- About this Journal ·
- Abstracting and Indexing ·
- Advance Access ·
- Aims and Scope ·
- Article Processing Charges ·
- Articles in Press ·
- Author Guidelines ·
- Bibliographic Information ·
- Citations to this Journal ·
- Contact Information ·
- Editorial Board ·
- Editorial Workflow ·
- Free eTOC Alerts ·
- Publication Ethics ·
- Reviewers Acknowledgment ·
- Submit a Manuscript ·
- Subscription Information ·
- Table of Contents
International Journal of Vascular Medicine
Volume 2013 (2013), Article ID 963596, 10 pages
Glycoconjugates and Related Molecules in Human Vascular Endothelial Cells
Research Team for Geriatric Medicine (Vascular Medicine), Tokyo Metropolitan Institute of Gerontology, Sakaecho 35-2, Itabashi-ku, Tokyo 173-0015, Japan
Received 2 August 2013; Accepted 12 August 2013
Academic Editor: Yoshitaka Iso
Copyright © 2013 Norihiko Sasaki and Masashi Toyoda. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
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.
Vascular endothelial cells (ECs) constitute the inner lining (endothelium) of blood vessels that form an interface between the blood and the vessel wall. Blood vessels alter their morphology and function in response to changes in blood flow, and their responses are based on blood flow detection by the vascular endothelium. ECs sense shear stress generated by flowing blood and transmit the signal to the interior of the cell, thereby evoking a cellular response . The EC response to shear stress is closely linked to the regulation of vascular tone, blood coagulation and fibrinolysis, angiogenesis, and vascular remodeling. ECs also control vascular barrier regulation, passive diffusion, and active transport of substances from the blood . Thus, ECs play important roles in vascular homeostatic functions, and excess activation or dysfunction of ECs is considered to lead to the development of vascular-related diseases, such as restenosis, arteriosclerosis, and cancer.
Carbohydrate antigens (also called glycans) are expressed on the cell surface as components of glycoproteins, glycosphingolipids, and proteoglycans; these carbohydrate antigens contribute significantly to fundamental biological functions, such as cell differentiation, cell adhesion, cell-cell interaction, pathogen-host recognition, toxin-receptor interactions, cancer metastasis, immune responses, and regulation of signaling pathways . Several studies have revealed that glycoconjugates play key roles in vascular biology. In this paper, we describe the importance of glycoconjugates in human ECs, with respect to their regulated expression and functional roles, particularly under pathological conditions.
Glycoproteins are proteins that contain oligosaccharide chains (glycans) covalently attached to polypeptide side chains. The carbohydrate is attached to the protein as a cotranslational or posttranslational modification. This glycosylation of proteins is important for their physicochemical and biological properties, such as protein folding, stability, targeting, dynamics, and ligand binding .
The vascular endothelial cadherin (VE-cadherin), including seven potential N-glycosylation sites, is endothelium specific and belongs to endothelial adherens junctions. Human VE-cadherin was purified from cultured human umbilical cord vein endothelial cells (HUVECs), and its glycosylation pattern was analyzed in order to enable further functional investigations . The results revealed that VE-cadherin carries predominantly sialylated diantennary and hybrid-type glycans in addition to some triantennary and high-mannose-type species (sialylated hybrid type is shown in Figure 1(a)). Sialidase treatment of whole cells to remove cell surface sialic acids changed VE-cadherin immunofluorescence from a continuous netlike superstructural organization to an unevenly scattered one. These results indicate that cell surface sialic acids might play a role in VE-cadherin organization.
To date, several studies have been performed to unravel the relationship between changes in the expression of carbohydrate structures and the function of ECs in pathological conditions. TNF- is one of the inflammatory factors that activate endothelial cells at sites of injury to recruit immune cells in acute and chronic inflammatory processes. Treatment with TNF- differentially modulates a set of glycosylation-related genes, resulting in the increase of the cell membrane-associated glycans, such as -2,6-sialic acid and fucose--1,2-galactose-1,4-N-acetylglucosamine . Also, TNF- stimulates endothelial expression of N-glycans, specifically the high-mannose and/or the hybrid types (Figures 1(b) and 1(c)), at cell junctions, and these epitopes play a role in modulating monocyte rolling and adhesion to the endothelium .
In pathological conditions such as tumorigenesis and atherogenesis, endothelial dysfunction may be related to a change in cell surface glycans as follows. Using a flow cytometry assay with glycan-specific lectins, the expression profiles of a selected group of 9 carbohydrate structures (-1,6-GlcNAc branching, high-mannose N-glycans, -linked fucose residues, N-acetylglucosamine, -2,3-sialic acid, N-acetyllactosamine, -2,6-sialic acid, -mannose, and -1,4-galactose) were compared in HUVECs under control and tumor-conditioned medium- (TCM-) treated conditions. The expression of 6 of these structures (-1,6-GlcNAc branching, high-mannose N-glycans, N-acetyllactosamine, -2,6-sialic acid, -mannose, and -1,4-galactose) increased significantly after TCM treatment. In particular, the -1,6-GlcNAc branching glycan expression level was greatly elevated after the stimulation . This -1,6-GlcNAc branching glycan was demonstrated to initiate endothelial cell contraction and gap formation, and these events lead to subsequent biological events such as tumorigenesis. High-mannose-type N-glycans increase in HAECs exposed to oscillatory shear or TNF- . Increasing surface N-linked mannose by inhibiting N-glycan processing potentiated monocyte adhesion under flow during TNF- stimulation. Conversely, enzymatic removal of high-mannose N-glycans or masking mannose residues with lectins significantly decreased monocyte adhesion under flow. These results, therefore, indicate that surface N-linked mannose on ECs is a novel ligand for monocyte adhesion during atherogenesis.
A glycosphingolipid (GSL) is composed of a glycan structure attached to a lipid tail containing the sphingolipid ceramide. GSLs are widely expressed on cell membranes in lower and higher eukaryotic organisms. GSLs have frequently been used as important developmental marker molecules and have been suggested to have important biological functions [3, 9].
The expression profile of GSLs in HUVECs was investigated under normal conditions  and after activation by inflammatory stimuli . Inflammatory cytokines, such as IFN- and IL-1, have been known to alter expression of cell surface molecules in ECs. IFN- has a striking effect on the surface expression of GSLs, in particular on the surface expression of the major neutral GSL, globoside (globotetraosylceramide, Gb4Cer) (Figure 1(d)), but IFN- does not alter the total quantity of GSLs. By contrast, IL-1 increases the cell content of neutral and acidic GSLs but does not alter their surface expression.
