Human chondrocytes in tridimensional culture

Maternal Hyperthyroidism in Rats Alters the Composition and Gene Expression of the Matrix Produced In Vitro by Chondrocytes from Offspring with Intrauterine Growth Restriction

Herein, we aimed to evaluate cultures of femoral chondrocytes from offspring of rats with intrauterine growth restriction (IUGR) induced by maternal hyperthyroidism. Fourteen adult female Wistar rats were divided into two groups, a control group and a group treated with daily L-thyroxine administration using an orogastric tube (50 µg/animal/day) during pregnancy. Three days after birth, the offspring were euthanized for chondrocyte extraction. At 7, 14, and 21 days, viability and alkaline-phosphatase (ALP) activity were assessed using the MTT assay and BCIP/NBT method, respectively, in a 2D culture. Pellets (3D cultures) were stained with periodic acid Schiff (PAS) to assess the morphology and percentage of PAS+ areas. The gene transcripts for Col2, Col10, Acan, Sox9, and Runx2 were evaluated by qRT-PCR. The MTT and ALP-assay results showed no significant differences between the groups. Maternal hyperthyroidism did not alter the chondrocyte morphology, but significantly reduced the percentage of PAS+ areas, decreased the expression of the gene transcripts of Col2 and Acan, and increased Sox9 expression. Maternal hyperthyroidism in rats alters the composition and gene expression of the matrix produced by chondrocytes from offspring with IUGR. This may be one of the mechanisms through which excess maternal thyroid hormones reduce offspring bone growth.

Ethanol Alters Phenotype and Synthesis Activity of Rat Neonatal Articular Chondrocytes Grown in 2- and 3-Dimensional Culture

OBJECTIVE

We sought to evaluate the effect of different concentrations of ethanol on phenotype and activity of articular chondrocyte synthesis of neonatal rats in 2-dimensional (2D) and 3-dimensional (3D) culture.

METHODS

Chondrocytes were cultured in chondrogenic medium with different concentrations of ethanol: 0.0% v/v (control); 0.05% v/v (8.6 mM); 0.25% v/v (42.9 mM), and 0.5% v/v (85.7 mM). Chondrocytes under 2D culture were subjected to MTT assay, while chondrocytes under 3D culture were processed for paraffin inclusion and stained by periodic acid Schiff (PAS) to evaluate mean chondrocyte diameter and percentages of cells, nucleus, cytoplasm, well-differentiated matrix, and PAS+ areas. The expression of gene transcripts for aggrecan, Sox9, and type II collagen was evaluated by real-time quantitative polymerase chain reaction.

RESULTS

There was no difference between groups by the MTT assay. PAS staining revealed that chondrocytes treated with 0.5% v/v ethanol had higher percentages of cytoplasm and nuclear areas, but with a reduction in PAS+ matrix area. The mean diameter of chondrocytes was similar between groups. The expression of aggrecan in the group treated with 0.5% v/v ethanol was lower in comparison to that in the control. In the groups treated with 0.25% v/v and 0.5% v/v ethanol, the percentage of differentiated cartilage was lower in comparison with that in the control. The group treated with 0.05% v/v ethanol was similar to the control in all parameters.

CONCLUSIONS

Ethanol acted directly on in vitro cultured articular chondrocytes of newborn rats, altering the chondrocyte phenotype and its synthesis activity, and these effects were dose dependent.

Systematic Comparison of Protocols for the Preparation of Human Articular Cartilage for Use as Scaffold Material in Cartilage Tissue Engineering

