Quantification and immunolocalisation of porcine articular and growth plate cartilage collagens

Intra-Articular Atelocollagen Injection for the Treatment of Articular Cartilage Defects in Rabbit Model

BACKGROUND

Atelocollagen is widely recognized as a biomaterial for regenerative medicine because of its good compatibility and low antigenicity. Injury of the outermost layer of articular cartilage, known as the lamina splendens, can lead to osteoarthritis (OA) and eventually full-thickness cartilage loss. The intra-articular injection of atelocollagen has been designed to restore the cartilage layer and cartilage defects in OA joints. In this study, we investigated the efficacy of atelocollagen as a cartilage supplement for joint defects.

METHODS

In this study, we evaluated the therapeutic effects of atelocollagen in animals with cartilage defects. Femoral groove defects were artificially created in 12 male New Zealand white rabbits, which were treated with intra-articular injection of either atelocollagen (experimental) or normal saline (control). The results were observed 3, 6, 9, and 12 weeks following macroscopic and histological evaluations.

RESULTS

At 3 weeks, cartilage tissue was restored in the experimental group, whereas the control group did not show signs of restoration. At 12 weeks, defects in both groups were filled with regenerated tissue, but the experimental group displayed a morphologically better appearance. Histologically, the regenerated tissue in the experimental group showed statistically significant improvement compared to the control group, with a structure similar to that of normal articular cartilage.

CONCLUSION

The results showed that the intra-articular injection of atelocollagen enhanced cartilage regeneration following rabbit patellar groove defects. Therefore, intra-articular injection of atelocollagen can be used as an effective supplement for joint defects.

Non-Invasive Monitoring of Functional State of Articular Cartilage Tissue with Label-Free Unsupervised Hyperspectral Imaging

Damage and degradation of articular cartilage leads to severe pain and loss of mobility. The development of new therapies for cartilage regeneration for monitoring their effect requires further study of cartilage, ideally at a molecular level and in a minimally invasive way. Hyperspectral microscopy is a novel technology which utilises endogenous fluorophores to non-invasively assess the molecular composition of cells and tissue. In this study, we applied hyperspectral microscopy to healthy bovine articular cartilage and osteoarthritic human articular cartilage to investigate its capacity to generate informative molecular data and characterise disease state and treatment effects. We successfully demonstrated label-free fluorescence identification of collagen type I and II - isolated in cartilage here for the first time and the co-enzymes free NADH and FAD which together give the optical redox ratio that is an important measure of metabolic activity. The intracellular composition of chondrocytes was also examined. Differences were observed in the molecular ratios within the superficial and transitional zones of the articular cartilage which appeared to be influenced by disease state and treatment. These findings show that hyperspectral microscopy could be useful for investigating the molecular underpinnings of articular cartilage degradation and repair. As it is non-invasive and non-destructive, samples can be repeatedly assessed over time, enabling true time-course experiments with in-depth molecular data. Additionally, there is potential for the hyperspectral approach to be adapted for patient examination to allow the investigation of cartilage state. This could be of advantage for assessment and diagnosis as well as treatment monitoring.

Novel Technique for Suspension Culture of Autologous Chondrocytes Improves Cell Proliferation and Tissue Architecture

We have developed a new and simple method of chondrocyte suspension culture using a spinner bottle with rotation of the matrices. We compared the characteristics of chondrocytes cultured by this method with those grown in standard monolayer cultures. We also determined the optimal nutritional medium for suspension cultures. Periosteum explants seeded with chondrocytes were grown in monolayer and suspension cultures under three conditions: in medium with no additive (control), with 10% fetal bovine serum (FBS), or with 10% autologous serum (AS). After culturing, the explants were harvested, processed for histology, and stained with hematoxylin-eosin or TUNEL, or immunostained for type I, II, and III collagen, and Ki-67 antigen. In monolayer cultures, the attachment of the chondrocytes to the periosteum was weak and the superficial layer consisted of fibrotic tissue and few nucleated cells. Collagen type II staining was strong, but types I and III were weak. Among the suspension cultures the AS group produced the thickest layer of chondrocytes with the fewest apoptotic cells. The superficial layer of cartilage in these cultures stained positive for type I and III collagen and Ki-67 antigen. Among the suspension cultures, total chondroitin and chondroitin-4 sulfate (C-4S) concentration was highest in the AS group, while prostaglandin E2 (PGE2) was highest in the FBS group. In summary, our new method of suspension culture of periosteal explants using rotational matrices combined with AS nutritional media was the most effective method for maintaining the bond between the chondrocyte layer and periosteum, as well as the production of type I and III collagen in the superficial layer.

Second harmonic generation imaging reveals a distinct organization of collagen fibrils in locations associated with cartilage growth

PURPOSE

The articular-epiphyseal cartilage complex (AECC) is responsible for the expansion of the bone ends and serves the function of the articular cartilage in juvenile mammals. Bundles of collagen fibrils surrounding cells were in the literature observed more frequently near the articular surface of the AECC. The articular surface, the perichondrium, and cartilage canals are interfaces where appositional growth of the AECC has been demonstrated. The current study aimed to evaluate the potential of second harmonic generation (SHG) to locate the collagen fibril bundles near the articular surface and to examine whether a comparable collagen fibril organization could be observed near the other interfaces of the AECC.

MATERIALS AND METHODS

The study included the femoral condyle of four piglets aged 82-141 days. The forward and backward scattered SHG, and their ratio, was analyzed across the AECC using objectives with different numerical aperture. Two-photon-excited fluorescence was used to visualize cells.

RESULTS

A similar pattern of collagen fibril organization was observed near the articular surface, around cartilage canals, and adjacent to the perichondrium. The pattern consisted of a higher ratio of forward to backward scattered SHG that increased relative to the surrounding matrix at lower numerical aperture. This was interpreted to reflect collagen fibril bundles in the territorial matrix of cells in these areas.

CONCLUSIONS

The observed arrangement of collagen fibrils was suggested to be related to the presumed different growth activity in these areas and indicated that SHG may be used as an indirect and label-free marker for cartilage matrix growth.

