Synthesis of proteoglycans, collagen, and elastin by cultures of rabbit auricular chondrocytes--relation to age of the donor

Impact of Inter- and Intra-Donor Variability by Age on the Gel-to-Tissue Transition in MMP-Sensitive PEG Hydrogels for Cartilage Regeneration

Matrix metalloproteinase (MMP)-sensitive hydrogels are promising for cartilage tissue engineering due to cell-mediated control over hydrogel degradation. However, any variability in MMP, tissue inhibitors of matrix metalloproteinase (TIMP), and/or extracellular matrix (ECM) production among donors will impact neotissue formation in the hydrogels. The goal for this study was to investigate the impact of inter- and intra-donor variability on the hydrogel-to-tissue transition. Transforming growth factor β3 was tethered into the hydrogel to maintain the chondrogenic phenotype and support neocartilage production, allowing the use of chemically defined medium. Bovine chondrocytes were isolated from two donor groups, skeletally immature juvenile and skeletally mature adult donors (inter-donor variability) and three donors within each group (intra-donor group variability). While the hydrogel supported neocartilaginous growth by all donors, donor age impacted MMP, TIMP, and ECM synthesis rates. Of the MMPs and TIMPs studied, MMP-1 and TIMP-1 were the most abundantly produced by all donors. Adult chondrocytes secreted higher levels of MMPs, which was accompanied by higher production of TIMPs. Juvenile chondrocytes exhibited more rapid ECM growth. By day 29, juvenile chondrocytes had surpassed the gel-to-tissue transition. On the contrary, the adult donors had a percolated polymer network indicating that despite higher levels of MMPs the gel-to-transition had not yet been achieved. The intra-donor group variability of MMP, TIMP, and ECM production was higher in adult chondrocytes but did not impact the extent of the gel-to-tissue transition. In summary, age-dependent inter-donor variations in MMPs and TIMPs significantly impact the timing of the gel-to-tissue transition in MMP-sensitive hydrogels.

Hydrogel matrices based on elastin and alginate for tissue engineering applications

Hydrogels from natural polymers are widely used in tissue engineering due to their unique properties, especially when regarding the cell environment and their morphological similarity to the extracellular matrix (ECM) of native tissues. In this study, we describe the production and characterization of novel hybrid hydrogels composed of alginate blended with elastin from bovine neck ligament. The properties of elastin as a component of the native ECM were combined with the excellent chemical and mechanical stability as well as biocompatibility of alginate to produce two hybrid hydrogels geometries, namely 2D films obtained using sonication treatment and 3D microcapsules produced by pressure-driven extrusion. The resulting blend hydrogels were submitted to an extensive physico-chemical characterization. Furthermore, the biological compatibility of these materials was assessed using normal human dermal fibroblasts, indicating the suitability of this blend for soft tissue engineering.

Growth factor stimulation improves the structure and properties of scaffold-free engineered auricular cartilage constructs

The reconstruction of the external ear to correct congenital deformities or repair following trauma remains a significant challenge in reconstructive surgery. Previously, we have developed a novel approach to create scaffold-free, tissue engineering elastic cartilage constructs directly from a small population of donor cells. Although the developed constructs appeared to adopt the structural appearance of native auricular cartilage, the constructs displayed limited expression and poor localization of elastin. In the present study, the effect of growth factor supplementation (insulin, IGF-1, or TGF-β1) was investigated to stimulate elastogenesis as well as to improve overall tissue formation. Using rabbit auricular chondrocytes, bioreactor-cultivated constructs supplemented with either insulin or IGF-1 displayed increased deposition of cartilaginous ECM, improved mechanical properties, and thicknesses comparable to native auricular cartilage after 4 weeks of growth. Similarly, growth factor supplementation resulted in increased expression and improved localization of elastin, primarily restricted within the cartilaginous region of the tissue construct. Additional studies were conducted to determine whether scaffold-free engineered auricular cartilage constructs could be developed in the 3D shape of the external ear. Isolated auricular chondrocytes were grown in rapid-prototyped tissue culture molds with additional insulin or IGF-1 supplementation during bioreactor cultivation. Using this approach, the developed tissue constructs were flexible and had a 3D shape in very good agreement to the culture mold (average error <400 µm). While scaffold-free, engineered auricular cartilage constructs can be created with both the appropriate tissue structure and 3D shape of the external ear, future studies will be aimed assessing potential changes in construct shape and properties after subcutaneous implantation.

Development of scaffold-free elastic cartilaginous constructs with structural similarities to auricular cartilage

External ear reconstruction with autologous cartilage still remains one of the most difficult problems in the fields of plastic and reconstructive surgery. As the absence of tissue vascularization limits the ability to stimulate new tissue growth, relatively few surgical approaches are currently available (alloplastic implants or sculpted autologous cartilage grafts) to repair or reconstruct the auricle (or pinna) as a result of traumatic loss or congenital absence (e.g., microtia). Alternatively, tissue engineering can offer the potential to grow autogenous cartilage suitable for implantation. While tissue-engineered auricle cartilage constructs can be created, a substantial number of cells are required to generate sufficient quantities of tissue for reconstruction. Similarly, as routine cell expansion can elicit negative effects on chondrocyte function, we have developed an approach to generate large-sized engineered auricle constructs (≥3 cm(2)) directly from a small population of donor cells (20,000-40,000 cells/construct). Using rabbit donor cells, the developed bioreactor-cultivated constructs adopted structural-like characteristics similar to native auricular cartilage, including the development of distinct cartilaginous and perichondrium-like regions. Both alterations in media composition and seeding density had profound effects on the formation of engineered elastic tissue constructs in terms of cellularity, extracellular matrix accumulation, and tissue structure. Higher seeding densities and media containing sodium bicarbonate produced tissue constructs that were closer to the native tissue in terms of structure and composition. Future studies will be aimed at improving the accumulation of specific tissue constituents and determining the clinical effectiveness of this approach using a reconstructive animal model.

