Isolation and partial characterization of high-buoyant-density proteoglycans synthesized in ovo by embryonic chick skeletal muscle and heart

Vascular cell proteoglycans: evidence for metabolic modulation

Proteoglycans accumulate in the intimal layer of blood vessels during the early stages of atherosclerosis and predispose the vessel wall to further complications of this disease. Arterial endothelial and smooth muscle cell cultures have been used to study the metabolism of vessel wall proteoglycans in an attempt to determine whether cellular events associated with the genesis of this disease, such as cellular proliferation, ageing, migration and interaction with components of the extracellular matrix, influence the metabolism of arterial proteoglycans. Proteoglycan analyses of vascular cells reveal that endothelial cells synthesize multiple species of heparan sulphate proteoglycan while smooth muscle cells synthesize little heparan sulphate proteoglycan but significant quantities of chondroitin and dermatan sulphate proteoglycan. Each family of proteoglycans synthesized by each cell type differs with regard to charge density, hydrodynamic size, glycosaminoglycan type and size, oligosaccharide content and ability to form high molecular weight aggregates. A monoclonal antibody has been generated against the chondroitin sulphate proteoglycan and used to immunolocalize this antigen to the interstitial matrix of normal and diseased blood vessels. Experiments are presented to indicate that proteoglycan metabolism is modulated when cultured arterial cells are stimulated to proliferate and migrate. Other factors shown to influence proteoglycan metabolism include the age of the cell and the nature of the substratum upon which the cells are grown. These culture systems provide useful models with which to study the factors involved in the regulation of proteoglycan synthesis by vascular cells.

Common structures of the core proteins of interstitial proteoglycans

Connective tissues, with few exceptions, contain easily distinguishable large and small proteoglycans with chondroitin sulphate or dermatan sulphate side-chains. One group consists of the large aggregating proteoglycans that have the capacity to interact specifically with hyaluronate, thereby forming very large aggregates. These proteoglycans can be divided into two families which can be separated by electrophoresis. Preliminary results indicate that one of these may be derived from the other by processing in the extracellular matrix. Although most prominent in cartilage, similar proteoglycans are present in many types of tissue, such as aorta, sclera and tendon. Another population are the large non-aggregating proteoglycans, identified in cartilage. These proteoglycans show structural features partially different from any of the others. They may represent a distinct population of molecules present in many connective tissues. Many tissues contain major populations of small, non-aggregating proteoglycans. These can be divided into two major groups, differing in the composition of their core proteins, while having similar types of side-chain constituents. One group is represented by proteoglycans from nasal cartilage and aorta, while the other is represented by proteoglycans from tendon, bone, sclera and cornea.

Reduced Glycosaminoglycan Sulfation Diminishes the Agrin Signal Transduction Pathway

Proteoglycans consist of a protein core complexed to glycosaminoglycan (GAG) side chains, are abundant in skeletal muscle cell membranes and basal lamina, and have important functions in neuromuscular synapse development. Treatment with chlorate results in the undersulfation of heparan sulfate and chondroitin sulfate GAGs in cell culture. In addition, chlorate treatment decreases the frequency of spontaneous acetylcholine receptor (AChR) clustering in skeletal muscle cell culture. AChRs and other molecules cluster to form the postsynaptic component of neuromuscular synapses. Chlorate treatment is shown here to decrease the frequency of agrin-induced AChR clustering and agrin-induced tyrosine phosphorylation of the AChR beta-subunit. These data suggest that reduced GAG chain sulfation decreases the frequency of AChR clustering by diminishing the agrin signal transduction pathway.

The structure and functional significance of variations in the connective tissue within muscle

The amount of intramuscular connective tissue (IMCT) and its morphological distribution is highly variable between muscles of differing function. The functional roles of this component of muscle have been poorly understood, but a picture is gradually emerging of the central role this component has in growth, transmission of mechanical signals to muscle cells and co-ordination of forces between fibres within a muscle. The aim of this review is to highlight recent advances that begin to show the functional significance of some of the variability in IMCT. IMCT has a number of clearly defined roles. It patterns muscle development and innervation, and mechanically integrates the tissue. In developing muscles, proliferation and growth of muscle cells is stimulated and guided by cell-matrix interactions. Recent work has shown that the topography of collagen fibres is an important signal. The timing and rates of expression of connective tissue proteins also show differences between muscles. Discussion of mechanical roles for IMCT has traditionally been limited to the passive elastic response of muscle. However, it is now clear that IMCT provides a matrix to integrate the contractile function of the whole tissue. Mechanical forces are co-ordinated and passed between adjacent muscle cells via cell-matrix interactions and the endomysial connective tissue that links the cells together. An emerging concept is that division of a muscle into fascicles by the perimysial connective tissue is related to the need to accommodate shear strains as muscles change shape during contraction and extension.