Isolation and characterisation of collagen from elk antler velvet

Collagen was extracted from the antler velvet of elk (Cervus elaphus). Two types of collagen were prepared namely, acetic acid-soluble collagen and pepsin-soluble collagen. The electrophoretic patterns of both of the collagens showed that they were heterotrimeric, i.e. they consisted of α1α2α3. The total yield of the collagen obtained from the elk antler velvet was 12.1%. Amino acid analysis of the collagen by high-performance liquid chromatography showed that imino acid content such as that of proline and hydroxyproline was high, which might contribute to better visco-elastic properties. The peptide mapping of the collagens showed their similarity with porcine Type I collagen, thereby suggesting that the primary structure of both collagens is identical to that of porcine skin Type I collagen. The thermal denaturation temperature was 37°C, which is comparable to porcine Type I collagen and may also be as a result of high imino acid content.

TGF-ß1 enhances the BMP-2-induced chondrogenesis of bovine synovial explants and arrests downstream differentiation at an early stage of hypertrophy

Background

Synovial explants furnish an in-situ population of mesenchymal stem cells for the repair of articular cartilage. Although bone morphogenetic protein 2 (BMP-2) induces the chondrogenesis of bovine synovial explants, the cartilage formed is neither homogeneously distributed nor of an exclusively hyaline type. Furthermore, the downstream differentiation of chondrocytes proceeds to the stage of terminal hypertrophy, which is inextricably coupled with undesired matrix mineralization. With a view to optimizing BMP-2-induced chondrogenesis, the modulating influences of fibroblast growth factor 2 (FGF-2) and transforming growth factor beta 1 (TGF-ß1) were investigated.

Methodology/Principal Findings

Explants of bovine calf metacarpal synovium were exposed to BMP-2 (200 ng/ml) for 4 (or 6) weeks. FGF-2 (10 ng/ml) or TGF-ß1 (10 ng/ml) was introduced at the onset of incubation and was present either during the first week of culturing alone or throughout its entire course. FGF-2 enhanced the BMP-2-induced increase in metachromatic staining for glycosaminoglycans (GAGs) only when it was present during the first week of culturing alone. TGF-ß1 enhanced not only the BMP-2-induced increase in metachromasia (to a greater degree than FGF-2), but also the biochemically-assayed accumulation of GAGs, when it was present throughout the entire culturing period; in addition, it arrested the downstream differentiation of cells at an early stage of hypertrophy. These findings were corroborated by an analysis of the gene- and protein-expression levels of key cartilaginous markers and by an estimation of individual cell volume.

Conclusions/Significance

TGF-ß1 enhances the BMP-2-induced chondrogenesis of bovine synovial explants, improves the hyaline-like properties of the neocartilage, and arrests the downstream differentiation of cells at an early stage of hypertrophy. With the prospect of engineering a mature, truly articular type of cartilage in the context of clinical repair, our findings will be of importance in fine-tuning the stimulation protocol for the optimal chondrogenic differentiation of synovial explants.

Hyaline cartilage tissue is formed through the co-culture of passaged human chondrocytes and primary bovine chondrocytes

To circumvent the problem of a sufficient number of cells for cartilage engineering, the authors previously developed a two-stage culture system to redifferentiate monolayer culture-expanded dedifferentiated human articular chondrocytes by co-culture with primary bovine chondrocytes (bP0). The aim of this study was to analyze the composition of the cartilage tissue formed in stage 1 and compare it with bP0 grown alone to determine the optimal length of the co-culture stage of the system. Biochemical data show that extracellular matrix accumulation was evident after 2 weeks of co-culture, which was 1 week behind the bP0 control culture. By 3 to 4 weeks, the amounts of accumulated proteoglycans and collagens were comparable. Expression of chondrogenic genes, Sox 9, aggrecan, and collagen type II, was also at similar levels by week 3 of culture. Immunohistochemical staining of both co-culture and control tissues showed accumulation of type II collagen, aggrecan, biglycan, decorin, and chondroitin sulfate in appropriate zonal distributions. These data indicate that co-cultured cells form cartilaginous tissue that starts to resemble that formed by bP0 after 3 weeks, suggesting that the optimal time to terminate the co-culture stage, isolate the now redifferentiated cells, and start stage 2 is just after 3 weeks.

Differential limb loading in miniature pigs (Sus scrofa domesticus): a test of chondral modeling theory

Variation in mechanical loading is known to influence chondrogenesis during joint formation. However, the interaction among chondrocyte behavior and variation in activity patterns is incompletely understood, hindering our knowledge of limb ontogeny and function. Here, the role of endurance exercise in the development of articular and physeal cartilage in the humeral head was examined in 14 miniature swine (Sus scrofa domesticus). One group was subjected to graded treadmill running over a period of 17 weeks. A matched sedentary group was confined to individual pens. Hematoxylin and eosin staining was performed for histomorphometry of cartilage zone thickness, chondrocyte count and cell area, with these parameters compared multivariately between exercised and sedentary groups. Comparisons were also made with femora from the same sample, focusing on humerus-femur differences between exercised and sedentary groups, within-cohort comparisons of humerus-femur responses and correlated changes within and across joints. This study shows conflicting support for the chondral modeling theory. The humeral articular cartilage of exercised pigs was thinner than that of sedentary pigs, but their physeal cartilage was thicker. While articular and physeal cartilage demonstrated between-cohort differences, humeral physeal cartilage exhibited load-induced responses of greater magnitude than humeral articular cartilage. Controlling for cohort, the humerus showed increased chondrocyte mitosis and cell area, presumably due to relatively greater loading than the femur. This represents the first known effort to evaluate chondral modeling across multiple joints from the same individuals. Our findings suggest the chondral response to elevated loading is complex, varying within and among joints. This has important implications for understanding joint biomechanics and development.

The incorporation of a zone of calcified cartilage improves the interfacial shear strength between in vitro-formed cartilage and the underlying substrate

A major challenge for cartilage tissue engineering remains the proper integration of constructs with surrounding tissues in the joint. Biphasic osteochondral constructs that can be anchored in a joint through bone ingrowth partially address this requirement. In this study, a methodology was devised to generate a cell-mediated zone of calcified cartilage (ZCC) between the in vitro-formed cartilage and a porous calcium polyphosphate (CPP) bone substitute in an attempt to improve the mechanical integrity of that interface. To do so, a calcium phosphate (CaP) film was deposited on CPP by a sol-gel process to prevent the accumulation of polyphosphates and associated inhibition of mineralization as the substrate degrades. Cartilage formed in vitro on the top surface of CaP-coated CPP by deep-zone chondrocytes was histologically and biochemically comparable to that formed on uncoated CPP. Furthermore, the mineral in the ZCC was similar in crystal structure, morphology and length to that formed on uncoated CPP and native articular cartilage. The generation of a ZCC at the cartilage-CPP interface led to a 3.3-fold increase in the interfacial shear strength of biphasic constructs. Improved interfacial strength of these constructs may be critical to their clinical success for the repair of large cartilage defects.

