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PubMed1991

Age related changes in the turnover of proteoglycans from explants of bovine articular cartilage.

Articular cartilage in explant culture synthesized 2 proteoglycan types of different size. The proportion of 35S-sulfate incorporated into the small proteoglycan was higher in mature (17%) than in immature cartilage (11%). The chondroitin sulfate chains of both proteoglycans, synthesized by mature cartilage were shorter than those of immature cartilage, with a higher ratio of 6-sulfated over 4-sulfated disaccharides. Radiolabelled macromolecules from tissue of both ages were released in 2 phases: an initial fast release followed by a period of slow release. The half-lives of both proteoglycan populations were shorter in mature cartilage than in immature tissue (-45%). The amount of proteoglycans released during the initial short phase increases with age, from 23-24% in immature cartilage to 28-29% in mature tissue.

Aging↗
PubMed1977

Anaerobic and aerobic metabolism in articular cartilage.

Articular cartilage explants were incubated at various oxygen tensions and the results of 35SO4 and 3H-thymidine incorporation indicate that proteoglycan and DNA synthesis is depressed at low oxygen tensions. The studies of oxygen consumption and glucose/lactate metabolism in the cartilage suggest a shift in energy pathways as the oxygen environment is altered. In low O2 tensions chondrocytes follow anaerobic glycolysis while at physiologic oxygen tensions chondrocytes follow a combination of both aerobic and glycolytic metabolism. The data suggest that hypoxia, frequently found in inflammatory arthritides, would have deleterious effects on chondrocyte metabolism and would significantly impair any reparative potential of the injured chondrocytes.

Animals↗
PubMed1998

The compressive strength of articular cartilage.

Articular cartilage provides the smooth bearing surfaces in freely moving (synovial) joints. Its mechanical properties are important because structural failure of cartilage is closely associated with joint disorders, including osteoarthritis. Some mechanical properties of cartilage are well characterized, but little is known about its compressive strength. A technique for measuring cartilage compressive strength is evaluated, and an overview of experiments which relate strength to stiffness and tissue hydration is given. Specimens of bovine articular cartilage-on-bone, approximately 15 mm square, were loaded on a hydraulic materials testing machine using flat impermeable indentors. Linear-ramp loading/unloading cycles of 1 s duration, and of increasing severity, were applied until failure was evident on force-displacement graphs. Some specimens were tested following a 30 min period of creep loading. Inkstaining and histology were used to locate the site of initial damage to each specimen. Specimen failure occurred first in the cartilage surface layer at a nominal applied stress of 14-59 MPa (mean 35.7 MPa). Mechanical properties were little affected by specimen or indentor size, provided both remained within defined limits, and compressive strength could be measured to an accuracy of approximately +/- 5 per cent. Compressive stiffness was a significant predictor of strength, but only if it was measured at high levels of stress. Strength increased following creep-induced water loss, and initial mechanical damage could propagate under moderate cyclic loading. This technique for measuring cartilage compressive strength has potential for investigating the causes of cartilage failure in vivo.

Animals↗
PubMed1986

Structural consequences of traumatizing articular cartilage.

Articular cartilage-on-bone has been subjected to repeated impact loading in vitro and the associated structural changes occurring in the general matrix examined by optical and transmission electron microscopy (TEM). The study shows that repeated trauma transforms the pseudorandom arrangement of fibrils comprising the general matrix of normal articular cartilage into a structural configuration strongly aligned in the radial direction and displaying a prominent waveform or crimp. This stress-induced structural transformation can be predicted from the application of a recently developed structural model of articular cartilage. Further, this altered structure bears a close resemblance to that commonly observed in articular cartilage exhibiting both non-progressive degeneration and osteoarthritic changes.

Animals↗
PubMed1997

The effect of recombinant human bone morphogenetic protein-2 (rhBMP-2) on the healing of full-thickness defects of articular cartilage.

