The collagens of articular cartilage

Articular cartilage tensile integrity: modulation by matrix depletion is maturation-dependent

Articular cartilage function depends on the molecular composition and structure of its extracellular matrix (ECM). The collagen network (CN) provides cartilage with tensile integrity, but must also remodel during growth. Such remodeling may depend on matrix molecules interacting with the CN to modulate the tensile behavior of cartilage. The objective of this study was to determine the effects of increasingly selective matrix depletion on tensile properties of immature and mature articular cartilage, and thereby establish a framework for identifying molecules involved in CN remodeling. Depletion of immature cartilage with guanidine, chondroitinase ABC, chondroitinase AC, and Streptomyces hyaluronidase markedly increased tensile integrity, while the integrity of mature cartilage remained unaltered after depletion with guanidine. The enhanced tensile integrity after matrix depletion suggests that certain ECM components of immature matrix serve to inhibit CN interactions and may act as modulators of physiological alterations of cartilage geometry and tensile properties during growth/maturation.

Mandibular functional positioning only in vertical dimension contributes to condylar adaptation evidenced by concomitant expressions of L-Sox5 and type II collagen

OBJECTIVE

Concerted expressions of L-Sox5 and type II collagen play an important part in osteogenic transition in epiphyseal cartilage. This study was designed to elucidate the role of mandibular vertical functional positioning in condylar adaptive remodelling by examining L-Sox5 and type II collagen expressions in condylar cartilage.

DESIGN

40 female Sprague-Dawley rats at age of 5 weeks were randomly divided into the experimental (n=20) and control groups (n=20). Bite plates were fitted on the upper posterior teeth of the experimental animals to induce functional repositioning of mandible in vertical dimension. The animals in both experimental and matched control groups were sacrificed on days 3, 6, 9 and 12, respectively. Tissue sections were cut in the sagittal plane through the mandibular condyles and processed with histomorphological examination for cellular response and immunohistochemical test for expressions of L-Sox5 and type II collagen. Quantitative assessment was conducted with computer-assisted imaging system to reveal the correlation between these two factors.

RESULTS

(1) Both L-Sox5 and type II collagen were expressed in prechondroblastic cells and chondroblastic cells. (2) When mandible was downward positioned, the amount of L-Sox5 expression was significantly higher by 16.1% (day 9) and 24.2% (day 12) than that of the control (P<0.05); Similarly, type II collagen expression in the experimental group was also significantly stronger by 9.3% (day 9) and 12.3% (day 12) than control group (P<0.05), indicating an enhanced osteogenic transition occurring in condylar cartilage. (3) There was a similarity in temporospatial patterns between the expressions of these two factors, indicating their integral functions in facilitating condylar adaptation.

CONCLUSIONS

It is suggested that L-Sox5 plays a key role in adaptive remodelling of condylar cartilage resulting from downward positioning of the mandible. Integration with type II collagen enables L-Sox5 to induce osteogenic transition and consequently to encourage endochondral ossification.

Collagen XI chain misassembly in cartilage of the chondrodysplasia (cho) mouse

Molecular mechanisms controlling the assembly of cartilage-specific types II, IX and XI collagens into a heteropolymeric network of uniformly thin, unbanded fibrils are not well understood, but collagen XI has been implicated. The present study on cartilage from the homozygous chondrodysplasia (cho/cho) mouse adds support to this concept. In the absence of alpha1(XI) collagen chains, thick, banded collagen fibrils are formed in the extracellular matrix of cho/cho cartilage. A functional knock-out of the type XI collagen molecule has been assumed. We have re-examined this at the protein level to see if, rather than a complete knock-out, alternative type XI chain assemblies were formed. Mass spectrometry of purified triple-helical collagen from the rib cartilage of cho/cho mice identified alpha1(V) and alpha2(XI) chains. These chains were recovered in roughly equal amounts based on Coomassie Blue staining of SDS-PAGE gels, in addition to alpha1(II)/alpha3(XI) collagen chains. Using telopeptide-specific antibodies and Western blot analysis, it was further shown that type V/XI trimers were present in the matrix cross-linked to each other and to type II collagen molecules to form heteropolymers. Cartilage from heterozygous (cho/+) mice contained a mix of alpha1(V) and alpha1(XI) chains and a mix of thin and thick fibrils on transmission electron microscopy. In summary, the results imply that native type XI collagen molecules containing an alpha1(XI) chain are required to form uniformly thin fibrils and support a role for type XI collagen as the template for the characteristic type II collagen fibril network of developing cartilage.

Anabolic and catabolic function of chondrocyte ex vivo is reflected by the metabolic processing of type II collagen

OBJECTIVE

The aim of the present study was to investigate collagen metabolism after anabolic and catabolic stimulation of chondrocytes ex vivo.

DESIGN

Metabolic activities in ex vivo bovine cartilage explants were stimulated with insulin-like growth factor I (IGF-I) or a combination of tumor necrosis factor alpha (TNFalpha) and oncostatin M (OSM). Supernatants were assessed for changes in biochemical markers, N-terminal propeptide of type II (PIINP) collagen and fragments of C-telopeptide of type II collagen (CTX-II). Matrix metalloproteinases (MMP) were added to metabolic inactivated cartilage and evaluated by the two biochemical markers for formation or degradation, respectively. Finally, urinary CTX-II and PIINP were evaluated for assessment of type II collagen turnover in patients with rheumatoid arthritis (RA).

