Structural features in heparin that interact with VEGF165 and modulate its biological activity

Conformational preferences of heparan sulfate to recognize the CXCL8 dimer in aqueous medium: degree of sulfation and hydrogen bonds

The sulfation pattern and epimerization of the long-chain sulfated polysaccharide heparan sulfate (HS) cause structural diversity and regulate various physiological and pathological processes when binding with proteins. In this work, we performed a series of molecular dynamics simulations of three variants of the octadecasaccharide HS with varying sulfation positions in aqueous medium in their free forms and in the presence of the chemokine CXCL8 dimer. The free energy of binding depicts the sulfation at the 6-O position of GlcNAc (HS6S), and both 3-O and 6-O positions of GlcNAc (HS3S6S) of HS variants are more likely to bind with the CXCL8 dimer than the triply sulfated HS2S3S6S, which is sulfated at the 2-O position of GlcUA additionally along with 3-O and 6-O positions of GlcNAc. Binding between HS and CXCL8 was driven by electrostatic and van der Waals interactions predominantly regardless of the sulfation pattern; however, unfavorable entropic contribution suppressed the interaction between HS and CXCL8. The contribution of different amino acid residues to the binding energetics suggested that basic amino acids line up the binding site of CXCL8. This study further acknowledges the role of interfacial water that is structured and bound with HS through hydrogen bonds, exhibiting differential hydrogen bond relaxation dynamics compared to when the HS molecules are free. Moreover, this study identifies that with the increase in sulfation, the HS-water hydrogen bond relaxation occurs faster with the complexation, while the reverse trend is followed in their free forms. Significant structural adaptation of the different sulfated HS molecules, as verified from the free energy landscapes generated from various reaction coordinates, root-mean-square-deviations, end-to-end distances, including ring pucker angles, dihedral flexibility, and the high conformational entropy cost arising from the glycosidic bonds, suggests that the different sulfated variants of HS undergo significant structural transformation to bind with CXCL8. The presence of a CXCL8 dimer imposes the bound forms of HS to adopt non-linear structures with skew-boat conformations. The atomistic details of the study would help in understanding the selectivity and conformational diversity, as well as the role of solvents in the recognition of CXCL8 by different sulfated variants of HS molecules.

Galectin-3-Binding Protein Inhibits Extracellular Heparan 6-O-Endosulfatase Sulf-2

Human extracellular 6-O-endosulfatases Sulf-1 and Sulf-2 are the only enzymes that post-synthetically alter the 6-O sulfation of heparan sulfate proteoglycans (HSPG), which regulates interactions of HSPG with many proteins. Oncogenicity of Sulf-2 in different cancers has been documented, and we have shown that Sulf-2 is associated with poor survival outcomes in head and neck squamous cell carcinoma (HNSCC). Despite its importance, limited information is available on direct protein-protein interactions of the Sulf-2 protein in the tumor microenvironment. In this study, we used monoclonal antibody (mAb) affinity purification and mass spectrometry to identify galectin-3-binding protein (LG3BP) as a highly specific binding partner of Sulf-2 in the conditioned media of HNSCC cell lines. We validated their direct interaction in vitro using recombinant proteins and have shown that the chondroitin sulfate (CS) covalently bound to the Sulf-2 influences the binding to LG3BP. We confirmed the importance of the CS chain for the interaction by generating a mutant Sulf-2 protein that lacks the CS. Importantly, we have shown that the LG3BP inhibits Sulf-2 activity in vitro in a concentration-dependent manner. As a consequence, the addition of LG3BP to a spheroid cell culture inhibited the invasion of the HNSCC cells into Matrigel. Thus, Sulf-2 interaction with LG3BP may regulate the physiological activity of the Sulf-2 enzyme as well as its activity in the tumor microenvironment.

Galectin-3-binding protein inhibits extracellular heparan 6-O-endosulfatse Sulf-2

Human extracellular 6-O-endosulfatases Sulf-1 and Sulf-2 are the only enzymes that post-synthetically alter the 6-O sulfation of heparan sulfate proteoglycans (HSPG), which regulates interactions of HSPG with many proteins. Oncogenicity of Sulf-2 in different cancers has been documented and we have shown that Sulf-2 is associated with poor survival outcomes in head and neck squamous cell carcinoma (HNSCC). In spite of its importance, limited information is available on direct protein-protein interactions of the Sulf-2 protein in the tumor microenvironment. In this study, we used monoclonal antibody (mAb) affinity purification and mass spectrometry to identify galectin-3-binding protein (LG3BP) as a highly specific binding partner of Sulf-2 in the secretome of HNSCC cell lines. We validated their direct interaction in vitro using recombinant proteins and have shown that the chondroitin sulfate (CS) covalently bound to the Sulf-2 influences the binding to LG3BP. We confirmed importance of the CS chain for the interaction by generating a mutant Sulf-2 protein that lacks the CS. Importantly, we have shown that the LG3BP inhibits Sulf-2 activity in vitro in a concentration dependent manner. As a consequence, the addition of LG3BP to a spheroid cell culture inhibited invasion of the HNSCC cells into Matrigel. Thus, Sulf-2 interaction with LG3BP has functional relevance, and may regulate physiological activity of the Sulf-2 enzyme as well as its activity in the tumor microenvironment.

A 6-O-endosulfatase activity assay based on synthetic heparan sulfate oligomers

Sulf-2 is an extracellular heparan 6-O-endosulfatase involved in the postsynthetic editing of heparan sulfate (HS), which regulates many important biological processes. The activity of the Sulf-2 and its substrate specificity remain insufficiently characterized in spite of more than two decades of studies of this enzyme. This is due, in part, to the difficulties in the production and isolation of this highly modified protein and due to the lack of well-characterized synthetic substrates for the probing of its catalytic activity. We introduce synthetic HS oligosaccharides to fill this gap, and we use our recombinant Sulf-2 protein to show that a paranitrophenol (pNP)-labeled synthetic oligosaccharide allows a reliable quantification of its enzymatic activity. The substrate and products of the desulfation reaction are separated by ion exchange high-pressure liquid chromatography and quantified by UV absorbance. This simple assay allows the detection of the Sulf-2 activity at high sensitivity (nanograms of the enzyme) and specificity. The method also allowed us to measure the heparan 6-O-endosulfatase activity in biological samples as complex as the secretome of cancer cell lines. Our in vitro measurements show that the N-glycosylation of the Sulf-2 enzyme affects the activity of the enzyme and that phosphate ions substantially decrease the Sulf-2 enzymatic activity. This assay offers an efficient, sensitive, and specific measurement of the heparan 6-O-endosulfatase activity that could open avenues to in vivo activity measurements and improve our understanding of the enzymatic editing of the sulfation of heparan.

Case of subcutaneous insulin resistance syndrome treated with ultra-rapid insulin lispro

Subcutaneous insulin resistance syndrome is a rare condition that causes difficulty in glycemic control due to severe resistance to subcutaneous insulin injections. We herein present a case of a 40-year-old woman with type 2 diabetes mellitus who had been diagnosed with subcutaneous insulin resistance syndrome since the age of 29 years, and had been persistently treated with continuous subcutaneous insulin infusion using a mixture of insulin lispro and heparin. The patient was switched from insulin lispro plus heparin to ultra-rapid insulin lispro; given that it contains treprostinil and citrate, it is expected to have similar effects as heparin, and shows similar glucose-lowering effects and insulin absorption. Our results suggest that treatment with ultra-rapid insulin lispro is effective for subcutaneous insulin resistance syndrome.

