Comparative biochemistry of chondroitin sulphate-proteins of cartilage and notochord

Comprehensive analysis of chondroitin sulfate and aggrecan in the head cartilage of bony fishes: Identification of proteoglycans in the head cartilage of sturgeon

Cartilage in the head of sturgeon or salmon has been gaining attention as a rich source of functional chondroitin sulfate (CS) or proteoglycans. Although the cartilage was found in the heads of other bony fishes, the structure of CS and its core protein, especially aggrecan, was not fully investigated. In this study, comprehensive analysis of CS and aggrecan in the head cartilage of 10 bony fishes including sturgeon and salmon was performed. The 4-O-sulfation to 6-O-sulfation ratio (4S/6S ratio; S: sulfate residue) of CS in Perciformes was ≧1.0, while the 4S/6S ratios of CS from sturgeons and salmon were less than 0.5. Dot blotting and proteomic analysis revealed that aggrecan was a major core protein in head cartilage of all bony fishes. These results suggest that the head cartilage of bony fishes is a promising source for the preparation of CS or proteoglycans as a health food ingredient.

Notochord Cells in Intervertebral Disc Development and Degeneration

The intervertebral disc is a complex structure responsible for flexibility, multi-axial motion, and load transmission throughout the spine. Importantly, degeneration of the intervertebral disc is thought to be an initiating factor for back pain. Due to a lack of understanding of the pathways that govern disc degeneration, there are currently no disease-modifying treatments to delay or prevent degenerative disc disease. This review presents an overview of our current understanding of the developmental processes that regulate intervertebral disc formation, with particular emphasis on the role of the notochord and notochord-derived cells in disc homeostasis and how their loss can result in degeneration. We then describe the role of small animal models in understanding the development of the disc and their use to interrogate disc degeneration and associated pathologies. Finally, we highlight essential development pathways that are associated with disc degeneration and/or implicated in the reparative response of the tissue that might serve as targets for future therapeutic approaches.

Isolation and characterization of chondroitin sulfates from sturgeon (Acipenser sinensis) and their effects on growth of fibroblasts

Chondroitin sulfate (CS) is a glycosaminoglycan that composed of hexosamine (D-galactosamine) and hexuronic acid (D-glucuronic acid) unit arranged in an alternating unbranched sequence. CS is an essential component of the extracellular matrix (ECM) of connective tissue. It is mainly covalently attached to core proteins in the form of proteoglycans so that it exhibits specific interactions with proteins for cell growth, differentiation, division and migration. In this study, CSs were purified from the cartilage and backbone of sturgeon (Acipenser sinensis). To characterize their biochemical properties, we performed disaccharide compositional analysis after chondroitinase ABC digestion, high performance size exclusion chromatography (HPSEC) and (1)H-NMR spectroscopy. We also investigated the effects of CSs on fibroblast proliferation and adhesion to determine whether wound healing was accelerated in vitro and proliferation of different mitogen-activated protein kinases (MAPK) signaling pathways was facilitated. The CS purified from sturgeon cartilage was primarily composed of 4-sulfated CS (88.8%) and sturgeon backbone CS contains more than 60% 6-sulfated CS. The average molecular weights of CSs obtained from sturgeon cartilage and backbone were found to be 8 and 43 kDa, respectively. Our results showed that both CSs are able to increase cell adhesion, induce proliferation and migration on fibroblasts and may accelerate wound healing by inducing MAPK signaling pathways.

Hyaluronan, a common thread

Hyaluronan, nature's simplest, but still exceptionally versatile glycosaminoglycan, is currently the focus of attention across a wide front of research; from cell biology, morphogenesis, matrix organization, pathobiology to tissue engineering. This macromolecule has entangled me in a number of puzzling and challenging projects over the past 3 decades. These entertaining encounters are outlined in this retrospective.

Progressive polyarthritis induced in BALB/c mice by aggrecan from normal and osteoarthritic human cartilage

OBJECTIVE

To find an "unlimited" source of antigenic material (aggrecan) for arthritis induction in BALB/c mice; to analyze the specificities of immune reactions to aggrecan and type II collagen in 2 arthritis-susceptible murine strains, BALB/c mice for proteoglycan (aggrecan)-induced arthritis and DBA/1j mice for collagen-induced arthritis; to compare the histopathologic features of arthritis induced by purified aggrecans or total extracts of osteoarthritic (OA) cartilage; and to determine arthritis susceptibility in various BALB/c colonies.

