Proteoglycans in health and disease: structures and functions

Proteoglycan biosynthesis by rabbit articular chondrocytes treated with D-penicillamine

Rabbit articular chondrocytes in confluent monolayer cultures were treated with D-Penicillamine (D-Pen) during 3 or 5 days. The [35S]-sulfate incorporation in neosynthesized proteoglycans was not modified by D-Pen doses ranging from 50 to 800 micrograms/ml. After treatment during 5 days with D-Pen concentrations of 50 or 400 micrograms/ml, the chemical characteristics of proteoglycans from medium and cell-layer were determined. The aggregation capacity of proteoglycans from medium, the monomer molecular size, the glycosaminoglycan chain length and the relative rates of the different glycosaminoglycans (chondroitins, chondroitin 6-sulfate, chondroitin 4-sulfate, hyaluronic acid) remained unchanged. These results suggest that D-Pen does not alter some of the cartilage mechanical properties due to the presence of proteoglycans.

Formation of extracellular matrix in normal rat liver: lipocytes as a major source of proteoglycan

Proteoglycans are a major component of the normal hepatic extracellular matrix and undergo quantitative and qualitative changes in hepatic fibrosis. The cellular sources of proteoglycans are as yet incompletely defined. We examined this question using primary cultures of hepatocytes and lipocytes isolated from normal rat liver. Proteoglycan synthesis was assessed by measuring production of sulfated glycosaminoglycan, the polysaccharide moiety of proteoglycans. The findings indicate that lipocytes produce sixfold more glycosaminoglycan, per cell, than do hepatocytes. Two-thirds of the newly synthesized material is cell- or matrix-associated. Of the individual glycosaminoglycan species produced by lipocytes, dermatan sulfate represents 60% of the total; heparan sulfate and chondroitin sulfate are measurable but relatively minor. In hepatocyte cultures, heparan sulfate accounted for essentially all of the glycosaminoglycan detected. We conclude that lipocytes are an important source of proteoglycan in normal liver and may be the principal source of dermatan sulfate associated with hepatic fibrosis.

Immunohistochemical identification of heparan sulphate proteoglycan in secondary systemic amyloidosis

The distribution of proteoglycans in kidneys from patients with secondary (AA) systemic amyloidosis was investigated. Antisera reacting with the protein cores of chondroitin sulphate proteoglycan (CSPG), dermatan sulphate proteoglycan (DSPG) and heparan sulphate proteoglycan (HSPG) were used in conjunction with the peroxidase-antiperoxidase (PAP) method. HSPG was the only proteoglycan found to be specifically localized to the amyloid deposits. The staining was most intense on the endothelial side of the deposits in both the glomeruli and in the vessel walls. No staining was observed after absorption of the HSPG antiserum with a fraction of the amyloid preparations, corresponding in size to that reported for glomerular HSPG. The possible role of HSPG and endothelial cells in the pathogenesis of the amyloid deposits is discussed.

Electron probe X-ray microanalysis of the composition of hyaline articular and non-articular cartilage in young and aged rats

Blocks of articular cartilage were taken from tibiae of young adult (8 week) and aged adult (50-60 week) rats; xiphisternal cartilage was obtained from young adult rats. Specimens were quench-frozen in nitrogen slush, freeze-fractured and examined by low-temperature scanning electron microscopy. The results of X-ray microanalysis of frozen-hydrated bulk cartilage are semi-quantitative. The composition of chondrocyte nuclei and cytoplasm are only marginally different. Xiphisternal chondrocytes contain lipid inclusions which show an absence of element peaks and are designated as being neutral lipid. Intra- and extracellular Na, P, S, Cl, K and Ca count rates are significantly different. Cartilage from older rats contains more S and Ca, and less K and Cl in the intercellular matrix than that from young rats. Intracellular K levels are lower in aged than in young rats. The intercellular matrix of xiphisternal cartilage contains larger amounts of S, Na and K, and a smaller amount of Cl compared to that of tibial articular cartilage.