Articular cartilage has a limited capacity for repair. We investigated the effect of rhBMP-2 (recombinant human bone morphogenetic protein-2) on the healing of full-thickness osteochondral defects in adult New Zealand White rabbits. A single defect, three millimeters wide by three millimeters deep, was created in the trochlear groove of the right femur in eighty-nine rabbits. The defect was either left empty, filled with a plain collagen sponge, or filled with a collagen sponge impregnated with five micrograms of rhBMP-2. The animals were killed at four, eight, or twenty-four weeks, and the repair tissue was examined histologically and evaluated with use of a grading scale. The defects also were examined immunohistochemically for the presence of type-II collagen at four and eight weeks. The rate of bone repair was evaluated with fluorescent labeling of bone at two and four weeks and with use of fluorescence microscopy at eight weeks. Treatment with rhBMP-2 greatly accelerated the formation of new subchondral bone and improved the histological appearance of the overlying articular surface. At twenty-four weeks, the thickness of the repair cartilage was 70 per cent that of the normal adjacent cartilage and a new tidemark usually had formed between the repair cartilage and the underlying subchondral bone. The average total scores on the histological grading scale were significantly better (p < 0.01) for the defects treated with rhBMP-2 than for the untreated defects (those left empty or filled with a plain collagen sponge) at all time-points. Immunostaining with an antibody against type-II collagen showed the diffuse presence of this cartilage-specific collagen throughout the repair cartilage in the treated defects. The untreated defects demonstrated minimum staining with this antibody.

Animals↗
PubMed2006

Fatty acid transport in articular cartilage.

Articular cartilage extracellular matrix imposes a significant transport barrier to albumin, the principal carrier of fatty acids. It has not been previously established whether it also influences the transport of fatty acids important for chondrocyte metabolism. Albumin was labelled with rhodamine-maleimide and bound to NBD-labelled lauric acid. Plugs of fresh equine metacarpal-phalangeal cartilage and subchondral bone were incubated with the complex at 4 degrees C for 2-160 h. The fluorophore distribution was quantified using quantitative microscopy in histological sections. The fluorescence intensity of both fluorophores fell steeply over 300 microm below the articular surface and remained relatively uniform through the mid zone but the ratio of lauric acid to albumin was higher than in the incubation medium. The effective diffusivity of lauric acid in the mid zone was (2.2+/-0.7) x 10(-12) m2 s(-1) (n = 33), higher than that of the carrier albumin, suggesting dissociation in the surface layer. Lauric acid accumulated reversibly at the tidemark.

Animals↗
PubMed1999

Articular cartilage cells immortalized by a temperature sensitive mutant of SV40 large T antigen survive and form cartilage tissue in articular cartilage environment.

A chondrogenic cell line, TC6, was established by using cells derived from articular cartilage of transgenic mice harboring a temperature-sensitive mutant simian virus (SV) 40 large T-antigen gene. TC6 cells express genes encoding proteins related to cartilage phenotypes such as type II collagen. To examine the in vivo behavior of the TC6 cells, these cells were implanted into cavity-shaped full-thickness defects made in the articular cartilage of the central part of the patellar grooves of mouse femora. One week after implantation, the morphology of the cells was still fibroblastic but these cells were just about to start to form a cartilage-like matrix. By 6 weeks after implantation, the cells had produced abundant cartilaginous matrix and their morphology became closer to that of authentic chondrocytes. This was in sharp contrast to the fibroblastic morphology of these cells in an in vitro environment even after long-term culture. These observations indicate that a cartilage-matrix environment provides a scaffold for the TC6 cells to form cartilage tissues. Our data show that the genetically engineered chondrocytic cell line, TC6, can form a cartilage-like matrix in vivo.

Animals↗
PubMed1999

Expression of ADAMTS homologues in articular cartilage.

Articular chondrocytes possess the capacity to express a number of ADAM (A Disintegrin And Metalloproteinase) family members, thereby implicating a role for such proteins in the turnover of cartilage extracellular matrix molecules. Recently, the sequence for the human orthologue of an "aggrecanase" isolated from bovine nasal cartilage has been elucidated, and the recombinant protein product shown to be capable of cleaving aggrecan specifically at the relevant peptide bonds which are hydrolyzed in situ during cartilage degradation. The sequence for the human "aggrecanase" exhibits homology with that of murine ADAMTS-1, an ADAM with thrombospondin type I motifs. In the present study we have identified additional ADAMTS homologues and have examined their mRNA expression profiles in freshly excised human articular cartilage and in human cartilage explant cultures stimulated with IL-1, TNF-alpha, or retinoic acid, agents which enhance "aggrecanase" activity in vitro. Significantly, cartilage exposed to retinoic acid showed a marked increase in the release of "aggrecanase"-generated aggrecan catabolites with no concomitant increase in mRNA levels for any of the ADAMTS homologues investigated. These findings indicate that enhanced "aggrecanase" activity, which may be attributed to known ADAMTS homologues, may be predominantly regulated by post-transcriptional mechanism(s), and may raise the possiblility for the existence of other as yet unidentified "aggrecanase(s)."

