The effect of cell density on net rates of glycosaminoglycan synthesis and secretion by cultured rat fibroblasts

Fatty Acid Fingerprints and Hyaluronic Acid in Extracellular Vesicles from Proliferating Human Fibroblast-like Synoviocytes

Extracellular vesicles (EVs) function as conveyors of fatty acids (FAs) and other bioactive lipids and can modulate the gene expression and behavior of target cells. EV lipid composition influences the fluidity and stability of EV membranes and reflects the availability of lipid mediator precursors. Fibroblast-like synoviocytes (FLSs) secrete EVs that transport hyaluronic acid (HA). FLSs play a central role in inflammation, pannus formation, and cartilage degradation in joint diseases, and EVs have recently emerged as potential mediators of these effects. The aim of the present study was to follow temporal changes in HA and EV secretion by normal FLSs, and to characterize the FA profiles of FLSs and EVs during proliferation. The methods used included nanoparticle tracking analysis, confocal laser scanning microscopy, sandwich-type enzyme-linked sorbent assay, quantitative PCR, and gas chromatography. The expression of hyaluronan synthases 1-3 in FLSs and HA concentrations in conditioned media decreased during cell proliferation. This was associated with elevated proportions of 20:4n-6 and total n-6 polyunsaturated FAs (PUFAs) in high-density cells, reductions in n-3/n-6 PUFA ratios, and up-regulation of cluster of differentiation 44, tumor necrosis factor α, peroxisome proliferator-activated receptor (PPAR)-α, and PPAR-γ. Compared to the parent FLSs, 16:0, 18:0, and 18:1n-9 were enriched in the EV fraction. EV counts decreased during cell growth, and 18:2n-6 in EVs correlated with the cell count. To conclude, FLS proliferation was featured by increased 20:4n-6 proportions and reduced n-3/n-6 PUFA ratios, and FAs with a low degree of unsaturation were selectively transferred from FLSs into EVs. These FA modifications have the potential to affect membrane fluidity, biosynthesis of lipid mediators, and inflammatory processes in joints, and could eventually provide tools for translational studies to counteract cartilage degradation in inflammatory joint diseases.

Identification and regulation of the eukaryotic hyaluronate synthase

Hyaluronate synthesis is required for fibroblast detachment in mitosis and migration. It is regulated by the activity of the synthase which is localized at the inner side of plasma membranes. The synthase was identified as a 50 kDa protein by immunological cross-reaction with the streptococcal enzyme and by affinity labelling. Transformation of fibroblasts by Rous sarcoma virus activated the synthase by enhanced transcription and phosphorylation. The synthase was a natural target of pp60v-src kinase.

Hypoxia-induced alterations in hyaluronan and hyaluronidase

Hyaluronan (HA), a large negatively-charged polysaccharide, is a major component of vessel basal membrane. HA is expressed by a variety of cells, including tumor and endothelial cells. We hypothesized that HA could be up-regulated by hypoxia to enhance vessel formation. To determine the effect of hypoxia on the production of HA, tumor cells were treated with either media alone (control) or a hypoxia inducer (CoCl or NaN3) for 24 h. The level of HA in the media was then measured by ELISA. The results showed that both CoCl and NaN3 induced the production of HA. Since the low molecular weight form of HA (SMW) possesses pro-angiogenic properties, we investigated whether hypoxia-induced HA can be processed into SMW. Under hypoxic conditions, the activity of hyaluronidase, the enzyme responsible for degrading HA, was measured by an ELISA-like assay. The activity of hyaluronidase was shown to be up-regulated by hypoxia and, further, could carry out the function of processing HA into SMW. In addition, the hypoxic areas of tumor tissues were stained strongly with biotinylated HA-binding proteins, indicating that the level of HA was high compared to the oxic areas. This study demonstrates that hypoxia can stimulate the production of HA and the activity of hyaluronidase, which may promote angiogenesis as a compensation mechanism for hypoxia.

Growth Physiology of the Hyperthermophilic Archaeon Thermococcus litoralis: Development of a Sulfur-Free Defined Medium, Characterization of an Exopolysaccharide, and Evidence of Biofilm Formation

Nutritional characteristics of the hyperthermophilic archaeon Thermococcus litoralis have been investigated with emphasis on the development of a sulfur-free, defined growth medium, analysis of an exocellular polysaccharide, and formation of a biofilm. An artificial-seawater-based medium, containing 16 amino acids, adenine, uracil, vitamins, and trace elements, allowed T. litoralis to attain growth rates and cell densities similar to those found with complex media. Four amino acids (alanine, asparagine, glutamine, and glutamate) were not included due to their lack of effect on growth rates and cell yields. In this medium, cultures reached densities of 10(sup8) cells per ml, with doubling times of 55 min (without maltose) or 43 min (with maltose). Neither the addition of elemental sulfur nor the presence of H(inf2) significantly affected cell growth. A sparingly soluble exopolysaccharide was produced by T. litoralis grown in either defined or complex media. Analysis of the acid-hydrolyzed exopolysaccharide yielded mannose as the only monosaccharidic constituent. This exopolysaccharide is apparently involved in the formation of a biofilm on polycarbonate filters and glass slides, which is inhabited by high levels of T. litoralis. Biofilm formation by hyperthermophilic microorganisms in geothermal environments has not been examined to any extent, but further work in this area may provide information related to the interactions among high-temperature organisms.

