Structural features in heparin which modulate specific biological activities mediated by basic fibroblast growth factor

Exploring single-molecule interactions: heparin and FGF-1 proteins through solid-state nanopores

Detection and characterization of protein-protein interactions are essential for many cellular processes, such as cell growth, tissue repair, drug delivery, and other physiological functions. In our research, we have utilized emerging solid-state nanopore sensing technology, which is highly sensitive to better understand heparin and fibroblast growth factor 1 (FGF-1) protein interactions at a single-molecule level without any modifications. Understanding the structure and behavior of heparin-FGF-1 complexes at the single-molecule level is very important. An abnormality in their formation can lead to life-threatening conditions like tumor growth, fibrosis, and neurological disorders. Using a controlled dielectric breakdown pore fabrication approach, we have characterized individual heparin and FGF-1 (one of the 22 known FGFs in humans) proteins through the fabrication of 17 ± 1 nm nanopores. Compared to heparin, the positively charged heparin-binding domains of some FGF-1 proteins translocationally react with the pore walls, giving rise to a distinguishable second peak with higher current blockade. Additionally, we have confirmed that the dynamic FGF-1 is stabilized upon binding with heparin-FGF-1 at the single-molecule level. The larger current blockades from the complexes relative to individual heparin and the FGF-1 recorded during the translocation ensure the binding of heparin-FGF-1 proteins, forming binding complexes with higher excluded volumes. Taken together, we demonstrate that solid-state nanopores can be employed to investigate the properties of individual proteins and their complex interactions, potentially paving the way for innovative medical therapies and advancements.

Glycobiology in osteoclast differentiation and function

Glycans, either alone or in complex with glycan-binding proteins, are essential structures that can regulate cell biology by mediating protein stability or receptor dimerization under physiological and pathological conditions. Certain glycans are ligands for lectins, which are carbohydrate-specific receptors. Bone is a complex tissue that provides mechanical support for muscles and joints, and the regulation of bone mass in mammals is governed by complex interplay between bone-forming cells, called osteoblasts, and bone-resorbing cells, called osteoclasts. Bone erosion occurs when bone resorption notably exceeds bone formation. Osteoclasts may be activated during cancer, leading to a range of symptoms, including bone pain, fracture, and spinal cord compression. Our understanding of the role of protein glycosylation in cells and tissues involved in osteoclastogenesis suggests that glycosylation-based treatments can be used in the management of diseases. The aims of this review are to clarify the process of bone resorption and investigate the signaling pathways mediated by glycosylation and their roles in osteoclast biology. Moreover, we aim to outline how the lessons learned about these approaches are paving the way for future glycobiology-focused therapeutics.

Recent Progress on Heparin–Protamine Particles for Biomedical Application

Biomolecules are attractive building blocks with self-assembly ability, structural diversity, and excellent functionality for creating artificial materials. Heparin and protamine, a clinically relevant pair of biomolecules used in cardiac and vascular surgery, have been shown to coassemble into particulate polyelectrolyte complexes in vitro. The resulting heparin–protamine particles exhibit adhesive properties that enable advantageous interactions with proteins, cells, and various other substances and have been employed as functional materials for biomedical applications. In this review article, we summarize recent progress in research on the use of heparin–protamine particles as drug carriers, cell adhesives, and cell labels. Studies have demonstrated that heparin–protamine particles are potentially versatile in biomedical fields from drug delivery and regenerative medicine to plastic surgery.

Smart and Biomimetic 3D and 4D Printed Composite Hydrogels: Opportunities for Different Biomedical Applications

In recent years, smart/stimuli-responsive hydrogels have drawn tremendous attention for their varied applications, mainly in the biomedical field. These hydrogels are derived from different natural and synthetic polymers but are also composite with various organic and nano-organic fillers. The basic functions of smart hydrogels rely on their ability to change behavior; functions include mechanical, swelling, shaping, hydrophilicity, and bioactivity in response to external stimuli such as temperature, pH, magnetic field, electromagnetic radiation, and biological molecules. Depending on the final applications, smart hydrogels can be processed in different geometries and modalities to meet the complicated situations in biological media, namely, injectable hydrogels (following the sol-gel transition), colloidal nano and microgels, and three dimensional (3D) printed gel constructs. In recent decades smart hydrogels have opened a new horizon for scientists to fabricate biomimetic customized biomaterials for tissue engineering, cancer therapy, wound dressing, soft robotic actuators, and controlled release of bioactive substances/drugs. Remarkably, 4D bioprinting, a newly emerged technology/concept, aims to rationally design 3D patterned biological matrices from synthesized hydrogel-based inks with the ability to change structure under stimuli. This technology has enlarged the applicability of engineered smart hydrogels and hydrogel composites in biomedical fields. This paper aims to review stimuli-responsive hydrogels according to the kinds of external changes and t recent applications in biomedical and 4D bioprinting.

Heparan Sulfate Proteoglycans: Key Mediators of Stem Cell Function

Heparan sulfate proteoglycans (HSPGs) are an evolutionarily ancient subclass of glycoproteins with exquisite structural complexity. They are ubiquitously expressed across tissues and have been found to exert a multitude of effects on cell behavior and the surrounding microenvironment. Evidence has shown that heterogeneity in HSPG composition is crucial to its functions as an essential scaffolding component in the extracellular matrix as well as a vital cell surface signaling co-receptor. Here, we provide an overview of the significance of HSPGs as essential regulators of stem cell function. We discuss the various roles of HSPGs in distinct stem cell types during key physiological events, from development through to tissue homeostasis and regeneration. The contribution of aberrant HSPG production to altered stem cell properties and dysregulated cellular homeostasis characteristic of cancer is also reviewed. Finally, we consider approaches to better understand and exploit the multifaceted functions of HSPGs in influencing stem cell characteristics for cell therapy and associated culture expansion strategies.

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.

Fibroblast Growth Factor 2 Protein Stability Provides Decreased Dependence on Heparin for Induction of FGFR Signaling and Alters ERK Signaling Dynamics

Fibroblast growth factor 2 (FGF2) plays important roles in tissue development and repair. Using heparan sulfates (HS)/heparin as a cofactor, FGF2 binds to FGF receptor (FGFR) and induces downstream signaling pathways, such as ERK pathway, that regulate cellular behavior. In most cell lines, FGF2 signaling displays biphasic dose-response profile, reaching maximal response to intermediate concentrations, but weak response to high levels of FGF2. Recent reports demonstrated that the biphasic cellular response results from competition between binding of FGF2 to HS and FGFR that impinge upon ERK signaling dynamics. However, the role of HS/heparin in FGF signaling has been controversial. Several studies suggested that heparin is not required for FGF-FGFR complex formation and that the main role of heparin is to protect FGF from degradation. In this study, we investigated the relationship between FGF2 stability, heparin dependence and ERK signaling dynamics using FGF2 variants with increased thermal stability (FGF2-STABs). FGF2-STABs showed higher efficiency in induction of FGFR-mediated proliferation, lower affinity to heparin and were less dependent on heparin than wild-type FGF2 (FGF2-wt) for induction of FGFR-mediated mitogenic response. Interestingly, in primary mammary fibroblasts, FGF2-wt displayed a sigmoidal dose-response profile, while FGF2-STABs showed a biphasic response. Moreover, at low concentrations, FGF2-STABs induced ERK signaling more potently and displayed a faster dynamics of full ERK activation and higher amplitudes of ERK signaling than FGF2-wt. Our results suggest that FGF2 stability and heparin dependence are important factors in FGF-FGFR signaling complex assembly and ERK signaling dynamics.