Chondrogenic potential of bone marrow-derived mesenchymal stem cells on a novel, auricular-shaped, nanocomposite scaffold

Reconstruction of the human auricle remains a challenge to plastic surgeons, and current approaches are not ideal. Tissue engineering provides a promising alternative. This study aims to evaluate the chondrogenic potential of bone marrow-derived mesenchymal stem cells on a novel, auricular-shaped polymer. The proposed polyhedral oligomeric silsesquioxane-modified poly(hexanolactone/carbonate)urethane/urea nanocomposite polymer has already been transplanted in patients as the world's first synthetic trachea, tear duct and vascular bypass graft. The nanocomposite scaffold was fabricated via a coagulation/salt-leaching method and shaped into an auricle. Adult bone marrow-derived mesenchymal stem cells were isolated, cultured and seeded onto the scaffold. On day 21, samples were sent for scanning electron microscopy, histology and immunofluorescence to assess for neocartilage formation. Cell viability assay confirmed cytocompatability and normal patterns of cellular growth at 7, 14 and 21 days after culture. This study demonstrates the potential of a novel polyhedral oligomeric silsesquioxane-modified poly(hexanolactone/carbonate)urethane/urea scaffold for culturing bone marrow-derived mesenchymal stem cells in chondrogenic medium to produce an auricular-shaped construct. This is supported by scanning electron microscopy, histological and immunofluorescence analysis revealing markers of chondrogenesis including collagen type II, SOX-9, glycosaminoglycan and elastin. To the best of our knowledge, this is the first report of stem cell application on an auricular-shaped scaffold for tissue engineering purposes. Although many obstacles remain in producing a functional auricle, this is a promising step forward.

The tissue-engineered auricle: past, present, and future

The reconstruction, repair, and regeneration of the external auricular framework continue to be one of the greatest challenges in the field of tissue engineering. To replace like with like, we should emulate the native structure and composition of auricular cartilage by combining a suitable chondrogenic cell source with an appropriate scaffold under optimal in vitro and in vivo conditions. Due to the fact that a suitable and reliable substitute for auricular cartilage has yet to be engineered, hand-carved autologous costal cartilage grafts and ear-shaped porous polyethylene implants are the current treatment modalities for auricular reconstruction. However, over the last decade, significant advances have been made in the field of regenerative medicine and tissue engineering. A variety of scaffolds and innovative approaches have been investigated as alternatives to using autologous carved costal cartilage or porous polyethylene implants. A review of recent developments and the current state of the art and science is presented, focusing on scaffolds, cell sources, seeding densities, and mechanical characteristics of tissue-engineered auricular cartilage.

Age-related differences in human skin proteoglycans

Previous work has shown that versican, decorin and a catabolic fragment of decorin, termed decorunt, are the most abundant proteoglycans in human skin. Further analysis of versican indicates that four major core protein species are present in human skin at all ages examined from fetal to adult. Two of these are identified as the V0 and V1 isoforms, with the latter predominating. The other two species are catabolic fragments of V0 and V1, which have the amino acid sequence DPEAAE as their carboxyl terminus. Although the core proteins of human skin versican show no major age-related differences, the glycosaminoglycans (GAGs) of adult skin versican are smaller in size and show differences in their sulfation pattern relative to those in fetal skin versican. In contrast to human skin versican, human skin decorin shows minimal age-related differences in its sulfation pattern, although, like versican, the GAGs of adult skin decorin are smaller than those of fetal skin decorin. Analysis of the catabolic fragments of decorin from adult skin reveals the presence of other fragments in addition to decorunt, although the core proteins of these additional decorin catabolic fragments have not been identified. Thus, versican and decorin of human skin show age-related differences, versican primarily in the size and the sulfation pattern of its GAGs and decorin in the size of its GAGs. The catabolic fragments of versican are detected at all ages examined, but appear to be in lower abundance in adult skin compared with fetal skin. In contrast, the catabolic fragments of decorin are present in adult skin, but are virtually absent from fetal skin. Taken together, these data suggest that there are age-related differences in the catabolism of proteoglycans in human skin. These age-related differences in proteoglycan patterns and catabolism may play a role in the age-related changes in the physical properties and injury response of human skin.

Engineered fetal cartilage: structural and functional analysis in vitro

BACKGROUND/PURPOSE

This study was aimed at characterizing the structure and function of engineered fetal cartilage in vitro.

METHODS

Chondrocytes from ovine specimens of fetal elastic, fetal hyaline, and adult elastic cartilage were expanded in culture and their growth rates determined. Cells were seeded onto synthetic scaffolds, which were then maintained in a bioreactor. Matrix deposition was determined by specific staining and quantitative assays for glycosaminoglycans (GAG), type II collagen (CII), and elastin, as well as compared with native tissue. Statistical analysis was by analysis of variance (ANOVA) and Students' t test, with significance set at P less than.01.

RESULTS

Fetal elastic chondrocytes grew significantly faster than all other cell types. All fetal constructs resembled hyaline cartilage, regardless of the cell source. There were significantly higher levels of GAG and CII in fetal versus adult constructs, but no significant difference between fetal constructs from different sources. Unlike their adult counterparts, fetal constructs had GAG and CII levels similar to native tissues.

CONCLUSIONS

Fetal chondrocytes can be rapidly expanded in culture. Compared with adult constructs, matrix deposition is enhanced in engineered fetal cartilage, which closely resembles native tissue, regardless of the cell source. Engineered fetal cartilage may be a preferable option during surgical reconstruction of select congenital anomalies.

Effects of serial expansion of septal chondrocytes on tissue-engineered neocartilage composition

OBJECTIVES

Cartilage grafts for reconstructive surgery may someday be created from harvested autologous chondrocytes that are expanded and seeded onto biodegradable scaffolds in vitro. This study sought to quantify the biochemical composition of neocartilage engineered from human septal chondrocytes and to examine the effects of cell multiplication in monolayer culture on the ultimate composition of the neocartilage.