Effects of retinoids on glycosaminoglycan synthesis by human skin fibroblasts grown as monolayers and within contracted collagen lattices

Fibroblasts grown within contracted collagen lattices synthesize substantially less glycosaminoglycans than fibroblasts grown as monolayers on a plastic substrate. [3H]glucosamine incorporation into hyaluronate was reduced by 70%, and incorporation into sulphated glycosaminoglycans was reduced by 40%. However, incorporation into heparan sulphate and chondroitin sulphates was reduced by 14 and 49%, respectively, resulting in a substantial change in the proportions of the individual glycosaminoglycans. On the basis of [3H]glucosamine incorporation, hyaluronate constituted 80% of the total glycosaminoglycans synthesized in monolayer cultures, but only 67% in collagen lattice cultures. Incorporation of 35SO4 into chondroitin sulphates was reduced by 22%, whereas no change was observed in heparan sulphates following culture within collagen lattices. Exposure of the fibroblast cultures to retinoic acid (10(-6) mol/l) and retinyl propionate (2 x 10(-6) mol/l) resulted in a decrease in the incorporation of [3H]glucosamine into hyaluronate by up to 41% in monolayer cultures, and 25% in collagen lattice cultures. The retinoids stimulated the incorporation of [3H]glucosamine into heparan sulphate by up to 72%, and chondroitin sulphates by up to 30%, whereas 35SO4 incorporation remained essentially unaltered. Only modest changes in the incorporation of both isotopes into fibroblast sulphated glycosaminoglycans were observed following exposure to the retinoids in lattice cultures. Q-Sepharose ion-exchange chromatography at pH 2.0 revealed that there was no change in the degree of polymer sulphation of either chondroitin sulphate or heparan sulphate isolated from collagen lattice cultures compared with monolayer cultures. Retinoic acid (10(-6) mol/l) treatment did, however, reduce the degree of polymer sulphation of heparan sulphates and chondroitin sulphates in both monolayer and lattice cultures.(ABSTRACT TRUNCATED AT 250 WORDS)

Corticosteroid Suppression of TraumaInduced Hyaluronan in Rabbit Cornea and Aqueous

BACKGROUND

Corneal and aqueous hyaluronan have recently been shown to react in response to several different types of trauma, including cataract surgery. In order to find ways to influence the reaction, we have evaluated the effect of topical dexamethasone (Isopto-Maxidex, Alcon Universal Ltd, Fort Worth, Tex) or indomethacin (Confortid, Dumex Ltd, Copenhagen, Denmark) on the postoperative hyaluronan concentration in rabbit cornea and aqueous after extracapsular lens extraction.

METHODS

The drugs were administered as topical eye drops three times daily. The hyaluronan concentration in rabbit cornea and aqueous after extracapsular lens extraction was measured with a radioligand assay.

RESULTS

Dexamethasone treatment (1 mg/mL) significantly suppressed the increase in corneal hyaluronan seen after extracapsular lens extraction, 2 (p < or = 0.0022) and 3 weeks (p < or = 0.0002) after surgery, while indomethacin did not induce any significant difference at 2 weeks. When the dexamethasone concentration was lowered to 0.1 and 0.2 mg/mL, there was still a significant decrease (p < or = 0.009) in hyaluronan concentration, but at lower concentrations of dexamethasone (0.01 and 0.02 mg/mL), no significant decrease was seen. The increase in aqueous hyaluronan concentration seen 2 days after surgery in untreated eyes was significantly lowered by both dexamethasone (p < or = 0.0076) and indomethacin (p < 0.036).

CONCLUSIONS

Dexamethasone lowers reactive corneal and aqueous hyaluronan concentration in vivo after extracapsular lens extraction.

Stimulation of glycosaminoglycan synthesis in cultured fibroblasts by hyperbaric oxygen

In this study we examined the effect of hyperbaric oxygen treatment on the synthesis of glycosaminoglycans by fibroblasts isolated from wounds and normal skin. Fibroblast cultures were exposed to seven treatments of intermittent hyperbaric oxygen, and then metabolically labelled with D-[6-(3)H] glucosamine. Hyaluronic acid and proteoglycan synthesis were determined by measuring the radioactivity precipitated with cetylpyridinium chloride before and after digestion with hyaluronidase. Hyperbaric oxygen treatment resulted in an increased synthesis of hyaluronic acid and proteoglycans by fibroblasts from wounds and normal skin. Overall, the average increase in total glycosaminoglycan synthesis after hyperbaric oxygen treatment was 28%, whereas fibroblast proliferation was decreased by 7%. These results suggest that one of the effects of this treatment on a wound may be to increase the ratio of extracellular matrix to cells. Such a change could have important consequences for cellular activities essential for effective wound healing, such as migration of cells into the wound and control of cell function.