Biologic interaction of three-dimensional periodontal fibroblast spheroids with collagen-based and synthetic membranes

BACKGROUND

Cell-based therapy using autologous cells has been suggested as a potential approach for periodontal tissue regeneration. Spheroid systems are a form of three-dimensional cell culture that promotes cell matrix interaction, which could recapitulate the aspect of cell homeostasis in vivo. The aim of this study is to assess the interaction of periodontal fibroblast spheroids with synthetic and collagen-based membranes that have been used in guided tissue regeneration.

METHODS

Commercially available normal human periodontal ligament fibroblasts were grown in spheroid forms using a liquid overlay technique and then transplanted onto a collagen-based and a polyglycolic acid-based membrane. The biologic interaction of the spheroids with the membranes was assessed using basic histology, Alamar blue tissue viability assay, scanning electron microscopy, and immunohistochemical analysis.

RESULTS

Periodontal fibroblast spheroids adhered to both membranes, and the cells were able to proliferate and migrate from the spheroids both horizontally and vertically into the membrane scaffolds. Immunohistochemical analysis showed expression of collagen type I, periostin, and Runx2 by the periodontal fibroblasts.

CONCLUSION

Periodontal fibroblast spheroids were able to grow three-dimensionally on the biologic membranes and may have the potential to be used together with guided tissue regeneration approaches as an adjunct for periodontal regeneration.

Characterization of ex vivo-generated bovine and human cartilage by immunohistochemical, biochemical, and magnetic resonance imaging analyses

Osteoarthritis (OA) is a prevalent age-associated disease involving altered chondrocyte homeostasis and cartilage degeneration. The avascular nature of cartilage and the altered chondrocyte phenotype characteristic of OA severely limit the capacity for in vivo tissue regeneration. Cell- and tissue-based repair has the potential to revolutionize treatment of OA, but those approaches have exhibited limited clinical success to date. In this study, we test the hypothesis that bovine and human chondrocytes in a collagen type I scaffold will form hyaline cartilage ex vivo with immunohistochemical, biochemical, and magnetic resonance (MR) endpoints similar to the original native cartilage. Chondrocytes were isolated from 1- to 3-week-old calf knee cartilage or from cartilage obtained from human total knee arthroplasties, suspended in 2.7 mg/mL collagen I, and plated as 300 microL spot cultures with 5 x 10(6) each. Medium formulations were varied, including the amount of serum, the presence or absence of ascorbate, and treatments with cytokines. Bovine chondrocytes generated metachromatic territorial and interstitial matrix and accumulated type II collagen over time. Type VI collagen was confined primarily to the pericellular region. The ex vivo-formed bovine cartilage contained more chondroitin sulfate per dry weight than native cartilage. Human chondrocytes remained viable and generated metachromatic territorial matrix, but were unable to support interstitial matrix accumulation. MR analysis of ex vivo-formed bovine cartilage revealed evidence of progressively maturing matrix, but MR-derived indices of tissue quality did not reach those of native cartilage. We conclude that the collagen-spot culture model supports formation and maturation of three-dimensional hyaline cartilage from active bovine chondrocytes. Future studies will focus on determining the capacity of human chondrocytes to show comparable tissue formation.

Effect of decorin and dermatan sulfate on the mechanical properties of a neocartilage

Decorin is known to influence the size of collagen fibrils in ligaments and tendons and it has been hypothesized to provide a structural link between collagen fibrils in connective tissues, including cartilage. Coincidently, mechanical properties of skin, ligament, and tendons are altered in decorin knockout mice, suggesting it may influence the structural properties of tissue or tissue matrix organization. To further examine the role of decorin in the extracellular matrix development and subsequent material properties of cartilage, tissue (neocartilage) was grown in a 3D culture model using a pure population of genetically modified chondrocytes stably overexpressing decorin (DCN) or decorin lacking dermatan sulfate (MDCN). An empty vector (CON) served as a virus control. Following generation of the cartilage-like tissues, mechanical properties in tension and compression, collagen fibril diameter, matrix organization, and biochemistry of the tissue were determined. There were no differences between CON and DCN tissues in any parameter measured. In contrast, tissue generated in MDCN cultures was thinner, had higher collagen density, and higher elastic moduli as compared to both CON and DCN tissues. Considering there was no difference in stiffness between CON and DCN tissues, the notion that decorin contributes to the mechanical properties via load transfer was refuted in this model. However, contrasts in the mechanical properties of the MDCN tissue suggest that the dermatan sulfate chains on decorin influences the organization/maturation and resultant mechanical properties of the matrix by as an yet-unidentified regulatory mechanism.

Influence of bone morphogenetic protein-2 on the extracellular matrix, material properties, and gene expression of long-term articular chondrocyte cultures: loss of chondrocyte stability

The aim of this study was to determine the effects of bone morphogenetic protein-2 (BMP-2) on articular chondrocyte tissues grown as monolayers in vitro for up to 8 weeks. Articular chondrocytes were isolated from New Zealand White rabbits and plated in monolayer cultures. The cultures were supplemented with 100 ng/mL of BMP-2 for up to 8 weeks and the extracellular matrix (ECM) composition, material properties, and messenger RNA (mRNA) expression were analyzed. mRNA expression of cartilage-specific genes, type II collagen, and aggrecan showed that BMP-2 enhanced chondrocyte stability for up to 3 weeks. After 3 weeks in culture, there was substantially more type I collagen expression and more osteopontin and runt-related transcription factor 2 expression in 5- and 8-week cultures treated with BMP-2 than in controls. Additionally, matrix metalloproteinase-13 and ADAMTS-5 (A disintegrin-like and metalloproteinase with thrombospondin 5) were upregulated in 5- and 8-week cultures treated with BMP-2, coinciding with a loss of ECM density, collagen, and proteoglycan. Eight-week tissue stimulated with BMP-2 was more fragile and tore more easily when removed from the culture dish as compared to controls, suggesting temporal limitations to the effectiveness of BMP-2 in monolayer systems and perhaps other models to enhance the generation of a cartilage-like tissue for tissue engineering purposes.