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.

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.

Identification of decorin and chondroitin sulfate proteoglycans in turkey skeletal muscle

Turkey pectoral muscles were examined at 15 through 25 d of embryonic age in order to delineate the developmental pattern of proteoglycan expression during skeletal muscle development. Glycosaminoglycan concentration, decorin, and muscle chondroitin sulfate proteoglycan (M-CSPG) levels were measured at each developmental age. Glycosaminoglycan levels rose during the developmental period studied, whereas decorin and M-CSPG levels were initially high at Day 15 and then decreased. The results from this study demonstrate the presence of both decorin and M-CSPG during turkey skeletal muscle development.

Differential heparin inhibition of skeletal muscle alpha-dystroglycan binding to laminins

The laminin binding properties of alpha-dystroglycan purified from rabbit skeletal muscle membranes were examined. In a solid phase microtiter assay, 125I-laminin (laminin-1) bound to purified alpha-dystroglycan in a specific and saturable manner with a half-maximal concentration of 8 nM. The binding of 125I- alpha-dystroglycan to native laminin and merosin (a mixture of laminin-2 and -4) was also compared using the solid phase assay. The absolute binding of 125I- alpha-dystroglycan to laminin (6955 +/- 250 cpm/well) was similar to that measured for merosin (7440 +/- 970 cpm/well). However, inclusion of 1 mg/ml heparin in the incubation medium inhibited 125I-alpha-dystroglycan binding to laminin by 84 +/- 4.3% but inhibited 125I-alpha-dystroglycan binding to merosin by only 17 +/- 5.2%. Similar results were obtained with heparan sulfate, while de-N-sulfated heparin, hyaluronic acid, and chondroitin sulfate had no differential effect. These results were confirmed by iodinated laminin and merosin overlay of electrophoretically separated and blotted dystrophin-glycoprotein complex. In contrast to the results obtained with skeletal muscle alpha-dystroglycan, both laminin and merosin binding to purified brain alpha-dystroglycan was significantly inhibited by heparin. Our data support the possibility that one or more heparan sulfate proteoglycans may specifically modulate the interaction of alpha-dystroglycan with different extracellular matrix proteins in skeletal muscle.

The effects of beta-D-xyloside on the synthesis of proteoglycans by skeletal muscle: lack of effect on decorin and differential polymerization of core protein-bound and xyloside-linked chondroitin sulfate

Developing skeletal muscle cells, as both myoblasts and myotubules, synthesize a distinctive large chondroitin sulfate proteoglycan. To probe the role of this proteoglycan in myogenesis, chick embryonic muscle cells in culture were treated with beta-D-xyloside, a compound which interferes with proteoglycan synthesis by acting as an artificial acceptor for glycosaminoglycan synthesis and thereby competing with the proteoglycan core protein. Analysis of the proteoglycans indicates that with increasing concentrations of beta-D-xyloside, synthesis of the chondroitin sulfate proteoglycan is inhibited, with concomitant massive synthesis of xyloside-linked chondroitin sulfate glycosaminoglycans. Xyloside does not appear to inhibit glycosaminoglycan attachment onto the small heparan sulfate and dermatan sulfate proteoglycans which are synthesized in the muscle cultures, even though, because of the mechanism of action of beta-xyloside, these proteoglycans should be affected. At submaximal concentrations of beta-xyloside, there is synthesis of both large chondroitin sulfate proteoglycans and xyloside-linked chondroitin sulfate. The xyloside-linked chondroitin sulfate chains have the same sulfation pattern as the core protein-bound skeletal muscle chondroitin sulfate (90% 6-sulfated isomer), but are much smaller (24,000 vs. 65,000 in molecular weight). The discrepancy in size but identify of sulfation indicates that, although sulfation takes place normally on either the core protein or the xyloside acceptor, termination of glycosylation occurs earlier for xyloside-initiated chondroitin sulfate. In spite of these dramatic effects on chondroitin sulfate proteoglycan synthesis, beta-xyloside elicits no observable effects on in vitro myogenesis. This suggests that the function served by the large chondroitin sulfate proteoglycan is not required in the more simplified environment of the muscle cultures.

