The vascular endothelial growth factor VEGF165 induces perlecan synthesis via VEGF receptor-2 in cultured human brain microvascular endothelial cells

VEGFA Isoforms as Pro-Angiogenic Therapeutics for Cerebrovascular Diseases

Therapeutic angiogenesis has long been considered a viable treatment for vasculature disruptions, including cerebral vasculature diseases. One widely-discussed treatment method to increase angiogenesis is vascular endothelial growth factor (VEGF) A. In animal models, treatment with VEGFA proved beneficial, resulting in increased angiogenesis, increased neuronal density, and improved outcome. However, VEGFA administration in clinical trials has thus far failed to replicate the promising results seen in animal models. The lack of beneficial effects in humans and the difficulty in medicinal translation may be due in part to administration methods and VEGFA's ability to increase vascular permeability. One solution to mitigate the side effects of VEGFA may be found in the VEGFA isoforms. VEGFA is able to produce several different isoforms through alternative splicing. Each VEGFA isoform interacts differently with both the cellular components and the VEGF receptors. Because of the different biological effects elicited, VEGFA isoforms may hold promise as a tangible potential therapeutic for cerebrovascular diseases.

Sb-Phenyl-N-methyl-5,6,7,12-tetrahydrodibenz[c,f][1,5]azastibocine Induces Perlecan Core Protein Synthesis in Cultured Vascular Endothelial Cells

Vascular endothelial cells synthesize and secrete perlecan, a large heparan sulfate proteoglycan that increases the anticoagulant activity of vascular endothelium by inducing antithrombin III and intensifying fibroblast growth factor (FGF)-2 activity to promote migration and proliferation in the repair process of damaged endothelium during the progression of atherosclerosis. However, the exact regulatory mechanisms of endothelial perlecan expression remain unclear. Since organic-inorganic hybrid molecules are being developed rapidly as tools to analyze biological systems, we searched for a molecular probe to analyze these mechanisms using a library of organoantimony compounds and found that the Sb-phenyl-N-methyl-5,6,7,12-tetrahydrodibenz[c,f][1,5]azastibocine (PMTAS) molecule promotes the expression of perlecan core protein gene without exhibiting cytotoxicity in vascular endothelial cells. In the present study, we characterized proteoglycans synthesized by cultured bovine aortic endothelial cells using biochemical techniques. The results indicated that PMTAS selectively induced perlecan core protein synthesis, without affecting the formation of its heparan sulfate chain, in vascular endothelial cells. The results also implied that this process is independent of the endothelial cell density, whereas in vascular smooth muscle cells, it occurred only at high cell density. Thus, PMTAS would be a useful tool for further studies on the mechanisms underlying perlecan core protein synthesis in vascular cells, which is critical in the progression of vascular lesions, such as those during atherosclerosis.

Lead suppresses perlecan expression via EGFR-ERK1/2-COX-2-PGI2 pathway in cultured bovine vascular endothelial cells

Vascular endothelial cell growth is essential for the repair of intimal injury. Perlecan, a large heparan sulfate proteoglycan, intensifies fibroblast growth factor-2 (FGF-2) signaling as a co-receptor for FGF-2 and its receptor, and promotes the proliferation of vascular endothelial cells. Previously, we reported that 2 µM of lead, a toxic heavy metal, downregulated perlecan core protein expression and then suppressed the growth of vascular endothelial cells. However, since the mechanisms involved in the repression of perlecan by lead remains unclear, we analyzed its detailed signaling pathway using cultured bovine aortic endothelial cells. Our findings indicate that 2 µM of lead inhibited protein tyrosine phosphatase (PTP) activity and induced cyclooxygenase-2 (COX-2) via phosphorylation of the epidermal growth factor receptor (EGFR) and its downstream extracellular signal-regulated kinases (ERK1/2). In addition, among the prostanoids regulated by COX-2, prostaglandin I2 (PGI2) specifically contributes to the downregulation of perlecan expression by lead. This study revealed an intracellular pathway-the EGFR-ERK1/2-COX-2-PGI2 pathway activated by inhibition of PTP by lead-as a pathway that downregulates endothelial perlecan synthesis. The pathway is suggested to serve as a mechanism for the repression of perlecan expression, which leads to a delay in cell proliferation by lead.

