Structural analysis of chick-embryo cartilage proteoglycan by selective degradation with chondroitin lyases (chondroitinases) and endo-beta-D-galactosidase (keratanase)

Systemic administrations of protamine heal subacute spinal cord injury in mice

Spinal cord injury (SCI) results in damage to neural circuits that cause long-term locomotor and sensory disability. The objective of the present study is to evaluate whether a clinical drug, protamine, can be employed as a therapeutic agent for SCI. First, we examined the rescue effect of protamine on dystrophic endballs (DEs) cultured on a chondroitin sulfate (CS) gradient coating. Consequently, axons with DE, which are unable to grow through the CS barrier, resumed growth after protamine treatment and were able to pass through the barrier. In addition, we tested whether protamine resolves the DE phenotype, accumulation of autophagosomes. The results demonstrated that protamine has significantly reduced the density of LC3 in DEs. Subsequently, mice were administered 1 mg/kg protamine via the tail vein one week following a contusion injury to the thoracic spinal cord. The hindlimb movements of the mice were evaluated in order to assess the therapeutic effect of protamine. Eleven venous administrations of protamine improved the symptoms. The current study has demonstrated that protamine cancels the CS inhibitory effect on axonal regrowth. Administrations of protamine were observed to alleviate hindlimb motor dysfunction in SCI mice. Our results suggest an effective therapeutic agent for SCI and a possibility for drug repositioning. It would be of interest to see if protamine also exerts a therapeutic effect in brain injury.

Catabolism of Newly Synthesized Decorin in vitro by Human Peritoneal Mesothelial Cells

Objective

Previous studies have shown that decorin and biglycan account for over 70% of the proteoglycans (PGs) synthesized by human peritoneal mesothelial cells (HPMCs). Since these PGs are involved in the control of cell growth, cell differentiation, and matrix assembly, we investigated their turnover in cultured HPMCs.

Methods

Confluent HPMCs were metabolically labeled with [35S]-sulfate and the labeled products isolated from the cell medium and the cell layer characterized by sensitivity to bacterial eliminases. Experiments were undertaken with exogenous labeled decorin, and its metabolic state was studied.

Results

In a 24-hour labeling period, 75% of the newly synthesized chondroitin sulfate/dermatan sulfate (CS/DS) PGs appeared in the culture medium, the majority of which (90%) was decorin. In the cell layer, protein-free glycosaminoglycan (GAG) chains accounted for 21% of the total CS/DS at 24 hours and exhibited constant specific activity at 12 – 16 hours. The latter material was turned over with a half-life of approximately 2.5 hours. Exogenous decorin underwent receptor-mediated endocytosis and subsequent intracellular degradation. Uptake but not degradation could be inhibited by heparin.

Conclusions

HPMCs are distinguished by a rapid turnover of decorin. A characteristic metabolic feature is the existence of a large intracellular pool of protein-free DS-GAGs. Understanding the control of decorin turnover in HPMCs might lead to delineation of its potential role in both the physiology and pathophysiology of the membrane in PD patients.

Three-Dimensional Printed Polylactic Acid Scaffolds Promote Bone-like Matrix Deposition in Vitro

Large bone defects represent a significant challenge for clinicians and surgeons. Tissue engineering for bone regeneration represents an innovative solution for this dilemma and may yield attractive alternate bone substitutes. Three-dimensional (3D) printing with inexpensive desktop printers shows promise in generating high-resolution structures mimicking native tissues using biocompatible, biodegradable, and cost-effective thermoplastics, which are already FDA-approved for food use, drug delivery, and many medical devices. Microporous 3D-printed polylactic acid scaffolds, with different pore sizes (500, 750, and 1000 μm), were designed and manufactured using an inexpensive desktop 3D printer, and the mechanical properties were assessed. The scaffolds were compared for cell growth, activity, and bone-like tissue formation using primary human osteoblasts. Osteoblasts showed high proliferation, metabolic activity, and osteogenic matrix protein production, in which 750 μm pore-size scaffolds showed superiority. Further experimentation using human mesenchymal stem cells on 750 μm pore scaffolds showed their ability in supporting osteogenic differentiation. These findings suggest that even in the absence of any surface modifications, low-cost 750 μm pore-size 3D-printed scaffolds may be suitable as a bone substitute for repair of large bone defects.

N-acetylgalactosamine positive perineuronal nets in the saccade-related-part of the cerebellar fastigial nucleus do not maintain saccade gain

Perineuronal nets (PNNs) accumulate around neurons near the end of developmental critical periods. PNNs are structures of the extracellular matrix which surround synaptic contacts and contain chondroitin sulfate proteoglycans. Previous studies suggest that the chondroitin sulfate chains of PNNs inhibit synaptic plasticity and thereby help end critical periods. PNNs surround a high proportion of neurons in the cerebellar nuclei. These PNNs form during approximately the same time that movements achieve normal accuracy. It is possible that PNNs in the cerebellar nuclei inhibit plasticity to maintain the synaptic organization that produces those accurate movements.

We tested whether or not PNNs in a saccade-related part of the cerebellar nuclei maintain accurate saccade size by digesting a part of them in an adult monkey performing a task that changes saccade size (long term saccade adaptation). We use the enzyme Chondroitinase ABC to digest the glycosaminoglycan side chains of proteoglycans present in the majority of PNNs. We show that this manipulation does not result in faster, larger, or more persistent adaptation. Our result indicates that intact perineuronal nets around saccade-related neurons in the cerebellar nuclei are not important for maintaining long-term saccade gain.

Age-related nanostructural and nanomechanical changes of individual human cartilage aggrecan monomers and their glycosaminoglycan side chains

The nanostructure and nanomechanical properties of aggrecan monomers extracted and purified from human articular cartilage from donors of different ages (newborn, 29 and 38 year old) were directly visualized and quantified via atomic force microscopy (AFM)-based imaging and force spectroscopy. AFM imaging enabled direct comparison of full length monomers at different ages. The higher proportion of aggrecan fragments observed in adult versus newborn populations is consistent with the cumulative proteolysis of aggrecan known to occur in vivo. The decreased dimensions of adult full length aggrecan (including core protein and glycosaminoglycan (GAG) chain trace length, end-to-end distance and extension ratio) reflect altered aggrecan biosynthesis. The demonstrably shorter GAG chains observed in adult full length aggrecan monomers, compared to newborn monomers, also reflects markedly altered biosynthesis with age. Direct visualization of aggrecan subjected to chondroitinase and/or keratanase treatment revealed conformational properties of aggrecan monomers associated with chondroitin sulfate (CS) and keratan sulfate (KS) GAG chains. Furthermore, compressive stiffness of chemically end-attached layers of adult and newborn aggrecan was measured in various ionic strength aqueous solutions. Adult aggrecan was significantly weaker in compression than newborn aggrecan even at the same total GAG density and bath ionic strength, suggesting the importance of both electrostatic and non-electrostatic interactions in nanomechanical stiffness. These results provide molecular-level evidence of the effects of age on the conformational and nanomechanical properties of aggrecan, with direct implications for the effects of aggrecan nanostructure on the age-dependence of cartilage tissue biomechanical and osmotic properties.

FGF-2- and TGF-β1-induced downregulation of lumican and keratocan in activated corneal keratocytes by JNK signaling pathway

PURPOSE

Downregulation of lumican and keratocan expression is an undesirable phenotypic change that occurs during corneal wound healing. The present study was intended to determine whether the activation of Jun N-terminal kinase (JNK)-signaling pathway is involved in their downregulation in TGF-β1- and FGF-2-activated keratocytes.

METHODS

Keratocytes, isolated from rabbit corneal stroma, and cultured in a serum-free medium, pretreated or not treated with JNK inhibitor (SP600125), were activated with FGF-2/heparin sulfate (HS) or TGF-β1 in the presence or absence of SP600125. In another set of experiments, keratocytes were transfected with JNK1/2 Dicer-substrate RNA (DsiRNA) and then activated with TGF-β1 or FGF-2/HS. Specific phenotypic changes were analyzed immunocytochemically and correlated with Western blot analyses. The relative levels of specific mRNAs were estimated by quantitative RT-PCR using specific reagents.

RESULTS

The FGF-2/HS- or TGF-β-induced activation of corneal stromal keratocytes to fibroblast- or myofibroblast-phenotype, respectively, resulted in marked decreases in cell surface-associated and secreted keratan sulfate proteoglycans (KSPGs). Both keratocan and lumican proteins and their mRNAs were downregulated in the activated keratocytes. However, JNK inhibition during the activation of keratocytes, pretreated with the JNK inhibitor, suppressed the reduction in the cell-surface associated and secreted KSPGs (lumican and keratocan), and their mRNA transcripts. Downregulation of total KSPGs and their mRNAs was also inhibited by decreasing JNK1 and JNK2 levels via JNK1/2 DsiRNA transfection of keratocytes before their activation.

CONCLUSIONS

Extrapolating from the present study, FGF-2- and TGF-β1-activation of JNK signaling pathway may be partly responsible for the downregulation of keratocan and lumican expression in activated corneal keratocytes observed during corneal stromal wound healing.