ECs are believed to play an important role in the pathogenesis of hemolytic uremic syndrome (HUS). EC damage by Escherichia coli verocytotoxin in vitro is potentiated by additional exposure to inflammatory mediators such as TNF-. The inflammatory mediators TNF- and IL-1 make EC sensitive to verotoxin by elevation of verotoxin receptors such as GSL globotriaosylceramide (Gb3Cer/CD77) (Figure 1(e)) on the cell surface [12, 13]. ECs demonstrated that the level of EC sensitivity to verotoxin depends on the expression of Gb4Cer synthase .
Functional analysis of GSLs on human ECs in angiogenesis has been performed. The mechanism of VEGF-driven angiogenesis involving lactosylceramide (LacCer) (Figure 1(f)) was examined in HUVECs and HAECs by RNAi-mediated silencing of LacCer synthase expression (GalT-V) and by use of the pharmacological inhibitor of LacCer synthase, D-threo-1-phenyl-2-decanoylamino-3-morpholino-1-propanol (D-PDMP). LacCer contributes to VEGF-induced platelet EC adhesion molecule-1 (PECAM-1) expression and angiogenesis [15, 16]. This suggests that LacCer is important in VEGF-implicated angiogenesis associated with coronary heart disease, vascular complications in diabetes, inflammatory vascular diseases, and tumor metastases. The functional involvement of other GSLs in angiogenesis is also implied. Inhibition of ganglioside GM3 (Figure 1(g)) biosynthesis with the glucosyltransferase inhibitor, N-butyldeoxynojirimycin (NB-DNJ), increased the EC proliferation and the phosphorylation of VEGFR-2 and Akt. The effects of NB-DNJ were reversed by the addition of GM3 . Thus, this report concludes that GM3 has antiangiogenic action in ECs and may possess therapeutic potential for reducing tumor angiogenesis.
Sulfoglucuronosyl paragloboside (SGPG) (Figure 1(h)), a minor GSL in ECs, is a ligand for L-selectin. It has been implicated in neuroinflammatory diseases such as the Guillain-Barré syndrome. Inflammatory cytokines such as TNF- and IL-1 upregulate SGPG expression in human brain cerebromicrovascular ECs (SV-HCECs) by stimulating the gene expression of the P and S forms of glucuronosyltransferases (GlcATp and GlcATs) and the human natural killer antigen (HNK-1) sulfotransferase (HNK-1 ST) . Transfection of the SV-HCEC line with HNK-1 ST siRNA downregulated SGPG expression, inhibited cytokine-stimulated T-cell adhesion, and offered protection against apoptosis . This paper indicates the functional importance of SGPG expression for brain-associated ECs in neuroinflammatory diseases. Recently, the SGPG cell signaling pathways were investigated. SGPG expression was inhibited by transfecting the cells with HNK-1 ST gene siRNA, and SGPG synthesis was promoted by overexpressing GlcATp and GlcATs. And then, either up- or downregulation of SGPG reduces activation of the NF-B pathway, which is mediated by the accumulation of inhibitor of B (IB) .
Proteoglycans (PGs) are macromolecules composed of a specific core protein substituted with covalently linked glycosaminoglycan (GAG) chains, namely, chondroitin sulfate (CS), dermatan sulfate (DS), and heparan sulfate (HS). Hyaluronan (HA) is the only GAG synthesized in a free form not covalently bound to a core protein. GAGs are linear, negatively charged polysaccharides comprised of repeating disaccharides of acetylated hexosamines (N-acetyl-galactosamine or N-acetyl-glucosamine) and mainly uronic acids (D-glucuronic acid or L-iduronic acid) sulfated at various positions. In HA, there are no chemical modifications such as sulfation and epimerization.
PGs can be classified into two main groups according to their localization: those extracellularly secreted and those associated with the cell surface. The secreted group consists of PGs involving large aggregating PGs, namely, hyalectans (e.g., versican), small leucine-rich PGs (SLRPs), and basement membrane PGs (e.g., perlecan). Cell-surface-associated PGs are divided into two main subfamilies: syndecans and glypicans [21, 22]. PGs perform numerous biological functions, act as structural components in tissue organization, and affect several cellular parameters, such as cell proliferation, adhesion, migration, and differentiation. PGs interact with growth factors and cytokines, as well as with growth factor receptors, and they are implicated in cell signaling.
4.1.1. Heparan Sulfate (HS)
To clarify the roles of HS in endothelium under pathological conditions, HS expression on human ECs was studied following stimulation by inflammatory or hyperglycemic conditions. Inflammation is pivotal in atherosclerosis, and a key early step is endothelial dysfunction. It was found that IL-1, TNF-, and IFN- influence HS expression significantly in HUVECs . Also, C-reactive protein, the prototypic marker of inflammation and cardiovascular risk marker, has been shown to promote atherogenesis, and increased levels of C-reactive protein are associated with endothelial dysfunction. C-reactive protein treatment caused the expression of HS to significantly reduce . In diabetes, the endothelium is exposed chronically or transiently to hyperglycemic conditions. In addition, endothelial dysfunction in diabetes is related to changes in the inflammatory response and turnover of the extracellular matrix. In hyperglycemic conditions, short-term inflammatory stimuli affected both the size and the sulfation pattern of HS on ECs, with the outcome depending on the type of stimulus . Thus, modification of HS under pathological conditions is considered a major cause of endothelial dysfunction, resulting in the disturbance of vascular integrity and barrier properties, due to decreased negative charge and increased permeability, and the consequent release of bioactive substances such as cytokines, enzymes, and growth factors.
To date, several studies have investigated the binding capabilities of HS on human ECs. Adhesion of leukocyte to ECs is partly dependent on HS that binds to L-selectin . The S100 family heterodimer, MRP-8/14 complex, which is abundantly expressed in inflamed endothelium, binds to ECs via the MRP-14 subunit, interacting chiefly with HS . It has also been shown that HMGB1 (high-mobility-group protein B1), an inflammatory cytokine, and receptor for advanced glycation endproducts (RAGEs) bind to HS . In another study, P. falciparum-infected erythrocytes (parasitized red blood cells) adhere to HS on ECs . Binding via HS followed by sequestration may be related to the severity of the diseases.