Evaluation of the Structural, Physicochemical, and Biological Characteristics of SB11, as Lucentis® (Ranibizumab) Biosimilar

Introduction

SB11 was recently approved as a ranibizumab biosimilar by the US Food and Drug Administration (FDA) and the European Commission (EC) as a therapy for retinal vascular disorders under the brand name Byooviz™. This study was performed to assess the analytical similarity between SB11 and reference products from the European Union (EU-ranibizumab) and United States (US-ranibizumab).

Methods

A comprehensive structural, physicochemical, and biological characterization was performed utilizing state-of-the-art analytical methods. Comparisons included the following: primary structure related to amino acid sequence and post-translational modifications; higher order structure; product-related substances and purity/impurity including size and charge variants. In addition, biological characterization included a series of mechanism of action (MoA)-related bioassays such as vascular endothelial growth factor (VEGF)-A binding assay (VEGF-A 165 and its isoforms), cell-based VEGF-A 165 neutralization assay, and anti-proliferation assay using human umbilical vein endothelial cells (HUVEC).

Results

The amino acid sequence of SB11 was identical to that of reference products, and post-translational modification profiles and higher order structures of SB11 were shown to be indistinguishable from the reference products. Product-related size and charge variants and aggregates were also similar. Using a broad range of VEGF-related functional assays, we demonstrated that SB11 has similar biological properties to reference products in VEGF-A binding activities (VEGF-A 165 and isoforms (VEGF-A 110, VEGF-A 121, and VEGF-A 189)), VEGF-A 165 neutralization, and HUVEC anti-proliferation. Overall, SB11 exhibits high similarity compared to EU/US-ranibizumab.

Conclusion

Based on the comprehensive analytical similarity assessment, SB11 is highly similar to the EU/US-ranibizumab with respect to structural, physicochemical, and biological properties.

Mechanistic Illustration: How Newly-Formed Blood Vessels Stopped by the Mineral Blocks of Bone Substitutes Can Be Avoided by Using Innovative Combined Therapeutics

One major limitation for the vascularization of bone substitutes used for filling is the presence of mineral blocks. The newly-formed blood vessels are stopped or have to circumvent the mineral blocks, resulting in inefficient delivery of oxygen and nutrients to the implant. This leads to necrosis within the implant and to poor engraftment of the bone substitute. The aim of the present study is to provide a bone substitute currently used in the clinic with suitably guided vascularization properties. This therapeutic hybrid bone filling, containing a mineral and a polymeric component, is fortified with pro-angiogenic smart nano-therapeutics that allow the release of angiogenic molecules. Our data showed that the improved vasculature within the implant promoted new bone formation and that the newly-formed bone swapped the mineral blocks of the bone substitutes much more efficiently than in non-functionalized bone substitutes. Therefore, we demonstrated that our therapeutic bone substitute is an advanced therapeutical medicinal product, with great potential to recuperate and guide vascularization that is stopped by mineral blocks, and can improve the regeneration of critical-sized bone defects. We have also elucidated the mechanism to understand how the newly-formed vessels can no longer encounter mineral blocks and pursue their course of vasculature, giving our advanced therapeutical bone filling great potential to be used in many applications, by combining filling and nano-regenerative medicine that currently fall short because of problems related to the lack of oxygen and nutrients.

A 3D Fiber-Hydrogel Based Non-Viral Gene Delivery Platform Reveals that microRNAs Promote Axon Regeneration and Enhance Functional Recovery Following Spinal Cord Injury

Current treatment approaches toward spinal cord injuries (SCI) have mainly focused on overcoming the inhibitory microenvironment that surrounds lesion sites. Unfortunately, the mere modulation of the cell/tissue microenvironment is often insufficient to achieve desired functional recovery. Therefore, stimulating the intrinsic growth ability of injured neurons becomes crucial. MicroRNAs (miRs) play significant roles during axon regeneration by regulating local protein synthesis at growth cones. However, one challenge of using miRs to treat SCI is the lack of efficient delivery approaches. Here, a 3D fiber-hydrogel scaffold is introduced which can be directly implanted into a spinal cord transected rat. This 3D scaffold consists of aligned electrospun fibers which provide topographical cues to direct axon regeneration, and collagen matrix which enables a sustained delivery of miRs. Correspondingly, treatment with Axon miRs (i.e., a cocktail of miR-132/miR-222/miR-431) significantly enhances axon regeneration. Moreover, administration of Axon miRs along with anti-inflammatory drug, methylprednisolone, synergistically enhances functional recovery. Additionally, this combined treatment also decreases the expression of pro-inflammatory genes and enhance gene expressions related to extracellular matrix deposition. Finally, increased Axon miRs dosage with methylprednisolone, significantly promotes functional recovery and remyelination. Altogether, scaffold-mediated Axon miR treatment with methylprednisolone is a promising therapeutic approach for SCI.

Syndecans and Pancreatic Ductal Adenocarcinoma

Pancreatic Ductal Adenocarcinoma (PDAC) is a fatal disease with poor prognosis because patients rarely express symptoms in initial stages, which prevents early detection and diagnosis. Syndecans, a subfamily of proteoglycans, are involved in many physiological processes including cell proliferation, adhesion, and migration. Syndecans are physiologically found in many cell types and their interactions with other macromolecules enhance many pathways. In particular, extracellular matrix components, growth factors, and integrins collect the majority of syndecans associations acting as biochemical, physical, and mechanical transducers. Syndecans are transmembrane glycoproteins, but occasionally their extracellular domain can be released from the cell surface by the action of matrix metalloproteinases, converting them into soluble molecules that are capable of binding distant molecules such as extracellular matrix (ECM) components, growth factor receptors, and integrins from other cells. In this review, we explore the role of syndecans in tumorigenesis as well as their potential as therapeutic targets. Finally, this work reviews the contribution of syndecan-1 and syndecan-2 in PDAC progression and illustrates its potential to be targeted in future treatments for this devastating disease.

Heparan sulfate functions are altered in the osteoarthritic cartilage

BACKGROUND

Heparan sulfate (HS) proteoglycans (PG) may be found at the chondrocyte surface and in the pericellular cartilage matrix, and are involved in cell-cell and cell-matrix interactions. An important function of HS chains is to regulate cell fate through specific interactions with heparin-binding proteins (HBP) modulated by their complex sulfation pattern. Osteoarthritis (OA) is a joint disorder characterized by the degradation of articular cartilaginous extracellular matrix. The aim of this study was to investigate HS structure and functions in osteoarthritic cartilages compared to normal cartilages (controls).

METHODS

Glycosaminoglycans (GAG) were extracted from human macroscopically normal cartilages (controls, n = 7) and (OA cartilages n = 11). HS were isolated and quantified using the DMMB quantification method. Their structure and functions were then compared using respectively a HPLC analysis and HBP binding tests and their phenotypic effects on murine chondrocytes were studied by RQ-PCR. Statistical analyzes were performed using a one-way ANOVA followed by a Dunnett's test or a t test for pairwise comparisons.

RESULTS

In OA, HS were characterized by increased sulfation levels compared to controls. Moreover, the capacity of these HS to bind HBP involved in the OA pathophysiological process such as FGF2 and VEGF was reduced. Chondroitin sulfates and keratan sulfates regulated these binding properties. Finally, HS from OA cartilages induced the mRNA levels of catabolic markers such as MMP3, MMP13, and TS4 and inhibited the mRNA levels of anabolic markers such as COL2, ACAN, SOX9, and VEGF in murine articular chondrocytes.

CONCLUSION

The sulfation of HS chains was increased in OA cartilages with changes in HBP binding properties and biological effects on chondrocyte phenotypes. Thus, modified HS present in altered cartilages could be a novel therapeutic target in OA.