Cell density-dependent modulation of perlecan synthesis by dichloro(2,9-dimethyl-1,10-phenanthroline)zinc(II) in vascular endothelial cells

Proteoglycans that are synthesized by vascular endothelial cells contribute to the proliferation, migration, and blood coagulation-fibrinolytic system in vascular endothelial cells. Clarification of the molecular mechanisms for proteoglycan synthesis allows understanding of the regulation of endothelial functions. The research strategy of bioorganometallics analyzes biological systems using organic-inorganic hybrid molecules as tools. The present study found dichloro(2,9-dimethyl-1,10-phenanthroline)zinc(II) and its ligand-modulated perlecan expression in vascular endothelial cells, which depends on the cell density.

Cell Density-Dependent Fibroblast Growth Factor-2 Signaling Regulates Syndecan-4 Expression in Cultured Vascular Endothelial Cells

Syndecan-4 is a member of the syndecan family of transmembrane heparan sulfate proteoglycans, and is involved in cell protection, proliferation, and the blood coagulation-fibrinolytic system in vascular endothelial cells. Heparan sulfate chains enable fibroblast growth factor-2 (FGF-2) to form a complex with its receptor and to transduce the cell growth signal. In the present study, bovine aortic endothelial cells were cultured, and the intracellular signal pathways that mediate the regulation of syndecan-4 expression in dense and sparse cultures by FGF-2 were analyzed. We demonstrated the cell density-dependent differential regulation of syndecan-4 expression. Specifically, we found that FGF-2 upregulated the synthesis of syndecan-4 in vascular endothelial cells via the MEK1/2-ERK1/2 pathway in dense cell cultures, with only a transcriptional induction of syndecan-4 at a low cell density via the Akt pathway. This study highlights a critical mechanism underlying the regulation of endothelial cell functions by proteoglycans.

Hypotensive Snake Venom Components-A Mini-Review

Hypertension is considered a major public health issue due to its high prevalence and subsequent risk of cardiovascular and kidney diseases. Thus, the search for new antihypertensive compounds remains of great interest. Snake venoms provide an abundant source of lead molecules that affect the cardiovascular system, which makes them prominent from a pharmaceutical perspective. Such snake venom components include bradykinin potentiating peptides (proline-rich oligopeptides), natriuretic peptides, phospholipases A2, serine-proteases and vascular endothelial growth factors. Some heparin binding hypotensive factors, three-finger toxins and 5' nucleotidases can also exert blood pressure lowering activity. Great advances have been made during the last decade regarding the understanding of the mechanism of action of these hypotensive proteins. Bradykinin potentiating peptides exert their action primarily by inhibiting the angiotensin-converting enzyme and increasing the effect of endogenous bradykinin. Snake venom phospholipases A2 are capable of reducing blood pressure through the production of arachidonic acid, a precursor of cyclooxygenase metabolites (prostaglandins or prostacyclin). Other snake venom proteins mimic the effects of endogenous kallikrein, natriuretic peptides or vascular endothelial growth factors. The aim of this work was to review the current state of knowledge regarding snake venom components with potential antihypertensive activity and their mechanisms of action.

Brain heparan sulphate proteoglycans are altered in developing foetus when exposed to in-utero hyperglycaemia

In-utero exposure of foetus to hyperglycaemic condition affects the growth and development of the organism. The brain is one of the first organs that start to develop during embryonic period and glycosaminoglycans (GAGs) and proteoglycans (PGs) are one of the key molecules involved in its development. But studies on the effect of hyperglycaemic conditions on brain GAGs/PGs are few and far between. We, therefore, looked into the changes in brain GAGs and PGs at various developmental stages of pre- and post-natal rats from non-diabetic and diabetic mothers as well as in adult rats induced with diabetes using a diabetogenic agent, Streptozotocin. Increased expression of GAGs especially that of heparan sulphate class in various developmental stages were observed in the brain as a result of in-utero hyperglycaemic condition but not in that of adult rats. Changes in disaccharides of heparan sulphate (HS) were observed in various developmental stages. Furthermore, various HSPGs namely, syndecans-1 and -3 and glypican-1 were overexpressed in offspring from diabetic mother. However, in adult diabetic rats, only glypican-1 was overexpressed. The offsprings from diabetic mothers became hyperphagic at the end of 8 weeks after birth which can have implications in the long run. Our results highlight the likely impact of the in-utero exposure of foetus to hyperglycaemic condition on brain GAGs/PGs compared to diabetic adult rats.