Pericellular versican regulates the fibroblast-myofibroblast transition: a role for ADAMTS5 protease-mediated proteolysis

The cell and its glycosaminoglycan-rich pericellular matrix (PCM) comprise a functional unit. Because modification of PCM influences cell behavior, we investigated molecular mechanisms that regulate PCM volume and composition. In fibroblasts and other cells, aggregates of hyaluronan and versican are found in the PCM. Dermal fibroblasts from Adamts5(-/-) mice, which lack a versican-degrading protease, ADAMTS5, had reduced versican proteolysis, increased PCM, altered cell shape, enhanced α-smooth muscle actin (SMA) expression and increased contractility within three-dimensional collagen gels. The myofibroblast-like phenotype was associated with activation of TGFβ signaling. We tested the hypothesis that fibroblast-myofibroblast transition in Adamts5(-/-) cells resulted from versican accumulation in PCM. First, we noted that versican overexpression in human dermal fibroblasts led to increased SMA expression, enhanced contractility, and increased Smad2 phosphorylation. In contrast, dermal fibroblasts from Vcan haploinsufficient (Vcan(hdf/+)) mice had reduced contractility relative to wild type fibroblasts. Using a genetic approach to directly test if myofibroblast transition in Adamts5(-/-) cells resulted from increased PCM versican content, we generated Adamts5(-/-);Vcan(hdf/+) mice and isolated their dermal fibroblasts for comparison with dermal fibroblasts from Adamts5(-/-) mice. In Adamts5(-/-) fibroblasts, Vcan haploinsufficiency or exogenous ADAMTS5 restored normal fibroblast contractility. These findings demonstrate that altering PCM versican content through proteolytic activity of ADAMTS5 profoundly influenced the dermal fibroblast phenotype and may regulate a phenotypic continuum between the fibroblast and its alter ego, the myofibroblast. We propose that a physiological function of ADAMTS5 in dermal fibroblasts is to maintain optimal versican content and PCM volume by continually trimming versican in hyaluronan-versican aggregates.

Proteoglycans regulate the chemotaxis of dendritic cells derived from human peripheral blood monocytes

Dendritic cells (DCs) are a type of antigen-presenting cell which play an essential role in the immune system. The transition from immature DC (iDCs) to mature DCs (mDCs) requires appropriate maturation stimuli, such as pro-inflammatory cytokines or pathogen-derived components. Proteoglycans (PGs), which are composed of core proteins and the glycosaminoglycans that bind to them, are one of the main components of the extracellular matrix around pathogens such as bacteria. This study investigated the effects of PG extracted from the nasal septum cartilage of whale (W-PG) on the maturation of DCs derived from human peripheral blood monocytes. iDCs were prepared from human monocytes using granulocyte-macrophage colony-stimulating factor (GM-CSF) and interleukin-4 (IL-4). The iDCs were stimulated by W-PG alone. In another type of experiment, the iDCs were stimulated by MIX (tumor necrosis factor-alpha (TNF-alpha), IL-1beta, IL-6 and prostaglandin E(2) (PGE(2))) or a combination of MIX plus W-PG. The stimulation of W-PG alone did not induce the phenotypic maturation from iDCs. However, W-PG promoted the up-regulation of chemokine receptor CCR7-surface expression and the chemotactic responsiveness to CCR7 ligand macrophage inflammatory protein-3beta on MIX-stimulated mDCs although W-PG did not influence matrix metalloproteinase-9 activity which is an important factor in DC migration through the extracellular matrix. The findings that W-PG can selectively regulate the chemotactic activity of DCs in vitro under inflammatory conditions therefore indicate that the interaction of PGs with immune cells including DCs plays an important role in the immune response under the milieu of innate immunity.

Intraarticular injection of heparin-binding insulin-like growth factor 1 sustains delivery of insulin-like growth factor 1 to cartilage through binding to chondroitin sulfate

OBJECTIVE

Insulin-like growth factor 1 (IGF-1) stimulates cartilage repair but is not a practical therapy due to its short half-life. We have previously modified IGF-1 by adding a heparin-binding domain and have shown that this fusion protein (HB-IGF-1) stimulates sustained proteoglycan synthesis in cartilage. This study was undertaken to examine the mechanism by which HB-IGF-1 is retained in cartilage and to test whether HB-IGF-1 provides sustained growth factor delivery to cartilage in vivo and to human cartilage explants.

METHODS

Retention of HB-IGF-1 and IGF-1 was analyzed by Western blotting. The necessity of heparan sulfate (HS) or chondroitin sulfate (CS) glycosaminoglycans (GAGs) for binding was tested using enzymatic removal and cells with genetic deficiency of HS. Binding affinities of HB-IGF-1 and IGF-1 proteins for isolated GAGs were examined by surface plasmon resonance and enzyme-linked immunosorbent assay.

RESULTS

In cartilage explants, chondroitinase treatment decreased binding of HB-IGF-1, whereas heparitinase had no effect. Furthermore, HS was not necessary for HB-IGF-1 retention on cell monolayers. Binding assays showed that HB-IGF-1 bound both CS and HS, whereas IGF-1 did not bind either. After intraarticular injection in rat knees, HB-IGF-1 was retained in articular and meniscal cartilage, but not in tendon, consistent with enhanced delivery to CS-rich cartilage. Finally, HB-IGF-1 was retained in human cartilage explants but IGF-1 was not.

CONCLUSION

Our findings indicate that after intraarticular injection in rats, HB-IGF-1 is specifically retained in cartilage through its high abundance of CS. Modification of growth factors with heparin-binding domains may be a new strategy for sustained and specific local delivery to cartilage.

Ex vivo expansions of megakaryocytopoiesis from placental and umbilical cord blood CD34(+) cells in serum-free culture supplemented with proteoglycans extracted from the nasal cartilage of salmon heads and the nasal septum cartilage of whale

As a possible approach to the treatment of thrombopocytopenia, the ex vivo expansion of megakaryocytic progenitor cells may be a useful tool to accelerate platelet recovery in vivo. Our objective was to assess the promoting effect of proteoglycans in a serum-free culture condition using human cord blood CD34(+) cells. Highly purified proteoglycan (PG) extracted from the nasal cartilage of salmon heads and the nasal septum cartilage of a whale were applied to the ex vivo expansion of megakaryocytopoiesis and thrombopoiesis from placental and umbilical cord blood CD34(+) cells in serum-free cultures stimulated with a combination of thrombopoietin (TPO) and interleukin-3 (IL-3). Each PG (0.5 and 5 mug) was applied to the culture with three different concentrations of TPO (50, 5 and 0.5 ng/ml) and IL-3 (100, 10 and 1 ng/ml). Both of the PGs showed no promoting effects on the mononuclear cell proliferation rate in any of the cultures. However, the whale-PG promoted the generation of megakaryocytic progenitor cells and megakaryocytes in the culture with a lower dose of cytokines, respectively. In addition, whale-PG led to a significant increase in CD42a(+) particles which seemed to be platelets. While the salmon-PG failed to promote such production in almost all of the cultures. Although whale-PG is an attractive molecule for the ex vivo expansion of human megakaryocytopoiesis, its action may depend on the glycosaminoglycans sulfation pattern and the ability of the binding affinity and the kinetics to interact with the cytokines and hematopoietic stem/progenitor cells.

The effect of substitution of the N-acetyl groups of N-acetylgalactosamine residues in chondroitin sulfate on its degradation by chondroitinase ABC

Chondroitinase ABC is a lyase that degrades chondroitin sulfate, dermatan sulfate and hyaluronic acid into disaccharides. The purpose of this study was to determine the ability of chondroitinase ABC to degrade chondroitin sulfate in which the N-acetyl groups are substituted with different acyl groups. The bovine tracheal chondroitin sulfate A (bCSA) was N-deacetylated by hydrazinolysis, and the free amino groups derivatized into N-formyl, N-propionyl, N-butyryl, N-hexanoyl or N-benzoyl amides. Treatment of the N-acyl or N-benzoyl derivatives of bCSA with chondroitinase ABC and analysis of the products showed that the N-formyl, N-hexanoyl and N-benzoyl derivatives are completely resistant to the enzyme. In contrast, the N-propionyl or N-butyryl derivatives were degraded into disaccharides with slower kinetics compared to that of unmodified bCSA. The rate of degradation of bCSA derivatives by the enzyme was found to be in the order of N-acetyl>N-propionyl>>N-butyryl bCSA. These results have important implications for understanding the interaction of N-acetyl groups of glycosaminoglycans with chondroitinase ABC.

