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PubMed2004

The surface of articular cartilage contains a progenitor cell population.

It is becoming increasingly apparent that articular cartilage growth is achieved by apposition from the articular surface. For such a mechanism to occur, a population of stem/progenitor cells must reside within the articular cartilage to provide transit amplifying progeny for growth. Here, we report on the isolation of an articular cartilage progenitor cell from the surface zone of articular cartilage using differential adhesion to fibronectin. This population of cells exhibits high affinity for fibronectin, possesses a high colony-forming efficiency and expresses the cell fate selector gene Notch 1. Inhibition of Notch signalling abolishes colony forming ability whilst activated Notch rescues this inhibition. The progenitor population also exhibits phenotypic plasticity in its differentiation pathway in an embryonic chick tracking system, such that chondroprogenitors can engraft into a variety of connective tissue types including bone, tendon and perimysium. The identification of a chondrocyte subpopulation with progenitor-like characteristics will allow for advances in our understanding of both cartilage growth and maintenance as well as provide novel solutions to articular cartilage repair.

Amyloid Precursor Protein Secretases↗

PubMed2006

Basic fibroblast growth factor: an extracellular mechanotransducer in articular cartilage?

Mechanical stimuli are important signals in articular cartilage, but what mediates them is unknown. We have shown that extracellular-signal-regulated kinase was activated on cutting and loading articular cartilage, and deduced that this was due to the release of bFGF (basic fibroblast growth factor) from the tissue. bFGF was shown to be extracellular, and by immunohistochemistry, was present in the pericellular matrix of articular chondrocytes attached to the heparan sulphate proteoglycan perlecan. We propose a novel mechanotransduction model, whereby pericellular bFGF, a short distance from the cell surface, becomes available to the cell surface tyrosine kinase receptors when articular cartilage is loaded.

Animals↗

PubMed1988

Quantification and characterization of hyaluronic acid in different topographical areas of normal articular cartilage from dogs.

Normal articular cartilage from adult dogs was analyzed for hyaluronate, hexuronate and hydroxyproline. The low weight-bearing areas of both tibial plateaus and femoral condyles displayed a higher collagen content and a lower proteoglycan content than the regions of maximum contact. Both superficial and deeper layers contained more hyaluronate in areas of maximum than of minimum contact. On the other hand, in each weight-bearing area, the proportion of hyaluronate relative to total proteoglycan content appeared twice as much in the superficial layers than in their corresponding underlying zones. The molecular weight and in vitro aggregating capacity of the hyaluronate molecules were however quite similar in the different topographical areas of the articular tissue.

Animals↗

PubMed2006

Articular cartilage: injury pathways and treatment options.

Articular cartilage injury and degeneration is a frequent occurrence in synovial joints. Treatment of these articular cartilage lesions are a challenge because this tissue is incapable of quality repair and/or regeneration to its native state. Nonoperative treatments endeavor to control symptoms, and include anti-inflammatory medication, viscosupplementation, bracing, orthotics, and activity modification. Techniques to stimulate the intrinsic repair (fibrocartilage) process include drilling, abrasion, and microfracture of the subchondral bone. Currently, the clinical biologic approaches to treat cartilage defects include autologous chondrocyte implantation, periosteal transfer, and osteochondral autograft or allograft transplantation. Newer strategies employing tissue engineering being studied involve the use of combinations of progenitor cells, bioactive factors, and matrices, and the use of focal synthetic devices. Many new and innovative treatments are being explored in this exciting field. However, there is a paucity of prospective, randomized controlled clinical trials that have compared the various techniques, treatment options, indications and efficacy.

Arthroplasty, Replacement↗

PubMed1989

Articular cartilage and intervertebral disc proteoglycans differ in structure: an electron microscopic study.

Articular cartilage and the intervertebral disc tissues have different material and biological properties and different patterns of aging and degeneration. To determine if the proteoglycans of these tissues differ in structure, we used the electron microscopic monolayer technique to compare baboon articular cartilage proteoglycans with baboon annulus fibrosus, transition zone, and nucleus pulposus proteoglycans. Intervertebral disc and articular cartilage proteoglycans differed significantly. Articular cartilage contained large proteoglycan aggregates formed from hyaluronic acid central filaments, multiple monomers, and large nonaggregated monomers. These molecules were identical to those of nasal cartilage, growth plate cartilage, chondrosarcomas, or menisci. In contrast, the intervertebral disc tissues contained only nonaggregated proteoglycan monomers and clusters of monomers without apparent central filaments. Intervertebral disc nonaggregated monomers were shorter and more variable in length than those from articular cartilage, and nucleus pulposus nonaggregated monomers were even shorter and more variable in length than transition zone and annulus fibrosus monomers. These observations suggest that significant differences in proteoglycan metabolism exist between articular cartilage and intervertebral disc.

