Biosynthesis of hyaluronic acid in cultures of chondrocytes from the Swarm rat chondrosarcoma

Enhanced expression of hyaluronic acid in osteoarthritis-affected knee-cartilage chondrocytes during three-dimensional in vitro culture in a hyaluronic-acid-retaining polymer scaffold

BACKGROUND

Chondrocyte transplantation to address cartilage damage is an established solution. Because hyaluronic acid (HA) is an essential component for homeostasis of the cartilage, in order to arrive at methodologies to utilize its advantages in cell-based therapies, we compared the HA retention capability of a thermoreversible gelation polymer scaffold-based environment (3D-TGP) with conventional in vitro cell culture methodologies.

METHODS

Chondrocytes derived from osteoarthritis-affected knee joint cartilage of elderly patients were used and accomplished in three phases. In Phase I, the levels of HA secreted by chondrocytes were measured in culture supernatant. In Phase II, retention capacity of externally added HA was quantified indirectly by measuring the HA released in culture supernatant, and in Phase III, the expression of CD44 on cells was analysed by immunohistochemistry.

RESULTS

In Phase I, the average HA in the 3D supernatant was 3% that of 2D. In phase II, 80% of externally added HA was detected in the 2D on day 7, while in 3D-TGP, only 0.1% was released until day 21. In Phase III, 2D yielded individual cells that started degenerating from the third week; in 3D-TGP cells grew for a longer duration, formed a tissue-like architecture with extracellular matrix with significantly intense staining of CD44 than 2D.

CONCLUSION

The capability of the 3D-TGP culture environment to retain HA and support chondrocytes to grow with a tissue-like architecture expressing higher HA content is considered advantageous as it serves as an in vitro culture platform that enables tissue engineering of cartilage tissue with native hyaline phenotype and higher HA expression. The in vitro environment being conducive, based on this data, we also recommend that the TGP be tried as an encapsulation material in clinical studies of chondrocyte implantation for optimal clinical outcome.

Hyaluronan secretion by synoviocytes is mechanosensitive

Hyaluronan (HA) is an essential component of synovial interstitial matrix and synovial fluid, but the link between its production and joint use is unclear. HA secretion is enhanced by joint distension in vivo, but direct proof that synoviocytes exhibit mechanosensitive HA secretion is lacking. We tested this in vitro. Primary rabbit synoviocyte (PRS) cultures from microdissected synovial intima were subjected to 180 min of maintained 10% static stretch, or to 10 min of 10% static stretch followed by 170 min relaxation, in a Flexcell 2000 apparatus. Stretch stimulated HA secretion into the medium over 3 h by 57%. Notably, a short stretch (10 min) was as effective as sustained stretch. Actinomycin D and cycloheximide abolished stretch-stimulated HA secretion and also reduced basal HA secretion rate. RT-PCR showed that HAS2 was the major hyaluronan synthase expressed, but there was no increase in HAS2 mRNA (or other isoforms) in continuously stretched cells, and only a small increase (20%) at 180 min in cells stretched for the first 10-30 min. However HAS2 transcription increased 10-fold in response to TGF-beta1 and IL-1beta. Thus HA secretion by intimal synoviocytes is regulated by a mechanosensitive pathway which depends on transcription and de novo protein synthesis, possibly of HAS2, but also of other proteins involved in HA secretion.

The establishment and characterization of an immortal cell line with a stable chondrocytic phenotype

A cell line was developed from the transplantable Swarm rat chondrosarcoma (RCS) and has been maintained in continuous monolayer tissue culture for a number of years. This long term-cultured (LTC) cell line exhibits the morphological and biochemical characteristics of chondrocytes and resembles the RCS tumor by electron and light microscopy. The cell line differs from the original tumor cells in that about 90% of the sulfated macromolecules are retained in the LTC extracellular matrix as compared to 30% by primary cultures of cells from the RCS tumor. An interesting and useful feature of this cell line is that it contains clonal populations of cells which differ in the quality and quantity of matrix produced. Two such clones serve to illustrate the diversity of cell types within the LTC cell line. One termed Rex accumulates an intensely staining matrix around it, while the other, Ng, accumulates a matrix, that remains virtually unstained. The chondrocytic nature and ease of cloning make these cells ideal for biochemical analysis of the chondrocyte and its extracellular matrix.

Goto-Kakizaki rat is protected from proteinuria after induction of anti-Thy1 nephritis

Hyperglycemia, although necessary, alone is insufficient for the development of progressive diabetic nephropathy. Two factors implicated in its pathogenesis are mesangial cell activation and/or proliferation and monocyte/macrophage influx. We have shown that prolonged hyperglycemia in the Goto-Kakizaki (GK) rat is associated with renal structural changes similar to those in patients with diabetes before the onset of progressive nephropathy. The aim of the current study is to examine the role of mesangial cell injury and macrophage influx on renal structure and function. After induction of nephritis in either hyperglycemic GK rats or normoglycemic Wistar rats by the administration of Ox-7 antibody, the degree of mesangiolysis and subsequent mesangial proliferation was no different between GK and Wistar rats. Similarly, macrophage influx and mesangial cell activation (assessed by alpha-smooth actin expression) was no different between the two groups. Wistar rats developed marked albuminuria; conversely, no significant proteinuria or albuminuria was seen in GK rats. Analysis of glomerular proteoglycans (PGs) showed an increase in (35)S incorporation into heparan sulfate PGs of GK compared with Wistar rats, with no alteration in glycosaminoglycan chain size or charge density. These changes were kidney specific and not seen in spleen, lung, or heart tissue. Western blot analysis showed increased agrin core protein expression in whole-kidney homogenates of untreated GK rats. Induction of Thy1.1 nephritis was associated with reduced expression of agrin in both GK and Wistar rats. However, agrin expression was greater in GK rats at all times. In summary, acute mesangial cell injury associated with a macrophage influx did not initiate progressive diabetic nephropathy in GK rats. Despite a similar magnitude of glomerular/mesangial injury, GK rats, in contrast to normoglycemic Wistar rats, did not develop proteinuria after the administration of anti-Thy1 antibody. We postulate that altered expression of agrin in this model accounts for the lack of proteinuria and thus may protect against progressive nephropathy.

Cytokine regulation of facilitated glucose transport in human articular chondrocytes

Glucose serves as the major energy substrate and the main precursor for the synthesis of glycosaminoglycans in chondrocytes. Facilitated glucose transport represents the first rate-limiting step in glucose metabolism. This study examines molecular regulation of facilitated glucose transport in normal human articular chondrocytes by proinflammatory cytokines. IL-1beta and TNF-alpha, and to a lesser degree IL-6, accelerate facilitated glucose transport as measured by [(3)H]2-deoxyglucose uptake. IL-1beta induces an increased expression of glucose transporter (GLUT) 1 mRNA and protein, and GLUT9 mRNA. GLUT3 and GLUT8 mRNA are constitutively expressed in chondrocytes and are not regulated by IL-1beta. GLUT2 and GLUT4 mRNA are not detected in chondrocytes. IL-1beta stimulates GLUT1 protein glycosylation and plasma membrane incorporation. IL-1beta regulation of glucose transport in chondrocytes depends on protein kinase C and p38 signal transduction pathways, and does not require phosphoinositide 3-kinase, extracellular signal-related kinase, or c-Jun N-terminal kinase activation. IL-1beta-accelerated glucose transport in chondrocytes is not mediated by endogenous NO or eicosanoids. These results demonstrate that stimulation of glucose transport represents a component of the chondrocyte response to IL-1beta. Two classes of GLUTs are identified in chondrocytes, constitutively expressed GLUT3 and GLUT8, and the inducible GLUT1 and GLUT9.