Rat spongiotrophoblast-specific protein is predominantly a unique low sulfated chondroitin sulfate proteoglycan

We have previously demonstrated that the human placenta contains a uniquely low sulfated extracellular aggrecan family chondroitin sulfate proteoglycan (CSPG). This CSPG is a major receptor for the adherence of Plasmodium falciparum-infected red blood cells (IRBCs) in placentas, causing pregnancy-specific malaria. However, it is not known whether such low sulfated CSPGs occur in placentas of other animals and, if so, whether IRBCs bind to those CSPGs. In this study, we show that rat placenta contains a uniquely low sulfated extracellular CSPG bearing chondroitin sulfate (CS) chains, which comprise only approximately 2% 4-sulfated and the remainder nonsulfated disaccharides. Surprisingly, the core protein of the rat placental CSPG, unlike that of the human placental CSPG, is a spongiotrophoblast-specific protein (SSP), which is expressed in a pregnancy stage-dependent manner. The majority of rat placental SSP is present in the CSPG form, and only approximately 10% occurs without CS chain substitution. Of the total SSP-CSPG in rat placenta, approximately 57% is modified with a single CS chain, and approximately 43% carries two CS chains. These data together with the previous finding on human placental CSPG suggest that the expression of low sulfated CSPG is a common feature of animal placentas. Our data also show that the unique species-specific difference in the biology of the rat and human placentas is reflected in the occurrence of completely different CSPG core protein types. Furthermore, the rat SSP-CSPG binds P. falciparum IRBCs in a CS chain-dependent manner. Since IRBCs have been reported to accumulate in the placentas of malaria parasite-infected rodents, our results have important implications for exploiting pregnant rats as a model for studying chondroitin 4-sulfate-based therapeutics for human placental malaria.

Versican/PG-M regulates chondrogenesis as an extracellular matrix molecule crucial for mesenchymal condensation

Mesenchymal cell condensation is an essential step for cartilage development. Versican/PG-M, a large chondroitin sulfate proteoglycan, is one of the major molecules expressed in the extracellular matrix during condensation. However, its role, especially as an environment for cells being condensed, has not been elucidated. Here we showed several lines of evidence for essential roles of versican/PG-M in chondrogenic condensation using a new chondrocytic cell line, N1511. Chondrogenic stimuli (treatment with parathyroid hormone, dexamethasone, 10% serum) induced a marked increase in the transcription and protein synthesis of versican/PG-M. Stable antisense clones for versican/PG-M, depending on suppression of the expression of versican/PG-M, showed different capacities for chondrogenesis, as indicated by the expression and deposition of aggrecan, a major chondrocytic cell product. The cells in the early stages of the culture only expressed V0 and V1 forms, having more chondroitin sulfate chains among the four variants of versican/PG-M, and treatment of those cells with chondroitinase ABC suppressed subsequent chondrogenesis. Furthermore, treatment with beta-xyloside, an artificial chain initiator of chondroitin sulfate synthesis to consequently inhibit the synthesis on the core proteins, suppressed chondrogenesis. In addition, forced expression of the variant V3, which has no chondroitin sulfate chain, disrupted the deposition and organization of native versican/PG-M (V0/V1) and other extracellular matrix molecules known to be expressed during the mesenchymal condensation and resulted in the inhibition of subsequent chondrogenesis. These results suggest that versican/PG-M is involved in positively regulating the formation of the mesenchymal matrix and the onset of chondrocyte differentiation through the attached chondroitin sulfate chains.

The concentration, gene expression, and spatial distribution of aggrecan in canine articular cartilage, meniscus, and anterior and posterior cruciate ligaments: a new molecular distinction between hyaline cartilage and fibrocartilage in the knee joint

The concentration, spatial distribution, and gene expression of aggrecan in meniscus, articular cartilage, and the anterior and posterior cruciate ligaments (ACL and PCL) was determined in the knee joints of five mature dogs. An anti-serum against peptide sequences specific to the G1 domain of aggrecan was employed in competitive-inhibition ELISA of guanidine HCl extracts and immunofluorescence microscopy. Gene expression was determined by Taqman real-time PCR. The concentration of aggrecan in articular cartilage (240.1 +/- 32 nMol/g dry weight) was higher than that in meniscus (medial meniscus: 33.4 +/- 4.3 nMol/g) and ligaments (ACL: 6.8 +/- 0.9 nMol/g). Aggrecan was more concentrated in the inner than the outer zone of the meniscus. Aggrecan in meniscus showed an organized, spatial network, in contrast to its diffuse distribution in articular cartilage. Thus, differences in the concentration, gene expression, and spatial distribution of aggrecan constitute another molecular distinction between hyaline cartilage and fibrocartilage of the knee.

Chondroitin sulfate proteoglycans of bovine cornea: structural characterization and assessment for the adherence of Plasmodium falciparum-infected erythrocytes

The structures of the bovine corneal chondroitin sulfate (CS) chains and the nature of core proteins to which these chains are attached have not been studied in detail. In this study, we show that structurally diverse CS chains are present in bovine cornea and that they are mainly linked to decorin core protein. DEAE-Sephacel chromatography fractionated the corneal chondroitin sulfate proteoglycans (CSPGs) into three distinct fractions, CSPG-I, CSPG-II, and CSPG-III. These CSPGs markedly differ in their CS and dermatan sulfate (DS) contents, and in particular the CS structure-the overall sulfate content and 4- to 6-sulfate ratio. In general, the CS chains of the corneal CSPGs have low to moderate levels (15-64%) of sulfated disaccharides and 0-30% DS content. Structural analysis indicated that the DS disaccharide units in the CS chains are segregated as large blocks. We have also assessed the suitability of the corneal CSPGs as an alternative to placental CSPG or the widely used bovine tracheal chondroitin sulfate A (CSA) for studying the structural interactions involved in the adherence of Plasmodium falciparum-infected red blood cells (IRBCs) to chondroitin 4-sulfate. The data demonstrate that the corneal CSPGs efficiently bind IRBCs, and that the binding strength is either comparable or significantly higher than the placental CSPG. In contrast, the IRBC binding strength of bovine tracheal CSA is markedly lower than the human placental and bovine corneal CSPGs. Thus, our data demonstrate that the bovine corneal CSPG but not tracheal CSA is suitable for studying structural interactions involved in IRBC-C4S binding.

Plasmodium falciparum-infected erythrocytes adhere both in the intervillous space and on the villous surface of human placenta by binding to the low-sulfated chondroitin sulfate proteoglycan receptor

In pregnant women infected with Plasmodium falciparum, the parasite-infected red blood cells (IRBCs) sequester in the placenta through chondroitin 4-sulfate (C4S)-mediated adherence. The pattern of IRBC adherence in P. falciparum-infected placenta has been controversial. Moreover, the identity of the chondroitin sulfate proteoglycan (CSPG) receptor, that mediates IRBC adherence, and its location in the placenta have not been established. This study, using immunohistochemical techniques, clearly shows, for the first time, that the low-sulfated CSPGs of the placenta are localized predominantly in the intervillous space. Ex vivo IRBC adherence analyses demonstrate that the IRBCs are adhered to the CSPG receptors in the placenta in a C4S-dependent manner. This IRBC binding pattern was similar to that observed in P. falciparum-infected placentas. These data and the results of dual-fluorescence staining of the endogenous RBCs and syncytiotrophoblasts, and co-localization of CSPG and IRBC adherence unequivocally establish that the low-sulfated CSPGs are the major natural receptors for IRBC adherence in the placenta. Further, it was found that IRBCs adhere mainly in the intervillous space and also at significant levels to the syncytiotrophoblasts. Finally, the ex vivo IRBC adherence method described herein provides a reliable procedure for future studies for the assessment of the efficacy of C4S inhibitors and adhesion inhibitory antibodies.

High glucose-induced alterations in subendothelial matrix perlecan leads to increased monocyte binding

OBJECTIVE

Hyperglycemia is an independent risk factor for cardiovascular disease in diabetic patients, although the link between the two is unknown. These studies were designed to model effects of high glucose on an early event in atherogenesis: the binding of monocytes to subendothelial matrix (SEM).

METHODS AND RESULTS

SEM was prepared from human aortic endothelial cells (HAECs) and bovine aortic endothelial cells (BAECs) cultured in the presence of low (5 mmol/L) or high (30 mmol/L) glucose for 3 to 5 days. Monocyte binding was significantly higher (P<0.05) to the SEM of both HAEC and BAEC exposed to high glucose. This increase was a result of changes in SEM heparan sulfate proteoglycans (HSPGs). Metabolic radiolabeling of BAEC demonstrated a 24% decrease in [35S]sulfate incorporation into SEM HSPG produced by cells incubated in 30 mmol/L versus 5 mmol/L glucose, whereas no glucose-associated differences were measured in [35S]methionine incorporation into proteoglycans (PGs) or non-PG proteins. Autoradiography revealed 2 high-molecular weight SEM HSPGs. One was a hybrid PG that contained both heparan sulfate and chondroitin sulfate/dermatan sulfate chains. Both PGs were identified by Western blotting as perlecan.

CONCLUSIONS

These results illustrate that hyperglycemia-induced structural changes in perlecan may result in a SEM that is more favorable to retention of monocytes.

