The protective effect on Cu2+- and AAPH-mediated oxidation of human low-density lipoproteins depends on glycosaminoglycan structure

The effect of various glycosaminoglycans on Cu(2+)- and AAPH-induced oxidation of human low-density lipoprotein (LDL) was studied by monitoring conjugated diene formation. Heparin (Hep) increased the lag phase (t(lag)) of LDL oxidation, and fast moving and slow moving Hep species modified the kinetics of LDL oxidation to the same extent. Beef spleen heparan sulfate (HS) sample produced a significant increase of the t(lag) and a decrease of the conjugated diene formation of LDL whilst beef kidney HS species modified LDL oxidation kinetics to a lower extent. Dermatan sulfate (DS) from different sources caused a significant increase of the t(lag) and a decrease of the conjugated diene formation of LDL. Hyaluronic acid had no effect. Chondroitin sulfate (CS) from beef trachea produced a very strong protective antioxidant effect evaluated by increasing of the t(lag) and decreasing of the conjugated diene formation. Hep was completely ineffective in protecting LDL from 2, 2'-azobis(2-amidinopropane) hydrochloride (AAPH)-mediated oxidation, whilst DS was moderately effective. Beef trachea CS showed a very strong ability to protect LDL oxidation induced by 1 mM AAPH. The different protective effect on Cu(2+)- and AAPH-induced LDL oxidation by glycosaminoglycans is discussed considering their various structures and properties, and their capacity to interact to different extents with hydrophobic regions of LDL protein is confirmed by measuring the LDL-tryptophan fluorescence kinetics.

Inhibition of phosphodiesterase/pyrophosphatase activity of PC-1 by its association with glycosaminoglycans

PC-1 is a type II membrane-bound glycoprotein consisting of a short N-terminal cytoplasmic domain and a large C-terminal extracellular domain, which contains phosphodiesterase/pyrophosphatase activity. When Jurkat T cells were cultured with dibutyryl cAMP, the membrane-bound PC-1 and its soluble form were induced. They were purified as a homodimer of a 130 kDa peptide and a 120 kDa monomer, respectively, and the same two forms could also be obtained from COS-7 cells that had been transfected with PC-1 cDNA. The membrane-bound and soluble forms of PC-1 were indistinguishable from each other in terms of their enzyme kinetics and N-glycosylated moieties. Thus, the enzymatically active and fully glycosylated form of soluble PC-1 was utilized to search for its interacting molecules. The phosphodiesterase/pyrophosphatase activity of PC-1 was competitively inhibited by glycosaminoglycans, such as heparin and heparan sulfate, which are the major components of the extracellular matrix. PC-1 was capable of binding to heparin-Sepharose and the binding was inhibited in the presence of the enzyme substrate, ATP or its nonhydrolyzable analog. The enzyme activity of PC-1 itself, however, was not required for the binding to heparin-Sepharose. These results suggest that PC-1 might function as an adhesion molecule independent of its enzyme activity to associate with glycosaminoglycans in the extracellular matrix.

Heparan sulfate chains with antimitogenic properties arise from mesangial cell-surface proteoglycans

Heparan sulfate (HS) chains accumulate in both the medium and the cell layer of mesangial cell cultures. When given in fresh medium to quiescent cultures at naturally occurring concentrations, they suppress entry into the cell cycle and progression to DNA synthesis. We have attempted to identify the proteoglycan (PG) source of the antimitogenic HS chains from mesangial cell layers (HS(c)) and medium (HS(c)). When cells were labeled for 16 hours with [35S]sulfate, 25% of the label was found in intracellular HS chains and 5% in extracellular HSPGs. Cell-surface HSPGs accounted for the remaining 70% of the label associated with cell-layer HS and were released by either trypsin or 2% Triton X-100. About 20% of this cell-surface fraction was released by treatment with phosphatidylinositol-specific phospholipase C (PI-PLC), and probably represents glypican-like PG; glypican mRNA was present in the cells. The remainder of this fraction could be incorporated into liposomes, indicating the presence of hydrophobic transmembrane regions suggestive of syndecans. Upon purification and deglycosylation, an antiserum to rat liver HSPGs that reacts primarily with syndecan-2 showed a strong signal corresponding to this protein and three weaker bands that may represent additional syndecans. mRNAs for syndecan-1, -2, and -4 were present in the cultures. Syndecan-1 and -2 mRNAs were increased 30 minutes after stimulation of quiescent rat mesangial cells (RMCs) with serum. Heparin, HS(c), and HS(m) all prevented this increase. Syndecan-4 mRNA was not affected by serum, heparin, or HS. In pulse-chase experiments, the amount of 35S appearing in the cellular protein-free HS fraction was accounted for almost entirely by cell-surface PGs, as matrix-associated label was a minor contribution at the end of the pulse-labeling. The appearance of [35S]HS in cell extracts was unaffected by phospholipase C treatment, indicating that turnover of the newly labeled syndecan fraction is the source of the antimitogenic HS chains.