Dynamic expression of proteoglycans during chicken skeletal muscle development and maturation

Skeletal muscle development is a complex process in which cell migration and adhesion play important roles. Because these cellular activities involve cell surface and extracellular matrix molecules, proteoglycan analysis was performed for developing chick skeletal muscle. Proteoglycans are macromolecular conjugates of protein and carbohydrate found in the extracellular matrix and at the cell surface. In developing muscle, both in vivo and in vitro, there is a development-related progression from synthesis of primarily large proteoglycans at earlier stages to mainly small proteoglycans at later stages. This progression was demonstrated by radiolabeling developing muscle and extracting and characterizing the proteoglycans. The large proteoglycans synthesized earlier in myogenesis have been identified as the large chondroitin sulfate proteoglycan, versican. Among the small proteoglycans synthesized at later stages is the small dermatan sulfate proteoglycan, decorin. Immunolocalization of these proteoglycans shows that versican is initially present in pericellular locations around developing myotubes, whereas decorin is observed in the epimysium early in development, and then its distribution gradually spreads to also include the perimysium and endomysium. Studies of regenerating muscle show that there is a recapitulation of the embryonic pattern of proteoglycan synthesis, which, coupled with the results from embryonic muscle development, suggests a role for versican in some early aspect of myogenesis.

Absence of cell-surface annexin V is accompanied by defective collagen matrix binding in the Swarm rat chondrosarcoma

Annexin V has been characterized as a major collagen type II binding cell-surface component of normal chondrocytes and is also called anchorin CII in chondrogenic populations. Herein we present evidence that in vitro cultured Swarm rat chondrosarcoma cells are not capable of binding collagen type II in significant quantities to their surfaces, as compared to normal rat chondrocytes. This finding coincides with a deficiency of annexin V on the surface of these cells. A small quantity of an intracellular polypeptide could be detected which is immunologically cross-reactive with annexin V but displayed a mobility in SDS-PAGE of less than 34 kD compared to the M(r) 36 kD of intact rat annexin V. By immunohistochemistry the protein could be localized in the cytoplasm of in vitro and in vivo grown tumor cells. By reverse transcription-polymerase chain reaction and Northern blot analysis, a regular-sized mRNA for annexin V could be detected in the chondrosarcoma cells that is expressed in only slightly lower quantities than in normal chondrocytes. Taken together, the data suggest a modified processing or turnover for annexin V in the chondrosarcoma excluding it from being a functionally active collagen type II binding protein. The findings support the hypothesis of cell-surface annexin V as a key component for the formation of the pericellular matrix of chondrocytes.

Hyaluronan fragments induce nitric-oxide synthase in murine macrophages through a nuclear factor kappaB-dependent mechanism

Activated macrophages play a critical role in controlling chronic tissue inflammation through the release of a variety of mediators including cytokines, chemokines, growth factors, active lipids, reactive oxygen, and nitrogen species. The mechanisms that regulate macrophage activation in chronic inflammation are poorly understood. A hallmark of chronic inflammation is the turnover of extracellular matrix components, and recent work has suggested that interactions with the extracellular matrix can exert important influences on macrophage effector functions. We have examined the effect of low molecular weight fragments of the extracellular matrix glycosaminoglycan hyaluronan (HA) on the induction of nitric-oxide synthase (iNOS) in macrophages. We found that HA fragments induce iNOS mRNA, protein and activity alone, and markedly synergize with interferon-gamma to induce iNOS gene expression in murine macrophages. In addition, we found that resident tissue alveolar macrophages respond minimally, but inflammatory alveolar macrophages exhibit a marked induction in iNOS expression in response to HA fragments. Finally, we demonstrate that the mechanism of HA fragment-induced expression of iNOS requires activation of the transcriptional regulator nuclear factor kappaB. These data support the hypothesis that HA may be an important regulator of macrophage activation at sites of chronic tissue inflammation.

The recovery of articular cartilage in explant culture from interleukin-1 alpha: effects on proteoglycan synthesis and degradation

The cytokine interleukin-1 (IL-1) strongly inhibits proteoglycan biosynthesis and increases extracellular proteoglycan degradation in cartilage. In this study we investigated how quickly proteoglycan turnover recovered after IL-1 treatment. Porcine articular cartilage in explant culture was incubated with recombinant human (rh) IL-1 alpha, rh insulin-like growth factor (IGF)-1 or rh-transforming growth factor (TGF)-beta 1 for 3 days. RhIL-1 alpha strongly inhibited synthesis and promoted matrix degradation over 3 days, whereas rhIGF-1 stimulated proteoglycan synthesis, and rhTGF-beta 1 had no significant effect on synthesis. In the absence of serum, the recovery of proteoglycan synthesis after IL-1 treatment (10 ng/ml) for 3 days was extremely slow, and it remained 30% inhibited even after a further 8 days of recovery. Matrix degradation of proteoglycan assessed from the rate of release of glycosaminoglycan into the culture medium recovered more quickly and was greatly reduced within 3 days. Shorter exposure of explants to IL-1 alpha (8 h) resulted in less inhibition of synthesis, but it did not result in a more rapid rate of recovery following its removal. Treatment of cartilage with IGF-1 (20 ng/ml) or TGF-beta (10 ng/ml) during the recovery period increased the rate of recovery of both synthesis and degradation. Synthesis recovered to control rates within 6 days and degradation within 2 days. TGF-beta (10 ng/ml) was slightly more potent than IGF-1. Fetal calf serum (10% v/v) also promoted recovery in a similar way to the growth factors.(ABSTRACT TRUNCATED AT 250 WORDS)

Responses of articular cartilage explant cultures to different oxygen tensions

Bovine articular cartilage explants were cultured under atmospheres of 6, 10, 24, 66 and 91% oxygen. [35S]Glycosaminoglycan, chondroitin sulphate and keratan sulphate synthesis were measured together with the pool size of UDP-N-acetylhexosamines, UDP-hexoses and UDP-glucuronate. UDP-xylose was not detected. [35S]Glycosaminoglycan synthesis was maintained at the same level as in fresh tissue when cultured over 7 days with 20% foetal calf serum present and under a 6% oxygen tension. Under normal atmosphere (24%) synthesis was stimulated and remained elevated throughout the incubation period. Under higher oxygen tensions, initial stimulation of glycosaminoglycan synthesis was followed by progressive inhibition. The [35S]chondroitin sulphate/keratan sulphate ratio was constant (approximately 16:1) between 6 and 24% oxygen tension, but increased to 50:1 at 91% oxygen. The UDP-N-acetylhexosamine pool was larger under anaerobic (6, 10%) and excessively aerobic (66, 91%) oxygen tensions than under a normal atmosphere (24%). The UDP-hexose pool was expanded under anaerobic conditions. The UDP-glucuronate pool showed little variation between 6 and 24% oxygen tensions, but contracted under very aerobic conditions. We found no evidence indicating that keratan sulphate synthesis was favoured under anaerobic conditions to compensate for decreasing chondroitin sulphate synthesis.

