Heparanase is preferentially expressed in human psoriatic lesions and induces development of psoriasiform skin inflammation in mice.

Heparanase is the sole mammalian endoglycosidase that selectively degrades heparan sulfate, the key polysaccharide associated with the cell surface and extracellular matrix of a wide range of tissues. Extensively studied for its capacity to promote cancer progression, heparanase enzyme was recently implicated as an important determinant in several inflammatory disorders as well. Applying immunohistochemical staining, we detected preferential expression of heparanase by epidermal keratinocytes in human psoriatic lesions. To investigate the role of the enzyme in the pathogenesis of psoriasis, we utilized heparanase transgenic mice in a model of 12-O-tetradecanoyl phorbol 12-myristate 13-acetate-induced cutaneous inflammation. We report that over-expression of the enzyme promotes development of mouse skin lesions that strongly recapitulate the human disease in terms of histomorphological appearance and molecular/cellular characteristics. Importantly, heparanase of epidermal origin appears to facilitate abnormal activation of skin-infiltrating macrophages, thus generating psoriasis-like inflammation conditions, characterized by induction of STAT3, enhanced NF-κB signaling, elevated expression of TNF-α and increased vascularization. Taken together, our results reveal, for the first time, involvement of heparanase in the pathogenesis of psoriasis and highlight a role for the enzyme in facilitating abnormal interactions between immune and epithelial cell subsets of the affected skin. Heparanase inhibitors (currently under clinical testing in malignant diseases) could hence turn highly beneficial in psoriatic patients as well.

Inhibition of matrix metalloproteinase-2 by halofuginone is mediated by the Egr1 transcription factor.

Halofuginone, a low-molecular-weight quinazolinone alkaloid that inhibits collagen α1(I), has been shown to suppress cancer growth, metastasis, and angiogenesis. These activities were attributed in part to the inhibition of matrix metalloproteinase-2 (MMP-2). The present study was carried out to explore the molecular mechanism underlying this effect. We found a marked (50%) inhibition in MMP-2 gelatinolytic activity in human breast cancer MDA-MB-435 cells pretreated with as little as 50 ng/ml of halofuginone, a concentration that markedly inhibited their invasive and proliferative capacities. We further show that both early growth response 1 (Egr-1) and Nab-2 (corepressor of Egr1 activation) are upregulated by halofuginone in a dose-dependent and time-dependent (up to 5 h) manner. Using MMP-2 reporter gene and chromatin immunoprecipitation analyses, we found that Egr-1 binds to the MMP-2 promoter and inhibits its activity. Altogether, our results identify the downstream elements (Egr-1, Nab-2, and MMP-2) by which halofuginone exerts its antitumoral effect, thereby advancing its potential therapeutic application as an anticancer drug.

Heparanase overexpression impairs inflammatory response and macrophage-mediated clearance of amyloid-ß in murine brain.

Neuroinflammation is typically observed in neurodegenerative diseases such as Alzheimer's disease, as well as after traumatic injury and pathogen infection. Resident immune cells, microglia and astrocytes, are activated and joined by blood-borne monocytes that traverse the blood-brain barrier and convert into activated macrophages. The activated cells express various cytokines, chemokines and proteolytic enzymes. To study the role of heparan sulfate proteoglycans in neuroinflammation, we employed a transgenic mouse overexpressing heparanase, an endoglucuronidase that specifically degrades heparan sulfate side chains. Neuroinflammation was induced by systemic challenge with lipopolysaccharide, or by localized cerebral microinjection of aggregated amyloid-ß peptide, implicated in Alzheimer's disease. Lipopolysaccharide-treated control mice showed massive activation of resident microglia as well as recruitment of monocyte-derived macrophages into the brain parenchyma. Microinjection of aggregated amyloid-ß elicited a similar inflammatory response, albeit restricted to the injection site, which led to dispersion and clearance of the amyloid. In the heparanase-overexpressing mice, all aspects of immune cell recruitment and activation were significantly attenuated in both inflammation models, as was amyloid dispersion. Accordingly, an in vitro blood-brain barrier model constructed from heparanase-overexpressing cerebral vascular cells showed impaired transmigration of monocytes compared to a corresponding assembly of control cells. Our data indicate that intact heparan sulfate chains are required at multiple sites to mediate neuroinflammatory responses, and further point to heparanase as a modulator of this process, with potential implications for Alzheimer's disease.