METHODS

Human septal chondrocytes from 10 donors were either seeded immediately after harvest (passage 0 [P(0)]) onto polyglycolic acid (PGA) scaffolds or underwent multiplication in monolayer culture before scaffold seeding at passage 1 (P(1)) and passage 2 (P(2)). Cell/scaffold constructs were grown in vitro for 7, 14, and 28 days. Neocartilage constructs underwent histologic analysis for matrix sulfated glycosaminoglycan (S-GAG) and type II collagen as well as quantitative assessment of cellularity (Hoescht 33258 assay), S-GAG content (dimethylmethylene blue assay), and collagen content (hydroxyproline assay).

RESULTS

Histologic sections of constructs seeded with P(0) cells stained strongly for S-GAG and type II collagen, whereas decreased staining for both matrix components was observed in constructs derived from P(1) and P(2) cells. Cellularity, S-GAG content, and total collagen content of constructs increased significantly from day 7 to day 28. S-GAG accumulation in P(0) constructs was higher than in either P(1) (P < 0.05) or P(2) (P < 0.01) constructs, whereas cellularity and total collagen content showed no difference between passages.

CONCLUSION

Neocartilage created from chondrocytes that have undergone serial passages in monolayer culture exhibited decreased matrix S-GAG and type II collagen, indicative of cellular dedifferentiation.

SIGNIFICANCE

The alterations of matrix composition produced by dedifferentiated chondrocytes may limit the mechanical stability of neocartilage constructs.

Serum-free medium supplemented with high-concentration FGF2 for cell expansion culture of human ear chondrocytes promotes redifferentiation capacity

For tissue engineering of autologous cartilage, cell expansion is needed to obtain the cell numbers required. Standard expansion media contain bovine serum. This has several disadvantages, that is, the risk of transmitting diseases and serum-batch variations. The aim of this study was to find a serum-free medium with at least the same potential to expand cell numbers as serum-containing media. Ear chondrocytes of three young children were expanded in either serum-containing medium (SCM; DMEM with 10% fetal calf serum) or serum-free medium (SFM; DMEM with ITS+) supplemented with 5 or 100 ng/mL fibroblast growth factor-2 (FGF2). To promote cell adherence onto the culture flask, the serum-free conditions were cultured with 10% serum for 1 day after each trypsinization. After the fourth passage, the chondrocytes were encapsuled in alginate beads and redifferentiated in a SFM (DMEM with ITS+, hydrocortisone, and L-ascorbic acid) supplemented with 10 ng/mL IGF-I and 10 ng/mL TGFbeta-2. Results showed that expansion in SFM with 100 ng/mL FGF2 was comparable to expansion in SCM. Redifferentiation with SFM with IGF-I and TGFbeta-2 showed high collagen type II expression and high GAG/DNA production regardless of which expansion medium had been used. However, chondrocytes expanded in SFM with 100 ng/mL FGF2 resulted in less positive cells for collagen type I and 11-fibrau (a fibroblast membrane marker). The present study shows that it is possible to use serum-free medium for tissue engineering of cartilage. Expansion of immature ear chondrocytes in SFM supplemented with high-concentration FGF2 resulted in high cell numbers, which in addition had better redifferentiation capacity than cells expanded in medium with 10% serum.

A new in vivo model for testing cartilage grafts and biomaterials: the 'rabbit pinna punch-hole' model

In this study an animal model was developed for evaluation of the feasibility of cartilage grafts. In the cartilage of the external ear of the rabbit multiple holes, 6 mm in diameter, were punched, leaving the adherent skin intact. Different experimental groups were evaluated. First, the punch-hole model was validated under various conditions to study spontaneous or perichondrial initiated regeneration of the cartilage defect. When both cartilage and perichondrium was excised no spontaneous repair of the cartilage defect was observed. When perichondrium is present, variable patch-like closure of the punch hole was found. As 'golden standard' a punched out piece of cartilage was reimplanted directly. This condition showed adequate closure of the punch hole, however, no perfect integration of graft and surrounding cartilage was observed. Secondly, to evaluate the 'punch-hole model' a biomaterial, trabecular demineralized bovine bone matrix (DBM), was implanted and tested as a scaffold for tissue engineering techniques in vivo and in vitro. Direct implantation of DBM did not lead to any cartilage formation to close the defect. In vivo engineered cartilage, generated by enveloping DBM in perichondrium for 3 weeks, could adequately close the punch hole. When DBM was seeded with isolated chondrocytes in vitro before implantation in the defect, a highly fragmented graft, with some islets of viable cells was seen. To promote an efficient and reliable evaluation of cartilage grafts a semi-quantitative grading system was developed. Items such as quality, quantity and integrity of the cartilage graft were included in a histomorphological grading system to provide information about the properties of a specific cartilage graft. To validate the grading system, all conditions were scored by two independent observers. An excellent reliability (R = 0.96) was seen between the observers. In summary, the rabbit pinna punch-hole model is a reliable and efficient method for first evaluation of cartilage grafts. The results can be easily analyzed using a semi-quantitative grading system.

Bioengineering of elastic cartilage with aggregated porcine and human auricular chondrocytes and hydrogels containing alginate, collagen, and kappa-elastin

Transplantation of isolated chondrocytes has long been acknowledged as a potential method for rebuilding small defects in damaged or deformed cartilages. Recent advances in tissue engineering permit us to focus on production of larger amounts of cartilaginous tissue, such as might be needed for reconstructive surgery of the entire auricle. In this report we describe modification of the basic techniques that lead to production of a large amount of elastic cartilage originated from porcine and human isolated chondrocytes. Small fragments of auricular cartilage were harvested from children undergoing ear reconstruction for microtia or extirpation of preauricular tags and from ears of juvenile pigs. Enzymatically isolated elastic chondrocytes were then agitated in suspension to form the chondronlike aggregates, which were further embedded in molded hydrogel constructs made of alginate and type I collagen augmented with kappa-elastin. The constructs were then implanted in nude mice and harvested 4 and 12 weeks after heterotransplantation. The resulting neocartilage closely resembled native auricular cartilage at the gross, microscopic, and ultrastructural levels. Immunohistochemistry and electron microscopy additionally confirmed that the newly produced cartilage contained the major components of the elastic cartilage-specific matrix, including collagen type II, proteoglycans, and well-assembled elastic fibers.