The relationship between proteoglycan synthesis in Swarm chondrocytes and pathways of cellular energy and UDP-sugar metabolism

The effect of anaerobic culture conditions and various metabolic inhibitors on 35S-proteoglycan synthesis, UDP-sugar pools, and the ATP pool were investigated in confluent, primary, day 1 cultures of Swarm chondrosarcoma chondrocytes. (i) Incubation under a nitrogen atmosphere for 6 h did not affect 35S-proteoglycan synthesis or the pool size for UDP-glucuronate, other UDP-sugars, or ATP. Incubation with 5 mM sodium azide brought about a 40% reduction of proteoglycan synthesis in the first 30 min but no further change over the subsequent 90 min. UDP-Glucuronate, other UDP-sugar pools, and the ATP level were not affected by azide treatment. The results indicate that proteoglycan synthesis and its energy requirements can be supported entirely by anaerobic metabolism in these cells. (ii) 35S-Proteoglycan synthesis, UDP-sugar production, and nucleotide triphosphate pools were inhibited in a concentration-dependent fashion with sodium iodoacetate. A > 70% reduction of the ATP pool after 30 min treatment suggests that glycolysis is a major target for iodoacetate. Lactate production was inhibited by 40% after 3 h treatment with 10(-4) M iodoacetate. (iii) Glutamine deprivation resulted in a 60% contraction in the UDP-N-acetylhexosamine pool and markedly inhibited 35S-proteoglycan and 3H-protein synthesis. At the same time the UDP-glucose pool expanded to 200%, but the UDP-glucuronate pool was unchanged. The sum of the UDP-N-acetylhexosamine and UDP-hexose pools remained constant. Restoration of glutamine to previously depleted cultures resulted in excessive expansion of the UDP-N-acetylhexosamine pool and excessive contraction of the UDP-hexose pool before both adjusted to normal levels. The UDP-xylose pool was very small. No increases were observed during inhibition of proteoglycan synthesis induced by glutamine deprivation. (iv) 6-Diazo-5-oxo-L-norleucine (DON), a glutamine analogue and amino transferase inhibitor, induced a further contraction of the UDP-N-acetylhexosamine pool and a further decrease in proteoglycan synthesis in glutamine-deprived cultures. Thus cultures use endogenous glutamine during exogenous glutamine deprivation. DON unaccountably stimulated expansion of the UDP-glucuronate pool by 180%, irrespective of whether glutamine was present or not.

The effects of beta-D-xyloside on the synthesis of proteoglycans by skeletal muscle: lack of effect on decorin and differential polymerization of core protein-bound and xyloside-linked chondroitin sulfate

Developing skeletal muscle cells, as both myoblasts and myotubules, synthesize a distinctive large chondroitin sulfate proteoglycan. To probe the role of this proteoglycan in myogenesis, chick embryonic muscle cells in culture were treated with beta-D-xyloside, a compound which interferes with proteoglycan synthesis by acting as an artificial acceptor for glycosaminoglycan synthesis and thereby competing with the proteoglycan core protein. Analysis of the proteoglycans indicates that with increasing concentrations of beta-D-xyloside, synthesis of the chondroitin sulfate proteoglycan is inhibited, with concomitant massive synthesis of xyloside-linked chondroitin sulfate glycosaminoglycans. Xyloside does not appear to inhibit glycosaminoglycan attachment onto the small heparan sulfate and dermatan sulfate proteoglycans which are synthesized in the muscle cultures, even though, because of the mechanism of action of beta-xyloside, these proteoglycans should be affected. At submaximal concentrations of beta-xyloside, there is synthesis of both large chondroitin sulfate proteoglycans and xyloside-linked chondroitin sulfate. The xyloside-linked chondroitin sulfate chains have the same sulfation pattern as the core protein-bound skeletal muscle chondroitin sulfate (90% 6-sulfated isomer), but are much smaller (24,000 vs. 65,000 in molecular weight). The discrepancy in size but identify of sulfation indicates that, although sulfation takes place normally on either the core protein or the xyloside acceptor, termination of glycosylation occurs earlier for xyloside-initiated chondroitin sulfate. In spite of these dramatic effects on chondroitin sulfate proteoglycan synthesis, beta-xyloside elicits no observable effects on in vitro myogenesis. This suggests that the function served by the large chondroitin sulfate proteoglycan is not required in the more simplified environment of the muscle cultures.

The effect of heparin on cell proliferation and type-I collagen synthesis by adult human dermal fibroblasts

(1), A commercial heparin inhibited the proliferation of two normal human dermal fibroblast cultures in a dose-responsive manner. 300 micrograms heparin/ml gave the maximum inhibition of 65%. Proliferation of fibroblasts from a patient with progressive systemic sclerosis was similarly inhibited by heparin. Heparan sulphate, pentosan polysulphate and a fucoidan also inhibited proliferation of the fibroblast cultures but chondroitin sulphate, dermatan sulphate and hyaluronate had no effect. (2) Type-I collagen synthesis per cell was elevated by up to 1.5-fold in the normal fibroblast cultures when proliferation was inhibited by heparin, heparan sulphate, pentosan polysulphate and the fucoidan. Progressive systemic sclerosis fibroblasts synthesized more collagen than the normal cell cultures and this was further stimulated by heparin and pentosan polysulphate. In contrast, heparin and the other polysulphates inhibited type-I collagen synthesis by about 20-30% in normal confluent fibroblast cultures. Collagen synthesis by confluent systemic sclerosis fibroblasts was reduced by only about 10%. (3), Total [35S]proteoglycan synthesis per cell was greatly elevated (approx. 2.5-fold) in normal subconfluent cultures treated with heparin. In contrast, heparin stimulated only a small increase in [35S]sulphate incorporation into proteoglycans in confluent cultures.

Modulation of proteoglycan synthesis by bovine vascular smooth muscle cells during cellular proliferation and treatment with heparin

Proliferating cultures of bovine vascular smooth muscle cells synthesized a variety of proteoglycans corresponding closely to those reported previously for monkey smooth muscle cells. These included a chondroitin sulfate proteoglycan (CSPG) (47%), a dermatan sulfate proteoglycan (DSPG) (22%), and a heparan sulfate proteoglycan (HSPG) (6%) which were secreted into the medium. Heparan sulfate proteoglycan (6%) and a second dermatan sulfate proteoglycan (14%) were also present in the cell layer. Confluent cultures synthesized a similar spectrum of proteoglycans although the medium CSPG and DSPG were of smaller hydrodynamic size. The cell layer HSPG was much reduced relative to DSPG in early proliferating cultures. Previous reports have shown that heparin inhibits vascular smooth muscle cell proliferation. Heparin had two effects on proteoglycan synthesis. In control cultures, 35S-Labeled proteoglycan synthesis doubled during the first 12 h after releasing cells from growth arrest, decreasing during the following 12 h during which time cell division occurred. Treatment with heparin delayed the onset of proliferation by 24 h and this was accompanied by a corresponding delay in the increase in 35S-labeled proteoglycan synthesis associated with the early phase of the cell cycle. Secondly, heparin treatment resulted in an increase in the anionic properties of heparan sulfate proteoglycan synthesized by the cells. This was independent of the proliferative state of the cultures. Pentosan polysulfate, semi-synthetic heparin, and a highly sulfated heparan sulfate modulated both cell proliferation and heparan sulfate proteoglycan synthesis in the same way as heparin.

