Metabolism of glycosaminoglycans in cultured smooth muscle cells from pig aorta

Differential transport kinetics of chondroitin sulfate and dermatan sulfate proteoglycan by monkey aorta smooth muscle cells

Pulse-chase studies were performed to study the kinetics of chondroitin sulfate proteoglycan (CSPG) and dermatan sulfate proteoglycan (DSPG) transport in monkey aorta smooth muscle cells. During a short pulse (5 min) with [35S]Na2SO4 (500 microCi/ml), the cells synthesized 59% DSPG, 38% CSPG, and 3% heparan sulfate proteoglycan. Both DSPG and CSPG were transported out of the cell very rapidly after sulfate incorporation. At various chase times, proteoglycans (PGs) were isolated from four cellular compartments: (a) medium, (b) total cell lysate, (c) intracellular pool, and (d) extracellular pool. The PGs from the different pools were analyzed by Sepharose CL-2B column chromatography. The data of intracellular DSPG loss fitted a double exponential decay model: approximately 90% was secreted quickly with a t1/2 of 7 min, and the remaining 10% had a dramatically slower rate of secretion (t1/2 of 130 min). DSPG was rapidly secreted into the medium without prior accumulation in the extracellular matrix. In contrast, the loss of intracellular CSPG fitted a single exponential decay model with a t1/2 of 8 min; however, there was a significant accumulation of CSPG in the extracellular matrix compartment before release into the medium, resulting in a relatively slower secretion of CSPG into the medium (t1/2 of about 31 min). This delay in CSPG secretion into the medium is probably due to aggregation in the extracellular matrix, since addition of short hyaluronan oligomers (8-14 oligosaccharides) to the medium during the chase increased the rate of CSPG being secreted into the medium. We concluded that in aortic smooth muscle cell cultures, CSPG and DSPG are secreted via two distinct pathways through the cellular compartments.

Biosynthesis of sulfated proteoglycans in amphibian embryonal cells

The synthesis of sulfated proteoglycans in small explants from various parts of late blastulae from Ambystoma mexicanum or Xenopus laevis was investigated by incorporation of radioactive sulfate or glucosamine and galactosamine in media of low, normal or high tonicity. The explants differentiated into ciliated aggregates of fibroblast-like cells, or remained undifferentiated depending upon their origin in the embryo. High tonicity induces the explants to dissociate and prevents morphological differentiation, while low tonicity hardly affects this process. Yet, both types of media decrease the incorporation into glycosaminoglycans to various degrees, ranging from 40 to 80%, depending upon the species. In Xenopus, the uptake of sulfate is inhibited by as much as 90% in high tonicity media. The rate of incorporation of label is approximately twice as much in mesodermal as in animal or vegetal aggregates, which do not differ significantly. Animal aggregates from Ambystoma, however, revealed an exceptionally high uptake of sulfate. The relative distribution of chondroitin sulfates and heparan sulfates is not affected by changes in tonicity, except in Xenopus where high tonicity severely suppresses the synthesis of heparan sulfates, and is independent of the type of aggregate. The relationship between the synthesis of sulfated proteoglycans and processes involved in cell differentiation, especially cell adhesion, is discussed.

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.

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.

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.

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.

[35S]proteoglycan metabolism of arterial smooth muscle cells cultured from normotensive and hypertensive rats

Arterial smooth muscle cells cultured from normotensive and hypertensive rats incorporated [35S]sulfate into the extracellular and pericellular sulfated proteoglycans and endocytose extracellular [35S]proteoglycans at a significantly higher rate in the phase of logarithmic growth than did nondividing cells. 35S incorporation into proteoglycans was positively correlated with [3H]thymidine incorporation into the cellular TCA-precipitable material. The rates of [35S]proteoglycan synthesis and endocytosis per cell pr day were higher in smooth muscle cells from hypertensive than from normotensive animals, the observed differences being related to a higher average protein content of smooth muscle cells cultured from hypertensive rats as compared with cells of normotensive animals. Gel filtration under dissociative conditions separated the [35S]proteoglycans into high and low molecular weight fractions (A, B) differing in glycosaminoglycan composition and their ability to be endocytosed by smooth muscle cells. The relative proportion of the high molecular weight proteoglycan fraction A decreased continuously from sparse to confluent cell cultures.

A method to evaluate the biosynthesis of glycosaminoglycans by the aorta of Cynomolgus monkey

The biosynthesis of the glycosaminoglycans (GAGs) was investigated in vitro in the aortic tissue of the Cynomolgus monkey incubated with [14C]glucosamine. With the use of a new micromethod, it was possible to quantify the glycosaminoglycans and their radioactive distribution in the aortic tissue and incubation medium. Labeled and nonlabeled chondroitin 6-sulfate, dermatan sulfate, heparan sulfate and hyaluronic acid were measured. Since the sensitivity of this procedure is between 5 and 20 micrograms of GAGs, as little as 5 mg of dry defatted aortic tissue is sufficient for chemical and radioactive analyses.