Glycosaminoglycans in the human aorta in diabetes mellitus: a study of tunica media from areas with and without atherosclerotic plaque

Alterations in the connective tissue of the arterial wall have been suggested to play a role in the development of macrovascular disease in diabetes mellitus. The present study deals with changes in the content of GAG in aortic tunica media in human diabetes by separately analysing normal areas and areas with fibrous plaques. The thoracic aorta from 15 diabetic patients (7 with IDDM, 8 with NIDDM), and 30 sex- and age-matched non-diabetic subjects were collected at autopsy. Tunica intima was removed and GAG were isolated from the dried defatted and pulverized tunica media. GAG were quantified by uronic acid analysis and characterized by electrophoresis on cellulose acetate. Results showed that IDDM patients had a relative and absolute increase in hyaluronic acid in normal tunica media compared to non-diabetic subjects. There was a significant positive correlation between hyaluronic acid content of normal tunica media and duration of diabetes, but not between hyaluronic acid content and age. When tunica media from plaque areas was compared to normal areas the same pattern was evident in diabetic patients as in non-diabetic patients--significantly increased proportion of dermatan sulphate and reduced hyaluronic acid. The data agree with the notion that the arterial wall is subject to different pathological processes in diabetes, one of classical atherosclerosis with changes in GAG similar to non-diabetic subjects, and the other seen in areas without plaques with dissimilar alterations in GAG. These data therefore support the concept of the presence of a macrovascular disease in diabetes different from atherosclerosis.

Stimulatory effect of TGF-beta on anionic glycoconjugate synthesis by rat calvarial cells: specificity, uncoupling of cell density dependence, and modulation by chondroitin sulfate

Anchorage-dependent cultures of a population of cells derived from the outer part of the rat calvaria demonstrated decreased net accumulation of radiolabeled chondroitin sulfate (CS) and hyaluronic acid (HA) per cell as the cell density of the cultures increased. The addition of TGF-beta 1 resulted in large stimulations of the net CS, but not of the net HA, accumulating in the medium at all cell densities and an abolition of the density-dependent effect. These effects were largely due to increases in newly synthesized CS appearing in the medium. Supplementation of the culture media with CS had complex but relatively small effects on the stimulation of the net accumulation of radiolabeled medium CS by TGF-beta 1. The addition of TGF-beta 1 also resulted in a biphasic effect on cell growth that depended on the plating density, but cell growth differences could not account for the marked stimulation of CS synthesis by TGF-beta 1. Experiments with cycloheximide and beta-xyloside and isolation of the intact anionic glycoconjugates (AG) indicated that although synthesis of core protein was the limiting factor in CS synthesis, TGF-beta 1 stimulated the synthesis of CS chain when sufficient beta-xyloside acceptor was available. The overall results suggest that, in this cell system, the action of TGF-beta 1 on the synthesis of the major extracellular AGs is characterized by a relatively specific upregulation of CS proteoglycan (PG) synthesis and an uncoupling of the inhibitory effect of high cell density on CS PG synthesis.

Histochemical identification of hyaluronan in the rabbit anterior segment during the healing period after extracapsular lens extraction

Extracapsular lens extractions were performed in rabbits. The eyes were examined at different time intervals after surgery with a histochemical method visualizing hyaluronan. There was positive staining for hyaluronan in the wound region from 2 to 90 days postoperatively. The staining was most intense and widespread between 7 and 14 days after surgery. A hyaluronan staining in the corneal stroma extended from the wound towards the central cornea 4 to 14 days postoperatively. The iris showed increased staining on the second postoperative day, but much less so at the other times studied. Cells on the posterior lens capsule were surrounded by hyaluronan from the seventh postoperative day throughout the observation time up to 90 days postoperatively. It is concluded that hyaluronan reacts during corneal wound healing.

Stimulation of cell proliferation by hyaluronidase during in vitro aging of human skin fibroblasts

The effect of the degradation of extracellular hyaluronan on the proliferation of human skin fibroblasts in serial cultures during in vitro aging was investigated. Human skin fibroblasts at different time intervals from 3rd to 36th passages were exposed after plating to bovine testicular hyaluronidase. The enzyme treatment resulted in an increase in cell proliferation (cell number vs. time) as compared to the untreated control fibroblasts. The effect was dose dependent, reversible, and was independent of the type of the glycosidic linkage cleaved in hyaluronan. The increased proliferation was observed at all passages when untreated cells underwent mitosis. The degradation of hyaluronan induced cell proliferation up to the presenescent phase. Depletion of hyaluronan did not induce proliferation of postmitotic fibroblasts. The incorporation of 3H-glucosamine into hyaluronan decreased with increasing cell passages (increase of the number of population doublings). Twenty-fourth passage fibroblasts accumulated about two time less hyaluronan in the medium than ninth passage cultures. Following hyaluronidase treatment, the amount of newly synthesized, labeled hyaluronan increased in the medium. Accordingly, the fibroblasts restored the degraded hyaluronan even in the declining phase of proliferation (phase III according to Hayflick).