Comparison of proteoglycans synthesized by porcine normal and polycystic renal tubular epithelial cells in vitro

Newly synthesized porcine tubular epithelial cell proteoglycans were labeled in vitro with Na2[35S]SO4. At the beginning of the labeling period (24 h) [35S] sulfate incorporated into macromolecules was measured following PD-10 chromatography. There was a significant reduction in the amount of 35S-labeled macromolecules isolated from polycystic cells compared to that from normal cells. The distribution of recovered radiolabeled material among the medium, cell surface, and intracellular fractions was similar for both normal and polycystic cells. Analysis of the proteoglycans in polycystic cells demonstrated that 86 and 73% of 35S-labeled macromolecules were of the heparan sulfate type in polycystic and normal cells, respectively. The remainder was chondroitin sulfate. Proteoglycans were characterized using DEAE-Sephacel ion-exchange chromatography, chondroitinase ABC, heparitinase, and nitrous acid digestion followed by Sepharose CL-4B gel permeation chromatography. The majority of radiolabeled material in the medium, cell surface, and intracellular fractions eluted between 0.35 and 0.39 M NaCl. However, a second peak (peak II) that eluted at 0.25 M NaCl was found in the medium from polycystic cells. This peak accounted for 27% of the total macromolecules secreted into the medium. Proteoglycans in the major peak were susceptible to nitrous acid and chondroitinase ABC digestion. A similar proportion of peak II was degraded by chondroitinase ABC. However, the remainder was only slightly susceptible to treatment with nitrous acid or heparitase. In normal cells a small amount of material eluted at a similar low charge; the proteoglycans were the same as those found in the major peak and appeared as a shoulder on this peak.

Modulation of extracellular-matrix synthesized by cultured stromal cells from normal human breast tissue by epidermal growth factor

A routine, reproducible procedure was developed for the preparation and characterization of stromal cells from normal human breast tissue obtained by reduction mammaplasty. Isolates (n = 15) all exhibited enhanced rates of proliferation, even in the presence of 20% fetal calf serum, when exposed to epidermal growth factor or transforming growth factor a (both 10(-8) M). Cellular responsiveness to these growth factors was consistent with expression of specific surface receptors for epidermal growth factor (approximately 10(4)/cell). In cultures, stromal cells elaborated an extensive, cross-linked, insoluble extracellular matrix which remained firmly associated with the plastic surface of tissue culture ware upon lysis of cells. The insoluble matrix material was analyzed using enzymatic digestion procedures following incorporation of radiolabelled precursors into macromolecular material prior to lysis and preparation. The relative proportion of glycoconjugate (glycopeptides and proteoglycans) and collagenous material present in matrix material was approximately 45% and approximately 55%, respectively, and this was modulated by inclusion of epidermal growth factor into culture medium to approximately 60% and approximately 40%, respectively. Under similar culture conditions stromal cells synthesized twice as much hyaluronate as was produced by control cultures. By use of specific antibody preparations we identified at least four species of glycopeptide present in stromal matrices (namely, fibronectin, laminin, tenascin, and thrombospondin) as well as three types of collagen (types I, III, and IV). The rapid and reproducible procedure for the preparation of radiolabelled insoluble matrix material from normal human breast tissue allows for the study of cellular interaction involving extracellular matrix turnover and degradation.

Inhibition of sulphate incorporation by chondrocytes in intact cartilage by hyaluronate from foetal cartilage

A number of regulators are available in cartilage to effect the local control of matrix production by chondrocytes. A cartilage slice assay has been used in this study to investigate the influence of such regulators (extracted from foetal cartilage) on intact cartilage. A net inhibition of sulphation was found, rather than stimulation as reported for extracts rich in the somatomedin-like, cartilage derived factor (CDF). Inhibition was due, to a high molecular weight component identified as hyaluronic acid (based on enzyme sensitivity, chromatographic behaviour and temperature stability). Its inhibition of sulphation in intact cartilage was more profound than that produced by commercially available umbilical cord hyaluronate. We conclude that foetal cartilage hyaluronate is a far more potent inhibitor of sulphation than hyaluronate from other sources, suppressing sulphation even in the presence of a somatomedin-like activator and in intact cartilage, which responds poorly to commercial hyaluronate.

Altered cartilage proteoglycans synthesized by chick limb bud chondrocytes cultured in serum-free defined medium

Chick high-density culture chondrocytes synthesize cartilage-specific proteoglycans with much structural similarity to the proteoglycans made by cartilage in vivo. Such cultures can be maintained in a defined medium formulated in this laboratory in which chondrogenesis occurs without the addition of serum. The proteoglycans synthesized by the chondrocytes in the presence of defined medium are of a cartilage-specific structure but differ in some aspects from the proteoglycans made in serum-containing medium. While their buoyant density, ability to aggregate with hyaluronic acid, and keratan sulfate chain size are unchanged, the proteoglycans synthesized in defined medium have altered chondroitin sulfate chains. This chondroitin sulfate is of significantly larger size and has a different sulfation pattern relative to that produced in serum-containing medium. The larger size of the chondroitin sulfate results in a larger monomer size of the defined medium proteoglycans. These differences have implications about the regulation of the structure of chondroitin sulfate proteoglycans.

Influence of the fibroblast environment on the structure of mast cell proteoglycans

The structure of the proteoglycan synthesized by rodent mast cells has been a useful biochemical marker of mast cell subpopulations, since mucosal mast cells synthesize predominantly oversulfated chondroitin sulfate proteoglycan and connective tissue mast cells synthesize heparin proteoglycan. Mast cells are intimately associated with fibroblasts in tissues and fibroblasts maintain the connective tissue type mast cell ex vivo. Whereas mouse IL-3-dependent, immature mast cells synthesize predominantly chondroitin sulfate E proteoglycan, after coculture with fibroblasts, the proliferating mast cells (cloned or uncloned) synthesize heparin proteoglycans, as well as change their phenotype to resemble connective tissue mast cells. Although there is a single peptide core for both heparin and chondroitin sulfate secretory granule proteoglycans, the relative predominance of a specific glycosaminoglycan is determined by the microenvironment in which the cell resides. This microenvironment can regulate the phenotypic properties of mast cells including the expression of their cationic constituents such as neutral proteases and the structure of their anionic proteoglycans.

Does chondroitin sulfate have a role to play in the morphogenesis of the chick primary corneal stroma?

This paper makes three points about how the chick corneal epithelium lays down the primary stroma, an orthogonally arranged array of well-spaced, 20-nm-diameter collagen fibrils. (1) Isolated corneal epithelia will, when cultured, lay down de novo stromas whose fibril-diameter distribution, fibril spacing, and proteoglycan profile are similar to those laid down in vivo. They differ from embryonic stromas in two ways: first, much of the chondroitin sulfate is released to the medium and, second, there is a relatively small amount of orthogonal organization. Epithelia seem only to lay down such stromas if they are separated from their original stromas with dispase, which leaves an intact basal lamina, and spread out, basal lamina downward, on a Nuclepore filter (poresize, 0.1 micron). (2) Chondroitin sulfate (CS), the predominant proteoglycan (greater than 85%), seems to play no significant role in collagen fibrillogenesis in vitro. Stromas laid down in its absence were indistinguishable from controls as assayed by fibril diameter, organization, and spacing and the amount of collagen synthesized. For these experiments, epithelia were cultured in the presence of hyaluronidase, which degrades CS, and p-nitrophenyl beta-D-xyloside, which inhibits the formation of links between the core protein and glycosaminoglycan side chains in the PG; the absence of intact CS was confirmed by gel filtration. We suggest that, in vivo, CS may facilitate the interfibrillar movement that takes place as the cornea grows. We have also found that keratinase, which degrades the very small amount of keratan sulfate present in the primary stroma, has no effect on stromal deposition. (3) There are substantial amounts of unidentified matrix components in primary stromas laid down both in vivo and in vitro. This conclusion was drawn from SEM observations on both types of stroma after they had been freeze-dried, a process which does not condense hydrated macromolecules. Even after being treated with hyaluronidase to remove the CS, substantial amounts of interfibrillar matrix were still present. Until these components are identified and their interactions with collagen are understood, the mechanisms responsible for stromal morphogenesis are unlikely to be understood.