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.

Biological Effects of Heparan Sulfates and Regioselectively Modified Heparin-Heparan Mimetics

The heparan sulfates (HS) are structurally the most complex but information rich biopolymers known. They are composed of polysaccharides containing regioselectively distributed carboxyl, sulfate ester, acetyl, amino, and N-sulfonyl groups with sequence- and domain-like arrangements. HS are found ubiquitously on cell surfaces and in extracellular matrices where they are covalently anchored via restricted protein cores. They modulate numerous development cell processes and the pathology of living organisms. HS concentration is extremely low on endothelial cell surfaces (1 pmol/cm2), therefore, they are difficult to isolate and evaluate. Furthermore, their sequence variability is extremely high and the sequence analysis is in its infancy. HS acts as a low affinity receptor which plays a central role in the reception and modulation of a wide range of effector proteins such as growth factors, morphogens, chemokines, enzymes, protease inhibitors.

Water soluble fragments of HS and heparin (HE) enzymatically released or synthetic sequences, analogs of heparinoids and heparanoids (HH) mimetics regioselectively modified oligo- and polysaccharides with HE/HS like functional groups, and nonsaccharide containing structures can modulate effector proteins and influence some of the development and pathological processes. Modulation effects are described for anticoagulant antiproliferative properties, for reducing platelet and plasma protein adhesion as well as inhibition or activating growth factors by the influence of HH mimetics. The advantage of defined high molecular weight substrates are discussed and compared to the low molecular weight mimetics. The potential of HH mimetics opens new approaches and strategies for therapeutic treatment.

Glycoarray Technologies: Deciphering Interactions from Proteins to Live Cell Responses

Microarray technologies inspired the development of carbohydrate arrays. Initially, carbohydrate array technology was hindered by the complex structures of glycans and their structural variability. The first designs of glycoarrays focused on the HTP (high throughput) study of protein-glycan binding events, and subsequently more in-depth kinetic analysis of carbohydrate-protein interactions. However, the applications have rapidly expanded and now achieve successful discrimination of selective interactions between carbohydrates and, not only proteins, but also viruses, bacteria and eukaryotic cells, and most recently even live cell responses to immobilized glycans. Combining array technology with other HTP technologies such as mass spectrometry is expected to allow even more accurate and sensitive analysis. This review provides a broad overview of established glycoarray technologies (with a special focus on glycosaminoglycan applications) and their emerging applications to the study of complex interactions between glycans and whole living cells.

Incorporation of heparin into biomaterials

This review provides an overview of the incorporation of heparin into biomaterials with a focus on drug delivery and the use of heparin-based biomaterials for self-assembly of polymer networks. Heparin conjugation to biomaterials was originally explored to reduce the thrombogenicity of materials in contact with blood. Many of the conjugation strategies that were developed for these applications are still popular today for other applications. More recently heparin has been conjugated to biomaterials for drug delivery applications. Many of the delivery approaches have taken advantage of the ability of heparin to bind to a wide variety of growth factors, protecting them from degradation and potentiating interactions with cell surface receptors. More recently, the use of heparin as a base polymer for scaffold fabrication has also been explored, often utilizing non-covalent binding of heparin with peptides or proteins to promote self-assembly of hydrogel networks. This review will highlight recent advances in each of these areas.

Diamond squid (Thysanoteuthis rhombus)-derived chondroitin sulfate stimulates bone healing within a rat calvarial defect

Chondroitin sulfate (CS) has been suggested to be involved in bone formation and mineralization processes. A previous study showed that squid-derived CS (sqCS) has osteoblastogenesis ability in cooperation with bone morphogenetic protein (BMP)-4 in vitro. However, in vivo, osteogenic potential has not been verified. In this study, we created a critical-sized bone defect in the rat calvaria and implanted sqCS-loaded gelatin hydrogel sponges (Gel) into the defect with or without BMP-4 (CS/BMP/Gel and CS/Gel, respectively). At 15 weeks, bone repair rate of CS/Gel-treated defects and CS/BMP/Gel-treated defects were 47.2% and 51.1%, respectively, whereas empty defects and defects with untreated sponges showed significantly less bone ingrowth. The intensity of von Kossa staining of the regenerated bone was less than that of the original one. Mineral apposition rates at 9 to 10 weeks were not significantly different between all treatment groups. Although bone repair was not completed, sqCS stimulated bone regeneration without BMP-4 and without external mesenchymal cells or preosteoblasts. Therefore, sqCS is a promising substance for promotion of osteogenesis.

FGF-FGFR signaling mediated through glycosaminoglycans in microtiter plate and cell-based microarray platforms

Fibroblast growth factor (FGF) signals cell growth through its interaction with a fibroblast growth factor receptor (FGFR) and a glycosaminoglycn (GAG) coreceptor. Here, we examine the signaling of five different FGFs (1, 2, 6, 8, and 8b) through FGFR3c. A small library of GAG and GAG-derivative coreceptors are screened to understand better the structure-activity relationship of these coreceptors on signaling. Initially, data were collected in a microtiter plate well-based cell proliferation assay. In an effort to reduce reagent requirements and improve assay throughput, a cell-based microarray platform was developed. In this cell-based microarray, FGFR3c-expressing cells were printed in alginate hydrogel droplets of ∼30 nL and incubated with FGF and GAG. Heparin was the most effective GAG coreceptor for all FGFs studied. Other GAGs, such as 2-O-desulfated heparin and chondroitin sulfate B, were also effective coreceptors. Signaling by FGF 8 and FGF 8b showed the widest tolerance for coreceptor structure. Finally, this on-chip cell-based microarray provides comparable data to a microtiter plate well-based assay, demonstrating that the coreceptor assay can be converted into a high-throughput assay.