Increased bleeding risk associated with concurrent vascular endothelial growth factor receptor tyrosine kinase inhibitors and low-molecular-weight heparin

BACKGROUND

Some cancer patients who are diagnosed with thromboembolism may require dual treatment with vascular endothelial growth factor receptor (VEGFR) tyrosine kinase inhibitors (TKIs) and factor Xa inhibitors (low-molecular-weight heparin [LMWH] or direct oral anticoagulants [DOACs]). However, to the authors' knowledge, the safety of such combinations has not been well characterized.

METHODS

Patients with advanced cancer who were treated with concurrent VEGFR TKIs and factor Xa inhibitors between 2010 and 2018 at The Ohio State University Comprehensive Cancer Center were included. Charts were reviewed retrospectively for clinically significant bleeding events occurring during concurrent treatment compared with those occurring during factor Xa inhibitor therapy alone, using each patient as their own control. The Fisher exact test was used to compare distribution of bleeding severities. The Cox proportional hazards model was used to compare bleeding risk between groups.

RESULTS

Among 86 patients, there were 29 clinically significant bleeding events (including 8 major bleeding events) reported during concurrent treatment and 17 events (including 4 major bleeding events) reported during factor Xa inhibitor therapy alone over a median follow-up of 63 days. Concurrent treatment was associated with significantly higher risks of overall bleeding (hazard ratio, 2.45; 95% confidence interval, 1.28-4.69 [P = .007]) and first-onset bleeding (hazard ratio, 2.23; 95% confidence interval, 1.13-4.42 [P = .02]). Analysis of 6-month bleeding risk and the subgroups of patients treated with concurrent TKIs and LMWH versus LMWH alone demonstrated a similar trend. The sample size was inadequate for comparisons between treatment with concurrent TKIs and DOACs versus DOACs alone.

CONCLUSIONS

Concurrent treatment with VEGFR TKIs and LMWH was found to be associated with a significantly increased risk of bleeding events when compared with LMWH therapy alone.

Heparinoid Complex-Based Heparin-Binding Cytokines and Cell Delivery Carriers

Heparinoid is the generic term that is used for heparin, heparan sulfate (HS), and heparin-like molecules of animal or plant origin and synthetic derivatives of sulfated polysaccharides. Various biological activities of heparin/HS are attributed to their specific interaction and regulation with various heparin-binding cytokines, antithrombin (AT), and extracellular matrix (ECM) biomolecules. Specific domains with distinct saccharide sequences in heparin/HS mediate these interactions are mediated and require different highly sulfated saccharide sequences with different combinations of sulfated groups. Multivalent and cluster effects of the specific sulfated sequences in heparinoids are also important factors that control their interactions and biological activities. This review provides an overview of heparinoid-based biomaterials that offer novel means of engineering of various heparin-binding cytokine-delivery systems for biomedical applications and it focuses on our original studies on non-anticoagulant heparin-carrying polystyrene (NAC-HCPS) and polyelectrolyte complex-nano/microparticles (N/MPs), in addition to heparin-coating devices.

PEG grafted chitosan scaffold for dual growth factor delivery for enhanced wound healing

Application of growth factors at wound site has improved the efficiency and quality of healing. Basic fibroblast growth factor (bFGF) and vascular endothelial growth factor (VEGF) induce proliferation of various cells in wound healing. Delivery of growth factor from controlled release systems protect it from degradation and also result in sustained delivery of it at the site of injury. The goal of the study was to develop a Polyethylene glycol (PEG) cross-linked cotton-like chitosan scaffold (CS-PEG-H) by freeze-drying method and chemically conjugate heparin to the scaffold to which the growth factors can be electrostatically bound and evaluate its wound healing properties in vitro and in vivo. The growth factor containing scaffolds induced increased proliferation of HaCaT cells, increased neovascularization and collagen formation seen by H and E and Masson's trichrome staining. Immunohistochemistry was performed using the Ki67 marker which increased proliferation of cells in growth factor containing scaffold treated group. Frequent dressing changes are a major deterrent to proper wound healing. Our system was found to release both VEGF and bFGF in a continuous manner and attained stability after 7 days. Thus our system can maintain therapeutic levels of growth factor at the wound bed thereby avoiding the need for daily applications and frequent dressing changes. Thus, it can be a promising candidate for wound healing.

Dual Action of Sulfated Hyaluronan on Angiogenic Processes in Relation to Vascular Endothelial Growth Factor-A

Pathological healing characterized by abnormal angiogenesis presents a serious burden to patients’ quality of life requiring innovative treatment strategies. Glycosaminoglycans (GAG) are important regulators of angiogenic processes. This experimental and computational study revealed how sulfated GAG derivatives (sGAG) influence the interplay of vascular endothelial growth factor (VEGF)₁₆₅ and its heparin-binding domain (HBD) with the signaling receptor VEGFR-2 up to atomic detail. There was profound evidence for a HBD-GAG-HBD stacking configuration. Here, the sGAG act as a “molecular glue” leading to recognition modes in which sGAG interact with two VEGF₁₆₅-HBDs. A 3D angiogenesis model demonstrated the dual regulatory role of high-sulfated derivatives on the biological activity of endothelial cells. While GAG alone promote sprouting, they downregulate VEGF₁₆₅-mediated signaling and, thereby, elicit VEGF₁₆₅-independent and -dependent effects. These findings provide novel insights into the modulatory potential of sGAG derivatives on angiogenic processes and point towards their prospective application in treating abnormal angiogenesis.

Glycosaminoglycan-based biomaterials for growth factor and cytokine delivery: Making the right choices

Controlled, localized drug delivery is a long-standing goal of medical research, realization of which could reduce the harmful side-effects of drugs and allow more effective treatment of wounds, cancers, organ damage and other diseases. This is particularly the case for protein "drugs" and other therapeutic biological cargoes, which can be challenging to deliver effectively by conventional systemic administration. However, developing biocompatible materials that can sequester large quantities of protein and release them in a sustained and controlled manner has proven challenging. Glycosaminoglycans (GAGs) represent a promising class of bio-derived materials that possess these key properties and can additionally potentially enhance the biological effects of the delivered protein. They are a diverse group of linear polysaccharides with varied functionalities and suitabilities for different cargoes. However, most investigations so far have focused on a relatively small subset of GAGs - particularly heparin, a readily available, promiscuously-binding GAG. There is emerging evidence that for many applications other GAGs are in fact more suitable for regulated and sustained delivery. In this review, we aim to illuminate the beneficial properties of various GAGs with reference to specific protein cargoes, and to provide guidelines for informed choice of GAGs for therapeutic applications.

Polyelectrolyte Complexes of Natural Polymers and Their Biomedical Applications

Polyelectrolyte complexes (PECs), composed of natural and biodegradable polymers, (such as positively charged chitosan or protamine and negatively charged glycosaminoglycans (GAGs)) have attracted attention as hydrogels, films, hydrocolloids, and nano-/micro-particles (N/MPs) for biomedical applications. This is due to their biocompatibility and biological activities. These PECs have been used as drug and cell delivery carriers, hemostats, wound dressings, tissue adhesives, and scaffolds for tissue engineering. In addition to their comprehensive review, this review describes our original studies and provides an overview of the characteristics of chitosan-based hydrogel, including photo-cross-linkable chitosan hydrogel and hydrocolloidal PECs, as well as molecular-weight heparin (LH)/positively charged protamine (P) N/MPs. These are generated by electrostatic interactions between negatively charged LH and positively charged P together with their potential biomedical applications.

