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PubMed1992

Morphometry of cupromeronic blue-stained proteoglycan molecules in animal corneas, versus that of purified proteoglycans stained in vitro, implies that tertiary structures contribute to corneal ultrastructure.

Isolated, purified small chondroitin (dermatan) sulphate proteoglycans from corneas of cow and rabbit and cow sclera were stained with Cupromeronic blue in 'model' experiments. The lengths and thicknesses of the images were compared with those of the same proteoglycans stained in the tissue, using the critical electrolyte concentration principle to give specificity for sulphated proteoglycans, and keratanase 1 or chondroitinase ABC digestion to distinguish between chondroitin and keratan sulphate. Corrections for orientation of the stained glycan filaments within the section plane were made to convert the observed lengths to true average lengths. Observed lengths of stained chondroitin (dermatan) sulphate were greater than those of keratan sulphate, both in models and tissues, in agreement with published data from biochemical and rotary-shadowing studies, in both species. Corrected (true) average lengths of stained isolated chondroitin (dermatan) sulphate proteoglycans were slightly, but not significantly, longer than expected from rotary shadowing or biochemical measurements. Keratan sulphate lengths were similarly somewhat longer. The data support the idea that Cupromeronic blue acts as a scaffold that helps maintain polyanion shape against distortion on staining. Stained filaments in tissues were sometimes over twice the length of isolated stained proteoglycans, suggesting that 2 glycan chains were aligned end-to-end. Thicknesses of proteoglycan filaments suggested that at least 2 glycan chains were aligned side-by-side, both in models and in tissues. A scheme for proteoglycan tertiary structure in cornea is proposed, in which glycan chains may bridge collagen fibrils in duplexed forms similar to those observed in rotary shadowed preparations.

Animals↗

PubMed1976

Proteoglycans from bovine proximal humeral articular cartilage. Structural basis for the polydispersity of proteoglycan subunit.

Polydisperse proteoglycan subunit from bovine proximal humeral articular cartilage has been separated into a series of relatively monodisperse fractions which have been chemically and physically characterized. The proteoglycan subunit species of the lowest molecular weight contains the least chondroitin sulfate and had an amino acid composition relatively low in serine and glycine and relatively high in cysteine, methionine, and aspartic acid, almost identical to that of the hyaluronic acid-binding region of proteoglycan subunit isolated by Heinegard and Hascall (Heinegard, D., and Hascall, V.C. (1974) J. Biol. Chem. 249, 4250-4256). The molecular weight of proteoglycan subunit increases in proportion to its chondroitin sulfate content. As the molecular weight and chondroitin sulfate content of proteoglycan subunit increase, there is a parallel increase in the serine and glycine contents, and a decrease in the cysteine, methionine, and aspartic acid contents of proteoglycan subunit core protein. The pattern of polydispersity observed strongly supports the concept that proteoglycan subunit core protein contains a hyaluronic acid-binding region of constant size and composition and a polysaccharide attachment region of variable length and composition, composed of repeating peptide sequences containing serine and glycine in equimolar amounts.

Amino Acids↗

PubMed1991

Proteoglycans in the mouse interphotoreceptor matrix. IV. Retinal synthesis of chondroitin sulfate proteoglycan.

To determine whether the mouse retina contributes chondroitin sulfate proteoglycan (CS-PG) to the interphotoreceptor matrix (IPM), 35SO4(2-) was used as a tracer for newly synthesized proteoglycan by retinas maintained in vitro in the absence of pigment epithelium. Following incubation with the tracer for 3 hr, the 35S-labeled proteoglycans present in the incubation medium and associated with isolated photoreceptor outer segments were analyzed separately. Proteoglycan was extracted with 4 M guanidine, and then separated on a G-25 column followed by DEAE ion exchange chromatography in the presence of 8 M urea. The proteoglycan fraction was eluted with a linear NaCl gradient of 0.15-1.0 M. Eluted 35S-labeled macromolecules were susceptible to chondroitinase AC and ABC degradation, indicating that virtually all the 35S-labeled proteoglycan synthesized by the mouse retina and secreted into the incubation media is of the chondroitin sulfate type. In parallel autoradiographic analysis of retinas following 35SO4(2-) incubation, silver grains were present over all retinal compartments, with 41-48% associated with the photoreceptor layer. Quantitative autoradiography of retinas following chondroitinase AC digestion of fixed retinas revealed significant (P less than 0.025) reduction in silver grains associated with the photoreceptor outer segment layer as compared to controls. These combined biochemical and autoradiographic studies indicate that the retina, possibly the photoreceptors, synthesize at least a portion of the CS-PG present in the IPM of the mouse.