Convergent stereoselective synthesis of multiple sulfated GlcNα(1,4)GlcAβ(1,4) dodecasaccharides

In this paper, we describe an effective method for the elongation of a GlcNα(1,4)GlcAβ(1,4) sequence using a GlcNTrocα(1,4)GlcA disaccharide unit and the synthesis of the N- and/or O-sulfated GlcNα(1,4)GlcAβ(1,4) oligosaccharides. N-Troc protection of GlcNα(1,4)GlcA units was effective for the synthesis of the GlcNα(1,4)GlcAβ(1,4) oligosaccharides in comparison with the azido substituent. The GlcNα(1,4)GlcAβ(1,4) dodecasaccharide was successfully prepared by the direct β-selective glycosidation of glucuronate in the GlcNα(1,4)GlcAβ(1,4)GlcNα(1,4)GlcAβ(1,4) tetrasaccharide. In addition, the synthesis of the N- and/or O-sulfated GlcNα(1,4)GlcAβ(1,4) oligosaccharides was accomplished by fluorous-assisted deprotection and sulfation. The fluorous-assisted synthetic technology applied to the highly polar sulfated oligosaccharide permits it to be more easily separated from the highly polar reagents, such as SO(3)·NEt(3).

In vivo bioactivity of rhBMP-2 delivered with novel polyelectrolyte complexation shells assembled on an alginate microbead core template

Electrostatic interactions between polycations and polyanions are being explored to fabricate polyelectrolyte complexes (PEC) that could entrap and regulate the release of a wide range of biomolecules. Here, we report the in vivo application of PEC shells fabricated from three different polycations: poly-l-ornithine (PLO), poly-l-arginine (PLA) and DEAE-dextran (DEAE-D) to condense heparin on the surface of alginate microbeads and further control the delivery of recombinant human bone morphogenetic protein 2 (rhBMP-2) in spinal fusion application. We observed large differences in the behavior of PEC shells fabricated from the cationic polyamino acids (PLO and PLA) when compared to the cationic polysaccharide, DEAE-D. Whereas DEAE-D-based PEC shells eroded and released rhBMP-2 over 2 days in vitro, PLO- and PLA-based shells retained at least 60% of loaded rhBMP-2 after 3 weeks of incubation in phosphate-buffered saline. In vivo implantation in a rat model of posterolateral spinal fusion revealed robust bone formation in the PLO- and PLA-based PEC shell groups. This resulted in a significantly enhanced mechanical stability of the fused segments. However, bone induction and biomechanical stability of spine segments implanted with DEAE-D-based carriers were significantly inferior to both PLO- and PLA-based PEC shell groups (p<0.01). From these results, we conclude that PEC shells incorporating native heparin could be used for growth factor delivery in functional bone tissue engineering application and that PLA- and PLO-based complexes could represent superior options to DEAE-D for loading and in vivo delivery of bioactive BMP-2 in this approach.

The tissue engineering of articular cartilage: cells, scaffolds and stimulating factors

Damage or loss of articular cartilage as a consequence of congenital anomaly, degenerative joint disease or injury leads to progressive debilitation, which has a negative impact on the quality of life of affected individuals in all age groups. Classical surgical techniques for hyaline cartilage reparation are frequently insufficient and in many cases it is not possible to obtain the expected results. For this reason, researchers and surgeons are forced to find a method to induce complete cartilage repair. Recently, the advent of tissue engineering has provided alternative possibilities for the treatment of these patients by application of cell-based therapy (e.g. chondrocytes and adult stem cells) combined with synthetic substitutes of the extracellular matrix and bioactive factors to prepare functional replacement of hyaline cartilage. This communication is aimed at a brief review of the current status of cartilage tissue engineering and recent advances in the field.

Synergism between Wnt3a and heparin enhances osteogenesis via a phosphoinositide 3-kinase/Akt/RUNX2 pathway

A new strategy has emerged to improve healing of bone defects using exogenous glycosaminoglycans by increasing the effectiveness of bone-anabolic growth factors. Wnt ligands play an important role in bone formation. However, their functional interactions with heparan sulfate/heparin have only been investigated in non-osseous tissues. Our study now shows that the osteogenic activity of Wnt3a is cooperatively stimulated through physical interactions with exogenous heparin. N-Sulfation and to a lesser extent O-sulfation of heparin contribute to the physical binding and optimal co-stimulation of Wnt3a. Wnt3a-heparin signaling synergistically increases osteoblast differentiation with minimal effects on cell proliferation. Thus, heparin selectively reduces the effective dose of Wnt3a needed to elicit osteogenic, but not mitogenic responses. Mechanistically, Wnt3a-heparin signaling strongly activates the phosphoinositide 3-kinase/Akt pathway and requires the bone-related transcription factor RUNX2 to stimulate alkaline phosphatase activity, which parallels canonical beta-catenin signaling. Collectively, our findings establish the osteo-inductive potential of a heparin-mediated Wnt3a-phosphoinositide 3-kinase/Akt-RUNX2 signaling network and suggest that heparan sulfate supplementation may selectively reduce the therapeutic doses of peptide factors required to promote bone formation.

Specific inhibition of FGF-2 signaling with 2-O-sulfated octasaccharides of heparan sulfate

In fibroblast growth factor (FGF)-2 signaling, the formation of a ternary complex of FGF-2, tyrosine-kinase fibroblast growth factor receptor (FGFR)-1, and cell surface heparan sulfate (HS) proteoglycan is known to be critical for the activation of FGFR-1 and downstream signal transduction. Exogenous heparin polymer and some octasaccharides inhibited FGF-2-induced phosphorylation both of FGFR-1 and of extracellular signal-regulated kinase (ERK1/2) in Chinese hamster ovary (CHO)-K1 cells transfected with FGFR-1, which present HS on their cell surface. The inhibitory effect of octasaccharide was dependent on the number of 2-O-sulfate groups within a molecule but independent of the number of 6-O-sulfate groups. Sulfation at the 2-O-position was a prerequisite not only for the binding of HS to FGF-2 but also for regulation of FGF-2 signaling and competitive inhibition with endogenous HS. Interestingly, FGF-4-induced phosphorylation was impeded only by specific octasaccharides containing both 2-O- and 6-O-sulfated groups, which were necessary for binding FGF-4. In CHO-677 cells deficient in HS biosynthesis, heparin enhanced FGF-2-induced phosphorylation of ERK1/2. On the other hand, an FGF-2-binding octasaccharide inhibited the phosphorylation. Our data suggest that the activity of particular heparin-binding factors can be inhibited by distinctive oligosaccharides that can bind the factors but cannot form functional signaling complexes irrespective of whether cells have a normal complement of HS or lack HS.