Natural extracellular matrix-derived biomaterials from decellularized allogenic tissues are of increasing interest for tissue engineering because their structure and composition provide a complexity that is not achievable with current manufacturing techniques. The prerequisite to bring allogenic tissue from bench to bedside as a functional biomaterial is the full removal of cells while preserving most of its native characteristics such as structure and composition. The exceptionally dense structure of articular cartilage, however, poses a special challenge for decellularization, scaffold preparation, and reseeding. Therefore, we tested 24 different protocols aiming to remove cells and glycosaminoglycans (GAG) while preserving the collagen backbone and ultrastructure. The resulting matrices were analyzed for cell removal (DNA quantification, haematoxylin and eosin staining), GAG content (dimethyl methylene blue assay, Alcian blue staining and micro-computed tomography), collagen integrity (immunohistochemistry and ultrastructure), and biomechanics (compression test). Furthermore, seeding tests were conducted to evaluate cell viability and attachment to the scaffolds. Sodium dodecyl sulfate-based protocols yielded satisfactory reduction of DNA content, yet had negative effects on cell viability and attachment. Hydrochloric acid efficiently decellularized the scaffold and pepsin emerged as best option for GAG depletion. Combining these two reagents led to our final protocol, most efficient in DNA and GAG depletion while preserving the collagen architecture. The compressive modulus decreased in the absence of GAG to ∼1/3 of native cartilage, which is significantly higher than that by commercially available scaffolds tested as a reference (ranging from 1/25 to 1/100 of native cartilage). Cytocompatibility tests showed that human adipose-derived stromal cells readily adhered to the scaffold. In this study, we established a protocol combining freeze-thaw cycles, osmotic shock, and treatment with hydrochloric acid followed by a pepsin digestion step, achieving successful decellularization and GAG depletion within 1 week, resulting in a cytocompatible material with intact collagen structure. The protocol provides a basis for the generation of allogeneic scaffolds, potentially substituting manufactured scaffolds currently used in clinical articular cartilage treatment.

Human chondrocyte cultures as models of cartilage-specific gene regulation

The human adult articular chondrocyte is a unique cell type that has reached a fully differentiated state as an end point of development. Within the cartilage matrix, chondrocytes are normally quiescent and maintain the matrix constituents in a low-turnover state of equilibrium. Isolated chondrocytes in culture have provided useful models to study cellular responses to alterations in the environment such as those occurring in different forms of arthritis. However, expansion of primary chondrocytes in monolayer culture results in the loss of phenotype, particularly if high cell density is not maintained. This chapter describes strategies for maintaining or restoring differentiated phenotype by culture in suspension, gels, or scaffolds. Techniques for assessing phenotype involving primarily the analysis of synthesis of cartilage-specific matrix proteins as well as the corresponding mRNAs are also described. Approaches for studying gene regulation, including transfection of promoter-driven reporter genes with expression vectors for transcriptional and signaling regulators, chromatin immunoprecipitation, and DNA methylation are also described.

Nanog maintains human chondrocyte phenotype and function in vitro

Previous work showed that Nanog, a homeobox family transcription factor, maintains embryonic stem cell pluripotency, suggesting that it has a role in stabilizing cell phenotype. Human chondrocytes lose their phenotype and dedifferentiate after relatively few passages in culture, changes that may limit their value in restoring damaged articular cartilage. We hypothesized that Nanog could stabilize the phenotype of cultured human chondrocytes in long-term monolayer cultures. To test this hypothesis, the human Nanog gene was stably transduced into human chondrocytes using a retroviral vector. Chondrocyte-specific gene expression (collagen type II, aggrecan, cartilage link protein, and Sox9) was measured by reverse transcription-polymerase chain reaction (RT-PCR) and real-time PCR in monolayer cultured chondrocytes transduced with Nanog and in control chondrocytes transduced with empty vector. In vitro cartilage matrix protein formation by Nanog-transduced and control cells was compared using Safranin-O and immunofluorescence stains. We found that after 25 passages, Nanog-transduced chondrocytes maintained significantly higher expression of collagen type II, aggrecan, and cartilage link protein genes than controls. Under chondrogenic conditions, Nanog-transduced cells produced significantly more cartilage-specific matrix than control cells. These findings support the hypothesis that Nanog maintains the human chondrocyte phenotype and function after long-term monolayer culture. Preservation of the chondrocyte phenotype may improve the ability of cultured chondrocytes to repair or restore articular cartilage.