Animals↗

PubMedDate not supplied

Biological functions of proteoglycans: use of specific inhibitors of proteoglycan synthesis.

The use of specific inhibitors of proteoglycan synthesis have demonstrated essential functions for these molecules. Proteoglycans do not appear to be essential for cell viability or proliferation but are necessary for stable assembly of ECM and functional cell-ECM interaction. Because of their ability to nearly completely abolish ECM assembly in cell culture systems, proteoglycan synthesis inhibitors are useful tools to examine effects of ECM on the phenotypic behavior of cells. Despite its usefulness, the use of proteoglycan synthesis inhibitors has some drawbacks. The most significant of these is the fact that synthesis of all proteoglycans is inhibited, making it difficult to assign a particular function to a specific proteoglycan type. For this reason, inhibition studies need to be done in conjunction with additional biochemical, immunological or molecular biological studies.

Animals↗

PubMed1980

Proteoglycan complex and proteoglycan subunit polydispersity. Study by isopycnic centrifugation in cesium sulfate density gradients.

A true isopycnic centrifugation method for the study of the bovine nasal cartilage proteoglycan polydispersity is presented. The use of cesium sulfate as gradient forming salt instead of cesium chloride allowed proteoglycan banding without any sedimentation at the bottom of the centrifuge tube. Apparent buoyant densities of proteoglycan monomer and proteoglycan aggregate were different. The present method provides a useful tool for the study of proteoglycan polydispersity and also allows us to follow the distribution of the link proteins in different proteoglycan extracts.

Amino Acids↗

PubMed1980

Molecular size distribution of proteoglycan subunits and glycosaminoglycans synthesized by chondrocytes under conditions of reduced proteoglycan synthesis.

The rate of proteoglycan synthesis by chondrocytes in vitro was depressed by either omitting L-glutamine from the incubation medium or by addition of proteoglycan subunit to the medium. The molecular size distribution on Sepharose 2B of the proteoglycan subunits synthesized by the chondrocytes under these conditions of reduced proteoglycan synthesis was found to be the same as those synthesized by the control cells. Likewise, the molecular size distribution on Sepharose 6B CL of the glycosaminoglycan chains synthesized by the depressed cells was found to be similar to that observed in untreated chondrocytes. This work demonstrates that, under conditions of reduced proteoglycan synthesis, fewer proteoglycan subunits are synthesized by chondrocytes and that the molecular size distribution of these macromolecules is similar to those synthesized by untreated cells.

Animals↗

PubMed1984

Distribution in caesium chloride gradients of proteoglycans secreted by bovine aorta smooth muscle cells and study of their aggregation with hyaluronate and cartilage proteoglycan.

Smooth muscle cells from media of bovine aorta were cultured with [35S] sulphate and [3H]glucosamine. The 4 M guanidinium chloride extract of cell layer had a greater proportion of its glycosaminoglycans as hyaluronic acid, heparan sulphate and dermatan sulphate than did medium, which contained relatively more chondroitin sulphate. Fractionation of medium and cell layer extract by caesium chloride density gradient centrifugation, under associative and dissociative conditions, respectively, established that heparan sulphate and dermatan sulphate proteoglycans had lower buoyant densities than chondroitin sulphate proteoglycans. Chromatography on Sepharose CL2B showed that chondroitin sulphate-rich proteoglycan from medium bottom fraction contained no high molecular weight aggregate but underwent partial reaggregation with hyaluronic acid. A slight shift to higher molecular weight occurred if cartilage proteoglycan monomer was added to medium bottom fraction, but if both hyaluronic acid and cartilage proteoglycan monomer were added, a high degree of aggregation took place. These observations could be explained if medium bottom fraction contained a proteoglycan-deficient aggregate with a low molecular weight hyaluronate species. Bottom fraction from cell layer extract showed none of these properties.

