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PubMed2003

Changes in the antiangiogenic properties of articular cartilage in osteoarthritis.

Avascularity is important for the unique biomechanical properties of articular cartilage, and normal cartilage actively repels vascular invasion. This study investigated whether the antiangiogenic properties changed in the presence of osteoarthritis (OA) by culturing explants of human articular cartilage on the chorioallantoic membrane (CAM) of chick embryos and investigating the incidence of vascular invasion and the effects of exogenous vascular endothelial growth factor (VEGF) and matrix metalloproteinase-9 (MMP-9). The results were compared with those of non-OA cartilage obtained after femoral neck fractures. Altogether, 72% of OA samples but only 5% of non-OA samples were invaded by the CAM, indicating that changes in the antiangiogenic properties represented a fundamental difference between control and OA cartilage. Exogenous VEGF or MMP-9 increased the frequency of invasion to 70%-100%. Invasion most frequently occurred into cartilage matrix from which proteoglycans had been lost, the latter being detectable by sirius red staining of cartilage collagen. VEGF was synthesized by chondrocytes in proportion to the severity of degradation and might exacerbate the loss of resistance to invasion. These results indicate that loss of resistance to vascular invasion distinguishes OA cartilage from normal articular cartilage, which may be important in the pathogenesis of OA.

Aged↗
PubMed1999

New developments in the pathogenesis of articular cartilage calcification.

Articular cartilage, unlike growth plate cartilage, is specialized to not undergo matrix calcification. However, articular cartilage mineralization, in the form of CPPD (chondrocalcinosis) and hydroxyapatite crystals, frequently accompanies and complicates osteoarthritis and aging. Recent work has demonstrated that certain features of growth cartilage development and mineralization are shared in degenerative cartilage. These include chondrocyte proliferation, hypertrophy and increased apoptosis. Moreover, parathyroid hormone related protein (PTHrP), one of the central mediators of endochondral development, is abundant in osteoarthritic cartilage. Cartilage PPi elaboration and cytosolic transglutaminase activity are markedly increased with aging. Only recently have the molecular identities been defined for the chondrocyte inorganic pyrophosphate (PPi)-generating isozymes of the phosphodiesterase nucleotide pyrophosphatase (PDNP) family (including PC-1 and B10), and for transglutaminase in articular cartilage. This review focuses on the evolving understanding of the potential roles, in articular cartilage calcification, of PTHrP, PDNP family enzymes, PPi metabolism, and transglutaminase activity.

Age Factors↗
PubMed1991

Effect of insulin on the altered production of proteoglycans in rib cartilage of experimentally diabetic rats.

Costal cartilage from experimentally diabetic rats, labeled in vivo or in vitro with [35S]sulfate, was shown to incorporate less label into proteoglycans than cartilage from nondiabetic rats. Analyses of guanidine HCl cartilage extracts by gel chromatography on Sepharose CL-2B showed two major peaks at Kav approximately 0.4 and 0.8 (peaks I and II, respectively). Cartilage extracts from the diabetic rats contained predominantly peak II proteoglycans, while 60 and 55%, respectively, of the total 35S-labeled proteoglycans extracted from control cartilage labeled in vivo and in vitro with [35S]sulfate were present in peak I. After insulin treatment of the diabetic rats, the relative amount of peak I 35S-labeled proteoglycans synthesized in vivo was increased to 70%. The overall in vivo incorporation of [35S]sulfate into proteoglycans was also stimulated in diabetic rats treated with insulin to levels above those found for control rats. Thus, diabetes-induced changes in the biosynthesis of rat costal cartilage proteoglycans may be alleviated by normalization of the diabetic state by insulin treatment. However, addition of insulin (10(-5)-10(-9) M) to the culture medium did not affect the amount of 35S-labeled proteoglycans synthesized in vitro or the relative amounts of peak I proteoglycans produced by control or diabetic cartilage, suggesting that insulin does not have a direct effect on proteoglycan production. Moreover, no decrease in the amount of 35S-labeled proteoglycans produced was found when glucose at high concentrations was present in the culture medium. However, the presence of rat serum resulted in an increase in the amount of 35S-labeled proteoglycans produced by both control and diabetic cartilage, demonstrating that the cartilage explants were metabolically responsive to stimulatory factors.