Interactions of hepatocyte growth factor/scatter factor with various glycosaminoglycans reveal an important interplay between the presence of iduronate and sulfate density

Hepatocyte growth factor/scatter factor (HGF/SF) has a cofactor requirement for heparan sulfate (HS) and dermatan sulfate (DS) in the optimal activation of its signaling receptor MET. However, these two glycosaminoglycans (GAGs) have different sugar backbones and sulfation patterns, with only the presence of iduronate in common. The structural basis for GAG recognition and activation is thus very unclear. We have clarified this by testing a wide array of natural and modified GAGs for both protein binding and activation. Comparisons between Ascidia nigra (2,6-O-sulfated) and mammalian (mainly 4-O-sulfated) DS species, as well as between a panel of specifically desulfated heparins, revealed that no specific sulfate isomer, in either GAG, is vital for interaction and activity. Moreover, different GAGs of similar sulfate density had comparable properties, although affinity and potency notably increase with increasing sulfate density. The weaker interaction with CS-E, compared with DS, shows that GlcA-containing polymers can bind, if highly sulfated, but emphasizes the importance of the flexible IdoA ring. Our data indicate that the preferred binding sites in DS in vivo will be comprised of disulfated, IdoA(2S)-containing motifs. In HS, clustering of N-/2-O-/6-O-sulfation in S-domains will lead to strong reactivity, although binding can also be mediated by the transition zones where sulfates are mainly at the N- and 6-O- positions. GAG recognition of HGF/SF thus appears to be primarily driven by electrostatic interactions and exhibits an interesting interplay between requirements for iduronate and sulfate density that may reflect in part a preference for particular sugar chain conformations.

Effects of growth factors on heparin-carrying polystyrene-coated atelocollagen scaffold for articular cartilage tissue engineering

The specific aim of our investigation is to study the potential use of a collagen/heparin-carrying polystyrene (HCPS) composite extracellular matrix for articular cartilage tissue engineering. Here, we created a high-performance extracellular matrix (HpECM) scaffold to build an optimal extracellular environment using an HCPS we originally developed, and an atelocollagen honeycomb-shaped-scaffold (ACHMS-scaffold) with a membrane seal. This scaffold was coated with HCPS to enable aggregation of heparin-binding growth factors such as FGF-2 and TGF-beta1 within the scaffold. Three-dimensional culture of rabbit articular chondrocytes within the HpECM-scaffold and subsequent preparation of a tissue-engineered cartilage were investigated. The results showed remarkably higher cell proliferative activity within the HpECM-pretreated-FGF-2 scaffold and the sustenance of phenotype within the HpECM-pretreated-TGF-beta1 scaffold. It was thought that both FGF-2 and TGF-beta1 were stably immobilized in the HpEMC-scaffold since HCPS generated an extracellular environment similar to that of heparan sulfate proteoglycan within the scaffold. These results suggest that an ACHMS-scaffold immobilized with HCPS can be a HpECM for cartilage regeneration to retain the heparin-binding growth factors within the scaffolds.

Acellular biological tissues containing inherent glycosaminoglycans for loading basic fibroblast growth factor promote angiogenesis and tissue regeneration

It was found in our previous study that acellular tissues derived from bovine pericardia consist primarily of insoluble collagen, elastin, and tightly bound glycosaminoglycans (GAGs). It is speculated that the inherent GAGs in acellular tissues may serve as a reservoir for loading basic fibroblast growth factor (bFGF) and promote angiogenesis and tissue regeneration. This study was therefore designed to investigate effects of the content of GAGs in acellular bovine pericardia on the binding of bFGF and its release profile in vitro while its stimulation in angiogenesis and tissue regeneration in vivo were evaluated subcutaneously in a rat model. To control the content of GAGs, acellular tissues were treated additionally with hyaluronidase for 1 (Hase-D1), 3 (Hase-D3), or 5 days (Hase-D5). The in vitro results indicated that a higher content of GAGs in the acellular tissue resulted in an increase in bFGF binding and in a more gradual and sustained release of the growth factor. The in vivo results obtained at 1 week postoperatively showed that the density and the depth of neo-vessels infiltrated into the acellular tissue loaded with bFGF (acellular/bFGF) were significantly greater than the other test samples. At 1 month postoperatively, vascularized neo-connective tissues were found to fill the pores within each test sample, particularly for the acellular/bFGF tissue. These results suggested that the sustained release of bFGF from the acellular/ bFGF tissue continued to be effective in enhancing angiogenesis and generation of new tissues. In conclusion, the inherent GAGs present in acellular tissues may be used for binding and sustained release of bFGF to enhance angiogenesis and tissue regeneration.

Heparin structures in FGF-2-dependent morphological transformation of astrocytes

Fibroblast growth factor-2 (FGF-2) participates in the morphological transformation of astrocytes (stellation) during the formation of glial scars in injured brains. In the current study, we used quantitative morphometric analysis to investigate the structural requirements for heparin's enhancement of FGF-2-induced stellation of cultured cortical astrocytes. Native heparin significantly promoted FGF-2-dependent astrocytic stellation, whereas heparin hexasaccharide inhibited FGF-2-dependent stellation. Furthermore, 2-O-, 6-O-, and N-desulfated heparins were unable to promote FGF-2-dependent stellation. The stellation induced by FGF-2 or by a combination of FGF-2 and native heparin was inhibited by SU5402, an FGF receptor inhibitor. These results demonstrate that the length and sulfated position of heparin are important for its enhancement of FGF-2-dependent astrocyte stellation. In addition, our findings show that heparin oligosaccharides are useful for regulating the FGF-2-dependent astrocytic transformation.

Structural determinants of heparan sulphate modulation of GDNF signalling

Glial cell line-derived neurotrophic factor (GDNF) has many functions including regulation of kidney morphogenesis and of neuron growth and survival in the enteric, sensory and central nervous systems. Reports of GDNF being used against Parkinson's disease in human patients have sparked intense clinical interest in GDNF signalling. We recently showed that GDNF signalling requires cell surface heparan sulphate glycosaminoglycans (Barnett et al., 2002, J. Cell Sci. 115, 4495-4503). Here we use exogenous modified heparins to determine those structural features required to inhibit GDNF signalling in ex vivo assays. 2-O-sulphate groups were found to impart high activity but were not absolute requirements for the inhibition of GDNF signalling. These findings may explain the similarities between the phenotypes of transgenic mice lacking GDNF and those lacking heparan sulphate 2-sulphotransferase, the enzyme responsible for achieving 2-O-sulphation of uronic acids in vivo.