Long-term neuroprotective effects of glycosaminoglycans-IGF-I cotreatment in the motor neuron degeneration (mnd) mutant mouse

This study shows that cotreatment with insulin-like growth factor-I (IGF-I) and glycosaminoglycans (GAGs) prevents the onset of neuromuscular deficit in the m/m mutant mouse. These mice show a mid-to-late-life onset of progressive paralysis of the hind limb, that is correlated with altered innervation and reduced nerve-evoked isometric twitch tension in the extensor digitorum longus (EDL) muscle. Almost 50% of EDL nerve endings are negative for antisynaptophysin staining, while retrograde labelling with beta-cholera-toxin coupled to type IV horseradish and quantitative histological analysis show a small loss of EDL and lumbar cord motor neurons. At 10 months of age also forelimb function evaluated as grip strength is significantly reduced. Animals treated either with glycosaminoglycans alone or with IGF-I alone at low and high doses showed only a partial improvement of their condition. However, cotreatment of m/m mice with IGF-I and GAGs fully prevented the neuromuscular abnormalities, the twitch tension loss, the motor neuron decrease and the reduction of forelimb grip strength.

Comparison of heparin- and dermatan sulfate-mediated catalysis of thrombin inactivation by heparin cofactor II

Heparin and dermatan sulfate activate heparin cofactor II (HCII) comparably, presumably by liberating the amino terminus of HCII to bind to exosite I of thrombin. To explore this model of activation, we systematically substituted basic residues in the glycosaminoglycan-binding domain of HCII with neutral amino acids and measured the rates of thrombin inactivation by the mutants. Mutant D, with changes at Arg(184), Lys(185), Arg(189), Arg(192), Arg(193), demonstrated a approximately 130-fold increased rate of thrombin inactivation that was unaffected by the presence of glycosaminoglycans. The increased rate reflects displacement of the amino terminus of mutant D because (a) mutant D inactivates gamma-thrombin at a 65-fold slower rate than alpha-thrombin, (b) hirudin-(54-65) decreases the rate of thrombin inactivation, and (c) deletion of the amino terminus of mutant D reduces the rate of thrombin inactivation approximately 100-fold. We also examined the contribution of glycosaminoglycan-mediated bridging of thrombin to HCII to the inhibitory process. Whereas activation of HCII by heparin was chain-length dependent, stimulation by dermatan sulfate was not, suggesting that dermatan sulfate does not utilize a template mechanism to accelerate the inhibitory process. Fluorescence spectroscopy revealed that dermatan sulfate evokes greater conformational changes in HCII than heparin, suggesting that dermatan sulfate stimulates HCII by producing more effective displacement of the amino terminus.

Modulation of macrophage and B cell function by glycosaminoglycans

There is increasing evidence that the behavior of antigen-presenting cells may be regulated, in part, by the surrounding microenvironment. Components of the microenvironment of solid tissues that might influence antigen-presenting cell functions include glycosaminoglycans. We previously showed that heparan sulfate glycosaminoglycans activate macrophages, leading to profound alterations in T cell responses. Here we demonstrate the functional changes that occur in murine antigen-presenting cells induced by heparan sulfate and other glycosaminoglycans, and postulate how these functional changes influence the nature of local immune responses. Heparan sulfate triggered up-regulation of ICAM-1 and I-A, caused the release by antigen-presenting cells of interleukin (IL)-1, IL-6, tumor necrosis factor, IL-12, transforming growth factor beta, and prostaglandin E2 (PGE2), and (in macrophages) induced cytotoxic capability. Heparin induced IL-12 and interferon-gamma production but did not promote the release of other cytokines. Chondroitin sulfate and dermatan sulfate, although not stimulating the production of cytokines or of PGE2, elicited the production by macrophages of nitric oxide. These findings support a model in which the glycosaminoglycan composition of a given tissue, which may be altered by inflammatory processes, helps to regulate the behavior of antigen-presenting cells, which in turn determines the characteristics of the immune response that ensues.