The low sulfated chondroitin sulfate proteoglycans of human placenta have sulfate group-clustered domains that can efficiently bind Plasmodium falciparum-infected erythrocytes

Plasmodium falciparum infection in pregnant women results in the chondroitin 4-sulfate-mediated adherence of the parasite-infected red blood cells (IRBCs) in the placenta, adversely affecting the health of the fetus and mother. We have previously shown that unusually low sulfated chondroitin sulfate proteoglycans (CSPGs) in the intervillous spaces of the placenta are the receptors for IRBC adhesion, which involves a chondroitin 4-sulfate motif consisting of six disaccharide moieties with approximately 30% 4-sulfated residues. However, it was puzzling how the placental CSPGs, which have only approximately 8% of the disaccharide 4-sulfated, could efficiently bind IRBCs. Thus, we undertook to determine the precise structural features of the CS chains of placental CSPGs that interact with IRBCs. We show that the placental CSPGs are a mixture of two major populations, which are similar by all criteria except differing in their sulfate contents; 2-3% and 9-14% of the disaccharide units of the CS chains are 4-sulfated, and the remainder are nonsulfated. The majority of the sulfate groups in the CSPGs are clustered in CS chain domains consisting of 6-14 repeating disaccharide units. While the sulfate-rich regions of the CS chains contain 20-28% 4-sulfated disaccharides, the other regions have little or no sulfate. Further, we find that the placental CSPGs are able to efficiently bind IRBCs due to the presence of 4-sulfated disaccharide clusters. The oligosaccharides corresponding to the sulfate-rich domains of the CS chains efficiently inhibited IRBC adhesion. Thus, our data demonstrate, for the first time, the unique distribution of sulfate groups in the CS chains of placental CSPGs and that these sulfate-clustered domains have the necessary structural elements for the efficient adhesion of IRBCs, although the CS chains have an overall low degree of sulfation.

Latent transforming growth factor beta-binding protein 1 interacts with fibrillin and is a microfibril-associated protein

Latent transforming growth factor beta-binding protein 1 (LTBP-1) targets latent complexes of transforming growth factor beta to the extracellular matrix, where the latent cytokine is subsequently activated by several different mechanisms. Fibrillins are extracellular matrix macromolecules whose primary function is architectural: fibrillins assemble into ultrastructurally distinct microfibrils that are ubiquitous in the connective tissue space. LTBPs and fibrillins are highly homologous molecules, and colocalization in the matrix of cultured cells has been reported. To address whether LTBP-1 functions architecturally like fibrillins, microfibrils were extracted from tissues and analyzed immunochemically. In addition, binding studies were conducted to determine whether LTBP-1 interacts with fibrillins. LTBP-1 was not detected in extracted beaded-string microfibrils, suggesting that LTBP-1 is not an integral structural component of microfibrils. However, binding studies demonstrated interactions between LTBP-1 and fibrillins. The binding site was within three domains of the LTBP-1 C terminus, and in fibrillin-1 the site was defined within four domains near the N terminus. Immunolocalization data were consistent with the hypothesis that LTBP-1 is a fibrillin-associated protein present in certain tissues but not in others. In tissues where LTBP-1 is not expressed, LTBP-4 may substitute for LTBP-1, because the C-terminal end of LTBP-4 binds equally well to fibrillin. A model depicting the relationship between LTBP-1 and fibrillin microfibrils is proposed.

Inhibition of scleral proteoglycan synthesis blocks deprivation-induced axial elongation in chicks

A specific inhibitor of proteoglycan synthesis was administered to chicks undergoing the development of form deprivation myopia in order to test the hypothesis that increases in proteoglycan synthesis are responsible for normal and/or deprivation-induced ocular elongation in chicks. Chicks undergoing monocular form deprivation were treated with p-nitrophenyl-beta-D-xylopyranoside (beta-xyloside) via i.p. injection every 8 hr for 5-11 days. Ocular measurements were made at the end of the experiment using high frequency A-scan ultrasound in conjunction with a LabView (v. 5.0) analysis program. Following ultrasound measurements, sclera were isolated and proteoglycans characterized by Sepharose CL-2B and Western blot analyses. Preliminary studies indicated that i.p. administration of beta-xyloside maximally inhibited sulfate incorporation into proteoglycans 8 hr after administration. Beta-xyloside treatment resulted in a significant reduction in the axial length, vitreous chamber depth, and rate of axial elongation of form deprived eyes as compared with form deprived eyes from vehicle treated chicks (P < 0.01, P < 0.05, P < 0.05, respectively). No significant differences were detected in anterior chamber depth, lens thickness, choroid thickness or retina thickness in form deprived eyes of beta-xyloside treated chicks as compared with that of vehicle controls. No significant differences were detected in contralateral non-deprived fellow eyes between beta-xyloside treated and vehicle treated chicks for any ocular measurement. Analysis of proteoglycans indicated that the xyloside treatment resulted in the accumulation of smaller proteoglycans due, in part, to the presence of underglycosylated aggrecan within the scleral matrix. These results indicate that interruption of normal scleral proteoglycan synthesis inhibits form deprivation-induced ocular elongation, supporting the hypothesis that scleral proteoglycan synthesis and accumulation are largely responsible for increases in axial length in form deprived chick eyes.

Role of uppermost superficial surface layer of articular cartilage in the lubrication mechanism of joints

The uppermost superficial surface layer of articular cartilage, the 'lamina splendens' which provides a very low friction lubrication surface in articular joints, was investigated using atomic force microscopy (AFM). Complementary specimens were also observed under SEM at -10 degrees C without dehydration or sputter ion coating. Fresh adult pig osteochondral specimens were prepared from the patellas of pig knee joints and digested with the enzymes, hyaluronidase, chondroitinase ABC and alkaline protease. Friction coefficients between a pyrex glass plate and the osteochondral specimens digested by enzymes as well as natural (undigested) specimens were measured, using a thrust collar apparatus. Normal saline, hyaluronic acid (HA) and a mixture of albumin, globulin, HA (AGH) were used as lubrication media. The surface irregularities usually observed in SEM studies were not apparent under AFM. The articular cartilage surface was resistant to hyaluronidase and also to chondroitinase ABC, but a fibrous structure was exhibited in alkaline protease enzymes-digested specimens. AFM analysis revealed that the thickness of the uppermost superficial surface layer of articular cartilage was between 800 nm and 2 microm in adult pig articular cartilage. The coefficient of friction (c.f.) was significantly higher in chondroitinase ABC and alkaline protease enzymes digested specimens. Generally, in normal saline lubrication medium, c.f. was higher in comparison to HA and AGH lubrication media. The role of the uppermost, superficial surface layer of articular cartilage in the lubrication mechanism of joints is discussed.

The characterization of angiogenesis inhibitor from shark cartilage

An angiogenesis inhibitor isolated from shark cartilage, SCF2, has been characterized. SCF2 was shown to have specific angiogenesis-inhibiting activity in endothelial cell culture assays. Results of structural and functional studies indicate that the inhibitor is not a typical protein. It is a heat-stable proteoglycan, which contains keratan sulfate units and peptide. Gel filtration chromatography shows that the molecular weight of the angiogenesis inhibitor is about 10 kd.

Structural requirements for the adherence of Plasmodium falciparum-infected erythrocytes to chondroitin sulfate proteoglycans of human placenta

Plasmodium falciparum infection during pregnancy results in the accumulation of infected red blood cells (IRBCs) in the placenta, leading to poor pregnancy outcome. In the preceding paper (Achur, R. N., Valiyaveettil, M., Alkhalil, A., Ockenhouse, C. F., and Gowda, D. C. (2000) J. Biol. Chem. 275, 40344-40356), we reported that unusually low sulfated chondroitin sulfate proteoglycans (CSPGs) in the intervillous spaces of the placenta mediate the IRBC adherence. In this study, we report the structural requirements for the adherence and the minimum chondroitin 4-sulfate (C4S) structural motif that supports IRBC adherence. Partially sulfated C4Ss with varying sulfate contents were prepared by solvolytic desulfation of a fully sulfated C4S. These and other nonmodified C4Ss, with different proportions of 4-, 6-, and nonsulfated disaccharide repeats, were analyzed for inhibition of IRBC adherence to the placental CSPG. C4Ss containing 30-50% 4-sulfated and 50-70% nonsulfated disaccharide repeats efficiently inhibited IRBC adherence; C6S had no inhibitory activity. Oligosaccharides of varying sizes were prepared by the partial depolymerization of C4Ss containing varying levels of 4-sulfation, and their ability to inhibit the IRBC adherence was studied. Oligosaccharides with six or more disaccharide repeats inhibited IRBC adherence to the same level as that of the intact C4Ss, indicating that a dodecasaccharide is the minimum structural motif required for optimal IRBC adherence. Of the C4S dodecasaccharides, only those with two or three sulfate groups per molecule showed maximum IRBC inhibition. These data define the structural requirements for the IRBC adherence to placental CSPGs with implications for the development of therapeutics for maternal malaria.