Identification of specific binding sites for keratan sulphate proteoglycans and chondroitin-dermatan sulphate proteoglycans on collagen fibrils in cornea by the use of cupromeronic blue in 'critical-electrolyte-concentration' techniques

Proteoglycans (PGs) in bovine corneal stroma were stained with Cupromeronic Blue in 'critical-electrolyte-concentration' (CEC) methods for electron microscopy, and were located vis-à-vis collagen fibril a-e banding patterns. Keratanase and chondroitin ABC lyase digestion showed that a + c-band- and d + e-band-associated PGs were keratan sulphate-rich and chondroitin (dermatan) sulphate-rich respectively. The CEC pattern proved that the keratan sulphate PGs at the a and c bands differed. Comparison of their CECs with their behaviour on anion-exchange chromatography confirmed previous (indirect) attempts at identification [Scott & Haigh (1985) Biosci. Rep. 5, 765-774]. Similar arguments were applied to the dermatan sulphate PGs at the d and e bands. These results strongly support the one-PG-one-binding-site hypothesis [e.g. Scott (1988) Biochem. J. 252, 313-323]. Remarkable inter-species variations in the keratan sulphate PG patterns contrast with the relatively constant picture of dermatan sulphate PG-collagen fibril interactions.

Extraction and fractionation of proteoglycans from squid skin

The extractability of squid skin proteoglycans with solutions of varying concentrations of guanidine-HCl, urea and SDS was studied; 4 M guanidine-HCl, being the best extractant, removed 95% of the tissue proteoglycans (glycosaminoglycan uronic acid). The proteoglycans in the 4 M guanidine-HCl extract were fractionated by repeated ion exchange and gel chromatography on Sepharose CL-4B to give three main populations, all being present in about equal proportions. Two populations (Kd 0.34 and 0.56) contained only chondroitin (proteochondroitin) and the other (Kd 0.50) only oversulphated chondroitin sulphate (oversulphated proteochondroitin sulphate). Two minor populations, one containing chondroitin and chondroitin sulphate and the other chondroitin sulphate and oversulphated chondroitin sulphate, were also identified.

Proteoglycan-fibrillar collagen interactions

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Ultrastructure of matrix vesicles in chick growth plate as revealed by quick freezing and freeze substitution

The ultrastructure of extracellular membrane-bound matrix vesicles (MVs), their biogenesis, and the surrounding matrix in chick tibial growth plate were studied after quick freezing and freeze substitution (FS) in an organic solvent. There were several notable differences in the ultrastructural preservation of cartilage when FS was used as compared with conventional fixation. The ultrastructural appearance of MVs after FS was extremely variable. Within the MVs, intravesicular filaments, amorphous material, and membrane-associated undercoat structures were observed. Intravesicular filaments, similar in diameter to microfilaments seen in the cytoplasm, were attached to the inside of MV membranes. This observation indicates the similarity of MV membranes and the plasma membrane. In some MVs in the proliferative zone an electron-dense material was present along the inner side of the MV membrane. In the prehypertrophic zone, crystalline material often appeared within the electron-dense material, which may be a precursor form of hydroxyapatite. The earliest crystals observed were in MVs but not in the extracellular matrix. Regarding MV formation, in addition to budding from cell surfaces and to cellular disintegration, this study also indicates that a sequential process of extrusion of preformed cytoplasmic structures may occur. Also, small MVs measuring 25-40 nm seem to arise from the disruption of large MVs. This is a previously unreported observation on MV biogenesis. FS preserves proteoglycans in the cartilage matrix as a fine, filamentous network. Initial extracellular calcification was not associated with this network.

Expression of cartilage-matrix genes and localization of their translation products in the embryonic chick eye

The presence of cartilage-matrix molecules in the embryonic chick eye was shown by means of measuring RNA expression and immunostaining studies. The molecules examined were proteoglycan core protein (PG-core), link protein (LP), cartilage-matrix protein (CMP) and type II collagen. The genes encoding these proteins are expressed in 8- to 11-day embryonic chick eyes at constant steady-state levels. Immunopositive stained tissues include sclera, choroid, cornea, lens capsule (PG-core, LP, CMP), lens epithelium, lens fibers (LP, CMP) and the membranes in the retina (LP). In addition, data from comparative studies employing the eyes from the proteoglycan core-protein-deficient mutant, nanomelia, indicate that levels of mRNA for core protein are almost absent and that CMP is reduced in the above-mentioned tissues.