Chromatin clearance in C57Bl/10 mice: interaction with heparan sulphate proteoglycans and receptors on Kupffer cells

Chromatin is an important autoantigen in the pathogenesis of systemic lupus erythematosus (SLE) as an immunogen and as a part of nephritogenic immune complexes. Earlier studies focused on clearance of DNA. However, DNA released into the circulation from dying cells is found associated with histones in nucleosomes. The liver is the major organ involved in clearance of chromatin from the circulation of mice. Heparan sulphate proteoglycans (HSPG) have been implicated in the clearance of various charged molecules. Receptor-mediated clearance of ssDNA by the liver has also been reported. Because chromatin contains positively charged histones in addition to DNA, we wished to determine if HSPG and/or DNA receptors are involved in chromatin clearance. The rate of clearance of H1-stripped chromatin from the bloodstream of C57Bl/10 mice was markedly decreased by prior treatment of mice with Heparinase I. Clearance was also inhibited by heparin, heparan sulphate, and DNA, but not by colominic acid. DNA was the most effective inhibitor of clearance and released chromatin from sites of clearance. Depletion of Kupffer cells and splenic macrophages using liposome-encapsulated Clodronate (dichloromethylene bisphosphonate) markedly inhibited chromatin clearance. These data suggest that chromatin clearance is mediated by charge interactions with cell surface HSPG and by DNA receptors. Clearance and degradation of chromatin require functional macrophages in the liver and spleen.

Endostatin binds to blood vessels in situ independent of heparan sulfate and does not compete for fibroblast growth factor-2 binding

Endostatin is a carboxyl-terminal proteolytic fragment of collagen XVIII and a potent inhibitor of angiogenesis. The mechanism of action is unknown, but the crystal structure of endostatin predicts a prominent heparan sulfate binding site, suggesting that endostatin competitively inhibits heparin-binding angiogenic factors, such as basic fibroblast growth factor (FGF-2). The goal of the study was to map endostatin binding sites in intact human tissues and to determine whether this binding is heparan sulfate dependent. In situ binding was performed with recombinant epitope-tagged murine endostatin. Endostatin predominantly binds to blood vessels of different calibers in a saturable fashion. In addition, binding to some epithelial basement membranes is seen. The localization pattern is similar to that reported for collagen XVIII, endostatin's parent molecule. In breast carcinomas, endostatin co-localizes largely with FGF-2. In a surprising contrast to FGF-2, endostatin binding is resistant to treatment with heparitinase, demonstrating that binding is not mediated by heparan sulfate proteoglycans. Furthermore, FGF-2 and heparin do not compete for endostatin binding, providing additional evidence for the discreteness of endostatin and FGF-binding sites.

Initiation of mammalian liver development from endoderm by fibroblast growth factors

The signaling molecules that elicit embryonic induction of the liver from the mammalian gut endoderm or induction of other gut-derived organs are unknown. Close proximity of cardiac mesoderm, which expresses fibroblast growth factors (FGFs) 1, 2, and 8, causes the foregut endoderm to develop into the liver. Treatment of isolated foregut endoderm from mouse embryos with FGF1 or FGF2, but not FGF8, was sufficient to replace cardiac mesoderm as an inducer of the liver gene expression program, the latter being the first step of hepatogenesis. The hepatogenic response was restricted to endoderm tissue, which selectively coexpresses FGF receptors 1 and 4. Further studies with FGFs and their specific inhibitors showed that FGF8 contributes to the morphogenetic outgrowth of the hepatic endoderm. Thus, different FGF signals appear to initiate distinct phases of liver development during mammalian organogenesis.

Heparan sulphates upregulate regeneration of transected sciatic nerves of adult guinea-pigs

The increased content of soluble glycosaminoglycan-containing forms in sciatic nerves during recovery from crush injury [Shum & Chau (1996) J. Neurosci. Res., 46, 465] suggests that the glycosaminoglycans modulate the environment for post-traumatic tissue remodelling and axonal regrowth. To test this, defined amounts of soluble heparan sulphates from bovine kidney or guinea-pig nerve were introduced into the regenerating environment via silicone conduits that bridged 8-mm gaps of transected sciatic nerves of adult guinea-pigs. Controls were bridged using the phosphate-buffered saline (PBS) vehicle or a chondroition sulphate preparation from whale cartilage. After timed periods of recovery, the animals were assessed for electromyographic signals at the target gastrocnemius muscle to determine the conduction velocity across the bridged nerve. Sections of the bridge were also histologically examined for nerve fibres. Transected sciatic nerves bridged with heparan sulphates or chondroitin sulphate showed earlier stimulated myelination of axons (week 5-6) than PBS-bridged nerves (week 9). Initial electromyographic indication of reconnection with the target was at week 9 post-transection. In the course of 20 weeks, transected sections of the bridge indicated similar numbers of unmyelinated axons irrespective of bridge material, but distinctly higher numbers of myelinated axons in heparan sulphate-bridged nerves than either PBS- or chondroitin sulphate-bridged nerves. At the end of the same period, heparan sulphate-bridged nerves resumed normal conduction velocities, but both PBS- and chondroitin sulphate-bridged nerves remained at 50% of that of the intact contralateral nerves. These results are the first to demonstrate that supplementation of soluble heparan sulphate to the fluid regenerative neural environment can restore functional, axonal reconnection of the severed nerve with the target muscle.