Growth-related production of proteoglycans and hyaluronic acid in synchronous arterial smooth muscle cells

1. The growth-stimulating effect of serum on the proteoglycan and hyaluronic acid production in arterial smooth muscle cells was investigated, using cells synchronized by serum deprivation. 2. After stimulation, synthesis of [35S]sulfated proteoglycans and [14C]hyaluronic acid increased during G1 and G2 phases (about 2- and 5-fold, respectively, in the culture medium), in comparison with quiescent cells. 3. Neither the size, nor the charge, nor the relative proportions of [35S]glycosaminoglycans of the proteoglycans were modified. 4. However, when the cells were stimulated to divide, increased synthesis of large [14C]hyaluronic acid was observed concomitantly with the production of higher hydrodynamic size [35S]proteoglycans, which aggregated with hyaluronic acid (20%).

Circulating hyaluronic acid in nonpregnant, pregnant, and postpartum guinea pigs: elevated levels observed at parturition

OBJECTIVE

Dilatation of the uterine cervix at parturition is associated with an increase in cervical hyaluronic acid content. The objective is to test the hypothesis that circulating hyaluronic acid is increased at parturition.

STUDY DESIGN

Serum hyaluronic acid levels from nonpregnant (n = 5), pregnant (n = 13), and postpartum (n = 4) adult Hartley guinea pigs were determined with a radiometric assay that utilizes iodine 125-labeled hyaluronic acid-binding protein. Results were analyzed for statistical significance with Student's paired t test and regression analysis.

RESULTS

The serum hyaluronic acid level in nonpregnant animals was 238 +/- 88 ng/ml (mean +/- SEM). During pregnancy, serum hyaluronic acid levels were 127 +/- 12 and 126 +/- 34 ng/ml at 25 and 50 to 63 days' gestation, respectively. At parturition, hyaluronic acid levels increased fivefold to 765 +/- 111 ng/ml (p less than 0.001). Hyaluronic acid levels returned to antepartum values 2 days post partum (153 +/- 27 ng/ml). There was no significant difference between arterial and venous levels.

CONCLUSION

Circulating hyaluronic acid levels increase significantly at parturition in the guinea pig.

Heterogeneity amongst fibroblasts in the production of migration stimulating factor (MSF): implications for cancer pathogenesis

Fetal skin fibroblasts migrate into 3D collagen gels to a significantly greater extent than do adult cells. This enhanced motility of fetal fibroblasts appears to result from the production of a "migration stimulating factor" (MSF) which is not made by their normal adult counterparts. Adult skin fibroblasts retain responsiveness to MSF and cells exposed to this factor achieve the elevated levels of migration characteristic of fetal cells. MSF has been purified to homogeneity, has an apparent molecular mass of 70 kD and has been further characterized in terms of a number of biochemical parameters. Studies concerned with the mechanism of action of MSF indicate that it stimulates the production of a high molecular weight class of hyaluronic acid (HA). Concurrent exposure of cells to Streptomyces hyaluronidase blocks the stimulation of adult fibroblast migration by MSF. In a related series of experiments, we have shown that TGF-beta inhibits the effects of MSF on both cell migration and HA production. Taken together, these data suggest that the stimulation of fibroblast migration by MSF is dependent upon (and may directly result from) a primary induction of HA synthesis. We have previously reported that skin fibroblasts obtained from patients with sporadic and familial breast cancer, as well as the unaffected first-degree relatives of familial breast cancer patients, commonly display a fetal-like migratory phenotype. Subsequent work has indicated that (a) these fetal-like cells also produce MSF, and (b) detectable levels of MSF are present in the serum of sporadic breast cancer patients both prior to and following surgical resection of the primary tumor mass. On the basis of these and related observations, we have put forward an hypothesis suggesting that the disruption in normal epithelial-mesenchymal interactions caused by the persistent production of MSF by fibroblasts in the adult may contribute directly to the pathogenesis of an epithelial cancer. The demonstration of aberrant fibroblasts in sporadic cancer patients (both in our own and independent studies) is not consistent with the "germ-line genetic lesion" model commonly invoked to account for the presence of such cells in patients with hereditary cancer syndromes.(ABSTRACT TRUNCATED AT 400 WORDS)

Influence of cell culture conditions on aromatase activity in human genital skin fibroblasts

