Isolation and characterization of proteoglycans from pig arterial wall

Changes in proteoglycans of cultured pig aortic smooth muscle cells during subculture

Smooth muscle cells were cultured from pig aorta. Changes in both the growth and the properties of sulfated proteoglycans were observed during passage. The population doubling time during log phase growth was 34 h from Passages 3 to 7-8 but 20 h at the Passage 11, and the cell density at the stationary phase, was 86,000 and 136,000 cells/cm2 at Passages 3 and 11, respectively. Structural characteristics of sulfated proteoglycans secreted into the medium were investigated after metabolic labeling with [35S]-sulfate. Significant differences were observed with age in vitro: a) [35S]proteoglycan complexes were in a greater amount at Passage 10 than at Passage 3; b) the hydrodynamic size of at least 45% of subunits and about 90% of monomers decreased with in vitro aging; c) this decrease in the size of proteoglycans was partly due to a decrease in the size of their glycanic chains; d) an increase of 15% in the proportion of dermatan sulfate was observed when cells were subjected to 10 passages.

Evidence for an interaction of lipoprotein lipase with artery wall proteoglycans

1. Artery wall proteoglycans-lipoprotein lipase binding characteristics were studied using bovine milk 125I-labelled lipoprotein lipase (LPL) and chondroitin sulphate-dermatan sulphate proteoglycans (PGs) purified from pig aorta. 2. The binding process was studied either by a soluble assay (gel filtration) or by an immobilized proteoglycan assay (ELISA). 3. The binding process was reversible, saturable and occurred at a stoichiometry 1:1. 4. The binding process involved ionic interactions between the positively charged groups of LPL and the negatively charged groups of PG carbohydrate chains. 5. The complex PG-LPL may lead to the production of remnant lipoproteins and, thereby, contribute to cholesteryl ester accumulation in the arterial wall.

Effect of endothelial-cell-conditioned medium on proteoglycan synthesis in cultured smooth muscle cells from pig aorta

The effect of porcine endothelial-cell-conditioned medium on proteoglycan synthesis by pig aorta smooth muscle cells was studied under serum-free conditions. Maximal stimulation of [35S]-sulfate incorporation (50%) into medium-secreted and cell layer proteoglycans was observed after 20 min and 4 h incubation, respectively. This stimulation can be explained neither by increased secretion nor by oversulfation of medium-secreted [35S]-labeled proteoglycans. Those [35S]-proteoglycans secreted (for 24 h) in the presence of endothelial cell-conditioned medium were characterized by a higher hydrodynamic size than those secreted in the presence of control medium, without modification of glycosaminoglycan chain length. Agreement between the stimulation of incorporation of [35S]-sulfate into glycanic chains (50.1%) and [14C]-serine residues associated with glycosaminoglycans (49.9%) involved an increase in the number of glycanic chains linked to protein cores. The lesser stimulation of [14C]-serine incorporation into secreted proteins (18%) suggested that stimulation of glycosaminoglycan synthesis was not the direct consequence of enhanced protein synthesis. Proteoglycan synthesis was studied in the presence of para-nitrophenyl-beta-D-xyloside. Fractionation of medium-secreted [35S]-proteoglycans and xyloside-initiated glycosaminoglycans revealed that stimulation of [35S]-glycosaminoglycan protein core acceptor for glycanic chain initiation. Our results suggest that the factor(s) secreted by endothelial cells are able to modify smooth muscle cell proteoglycan synthesis by stimulating the first step of protein core glycosylation. This stimulation was accompanied by an increase in proteoglycan hydrodynamic size.