Animals↗
PubMed1975

Comparison of proteoglycans from bovine articular cartilage.

Four bovine articular cartilages have been compared with regard to the chemical composition of the whole cartilages, the amount of proteoglycan selectively extracted with 3 M MGCl2 or with 3 M guanidine-HCl, and the compositions and physical properties of the isolated proteoglycans. The whole cartilages differ but slightly in composition. Occipital condylar cartilage, a thin cartilage from the smallest joint, contains 4% more collagen and proportionately less proteoglycan than proximal humeral, the thickest cartilage from the largest joint. Each cartilage contains a pool of proteoglycan that resists extraction with 3 M MgCl2 but is extracted with 3 M guanidine-HCl. The proteoglycan extracted from each cartilage with 3 M guanidine-HCl contains a high molecular weight proteoglycan-collagen complex demonstrated by analytical ultracentrifugation and by the turbidity of its visible and ultra-violet spectra. The four cartilages appear to differ most remarkably in the fraction of total proteoglycan extracted from each as proteoglycan-collagen complex.

Animals↗
PubMed1984

Appearance of distinct types of proteoglycan in a well-defined temporal and spatial pattern during early cartilage formation in the chick limb.

Our recent studies have shown that chick embryo epiphyseal cartilage synthesizes three distinct species of proteoglycan (PG-H, PG-Lb, and PG-Lt) which are analogous in having glycosaminoglycan side chains of the chondroitin (dermatan) sulfate type but different from one another in regard to the structure of core protein. In the present report, the expression of PG-H and PG-Lb has been studied in developing chick hind limbs (stages 19-33), using antibodies specific for these substances in indirect immunofluorescence. At the onset of cartilage morphogenesis (stage 24), PG-H became recognizable in the cartilage primordia, whereas a parallel section stained for PG-Lb showed no reaction. The first evidence of PG-Lb appearance was seen in a stage 28 cartilage (e.g., tibia) in which the cells in the middiaphysis became elongated in a direction perpendicular to the long axis of the cartilage. The PG-Lb fluorescence was confined to the zone of these flattened, disc-like cells, whereas the fluorescence for PG-H was uniformly distributed throughout the cartilage. With further development of cartilage (stage 29 approximately), the zone of flattened cells spread proximally and distally, and simultaneously large hypertrophied cells appeared at the diaphyseal region. During these zonal changes of cell morphology, the PG-Lb fluorescence remained restricted to the zone of flattened cells. Parallel sections stained for PG-H, in contrast, showed an evenly distributed pattern of the PG-H fluorescence throughout the cartilage. The results indicate that the appearance of PG-Lb is closely associated with the zonal changes of cell shape and orientation along the proximal-distal axis of the developing limb cartilage, and further suggest that the flattened chondrocytes in this particular zone have undergone additional changes in gene expression to form an extracellular matrix of still another chemical property.

Animals↗
PubMed1988

Temporal and spatial analysis of cartilage proteoglycan core protein gene expression during limb development by in situ hybridization.