Functional studies of HS on human ECs have been performed. In HUVECs, RNAi-mediated downregulation of HSulf-1, which selectively removes 6-O-sulfate from HS, resulted in increased proliferation mediated by HS-dependent FGF-2, hepatocyte growth factor, and VEGF165. HSulf-1 downregulation also enhanced downstream signaling through the extracellular signal-regulated kinase pathway, when compared with untreated cells . Another study confirmed the importance of HS 6-O-sulfate in EC function . Reducing HS 6-O-sulfotransferase-1 (HS6ST-1) or 6-O-sulfotransferase-2 (HS6ST-2) expression in ECs with RNAi affected the prevalence of HS 6-O-sulfate moieties in HS sequences; 1%–40% reduction in 6-O-sulfates significantly compromised FGF-2- and VEGF165-induced EC sprouting and tube formation. These data indicate that 6-O-sulfate moieties in endothelial HS are of major importance in regulating FGF2- and VEGF165-dependent EC functions.
4.1.2. Chondroitin Sulfate (CS)
CD97, which is highly expressed on various inflammatory cells and some carcinomas, contributes to inflammation-mediated angiogenesis and possibly tumor progression. CD97 acts as a potent chemoattractant for the migration and invasion of ECs, and this function is integrin dependent. CD97 EGF-like repeat 4 is known to bind CS. One study  showed that coengagement of 51 and CS proteoglycan by CD97 synergistically initiates EC invasion.
4.1.3. Hyaluronan (HA)
Chronic inflammation has a critical role in the onset of several diseases, including atherosclerosis, and endothelial dysfunction is a key early step in these diseases. A study  has shown that the expression of HA on HUVECs is induced by IL-15, which has been suggested to play a role in the setting of the chronic autoimmune disease, particularly in the recruitment and activation of synovial T-cells. The results of the study suggest that IL-15 can regulate EC function and thereby enable a CD44-initiated adhesion pathway that facilitates the entry of activated T lymphocytes into inflammatory sites. In HAECs, C-reactive protein, the expression of which is related to inflammation as well as endothelial dysfunction, dose dependently increased HA release. This is thought to result in EC dysfunction by, for example, increasing monocyte-EC adhesion . Another study found that IL-1, TNF-, and TNF- strongly induce HA synthesis via the NF-B pathway. Moreover, it has been verified that U937 monocyte adhesion to stimulated ECs depends strongly on HA . Thus, in chronic inflammation, elevation of HA expression via inflammatory stimulation promotes adhesion of leucocytes to ECs, resulting in vascular-related diseases, such as atherosclerosis.
Recent in vivo studies revealed that the inner blood vessel surface is lined with an endothelial surface layer at least 0.5 m thick, which serves as a shield protecting the vessel wall from arteriosclerosis. HA seems to be an essential component that is related to the atheroprotective properties of this surface structure. It has also been shown that HA is increased in a shear-stress-dependent manner via the phosphatidylinositol 3-kinase-Akt pathway [35, 36]. In particular, pulsatile, arterial-like shear stress conditions effectively induced HA . Thus, fluid shear stress stimulates the incorporation of HA into the glycocalyx, which may contribute to its vasculoprotective effects against proinflammatory and pro-atherosclerotic stimuli.
4.2. Extracellularly Secreted PGs
It has been reported that the amounts of heparan sulfate (HS) in perlecan (an HSPG) are different in HUVECs and HAECs and that HS expression affects perlecan-dependent adhesion of vascular cells . The functions of HS in endothelial perlecan were further investigated [38, 39]. The studies show that the binding abilities of FGF-1 and FGF-2 to endothelial perlecan differ depending on the HS structures in the different cell types.
Hyperglycemia is an independent risk factor for diabetes-associated cardiovascular disease. One potential mechanism involves hyperglycemia-induced changes in arterial wall extracellular matrix components leading to increased atherosclerosis susceptibility. A decrease in HS GAG has been reported in the arteries of diabetics. In HAECs, high glucose induced modification in HS but not in perlecan core protein levels . In addition, endothelial dysfunction in diabetes is related to changes in the inflammatory response and the turnover of extracellular matrix. In hyperglycemic conditions, secretion of perlecan from ECs was increased after IL-1 stimulation .
Perlecan, but not other HSPGs, is dramatically downregulated in ECs treated with antiangiogenic cleaved and latent forms of antithrombin [41, 42]. The previously established key role of perlecan in mediating FGF-2 stimulation of EC proliferation and angiogenesis suggests that a primary mechanism by which antiangiogenic antithrombins exert their effects is through the downregulation of perlecan expression. The role of perlecan in the antiangiogenesis function of NK4, an angiogenesis inhibitor, was also studied . In this study, knockdown of perlecan expression in ECs by RNAi significantly reduced the inhibitory effect of NK4 on fibronectin assembly and cell spreading. Thus, this study indicates that the association of NK4 with perlecan plays a key role in angiogenesis inhibition by NK4.
Endocan is a novel small soluble dermatan sulfate proteoglycan (DSPG) produced specially by ECs. In SV40-transfected human ECs (SV1 cells), endocan regulates HGF/SF-mediated mitogenic activity and may support the function of HGF/SF, not only in embryogenesis and tissue repair after injury but also in tumor progression . Additionally, endocan expression in HUVECs is upregulated by tumor-cell-conditioned medium . Moreover, treatment with VEGF resulted in dose- and time-dependent increases in endocan mRNA. The results suggest that endocan is preferentially expressed in tumor endothelium in vivo and that its expression is regulated by tumor-derived factors. Now, it is highlighted that endocan is a marker of EC activation during growth of the new vessels required for tumor progression .
Decorin, a member of the small leucine-rich repeat proteoglycan (SLRP) family, is expressed by sprouting ECs during inflammation-induced angiogenesis in vivo and by human ECs cocultured with fibroblasts in a collagen lattice. Activation with IL-10 or IL-6 treatment induces decorin mRNA in human ECs . As function of decorin in human ECs, it has been reported that decorin core protein can bind to and activate insulin-like growth factor-I receptor (IGF-IR)  and that decorin promotes 21 integrin-dependent EC adhesion and migration on fibrillar collagen type I . It is now understood that modulation of cell-matrix interactions by decorin plays a key role during angiogenesis .