In vivo turnover of the basement membrane and other heparan sulfate proteoglycans of rat glomerulus

The metabolic turnover of rat glomerular proteoglycans in vivo was investigated. Newly synthesized proteoglycans were labeled during a 7-h period after injecting sodium [35S]sulfate intraperitoneally. At the end of the labeling period a chase dose of sodium sulfate was given. Subsequently at defined times (0-163 h) the kidneys were perfused in situ with 0.01% cetylpyridinium chloride in phosphate-buffered saline to maximize the recovery of 35S-proteoglycans. Glomeruli were isolated from the renal cortex and analyzed for 35S-proteoglycans by autoradiographic, biochemical, and immunochemical methods. Grain counting of autoradiographs revealed a complex turnover pattern of 35S-labeled macromolecules, commencing with a rapid phase followed by a slower phase. Biochemical analysis confirmed the biphasic pattern and showed that the total population of [35S]heparan sulfate proteoglycans had a metabolic half-life (t1/2) of 20 and 60 h in the early and late phases, respectively. Heparan sulfate proteoglycans accounted for 80% of total 35S-proteoglycans, the remainder being chondroitin/dermatan sulfate proteoglycans. Whole glomeruli were extracted with 4% 3-[(cholamidopropyl)dimethy-lammonio]-1-propanesulfonate-4 M guanidine hydrochloride, a procedure which solubilized greater than 95% of the 35S-labeled macromolecules. Of these 11-13% was immunoprecipitated by an antiserum against heparan sulfate proteoglycan which, in immunolocalization experiments, showed specificity for staining the basement membrane of rat glomeruli. Autoradiographic analysis showed that 18% of total radioactivity present at the end of the labeling period was associated with the glomerular basement membrane. The glomerular basement membrane [35S]heparan sulfate proteoglycans, identified by immunoprecipitation, have a very rapid turnover with an initial phase, t1/2 = 5 h, and a later phase t1/2 = 20 h.

Effects of vanadate on tyrosine phosphorylation and the pattern of glycosaminoglycan synthesis in rabbit chondrocytes in culture

The present study examined the effects of high doses of vanadate on glycosaminoglycan (GAG) synthesis and tyrosine phosphorylation in rabbit chondrocytes in confluent cultures. Although 6 microM vanadate increased the incorporation of [3H]glucosamine into chondroitin sulfate proteoglycans twofold, 40-60 microM vanadate suppressed this incorporation fourfold. Although 6 microM vanadate had little effect on [3H]glucosamine incorporation into hyaluronate, 40-60 microM vanadate increased this incorporation threefold. Chemical analyses confirmed that the increase in [3H]glucosamine incorporation into hyaluronate and the decrease in the incorporation into chondroitin sulfate proteoglycan correlated with increased hyaluronate content and decreased chondroitin sulfate content in the cell layers of vanadate-transformed cells. Chondrocytes exposed to 40-60 microM vanadate became typically transformed spindlelike cells. Furthermore, vanadate, at 6 and 60 microM, increased the overall level of phosphotyrosine by 8- and 31-fold, respectively, and 60 microM vanadate enhanced phosphorylation of many phosphotyrosine-containing proteins. These observations suggest that vanadate induces transformation-associated changes in the pattern of GAG synthesis when it induces excess phosphorylation on tyrosine in chondrocyte proteins.

Secretions from primary hamster tracheal surface epithelial cells in culture: mucin-like glycoproteins, proteoglycans, and lipids

Surface epithelial cells dissociated from hamster tracheas and grown on a thick collagen gel in the presence of 5% fetal bovine serum become highly enriched with secretory cells at confluence. In the present communication, we have analyzed secretory products from this primary hamster tracheal surface epithelial (HTSE) cell culture. The secreted glycoconjugates included high-molecular-weight mucin-like glycoproteins (HMW MLGP) and proteoglycans that comprised 22% and 5% of the total [3H]glycoconjugates secreted when [3H]glucosamine was added as a metabolic precursor. Among the proteoglycans were hyaluronic acids (53%), heparan sulfate proteoglycans (29%), and chrondroitin sulfate proteoglycans (18%). Chondroitin sulfates were mostly 4-sulfated. On the other hand, the secreted lipids included cholesterol, phospholipids, and glycolipids, and most of them were associated with HMW MLGP.

Stimulation of cartilage-matrix proteoglycan synthesis by morphologically transformed chondrocytes grown in the presence of fibroblast growth factor and transforming growth factor-beta

The effects of transforming growth factor-beta (TGF-beta) on the synthesis of cartilage-matrix proteoglycan by cultured rabbit chondrocytes were examined. Rabbit chondrocytes were seeded at low density and exposed to a 1:1 mixture of Dulbecco's modified Eagle's medium and Ham's F-12 medium supplemented with 0.5% fetal bovine serum, 1% bovine serum albumin, 50 micrograms/ml ascorbic acid, and 2 x 10(-7) M hydrocortisone (Medium A). Various combinations of TGF-beta, insulin-like growth factor-I (IGF-I), and fibroblast growth factor (FGF) were also added to Medium A, and the chondrocytes were grown to confluency. Chondrocytes grown with TGF-beta or FGF alone became flat or fibroblastic, those grown with FGF and TGF-beta became very elongated and formed distinct foci, and those grown with FGF and IGF-I showed the spherical configuration characteristic of overtly differentiated chondrocytes. Nevertheless, the incorporation of 3H with glucosamine into the large, chondroitin sulfate proteoglycan synthesized by cultures with FGF and TGF-beta was similar to that in cells grown with FGF and IGF-I and five times that in cells cultured with FGF alone. The increases in incorporation of 3H reflected real increases in proteoglycan synthesis, because chemical analyses showed an increase in the accumulation of macromolecules containing uronic acid in cultures with FGF and TGF-beta or with FGF and IGF-I. However, FGF in combination with either TGF-beta or IGF-I had little effect on the incorporation of 3H into small proteoglycans or hyaluronic acid. These results indicate that chondrocytes morphologically transformed with TGF-beta and FGF fully express the differentiated proteoglycan phenotype rather than the transformed glycosaminoglycan phenotype.