Dissociation between mature phenotype and impaired transmigration in dendritic cells from heparanase-deficient mice.

To reach the lymphatics, migrating dendritic cells (DCs) need to interact with the extracellular matrix (ECM). Heparanase, a mammalian endo-ß-D-glucuronidase, specifically degrades heparan sulfate proteoglycans ubiquitously associated with the cell surface and ECM. The role of heparanase in the physiology of bone marrow-derived DCs was studied in mutant heparanase knock-out (Hpse-KO) mice. Immature DCs from Hpse-KO mice exhibited a more mature phenotype; however their transmigration was significantly delayed, but not completely abolished, most probably due to the observed upregulation of MMP-14 and CCR7. Despite their mature phenotype, uptake of beads was comparable and uptake of apoptotic cells was more efficient in DCs from Hpse-KO mice. Heparanase is an important enzyme for DC transmigration. Together with CCR7 and its ligands, and probably MMP-14, heparanase controls DC trafficking.

Heparanase regulates thrombosis in vascular injury and stent-induced flow disturbance.

OBJECTIVES: The purpose of this study was to examine the role of heparanase in controlling thrombosis following vascular injury or endovascular stenting. BACKGROUND: The use of endovascular stents are a common clinical intervention for the treatment of arteries occluded due to vascular disease. Both heparin and heparan sulfate are known to be potent inhibitors of thrombosis. Heparanase is the major enzyme that degrades heparan sulfate in mammalian cells. This study examined the role of heparanase in controlling thrombosis following vascular injury and stent-induced flow disturbance. METHODS: This study used mice overexpressing human heparanase and examined the time to thrombosis using a laser-induced arterial thrombosis model in combination with vascular injury. An ex vivo system was used to examine the formation of thrombus to stent-induced flow disturbance. RESULTS: In the absence of vascular injury, wild type and heparanase overexpressing (HPA Tg) mice had similar times to thrombosis in a laser-induced arterial thrombosis model. However, in the presence of vascular injury, the time to thrombosis was dramatically reduced in HPA Tg mice. An ex vivo system was used to flow blood from wild type and HPA Tg mice over stents and stented arterial segments from both animal types. These studies demonstrate markedly increased thromboses on stents with blood isolated from HPA Tg mice in comparison to blood from wild type animals. We found that blood from HPA Tg animals had markedly increased thrombosis when applied to stented arterial segments from either wild type or HPA Tg mice. CONCLUSIONS: Taken together, this study's results indicate that heparanase is a powerful mediator of thrombosis in the context of vascular injury and stent-induced flow disturbance.

Heparanase is essential for the development of diabetic nephropathy in mice.

Diabetic nephropathy (DN) is the major life-threatening complication of diabetes. Abnormal permselectivity of glomerular basement membrane (GBM) plays an important role in DN pathogenesis. Heparanase is the predominant enzyme that degrades heparan sulfate (HS), the main polysaccharide of the GBM. Loss of GBM HS in diabetic kidney was associated with increased glomerular expression of heparanase; however, the causal involvement of heparanase in the pathogenesis of DN has not been demonstrated. We report for the first time the essential involvement of heparanase in DN. With the use of Hpse-KO mice, we found that deletion of the heparanase gene protects diabetic mice from DN. Furthermore, by investigating the molecular mechanism underlying induction of the enzyme in DN, we found that transcription factor early growth response 1 (Egr1) is responsible for activation of heparanase promoter under diabetic conditions. The specific heparanase inhibitor SST0001 markedly decreased the extent of albuminuria and renal damage in mouse models of DN. Our results collectively underscore the crucial role of heparanase in the pathogenesis of DN and its potential as a highly relevant target for therapeutic interventions in patients with DN.