Smurf2 induces degradation of GSK-3beta and upregulates beta-catenin in chondrocytes: a potential mechanism for Smurf2-induced degeneration of articular cartilage

We have previously demonstrated that Smurf2 is highly expressed in human osteoarthritis (OA) tissue, and overexpression of Smurf2 under the control of the type II collagen promoter (Col2a1) induces an OA-like phenotype in aged Col2a1-Smurf2 transgenic mice, suggesting that Smurf2 is located upstream of a signal cascade which initiates OA development. However, the factors downstream of Smurf2 in this signal cascade and how Smurf2-induced OA is initiated are largely unknown. In this study, we further characterized the phenotypic changes in Col2a1-Smurf2 transgenic and WT articular cartilage from the postnatal stage to adulthood. We found that the articular cartilage degeneration occurring at the cartilage surface in 6 month-old Col2a1-Smurf2 transgenic mice progressed from an expanded hypertrophic domain in the basal layer of the deep articular cartilage at 2.5 weeks of age, which may lead to an accelerated calcification and ectopic ossification of this region at 1 month of age, and aggregation and maturation of articular chondrocytes in the middle and deep zones at 2 months and 4.5 months of age, respectively. Furthermore, we discovered that ectopically expressed Smurf2 interacted with GSK-3beta and induced its ubiquitination and subsequent proteasomal degradation, and hence upregulated beta-catenin in Col2a1-Smurf2 transgenic chondrocytes ex vivo. It is therefore likely that Smurf2-mediated upregulation of beta-catenin through induction of proteasomal degradation of GSK-beta in chondrocytes may activate articular chondrocyte maturation and associated alteration of gene expression, the early events of OA.

Nanostructure of the neurocentral growth plate: Insight from scanning small angle X-ray scattering, atomic force microscopy and scanning electron microscopy

In this study, the experimental techniques scanning electron microscopy (SEM) including energy-dispersive X-ray analysis, atomic force microscopy (AFM) and scanning small angle X-ray scattering (SAXS) have been exploited to characterize the organization of large molecules and nanocrystallites in and around the neurocentral growth plate (NGP) of a pig vertebrae L4. The techniques offer unique complementary information on the nano- to micrometer length scale and provide new insight in the changes in the matrix structure during endochondral bone formation. AFM and SEM imaging of the NGP reveal a fibrous network likely to consist of collagen type II and proteoglycans. High-resolution AFM imaging shows that the fibers have a diameter of approximately 100 nm and periodic features along the fibers with a periodicity of 50-70 nm. This is consistent with the SAXS analysis that yields a cross-sectional diameter of the fibers in the range of 90 to 112 nm and a predominant orientation in the longitudinal direction of the NGP. Furthermore, we find inhomogeneities around 7 nm in the NGP by SAXS analysis. Moving towards the bone in the direction perpendicular to the growth plate, a systematic change in apparent thickness is observed, while the large-scale structural features remain constant. In the region of bone, the apparent thickness equals the mean mineral thickness and increases from 2 nm to approximately 3.5 nm as a function distance from the NGP. The mineral particles are organized as plates in a rather compact network structure. We have demonstrated that SEM, AFM and SAXS are valuable tools for the investigation of the organization of large molecules and nanocrystallites in the NGP and adjacent trabecular bone. Our findings will be an important basis for future work into identifying the defects on nanometer length scale responsible for idiopathic scoliosis and other growth-plate-related diseases.

Distribution of Type VI Collagen in the Cartilaginous Tissue of the Proximal Tibia in the Domestic Cat

To investigate the distribution of the early stage chondrocytes during the formation and closure of epiphyseal growth plate (EGP) of the domestic cat, we examined the EGP of proximal tibiae by immunohistochemistry for type VI collagen. In the epiphyseal cartilage without the secondary ossification center (SOC) and EGP in newborn cats aged 1 and 10 days, type VI collagen-positive chondrocytes were located around the cartilage canals and articular surface. In the epiphyseal cartilage with the SOC and EGP in young cats aged 1 to 3 months, type VI collagen-positive chondrocytes were located in the upper resting zone of the EGP, and then increased throughout the resting zone along with maturation. In the adult cats with the partially closed EGP, type VI collagen-positive chondrocytes were distributed throughout the remaining EGP. These findings indicate that the early stage chondrocytes characterized with type VI collagen are continuously located in the EGP during maturation. In addition, the increase of the early stage chondrocytes and the decrease of the reserve chondrocytes in the EGP along with maturation may cause the cessation of the longitudinal growth of the EGP, and finally bring about the EGP closure.

Immunochemical and mechanical characterization of cartilage subtypes in rabbit

Cartilage is categorized into three general subgroups, hyaline, elastic, and fibrocartilage, based primarily on morphologic criteria and secondarily on collagen (Types I and II) and elastin content. To more precisely define the different cartilage subtypes, rabbit cartilage isolated from joint, nose, auricle, epiglottis, and meniscus was characterized by immunohistochemical (IHC) localization of elastin and of collagen Types I, II, V, VI, and X, by biochemical analysis of total glycosaminoglycan (GAG) content, and by biomechanical indentation assay. Toluidine blue staining and safranin-O staining were used for morphological assessment of the cartilage subtypes. IHC staining of the cartilage samples showed a characteristic pattern of staining for the collagen antibodies that varied in both location and intensity. Auricular cartilage is discriminated from other subtypes by interterritorial elastin staining and no staining for Type VI collagen. Epiglottal cartilage is characterized by positive elastin staining and intense staining for Type VI collagen. The unique pattern for nasal cartilage is intense staining for Type V collagen and collagen X, whereas articular cartilage is negative for elastin (interterritorially) and only weakly positive for collagen Types V and VI. Meniscal cartilage shows the greatest intensity of staining for Type I collagen, weak staining for collagens V and VI, and no staining with antibody to collagen Type X. Matching cartilage samples were categorized by total GAG content, which showed increasing total GAG content from elastic cartilage (auricle, epiglottis) to fibrocartilage (meniscus) to hyaline cartilage (nose, knee joint). Analysis of aggregate modulus showed nasal and auricular cartilage to have the greatest stiffness, epiglottal and meniscal tissue the lowest, and articular cartilage intermediate. This study illustrates the differences and identifies unique characteristics of the different cartilage subtypes in rabbits. The results provide a baseline of data for generating and evaluating engineered repair cartilage tissue synthesized in vitro or for post-implantation analysis.