Biosynthetic oligosaccharide libraries for identification of protein-binding heparan sulfate motifs. Exploring the structural diversity by screening for fibroblast growth factor (FGF)1 and FGF2 binding

Heparan sulfate is crucial for vital reactions in the body because of its ability to bind various proteins. The identification of protein-binding heparan sulfate sequences is essential to our understanding of heparan sulfate biology and raises the possibility to develop drugs against diseases such as cancer and inflammatory conditions. We present proof-of-principle that in vitro generated heparan sulfate oligosaccharide libraries can be used to explore interactions between heparan sulfate and proteins, and that the libraries expand the available heparan sulfate sequence space. Oligosaccharide libraries mimicking highly 6-O-sulfated domains of heparan sulfate were constructed by enzymatic O-sulfation of O-desulfated, end-group (3)H-labeled heparin octasaccharides. Acceptor oligosaccharides that were 6-O-desulfated but only partially 2-O-desulfated yielded oligosaccharide arrays with increased ratio of iduronyl 2-O-sulfate/glucosaminyl 6-O-sulfate. The products were probed by affinity chromatography on immobilized growth factors, fibroblast growth factor-1 (FGF1) and FGF2, followed by sequence analysis of trapped oligosaccharides. An N-sulfated octasaccharide, devoid of 2-O-sulfate but with three 6-O-sulfate groups, was unexpectedly found to bind FGF1 as well as FGF2 at physiological ionic strength. However, a single 2-O-sulfate group in the absence of 6-O-sulfation gave higher affinity for FGF2. FGF1 binding was also augmented by 2-O-sulfation, preferentially in combination with an adjacent upstream 6-O-sulfate group. These results demonstrate the potential of the enzymatically generated oligosaccharide libraries.

Fibroblast growth factor-2 binds to small heparin-derived oligosaccharides and stimulates a sustained phosphorylation of p42/44 mitogen-activated protein kinase and proliferation of rat mammary fibroblasts

We examine the relationship between the chain length of heparin-derived oligosaccharides, fibroblast growth factor (FGF)-2 binding kinetics and the ability of the oligosaccharides to allow FGF-2-induced proliferation of chlorate-treated rat mammary fibroblasts. First, using an optical biosensor, we show that FGF-2 did not bind disaccharides, but definitively bound to tetrasaccharides. As the chain length increased from tetrasaccharide to octasaccharide, there was a substantial increase in k(ass) (564000 M(-1) x s(-1) to 2000000 M(-1) x s(-1), respectively) and affinity (K(d) 77 nM to 11 nM, respectively) for FGF-2. From decasaccharides and longer, the k(ass) and affinity for FGF-2 was reduced substantially (tetradecasaccharide k(ass) 470000 M(-1) x s(-1), K(d) 30 nM). In chlorate-treated, and hence sulphated, glycosaminoglycan-deficient cells, FGF-2 alone or in the presence of disaccharides did not stimulate DNA synthesis and it only elicited an early transient dual phosphorylation of p42/44 mitogen-activated protein kinase (MAPK). In the same cells FGF-2 in the presence of tetrasaccharides and longer oligosaccharides was able to restore DNA synthesis and enable the sustained dual phosphorylation of p42/44(MAPK). However, the oligosaccharides from tetrasaccharides to octasaccharides were less potent in proliferation assays than deca- and longer oligosaccharides. Therefore, there was no correlation between the binding parameters and the potency of the oligosaccharides in DNA synthesis assays. These results demonstrate that tetrasaccharides are able to bind FGF-2 and enable FGF-2 to stimulate cell proliferation, which sets important boundary conditions for models of the FGF-2-heparan sulphate-FGF receptor complex.

Effect of heparin chain length on the interaction with tissue factor pathway inhibitor (TFPI)

Tissue factor pathway inhibitor (TFPI) is a heparin-binding protein involved in the extrinsic blood coagulation system. In order to elucidate the minimal size of heparin chain required for the interaction with TFPI, we prepared a series of heparin-derived oligosaccharides with tailored chain length ranged from disaccharide to eicosasaccharide after the successive treatments of heparin, including partial N-desulphation, deaminative cleavage with nitrous acid and gel-filtration. Affinity chromatography study of each oligosaccharide fraction using TFPI as the ligand indicated that increasing the degree of polymerisation causes increased affinity, and that a remarkable change in the affinity occurs between the decamers and dodecamers. Measurement of factor Xa inhibitory activity of TFPI in the presence of each oligosaccharide fraction indicated that the fractions shorter than dodecamers only slightly enhanced the TFPI activity for factor Xa inhibition, while the fractions larger than octadecamers had an effect comparable to full-length heparin. These were compatible to the results from the kinetic analyses of the interaction between TFPI and heparin-derived oligosaccharide with an evanescent wave-based biosensor system, IAsys, using a TFPI C-terminal peptide as the ligand.

Regulation of renal proximal tubular epithelial cell fibroblast growth factor-2 generation by heparin

Progression of renal disease is closely correlated to the degree of renal interstitial fibrosis, and evidence is increasing that epithelial cells of the renal proximal tubule (PTCs) may contribute to its pathogenesis. Such cytokines as basic fibroblast growth factor (FGF-2) have been implicated in progressive renal injury, and we previously showed that PTCs are a source of this cytokine. FGF-2 is characterized by its high affinity for heparin, and numerous studies have suggested that heparin may modify the progression of renal disease. The current study examined how heparin influenced FGF-2 generation and bioactivity in the human renal epithelial PTC line, HK-2. Incubation of HK-2 cells with heparin led to a dose- and time-dependent increase in FGF-2 concentration in the culture supernatant that was not accompanied by alterations in FGF-2 messenger RNA expression, assessed by reverse-transcriptase polymerase chain reaction and Northern analysis. The heparin-induced increase in FGF-2 concentration was accompanied by a decrease in the amount of FGF-2 bound to the extracellular matrix, although this accounted for only a small proportion of the total FGF-2 generated. Induction of FGF-2 by 2-O-desulfated heparin, together with a reduction in total cell-associated FGF-2 and anti-FGF-2 antibody binding to fixed permeabilized cells after the addition of heparin, suggested that the FGF-2 released was mainly derived from a preformed intracellular source. That FGF-2 was predominantly derived from an intracellular pool was also confirmed by pulse chase experiments. The addition of heparin resulted in the generation of bioinactive FGF-2, judged by in vitro fibroblast proliferation. Conversely, heparitinase treatment of supernatant samples from heparin-treated cells and the addition of 2-O-desulfated heparin resulted in the generation of active FGF-2, suggesting that the generation of bioinactive FGF-2 was related to binding of FGF-2 by extracellular heparin after its release from cells. These data show that heparin depletes both the cell and surrounding matrix of FGF-2 and suggest that FGF-2 released from cells was mainly derived from a preformed intracellular source. Furthermore, FGF-2 released from epithelial PTCs after the application of heparin was bioinactive. This likely resulted from released FGF-2 binding to an excess of extracellular heparin. Results presented here therefore suggest a mechanism by which heparin, through its effect on depletion of matrix and cells of FGF-2 and its generation in an inactive form, may influence progressive renal interstitial fibrosis.