beta-amyloid activates the O-2 forming NADPH oxidase in microglia, monocytes, and neutrophils. A possible inflammatory mechanism of neuronal damage in Alzheimer's disease

The deposition of beta-amyloid in the brain is the key pathogenetic event in Alzheimer's disease. Among the various mechanisms proposed to explain the neurotoxicity of beta-amyloid deposits, a new one, recently identified in our and other laboratories, suggests that beta-amyloid is indirectly neurotoxic by activating microglia to produce toxic inflammatory mediators such as cytokines, nitric oxide, and oxygen free radicals. Three findings presented here support this mechanism, showing that beta-amyloid peptides (25-35), (1-39), and (1-42) activated the classical NADPH oxidase in rat primary culture of microglial cells and human phagocytes: 1) The exposure of the cells to beta-amyloid peptides stimulates the production of reactive oxygen intermediates; 2) the stimulation is associated with the assembly of the cytosolic components of NADPH oxidase on the plasma membrane, the process that corresponds to the activation of the enzyme; 3) neutrophils and monocytes of chronic granulomatous disease patients do not respond to beta-amyloid peptides with the stimulation of reactive oxygen intermediate production. Data are also presented that the activation of NADPH oxidase requires that beta-amyloid peptides be in fibrillary state, is inhibited by inhibitors of tyrosine kinases or phosphatidylinositol 3-kinase and by dibutyryl cyclic AMP, and is potentiated by interferon-gamma or tumor necrosis factor-alpha.

Regulation of basic fibroblast growth factor binding and activity by cell density and heparan sulfate

The role of cell density in modulating basic fibroblast growth factor binding and activity was investigated. A primary corneal stromal fibroblast cell culture system was used, since these cells do not constitutively express heparan sulfate proteoglycans in vivo except after injury. A 3-5-fold reduction in bFGF binding per cell was observed as cell density increased from 1000 to 35,000 cells/cm2. The cell density-dependent change in bFGF binding was not the result of altered FGFR expression as determined by equilibrium binding experiments and by immunoblot analysis. However, bFGF-cell surface receptor binding affinities were measured to be 10-20-fold higher at low cell densities than at intermediate and high cell density. bFGF-induced cell proliferation was also cell density-dependent, with maximal stimulation of proliferation 190-280% greater at intermediate densities (15,000 cells/cm2) than at other cell densities. This effect was specific to bFGF as serum, epidermal growth factor, and transforming growth factor-beta did not exhibit the same density-dependent profile. Further, heparan sulfate proteoglycans and, specifically, syndecan-4 were implicated as the modulator of bFGF binding and activity. Pretreatment of cell cultures with heparinase resulted in reduced bFGF binding to the cells and abrogated bFGF induced proliferation. These data suggest a mechanism by which cell density regulates heparan sulfate proteoglycan expression and modulates the cellular response to bFGF. Modulation of heparan sulfate proteoglycan expression might be an important aspect of the regulation of stromal cell migration and proliferation during wound healing.

Proteoglycan involvement in polyamine uptake

We have evaluated the possible role of proteoglycans in the uptake of spermine by human lung fibroblasts. Exogenous glycosaminoglycans behaved as competitive inhibitors of spermine uptake, the most efficient being heparan sulphate (Ki=0.16+/-0.04 microM). Treatment of fibroblasts with either heparan sulphate lyase, p-nitrophenyl-O-beta-D-xylopyranoside or chlorate reduced spermine uptake considerably, whereas chondroitin sulphate lyase had a limited effect. Inhibition of polyamine biosynthesis with alpha-difluoromethylornithine resulted in an increase of cell-associated heparan sulphate proteoglycans exhibiting higher affinity for spermine. The data indicate a specific role for heparan sulphate proteoglycans in the uptake of spermine by fibroblasts. Spermine uptake by pgsD-677, a mutant Chinese hamster ovary cell defective in heparan sulphate biosynthesis, was only moderately reduced (20%) compared with wild-type cells. Treatment of mutant cells with the above-mentioned xyloside resulted in a greater reduction of endogenous proteoglycan production as well as a higher inhibition of spermine uptake than in wild-type cells. Moreover, treatment with chondroitin sulphate lyase resulted in a selective inhibition of uptake in mutant cells, indicating a role for chondroitin/dermatan sulphate proteoglycans in the uptake of spermine by these cells. Fibroblasts, made growth-dependent on exogenous spermine by alpha-difluoromethylornithine treatment, were growth-inhibited by heparan sulphate or beta-D-xyloside, which might have future therapeutical implications.