Heparanase affects secretory granule homeostasis of murine mast cells through degrading heparin.

BACKGROUND: Heparanase degradation of heparan sulfate plays important roles in a number of pathological processes, including inflammation. In vitro experiments show that heparanase is capable of degrading heparin, a polysaccharide present in mast cells (MCs), in which it has a key role in promoting the storage of secretory granule compounds. OBJECTIVE: We sought to investigate the functions of heparanase in MCs. METHODS: Primarily cultured fetal skin-derived mast cells (FSMCs) isolated from embryos and adult peritoneal MCs were analyzed for storage and release of granule molecules in response to MC activation. RESULTS: FSMCs from heparanase-overexpressing mice contained substantially shorter heparin chains and significantly less proteases than control cells. Conversely, FSMCs lacking heparanase contained heparin of larger size and more proteases than control cells. Correspondingly, heparanase-overexpressing adult MCs exhibited reduced release of heparin-bound proteases, a finding that could be attributed to spontaneous release of granular compounds. Heparanase was found to be upregulated in MCs on activation. CONCLUSION: These findings reveal a novel function of heparanase in maintaining MC homeostasis through controlled degradation of heparin present in the MC secretory granules.

Heparanase powers a chronic inflammatory circuit that promotes colitis-associated tumorigenesis in mice.

Ulcerative colitis (UC) is a chronic inflammatory bowel disease that is closely associated with colon cancer. Expression of the enzyme heparanase is clearly linked to colon carcinoma progression, but its role in UC is unknown. Here we demonstrate for what we believe to be the first time the importance of heparanase in sustaining the immune-epithelial crosstalk underlying colitis-associated tumorigenesis. Using histological specimens from UC patients and a mouse model of dextran sodium sulfate-induced colitis, we found that heparanase was constantly overexpressed and activated throughout the disease. We demonstrate, using heparanase-overexpressing transgenic mice, that heparanase overexpression markedly increased the incidence and severity of colitis-associated colonic tumors. We found that highly coordinated interactions between the epithelial compartment (contributing heparanase) and mucosal macrophages preserved chronic inflammatory conditions and created a tumor-promoting microenvironment characterized by enhanced NF-κB signaling and induction of STAT3. Our results indicate that heparanase generates a vicious cycle that powers colitis and the associated tumorigenesis: heparanase, acting synergistically with the intestinal flora, stimulates macrophage activation, while macrophages induce production (via TNF-α-dependent mechanisms) and activation (via secretion of cathepsin L) of heparanase contributed by the colon epithelium. Thus, disruption of the heparanase-driven chronic inflammatory circuit is highly relevant to the design of therapeutic interventions in colitis and the associated cancer.

Role of heparanase on hepatic uptake of intestinal derived lipoprotein and fatty streak formation in mice.

BACKGROUND: Heparanase modulates the level of heparan sulfate proteoglycans (HSPGs) which have an important role in multiple cellular processes. Recent studies indicate that HSPGs have an important function in hepatic lipoprotein handling and processes involving removal of lipoprotein particles. PRINCIPAL FINDINGS: To determine the effects of decreased HSPGs chain length on lipoprotein metabolism and atherosclerosis, transgenic mice over-expressing the human heparanase gene were studied. Hepatic lipid uptake in hpa-Tg mice were evaluated by giving transgenic mice oral fat loads and labeled retinol. Sections of aorta from mice over-expressing heparanase (hpa-Tg) and controls (C57/BL6) fed an atherogenic diet were examined for evidence of atherosclerosis. Heparanase over-expression results in reduced hepatic clearance of postprandial lipoproteins and higher levels of fasting and postprandial serum triglycerides. Heparanase over-expression also induces formation of fatty streaks in the aorta. The mean lesion cross-sectional area in heparanase over-expressing mice was almost 6 times higher when compared to control mice (23,984 µm(2)±5,922 vs. 4,189 µm(2)±1,130, p<0.001). CONCLUSIONS: Over-expression of heparanase demonstrates the importance of HSPGs for the uptake of intestinal derived lipoproteins and its role in the formation of fatty streaks.

