migration. Using a recently published rapid, quantitative assay for heparanase activity towards HS [Freeman, C. and Parish, C.R. (1997), Biochem. J., 325, 229-237], human platelet heparanase has now been purified 1700-fold to homogeneity in 19% yield by a five column procedure, which consists of concanavalin A-Sepharose, Zn2+-chelating-Sepharose, Blue A-agarose, octyl-agarose and gel filtration chromatography. The enzyme, which was shown to be an endoglucuronidase that degrades both heparin and HS, has a native molecular mass of 50 kDa when analysed by gel filtration chromatography and by SDS/PAGE. Platelet heparanase degraded porcine mucosal HS in a stepwise fashion from a number average molecular mass of 18.5 to 13, to 8 and finally to 4.5 kDa fragments as determined by gel filtration analysis. Bovine lung heparin was degraded from 8.9 to 4.8 kDa while porcine mucosal heparin was degraded from 8.1 kDa to 3.8 and finally to 2.9 kDa fragments. Studies of the enzyme's substrate specificity using modified heparin analogues showed that substrate cleavage required the presence of carboxyl groups, but O- and N-sulphation were not essential. Inhibition studies demonstrated an absolute requirement for the presence of O-sulphate groups. Platelet heparanase was inhibited by heparin analogues which also inhibited tumour heparanase, suggesting that sulphated polysaccharides which inhibit tumour metastasis may act to prevent both tumour cell and platelet heparanase degradation of endothelial cell surface HS and the basal laminar.

A rapid quantitative assay for the detection of mammalian heparanase activity

Heparan sulphate (HS) is an important component of the extracellular matrix and the vasculature basal laminar which functions as a barrier to the extravasation of metastatic and inflammatory cells. Cleavage of HS by endoglycosidase or heparanase activity produced by invading cells may assist in the disassembly of the extracellular matrix and basal laminar, and thereby facilitate cell migration. Heparanase activity has previously been shown to be related to the metastatic potential of murine and human melanoma cell lines [Nakajima, Irimura and Nicolson (1988) J. Cell. Biochem. 36, 157-167]. To determine heparanase activity, porcine mucosal HS was partially de-N-acetylated and re-N-acetylated with [3H]acetic anhydride to yield a radiolabelled substrate. This procedure prevented the masking of, or possible formation of, new heparanase-sensitive cleavage sites as has been observed with previous methods of radiolabelling. Heparanase activity in a variety of tissues and cell homogenates including human platelets, colonic carcinoma cells, umbilical vein endothelial cells and rat mammary adenocarcinoma cells (both metastatic and non-metastatic variants) and liver homogenates all degraded the substrate in a stepwise fashion from 18.5 to approximately 13, 8 and finally to 4.5 kDa fragments, as assessed by gel-filtration analysis, confirming the substrate as suitable for the detection of heparanase activity present in a variety of cells and tissues. A rapid quantitative assay was developed with the HS substrate using a novel method for separating degradation products from the substrate by taking advantage of the decreased affinity of the heparanase-cleaved products for the HS-binding plasma protein chicken histidine-rich glycoprotein (cHRG). Incubation mixtures were applied to cHRG-Sepharose columns, with unbound material corresponding to heparanase-degradation products. Heparanase activity was determined for a variety of human, rat and murine cell and tissue homogenates. The highly metastatic rat mammary adenocarcinoma and murine lung carcinoma cell lines had four to ten times the heparanase activity of non-metastatic variants, confirming the correlation of heparanase activity with metastatic potential. Human cancer patients had twice the serum heparanase levels of normal healthy adults. The assay will be valuable for the determination of heparanase activity from a variety of tissue and cell sources, as a diagnostic tool for the determination of heparanase potential, and for the development of specific inhibitors of heparanase activity and metastasis.