Transforming Growth Factor-β1 Modulates the Expression of Syndecan-4 in Cultured Vascular Endothelial Cells in a Biphasic Manner

Proteoglycans are macromolecules that consist of a core protein and one or more glycosaminoglycan side chains. Previously, we reported that transforming growth factor‐β₁ (TGF‐β₁) regulates the synthesis of a large heparan sulfate proteoglycan, perlecan, and a small leucine‐rich dermatan sulfate proteoglycan, biglycan, in vascular endothelial cells depending on cell density. Recently, we found that TGF‐β₁ first upregulates and then downregulates the expression of syndecan‐4, a transmembrane heparan sulfate proteoglycan, via the TGF‐β receptor ALK5 in the cells. In order to identify the intracellular signal transduction pathway that mediates this modulation, bovine aortic endothelial cells were cultured and treated with TGF‐β₁. Involvement of the downstream signaling pathways of ALK5—the Smad and MAPK pathways—in syndecan‐4 expression was examined using specific siRNAs and inhibitors. The data indicate that the Smad3–p38 MAPK pathway mediates the early upregulation of syndecan‐4 by TGF‐β₁, whereas the late downregulation is mediated by the Smad2/3 pathway. Multiple modulations of proteoglycan synthesis may be involved in the regulation of vascular endothelial cell functions by TGF‐β₁. J. Cell. Biochem. 118: 2009–2017,2017. © 2016 The Authors. Journal of Cellular Biochemistry Published by Wiley Periodicals, Inc.

Induction of Syndecan-4 by Organic-Inorganic Hybrid Molecules with a 1,10-Phenanthroline Structure in Cultured Vascular Endothelial Cells

Organic-inorganic hybrid molecules constitute analytical tools used in biological systems. Vascular endothelial cells synthesize and secrete proteoglycans, which are macromolecules consisting of a core protein and glycosaminoglycan side chains. Although the expression of endothelial proteoglycans is regulated by several cytokines/growth factors, there may be alternative pathways for proteoglycan synthesis aside from downstream pathways activated by these cytokines/growth factors. Here, we investigated organic-inorganic hybrid molecules to determine a variant capable of analyzing the expression of syndecan-4, a transmembrane heparan-sulfate proteoglycan, and identified 1,10-phenanthroline (o-Phen) with or without zinc (Zn-Phen) or rhodium (Rh-Phen). Bovine aortic endothelial cells in culture were treated with these compounds, and the expression of syndecan-4 mRNA and core proteins was determined by real-time reverse transcription polymerase chain reaction and Western blot analysis, respectively. Our findings indicated that o-Phen and Zn-Phen specifically and strongly induced syndecan-4 expression in cultured vascular endothelial cells through activation of the hypoxia-inducible factor-1α/β pathway via inhibition of prolyl hydroxylase-domain-containing protein 2. These results demonstrated an alternative pathway involved in mediating induction of endothelial syndecan-4 expression and revealed organic-inorganic hybrid molecules as effective tools for analyzing biological systems.

Biglycan Intensifies ALK5-Smad2/3 Signaling by TGF-β1 and Downregulates Syndecan-4 in Cultured Vascular Endothelial Cells

Proteoglycans are macromolecules that consist of a core protein and one or more glycosaminoglycan side chains. A small leucine‐rich dermatan sulfate proteoglycan, biglycan, is one of the predominant types of proteoglycans synthesized by vascular endothelial cells; however, the physiological functions of biglycan are not completely understood. In the present study, bovine aortic endothelial cells in culture were transfected with small interfering RNAs for biglycan, and the expression of other proteoglycans was examined. Transforming growth factor‐β₁ signaling was also investigated, because the interaction of biglycan with cytokines has been reported. Biglycan was found to form a complex with either transforming growth factor‐β₁ or the transforming growth factor‐β₁ type I receptor, ALK5, and to intensify the phosphorylation of Smad2/3, resulting in a lower expression of the transmembrane heparan sulfate proteoglycan, syndecan‐4. This is the first report to clarify the function of biglycan as a regulatory molecule of the ALK5–Smad2/3 TGF‐β₁ signaling pathway that mediates the suppression of syndecan‐4 expression in vascular endothelial cells. J. Cell. Biochem. 118: 1087–1096, 2017. © 2016 Wiley Periodicals, Inc.