Primary human ECs, if stimulated with TNF- or VEGF, alter their expression of versican (a large aggregating CSPG) by de novo transcription of the V3 isoform and by exhibiting a moderate V1/V2 production. Induced versican synthesis and de novo V3 expression were also observed in ECs induced to migrate in a wound-healing model in vitro and in angiogenic ECs forming tubule-like structures in Matrigel or fibrin clots. Thus, in activated conditions, versican expression in human ECs is altered . This study indicates that versican produced from ECs plays a key role in the pathological conditions such as inflammation, angiogenesis, and wound healing.
4.2.5. Biglycan and PG-100
When EA.hy 926 cells, one of human ECs, form monolayer cultures typical of macrovascular ECs, they express and synthesize detectable amounts of biglycan and PG-100 (members of the small leucine-rich repeat proteoglycan family). TNF-, responsible for changing the morphology of the cells from a polygonal to a spindle shape and for stimulating the detachment of the cells from the culture dish, markedly decreased the synthesis of biglycan. By contrast, PG-100 expression was increased in response to FGF-2, FGF-7, TNF-, and TGF- . Although the functional roles of biglycan and PG-100 are not yet clearly understood, their different responses to the stimuli may be critical for the progression of vascular diseases. Another study has shown that antiangiogenic antithrombin treatment significantly decreases biglycan in HUVECs , suggesting that a mechanism of antiangiogenic antithrombins is through the downregulation of proangiogenic biglycan.
4.3. Cell Surface PGs
Glypican-1 is the only glypican expressed in the vascular system. VEGF165 interacts with EC-derived glypican-1 dependent on HS . Recently, the contribution of glypican-1 to the cell cycle and proliferation has been demonstrated in ECs .
Proteoglycans (PGs) are important constituents of the plasma membrane and of the basement membrane supporting the EC layer. Changes in the amounts or the structures of PGs in the endothelium may affect important functions, such as turnover of lipoproteins, filtration properties, and regulation of chemokines during inflammation, which are all relevant to diabetes. In HUVECs, exposure to high glucose (hyperglycemic condition) leads to decreased secretion of syndecan-1 . Thrombospondin-1 (TSP-1), an extracellular matrix protein, modulates focal adhesion in mammalian cells and exhibits dual roles in angiogenesis. There are indications that binding of TSP-1 to syndecan-4 proteoglycan mediates tubulogenesis and their protection from apoptosis . Syndecan-2, the major syndecan expressed by human microvascular ECs (HMECs), is regulated by growth factors and extracellular matrix proteins, in both bidimensional and tridimensional culture conditions . Downregulation of syndecan-2 reduced the spreading and adhesion of HMECs, and it not only enhanced their migration but also impaired the formation of capillary-like structures. Therefore, syndecan-2 has an important function in some of the necessary steps in the angiogenic process. Syndecan-1 is a critical regulator of v3 and v5 integrins during angiogenesis and tumorigenesis, and it is inhibited by the novel peptide called synstatin .
5. Glycoconjugate-Related Molecules: Galectins
Galectins are a family of lectins that bind to -galactosides via a carbohydrate recognition domain containing many conserved sequence elements . There are currently 15 known mammalian galectins , which are involved in a variety of biological processes . Expression of galectin-1 in cultured human ECs was first shown in 1995 by Baum et al. . They also showed that activation of cultured ECs by minimally oxidized low-density lipoprotein (MM-LDL) or cytokines and LPS increases galectin-1 expression, as determined by ELISA, northern blot analysis, and high-throughput cDNA sequencing. Another study found that poly IC, a synthetic analog of double-stranded RNA (dsRNA), enhances the expression of galectin-9 mRNA and protein in ECs in concentration- and time-dependent manners . Treatment of cells with dsRNA in vitro mimics viral infection and regulates the expression of various genes. Thus, it has been proposed that upregulation of galectin-9 expression by poly IC in the vascular endothelium may be part of the mechanism for leukocyte trafficking through the vascular wall after viral infection. Subsequently, galectin-1, -3, -8, and -9 expression levels in quiescent ECs were measured, and the expression and distribution of these galectins changed after activation with tumor-derived culture medium . Recently, it was reported that galectin-9 protein expression is positively regulated by histone deacetylase 3 in ECs . This study provides new evidence that HDAC3 regulates galectin-9 expression in ECs via interaction with the PI3K-IRF3 signaling pathway.
Some functional analyses of galectins in human ECs have been reported. Cancer-associated carbohydrate T antigen plays a leading role in docking breast and prostate cancer cells onto endothelium by specifically interacting with EC-expressed galectin-3 . One of the low-molecular-weight synthetic lactulose amines (SLAs), N, N′-dilactulose-octamethylenediamine (D-LDO), severely impaired tube formation of ECs. This inhibitory effect is thought to occur by inhibition of galectin-1- and/or galectin-3-mediated functions. D-LDO inhibited the binding of galectin-1 and/or galectin-3 to the highly glycosylated protein 90 K. Thus, D-LDO may be a new galectin inhibitor for blocking angiogenesis . In HUVECs, knockdown of galectin-3 and Mgat5, an enzyme that synthesizes high-affinity glycan ligands of galectin-3, reduced VEGF-A-mediated angiogenesis in vitro. A direct interaction was detected on the plasma membrane between galectin-3 and VEGF-R2, and this interaction was dependent on the expression of Mgat5. Using immunofluorescence and cell surface labeling, an increase in the level of internalized VEGF-R2 was observed in both Mgat5 and galectin-3 knockdown cells, suggesting that galectin-3 retains the receptor on the plasma membrane via lattice formation. Thus, galectin-3 contributes to the plasma membrane retention and proangiogenic functions of VEGF-R2 in ECs .
6. Glycan-Degrading Enzymes
Heparanase is an endo--D-glucuronidase responsible for heparan sulfate (HS) degradation at a limited number of sites, yielding HS fragments of an appreciable size (5–7 kDa) and with biological potency [69, 70]. In 1991, heparanase activity was observed in human ECs . Few reports of functional analyses of endogenous heparanase have since been published. The HS content of the endothelium is reduced under hyperglycemic conditions, and it may contribute to the pathogenesis of atherosclerosis. This suggests that HS reduction in ECs is due to increased heparanase production under hyperglycemic conditions. Recently, high-glucose-induced heparanase production and HS degradation were detected in human several types of ECs [72, 73]. In fact, functional analyses revealed that the expression of heparanase contributed to EC migration and proliferation. Furthermore, it has been shown that EC proliferation and migration correlate with Akt and ERK phosphorylation levels .