Binding of interleukin-8 to heparan sulphate enhances cervical maturation in rabbits

Cervical ripening is a cytokine-triggered process with substantial remodelling of the cervical extracellular matrix. Interleukin-8 (IL-8) is an important cytokine in cervical maturation. Glycosaminoglycans are also included in this process, but their role in not clearly understood. The effects of heparan sulphate (HS), hyaluronic acid (HA), IL-8, HS + IL-8 and HA + IL-8 on biochemical properties of the cervix were examined in non-pregnant rabbits. The changes in vascular pattern with collagen structure of the cervices and immunohistochemical studies, together with the relative collagen concentrations, were determined. A reduction in relative collagen concentration was significant after HS + IL-8, IL-8 and HA + IL-8 treatment (all P < 0.0001). Gel electrophoresis analysis showed that IL-8 bound preferentially to HS than to HA. Neutrophils were significantly increased in number (P < 0.0001) and located predominantly beneath the glandular epithelium and around the blood vessels after HS + IL-8 treatment. HS + IL-8 treatment caused cervices to increase their water content and become oedematous. The collagen fibres were considerably dissociated, the interfibrillar spaces markedly dilated, and the blood vessels notably increased and dilated. We conclude that binding to HS enhances the activity of IL-8 in inducing cervical maturation.

Impact of various glycosaminoglycans upon cAMP-dependent protein kinase

The physiological effects of the second messenger cAMP are displayed by cAMP-dependent protein kinase-medicated phosphorylation of specific target proteins which in turn control diverse cellular functions. We have determined this enzyme substrate phosphorylation in the presence of various glycosaminoglycans using a cAMP-dependent protein kinase isolated from rat liver. The results indicate that sulfated and unsulfated polysaccharides are able to inhibit phosphorylation of histone type IIa catalysed by cAMP-dependent protein kinase. Based on their impact upon substrate phosphorylation, glycosaminoglycans can be divided into three groups: group I with the highest inhibitory effect: dermatan sulfate and heparan sulfate; group II: chondroitin 4-sulfate and group III with the lowest inhibitory effect: chondroitin 6-sulfate, keratan sulfate and hyaluronic acid.

Plasmodium falciparum: molecular background to strain-specific rosette disruption by glycosaminoglycans and sulfated glycoconjugates

Rosetting, the adhesion of Plasmodium falciparum-infected erythrocytes to uninfected erythrocytes, is a virulent parasite phenotype associated with the occurrence of severe malaria, e.g., cerebral malaria. Compounds with specific anti-rosetting activity are potential therapeutic agents. Glycosaminoglycans and sulfated glycoconjugates were found to disrupt rosettes in a strain- and isolate-specific manner. Rosette disruption was strongly connected to the presence of N-sulfate groups in heparin/heparan sulfate as demonstrated by modified heparin preparations. This finding was corroborated by the disruption of rosettes with mono- and disaccharides derived from heparin/heparan sulfate that contained N-sulfated glucosamine. Furthermore, heparinase III treatment of erythrocyte cultures infected by FCR3S1 (and to some extent TM 284) P. falciparum strains abolished rosetting. Heparinase III treatment of the uninfected erythrocytes prior to mixing with the infected culture impeded formation of rosettes, indicating that the rosetting receptors at least partially are of glycosaminoglycan nature.

Heparan sulphate and HB-GAM (heparin-binding growth-associated molecule) in the development of the thalamocortical pathway of rat brain