Animals↗

PubMed2002

Magnetic resonance imaging for articular cartilage: cartilage-bone mismatch.

The authors studied the articular cartilage surface anatomy of the patellofemoral joint in the sagittal and axial planes. On sagittal and axial cryosections and on multiplanar MR arthrotomograms, biplanar contour differences of the retropatellar articular cartilage surfaces and curvatures with respect to the corresponding subchondral osseous contours of the patellofemoral joint were determined. On multiplanar arthrotomograms, the surface geometry of the articular cartilage of the patella and of the femoral trochlea were compared.

Adult↗

PubMed2006

Regional gene therapy for full-thickness articular cartilage lesions using naked DNA with a collagen matrix.

A novel gene therapy approach for treating damaged cartilage is proposed that involves placing endotoxin-free cDNA containing the gene for bone morphogenetic protein-2 (BMP-2) in type I collagen sponges and then transferring the naked plasmid DNA construct to the injury site. A full-thickness cartilaginous defect in rabbits implanted with plasmid containing a marker gene (beta-galactosidase) showed expressed protein as detected by immunostaining. At 1 week postimplantation, mesenchymal cells subjacent to the defect had incorporated the implanted naked plasmid DNA and, once transfected, served as local bioreactors, transiently producing the gene product. Plasmids containing the gene for BMP-2 implanted in collagen sponges in cartilage lesions stimulated hyalinelike articular cartilage repair at 12 weeks postimplantation, nearly equivalent in quality to that induced by collagen sponges with recombinant BMP-2 protein. Our approach circumvents the risks of inflammation and immunogenic response associated with the use of viral vectors. Naked plasmid DNA as a vehicle for transferring therapeutic genes has been shown to be effective in a therapeutic model within rabbit articular cartilage and appears to be safe and cost effective.

Animals↗

PubMed1992

Evaluation of intra-articularly administered sodium monoiodoacetate-induced chemical injury to articular cartilage of horses.

Three doses of sodium monoiodoacetate (MIA) were used to induce degenerative changes in articular cartilage in middle carpal joints of horses. Twelve young (2- to 5-year-old) horses, free of lameness, were randomly allotted to 3 groups. One middle carpal joint of each horse was injected with 0.9% NaCl solution (control joint). The contralateral middle carpal joint was injected with 0.09 mg of MIA/kg of body weight (group 1); 0.12 mg/kg (group 2); or 0.16 mg/kg (group 3). After MIA administration, horses were allowed ad libitum exercise in a 2-acre paddock for 12 weeks. At the end of the study, gross and microscopic tissue changes were evaluated and biochemical analyses of articular cartilage were done. Grossly, diffuse partial-thickness articular cartilage lesions were observed in group-2 (n = 2) and group-3 (n = 4) horses, but not in group-1 horses. Articular cartilage uronic acid content was significantly (P less than 0.03) decreased in all MIA-injected joints, compared with controls. Articular cartilage matrix staining with safranin-O was decreased in 3 of 4 MIA-injected joints of group-1 horses and in all MIA-injected joints of group-2 and group-3 horses, compared with controls (P less than 0.06). Microscopic degenerative changes in articular cartilage were not significantly different between MIA-injected and control joints in group-1 horses, but were increased (P less than 0.06) in all MIA-injected joints of group-2 and group-3 horses, compared with controls. Qualitatively, decreased matrix staining and degenerative changes were more severe in group-3 horses. On the basis of articular cartilage gross and microscopic changes, as well as biochemical changes, 0.12 mg of MIA/kg injected intra-articularly was determined to induce moderate degrees of articular cartilage degeneration. This model of chemically induced articular cartilage injury could be useful for evaluating treatment effects of anti-arthritic drugs in horses.

Animals↗

PubMed2003

Homeostasis of the extracellular matrix of normal and osteoarthritic human articular cartilage chondrocytes in vitro.