Effects of ethanol, acetaldehyde, and lactate on proteoglycan synthesis and proliferation of cultured rat liver fat-storing cells

The hypothesis that ethanol and some of its metabolites are directly involved in the process of fat-storing cell activation and stimulated proteoglycan synthesis in alcoholic liver injury was investigated. The effects of short-term (24 h) and long-term (4 days) exposure of rat liver fat-storing cells at various times of culture to ethanol, acetaldehyde, and lactate on the synthesis of proteoglycans and total protein and on the proliferation activity of the cells were studied. Ethanol and lactate did not stimulate the incorporation of [35S]sulfate into glycosaminoglycans. Acetaldehyde inhibited strongly glycosaminoglycan synthesis, reaching 50% inhibition at 330 mumol/L. The compound preferentially inhibited the synthesis of dermatan sulfate. No significant changes of glycosaminoglycan chain length or of the degree of polysaccharide sulfation were noted in acetaldehyde-treated cultures. The inhibition was reversed by the addition of beta-D-xylopyranoside (0.5 mmol/L), an artificial initiator of chain elongation, to the medium. Total protein synthesis, cell number, deoxyribonucleic acid content of the cultures, and [3H]thymidine incorporation were not affected by the compounds. The results do not support the view that ethanol, its oxidation product acetaldehyde, or lactate are directly involved in the activation of fat-storing cells and in enhanced matrix proteoglycan synthesis and secretion.

Glomerular basement membrane proteoglycans are derived from a large precursor

The basement membrane heparan sulfate proteoglycan produced by the Englebreth-Holm-Swarm (EHS) tumor and by glomeruli were compared by immunological methods. Antibodies to the EHS proteoglycan immunoprecipitated a single precursor protein (Mr = 400,000) from [35S]methionine-pulsed glomeruli, the same size produced by EHS cells. These antibodies detected both heparan sulfate proteoglycans and glycoproteins in extracts of unlabeled glomeruli and glomerular basement membrane. The proteoglycans contained core proteins of varying size (Mr = 150,000 to 400,000) with a Mr = 250,000 species being predominant. The glycoproteins are fragments of the core protein which lack heparan sulfate side chains. Antibodies to glomerular basement membrane proteoglycan immunoprecipitated the precursor protein (Mr = 400,000) synthesized by EHS cells and also reacted with most of the proteolytic fragments of the EHS proteoglycan. This antibody did not, however, react with the P44 fragment, a peptide situated at one end of the EHS proteoglycan core protein. These data suggest that the glomerular basement membrane proteoglycan is synthesized from a large precursor protein which undergoes specific proteolytic processing.

Identification of the glycosaminoglycan-attachment site of mouse invariant-chain proteoglycan core protein by site-directed mutagenesis

The invariant chain (Ii), a nonpolymorphic glycoprotein that associates with the immunoregulatory Ia proteins encoded by the major histocompatibility complex, has a proteoglycan form (Ii-CS) that bears a chondroitin sulfate glycosaminoglycan. In this proteoglycan form, Ii may remain associated with Ia at the cell surface. Inhibitors that prevent the addition of glycosaminoglycan to Ii have been found to depress antigen-presenting function. Ii does not have multiple candidate glycosaminoglycan-attachment sites, and we used site-directed mutagenesis to replace a candidate serine glycosaminoglycan-acceptor site with alanine at position 201 in the murine Ii protein. Transfection of the normal or altered gene into Ii-negative COS-7 cells showed that equivalent amounts of core Ii protein and its acidic, terminally glycosylated forms were synthesized, but the Ala-201 mutant Ii did not give rise to Ii-CS. The mutant protein had apparently normal transport through the Golgi compartment and associated stably with Ia molecules. Thus, this mutation directly identifies the site of glycosaminoglycan addition and shows that it can be eliminated without adversely affecting the overall biosynthesis of Ii.

Characterization and macromolecular association of proteoglycans produced by pig arterial smooth muscle cells in culture

1. Medium and cell-layer proteoglycans from pig aorta smooth muscle cells in culture were compared. In both compartments, the main proteoglycans contained chondroitin sulfate-dermatan sulfate chains of 40 kDalton. 2. However, cell-layer proteoglycans differed from those of the medium by the presence of: (a) some small-size proteoglycans; (b) a greater amount of heparan sulfate; (c) chondroitin sulfate-dermatan sulfate enriched in iduronate and in 4 sulfate- (instead of 6 sulfate-) residues. 3. During dissociation-reassociation assays of arterial proteoglycans with exogenous hyaluronate or "aggregate" proteoglycans, the in vitro formation of complexes appeared to involve inter-associations between proteoglycans molecules, in addition to aggregation with hyaluronate.