Sialidases are glycosidases that catalyze the removal of -glycosidically linked sialic acid residues from the carbohydrate groups of glycoproteins and glycolipids. To date, at least 4 mammalian sialidases, NEU1–4, have been identified [74, 75]. Whether the EC surface expresses sialidase activity was not known until recently. In human lung microvascular ECs (HMVEC-Ls) and human pulmonary artery ECs (HPAECs), NEU1–4 expression was examined, and functional analysis by knockdown and overexpression was performed. These ECs express catalytically active NEU1 and NEU3 sialidases, and NEU1 restrains the endothelial migratory response to wounding. It was concluded that NEU1 regulates endothelial remodeling in response to injury .
7. Closing Remark
In this paper, we described previous research about glycoconjugates in human ECs. To date, the functional roles of glycoconjugates in vivo have been investigated in animal disease models (e.g., atherosclerosis) (Figure 2(a)). In apoE-null mice, HS of perlecan contributes to the promotion of atherosclerosis . This contribution may involve increased LDL retention, altered vascular permeability, or other mechanisms. Additionally, a proatherosclerosis function of biglycan has been suggested by the retention of LDL . Abnormal angiogenesis plays a critical role in the pathogenesis of many diseases such as cancer, ischemic vascular disorders, and diabetic retinopathy . In particular, the importance of HS in tumor angiogenesis has been demonstrated by tumor-based studies in mice with endothelial-targeted genetic alterations in HS biosynthesis (Figure 2(a)) . Thus, the functional importance of glycoconjugates in vascular-related diseases has been demonstrated.
Glycoconjugates are markers for cell context, and they play biological roles. Increasing evidence from examination of human ECs indicates that glycoconjugates also serve as biomarkers and functional players in the human endothelium under pathological conditions as described here (Figure 2(b)). Therefore, although many issues await clarification, glycoconjugates are attractive potential targets for the prevention and treatment of vascular-related diseases. In recent years, the incidence of vascular-related diseases, such as cancer, cardiac disease, and cerebrovascular disease, has increased with an aging population, and prompt countermeasures are sought. Hence, further study of the functional roles of glycoconjugates in human ECs and identification of specific glycoconjugates related to disease are required in order to develop therapeutic strategies for vascular-related diseases, such as peripheral artery disease (PAD) (Figure 2(c)).
This work was supported by JSPS KAKENHI Grants nos. 24890298 (Grant-in-Aid for Young Scientists (Startup)), 22591557 (Grant-in-Aid for Scientific Research (C)), and 25670182 (Grant-in-Aid for Challenging Exploratory Research).
- Y.-S. J. Li, J. H. Haga, and S. J. Chien, “Molecular basis of the effects of shear stress on vascular endothelial cells,” Journal of Biomechanics, vol. 38, no. 10, pp. 1949–1971, 2005.
- W. C. Aird, “Phenotypic heterogeneity of the endothelium: I. Structure, function, and mechanisms,” Circulation Research, vol. 100, no. 2, pp. 158–173, 2007.
- Essentials of Glycobiology, Cold Spring Harbor Laboratory Press, Cold Spring Harbor, NY, USA, 2nd edition, 2008.
- H. Geyer, R. Geyer, M. Odenthal-Schnittler, and H.-J. Schnittler, “Characterization of human vascular endothelial cadherin glycans,” Glycobiology, vol. 9, no. 9, pp. 915–925, 1999.
- B. K. Chacko, D. W. Scott, R. T. Chandler, and R. P. Patel, “Endothelial surface N-glycans mediate monocyte adhesion and are targets for anti-inflammatory effects of peroxisome proliferator-activated receptor γ ligands,” Journal of Biological Chemistry, vol. 286, no. 44, pp. 38738–38747, 2011.
- J. J. García-Vallejo, W. van Dijk, B. van Het Hof et al., “Activation of human endothelial cells by tumor necrosis factor-α results in profound changes in the expression of glycosylation-related genes,” Journal of Cellular Physiology, vol. 206, no. 1, pp. 203–210, 2006.
- Y. Peng, J. Li, and M. Geng, “The glycan profile of endothelial cells in the present of tumor-conditioned medium and potential roles of β-1,6-GlcNAc branching on HUVEC conformation,” Molecular and Cellular Biochemistry, vol. 340, no. 1-2, pp. 143–152, 2010.
- D. W. Scott, J. Chen, B. K. Chacko, et al., “Role of endothelial N-glycan mannose residues in monocyte recruitment during atherogenesis,” Arteriosclerosis, Thrombosis, and Vascular Biology, vol. 32, no. 8, pp. e51–e59, 2012.
- C. A. Lingwood, “Glycosphingolipid functions,” Cold Spring Harbor Perspectives in Biology, vol. 3, no. 7, pp. 1–26, 2011.
- B. K. Gillard, M. A. Jones, and D. M. Marcus, “Glycosphingolipids of human umbilical vein endothelial cells and smooth muscle cells,” Archives of Biochemistry and Biophysics, vol. 256, no. 2, pp. 435–445, 1987.
- B. K. Gillard, M. A. Jones, A. A. Turner, D. E. Lewis, and D. M. Marcus, “Interferon-γ alters expression of endothelial cell-surface glycosphingolipids,” Archives of Biochemistry and Biophysics, vol. 279, no. 1, pp. 122–129, 1990.
- N. C. A. J. van de Kar, L. A. H. Monnens, M. A. Karmali, and V. W. M. van Hinsbergh, “Tumor necrosis factor and interleukin-1 induce expression of the verocytotoxin receptor globotriaosylceramide on human endothelial cells: implications for the pathogenesis of the hemolytic uremic syndrome,” Blood, vol. 80, no. 11, pp. 2755–2764, 1992.
- P. B. Eisenhauer, P. Chaturvedi, R. E. Fine et al., “Tumor necrosis factor alpha increases human cerebral endothelial cell Gb3 and sensitivity to Shiga toxin,” Infection and Immunity, vol. 69, no. 3, pp. 1889–1894, 2001.