Differentiated cellular function in fetal chondrocytes cultured with insulin-like growth factor-I and transforming growth factor-beta

This study examined fetal chondrocyte proliferation and function following exposure to transforming growth factor-beta and insulin-like growth factor-I. Fetal equine articular chondrocytes of the early third-trimester were isolated and cultured in monolayer conditions, then exposed to 0, 1, 5, or 10 ng/ml transforming growth factor-beta or 0, 10, 50, or 100 ng/ml insulin-like growth factor-I for 48 hours. Proliferative responses were assessed by cell counts and [3H]thymidine uptake into precipitable DNA. Differentiated chondrocyte metabolic activity was determined by sulfated glycosaminoglycan quantitation, 35[SO4] incorporation into precipitable glycosaminoglycan, and proteoglycan molecular sizing by CL-2B column chromatography. Morphological changes seen on phase-contrast microscopy included a larger proportion of rounded cells in monolayer cultures supplemented with insulin-like growth factor-I and cytotoxic changes in cells treated with transforming growth factor-beta. Both insulin-like growth factor-I and transforming growth factor-beta resulted in significant elevations of [3H]thymidine uptake; however, cell numbers did not rise sufficiently over the 48-hour culture period to reach significant levels. Maximum mitogenic responses were evident at 50 and 100 ng/ml insulin-like growth factor-I and 5 ng/ml transforming growth factor-beta. The production of proteoglycan was also enhanced (435%) by exposure to 50 ng/ml insulin-like growth factor-I, and an increased proportion of larger proteoglycan monomer species was evident in cultures treated with 50 and 100 ng/ml insulin-like growth factor-I. A similar dose-response was also evident in cultures treated with transforming growth factor-beta (maximal 164% increase with 5 ng/ml), although the presence of serum in the culture medium altered the pattern of enhanced proteoglycan synthesis to favor the lower concentration of 1 ng/ml (191%). Additionally, larger proteoglycan molecules were synthesized in response to high concentrations of transforming growth factor-beta in serum-free cultures. Significant biochemical changes resulted from the addition of transforming growth factor-beta to fetal chondrocyte cultures; however, monolayer cultures that were treated with transforming growth factor-beta and supplemented with serum began to develop cellular toxicity, including nuclear pyknosis and cytoplasmic fragmentation. Degenerative cellular changes were not evident in cultures treated with insulin-like growth factor-I, and significant differentiated metabolic activity resulted from the presence of insulin-like growth factor-I in the culture medium. These data suggest that the responses of fetal chondrocytes to insulin-like growth factor-I and transforming growth factor-beta were enhanced compared with the responses of chondrocytes derived from postnatal animals and that these metabolically active cells can be primed by endogenous or exogenous growth factors to provide enhanced articular function and repair.

TSG-6 expression in human articular chondrocytes. Possible implications in joint inflammation and cartilage degradation

OBJECTIVE

The hyaluronan-binding protein TSG-6 (tumor necrosis factor-stimulated gene 6) forms a stable complex with the serine protease inhibitor, inter-alpha-inhibitor, potentiates the inhibition of plasmin activity, and has antiinflammatory effects in vivo. This study examines the expression of TSG-6 in human articular chondrocytes and cartilage.

METHODS

Human articular chondrocytes and cartilage explants were stimulated with cytokines, growth factors, and other agents. TSG-6 expression was analyzed by imaging-assisted Northern and Western blotting.

RESULT

TSG-6 messenger RNA (mRNA) expression was upregulated by cytokines and growth factors, predominantly interleukin-1 beta (IL-1 beta), tumor necrosis factor alpha (TNF alpha), platelet-derived growth factor AA (PDGF-AA), and transforming growth factor beta 1 (TGF beta 1). TSG-6 mRNA induction by TGF beta 1 was delayed as compared with IL-1beta. Treatment of the cells with the glucocorticoid dexamethasone neither induced TSG-6 mRNA nor did it affect IL-1 beta-induced transcript levels. TSG-6 mRNA induction may involve several signal transduction pathways. The strong transcriptional stimulation by phorbol myristate acetate suggests protein kinase C (PKC)-mediated signaling. In contrast, PKA- and Ca- dependent signals are only marginally involved as messengers leading to increased TSG-6 levels after IL-1beta and TNF alpha treatment. In chondrocyte and cartilage organ cultures, both free TSG-6 (35 kd) and the complex with inter-alpha-inhibitor (120 kd) were present and upregulated by IL-1 beta, TNF alpha, or TGF beta 1.

CONCLUSION

Chondrocytes are a source of TSG-6 which may play a role in cartilage remodeling and joint inflammation.

Chondrocyte-laden collagen scaffolds for resurfacing extensive articular cartilage defects

Chondrocyte-collagen composites were evaluated for resurfacing of large articular defects. Isolated chondrocytes were cultured in expanded collagen scaffolds for 7-10 days to provide a composite containing 3.6 x 10(4) cells/mm3. The graft was transplanted into 15 mm full thickness articular defects in the femoropatellar joint of 12 horses using arthroscopic techniques. Ungrafted defects in the opposite femoropatellar joint served as controls. Synovial fluid, clinical progress and pain responses were evaluated in groups of 6 horses over 4-month and 8-month periods. Following termination, gross, histochemical and histologic evaluations of the repair tissues and synovial membrane were performed. Arthroscopic defect debridement and chondrocyte implantation resulted in minimal post-operative effusion or pain, and synovial fluid constituents were not significantly different in grafted and ungrafted joints. Gross differences in grafted defects were not apparent. Increased chondrocyte numbers and cartilage histochemical staining were evident in the deeper layers of grafted defects, whereas ungrafted defects were almost entirely fibrous tissue. The surface layers of grafted defects were fibrous tissue. There were no synovial fluid cellular responses, synovial membrane histiocytic reaction or subchondral bone infiltrates to suggest immune-related reaction to the allograft cells. Chondrocyte-collagen grafts were arthroscopically implanted and resulted in improved cartilage healing in extensive defects. However, the structural organization of the surface layers was inadequate and suggested poor long-term durability.