Effect of insulin on sulfated proteoglycan synthesis in cultured smooth muscle cells from pig aorta

The effect of insulin upon proteoglycan synthesis was studied in cultured smooth muscle cells from pig aorta blocked in the G0 phase by serum deprivation. Insulin enhanced [35S]sulfate incorporation into cell layer and medium-secreted proteoglycans. The increase in incorporation of the precursor was not due to a mitogenic response by smooth muscle cells to the hormone and the specific radioactivity of proteoglycans showed that the stimulation reflected a real increase in sulfated proteoglycan synthesis. Maximal stimulation was observed, for the cell layer as well as for the medium, 40 h after the addition of 1.7 x 10(-7) M insulin and reached respectively 65 and 53%. This stimulation was about 80 and 60% of the level achieved with 10% fetal calf serum for cell layer and medium-secreted proteoglycans, respectively. The half-maximal effect was attained, for both the cell layer and the medium, in the presence of 2.1 x 10(-9) M insulin. Proteoglycans secreted into the medium, in the presence of 1.7 x 10(-8) M insulin for 40 h, showed a higher proportion of complexes (24%) than those synthesized in control medium (11%) and at least 95% of the monomers from culture treated with insulin were characterized by a smaller hydrodynamic size than those synthesized by cells maintained in control medium. This decrease in the size of proteoglycans was partly due to a decrease in the size of their glycanic chains.

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.

The structures of N- and O-glycosidic carbohydrate chains of a chondroitin sulfate proteoglycan isolated from the media of the human aorta

A large Mr chondroitin sulfate proteoglycan was extracted from the media of human aorta under dissociative conditions and purified by density-gradient centrifugation, ion-exchange chromatography, and gel filtration chromatography. Removal of a contaminating dermatan sulfate proteoglycan was accomplished by reduction, alkylation and rechromatography on the gel filtration column. After chondroitinase ABC treatment, the proteoglycan core was separated from a residual heparan sulfate proteoglycan by a third gel filtration chromatography step. As assessed by radioimmunoassay, the isolated proteoglycan core was free of link protein, but possessed epitopes that were recognized by antisera against the hyaluronic acid binding region of bovine cartilage proteoglycan as well as those that were weakly recognized by anti-keratan sulfate antisera. Following beta-elimination of the protein core, the liberated low Mr oligosaccharides were partially resolved by Sephadex G-50 chromatography, and their primary structure was determined by 500-MHz1H NMR spectroscopy in combination with compositional sugar analysis. The N-glycosidic carbohydrate chains, which were obtained as glycopeptides, were all biantennary glycans containing NeuAc and Fuc; microheterogeneity in the NeuAc----Gal linkage was detected in one of the branches. The N-glycosidic glycans have the following overall structure: (Formula: see text). The majority of the O-glycosidic carbohydrate chains bound to the protein core were found to be of the mucin type. They were obtained as glycopeptides and oligosaccharide alditols, and possessed the following structures: NeuAc alpha(2----3)Gal beta(1----3)GalNAc-ol, [NeuAc alpha(2----3)Gal beta(1----3)[NeuAc alpha(2----6)]GalNAc-ol, and NeuAc alpha-(2----3) Gal beta(1----3)[NeuAc alpha(2----3)Gal beta(1----4)GlcNAc beta(1----6)] GalNAc-ol. The remainder of the O-glycosidic carbohydrate chains bound to the isolated proteoglycan were the hexasaccharide link regions of the chondroitin sulfate chains that remained after chondroitinase ABC treatment of the native molecule. These latter glycans, which were obtained as oligosaccharide alditols, had the following structure (with GalNAc free of sulfate or containing sulfate bound at either C-4 or C-6): delta 4,5GlcUA beta(1----3)GalNAc beta(1----4)GlcUA beta(1----3)Gal beta(1----3)Gal beta(1----4)Xyl-ol.