- C. H. Schweppe, M. Bielaszewska, G. Pohlentz et al., “Glycosphingolipids in vascular endothelial cells: relationship of heterogeneity in Gb3Cer/CD77 receptor expression with differential Shiga toxin 1 cytotoxicity,” Glycoconjugate Journal, vol. 25, no. 4, pp. 291–304, 2008.
- M. Rajesh, A. Kolmakova, and S. Chatterjee, “Novel role of lactosylceramide in vascular endothelial growth factor-mediated angiogenesis in human endothelial cells,” Circulation Research, vol. 97, no. 8, pp. 796–804, 2005.
- A. Kolmakova, M. Rajesh, D. Zang, R. Pili, and S. Chatterjee, “VEGF recruits lactosylceramide to induce endothelial cell adhesion molecule expression and angiogenesis in vitro and in vivo,” Glycoconjugate Journal, vol. 26, no. 5, pp. 547–558, 2009.
- P. Mukherjee, A. C. Faber, L. M. Shelton, R. C. Baek, T. C. Chiles, and T. N. Seyfried, “Thematic review series: sphingolipids. Ganglioside GM3 suppresses the proangiogenic effects of vascular endothelial growth factor and ganglioside GD1a,” Journal of Lipid Research, vol. 49, no. 5, pp. 929–938, 2008.
- S. Dasgupta, M. Yanagisawa, K. Rrishnamurthy, S. S. Liour, and R. K. Yu, “Tumor necrosis factor-α up-regulates glucuronosyltransferase gene expression in human brain endothelial cells and promotes T-cell adhesion,” Journal of Neuroscience Research, vol. 85, no. 5, pp. 1086–1094, 2007.
- S. Dasgupta, J. Silva, G. Wang, and R. K. Yu, “Sulfoglucuronosyl paragloboside is a ligand for T cell adhesion: regulation of sulfoglucuronosyl paragloboside expression via nuclear factor κB signaling,” Journal of Neuroscience Research, vol. 87, no. 16, pp. 3591–3599, 2009.
- S. Dasgupta, G. Wang, and R. K. Yu, “Sulfoglucuronosyl paragloboside promotes endothelial cell apoptosis in inflammation: elucidation of a novel glycosphingolipid-signaling pathway,” Journal of Neurochemistry, vol. 119, no. 4, pp. 749–759, 2011.
- R. V. Iozzo, “Matrix proteoglycans: from molecular design to cellular function,” Annual Review of Biochemistry, vol. 67, pp. 609–652, 1998.
- L. Schaefer and R. M. Schaefer, “Proteoglycans: from structural compounds to signaling molecules,” Cell and Tissue Research, vol. 339, no. 1, pp. 237–246, 2010.
- N. J. Klein, G. I. Shennan, R. S. Heyderman, and M. Levin, “Alteration in glycosaminoglycan metabolism and surface charge on human umbilical vein endothelial cells induced by cytokines, endotoxin and neutrophils,” Journal of Cell Science, vol. 102, part 4, pp. 821–832, 1992.
- S. Devaraj, J.-M. Yun, G. Adamson, J. Galvez, and I. Jialal, “C-reactive protein impairs the endothelial glycocalyx resulting in endothelial dysfunction,” Cardiovascular Research, vol. 84, no. 3, pp. 479–484, 2009.
- T. M. Reine, M. Kusche-Gullberg, A. Feta, T. Jenssen, and S. O. Kolset, “Heparan sulfate expression is affected by inflammatory stimuli in primary human endothelial cells,” Glycoconjugate Journal, vol. 29, no. 1, pp. 67–76, 2012.
- K. Norgard-Sumnicht and A. Varki, “Endothelial heparan sulfate proteoglycans that bind to L-selectin have glucosamine residues with unsubstituted amino groups,” Journal of Biological Chemistry, vol. 270, no. 20, pp. 12012–12024, 1995.
- M. J. Robinson, P. Tessier, R. Poulsom, and N. Hogg, “The S100 family heterodimer, MRP-8/14, binds with high affinity to heparin and heparan sulfate glycosaminoglycans on endothelial cells,” Journal of Biological Chemistry, vol. 277, no. 5, pp. 3658–3665, 2002.
- D. Xu, J. Young, D. Song, and J. D. Esko, “Heparan sulfate is essential for high mobility group protein 1 (HMGB1) signaling by the receptor for advanced glycation end products (RAGE),” Journal of Biological Chemistry, vol. 286, no. 48, pp. 41736–41744, 2011.
- A. M. Vogt, A. Barragan, Q. Chen, F. Kironde, D. Spillmann, and M. Wahlgren, “Heparan sulfate on endothelial cells mediates the binding of Plasmodium falciparum-infected erythrocytes via the DBL1α domain of PfEMP1,” Blood, vol. 101, no. 6, pp. 2405–2411, 2003.
- K. Narita, J. Staub, J. Chien et al., “HSulf-1 inhibits angiogenesis and tumorigenesis in vivo,” Cancer Research, vol. 66, no. 12, pp. 6025–6032, 2006.
- C. Ferreras, G. Rushton, C. L. Cole, et al., “Endothelial heparan sulfate 6-O-sulfation levels regulate angiogenic responses of endothelial cells to fibroblast growth factor 2 and vascular endothelial growth factor,” Journal of Biological Chemistry, vol. 287, no. 43, pp. 36132–36146, 2012.
- T. Wang, Y. Ward, L. Tian et al., “CD97, an adhesion receptor on inflammatory cells, stimulates angiogenesis through binding integrin counterreceptors on endothelial cells,” Blood, vol. 105, no. 7, pp. 2836–2844, 2005.
- P. Estess, A. Nandi, M. Mohamadzadeh, and M. H. Siegelman, “Interleukin 15 induces endothelial hyaluronan expression in vitro and promotes activated T cell extravasation through a CD44-dependent pathway in vivo,” Journal of Experimental Medicine, vol. 190, no. 1, pp. 9–19, 1999.
- D. Vigetti, A. Genasetti, E. Karousou et al., “Proinflammatory cytokines induce hyaluronan synthesis and monocyte adhesion in human endothelial cells through hyaluronan synthase 2 (HAS2) and the nuclear factor-κB (NF-κB) pathway,” Journal of Biological Chemistry, vol. 285, no. 32, pp. 24639–24645, 2010.