Extracellular matrix (ECM) molecules, such as laminin, tenascin, chondroitin sulphate proteoglycans and heparan sulphate proteoglycans have been suggested to have 'signpost' and directing roles in the formation of axonal projections in cortical development. We show here that the expression of the neurite outgrowth-promoting protein heparin-binding growth-associated molecule (HB-GAM) and N-syndecan, a transmembrane heparan sulphate proteoglycan previously isolated as a receptor for HB-GAM, is spatiotemporally associated with the developing thalamocortical pathway in the rat brain. Using in situ hybridization, thalamic neurons were shown to express mRNA for N-syndecan, and in vitro, thalamic neurons grew more neurites on HB-GAM than on laminin. The HB-GAM-induced neurite outgrowth in thalamic neurons was inhibited by heparitinase, heparin, soluble N-syndecan and by an excess of soluble HB-GAM in the culture medium. In a pathway assay, thalamic neurons selectively preferred attaching and growing neurites on matrices containing HB-GAM than on those containing fibronectin or laminin alone, suggesting that HB-GAM may modulate the effect of other ECM proteins. On an unfixed brain slice preparation, thalamic neurons repeatedly showed a typical neurite outgrowth and attachment pattern resembling the expression pattern of HB-GAM. On the brain slices, the neurite outgrowth was significantly inhibited by heparitinase, heparin and soluble HB-GAM, thus displaying features of neurite outgrowth on matrix-bound HB-GAM. Our results suggest that HB-GAM is important for the neurite outgrowth of thalamic neurons and it may function as an ECM-bound guidance cue for thalamic neurons that possess HB-GAM-binding heparan sulphates on their cell membrane.

The V3 region of gp120 is responsible for anti-HIV-1 activity of heparin sulphate

The effect of heparin sulphate on the infection of CD4+ lymphocytes by recombinant HIV-1 clones pIIIB and by pIIIB/V3-BaL was investigated. It was demonstrated that heparin sulphate decreased the infectivity of CD4+ lymphocytes by the pIIIB virus stronger than by the pIIIB/V3-BaL clone, and that the effect of heparin was concentration-dependent. This was accompanied by an inhibition of binding of the monoclonal antibodies 447-52-D to the V3 region and G45-60 to the C4 region of oligomeric glycoprotein 120 (gp120). It has been concluded that the inhibitory effect of heparin sulphate on the infection of CD4+ lymphocytes by recombinant HIV-1 clones is mediated mainly by the V3 region of gp120. However, the C4 region contributes to the inhibitory effect of heparin sulphate.

Heparan sulfate proteoglycans mediate interleukin-7-dependent B lymphopoiesis

Heparin/heparan sulfate proteoglycans (HSPGs) have the potential to bind and directly regulate the bioactivity of hematopoietic growth factors including interleukin-7 (IL-7), a cytokine critical for murine B-cell development. We examined the consequence of manipulating soluble heparin and cell-surface heparan sulfate to IL-7-dependent responses of B-cell precursors. Soluble heparin was found to inhibit production of lymphoid, but not myeloid, cells in long-term bone marrow cultures. Analysis of pro-B cells lacking plasma membrane HS suggests that this glycosaminoglycan is required for efficient binding and responsiveness to IL-7. By contrast, responses of hematopoietic cells to other cytokines were not influenced by heparin addition or HS removal. Therefore, HSPGs on B-lineage precursors may function as IL-7 receptor components similar to HSPGs known to be important for the bFGF receptor. Other experiments suggest that HSPGs on the surface of stromal cells provide a weakly associating docking site for IL-7, possibly controlling availability of this cytokine to B-cell precursors. Together these data demonstrate a direct role for heparinlike molecules in regulating the IL-7-dependent stages of murine B lymphopoiesis.

Structurally specific heparan sulfates support primitive human hematopoiesis by formation of a multimolecular stem cell niche

Stem cell localization, conservation, and differentiation is believed to occur in niches in the marrow stromal microenvironment. Our recent observation that long-term in vitro human hematopoiesis requires a stromal heparan sulfate proteoglycan (HSPG) led us to hypothesize that such HSPG may orchestrate the formation of the stem cell niche. We compared the structure and function of HS from M2-10B4, a hematopoiesis-supportive cell line, with HS from a nonsupportive cell line, FHS-173-We. Long-term culture-initiating cell (LTC-IC) maintenance was enhanced by PG from supportive cells but not by PG from nonsupportive cells (P <.005). The supportive HS were significantly larger and more highly sulfated than the nonsupportive HS. Specifically, supportive HS contained higher 6-O-sulfation on the glucosamine residues. In agreement with these observations, purified 6-O-sulfated heparin and highly 6-O-sulfated bovine kidney HS similarly maintained LTC-IC. In contrast, completely desulfated heparin, N-sulfated heparin, and unmodified heparin did not support LTC-IC maintenance. Moreover, the supportive HS promoted LTC-IC maintenance but not differentiation of CD34(+)/HLA-DR- cells into colony-forming cells (CFCs) and mature blood cells. The supportive HS but not the nonsupportive HS bound both cytokines and matrix components critical for hematopoiesis, including interleukin-3 (IL-3), macrophage inflammatory protein-1 (MIP-1), and thrombospondin (TSP). Significantly more CD34(+) cells adhered directly to immobilized O-sulfated heparin than to N-sulfated or desulfated heparin. Thus, hematopoiesis-supportive stromal HSPG possessing large, highly 6-O-sulfated HS mediate the juxtaposition of hematopoietic progenitors with stromal cells, specific growth-promoting (IL-3) and growth-inhibitory (MIP-1 and platelet factor 4 [PF4]) cytokines, and extracellular matrix (ECM) proteins such as TSP. We conclude that the structural specificity of stromal HSPG that determines the selective colocalization of cytokines and ECM components leads to the formation of discrete niches, thereby orchestrating the controlled growth and differentiation of stem cells. These findings may have important implications for ex vivo expansion of and gene transfer into primitive hematopoietic progenitors.

