Analysis of types I, II, III, IX and XI collagens synthesized by fetal bovine chondrocytes in high-density culture

Modulation of Canine Adipose-Derived Mesenchymal Stem/Medicinal Signalling Cells with Ascorbic Acid: Effect on Proliferation and Chondrogenic Differentiation on Standard Plastic and Silk Fibroin Surfaces

Ascorbic acid (AA) plays a crucial role in both the proliferation and chondrogenic differentiation potential of mesenchymal stem/medicinal signalling cells (MSCs); these are both key aspects of their general therapeutic use and their increasing use in veterinary medicine. Current immunomodulatory therapies require efficient expansion of MSCs in the laboratory, while emerging tissue regeneration strategies, such as cartilage or bone repair, aim to use differentiated MSCs and modulate the expression of chondrogenic and hypertrophic markers. Our aim was to investigate whether the addition of AA to the growth medium enhances the proliferation of canine adipose-derived MSCs (cAMSCs) grown on standard plastic surfaces and whether it affects chondrogenic differentiation potential on silk fibroin (SF) films. We assessed cell viability with trypan blue and proliferation potential by calculating population doubling. Chondrogenic induction on SF films was assessed by Alcian blue staining and gene expression analysis of chondrogenic and hypertrophic genes. The results showed that growth medium with AA significantly enhanced the proliferation of cAMSCs without affecting cell viability and modulated the expression of chondrogenic and hypertrophic genes of cAMSCs grown on SF films. Our results suggest that AA may be used in growth medium for expansion of cAMSCs and, at the same time, provide the basis for future studies to investigate the role of AA and SF in chondrogenic differentiation of MSCs.

Validation of COL11A1/procollagen 11A1 expression in TGF-β1-activated immortalised human mesenchymal cells and in stromal cells of human colon adenocarcinoma

Background

The human COL11A1 gene has been shown to be up-regulated in stromal cells of colorectal tumours, but, so far, the immunodetection of procollagen 11A1, the primary protein product of COL11A1, has not been studied in detail in human colon adenocarcinomas. Some cancer-associated stromal cells seem to be derived from bone marrow mesenchymal cells; the expression of the COL11A1 gene and the parallel immunodetection of procollagen 11A1 have not been evaluated in these latter cells, either.

Methods

We used quantitative RT-PCR and/or immunocytochemistry to study the expression of DES/desmin, VIM/vimentin, ACTA2/αSMA (alpha smooth muscle actin) and COL11A1/procollagen 11A1 in HCT 116 human colorectal adenocarcinoma cells, in immortalised human bone marrow mesenchymal cells and in human colon adenocarcinoma-derived cultured stromal cells. The immunodetection of procollagen 11A1 was performed with the new recently described DMTX1/1E8.33 mouse monoclonal antibody. Human colon adenocarcinomas and non-malignant colon tissues were evaluated by immunohistochemistry as well. Statistical associations were sought between anti-procollagen 11A1 immunoscoring and patient clinicopathological features.

Results

Procollagen 11A1 was immunodetected in human bone marrow mesenchymal cells and in human colon adenocarcinoma-associated spindle-shaped stromal cells but not in colon epithelial or stromal cells of the normal colon. This immunodetection paralleled, in both kinds of cells, that of the other mesenchymal-related biomarkers studied: vimentin and alpha smooth muscle actin, but not desmin. Thus, procollagen 11A1⁺ adenocarcinoma-associated stromal cells are similar to “activated myofibroblasts”. In the series of human colon adenocarcinomas here studied, a high procollagen 11A1 expression was associated with nodal involvement (p = 0.05), the development of distant metastases (p = 0.017), and advanced Dukes stages (p = 0.047).

Conclusion

The immunodetection of procollagen 11A1 in cancer-associated stromal cells could be a useful biomarker for human colon adenocarcinoma characterisation.

Electronic supplementary material

The online version of this article (doi:10.1186/1471-2407-14-867) contains supplementary material, which is available to authorized users.