- M. Gouverneur, J. A. E. Spaan, H. Pannekoek, R. D. Fontijn, and H. Vink, “Fluid shear stress stimulates incorporation of hyaluronan into endothelial cell glycocalyx,” American Journal of Physiology—Heart and Circulatory Physiology, vol. 290, no. 1, pp. H458–H462, 2006.
- J. Maroski, B. J. Vorderwülbecke, K. Fiedorowicz et al., “Shear stress increases endothelial hyaluronan synthase 2 and hyaluronan synthesis especially in regard to an atheroprotective flow profile,” Experimental Physiology, vol. 96, no. 9, pp. 977–986, 2011.
- J. M. Whitelock, L. D. Graham, J. Melrose, A. D. Murdoch, R. V. Iozzo, and P. Anne Underwood, “Human perlecan immunopurified from different endothelial cell sources has different adhesive properties for vascular cells,” Matrix Biology, vol. 18, no. 2, pp. 163–178, 1999.
- S. Knox, J. Melrose, and J. Whitelock, “Electrophoretic, biosensor, and bioactivity analyses of perlecans of different cellular origins,” Proteomics, vol. 1, no. 12, pp. 1534–1541, 2001.
- S. Knox, C. Merry, S. Stringer, J. Melrose, and J. Whitelock, “Not all perlecans are created equal. Interactions with fibroblast growth factor (FGF) 2 and FGF receptors,” Journal of Biological Chemistry, vol. 277, no. 17, pp. 14657–14665, 2002.
- C. A. Vogl-Willis and I. J. Edwards, “High-glucose-induced structural changes in the heparan sulfate proteoglycan, perlecan, of cultured human aortic endothelial cells,” Biochimica et Biophysica Acta, vol. 1672, no. 1, pp. 36–45, 2004.
- W. Zhang, Y.-J. Chuang, R. Swanson et al., “Antiangiogenic antithrombin down-regulates the expression of the proangiogenic heparan sulfate proteoglycan, perlecan, in endothelial cells,” Blood, vol. 103, no. 4, pp. 1185–1191, 2004.
- W. Zhang, Y.-J. Chuang, T. Jin et al., “Antiangiogenic antithrombin induces global changes in the gene expression profile of endothelial cells,” Cancer Research, vol. 66, no. 10, pp. 5047–5055, 2006.
- K. Sakai, T. Nakamura, K. Matsumoto, and T. Nakamura, “Angioinhibitory action of NK4 involves impaired extracellular assembly of fibronectin mediated by Perlecan-NK4 association,” Journal of Biological Chemistry, vol. 284, no. 33, pp. 22491–22499, 2009.
- D. Béchard, T. Gentina, M. Delehedde et al., “Endocan is a novel chondroitin sulfate/dermatan sulfate proteoglycan that promotes hepatocyte growth factor/scatter factor mitogenic activity,” Journal of Biological Chemistry, vol. 276, no. 51, pp. 48341–48349, 2001.
- M. R. Abid, X. Yi, K. Yano, S.-C. Shih, and W. C. Aird, “Vascular endocan is preferentially expressed in tumor endothelium,” Microvascular Research, vol. 72, no. 3, pp. 136–145, 2006.
- M. Delehedde, L. Devenyns, C. A. Maurage, and R. R. Vivès, “Endocan in cancers: a lesson from a circulating dermatan sulfate proteoglycan,” International Journal of Cell Biology, vol. 2013, Article ID 705027, 11 pages, 2013.
- M. Strazynski, J. A. Eble, H. Kresse, and E. Schönherr, “Interleukin (IL)-6 and IL-10 induce decorin mRNA in endothelial cells, but interaction with fibrillar collagen is essential for its translation,” Journal of Biological Chemistry, vol. 279, no. 20, pp. 21266–21270, 2004.
- E. Schönherr, C. Sunderkötter, R. V. Iozzo, and L. Schaefer, “Decorin, a novel player in the insulin-like growth factor system,” Journal of Biological Chemistry, vol. 280, no. 16, pp. 15767–15772, 2005.
- L. R. Fiedler, E. Schönherr, R. Waddington et al., “Decorin regulates endothelial cell motility on collagen I through activation of insulin-like growth factor I receptor and modulation of α2β1 integrin activity,” Journal of Biological Chemistry, vol. 283, no. 25, pp. 17406–17415, 2008.
- L. R. Fiedler and J. A. Eble, “Decorin regulates endothelial cell-matrix interactions during angiogenesis,” Cell Adhesion and Migration, vol. 3, no. 1, pp. 3–6, 2009.
- S. Cattaruzza, M. Schiappacassi, Å. Ljungberg-Rose et al., “Distribution of PG-M/versican variants in human tissues and de novo expression of isoform V3 upon endothelial cell activation, migration, and neoangiogenesis in vitro,” Journal of Biological Chemistry, vol. 277, no. 49, pp. 47626–47635, 2002.
- L. Nelimarkka, V. Kainulainen, E. Schönherr et al., “Expression of small extracellular chondroitin/dermatan sulfate proteoglycans is differentially regulated in human endothelial cells,” Journal of Biological Chemistry, vol. 272, no. 19, pp. 12730–12737, 1997.
- S. Gengrinovitch, B. Berman, G. David, L. Witte, G. Neufeld, and D. Ron, “Glypican-1 is a VEGF165 binding proteoglycan that acts as an extracellular chaperone for VEGF165,” Journal of Biological Chemistry, vol. 274, no. 16, pp. 10816–10822, 1999.
- D. Qiao, K. Meyer, and A. Friedl, “Glypican-1 stimulates Skp2 autoinduction loop and G1/S transition in endothelial cells,” Journal of Biological Chemistry, vol. 287, no. 8, pp. 5898–5909, 2012.
- S. Gharagozlian, J. Borrebæk, T. Henriksen, T. K. Omsland, H. Shegarfi, and S. O. Kolset, “Effect of hyperglycemic condition on proteoglycan secretion in cultured human endothelial cells,” European Journal of Nutrition, vol. 45, no. 7, pp. 369–375, 2006.
- S. S. Nunes, M. A. F. Outeiro-Bernstein, L. Juliano et al., “Syndecan-4 contributes to endothelial tubulogenesis through interactions with two motifs inside the pro-angiogenic N-terminal domain of thrombospondin-1,” Journal of Cellular Physiology, vol. 214, no. 3, pp. 828–837, 2008.