Physical properties of chondroitin sulphate/dermatan sulphate proteoglycans from bovine aorta

Bovine aortic chondroitin sulphate/dermatan sulphate proteoglycans (PG-25, PG-35 and PG-50) were differentially precipitated with ethanol and analysed by a variety of chemical and physical techniques. The glycosaminoglycan chains of PG-25 and PG-35 contained a mixture of glucuronic acid and iduronic acid, whereas the uronic acid component of PG-50 was primarily glucuronic acid. In addition, various amounts of oligosaccharides containing small amounts of mannose, a galactose/hexosamine ratio of 1:1 and an absence of uronic acid were covalently linked to the core protein of all proteoglycans. The weight-average Mr (Mw) values of the proteoglycans determined by light-scattering in 4 M-guanidinium chloride were 1.3 X 10(6) (PG-25), 0.30 X 10(6) (PG-35) and 0.88 X 10(6) (PG-50). The s0 values of the proteoglycans were distributed between 7 and 8 S, and the reduced viscosities, eta sp./c, of all proteoglycans were dependent on the shear rate and polymer concentration. Electron microscopy of spread molecules revealed that PG-25 contained small structural units that appeared to self-associate into large aggregates, whereas PG-35 and PG-50 appeared mainly as monomers consisting of a core with various numbers of side projections. Hyaluronic acid-proteoglycan complexes occurred only with a small proportion of the molecules present in PG-35, and their formation could be inhibited by oligosaccharides. These results suggest the presence in the aorta of subspecies of chondroitin sulphate and dermatan sulphate proteoglycans, which show large variations in their physicochemical and inter- and intra-molecular association properties.

Synthesis of sulfated proteoglycans throughout the cell cycle in smooth muscle cells from pig aorta

Cultured smooth muscle cells from pig aorta arrested in G0 phase by serum deprivation were stimulated to proliferate by replacing the medium with one containing 10% serum. Studies in DNA replication and proliferation of cells showed a relatively good synchrony: 90% of the cells were in G1 phase for 16 h after addition of serum; they entered S phase between 18 and 24 h, completed S phase and traversed G2 phase between 24 and 30-32 h; 75% of these cells multiplied after 30-32 h and the remainder were blocked at the end of G2 phase. The synthesis and secretion of sulfated proteoglycans were examined throughout a full cell cycle using metabolic labelling with [35S]sulfate. Smooth muscle cells in G1 or G2 phase synthesized and secreted sulfated proteoglycans with a possible pause at the end of the G2 phase but at the beginning of the S phase and during mitosis the incorporation of [35S]sulfate into these macromolecules stopped entirely. Structural characteristics of sulfated proteoglycans secreted into the medium during G1 phase and an entire cell cycle were investigated. The proportion of proteoglycan complexes and the relative hydrodynamic size of monomers and of constituent subunits of complexes were determined after chromatography on Sepharose CL-2B and CL-6B columns run under both associative and dissociative conditions. No significant differences were observed for the periods of the cell cycle that were studied: [35S]Proteoglycan complexes represented at the end of G1 phase and of the cell cycle respectively 19 and 16% of the total [35S]proteoglycans secreted into the medium. More than 90% of the subunits, obtained after dissociation of complexes, were characterized by a similar kav after chromatography on Sepharose CL-2B columns eluted under dissociative conditions (kav 0.68 at the end of G1 phase and 0.65 at the end of full cell cycle). About 95% of monomers synthesized at the two stages of the cell cycle were eluted at kav 0.25 after chromatography on Sepharose CL-6B column run under associative conditions and were characterized by a similar glycosaminoglycan distribution. These results suggest that smooth muscle cells in culture liberate similar populations of proteoglycans into the medium during the G1 and G2 phases.

Proteoglycans and hypertension. II. [35S]sulfate incorporation into aorta proteoglycans of spontaneously hypertensive rats