METHODS

Aggrecans from total extracts of human fetal, normal adult, OA, and rheumatoid cartilage samples and from osteophytes were isolated, purified by gradient centrifugation, deglycosylated, characterized, and tested for arthritis induction. Purified type II collagen and salt-soluble collagens from OA cartilage were denatured, stromelysin treated, and used for immunization and arthritis induction in arthritis-susceptible (DBA/1j and BALB/c) murine strains.

RESULTS

Chondrocytes from OA cartilage synthesize predominantly fetal-type aggrecan, which is the most efficient antigenic material for arthritis induction in BALB/c mice. The critical autoimmune/arthritogenic T cell epitopes of aggrecan are located in the G1 domain. Although most of the aggrecan molecules are heavily degraded and lost from OA cartilage, the G1 domain-containing fragments accumulate in OA cartilage. The amount of G1-containing fragments is approximately twice as much in OA than in normal adult articular cartilage, and the arthritogenic epitope(s) remains intact in G1-containing fragments retained in cartilage. Thus, total extracts of OA cartilage (without additional purification), if deglycosylated appropriately, can be used as arthritogenic material in BALB/c mice.

CONCLUSION

Predominantly G1 domain-containing fragments of aggrecan accumulate in OA cartilage, and these are the fragments which induce arthritis in BALB/c mice. Arthritis induction is highly specific for aggrecan epitopes and dictated by the genetic background of the BALB/c strain.

Anin vitro model for chick embryonic notochords

A two step method to obtain mesenchymal free 3.5 day old chick embryonic notochordsin vitro is presented. 1.) Notochords are isolated by mechanical microdissection from the embryos below the head and above the leg-buds. 2.) The dissected notochords are trypsinized to eliminate contaminating mesenchymal cells, while the perinotochordal sheath (PNS) is retained. After isolation and trypsinization, notochords are cut in standard 8mm lengths, explantedin vitro and incubated at 37°C. Immediately before incubation and after 3 and 6 daysin vitro, notochords are fixed and stained to follow the morphological changes. The total DNA content of notochords is measured before and during maintenancein vitro to evaluate their metabolic activities. Results show that during thein vitro period, the isolated mesenchymal free notochordal fragments can conserve their characteristic architecture. The total DNA content measurements indicate proliferative activity and a high viability of the notochords in ourin vitro system. In the present study, an isolation andin vitro method is offered which might be an effective tool to study the metabolic activities of chick embryonic notochordsin vitro in comparison toin vivo behaviour, in order to study the underlying mechanism of notochord regression.

Molecular cloning and analysis of the protein modules of aggrecans

The large aggregating chondroitin sulfate proteoglycan of cartilage, aggrecan, has served as a prototype of proteoglycan structure. Molecular cloning has elucidated its primary structure and revealed both known and unknown domains. To date the complete structures of chicken, rat and human aggrecans have been deduced, while partial sequences have been reported for bovine aggrecan. A related proteoglycan, human versican, has also been cloned and sequenced. Both aggrecan and versican have two lectin domains, one at the amino-terminus which binds hyaluronic acid and one at the carboxyl-terminus whose physiological ligand is unknown. Both lectins have homologous counterparts in other types of proteins. Within the aggrecans the keratan sulfate domain may be variably present and also has a prominent repeat in some species. The chondroitin sulfate domain has three distinct regions which vary in their prominence in different species. The complex molecular structure of aggrecans is consistent with the concept of exon shuffling and aggrecans serve as suitable prototypes for comprehending the evolution of multi-domain proteins.

Molecular cloning and analysis of the protein modules of aggrecans

The large aggregating chondroitin sulfate proteoglycan of cartilage, aggrecan, has served as a prototype of proteoglycan structure. Molecular cloning has elucidated its primary structure and revealed both known and unknown domains. To date the complete structures of chicken, rat and human aggrecans have been deduced, while partial sequences have been reported for bovine aggrecan. A related proteoglycan, human versican, has also been cloned and sequenced. Both aggrecan and versican have two lectin domains, one at the amino-terminus which binds hyaluronic acid and one at the carboxyl-terminus whose physiological ligand is unknown. Both lectins have homologous counterparts in other types of proteins. Within the aggrecans the keratan sulfate domain may be variably present and also has a prominent repeat in some species. The chondroitin sulfate domain has three distinct regions which vary in their prominence in different species. The complex molecular structure of aggrecans is consistent with the concept of exon shuffling and aggrecans serve as suitable prototypes for comprehending the evolution of multi-domain proteins.