Animals↗

PubMed1982

Proteoglycans of bovine periodontal ligament and skin. Occurrence of different hybrid-sulphated galactosaminoglycans in distinct proteoglycans.

A proteoglycan purified from 4 M-guanidinium chloride extracts of bovine periodontal ligament closely resembled that of bovine skin, except for a rather lower protein content and a higher molecular weight (120 000 compared with about 90 000) by sodium dodecyl sulphate/polyacrylamide-gel electrophoresis. The latter difference was explained by the molecular weights (29 000 and 16 000) of the respective dermatan sulphate components, each of which was rich in L-iduronate (about 75% of the total hexuronate). Significant amounts of other glycosaminoglycans did not occur in these proteoglycans, which were homogenous on gel chromatography and agarose/polyacrylamide-gel electrophoresis. Polydispersity was observed in sedimentation equilibrium experiments, but proteolysis or self-association of the proteodermatan sulphates may have affected these results. Ligament proteoglycans that were almost completely extracted with 0.1 M-NaCl contained less protein of a completely different amino acid composition than the proteodermatan sulphates. They were heterogeneous in size but generally smaller than cartilage proteoglycans and L-iduronate was a component, comprising about 7% of the total hexuronate of the sulphated galactosaminoglycan chains. The latter consisted of two fractions differing in molecular weight, but a dermatan sulphate with a high L-iduronate content was not present. These proteoglycans had some resemblance to D-glucuronate-rich proteoglycans of other non-cartilaginous tissues. Such compounds, however, are difficult to categorize at present.

Amino Acids↗

PubMed1989

Chondroitin 6-sulfate proteoglycan but not heparan sulfate proteoglycan is abnormally expressed in skin basement membrane from patients with dominant and recessive dystrophic epidermolysis bullosa.

Two distinct groups of proteoglycans, chondroitin 6-sulfate (C6-S) proteoglycan and heparan sulfate proteoglycan (HSPG), have been recently shown to reside within the lamina densa of normal human skin basement membrane (BM). To determine whether either or both antigens are normally expressed in one or more forms of epidermolysis bullosa (EB), a disease known to have specific alterations in skin BM, we have examined by indirect immunofluorescence 31 specimens of clinically normal skin from 28 EB patients (simplex, 5; junctional, 8; dominant dystrophic [DDEB], 9; recessive dystrophic [RDEB], 9) with monoclonal antibodies to C6-S and HSPG. HSPG was normally expressed in all EB and control skin specimens, whereas C6-S was absent along the dermoepidermal junction of 9 of 9 RDEB and 7 of 9 DDEB, and reduced in 2 of 9 DDEB cases. In contrast, C6-S was normally expressed in 5 of 5 EB simplex, 5 of 6 junctional EB, and all control skin specimens. We have subsequently extracted a greater than 400 kD C6-S proteoglycan from normal skin BM and have found that the core protein may also contain heparan sulfate side chains. Our findings suggest that 3B3 monoclonal antibody recognizes a hybrid proteoglycan in human skin, and that its absent or reduced binding in dystrophic EB skin BM may reflect either absence of associated core protein or posttranslational alterations in the proteoglycan side chains.

Basement Membrane↗

PubMed1986

A comparison of proteoglycan from chick cartilage of different types and a study of the effect of vitamin D on proteoglycan structure.

Normal chick growth cartilage contains mainly large proteoglycans that interact well with hyaluronic acid. In contrast normal articular and sternal cartilages contain mainly smaller molecules that interact poorly with hyaluronic acid. Similar smaller proteoglycans are present in all the cartilages in the rachitic state. The smaller proteoglycans all appear to be synthesized as such, and not to arise from degradation of larger molecules unless such degradation occurs extremely rapidly after synthesis. Supplementation of the vitamin D-deplete animals with calcium resulted in the production of large proteoglycans by the growth cartilage, but did not affect the size of the proteoglycan produced by the articular or sternal cartilages. It would appear that in these chicks the chondrocytes of the growth cartilage may be unique in their ability to produce large aggregating proteoglycans, and in their response to plasma calcium levels.