Sequence analysis of heparan sulfate epitopes with graded affinities for fibroblast growth factors 1 and 2

Proteins that belong to the fibroblast growth factor (FGF) family regulate proliferation, migration, and differentiation of many cell types. Several FGFs, including the prototype factors FGF-1 and FGF-2, depend on interactions with heparan sulfate (HS) proteoglycans for activity. We have assessed tissue-derived HS fragments for binding to FGF-1 and FGF-2 to identify the authentic saccharide motifs required for interactions. Sequence information on a range of N-sulfated HS octasaccharides spanning from low to high affinity for FGF-1 was obtained. All octasaccharides with high affinity for FGF-1 (> or =0.5 m NaCl required for elution) contained an internal IdoUA(2-OSO(3))-GlcNSO(3)(6-OSO(3))-IdoUA(2-OSO(3))-trisaccharide motif. Octasaccharides with a higher overall degree of sulfation but lacking the specific trisaccharide motif showed lower affinity for FGF-1. FGF-2 was shown to bind to a mono-O-sulfated HS 6-mer carrying a single internal IdoUA(2-OSO(3))-unit. However, a di-O-sulfated -IdoUA(2-OSO(3))-GlcNSO(3)-IdoUA(2-OSO(3))-trisaccharide sequence within a HS 8-mer gave stronger binding. These findings show that not only the number but also the positions of individual sulfate groups determine affinity of HS for FGFs. Our findings support the notion that FGF-dependent processes can be modulated in vivo by regulated expression of distinct HS sequences.

The analysis of heparin-protein interactions using evanescent wave biosensor with regioselectively desulfated heparins as the ligands

Evanescent wave biosensor has been recently employed as a powerful tool for analyses of macromolecular interactions. In the present study, evanescent wave biosensor analysis was developed to analyze the heparin-protein interaction using as ligands a series of heparin derivatives regioselectively desulfated by chemical methods, particularly to evaluate the effect of each sulfate group of heparin. The method for immobilizing heparin on the cuvette of the evanescent wave biosensor equipment was optimized to obtain the high response required for accurate measurement. The best result was achieved when the amino group introduced at the reducing end of heparin was coupled with carboxymethyl dextran on the surface of the cuvette using glycolchitosan as a multivalent linker. The established system appeared to describe well the interactions of heparin with such proteins as acidic and basic fibroblast growth factors and tissue factor pathway inhibitor.

Binding and release of basic fibroblast growth factor from heparinized collagen matrices

Endothelial cell seeding is a promising method to improve the performance of small-diameter vascular grafts. Growth of endothelial cells seeded on the luminal surface of synthetic vascular grafts, coated with a matrix suitable for cell seeding (e.g. collagen), can be accelerated by local, sustained release of basic fibroblast growth factor (bFGF). In this study two potential matrices for in vivo endothelial cell seeding were studied with respect to bFGF binding and release: collagen crosslinked using N-(3-dimethylaminopropyl)-N'-ethylcarbodiimide (EDC) and N-hydroxysuccinimide (NHS), as well as heparinized EDC/NHS-crosslinked collagen. bFGF binding was determined after incubation of circular samples (10 mm diameter) with 0.25 ml bFGF solution for 90 min. Immobilization of increasing amounts of heparin, also using EDC and NHS, to crosslinked collagen containing 14 free primary amino groups per 1000 amino acid residues (E/N14C) resulted in binding of increasing amounts of bFGF. A plateau in bFGF binding was observed for heparinized E/N14C containing approximately 2.0-3.0 wt% of immobilized heparin which was obtained using a molar ratio of EDC to heparin-carboxylic acid groups of 0.4 during heparin immobilization (E/N14C-H(0.4)). At concentrations up to 840 ng bFGF/ml, 10% of the added bFGF bound to E/N14C, while binding of bFGF to E/N14C-H(0.4) amounted to 22%. Both E/N14C and E/N14C-H(0.4) pre-loaded with bFGF showed sustained bFGF release. A burst release of 30% in endothelial cell culture medium (CM) was observed for E/N14C during the first 6 h, compared to 2% release from E/N14C-H(0.4). After 28 days, the bFGF release from E/N14C and E/N14C-H(0.4) in CM amounted to 100 and 65%, respectively. Combined results of binding and release of bFGF indicate that compared to E/N14C, E/N14C-H(0.4) is the substrate of choice for bFGF pre-loading and subsequent endothelial cell seeding.

Heparin inhibits allergen-induced eosinophil infiltration into guinea-pig lung via a mechanism unrelated to its anticoagulant activity

There is considerable interest in the discovery of novel molecules for the treatment of allergic diseases and several recent studies have demonstrated that heparin can inhibit airway responses in subjects with asthma. However, heparin is also an anticoagulant which is potentially an unwanted effect in a molecule for treating asthma and allergic diseases. Recently, though, there have been a number of molecules described that are heparin-like but devoid of anticoagulant activity. The aim of this study was to evaluate whether the ability of heparin to inhibit allergen-induced eosinophil infiltration could be mimicked by analogues of heparin, some of which lack anticoagulant activity. We evaluated the effects of heparin and a number of modified heparins for their ability to inhibit allergen induced eosinophil infiltration into airways of suitably sensitised guinea-pigs assessed by bronchoalveolar lavage. Heparin and various modified heparins inhibited allergen-induced eosinophil infiltration into guinea-pig lung, including modified heparin preparations lacking anticoagulant activity. Our results suggest that heparin can inhibit eosinophil infiltration into lung tissue via a mechanism unrelated to its ability to act as an anticoagulant. Our results suggest that it may be possible to develop novel antiinflammatory agents for the treatment of asthma and allergic diseases related to the structure of heparin.

Preparation of completely 6-O-desulfated heparin and its ability to enhance activity of basic fibroblast growth factor

Although regioselective removal of 6-O-sulfate groups of heparin has been undertaken by several researchers, complete 6-O-desulfation with little side reaction has not been attained successfully. In this work, a modified method with a certain silylating reagent, N-methyl-N-(trimethylsilyl)trifluoroacetamide, has been established to produce completely 6-O-desulfated heparin with few other chemical changes. The degrees of 6-O-desulfation were estimated by means of chemical disaccharide analyses and/or (13)C NMR spectra. Although the completely 6-O-desulfated heparin lost about 20% of 2-O-sulfate groups, any other chemical changes and depolymerization were not detected. The completely 6-O-desulfated heparin displayed strong inhibition of COS-1 cell adhesion to basic fibroblast growth factor (bFGF)-coated well in a dose-dependent manner, as was clarified by the competitive cell-adhesion assay. Furthermore, the completely 6-O-desulfated heparin was shown to promote in vitro A31 fibroblast proliferation in a dose-dependent manner in the presence of bFGF. These results suggest that signal transduction through bFGF/bFGF receptor in A31 cells occurs in the absence of 6-O-sulfate groups in heparin. The involvement of 6-O-sulfate group(s) of heparin/heparan sulfate in the promotion of bFGF mitogenic activity was reported by several groups. This discrepancy between our results and those of other groups would be due to the differences in molecular size of heparin/heparan sulfate derivatives and/or cell species used for the assay.