OBJECTIVE: In normal articular cartilage cells, the IGFRI/insulin-like growth factor 1 (IGF-1) autocrine pathway was shown to overrule the catabolic effects of the IL-1/IL-1RI pathway by up-regulation of the IL-1RII decoy receptor. The activity of the IGF-1/IGFR1 and IL-1/IL-1R pathways, and of the IL-1RII control mechanism in the synthesis and turnover of the extracellular matrix (ECM) by chondrocytes from normal and osteoarthritic (OA) articular cartilage was compared in order to identify possible therapeutic targets of this disease. METHODS: Phenotypically stable human articular cartilage cells were obtained from normal and OA cartilage of the same knee showing focal OA. The cells were cultured in alginate beads over 1 week to re-establish the intracellular cytokine and growth factors, to reexpress the respective plasma membrane receptors and to reach equilibrium in accumulated cell-associated matrix (CAM) compounds. Following liberation of the cells from the alginate beads, the levels of cell-associated matrix (CAM) aggrecan, type II collagen and fibronectin, of intracellular IGF-1, IL-1alpha and beta and of their respective plasma membrane-bound receptors, IGFR1, IL-1RI and the decoy receptor IL-1RII, were assayed using flow cytometry. RESULTS: Coordinated production and accumulation of CAM aggrecan and type II collagen under the effect of the IGFR1/IGF-1 autocrine pathway-as documented for chondrocytes from healthy controls-was absent when the chondrocytes had been obtained from OA joints. When compared with cells obtained from normal tissues, chondrocytes from fibrillated OA cartilage expressed significantly higher intracellular IGF-1 levels and plasma membrane-bound IGFR1. At the same time, significantly higher intracellular IL-1alpha and beta levels and upregulated plasma membrane-bound IL-1RI were observed. Plasma membrane-bound IL-1RII decoy receptor was downregulated in OA chondrocytes. The levels of CAM aggrecan, type II collagen and fibronectin were significantly reduced in the chondrocytes obtained from pathological tissue. CONCLUSION: Paired analysis of normal and OA chondrocytes from the same knee joint has shown an enhanced capacity of chondrocytes from OA cartilage to produce ECM macromolecules. However, the same cells have increased catabolic signalling pathways. As a consequence of this increased IL-1 activity and the reduced amounts of IL-1RII decoy receptor, less of the produced ECM macromolecules may persist in the CAM of the OA chondrocytes.

Adult↗

PubMed1997

The effect of strenuous versus moderate exercise on the metabolism of proteoglycans in articular cartilage from different weight-bearing regions of the equine third carpal bone.

Articular cartilage degeneration in the middle carpal joint is a common problem in racing horses. This study evaluated the effect of exercise on the in-vitro synthesis of the large aggregating proteoglycans (aggrecan) and two small proteoglycans, biglycan and decorin, in articular cartilage taken from three weight bearing regions of the third carpal bone of horses which were subjected to moderate or strenuous exercise. Twelve Standardbred horses free from clinical and radiographic disease of the middle carpal joint were subjected to an 8 week moderate exercise program. The horses were then randomly assigned to two groups: group A--continued moderate exercise and group B--strenuous exercise for 17 weeks. Horses were then rested for 16 weeks. Full-depth articular cartilage explants from the dorsal radial facet (DRF), dorsal intermediate facet (DIF) and palmar condyle (PC) of the third carpal bone were collected and cultured. Cartilage proteoglycan content and release into culture media were measured. Newly synthesized proteoglycans were labeled with 35SO4(2-) for 48 h and analyzed by size exclusion and hydrophobic chromatography, sodium dodecyl sulfate (SDS) polyacrylamide gel electrophoresis (PAGE) and autoradiography. Histologic sections of adjacent osteochondral regions were evaluated for evidence of arthritic change. No histologic abnormalities or differences in proteoglycan content were detected in any of the articular cartilage regions examined. There was however, a significant reduction (P < 0.05) in aggrecan synthesis and a concomitant increase in decorin synthesis (P < 0.05) in articular cartilage from the DRF of group B animals. There was no change in biglycan synthesis, aggrecan hydrodynamic size or ability to aggregate in any articular cartilage region. This study has demonstrated that strenuous exercise in horses can lead to a disturbance in the biosynthesis of proteoglycans in articular cartilage regions subjected to high contact stresses (DRF). These metabolic abnormalities, which persisted for 16 weeks after cessation of exercise, could have deleterious effects on the biomechanical properties of the tissue. We suggest that the observed alteration in articular cartilage metabolism in CRF cartilage of strenuously exercised horses could represent a predisposing factor for cartilage degeneration and osteoarthritis at a later stage.