N-terminal syndecan-2 domain selectively enhances 6-O heparan sulfate chains sulfation and promotes VEGFA165-dependent neovascularization

The proteoglycan Syndecan-2 (Sdc2) has been implicated in regulation of cytoskeleton organization, integrin signaling and developmental angiogenesis in zebrafish. Here we report that mice with global and inducible endothelial-specific deletion of Sdc2 display marked angiogenic and arteriogenic defects and impaired VEGFA165 signaling. No such abnormalities are observed in mice with deletion of the closely related Syndecan-4 (Sdc4) gene. These differences are due to a significantly higher 6-O sulfation level in Sdc2 versus Sdc4 heparan sulfate (HS) chains, leading to an increase in VEGFA165 binding sites and formation of a ternary Sdc2-VEGFA165-VEGFR2 complex which enhances VEGFR2 activation. The increased Sdc2 HS chains 6-O sulfation is driven by a specific N-terminal domain sequence; the insertion of this sequence in Sdc4 N-terminal domain increases 6-O sulfation of its HS chains and promotes Sdc2-VEGFA165-VEGFR2 complex formation. This demonstrates the existence of core protein-determined HS sulfation patterns that regulate specific biological activities.

Chitosan sulfate inhibits angiogenesis via blocking the VEGF/VEGFR2 pathway and suppresses tumor growth in vivo

SCTS inhibits neovascularization by blocking the VEGF/VEGFR2 signal pathway and exerts anti-tumor effects.

The Role of Endothelial Surface Glycocalyx in Mechanosensing and Transduction

The endothelial cells (ECs) forming the inner wall of every blood vessel are constantly exposed to the mechanical forces generated by blood flow. The EC responses to these hemodynamic forces play a critical role in the homeostasis of the circulatory system. A variety of mechanosensors and transducers, locating on the EC surface, intra- and trans-EC membrane, and within the EC cytoskeleton, have thus been identified to ensure proper functions of ECs. Among them, the most recent candidate is the endothelial surface glycocalyx (ESG), which is a matrix-like thin layer covering the luminal surface of the EC. It consists of various proteoglycans, glycosaminoglycans, and plasma proteins and is close to other prominent EC mechanosensors and transducers. This chapter summarizes the ESG composition, thickness, and structure observed by different labeling and visualization techniques and in different types of vessels. It also presents the literature in determining the ESG mechanical properties by atomic force microscopy and optical tweezers. The molecular mechanisms by which the ESG plays the role in EC mechanosensing and transduction are described as well as the ESG remodeling by shear stress, the actin cytoskeleton, the membrane rafts, the angiogenic factors, and the sphingosine-1-phosphate.

Small Molecule Antagonist of Cell Surface Glycosaminoglycans Restricts Mouse Embryonic Stem Cells in a Pluripotent State

Recently, the field of stem cell-based regeneration has turned its attention toward chemical approaches for controlling the pluripotency and differentiation of embryonic stem cells (ESCs) using drug-like small molecule modulators. Growth factor receptors or their associated downstream kinases that regulate intracellular signaling pathways during differentiation are typically the targets for these molecules. The glycocalyx, which plays an essential role in actuating responses to growth factors at the cellular boundary, offers an underexplored opportunity for intervention using small molecules to influence differentiation. Here, we show that surfen, an antagonist of cell-surface glycosaminoglycans required for growth factor association with cognate receptors, acts as a potent and general inhibitor of differentiation and promoter of pluripotency in mouse ESCs. This finding shows that drugging the stem cell Glycome with small molecules to silence differentiation cues can provide a powerful new alternative to existing techniques for controlling stem cell fate. Stem Cells 2018;36:45-54.

A glycan-based approach to therapeutic angiogenesis

Angiogenesis, the sprouting of new blood vessels from existing vasculature, involves multiple complex biological processes, and it is an essential step for hemostasis, tissue healing and regeneration. Angiogenesis stimulants can ameliorate human disease conditions including limb ischemia, chronic wounds, heart disease, and stroke. The current strategies to improve the bioavailability of pro-angiogenic growth factors, including VEGF and FGF2, have remained largely unsuccessful. This study demonstrates that small molecules, termed click-xylosides, can promote angiogenesis in the in vitro matrigel tube formation assay and the ex ovo chick chorioallantoic membrane assay, depending on their aglycone moieties. Xyloside treatment enhances network connectivity and cell survivability, thereby, maintaining the network structures on matrigel culture for an extended period of time. These effects were achieved via the secreted xyloside-primed glycosaminoglycans (GAG) chains that in part, act through an ERK1/2 mediated signaling pathway. Through the remodeling of GAGs in the extracellular matrix of endothelial cells, the glycan approach, involving xylosides, offers great potential to effectively promote therapeutic angiogenesis.

Sulfated Hyaluronan Alters Endothelial Cell Activation in Vitro by Controlling the Biological Activity of the Angiogenic Factors Vascular Endothelial Growth Factor-A and Tissue Inhibitor of Metalloproteinase-3

Several pathologic conditions such as rheumatoid arthritis, ocular neovascularization, cancer, or atherosclerosis are often associated with abnormal angiogenesis, which requires innovative biomaterial-based treatment options to control the activity of angiogenic factors. Here, we studied how sulfated hyaluronan (sHA) and oversulfated chondroitin sulfate derivatives as potential components of functional biomaterials modulate vascular endothelial growth factor-A (VEGF-A) signaling and endothelial cell activity in vitro. Tissue inhibitor of metalloproteinase-3 (TIMP-3), an effective angiogenesis inhibitor, exerts its activity by competing with VEGF-A for binding to VEGF receptor-2 (VEGFR-2). However, even though TIMP-3 and VEGF-A are known to interact with glycosaminoglycans (GAGs), the potential role and mechanism by which GAGs alter the VEGF-A/TIMP-3 regulated VEGFR-2 signaling remains unclear. Combining surface plasmon resonance, immunobiochemical analysis, and molecular modeling, we demonstrate the simultaneous binding of VEGF-A and TIMP-3 to sHA-coated surfaces and identified a novel mechanism by which sulfated GAG derivatives control angiogenesis: GAG derivatives block the binding of VEGF-A and TIMP-3 to VEGFR-2 thereby reducing their biological activity in a defined, sulfation-dependent manner. This effect was stronger for sulfated GAG derivatives than for native GAGs. The simultaneous formation of TIMP-3/sHA complexes partially rescues the sHA inhibited VEGF-A/VEGFR-2 signaling and endothelial cell activation. These results provide novel insights into the regulation of angiogenic factors by GAG derivatives and highlight the potential of sHA derivatives for the treatment of diseases associated with increased VEGF-A and VEGFR-2 levels.

The "in and out" of glucosamine 6-O-sulfation: the 6th sense of heparan sulfate

The biological properties of Heparan sulfate (HS) polysaccharides essentially rely on their ability to bind and modulate a multitude of protein ligands. These interactions involve internal oligosaccharide sequences defined by their sulfation patterns. Amongst these, the 6-O-sulfation of HS contributes significantly to the polysaccharide structural diversity and is critically involved in the binding of many proteins. HS 6-O-sulfation is catalyzed by 6-O-sulfotransferases (6OSTs) during biosynthesis, and it is further modified by the post-synthetic action of 6-O-endosulfatases (Sulfs), two enzyme families that remain poorly characterized. The aim of the present review is to summarize the contribution of 6-O-sulfates in HS structure/function relationships and to discuss the present knowledge on the complex mechanisms regulating HS 6-O-sulfation.