Cloning and sequence analysis of a partial cDNA for chicken cartilage proteoglycan core protein

A chicken embryo sternal cartilage cDNA library, created in the plasmid expression vector pUC9, was screened for sequences coding for immunologically detectable core protein of the large, major proteoglycan of cartilage. A 1229-base-pair cDNA clone was isolated that contained only one extended open reading frame, which had sequences coding for a polypeptide of 379 amino acid residues. These deduced sequences corresponded to those anticipated from current models of proteoglycan structure; a deduced sequence encompassing 21 amino acids was almost identical to a known sequence of bovine nasal cartilage proteoglycan. Significant homology was found between the deduced amino acid sequence of the proteoglycan and two regions of a chicken hepatic lectin. Immunoprecipitation of the products of cell-free translation yielded a component of about 340 kDa, and transfer blot hybridization of sternal cartilage RNA showed a single mRNA of about 8.1 kilobases. Hybridizable mRNA sequences were readily detectable by dot-blot analyses of the cytoplasm of cartilaginous tissues of the chicken embryo, whereas similar analyses of prechondrogenic limb mesenchymal cells did not demonstrate such hybridizable mRNA signals.

Immunological analysis of chick notochord and cartilage matrix development with antisera to cartilage matrix macromolecules

Transverse frozen sections from the postcephalic region of stage 9-16 chick embryos and from the wing bud region of stage 17-31 embryos were stained with antibodies to the major extracellular matrix components of cartilage. These probes included unfractionated A1 and A2 antisera to the major cartilage proteoglycan, affinity-purified purified antibodies to the proteoglycan core protein and to Type II collagen, and a monoclonal antibody to keratan sulfate. In embryos as early as stage 10, notochord stained specifically with the keratan sulfate monoclonal antibody. At this stage the notochord, as well as surrounding tissues, were negative to cartilage proteoglycan and collagen antibodies. Positive staining with the latter probes was coordinately acquired by notochord cells and their accompanying sheath around stage 15, while surrounding tissues remained negative. At this stage, the ventral region of the perispinal cord sheath exhibited light staining with the proteoglycan and keratan sulfate antibodies though failing to react to Type II collagen antibodies. Positive staining of notochord and ventral spinal cord persisted through later developmental stages. As revealed by immunofluorescence, definitive vertebral chondroblasts first emerged at approximately stage 23 and definitive limb chondroblasts at stage 25. The results are discussed in terms of the possible multiple roles of notochord in early embryogenesis.

The effects of trypsin treatment on proteoglycan biosynthesis by bovine articular cartilage

The effects of mild or severe trypsin treatment of bovine articular-cartilage slices in tissue culture were studied by monitoring the incorporation of [35S]sulphate into proteoglycans. Moderate trypsin treatment caused a subsequent marked inhibition of proteoglycan biosynthesis, which was reversible with time. Analysis on Sepharose CL-2B of the proteoglycan species synthesized showed that, directly after trypsin treatment, there was a 30% increase in the synthesis of the low-Mr proteoglycan (Kav. 0.71), and the total decrease in proteoglycan biosynthesis was reflected in a decrease in the synthesis of the high-Mr proteoglycan species (Kav. 0.31). The small proteoglycan was partially characterized and shown to be a true biosynthetic product and not a breakdown product. Trypsin treatment (20 micrograms/ml per 100 mg of tissue) of cartilage slices also resulted in an increase in the glycosaminoglycan chain size of the large proteoglycan, but not of the small proteoglycan.