RESULTS

In the bovine articular cartilage explants, IGF-I induced an increase in PIINP level up to 4.8+/-1.1[ng/ml]/mg cartilage whereas CTX-II remained below 0.1+/-0.1[ng/ml]/mg cartilage. In the catabolic stimulated explants both PIINP and CTX-II were released to the supernatant, reaching concentrations of 9.0+/-1.4 and 9.1+/-2.2[ng/ml]/mg cartilage, respectively. RA patients had significantly lower serum concentrations of PIINP (3.4+/-3.7 ng/ml) compared with those healthy individuals (18.7+/-12.41 ng/ml, P<0.001). In contrast, RA patients had significantly higher urinary CTX-II (0.8+/-0.8 mg/mmol) compared to the healthy controls (0.1+/-0.08 mg/mmol, P=0.004).

CONCLUSIONS

This study is the first to demonstrate that precursors and degradation products of type II collagen released into the supernatant can effectively reflect the anabolic and catabolic activities of stimulated cartilage explants.

Biochemical and functional modulation of the cartilage collagen network by IGF1, TGFbeta2 and FGF2

OBJECTIVE

Examine effects of insulin-like growth factor 1 (IGF1), transforming growth factor beta2 (TGFbeta2) and fibroblast growth factor 2 (FGF2) on proteoglycan and collagen network and biomechanical properties of the newly formed cartilage matrix.

METHODS

Bovine articular chondrocytes were cultured in alginate beads for 3 weeks with or without FGF2, TGFbeta2 or IGF1 in the presence of 10% FCS. Proteoglycan content, collagen content, hydroxylysylpyridinoline cross-links and overall matrix metalloproteinase (MMP) activity in the culture medium were measured. Alginate disks cultured for 5 weeks were used to evaluate the effect of growth factors on mechanical properties of the construct by determining the equilibrium aggregate modulus and secant modulus.

RESULTS

IGF1 increased collagen and proteoglycan deposition. FGF2 mainly decreased collagen deposition and TGFbeta2 proteoglycan deposition. A decrease in cross-links was observed in matrix produced by chondrocytes cultured in the presence of TGFbeta2. IGF1 and FGF2 had no influence on the number of cross-links per collagen molecule. Overall MMP activity was significantly higher in culture medium of cells cultured with FGF2. TGFbeta2 and IGF1 had no effect on MMP activity. After 35 days of culture, the matrix produced under influence of IGF1 had a lower permeability and a trend to increase stiffness. FGF2 showed a trend to lower both properties. TGFbeta2 had no effect on these parameters.

CONCLUSION

IGF1, TGFbeta2 and FGF2 had differential effects on collagen network formation. Of the three growth factors tested, IGF1 seems to be best in promoting the formation of a functional collagen network since it increased proteoglycan and collagen deposition and improved the mechanical properties.

The role of computational models in the search for the mechanical behavior and damage mechanisms of articular cartilage

Articular cartilage plays a vital role in the function of diarthrodial joints. Due to osteoarthritis degeneration of articular cartilage occurs. The initial event that triggers the pathological process of cartilage degeneration is still unknown. Cartilage damage due to osteoarthritis is believed to be mechanically induced. Hence, to investigate the initiation of osteoarthritis the stresses and strains in the cartilage must be determined. So far the most common method to accomplish that is finite element analysis. This paper provides an overview of computational descriptions developed for this purpose, and what they can be used for. Articular cartilage composition and structure are discussed in relation with degenerative changes, and how these affect mechanical properties.

The influence of mechanical compression on the induction of osteoarthritis-related biomarkers in articular cartilage explants

OBJECTIVE

Macromolecules of the articular cartilage extracellular matrix released into synovial fluid, blood, or urine can serve as potentially useful biomarkers of the severity of osteoarthritis (OA). Biomechanical factors play an important role in OA pathogenesis, yet their influence on biomarker production is not well understood. The goal of this study was to examine the hypothesis that dynamic mechanical stress influences the release of these biomarkers from articular cartilage.

METHODS

Explants of porcine cartilage were subjected to dynamic compression at 0.5 Hz for 24h at stresses ranging from 0.006 to 0.1 MPa. The concentrations of cartilage oligomeric matrix protein (COMP), keratan sulfate (KS measured as the 5 D 4 epitope), total sulfated glycosaminoglycan (S-GAG), and the KS (keratanase-digestible) and chondroitin sulfate (CS) (chondroitinase-digestible) fractions of S-GAG were measured. Radiolabel incorporation was used to determine the rates of proteoglycan and protein synthesis.

RESULTS

The magnitudes of mechanical stress applied in this study induced nominal tissue strains of 4-23%, consistent with a range of physiological to hyperphysiologic strains measured in situ. COMP release increased in proportion to the magnitude of dynamic mechanical stress, while KS, CS and total S-GAG release increased in a bimodal pattern with increasing stress. Protein and proteoglycan synthesis were significantly decreased at the highest level of stress.

CONCLUSION

Mechanical stress differentially regulates the turnover of distinct pools of cartilage macromolecules. These findings indicate that mechanical factors, independent of exogenous cytokines or other stimulatory factors, can influence the production and release of OA-related biomarkers from articular cartilage.