- O. Noguer, J. Villena, J. Lorita, S. Vilaró, and M. Reina, “Syndecan-2 downregulation impairs angiogenesis in human microvascular endothelial cells,” Experimental Cell Research, vol. 315, no. 5, pp. 795–808, 2009.
- D. M. Beauvais, B. J. Ell, A. R. McWhorter, and A. C. Rapraeger, “Syndecan-1 regulates αvβ3 and αvβ5 integrin activation during angiogenesis and is blocked by synstatin, a novel peptide inhibitor,” Journal of Experimental Medicine, vol. 206, no. 3, pp. 691–705, 2009.
- D. N. W. Cooper, “Galectinomics: finding themes in complexity,” Biochimica et Biophysica Acta, vol. 1572, no. 2-3, pp. 209–231, 2002.
- D. N. W. Cooper and S. H. Barondes, “God must love galectins; he made so many of them,” Glycobiology, vol. 9, no. 10, pp. 979–984, 1999.
- R.-Y. Yang, G. A. Rabinovich, and F.-T. Liu, “Galectins: structure, function and therapeutic potential,” Expert Reviews in Molecular Medicine, vol. 10, p. e17, 2008.
- L. G. Baum, J. J. Seilhamer, M. Pang, W. B. Levine, D. Beynon, and J. A. Berlinger, “Synthesis of an endogeneous lectin, galectin-1, by human endothelial cells is up-regulated by endothelial cell activation,” Glycoconjugate Journal, vol. 12, no. 1, pp. 63–68, 1995.
- A. Ishikawa, T. Imaizumi, H. Yoshida et al., “Double-stranded RNA enhances the expression of galectin-9 in vascular endothelial cells,” Immunology and Cell Biology, vol. 82, no. 4, pp. 410–414, 2004.
- V. L. Thijssen, S. Hulsmans, and A. W. Griffioen, “The galectin profile of the endothelium: altered expression and localization in activated and tumor endothelial cells,” The American Journal of Pathology, vol. 172, no. 2, pp. 545–553, 2008.
- S. Alam, H. Li, A. Margariti et al., “Galectin-9 protein expression in endothelial cells is positively regulated by histone deacetylase 3,” Journal of Biological Chemistry, vol. 286, no. 51, pp. 44211–44217, 2011.
- V. V. Glinsky, G. V. Glinsky, K. Rittenhouse-Olson et al., “The role of Thomsen-Friedenreich antigen in adhesion of human breast and prostate cancer cells to the endothelium,” Cancer Research, vol. 61, no. 12, pp. 4851–4857, 2001.
- G. A. Rabinovich, A. Cumashi, G. A. Bianco et al., “Synthetic lactulose amines: novel class of anticancer agents that induce tumor-cell apoptosis and inhibit galectin-mediated homotypic cell aggregation and endothelial cell morphogenesis,” Glycobiology, vol. 16, no. 3, pp. 210–220, 2006.
- A. I. Markowska, K. C. Jefferies, and N. Panjwani, “Galectin-3 protein modulates cell surface expression and activation of vascular endothelial Growth factor receptor 2 in human endothelial cells,” Journal of Biological Chemistry, vol. 286, no. 34, pp. 29913–29921, 2011.
- C. R. Parish, C. Freeman, and M. D. Hulett, “Heparanase: a key enzyme involved in cell invasion,” Biochimica et Biophysica Acta, vol. 1471, no. 3, pp. M99–M108, 2001.
- I. Vlodavsky and Y. Friedmann, “Molecular properties and involvement of heparanase in cancer metastasis and angiogenesis,” Journal of Clinical Investigation, vol. 108, no. 3, pp. 341–347, 2001.
- K. Godder, I. Vlodavsky, A. Eldor, B. B. Weksler, A. Haimovitz-Freidman, and Z. Fuks, “Heparanase activity in cultured endothelial cells,” Journal of Cellular Physiology, vol. 148, no. 2, pp. 274–280, 1991.
- L. Yuan, J. Hu, Y. Luo, et al., “Upregulation of heparanase in high-glucose-treated endothelial cells promotes endothelial cell migration and proliferation and correlates with Akt and extracellular-signal-regulated kinase phosphorylation,” Molecular Vision, vol. 18, pp. 1684–1695, 2012.
- G. Rao, H. G. Ding, W. Huang et al., “Reactive oxygen species mediate high glucose-induced heparanase-1 production and heparan sulphate proteoglycan degradation in human and rat endothelial cells: a potential role in the pathogenesis of atherosclerosis,” Diabetologia, vol. 54, no. 6, pp. 1527–1538, 2011.
- K. E. Achyuthan and A. M. Achyuthan, “Comparative enzymology, biochemistry and pathophysiology of human exo-α-sialidases (neuraminidases),” Comparative Biochemistry and Physiology B, vol. 129, no. 1, pp. 29–64, 2001.
- E. Monti, A. Preti, B. Venerando, and G. Borsani, “Recent development in mammalian sialidase molecular biology,” Neurochemical Research, vol. 27, no. 7-8, pp. 649–663, 2002.
- A. S. Cross, S. W. Hyun, A. Miranda-Ribera, et al., “NEU1 and NEU3 sialidase activity expressed in human lung microvascular endothelia: NEU1 restrains endothelial cell migration, whereas NEU3 does not,” Journal of Biological Chemistry, vol. 287, no. 19, pp. 15966–15980, 2012.
- K. Tran-Lundmark, P.-K. Tran, G. Paulsson-Berne et al., “Heparan sulfate in perlecan promotes mouse atherosclerosis: roles in lipid permeability, lipid retention, and smooth muscle cell proliferation,” Circulation Research, vol. 103, no. 1, pp. 43–52, 2008.
- F. Huang, J. C. Thompson, P. G. Wilson, H. H. Aung, J. C. Rutledge, and L. R. Tannock, “Angiotensin II increases vascular proteoglycan content preceding and contributing to atherosclerosis development,” Journal of Lipid Research, vol. 49, no. 3, pp. 521–530, 2008.
- J. Folkman, “Angiogenesis in cancer, vascular, rheumatoid and other disease,” Nature Medicine, vol. 1, no. 1, pp. 27–31, 1995.
- M. M. Fuster and L. Wang, “Endothelial heparan sulfate in angiogenesis,” Progress in Molecular Biology and Translational Science, vol. 93, pp. 179–212, 2010.