In vitro effects of insulin on macromolecular events in newt limb regeneration blastemata

This work provides data demonstrating a stimulatory effect of insulin on macromolecular events occurring in cultured regeneration blastemata and demonstrates a synergistic interdependence between nerves and insulin in newt limb regeneration. The current experiments provide evidence for the following: (1) Insulin is paramount for expression of the mitogenic effect of nerves on cultures blastemata. (2) Insulin stimulates the incorporation of (3H)uridine into the acid-insoluble fraction of blastemal homogenates, but it does not alter the turnover rate of incorporated labeled uridine. (3) Insulin also stimulates the incorporation of 35SO4 and (3H)leucine into both chondroitinase-sensitive and chondroitinase-resistant blastemal proteoglycans. (4) Insulin increases the uptake of radiolabeled precursors by the blastemata, namely, (3H)leucine, (3H)uridine, 35SO4, (3H)alpha-aminoisobutyrate, and (3H)2-deoxy-D-glucose. The importance of insulin in the regulation of newt limb regeneration is discussed.

The structure of the linkage region of bovine nasal cartilage proteoglycan after beta-elimination and sulfite addition

A method of peptide "fingerprinting" has been developed allowing the separation of the majority of the tryptic peptides of purified proteoglycan subunit from bovine nasal cartilage. When this preparation was reacted with 0.2 M sodium sulfite at pH 11.5, beta-elimination of the substituted glycosaminoglycans and O-linked oligosaccharides and the quantitative addition of sulfite occurred in the serine and threonine residues of the linkage region. After elimination-addition studies with sodium [35S] sulfite, 6 radiolabelled linkage peptides were isolated by 2-dimensional "fingerprinting." Five of these peptides were derived from a section of the protein core in which each [35S] cysteic acid residue was separated by an average of 6-10 amino acid residues. Apart from [35S] cysteic acid, the predominant amino acids in the attached peptides were glycine and glutamic acid (or glutamine), suggesting that a combination of these amino acids in the nascent protein core may be important for the initiation of glycosaminoglycan chains during proteoglycan biosynthesis.

Identification of cyanogen bromide-fragments of the protein core of bovine nasal cartilage proteoglycan monomer

Cyanogen bromide treatment of bovine nasal cartilage proteoglycan monomer gave rise to three major fractions (CN-1 to CN-3), isolated by Sepharose CL-6B chromatography. The uronate-rich fraction in the void volume (CN-1) digested with chondroitinase ABC (C treatment) yielded a fragment (CN-1 C/6B) with a unique N-terminal sequence. The same fraction, when digested sequentially by chondroitinase ABC and trypsin (CT treatment), was resolved into two distinct fractions, CN-1 CT/6B-1 and CN-1 CT/6B-2. CN-1 CT/6B-1 consisted in a keratan sulfate-rich region, representing the N-terminal moiety of the CN-1 fraction; these data suggested, according to the model of the proteoglycan monomer structure described by Heinegard, D. and Axelsson, I. (1977) J. Biol. Chem. 252, 1971-1979, that its C-terminal moiety is localized at the end of the core bearing the chondroitin sulfate chains. CN-1 CT/6B-2 contained two fragments from the chondroitin sulfate-bearing region: one of them has been submitted to Edman degradation. The CN-2 fraction upon chondroitinase and trypsin treatments gave rise to a keratan-bearing region (CN-2 CT/6B-1) and a mannose-rich region (CN-2 CT/6B-2). After reduction and alkylation of CN-2, the N-terminal sequence of the isolated major fragment (CN-2 RA/6B-1) was determined. The CN-3 fraction revealed a pattern upon electrophoresis similar to that of the cyanogen bromide-treated hyaluronic acid-binding region.

Isolation and biochemical characterization of the tryptic fragments of bovine nasal-cartilage proteoglycan monomer of high buoyant density

Relatively homogeneous fractions of proteoglycan fragments were prepared from tryptic digests of the 4M-guanidinium chloride extract of bovine nasal cartilage. Glycosaminoglycan-containing fragments were separated from non-proteoglycan contaminants by ion-exchange chromatography and fractionated by equilibrium density-gradient centrifugation under dissociative conditions. The fractions of highest buoyant density were chromatographed on a column of Sepharose 4B, digested with chondroitinase ABC and chromatographed on a column of Sepharose 6B, yielding two distinct fractions: fraction B/6B-4 contained fragments from the chondroitin sulphate-bearing region of the proteoglycan monomer, and fraction B/6B-2 fragments from the keratan sulphate-rich region, most probably including a chondroitin sulphate-bearing monomer segment. By dansyl chloride analysis, fraction B/6B-2 had alanine and leucine as sole and fraction B/6B-4 had isoleucine and leucine as greatly predominant N-terminal amino acids, indicative of the relative homogeneity of these preparations of cartilage proteoglycan monomer fragments.