Mesenchymal stem cell therapy to rebuild cartilage

Disorders affecting cartilage touch almost the whole population and are one of the leading causes of invalidity in adults. To repair cartilage, therapeutic approaches initially focused on the implantation of autologous chondrocytes, but this technique proved unsatisfactory because of the limited number of chondrocytes obtained at harvest. The discovery that several adult human tissues contain mesenchymal stem cells (MSCs) capable of differentiating into chondrocytes raised the possibility of injecting MSCs to repair cartilages. The important data published recently on the factors controlling chondrocyte commitment must be thoroughly considered to make further progress towards this therapeutic approach. The potential application of MSC therapy provides new hope for the development of innovative treatments for the repair of cartilage disorders.

Multiple Signals Induce Endoplasmic Reticulum Stress in Both Primary and Immortalized Chondrocytes Resulting in Loss of Differentiation, Impaired Cell Growth, and Apoptosis

The endoplasmic reticulum is the site of synthesis and folding of secretory proteins and is sensitive to changes in the internal and external environment of the cell. Both physiological and pathological conditions may perturb the function of the endoplasmic reticulum, resulting in endoplasmic reticulum stress. The chondrocyte is the only resident cell found in cartilage and is responsible for synthesis and turnover of the abundant extracellular matrix and may be sensitive to endoplasmic reticulum stress. Here we report that glucose withdrawal, tunicamycin, and thapsigargin induce up-regulation of GADD153 and caspase-12, two markers of endoplasmic reticulum stress, in both primary chondrocytes and a chondrocyte cell line. Other agents such as interleukin-1beta or tumor necrosis factor alpha induced a minimal or no induction of GADD153, respectively. The endoplasmic reticulum stress resulted in decreased chondrocyte growth based on cell counts, up-regulation of p21, and decreased PCNA expression. In addition, perturbation of endoplasmic reticulum function resulted in decreased accumulation of an Alcian Blue positive matrix by chondrocytes and decreased expression of type II collagen at the protein level. Further, quantitative real-time PCR was used to demonstrate a down-regulation of steady state mRNA levels coding for aggrecan, collagen II, and link protein in chondrocytes exposed to endoplasmic reticulum stress-inducing conditions. Ultimately, endoplasmic reticulum stress resulted in chondrocyte apoptosis, as evidenced by DNA fragmentation and annexin V staining. These findings have potentially important implications regarding consequences of endoplasmic reticulum stress in cartilage biology.

Profiling genes expressed in human fetal cartilage using 13,155 expressed sequence tags

OBJECTIVE

To analyze the gene expression profile of human fetal cartilage by expressed sequence tags (ESTs).

METHODS

A human fetal cartilage (8-12 weeks) cDNA library was constructed using the lambda ZAP Express vector. ESTs were obtained by partial sequencing of cDNA clones. The basic local alignment search tool algorithm was used to compare all generated ESTs to known sequences.

RESULTS

A total of 13,155 ESTs were analyzed, of which 8696 ESTs (66.1%) matched known genes, 53 ESTs (0.4%) were putatively novel (with no match) and the rest matched other ESTs, genomic DNA and repetitive sequences. Importantly, we identified 2448 unique known genes through non-redundancy analysis of the known gene matches, which were then functionally categorized. The tissue specificity of this library was reflected by its EST profile of the extracellular matrix (ECM) proteins. Collagens were the major transcripts, representing 68.5% of the ECM proteins. Proteoglycans were the second most abundant, constituting 9.5%. Collagen type II was the most abundant gene of all. Glypican 3, decorin and aggrecan were the major transcripts of proteoglycans. Many genes involved in cartilage development were identified, such as insulin-like growth factor-II, its receptor and binding proteins, connective tissue growth factor and fibroblast growth factors. Proteases and their regulatory factors were also identified, including matrix metalloprotease 2 and tissue inhibitor of metalloproteinase 1.

CONCLUSIONS

The EST approach is an effective way of characterizing the genes expressed in cartilage. These data represent the most extensive molecular information on human fetal cartilage to date. The availability of this information will serve as a basis for further research to identify genes that are essential in cartilage development.

Mechano-electrochemical properties of articular cartilage: their inhomogeneities and anisotropies

In this chapter, the recent advances in cartilage biomechanics and electromechanics are reviewed and summarized. Our emphasis is on the new experimental techniques in cartilage mechanical testing, new experimental and theoretical findings in cartilage biomechanics and electromechanics, and emerging theories and computational modeling of articular cartilage. The charged nature and depth-dependent inhomogeneity in mechano-electrochemical properties of articular cartilage are examined, and their importance in the normal and/or pathological structure-function relationships with cartilage is discussed, along with their pathophysiological implications. Developments in theoretical and computational models of articular cartilage are summarized, and their application in cartilage biomechanics and biology is reviewed. Future directions in cartilage biomechanics and mechano-biology research are proposed.