Chondrocytes cultured in stirred suspension with serum-free medium containing pluronic-68 aggregate and proliferate while maintaining their differentiated phenotype

The study of chondrocyte biology requires culture conditions that maintain cell phenotype. Phenotype is rapidly lost in monolayer but is maintained in 3-dimensional scaffolds, which however, experience limited cell proliferation and limited mass transport. In this study, we cultured chondrocytes in aggregates in stirred spinner flask suspension cultures to control aggregate size and promote mass transport. A previously optimized serum-free medium, containing the following growth factors (GFs), epidermal growth factor, platelet-derived growth factor-BB, and basic fibroblast growth factor, all at 2 ng/mL, was used as a control medium. In addition, two modified media were tested: one containing Pluronic F-68 (PF-68) and the other containing PF-68 with 10 times greater GF concentration (20 ng/mL, medium PF-68/10 x GF). Chondrocytes formed limited-size aggregates within 24 h and exhibited high viability (>95%), and cell concentration doubled in 7 days in the presence of PF-68. Low or no collagen I expression was found for any of the three media, whereas collagen II accumulated between cells, as revealed by a dense immunostaining. Integrin alpha10, a marker of differentiated chondrocytes and chondrogenic cells, was also found to be highly expressed. Aggregates resulting from spinner culture were found to be relevant in vitro models and their use for cartilage repair to be also conceivable.

The role of tissue engineering in articular cartilage repair and regeneration

Articular cartilage repair and regeneration continue to be largely intractable because of the poor regenerative properties of this tissue. The field of articular cartilage tissue engineering, which aims to repair, regenerate, and/or improve injured or diseased articular cartilage functionality, has evoked intense interest and holds great potential for improving articular cartilage therapy. This review provides an overall description of the current state of and progress in articular cartilage repair and regeneration. Traditional therapies and related problems are introduced. More importantly, a variety of promising cell sources, biocompatible tissue engineered scaffolds, scaffoldless techniques, growth factors, and mechanical stimuli used in current articular cartilage tissue engineering are reviewed. Finally, the technical and regulatory challenges of articular cartilage tissue engineering and possible future directions are also discussed.

Down regulation of degenerative cartilage molecules in chondrocytes grown on a hyaluronan-based scaffold

Hyaluronic-acid-based biomaterials used for cartilage repair allow the expression of specific extracellular matrix molecules by human chondrocytes grown onto them. We investigated whether these biomaterials could also create an environment in which the cells downregulate the expression of some catabolic factors. Chondrocytes were isolated from human articular cartilage obtained from the knees of patients with a history of trauma. First, the cells were expanded in monolayers and then they were seeded on a hyaluronic-acid derivative scaffold. Constructs and surnatants were collected and analysed at 1, 3, 7, 14 and 21 days after seeding. Immunohistochemical analysis for CD44 and caspase was carried out on paraffin-embedded sections. The Tunel method was used to identify chondrocyte apoptosis status. Secretion of MMP-1 and MMP-13 in the surnatants of the cells grown onto the biomaterial was measured by enzyme-linked immunosorbent assay. Nitric oxide (NO) production was evaluated by estimating the stable NO metabolite nitrite by the Griess method. A real-time RT-PCR analysis was performed on the constructs to evaluate the expression of type I and II collagens, aggrecan, Sox-9, MMP-1 and MMP-13 mRNAs at the different experimental times evaluated. Decreased levels of metalloproteinases and nitric oxide were observed in the surnatants of chondrocytes grown onto the hyaluronan-based scaffold. This was also confirmed by real-time PCR analysis which showed that the cells expressed the specific differentiated phenotype downregulating the expression of some catabolic molecules. Cells apoptosis decreased during the culture period, which further supported the biochemical data. The ability of the hyaluronan scaffold to reduce the expression and production of molecules involved in cartilage degenerative diseases indicates its use to treat early lesions of osteoarthritic patients.

Microscale tissue engineering using gravity-enforced cell assembly

Designing artificial microtissues by reaggregation of monodispersed primary cells, neoplastic or engineered cell lines is providing insight into cell-cell interactions and underlying regulatory networks. Recent advances in microtissue production have highlighted the potential of scaffold-free cell aggregates in maintaining tissue-specific functionality, supporting seamless integration of implants into host tissues, and providing complex feeder structures for difficult-to-differentiate cell types. Furthermore, these tissues are amenable to therapeutic and phenotype-modulating interventions using latest-generation transduction technologies. Microtissues produce therapeutic transgenes at increased levels and offer tissue-like assay environments to improve drug-function correlations in current discovery programs. Here, we outline scaffold-free microtissue design in liver, heart and cartilage, and discuss how this technology could significantly impact regenerative medicine.