Hybrid Polycaprolactone/Alginate Scaffolds Functionalized with VEGF to Promote de Novo Vessel Formation for the Transplantation of Islets of Langerhans

Although regarded as a promising treatment for type 1 diabetes, clinical islet transplantation in the portal vein is still hindered by a low transplantation outcome. Alternative transplantation sites have been proposed, but the survival of extra-hepatically transplanted islets of Langerhans critically depends on quick revascularization after engraftment. This study aims at developing a new 3D scaffold platform that can actively boost vascularization and may find an application for extra-hepatic islet transplantation. The construct consists of a 3D ring-shaped polycaprolactone (PCL) scaffold with heparinized surface to electrostatically bind vascular endothelial growth factor (VEGF), surrounding a hydrogel core for islets encapsulation. Heparin immobilization improves the amount of VEGF retained by the construct, up to 3.6 fold, compared to untreated PCL scaffolds. In a chicken chorioallanthoic membrane model, VEGF immobilized on the construct enhances angiogenesis in close proximity and on the surface of the scaffolds. After 7 days, islets encapsulated in the alginate core show functional response to glucose stimuli comparable to free-floating islets. Thus, the developed platform has the potential to support rapid vascularization and islet endocrine function.

Synergistic Binding of Vascular Endothelial Growth Factor-A and Its Receptors to Heparin Selectively Modulates Complex Affinity

Angiogenesis is a highly regulated process orchestrated by the VEGF system. Heparin/heparan sulfate proteoglycans and neuropilin-1 (NRP-1) have been identified as co-receptors, yet the mechanisms of action have not been fully defined. In the present study, we characterized molecular interactions between receptors and co-receptors, using surface plasmon resonance and in vitro binding assays. Additionally, we demonstrate that these binding events are relevant to VEGF activity within endothelial cells. We defined interactions and structural requirements for heparin/HS interactions with VEGF receptor (VEGFR)-1, NRP-1, and VEGF165 in complex with VEGFR-2 and NRP-1. We demonstrate that these structural requirements are distinct for each interaction. We further show that VEGF165, VEGFR-2, and monomeric NRP-1 bind weakly to heparin alone yet show synergistic binding to heparin when presented together in various combinations. This synergistic binding appears to translate to alterations in VEGF signaling in endothelial cells. We found that soluble NRP-1 increases VEGF binding and activation of VEGFR-2 and ERK1/2 in endothelial cells and that these effects require sulfated HS. These data suggest that the presence of HS/heparin and NRP-1 may dictate the specific receptor type activated by VEGF and ultimately determine the biological output of the system. The ability of co-receptors to fine-tune VEGF responsiveness suggests the possibility that VEGF-mediated angiogenesis can be selectively stimulated or inhibited by targeting HS/heparin and NRP-1.

Enhancement of VEGF-Mediated Angiogenesis by 2-N,6-O-Sulfated Chitosan-Coated Hierarchical PLGA Scaffolds

Rapid and controlled vascularization within scaffolds remains one of the key limitations in tissue engineering applications. This study describes the fabrication and characterization of 2-N,6-O-sulfated chitosan (26SCS)-coated hierarchical scaffold composed of poly(lactic-co-glycolic acid) (PLGA) microspheres, as a desirable vehicle for vascular endothelial growth factor (VEGF) delivery and consequent angiogenic boosting in vitro. Owing to the hierarchical porous structure and high affinity between VEGF and 26SCS, the 26SCS-modified PLGA (S-PLGA) scaffold possesses excellent entrapment and sustained release of VEGF. Using human umbilical vein endothelial cells (HUVECs) as a cell model, the VEGF-loaded S-PLGA scaffold shows desirable cell viability and attachment. The bioactivity of released VEGF is validated by intracellular nitric oxide secretion and capillary tube formation, demonstrating the improved capacity of VEGF-mediated pro-angiogenesis ascribed to 26SCS incorporation. Such a strategy will afford an effective method to prepare a scaffold with promoted angiogenesis.

In-vitro suppression of IL-6 and IL-8 release from human pulmonary epithelial cells by non-anticoagulant fraction of enoxaparin

BACKGROUND

Enoxaparin, a mixture of anticoagulant and non-anticoagulant fractions, is widely used as an anticoagulant agent. However, it is also reported to possess anti-inflammatory properties. Our study indicated that enoxaparin inhibits the release of IL-6 and IL-8 from A549 pulmonary epithelial cells. Their release causes extensive lung tissue damage. The use of enoxaparin as an anti-inflammatory agent is hampered due to the risk of bleeding associated with its anticoagulant fractions. Therefore, we aimed to identify the fraction responsible for the observed anti-inflammatory effect of enoxaparin and to determine the relationship between its structure and biological activities.

METHODS

A549 pulmonary epithelial cells were pre-treated in the presence of enoxaparin and its fractions. The levels of IL-6 and IL-8 released from the trypsin-stimulated cells were measured by ELISA. The anticoagulant activity of the fraction responsible for the effect of enoxaparin was determined using an anti-factor-Xa assay. The fraction was structurally characterised using nuclear magnetic resonance. The fraction was 2-O, 6-O or N-desulfated to determine the position of sulfate groups required for the inhibition of interleukins. High-performance size-exclusion chromatography was performed to rule out that the observed effect was due to the interaction between the fraction and trypsin or interleukins.

RESULTS

Enoxaparin (60 μg/mL) inhibited the release of IL-6 and IL-8 by >30%. The fraction responsible for this effect of enoxaparin was found to be a disaccharide composed of α-L-iduronic-acid and α-D-glucosamine-6-sulfate. It (15 μg/mL) inhibited the release of interleukins by >70%. The 6-O sulphate groups were responsible for its anti-inflammatory effect. The fraction did not bind to trypsin or interleukins, suggesting the effect was not due to an artefact of the experimental model.

CONCLUSION

The identified disaccharide has no anticoagulant activity and therefore eliminates the risk of bleeding associated with enoxaparin. Future in-vivo studies should be designed to validate findings of the current study.

Heparin/Heparan sulfate proteoglycans glycomic interactome in angiogenesis: biological implications and therapeutical use

Angiogenesis, the process of formation of new blood vessel from pre-existing ones, is involved in various intertwined pathological processes including virus infection, inflammation and oncogenesis, making it a promising target for the development of novel strategies for various interventions. To induce angiogenesis, angiogenic growth factors (AGFs) must interact with pro-angiogenic receptors to induce proliferation, protease production and migration of endothelial cells (ECs). The action of AGFs is counteracted by antiangiogenic modulators whose main mechanism of action is to bind (thus sequestering or masking) AGFs or their receptors. Many sugars, either free or associated to proteins, are involved in these interactions, thus exerting a tight regulation of the neovascularization process. Heparin and heparan sulfate proteoglycans undoubtedly play a pivotal role in this context since they bind to almost all the known AGFs, to several pro-angiogenic receptors and even to angiogenic inhibitors, originating an intricate network of interaction, the so called "angiogenesis glycomic interactome". The decoding of the angiogenesis glycomic interactome, achievable by a systematic study of the interactions occurring among angiogenic modulators and sugars, may help to design novel antiangiogenic therapies with implications in the cure of angiogenesis-dependent diseases.