Animals↗

PubMed2003

Prolonged treatment of human osteoarthritic chondrocytes with insulin-like growth factor-I stimulates proteoglycan synthesis but not proteoglycan matrix accumulation in alginate cultures.

OBJECTIVE: To determine the level of anabolic response when chondrocytes isolated from human osteoarthritic cartilage are stimulated with 2 doses of insulin-like growth factor-I (IGF-I) for extended culture periods. METHODS: Human chondrocytes were isolated from knee cartilage removed at the time of joint replacement surgery for osteoarthritis (OA). The cells were cultured in alginate beads under serum-free conditions and treated with 100 ng/ml or 1000 ng/ml of human recombinant IGF-I. Response was measured during culture periods of 1 to 28 days by determining the level of radiolabeled sulfate incorporated into alcian blue precipitable material and by measuring the level of total proteoglycan accumulation using the dimethylmethylene blue (DMB) assay. For the latter assay, cultures treated with osteogenic protein-1 (OP-1) were used for comparison to IGF-I. Results were normalized to cell numbers using DNA measurements. RESULTS: The level of IGF-I stimulated sulfate incorporation relative to untreated controls increased with time in culture, with a peak response occurring between days 7 and 14 of culture. There was no significant difference between the 2 IGF-I doses. Despite the stimulation of sulfate incorporation, the DMB assay did not reveal a significant accumulation of proteoglycans in the cell-associated and further-removed matrix with either dose of IGF-I in cultures carried out to 21 days. In contrast, compared to controls, OP-1 at 100 ng/ml stimulated a 3-fold increase in matrix proteoglycan at day 21 of culture. CONCLUSION: Prolonged IGF-I treatment of human OA chondrocytes in serum-free alginate cultures stimulated sulfate incorporation without significant accumulation of a proteoglycan matrix in longterm cultures. However, significant proteoglycan accumulation was seen in cultures treated with OP-1, suggesting it is a better stimulator of proteoglycan production by OA chondrocytes.

Aged↗

PubMed1980

Immunological determinants of proteoglycans. Antibodies against the unsaturated oligosaccharide products of chondroitinase ABC-digested cartilage proteoglycans.

Bovine nasal cartilage proteoglycan monomer which had been digested with chondroitinase ABC to form the keratan sulfate-protein core was injected into rabbits. High titer antiserum was obtained as judged by the binding of 125I-labeled keratan sulfate-protein core. Native proteoglycan did not inhibit the interaction of the antiserum with labeled keratan sulfate-protein core. However, the disaccharide obtained from chondroitin 4-sulfate by the action of chondroitinase ABC, 2-acetamido-2-deoxy-3-O-(beta-D-gluco-4-enepyranosyluronic acid)-4-O-sulfo-D-galactose, inhibited the interaction 50% at a concentration of 500 microM. The corresponding 6-sulfated and nonsulfated disaccharides at the same concentration gave 15% and 10% inhibition, respectively. Chondroitinase-digested proteoglycan from Swarm rat chondrosarcoma was strongly inhibitory, while the hyaluronidase-digested chondrosarcoma proteoglycan exhibited no detectable inhibition. Evidently, the antiserum raised against chondroitinase ABC-digested bovine nasal cartilage proteoglycan contains antibodies which recognize the unsaturated uronic acid residue linked to N-acetylgalactosamine 4-sulfate. These antibodies will be valuable for identifying and quantitating chondroitin 4-sulfate-containing proteoglycans in tissues.

Animals↗

PubMed1983

The occurrence of three different proteoglycan species in chick embryo cartilage. Isolation and characterization of a second proteoglycan (PG-Lb) and its precursor form.