As limb mesenchymal cells differentiate into chondrocytes they initiate the synthesis of a cartilage-specific sulfated proteoglycan, cartilage-characteristic type II collagen, and other cartilage-specific proteins. In the present study, in situ hybridization with a 32P-labeled cloned cDNA probe complementary to mRNA encoding the core protein of cartilage proteoglycan has been used to visualize and localize the accumulation of cartilage proteoglycan core protein mRNA sequences during development of the chick limb bud in vivo. When the probe was hybridized to sections through 7-day (stage 32) limbs, an intense hybridization signal was observed over the well-differentiated cartilage rudiments of the limb, while no signal above background was observed over nonchondrogenic tissues including muscle, loose connective tissue, and epidermis. At early stages of limb development, an accumulation of silver grains representing hybridizable core protein mRNA first became detectable in the proximal central core of the limb where the prechondrogenic condensation of mesenchymal cells that characterizes the onset of cartilage differentiation was occurring. In fact, the pattern of silver grain accumulation closely followed the pattern of mesenchymal cell condensation, and no hybridizable core protein mRNA sequences were detectable in the limb bud prior to condensation. Cartilage-characteristic type II collagen mRNA was colocalized with core protein mRNA in the condensing central core of the limb suggesting that the genes for these two major constituents of cartilage matrix are coordinately regulated at the onset of chondrogenesis. Furthermore, the appearance of hybridizable core protein mRNA was closely followed by the appearance of the protein for which it codes as detected by immunohistochemical staining with monospecific antibody. These observations support the hypothesis that at the initial stages of limb chondrogenesis core protein gene expression is controlled primarily at the transcriptional level.

Aggrecans↗
PubMed1989

Biphasic indentation of articular cartilage--II. A numerical algorithm and an experimental study.

Part I (Mak et al., 1987, J. Biomechanics 20, 703-714) presented the theoretical solutions for the biphasic indentation of articular cartilage under creep and stress-relaxation conditions. In this study, using the creep solution, we developed an efficient numerical algorithm to compute all three material coefficients of cartilage in situ on the joint surface from the indentation creep experiment. With this method we determined the average values of the aggregate modulus. Poisson's ratio and permeability for young bovine femoral condylar cartilage in situ to be HA = 0.90 MPa, vs = 0.39 and k = 0.44 x 10(-15) m4/Ns respectively, and those for patellar groove cartilage to be HA = 0.47 MPa, vs = 0.24, k = 1.42 x 10(-15) m4/Ns. One surprising finding from this study is that the in situ Poisson's ratio of cartilage (0.13-0.45) may be much less than those determined from measurements performed on excised osteochondral plugs (0.40-0.49) reported in the literature. We also found the permeability of patellar groove cartilage to be several times higher than femoral condyle cartilage. These findings may have important implications on understanding the functional behavior of cartilage in situ and on methods used to determine the elastic moduli of cartilage using the indentation experiments.

Algorithms↗
PubMed1995

Dynamic behavior of a biphasic cartilage model under cyclic compressive loading.

It is well known that dynamic mechanical loads can stimulate the biosynthetic activity of articular cartilage. Studying the mechanical environment of chondrocytes under dynamic loading conditions can help to explain this mechano-biological phenomenon in articular cartilage. In this study, the linear biphasic theory was used to examine the dynamic mechanical behavior of articular cartilage under a cyclic compressive force. We first studied the dynamic confined compression of a cartilage disk as a simplified one-dimensional model and then investigated the role of the relatively impermeable subchondral bone structure on the dynamic behavior of the cartilage extracellular matrix (ECM). Under an assumption of articular cartilage as a biphasic composite structure of a porous elastic solid matrix and interstitial fluid, the porous ECM of the articular cartilage was repeatedly compressed and expanded during the loading-unloading phases of the cyclic compressive force. One interesting finding of this study was the oscillating positive (supra-ambient)-negative (sub-ambient) hydrostatic pressure within the cartilage ECM under cyclic compressive loading. The pattern of the dynamic behavior of the cartilage ECM strongly depended on the loading frequency and the primary diffusion characteristic time, tau d. This finding is consistent with those of previous studies (Guilak et al., 1990 Adv Biomech. ASME, 225-228; Mow et al., 1990, Biomechanics of Diarthrodial Joints, pp. 215-260.

Algorithms↗
PubMed1994

Ageing increases growth factor-induced inorganic pyrophosphate elaboration by articular cartilage.