Glycosaminoglycans and chondroitin/dermatan sulfate proteoglycans in the myocardium of a non-human primate

Lyophilized mid-wall left ventricular myocardial tissues of the long-tailed non-human primate, Macaca fascicularis, were examined for the presence of glycosaminoglycans and chondroitin/dermatan sulfate proteoglycans. Mean uronic acid concentration in all samples was 0.97 +/- 0.27 micrograms per mg dry weight myocardium. The distribution of the glycosaminoglycans in the myocardium, determined by cellulose acetate strip electrophoresis was 62 +/- 4% heparan sulfate, 20 +/- 6% hyaluronan, and 16 +/- 5% chondroitin/dermatan sulfate. The analysis of chondroitin/dermatan sulfate proteoglycans, done directly on the extracts of lyophilized myocardium using agarose-acrylamide gel electrophoresis and Western blotting with monoclonal antibodies to various carbohydrate epitopes and with polyclonal antibodies to the protein core, showed the presence of biglycan and decorin. That these two and no other chondroitin/dermatan sulfates were present was established by core protein analysis using SDS PAGE and Western blotting. Quantification of chondroitin/dermatan sulfate proteoglycans uncovered high individual specific variability of the chondroitin/dermatan sulfate epitopes, but only moderate variability of biglycan and decorin core proteins. The variability of the chondroitin/dermatan sulfate epitopes is most likely related to individual specific differences in chain number, iduronate content and sulfation patterns of biglycan and decorin.

Decorin, a chondroitin/dermatan sulfate proteoglycan is under neural control in rat skeletal muscle

Proteoglycans (PGs) are abundant components of the extracellular matrices (ECM) of skeletal muscle. We have previously found that the synthesis of skeletal muscle PGs present at the ECM increase after denervation. The experiments reported here were undertaken to identify which PG(s) increase after denervation of rat leg muscles. Incorporation of radioactive sulfate demonstrated the presence of a chondroitin/dermatan sulfate PG of 70-90 kDa in the skeletal muscle ECM, which increased after denervation. The PG has a core protein of 39-45 kDa after treatment with chondroitinase ABC. Antibodies against rat decorin, a chondroitin/dermatan sulfate PG synthesized by various cell types, specifically immunoprecipitated this PG from a mixture of PGs. Immunocytolocalization of this PG indicated that the chondroitin/dermatan sulfate PG accumulates at the perimysium of skeletal muscle after denervation. Finally, Northern blot analysis indicated an increase of muscle transcripts for decorin after denervation. The data reported here suggest that a chondroitin/dermatan sulfate PG present at the skeletal muscle ECM, very similar if not identical to decorin, increases after denervation.

Isolation of proteoglycans synthesized by rat heart: evidence for the presence of several distinct forms

1. The proteoglycans (Ps) synthesized by auricle and ventricle from adult rat heart were studied. 2. Auricle tissue incorporated over two times radioactive sulfate compared to ventricle tissue and the Ps were mainly found in the detergent insoluble fraction. 3. The Ps from both tissues were isolated by ion-exchange chromatography on DEAE-Sephacel, followed by gel filtration on Sepharose CL-6B and SDS-PAGE electrophoresis. 4. Enzymatic and chemical degradation of these Ps suggest that at least three and probably four different species of Ps can be observed in heart tissue. 4. A high molecular weight chondroitin sulfate-P, a high molecular weight heparan sulfate-P, a chondroitin/dermatan sulfate-P of 240-200 kDa and a dermatan sulfate of 115 kDa. 5. This latter P was specifically immunoprecipitated using rat decorin antiserum.

Glycosaminoglycans in thyroid-associated ophthalmopathy

Glycosaminoglycan (GAG) accumulation in the retrobulbar space of patients with thyroid-associated ophthalmopathy (TAO) has been documented in a number of immunohistochemical studies. In order to gain further insight into possible immunopathogenic mechanisms, the influence of humoral immunity on retrobulbar fibroblasts (RF) as GAG producing cells as well as on GAGs themselves was investigated. The effect of lymphocytes on hyaluronic acid (HA) synthesis of RF as well as in turn the influence of RF on lymphocytes were evaluated. In search of methods which would facilitate management of patients with TAO and allow assessment of disease activity, GAGs were determined in both urine and plasma. Immunoglobulin G (IgG) of patients with TAO were found to markedly stimulate the 3H-GAG secretion of RF. Patients with TAO exhibited significantly greater antibody values directed against HA than controls. Preliminary results concerning the influence of lymphocytes on RF indicate a tendency for patients' lymphocytes to increase the synthesis of HA. Furthermore, these lymphocytes in turn were stimulated more by irradiated autologous RF than by irradiated heterologous RF. Urine and plasma GAG determination proved to be suitable for the routine assessment of disease activity and outcome of therapy. In conclusion, GAGs seem to play an important role in the pathogenesis of the disease and their measurement may provide aid to the endocrinological evaluation of patients with TAO.