Aged↗
PubMed1997

The role of mandibular condylar cartilage in articular cartilage repair.

The articular hyaline cartilage of synovial joints has a very limited capacity for repair after injury. In contrast, the mandibular condylar cartilage of the temporomandibular joint possesses as intrinsic potential for regeneration. This study aimed to test the hypothesis that cultured allografts of mandibular condylar cartilage could be used to promote biological repair of injured orthotopic joint surfaces. Using a primate animal model, cultures of mandibular condylar cartilage cells were grafted into surgically created defects in a recipient hyaline cartilage joint surface. Articular wound healing was assessed macroscopically and histologically over a postoperative period of 52 weeks. Mandibular condylar cartilage cells scheduled for allogenous transplantation were initially characterised in vitro. Expansion of primary colonies in organ culture provided the allogenic cellular material for in vivo grafting. Grafting of osteochondral articular wounds with 5-week cultures of mandibular cartilage cells led to wound regeneration with complete reconstitution of articular surface continuity by 52 weeks. There was novel synthesis of cartilage collagens and sulphated glycosaminoglycans within the repair tissue and no evidence of immunological rejection. Healing of grafted defects was thought to occur by a combination of donor cell proliferation and ingress of host mesenchymal cells. In contrast, grafted control wounds underwent largely fibrous repair with incomplete articular regeneration. In conclusion, transplanted allografts of cultured mandibular condylar cartilage appeared to have the ability, in this primate model, to promote cartilaginous repair and regeneration of orthotopic articular wounds.

Animals↗
PubMed2003

Mechanical regulation of mitogen-activated protein kinase signaling in articular cartilage.

Articular chondrocytes respond to mechanical forces by alterations in gene expression, proliferative status, and metabolic functions. Little is known concerning the cell signaling systems that receive, transduce, and convey mechanical information to the chondrocyte interior. Here, we show that ex vivo cartilage compression stimulates the phosphorylation of ERK1/2, p38 MAPK, and SAPK/ERK kinase-1 (SEK1) of the JNK pathway. Mechanical compression induced a phased phosphorylation of ERK consisting of a rapid induction of ERK1/2 phosphorylation at 10 min, a rapid decay, and a sustained level of ERK2 phosphorylation that persisted for at least 24 h. Mechanical compression also induced the phosphorylation of p38 MAPK in strictly a transient fashion, with maximal phosphorylation occurring at 10 min. Mechanical compression stimulated SEK1 phosphorylation, with a maximum at the relatively delayed time point of 1 h and with a higher amplitude than ERK1/2 and p38 MAPK phosphorylation. These data demonstrate that mechanical compression alone activates MAPK signaling in intact cartilage. In addition, these data demonstrate distinct temporal patterns of MAPK signaling in response to mechanical loading and to the anabolic insulin-like growth factor-I. Finally, the data indicate that compression coactivates distinct signaling pathways that may help define the nature of mechanotransduction in cartilage.

Animals↗
PubMed2001

TGF-beta/Smad3 signals repress chondrocyte hypertrophic differentiation and are required for maintaining articular cartilage.

Endochondral ossification begins from the condensation and differentiation of mesenchymal cells into cartilage. The cartilage then goes through a program of cell proliferation, hypertrophic differentiation, calcification, apoptosis, and eventually is replaced by bone. Unlike most cartilage, articular cartilage is arrested before terminal hypertrophic differentiation. In this study, we showed that TGF-beta/Smad3 signals inhibit terminal hypertrophic differentiation of chondrocyte and are essential for maintaining articular cartilage. Mutant mice homozygous for a targeted disruption of Smad3 exon 8 (Smad3(ex8/ex8)) developed degenerative joint disease resembling human osteoarthritis, as characterized by progressive loss of articular cartilage, formation of large osteophytes, decreased production of proteoglycans, and abnormally increased number of type X collagen-expressing chondrocytes in synovial joints. Enhanced terminal differentiation of epiphyseal growth plate chondrocytes was also observed in mutant mice shortly after weaning. In an in vitro embryonic metatarsal rudiment culture system, we found that TGF-beta1 significantly inhibits chondrocyte differentiation of wild-type metatarsal rudiments. However, this inhibition is diminished in metatarsal bones isolated from Smad3(ex8/ex8) mice. These data suggest that TGF-beta/Smad3 signals are essential for repressing articular chondrocyte differentiation. Without these inhibition signals, chondrocytes break quiescent state and undergo abnormal terminal differentiation, ultimately leading to osteoarthritis.