Because the measurement of aromatase activity in cultured human genital skin fibroblasts has been proposed as a means of studying estrogen production in men, we investigated the influence of culture conditions on aromatase activity. Genital skin fibroblasts were seeded onto culture plates at a density of 1 X 10(6) cells/plate and aromatase activity was determined over a 1-mo. period. Enzyme activity rose slowly over the first 14 d but then rose rapidly to a 10-fold higher plateau by Day 28. The rise in aromatase activity was similar whether activity was normalized for protein or for DNA content. When cells were seeded at the usual density of 1 X 10(6) or at 0.25 X 10(6) cells/plate, aromatase activity was consistently lower during the first 2 wk in cells plated at lower density, but thereafter the levels of enzyme activity in the two groups converged. In cells plated at the lower density, the lower activity observed in the first 2 wk was associated with a lower Vmax. Preincubation of cells plated at one density with conditioned medium from cells plated at the other density did not change the relative levels of activity in the two groups. By contrast, dihydrotestosterone (DHT) receptor binding and 5 alpha-reductase activity were similar at all time points, despite differences in plating density. In additional experiments, the culture medium was replaced daily rather than every 3rd d, and aromatase activity was assayed on Day 7. In cells fed daily, DNA and protein content were twice that of cells fed every 3rd d. By contrast, aromatase activity declined to 30% of that in the latter group. DHT and dexamethasone receptor binding and 5 alpha-reductase activity were similar in the two groups. In summary, factors such as plating density, culture density, and frequency of media replacement dramatically influence aromatase activity in cultured human genital skin fibroblasts. Therefore, the interpretation of aromatase activity data obtained from cultured cells in relation to physiologic or pathologic states should be viewed with appropriate caution.

Concentration of hyaluronan in the serum of untreated cancer patients with special reference to patients with mesothelioma

The concentration of hyaluronan was measured in the serum from patients with tumors. The patients were divided into nine groups: two control groups, i.e., those with benign tumors and those having undergone radical surgery; and seven groups of patients with untreated malignant conditions, i.e., mesotheliomas, sarcomas, lymphomas, breast carcinomas, brain tumors, bronchial carcinomas, and a group of various malignancies. As an additional control group, subjects with benign pulmonary diseases were investigated. The control groups and all the groups with malignant tumors except the mesotheliomas had serum hyaluronan values equal to or only slightly higher than those of healthy volunteers of the same age. The patients with mesotheliomas had significantly elevated hyaluronan levels (287 +/- 282 [Standard deviation] micrograms/l; n = 35; P less than 0.001) compared with healthy volunteers (54 +/- 28 micrograms/l in the age group of 51 to 60 years). Patients with asbestosis do not exhibit increased serum hyaluronan. The analysis of serum hyaluronan should therefore be of value in the diagnosis of mesothelioma.

The effect of the outer membrane fraction of Bacteroides gingivalis W50 on glycosaminoglycan metabolism by human gingival fibroblasts in culture

The synthesis of extracellular [35S]-SO4- and [3H]-glucosamine-labelled glycosaminoglycan (GAG) was studied in confluent human gingival fibroblast cultures in vitro. The differential synthesis of the total chondroitin sulphate/dermatan sulphate (CS/DS) and heparan-sulphate (HS) fraction was measured following chondroitinase-ABC digestion, nitrous-acid treatment and column chromatography on Sephadex G50. Control cultures synthesized a CS/DS fraction that represented 78 per cent of the total [35S]-SO4-GAG; the residual 22 per cent was heparan sulphate. Similar cultures were labelled with [3H]-glucosamine and the proportions of a high molecular-weight hyaluronic acid (HA) and proteoglycan fractions measured by gel-filtration HPLC after papain and hyaluronidase digestions. The HA fraction represented 66 per cent of the total isotope incorporated in control cultures. GAG chains released on treatment with papain (24 per cent of the total label incorporated) were of apparent molecular weight 17-20 kDa. All cultures exposed to Bacteroides gingivalis W50 outer membrane at concentrations between 2 and 50 micrograms ml-1 displayed a decrease in the CS/DS fraction and a reciprocal increase in the HS. However, the proportion of HA synthesized was slightly enhanced with a reciprocal decrease in the proteoglycan (papain-digestible) fraction. There was no alteration in the molecular weight of the papain-digestion products or the size distribution of the hyaluronic-acid fraction.

Hyaluronate inhibition of cell proliferation

The proliferation of rabbit synovial cells, 3T3 cells, or simian virus-transformed 3T3 cells in cell culture was inhibited by the addition of hyaluronate to the culture medium. This effect was markedly dependent on the molecular weight and concentration of the hyaluronate. At the molecular weight and concentration of hyaluronate present in normal synovial fluid, proliferation was inhibited. At lower molecular weights or concentrations, as found in rheumatoid synovial fluid, hyaluronate was significantly less inhibitory. Thus, the changes in synovial fluid hyaluronate that are associated with arthropathies may contribute to a favorable environment for rheumatoid pannus expansion.