Three different molecular species of proteoglycan (designated PG-H, PG-Lb, and PG-Lt) have been isolated from chick embryo epiphyseal cartilage. PG-H is a major proteoglycan of the tissue and identical, or nearly identical, with so-called cartilage-characteristic proteoglycan previously described in mammalian and avian cartilages. The third proteoglycan, PG-Lt, differs from the other two in containing disulfide-bonded collagenous polypeptides (Noro, A., Kimata, K., Oike, Y., Shinomura, T., Maeda, N., Yano, S., Takahashi, N., and Suzuki, S. (1983) J. Biol. Chem. 258, 9323-9331). The second proteoglycan, PG-Lb, consists of a core protein with Mr congruent to 52,000 dermatan sulfate copolymer chains with glucuronic acid/iduronic acid residues. Upon chondroitinase ABC digestion, the proteoglycan yields a protein-enriched core fraction of Mr congruent to 43,000. Its amino acid composition, tryptic peptide profile, and immunochemical properties indicate that PG-Lb is distinctly different from PG-H and PG-Lt in core protein structure. PG-Lb shows no specific binding with hyaluronic acid. Pulse-chase experiments with [3H]serine indicate that PG-Lb is first synthesized as a precursor form (pro-PG-Lb) that can be distinguished from PG-Lb by the production of a core molecule of Mr congruent to 52,000 after chondroitinase ABC digestion. This core molecule is labeled when [2-3H]mannose is used as a precursor, suggesting that it contains a glycoprotein type oligosaccharide. Since the core molecule from pro-PG-Lb is significantly larger in molecular weight than that from PG-Lb, the conversion of pro-PG-Lb to PG-Lb should involve scission of the polypeptide or possibly removal of mannose-containing oligosaccharide chain.

Amino Acids↗

PubMed1996

Perlecan and basement membrane-chondroitin sulfate proteoglycan (bamacan) are two basement membrane chondroitin/dermatan sulfate proteoglycans in the Engelbreth-Holm-Swarm tumor matrix.

The presence of proteoglycans bearing galactosaminoglycan chains has been reported, but none has been identified previously in the matrix of the Engelbreth-Holm-Swarm tumor, which is a source of several basement membrane components. This tumor matrix contains perlecan, a large, low buoyant density heparan sulfate proteoglycan, widespread in many basement membranes and connective tissues. We now identify two distinct proteoglycan species from this tumor source, which are substituted with galactosaminoglycans and which show basement membrane localization by immunohistochemistry. One species is perlecan but, in addition to being present as a heparan sulfate proteoglycan, it is also present as a hybrid molecule, with dermatan sulfate chains. A minor population of perlecan apparently lacks heparan sulfate chains totally, and some of this is substituted with chondroitin sulfate. The second species is immunologically related to basement membrane-chondroitin sulfate proteoglycan (BM-CSPG) and bears chondroitin sulfate chains. No BM-CSPG was detectable which was substituted with heparan sulfate chains. A combination of immunological and molecular approaches, including cDNA cloning, showed that perlecan and BM-CSPG are distinct in core protein structure. Both are, however, basement membrane components, although there are tissue-specific differences in their distribution.

Animals↗

PubMed1985

Heparan sulfate proteoglycans from mouse mammary epithelial cells. Cell surface proteoglycan as a receptor for interstitial collagens.

A heparan sulfate-rich proteoglycan is on the surface of NMuMG mouse mammary epithelial cells apparently intercalated into their plasma membranes. Mild treatment of the cells with trypsin releases the GAG-bearing region (ectodomain) of this molecule as a discrete proteoglycan which is readily purified. At physiological pH and ionic strength, the ectodomain binds collagen types I, III, and V but not types II, IV, or denatured type I. The proteoglycan binds to a single class of high affinity saturable sites on type I collagen fibrils, sites which are selective for heparin-like glycosaminoglycans. The binding of NMuMG cells to type I collagen duplicates that of their cell surface proteoglycan; cells bind to native but not denatured collagen, and binding is inhibited by heparin but not by other glycosaminoglycans. These binding properties suggest that cell surface heparan sulfate proteoglycans could act as receptors for interstitial collagens and mediate changes in cell behavior induced by collagenous matrices.

Animals↗

PubMed1984

Heparan sulfate proteoglycans from mouse mammary epithelial cells. Basal extracellular proteoglycan binds specifically to native type I collagen fibrils.