Possible relationship between micronucleated and binucleated cells induced by cisplatin in cultured CHO cells

Chinese hamster ovary (CHO) cells were treated with a single dose (10 micrograms/ml) of cis-diamminodichloroplatinum (II) (cisplatin) for 1 h and the effect of the drug on the kinetics of proliferation of the cultures was studied. It was found that the drug produces a delay in the proliferation rates of the treated cultures. The induction of micronuclei and binucleated cells (BC) at different times after treatment have also been studied, and the ability of these cells to undergo DNA synthesis (measured as the ability to incorporate [3H]thymidine) is shown. It was also found that cisplatin induced a particular type of BC that contains one or more micronuclei rather than a pure population of BC. The results obtained show a possible relationship between micronuclei and BC. The possibility that some of the micronucleated cells evolve in subsequent cell divisions to BC with micronuclei is suggested.

Glycosaminoglycan patterns in gingival proteoglycans of rat with age

Among the potential biochemical indices that are closely associated with craniofacial development are the proteoglycans. Gingival segments from the palate of 4-, 6-, 8-, 12- and 18-week-old rats were incubated for 4 h in medium containing [3H]-glucosamine and [35S]-Na2SO4, and subjected to proteoglycan isolation and glycosaminoglycan analysis. Two distinct proteoglycan fractions differing in the degree of sulphation were obtained by ion-exchange chromatography. The incorporation of both labels in the undersulphated fraction increased with age; there was a pronounced decrease with age in the sulphated proteoglycan fraction. The undersulphated proteoglycans showed an age-dependent decrease in hyaluronic acid, and increase in dermatan sulphate and chondroitin 4- and 6-sulphates. Gel filtration of the sulphated proteoglycan fraction yielded high and low molecular-weight proteoglycans, the glycosaminoglycans of which were particularly rich (61-76%) in dermatan sulphate. Smaller quantities of chondroitin 4- and 6-sulphates, and heparan sulphate were also present. All glycosaminoglycans showed a decrease in content with age. The findings suggest a possible correlation between gingival proteoglycan/glycosaminoglycan patterns and development.

Basic fibroblast growth factor is synthesized and released by isolated ovine fetal growth plate chondrocytes: potential role as an autocrine mitogen

Basic fibroblast growth factor (basic FGF) is a mitogen for isolated epiphyseal growth plate chondrocytes. To determine whether basic FGF might function as an autocrine stimulus to longitudinal skeletal growth in utero, we investigated the synthesis and release of basic FGF by isolated growth plate chondrocytes from the ovine fetus, the expression of mRNA for a high affinity basic FGF receptor by these cells, and the contribution of endogenous basic FGF to the DNA synthetic rate of the cells in vitro. Chondrocytes were isolated from the proximal tibial growth plate of the lamb fetuses between 35 and 132 days' gestation using collagenase, and were cultured in monolayer before use between passages 3 and 6. Viability was confirmed over the duration of the experiments by the exclusion of trypan blue, and an absence of lactate dehydrogenase accumulation in conditioned medium. Immunocytochemistry of chondrocyte monolayers showed immunoreactive basic FGF to be present in the cytoplasm of approximately 80% of sub-confluent cells which was accompanied by pronounced nuclear staining in approximately 30% of cells. Serum-free, conditioned culture medium, extracellular matrix and chondrocyte cytoplasm contained 52 +/- 2 pM/micrograms DNA, 66 +/- 2 pM/micrograms DNA and 22 +/- 3 pM/micrograms DNA basic FGF, respectively (mean +/- S.E.M., n = 8 fetuses), for cells obtained from animals of 35-40 days' gestation when assessed by radioimmunoassay. Chondrocyte-conditioned medium increased endothelial cell proliferation in vitro (a specific bio-assay for basic FGF and related peptides); and the mitogenic activity was removed from conditioned medium by incubation with heparin-Sepharose demonstrating that this was due to heparin-binding protein(s). Western blot analysis of conditioned medium using a specific basic FGF antibody revealed a single immunoreactive protein of approximately 18 kDa molecular size. The appearance of radiommunoassayable basic FGF in conditioned medium, extracellular matrix, and chondrocyte cytoplasm observed during culture was blocked by co-incubation with cycloheximide. The levels of immunoreactive basic FGF present in each compartment decreased with gestational age as did basal DNA synthetic rate assessed by the incorporation of [3H] thymidine. Incubation of chondrocytes with transforming growth factor beta, resulted in a significant increase while exposure to insulin-like growth factors or insulin caused a decrease, in the content and release of basic FGF. Basic FGF presence was unaltered when medium was supplemented with varying amounts of glucose (2.7-16.7 mM). In situ hybridization on cell monolayers using a cRNA probe encoding the high affinity flg receptor for FGFs showed an abundant expression of mRNA for the receptor.(ABSTRACT TRUNCATED AT 400 WORDS)

The relationship between the rate of entry into S phase, concentration of DNA polymerase alpha, and cell volume in human diploid fibroblast-like monokaryon cells

We have examined the kinetic relationship between the rate of entry into the S phase in human diploid fibroblast-like (HDFL) monokaryon cells and (1) the concentration of DNA polymerase alpha activity and (2) the cell volume. In the former studies, a first-order dependence between the rate of entry into the S phase and the concentration of DNA polymerase alpha activity was observed, consistent with the enzyme, or a coregulated factor, being rate limiting for this metabolic process. Examination of the nature of the dependence of the rate of entry into the S phase upon cell volume revealed a more complex relationship. The results obtained in studies with synchronized cultures are consistent with the presence of two to three rate-limiting reactants when cell volume is the independent variable. Studies with asynchronous HDFL cell cultures revealed that the smallest cells in the G1 population, presumably the early G1 cells, enter the S phase at an increasing rate as a function of cell volume up to a certain size, beyond which the cells enter at a decreasing rate similar to that observed in the studies with the synchronized cultures. Similar studies examining the relationship between cell volume and the rate of entry into S phase in three established immortal cell lines revealed positive correlation between the rate of entry into S phase and cell volume throughout the size range of the G1 population. This latter observation suggests that the factors involved in the initiation of the S phase may be present in concentrations that are not rate limiting in immortal cell lines.