Downregulation of Col1a1 induces differentiation in mouse spermatogonia

Col1a1 (one of the subunit of collagen type I) is a collagen, which belongs to a family of extracellular matrix (ECM) proteins that play an important role in cellular proliferation and differentiation. However, the role of Col1a1 in spermatogenesis, especially in the control of proliferation and differentiation of spermatogonial stem cells (SSCs), remains unknown. In this study, we explored effects of downregulation of Col1a1 on differentiation and proliferation of mouse spermatogonia. Loss-of-function study revealed that Oct4 and Plzf, markers of SSC self-renewal, were significantly decreased, whereas the expression of c-kit and haprin, hallmarks of SSC differentiation, was enhanced after Col1a1 knockdown. Cell cycle analyses indicated that two-thirds of spermatogonia were arrested in S phase after Col1a1 knockdown. In vivo experiments, DNA injection and electroporation of the testes showed that spermatogonia self-renewal ability was impaired remarkably with the loss-of-function of Col1a1. Our data suggest that silencing of Col1a1 can suppress spermatogonia self-renewal and promote spermatogonia differentiation.

Chondrocytes or adult stem cells for cartilage repair: the indisputable role of growth factors

Articular cartilage is easily injured but difficult to repair and cell therapies are proposed as tools to regenerate the defects in the tissue. Both differentiated chondrocytes and adult mesenchymal stem cells (MSCs) are regarded as cells potentially able to restore a functional cartilage. However, it is a complex process from the cell level to the tissue end product, during which growth factors play important roles from cell proliferation, extracellular matrix synthesis, maintenance of the phenotype to induction of MSCs towards chondrogenesis. Members of the TGF-β superfamily, are especially important in fulfilling these roles. Depending on the cell type chosen to restore cartilage, the effect of growth factors will vary. In this review, the roles of these factors in the maintenance of the chondrocyte phenotype are discussed and compared with those of factors involved in the repair of cartilage defects, using chondrocytes or adult mesenchymal stem cells.

[New strategies for tissue replacement in the head and neck region]

In recent years there has been an increase in the need for tissue replacement in the head and neck region. The disadvantages of classical reconstructive procedures are donor site morbidity for autologous transplants and the immunogenity of allogenous transplants. Tissue engineering is a promising method for the generation of autologous cartilagenous transplants for plastic and reconstructive surgery for closure of large defects by the use of minimal amounts of material for reconstruction. For this purpose harvested material must be cultivated in suitable culture/carrier systems. One obstacle is the loss of phenotype and function once the cells are detached from their environment (dedifferentiation). Adult mesenchymal stem cells are a valuable cell source for tissue engineering. The underlying strategy of using stem cells is the replacement of functionally compromised cells either by in vitro expanded stem cells or activation of stem cells in the tissue. However, there are still problems regarding valuable markers for cellular differentiation and the controlled differentiation towards a specific phenotype.

Chondrocytes harvested from osteochondritis dissecans cartilage are able to undergo limited in vitro chondrogenesis despite having perturbations of cell phenotype in vivo

Our objective was to characterize the variation in gene expression for key genes associated with chondrogenic phenotype of osteochondrosis (OC)-affected and normal chondrocytes, and to identify whether OC chondrocytes can redifferentiate and regain a phenotype similar to normal chondrocytes if appropriate chondrogenic signals are given. Equine articular cartilage removed at surgery to treat clinically significant OC lesions was collected (n = 10), and the gene expression evaluated and compared to aged-matched normal samples (n = 10). Cartilage was harvested from normal (n = 4) and OC (n = 3) joints from horses at necropsy. Chondrogenic pellet cultures were established following monolayer proliferation. After 14 days in culture, the pellets were assessed by histochemical and pellet weight analysis, assay of glycosaminoglycan (GAG) content, and gene expression. Chondrocytes from OC cartilage expressed significantly more Coll-I, -II, -III, and -X than chondrocytes from normal cartilage (all p < 0.0001). Furthermore, OC chondrocytes expressed significantly more MMP-13, ADAMTS-4 (both p < 0.0001), and TIMP-1 (p < 0.001) and significantly less TIMP-2 and TIMP-3. Pellets created from OC chondrocytes contained significantly less GAG (p = 0.0069) and expressed significantly less Sox9 and significantly more superficial zone protein (SZP) (p = 0.0105) than pellets created from normal cartilage. The results suggest that chondrocytes from OC cartilage at the time of surgical treatment have perturbations in phenotype compared to cells from normal cartilage. Despite these differences, following monolayer expansion and pellet culture under chondrogenic conditions, chondrocytes derived from OC cartilage retain some ability to undergo chondrogenic differentiation and synthesize an appropriate cartilage-like matrix. However, this chondrogenic differentiation potential is inferior to that seen in aged-matched normal chondrocytes.