Comparison of the stimulation of glycosaminoglycan synthesis in cultures of mononuclear cells from blood and of fibroblastic cells

A small molecular weight factor, derived from bovine bone ('matrigenin'), stimulated glycosaminoglycan and proteoglycan synthesis of cultured human fibroblastic cells but not of mononuclear cells from human blood. However, proteoglycan synthesis and secretion by the mononuclear cells was stimulated by the addition of concanavalin A. The proteoglycan from the concanavalin-A-stimulated mononuclear cells was of smaller molecular weight than the proteoglycan from the 'matrigenin'-stimulated fibroblastic cells. The major increase in proteoglycan synthesis and secretion occurred much later during the culture period for concanavalin-A-stimulated mononuclear cells than for 'matrigenin'-stimulated fibroblastic cells.

Effects of colchicine on sulfated glycosaminoglycan production and cell detachment in pre-capillary pulmonary endothelial cells

The effects of colchicine on the morphology, substrate adhesiveness, and production of glycosaminoglycan (GAG) macromolecules by cultured pre-capillary pulmonary endothelial cell were studied. Colchicine-treated cells demonstrated altered morphology and decreased substrate adhesiveness compared to untreated cells. In addition, [35S]sulfate incorporation into glycosaminoglycans was decreased 33% after treatment with colchicine. Spectrophotometric measurement of total cellular GAG revealed a similar GAG reduction in colchicine-treated cells. The composition of [35S]sulfate radiolabelled GAG was similar in cultures with and without colchicine, consisting of approximately 56% chondroitin sulfate and the remainder heparin/heparan sulfate. The results indicate that colchicine influences the biological behavior of pre-capillary endothelial cells, in part by altering the amount of glycosaminoglycan molecules produced.

Biochemistry of hyaluronan

Hyaluronan (hyaluronic acid) is a linear polysaccharide formed from disaccharide units containing N-acetylglucosamine and glucuronic acid. It is ubiquitously distributed in the organism but is found in the highest concentrations in soft connective tissues. The molecular weight of hyaluronan is usually in the order of 10(6) to 10(7). Due to hydrogen bonding, the chain is rather stiff and the molecule behaves in solution as an extended, randomly kinked coil. Molecules of hyaluronan start to entangle already at concentrations of less than 1 g/l and form a continuous polymer network. Some of the functions of the polysaccharide have been connected with the unique physical chemical characteristics of the network such as its rheological properties, flow resistance, osmotic pressure, exclusion properties and filter effect. Hyaluronan is synthesized in the cell membrane by adding monosaccharides to the reducing end of the chain. The precursors are UDP-glucuronic acid and UDP-N-acetylglucosamine. The polysaccharide grows out from the cell surface and it can be shown that fibroblasts, for example, surround themselves with a coat of hyaluronan. The rate of biosynthesis is regulated by various factors, such as growth factors, hormones, inflammatory mediators, etc. The responsible enzyme, hyaluronan synthase, is a phosphoprotein and the regulation of the synthetic rate is apparently via phosphorylation. The hyaluronan is at least partly carried by lymph flow from the tissues. Part of the material is taken up and degraded in the lymph nodes. Another part is carried to the general circulation and taken up in the endothelial cells in the liver sinusoids. These cells have specific receptors for hyaluronan, which also recognize chondroitin sulphate. The uptake in the liver of high-molecular weight hyaluronan is very efficient and its normal half-life in serum is only in the order of 2 to 5 min. The polysaccharide is rapidly degraded in the lysosomes to low-molecular weight products, lactate and acetate. The total turnover of hyaluronan in serum is in the order of 10-100 mg/24 h. The normal concentration of hyaluronan in serum is less than 100 micrograms/l with a mean of 30-40 micrograms/l. High serum levels have been noted in liver cirrhosis (impaired uptake in the liver) and rheumatoid arthritis (increased synthesis in the tissues). Hyaluronan has been shown to interact specifically with certain proteins and cell surfaces. It binds to proteoglycans in cartilage and other tissues and fills an important structural role in the organization of the extra-cellular matrix.(ABSTRACT TRUNCATED AT 400 WORDS)

Glycosaminoglycan metabolism of HL-60 cells during differentiation induction by tetradecanoylphorbol-13-acetate

Many biochemical responses to phorbol ester differentiation inducers have been reported, including alterations in synthesis of specific gene products such as glycoproteins. Stage-specific glycosaminoglycan changes have previously been associated with the differentiation process, including a dramatic reduction in cellular chondroitin 4-sulfate during human myeloid leukemia cell maturation induced by 12-O-tetradecanoylphorbol-13-acetate (TPA). We have demonstrated that treatment of HL-60 human promyelocytic leukemia cells with 4-methyl-umbelliferyl-beta-D-xyloside increases precursor incorporation into glycosaminoglycans linked to beta-D-xyloside, rather than core protein, eliminating the need for core protein and xylosyltransferase. Therefore, these beta-D-xyloside-treated cells were used to study the decreased glycosaminoglycan production during TPA-induced HL-60 differentiation. Exposure of these pretreated HL-60 cells to TPA, which induces macrophage-like maturation, resulted in a 70% reduction of incorporation of [35S]sulfate into cell-associated glycosaminoglycans. Thus, even in HL-60 cells in which glycosaminoglycan production is maximally stimulated by beta-D-xyloside, TPA is a strong inhibitor of free glycosaminoglycan chain production, and this biochemical effect is associated with other features of leukocyte maturation.