Stimulation of matrix formation in rabbit chondrocyte cultures by ascorbate. 2. Characterization of proteoglycans

The effect of ascorbate on the proteoglycans synthesized by rabbit articular chondrocytes was studied in first- and third-passage cultures for 12 and 26 days total duration, respectively. L-Ascorbate (0.2 mM) was added daily to half of the flasks after attachment of the cells. The cultures were labeled with Na2[35S]O4 or [14C]-glucosamine and [3H]-proline. Proteoglycans were isolated from the media and pericellular matrices by dissociative extraction and associative density gradient centrifugation. There was a large decline in the amount of proteoglycan synthesized between early and late cultures. Ascorbate increased the DNA content, amount of radiosulfate incorporated into glycosaminoglycans per microgram of DNA, and the proportion of labeled proteoglycan in the pericellular fraction of both short- and long-term cultures. The proteoglycans of the media and matrices of all cultures, with and without ascorbate, eluted as aggregates under associative column chromatographic conditions. The proteoglycans of 26-day cultures exhibited a higher degree of polydispersity in size than those of the short-term culture and contained small amounts of keratan (2-5%) and dermatan sulfate (4-8%) as assessed by keratanase and chondroitinase digestions, respectively. The effect of ascorbate, therefore, was to increase the amount of proteoglycan formed and to direct it into matrix deposition rather than to alter its quality.

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.

Insulin-like growth factor I, somatomedin C, induces the synthesis of tropoelastin in aortic tissue

The action of IGF-I (insulin-like growth factor I) on the synthesis of tropoelastin in chick embryonic aortae was examined. Maximal and selective stimulation of the relative (40%) and absolute (145%) rates of tropoelastin synthesis over control occurred at an IGF-I concentration of 100 ng/ml of medium. Parallel to the increase in synthesis was a 92% increase in the amount of tropoelastin activity per 100 ng of poly (A)+ RNA translated in a cell-free system. The relative rate of tropoelastin synthesis achieved at maximal stimulation is greater than that observed during normal aortic embryogenesis. The stimulatory action of the hormone on elastin synthesis appears to be at a pretransitional level perhaps involving increased transcription or stabilization of the tropoelastin mRNAs. These results suggest that IGF-I may play a key role in the regulation of elastogenesis in arterial tissue.

Cell fractions from rat rib growth cartilage. Biochemical characterization of matrix molecules

In an attempt to isolate and characterize the putative target cells for growth hormone, chondrocytes were isolated from rat rib growth cartilage and fractionated by centrifugation in a discontinuous Percoll gradient. This resulted in three cell fractions with differing properties. The fraction with the lowest density consisted mainly of large, lipid-containing cells which became flattened in subsequent culture. The cells in this fraction were fair collagen producers but synthesized only minor amounts of proteoglycans and apparently no proteoglycan aggregates. These cells probably originate in the hypertrophy zone of the growth plate. The fraction with highest density, on the other hand, consisted of small cells which upon cell culture became polygonal and surrounded with refractile matrix. They synthesized less collagen, but more proteoglycans than the low-density fraction. The proportion of proteoglycan aggregates was rather low (10-20%) but otherwise the proteoglycans were similar to those synthesized by other chondrocytes. This cell fraction was tentatively identified as cells from the upper part of the growth plate. Finally, the middle fraction was heterogeneous, consisting of cells of varying shape. This fraction synthesized large amounts of both collagen and proteoglycans. In all three cell fractions, type II collagen predominated. There were also minor amounts of (1a, 2a, 3a) collagen, and, in the two denser fractions, of type I collagen.

Elastin production in human skin fibroblast cultures and its decline with age

Recent studies have established that cultured human skin fibroblasts secrete the soluble precursor of elastin, tropoelastin (TE). The present studies evaluate, by an enzyme-linked immunosorbent assay, the stability of the TE phenotype and the effect of culture conditions and donor age on TE accumulation by human skin fibroblasts. Tropoelastin was maximally produced by 2 control fibroblast strains at early confluency (32-49 X 10(3) molecules/cell/h), and its serum-dependent accumulation in the medium was linear for at least 72 h. Inhibition of cross-linking had no effect on the rate of elastin production. Optimum serum concentrations for TE production differed for fibroblast cell strains derived from foreskin and trunk skin fibroblasts. Production of TE by human skin fibroblasts was stable through nearly 30 population doublings after which there was a greater than 2-fold decline in the rate of accumulation. In a cohort of donor strains, TE production appeared to decline at donor ages greater than or equal to 70 years. Under standard culture conditions, cell strains from normal donors of various ages produced TE at rates ranging from 25-69 X 10(3) molecules/cell/h. Rates of TE accumulation in medium were not significantly altered by degradation of TE, as a variety of cell strains tested exhibited minimal cell-associated elastolytic activity. Based on the demonstration of a stable elastin phenotype, skin fibroblast cultures provide a new system for studying regulation of elastin biosynthesis and evaluating potential defects in elastin metabolism associated with certain connective tissue disorders.

In-vitro culture of human chondrocytes from adult subjects

An agarose gel matrix was utilized to grow chondrocytes from human donors of various ages in cell culture. The chondrocytes produced the pericellular matrix characteristic for such cells and synthesized collagen type II as well as glyco-saminoglycans. The latter exhibit the typical distribution pattern of the respective articular cartilage matrix. The electron-microscopic appearance of the cultured chondrocytes closely resembles that of chondrocytes in sections of the original cartilage.