The influence of fluoride administration on the structure of proteoglycans in the developing rat incisor

1. 35S-labelled chondroitin 4-sulphate proteoglycan was isolated from the mineralized elements of the developing incisor teeth of Harvard rats receiving intraperitoneal administration of Na235SO4. 2. The chondroitin 4-sulphate proteoglycan underwent a decrease in molecular size in fluorotic teeth as judged by gel filtration on Sepharose 2B. 3. When examined by anion-exchange chromatography on DEAE cellulose-52, the proteoglycan from fluorotic teeth resolved into four peaks in comparison with the material from non-fluorotic teeth, which exhibited only a single major peak. 4. Both the single peak from non-fluoridated teeth and the four peaks from the fluorotic teeth were further resolved on cellulose acetate electrophoresis. 5. Isolated chondroitin 4-sulphate chains obtained from fluorotic teeth also were of smaller molecular size as judged by gel filtration on Sephadex G-150. 6. Some possible influences of fluoride on the metabolism of these connective-tissue components in the developing rat incisor are discussed.

Biochemical studies of the matrix of craniovertebral chordoma and a metastasis

Glycosaminoglycans of human chordoma and a metastasis were studied. The glycosaminoglycans were derived from the extracellular matrix and consisted of chondroitin 4- and 6-sulphate, keratan sulphate and hyaluronate. The ratio of chondroitin sulphate to keratan sulphate was much lower in the metastasis than in the primary. Proteoglycan extracted with 4M guanidinium chloride and purified by associative density-gradient centrifugation was assessed on Sepharose 2B before and after reduction and alkylation. The result of this experiment suggested that only a small proportion of the proteoglycans were aggregated.

Hyaluronic acid in the pulmonary secretions of patients with asthma

Hyaluronic acid was the only glycosaminoglycan found in the pulmonary secretions of patients with asthma. The compound had a hexuronate/hexosamine molar ratio of about 1:1. Glucosamine constituted over 98% of the hexosamines, the remaining being galactosamine. The compound moved as a single spot with the mobility of standard hyaluronic acid on cellulose acetate electrophoresis, and this spot disappeared after digestion with testicular hyaluronidase. Even after extensive proteolysis and purification, the compound was associated with small amounts of protein, the major amino acids of which were aspartic acid, threonine, serine, glutamic acid, glycine and valine.

Hyaluronic acid in the pulmonary secretions of patients with alveolar proteinosis

Hyaluronic acid was the only glycosaminoglycan found in the pulmonary secretions of patients with alveolar proteinosis. The compound gave a hexouronate/hexosamine molar ratio of about 1:1. Glucosamine constituted over 98% of the hexosamines, the remaining being galactosamine. It moved as a single spot with the mobility of standard hyaluronic acid on cellulose acetate electrophoresis, and this spot disappeared after digestion with hyaluronidase. It was associated with small amounts of proteins, the major amino acids of which are aspartic acid, glutamic acid, glycine, alanine, and leucine.

The simultaneous release by bone explants in culture and the parallel activation of procollagenase and of a latent neutral proteinase that degrades cartilage proteoglycans and denatured collagen

1. A latent neutral proteinase was found in culture media of mouse bone explants. Its accumulation during the cultures is closely parallel to that of procollagenase; both require the presence of heparin in the media. 2. Latent neutral proteinase was activated by several treatments of the media known to activate procollagenase, such as limited proteolysis by trypsin, chymotrypsin, plasmin or kallikrein, dialysis against 3 M-NaSCN at 4 degrees C and prolonged preincubation at 25 degrees C. Its activation often followed that of the procollagenase present in the same media. 3. Activation of neutral proteinase (as does that of procollagenase) by trypsin or plasmin involved two successive steps: the activation of a latent endogenous activator present in the media followed by the activation of neutral proteinase itself by that activator. 4. The proteinase degrades cartilage proteoglycans, denatured collagen (Azocoll) and casein at neutral pH; it is inhibited by EDTA, cysteine or serum. Collagenase is not inhibited by casein or Azocoll and is less resistant to heat or to trypsin than is the proteinase. Partial separation of the two enzymes was achieved by gel filtration of the media but not by fractional (NH4)2SO4 precipitation, by ion exchange or by affinity chromatography on Sepharose-collagen. These fractionations did not activate latent enzymes. 5. Trypsin activation decreases the molecular weight of both latent enzymes (60 000-70 000) by 20 000-30 000, as determined by gel filtration of media after removal of heparin. 6. The latency of both enzymes could be due either to a zymogen or to an enzyme-inhibitor complex. A thermostable inhibitor of both enzymes was found in some media. However, combinations of either enzyme with that inhibitor were not reactivated by trypsin, indicating that this inhibitor is unlikely to be the cause of the latency.