Effects of interleukin-1 and lipopolysaccharides on protein and carbohydrate metabolism in bovine articular cartilage organ cultures

The long term (18 day) metabolic response of bovine articular cartilage to treatment with either E. Coli lipopolysaccharide (LPS) or interleukin 1 was studied. For LPS treatment, incorporation of [35S]sulfate into the large proteoglycan population was inhibited 80% while that into the small interstitial proteoglycans was only inhibited 40%. Incorporation of [3H]serine into the large proteoglycan population was inhibited approximately 72% while incorporation into other protein was inhibited only 16%. Furthermore, the rate of catabolism of [3H]serine labeled proteoglycans was increased 2-fold by LPS treatment while the rate of 3H-labeled general protein catabolism was not affected. Incorporation of [3H]glucosamine into hyaluronate was increased; however a correction for changes in the specific activity of the intracellular [3H]glucosamine precursor pool in LPS-treated cultures indicated that the net amount of hyaluronate synthesized was not altered by LPS treatment. The 3H/35S ratios in isolated chondroitin sulfate disaccharides labeled with [35S]sulfate and [3H]glucosamine precursors were significantly changed during long term LPS treatment, suggesting that general carbohydrate pathways are altered. The 3H/35S changes were larger in the disaccharides isolated from the small proteoglycans indicating that different precursor pools, probably in different cell populations, preferentially synthesize this proteoglycan population. Interleukin-1 affected the same chondrocytic pathways as LPS as shown by a) the extent of inhibition of proteoglycan synthesis, b) the selective inhibition of synthesis of the large proteoglycan species, c) acceleration of proteoglycan catabolism, d) net depletion of proteoglycans from the tissue, e) increases in guanidine HCl extractable [3H]hyaluronate, f) increases in levels of prostaglandin E2 synthesis, g) changes in 3H/35S ratios in glycosaminoglycan chains and, h) minimal effects on general protein synthesis.

Proteoglycan synthesis in vitamin D-deficient cartilage: recovery from vitamin D deficiency

Vitamin D appears to be required for mineralization of skeletal elements. There is also evidence that cartilage proteoglycans may be involved in the regulation of mineralization. Previous studies have shown an alteration in the structure of the proteoglycans of the epiphyseal growth cartilage as a result of the decrease in serum calcium related to deficiency of dietary vitamin D. Vitamin D deficiency also induces a thickening of the epiphyseal growth plate presumably because of the inhibition of maturation of the growth plate chondrocytes. In order to compare the effect on proteoglycan structure with that on growth plate morphology, the proteoglycans of healing epiphyseal cartilage were characterized. The results indicate that, consistent with previous data, in vitamin D-deficient hatching chicks, the proteoglycans of the growth cartilage, but not of the articular cartilage, are smaller in monomer size with slightly smaller chondroitin sulfate chains whose sulfation pattern is unaltered. Sternal cartilage proteoglycans are unaffected. During recovery from vitamin D deficiency, the proteoglycans isolated from the growth cartilage are still not completely normal one day after supplementation with vitamin D, but are indistinguishable from normal by four days. In addition, the results conflict with those of a previous study in which only growth cartilage of hatchling chicks, not sternal or articular cartilage, was reported to synthesize large proteoglycans. Instead, all of these cartilages in the normal chicken have been found in this study to produce large proteoglycans of a size typical for mammalian cartilage and embryonic chick cartilage.

Dog mastocytoma proteoglycans: occurrence of heparin and oversulfated chondroitin sulfates, containing trisulfated disaccharides, in three cell lines

The cell-associated proteoglycans synthesized by three dog mastocytoma cell lines were isolated and their structural features compared. The lines were propagated as subcutaneous tumors in athymic mice for over 25 generations. In primary cell culture, all three lines incorporated [35S]sulfate into high molecular weight proteoglycans which were heterogeneous in size and glycosaminoglycan content. Two lines, BR and G, synthesized both a heparin proteoglycan (HPG) and a chondroitin sulfate proteoglycan (ChSPG) in different proportions. The third line, C2, synthesized predominantly a ChSPG with little or no detectable heparin. Gel filtration of the 35S-labeled HPG and ChSPG from the BR line on Sepharose CL-4B in dissociative conditions (4 M guanidine, Triton X-100) yielded a major polydisperse peak (Kav = 0.22) accounting for 70% of 35S activity. Under aggregating conditions (0.1 M sodium acetate) on Sepharose CL-4B, the BR proteoglycans eluted in the excluded volume. Proteoglycans from lines G and C2 also eluted in the void volume under nondissociative conditions, however the C2 line yielded additional fractions of smaller hydrodynamic size (Kav = 0.81) suggesting the presence of intracellular proteoglycan cleavage products or incompletely processed proteoglycans. As assessed by dissociative chromatography on Sepharose CL-4B, proteoglycans from the BR line were resistant to proteinase cleavage under conditions which degraded a rat chondrosarcoma proteoglycan. For all lines, glycosaminoglycans released by pronase/alkaline-borohydride had molecular weights ranging from 20,000 to 50,000 on gel filtration. For line BR, 75% of 35S-labeled glycosaminoglycans were degraded to oligosaccharides by nitrous acid, and the remaining 25% were degraded by chondroitinase ABC. Corresponding percentages for line G were 89% and 11%, and for line C2, 2% and 98%. Paper chromatography of the chondroitinase digestion products from lines BR and C2 showed products corresponding to unsaturated standards delta Di-diSB and delta Di-diSE, derived from the disaccharides IdoUA-2-SO4----GalNAc-4-SO4 and GlcUA----GalNAc-4,6-diSO4 respectively, in addition to smaller amounts of monosulfated disaccharides. Glycans from lines C2 and BR contained small quantities of a trisulfated disaccharide which was degraded to delta Di-diSB upon incubation with chondro-6-sulfatase. The results demonstrate the simultaneous presence of heparin and polysulfated chondroitin sulfate in dog mast cells of clonal origin.

Pharmacological actions of 17 beta-oestradiol on articular cartilage chondrocytes and chondrosarcoma chondrocytes in the absence of oestrogen receptors

(1) Pharmacological concentrations (greater than 10(-5) M) of 17 beta-oestradiol inhibited 35S-labelled proteoglycan synthesis in bovine articular cartilage explant cultures. They also inhibited 35S-labelled proteoglycan synthesis and 3H-labelled protein synthesis in cell cultures of chondrocytes from bovine articular cartilage and Swarm rat chondrosarcoma. Maximal inhibition was about 30-50%. Physiological concentrations (10(-9)-10(-8) M) of oestradiol had no effect on the synthesis of either protein or proteoglycan. (2) The inhibitory action of high concentrations of oestradiol on these biosynthetic pathways is not common to all steroids since 10(-4) M cortisol had no effect on articular chondrocyte cell cultures. 10(-4) M testosterone had a similar action to oestradiol. (3) Neither physiological nor pharmacological concentrations of 17 beta-oestradiol had any effect on 35S-labelled proteoglycan turnover in the cartilage explant system. (4) 10(-5) M oestradiol inhibited cell division in cultures of articular chondrocytes which had entered the log growth phase. 10(-7) M oestradiol had no effect on articular chondrocyte growth. (5) In male rats implanted with silastic capsules releasing 17 beta-oestradiol, increase in body weight was retarded by about 25% over a period of 6 weeks, compared to control rats. Rat chondrosarcoma grew to the same size in oestrogen-treated rats as it did in controls. (6) Oestrogen receptors could not be detected in freshly isolated bovine articular chondrocytes or in rat chondrosarcoma. (7) In conclusion, neither the mitotic rate of articular chondrocytes nor their proteoglycan metabolism is under the direct physiological control of oestradiol. Growth and biosynthetic activity of the rat chondrosarcoma chondrocytes are independent of either direct control by the hormone or control effected by oestradiol regulation of a second hormone or growth factor.