Engineering cartilage with human nasal chondrocytes and a silanized hydroxypropyl methylcellulose hydrogel

Tissue engineering strategies, based on developing three-dimensional scaffolds capable of transferring autologous chondrogenic cells, holds promise for the restoration of damaged cartilage. In this study, the authors aimed at determining whether a recently developed silanized hydroxypropyl methylcellulose (Si-HPMC) hydrogel can be a suitable scaffold for human nasal chondrocytes (HNC)-based cartilage engineering. Methyltetrazolium salt assay and cell counting experiments first revealed that Si-HPMC enabled the proliferation of HNC. Cell tracker green staining further demonstrated that HNC were able to form nodular structures in this three-dimensional scaffold. HNC phenotype was then assessed by RT-PCR analysis of type II collagen and aggrecan expression as well as alcian blue staining of extracellular matrix. Our data indicated that Si-HPMC allowed the maintenance and the recovery of a chondrocytic phenotype. The ability of constructs HNC/Si-HPMC to form a cartilaginous tissue in vivo was finally investigated after 3 weeks of implantation in subcutaneous pockets of nude mice. Histological examination of the engineered constructs revealed the formation of a cartilage-like tissue with an extracellular matrix containing glycosaminoglycans and type II collagen. The whole of these results demonstrate that Si-HPMC hydrogel associated to HNC is a convenient approach for cartilage tissue engineering.

Histological and cell biological characterization of dissected cartilage fragments in human osteochondritis dissecans of the femoral condyle

INTRODUCTION

Osteochondritis dissecans (OCD) within the weight-bearing femoral condyle carries a high risk of osteoarthritis. The definitive pathogenetic cause is unclear. Therefore biochemical and cellular features of OCD were analyzed and compared to macroscopically normal cartilage of the same joint surface.

MATERIALS AND METHODS

Dissected fragments from 14 patients and biopsies of normal cartilage from the intercondylar notch as controls were harvested at arthroscopy. Staining with safranin O to monitor proteoglycan content, alkaline phosphatase activity, and immunohistochemistry with mouse monoclonal antibodies to collagen types I, II, and X. Chondrocytes were isolated for RT-PCR to detect GAPDH, collagen types I, II, X, aggrecan, TGF-beta, BMP-7, bFGF, VEGF and IL-1.

RESULTS

The dissected cartilage displayed significant variability. Apart from normal cartilage matrix components also atypical molecules such as collagen type X and alkaline phosphatase were detected at the tidemark but also across the entire dissecate, suggesting chondrocyte hypertrophy. Extended fibrous degeneration associated with collagen type I deposition was observed at the surface and may indicate chondrocyte dedifferentiation. Viable cells could be extracted from OCD and notch. Both expressed similar mRNA levels for matrix molecules, growth factors, and interleukin-1 (IL-1), however significantly more Col X mRNA was detected in dissecates.

CONCLUSION

Histology suggests focal alteration of cartilage matrix originating from the basis of the joint cartilage, potentially the mineralized layer or subchondral bone. The molecular analysis indicates a disorganization of cartilage homeostasis across the joint accompanied by embryogenetic processes. The surprisingly high viability and quality of the extracted cells suggests a still preserved intrinsic repair capacity of those vital dissecates.

Bovine chondrocyte behaviour in three-dimensional type I collagen gel in terms of gel contraction, proliferation and gene expression

This study evaluated the in vitro behaviour of bovine chondrocytes seeded in collagen gels, promising recently reported scaffolds for the treatment of full-thickness cartilage defects. To determine how chondrocytes respond to a collagen gel environment, 2 x 10(6) chondrocytes isolated from fetal, calf and adult bovine cartilage were seeded within type I collagen gels and grown for 12 days in both attached and floating (detached from the culture dish after polymerisation) conditions. Monolayer cultures were performed in parallel. All chondrocytes contracted floating gels to 55% of the initial size, by day 12. Contraction was dependent on initial cell density and inhibited by the presence of dihydrocytochalasin B as previously observed with fibroblasts. Gene expression was determined using conventional and real-time PCR. The chondrocyte phenotype was better maintained in floating gels compared to attached gels and monolayers. This was demonstrated by comparing the ratio of COL2A1/ COL1A2 mRNA and also of alpha10/alpha11 integrin mRNA. A strong up-regulation of MMP13 expression was measured at day 12 in floating gels. The composition of cartilage-like tissue obtained by growing chondrocytes in a collagen gel varied depending on the floating or attached conditions and initial cell density. It is thus important to consider these parameters when using this culture system in order to prepare a well-defined implant for cartilage repair.