Oxidized lipid-mediated alterations in proteoglycan metabolism in cultured pulmonary endothelial cells

Compared to cholesterol or linoleic acid (18:2), oxidized lipids such as cholestan-3 beta, 5 alpha, 6 beta-triol (triol) and hydroperoxy linoleic acid (HPODE) markedly impair endothelial barrier function in culture [Hennig and Boissonneault, 1987; Hennig et al. 1986]. Because proteoglycans contribute to vascular permeability properties, the effects of cholesterol and 18:2 and their oxidation products, triol and HPODE, on endothelial proteoglycan metabolism were determined. While cholesterol was without effect, a concentration-dependent decrease in cellular proteoglycans (measured by 35S incorporation) was observed after exposure to triol. Compared to control cultures, cholesterol reduced mRNA levels for the proteoglycans, perlecan and biglycan. Triol had a similar effect on biglycan but not an perlecan mRNA levels. Compared to 18:2, 1,3 and 5 microM HPODE depressed cellular proteoglycans. Perlecan mRNA levels were reduced more by HPODE when compared to 18:2. Biglycan mRNA levels were reduced by 3 microM, but not by 5 microM HPODE. These data demonstrate that oxidized lipids such as triol and HPODE can decrease cellular proteoglycan metabolism in endothelial monolayers and alter mRNA levels of major specific proteoglycans in a concentration-dependent manner. This may have implications in lipid-mediated disruption of endothelial barrier function and atherosclerosis.

Comparative analysis of the ability of leucocytes, endothelial cells and platelets to degrade the subendothelial basement membrane: evidence for cytokine dependence and detection of a novel sulfatase

The subendothelial basement membrane (BM) is regarded as an important barrier to the entry of leucocytes into inflammatory sites. This study compares the ability of leucocytes, platelets and endothelial cells (EC) to degrade a [35SO4]-labelled subendothelial extracellular matrix (ECM) and assesses the effect of PMA and various pro-inflammatory cytokines on this degradative activity. The different products of degradation, identified by fast protein liquid chromatography (FPLC) gel filtration chromatography, were indicative of protease, endoglycosidase (heparanase) and exoglycosidase and/or sulfatase activity. In terms of ECM degradation, EC and platelets were the most active, with PMA stimulation further enhancing the degradative activity of these two cell types. Platelets exhibited predominantly heparanase activity whereas the EC degradation products suggested a range of enzymic activities, namely proteases, heparanases and sulfatases. Interestingly, EC in suspension expressed these three enzymic activities whereas confluent EC monolayers only exhibited sulfatase activity, suggesting that the former situation might represent an angiogenic response. In the case of leucocytes, neutrophils and lymphocytes degraded the ECM to a much greater extent than monocytes. Each cell type also differed in the predominant enzymic activities it expressed, for example, heparanase activity by lymphocytes, protease activity by neutrophils and sulfatase activity by monocytes. Furthermore, PMA stimulation was shown to have differential effects on these enzymic activities. Some pro-inflammatory cytokines were found to be cell-type specific in their effects on ECM degradation. Thus, IL-1 + TNF enhanced neutrophil and EC degradation of the ECM but inhibited lymphocyte ECM degradation. In contrast, the chemokine IL-8 enhanced ECM degradation by neutrophils, lymphocytes and EC. Of particular interest was the unique sulfatase activity expressed by EC and monocytes which was induced in EC by TNF + IL-1 and IL-8, whereas in monocytes the sulfatase activity was exclusively induced by the chemokine monocyte chemotactic and activating factor (MCAF). Collectively, the results of this study show that leucocytes differ markedly in the enzymes they express to degrade the BM during extravasation and that PMA and cytokines are cell-type specific in their induction of hydrolytic enzyme activity. These results also indicate that EC may play an important role, not only in the recruitment of leucocytes, but also via sulfatase activity in the preparation of vascular BM for leucocyte extravasion.

Enzymatic degradation of glycosaminoglycans

Glycosaminoglycans (GAGs) play an intricate role in the extracellular matrix (ECM), not only as soluble components and polyelectrolytes, but also by specific interactions with growth factors and other transient components of the ECM. Modifications of GAG chains, such as isomerization, sulfation, and acetylation, generate the chemical specificity of GAGs. GAGs can be depolymerized enzymatically either by eliminative cleavage with lyases (EC 4.2.2.-) or by hydrolytic cleavage with hydrolases (EC 3.2.1.-). Often, these enzymes are specific for residues in the polysaccharide chain with certain modifications. As such, the enzymes can serve as tools for studying the physiological effect of residue modifications and as models at the molecular level of protein-GAG recognition. This review examines the structure of the substrates, the properties of enzymatic degradation, and the enzyme substrate-interactions at a molecular level. The primary structure of several GAGs is organized macroscopically by segregation into alternating blocks of specific sulfation patterns and microscopically by formation of oligosaccharide sequences with specific binding functions. Among GAGs, considerable dermatan sulfate, heparin and heparan sulfate show conformational flexibility in solution. They elicit sequence-specific interactions with enzymes that degrade them, as well as with other proteins, however, the effect of conformational flexibility on protein-GAG interactions is not clear. Recent findings have established empirical rules of substrate specificity and elucidated molecular mechanisms of enzyme-substrate interactions for enzymes that degrade GAGs. Here we propose that local formation of polysaccharide secondary structure is determined by the immediate sequence environment within the GAG polymer, and that this secondary structure, in turn, governs the binding and catalytic interactions between proteins and GAGs.