A current view of perlecan in physiology and pathology: A mosaic of functions

Perlecan, a large basement membrane heparan sulfate proteoglycan, is expressed in a wide array of tissues where it regulates diverse cellular processes including bone formation, inflammation, cardiac development, and angiogenesis. Here we provide a contemporary review germane to the biology of perlecan encompassing its genetic regulation as well as an analysis of its modular protein structure as it pertains to function. As perlecan signaling from the extracellular matrix converges on master regulators of autophagy, including AMPK and mTOR, via a specific interaction with vascular endothelial growth factor receptor 2, we specifically focus on the mechanism of action of perlecan in autophagy and angiogenesis and contrast the role of endorepellin, the C-terminal fragment of perlecan, in these cellular and morphogenic events.

Endorepellin-evoked Autophagy Contributes to Angiostasis

Endorepellin, the C-terminal domain of perlecan, is an angiostatic molecule that acts as a potent inducer of autophagy via its interaction with VEGFR2. In this study, we examined the effect of endorepellin on endothelial cells using atomic force microscopy. Soluble endorepellin caused morphological and biophysical changes such as an increase in cell surface roughness and cell height. Surprisingly, these changes were not accompanied by alterations in the endothelial cell elastic modulus. We discovered that endorepellin-induced autophagic flux led to co-localization of mammalian target of rapamycin with LC3-positive autophagosomes. Endorepellin functioned upstream of AMP-activated kinase α, as compound C, an inhibitor of AMP-activated kinase α, abrogated endorepellin-mediated activation and co-localization of Beclin 1 and LC3, thereby reducing autophagic progression. Functionally, we discovered that both endorepellin and Torin 1, a canonical autophagic inducer, blunted ex vivo angiogenesis. We conclude that autophagy is a novel mechanism by which endorepellin promotes angiostasis independent of nutrient deprivation.

Heparan sulfate proteoglycans and heparin regulate melanoma cell functions

BACKGROUND

The solid melanoma tumor consists of transformed melanoma cells, and the associated stromal cells including fibroblasts, endothelial cells, immune cells, as well as, soluble macro- and micro-molecules of the extracellular matrix (ECM) forming the complex network of the tumor microenvironment. Heparan sulfate proteoglycans (HSPGs) are an important component of the melanoma tumor ECM. Importantly, there appears to be both a quantitative and a qualitative shift in the content of HSPGs, in parallel to the nevi-radial growth phase-vertical growth phase melanoma progression. Moreover, these changes in HSPG expression are correlated to modulations of key melanoma cell functions.

SCOPE OF REVIEW

This review will critically discuss the roles of HSPGs/heparin in melanoma development and progression.

MAJOR CONCLUSIONS

We have correlated HSPGs' expression and distribution with melanoma cell signaling and functions as well as angiogenesis.

GENERAL SIGNIFICANCE

The current knowledge of HSPGs/heparin biology in melanoma provides a foundation we can utilize in the ongoing search for new approaches in designing anti-tumor therapy. This article is part of a Special Issue entitled Matrix-mediated cell behaviour and properties.

Novel insight into the biological functions of syndecan ectodomain core proteins

Syndecans are a four member family of multifunctional transmembrane heparan sulphate bearing cell surface receptors. Each family member has common molecular architecture but a distinct expression profile. Numerous molecular interactions between syndecan heparan sulphate chains, growth factors, cytokines, and extracellular matrix molecules have been reported and syndecans are intimately associated with cell adhesion and migration. Here, we describe the important emerging concept that contained within syndecan extracellular core proteins are "adhesion regulatory domains." Cell adhesion is driven by the integrins and syndecan ectodomain adhesion regulatory domains can alter integrin driven cellular responses. Cell adhesion and migration is central to numerous pathologies and an understanding of how syndecan ectodomains influence integrins will lead to novel therapeutic strategies.