Injectable gelatin derivative hydrogels with sustained vascular endothelial growth factor release for induced angiogenesis

Injectable biomaterials are attractive for soft tissue regeneration because they are handled in a minimally invasive manner and can easily adapt to complex defects. However, inadequate vascularization of the injectable constructs has long been a barrier, leading to necrosis or volume reduction after implantation. In this work, we developed a three-step process to synthesize injectable gelatin-derived hydrogels that are capable of controlling growth factor delivery to induce angiogenesis. In our approach, tyramine was first introduced into gelatin chains to provide enzymatic crosslinking points for gel formation after injection. Next, heparin, a polysaccharide with binding domains to many growth factors, was covalently linked to the tyramine-modified gelatin. Finally, vascular endothelial growth factor (VEGF) was incorporated into the gelatin derivative by binding with the heparin in the gelatin derivative, and an injectable gel with controlled VEGF release was formed by an enzymatic catalytic reaction with hydrogen peroxide (H2O2) and horseradish peroxidase (HRP). The gelation time, mechanical properties and degradation of the gel was readily tailored by the gelatin concentration and the ratio of H2O2/HRP. Binding VEGF to heparin stabilizes this growth factor, protects it from denaturation and proteolytic degradation and subsequently prolongs the sustained release. An in vitro release study and bioactivity assay indicated that the VEGF was released in a sustained manner with high bioactivity for over 3 weeks. Furthermore, a chicken chorioallantoic membrane (CAM) assay and animal experiments were performed to evaluate in vivo bioactivity of the VEGF released from the hydrogels. After 5 days of incubation on CAM, the number of blood vessels surrounding the heparin-modified hydrogels was increased by 2.4-fold compared with that of the control group. Deeper and denser cell infiltration and angiogenesis in the heparin-modified gelatin/VEGF gels were observed compared to the controls after being subcutaneously injected in the dorsal side of the mice for 2 weeks. Interestingly, even without the incorporation of VEGF, the heparin-modified gelatin derivative still had the capability to induce angiogenesis to a certain degree. Our results suggest that the gelatin derivative/VEGF is an excellent injectable delivery system for induced angiogenesis of soft tissue regeneration.

Glycosaminoglycan mimetic improves enrichment and cell functions of human endothelial progenitor cell colonies

Human circulating endothelial progenitor cells isolated from peripheral blood generate in culture cells with features of endothelial cells named late-outgrowth endothelial colony-forming cells (ECFC). In adult blood, ECFC display a constant quantitative and qualitative decline during life span. Even after expansion, it is difficult to reach the cell dose required for cell therapy of vascular diseases, thus limiting the clinical use of these cells. Glycosaminoglycans (GAG) are components from the extracellular matrix (ECM) that are able to interact and potentiate heparin binding growth factor (HBGF) activities. According to these relevant biological properties of GAG, we designed a GAG mimetic having the capacity to increase the yield of ECFC production from blood and to improve functionality of their endothelial outgrowth. We demonstrate that the addition of [OTR(4131)] mimetic during the isolation process of ECFC from Cord Blood induces a 3 fold increase in the number of colonies. Moreover, addition of [OTR(4131)] to cell culture media improves adhesion, proliferation, migration and self-renewal of ECFC. We provide evidence showing that GAG mimetics may have great interest for cell therapy applied to vascular regeneration therapy and represent an alternative to exogenous growth factor treatments to optimize potential therapeutic properties of ECFC.

Post-Synthetic Regulation of HS Structure: The Yin and Yang of the Sulfs in Cancer

Heparan sulfate (HS) is a complex polysaccharide that takes part in most major cellular processes, through its ability to bind and modulate a very large array of proteins. These interactions involve saccharide domains of specific sulfation pattern (S-domains), the assembly of which is tightly orchestrated by a highly regulated biosynthesis machinery. Another level of structural control does also take place at the cell surface, where degrading enzymes further modify HS post-synthetically. Amongst them are the Sulfs, a family of extracellular sulfatases (two isoforms in human) that catalyze the specific 6-O-desulfation of HS. By targeting HS functional sulfated domains, Sulfs dramatically alter its ligand binding properties, thereby modulating a broad range of signaling pathways. Consequently, Sulfs play major roles during development, as well as in tissue homeostasis and repair. Sulfs have also been associated with many pathologies including cancer, but despite increasing interest, the role of Sulfs in tumor development still remains unclear. Studies have been hindered by a poor understanding of the Sulf enzymatic activities and conflicting data have shown either anti-oncogenic or tumor-promoting effects of these enzymes, depending on the tumor models analyzed. These opposite effects clearly illustrate the fine tuning of HS functions by the Sulfs, and the need to clarify the mechanisms involved. In this review, we will detail the present knowledge on the structural and functional properties of the Sulfs, with a special focus on their implication during tumor progression. Finally, we will discuss attempts and perspectives of using the Sulfs as a biomarker of cancer prognosis and diagnostic and as a target for anti-cancer therapies.

Non-anticoagulant derivatives of heparin for the management of asthma: distant dream or close reality?

INTRODUCTION

Approximately 300 million people worldwide are currently affected by asthma. Improvements in the understanding of the mechanisms involved in such inflammatory airway disorders has led to the recognition of new therapeutic approaches. Heparin, a widely used anticoagulant, has been shown to be beneficial in the management of asthma. It belongs to the family of highly sulphated polysaccharides referred to as glycosaminoglycans, containing a heterogeneous mixture of both anticoagulant and non-anticoagulant polysaccharides. Experimental findings have suggested that heparin has potential anti-asthmatic properties owing to the ability of its non-anticoagulant oligosaccharides to bind and modulate the activity of a wide range of biological molecules involved in the inflammatory process.

AREAS COVERED

This review focuses on the potential mechanisms of action and clinical application of heparin as an anti-inflammatory agent for the management of asthma.

EXPERT OPINION

Heparin may play a significant role in the management of asthma. However, these properties are often hindered by the presence of anticoagulant oligosaccharides, which possess a significant risk of bleeding. Therefore, its therapeutic potential must be explored using well-designed clinical studies that focus on identifying and isolating the anti-inflammatory oligosaccharides of heparin and further elucidating the structure and mechanisms of actions of these non-anticoagulant oligosaccharides.

Multifunctional silk-heparin biomaterials for vascular tissue engineering applications

Over the past 30 years, silk has been proposed for numerous biomedical applications that go beyond its traditional use as a suture material. Silk sutures are well tolerated in humans, but the use of silk for vascular engineering applications still requires extensive biocompatibility testing. Some studies have indicated a need to modify silk to yield a hemocompatible surface. This study examined the potential of low molecular weight heparin as a material for refining silk properties by acting as a carrier for vascular endothelial growth factor (VEGF) and improving silk hemocompatibility. Heparinized silk showed a controlled VEGF release over 6 days; the released VEGF was bioactive and supported the growth of human endothelial cells. Silk samples were then assessed using a humanized hemocompatibility system that employs whole blood and endothelial cells. The overall thrombogenic response for silk was very low and similar to the clinical reference material polytetrafluoroethylene. Despite an initial inflammatory response to silk, apparent as complement and leukocyte activation, the endothelium was maintained in a resting, anticoagulant state. The low thrombogenic response and the ability to control VEGF release support the further development of silk for vascular applications.

Age-related impairment of endothelial progenitor cell migration correlates with structural alterations of heparan sulfate proteoglycans

Aging poses one of the largest risk factors for the development of cardiovascular disease. The increased propensity toward vascular pathology with advancing age maybe explained, in part, by a reduction in the ability of circulating endothelial progenitor cells to contribute to vascular repair and regeneration. Although there is evidence to suggest that colony forming unit-Hill cells and circulating angiogenic cells are subject to age-associated changes that impair their function, the impact of aging on human outgrowth endothelial cell (OEC) function has been less studied. We demonstrate that OECs isolated from cord blood or peripheral blood samples from young and old individuals exhibit different characteristics in terms of their migratory capacity. In addition, age-related structural changes were discovered in OEC heparan sulfate (HS), a glycocalyx component that is essential in many signalling pathways. An age-associated decline in the migratory response of OECs toward a gradient of VEGF significantly correlated with a reduction in the relative percentage of the trisulfated disaccharide, 2-O-sulfated-uronic acid, N, 6-O-sulfated-glucosamine (UA[2S]-GlcNS[6S]), within OEC cell surface HS polysaccharide chains. Furthermore, disruption of cell surface HS reduced the migratory response of peripheral blood-derived OECs isolated from young subjects to levels similar to that observed for OECs from older individuals. Together these findings suggest that aging is associated with alterations in the fine structure of HS on the cell surface of OECs. Such changes may modulate the migration, homing, and engraftment capacity of these repair cells, thereby contributing to the progression of endothelial dysfunction and age-related vascular pathologies.