Advanced age is the most common risk factor for the development of calcium pyrophosphate dihydrate (CPPD) crystal-associated arthritis. However, the link between ageing and CPPD crystal formation in cartilage remains unexplained. In CPPD deposition disease, excess extracellular inorganic pyrophosphate (ePPi), generated by articular chondrocytes, accumulates in affected joints and contributes to CPPD crystallogenesis. Transforming growth factor beta 1 (TGF beta 1) is the first known physiologic stimulant of ePPi elaboration by adult porcine and human cartilage. We hypothesized that sensitivity of articular cartilage to the ePPi-stimulatory effects of TGF beta 1 may increase with ageing. Accordingly, we compared the effects of TGF beta 1 on cartilage ePPi elaboration from juvenile, young adult, and old adult pigs. Cartilage organ cultures from old animals increased ePPi elaboration in response to TGF beta 1 to a greater extent than did cartilage from juvenile and young adult animals. Similar results were seen in chondrocyte monolayers. Concurrent exposure to epidermal growth factor (EGF) augmented, but was not necessary for TGF beta 1-induced ePPi elaboration by adult cartilage. In contrast, in juvenile cartilage, concurrent exposure to EGF was required to permit TGF beta 1-induced ePPi elaboration. Thus, increased cartilage responsiveness to the ePPi-stimulatory effects of TGF beta 1 occurs with ageing, and may explain the link between advanced age and CPPD deposition disease.

Aging↗
PubMed1989

Cartilage resorption and endochondral bone formation during the development of long bones in chick embryos.

Cartilage resorption during long bone development in the chick embryo varies in several crucial aspects from that in mammals. Cartilage does not calcify prior to resorption, the pattern of vascular tunnelling is not as regular as that in mammals and no distinct growth plate or secondary ossification centre is apparent. Primary cartilage resorption is preceded by diffusion of substances which produce a change in the cartilage matrix and necrosis of adjacent chondrocytes. Mononuclear phagocytes resorb the bulk of uncalcified cartilage, but resorption is slowed down by the formation of an osteoid band along the walls of the marrow tunnels. This prevents resorbing cells from gaining access to the cartilage matrix. If this osteoid band is in alignment with the trabecular structure, it may contribute to structural bone. In some areas chondrocytes transform into, or are replaced by, bone-producing cells and osteoid is observed within the chondrocyte lacunae. Some calcification of cartilage is observed after 16 days in ovo, but this is independent of cartilage resorption. Remnants of calcified cartilage frequently persist in the marrow cavity and multinucleated chondroclasts are required to resorb these remnants.

Acid Phosphatase↗
PubMed1994

Temporomandibular joint disc replacement made by tissue-engineered growth of cartilage.

OBJECTIVE: To test the effectiveness of the new technique of tissue-engineered growth of cartilage, temporomandibular joint (TMJ) disc replacements were created by seeding dissociated chondrocytes on synthetic, three-dimensional, bioresorbable polymer constructs of a predetermined anatomic shape, incubating the cell-polymer constructs in vitro, and transplanting them into test animals. MATERIALS AND METHODS: Twelve highly porous and bioresorbable cell-transplantation devices in the shape of TMJ discs were created using biodegradable polylactid and polyglycolic acid fibers. Bovine articular cartilage was dissociated into chondrocytes and the cells were allowed to attach to the three-dimensional polymer scaffolds and multiply in vitro. After 1 week, the cell-polymer constructs were implanted subcutaneously into nude mice. The neocartilage was assessed by magnetic resonance imaging (MRI) techniques, gross inspection, histology, and biomechanical and biochemical analysis after 12 weeks. RESULTS: All implants seeded with chondrocytes showed gross evidence of histologically organized hyaline cartilage. The scaffolds maintained their specific shape. They not only showed appropriate intrinsic stability during neomorphogenesis of cartilage in vitro and in vivo, but also seemed to guide the growth of cartilage. The presence of sulfated glycosaminoglycans was shown by aldehyde fuchsin alcian blue staining of the specimens. Type II collagen, considered to be indicative of cartilage formation, was found in the specimens tested. MRI showed signal characteristics similar to those of hyaline cartilage. Analysis of neocartilage force/displacement curves and aqueous phase compliance using a closed compression chamber suggested that the ability of the constructs to resist deformation was similar to that of native donor cartilage. CONCLUSION: The technology of tissue-engineered growth of cartilage on individually designed scaffolds may have many applications not only in reconstructive surgery of the TMJ, but also in craniomaxillofacial, plastic, and orthopedic surgery.