Aggrecans↗

PubMed1987

Chondrons in cartilage: ultrastructural analysis of the pericellular microenvironment in adult human articular cartilages.

A combination of scanning and transmission electron microscopy was used to investigate the morphology and ultrastructure of normal human articular cartilage sampled from adult amputation specimens. This study confirms our previous observations on canine articular cartilage, which showed middle and deep layer chondrocytes surrounded by a pericellular matrix and enclosed within a pericellular capsule composed of filamentous and fine fibrillar materials. Pores in the "felt-like" organization of the capsular weave progressively decreased in size from the inner to the outer border of the capsule. Matrix vesicles were found embedded within the capsular weave and distributed throughout the territorial matrix. It is suggested that the chondrocyte, its pericellular matrix, and capsule together constitute the "chondron," a primary functional and metabolic unit of cartilage that acts hydrodynamically to protect the integrity of the chondrocyte and its pericellular microenvironment during compressive loading.

Adult↗

PubMed1978

Subchondral route for nutrition to articular cartilage in the rabbit. Measurement of diffusion with hydrogen gas in vivo.

The route of nutrients going to articular cartilage was studied by determining the diffusion of hydrogen molecules from the subchondral circulation to the articular cartilage in rabbits. In all immature animals there was diffusion of hydrogen from subchondral bone into articular cartilage, while in the older immature animals the results were variable. None of the mature animals showed any diffusion of hydrogen into articular cartilage. The rate of diffusion of hydrogen was significantly lower in the articular cartilage than in the subchondral bone in the immature animals while the concentrations of hydrogen in the articular cartilage were only fractions of those in the subchondral bone at the same instant. Histologically, the deep layers of immature cartilage are penetrated extensively by vascular buds from the ossified portion of the epiphysis, while in adults the articular cartilage is separated from subchondral vascular spaces by an end-plate of bone. Blood vessels penetrating into the basilar layer of articular cartilage in immature animals appear to play an important role in the nutrition of articular cartilage coming from the subchondral region.

Animals↗

PubMed2004

Cryoprotectant permeation through human articular cartilage.

OBJECTIVE: The cryopreservation of intact articular cartilage is constrained by minimal chondrocyte survival. It was the aim of the present study to gain an insight into the permeation kinetics of cryoprotectants through cartilage. This knowledge is essential for achieving adequate tissue permeation prior to cooling. DESIGN: The diffusion coefficients and penetration rates through human articular cartilage of dimethyl sulfoxide (Me(2)SO) and glycerol at different temperatures (4 degrees C, 17 degrees C, 27 degrees C and 37 degrees C) and at two concentrations [10% (v/v) and absolute state] were measured using diffusion nuclear magnetic imaging. Deuterated water (D(2)O) was used as a control substance. RESULTS: Glycerol penetrated faster than Me(2)SO at all temperatures and at rates that were comparable to those for D(2)O. The penetration rate of each agent increased with increasing temperature. The diffusion coefficients for glycerol and Me(2)SO increased with increasing temperature and decreased at the higher concentration, but the differences between each agent were not significant. CONCLUSIONS: The classical cryopreservation protocols expose cartilage samples to Me(2)SO at a too low temperature and/or for an insufficient time period for optimal cell survival. When considering the penetration rate, glycerol appears to be a more efficient cryoprotective agent than Me(2)SO. The present study demonstrates the power of nuclear magnetic resonance technology to elucidate key physiological factors in cryobiology.

Adult↗

PubMed2006

The effects of exercise on human articular cartilage.

The effects of exercise on articular hyaline articular cartilage have traditionally been examined in animal models, but until recently little information has been available on human cartilage. Magnetic resonance imaging now permits cartilage morphology and composition to be analysed quantitatively in vivo. This review briefly describes the methodological background of quantitative cartilage imaging and summarizes work on short-term (deformational behaviour) and long-term (functional adaptation) effects of exercise on human articular cartilage. Current findings suggest that human cartilage deforms very little in vivo during physiological activities and recovers from deformation within 90 min after loading. Whereas cartilage deformation appears to become less with increasing age, sex and physical training status do not seem to affect in vivo deformational behaviour. There is now good evidence that cartilage undergoes some type of atrophy (thinning) under reduced loading conditions, such as with postoperative immobilization and paraplegia. However, increased loading (as encountered by elite athletes) does not appear to be associated with increased average cartilage thickness. Findings in twins, however, suggest a strong genetic contribution to cartilage morphology. Potential reasons for the inability of cartilage to adapt to mechanical stimuli include a lack of evolutionary pressure and a decoupling of mechanical competence and tissue mass.