Expression of Col1a1, Col1a2 and procollagen I in germ cells of immature and adult mouse testis

The objective of this study was to compare the expression of Col1a1, Col1a2, and procollagen I in the seminiferous tubules of immature and adult mice and to characterize the cellular expression pattern of procollagen I in germ cells during spermatogenesis in order to provide necessary groundwork for further functional studies in the process of spermatogenesis. Microarray analysis demonstrated that Col1a1 and Col1a2 were abundantly expressed in the seminiferous tubules of 6-day-old mice compared with 60-day-old mice, and the expression levels of Col1a1 and Col1a2 mRNA were validated using a semi-quantitative RT-PCR assay. Western blot analysis further confirmed that procollagen I was expressed at a higher level in the seminiferous tubules of 6-day-old mice compared with 60-day-old mice. Immunohistochemical analysis revealed that type A spermatogonia were positive for procollagen I in the testis of 6-day-old mice, whereas Sertoli cells were negative for this protein. The in vivo procollagen I staining in type A spermatogonia was corroborated in spermatogonia exhibiting a high potential for proliferation and the ability to form germ cell colonies in in vitro culture. Moreover, procollagen I was also detected in type A spermatogonia, intermediate spermatogonia, type B spermatogonia, and preleptotene spermatocytes in the adult mouse testes, but positive staining disappeared in more differentiated germ cell lineages detaching from the basement membrane, including leptotene spermatocytes, pachytene spermatocytes, round spermatids and elongated spermatids. These data suggest that Col1a1, Col1a2 and procollagen I are associated with type A spermatogonia and play a potential role in mediating the detachment and migration of germ cells during spermatogenesis.

A silanized hydroxypropyl methylcellulose hydrogel for the three-dimensional culture of chondrocytes

Articular cartilage has limited intrinsic repair capacity. In order to promote cartilage repair, the amplification and transfer of autologous chondrocytes using three-dimensional scaffolds have been proposed. We have developed an injectable and self-setting hydrogel consisting of hydroxypropyl methylcellulose grafted with silanol groups (Si-HPMC). The aim of the present work is to assess both the in vitro cytocompatibility of this hydrogel and its ability to maintain a chondrocyte-specific phenotype. Primary chondrocytes isolated from rabbit articular cartilage (RAC) and two human chondrocytic cell lines (SW1353 and C28/I2) were cultured into the hydrogel. Methyl tetrazolium salt (MTS) assay and cell counting indicated that Si-HPMC hydrogel did not affect respectively chondrocyte viability and proliferation. Fluorescent microscopic observations of RAC and C28/I2 chondrocytes double-labeled with cell tracker green and ethidium homodimer-1 revealed that chondrocytes proliferated within Si-HPMC. Phenotypic analysis (RT-PCR and Alcian blue staining) indicates that chondrocytes, when three-dimensionnally cultured within Si-HPMC, expressed transcripts encoding type II collagen and aggrecan and produced sulfated glycosaminoglycans. These results show that Si-HPMC allows the growth of differentiated chondrocytes. Si-HPMC therefore appears as a potential scaffold for three-dimensional amplification and transfer of chondrocytes in cartilage tissue engineering.

Chondrocyte phenotypes on different extracellular matrix monolayers

Chondrocytes undergo a process of dedifferentiation in monolayer culture that is characterized by a transition to a fibroblast-like phenotype. This behavioral change poses a challenge for tissue-engineered cartilage constructs, as approaches using autologous cells require expansion in vitro. Because chondrocytes express a variety of integrin receptors specific to different adhesive proteins, we hypothesized that chondrocytes expanded on various underlying protein monolayers would have different phenotypic responses. Bovine articular chondrocytes were cultured for up to 2 weeks on tissue culture plastic, fibronectin, collagen type I or collagen type II substrate in the presence or absence of ascorbate. Contrary to our hypothesis, the extracellular matrix protein substrates used in this study did not significantly alter the changes in chondrocyte morphology, gene expression, matrix formation, or cytoskeletal organization. Cells on all substrates assembled equivalent matrices, which may have subsequently regulated cell behavior. In cultures with ascorbate, populations of round and spread cells emerged after 1 week, with round cells expressing collagen type II and the differentiated phenotype and spread cells dedifferentiating. In cultures without ascorbate, chondrocytes rapidly adhered and spread onto organized fibronectin matrices via the alpha5beta1 integrin, which has been associated with survival and proliferation of chondrocytes in vitro. These findings indicate that expanding chondrocytes on protein monolayers may not be an effective solution to preventing dedifferentiation and improving autologous chondrocyte transplantation.