Endorepellin, the angiostatic module of perlecan, interacts with both the α2β1 integrin and vascular endothelial growth factor receptor 2 (VEGFR2): a dual receptor antagonism

Endorepellin, the C-terminal module of perlecan, negatively regulates angiogenesis counter to its proangiogenic parental molecule. Endorepellin (the C-terminal domain V of perlecan) binds the α2β1 integrin on endothelial cells and triggers a signaling cascade that leads to disruption of the actin cytoskeleton. Here, we show that both perlecan and endorepellin bind directly and with high affinity to both VEGF receptors 1 and 2, in a region that differs from VEGFA-binding site. In both human and porcine endothelial cells, this interaction evokes a physical down-regulation of both the α2β1 integrin and VEGFR2, with concurrent activation of the tyrosine phosphatase SHP-1 and downstream attenuation of VEGFA transcription. We demonstrate that endorepellin requires both the α2β1 integrin and VEGFR2 for its angiostatic activity. Endothelial cells that express α2β1 integrin but lack VEGFR2, do not respond to endorepellin treatment. Thus, we provide a new paradigm for the activity of an antiangiogenic protein and mechanistically explain the specificity of endorepellin for endothelial cells, the only cells that simultaneously express both receptors. We hypothesize that a mechanism such as dual receptor antagonism could operate for other angiostatic fragments.

Perlecan domain V is neuroprotective and proangiogenic following ischemic stroke in rodents

Stroke is the leading cause of long-term disability and the third leading cause of death in the United States. While most research thus far has focused on acute stroke treatment and neuroprotection, the exploitation of endogenous brain self-repair mechanisms may also yield therapeutic strategies. Here, we describe a distinct type of stroke treatment, the naturally occurring extracellular matrix fragment of perlecan, domain V, which we found had neuroprotective properties and enhanced post-stroke angiogenesis, a key component of brain repair, in rodent models of stroke. In both rat and mouse models, Western blot analysis revealed elevated levels of perlecan domain V. When systemically administered 24 hours after stroke, domain V was well tolerated, reached infarct and peri-infarct brain vasculature, and restored stroke-affected motor function to baseline pre-stroke levels in these multiple stroke models in both mice and rats. Post-stroke domain V administration increased VEGF levels via a mechanism involving brain endothelial cell α5β1 integrin, and the subsequent neuroprotective and angiogenic actions of domain V were in turn mediated via VEGFR. These results suggest that perlecan domain V represents a promising approach for stroke treatment.

Proteoglycans in cancer biology, tumour microenvironment and angiogenesis

Proteoglycans, key molecular effectors of cell surface and pericellular microenvironments, perform multiple functions in cancer and angiogenesis by virtue of their polyhedric nature and their ability to interact with both ligands and receptors that regulate neoplastic growth and neovascularization. Some proteoglycans such as perlecan, have pro- and anti-angiogenic activities, whereas other proteoglycans, such as syndecans and glypicans, can also directly affect cancer growth by modulating key signalling pathways. The bioactivity of these proteoglycans is further modulated by several classes of enzymes within the tumour microenvironment: (i) sheddases that cleave transmembrane or cell-associated syndecans and glypicans, (ii) various proteinases that cleave the protein core of pericellular proteoglycans and (iii) heparanases and endosulfatases which modify the structure and bioactivity of various heparan sulphate proteoglycans and their bound growth factors. In contrast, some of the small leucine-rich proteoglycans, such as decorin and lumican, act as tumour repressors by physically antagonizing receptor tyrosine kinases including the epidermal growth factor and the Met receptors or integrin receptors thereby evoking anti-survival and pro-apoptotic pathways. In this review we will critically assess the expanding repertoire of molecular interactions attributed to various proteoglycans and will discuss novel proteoglycan functions modulating cancer progression, invasion and metastasis and how these factors regulate the tumour microenvironment.