Characterization of proteoglycans of human placenta and identification of unique chondroitin sulfate proteoglycans of the intervillous spaces that mediate the adherence of Plasmodium falciparum-infected erythrocytes to the placenta

In pregnant women infected with Plasmodium falciparum, the infected red blood cells (IRBCs) selectively accumulate in the intervillous spaces of placenta, leading to poor fetal outcome and severe health complications in the mother. Although chondroitin 4-sulfate is known to mediate IRBC adherence to placenta, the natural receptor has not been identified. In the present study, the chondroitin sulfate proteoglycans (CSPGs) of human placenta were purified and structurally characterized, and adherence of IRBCs to these CSPGs investigated. The data indicate that the placenta contains three distinct types of CSPGs: significant quantities of uniquely low sulfated, extracellular CSPGs localized in the intervillous spaces, minor amounts of two cell-associated CSPGs, and major amounts of dermatan sulfate-like CSPGs of the fibrous tissue. Of the various CSPGs isolated from the placenta, the low sulfated CSPGs of the intervillous spaces most efficiently bind IRBCs. Based on IRBC adherence capacities and localization patterns of various CSPGs, we conclude that the CSPGs of the intervillous spaces are the receptors for placental IRBC adherence. The identification and characterization of these CSPGs provide a valuable tool for understanding the precise molecular interactions involved in placental IRBC adherence and for the development of therapeutic strategies for maternal malaria. In the accompanying paper (Alkhalil, A., Achur, R. N., Valiyaveettil, M., Ockenhouse, C. F., and Gowda, D. C. (2000) J. Biol. Chem. 275, 40357-40364), we report the structural requirements for the IRBC adherence.

Cartilage formation by cultured chondrocytes in a new scaffold made of poly(L-lactide-epsilon-caprolactone) sponge

PURPOSE

This study investigated the ability of chondrocytes grown in culture and inoculated into a newly developed biodegradable sponge to form ectopic cartilage tissue.

MATERIALS AND METHODS

Chondrocytes obtained from costochondral cartilage dissected from Lewis rats were cultured to allow proliferation and then were inoculated into a sponge consisting of a biodegradable polymer, poly (L-lactide-epsilon-caprolactone). The composites of chondrocytes and sponge were transplanted subcutaneously into Nude mice and removed after 4 weeks for histologic and Northern blot analysis.

RESULTS

Staining with hematoxylin and eosin showed the formation of a cartilage-like structure in the sponge. Northern blot analysis of the total RNA in the composites showed the presence of aggrecan transcripts of about 9 kb.

CONCLUSION

The poly (L-lactide-epsilon-caprolactone) sponge system, is suitable as a matrix for tissue-engineered cartilage.

Expression of the keratan sulfate proteoglycans lumican, keratocan and osteoglycin/mimecan during chick corneal development

The corneal proteoglycans belong to the Leu-rich proteoglycan (LRP) gene family and contain chondroitin/dermatan (CS/DS) or keratan sulfate (KS) chains. These proteoglycans play a critical role in generating and maintaining a transparent matrix within the corneal stroma. Decorin which has CS/DS chains and lumican which has KS chains, were first to be identified in the cornea. Two other corneal KS proteoglycans (KSPGs), keratocan and osteoglycin/mimecan were recently identified in bovine corneas. We cloned and sequenced chick osteoglycin/mimecan and found it to contain a stretch of 60 amino acids that showed no identity to the presumed mammalian homolog. The 177 base pair DNA coding for this unique sequence shows 47% identity to an 189 base pair sequence between exons 4 and 5 of the bovine osteoglycin/mimecan gene. This indicates that this cDNA represents an alternatively spliced form of osteoglycin/mimecan containing a unique N-terminal sequence. The expression of each of the three corneal KSPGs in the developing and mature chick cornea was investigated by competitive PCR and immuno-biochemical analysis of corneal extracts. Competitive PCR was used to determine the message levels for chick lumican, keratocan and osteoglycin in embryonic day 9, 12, 15, 18 and adult corneas. Results showed that lumican mRNA fluctuated during development but remained at a relatively high level while keratocan and osteoglycin message levels declined steadily from day 9 to adult. Additionally, lumican mRNA was present at higher levels, during all stages of corneal development, than keratocan and at much higher levels than osteoglycin. Antibodies shown to be specific for each KSPG were used to characterize proteoglycans isolated from embryonic and adult chick corneas. KSPGs from embryonic corneas eluted 1-2 fractions earlier on Q-Sepharose than KSPG from adult corneas. Additionally, Western blot analysis showed that embryonic KSPGs were more keratanase-resistant, endo-beta-galactosidase sensitive than adult KSPGs. The results of this study indicate an alteration in sulfation or the fine structure of the glycosaminoglycan chains occurs during corneal maturation for the 3 KSPGs.

Gene expression and immunohistochemical localization of biglycan in association with mineralization in the matrix of epiphyseal cartilage

This study has used in situ hybridization, Northern blot analysis, and immunohistochemistry at the light and electron microscope levels to localize mRNAs and core proteins of biglycan in developing tibial epiphyseal cartilage of 10-day old Wistar rats. The expression of mRNAs and core proteins of biglycan appeared prominent in hypertrophic and degenerative chondrocytes associated with the epiphyseal ossification centre and the growth plate cartilage, but was not seen in the rest of epiphyseal cartilage. Northern blot analysis confirmed biglycan mRNA expression in the epiphyseal cartilage. Ultrastructural immunogold cytochemistry of the growth plate revealed that prominent immunolabelling was confined to the Golgi apparatus and cisternae of rough-surfaced endoplasmic reticulum of the hypertrophic and the degenerating chondrocytes, the early mineralized cartilage matrices of the longitudinal septum of the lower hypertrophic and the calcifying zones, and fully mineralized cartilage mitrices, which were present in the metaphyseal bone trabeculae. Furthermore, Western blot analysis of biglycan in extracts of fresh epiphyseal cartilage revealed that an EDTA extract, after chondroitinase ABC digestion, contains core proteins of biglycan, indicating the presence of biglycan in mineralized cartilage matrices. These results indicate that the distribution of biglycan is associated with cartilage matrix mineralization.

Age-related changes in the proteoglycans of human skin

Skin undergoes dramatic age-related changes in its mechanical properties, including changes in tissue hydration and resiliency. Proteoglycans are macromolecular conjugates of protein and carbohydrate (glycosaminoglycan) which are involved in these tissue properties. In order to examine whether age-related changes in skin proteoglycans may contribute to the age-related changes in the mechanical properties of skin, proteoglycans from human skin of various ages were extracted and analyzed. Samples were obtained from two different fetal ages, from mature skin, and from senescent skin. As a function of age, there is a decrease in the proportion of large chondroitin sulfate proteoglycans (versican) and a concomitant increase in the proportion of small dermatan sulfate proteoglycans (decorin). Based on reactivity with antibodies to various chondroitin sulfate epitopes, fetal versican differs from the versican found in older skin with respect to the chondroitin sulfate chains. Also, the decorin of fetal skin is slightly larger, while the decorin of older skin shows greater polydispersity in both its size and its charge to mass ratio. There are also age-related differences in the size and polydispersity of the core proteins of decorin. The most pronounced change in skin proteoglycans is the appearance in mature skin of a proteoglycan which is smaller than decorin, but which has the same amino terminal amino acid sequence as decorin. This small proteoglycan is abundant in mature skin and may be a catabolic fragment of decorin or an alternatively spliced form of decorin. In light of the known ability of decorin to influence collagen fibrillogenesis and fibril diameter, the appearance of this small decorin-related proteoglycan may have a significant effect on skin elasticity. The observation that proteoglycans in skin show dramatic age-related differences suggests that these changes may be involved in the age-related changes in the physical properties of skin.

Heparan sulfate in the inner limiting membrane of embryonic chicken retina binds basic fibroblast growth factor to promote axonal outgrowth

During neural development retinal ganglion cell axons migrate over the retinal basal lamina (inner limiting membrane, ILM) in directed growth toward the optic nerve. We found that both growth rate and distribution density of the ganglion cell axons on isolated cell-free ILM was greatly inhibited by pretreatment with heparitinase but not with chondroitinase ABC. The persistence of radioactively labeled proteoglycans added to the culture medium eliminated residual heparitinase as an explanation for the inhibition. A cell binding assay showed that heparitinase acted on the ILM to influence axonal behavior without apparent inhibition of cell adhesion. These results indicated that the neurite outgrowth promoting activity of the ILM depended on the heparan sulfate (HS) side chains of its proteoglycans. Basic fibroblast growth factor (bFGF) stimulated additional neuronal sprouting and neurite elongation on the ILM. This neurotropic activity of bFGF was inhibited by heparitinase pretreatment of the ILM, suggesting that bFGF bound to HS on the ILM. The activity of bFGF was enhanced by exogenous heparin added to the culture medium; although heparin alone failed to stimulate either neurite extension or neuronal cell sprouting. These results demonstrate that HS in the ILM possesses neurotropic activity for axons of the ganglion cells by binding bFGF for presentation to cell-surface receptors and may, therefore, play a significant role in stimulating axonal outgrowth during development.