Degradation of cartilage proteoglycans by a neutral proteinase secreted by rabbit bone-marrow macrophages in culture

When cultivated together with pieces of cartilage biosynthetically labelled with 35S in their proteoglycans, rabbit macrophages, differentiated in vitro from bone-marrow cells, cause the release of soluble 35S-labelled material into the culture medium. This process is inhibited by killing the macrophages or by cycloheximide treatment, and is due to the secretion by the cells of a metal-dependent neutral proteinase capable of degrading cartilage proteoglycan subunits into fragments of high molecular weight. Enzyme activity is optimum at about pH7, and is inhibited by EDTA, o-phenanthroline, cysteine or serum, but not by di-isopropyl phosphorofluoridate nor by 4-hydroxymercuribenzoate. The effect of EDTA is partially reversed by Co2+ or Zn2+ ions. The enzyme is eluted from Sephadex G-150 columns as a single peak of material (apparent mol.wt. 17000) that contains also most of the proteolytic activity exerted by culture media on Azocoll (denatured collagen) or on casein. The possible role of this metalloproteinase in chronic inflammatory processes is discussed, particularly in connection with joint erosions in rheumatoid arthritis.

The degradation of cartilage proteoglycans by tissue proteinases. Proteoglycan structure and its susceptibility to proteolysis

1. Proteoglycan was obtained from bovine nasal cartilage by a procedure involving sequential extraction with a low-ionic-strength KCl solution, then a high-ionic-strength CaCl2 solution. Purification was by CsCl-density-gradient centrifugation. 2. The CaCl2- extracted proteoglycan was subjected to proteolytic degradation by papain, trypsin, cathepsin D, cathepsin B, lysosomal elastase or cathepsin G. Degradation was allowed to proceed until no further decrease in viscosity was detectable. 3. The size and chemical composition of the final degradation products varied with the different proteinases. Cathepsin D and cathepsin G produced glycosaminoglycan-peptides of largest average size, and papain produced the smallest product. 4. The KCl-extracted proteoglycan was intermediate in molecular size and composition between the CaCl2-extracted proteoglycan and the largest final degradation products, and may have been formed by limited proteolysis during the extraction procedure. 5. It is postulated that the glycosaminoglycan chains are arranged in groups along the proteoglycan core protein. Proteolytic cleavage between the groups may be common to the majority of proteinases, whereas clevage within the groups is dependent on the specificity of each individual proteinase.

Biosynthesis and release of glycoproteins by human skin fibroblasts in culture

1. Confluent human skin fibroblasts maintained in a chemically defined medium incorporate l-[1-(3)H]fucose in a linear manner with time into non-diffusible macromolecules for up to 48h. Chromatographic analysis demonstrated that virtually all the macromolecule-associated (3)H was present as [(3)H]fucose. 2. Equilibrium CsCl-density-gradient centrifugation established that [(3)H]fucose-labelled macromolecules released into the medium were predominantly glycoproteins. Confirmation of this finding was provided by molecular-size analyses of the [(3)H]fucose-labelled material before and after trypsin digestion. 3. The [(3)H]fucose-labelled glycoproteins released into fibroblast culture medium were analysed by gel-filtration chromatography and sodium dodecyl sulphate/polyacrylamide-gel electrophoresis. These techniques demonstrated that the major fucosylated glycoprotein had an apparent mol.wt. of 230000-250000; several minor labelled species were also detected. 4. Dual-labelling experiments with [(3)H]fucose and (14)C-labelled amino acids indicated that the major fucosylated glycoprotein was synthesized de novo by cultured fibroblasts. The non-collagenous nature of this glycoprotein was established by three independent methods. 5. Gel-filtration analysis before and after reduction with dithiothreitol showed that the major glycoprotein occurs as a disulphide-bonded dimer when analysed under denaturing conditions. Further experiments demonstrated that this glycoprotein was the predominant labelled species released into the medium when fibroblasts were incubated with [(35)S]cysteine. 6. The relationship between the major fucosylated glycoprotein and a glycoprotein, or group of glycoproteins, variously known as fibronectin, LETS protein, cell-surface protein etc., is discussed.