Mouse mammary epithelial cells (NMuMG cells) deposit at their basal surfaces an extracellular heparan sulfate-rich proteoglycan that binds to type I collagen. The binding of the purified proteoglycan to collagen was studied by (i) a solid phase assay, (ii) a suspension assay using preformed collagen fibrils, and (iii) a collagen fibril affinity column. The binding interaction occurs at physiological pH and ionic strength and can be inhibited only by salt concentrations that greatly exceed those found physiologically. Binding requires the intact proteoglycan since the protein-free glycosaminoglycan chains will not bind under the conditions of these assays. However, binding is mediated through the heparan sulfate chains as it can be inhibited by block-sulfated polysaccharides, including heparin. Binding requires native collagen structure which may be optimal when the collagen is in a fibrillar configuration. Binding sites on collagen fibrils are saturable, high affinity (Kd approximately 10(-10) M), and selective for heparin-like glycosaminoglycans. Because a culture substratum of type I collagen fibrils causes NMuMG cells to accumulate heparan sulfate proteoglycan into a basal lamina-like layer, binding of heparan sulfate proteoglycans to type I collagen may lead to the formation of a basal lamina and may link the basal lamina to the connective tissue matrix, an association found in basement membranes.

Animals↗

PubMed1989

Proteoglycans of the articular disc of the bovine temporomandibular joint. I. High molecular weight chondroitin sulphate proteoglycan.

Proteoglycans were extracted from articular discs with 4 M guanidinium chloride and separated by ion-exchange and gel-filtration chromatography into high molecular weight (Mr greater than 1,000,000) species containing chondroitin sulphate (predominantly chondroitin 6-sulphate) and low molecular weight iduronic acid-rich dermatan sulphate proteoglycan(s). The chondroitin sulphate proteoglycan contained 21% uronic acid and 17% protein. It gave rise on digestion with chondroitinase ABC to a protein core of apparent Mr 350,000 with an amino acid composition closely resembling that of the cartilage-type proteoglycans. Other characteristics shared with previously-described cartilage proteoglycans include the presence of keratan sulphate and the ability to aggregate with hyaluronic acid.

Amino Acids↗

PubMed1995

Effect of transforming growth factor-beta 1 and basic fibroblast growth factor on the expression of cell surface proteoglycans in human lung fibroblasts. Enhanced glycanation and fibronectin-binding of CD44 proteoglycan, and down-regulation of glypican.

We have tested the effects of transforming growth factor-beta 1 (TGF-beta 1), basic fibroblast growth factor (bFGF) and TGF-beta 1 + bFGF on the expression of the cell surface proteoglycans (CD44, syndecans and glypican) in cultures of human lung fibroblasts (HLF). Cell surface proteoglycan expression was monitored by quantitative immunoprecipitation from metabolically labelled cells. Western and Northern blotting and evaluation of the glycanation of the proteoglycans. Stimulation of the cells with TGF-beta 1 increased the length of the chondroitin sulphate (CS) chains on CD44 (approximately 1.6-fold). bFGF, administered solely, also increased the length of the CS chains on CD44 (approximately 1.4-fold), whereas the combination of TGF-beta 1 + bFGF nearly doubled both the length and the number of the CS chains on CD44. None of these treatments lead to changes in CD44 message or core-protein expression. This enhanced glycanation of CD44 after the TGF-beta 1, bFGF and combined treatments correlated with a 2-fold increase in the affinity of the proteoglycan for fibronectin but had no influence on the binding to type I collagen. TGF-beta 1, alone or in combination with bFGF, also stimulated the CS content of syndecan-1, but none of the other syndecans was significantly affected by any of the factors or combinations tested. The expression of glypican however was significantly decreased (nearly halved) by the combination of TGF-beta 1 + bFGF, less so by TGF-beta 1 and not at all by bFGF. This decrease occurred both at the level of the message and of the core protein. These data demonstrate specific and differential effects of TGF-beta 1 and bFGF on the structure, expression and interactions of the cell surface proteoglycans of HLF.

Base Sequence↗