Immunization of rats with homologous type XI collagen leads to chronic and relapsing arthritis with different genetics and joint pathology than arthritis induced with homologous type II collagen

The most commonly used animal model for rheumatoid arthritis (RA) is collagen-induced arthritis (CIA), induced by immunization with type II collagen (CII), a cartilage restricted protein. In this work we show that type XI collagen (CXI), which is a minor component in cartilage, induces a different form of erosive and chronic relapsing polyarthritis in rats. Using a series of inbred rat strains involving various genetic backgrounds (DA, LEW, E3), and congenic MHC regions (a, u, f, n, c, d), we found that CXI induced arthritis (C(XI)IA) is associated with the RT1f haplotype in contrast to CII induced arthritis (C(II)IA), which is associated with the RT1a and RT1u haplotypes. The C(XI)IA follows a chronic disease course affecting peripheral joints with both progression and relapses, which appear not to cease (occurring >800 days). Susceptible strains showed a sustained antibody response to CXI with time indicating that the autoimmune response was self-perpetuated. Microscopic analysis of the joints at different stages demonstrated the severe destruction of bone and cartilage by pannus tissue consisting of activated macrophages and T cells. The main difference to joints from rats with C(II)IA was larger numbers of infiltrating lymphocytes and these tended to form follicle-like aggregates. Surprisingly, males were more susceptible to C(XI)IA than females whereas the opposite has been observed in other rat arthritis models, including C(II)IA. Taken together, C(XI)IA is a chronic relapsing and erosive polyarthritis that is MHC associated, which in fact fulfills the criteria for diagnosis of RA. Thus the C(XI)IA model will be useful as a novel and relevant animal model for RA.

The involvement of beta1 integrin in the modulation by collagen of chondrocyte-response to transforming growth factor-beta1

The physiologic response of chondrocytes to maintenance of the matrix and response to injury likely involves signaling from multiple sources including soluble cytokines, mechanical stimulation, and signaling from the extracellular matrix. The signaling from the extracellular matrix may serve to effect cell differentiation and to modulate the response to cytokines. We have previously reported that type II collagen modulates the response of bovine articular chondrocytes to TGF-beta1. The molecular nature of the signaling mechanism has not been elucidated but presumably involves a similar mechanism by which the cell attaches to the surrounding matrix. An alginate bead culture system is utilized to which exogenous type II collagen is added. The inclusion of type II collagen results in an alteration of integrin expression with a down regulation of alpha2. The response of the chondrocyte to TGF-beta1 can be modulated by the inclusion of exogenous type II collagen. The modulation of DNA and proteoglycan synthesis was blocked by the treatment of anti-beta1 integrin antibody (4B4) or by cyclic RGD containing peptides. These events occur at concentrations that block cell adhesion to type II collagen. Linear RGD containing peptides and anti-anchorin antibodies had no effect on the modulation by type II collagen. These results suggest that type II collagen binding by chondrocytes at least in part occurs through the beta1 integrin. This binding results in modulation of the cell response to TGF-beta1. This modulation may serve to provide physiologic specificity to the cytokine-signaling cascade. An understanding of the regulatory milieu of the chondrocyte may permit the stimulation of an intrinsic repair of articular cartilage in the future. A near term application of this understanding can be made to tissue engineering attempts at articular cartilage repair.

Collagen type II C-telopeptide fragments as an index of cartilage degradation

We report the development of an assay for measurement of the urinary concentration of collagen type II C-telopeptide fragments. This assay was developed for providing a specific marker of joint metabolism. A monoclonal antibody, recognizing a linear six amino acid epitope from the middle region of the collagen type II C-telopeptide was used in a competitive enzyme-linked immunoassay (ELISA) format for measurement of urine samples. The technical performance and specificity of the assay was evaluated and a panel of samples from patients with rheumatoid arthritis (RA) (n = 27), osteoarthritis (OA) (n = 29), Paget's disease (n = 9), and healthy controls (n = 428) was measured in the assay. The ELISA was specific for the peptide EKGPDP derived from collagen type II C-telopeptide: it did not recognize peptides from the N-telopeptide of the molecule or from other collagen types. Collagen type II C-telopeptide fragments measured in the assay resisted seven freeze-thaw cycles and >20 h of storage at room temperature. RA and OA patients showed significant 2.33-fold (95% confidence interval [CI] 1.50-3.16) and 1.53-fold (CI 1.24-1.82) elevations in CartiLaps concentration, respectively. Paget's disease patients did not have elevated CartiLaps levels. RA patients with radiological evidence of cartilage damage had significantly higher (1.79-fold, CI 1.04-2.54) CartiLaps levels than RA patients without radiological evidence of cartilage destruction. The Cartilaps assay showed high technical precision and an ability to differentiate populations with an elevated joint metabolism from normal controls. This suggests that the assay may have clinical value in assisting in the diagnosis of joint diseases and in monitoring progression and therapy in RA and OA.

Integrative cartilage repair: inhibition by beta-aminopropionitrile

The effects of beta-aminopropionitrile, a known inhibitor of lysyl oxidase, on the extractability of newly synthesized collagen and integrative cartilage repair were determined in explant cultures of adult bovine articular cartilage. Dose-escalation studies indicated that treatment of cartilage explants for 6 days with beta-aminopropionitrile caused a dose-dependent inhibition of proteoglycan synthesis ([35S]sulfate incorporation) with a 50% inhibition at 2.2 mM. However, 0.25 mM beta-aminopropionitrile had no detectable effect on proteoglycan synthesis and was thus used for subsequent experiments. Treatment of cartilage with beta-aminopropionitrile for 14 days increased the extractability of newly synthesized collagen with 4 M guanidine-HCl while having little effect on proteoglycan synthesis, proteoglycan deposition, collagen synthesis (formation of [3H]hydroxyproline after labeling with [3H]proline), collagen deposition, or cartilage cellularity (DNA content). In untreated cultures, the percentage of radiolabeled collagen ([3H]hydroxyproline) that was extractable after 1 day of radiolabeling, 6 days of radiolabeling, or 6 days of label and 6 days of chase decreased from 81 to 25 and 9%, respectively. In beta-aminopropionitrile-treated cultures, the extractability was relatively higher (96, 62, and 47%, respectively). Treatment with beta-aminopropionitrile after radiolabeling with [14C]lysine also significantly inhibited the formation of the reducible crosslink [14C]dihydroxylysinonorleucine without affecting the overall deposition in cartilage of [14C]lysine and [14C]hydroxylysine. In functional repair studies, treatment with beta-aminopropionitrile caused an almost complete inhibition of integration between pairs of cartilage explants maintained in apposition for 2 weeks. These results indicate that beta-aminopropionitrile blocks the formation of collagen crosslinks in cartilage explants and suggest that such crosslinks are critical to integrative cartilage repair.