Differential Behavior Between Isolated and Aggregated Rabbit Auricular Chondrocytes on Plastic Surfaces

A knowledge of the behavior of chondrocytes in culture is relevant for tissue engineering. Chondrocytes dedifferentiate to a fibroblast-like phenotype on plastic surfaces. Dedifferentiation is reversible if these cells are then cultured in suspension. In this report a description is given of how when chondrocyte aggregates formed in suspension are next seeded on plastic, most of them attach as round or polygonal cells. This morphological differentiation, with synthesis of type II collagen, is stable for long culture periods. This simple method can be of use as a model for studies of chondrocyte behavior on plastic. The results indicate that in addition to culture conditions, such as cell isolation method or cell density, chondrocyte behavior on plastic depends on the presence of aggregates.

Collagen expression in tissue engineered cartilage of aged human articular chondrocytes in a rotating bioreactor

This study describes the culture and three-dimensional assembly of aged human articular chondrocytes under controlled oxygenation and low shear stress in a rotating-wall vessel. Chondrocytes cultured in monolayer were released and placed without any scaffold as a single cell suspension in a rotating bioreactor for 12 weeks. Samples were analyzed with immunohistochemistry, molecular biology and electron microscopy. During serial monolayer cultures chondrocytes dedifferentiated to a "fibroblast-like" structure and produced predominantly collagen type I. When these dedifferentiated cells were transferred to the rotating bioreactor, the cells showed a spontaneous aggregation and formation of solid tissue during the culture time. Expression of collagen type II and other components critical for the extracellular cartilage matrix could be detected. Transmission electron microscopy revealed a fine network of randomly distributed collagen fibrils. This rotating bioreactor proves to be a useful tool for providing an environment that enables dedifferentiated chondrocytes to redifferentiate and produce a cartilage-specific extracellular matrix.

In vitro engineering of human autogenous cartilage

A challenge in tissue engineering is the in vitro generation of human cartilage. To meet standards for in vitro-engineered cartilage, such as prevention of immune response and structural as well as functional integration to surrounding tissue, we established a three-dimensional cell culture system without adding exogenous growth factors or scaffolds. Human chondrocytes were cultured as spheroids. Tissue morphology and protein expression was analyzed using histological and immunohistochemical investigations on spheroid cryosections. A cartilage-like tissue similar to naturally occurring cartilage was generated when spheroids were cultured in medium supplemented only with human serum. This in vitro tissue was characterized by the synthesis of the hyaline-specific proteins collagen type II and S-100, as well as the synthesis of hyaline-specific mucopolysaccharides that increased with prolonged culture time. After 3 months, cell number in the interior of in vitro tissues was diminished and was only twice as much as in native cartilage. Additionally, spheroids quickly adhered to and migrated on glass slides and on human condyle cartilage. The addition of antibiotics to autologous spheroid cultures inhibited the synthesis of matrix proteins. Remarkably, replacing human serum by fetal calf serum resulted in the destruction of the inner part of the spheroids and only a viable rim of cells remained on the surface. These results show that the spheroid culture allows for the first time the autogenous in vitro engineering of human cartilage-like tissue where medium supplements were restricted to human serum.

Evidence for redifferentiation of human chondrocytes grown on a hyaluronan-based biomaterial (HYAff 11): molecular, immunohistochemical and ultrastructural analysis

Association of biomaterials with autologous cells can provide a new generation of implantable devices for cartilage repair. Such scaffolds should provide a preformed three-dimensional shape and prevent cells from escaping into the articular cavity. Furthermore, these constructs should have sufficient mechanical strength to facilitate handling in a clinical setting and stimulate the uniform spreading of cells and their phenotype redifferentiation. The aim of this study was to verify the ability of HYAFF 11, a recently developed hyaluronic-acid-based biodegradable polymer, to support the growth of human chondrocytes and to maintain their original phenotype. This capability was assessed by the evaluation of collagen types I, II and aggrecan mRNA expression. Immunohistochemical analyses were also performed to evaluate collagen types I, II and proteoglycans synthesis. A field emission in lens scanning microscopy was utilized to verify the interactions between the cells and the biomaterial. Our data indicate that human chondrocytes seeded on HYAFF 11 express and produce collagen type II and aggrecan and downregulate the production of collagen type I. These results provide an in vitro demonstration for the therapeutic potential of HYAFF 11 as a delivery vehicle in a tissue-engineered approach towards the repair of articular cartilage defects.