Effect of thyroid hormone deficiency on proteoglycan synthesis by human skin fibroblast cultures

Proteoglycans and hyaluronic acid synthesized by human skin fibroblasts in culture were characterized, and the effect of thyroid hormone deficiency was examined. The fibroblasts in culture synthesize hyaluronic acid, dermatan sulfate (DS) proteoglycans and heparan sulfate (HS) proteoglycans. Hyaluronic acid is almost exclusively secreted into the medium. Among the proteoglycans synthesized during 24 h label, about 70% were secreted into the medium and the remaining 30% were associated with the cell layer. About 70% of proteoglycans secreted into the medium contained DS and the remaining 30% contained HS. For cell-associated proteoglycans, 60% contained HS and the remainder contained DS. The size distributions of the glycosaminoglycans from both DS and HS proteoglycans were similar, with an average Mr of approximately 30,000. Incubation of fibroblasts in thyroid hormone deficient medium increased net synthesis of hyaluronic acid (approximately 50%) and all species of proteoglycans (approximately 85%). 3H/35S ratios in the chondroitin 4-sulfate disaccharide isolated with HPLC were not altered in thyroid hormone deficient cultures, indicating that the specific activity of 3H in UDP-N-acetylhexosamine precursors did not change. The increased incorporation of 3H into hyaluronic acid and of 3H and 35S into DS and HS proteoglycans thus indicates increased net synthesis. Degradation of cell-associated proteoglycans was not influenced by thyroid hormone deficiency.

Glycoconjugates secreted by bovine tracheal serous cells in culture

Glycoconjugates secreted by bovine tracheal gland serous cells in culture were characterized after incorporation of radioactive precursor [1-14C]glucosamine and stimulation with isoproterenol. Under dissociative conditions, glycoconjugates eluted in both the void and included volumes on Sepharose Cl-4B. Fractionated by anion-exchange chromatography, the high-molecular-weight (Sepharose Cl-4B; V0) glycoconjugates gave two acidic fractions eluting at 0.5 and 2.0 M NaCl; low-molecular-weight glycoconjugates of the included volumes gave a neutral fraction and two acidic fractions eluting at 0.5 and 2.0 M NaCl. Based on chemical analysis and specific enzymatic digestions, the material eluting in the void volume was shown to contain hyaluronic acid and chondroitin sulfate proteoglycan. In addition, the presence of small amounts of galactose, fucose, sialic acid, glucosamine, and galactosamine suggest the presence of O-glycosidically linked glycoproteins in the void volume. The identification of galactosaminitol in beta-eliminated oligosaccharides from this material confirms this notion. The material eluting in the included volume was shown to contain N-linked glycoproteins with glycans of complex type in the neutral fraction and chondroitin sulfate proteoglycans in the two acidic fractions. Significant N-sulfation of amino sugars was detected in the 0.5 M acidic fraction, indicating the presence of heparan sulfate. Hyaluronic acid and chondroitin sulfate proteoglycan have recently been identified in tracheal secretions; our results suggest that these components originate at least in part from tracheal gland serous cells.

Fibroblast growth factor stimulates colony formation of differentiated chondrocytes in soft agar

The effect of fibroblast growth factor (FGF) on the growth of chondrocytes in soft agar was examined. FGF induced colony formation by chick embryo and rabbit chondrocytes. The colony-forming efficiency of FGF-exposed chondrocytes was similar to that of Rous sarcoma virus-transformed chondrocytes (15-20%). Other mitogenic agents tested, such as epidermal growth factor, insulin, insulin-like growth factor-l, and platelet-derived growth factor, induced very low levels of colony formation. The induction of growth in soft agar of chondrocytes by FGF was not due to cells' phenotypic transformation, because chondrocytes grown in soft agar with FGF retained the ability to synthesize cartilage-characteristic proteoglycan. FGF did not induce growth in soft agar of chondrocytes whose phenotypic expression was suppressed by retinoic acid or 5-bromodeoxyuridine. In addition, FGF did not induce growth in soft agar of primary fibroblasts and normal rat kidney (NRK) cells. These results suggest that FGF selectively stimulates growth of differentiated chondrocytes in soft agar.

Tunicamycin partially delays release of newly synthesized hyaluronate from Swarm rat chondrosarcoma chondrocytes

Tunicamycin (5-100 micrograms/ml) inhibits total [3H]hyaluronate synthesis in cultures of Swarm rat chondrosarcoma chondrocytes by approx. 15%. In agreement with previous results (Lohmander, L.S., Fellini, S.K., Kimura, J.H., Stevens, R.L. and Hascall, V.C. (1983) J. Biol. Chem. 258, 12280-12286) the relative decrease in [3H]hyaluronate radioactivity in the culture medium was greater than in the cell layer. Treated cultures show a concentration-related decrease in the proportion of medium 35S-labelled proteoglycans forming 'natural aggregates'. Pulse-chase experiments in cultures pretreated with tunicamycin (100 micrograms/ml, 13 h) showed that 30-40% of the total [3H]hyaluronate synthesized is released more slowly from these chondrocytes than from control culture chondrocytes. Release of some hyaluronate molecules may be delayed by 6 h or more. After a 24 h chase period almost all the [3H]hyaluronate is released from the cells. The proportion of 35S-labelled proteoglycans present as aggregates in the 24 h chase medium (57%) remained depressed compared to controls (81%), although the monomers could form aggregates if exogenous hyaluronate was added. Hyaluronate synthesized in the presence of tunicamycin has the same hydrodynamic size as control culture hyaluronate, as assessed by its sedimentation profile in CsSO4 gradients and its chromatographic profile on a dissociative Sephacryl S-1000 column.

Thermal and solvent stability of proteoglycan aggregates by quasielastic laser light-scattering

The dissociation behavior of several species of proteoglycan aggregates (PGA) has been studied quantitatively by monitoring the changes in particle size by dynamic laser light-scattering. Firstly, studies of the thermal dissociation of reconstituted PGA from bovine nasal septum and bovine fetal epiphysus are described. The effect of link protein in stabilizing reconstituted PGA against changes in temperature has been demonstrated. It was also confirmed that, upon prolonged heating at 70 degrees, the dissociation of link-containing, reconstituted PGA is effectively irreversible. Secondly, the dissociation characteristics of native PGA isolated from chick chondrocyte and rat chondrosarcoma cell-cultures were investigated in aqueous solvents containing increasing concentrations of guanidine hydrochloride. It was found that the more densely packed, native, aggregate structure has a higher susceptibility to thermal disruption than the reconstituted, link-containing material. Considerable loss of subunits from the native aggregates occurs at temperature where the link protein retains its activity. The dissociation of native PGA is irreversible, in the sense that reconstituted PGA always exhibits smaller sizes than the native PGA, reflecting a smaller degree of aggregation of the subunits.