Identification of a signaling pathway activated specifically in the somatodendritic compartment by a heparan sulfate that regulates dendrite growth

In two earlier reports we demonstrated that natural heparan sulfate, but not dermatan or chondroitin sulfate glycosaminoglycans, stimulate axonal elongation and inhibit dendrite growth in vitro (Lafont et al., 1992). The latter specific effect on dendrite elongation was reproduced by chemically synthesized heparan sulfates and by SR 80037A, a purified sulfated and hexanoylated heparin fragment (Lafont et al., 1994). Adding radioactive SR 80037A to purified neurons demonstrated the existence, at the neuronal surface, of heparan sulfate-specific and saturable binding sites, suggesting that SR 80037A activates specific signal transduction pathways. In the present study, using rat or mouse neurons from the embryonic cortex, we show that SR 80037A signaling involves one or several G-coupled receptor or receptors, small GTPases rhoA and/or rhoC, and one or several PKCs. We also demonstrate that the rapid soma rounding elicited by SR 80037A does not require protein synthesis but that the long-term effect on dendrite initiation requires protein synthesis in a short period after the addition of the heparan sulfate. Finally, by preparing membranes from the somatodendritic or axonal compartments we demonstrate that the identified signaling pathway is activated by SR 80037A primarily in the somatodendritic compartment and is not sensitive to the addition of a dermatan sulfate glycosaminoglycan that does not induce the axonal phenotype by impairing dendrite initiation and elongation.

Heparan sulfate upregulates platelet-derived growth factor receptors on human lung fibroblasts

Heparan sulfate is a molecule that possesses a large structural variability and which has been shown to inhibit the proliferation of fibroblasts in vitro. The aim of this study was to determine whether the anti-proliferative effects of heparan sulfate were exerted by regulation of the activity of the platelet-derived growth factor and/or of the platelet-derived growth factor receptors. Both l-iduronate-rich, anti-proliferative and the l-iduronate-poor, non-anti-proliferative heparan sulfate species, were incubated with confluent human embryonic lung fibroblasts for 24 h. The mRNA levels for PDGF-AA, PDGF-BB, and their receptors were measured. Binding studies were performed with [125I]-PDGF-BB and [125I]-EGF for 2 h at 4 degreesC in cultures preincubated with both types of heparan sulfate for 24 h. In separate experiments, cultures were incubated together with heparan sulfate and [125I]-PDGF-BB for 2 h at 4 degreesC. Increases of two- to threefold in the mRNA levels for both the alpha- and the beta-receptors of PDGF was obtained after treatment with both types of heparan sulfate, whereas the mRNA levels of both the PDGF-AA and the PDGF-BB were essentially unaffected. A sixfold increase in binding was only noted for [125I]-PDGF-BB in cultures pre-treated with the anti-proliferative heparan sulfate for 24 h, whereas no effect was noted with use of the non-anti-proliferative heparan sulfate. Incubating the [125I]-PDGF-BB and the anti-proliferative heparan sulfate together for 2 h resulted in a smaller, threefold increase in binding. This indicates that the anti-proliferative heparan sulfate both stabilizes and increases expression of the PDGF receptors. To investigate whether the increased number of PDGF receptors could affect cell activity, cells were preincubated with anti-proliferative heparan sulfate and then treated with PDGF-BB. This resulted in an increase in mitogenicity compared to cells treated only with PDGF-BB. Neither an increase in binding for [125I-EGF] nor an increase in the mitogenic response of EGF could be observed in cultures pre-treated with the anti-proliferative heparan sulfate. The results indicate that the extracellular matrix itself may regulate important biological phenomena such as cell proliferation and matrix production through affecting the expression of receptors of PDGF, which initiate both stimulatory and inhibitory signals.