Novel therapeutic targets in the brain tumor microenvironment

Glioblastoma (GBM), a highly malignant brain tumor of adults and children, diffusely invades within the non-neoplastic brain. Despite aggressive current therapeutic interventions, improved therapeutic strategies are greatly needed. Interactions between the tumor and constituents of its microenvironment are known to regulate malignancy, and heparan sulfate proteoglycans (HSPGs) are important as they bind diverse extracellular proteins, including growth factors and cell adhesion molecules, regulating the activity of several ligand-mediated signaling pathways. Recent work from our group described a mechanism by which GBM regulates PDGFR-alpha signaling via enzymatic alteration of heparan sulfate proteoglycans (HSPGs) in the extracellular microenvironment. Blocking tumor-induced alterations of HSPGs, which can be achieved by pharmacological strategies, would potentially inhibit multiple oncogenic signaling pathways in tumor cells and disrupt critical tumormicroenvironment interactions. Here we examine HSPGs and the enzymes that modify them in GBM. We compare their expression across tumor subtypes, their potential roles in oncogenesis, and their potential as novel therapeutic targets in GBM.

Potentiation of anti-angiogenic activity of heparin by blocking the ATIII-interacting pentasaccharide unit and increasing net anionic charge

Heparin, a potent anticoagulant used for the prevention of venous thromboembolism, has been recognized as a tumor angiogenesis inhibitor. Its limitation in clinical application for cancer therapy, however, arises from its strong anticoagulant activity, which causes associated adverse effects. In this study, we show the structural correlation of LHT7, a previously developed heparin-based angiogenesis inhibitor, with its influence on VEGF blockade and its decreased anticoagulant activity. LHT7 was characterized as having average seven molecules of sodium taurocholates conjugated to one molecule of low-molecular-weight heparin (LMWH). This study showed that the conjugation of sodium taurocholates selectively blocked interaction with antithrombin III (ATIII) while enhancing the binding with VEGF. This resulted in LHT7 to have negligible anticoagulant activity but potent anti-angiogenic activity. Following up on this finding, we showed that the bidirectional effect of sodium taurocholate conjugation was due to its unique structure, that is, the sterane core hindering the ATIII-binding pentasaccharide unit of LMWH with its bulky and rigid structural characteristics while the terminal sulfate group interacts with VEGF to produce stronger binding. In addition, we showed that LHT7 was localized in the tumor, especially on the endothelial cells. One explanation for this might be that LHT7 was delivered to the tumor via platelets.

Novel therapeutic targets in the brain tumor microenvironment

Glioblastoma (GBM), a highly malignant brain tumor of adults and children, diffusely invades within the non-neoplastic brain. Despite aggressive current therapeutic interventions, improved therapeutic strategies are greatly needed. Interactions between the tumor and constituents of its microenvironment are known to regulate malignancy, and heparan sulfate proteoglycans (HSPGs) are important as they bind diverse extracellular proteins, including growth factors and cell adhesion molecules, regulating the activity of several ligand-mediated signaling pathways. Recent work from our group described a mechanism by which GBM regulates PDGFR-alpha signaling via enzymatic alteration of heparan sulfate proteoglycans (HSPGs) in the extracellular microenvironment. Blocking tumor-induced alterations of HSPGs, which can be achieved by pharmacological strategies, would potentially inhibit multiple oncogenic signaling pathways in tumor cells and disrupt critical tumormicroenvironment interactions. Here we examine HSPGs and the enzymes that modify them in GBM. We compare their expression across tumor subtypes, their potential roles in oncogenesis, and their potential as novel therapeutic targets in GBM.

Binding affinities of vascular endothelial growth factor (VEGF) for heparin-derived oligosaccharides

Heparin and HS (heparan sulfate) exert their wide range of biological activities by interacting with extracellular protein ligands. Among these important protein ligands are various angiogenic growth factors and cytokines. HS binding to VEGF (vascular endothelial growth factor) regulates multiple aspects of vascular development and function through its specific interaction with HS. Many studies have focused on HS-derived or HS-mimicking structures for the characterization of VEGF165 interaction with HS. Using a heparinase 1-prepared small library of heparin-derived oligosaccharides ranging from hexasaccharide to octadecasaccharide, we systematically investigated the heparin-specific structural features required for VEGF binding. We report the apparent affinities for the association between the heparin-derived oligosaccharides with both VEGF165 and VEGF55, a peptide construct encompassing exclusively the heparin-binding domain of VEGF165. An octasaccharide was the minimum size of oligosaccharide within the library to efficiently bind to both forms of VEGF and a tetradecasaccharide displayed an effective binding affinity to VEGF165 comparable to unfractionated heparin. The range of relative apparent binding affinities among VEGF and the panel of heparin-derived oligosaccharides demonstrate that the VEGF binding affinity likely depends on the specific structural features of these oligosaccharides, including their degree of sulfation, sugar-ring stereochemistry and conformation. Notably, the unique 3-O-sulfo group found within the specific antithrombin binding site of heparin is not required for VEGF165 binding. These findings afford new insight into the inherent kinetics and affinities for VEGF association with heparin and heparin-derived oligosaccharides with key residue-specific modifications and may potentially benefit the future design of oligosaccharide-based anti-angiogenesis drugs.

Heparan sulfate sulfatase SULF2 regulates PDGFRα signaling and growth in human and mouse malignant glioma

Glioblastoma (GBM), a uniformly lethal brain cancer, is characterized by diffuse invasion and abnormal activation of multiple receptor tyrosine kinase (RTK) signaling pathways, presenting a major challenge to effective therapy. The activation of many RTK pathways is regulated by extracellular heparan sulfate proteoglycans (HSPG), suggesting these molecules may be effective targets in the tumor microenvironment. In this study, we demonstrated that the extracellular sulfatase, SULF2, an enzyme that regulates multiple HSPG-dependent RTK signaling pathways, was expressed in primary human GBM tumors and cell lines. Knockdown of SULF2 in human GBM cell lines and generation of gliomas from Sulf2(-/-) tumorigenic neurospheres resulted in decreased growth in vivo in mice. We found a striking SULF2 dependence in activity of PDGFRα, a major signaling pathway in GBM. Ablation of SULF2 resulted in decreased PDGFRα phosphorylation and decreased downstream MAPK signaling activity. Interestingly, in a survey of SULF2 levels in different subtypes of GBM, the proneural subtype, characterized by aberrations in PDGFRα, demonstrated the strongest SULF2 expression. Therefore, in addition to its potential as an upstream target for therapy of GBM, SULF2 may help identify a subset of GBMs that are more dependent on exogenous growth factor-mediated signaling. Our results suggest the bioavailability of growth factors from the microenvironment is a significant contributor to tumor growth in a major subset of human GBM.