The effects of pH and ionic strength on intrafibrillar hydration in articular cartilage

The hydration of articular cartilage is an essential determinant of its load bearing capacity. Here we have examined the dependence of the amount of intrafibrillar water, associated with the collagen molecules in both native and PG-depleted cartilage specimens, on the pH and ionic strength of the bathing solution, in the presence and absence of an externally applied pressure. We found that high ionic strength reduces the collagen intermolecular spacing over a large pH range: this is consistent with the electrostatic nature of the interactions between the charged groups within the intrafibrillar space. We also found that as the pH is lowered from neutral to approximately 3, there is, as expected, a gradual increase in the overall positive charge of the intrafibrillar compartment. However, surprisingly, this is not accompanied by an increase in the intrafibrillar hydration; only at pH 1.8 does the amount of intrafibrillar water increase markedly. We suggest that, rather than overall intrafibrillar charge, it is specific local axial and azimuthal relationships among collagen molecules in the fibril, and more particularly, among their charged amino acid residues, that determine the intermolecular collagen spacing, and hence intrafibrillar hydration.

Collagenase 1 and collagenase 3 expression in a guinea pig model of osteoarthritis

OBJECTIVE

To analyze the in vivo compartmental expression of collagenases 1 and 3 (MMP-1 and MMP-13) in the Hartley guinea pig model of spontaneously occurring osteoarthritis (OA) for the purpose of elucidating their roles in the pathogenesis of OA.

METHODS

Competitive reverse transcription-polymerase chain reaction (RT-PCR) and immunohistochemistry quantification of messenger RNA (mRNA) and protein levels in medial and lateral tibial cartilage obtained from the knee joints of 2-month-old (no OA) and 12-month-old (OA) guinea pigs.

RESULTS

The patterns of mRNA expression of collagenases 1 and 3 varied with the age of the animal and the compartment of the knee. We also found focal areas of collagenase 1 and collagenase 3 proteins localized to the extracellular matrix of OA lesion sites, coincident with three-quarter/one-quarter collagen cleavage. Collagenase 3 protein was also abundant throughout the medial tibial cartilage of 2-month-old animals.

CONCLUSION

This represents the first description of bona fide collagenase 1 in a rodent species. Recent evidence, however, based on analysis of mitochondrial DNA homologies, suggests that the guinea pig is not a member of the order Rodentia and may be more closely allied with lagomorphs. This taxonomic controversy leaves open to question the issue of the expression of collagenase 1 in other rodents, such as mice and rats. The presence of active collagenases 1 and 3 at OA lesion sites is consistent with an important role of these enzymes in the cartilage degradation of OA in guinea pigs. The expression of collagenase 3 in medial tibial cartilage from 2-month-old guinea pigs may signify a role of this enzyme in cartilage remodeling with growth and development, or it may represent an early molecular manifestation of OA.

Electron microscopical study in multiple epiphyseal dysplasia type II

An electron microscopic examination of articular cartilage of two cases with multiple epiphyseal dysplasia type II was performed. The cartilage had a normal cell distribution and no signs of gross degeneration were found. Chondrocytes showed normal ultrastructural characteristics without dilation of the rough endoplasmic reticulum. The matrix contained normal banded collagen fibrils, proteoglycans, and aggregated fibrils.

Increased content of type-VI collagen epitopes in human osteoarthritic cartilage: quantitation by inhibition ELISA

Type-VI collagen is an integral part of the extracellular cartilage matrix. However, the exact amounts of type-VI collagen in normal and osteoarthritic human cartilage still are not known. In this study, we describe an inhibition enzyme-linked immunosorbent assay that was developed to quantitate type-VI collagen epitopes found in guanidinium chloride extracts from normal and osteoarthritic human cartilage. In 31 cartilage samples from various localizations of healthy adult human knees, type-VI collagen epitopes accounted for approximately 0.40% of the total collagen content. Interestingly, type-VI collagen epitopes increased about 4-fold in osteoarthritic cartilage. A statistically significant increase of type-VI collagen epitopes was found during early stages of the disease, with only a superficial roughening of the cartilage surface and a loss of proteoglycans. Thus, these findings indicate that type-VI collagen is a minor component of normal human articular cartilage and that the amount of type-VI collagen epitopes increases significantly during early stages of osteoarthritis.