Cellular adhesion mediated by factor J, a complement inhibitor. Evidence for nucleolin involvement

Factor J (FJ) is a complement inhibitor that acts on the classical and the alternative pathways. We demonstrated FJ-cell interactions in fluid phase by flow cytometry experiments using the cell lines Jurkat, K562, JY, and peripheral blood lymphocytes. FJ bound to plastic plates was able to induce in vitro adhesion of these cells with potency equivalent to fibronectin. As evidence for the specificity of this reaction, the adhesion was blocked by MAJ2, an anti-FJ monoclonal antibody, and by soluble FJ. Attachment of the cells required active metabolism and cytoskeletal integrity. The glycosaminoglycans heparin, heparan sulfate, or chondroitin sulfates A, B, and C inhibited to varying degrees the binding of FJ to cells, as did treatment with chondroitinase ABC. In the search for a putative receptor, a protein of 110 kDa was isolated by affinity chromatography, and microsequence analysis identified this protein as nucleolin. Confocal microscopy evidenced the presence of nucleolin in cell membrane by immunofluorescence with monoclonal (D3) and polyclonal anti-nucleolin antibodies in Jurkat cells. The interaction FJ-nucleolin was evidenced by Western blot and enzyme-linked immunosorbent assay. Furthermore, purified nucleolin and D3 inhibited adhesion of Jurkat cells to immobilized FJ, suggesting that the interaction was specific and that nucleolin mediated the binding.

Sulfation-dependent down-regulation of interferon-gamma-induced major histocompatibility complex class I and II and intercellular adhesion molecule-1 expression on tubular and endothelial cells by glycosaminoglycans

BACKGROUND

Previously, it has been demonstrated that heparin inhibits major histocompatibility complex (MHC) class II and intercellular adhesion molecule-1 (ICAM-1) expression on interferon-gamma (IFN-gamma)-stimulated human umbilical vein endothelial cells (HUVECs). Inasmuch as proximal tubular epithelial cells (PTECs) are prime targets in acute renal allograft rejection, we investigated whether there is a difference in the ability of heparin to influence MHC and ICAM-1 expression on PTECs as compared to HUVECs. We also studied whether the degree of sulfation of heparin is of relevance for the binding to IFN-gamma and inhibition of MHC and ICAM-1 expression after IFN-gamma stimulation.

METHODS

Cultured HUVECs and PTECs were stimulated with IFN-gamma for 72 hr in the presence or absence of various heparinoids. MHC and ICAM-1 expression were thereafter determined by fluorescence-activated cell sorting.

RESULTS

Heparin was able to inhibit the up-regulation of MHC and ICAM-1 in a dose-dependent fashion on both IFN-gamma-stimulated HUVECs and PTECs. In PTEC cultures, higher concentrations of heparin were required for the inhibition of MHC class I. Heparin and supersulfated glycosaminoglycans (GAGs) were able to bind to IFN-gamma, whereas N-desulfated N-acetylated GAGs with a low amount of sulfate were not. Inhibition of cell-bound heparan sulfate proteoglycan sulfation with NaClO3 resulted in an impaired MHC and ICAM-1 expression after IFN-gamma stimulation.

CONCLUSION

We postulate that IFN-gamma binds to cell-bound heparan sulfate proteoglycan in a sulfation-dependent fashion. This binding may facilitate the interaction of IFN-gamma with its receptor. Supersulfated GAGs with low anti-coagulant activity could be used therapeutically to decrease MHC and ICAM-1 expression on organ grafts.

Focal delivery of fibroblast growth factor-1 by transfected cells induces spiral ganglion neurite targeting in vitro

Sensory cells in the cochlea of the rat transiently express acidic fibroblast growth factor (FGF-1) during the developmental period of terminal innervation in the sensory epithelium. To explore the potential role of FGF-1 in terminal innervation events, the response of cochlear ganglion neurons to FGF-1 was evaluated in culture. Explants from the spiral ganglion of postnatal day 5 rats were cultured in the presence of exogenous FGF-1, with or without heparin. FGF-1 in the culture medium produced a dose-dependent increase in the number and length of neurites produced by spiral ganglion neurons, a response that was enhanced by heparin. To assess the effects of FGF-1 produced by a focal, cellular source, additional explants were cocultured with 3T3 cell transfectants that secrete FGF-1. Neurites that came into contact with FGF-1 secreting cells branched, formed bouton-like terminal swellings on the surface of the transfectants, and stopped extending. The results suggest that FGF-1 may stimulate neurite extension into the sensory epithelium of the cochlea and that focal production of FGF-1 may contribute to the formation of contacts on sensory cells by developing neurites.