Heparan Sulfate Proteoglycan Expression Is Induced During Early Erythroid Differentiation of Multipotent Hematopoietic Stem Cells

Heparan sulfate (HS) proteoglycans of bone marrow (BM) stromal cells and their extracellular matrix are important components of the microenvironment of hematopoietic tissues and are involved in the interaction of hematopoietic stem and stromal cells. Although previous studies have emphasized the role of HS proteoglycan synthesis by BM stromal cells, we have recently shown that the human hematopoietic progenitor cell line TF-1 also expressed an HS proteoglycan. Immunochemical, reverse transcriptase-polymerase chain reaction (RT-PCR), and Northern blot analysis of this HS proteoglycan showed that it was not related to the syndecan family of HS proteoglycans or to glypican. To answer the question of whether the expression of HS proteoglycans is associated with the differentiation state of hematopoietic progenitor cells, we have analyzed the proteoglycan synthesis of several murine and human hematopoietic progenitor cell lines. Proteoglycans were isolated from metabolically labeled cells and purified by several chromatographic steps. Isolation and characterization of proteoglycans from the cell lines HEL and ELM-D, which like TF-1 cells have an immature erythroid phenotype, showed that these cells synthesize the same HS proteoglycan, previously detected in TF-1 cells, as a major proteoglycan. In contrast, cell lines of the myeloid lineage, like the myeloblastic/promyelocytic cell lines B1 and B2, do not express HS proteoglycans. Taken together, our data strongly suggest that expression of this HS proteoglycan in hematopoietic progenitor cell lines is associated with the erythroid lineage. To prove this association we have analyzed the proteoglycan expression in the nonleukemic multipotent stem cell line FDCP-Mix-A4 after induction of erythroid or granulocytic differentiation. Our data show that HS proteoglycan expression is induced during early erythroid differentiation of multipotent hematopoietic stem cells. In contrast, during granulocytic differentiation, no expression of HS proteoglycans was observed.

Dynamic expression of proteoglycans during chicken skeletal muscle development and maturation

Skeletal muscle development is a complex process in which cell migration and adhesion play important roles. Because these cellular activities involve cell surface and extracellular matrix molecules, proteoglycan analysis was performed for developing chick skeletal muscle. Proteoglycans are macromolecular conjugates of protein and carbohydrate found in the extracellular matrix and at the cell surface. In developing muscle, both in vivo and in vitro, there is a development-related progression from synthesis of primarily large proteoglycans at earlier stages to mainly small proteoglycans at later stages. This progression was demonstrated by radiolabeling developing muscle and extracting and characterizing the proteoglycans. The large proteoglycans synthesized earlier in myogenesis have been identified as the large chondroitin sulfate proteoglycan, versican. Among the small proteoglycans synthesized at later stages is the small dermatan sulfate proteoglycan, decorin. Immunolocalization of these proteoglycans shows that versican is initially present in pericellular locations around developing myotubes, whereas decorin is observed in the epimysium early in development, and then its distribution gradually spreads to also include the perimysium and endomysium. Studies of regenerating muscle show that there is a recapitulation of the embryonic pattern of proteoglycan synthesis, which, coupled with the results from embryonic muscle development, suggests a role for versican in some early aspect of myogenesis.

Heparan Sulfate Proteoglycan Expression Is Induced During Early Erythroid Differentiation of Multipotent Hematopoietic Stem Cells

Heparan sulfate (HS) proteoglycans of bone marrow (BM) stromal cells and their extracellular matrix are important components of the microenvironment of hematopoietic tissues and are involved in the interaction of hematopoietic stem and stromal cells. Although previous studies have emphasized the role of HS proteoglycan synthesis by BM stromal cells, we have recently shown that the human hematopoietic progenitor cell line TF-1 also expressed an HS proteoglycan. Immunochemical, reverse transcriptase-polymerase chain reaction (RT-PCR), and Northern blot analysis of this HS proteoglycan showed that it was not related to the syndecan family of HS proteoglycans or to glypican. To answer the question of whether the expression of HS proteoglycans is associated with the differentiation state of hematopoietic progenitor cells, we have analyzed the proteoglycan synthesis of several murine and human hematopoietic progenitor cell lines. Proteoglycans were isolated from metabolically labeled cells and purified by several chromatographic steps. Isolation and characterization of proteoglycans from the cell lines HEL and ELM-D, which like TF-1 cells have an immature erythroid phenotype, showed that these cells synthesize the same HS proteoglycan, previously detected in TF-1 cells, as a major proteoglycan. In contrast, cell lines of the myeloid lineage, like the myeloblastic/promyelocytic cell lines B1 and B2, do not express HS proteoglycans. Taken together, our data strongly suggest that expression of this HS proteoglycan in hematopoietic progenitor cell lines is associated with the erythroid lineage. To prove this association we have analyzed the proteoglycan expression in the nonleukemic multipotent stem cell line FDCP-Mix-A4 after induction of erythroid or granulocytic differentiation. Our data show that HS proteoglycan expression is induced during early erythroid differentiation of multipotent hematopoietic stem cells. In contrast, during granulocytic differentiation, no expression of HS proteoglycans was observed.

Spatial and temporal changes in chondroitin sulfate distribution in the sclerotome play an essential role in the formation of migration patterns of mouse neural crest cells

We have examined the roles of pertinent extracellular matrix molecules in the formation of the neural crest cell migration patterns in the sclerotome of the mouse embryo. The present data indicate that permissiveness for migration is inversely correlated with chondroitin sulfate content. Experimental removal of chondroitin sulfate proteoglycans in the embryo causes neural crest cells to migrate even within the posterior half of the somite, which they do not invade ordinarily. Moreover, three different sclerotomal regions defined by the presence or absence of the ventromedial and/or ventrolateral pathways are present along the anteroposterior axis and undergo systematic temporal changes that affect migration patterns. The most anterior portion of the sclerotome is conducive to both ventromedial and ventrolateral migration (Anterior Region). The intermediate portion is conducive to ventromedial migration only (Intermediate Region). No neural crest cells are seen within the posterior portion of the sclerotome (Posterior Region). At this level, they are observed exclusively in the dorsolateral space adjacent to the roof of the neural tube. With advancing embryonic development, the rostrocaudal length of the Anterior Region decreases and is accompanied by a corresponding enlargement of the Intermediate Region. These results suggest that temporal and regional differences in the sclerotome contribute to the neural crest cell migration patterns in the mouse. To refine our understanding of the underlying mechanisms, regional differences and temporal changes in the distribution of extracellular matrix molecules have been examined during migration. In the sclerotome, chondroitin sulfate displays distinct distribution patterns that are closely correlated with the migration patterns of mouse neural crest cells. Furthermore, their migration patterns are altered in embryos treated with the inhibitors of chondroitin sulfate proteoglycan biosynthesis, sodium chlorate, and beta-D-xyloside. In inhibitor-treated embryos, neural crest cell migration occurs even in the posterior portion of the sclerotome. The metameric organization of dorsal root ganglia is disturbed in these embryos. Our observations provide novel evidence for the importance of sclerotomal chondroitin sulfate distribution patterns in mouse crest cell migration patterns. We conclude that systematic spatiotemporal changes in the distribution of chondroitin sulfate proteoglycans are a key requisite for the formation of migration patterns of mouse neural crest cells in the sclerotome.

The soft tissue cover of the mandibular condyle. Differentiation in histological forms and age-related changes of aggrecan- and versican-like proteoglycans

Age-related changes of the composition of the extracellular matrix of the soft tissue cover of the mandibular condyle (STC), especially of the large proteoglycans, have been investigated. Proteoglycans were extracted from the STC of neonatal, juvenile and adult domestic pigs, fractionated by density gradient centrifugation and analyzed by electrophoresis/Western blotting. Experiments revealed firstly that a large CS/KS proteoglycan (aggrecan) is an essential constituent of the STC at all ages. This proteoglycan is required for nutrition of avascular tissues, and age-related changes in its average size and substitution with KS (keratan sulfate) may be a response to altered functional loading and tissue architecture of the STC. Secondly it was shown that a large CS/DS (chondroitin sulfate/dermatan sulfate) proteoglycan characterized by a doublet of core proteins at 200 and 250 kDa, thereby resembling perlecan, is present in the tissue of adults, but not of neonates and juveniles. Thirdly a large CS/DS proteoglycan characterized by core proteins at 350, 450 and 550 kDa, thereby resembling versican, was present in juveniles. It was detectable only weakly in neonates and not in adults. Results of core protein analysis were confirmed by results of agarose gel electrophoresis/Western blotting of the undigested proteoglycans isolated directly from the tissue extracts. Versican is believed to destabilize cell-matrix interactions required for cell proliferation and differentiation. In this context, presence of versican-like proteoglycans in the STC of growing individuals and its disappearance in adults appears to be related to the growth potential of the mandibular condyle.