Role of heparanase in radiation-enhanced invasiveness of pancreatic carcinoma.

Pancreatic cancer is characterized by very low survival rates because of high intrinsic resistance to conventional therapies. Ionizing radiation (IR)-enhanced tumor invasiveness is emerging as one mechanism responsible for the limited benefit of radiotherapy in pancreatic cancer. In this study, we establish the role of heparanase-the only known mammalian endoglycosidase that cleaves heparan sulfate-in modulating the response of pancreatic cancer to radiotherapy. We found that clinically relevant doses of IR augment the invasive capability of pancreatic carcinoma cells in vitro and in vivo by upregulating heparanase. Changes in the levels of the transcription factor Egr-1 occurred in pancreatic cancer cells following radiation, underlying the stimulatory effect of IR on heparanase expression. Importantly, the specific heparanase inhibitor SST0001 abolished IR-enhanced invasiveness of pancreatic carcinoma cells in vitro, whereas combined treatment with SST0001 and IR, but not IR alone, attenuated the spread of orthotopic pancreatic tumors in vivo. Taken together, our results suggest that combining radiotherapy with heparanase inhibition is an effective strategy to prevent tumor resistance and dissemination, observed in many IR-treated pancreatic cancer patients. Further, the molecular mechanism underlying heparanase upregulation in pancreatic cancer that we identified in response to IR may help identify patients in which radiotherapeutic intervention may confer increased risk of metastatic spread, where antiheparanase therapy may be particularly beneficial.

Local retention versus systemic release of soluble VEGF receptor-1 are mediated by heparin-binding and regulated by heparanase.

RATIONALE: The vascular endothelial growth factor (VEGF) decoy receptor soluble VEGF-R1 (sVEGF-R1) is thought to protect the cells that produce it from adverse VEGF signaling. To accomplish this role, a mechanism for pericellular retention of sVEGF-R1 is required. Local retention may also prevent the accumulation of high circulating levels of sVEGF-R1 and resulting interference with homeostatic VEGF functions in remote organs. OBJECTIVE: To reveal natural storage depots of sVEGF-R1 and determine mechanisms underlying its pericellular retention. To uncover natural mechanisms regulating its systemic release. METHODS AND RESULTS: We show that both the canonical and human-specific isoforms of sVEGF-R1 are strongly bound to heparin. sVEGF-R1 produced by vascular smooth muscle cells is stored in the vessel wall and can be displaced from isolated mouse aorta by heparin. Another major reservoir of sVEGF-R1 is the placenta. Heparin increases the level of sVEGF-R1 released by cultured human placental villi, and pregnant women treated with low molecular weight heparin showed markedly elevated levels of sVEGF-R1 in the circulation. Heparanase is expressed in human placenta at the same locales as sVEGF-R1, and its transgenic overexpression in mice resulted in a marked increase in the levels of circulating sVEGF-R1. Conversely, heparanase inhibition, by either a neutralizing antibody or by inhibition of its maturation, reduced the amounts of sVEGF-R1 released from human placental villi, indicating a natural role of heparanase in sVEGF-R1 release. CONCLUSIONS: Together, the findings uncover a new level of regulation governing sVEGF-R1 retention versus release and suggest that manipulations of the heparin/heparanase system could be harnessed for reducing unwarranted release of sVEGF-R1 in pathologies such as preeclampsia.

Involvement of heparanase in vaginal and cesarean section deliveries.