Generation of a monoclonal antibody against avian small dermatan sulfate proteoglycan: immunolocalization and tissue distribution of PG-II (decorin) in embryonic tissues

Chick embryonic skeletal muscle synthesizes three major types of proteoglycans: large chondroitin sulfate proteoglycans, small dermatan sulfate proteoglycans and small heparan sulfate proteoglycans. A monoclonal antibody has been raised which recognizes the small dermatan sulfate proteoglycan. Immunoblot analysis of a partially purified preparation of skeletal muscle proteoglycans indicates that the antibody reacts with a molecule which migrates with an estimated Mr of 100,000. Prior treatment of the proteoglycans with chondroitinase results in immunostaining of a species of estimated Mr 45,000. These values for the intact proteoglycan and its core protein suggest that the antibody is directed against a proteoglycan of the PG-II or decorin class. Immunohistochemistry indicates a widespread distribution of the proteoglycan, which is localized in connective tissue septa of skeletal and cardiac muscle, dermis, tendon, bone, perichondrium and cornea. Immunoblot analysis of the proteoglycan core proteins from these tissues demonstrates that the antibody recognizes the same 45,000-dalton band in each tissue. The widespread tissue distribution is also consistent with the antibody being directed against an epitope of PG-II. Neither the glycosaminoglycan chains nor N-linked oligosaccharides are required for reactivity and the antibody cross-reacts with other avian material, but not mammalian. This antibody, which has been designated CB-1, reveals developmental stage-specific changes in the deposition of PG-II in embryonic limb bud and skeletal muscle.

The dynamics of compartmentalization of embryonic muscle by extracellular matrix molecules

In order to delineate the role of proteoglycans in muscle development, the immunohistological localization of glycosaminoglycans and proteoglycan core proteins was studied in embryonic chick leg at Hamburger-Hamilton stages (St.) 36, 39, 43, and 46, and at 2 weeks posthatching. A specific anatomical landmark was chosen (the junction between the pars pelvica and the pars accessoria of the flexor cruris lateralis muscle) in order to ensure the study of anatomically equivalent sites. Frozen cross sections were immunostained with monoclonal antibodies to chondroitin-4-sulfate, chondroitin-6-sulfate, dermatan sulfate, and keratan sulfate glycosaminoglycans; to the core proteins of muscle/mesenchymal chondroitin sulfate proteoglycan, dermatan sulfate proteoglycan, and basement membrane heparan sulfate proteoglycan; and to laminin and tenascin. Extracellular matrix zones corresponding to the endomysium, perimysium, epimysium, basement membrane, and myotendinous junction each show characteristic immunostaining patterns from St. 36 to St. 46 and have unique matrix compositions by St. 46. In some cases, there is a sequential or coordinate expression of epitopes, first in the epimysium, then the perimysium, and last in the endomysium. Dermatan sulfate proteoglycan is detected in the epimysium at St. 36, in the perimysium at St. 39 (there is no perimysium structure at St. 36), and is not detected in the endomysium until St. 43. A putative mesenchymal proteoglycan core protein (reactive to the monoclonal antibody MY-174) is detected at St. 39 in both epimysium and perimysium, but is not detected in the endomysium until St. 43. Keratan sulfate antibody immunostains epimysium at St. 39 and perimysium at St. 46, but is never detected in the endomysium. Some epitopes are expressed independently in each of the extracellular matrix zones: antibody to tenascin stains only a subset of the epimysium, at the myotendinous junction; and heparan sulfate proteoglycan and laminin are detected only in the endomysium. Between St. 36 and St. 39, the muscle/MY-174-reactive proteoglycan core protein staining decreases in intensity in the endomysium and becomes positive in the epimysium and perimysium. An inverse relationship is found between (1) the disappearance of muscle/MY-174-reactive proteoglycan core protein staining at the surface of myotubes from St. 36 to St. 39 and (2) the infiltration of laminin and heparan sulfate proteoglycan staining encompassing groups of myotubes (St. 36) to circumferential staining of all myotubes (St. 39).(ABSTRACT TRUNCATED AT 400 WORDS)

Proteoglycan synthesis by clonal skeletal muscle cells during in vitro myogenesis: differences detected in the types and patterns from primary cultures