Expression of adhesion molecules by lp(a): a potential novel mechanism for its atherogenicity

Lp(a) is a major inherited risk factor for premature atherosclerosis. The mechanism of Lp(a) atherogenicity has not been elucidated, but likely involves both its ability to interfere with plasminogen activation and its atherogenic potential as a lipoprotein particle after receptor-mediated uptake. We demonstrate that Lp(a) stimulates production of vascular cell adhesion molecule 1 (VCAM-1) and E-selectin in cultured human coronary artery endothelial cells (HCAEC). This effect resulted from a rise in intracellular free calcium induced by Lp(a) and could be inhibited by the intracellular calcium chelator, BAPTA/AM. The involvement of the LDL and VLDL receptors in Lp(a) activation of HCAEC were ruled out since Lp(a) induction of adhesion molecules was not prevented by an antibody (IgGC7) to the LDL receptor or by receptor-activating protein, an antagonist of ligand binding to the VLDL receptor. Addition of alpha2-macroglobulin as well as treatment with heparinase, chondroitinase ABC, and sodium chlorate did not decrease levels of VCAM-1 and E-selectin stimulated by Lp(a), suggesting that neither the low density lipoprotein receptor-related protein nor cell-surface proteoglycans are involved in Lp(a)-induced adhesion molecule production. Neither does the binding site on HCAEC responsible for adhesion molecule production by Lp(a) appear to involve plasminogen receptors, as levels of VCAM-1 and E-selectin were not significantly decreased by the addition of glu-plasminogen, the lysine analog epsilon-aminocaproic acid, or by trans-4-(aminomethyl)-cyclohexanecarboxymethylic acid (tranexamic acid), which acts by binding to the lysine binding sites carried on the kringle structures in plasminogen. In contrast, recombinant apolipoprotein (a) [r-apo(a)] competed with Lp(a) and attenuated the expression of VCAM-1 and E-selectin. In summary, we have identified a calcium-dependent interaction of Lp(a) with HCAEC capable of inducing potent surface expression of VCAM-1 and E-selectin that does not appear to involve any of the known potential Lp(a) binding sites. Because leukocyte recruitment to the vessel wall appears to represent one of the important early events in atherogenesis, this newly described endothelial cell-activating effect of Lp(a) places it at a crucial juncture in the initiation of atherogenic disease and may lead to a better understanding of the role of Lp(a) in the vascular biology of atherosclerosis.

Oligosaccharide sequence of human breast cancer cell heparan sulfate with high affinity for laminin

Laminin-1 is a basement membrane glycoprotein implicated in tumor-host adhesion, which involves the cell-binding domain(s) of laminin-1 and tumor cell surface heparan sulfate (HS). The specific tumor cell surface HS oligosaccharide sequences that are necessary for binding to laminin-1 have not been characterized. To identify this laminin-binding oligosaccharide sequence, GlcNSO4-rich oligosaccharides terminating with [3H]2,5-anhydromannitol (AManR) residues were isolated from human breast cancer cell (MCF-7)-derived HS through hydrazinolysis/high pH (4.0) nitrous acid treatment/[3H]NaBH4 reduction. These oligosaccharides were chromatographed on a laminin-1 affinity column. A high affinity dodecasaccharide was isolated and characterized. Disaccharide analysis yielded IdoA(2-SO4) --> AManR(6-SO4) as the only disaccharide upon treatment of this dodecasaccharide with nitrous acid at low pH (1.5). The sequence of laminin-binding high affinity oligosaccharide is therefore [IdoA(2-SO4) --> GlcNSO4(6-SO4)]5[IdoA(2-SO4) --> AManR(6-SO4)]. Low affinity dodecasaccharides composed of [IdoA(2-SO4) --> GlcNSO4(6-SO4)]5, [IdoA(2-SO4) --> GlcNSO4] were also isolated by laminin-1 affinity chromatography. Molecular modeling studies indicate that a heparin-binding peptide sequence corresponding to amino acid residues 3010-3031 (KQNCLSSRASFRGCVRNLRLSR) in the G domain of laminin-1, modeled as a right-handed alpha-helix, carries an array of basic residues well placed to bind to clusters of sulfate groups on the high affinity dodecasaccharide.

Identification of the N-linked oligosaccharide sites in chick corneal lumican and keratocan that receive keratan sulfate

Corneal proteoglycans have chondroitin/dermatan and keratan sulfate (KS) chains and belong to the leucine-rich proteoglycan gene family. Corneal KS is N-linked to Asn of an NX(S/T) site through a complex oligosaccharide linkage region. Only some sites receive KS, whereas others remain in a high mannose form. To determine whether the attachment of KS was biased toward specific sites, we isolated trypsin-digested KS-containing fragments of chick corneal proteoglycans and sequenced the peptides. Results showed that all of the peptides sequenced aligned to the deduced amino acid sequence of either chick lumican or chick keratocan at the first, third, and fourth potential N-linked sites. Sites 1 and 4 in lumican and keratocan are in a homologous location. By analogy with the structure of ribonuclease inhibitor (a Leu-rich repeat containing protein), the KS chains would extend outward on the outer face of a horseshoe-like structure. The amino acid sequences surrounding the potential N-linked sites were also compared. Sites receiving KS tend to have a higher occurrence of aromatic residues, in particular Phe, located within 3 amino acids of NX(S/T). These conserved Phe residues may have a role in the conversion of high mannose N-linked oligosaccharides to polylactosamine and/or keratan sulfate.

Arthritis induced by proteoglycan aggrecan G1 domain in BALB/c mice. Evidence for t cell involvement and the immunosuppressive influence of keratan sulfate on recognition of t and b cell epitopes

Our previous work showed that the proteoglycan aggrecan can induce erosive polyarthritis and spondylitis in BALB/c mice, and that the G1 domain of the proteoglycan aggrecan (G1) is the arthritogenic region. In this study, two T cell epitopes residing on G1 within residues 70-84 (peptide G5) and 150-169 (peptide G9) were identified using synthetic peptides and aggrecan-specific T cell lines. Two G1-specific T cell hybridomas exclusively responded to peptide G5. When the G5-specific T cell line was injected intraperitoneally into BALB/c mice, it induced acute inflammatory arthritis in joints, but only in those that had been injected with the epitope recognized by these T cells. Furthermore, we also demonstrate that the keratan sulfate chain(s) (KS) on G1 possess immunosuppressive properties with respect to T and B cell epitope recognition. T cell lines that recognize both G1 and peptide G5 show an increased response to G1 after KS is removed. Antibodies in hyperimmune sera of mice immunized with G1 show increased epitope recognition (quantitative and qualitative) after KS removal before immunization. These studies reveal that a T cell line specific to an epitope on the G1 domain of aggrecan, also recognizing a corresponding mouse G1 epitope, can induce arthritis by adoptive transfer and homing to the intraarticular epitope, thereby implicating T cells in arthritis development caused by immunity to the G1 domain of aggrecan. Moreover, the presence of KS on G1 can inhibit arthritis development by suppressing T and B cell epitope recognition.

Dysregulation of proteoglycan production by intrahepatic biliary epithelial cells bearing defective (delta-f508) cystic fibrosis transmembrane conductance regulator

Hepatic dysfunction in cystic fibrosis (CF) has been attributed to accumulation of viscous mucoid secretions in intrahepatic bile ducts. The purpose of our study was to compare glycoconjugate secretion by intrahepatic biliary epithelial (IBE) cells derived from normal livers and livers of CF patients with the delta F508 mutation of the cystic fibrosis transmembrane conductance regulator (CFTR). Confluent cells were incubated with 3H-glucosamine (GlcN) for 16 hours, and radiolabeled macromolecules were analyzed for the amount and type of glycoconjugates. Incorporation of 3H-GlcN into macromolecular glycoconjugates was two- to threefold higher in CF cells versus normals, as was uptake of 3H-Glcn into the cytoplasm of CF cells. Gel exclusion chromatography on Sepharose Cl 4B revealed that the secreted glycoconjugates from CF cells eluted entirely in the excluded fraction (molecular weight > 2 x 10(6)), while, in the normal cells, 60% of the glycoconjugates eluted as lower-molecular-weight species. The high-molecular-weight glycoconjugates in both CF and normal cells were identified as chondroitin sulfates, as evidenced by susceptibility to beta elimination, chondroitinase digestion, and amino acid composition. Western blotting of IBE cell secretions with a polyclonal antibody to chondroitin sulfate revealed proteoglycan bands at 100 and 210 kd. Our results indicate that secretion of chondroitin sulfate is markedly increased in CF biliary epithelium in vitro compared with non-CF cells. Increased uptake of precursor 3H-GlcN may contribute to enhanced glycosylation of chondroitin sulfate in CF cells.

Isolation and characterization of chondroitin sulfate proteoglycans from embryonic quail that influence neural crest cell behavior

The movement of neural crest cells is controlled in part by extracellular matrix. Aggrecan, the chondroitin sulfate proteoglycan from adult cartilage, curtails the ability of neural crest cells to adhere, spread, and move across otherwise favorable matrix substrates in vitro. Our aim was to isolate, characterize, and compare the structure and effect on neural crest cells of aggrecan and proteoglycans purified from the tissues through which neural crest cells migrate. We metabolically radiolabeled proteoglycans in E2.5 quail embryos and isolated and characterized proteoglycans from E3.3 quail trunk and limb bud. The major labeled proteoglycan was highly negatively charged, similar in hydrodynamic size to chick limb bud versican/PG-M, smaller than adult cartilage aggrecan but larger than reported for embryonic sternal cartilage aggrecan. The molecular weight of the iodinated core protein was about 400 kDa, which is more than reported for aggrecan but less than that of chick versican/PG-M. The proteoglycan bore chondroitin sulfate glycosaminoglycan chains of 45 kDa, which is larger than those of aggrecan. It lacked dermatan sulfate, heparan sulfate, or keratan sulfate chains. It bound to collagen type I, like aggrecan, but not to fibronectin (unlike versican/PG-M), collagen type IV, or laminin-1 in solid-phase assays and it bound to hyaluronate in gel-shift assays. When added at concentrations between 10 and 30 microg/ml to substrates of fibronectin, trunk proteoglycan inhibited neural crest cell spreading and migration. Attenuation of cell spreading was shown to be the most sensitive and titratable measure of the effect on neural crest cells. This effect was sensitive to digestion with chondroitinase ABC. Similar cell behavior was also produced by aggrecan and the small dermatan sulfate proteoglycan decorin; however, 30-fold more aggrecan was required to produce an effect of similar magnitude. When added in solution to neural crest cells which were already spread and migrating on fibronectin, the embryonic proteoglycan rapidly and reversibly caused complete rounding of the cells, being at least 30-fold more potent than aggrecan in this activity.