A simplified measurement of degraded collagen in tissues: application in healthy, fibrillated and osteoarthritic cartilage

Intact triple helical collagen molecules are highly resistant to proteolytic enzymes, whereas degraded (unwound) collagen is easily digested. This fact was exploited to develop a simplified method for the quantification of the amount of degraded collagen in the collagen network of connective tissues. Essentially, the method involves extraction of proteoglycans with 4 M guanidinium chloride, selective digestion of degraded collagen by alpha-chymotrypsin, hydrolysis in 6 M HCl of the released fragments as well as the residual tissue, and then measurement of the amount of hydroxyproline in both pools. Since the digestion of degraded collagen by alpha-chymotrypsin and measurement of hydroxyproline is not restricted to a specific collagen type, this technique can be applied to a wide variety of connective tissues. The method was validated with articular cartilage. Levels of in situ degraded collagen were about four-fold higher in degenerated (fibrillated) cartilage than in its healthy counterpart derived from the same donor. More detailed investigations revealed that the collagen damage in degenerated cartilage is more extensive at the cartilage surface than in the region adjacent to bone. This was not the case in healthy cartilage; identical low values were obtained at the surface and close to the bone. An impaired collagen network has been hypothesized to be the reason for the swelling of cartilage in osteoarthritis (OA). The present paper presents the first experimental evidence to support this hypothesis: more damage to the collagen network (i.e., more degraded collagen molecules within fibrils) is linearly related to more extensive swelling of the OA tissue in hypotonic saline.

Extracellular collagen modulates the regulation of chondrocytes by transforming growth factor-beta 1

This article describes the modulation, by extracellular collagen, of DNA and proteoglycan synthesis in articular chondrocytes stimulated with transforming growth factor-beta 1. Type-I and type-II collagen, heat-denatured type-II collagen, and bovine serum albumin were each incorporated into alginate in increasing concentrations. Bovine articular chondrocytes were isolated and were resuspended in the alginate, yielding alginate beads with final extracellular protein concentrations of 0-1.5% (wt/vol) for the collagens and 0-2.5% (wt/vol) for bovine serum albumin. Cultures of beads were maintained for 7 days in basal Dulbecco's modified Eagle medium or in medium supplemented with 10 ng/ml transforming growth factor-beta 1. Subsequently, the synthesis of DNA and proteoglycan was measured by radiolabel-incorporation methods with [35S]sulfate and [3H]thymidine, and the values were normalized to the DNA content. Transforming growth factor-beta 1 stimulated the synthesis of both DNA and proteoglycan in a bimodal fashion. The presence of extracellular type-II collagen increased the rate of DNA and proteoglycan synthesis in a dose-dependent fashion in cultures stimulated by transforming growth factor-beta 1, whereas heat-inactivated type-II collagen abrogated the effects observed with type-II collagen for synthesis of both DNA and proteoglycan. In contrast, the presence of extracellular type-I collagen caused a dose-dependent inhibition of synthesis of both DNA and proteoglycan in cultures stimulated with transforming growth factor-beta 1. Extracellular bovine serum albumin brought about a limited increase in synthesis rates, presumably by blocking nonspecific cytokine binding. These results suggest that type-II collagen has a specific role in chondrocyte regulation and serves to mediate the response of chondrocytes to transforming growth factor-beta 1.

Characterization of human type II procollagen and collagen-specific antibodies and their application to the study of human type II collagen processing and ultrastructure

Type II collagen is the most abundant collagen in articular cartilage and, together with other tissue-specific collagens and proteoglycans, provides the tissue with its shock-absorbing properties and its resiliency to stress. Specific antibodies which recognize various collagen types have been very useful in the study of collagen biosynthesis, structure and metabolism in normal and pathological conditions. Antibodies which recognize epitopes of type II collagen have been described previously; however, many of these antibodies display cross-reactivity with other collagens or with type II collagen from other species, reflecting the high degree of homology of the helical domains of fibrillar collagens. In this study, we prepared antibodies to sequential determinants of human type II procollagen employing synthetic peptides with sequences deduced from the nucleotide sequence of the human alpha 1 (II) procollagen cDNA. The antibodies were highly specific for epitopes in either the C-terminal propeptide or the telopeptide of the human type II collagen and did not cross-react with other human interstitial collagens or with murine type II collagen. These antibodies were used in conjunction with biosynthetic labeling to study the secretion and processing of human type II procollagen and collagen in human chondrocytes in vitro. The results indicated that a lag period of about 90 min was required for the secretion of newly synthesized type II procollagen. Conversion of the secreted procollagen into fully processed alpha-chains and their deposition in the cell layer were first apparent 240 min following the initiation of biosynthetic labeling. The antibodies were also used to examine, by immunoelectron microscopy, the structure of the extracellular matrix produced by human chondrocytes maintained in long-term cultures under conditions which permit the preservation of the cartilage-specific phenotype. These highly specific antibodies provide valuable tools to study the metabolism and structure of human type II procollagen and collagen in normal and pathologic conditions.

The mouse col11a2 gene. Some transcripts from the adjacent rxr-beta gene extend into the col11a2 gene

Type XI collagen is present in small amounts in cartilage, together with small amounts of type IX and type V collagens and large amounts of type II collagen. Here, primers based on the nucleotide sequences of partial human cDNAs and mouse genomic DNAs that were analyzed by other investigators were used to isolate a cDNA for the mouse col11a2 gene. Cosmid clones for the mouse col11a2 gene were isolated, and 12.4 kb of the nucleotide sequences were defined. Analysis of the genomic sequences identified three exons in the mouse gene that were recently shown to undergo alternative splicing (Tsumaki and Kimura, J. Biol. Chem. 270, 2372-2378, 1995; Zhidkova et al., J. Biol. Chem. 270, 94886-9493, 1995). In addition, analysis of the cosmid clones revealed that the 5' end of the mouse col11a2 gene was located head-to-tail with the mouse retinoic X receptor beta gene. RT-PCR assays demonstrated that some transcripts from the retinoic X receptor beta gene extend into the col11a2 gene. Therefore, there may be coordinate expression of the two genes.