Proteoglycan synthesis by two clonal murine skeletal muscle cell lines, G8-1 and C2, was examined. Cultures of skeletal muscle cells at both the myoblast and myotube stages were radiolabeled using [35S]sulfate as a precursor. The proteoglycans of the cell layer and medium were separately extracted and isolated by ion exchange chromatography on DEAE-Sephacel followed by gel filtration chromatography on Sepharose CL-2B. The cell layer proteoglycans eluted from Sepharose CL-20 as a single peak with a Kav of 0.66 and contained glycosaminoglycan chains with an average molecular weight of 20,000. The glycosaminoglycan chains were composed of nearly equal mixtures of chondroitin sulfate and heparan sulfate with the exception that C2 myoblast cultures contained larger amounts of heparan sulfate. Of interest, this line differentiates more rapidly in our laboratory than G8-1. The medium proteoglycans also eluted from Sepharose CL-2B as a single peak with a Kav of 0.66 but contained glycosaminoglycan chains with an average molecular weight of 32,000. Based upon enzymatic and chemical analysis, the medium glycosaminoglycan chains were composed of a mixture of chondroitin sulfate (71-80%) and heparin sulfate (19-22%). Following chondroitinase ABC digestion, the predominant disaccharide released from all glycosaminoglycan fractions was chondroitin-4-sulfate. When the extracted cell layer proteoglycans were chromatographed on Sepharose CL-28 in the absence of detergent, a small but consistent proportion (14-18%) eluted in the void volume, suggesting the association of at least a portion of this proteoglycan with cellular lipid. These differences distinguish proteoglycan metabolism in fusing clonal lines from primary muscle cell cultures suggesting their utility in evaluating the contribution of these macromolecules in myogenesis.

Isolation and characterization of rat skeletal muscle proteoglycan decorin and comparison with the human fibroblast decorin

1. The extracellular matrix (ECM) of rat skeletal muscle contains several proteoglycans (PGs). The more abundant correspond to a chondroitin/dermatan sulfate PG or decorin. 2. Decorin isolated from rat skeletal muscle ECM has a smaller molecular size than human fibroblast decorin. 3. The difference in size is mainly due to the glycosaminoglycan (GAG) chain length rather than the core protein size. 4. Peptide analysis of trypsin treated decorins shows at least three peptides with the same electrophoretic mobility.

Change in synthesis of sulfated glycoconjugates during muscle development, maturation and aging in embryonic to senescent CBF-1 mouse

Previous biochemical and morphological studies have demonstrated a change in the synthetic pattern of sulfated proteoglycans during skeletal musculogenesis in the embryonic chick. These studies revealed that a transition occurs in both composition and deposition of sulfated glycoconjugates that parallels the developmental state of the tissue. The current study was undertaken to ascertain whether this transition in the embryonic chick is a conserved developmental process during musculogenesis in the mouse. Leg musculature from embryonic, newborn, juvenile, adolescent, young adult, mature adult and senescent mice, radiolabeled in vivo with [35S]sulfate, was analyzed for relative size and composition of newly synthesized sulfated macromolecules. The data reveal a transition in the synthesis of sulfated proteoglycans and glycoproteins that parallels the myogenic differentiative state of the mouse leg muscle. Embryonic mouse leg musculature synthesizes relatively large proteoglycans consisting of large chondroitin sulfate glycosaminoglycan chains. Subsequently, these major newly synthesized proteoglycans are replaced synthetically by smaller molecules composed of mixtures of dermatan sulfate, chondroitin sulfate and heparan sulfate glycosaminoglycans (newborn through 2 weeks); dermatan sulfate, heparan sulfate and chondroitin sulfate glycosaminoglycans (13 months) and heparan sulfate and dermatan sulfate glycosaminoglycans (25-26 months). The sulfated glycoproteins demonstrate a reciprocal synthetic pattern. Early in development sulfated glycoproteins form a small proportion of the newly synthesized sulfated material. With increasing developmental and maturational age, the proportion of sulfated glycoproteins increases. This continues until they become the predominant sulfated moieties synthesized by senescent mouse muscle. The results from this study thus extend observations initially made in chick to muscle development in the mouse and, therefore, suggest that the transition in synthesis of sulfated glycoconjugates is a conserved developmental process during musculogenesis.

Immunohistochemical localization of proteoglycans in interstitial elements of human pancreas and biliary system

The immunohistochemical localization of large proteoglycan and small proteoglycan was observed, using antibodies 2B1 and 6B6 (Sobue et al., 1988, 1989a), in fetal and adult pancreas and biliary system as well as in tumour tissues, obtained from 11 autopsies and 74 biopsies. The distribution of chondroitin 4- and 6-sulphate side chains, type I and IV collagen and elastin were also studied. In adult pancreas and all the biliary tracts examined, periductal fibrous tissues consisted mainly of dermatan sulphate small proteoglycan with networks of fibrous elements, which were composed of large proteoglycan, elastin, type I collagen and type IV collagen. In the interstitial components of cystadenoma of pancreas and biliary duct carcinoma, similar small proteoglycan-rich components were relatively abundant, although large proteoglycan was present in much larger amounts than that in non-neoplastic adult tissues. In some cholangiomas, the extra- and intracellular hyaline globules formed by the carcinoma cells were found to contain chondroitin sulphate large proteoglycan, laminin and fibronectin. The distribution of proteoglycans was observed to be different in the arterial walls of the interlobular tissues of the adult and the fetal pancreas. The biological significance of large and small proteoglycans in the interstitial connective tissues was discussed.