Participation of syndecan 2 in the induction of stress fiber formation in cooperation with integrin alpha5beta1: structural characteristics of heparan sulfate chains with avidity to COOH-terminal heparin-binding domain of fibronectin

The present study provides direct evidence that syndecan 2 participates selectively in the induction of stress fiber formation in cooperation with integrin alpha5beta1 through specific binding of its heparan sulfate side chains to the fibronectin substrate. Our previous study with Lewis lung carcinoma-derived P29 cells demonstrated that the cell surface heparan sulfate proteoglycan, which binds to fibronectin, is syndecan 2 (N. Itano et al., 1996, Biochem. J. 315, 925-930). We here report that in vitro treatment of the cells by antisense oligonucleotide for syndecan 2 resulted in a failure to form stress fibers on fibronectin substrate in association with specific suppression of its cell surface expression. Instead, localization of actin filaments in the cytoplasmic cortex occurred. A similar response of the cells was observed when the cells were treated to eliminate functions of cell surface heparan sulfates, including exogenous addition of heparin and pretreatment with anti-heparan sulfate antibody, F58-10E4, and with proteinase-free heparitinase I. Size- and structure-defined oligosaccharides prepared from heparin and chemically modified heparins were utilized as competitive inhibitors to examine the structural characteristics of the cell surface heparan sulfates involved in organization of the actin cytoskeleton. Their affinity chromatography on a column linked with a recombinant H-271 peptide containing a C-terminal heparin-binding domain of fibronectin demonstrated that 2-O-sulfated iduronates were essential for the binding. Inhibition studies revealed that a heparin-derived dodecasaccharide sample enriched with an IdoA(2OS)-GlcNS(6OS) disaccharide completely blocked binding of the syndecan 2 ectodomain to immobilized H-271 peptide. Finally, the dodecasaccharide sample was shown to inhibit stress fiber formation, triggered by adhesion of P29 cells to a CH-271 polypeptide consisting of both the RGD cell-binding and the C-terminal heparin-binding domains of fibronectin in a fused form. All these results consistently suggest that syndecan 2 proteoglycan interacts with the C-terminal heparin-binding domain of fibronectin at the highly sulfated cluster(s), such as [IdoA(2OS)-GlcNS(6OS)](6) present in its heparan sulfate chains, to result in the induction of stress fiber formation in cooperation with integrin alpha5beta1.

Elucidation of the structural features of heparan sulfate important for interaction with the Hep-2 domain of fibronectin

The interaction of fibronectin with cell surface heparan sulfate proteoglycans is important biologically in inducing reorganization of the cytoskeleton and the assembly of focal adhesions. The major heparan sulfate-binding site in fibronectin, which is also implicated in these morphological events, is the COOH-terminal Hep-2 domain. We describe the first extensive study of the structural determinants required for the interaction between heparan sulfate/heparin and Hep-2. It is clear that, in heparan sulfate, there is a very prominent role for N-sulfate groups, as opposed to a relatively small apparent contribution from carboxyl groups. Furthermore, a minimal octasaccharide binding sequence appeared to contain at least two 2-O-sulfated iduronate residues, but no 6-O-sulfate groups. However, affinity was enhanced by the presence of 6-O-sulfates, and the interaction with Hep-2 also increased progressively with oligosaccharide size up to a maximum length of a tetradecasaccharide. This overall specificity is compatible with recent information on the structure of Hep-2 (Sharma, A., Askari, J. A., Humphries, M. J., Jones, E. Y., and Stuart, D. I. (1999) EMBO J. 18, 1468-1479) in which two separate, positively charged clusters, involving up to 11 basic amino acid residues (mostly arginines with their preferential ability to co-ordinate sulfate groups), could form a single extended binding site.

Improved endothelialization of vascular grafts by local release of growth factor from heparinized collagen matrices

Endothelial cell seeding, a promising method to improve the performance of small-diameter vascular grafts, requires a suitable substrate, e.g. crosslinked collagen. In addition, the growth of seeded endothelial cells can be improved by local release of a heparin-binding protein, basic fibroblast growth factor (bFGF). In this study, the influence of immobilization of heparin to collagen, crosslinked using N-(3-dimethylaminopropyl)-N'-ethylcarbodiimide (EDC) in combination with N-hydroxysuccinimide (NHS), on the binding and release of bFGF was determined. Heparin was immobilized also using EDC and NHS. Furthermore, the effects of the release of bFGF from (heparinized) EDC/NHS-crosslinked collagen on the proliferation of seeded endothelial cells was studied in vitro. Immobilization of increasing amounts of heparin to EDC/NHS-crosslinked collagen (containing 14 free epsilon-amino groups per 1000 amino acid residues, E/N14C) resulted in binding of increasing amounts of bFGF to the material. Maximal bFGF binding was observed for E/N14C containing 20-30 mg heparin immobilized per gram of collagen which was obtained using a molar ratio of EDC to heparin-carboxylic acid groups of 0.4 for heparin immobilization (E/N14C-H(0.4)). Up to concentrations of 320 ng bFGF/ml, 10% of the added bFGF bound to E/N14C, while binding of bFGF to E/N14C-H(0.4) was 22%. The initial release rate of bFGF bound to E/N14C was much higher compared to bFGF bound to E/N14C-H(0.4): respectively, 30 vs. 2% in the first 6 h. After 10 days, the bFGF release from E/N14C and E/N14C-H(0.4) amounted to 83 vs. 42%, respectively. Binding of increasing amounts of bFGF resulted in increased growth of human umbilical vein endothelial cells (HUVECs) seeded on both E/N14C and E/N14C-H(0.4). Nevertheless, after 6 and 10 days of proliferation cell numbers on E/N14C-H(0.4) where higher than cell numbers on E/N14C, irrespective of the bFGF concentration used for loading of the matrix. It is concluded that heparinized, EDC/NHS-crosslinked collagen is a good synthetic vascular graft coating for in vivo endothelial cell seeding.