The role of histamine in wound healing I. The effect of high doses of histamine on collagen and glycosoaminoglycan content in wounds

The effect of high doses of histamine (Hi) on collagen and glycosoaminoglycan (GAG) content in skin wounds of rats was studied on days 1, 3, 5, 10 and 14 after wounding. Injection of high doses of Hi into the wounded area inhibited colagen production, collagen polymerization and GAG synthesis; levels of chondroitin sulphates (chondroitin-4,6-sulphate and dermatan sulphate) and hyaluronic acid were decreased.

Comparative studies of water sorption of hyaline cartilage

Vapor phase, water sorption isotherms were obtained for specimens of bovine, sturgeon and shark cartilage and for membranes composed of collagen and various proportions of cartilage proteoglycan. The data were interpreted in the light of an elementary model for swelling of gels which regards equilibrium swelling a resultant of a balance between contractile forces of an elastic matrix and expansive forces, principally osmotic in nature. Swelling ratios for bovine and sturgeon cartilage compared at the same water vapor pressure are nearly identical, whereas the swelling ratios for shark cartilage are elevated. These high values are due principally to a higher ratio of glycosaminoglycan to collagen but also reflect a higher salt and urea content and possibly also a different type of collagen fibril network.

Proteoglycans of dentine and predentine

A density gradient system is presented by which dentine and predentine are separated, leaving an intermediate fraction, which contains material from the mineralization front. From the fractions thus obtained the proteoglycans were extracted with 4 M guanidinium chloride and further purified in urea on a DEAE column. The glycosaminoglycans extracted from dentine appeared to be protein-bound, as judged from papain digestion experiments. The polydispersity of dentine proteoglycans seemed to depend, at least partly, upon the polydispersity of its glycosaminoglycans. The materials extracted from the three tissue fractions were ellted in a similar way from Sepharose 6 B, and the amino acid composition of the preparation was determined. The differing proteoglycan patterns of the three tissue fractions indicate a metabolism related to the mineralization front.

The chemical constitution of the proteoglycan of human intervertebral disc

Proteoglycan was prepared from three pools of normal human intervertebral discs by extraction with buffered 4M-guanidinium chloride followed by CsCl-density-gradient ultracentrifugation. Chromatography on agarose (Bio-Gel A-150m) and on DEAE-cellulose suggested a single polydisperse proteoglycan species. The intrinsic viscosities of three preparations were 166, 122 and 168 ml/g. After degradation with 0.5M-KOH containing 0.02M-NaBH4, the glycosaminoglycans were recovered quantitatively and their Ca2+ salts separated into a hexuronate-rich fraction (fraction 1), which was precipitated in 0-45% (v/v) ethanol, and a hexose-rich fraction (fraction2), which was precipitated in 45-70% (v/v) ethanol. Qualitative and quantitative analyses of the glycosaminoglycans revealed fraction 1 to be chondroitin sulphate, and fraction 2 to be keratan sulphate; the latter was contaminated with protein and possibly a small amount of another glycosaminoglycan. For both glycosaminoglycans, plots of log(mol.wt.) against weight fell close to a normal distribution. The mode for chondroitin sulphate was close to 20000; that for keratan sulphate, 10000. A threefold range of molecular weight included the central 16-84% [+/- 1 S.D. of log(mol.wt.)] of the weight of both fractions.