Adaptation, Physiological↗

PubMed1999

Articular cartilage biomechanics: theoretical models, material properties, and biosynthetic response.

Articular cartilage has unique material properties that enable the cartilage to perform its physiological functions over a lifetime and under a wide range of loading conditions. Numerous studies have investigated the relationship between cartilage properties and composition/structure. For cartilage transplantation and regeneration, it is necessary to know how cartilage maintains its functionality and how cartilage responds to the ever-changing mechanical environment. In this review, we discuss theoretical and experimental studies on the behavior of articular cartilage to load. In the first part, the composition and structure of articular cartilage is presented. In the second part, theoretical models of the mechanical behavior of cartilage, experimental methods for the determination of cartilage properties, and material properties for normal, pathologic, and repair cartilage are summarized. In the third part, the relationship between mechanical loading of the cells and their corresponding biological responses are discussed. The goal for treating joint degeneration in the future lies in cartilage regeneration rather than prosthetic replacement. In order to achieve this goal, it has to be understood how structure and function, metabolic and biochemical properties, and biomechanical performance of articular cartilage can be restored.

Animals↗

PubMed1990

Subpopulations of chondrocytes from different zones of pig articular cartilage. Isolation, growth and proteoglycan synthesis in culture.

Articular cartilage varies in ultrastructure and composition with distance from the articular surface. We have cultured chondrocytes from different zones of pig articular cartilage and investigated whether there are intrinsic differences in their behaviour that might account for the variation observed in intact tissue. On isolation, cells from the upper third of the cartilage were smaller than those of the lower third, but this difference was not maintained in culture. Upper zone cells attached and spread more slowly than lower zone cells; morphological differences between the two populations could be seen for several weeks. The growth rates of the two populations were similar, but upper zone cells reached a lower confluent density. Levels of protein synthesis were similar for both populations, but upper zone cells deposited less proteoglycan in the cell layer. On isolation, the percentage of upper zone cells that stained positive with MZ15, a monoclonal antibody to keratan sulphate, was smaller than the percentage of lower zone cells, but this difference was lost after several days in culture. Nevertheless, the keratan sulphate content of proteoglycan synthesised by lower zone chondrocytes at high density was greater than of that synthesised by upper zone cells. The proportion of nonaggregating proteoglycan was greater in upper than lower zone cartilage and this difference was also observed in long-term cultures. proteoglycans were further characterised by composite and polyacrylamide gel electrophoresis and by immunoblotting; differences detected in cartilage extracts were not, however, maintained in culture; instead, the small proteoglycans synthesised by both upper and lower zone cells varied with plating density. Finally, alkaline phosphatase, a marker of hypertrophic, calcifying cartilage, was only expressed in lower zone cultures. We conclude that some of the observed heterogeneity of articular cartilage reflects intrinsic differences between the cells of different zones, whereas some may reflect the response of chondrocytes to different environmental conditions.

Alkaline Phosphatase↗

PubMed1998

Isolation and differential secretion of metalloproteinase by superficial chondrocytes in articular cartilage.

Chondrocytes from superficial layers of articular cartilage have distinct phenotypic properties which are different from those of cells obtained from the deeper areas. We describe a method that isolates highly purified articular cartilage chondrocytes from the superficial layers. When the superficial cells are stimulated in vitro with a source of cytokines, they secrete greater amounts of metalloproteinase compared to chondrocytes obtained from a deeper area.

Animals↗

PubMed1992

Localized deposition of amyloid in articular cartilage.

The frequency, nature and tissue distribution of localized amyloid deposits in articular cartilage of young and elderly patients, with and without evidence of arthritic disease, was determined. Localized amyloid deposits in articular cartilage were not found in young patients with osteoarthritis of the hip or chondromalacia/osteoarthritis of the patella. However, in elderly patients with osteoarthritis of the hip, amyloid deposits were commonly found, although at no greater frequency than in elderly patients with no evidence of arthritis. Amyloid deposits were commonly present (in 95% of cases) in osteoarthritis of the knee joint and in the articular cartilage of all joints containing pyrophosphate deposits. Similar deposits of amyloid were also found in the articular cartilage of 40-45% of rheumatoid joints. These findings indicate that localized amyloid deposits in the articular cartilage are largely age-related and not due to specific pathological alterations affecting articular cartilage.

Adolescent↗