Inhibition of lysyl oxidase activity can delay phenotypic modulation of chondrocytes in two-dimensional culture

OBJECTIVE

Chondrocytes frequently de-differentiate in two-dimensional (2D) culture, especially in the presence of serum. To examine the role of lysyl oxidase (LOX) induced cross-linking in this phenomenon, the effect of the specific LOX inhibitor beta-aminopropionitrile (BAPN) was studied in 2D chondrocyte culture.

DESIGN

Chick embryo sternal chondrocytes (both proliferative and hypertrophic, from caudal and cranial zones, respectively) were cultured in the presence and absence of BAPN. The production and activities of LOX and LOX-like (LOXL) were assessed by enzyme assay and the use of specific antibodies. Seventeen batches of serum of different origin were compared. Chondrocyte phenotype was assessed both morphologically and biochemically, the latter by quantitative analysis of production of radiolabeled cartilage collagens II, IX, X and XI, and the de-differentiation marker collagen I, for up to 4 weeks in culture.

RESULTS

LOX and LOXL were identified, by Western blotting and immunofluorescence, and LO activity was measured in the medium, with both proliferative and hypertrophic chondrocytes. Inhibition of LO activity prevented or delayed chondrocyte de-differentiation, as characterized by changes in cell shape and synthesis of the five different collagen types, from the first days of culture for up to 4 weeks, depending on the origin of the serum added to the culture medium.

CONCLUSION

LO activity may be involved in the control of chondrocyte phenotype, in addition to serum factors. Inhibition of LO activity by BAPN may be useful for the maintenance of the chondrocyte phenotype in 2D culture. Specific variations in the relative proportions of collagens II, IX and XI could be involved in the mechanism underlying these observations.

Cell lines and primary cell cultures in the study of bone cell biology

Bone is a metabolically active and highly organized tissue consisting of a mineral phase of hydroxyapatite and amorphous calcium phosphate crystals deposited in an organic matrix. Bone has two main functions. It forms a rigid skeleton and has a central role in calcium and phosphate homeostasis. The major cell types of bone are osteoblasts, osteoclasts and chondrocytes. In the laboratory, primary cultures or cell lines established from each of these different cell types provide valuable information about the processes of skeletal development, bone formation and bone resorption, leading ultimately, to the formulation of new forms of treatment for common bone diseases such as osteoporosis.

Influence of medium composition, static and stirred conditions on the proliferation of and matrix protein expression of bovine articular chondrocytes cultured in a 3-D collagen scaffold

Interest in chemical and physical modifications of culture conditions and composition, as a way to improve engineered cartilage, has grown over the last decade. To address some of these aspects, articular bovine chondrocytes seeded in collagen sponges (2.3x10(6) cells/cm(3), whose growth and metabolism have been previously reported) were grown under static or stirred conditions (orbital shaker at 30 rpm), in either 10% FCS-supplemented or serum-free media (1% ITS+1mM cysteine). Under stirred conditions, we observed a 2-fold increase in both cell proliferation and sulphated glycosaminoglycan deposition after 1 month of culture, compared to static conditions, and after 3 months, a more homogeneous distribution of both cells and neomatrix in the constructs. During the first month of culture, the substitution of FCS by ITS led to low cell proliferation and poor neomatrix deposition but, after 2 months a steep increase was observed with ITS for these two parameters that reached, after 3 months the levels observed with FCS. Aggrecan was the more abundant component at both gene and protein levels, whereas the collagenous network formed was looser than with FCS. In conclusion, the use of these simple culture conditions should improve, in long-term culture, the quality of the cartilage construct.

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.