Spontaneously hypertensive (SH) rats are known to have an increased content of chondroitin sulfate (CS) proteoglycans (PG) in the aorta as compared to normotensive Wistar Kyoto (WKY) rats. In the present study we have compared WKY and SH rat aortas with respect to [35S]sulfate incorporation in vivo and in vitro. The specific activity (cpm/mg aorta) of the total glycosaminoglycan (GAG) pool from SH rat aorta, measured 48 h after intraperitoneal injection of [35S]sulfate, was twice as high as that of WKY aorta GAG. After in vitro incubation of aortas for 4 or 6 h, the specific activity (cpm/mg aorta) of glycosaminoglycans from SH rat was 2.4- to 7.1-fold higher than in controls. Labeled PG were extracted with 4 M guanidine from aortas which had been incubated with [35S]sulfate, and chromatography of the extract on Sepharose CL-6B yielded two incompletely resolved peaks, one emerging with the void volume (peak I) and one in a more retarded position (peak II). Peak I (WKY) contained nearly equal amounts of CS and HS (53 and 46%, respectively) and a small amount of DS (8%). Peak II (WKY) (Kav, 0.34) was divided into two fractions; the fraction of larger molecular weight (II A) contained 43% CS, 35% DS, and 20% HS, whereas the smaller fraction (II B) contained 40% CS, 51% DS, and 5% HS. In each corresponding pool from SH rat aorta, a similar proportion of HS was found, but the DS content was approximately half, and the CS content was correspondingly greater. The estimated molecular weights of the CS/DS chains in peaks I, II A, and II B from WKY aorta were 34,600, 18,800, and 11,600 daltons, respectively, whereas the corresponding values for the SH rat aorta pools were 32,300, 24,700, and 17,000 daltons, respectively. The proportions of 4- and 6-sulfated galactosamine residues as well as the degree of sulfation of the CS/DS PG were similar in the two strains. The HS-PG was larger in the WKY rat aorta and was made up of larger HS chains (Mr 26,600 vs. 16,100); however, the degree of sulfation was apparently similar in the two strains. These results suggest that the rates of PG synthesis and/or degradation and the PG structure are altered in the SH rat aorta.

Investigation of relationships between collagens, elastin and proteoglycans in bovine thoracic aorta by immunofluorescence techniques

Types I, III and V collagens and proteoglycan were localized in the aorta by indirect immunofluorescence techniques. Type I collagen was more prominent in media and adventitia than in intima while type III collagen predominated in intima and media but appeared less significant in adventitia. Type V collagen was observed in intima and media only and was seen surrounding smooth muscle cells. Type I collagen was located between elastic fibres but type III collagen appeared to envelop the fibres, suggesting an interaction between elastic fibres and type III collagen. Pretreatment of sections with testicular hyaluronidase caused no changes in staining for type I collagen, but adventitial areas showed increased staining for type III collagen. After digestion with chondroitinase ABC, intimal and medial areas showed increased staining for type III collagen. Therefore, type III collagen forms stronger interactions with proteoglycans and hyaluronic acid than does type I collagen and type III collagen in adventitia is largely masked by hyaluronic acid, while type III collagen in intima and media is associated with proteoglycan. Thus, type III collagen is a more significant component of adventitia than previously recognized. Proteoglycan was also partly localized along elastic fibres. It is, therefore, suggested that elastic fibres are coated with type III collagen, which itself is coated with proteoglycan.

Distribution of proteoglycans and hyaluronic acid in transverse sections of bovine thoracic aorta

The distribution of hyaluronic acid and proteoglycans in bovine thoracic aorta was studied by Alcian Blue staining of frozen tissue sections under controlled electrolyte conditions with and without prior enzymic digestion. Some sections were digested with chondroitinase ABC, testicular hyaluronidase or bacterial collagenase and subsequent staining permitted conclusions to be drawn about the distribution of specific glycosaminoglycans within the tissue. The total glycosaminoglycan content was maximal in the intima and decreased across the arterial wall to the outermost adventitial layer. The content of proteoglycan containing chondroitin sulphate and/or dermatan sulphate chains paralleled this distribution. However, other glycosaminoglycans also contributed significantly to staining, although there was no evidence for any appreciable concentration of heparin or highly sulphated heparan sulphate. Several experiments indicated that proteoglycan containing chondroitin sulphate and/or dermatan sulphate was associated with elastic laminae which were often seen stained along their periphery. Hyaluronic acid was present at significant concentrations in all locations of the aorta and there was evidence for a similar distribution of heparan sulphate which was possible also present at a high concentration in the endothelium. Staining of sections after treatment with 4 M guanidinium chloride confirmed that this extractant removed most of the proteoglycan from the tissue section.