Effects of preservation on the mechanical strength and chemical composition of cortical bone: an experimental study in sheep femora

Preservation methods have enabled bone banks to furnish cortical bone grafts to orthopaedic surgeons. However, cortical bone preserved by freezing and autoclaving, may be weakened by these treatments. To test this hypothesis we compared the ultimate tensile strength of freshly harvested sheep femora with that of femora which were frozen at -20 degrees C for 60 days, or autoclaved at 134 degrees C for 8 min. We measured the collagen and mineral contents (calcium, phosphorus, magnesium) and hydroxyproline of the specimens and tested for changes induced by preservation. Mechanical three point tests showed that frozen femora were significantly stronger than either fresh or autoclaved femora (p<0.05). Frozen specimens also had the highest phosphorus level, indicating these measures are related to strength. Cortical bone is not significantly weakened by autoclaving or freezing. This result does not imply that preserved grafts are clinically interchangeable with fresh grafts, rather, it suggests that future studies should focus on post surgical issues, such as the rate of remodeling and integration, which may be sensitive to preservation technique.

Growth factors for sequential cellular de- and re-differentiation in tissue engineering

A model system for the in vitro generation of cartilaginous constructs was used to study a tissue engineering paradigm whereby sequentially applied growth factors promoted chondrocytes to first de-differentiate into a proliferative state and then re-differentiate and undergo chondrogenesis. Early cultivation in medium with supplemental TGF-beta1/FGF-2 doubled cell fractions in 2-week constructs compared to unsupplemented controls. Subsequent culture with supplemental IGF-I yielded large 4-week constructs with high fractions of cartilaginous extracellular matrix (ECM) and high compressive moduli, whereas prolonged culture with supplemental FGF-2 yielded small 4-week constructs with low ECM fractions and moduli. Sequential supplementation with TGF-beta1/FGF-2 and then IGF-I yielded 4-week constructs with type-specific mRNA expression and protein levels that were high for type II and negligible for type I collagen, in contrast to other growth factor regimens studied. The data demonstrate that structural, functional, and molecular properties of engineered cartilage can be modulated by sequential application of growth factors.

Targeted disruption of Col11a2 produces a mild cartilage phenotype in transgenic mice: comparison with the human disorder otospondylomegaepiphyseal dysplasia (OSMED)

Transgenic mice were prepared by homologous recombination with a Col11a2 targeting gene in which an inverted neomycin-resistant gene was inserted between restriction sites in exons 27 and 28. The targeted allele was transcribed in shortened mRNAs, which could be detected by Northern blotting. However, translation of the full-length Col11a2 chain was unable to occur because of the presence of premature termination codons within the inverted neomycin-resistant gene. Analysis of pepsin-resistant collagen chains from rib cartilage of homozygous mice demonstrated the lack of synthesis of intact alpha2(XI) chains. However, pepsin-resistant collagen chains of either alpha1(XI) or alpha1(V) were still detected on sodium dodecyl sulfate polyacrylamide gel electrophoresis. Therefore, alpha2(XI) chains are not essential for the assembly of some molecular forms of triple-helical type V/XI collagen. The phenotype was milder than in the cho/cho mouse in which, as the result of mutation, translation of the full-length alpha1(XI) chain fails to occur and the mice die at birth (Li et al., 1995). Homozygous mice without expression of an alpha2(XI) chain had a smaller body size, receding snouts, and deafness. Nasal bones in the homozygous transgenic mice were specifically shorter and dimpled on their external surfaces. Chondrocytes in growth plates of all long bones were markedly disorganized and failed to align in columns. Analysis of growth plates from transgenic mice by in situ hybridization showed expression of alpha1(II) and alpha1(XI) but not of alpha1(I) or alpha1(V) which, in contrast, were expressed in the developing bone and in the bone collar. Expression of alpha1(X) specifically in the hypertrophic cartilage was observed in normal and transgenic mice. No obvious osteoarthritis was observed throughout the life of homozygous mice up to 1 year of age, although minor morphologic anomalies in the articular cartilages were discernible. The mild phenotype is consistent with similar mutations in the COL11A2 gene seen in patients with nonocular Stickler syndrome and some patients with otospondylomegaepiphyseal dysplasia (OSMED), as well as in patients with a nonsyndromic form of deafness called DFNA13.

Biochemical characterization of cartilage affected by osteochondritis dissecans in the humeral head of dogs

OBJECTIVE

To determine glycosaminoglycan (GAG) concentration and immunohistochemical staining characteristics of type-I, -II, and -X collagen from cartilage affected by osteochondritis dissecans (OCD) in dogs.

ANIMALS

31 dogs with OCD and 11 clinically normal purpose-bred dogs.

PROCEDURE

Cartilage samples were evaluated microscopically, and GAG content was determined. Immunohistochemical staining was performed for type-I, -II, and -X collagen. Sections were subjectively evaluated for location and intensity of staining.

RESULTS

Cartilage affected by OCD had a variety of pathologic changes and significantly lower GAG concentrations than did normal cartilage. Normal cartilage had no detectable type-I collagen. For dogs < 9 months of age, cartilage affected by OCD had significantly more type-I collagen but significantly less type-X collagen than did control cartilage. For dogs > 12 months of age, cartilage affected by OCD contained significantly more type-I collagen than did control cartilage. There was a significant negative correlation between immunoreactivity of type-I collagen and that of type-II and -X collagen. A significant positive correlation was found between immunoreactivity of type-II and -X collagen.

CONCLUSIONS AND CLINICAL RELEVANCE

Cartilage affected by OCD contains less GAG, more type-I collagen, and less type-X collagen, compared with normal cartilage. A direct correlation between these changes and the etiopathogenesis of OCD was not established.