BACKGROUND: Heparanase is an endo-ß-D-glucuronidase dominantly involved in cell invasion, tumor angiogenesis and metastasis. Recently, we demonstrated increased levels of heparanase, tissue factor pathway inhibitor (TFPI)-2 and vascular endothelial growth factor (VEGF)-A in early miscarriages (Nadir et al., Thromb Res, 2010). Herein, we investigated the role of heparanase in third trimester placentas, in correlation to tissue factor (TF), TFPI, TFPI-2, and VEGF-A. METHODS: Twenty five third-trimester placenta samples (weeks 36-41) were studied applying real time RTPCR and immunostaining. Ten cases were placentas of elective cesarean sections, 8 cases were of normal vaginal deliveries and 7 samples were placentas of intra-uterine growth restriction (IUGR) fetuses. Skin and lung tissues of heparanase over-expressing mice and heparanase knock-out mice were subjected to immunostaining. RESULTS: Sections obtained from vaginal and IUGR placentas revealed 2 folds increased levels of heparanase, TFPI-2 and VEGF-A compared to placentas from elective cesarean sections in maternal decidua as well as in fetal placenta elements. Interestingly, abundance of TFPI staining in the intra-villous blood was observed in placentas of vaginal and IUGR deliveries. Heparanase effect on TFPI release to the blood was supported by immunostaining of heparanase over-expressing and heparanase knock-out mice tissues. CONCLUSIONS: In regard to our previous data on early pregnancy losses, the present data strengthen the understanding that in placental vascular complications levels of heparanase, TFPI-2 and VEGF-A increase. In the process of delivery, heparanase may have a regulatory role on TFPI release to fetal circulation.

A chemotactic gradient sequestered on endothelial heparan sulfate induces directional intraluminal crawling of neutrophils.

During infection, chemokines sequestered on endothelium induce recruitment of circulating leukocytes into the tissue where they chemotax along chemokine gradients toward the afflicted site. The aim of this in vivo study was to determine whether a chemokine gradient was formed intravascularly and influenced intraluminal neutrophil crawling and transmigration. A chemokine gradient was induced by placing a macrophage inflammatory protein-2 (MIP-2)-containing (CXCL2) gel on the cremaster muscle of anesthetized wild-type mice or heparanase-overexpressing transgenic mice (hpa-tg) with truncated heparan sulfate (HS) side chains. Neutrophil-endothelial interactions were visualized by intravital microscopy and chemokine gradients detected by confocal microscopy. Localized extravascular chemokine release (MIP-2 gel) induced directed neutrophil crawling along a chemotactic gradient immobilized on the endothelium and accelerated their recruitment into the target tissue compared with homogeneous extravascular chemokine concentration (MIP-2 superfusion). Endothelial chemokine sequestration occurred exclusively in venules and was HS-dependent, and neutrophils in hpa-tg mice exhibited random crawling. Despite similar numbers of adherent neutrophils in hpa-tg and wild-type mice, the altered crawling in hpa-tg mice was translated into decreased number of emigrated neutrophils and ultimately decreased the ability to clear bacterial infections. In conclusion, an intravascular chemokine gradient sequestered by endothelial HS effectively directs crawling leukocytes toward transmigration loci close to the infection site.

Heparanase promotes engraftment and prevents graft versus host disease in stem cell transplantation.

BACKGROUND: Heparanase, endoglycosidase that cleaves heparan sulfate side chains of heparan sulfate proteoglycans, plays important roles in cancer metastasis, angiogenesis and inflammation. DESIGN AND METHODS: Applying a mouse model of bone marrow transplantation and transgenic mice over-expressing heparanase, we evaluated the effect of heparanase on the engraftment process and the development of graft-versus-host disease. RESULTS: Analysis of F1 mice undergoing allogeneic bone marrow transplantation from C57BL/6 mice demonstrated a better and faster engraftment in mice receiving cells from donors that were pretreated with heparanase. Moreover, heparanase treated recipient F1 mice showed only a mild appearance of graft-versus-host disease and died 27 days post transplantation while control mice rapidly developed signs of graft-versus-host disease (i.e., weight loss, hair loss, diarrhea) and died after 12 days, indicating a protective effect of heparanase against graft-versus-host disease. Similarly, we applied transgenic mice over-expressing heparanase in most tissues as the recipients of BMT from C57BL/6 mice. Monitoring clinical parameters of graft-versus-host disease, the transgenic mice showed 100% survival on day 40 post transplantation, compared to only 50% survival on day 14, in the control group. In vitro and in vivo studies revealed that heparanase inhibited T cell function and activation through modulation of their cytokine repertoire, indicated by a marked increase in the levels of Interleukin-4, Interleukin-6 and Interleukin-10, and a parallel decrease in Interleukin-12, tumor necrosis factor-alfa and interferon-gamma. Using point mutated inactive enzyme, we found that the shift in cytokine profile was independent of heparanase enzymatic activity. CONCLUSIONS: Our results indicate a significant role of heparanase in bone marrow transplantation biology, facilitating engraftment and suppressing graft-versus-host disease, apparently through an effect on T cell activation and cytokine production pattern.