The structural characterization of proteoglycans of cultured aortic smooth muscle cells and arterial wall of the pig

Aortic proteoglycans, from the growth medium of cultured smooth muscle cells and from sequential associative and dissociative extracts of the tissue of origin, the pig aorta, were isolated and purified by precipitation with cetylpiridinium chloride. After isopycnic CsCl gradient centrifugation under associative conditions 94% of the cell-secreted proteoglycans were recuperated in the bottom one fifth (rho av = 1.62 g/ml) fraction. In contrast 80% of the tissue proteoglycans of both extracts, fractionated into two fractions: the bottom one fifth (rho av = 1.60 g/ml) fraction and three fifths (rho av = 1.42 g/ml) fraction. Fractionated tissue proteoglycans were composed predominantly of chondroitin sulfate-dermatan sulfate (83-90%) with lower proportions of heparan sulfate (5-11%) and hyaluronic acid (3-6%) whilst cell-secreted proteoglycans showed a similar glycosaminoglycan composition but with a higher proportion of hyaluronic acid (11-13%). Sepharose 2B and C1-2B chromatography of tissue proteoglycans of high buoyant density showed the presence of only subunit proteoglycans whilst those of intermediate density contained a complex species, partially dissociable in 4 M guanidinium chloride, along with Kav 0.50 subunit species. The latter was also observed for cell-secreted proteoglycans although obtained at high buoyant density. The cell-secreted subunit proteoglycans became separated into two distinct populations when chromatographed on Sepharose 4B and C1-4B, half of which eluted in the column Vo and the rest at a Kav of 0.34. The majority of subunit macromolecules eluted at the Vo fractions of Sepharose 6B and C1-6B columns. Unlike the major species of cartilage proteoglycans, only approx. 20% of purified arterial proteoglycans formed complexes. This proportion could be increased by only 4-7% by interaction, of a mixture of subunit cell-secreted and tissue-extracted proteoglycans, with hyaluronic acid. These results suggest that proteoglycans secreted by cultured aortic smooth muscle cells and present in the aortic tissue possess certain similar physicochemical properties and are present in the form of complex and several subunit species.

High molecular weight proteoglycans biosynthesized in culture by pigeon aortas

The properties of aortic proteoglycans synthesized in vitro were examined to demonstrate synthesis of intact proteoglycans by aortic tissue in culture and to compare labeling and synthetic rates of two different populations of proteoglycan. Following 3, 6, or 9 h of incubation in medium containing [35S]sodium sulfate and [3H]serine, the tissue was extracted with 4.0 M guanidine hydrochloride containing protease inhibitors. Extracts were chromatographed on Sepharose CL-4B and subjected to buoyant density centrifugation under dissociative conditions. Radioactive precursors were incorporated into two major populations of aortic proteoglycan, one of high molecular weight eluting near the void volume of Sepharose CL-4B (Proteoglycan I) and one of lower molecular weight (Proteoglycan II) having a Kav of 0.40-0.44. The radioactively labeled proteoglycans were localized at densities 1.50-1.56 g/ml (Preparation 1) and 1.43-1.49 g/ml (Preparation 2) following CsCl buoyant density centrifugation. Both proteoglycan populations had increased incorporation of 35S and 3H over time. At all times the lower molecular weight proteoglycan had a higher specific activity (dpm 35S and 3H/micrograms hexuronic acid). At 3, 6, and 9 h, the specific activity of Proteoglycan II was 8.2-, 6.7- and 3.0-fold higher than Proteoglycan I using 35S and 13.0-, 8.1- and 2.7-fold higher using 3H, suggesting different synthetic rates for the two proteoglycans. The results illustrate synthesis of intact proteoglycans during short-term artery culture. The proteoglycan types have size and buoyant density characteristics as described for artery, but based upon changes in specific activity ratios, the two proteoglycan populations differ in rates of synthesis.