The effects of ascorbic acid on cartilage metabolism in guinea pig articular cartilage explants

Ascorbic acid has been associated with the slowing of osteoarthritis progression in guinea pig and man. The goal of this study was to evaluate transcriptional and translational regulation of cartilage matrix components by ascorbic acid. Guinea pig articular cartilage explants were grown in the presence of L-ascorbic acid (L-Asc), D-isoascorbic acid (D-Asc), sodium L-ascorbate (Na L-Asc), sodium D-isoascorbate (Na D-Asc), or ascorbyl-2-phosphate (A2P) to isolate and analyze the acidic and nutrient effects of ascorbic acid. Transcription of type II collagen, prolyl 4-hydroxylase (alpha subunit), and aggrecan increased in response to the antiscorbutic forms of ascorbic acid (L-Asc, Na L-Asc, and A2P) and was stereospecific to the L-forms. Collagen and aggrecan synthesis also increased in response to the antiscorbutic forms but only in the absence of acidity. All ascorbic acid forms tended to increase oxidative damage over control. This was especially true for the non-nutrient D-forms and the high dose L-Asc. Finally, we investigated the ability of chondrocytes to express the newly described sodium-dependent vitamin C transporters (SVCTs). We identified transcripts for SVCT2 but not SVCT1 in guinea pig cartilage explants. This represents the first characterization of SVCTs in chondrocytes. This study confirms that ascorbic acid stimulates collagen synthesis and in addition modestly stimulates aggrecan synthesis. These effects are exerted at both transcriptional and post-transcriptional levels. The stereospecificity of these effects is consistent with chondrocyte expression of SVCT2, shown previously to transport L-Asc more efficiently than D-Asc. Therefore, this transporter may be the primary mechanism by which the L-forms of ascorbic acid enter the chondrocyte to control matrix gene activity.

Physiological and cell biological aspects of perfusion culture technique employed to generate differentiated tissues for long term biomaterial testing and tissue engineering

Optimal results in biomaterial testing and tissue engineering under in vitro conditions can only be expected when the tissue generated resembles the original tissue as closely as possible. However, most of the presently used stagnant cell culture models do not produce the necessary degree of cellular differentiation, since important morphological, physiological, and biochemical characteristics disappear, while atypical features arise. To reach a high degree of cellular differentiation and to optimize the cellular environment, an advanced culture technology allowing the regulation of differentiation on different cellular levels was developed. By the use of tissue carriers, a variety of biomaterials or individually selected scaffolds could be tested for optimal tissue development. The tissue carriers are to be placed in perfusion culture containers, which are constantly supplied with fresh medium to avoid an accumulation of harmful metabolic products. The perfusion of medium creates a constant microenvironment with serum-containing or serum-free media. By this technique, tissues could be used for biomaterial or scaffold testing either in a proliferative or in a postmitotic phase, as is observed during natural development. The present paper summarizes technical developments, physiological parameters, cell biological reactions, and theoretical considerations for an optimal tissue development in the field of perfusion culture.

Native and DPPA cross-linked collagen sponges seeded with fetal bovine epiphyseal chondrocytes used for cartilage tissue engineering

Collagen-based biomaterials in the form of sponges (bovine type I collagen, both native and cross-linked by treatment with diphenylphosphorylazide, noted control and DPPA sponges respectively) were tested as three-dimensional scaffolds to support chondrocyte proliferation with maintenance of the phenotype in order to form neocartilage. Control and DPPA sponges were initially seeded with 10(6) or 10(7) foetal bovine epiphyseal chondrocytes and maintained for 4 weeks in culture under static conditions in RPMI/NCTC medium with 10% FCS and without addition of fresh ascorbic acid. Both supports were always present during the study and a partial decrease in size and weight was detected only with control sponges, both seeded and unseeded. Cell proliferation was only noted in the 10(6) cells-seeded sponges (4-fold increase after 4 weeks of culture). Specific cartilage collagens (types II and XI) were deposited in the matrix throughout the culture and traces of type I collagen were noticed only in the culture medium after 2-3 weeks and 4 weeks in the case of 10(6) and 10(7) cells-seeded sponges, respectively. Glycosaminoglycans accumulated in the matrix, up to 1.8 and 9.8% of total dry weight after one month with both seeding conditions, which was much lower than in the natural tissue. In the 10(7) cells-seeded sponges, mineral deposition, observed with unseeded sponges, was significantly decreased (2- to 3-fold). These in vitro results indicate that both collagen matrices can support the development of tissue engineered cartilage.