Changes of the elastin compartment in the human meniscus

We report on the elastin, collagen and ground substance compartments in the human meniscus and their interrelationships. Elastin is found in neonates and shows both an arrangement parallel to the collagen fibre and into net-like structures. Branching, caliber inconstancy, rupture and the phenomenon of the "rubber band" are findings within the different forms of the meniscopathy. The function of the elastin compartment cannot be visualised without suggesting "puncta fixa". The morphology of the collagen-elastin-junctions has been described and their possible mode of function is discussed with the help of a model.

Stable phenotypic expression by chick chondroblasts in long-term suspension cultures as determined by proteoglycan analysis

The influence of cell shape on phenotypic expression was studied in chick vertebral chondroblasts maintained for several weeks in suspension culture. To monitor phenotypic expression, synthesis of proteoglycans was studied in cultures of freshly-isolated 1-day-old chondroblasts and 1-to-6-week-old chondroblasts. The rate of proteoglycan synthesis was virtually identical in 1-week or older chondroblasts; however, this rate was 3- to 5-fold higher than in 1-day-old cells. When compared to the latter cells, the various populations of older chondroblasts synthesized monomers of the major cartilage proteoglycan (KS: CS-PG) of slightly lower molecular size and a lower level of unsubstituted N-acetylgalactosamine residues on their core protein but with similar chondroitin sulfate chains and levels of O-linked oligosaccharides. At no time of culture were changes in the proportions of the major vs the minor cartilage proteoglycans detected. The results suggest that in contrast to epithelioid chondroblasts in standard monolayer cultures studied previously, the round floating chondroblasts express very stable biosynthetic properties for a prolonged time in suspension. The distinct biosynthetic properties of 1-day-old chondroblasts are discussed in terms of an initial, transitory response to the culture condition and in relation to regulatory mechanisms for proteoglycan elaboration.

Absence of keratan sulphate from skeletal tissues of mouse and rat

The absence of keratan sulphate synthesis from skeletal tissues of young and mature mice and rats has been confirmed by (1) analysis of specific enzyme degradation products of newly synthesized glycosaminoglycans, and (2) immunohistochemistry and radioimmunoassay using a monoclonal antibody directed against keratan sulphate. Approx. 98% of the [35S]glycosaminoglycans synthesized in vivo by mouse and rat costal cartilage, and all of those of lumbar disc, are chondroitin sulphate. The remainder in costal cartilage were identified as heparan sulphate in mature rats. In contrast, [35S]glycosaminoglycans synthesized by cornea of both species comprised both chondroitin sulphate and keratan sulphate. In mice keratan sulphate accounted for 12-25% and in rats 40-50% of the total [35S]glycosaminoglycans, depending on the age of the animal. Experiments in vitro with organ culture of cartilage and cornea confirm these results. Absence of keratan sulphate from mouse costal cartilage and lumbar disc D1-proteoglycans was corroborated by inhibition radioimmunoassay with the monoclonal antibody MZ15 and by lack of staining for keratan sulphate in indirect immunofluorescence studies using the same antibody.

Effect of exogenous extracellular matrices on proteoglycan synthesis by cultured rabbit costal chondrocytes

We examined the effect of an extracellular matrix (ECM), produced by either bovine corneal endothelial (BCE) cells or mouse PF HR-9 teratocarcinoma cells, on the ability of rabbit costal chondrocytes to re-express their phenotype once confluent. Rabbit chondrocytes seeded at low densities and grown on plastic tissue culture dishes produced a heterogeneous cell population composed of both overtly differentiated and poorly differentiated chondrocytes, as well as fibroblastic cells. On the other hand, cultures grown on BCE-ECM- or HR-9-ECM-coated dishes reorganized into a homogeneous cartilage-like tissue composed of round cells surrounded by a refractile matrix that stained intensely with alcian green. The cell ultrastructure and that of their pericellular matrix were similar to those seen in vivo. The differentiation of chondrocyte cultures grown on the ECMs vs. plastic was reflected by a two- to three-fold increase in the maximal rate of incorporation of [35S]sulfate and [3H]glucosamine into proteoglycans. Furthermore, the ratio of 35S-labeled proteoglycans incorporated in the cell layer vs. those released into the medium was 1.5-2.5-fold higher when cultures were grown on the ECMs than on plastic. This suggests that the ECMs stimulate the incorporation of newly synthesized proteoglycans into a cartilaginous matrix. Since chondrocyte cultures grown on BCE-ECM or HR-9-ECM give rise to a homogeneous cartilage-like tissue even when seeded at low cell densities, they provide a model for the study of cell-substrate interactions that are responsible for the maintenance of the differentiated phenotype of chondrocytes.

Sulfated proteoglycan synthesis by confluent cultures of rabbit costal chondrocytes grown in the presence of fibroblast growth factor

We examined the effect of fibroblast growth factor (FGF) on proteoglycan synthesis by rabbit costal chondrocyte cultures maintained on plastic tissue culture dishes. Low density rabbit costal chondrocyte cultures grown in the absence of FGF gave rise at confluency to a heterogeneous cell population composed of fibroblastic cells and poorly differentiated chondrocytes. When similar cultures were grown in the presence of FGF, the confluent cultures organized into a homogenous cartilage-like tissue composed of rounded cells surrounded by a refractile matrix. The cell ultrastructure and that of the pericellular matrix were similar to those seen in vivo. The expression of the cartilage phenotype in confluent chondrocyte cultures grown from the sparse stage in the presence vs. absence of FGF was reflected by a fivefold increase in the rate of incorporation of [35S]sulfate into proteoglycans. These FGF effects were only observed when FGF was present during the cell logarithmic growth phase, but not when it was added after chondrocyte cultures became confluent. High molecular weight, chondroitin sulfate proteoglycans synthesized by confluent chondrocyte cultures grown in the presence of FGF were slightly larger in size than that produced by confluent cultures grown in the absence of FGF. The major sulfated glycosaminoglycans associated with low molecular weight proteoglycan in FGF-exposed cultures were chondroitin sulfate, while in cultures not exposed to FGF they were chondroitin sulfate and dermatan sulfate. Regardless of whether or not cells were grown in the presence or absence of FGF, the 6S/4S disaccharide ratio of chondroitin sulfate chains associated with high and low molecular weight proteoglycans synthesized by confluent cultures was the same. These results provide evidence that when low density chondrocyte cultures maintained on plastic tissue culture dishes are grown in the presence of FGF, it results in a stimulation of the expression and stabilization of the chondrocyte phenotype once cultures become confluent.