Culture of organized cell communities

Cells cultured in vitro will tend to retain their differentiated phenotype under conditions that resemble their natural in vivo environment, for example, when cultured on polymer scaffolds in tissue culture bioreactors. In this chapter, we define organized cell communities as three-dimensional in vitro grown cell-polymer constructs that display important structural and functional features of the natural tissue. We review representative studies in which the research goal was to culture organized cell communities resembling cartilage, bone, skeletal muscle or cardiac-like tissue. These constructs can potentially serve as tissue equivalents for in vivo transplantation or as a model system for the in vitro testing of cell and tissue-level responses to molecular, mechanical or genetic manipulations.

Cartilage fibronectin isoforms: in search of functions for a special population of matrix glycoproteins

Fibronectins are a part of the repertoire of matrix molecules produced by the chondrocyte in order to assemble a functional cartilage matrix. They are encoded by a single gene, but significant protein heterogeneity results from alternative RNA splicing. The population of fibronectin isofroms in adult cartilage is significantly different from fibronectins in other tissues and includes relatively high levels (20-30%) of ED-B(+) fibronectins and high levels (50-80%) of the cartilage specific (V + C)- isoform which lacks the V, III-15 and I-10 segments. Less than 4% of the fibronectins in cartilage are ED-A(+). The synthesis and accumulation of cartilage fibronectins are modulated in response to matrix pathology and to biochemical and mechanical mediators. In addition, alternative splicing patterns are altered when chondrocytes are allowed to dedifferentiate in monolayer culture such that the (V + C)- isoform is lost but the ED-A(+) isoform is reexpressed at high levels. Cartilage fibronectins have the potential to participate in cell signalling via integrin mediated pathways and to interact with other cartilage matrix macromolecules. The tissue-specific splicing pattern gives rise to a unique population of fibronectins within the cartilage. Together, this points to a critical role for cartilage fibronectins in chondrocyte cell biology and the organization of a biomechanically sound matrix. However, the precise function (or functions) of the cartilage fibronectins has (or have) not been defined. This minireview examines current information about the structure, synthesis and interactions of cartilage fibronectins. When possible, potential consequences of the inclusion of the ED-B segment or the exclusion of the V, III-15 and I-10 segments are discussed. The goal is to stimulate critical thought and discussion in the field about cartilage fibronectin isoforms, their function(s) in normal cartilage, and their role(s) in the pathogenesis of cartilage diseases.

Effects of ipriflavone and its metabolites on human articular chondrocytes cultivated in clusters

Ipriflavone (IP) is an isoflavone derivative that was suggested to have bone-sparing effects in post-menopausal and senile osteoporosis. A moderate stimulatory effect of IP and its metabolites on proliferation of osteoblastic cells was reported in rat osteoblastic osteosarcoma cell line. We investigated the effects of different concentrations (0, 1, 10 and 100 micrograms/ml) of IP and its metabolites (MET I, II, III and V) on the incorporation of [3H] thymidine and production of proteoglycans (PG) and type II collagen (COL II) by human articular chondrocytes during a 12-day period, in a three-dimensional chondrocyte culture model. [3H]thymidine uptake was measured in chondrocyte clusters, and specific PG and COL II radioimmunoassays were performed every 4 days on the culture medium and cell clusters. Incubation with IP or its metabolites did not affect [3H]thymidine uptake regardless of the dose. PG released into the culture medium and PG cluster content rose significantly (P < 0.025) in presence of IP (1, 10 and 100 micrograms/ml). MET I increased PG release in culture medium (10 and 100 micrograms/ml) and PG cluster content (100 micrograms/ml). MET II has no effect on PG production. MET III increased PG in culture medium (100 microgram/ml) but did not influence PG cluster content while MET V (100 micrograms/ml) increased both PG release in culture medium and PG cluster content. COL II release in culture medium and COL II cluster content were significantly (P < 0.025) increased in presence of IP (10 and 100 micrograms/ml), MET III (1, 10 and 100 micrograms/ml) or MET V (100 micrograms/ml). MET I and II did not significantly affect COL II production.