Density-dependent regulation of skin-fibroblast glycosaminoglycans in vitro: control by a secreted factor

Glycosaminoglycans (GAG) secretion by human skin fibroblasts in monolayer culture was inversely proportional to cell density, the relationship applying both within and between cultures of different fibroblast lines. There was neither substantial extracellular degradation nor significant endocytosis of the GAG from the culture medium. The mechanism controlling the inhibition of secretion did not involve the exhaustion of serum in the culture medium, a decline in cell viability or a negative feedback related to hyaluronic-acid concentration, and did not require intercellular contact. The inhibitory factor could be transferred from one culture to another and appeared to be secreted by the fibroblasts concomitantly with the GAG. The effect of cell density on GAG must be considered in future studies of drugs in vitro or other manipulations of the cellular environment.

An electron microscopic demonstration of induction of chondrogenesis in neonatal rat muscle outgrowth cells in monolayer cultures

Second passage fibroblast-like cells grown from explants of neonatal rat muscle continue to demonstrate fibroblast-like properties for many days when cultured on plastic surfaces. Such cells can be induced to change to a chondrocyte-like mode of expression by the addition of effector materials prepared from bovine cortical bone decalcified with 0.6 N HCl. Other studies show that similar demineralized bone particles and extracts from them have, in vivo, osteoinductive properties. Optimum conditions for this differentiation in monolayer culture were found in the use of 2% fetal calf serum with Dulbecco's modified Eagles medium. At 10% fetal calf serum the chondrogenic changes could not be detected. Light microscopy showed a sequence of morphological changes, after 36 h in culture, which resembled those seen at the beginning of osteogenesis in vivo. Induced cultures showed abundant extracellular proteoglycan production. Isotope incorporation studies showed stimulation of glycosaminoglycan synthesis in response to effector materials in soluble form. Type II collagen could be detected after three days. Electron microscopic analysis of induced and control cultures showed unequivocal evidence for marked production of an extensive extracellular matrix in the region of effector particles. The cells themselves change shape and develop an abundant system of lysosome-like vesicles and a very active, highly engorged endoplasmic reticulum and Golgi apparatus. After nine days in culture, evidence for the formation of a ruthenium red stained structure on the surface of the cells in contact with inductive particles, was observed. The simple monolayer culture system described provides a direct means by which the presence of active chondrogenic fractions may be assessed, and in which the mechanism of action of the effectors can be studied.

Synthesis of glycosaminoglycans and collagen in skin fibroblasts cultured from a patient with lichen myxedematosus

A patient is described with typical skin lesions of lichen myxedematosus and IgG-type lambda paraproteinemia. Fibroblasts cultured from the skin of the patient and from the skin of control persons were used to study glycosaminoglycan and collagen synthesis; the cultures were labelled with 3H-glucosamine and 3H-proline, respectively. Fibroblasts from the patient grew to a cell density which was lower than that of the control fibroblasts. The production of glycosaminoglycans was increased in lichen myxedematosus cultures, so that the ratio of hyaluronic acid to sulphated glucosaminoglycans was higher in the patient's cultures than in control cultures. Collagen production in the patient's cultures was about half of that in control cultures, whereas the ratio of type III to type I collagen was normal.

Glycosaminoglycan synthesis by rat fibroblast monolayers: effects of serum and solubilized bone matrix fractions

Glycosaminoglycan synthesis by fibroblasts, from skeletal muscle of the neonatal rat, is stimulated by a bone matrix preparation, soluble in isotonic medium, obtained by extracting decalcified rat bone with 4 M guanidine HCl. The stimulation in glycosaminoglycan synthesis is dependent on the presence of serum in the culture, but the stimulatory effect can be clearly distinguished from that of serum. The stimulatory activity in the bone matrix has been fractionated by ion-exchange chromatography and coelutes largely with anionic, non-collagenous matrix glycoproteins.

Synthesis and secretion of sulphated glycosaminoglycans by bovine peridontal ligament fibroblast cultures

The cultures were allowed to incorporate 35SO2-4 for various periods of time. 35S-labelled macromolecules were isolated from the medium, a trypsin digest of the cells and the cell residue. Ion-exchange chromatography separated the radioactive polysaccharides into heparan sulphate and a galactosaminoglycan population. Most heparan sulphate was in the trypsin digest and cell residue fractions. The galactosaminoglycan fractions were investigated by differential degradations with chondroitinase ABC and AC and ethanol fractionation. The medium galactosaminoglycans contained both glucuronic and iduronic acid residues and existed in copolymeric structures as chondroitin sulphate/dermatan sulphate hybrid molecules. Dermatan sulphate was also detected. In contrast, the trypsin-digest fraction contained mainly chondroitin sulphate-like molecules.