The expression of types X and VI collagen and fibrillin in rat mandibular condylar cartilage. Response to mastication forces

Types X and VI collagen and fibrillin were localized by in situ hybridization and immunohistochemical methods in the mandibular condyles of rats, and the response of these molecules to post-weaning diets of soft food, ordinary pellets, or hardened pellets was studied. Type X collagen was synthesized, particularly in conditions of soft food consistency, by cells in the perichondrium-periosteum and in the bone and by cells at the erosion front between cartilage and bone. Type X collagen synthesis diminished under higher compression forces due to mastication and with increasing age. Type VI collagen and fibrillin were synthesized by cells in the perichondrium-periosteum and by chondrocytes and by stromal osteoblasts and were not modified by higher mechanical forces. In contrast to previous findings in the growth plate of long bones, type X collagen in the mandibular condyle was not synthesized by hypertrophic chondrocytes but was associated with cells of the osteoblastic rather than the chondroblastic phenotype.

Collagen type IX from human cartilage: a structural profile of intermolecular cross-linking sites

Type IX collagen, a quantitatively minor collagenous component of cartilage, is known to be associated with and covalently cross-linked to type II collagen fibrils in chick and bovine cartilage. Type IX collagen molecules have also been shown to form covalent cross-links with each other in bovine cartilage. In the present study we demonstrate by structural analysis and location of cross-linking sites that, in human cartilage, type IX collagen is covalently cross-linked to type II collagen and to other molecules of type IX collagen. We also present evidence that, if the proteoglycan form of type IX collagen is present in human cartilage, it can only be a minor component of the matrix, similar to findings with bovine cartilage.

Effects of fluid-induced shear on articular chondrocyte morphology and metabolism in vitro

This study tested the effects of fluid-induced shear on high density monolayer cultures of adult articular chondrocytes. Fluid-induced shear (1.6 Pa) was applied by cone viscometer to normal human and bovine articular chondrocytes for periods of 24, 48, and 72 hours. At 48 and 72 hours, fluid-induced shear caused individual chondrocytes to elongate and align tangential to the direction of cone rotation. Fluid-induced shear stimulated glycosaminoglycan synthesis by 2-fold (p < 0.05) and increased the length of newly synthesized chains in human and bovine chondrocytes. In human chondrocytes, the hydrodynamic size of newly synthesized proteoglycans also was increased. After 48 hours of fluid-induced shear, the release of prostaglandin E2 from the chondrocytes was increased 10 to 20-fold. In human chondrocytes, mRNA signal levels for tissue inhibitor of metalloproteinase increased 9-fold in response to shear compared with the controls. In contrast, mRNA signal levels for the neutral metalloproteinases, collagenase, stromelysin, and 72 kD gelatinase, did not show such major changes. This study demonstrated that articular chondrocyte metabolism responds directly to physical stimulation in vitro and suggests that mechanical loading may directly influence cartilage homeostasis in vivo.

The human COL11A2 gene structure indicates that the gene has not evolved with the genes for the major fibrillar collagens

The human COL11A2 gene was analyzed from two overlapping cosmid clones that were previously isolated in the course of searching the human major histocompatibility region (Janatipour, M., Naumov, Y., Ando, A., Sugimura, K., Okamoto, N., Tsuji, K., Abe, K., and Inoko, H. (1992) Immunogenetics 35, 272-278). Nucleotide sequencing defined over 28,000 base pairs of the gene. It was shown to contain 66 exons. As with most genes for fibrillar collagens, the first intron was among the largest, and the introns at the 5'-end of the gene were in general larger than the introns at the 3'-end. Analysis of the exons coding for the major triple helical domain indicated that the gene structure had not evolved with the genes for the major fibrillar collagens in that there were marked differences in the number of exons, the exon sizes, and codon usage. The gene was located close to the gene for the retinoic X receptor beta in a head-to-tail arrangement similar to that previously seen with the two mouse genes (P. Vandenberg and D. J. Prockop, submitted for publication). Also, there was marked interspecies homology in the intergenic sequences. The amino acid sequences and the pattern of charged amino acids in the major triple helix of the alpha 2(XI) chain suggested that the chain can be incorporated into the same molecule as alpha 1(XI) and alpha 1(V) chains but not into the same molecule as the alpha 3(XI)/alpha 1(II) chain. The structure of the carboxyl-terminal propeptide was similar to the carboxyl-terminal propeptides of the pro alpha 1(XI) chain and pro alpha chains of other fibrillar collagens, but it was shorter because of internal deletions of about 30 amino acids.