Characterization of type XI collagen-glycosaminoglycan interactions

Using competitive binding experiments, it was found that native type XI collagen binds heparin, heparan sulfate, and dermatan sulfate. However, interactions were not evident with hyaluronic acid, keratan sulfate, or chondroitin sulfate chains over the concentration range studied. Chondrocyte-matrix interactions were investigated using cell attachment to solid phase type XI collagen. Pretreatment of chondrocytes with either heparin or heparinase significantly reduced attachment to type XI collagen. Incubation of denatured and cyanogen bromide-cleaved type XI collagen with radiolabeled heparin identified sites of interaction on the alpha1(XI) and alpha2(XI) chains. NH(2)-terminal sequence data confirmed that the predominant heparin-binding peptide contained the sequence GKPGPRGQRGPTGPRGSRGAR from the alpha1(XI) chain. Using rotary shadowing electron microscopy of native type XI collagen molecules and heparin-bovine serum albumin conjugate, an additional binding site was identified at one end of the triple helical region of the collagen molecule. This coincides with consensus heparin binding motifs present at the amino-terminal ends of both the alpha1(XI) and the alpha2(XI) chains. The contribution of glycosaminoglycan-type XI collagen interactions to cartilage matrix stabilization is discussed.

Characterization of a biomaterial with cartilage-like properties expressing type X collagen generated in vitro using neonatal porcine articular and growth plate chondrocytes

OBJECTIVE

The availability of cartilage with or without the potential to ossify and suitable for surgical restoration and resurfacing of joints is an important clinical problem in arthritis-related pathology, trauma and reconstructive surgery. Here, we designed experiments to generate a biomaterial with cartilage-like properties by culturing neonatal porcine articular and growth plate chondrocytes on a hydrogel substrate and to examine the biochemical and histological characteristics of the resulting tissue.

DESIGN

Neonatal porcine epiphyseal and growth plate chondrocytes were cultured on poly(2-hydroxyethyl methacrylate) (polyHEMA)-coated dishes to prevent their adherence to plastic. We previously described that this procedure allows the maintenance of the chondrocyte-specific phenotype for > or = 8 months. Chondrocytes were isolated by successive enzymatic digestions and cultured at high density (>2.0 x 10(7) cells/ml) in DMEM with 10% FBS, 50 microg/ml ascorbic acid, glutamine, vitamins, and antibiotics for up to 10 weeks on 60 mm plastic culture dishes coated with polyHEMA. The tissues produced during culture were studied histologically and biochemically and were examined for cellular proliferation employing(3)H-thymidine incorporation and for their collagen production employing biosynthetic labeling with(14)C-proline and Western blot with specific antibodies. The expression of relevant collagen genes was examined employing RT-PCR.

RESULTS

Within 24 h of culture, isolated chondrocytes organized into well-formed clusters and in 2 weeks formed structures with gross appearance and consistency similar to those of natural cartilage. The wet weight of the tissue formed in vitro increased six-fold during the 10-week period of study. Cell proliferation measured by the incorporation of(3)H-thymidine increased during the first 3 weeks and reached a plateau in subsequent weeks. Histological examination showed that the cultures contained rounded chondrocytes embedded in an abundant cartilaginous extracellular matrix. The cartilage formed contained large amounts of collagen and sulfated proteoglycans as examined by staining with Masson's Trichrome and Alcian blue, respectively. Deposition of calcium in the deeper layers of the tissue was demonstrated with the von Kossa stain. Western analyses with specific antibodies showed that type II collagen was present from the first week and progressively increased in the cultures, whereas type X collagen was first detected at 4 weeks and increased with length of culture. When chondrocytes isolated from the growth plate were included, small amounts of type I collagen were detected in the medium of cultured biomaterial as expected. Type III collagen was not detected by Western blot over the 10-week period. High levels of type II and type X collagen gene expression were demonstrated by RT-PCR.

CONCLUSION

These studies demonstrate the production in vitro of cartilage-like tissue with similar morphological, histochemical and biochemical characteristics to those of natural growth plate cartilage. The cartilage generated in vitro has the potential to be used in reconstructive surgery and in joint resurfacing and restoration of skeletal defects.

Deep zone articular chondrocytes in vitro express genes that show specific changes with mineralization

We have developed a method to form reconstituted mineralized articular cartilagenous tissue in vitro from isolated deep zone chondrocytes. The aim of this study was to characterize further these cultures prior to and during mineralization. Histologic examination of the cells up to 8 days in culture showed that the chondrocytes had formed cartilagenous tissue. Similar to the in vivo cartilage, the chondrocytes expressed aggrecan, types II, I, and X collagens, osteopontin, and alkaline phosphatase (ALP). No osteocalcin mRNA expression was detected in either the in vivo cartilage or in vitro-generated tissue. Addition of beta-glycerophosphate (beta-GP) to the medium on day 5 induced mineralization and changes in gene expression. Expression of type X collagen, type II collagen, aggrecan core protein, and ALP were inhibited significantly between 2 h and 24 h after the addition of beta-GP. At 72 h, expression of these genes were still significantly depressed. These changes correlated with a decrease in collagen and proteoglycan synthesis, and ALP activity. Osteopontin expression increased within 8 h but returned to constitutive levels by 72 h. No change in type I collagen expression was detected. The changes in gene expression were not due to a direct effect of beta-GP itself, because similar gene changes occurred in the presence of phosphoethanolamine, another agent which induces mineralization. No changes in gene expression were seen in nonmineralizing cultures. In summary, articular chondrocytes grown on filter culture show expression of similar genes to the chondrocytes in the deep zone of articular cartilage and that changes in expression of specific genes were observed during tissue mineralization, suggesting that it is a suitable model to use to study the mechanism(s) regulating the localized mineralization of articular cartilage.

Deer antler does not represent a typical endochondral growth system: immunoidentification of collagen type X but little collagen type II in growing antler tissue

The collagen isotypes present at early (6 week) and late (5 month) stages of growing deer antler were isolated and identified. Pepsin-digested collagens were separated by differential salt fractionation, SDS-PAGE and Western blotting and subsequently identified by immunostaining. Cyanogen bromide digestion of antler tissue was used to establish a collagen type-specific pattern of peptides, and these were also identified by immunoblotting. Collagen type I was found to be the major collagen in both early- and late-stage antler. Collagen type II was present in the young antler in small amounts but was not confined to the soft "cartilaginous" tip of the antler. Collagen type XI was found in the pepsin digest of the young antler, but collagen type IX was not present at either stage of antler growth. Collagen type X was found in the young antler in all fractions studied. Microscopic study showed that the deer antler did not possess a discrete growth plate as found in endochondral bone growth. Unequivocal immunolocalization of the different collagen types in the antler were unsuccessful. These results show that, despite the presence in the antler of many cartilage collagens, growth does not occur through a simple endochondral process.