Anti-tumor effects of a novel chimeric peptide on S180 and H22 xenografts bearing nude mice

In recent years, many endogenous peptides have been identified by screening combinatory phage display peptide library, which play important roles in the process of angiogenesis. A heptapeptide, ATWLPPR, binds specifically to NRP-1 and selectively inhibits VEGF165 binding to VEGFR-2. Another heptapeptide, NLLMAAS, blocks both Ang-1 and Ang-2 binding to Tie-2 in a dose-dependent manner. In the present study, we aimed to connect ATWLPPR (V1) with NLLMAAS (V2) via a flexible linker, Ala-Ala, to reconstruct a novel peptide ATWLPPRAANLLMAAS (V3). We firstly investigated the anti-tumor and anti-angiogenic effects of peptide V3 on sarcoma S180 and hepatoma H22 bearing BALB/c nude mice. Mice were continuously subcutaneously administrated with normal saline, V1 (320microg/kg/d), V2 (320microg/kg/d), V1+V2 (320microg/kg/d), and V3 (160, 320 and 480microg/kg/d), for 7 days. Treatment with peptide V3 could significantly reduce the tumor weight and volume. Pathological examination showed that the tumors treated with peptide V3 had a larger region of necrosis than that of peptide V1, V2, and V1+V2 at the same dose. A significant decrease of microvessel density (MVD) in a dose-dependent manner was observed in each group of peptide V3. The results of pathological examination on normal tissue, lung, heart, liver, spleen, kidney and white blood cells showed that peptide V3 might have no significant toxicity. In conclusion, our results demonstrated that peptide V3 could be more effective on inhibiting tumor growth and angiogenesis than that of V1, V2, and V1+V2. Peptide V3 could be considered as a novel chimeric peptide with potent anti-tumor activity.

Overexpression of VEGF-A in podocytes of adult mice causes glomerular disease

We sought to examine the pathogenic role of excessive VEGF-A expression in podocytes, since it has been reported that diabetic nephropathy and other glomerular diseases are associated with increased VEGF-A expression. The induction of podocyte-specific VEGF164 overexpression in adult transgenic mice led to proteinuria, glomerulomegaly, glomerular basement membrane thickening, mesangial expansion, loss of slit diaphragms, and podocyte effacement. When doxycycline-mediated VEGF164 was stopped, these abnormalities reversed. These findings were associated with reversible downregulation of metalloproteinase 9 and nephrin expression. Using transmission electron microscopy, we established that VEGF-A receptor-2 (VEGFR2) was expressed in podocytes and glomerular endothelial cells. We also found that VEGF164 induced VEGFR2 phosphorylation in podocytes. Further, we were able to co-immunoprecipitate VEGFR2 and nephrin using whole kidney lysates, confirming interaction in vivo. This implies that autocrine and paracrine VEGF-A signaling through VEGFR2 occurs in podocytes and may mediate the glomerular phenotype caused by VEGF164 overexpression. Thus, we suggest that podocyte VEGF164 overexpression in adult mice is sufficient to induce glomerular filtration barrier structural and functional abnormalities similar to those present in murine diabetic nephropathy.

Conjugation of bevacizumab to cationic liposomes enhances their tumor-targeting potential

Aims: Cationic liposomes have been shown to preferentially target the tumor vasculature, but not uniformly. Bevacizumab antibody selectively accumulates in tumors expressing VEGF. We thus developed bevacizumab-modified, pegylated cationic liposomes (PCLs) to improve the distribution of liposomes along tumor vessels, and to enhance tumor targeting. Materials & methods: We evaluated the delivery vehicle both in the absence and presence of VEGF, using human pancreatic cancer (Capan-1, HPAF-II and PANC-1) and endothelial (MS1-VEGF and HMEC-1) cell lines. Results: All cell lines except for HMEC-1 secreted VEGF. Modification of PCLs with bevacizumab did not alter ζ-potential, but increased overall liposome size. The toxicity profile for bevacizumab-modified PCLs was cell line dependent and, in general, bevacizumab improved cellular uptake and tumor targeting of PCLs. Conclusion: Bevacizumab-modified PCLs represent a potential improvement over the unmodified variety, supporting their future development for the treatment of cancer.