Glycosaminoglycan content in neonatal rat aortic smooth muscle cell cultures

In the present study the biosynthesis of glycosaminoglycans (GAGs) by neonatal rat aortic smooth muscle cells in culture was studied. Heparan sulfate (HS) was the predominant GAG of the cell layer accounting for 32-49% of the total GAGs depending on the time in culture. The presence of low sulfated chondroitin sulfate (LSC) in aortic smooth muscle cell cultures is reported here for the first time. The effect of ascorbate on the synthesis and accumulation of these macromolecules resulted in a relative increase of C4S and DS in the cell layer. In contrast, the distribution of the GAGs which were secreted into the medium was not significantly effected by the addition of ascorbate. While HS was always found to be a minor component, the other GAGs were present in about equal concentrations. The total GAG accumulation in the medium was much greater (91-97%) than that of the cell layer (3-9%) indicating that the cells are synthesizing relatively large amounts of GAGs, although incorporation of these macromolecules into the extracellular matrix was consistently low.

Isolation and characterization of a collagen fibril-associated dermatan sulphate proteoglycan from bovine lung

Dermatan sulphate proteoglycans have been extracted from bovine lung with 2.0 M CaCl2 and isolated using CsCl density gradient centrifugation, DEAE ion-exchange chromatography, gel chromatography and preparative sodium dodecyl sulphate-polyacrylamide gel electrophoresis. Ultrastructurally these proteoglycans are specifically associated with collagen fibrils. Dermatan sulphate (Mr 15.10(3)-35.10(3), with a strong prevalence for the higher Mr) is link via an O-glycosidic bond to a protein core, which is rich in Asx, Glx and Leu. Of the total uronic acid, 91% is iduronic acid. A part of the glucuronic acid residues is located near the protein core and a large cluster of disaccharides is devoid of glucuronic acid residues. An inhibition enzyme immunoassay has been developed to quantitate the proteoglycan. A model for the interaction between dermatan sulphate proteoglycans and collagen fibrils is proposed.

Kupffer cell-mediated induction of synthesis and secretion of proteoglycans by rat liver fat-storing cells in culture

The effect of conditioned media from Kupffer cells of normal, D-galactosamine- and thioacetamide-treated rats on the synthesis of proteoglycans by rat liver fat-storing cells in culture was studied in order to elucidate some of the mechanisms initiating enhanced connective tissue proteoglycan synthesis in injured liver. The incorporation of [35S]sulfate and [3H]glucosamine into proteoglycans was 2.1-2.5 fold (P less than 0.005) stimulated by the additions of normal, D-galactosamine- and thioacetamide-exposed Kupffer cell media. The concentrations of hexuronic acid and amino sugars in the medium glycosaminoglycan fraction were enhanced 5-fold and 4.5-fold, respectively, if the fat-storing cells were cultured in the presence of normal Kupffer cell conditioned medium. Treatment of normal Kupffer cells in culture with zymosan and phorbol esters, but not the addition of lipopolysaccharide, enhanced further the proteoglycan synthesis-stimulating effect of normal (untreated) Kupffer cells. The pattern of newly formed [35S]sulfate-labeled proteoglycans was changed in the presence of Kupffer cell media, showing a strong fractional increase of chondroitin sulfate and a relative decrease of dermatan sulfate, but the fraction of heparan sulfate was almost unaffected. In absolute terms Kupffer cells stimulated the total (medium and cell fraction) synthesis of chondroitin sulfate 2.8-fold and that of dermatan sulfate 1.5-fold. Although the DNA content of fat-storing cell cultures was increased by incubation with Kupffer cell media, an enhancement of proteoglycan synthesis was also observed when related to the DNA content of the cultures. The stimulation of proteoglycan synthesis was not dependent on the induction of cell proliferation. Gel chromatography and beta-elimination of medium proteoglycans revealed no changes of the molecular weight distribution profile of native proteoglycans and glycosaminoglycan chains synthesized under the influence of the various Kupffer cell media. Activation of proteoglycan synthesis and secretion in fat-storing cells by Kupffer cell-derived factor(s) might be an important mechanism of their strong accumulation in the connective tissue of fibrotic livers.