Heparanase upregulates Th2 cytokines, ameliorating experimental autoimmune encephalitis.

Heparanase is an endo-beta-d-glucuronidase that cleaves heparan sulfate (HS) saccharide chains. The enzyme promotes cell adhesion, migration and invasion and plays a significant role in cancer metastasis, angiogenesis and inflammation. The present study focuses on the involvement of heparanase in autoimmunity, applying the murine experimental autoimmune encephalitis (EAE) model, a T-cell dependent disease often used to investigate the pathophysiology of multiple sclerosis (MS). Intraperitoneal administration of recombinant heparanase ameliorated, in a dose dependent manner, the clinical signs of the disease. In vitro and in vivo studies revealed that heparanase inhibited mitogen induced splenocyte proliferation and mixed lymphocyte reaction (MLR) through modulation of their repertoire of cytokines indicated by a marked increase in the levels of IL-4, IL-6 and IL-10, and a parallel decrease in IL-12 and TNF-alpha. Similar results were obtained with active, latent, or point mutated inactive heparanase, indicating that the observed inhibitory effect is attributed to a non-enzymatic activity of the heparanase protein. We suggest that heparanase induces upregulation of Th2 cytokines, resulting in inhibition of the inflammatory lesion of EAE.

Accumulation of Ym1 and formation of intracellular crystalline bodies in alveolar macrophages lacking heparanase.

Heparanase is a heparan sulfate (HS) degrading endoglucuronidase that has been implicated in cell migration and inflammatory conditions. Here we used mice deficient of heparanase (Hpse(-/-)) to study the impact of heparanase on airway leukocytes. Normal numbers of macrophages and lymphocytes were present in bronchoalveolar lavage fluid of Hpse(-/-) mice, indicating that heparanase is not essential for proper homing of leukocytes to airways. While lymphocytes from Hpse(-/-) mice displayed normal morphology, Hpse(-/-) alveolar macrophages showed a striking, age-dependent appearance of granule-like structures in the cytoplasm. Transmission electron microscopy revealed that these structures corresponded to membrane-enclosed crystalline bodies that closely resembled the intracellular crystals known to be formed by the HS-binding protein Ym1, suggesting that heparanase deficiency is associated with intracellular Ym1 deposition. Indeed, applying immunocytochemistry, we found markedly higher levels of intracellular Ym1 protein in Hpse(-/-) versus WT alveolar macrophages, and there was a significant correlation between levels of Ym1 protein detected by immunoblotting and amounts of crystalline material in BAL cells. Biosynthetic radio-labeling of the macrophages revealed accumulation of non-degraded HS chains in Hpse(-/-) macrophages. Together, these findings implicate heparanase in normal processing of HS in macrophages, and indicate that heparanase regulates intracellular Ym1 accumulation and crystal formation in airways.

Newly generated heparanase knock-out mice unravel co-regulation of heparanase and matrix metalloproteinases.