Specificities of heparin-binding sites from the amino-terminus and type 1 repeats of thrombospondin-1

Interactions of heparin with intact human thrombospondin-1 (TSP1) and with two heparin-binding fragments of TSP1 were characterized using chemically modified heparins, a vascular heparan sulfate proteoglycan, and a series of heparin oligosaccharides prepared by partial deaminative cleavage. The avidity of TSP1 binding increased with oligosaccharide size, with plateaus at 4 to 6 and at 8 to 10 monosaccharide units. The dependence on oligosaccharide size for binding to the recombinant amino-terminal heparin-binding domain of TSP1 was the same as that of the intact TSP1 molecule but differed from that of a synthetic heparin-binding peptide from the type 1 repeats, suggesting that the interaction between intact TSP1 and heparin is primarily mediated by the amino-terminal domain. Based on activities of chemically modified heparins, binding to TSP1 depended primarily on 2-N- and 6-O-sulfation of glucosamine and to a lesser degree on 2,3-O-sulfation and the carboxyl residues of the uronic acids. In contrast, all of these modifications were required for binding of heparin to the type 1 repeat peptides. Affinity purification of heparin octasaccharides on immobilized TSP1 type 1 repeat peptides revealed a preference for oligosaccharides containing the disaccharide sequence IdoA(2-OSO(3))alpha1-4-GlcNS(6-OSO(3)). Binding of these oligosaccharides to the peptide required the Trp residues. These data demonstrate that the heparin-binding specificities of intact TSP1 and peptides from the type 1 repeats overlap with that of basic fibroblast growth factor (FGF2) and are consistent with the ability of these TSP1-derived molecules to inhibit FGF2-stimulated angiogenesis.

Effects of the binding of a dextran derivative on fibroblast growth factor 2: secondary structure and receptor-binding studies

CMDB (carboxymethyldextran-benzylamide) are dextrans statistically substituted with carboxymethyl and benzylamide groups which can mimick some of the biological properties of heparin. It has previously been shown that CMDB inhibit autocrine growth of breast tumor cells (Bagheri-Yarmand et al., Biochem. Biophys. Res. Commun. 239: 424-428, 1997) and selectively displace fibroblast growth factor 2 (FGF-2) from its receptor. Here, we used circular dichroism and fluorescence anisotropy measurements to show that the conformation of FGF-2 was significantly altered upon its binding to CMDB and to short CMDB fragments prepared within this study. CMDB and fragments formed a stable 1:1 complex with FGF-2, with affinities being estimated as 20+/-10 nM from fluorescence anisotropy analysis. No such a complex was formed with insulin-like growth factor (IGF-1) or epidermal growth factor (EGF). CMDB competed with the FGF-2 receptor for binding to FGF-2 but did not disturb the binding of IGF-1 and EGF to their receptors. Thus, our results highlight the selectivity of CMDB and their fragments towards FGF-2. Heparin, however, competes with CMDB and their fragments for binding to FGF-2. The carboxymethyl and benzylamide groups of these molecules likely interact directly with a heparin-binding region of FGF-2. The resulting change in conformation disturbs the binding of FGF-2 to its receptor and consecutively its mitogenic activity.

Monomer complexes of basic fibroblast growth factor and heparan sulfate oligosaccharides are the minimal functional unit for cell activation

The interaction of basic fibroblast growth factor (bFGF) with heparan sulfate (HS)/heparin has been shown to strongly enhance the activity of the growth factor although the mechanism of activation is unclear. We have addressed the issue of the minimal stoichiometry of an active HS oligosaccharide.bFGF complex by chemically cross-linking the two components to form novel covalent conjugates. The cross-linking procedure produced both monomeric and dimeric bFGF. oligosaccharide complexes, which were purified to homogeneity. Dimer conjugates were shown to have been formed as a result of disulfide bridging of monomer conjugates. These monomer conjugates were subsequently found to be biologically active in a mitogenesis assay. We therefore conclude that a monomeric bFGF.oligosaccharide complex is the minimal functional unit required for mitogenic stimulation.

Binding of interferon gamma by glycosaminoglycans: a strategy for localization and/or inhibition of its activity

Glycosaminoglycans (GAGs) are a group of negatively charged molecules present in many tissues as components of the extracellular matrix, basement and cellular membranes. This work analysed the ability of this group of substances to interact with human interferon gamma and the effect of those interactions on its biologic activity. A variety of GAGs (heparin, heparan sulfate, chondroitin sulfate and hyaluronic acid), and a related sulfated polysaccharide (dextran sulfate), were found to interact with IFN-gamma as determined by inhibition of the binding of [125I]IFN-gamma to COLO-205 cells and binding to wells coated with GAGs. These interactions were inhibited by synthetic peptides mimicking the sequences of the basic amino acid cluster located at the C-terminal end of mouse and human IFN-gamma, or by poly-L-lysine, suggesting that ionic interactions between the positively-charged C-terminus and negatively charged groups in GAGs were involved. IFN-gamma molecules bound to plate-immobilized or endothelial cell surface GAGs retained biological activity, since they could induce major histocompatibility complex (MHC) class II expression on COLO-205 cells, suggesting that cell surface GAGs might be able to present IFN-gamma to its receptors. These results suggest important regulatory roles for GAGs on the activity of IFN-gamma in vivo.

Functional analysis of conserved cysteines in heparan sulfate N-deacetylase-N-sulfotransferases

N-Deacetylase-N-sulfotransferases (NDANST) catalyze the two initial modifications of the polysaccharide precursor in the biosynthesis of heparin and heparan sulfate. These modifications are the gating steps in establishing growth factor protein-binding domains of these glycosaminoglycans. We have undertaken a structure-activity analysis of the 841-amino acid Golgi-luminal portion of the rat liver NDANST to localize the two enzymatic functions. Each activity can be assayed in vitro independently of the other when provided with the appropriate substrate, and N-ethylmaleimide treatment selectively inactivates the deacetylase activity. In this study, dithiothreitol treatment of the rat liver NDANST was shown to inactivate the sulfotransferase function, while stimulating deacetylase activity 2-3-fold over the native protein. Site-directed mutagenesis of the eight cysteine (Cys) residues in the rat liver NDANST that are conserved in the mouse mastocytoma protein produced three important findings regarding the localization of each enzymatic function: 1) derivatization of Cys486 with N-ethylmaleimide resulted in total inactivation of the deacetylase activity based on steric hindrance of the active site (this residue was shown not to be involved in enzymatic catalysis), 2) substitution of either Cys159 or Cys486 with alanine resulted in enhanced activity of the deacetylase to the level obtained by dithiothreitol treatment, and 3) alanine substitution of Cys818 or Cys828 completely inactivated the sulfotransferase activity, while substitution of Cys586 or Cys601 resulted in a 90% loss in activity. These findings suggest that the two enzymatic domains within the NDANST localize to different portions of the protein, with two disulfide pairs toward the COOH-terminal half of the protein necessary for the sulfotransferase activity, and Cys residues within the NH2-terminal half influencing or located near the active site of the deacetylase functionality.