Magnetization transfer in cartilage and its constituent macromolecules

The goal of this work was to investigate magnetization transfer (MT) in cartilage by measuring water proton signals Ms/Mo, as an indicator of MT, in (i) single-component systems of the tissue's constituent macromolecules and (ii) intact cartilage under control conditions and after two pathomimetic interventions. Ms/Mo was quantified with a 12-microT saturation pulse applied 6 kHz off resonance. Both glycosaminoglycans (GAG) and collagen exhibited concentration dependent effects on Ms/Mo, being approximately linear for GAG solutions (Ms/Mo = -0.0137[% GAG] + 1.02) and exponential for collagen suspensions (Ms/Mo = 0.80 x exp[-(%collagen)/6.66] + 0.20); the direct saturation of water could not account for the measured Ms/Mo. Although the effect of collagen on Ms/Mo is much stronger than for a corresponding concentration of GAG, Ms/Mo is not very sensitive to changes in collagen concentration in the physiological range. Tissue degradation with 25 mg/ml trypsin led to an increase in Ms/Mo from the baseline value of 0.2 (final/initial values = 1.15 +/- 0.13, n = 11, P < 0.001). In contrast, a 10-day treatment of cartilage with 100 ng/ml of interleukin-1 beta (IL-1 beta) caused a 19% decrease in Ms/Mo (final/initial values = 0.81 +/- 0.08, n = 3, P = 0.085). The changes in hydration and macromolecular content for the two treatments were comparable, suggesting that Ms/Mo is sensitive to macromolecular structure as well as concentration. In conclusion, whereas the baseline Ms/Mo value in cartilage may be primarily due to the tissue collagen concentration, changes in Ms/Mo may be due to physiological or pathophysiological changes in GAG concentration and tissue structure, and the measured Ms/Mo may differentiate between various pathomimetic degradative procedures.

Local and remote matrix responses to chondrocyte-laden collagen scaffold implantation in extensive articular cartilage defects

Chondrocyte-laden collagen scaffolds were evaluated in extensive cartilage defects in an equine model. Arthroscopic techniques were used to implant a chondrocyte-collagen culture product in 15-mm defects in the lateral trochlear ridge of the femoropatellar joint of 12 horses. Ungrafted control defects were formed in the opposite joint. Groups of six horses were terminated at 4 and 8 months after implantation and the repair sites, adjacent cartilage, and remote cartilage within each femoropatellar joint examined biochemically. Eight months following surgery the relative proportions of type II collagen in grafted and ungrafted defects, determined using the ratio of cyanogen bromide cleavage products alpha 1(II)CB10/alpha 2(I)CB3,5, were not significantly different (31.57 +/- 2.76% and 26.88 +/- 2.76%, respectively). Aggrecan content was significantly improved in grafted defects (85.61 +/- 6.51 and 74.91 +/- 10.31 micrograms/mg dry weight). Cartilage surrounding grafted defects also showed improved maintenance of cartilage glycosaminoglycan content. Thus, chondrocyte grafting in collagen scaffold vehicles improved the aggrecan content in extensive cartilage defects and surrounding normal cartilage. However, given the continued disparity between repair tissue and normal cartilage aggrecan content, and the low proportion of type II collagen in grafted defects, the utility of collagen scaffolds for chondrocyte grafting of large cartilage defects seems limited.

The diastrophic dysplasia gene encodes a novel sulfate transporter: positional cloning by fine-structure linkage disequilibrium mapping

Diastrophic dysplasia (DTD) is a well-characterized autosomal recessive osteochondrodysplasia with clinical features including dwarfism, spinal deformation, and specific joint abnormalities. The disease occurs in most populations, but is particularly prevalent in Finland owing to an apparent founder effect. DTD maps to distal chromosome 5q and, based on linkage disequilibrium studies in the Finnish population, we had previously predicted that the DTD gene should lie about 64 kb away from the CSF1R locus. Here, we report the positional cloning of the DTD gene by fine-structure linkage disequilibrium mapping. The gene lies in the predicted location, approximately 70 kb proximal to CSF1R, and encodes a novel sulfate transporter. Impaired function of its product is likely to lead to undersulfation of proteoglycans in cartilage matrix and thereby to cause the clinical phenotype of the disease. These results demonstrate the power of linkage disequilibrium mapping in isolated populations for positional cloning.

A microstructural model for the elastic response of articular cartilage

A model of articular cartilage is developed in which the continuum stiffness tensor is related to the tissue's microstructure. The model consists of bilinear elastic fibers embedded in an elastic matrix. Homogenization techniques are used to relate this level of organization to the macroscopic response of the tissue. The model includes the effects of spatial orientation of fibers, pre-stress in the fibers and matrix resulting from matrix swelling, slipping at the interface between the fibers and the matrix, fiber buckling in compression, and deformation-induced fiber reorientation. The model predicts increased axial stiffness with increasing stretch due to fiber reorientation, reduced axial and shear stiffness with slipping between fiber and matrix and a sensitivity of the tissue response to the swelling pressure in the matrix, the matrix modulus and the bonding of the fiber matrix interface.

Abnormality of type IX collagen in a patient with diastrophic dysplasia

There is growing evidence that a spectrum of chondrodysplasias are caused by mutations in the gene coding for type II collagen. The basic molecular defect in diastrophic dysplasia has not been defined, but it appears not to be in collagen type II. Cartilage contains other tissue-specific collagens, types IX, X, and XI, but no mutations have yet been found in their genes in clinical disease. Type IX collagen is hypothesized to play a role in the regulation of type II collagen fibril organization and structure in cartilage extracellular matrix. In this study, we have examined iliac crest growth cartilage from a patient with diastrophic dysplasia. Although collagen fibrils were markedly increased in diameter on transmission electron microscopy, type II collagen appeared to be normal biochemically. Type XI collagen was also normal. However, type IX collagen appeared abnormal on sodium dodecyl sulfate polyacrylamide gel electrophoresis with a pronounced excess of the COL1 domain of the molecule in pepsin extracts. The findings point to an abnormality in structure or metabolism of type IX collagen in diastrophic dysplasia.