Phenotypic stability of articular chondrocytes in vitro: the effects of culture models, bone morphogenetic protein 2, and serum supplementation

Numerous in vitro culture models have been developed for the investigation of chondrocyte and cartilage biology. In this study, we investigated the stability of the chondrocytic phenotype in monolayer, aggregate, pellet, and explant culture models and assessed the effects of recombinant human bone morphogenetic protein 2 (rhBMP-2) and serum supplementation on the phenotype in each model. Phenotypic effects were assessed by analyses of procollagen type II, aggrecan, (V + C)- fibronectin, and procollagen type I messenger RNA expression. In monolayer cultures, we noted a characteristic loss of procollagen type II and induction of procollagen type I expression. The aggregate and pellet culture models supported matrix protein gene expression profiles more reflective of in vivo levels. In explant cultures, expression of matrix protein genes was consistently depressed. Treatment with rhBMP-2 significantly increased the expression of procollagen type II and aggrecan in monolayer cultures; however, other models showed comparatively little response. Similarly, serum supplementation significantly down-regulated procollagen type II and aggrecan expression in monolayer cultures but had less effect on gene expression in the other models. Serum supplementation increased procollagen type I expression in monolayer and aggregate cultures. These results suggest that the influence of exogenous BMP-2 and serum on expression of chondrocyte-specific matrix protein genes is influenced by aspects of substrate attachments, cellular morphology, and/or cytoskeletal organization. Finally, the analyses of fibronectin expression suggest that V and C region alternative splicing in chondrocytes is linked to the establishment of a three-dimensional multicellular complex.

Lineage-dependent collagen expression and assembly during osteogenic or chondrogenic differentiation of a mesoblastic cell line

The mesoblastic clone, C1, behaves as a tripotential progenitor able to self-renew and to differentiate toward osteogenesis, chondrogenesis, or adipogenesis in response to specific inducers. In this study, expression and deposition by the C1 cells of essential components of the extracellular matrix, collagens type I, II, III, V, XI, VI, IX, and X were followed along the osteogenic and chondrogenic pathways, through biochemical, immunochemical, and electron microscopy analyses. Implementation of each program involves profiles of collagen synthesis and matrix assembly close to those documented in vivo. Depending on the applied inducers, cells adopt a defined identity and, controls acting at transcriptional and posttranslational levels adapt the set of deposited collagens to one particular cell fate. Osteogenic C1 cells selectively build a type I collagen matrix also containing type III, V, and XI collagens but selectively exclude type II collagen. Chondrogenic C1 cells first elaborate a type II collagen network and then acquire hypertrophic chondrocyte properties while assembling a type X collagen matrix as in the growth plate. This study provides an example of how a mesoblastic cell line can develop, in vitro, each of its genetic programs up to terminal differentiation. Intrinsic factors and time-dependent cell-matrix interactions might, as in vivo, underline the implementation of an entire differentiation program.

Regulation of growth, protein synthesis, and maturation of fetal bovine epiphyseal chondrocytes grown in high-density culture in the presence of ascorbic acid, retinoic acid, and dihydrocytochalasin B

Phenotypic expression of chondrocytes can be modulated in vitro by changing the culture technique and by agents such vitamins and growth factors. We studied the effects of ascorbic acid, retinoic acid (0.5 and 10 microM), and dihydrocytochalasin B (3, 10, 20 microM DHCB), separately or in combination (ascorbic acid + retinoic acid or ascorbic acid + DHCB), on the induction of maturation of fetal bovine epiphyseal chondrocytes grown for up to 4 weeks at high density in medium containing 10% fetal calf serum and the various agents. In the absence of any agent or with retinoic acid or DHCB alone, the metabolic activity of the cells remained very low after day 6, with no induction of type I or X collagen synthesis nor increase in alkaline phosphatase activity. Chondrocytes treated with fresh ascorbic acid showed active protein synthesis associated with expression of types I and X after 6 and 13 days, respectively. This maturation was not accompanied by obvious hypertrophy of the cells or high alkaline phosphatase activity. Addition of retinoic acid to the ascorbic acid-treated cultures decreased the level of type II collagen synthesis and delayed the induction of types I and X collagen, which were present only after 30 days. A striking increase in alkaline phosphatase activity (15-20-fold) was observed in the presence of both ascorbic acid and the highest dose of retinoic acid (10 microM). DHCB was also a potent inhibitor of the maturation induced by treatment with ascorbic acid, as the chondrocytes maintained their rounded shape and synthesized type II collagen without induction of type I or X collagen. The pattern of protein secretion was compared under all culture conditions by two-dimensional gel electrophoresis. The different regulations of chondrocyte differentiation by ascorbic acid, retinoic acid, and DHCB were confirmed by the important qualitative and quantitative changes in the pattern of secreted proteins observed by two-dimensional gel electrophoresis along the study.