The effect of solubilized bone matrix fractions from different mammalian species on glycosaminoglycan synthesis by cultured fibroblasts

Human and bovine bone matrices were extracted with salt solutions of different composition and the extracts tested for stimulation of incorporation of radioactivity from [3H]glucosamine and [35S]SO4 into the hyaluronic acid and chondroitin sulfate of the cell pellet, the cell surface and the medium fractions of human synovial cells in culture. Stimulatory activity was extracted with a solution of 0.3 M EDTA in 2.5 M NaCl from bovine but not human bone. Subsequent extraction of the residues with 4 M guanidinium hydrochloride yielded activity from both matrices. A major stimulation of incorporation of radioactivity was observed in the cell surface fractions. Human synovial cells constitute a more sensitive assay system for the stimulatory activity than rabbit synovial cells.

Incorporation of radioactive precursors into glycosaminoglycans by rat muscle fibroblasts exposed to a solubilized rat bone matrix fraction

Confluent cultures of rat muscle fibroblastic cells respond by increased glycosaminoglycan (GAG) synthesis when cultured in medium containing a solubilized bone matrix fraction (SBM) at a concentration of 100 micrograms/ml. The metabolism of the GAG associated with the cell pellet, the cell surface and the tissue culture medium fractions was studied, in the presence and absence of SBM, by measuring the incorporation of radioactivity from [3H]glucosamine and [35S]SO4 into the isolated GAG. Net synthesis of hyaluronic acid and of chondroitin sulfate in the medium fraction increased more rapidly in cultures containing SBM compared to controls, and the accumulation of labelled GAG in the medium of the treated cultures was approximately linear with respect to the length of incubation. The addition of SBM also resulted in increased incorporation of 3H and of 35S into the GAG of the cell surface and cell pellet fractions. In these fractions, stimulation of incorporation of radioactivity occurred in two waves: an early, relatively minor increase and a later relatively major increase. The relatively major stimulation of radioactivity into the GAG of the cell surface fraction occurred between 24 and 48 h and was independent of any apparent effect of serum.

Hyperactivity of fibroblasts cultured from psoriatic skin: II. Synthesis of macromolecules

Glycosaminoglycans and protein synthesis were assessed in fibroblasts cultured from the involved (PSA strains) and uninvolved (PSB strains) forearm skin of patients with severe generalized psoriasis and compared with that in fibroblasts from the forearm skin of control subjects of similar ages (NSF strains). Average rates of glycosaminoglycan secretion were 19% (PSA) and 28% higher (PSB) in psoriatic strains. Although these differences were not significant in themselves, the relationship between glycosaminoglycan secretion and fibroblast density (cells/cm2) was significantly different (P = 0.02) for the psoriatic and control groups, with the psoriatic cells secreting appreciably more glycosaminoglycans at higher cell densities. The nature of the glycosaminoglycans produced was the same in psoriatic and normal strains; 90% was recovered in the culture medium and the bulk of this appeared to be hyaluronic acid with only small amounts of sulphated components. Collagen synthesis was 77% higher in PSA and PSB strains (P less than 0.01), while other protein synthesis was increased by 44% (P less than 0.05). These findings confirm that fibroblasts from psoriatic skin are hyperactive in vitro. The data are compatible with the results of studies of psoriatic skin in vivo and suggest that the entire skin is abnormal.

Glycosaminoglycan and surface glycoprotein syntheses by rat muscle fibroblast monolayers: response to solubilized bone matrix and effect of serum

Glycosaminoglycan synthesis by muscle fibroblasts derived from neonatal rats has been studied using a sensitive radioisotope method. Feeding the cultures with serum-containing medium supplemented with 80 micrograms/ml of a solubilized bone matrix (SBM) preparation results in an initial enhancement of net glycosaminoglycan secretion and a later additional response, not seen in controls. A pronounced dilution of the specific radioactivity of secreted chondroitin sulfate characterizes the latter response. SBM-treated cultures (100 micrograms/ml) also demonstrate increased incorporation of radioactive glucosamine into a large molecular weight cell surface glycoprotein. SBM suppresses the growth rate and final cell densities at all serum concentrations tested. However, at similar cell densities, higher serum concentrations tend to minimize the relative stimulation of incorporation of radioactivity into the secreted glycosaminoglycans by SBM-treated cultures, compared to controls.

Synthesis of underpolymerized hyaluronic acid by fibroblasts cultured from rheumatoid and non-rheumatoid synovitis

Fibroblast cultures were started from synovial tissue of normal controls and patients with seronegative and seropositive rheumatoid arthritis, juvenile rheumatoid arthritis and chronic non-rheumatoid synovitis. Glycosaminoglycan synthesis of the cultures was studied by metabolic labeling with 3H-glucosamine. Molecular weight of hyaluronic acid produced and secreted into culture medium by these fibroblast strains was studied by gel filtration in a Sepharose 2 B column. All fibroblast strains from joints with active inflammation produced hyaluronate with decreased molecular weight. The synthesis of underpolymerized hyaluronate thus appears to be a property of activated synovial fibroblasts common to rheumatoid and non-rheumatoid inflammation.