Analysis of collagen types synthesized by rabbit ear cartilage chondrocytes in vivo and in vitro

This study compares the collagen types present in rabbit ear cartilage with those synthesized by dissociated chondrocytes in cell culture. The cartilage was first extracted with 4M-guanidinium chloride to remove proteoglycans. This step also extracted type I collagen. After pepsin solubilization of the residue, three additional, genetically distinct collagen types could be separated by fractional salt precipitation. On SDS (sodium dodecyl sulphate)/polyacrylamide-gel electrophoresis they were identified as type II collagen, (1 alpha, 2 alpha, 3 alpha) collagen and M-collagen fragments, a collagen pattern identical with that found in hyaline cartilage. Types I, II, (1 alpha, 2 alpha, 3 alpha) and M-collagen fragments represent 20, 75, 3.5, and 1% respectively of the total collagen. In frozen sections of ear cartilage, type II collagen was located by immunofluorescence staining in the extracellular matrix, whereas type I collagen was closely associated with the chondrocytes. Within 24h after release from elastic cartilage by enzymic digestion, auricular chondrocytes began to synthesize type III collagen, in addition to the above-mentioned collagens. This was shown after labelling of freshly dissociated chondrocytes with [3H]proline 1 day after plating, fractionation of the pepsin-treated collagens from medium and cell layer by NaCl precipitation, and analysis of the fractions by CM(carboxymethyl)-cellulose chromatography and SDS/polyacrylamide-gel electrophoresis. The 0.8 M-NaCl precipitate of cell-layer extracts consisted predominantly of type II collagen. The 0.8 M-NaCl precipitate obtained from the medium contained type I, II, and III collagen. In the supernatant of the 0.8 M-NaCl precipitation remained, both in the cell extract and medium, predominantly 1 alpha-, 2 alpha-, and 3 alpha-chains and M-collagen fragments. These results indicate that auricular chondrocytes are similar to chondrocytes from hyaline cartilage in that they produce, with the exception of type I collagen, the same collagen types in vivo, but change their cellular phenotype more rapidly after transfer to monolayer culture, as indicated by the prompt onset of type III collagen synthesis.

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.

Enhanced endocytosis by aging chondrocytes and fibroblasts

We have compared the uptake of latex beads by cultures of old and young chondrocytes and fibroblasts. In each case, their phagocytic rates increased with cellular age.

Synthesis and secretion of proteoglycans by cultured chondrocytes. Effects of monensin, colchicine and beta-D-xyloside

Chondrocytes, isolated from elastic ear cartilage of young rabbits, were grown in monolayer cultures in Ham's F-12 medium. Synthesis and secretion of macromolecules were monitored by labelling with radioactive precursors and the effect of monensin and other experimental agents was investigated. Monensin caused an inhibition of the incorporation of precursors into macromolecular material and a moderate intracellular accumulation when used in higher concentrations. The effect was more pronounced for 35SO4 than for 3H-labelled glucose or proline. p-Nitrophenyl-beta-D-xyloside alleviated this inhibition to some extent, but there was a concomitant increase in the amount of intracellular labelled material. Colchicine and monensin together caused a severe inhibition of the incorporation of 35SO4 and a marked shift of the label to the intracellular compartment. Colchicine also increased the sensitivity of the cells to monensin, lowering the minimal effective concentration about one order of magnitude. The latter results are consistent with the idea that cytoplasmic microtubules have a stabilizing function on the secretory pathways and, that their removal by colchicine, causing a 'randomizing' of the Golgi complex, makes these pathways more vulnerable to monensin.

Influence of beta-aminoproprionitrile (BAPN) on cell growth and elastic fiber formation in cultures of auricular chondrocytes

Auricular chondrocytes isolated from 4-day-old rabbits and grown in vitro for 14 days, proliferated rapidly and produced a conspicuous network of elastic fibers. Beta-aminoproprionitrile (BAPN), which in vivo inhibits cross-linking of elastin, decreased the formation of elastic fibers at a concentration of 10-20 micrograms/ml and prevented formation at 40 micrograms/ml. At a concentration of 5 micrograms/ml only the so-called patches of elastin appeared to be absent. The inhibitory effect of BAPN on cell growth did not exceed 10%, which indicates that BAPN is only slightly harmful to auricular chondrocytes and can safely be used in studies on elastin deposition by these cells in vitro.

Growth hormone stimulates the proliferation of cultured chondrocytes from rabbit ear and rat rib growth cartilage

The effect of growth hormone (GH) on various growth processes is generally considered to be indirect, mediated by GH-dependent plasma factors--somatomedins--which are produced mainly in the liver. In vitro, somatomedins stimulate a number of processes that apparently are associated with cell growth. It has been difficult, however, to induce skeletal growth by the administration of somatomedins in vivo. Daily injections of a partially purified somatomedin preparation failed to induce accumulated longitudinal bone growth using the intravital marker tetracycline or by measuring the nose-to-tail length. Administration of insulin-like growth factor I (IGF I) which is probably identical to somatomedin C, to hypophysectomized rats has been reported to increase the width of the epiphyseal plate. But although this suggests an in vivo effect of IGF I on longitudinal bone growth, such an effect has not been directly demonstrated. Recently, we reported that local administration of human GH (hGH) into the proximal cartilage growth plate of the tibia of hypophysectomized rats stimulated longitudinal bone growth on the side injected with the hormone. Furthermore, we have identified specific binding sites for hGH in cultured chondrocytes from rabbit ear and epiphyses. Here, we show that hGH, but not the structurally related polypeptides ovine prolactin or human prolactin, stimulates DNA synthesis in chondrocytes from rabbit ear and from rat rib growth plate, cultured in a chemically defined medium without the addition of serum. Our results suggest that GH directly initiates proliferation in mammalian chondrocytes.