Tissue factor pathway inhibitor blocks angiogenesis via its carboxyl terminus

OBJECTIVE

Tissue factor pathway inhibitor (TFPI) is the primary regulator of the tissue factor (TF) coagulation pathway. As such, TFPI may regulate the proangiogenic effects of TF. TFPI may also affect angiogenesis independently of TF, through sequences within its polybasic carboxyl terminus (TFPI C terminus [TFPIct]). We aimed to determine the effects of TFPI on angiogenesis and the role of TFPIct.

METHODS AND RESULTS

Transgenic overexpression of TFPI attenuated angiogenesis in the murine hindlimb ischemia model and an aortic sprout assay. In vitro, TFPI inhibited endothelial cell migration. Peptides within the human TFPIct inhibited endothelial cell cord formation and migration in response to vascular endothelial growth factor (VEGF) 165 but not VEGF121. Furthermore, exposure to human TFPIct inhibited the phosphorylation of VEGF receptor 2 at residue Lys951, a residue known to be critical for endothelial cell migration. Finally, systemic delivery of a murine TFPIct peptide inhibited angiogenesis in the hindlimb model.

CONCLUSION

These data demonstrate an inhibitory role for TFPI in angiogenesis that is, in part, mediated through peptides within its carboxyl terminus. In addition to its known role as a TF antagonist, TFPI, via its carboxyl terminus, may regulate angiogenesis by directly blocking VEGF receptor 2 activation and attenuating the migratory capacity of endothelial cells.

Heparan sulfate proteoglycans mediate the angiogenic activity of the vascular endothelial growth factor receptor-2 agonist gremlin

OBJECTIVE

Heparan sulfate proteoglycans (HSPGs) modulate the interaction of proangiogenic heparin-binding vascular endothelial growth factors (VEGFs) with signaling VEGF receptor-2 (VEGFR2) and neuropilin coreceptors in endothelial cells (ECs). The bone morphogenic protein antagonist gremlin is a proangiogenic ligand of VEGFR2, distinct from canonical VEGFs. Here we investigated the role of HSPGs in VEGFR2 interaction, signaling, and proangiogenic capacity of gremlin in ECs.

METHODS AND RESULTS

Surface plasmon resonance demonstrated that gremlin binds heparin and heparan sulfate, but not other glycosaminoglycans, via N-, 2-O, and 6-O-sulfated groups of the polysaccharide. Accordingly, gremlin binds HSPGs of the EC surface and extracellular matrix. Gremlin/HSPG interaction is prevented by free heparin and heparan sulfate digestion or undersulfation following EC treatment with heparinase II or sodium chlorate. However, at variance with canonical heparin-binding VEGFs, gremlin does not interact with neuropilin-1 coreceptor. On the other hand, HSPGs mediate VEGFR2 engagement and autophosphorylation, extracellular signaling-regulated kinase(1/2) and p38 mitogen-activated protein kinase activation, and consequent proangiogenic responses of ECs to gremlin. On this basis, we evaluated the gremlin-antagonist activity of a panel of chemically sulfated derivatives of the Escherichia coli K5 polysaccharide. The results demonstrate that the highly N,O-sulfated derivative K5-N,OS(H) binds gremlin with high potency, thus inhibiting VEGFR2 interaction and angiogenic activity in vitro and in vivo.

CONCLUSIONS

HSPGs act as functional gremlin coreceptors in ECs, affecting its productive interaction with VEGFR2 and angiogenic activity. This has allowed the identification of the biotechnological K5-N,OS(H) as a novel angiostatic gremlin antagonist.

Heparan sulfate proteoglycans

Heparan sulfate proteoglycans are found at the cell surface and in the extracellular matrix, where they interact with a plethora of ligands. Over the last decade, new insights have emerged regarding the mechanism and biological significance of these interactions. Here, we discuss changing views on the specificity of protein-heparan sulfate binding and the activity of HSPGs as receptors and coreceptors. Although few in number, heparan sulfate proteoglycans have profound effects at the cellular, tissue, and organismal level.

Heparan sulfate proteoglycans

Heparan sulfate proteoglycans are found at the cell surface and in the extracellular matrix, where they interact with a plethora of ligands. Over the last decade, new insights have emerged regarding the mechanism and biological significance of these interactions. Here, we discuss changing views on the specificity of protein-heparan sulfate binding and the activity of HSPGs as receptors and coreceptors. Although few in number, heparan sulfate proteoglycans have profound effects at the cellular, tissue, and organismal level.

Lymphatic endothelial heparan sulfate deficiency results in altered growth responses to vascular endothelial growth factor-C (VEGF-C)

Growth and remodeling of lymphatic vasculature occur during development and during various pathologic states. A major stimulus for this process is the unique lymphatic vascular endothelial growth factor-C (VEGF-C). Other endothelial growth factors, such as fibroblast growth factor-2 (FGF-2) or VEGF-A, may also contribute. Heparan sulfate is a linear sulfated polysaccharide that facilitates binding and action of some vascular growth factors such as FGF-2 and VEGF-A. However, a direct role for heparan sulfate in lymphatic endothelial growth and sprouting responses, including those mediated by VEGF-C, remains to be examined. We demonstrate that VEGF-C binds to heparan sulfate purified from primary lymphatic endothelia, and activation of lymphatic endothelial Erk1/2 in response to VEGF-C is reduced by interference with heparin or pretreatment of cells with heparinase, which destroys heparan sulfate. Such treatment also inhibited phosphorylation of the major VEGF-C receptor VEGFR-3 upon VEGF-C stimulation. Silencing lymphatic heparan sulfate chain biosynthesis inhibited VEGF-C-mediated Erk1/2 activation and abrogated VEGFR-3 receptor-dependent binding of VEGF-C to the lymphatic endothelial surface. These findings prompted targeting of lymphatic N-deacetylase/N-sulfotransferase-1 (Ndst1), a major sulfate-modifying heparan sulfate biosynthetic enzyme. VEGF-C-mediated Erk1/2 phosphorylation was inhibited in Ndst1-silenced lymphatic endothelia, and scratch-assay responses to VEGF-C and FGF-2 were reduced in Ndst1-deficient cells. In addition, lymphatic Ndst1 deficiency abrogated cell-based growth and proliferation responses to VEGF-C. In other studies, lymphatic endothelia cultured ex vivo from Ndst1 gene-targeted mice demonstrated reduced VEGF-C- and FGF-2-mediated sprouting in collagen matrix. Lymphatic heparan sulfate may represent a novel molecular target for therapeutic intervention.

Multiple mechanisms for exogenous heparin modulation of vascular endothelial growth factor activity

Heparin and heparin-like molecules are known to modulate the cellular responses to vascular endothelial growth factor-A (VEGF-A). In this study, we investigated the likely mechanisms for heparin's influence on the biological activity of VEGF-A. Previous studies have shown that exogenous heparin's effects on the biological activity of VEGF-A are many and varied, in part due to the endogenous cell-surface heparan sulfates. To circumvent this problem, we used mutant endothelial cells lacking cell-surface heparan sulfates. We showed that VEGF-induced cellular responses are dependent in part on the presence of the heparan sulfates, and that exogenous heparin significantly augments VEGF's cellular effects especially when endogenous heparan sulfates are absent. Exogenous heparin was also found to play a cross-bridging role between VEGF-A(165) and putative heparin-binding sites within its cognate receptor, VEGFR2 when they were examined in isolation. The cross-bridging appears to be more dependent on molecular weight than on a specific heparin structure. This was confirmed by surface plasmon resonance binding studies using sugar chips immobilized with defined oligosaccharide structures, which showed that VEGF-A(165) binds to a relatively broad range of sulfated glycosaminoglycan structures. Finally, studies of the far-UV circular dichroism spectra of VEGF-A(165) showed that heparin can also modulate the conformation and secondary structure of the protein.