Animals↗
PubMed1982

Reduced deposition of collagen in the degenerated articular cartilage of dogs with degenerative joint disease.

Collagen metabolism in the focal degenerated cartilage from immature dogs with degenerative joint disease was compared with that in the adjacent 'normal' cartilage of the same joint surface. The deposition of collagen into the cartilage in vitro as measured by accumulation of hydroxy[14C]proline was decreased in the early and in advanced stages of cartilage degeneration. The deposition of collagen into cartilage in vivo as measured by the accumulation of hydroxy[3H]proline (intravenously injected [3H]proline) also was reduced in the degenerated cartilages of a dog with degenerative joint disease. Gel electrophoretic analysis revealed that degenerated cartilage contained less alpha 1 II collagen chains, but increased amounts of larger proteins. Degenerated cartilage contained more water, increased amounts of unidentified, non-collagenous protein, increased collagenolytic enzyme activity and fewer chondrocytes. Decreased deposition of collagen would result in collagen depletion in the foci of degenerated cartilage in joints of dogs with degenerative joint disease.

Animals↗
PubMed1986

In vitro effect of multiplication stimulating activity (MSA) on human fetal and postnatal cartilage.

Although insulin-like growth factors may have a physiological role in fetal growth, little is known of their biological action on human fetal tissues. In the present study, the action of multiplication stimulating activity (MSA) on human fetal cartilage in vitro, has been examined and compared with its effect on postnatal cartilage. Addition of MSA (10-100 ng/ml) resulted in a dose dependent increase in [3H]thymidine incorporation into fetal cartilage aged between 15 and 18 weeks of gestation. The mean response with 100 ng/ml was 143 +/- 18% (n = 10) of basal levels. The increase in [35S]sulphate incorporation was variable, the mean (131 +/- 36%, n = 5) being not significantly greater than in controls. The increase in [3H]thymidine incorporation on addition of MSA was not seen in fetal cartilage of earlier (13/14 wk) or later (19 wk) gestational age. MSA-III (a highly purified component of MSA) at 100 ng/ml increased [3H]thymidine and [35S]sulphate incorporation into cartilage from a fetus of 17 weeks to 165% and 150%, respectively, but had no effect on the incorporation of either isotope into cartilage from a fetus of 19 weeks gestation. In contrast to the mitogenic effects of MSA on fetal cartilage, the same preparation had no effect on either [3H]thymidine or [35S]sulphate incorporation into postnatal cartilage. These results may reflect developmental changes in cartilage response to insulin-like growth factors similar to those reported in human brain.

Aging↗
PubMed2004

Characteristics of tissue-engineered cartilage from human auricular chondrocytes.

This study was done to define the mechanical and histological properties of tissue-engineered cartilage (TEC) derived from human chondrocytes and to compare these findings with those of native cartilage. Chondrocytes were obtained from 10 human auricular cartilages and seeded onto a biodegradable template of polyglycolic acid and poly L-lactic acid. Each template was shaped into a 1 cm x 2 cm rectangle. The templates were implanted in athymic mice for 8 weeks. Eight human auricular cartilages were used for comparison. Mechanical analysis with a tensile testing device provided values of ultimate tensile strength (UTS), stiffness, and resilience. Statistical analysis was performed with the Student's t-test. Histological assessment was done with hematoxylin-eosin staining along with other special stains. The TEC had UTS of 2.07 MPa, stiffness of 3.7 MPa, and resilience of 0.37 J/m3. The control specimens had UTS of 2.18 MPa, stiffness of 5.11 MPa, and resilience of 0.42 J/m3. No statistical difference was found between the experimental and control groups for each of the three parameters. Histological analysis showed mature cartilage with characteristic collagen, glycosaminoglycans, and elastin in the TEC. The neo-cartilage showed slightly smaller size and more irregular distribution of chondrocytes and unique fibrous capsule formation with peripheral infiltration of fibrous tissue. This study showed that the mechanical qualities of TEC from human chondrocytes are similar to those of native auricular cartilage. It suggests that the engineered cartilage from human chondrocytes may have sufficient strength and durability for clinical uses. The histological findings revealed some differences with neo-cartilage.