Developmental changes in glycosaminoglycan sulfotransferase activities in animal sera

Glycosaminoglycan sulfotransferase activities in sera during the prenatal and postnatal development of the ox, rat, and chicken were systematically measured with chemically desulfated cartilage chondroitin 4-sulfate, cornea keratan sulfate, and kidney heparan sulfate as exogenous sulfate acceptors and with [35S]sulfate-labeled 3'-phosphoadenosine 5'-phosphosulfate as a sulfate donor. The results of specificity studies and product analyses indicated that these enzymes introduce sulfates at position 6 of the internal N-acetylgalactosamine units of chondroitin, position 6 of the galactose units of keratan sulfate, and position 2 (an amino group) of the glucosamine units of heparan sulfate, respectively. The results of the enzyme assays indicated that (1) the three activities change in a development-associated manner in each animal species, (2) generally, the activities of the former two enzymes decrease with embryonic development and aging after birth, although in chicken serum they increase transiently at the late prenatal stage and decrease thereafter, and (3) the pattern of the changes in heparan sulfate sulfotransferase activity is species-dependent: the activity increases in the rat, decreases in the ox, and does not significantly change in the chicken during prenatal or postnatal development. These alterations may reflect development-associated biosynthesis of the corresponding glycosaminoglycans or maturation of the proteoglycans in some tissues.

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.

Paper disk assay for glycosaminoglycan sulfotransferases

A method is described for the assay of sulfotransferases, which transfer sulfate from 3'-phosphoadenosine-5'-phosphosulfate (PAPS) to glycosaminoglycan acceptors. Following the sulfation reactions, the [35S]sulfate-labeled products are precipitated and then separated from a sulfate donor ([35S]PAPS) and its degradation products by a paper disk method, and then the radioactivity remaining on the paper disk is subsequently determined by liquid scintillation counting. The rapidity and simplicity of the method are advantageous for multiple assays and have allowed us to establish assay conditions for serum sulfotransferases which introduce sulfate at position 6 of the internal N-acetylgalactosamine units of chondroitin, position 2 (amino group) of the glucosamine units of heparan sulfate and sugar units of keratan sulfate, respectively. The assay method will be applicable with modification to the assay of other glycosaminoglycan sulfotransferases and glycoprotein sulfotransferases.

Detection by 125I-cationized cytochrome c of proteoglycans and glycosaminoglycans immobilized on unmodified and on positively charged nylon 66

We have examined the detection by a 125I-labeled basic protein, cationized cytochrome c, of selected proteoglycans (PGs) and standard preparations of glycosaminoglycans (GAGs) immobilized on Nylon 66 and also on positively charged Nylon 66. Immobilization on Nylon 66 appears to allow a relative freedom of interaction between PGs or GAGs and 125I-cationized cytochrome c, but a more restricted reaction was observed when PGs and GAGs were immobilized to positively charged Nylon 66. On this support PGs with large numbers of GAG side chains reacted well with 125I-cationized cytochrome c, but GAGs were minimally reactive. By taking advantage of some of the properties of large-pore agarose-acrylamide gels, rapid partial characterization of some PGs can be accomplished in the 10-ng range, and therefore at a sensitivity equal to PGs with internal biosynthetic labels.

Effects of glycosaminoglycan polysulfate treatment on soundness, hyaluronic acid content of synovial fluid and proteoglycan aggregate in articular cartilage of lame boars

Eighteen lame boars were equally assigned to two treatment groups based on initial bodyweight and leg soundness. The boars were injected intramuscularly with an aqueous solution of glycosaminoglycan polysulfate or saline on day 0, 5, 10, 15, 20 and 25 and killed on day 27. The glycosaminoglycan polysulfate treatment significantly (P less than 0.05) improved leg soundness score, and resulted in an increase (P less than 0.06) in the hyaluronic acid concentration of the cubitus joint synovial fluid, and an increase (P less than 0.05) in the proportion of aggregated proteoglycans in the articular cartilage of the medial femoral condyle. Feed intake, growth rate and articular cartilage soundness score for the cubitus and stifle joints were not significantly (P greater than 0.10) affected by the treatment.

Hyaluronate synthetase inhibition by normal and transformed human fibroblasts during growth reduction

To establish the relation of glycosaminoglycan synthesis to cell proliferation, we investigated the synthesis of individual glycosaminoglycan species by intact cells and in a cell-free system, using normal and transformed human fibroblasts under differing culture conditions. Reducing serum concentration brought about a marked decline in the synthesis of hyaluronate (HA) as well as cell proliferation on both normal and transformed cells. Both HA synthesis and proliferation decreased with increasing cell densities markedly (in inverse proportion to cell density) in normal cells but gradually in transformed cells. This noticeable congruity of the changes in HA synthesis and proliferation indicates that the change in HA synthesis is related primarily to cell proliferation rather than to cell density or cellular transformation. Examination of HA synthesis in a cell-free system demonstrated that the activity of HA synthetase also fluctuated in conjunction with cell proliferation. Furthermore, growth-reduced cells (except crowded transformed cells) inhibited cell-free HA synthesis and this inhibition was induced coincidentally with a decrease in both HA synthetase activity and proliferation. These findings suggest that the change in HA synthesis is significant in the regulation of cell proliferation.