Immunolocalization of type IX collagen in normal and spontaneously osteoarthritic canine tibial cartilage and isolated chondrons

OBJECTIVE

The pericellular localization of type IX collagen in avian and mammalian hyaline cartilages remains controversial, while its distribution during osteoarthritic degeneration is poorly understood. This study aimed to compare and contrast the immunohistochemical distribution of type IX collagen in normal mature and spontaneously osteoarthritic canine tibial cartilage.

DESIGN

Thick vibratome sectioning techniques were evaluated and compared with isolated chondrons using a range of streptavidin-linked probes in combination with light, confocal and transmission electron microscopy.

RESULTS

In normal intact samples, type IX collagen was concentrated in the pericellular microenvironment, while a weaker extracellular reaction around each chondron separated the territorial matrix from the unstained interterritorial matrix. Further differentiation was evident in isolated chondrons where the fibrous pericellular capsule stained more intensely than the tail and interconnecting segments between columnated chondrons. Two regions of type IX reactivity were identified in osteoarthritic tissue: an intensely stained superficial reactive region below the eroding margins, and normal deep layer cartilage where pericellular staining persists. The superficial reactive region was characterized by chondron swelling and chondrocyte cluster formation, a loss of pericellular type IX staining, and a significant increase in matrix staining between clusters. Disintegration and loss of fibrillar collagens was evident in both the swollen microenvironment and adjacent territorial matrices.

CONCLUSIONS

The results suggest that changes in type IX distribution, expansion of the pericellular microenvironment and chondrocyte proliferation represent key elements in the chondron remodeling and chondrocyte cluster formation associated with osteoarthritic degeneration.

Retinoic acid stimulates matrix calcification and initiates type I collagen synthesis in primary cultures of avian weight-bearing growth plate chondrocytes

The effect of retinoic acid (RA) on primary cultures of growth plate chondrocytes obtained from weight-bearing joints was examined, Chondrocytes were isolated from the tibial epiphysis of 6- to 8-week-old broiler-strain chickens and cultured in either serum-containing or serum-free media. RA was administered at low levels either transiently or continuously after the cells had become established in culture. Effects of RA on cellular protein levels, alkaline phosphatase (AP) activity, synthesis of proteoglycan (PG), matrix calcification, cellular morphology, synthesis of tissue-specific types of collagen, and level of matrix metalloproteinase (MMP) activity were explored. RA treatment generally increased AP activity and stimulated mineral deposition, especially if present continuously. RA also caused a shift in cell morphology from spherical/polygonal to spindle-like. This occurred in conjunction with a change in the type of collagen synthesized: type X and II collagens were decreased, while synthesis of type I collagen was increased. There was also a marked increase in the activity of MMP. Contrasting effects of continuous RA treatment on cellular protein levels were seen: they were enhanced in serum-containing media, but decreased in serum-free HL-1 media. Levels of RA as low as 10 nM significantly inhibited PG synthesis and caused depletion in the levels of PG in the medium and cell-matrix layer. Thus, in these appendicular chondrocytes, RA suppressed chondrocytic (PG, cartilage-specific collagens) and enhanced osteoblastic phenotype (cell morphology, type I collagen, alkaline phosphatase, and mineralization).

In vitro formation of mineralized cartilagenous tissue by articular chondrocytes

Study of the deep articular cartilage and adjacent calcified cartilage has been limited by the lack of an in vitro culture system which mimics this region of the cartilage. In this paper we describe a method to generate mineralized cartilagenous tissue in culture using chondrocytes obtained from the deep zone of bovine articular cartilage. The cells were plated on Millipore CMR filters. The chondrocytes in culture accumulated extracellular matrix and formed cartilagenous tissue which calcified when beta-glycerophosphate was added to the culture medium. The cartilagenous tissue generated in vitro contains both type II and type X collagens, large sulfated proteoglycans, and alkaline phosphatase activity. Ultrastructurally, matrix vesicles were seen in the extracellular matrix. Selected area electron diffraction confirmed that the calcification was composed of hydroxyapatite crystals. The chondrocytes, as characterized thus far, appear to maintain their phenotype under these culture conditions which suggests that these cultures could be used as a model to examine the metabolism of cells from the deep zone of cartilage and mineralization of cartilagenous tissue in culture.

Expression and distribution of two alternatively spliced transcripts from the chicken alpha 2 (VI) collagen gene

Two types of mRNA molecules with different 3' ends are transcribed from the chicken alpha 2(VI) collagen gene. The major splice variant encodes a polypeptide with a von Willebrand factor A domain at its carboxyl terminus. In the minor splice variant, this A domain is replaced by a novel motif which reveals some similarity to a fibronectin type III repeat. In situ hybridization experiments demonstrate that the major transcript is ubiquitously expressed. Substantial amounts are found in skeletal and cardiac muscle, gizzard, skin, tendon, liver, the wall of blood vessels, and the connective tissue of peripheral nerves. In contrast, the minor transcript is expressed at a very low level and can hardly be detected in any tissue by in situ hybridization. Only the aortic wall contains a considerable amount of this splice variant. However, no difference is observed by Northern blotting and the polymerase chain reaction in the ratio of the two transcripts when aorta and the other tissues are compared. Thus, the minor splice variant is not expressed in a tissue specific manner and, consequently, it is unlikely that it plays a tissue specific role. It might rather serve a general function in the structure and assembly of type VI collagen microfibrils.

A multiwell plate procedure for immunohistochemical and histochemical staining of constituents of articular cartilage

A multiwell plate procedure was tested for its applicability to determine immunohistochemically the noncollagenous matrix protein COMP (cartilage oligomeric matrix protein) and histochemically the proteoglycans of the matrix of articular cartilage. Fixed and decalcified cartilage-bone sections were treated with buffer, antisera, substrate or staining solutions in the wells of an assay plate under shaking on a rocking table. This floating procedure results in a reproducible histochemical or immunohistochemical staining and might therefore be valuable to determine or to detect other constituents of the matrix of these connective tissues under comparable conditions.