Glycosaminoglycan variants in the C2 muscle cell line

Using a replica technique, we have isolated and characterized five genetic variants of the C2 mouse muscle cell line that are defective in incorporation of radiolabeled sulfate into glycosaminoglycans (GAGs). The variants incorporate free sulfate into GAGs at 5-20% of wild-type levels. None of the variants is defective in sulfate transport across the cell membrane, and in no case could the deficit in incorporation of sulfate be reversed by addition of an artificial initiator of GAG biosynthesis, p-nitrophenyl beta-D-xyloside. Analysis of the incorporation of [3H]glucosamine into GAGs by the variants revealed three different patterns: one variant incorporated [3H]glucosamine at the wild-type level; one, S27, at a severely reduced level; and three at intermediate levels. Four of the five variants showed marked deficits in their ability to differentiate and fuse. The remaining variant, S27, formed multinucleated myotubes and expressed acetylcholine receptor with a normal time course. Differentiation of the first four variants could not be restored by addition of exogenous GAGs or extracellular matrix. Because of the important roles that GAGs and proteoglycans are thought to play in the differentiation of muscle, these genetic variants should serve as useful tools in functional analyses of these molecules.

Production and immunohistochemical characterization of a monoclonal antibody raised to proteoglycan purified from a human yolk sac tumour

A large proteoglycan with chondroitin sulphate and dermatan sulphate side chains has been isolated and purified from a yolk sac tumour of the left ovary from a 23-year-old female. A monoclonal antibody, designated 2B1, was produced which reacted specifically with the intact molecule of the large proteoglycan and the chondroitinase ABC-treated core molecule. The localization of substances showing cross-reactivity to this antibody was studied in a variety of human tissues by means of indirect immunohistochemistry. The interstitial elements of nearly all tissues of a 5-month-old foetus were intensely reactive with the antibody, but in adult tissues structures that gave positive reactions were limited; only the perivascular and perimuscular fibrous elements were reactive, except for the aorta, which reacted extensively. In contrast, the interstitial elements of the carcinoma tissues tested were intensely reactive. Thus antibody 2B1 can be regarded as a useful tool for studies on the immunohistochemical localization of large proteoglycan in various human tissues.

Histochemical analysis of newly synthesized and accumulated sulfated glycosaminoglycans during musculogenesis in the embryonic chick leg

The leg musculature from 11, 14, and 17 day chick embryos was analyzed histochemically to investigate the temporal and spatial distribution of various types of sulfated glycosaminoglycans present during skeletal muscle development. Types of glycans were identified by selective degradation with specific glycosidases and nitrous acid coupled with Alcian blue staining procedures for sulfated polyanions and with [35S]sulfate autoradiography. On day 11, radiolabeled chondroitin sulfate glycosaminoglycans are localized extracellularly in both the myogenic and connective tissue cell populations. By day 17, incorporation of [35S]sulfate into chondroitin sulfate is substantially reduced, although Alcian blue-stained chondroitin sulfate molecules are still detectable. With increasing age and developmental state of the tissues, radiolabeled and stained dermatan sulfate and heparan sulfate progressively increase in relative quantity compared to chondroitin sulfate both in muscle and in associated connective tissue elements. These changes in glycosaminoglycans correlate well with similar changes previously determined biochemically and further document the alterations in extracellular matrix components during embryonic skeletal myogenesis.

Altered cartilage proteoglycans synthesized by chick limb bud chondrocytes cultured in serum-free defined medium

Chick high-density culture chondrocytes synthesize cartilage-specific proteoglycans with much structural similarity to the proteoglycans made by cartilage in vivo. Such cultures can be maintained in a defined medium formulated in this laboratory in which chondrogenesis occurs without the addition of serum. The proteoglycans synthesized by the chondrocytes in the presence of defined medium are of a cartilage-specific structure but differ in some aspects from the proteoglycans made in serum-containing medium. While their buoyant density, ability to aggregate with hyaluronic acid, and keratan sulfate chain size are unchanged, the proteoglycans synthesized in defined medium have altered chondroitin sulfate chains. This chondroitin sulfate is of significantly larger size and has a different sulfation pattern relative to that produced in serum-containing medium. The larger size of the chondroitin sulfate results in a larger monomer size of the defined medium proteoglycans. These differences have implications about the regulation of the structure of chondroitin sulfate proteoglycans.