Animals↗
PubMed1993

Collagen II from articular cartilage and annulus fibrosus. Structural and functional implication of tissue specific posttranslational modifications of collagen molecules.

Collagen II was isolated and characterized from hyaline cartilage (articular cartilage) and fibro-cartilage (annulus fibrosus). Collagen II from the latter tissue has a substantially higher degree of hydroxylation and glycosylation than that isolated from articular cartilage. The higher degree of posttranslational modification was associated with a slower electrophoretic mobility, a greater resistance to mammalian collagenase digestion and a higher thermal stability. An increase of glycosylation accelerates the initial steps in fibril formation of collagen molecules but slows down the following lateral growth. The newly formed aggregates of collagen II from annulus fibrosus consisted of fibrils with a smaller diameter.

Amino Acid Sequence↗
PubMedDate not supplied

Temperature requirements for altering the morphology of osteoarthritic and nonarthritic articular cartilage: in vitro thermal alteration of articular cartilage.

BACKGROUND: Radiofrequency and laser thermal chondroplasty procedures are performed to debride and smooth fibrillated, articular cartilage. HYPOTHESIS: Temperature requirements necessary to achieve morphological change will be lower in fibrillated arthritic cartilage as compared with nonarthritic articular cartilage. STUDY DESIGN: Controlled laboratory study. METHODS: A thermal cell-culture chamber was mounted on a stereoscopic microscope and coordinated with a custom temperature-control program. Nonarthritic and osteoarthritic articular cartilage specimens were sectioned into full-thickness slices. The articular sections were exposed to temperatures incrementally from 37 masculine C to 75 masculine C. Real-time, digital capture microscopy was used to visualize and analyze the morphological changes undergone by the articular cartilage specimens. RESULTS: Arthritic articular cartilage displayed morphological change at 56.5 +/- 1.7 masculine C. Loss of fibrillation was the initial morphological change visualized. Continued thermal exposure caused a shrinkage effect of the entire tissue section that was similar to the change seen in nonarthritic sections. Nonarthritic cartilage displayed morphological change at 60.9 +/- 1.9 masculine C. CONCLUSIONS: Consistent characteristic morphological changes were found at distinct temperatures in osteoarthritic and nonarthritic articular cartilage. CLINICAL RELEVANCE: This information begins to establish the thermal parameters required for morphological change of osteoarthritic articular cartilage.

Cartilage, Articular↗
PubMed1979

Articular cartilage preservation and storage. I. Application of tissue culture techniques to the storage of viable articular cartilage.

Articular cartilage slice explants were stored under various conditions, including freezing-thawing at various rates by using dimethyl sulfoxide (DMSO) as a cryoprotective agent, incubating in standard tissue culture medium (MEM Eagle:NCTC 135:15% fetal calf serum) in 5% CO2 and air at 4 degrees, 21 degrees, and 37 degrees C, and incubating in standard tissue culture medium containing 200 micrograms/ml alpha-tocopherol (vitamin E) at 37 degrees C after first ascertaining a dose-response curve of vitamin E. Results indicated that articular cartilage slice explants did not survive freezing or storage at 4 degrees and 21 degrees C as measured by 35S uptake. When stored at 37 degrees C in standard tissue culture in 5% CO2 and air, the slice explants remained viable for up to 60 days. The addition of alpha-tocopherol to the medium resulted in significantly less release of previously incorporated 35Sin stored cartilage slices and significantly less reduction of the amount of hexosamine present in the stored explants. alpha-Tocopherol in the medium also preserved safranin O staining. Thus, the application of tissue culture techniques to the storage of articular cartilage made it possible to preserve cartilage slice explants in a viable, biochemically "normal" state.