The electrophoretic heterogeneity of bovine nasal cartilage proteoglycans

1. Proteoglycans were extracted from bovine nasal cartilage with 2.0M-CaC2 or with 0.15M-KCl followed by 2.0M-CaC2.. Proteoglycan fractions were prepared from the extracts by density-gradient centrifugation in CsCl under 'associative' and 'dissociative' conditions. 2. The heterogeneity of the proteoglycan fractions was investigated by large-pore-gel electrophoresis. It was concluded that extracts made with 2.0M-CaCl2 or sequential 2.0M-CaCl2 contain two major species of proteoglycan 'subunit' of different hydrodynamic size, together with proteoglycan aggregates. Both 'subunits' have mobilities that are greater than those of proteoglycans obtained from pig articular cartilage McDevitt & Muir (1971) Anal. Biochem. 44, 612-622] and are therefore probably smaller in size than the latter. 3. Proteoglycan fractions isolated from cartilage extracted lith 0.15M-KCl separated into two main components on large-pore-gel electrophoresis with mobilities greater than those of proteoglycans extracted with 2.0M-CaCl2. Proteoglycans extracted at low ionic strength from bovine nasal cartilage are of similar hydrodynamic size to those extracted from pig articular cartilage under the same conditions [McDevitt & Muir (1971) Anal. Biochem. 44, 612-622]. 4. The role of endogenous proteolytic enzymes in producing proteoglycan heterogeneity, particularly in low-ionic-strength cartilage extracts is discussed. 5. Hyaluronic acid and 'link proteins' were present in the proteoglycan fraction separated from KCl extracts as well as in the fraction separated from CaCl2 extracts. Hyaluronic acid can only be identified in proteoglycan fractions by large-pore-gel electrophoresis after proteolysis and further purification of the fraction. 6. Collagen was extracted by both salt solutions and was tentatively identified as type II. Small amounts of collagen appear to be associated with the proteoglycan-aggregate fraction from the high-ionic-strength extract but not with the corresponding fraction from the KCl extract.

Cartilage proteoglycans. Structure and heterogeneity of the protein core and the effects of specific protein modifications on the binding to hyaluronate

Purified proteoglycans extracted from pig laryngeal cartilage in 0.15 M-NaCl and 4 M-guanidinium chloride were analysed and their amino acid compositions determined. Selective modification of amino acid residues on the protein core confirmed that binding to hyaluronate was a function of the protein core, and was dependent on disulphide bridges, intact arginine and tryptophan residues, and epsilon-amino groups of lysine. Fluorescence measurement suggested that tryptophan was not involved in direct subsite interactions with the hyaluronate. The polydispersity in size and heterogeneity in composition of the aggregating proteoglycan was compatible with a structure based on a protein core containing a globular hyaluronate-binding region and an extended region of variable length also containing a variable degree of substitution with chondroitin sulphate chains. The non-aggregated proteoglycan extracted preferentially in 0.15 M-NaCl, which was unable to bind to hyaluronate, contained less cysteine and tryptophan than did other aggregating proteoglycans and may be deficient in the hyaluronate-binding region. Its small average size and low protein and keratan sulphate contents suggest that it may be a fragment of the chondroitin sulphate-bearing region of aggregating proteoglycan produced by proteolytic cleavage of newly synthesized molecules before their secretion from the cell.

Content and synthesis of glycosaminoglycans in the developing lung

The function of lung is fundamentally linked to the connective tissue composition of the alveolar interstitium. The composition and synthesis of one class of interstitial connective tissue components, the glycosaminoglycans (GAG), was determined in lung parenchyma of rabbits at different stages of development. Parenchymal GAG content ranged between 0.2 and 0.4% (wt/wt) of dry weight, with highest concentration in adult lung. There were significant changes in types of GAG present at different ages. Fetal lungs contained a relatively high proportion of chondroitin 4-sulfate while the GAG in lung parenchyma of older animals was predominantly dermatan sulfate, heparan sulfate, and heparin. Methods were developed for the study of rates of synthesis of GAG by incorporation of [1-14C]glucosamine into lung explants. The rate of synthesis of total GAG per cell increased with development to a maximum in lung from weanling rabbits and fell to low rates of synthesis in mature rabbits. Fetal rabbit lung parenchyma synthesized mostly hyaluronic acid and heparan sulfate, while in weanling rabbit parenchyma hyaluronic acid and chondroitin 4/6-sulfate synthesis was greatest. In mature animals, the rates of synthesis of all types of GAG were relatively low but there was a relatively greater emphasis on synthesis of dermatan sulfate and heparin. These results may have significance in changes in lung function during development and in effects on other connective tissue components.