The modulation of platelet and endothelial cell adhesion to vascular graft materials by perlecan

Controlled neo-endothelialisation is critical to the patency of small diameter vascular grafts. Endothelialisation and platelet adhesion to purified endothelial cell-derived perlecan, the major heparan sulfate (HS) proteoglycan in basement membranes, were investigated using in vivo and in vitro assays. Expanded polytetrafluoroethylene (ePTFE) vascular grafts were coated with perlecan and tested in an ovine carotid interposition model for a period of 6 weeks and assessed using light and scanning microscopy. Enhanced endothelial cell growth and reduced platelet adhesion were observed on the perlecan coated grafts when compared to uncoated controls implanted in the same sheep (n=5). Perlecan was also found to stimulate endothelial cell proliferation in vitro over a period of 6 days in the presence of plasma proteins and fibroblastic growth factor 2 (FGF-2), however in the absence of FGF-2 endothelial cell growth could not be maintained during this period. Perlecan was found to be anti-adhesive for platelets, however after removal of the HS chains attached to perlecan, platelet adhesion and aggregation were supported. These results suggest a role for HS chains of perlecan in improving graft patency by selectively promoting endothelial cell proliferation while modulating platelet adhesion.

Perlecan regulates developmental angiogenesis by modulating the VEGF-VEGFR2 axis

Using the zebrafish, we previously identified a central function for perlecan during angiogenic blood vessel development. Here, we explored the nature of perlecan function during developmental angiogenesis. A close examination of individual endothelial cell behavior revealed that perlecan is required for proper endothelial cell migration and proliferation. Because these events are largely mediated by VEGF-VEGFR2 signaling, we investigated the relationship between perlecan and the VEGF pathway. We discovered that perlecan knockdown caused an abnormal increase and redistribution of total VEGF-A protein suggesting that perlecan is required for the appropriate localization of VEGF-A. Importantly, we linked perlecan function to the VEGF pathway by efficiently rescuing the perlecan morphant phenotype by microinjecting VEGF-A(165) protein or mRNA. Combining the strategic localization of perlecan throughout the vascular basement membrane along with its growth factor-binding ability, we hypothesized a major role for perlecan during the establishment of the VEGF gradient which provides the instructive cues to endothelial cells during angiogenesis. In support of this hypothesis we demonstrated that human perlecan bound in a heparan sulfate-dependent fashion to VEGF-A(165). Moreover, perlecan enhanced VEGF mediated VEGFR2 activation of human endothelial cells. Collectively, our results indicate that perlecan coordinates developmental angiogenesis through modulation of VEGF-VEGFR2 signaling events. The identification of angiogenic factors, such as perlecan, and their role in vertebrate development will not only enhance overall understanding of the molecular basis of angiogenesis, but may also provide new insight into angiogenesis-based therapeutic approaches.

Thematic review series: sphingolipids. Ganglioside GM3 suppresses the proangiogenic effects of vascular endothelial growth factor and ganglioside GD1a

Gangliosides are sialic acid-containing glycosphingolipids that have long been associated with tumor malignancy and metastasis. Mounting evidence suggests that gangliosides also modulate tumor angiogenesis. Tumor cells shed gangliosides into the microenvironment, which produces both autocrine and paracrine effects on tumor cells and tumor-associated host cells. In this study, we show that the simple monosialoganglioside GM3 counteracts the proangiogenic effects of vascular endothelial growth factor (VEGF) and of the complex disialoganglioside GD1a. GM3 suppressed the action of VEGF and GD1a on the proliferation of human umbilical vein endothelial cells (HUVECs) and inhibited the migration of HUVECs toward VEGF as a chemoattractant. Enrichment of added GM3 in the HUVEC membrane also reduced the phosphorylation of vascular endothelial growth factor receptor 2 (VEGFR-2) and downstream Akt. Moreover, GM3 reduced the proangiogenic effects of GD1a and growth factors in the in vivo Matrigel plug assay. Inhibition of GM3 biosynthesis with the glucosyl transferase inhibitor, N-butyldeoxynojirimycin (NB-DNJ), increased HUVEC proliferation and the phosphorylation of VEGFR-2 and Akt. The effects of NB-DNJ on HUVECs were reversed with the addition of GM3. We conclude that GM3 has antiangiogenic action and may possess therapeutic potential for reducing tumor angiogenesis.