Different growth rates of swarm chondrosarcoma in Lewis and Wistar rats correlate with different thyroid hormone levels

The transplantable Swarm rat chondrosarcoma grew to twice the weight in 5 weeks in Lewis strain rats (approximately 80 g) as it did in Wistar strain rats (approximately 40 g). Wistar tumor passaged into Lewis rats adopted the accelerated growth rate of the Lewis tumor on the second passage. Conversely Lewis tumor passaged into Wistar rats grew like Wistar lineage chondrosarcoma after two passages. Lewis and Wistar tumors had a similar histological appearance. The extracellular matrix composition of the two tumors was very similar. Tumor explant cultures synthesized about the same amount of 35S-proteoglycans and the same proportion of 3H-hyaluronate: 3H-chondroitin sulfate. Serum levels of growth hormone and insulin were the same in the two strains but T3 and T4 levels were 50% higher in Lewis rats compared to Wistar rats. It is likely that accelerated tumor growth in Lewis strain rats is related to the higher thyroid hormone levels.

Tunicamycin inhibits proteoglycan synthesis in rat ovarian granulosa cells in culture

The effects of tunicamycin, an inhibitor of N-linked oligosaccharide biosynthesis, on the synthesis and turnover of proteoglycans were investigated in rat ovarian granulosa cell cultures. The synthesis of proteoglycans was inhibited (40% of the control at 1.6 micrograms/ml tunicamycin) disproportionately to that of general protein synthesis measured by [3H]serine incorporation (80% of control). Proteoglycans synthesized in the presence of tunicamycin lacked N-linked oligosaccharides but contained apparently normal O-linked oligosaccharides. The dermatan sulfate and heparan sulfate chains of the proteoglycans had the same hydrodynamic size as control when analyzed by Sepharose 6B chromatography. However, the disulfated disaccharide content of the dermatan sulfate chains was reduced by tunicamycin in a dose-dependent manner, implying that the N-linked oligosaccharides may be involved in the function of a sulfotransferase which is responsible for sulfation of the iduronic acid residues. When [35S]sulfate and [3H]glucosamine were used as labeling precursors, the ratio of 35S/3H in chondroitin 4-sulfate was reduced to approximately 50% of the control by tunicamycin, indicating that the drug reduced the supply of endogenous sugar to the UDP-N-acetylhexosamine pool. Neither transport of proteoglycans from Golgi to the cell surface nor their turnover from the cell surface (release into the medium, or internalization and subsequent intracellular degradation) was affected by the drug. Addition of mannose 6-phosphate to the culture medium did not alter the proteoglycan turnover. When granulosa cells were treated with cycloheximide, completion of proteoglycan diminished with a t1/2 of approximately 12 min, indicating the time required for depleting the core protein precursor pool. The glycosaminoglycan synthesizing capacity measured by the addition of p-nitrophenyl-beta-xyloside, however, lasted longer (t1/2 of approximately 40 min). Tunicamycin decreased the core protein precursor pool size in parallel to decreased proteoglycan synthesis, both of which were significantly greater than the inhibition of general protein synthesis. This suggests two possibilities: tunicamycin specifically inhibited the synthesis of proteoglycan core protein, or more likely a proportion of the synthesized core protein precursor (approximately 50%) did not become accessible for post-translational modifications, and was possibly routed for premature degradation.

Two species of dermatan sulfate proteoglycans with different molecular sizes from newborn calf skin

Two species of dermatan sulfate-proteoglycans (DS-PGs) were isolated from calf skin. The first species, PDS-H (high-molecular-weight proteodermatan sulfate), contains the core protein with a molecular weight of either about 55,000 or 53,000. Both the core proteins are capable of binding to concanavalin A (Con A). The second species, PGs-L (low-molecular-weight proteoglycan containing dermatan sulfate and/or chondroitin sulfate), contains a core protein of Mr = 20,000 that did not bind to Con A. Tryptic peptide mappings revealed that Mr = 55,000 core protein and Mr = 53,000 core protein were of the same origin. However, the tryptic peptides and the amino acid composition of PGs-L core protein were completely different from those of PDS-H core proteins. The polyclonal antibodies against Mr = 55,000 core protein reacted with both the core proteins of Mr = 55,000 and Mr = 53,000 but not with the core protein from PGs-L. The DS was found to be the only glycosaminoglycan component of PDS-H. That is, the glycosaminoglycan from PDS-H was composed of 46% iduronosylhexosamine units and 54% glucuronosylhexosamine units, while the glycosaminoglycan of PGs-L was composed of 30% iduronosylhexosamine units and 70% glucuronosylhexosamine units.

Effects of complex extracellular matrices on 5-azacytidine-induced myogenesis

Culture dishes coated with extracellular matrix material synthesized by bovine endothelial cells, rat smooth muscle cells or human fibroblasts were used to study proliferation and myogenesis in C3H/10T1/2 C18 (10T1/2) cells primed to differentiate with 5-azacytidine (5-aza-CR). Endothelial and smooth muscle matrices were permissive for growth and myogenic differentiation of treated 10T1/2 cells, whereas the fibroblast matrix was inhibitory. All three types of matrix-coated dishes were refractory for myogenesis after brief exposure to trypsin. Analysis of the matrix glycosaminoglycans showed that high chondroitin sulfate relative to hyaluronic acid (HA) levels were favorable for the myogenic response. The ratio between these two glycosaminoglycans therefore had a major influence on mesenchymal differentiation. These results using complex extracellular matrices produced in vitro may be useful in understanding cell-matrix interactions during embryogenesis.

Synthesis of hyaluronic acid is decreased and synthesis of proteoglycans is increased when cultured mouse epidermal cells differentiate

Newborn mouse epidermal cells proliferate when cultured in 0.05 mM Ca++ medium and terminally differentiate when the Ca++ is increased to about 1.2 mM, the level found in most cell culture media. We found that hyaluronic acid and proteoglycans were synthesized by isolated cultured newborn mouse epidermal cells and that quantitative and qualitative changes in these macromolecules appeared when proliferating epidermal cultures were induced to differentiate by calcium. A major change that occurred with differentiation was a reduction in synthesis of hyaluronic acid while synthesis of proteoglycans and glycoproteins increased. The proteoglycans synthesized in these cultures were heparan sulfate-proteoglycan (90%) and chondroitin sulfate-proteoglycan (10%), regardless of the calcium level.

Biosynthesis and fate of proteoglycans in cartilage and bone during development and mineralization

Subcutaneous implantation of demineralized bone matrix in rats induces migration of host cells into the site and results in the sequential development of cartilage and bone. The biosynthesis and metabolic fate of proteoglycans in the plaques at the bone matrix implantation site were investigated by [35S]sulfate labeling in vivo. 35S-Labeled proteoglycans were extracted with 4 M guanidine HCl and purified by DEAE-Sephacel chromatography. Analysis of proteoglycans on Sepharose CL-2B chromatography showed two major peaks at Kd = 0.28 and 0.68 (peaks I and II, respectively). Peak I proteoglycan has a high buoyant density and contains chondroitin sulfate chains of average Mr = 20,000. Peak II proteoglycan has a lower average buoyant density and contains dermatan sulfate chains of average Mr = 33,000. Throughout the endochondral bone development sequence, peak II proteoglycan predominates. Peak I was low on Day 3, became prominent on Day 7 (approximately 30% of the total radioactivity), and declined after Day 9. The calculated half-lives of peak I and II proteoglycans labeled on Day 7 were about 1.8 and 2.8 days, respectively. After the initiation of osteogenesis, a species of mineral-associated proteoglycan was extracted with a 4 M guanidine HCl solvent containing 0.5 M EDTA. This proteoglycan has a small hydrodynamic size (Kd = 0.38 on Sepharose CL-6B chromatography) and shows a long half-life, about 6 days.