Dermatan sulphate proteoglycans from sclera examined by rotary shadowing and electron microscopy

Two dermatan sulphate-containing proteoglycans from bovine sclera were examined by rotary shadowing and electron microscopy, and the results were compared with previous biochemical findings. Both the large iduronate-poor proteoglycan (PGI) and the small iduronate-rich proteoglycan (PGII) possessed a globular proteinaceous region. Whereas PGI had a branched extension from the globular region, with five to eight side chains attached to it, PGII had only a single tail, which was of glycosaminoglycuronan. PGII aggregated via globular-region interactions, which were much diminished by reduction and alkylation. PGI aggregated via side chains and globular-region interactions. Although a few PGI aggregates were large, and similar to the hyaluronan-cartilage proteoglycan aggregates [Weidemann, Paulsson, Timpl, Engel & Heinegård (1984) Biochem. J. 224, 331-333], hyaluronan did not cause enhanced aggregation. PGII is very similar in shape to the small cartilage chondroitin sulphate proteoglycan, whereas PGI somewhat resembles the large cartilage chondroitin sulphate proteoglycan, although with many fewer glycosaminoglycan side chains, and probably only one globular region as opposed to two in the cartilage proteoglycan.

Glycosaminoglycan composition of electric organ basement membranes

The basement membranes of the innervated surface of the electric organ of Discopyge tschudii present a high concentration of mucopolysaccharides as revealed by intense ruthenium red-positive reaction. Glycosaminoglycans (GAGs) were isolated and characterized from these pure basement membranes by using a combination of agarose gel electrophoresis and enzymatic degradation with specific enzymes. The isolated basement membrane showed a high concentration of GAGs (130 mg/g of dry tissue); of this amount 49% was hyaluronic acid, 24% was chondroitin-6-sulfate, 12% was heparan sulfate, and 14% was dermatan sulfate. Controlled digestion with heparinase and heparitinases I and II was used to study the structural features of the heparan sulfate. Four unsaturated disaccharide units were found in the heparan sulfate: disulfated, N-sulfated, N-acetylated, and N-acetylated O-sulfated disaccharides. The disaccharide units of the cholinergic heparan sulfate present a high amount of disulfated disaccharides and a low amount of N-acetylated O-sulfated disaccharides. The N-sulfated disaccharides, in contrast to the N-acetylated ones, were found through all the structure of the cholinergic heparan sulfate. Finally our work shows for the first time the presence of dermatan sulfate in the basal lamina of the electric organ.

Characterization of bone PG II cDNA and its relationship to PG II mRNA from other connective tissues

Two cDNA clones encoding the small proteoglycan II (PG II) of bone were isolated from a lambda gt11 expression library. These clones expressed recombinant protein which was cross-reactive with polyclonal and monoclonal antisera to PG II molecules from several connective tissues. The longest clone, lambda Pg 20 was studied in detail. The clone was shown to encode PG II by hybrid selected translation and immunoprecipitation. Northern analysis showed two species of the PG II message of approximately 1.4 and 1.8 kb. Substantial amounts of PG II message were found in bone, tendon, articular cartilage, skin, smooth muscle and cornea. Trace amounts of message were also detected in liver and brain. Radiolabeled bovine PG II cDNA hybridized to RNA from several other species including the human, rat and chicken. The level of PG II mRNA in chick embryonic fibroblasts was sensitive to transformation by Rous sarcoma virus.

Internalization and metabolism of endogenous heparin by cultured endothelial cells

We have studied the ability of bovine adrenal capillary cells cultured in vitro to uptake and metabolize heparin. We have previously demonstrated that endogenous heparin can be extracted from human plasma (Vannucchi, S. et al., (1985) Biochem. J. 227, 57-65), and here we show that also endothelial cells contain heparin. However, experiments with (35S)sodium sulfate labeling indicate that these cells do not synthesize de novo heparin, but they uptake it from culture serum. Bovine adrenal capillary endothelial cells are able to bind and uptake (3H)heparin added to culture medium and they also release its low molecular weight degradation products, thus indicating a metabolism of heparin. We discuss about the role of endothelial cell-mediated uptake and metabolism of endogenous heparin in relationship with circulating heparin. We also discuss about these events as related to some of the antithrombogenic properties of the endothelium.