Animals↗
PubMed1989

Immunohistochemical detection and immunochemical analysis of type II collagen degradation in human normal, rheumatoid, and osteoarthritic articular cartilages and in explants of bovine articular cartilage cultured with interleukin 1.

Articular cartilage destruction and loss of function in arthritic diseases involves proteolytic degradation of the connective tissue matrix. We have investigated the degradation of cartilage collagen by developing immunochemical methods that permit the identification and analysis of type II collagen degradation in situ. Previously, a technique to specifically identify type II collagen degradation in situ in articular cartilage did not exist. These methods utilize a polyclonal antiserum (R181) that specifically reacts with unwound alpha-chains and CNBr-derived peptides, alpha 1(II)CB11 and alpha 1(II)CB8, of human and bovine type II collagens. The experimental approach is based on the fact that when fibrillar collagens are cleaved the helical collagen molecule unwinds, exposing hidden epitopes. Here we demonstrate the use of R181 in studying type II collagen degradation in bovine articular cartilage that has been cultured with or without IL-1 and in human normal, rheumatoid, and osteoarthritic articular cartilages. Compared to cartilages either freshly isolated or cultured without IL-1, bovine cartilage cultured with IL-1 for 3-5 d showed an increase in both pericellular and intercellular immunohistochemical staining. Extracts of these cartilages contained type II collagen alpha chains that were increased in amount after culture with IL-1 for 11 d. In addition, culture with IL-1 resulted in the appearance of alpha chain fragments of lower molecular weight. All human arthritic tissues examined showed areas of pronounced pericellular and territorial staining for collagen degradation as compared with non-diseased tissues, indicating that chondrocytes are responsible in part for this degradation as compared with non-diseased tissues. In most cases rheumatoid cartilage was stained most intensely at the articular surface and in the deep and mid-zones, whereas osteoarthritic cartilage usually stained more in the superficial and mid-zones, but less intensely. Distinct patterns of sites of collagen degradation reflect differences in collagen destruction in these diseases, suggesting possible different sources of chondrocyte activation. These experiments demonstrate the application of immunological methods to detect collagen degradation and demonstrate an increase of collagen degradation in human arthritides and in IL-1-treated viable bovine cartilage.

Animals↗
PubMed2006

A theoretical study of the distribution of insulin-like growth factor in human articular cartilage.

We present a mathematical simulation which integrates the mechanisms that are currently believed to govern the concentration of the growth factor, IGF1, in cartilage. Articular cartilage is treated as a two-layer continuum: a thin surface layer, exposed to synovial fluid, with a higher cell density, and a deeper layer with impermeable bony endplate. A system of differential equations accounts for diffusion of IGF1 from synovial fluid into, and throughout, the cartilage; IGF1 synthesis, its reactions with soluble binding protein, with cell receptors, and with immobile binding sites on the extracellular matrix. We have collected all available physiologic data relevant to the solution of these equations and used it to compute numerical solutions that yield time dependent profiles for free and complex IGF1 throughout the depth of normal cartilage. Equations for osteoarthritic cartilage were formulated as well. Numerical results indicate a time-scale of several days for IGF1 profiles to settle down after a disturbance. The number of cell receptors for IGF1 appears to be more important than their rate of internalization. There is a lower bound to the number of cell receptors and of immobile binding sites. Parameters that await experimental determination are identified.

Carrier Proteins↗
PubMed1980

[Glucosamine: its importance for the metabolism of articular cartilage. 2. Studies on articular cartilage].

In healthy individuals there exists a balance between cartilage proteoglycan synthesis and degradation. In arthrotic cartilage this metabolic balance is deteriorated in spite of a sometimes enhanced proteoglycan synthesis, since the catabolic rate exceeds the anabolic rate corresponding to the severity of the disease. The extracellular organic matrix of the cartilage is destroyed. With different experimental models it could be demonstrated, that the non steroidal anti-inflammatory drugs commonly used in the treatment of arthrosis inhibit the synthesis of mucopolysaccharides, intensify the already existing metabolic disorder, prevent a normalization of cartilage composition and thus impair the function of the cartilage. Glucosamine on the other hand increases in a dose-dependent way the ability of cartilage to synthesize both sulfated mucopolysaccharides and protein, thus restoring the catabolic-anabolic balance of the cartilage.

Animals↗