Role of heparan sulfate in immune system-blood vessel interactions

Heparan sulfate proteoglycan, a component of endothelial cell membranes and extracellular matrices, is involved in a number of the critical functions of endothelium and of antigen-presenting cells. This review discusses how heparan sulfate is released from endothelial cells during inflammation, how the loss of heparan sulfate potentially alters endothelial cell physiology, and how the presence of heparan sulfate in a soluble form might regulate the functioning of lymphocytes at sites of inflammation.

Accumulation of PDGF B and cell-binding forms of PDGF A in the extracellular matrix

PDGF is a powerful mitogen initially identified within platelets, but also shown to be produced by a wide variety of cell types. PDGF is encoded on two separate genes. These give rise to three polypeptides, PDGF B and two forms of PDGF A (SA and LA), resulting from alternative splicing of the PDGF A gene primary transcript. We report that in CHO cells transfected with PDGF gene constructs and producing moderate levels of PDGF homodimers, much of the PDGF LA and B produced, but little if any SA, is found in the matrix laid down beneath the cells. Immunoreactive PDGF in cells, and in matrix below expressing cells, was visualized by laser confocal microscopy. Western blotting of protein in matrix extracts, cell extracts, and secreted into the growth medium was used to demonstrate that the range of PDGF A polypeptides seen in the matrix was overlapping with those reported previously to be cell associated in cell types such as NIH3T3 and COS 7. This suggests that attachment to matrix or cell surface may be alternative fates for these polypeptides, with fate dependent on the characteristics of the producing cells. Immunoreactive PDGF A and B could be partially released by incubation of matrix material with heparin but not with other glycosaminoglycans. Digestion of matrix with chondroitin ABC lyase but not heparitinase or collagenase displaced some PDGF from its attachment sites. The results indicate attachment of PDGF to matrix proteoglycans, at least partly through the glycosaminoglycan moieties, and perhaps to additional components. The significance of matrix deposition for PDGF action is discussed.

Differential effects of SPARC and cationic SPARC peptides on DNA synthesis by endothelial cells and fibroblasts

SPARC (secreted protein, acidic and rich in cysteine), also known as osteonectin, is an extracellular Ca+2-binding glycoprotein that inhibits the incorporation of [3H]-thymidine and delays the onset of S-phase in synchronized cultures of bovine aortic endothelial (BAE) cells. This effect appears not to be dependent on the functional properties of SPARC associated with changes in cell shape or inhibition of cell spreading. In this study we investigate the conditions under which cell cycle modulation occurs in different types of cells. Human umbilical vein endothelial cells, a transformed fetal BAE cell line, and bovine capillary endothelial cells exhibited a sensitivity to SPARC and a cationic peptide from a non-Ca+2-binding region of SPARC (peptide 2.1, 0.2-0.8 mM) similar to that observed in BAE cells. In contrast, human foreskin fibroblasts and fetal bovine ligament fibroblasts exhibited an increase in the incorporation of [3H]-thymidine in the presence of 25 microM-0.2 mM peptide 2.1; inhibition was observed at concentrations in excess of 0.4 mM. This biphasic modulation could be further localized to a sequence of 10 amino acids comprising the N-terminal half of peptide 2.1. A synthetic peptide from another cationic region of SPARC (peptide 2.3) increased [3H]-thymidine incorporation by BAE cells and fibroblasts in a dose-dependent manner. In endothelial cells, a stimulation of 50% was observed at a concentration of 0.01 mM; fibroblasts required approximately 100-fold more peptide 2.3 for levels of stimulation comparable to those obtained in endothelial cells. The observation that SPARC and unique SPARC peptides can differentially influence the growth of fibroblasts and endothelial cells in a concentration-dependent manner suggests that SPARC might regulate proliferation of specific cells during wound repair and remodeling.