Structural characterization of chick embryonic skeletal muscle chondroitin sulfate proteoglycan

Embryonic chick skeletal muscle has been shown to synthesize a distinct proteoglycan of large size with relatively large, highly 6-sulfated chondroitin sulfate glycosaminoglycans. Further analysis of these proteoglycans indicates that tryptic digestion gives rise to fragments with an average of two chondroitin sulfate chains per peptide. The skeletal muscle chondroitin sulfate proteoglycan also contains oligosaccharides whose characteristics suggest the presence of both O-linked and N-linked oligosaccharides. These characteristics include the average hydrodynamic size of the oligosaccharides as well as their localization. Approximately 10% of the putative O-linked oligosaccharides reside on the same tryptic fragments which contain the chondroitin sulfate chains, while the presumptive N-linked oligosaccharides appear to be present at sites distant from the chondroitin sulfate. Further support for this identification comes from radioisotopic labeling with [3H]mannose, which is incorporated exclusively into the putative N-linked oligosaccharides. Some of the O-linked oligosaccharides which are not in close apposition to the chondroitin sulfate seem to occur in clusters. The skeletal muscle chondroitin sulfate proteoglycan has the ability to interact in a link protein-stabilized fashion with hyaluronic acid. This ability as well as the estimated number of chondroitin sulfate chains per cluster and the estimated number of oligosaccharides per chondroitin sulfate chain have implications about the structure of the core protein of the skeletal muscle proteoglycan. The information presented is used to construct a model of these molecules; with this detailed model, attention can now be directed at other aspects of the skeletal muscle chondroitin sulfate proteoglycan, such as its role in myogenesis.

A search for the osteogenic factor in dentin. Rat incisor dentin contains a factor stimulating rat muscle cells in vitro to incorporate sulfate into an altered proteoglycan

Demineralized dentin matrix has the capacity to induce bone formation via a chondrogenic pathway when implanted into muscle, in a fashion entirely analogous to bone matrix implants. In this work we have attempted to isolate, from rat incisor dentin, the matrix factor responsible for initiating osteogenesis. Rat incisor dentin was demineralized with EDTA plus 4.0 M guanidine. HCl. The proteins in the extracts were collected and, after a CaCl2 precipitation step, fractionated on Sephacryl S-200 in 6.0 M guanidine. HCl. The primary assay for activity was the incorporation of 35S-sulfate into proteoglycan in cultures of the fibroblast-like outgrowth cells from explants of neonatal rat muscle. Two Sephacryl S-200 fractions showed enhanced sulfate incorporating activity, but only one showed enhanced incorporation without a concomitant increase in cell number. In the presence of this fraction, the cell cultures produced a larger amount of a new small proteoglycan, as compared to controls, and a significant amount of a much larger proteoglycan. The active fraction had proteins in the Mr range from 8,000 to 15,000 as the major components. These data suggest that the fraction identified may contain the factors responsible for initiating the osteogenic response to dentin matrix upon its implantation in muscle in vivo.

Proteoglycan synthesis in vitamin D-deficient cartilage: recovery from vitamin D deficiency

Vitamin D appears to be required for mineralization of skeletal elements. There is also evidence that cartilage proteoglycans may be involved in the regulation of mineralization. Previous studies have shown an alteration in the structure of the proteoglycans of the epiphyseal growth cartilage as a result of the decrease in serum calcium related to deficiency of dietary vitamin D. Vitamin D deficiency also induces a thickening of the epiphyseal growth plate presumably because of the inhibition of maturation of the growth plate chondrocytes. In order to compare the effect on proteoglycan structure with that on growth plate morphology, the proteoglycans of healing epiphyseal cartilage were characterized. The results indicate that, consistent with previous data, in vitamin D-deficient hatching chicks, the proteoglycans of the growth cartilage, but not of the articular cartilage, are smaller in monomer size with slightly smaller chondroitin sulfate chains whose sulfation pattern is unaltered. Sternal cartilage proteoglycans are unaffected. During recovery from vitamin D deficiency, the proteoglycans isolated from the growth cartilage are still not completely normal one day after supplementation with vitamin D, but are indistinguishable from normal by four days. In addition, the results conflict with those of a previous study in which only growth cartilage of hatchling chicks, not sternal or articular cartilage, was reported to synthesize large proteoglycans. Instead, all of these cartilages in the normal chicken have been found in this study to produce large proteoglycans of a size typical for mammalian cartilage and embryonic chick cartilage.