Absorbable Implants↗
PubMed2005

Characterization of articular cartilage and subchondral bone changes in the rat anterior cruciate ligament transection and meniscectomized models of osteoarthritis.

Osteoarthritis (OA) is a chronic joint disease characterized by cartilage destruction, subchondral bone sclerosis, and osteophyte formation. Subchondral bone stiffness has been proposed to initiate and/or contribute to cartilage deterioration in OA. The purpose of this study was to characterize subchondral bone remodeling, cartilage damage, and osteophytosis during the disease progression in two models of surgically induced OA. Rat knee joints were subjected either to anterior cruciate ligament transection (ACLT) alone or in combination with resection of medial menisci (ACLT + MMx). Histopathological changes in the surgical joints were compared with sham at 1, 2, 4, 6, and 10 weeks post-surgery. Using a modified Mankin scoring system, we demonstrate that articular cartilage damage occurs within 2 weeks post-surgery in both surgical models. Detectable cartilage surface damage and proteoglycan loss were observed as early as 1 week post-surgery. These were followed by the increases in vascular invasion into cartilage, in loss of chondrocyte number and in cell clustering. Histomorphometric analysis revealed subchondral bone loss in both models within 2 weeks post-surgery followed by significant increases in subchondral bone volume relative to sham up to 10 weeks post-surgery. Incidence of osteophyte formation was optimally observed in ACLT joints at 10 weeks and in ACLT + MMx joints at 6 weeks post-surgery. In summary, the two surgically induced rat OA models share many characteristics seen in human and other animal models of OA, including progressive articular cartilage degradation, subchondral bone sclerosis, and osteophyte formation. Moreover, increased subchondral bone resorption is associated with early development of cartilage lesions, which precedes significant cartilage thinning and subchondral bone sclerosis. Together, these findings support a role for bone remodeling in OA pathogenesis and suggest that these rat models are suitable for evaluating bone resorption inhibitors as potential disease-modifying pharmaco-therapies.

Animals↗
PubMed2005

Formation of cartilage in congenital bicuspid aortic valves of Syrian hamsters (mesocricetus auratus).

The formation, topographical location and calcification of cartilage in congenital bicuspid aortic valves of 235 Syrian hamsters aged 0--173 days were studied by histological, histochemical and immunohistochemical techniques. In all animals the aortic valve was bicuspid; it had two leaflets, ventral and dorsal, each supported by its own aortic sinus. In 141 valves, a more or less developed raphe was located in the ventral sinus. The remaining 94 valves were devoid of any raphe. The first sign of valvular chondrogenesis was the presence of small groups of cells embedded in a type II collagen-positive extracellular matrix. These cellular groups, which appeared as early as 2 days after birth, became converted into hyaline cartilage or fibrocartilage. A considerable proportion (67%) of the valvular cartilages developed within the first 6 weeks of life. The cartilaginous tissue was capable of forming anywhere along the attachments of the valve leaflets to their supporting sinuses. However, statistical analyses substantiated the observation that the bases of the sinuses and raphes were the valvular regions particularly prone to the development of cartilage. At these sites, the cartilage was usually hyaline and often became calcified. The findings were consistent with the assumption that intense mechanical stimulation plays an important role in the formation of the valvular cartilage. Moreover, these findings supplied new evidence that in the cardiac semilunar valves of Syrian hamsters, cartilage formation does not involve the aggregation of large numbers of cells before their differentiation into chondrocytes. The valvular hyaline cartilages appear to act as competent pivots, resisting mechanical tensions generated during the cardiac cycle. Deposition of calcium in the matrix can be regarded as a reinforcement process of the cartilaginous tissue. Finally, it is hypothesized that the formation of cartilage in the aortic valves of hamsters prevents dystrophic calcification of the valve, a pathological change that causes aortic stenosis in man, especially in patients with a bicuspid aortic valve.