Collagen expression in chicken tibial dyschondroplasia

Collagen expression in growth plate cartilage derived from broiler chickens with tibial dyschondroplasia was studied and compared with samples from unaffected birds. Normal growth plate contains 12% collagen (dry weight) and dyschondroplastic growth plate 19% collagen compared with articular cartilage, which contains 55%. Dyschondroplastic growth plate collagens were more resistant to extraction by pepsin treatment than were those from unaffected growth plate. Normal and dyschondroplastic growth plate cartilages contain similar amounts of type I collagen (5% of the total collagen) but dyschondroplastic growth plate cartilage contains slightly less type II and type XI collagens, and significantly more type X collagen (25% as compared to 11%) than in normal growth plate. The levels of the mature collagen cross-link, hydroxylysyl-pyridinoline, are very low in normal growth plate but are six times higher in dyschondroplastic lesions. Immunolocalisation studies show that there is little change to the normal patterns of collagen organisation in dyschondroplastic growth plate. Investigation of metalloproteinase activity showed there to be a reduction in MMP-2 levels in dyschondroplastic growth plate compared to normal growth plate. In vitro studies on articular, normal growth plate and dyschondroplastic growth plate chondrocytes cultured in alginate or on plastic revealed differences between the cell types. When plated on plastic, articular chondrocytes rapidly assume a fibroblastic morphology. In contrast, normal growth plate chondrocytes retain their polygonal morphology whereas chondrocytes derived from dyschondroplastic cartilage initially exhibit both fibroblastic and polygonal phenotypes but gradually change to totally fibroblastic. These morphological changes are reflected by the collagen synthesis in vitro. Chondrocytes derived from normal articular cartilage synthesised collagen types I, II and X when cultured in alginate but type X synthesis was lost when cultured on plastic. Chondrocytes derived from normal growth plate cartilage synthesised predominantly type X collagen when cultured in either system. Chondrocytes derived from dyschondroplastic growth plate exhibited a similar phenotype to normal growth plate chondrocytes when cultured in alginate beads, but showed signs of dedifferentiation with reduced type X collagen and increased type I collagen when plated on plastic. These results suggest that the chondrocytes in dyschondroplastic growth plate cartilage are at a different stage of maturity than normal resulting in a cartilage that is failing to turn over at a normal rate.

Morphological and biochemical characterization of mineralizing primary cultures of avian growth plate chondrocytes: evidence for cellular processing of Ca2+ and Pi prior to matrix mineralization

Advances in the culture of mineralizing growth plate chondrocytes provided an opportunity to study endochondral calcification under controlled conditions. Here we report that these cultures synthesize large amounts of proteins characteristically associated with mineralization: type II and X collagens, sulfated proteoglycans, alkaline phosphatase, and the bone-related proteins, osteonectin and osteopontin. Certain chondrocytes appeared to accumulate large amounts of Ca2+ and Pi during the mineralization process: laser confocal imaging revealed high levels of intracellular Ca2+ in their periphery and X-ray microanalytical mapping revealed the presence of many Ca(2+)- and Pi-rich cell surface structures ranging from filamentous processes 0.14 +/- 0.02 microns by 0.5-2.0 microns, to spherical globules 0.70 +/- 0.27 microns in diameter. Removal of organic matter with alkaline sodium hypochlorite revealed numerous deposits of globular (0.77 +/- 0.19 micron) mineral (calcospherites) in the lacunae around these cells. The size and spatial distribution of these mineral deposits closely corresponded to the Ca(2+)-rich cell surface blebs. The globular mineral progressively transformed into clusters of crystallites. Taken with earlier studies, these findings indicate that cellular uptake of Ca2+ and Pi leads to formation of complexes of amorphous calcium phosphate, membrane lipids, and proteins that are released as cell surface blebs analogous to matrix vesicles. These structures initiate development of crystalline mineral. Thus, the current findings support the concept that the peripheral intracellular accumulation of Ca2+ and Pi is directly involved in endochondral calcification.

Type III collagen in normal human articular cartilage

Type III collagen in normal human articular cartilage has been detected biochemically and its location in a diffuse area around the chondrocytes demonstrated by immunofluorescence. It can be found pericellularly throughout the depth of the cartilage and is evident in specimens ranging in age from 17 to 81 years.

Characterisation of articular and growth plate cartilage collagens in porcine osteochondrosis

The articular and growth plate cartilages of osteochondrotic pigs were examined and compared with those from clinically normal animals. Both types of osteochondrotic cartilage showed considerable localised thickening apparently due to a lack of ossification. Histological examination of cartilage lesions demonstrated a breakdown in the normal pattern of chondrocyte maturation. Articular cartilage lesions lacked mature clones of chondrocytes in the calcifying region. Growth plate cartilage showed an accumulation of disorganised hypertrophic chondrocytes rather than the well-defined columns seen in normal tissue. The overall percentages of collagen in osteochondrotic lesions from both articular and growth plate cartilage were significantly reduced compared with levels in unaffected cartilage. There were substantial increases in the proportion of type I collagen in lesions from both osteochondrotic articular and growth plate cartilages and a reduction in the proportion of type II collagen. Type X collagen was detected in osteochondrotic but not normal articular cartilage. The proportion of type X collagen was unchanged in osteochondrotic growth plate cartilage. The levels of the collagen cross-links, hydroxylysylpyridinoline, hydroxylysyl-ketonorleucine and dehydrohydroxylysinonorleucine were radically reduced in samples from osteochondrotic growth-plate cartilage lesions when compared with normal tissue. Less dramatic changes were observed in articular cartilage although there was a significant decrease in the level of hydroxylysylketonorleucine in osteochondrotic lesions. Immunofluorescence examination of osteochondrotic lesions showed a considerable disruption of the organisation of the collagenous components within both articular and growth-plate cartilages. Normal patterns of staining of types I and VI collagen seen at the articular surface in unaffected tissue were replaced by a disorganised, uneven stain in osteochondrotic articular cartilage lesions. Incomplete removal of cartilage at the ossification front of osteochondrotic growth plate was demonstrated by immunofluorescence staining of type IX collagen. Type X collagen was produced in the matrix of the calcifying region of osteochondrotic articular cartilage by small groups of hypertrophic chondrocytes, but was not detected in normal articular cartilage. The distribution of type X collagen was unchanged in osteochondrotic growth plate cartilage.