BACKGROUND: Heparanase, a mammalian endo-beta-D-glucuronidase, specifically degrades heparan sulfate proteoglycans ubiquitously associated with the cell surface and extracellular matrix. This single gene encoded enzyme is over-expressed in most human cancers, promoting tumor metastasis and angiogenesis. PRINCIPAL FINDINGS: We report that targeted disruption of the murine heparanase gene eliminated heparanase enzymatic activity, resulting in accumulation of long heparan sulfate chains. Unexpectedly, the heparanase knockout (Hpse-KO) mice were fertile, exhibited a normal life span and did not show prominent pathological alterations. The lack of major abnormalities is attributed to a marked elevation in the expression of matrix metalloproteinases, for example, MMP2 and MMP14 in the Hpse-KO liver and kidney. Co-regulation of heparanase and MMPs was also noted by a marked decrease in MMP (primarily MMP-2,-9 and 14) expression following transfection and over-expression of the heparanase gene in cultured human mammary carcinoma (MDA-MB-231) cells. Immunostaining (kidney tissue) and chromatin immunoprecipitation (ChIP) analysis (Hpse-KO mouse embryonic fibroblasts) suggest that the newly discovered co-regulation of heparanase and MMPs is mediated by stabilization and transcriptional activity of beta-catenin. CONCLUSIONS/SIGNIFICANCE: The lack of heparanase expression and activity was accompanied by alterations in the expression level of MMP family members, primarily MMP-2 and MMP-14. It is conceivable that MMP-2 and MMP-14, which exert some of the effects elicited by heparanase (i.e., over branching of mammary glands, enhanced angiogenic response) can compensate for its absence, in spite of their different enzymatic substrate. Generation of viable Hpse-KO mice lacking significant abnormalities may provide a promising indication for the use of heparanase as a target for drug development.

Alternatively spliced Spalax heparanase inhibits extracellular matrix degradation, tumor growth, and metastasis.

Heparanase is an endoglycosidase that degrades heparan sulfate (HS) at the cell surface and in the extracellular matrix. Heparanase is expressed mainly by cancer cells, and its expression is correlated with increased tumor aggressiveness, metastasis, and angiogenesis. Here, we report the cloning of a unique splice variant (splice 36) of heparanase from the subterranean blind mole rat (Spalax). This splice variant results from skipping part of exon 3, exons 4 and 5, and part of exon 6 and functions as a dominant negative to the wild-type enzyme. It inhibits HS degradation, suppresses glioma tumor growth, and decreases experimental B16-BL6 lung colonization in a mouse model. Intriguingly, Spalax splice variant 7 of heparanase (which results from skipping of exon 7) is devoid of enzymatic activity, but unlike splice 36 it enhances tumor growth. Our results demonstrate that alternative splicing of heparanase regulates its enzymatic activity and might adapt the heparanase function to the fluctuating normoxic-hypoxic subterranean environment that Spalax experiences. Development of anticancer drugs designed to suppress tumor growth, angiogenesis, and metastasis is a major challenge, of which heparanase inhibition is a promising approach. We anticipate that the heparanase splicing model, evolved during 40 million years of Spalacid adaptation to underground life, would pave the way for the development of heparanase-based therapeutic modalities directed against angiogenesis, tumor growth, and metastasis.

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.

Heparanase regulates retention and proliferation of primitive Sca-1+/c-Kit+/Lin- cells via modulation of the bone marrow microenvironment.

Heparanase is involved in tumor growth and metastasis. Because of its unique cleavage of heparan sulfate, which binds cytokines, chemokines and proteases, we hypothesized that heparanase is also involved in regulation of early stages of hematopoiesis. We report reduced numbers of maturing leukocytes but elevated levels of undifferentiated Sca-1(+)/c-Kit(+)/Lin(-) cells in the bone marrow (BM) of mice overexpressing heparanase (hpa-Tg). This resulted from increased proliferation and retention of the primitive cells in the BM microenvironment, manifested in increased SDF-1 turnover. Furthermore, heparanase overexpression in mice was accompanied by reduced protease activity of MMP-9, elastase, and cathepsin K, which regulate stem and progenitor cell mobilization. Moreover, increased retention of the progenitor cells also resulted from up-regulated levels of stem cell factor (SCF) in the BM, in particular in the stem cell-rich endosteum and endothelial regions. Increased SCF-induced adhesion of primitive Sca-1(+)/c-Kit(+)/Lin(-) cells to osteoblasts was also the result of elevation of the receptor c-Kit. Regulation of these phenomena is mediated by hyperphosphorylation of c-Myc in hematopoietic progenitors of hpa-Tg mice or after exogenous heparanase addition to wildtype BM cells in vitro. Altogether, our data suggest that heparanase modification of the BM microenvironment regulates the retention and proliferation of hematopoietic progenitor cells.