Proteoglycan synthesis in haematopoietic cells: isolation and characterization of heparan sulphate proteoglycans expressed by the bone-marrow stromal cell line MS-5

Proteoglycans of bone-marrow stromal cells and their extracellular matrix are important components of the haematopoietic microenvironment. Recently, several studies have indicated that they are involved in the interaction of haematopoietic stem and stromal cells. However, a detailed characterization of the heparan sulphate proteoglycans synthesized by bone-marrow stromal cells is still lacking. Here we report on the isolation and characterization of proteoglycans from the haematopoietic stromal cell line MS-5, that efficiently supports the growth and differentiation of human and murine haematopoietic progenitor cells. Biochemical characterization of purified proteoglycans revealed that the haematopoietic stromal cell line MS-5 synthesizes, in addition to chondroitin sulphate proteoglycans, several different heparan sulphate proteoglycans. Immunochemical analysis, using specific antibodies against the different members of the syndecan family, glypican, betaglycan and perlecan, showed that MS-5 cells synthesize all these different heparan sulphate proteoglycans. These data were further supported by reverse-transcriptase PCR and confirmed by sequence and Northern blot analysis. The relative abundance of the different heparan sulphate proteoglycans was estimated on the protein and mRNA levels.

Localization of a binding site for the proteoglycan decorin on collagen XIV (undulin)

Through its ability to bind extracellular matrix constituents and growth factors the small leucine-rich chondroitin/dermatan sulfate proteoglycan decorin which is present in many types of connective tissues may play an important biological role in remodeling and maintenance of extracellular matrices during inflammation, fibrosis, and cancer growth. In this study we investigated the known binding of decorin to human collagen XIV. This binding was unaffected when the small collagenous moiety of collagen XIV was removed with collagenase. Therefore, fragments covering the large noncollagenous domain NC3 of collagen XIV were expressed in Escherichia coli, each fused to a 26-kDa fragment of glutathione S-transferase. Using radioiodinated decorin as ligand for the immobilized fusion proteins, a binding site that interacted with the decorin core protein could be assigned to the NH2-terminal fibronectin type III repeat of collagen XIV. In addition, an auxiliary binding site located COOH-terminal to this fibronectin type III repeat interacted with the glycosaminoglycan component of decorin.

Role of heparan sulfate proteoglycans in the uptake and degradation of tissue factor pathway inhibitor-coagulation factor Xa complexes

Tissue factor pathway inhibitor (TFPI) is a potent inhibitor of blood coagulation factor Xa (fXa) and factor VIIa. We have recently shown that fXa binding stimulates the uptake and degradation of cell surface-bound 125I-TFPI (Ho, G., Toomey, J. R., Broze, G. J., Jr., and Schwartz, A. L. (1996) J. Biol. Chem. 271, 9497-9502). In the present study we examined the role of cell surface glycosaminoglycans (GAGs) in this process. Removal of cell surface GAG chains by treatment of cells with heparinase or heparitinase but not chondroitinase markedly reduced fXa-stimulated 125I-TFPI uptake and degradation. Inhibition of GAG sulfation by growth of cells in chlorate-containing medium similarly decreased fXa-stimulated 125I-TFPI degradation. These results suggest that heparan sulfate proteoglycans (HSPGs) are required for the uptake and degradation of 125I-TFPI.fXa complexes. Chemical cross-linking/immunoprecipitation analyses revealed that 125I-TFPI was directly associated with HSPGs on the cell surface and that fXa binding increased the amount of 125I-TFPI bound. Of the several cell lines evaluated, bend endothelial cells demonstrated the greatest fXa stimulation of 125I-TFPI uptake and degradation. Cross-linking/immunoprecipitation analyses on bend cells also revealed that HSPGs were specifically associated with TFPI and fXa. These data suggest that HSPGs may directly act as the uptake and degradation receptor for TFPI.fXa complexes.

Two distinct chondroitin sulfate ABC lyases. An endoeliminase yielding tetrasaccharides and an exoeliminase preferentially acting on oligosaccharides

Crude enzyme obtained from chondroitin sulfate-induced Proteus vulgaris NCTC 4636 has been fractionated into 1) an endoeliminase capable of depolymerizing chondroitin sulfate and related polysaccharides to produce, as end products, a mixture of Delta4-unsaturated tetra- and disaccharides and 2) an exoeliminase preferentially acting on chondroitin sulfate tetra- and hexasaccharides to yield the respective disaccharides. Isolation of the two enzymes was achieved by a simple two-step procedure: extracting the enzymes from intact P. vulgaris cells with a buffer solution of nonionic surfactant and then treating the extract by cation-exchange chromatography. Each of the enzymes thus prepared was apparently homogeneous as assessed by SDS-polyacrylamide gel electrophoresis and readily crystallized from polyethylene glycol solutions. Both enzymes acted on various substrates such as chondroitin sulfate, chondroitin sulfate proteoglycan, and dermatan sulfate at high, but significantly different, initial rates. They also attacked hyaluronan but at far lower rates and were inactive to keratan sulfate, heparan sulfate, and heparin. Our results show that the known ability of the conventional enzyme called "chondroitinase ABC" to catalyze the complete depolymerization of chondroitin sulfates to unsaturated disaccharides may actually result from the combination reactions by endoeliminase (chondroitin sulfate ABC endolyase) and exoeliminase (chondroitin sulfate ABC exolyase).

Inhibition of experimental metastasis and cell adhesion of murine melanoma cells by chondroitin sulfate-derivatized lipid, a neoproteoglycan with anti-cell adhesion activity

Chondroitin sulfate dipalmitoylphosphatidylethanolamine (CS-PE), when immobilized onto substratum, inhibited the adhesion of B16F10 mouse melanoma cells to fibronectin-coated dishes (anti-adhesion activity). CS-PE showed the most potent anti-adhesion activity for the melanoma cells among various GAG-PEs. CS-PE also inhibited the adhesion of B16F10 cells to Matrigel and the invasion of the cells into Matrigel. In the in vivo system of experimental metastasis, administration of B16F10 cells with CS-PE into C57BL/6 mice significantly inhibited lung metastasis. The inhibition degree of CS or hyaluronic acid-PE was lower than CS-PE. CS-PE administered intravenously into mice before the injection of B16F10 cells also inhibited metastasis. Pretreatment of B16F10 cells with CS-PE caused some but a lower degree of inhibition. When CS-PE was injected intravenously into mice, more binding in the lung was found than when CS was injected. CS-PE but not CS inhibited the retention in the lung of fluorochrome-labeled B16F10 cells when injected intravenously into mice. Since there was no significant effect of CS-PE on the viability and growth of B16F10 cells, the results suggest that CS-PE immobilized onto the subendothelial matrix may prevent melanoma cells from adhering to the subendothelial substrata of lung capillaries and inhibit subsequent invasion processes of metastasis.

Evidence for the presence of a large keratan sulphate proteoglycan in the human uterine cervix

Profound changes occur in the uterine cervix during pregnancy. In particular, the extracellular matrix of the connective tissue is remodelled extensively. To elucidate the mechanisms involved in this process, we have analysed the proteoglycan pattern in the human cervix from pregnant and non-pregnant women. Proteoglycans of the cervix tissue specimen were extracted with 4 M guanidine hydrochloride and precipitated with 80% ethanol. Purification of proteoglycans was performed by several chromatographic steps. Characterization of proteoglycans was done by SDS/PAGE before and after digestion with glycosaminoglycan-specific enzymes. Proteoglycans were detected by combined Alcian Blue/silver staining or, after blotting of biotin-labelled proteoglycans on to poly(vinylidene difluoride) membrane, with peroxidase-conjugated avidin or by the use of keratan sulphate- or decorin-specific monoclonal antibodies. In contrast with previous reports, where only chondroitin/dermatan sulphate proteoglycans have been found in the uterine cervix, we have shown in the present study the existence of a large keratan sulphate proteoglycan with an M(r) > 220,000 in cervix samples from non-pregnant and pregnant women. This proteoglycan showed a strong reaction with the keratan sulphate-specific monoclonal antibody 5D4 and could be degraded by keratanases. The size of the core protein of this keratan sulphate proteoglycan was estimated to be about M(r) 220,000.