Tissue engineering and autologous transplant formation: practical approaches with resorbable biomaterials and new cell culture techniques

The engineering of living tissues in vivo requires new concepts in cell culture technology. In contrast to conventional cell cultures, the development of tissues depends on a three-dimensional arrangement of cells and the formation or synthesis of an appropriate extracellular matrix. Special emphasis is given to the major role of the extracellular matrix and cell differentiation in an artificial tissue. New technical approaches of in vitro tissue engineering are compared to the natural development of tissues in vivo. Current methods using resorbable biomaterials, tissue encapsulation and perfusion culture are discussed. Major consideration is given to scaffold structures of biomaterials that define a three-dimensional shape of a tissue or guide matrix formation. The different goals of tissue engineering such as in vitro models and transplant production are taken into account in the described techniques. Practical concepts comprising cell multiplication and differentiation in subsequent steps for future clinical applications are outlined.

Proteoglycan synthesis by cultured human chondrocytes

Iliac crest biopsies are important in the detection of human skeletal dysplasias. Therefore, culture of these cells may serve as a valuable method for studying proteoglycan metabolism in chondrocytes of individuals with skeletal abnormalities. Morphological and biochemical studies were performed on human iliac crest chondrocytes grown in monolayer and in agarose gels. Two proteoglycan populations of different hydrodynamic size and glycosaminoglycan composition were synthesized by cells grown in monolayer. Chondrocytes cultured in an agarose gel for 2 weeks synthesized proteoglycans identical to those of the native tissue with respect to hydrodynamic size and glycosaminoglycan chain length. However, the ratio of chondroitin-6-sulfate to chondroitin-4-sulfate was higher than in the native tissue. This ratio was not influenced by different sulfate concentrations in the medium. Moreover, treatment with ascorbic acid did not influence proteoglycan synthesis; however, there was a pericellular accumulation of proteoglycans.

Cartilage oligomeric matrix protein and thrombospondin 1. Purification from articular cartilage, electron microscopic structure, and chondrocyte binding

Cartilage oligomeric matrix protein (COMP) and thrombospondin 1 (TSP1) were purified in a native form from normal bovine articular cartilage. The key step in the purification scheme was selective extraction with EDTA-containing buffer. Final separation of these two molecules was achieved by heparin affinity chromatography. Particles viewed by electron microscopy after rotary shadowing and negative staining revealed structures similar to their prototype molecules; from the Swarm rat chondrosarcoma for COMP, or from platelets for TSP1. Attachment of primary bovine chondrocytes to purified matrix proteins was investigated. Cells attached to COMP but not to the structurally related TSP1 indicating separate functions for these proteins in cartilage.

Effects of sodium naproxen on differentiated human chondrocytes cultivated in clusters

The effects of different pharmacological concentrations of the non-steroidal anti-inflammatory drug (NSAID) sodium naproxen (NAP) were tested on several metabolic functions of differentiated human chondrocytes cultivated in clusters and compared with the action of acetylsalicylic acid (ASA). DNA synthesis was significantly inhibited by ASA but not by NAP. Proteoglycan production was also markedly decreased by ASA, while synthesis of type II collagen was not modified. By contrast, NAP did not affect these chondroformative processes. Both NSAIDs were potent inhibitors of prostaglandin E2 production. These results indicate that in terms of the parameters tested NAP does not lead to deleterious effects on human articular chondrocytes cultured in vitro.

Effects of etodolac on human chondrocytes cultivated in three dimensional culture

Human chondrocytes in three-dimensional culture were incubated for up to 20 days in the presence of etodolac, a nonsteroidal anti-inflammatory drug which penetrates readily into the synovial fluid. Even at an etodolac concentration of 80 micrograms/ml, DNA synthesis, proteoglycan synthesis, and type-II collagen synthesis were unchanged. Collagenase production was also unaffected by etodolac (60 micrograms/ml). In contrast, prostaglandin E2 production was reduced by 84% in the presence of 60 micrograms/ml of etodolac. The 80 micrograms/ml concentration is 5 times that found in the serum of subjects treated with 200 mg of etodolac twice a day for 6 days, and 33 times the concentration in synovial fluid of arthritic patients treated with etodolac 200 mg twice a day for 7 days. These in vitro results indicate that anti-inflammatory levels of etodolac may not damage articular cartilage in vivo.