Age Factors↗
PubMed2004

Three-dimensional distribution of acetabular cartilage thickness in patients with hip dysplasia: a fully automated computational analysis of MR imaging.

OBJECTIVE: The aim of this study was to evaluate three-dimensional (3D) distribution of acetabular articular cartilage thickness in patients with hip dysplasia using in vivo magnetic resonance (MR) imaging, and to compare cartilage thickness distribution between normal and dysplastic hips. DESIGN: Forty-five dysplastic hips without joint space narrowing on radiographs and 13 normal hips underwent MR imaging with fat-suppressed 3D fast spoiled gradient echo (SPGR) sequence. Acetabular cartilage thickness was measured with a fully automated segmentation technique, and cartilage thickness distribution was compared between the dysplastic and normal hips on the celestial spherical coordinate system. RESULTS: Average cartilage thickness was significantly greater for the dysplastic hips than the normal hips (1.77 mm vs 1.34 mm). There was a general trend of gradient increase of cartilage thickness at the superolateral area in normal and dysplastic hips. The gradient increase of cartilage thickness was significantly greater in the dysplastic hips than the normal hips. CONCLUSIONS: Dysplastic hips have general thick cartilage distribution as well as more prominent gradient increase of thickness at the superolateral portion. The knowledge of fundamental morphological feature of dysplastic hips at a preradiologic stage may aid early detection of cartilage thinning in association with osteoarthritic progression, accurate computational biomechanical analysis in the hip joint, and planning periacetabular osteotomy with satisfactory cartilaginous congruency.

Acetabulum↗
PubMed2004

Characterization of mature vs aged rabbit articular cartilage: analysis of cell density, apoptosis-related gene expression and mechanisms controlling chondrocyte apoptosis.

OBJECTIVE: The prevalence of osteoarthritis (OA) is increased in aged individuals and a direct correlation between chondrocyte apoptosis and cartilage degradation secondary to OA has been demonstrated. To address the question of whether age predisposes articular cartilage to apoptosis, the objective of the present study was to characterize and compare in aged and mature non-OA rabbit articular cartilage, cell density and expression levels of specific genes associated with apoptosis. Mechanistic studies on the inhibition of induced apoptosis were also carried out. METHODS: Grade I (non-OA) femoral condyles and tibial plateaus from mature and aged rabbits were taken for assessment of viable cell density (VCD) and mRNA (reverse transcription-polymerase chain reaction) expression levels of the pro-apoptotic genes, Fas, Fas ligand (FasL), caspase-8, inducible nitric oxide synthase (iNOS) and p53. In vitro insulin-like growth factor (IGF-1)-mediated inhibition of nitric oxide (NO)-induced apoptosis was also examined using sodium nitroprusside (SNP) as NO donor. RESULTS: VCD was decreased 50-70% in aged articular cartilage relative to mature cartilage. mRNA expression levels of Fas, FasL, caspase-8 and p53 were higher in aged cartilage than in mature cartilage. iNOS expression was unchanged. IGF-1-mediated inhibition of NO-induced apoptosis was dose-dependent and reversed with addition of phosphatidylinositol-3 kinase inhibitor. CONCLUSIONS: This controlled animal model study demonstrates that age predisposes articular cartilage to changes in VCD and expression levels of specific pro-apoptotic genes. It is significant that these findings were demonstrated on cartilage that showed no prior signs of OA; it is also possible that such changes are a prelude to the age-related development of OA.

Aging↗