Initial characterization of small proteoglycans synthesized by embryonic chick leg muscle-associated connective tissues

Muscle development in the embryonic chick involves the interfacing of two different cell types: myogenic cells forming the contractile network and connective tissue cells which wrap this network into discrete morphologies. Previous reports from this laboratory detailed the characterization of large extracellular matrix proteoglycans synthesized by skeletal muscle. This report describes the initial characterization of small muscle-associated connective tissue proteoglycans synthesized in embryonic chick leg in ovo and by embryonic leg muscle-associated secondary fibroblasts in vitro by CsCl equilibrium density gradient centrifugation. Analysis of the D1 gradient fractions from the in ovo and in vitro material revealed that the proteoglycans were of relatively small size. These molecules eluted from Sepharose CL-2B through a Kav range of 0.6-0.8. Analysis of alkaline borohydride-released glycosaminoglycan chains by Sepharose CL-6B, Sephadex G-25, and thin layer chromatography demonstrated a mixture of three proteoglycan families composed of chondroitin sulfate, dermatan sulfate, and heparan sulfate glycosaminoglycans.

Proteoglycan synthesis by primary chick skeletal muscle during in vitro myogenesis

The proteoglycans synthesized by primary chick skeletal muscle during in vitro myogenesis were compared with those of muscle-specific fibroblasts. Cultures of skeletal muscle cells and muscle fibroblasts were separately labeled using [35S] sulfate as a precursor. The proteoglycans of the cell layer and medium were separately extracted and isolated by ion-exchange chromatography on DEAE-Sephacel followed by gel filtration chromatography on Sepharose CL-2B. Two cell layer-associated proteoglycans synthesized both by skeletal muscle cells and muscle fibroblasts were identified. The first, a high molecular weight proteoglycan, eluted from Sepharose CL-2B with a Kav of 0.07 and contained exclusively chondroitin sulfate chains with an average molecular weight greater than 50,000. The second, a relatively smaller proteoglycan, eluted from Sepharose CL-2B with a Kav of 0.61 and contained primarily heparan sulfate chains with an average molecular weight of 16,000. Two labeled proteoglycans were also found in the medium of both skeletal muscle and muscle fibroblasts. A high molecular weight proteoglycan was found with virtually identical properties to that of the high molecular weight chondroitin sulfate proteoglycan of the cell layer. A second, smaller proteoglycan had a similar monomer size (Kav of 0.63) to the cell layer heparan sulfate proteoglycan, but differed from it in that this molecule contained primarily chondroitin sulfate chains with an average molecular weight of 32,000. Studies on the distribution of these proteoglycans in muscle cells during in vitro myogenesis demonstrated that a parallel increase in the relative amounts of the smaller proteoglycans occurred in both the cell layer and medium compared to the large chondroitin sulfate proteoglycan in each compartment. In contrast, muscle-derived fibroblasts displayed a constant ratio of the small proteoglycans of the cell layer and medium fractions, compared to the larger chondroitin sulfate proteoglycan of the respective fraction as a function of cell density. Our results support the concept that proteoglycan synthesis is under developmental regulation during skeletal myogenesis.

Isolation of the heparan sulfate proteoglycans from the extracellular matrix of rat skeletal muscle

We have previously shown that asymmetric collagen-tailed acetylcholinesterase (AChE) is anchored to the extracellular matrix (ECM) by heparan sulfate proteoglycans (HSPGs). Here we present our studies on the characterization of such PGs from the ECM of rat skeletal muscles. After radiolabeling with 35SO4 for 24h, PGs were extracted from the muscle ECM with 4.0 M guanidine-HCl containing protease inhibitors. PGs were subsequently isolated using sequential DEAE-Sephacel chromatography, digestion with chondroitinase ABC, and Sepharose CL-4B. Two different hydrodynamic size species of HSPGs were found. One type had a Mr of 4-6 X 10(5) (Kav = 0.25) as estimated by gel chromatography in the presence of 1% SDS and accounted for 75% of the total HSPGs. The other HSPG had a Mr 1.5-2.5 X 10(5) (Kav = 0.41). The glycosaminoglycan (GAG) side chains (Mr 20,000 and 12,000) were found composed only of heparan sulfate as determined by nitrous acid oxidation and heparitinase treatment. The large-sized HSPG, which is concentrated in synaptic regions, contains only GAG chains of Mr 20,000, suggesting that each HSPG contains only one kind of heparan sulfate chain in its structure. Our results definitively establish by biochemical criteria that the basement membrane of mammalian skeletal muscle contains HSPGs, the likely matrix receptor for the immobilization of the asymmetric collagen-tailed AChE at the neuromuscular junction.