The c-Jun N-terminal kinases (JNK) are members of the mitogen-activated protein kinase family and are activated by environmental stress. Se plays an important role in the biological pathways by forming selenoprotein. Selenoproteins have been shown to exhibit a variety of biological functions including antioxidant functions and maintaining cellular redox balance, and compromise of such important proteins would lead to oxidative stress and apoptosis. We examined the expression levels of JNK in Kashin–Beck disease (KBD) patients, tested the potential protective effects of sodium selenite on tert-butyl hydroperoxide (tBHP)-induced oxidative injury and apoptosis in human chondrocytes as well as its underlying mechanism in this study. We produced an oxidative damage model induced by tBHP in C28/I2 human chondrocytes to test the essential anti-apoptosis effects of Se in vitro. The results indicated that the expression level of phosphorylated JNK was significantly increased in KBD patients. Cell apoptosis was increased and molecule expressions of the JNK signalling pathway were activated in the tBHP-injured chondrocytes. Na2SeO3 protected against tBHP-induced oxidative stress and apoptosis in cells by increasing cell viability, reducing reactive oxygen species generation, increasing Glutathione peroxidase (GPx) activity and down-regulating the JNK pathway. These results demonstrate that apoptosis induced by tBHP in chondrocytes might be mediated via up-regulation of the JNK pathway; Na2SeO3 has an effect of anti-apoptosis by down-regulating the JNK signalling pathway.

Although the clinical benefits of dietary supplementation with n-3 polyunsaturated fatty acids (PUFA) has been recognised for a number of years, the molecular mechanisms by which particular PUFA affect metabolism of cells within the synovial joint tissues are not understood. This study set out to investigate how n-3 PUFA and other classes of fatty acids affect both degradative and inflammatory aspects of metabolism of articular cartilage chondrocytes using an in vitro model of cartilage degradation. Using well-established culture models, cartilage explants from normal bovine and human osteoarthritic cartilage were supplemented with either n-3 or n-6 PUFA, and cultures were subsequently treated with interleukin 1 to initiate catabolic processes that mimic cartilage degradation in arthritis. Results show that supplementation specifically with n-3 PUFA, but not n-6 PUFA, causes a decrease in both degradative and inflammatory aspects of chondrocyte metabolism, whilst having no effect on the normal tissue homeostasis. Collectively, our data provide evidence supporting dietary supplementation of n-3 PUFA, which in turn may have a beneficial effect of slowing and reducing inflammation in the pathogenesis of degenerative joint diseases in man.

Tibial Dyschondroplasia (TD) is one of the most prevalent skeletal abnormalities observed in avian species; it causes enormous economic losses and is a major animal welfare problem. It is characterized by lesions composed of uncalcified, unvascularized cartilage that can extend from the epiphyseal growth plate into the metaphysis. The disease development and progress have been attributed to dietary, environmental and genetic factors. Irregular cell differentiation of the chondrocytes that populate the growth plate, with consequently aberrant cartilage vascularization and mineralization, has been hypothesized to be involved in the etiology of the disease.

Various tools available for the study of TD are described in the present review, and their advantages and limitations are discussed. We describe the morphology of the growth plate, with especial emphasis on the differences between the mammalian and the avian ones. We highlight vascularization as a possible cause of TD, and suggest that matrix metalloproteinases (MMPs) play an important role in cartilage vascularization and TD development. The disparity between broilers and turkeys MMPs suggests that they differ in their regulation of vascularization, so that different strategies may be required in dealing with TD in broilers and in turkeys. The high body mass of the modern meat-type birds has been implicated in the development of TD. A model was established to evaluate the effect of mechanical loading on the bones of young chickens, without any dietary manipulations: increased loading caused enhanced vascularization of the growth plate together with increased MMP-9 expression, without any changes in the incidence of TD, which suggests that the increased loading is not in itself the cause of TD.

At present, the cause of TD is not known, but multidisciplinary research at various levels such as a genomic approach based on microarray technology and the chicken genome project, together with cell and organ culture methodology, genetic selection, nutritional manipulation and environmental approaches will provide us with better understanding of the molecular mechanisms underlying TD, and should pave the way for future reduction in its incidence.

The aim of this study was to investigate the developmental characteristics of the mandibular condyle in sequential phases at the gene level using in situ hybridisation. At d 14.5 of gestation, although no expression of type II collagen mRNA was observed, aggrecan mRNA was detected with type I collagen mRNA in the posterior region of the mesenchymal cell aggregation continuous with the ossifying mandibular bone anlage prior to chondrogenesis. At d 15.0 of gestation, the first cartilaginous tissue appeared at the posterior edge of the ossifying mandibular bone anlage. The primarily formed chondrocytes in the cartilage matrix had already shown the appearance of hypertrophy and expressed types I, II and X collagens and aggrecan mRNAs simultaneously. At d 16.0 of gestation, the condylar cartilage increased in size due to accumulation of hypertrophic chondrocytes characterised by the expression of type X collagen mRNA, whereas the expression of type I collagen mRNA had been reduced in the hypertrophic chondrocytes and was confined to the periosteal osteogenic cells surrounding the cartilaginous tissue. At d 18.0 of gestation before birth, cartilage-characteristic gene expression had been reduced in the chondrocytes of the lower half of the hypertrophic cell layer. The present findings demonstrate that the initial chondrogenesis for the mandibular condyle starts continuous with the posterior edge of the mandibular periosteum and that chondroprogenitor cells for the condylar cartilage rapidly differentiate into hypertrophic chondrocytes. Further, it is indicated that sequential rapid changes and reductions of each mRNA might be closely related to the construction of the temporal mandibular ramus in the fetal stage.

Angiogenesis is essential for the replacement of cartilage by bone during growth and repair. In order to obtain a better understanding of the mechanisms regulating vascular invasion at sites of endochondral ossification we have investigated the expression of the endothelial cell-specific mitogen, vascular endothelial growth factor (VEGF), by chondrocytes in human neonatal growth plates. VEGF was absent from chondrocytes in the resting zone and only weakly expressed by occasional chondrocytes in the proliferating region. In the hypertrophic zone the number of chondrocytes stained and the intensity of staining for VEGF increased with chondrocyte hypertrophy, maximum expression of VEGF being observed in chondrocytes in the lower hypertrophic and mineralised regions of the cartilage. These observations provide the first demonstration of the presence of VEGF in situ in developing human bone and are consistent with in vitro observations demonstrating the upregulation of proangiogenic growth factor production with increasing chondrocyte hypertrophy. The presence of numerous small blood vessels and vascular structures in the subchondral region where VEGF expression was maximal indicates that VEGF produced by hypertrophic chondrocytes may play a key role in the regulation of vascular invasion of the growth plate.

We examined cells from the nucleus pulposus and annulus fibrosus of adult bovine intervertebral discs, using confocal laser scanning microscopy on living unfixed tissue. These cells were visualised using chloromethyl fluorescein diacetate, a membrane-impermeant fluorescent dye. The organisation of cells from the outer annulus was also determined using confocal microscopy after fixation and staining the actin-filaments with FITC-phalloidin. We found that cellular processes were a dominant feature of cells from all regions of the disc including the cells of the nucleus pulposus and inner annulus. These processes were also visible in histological sections of disc examined both at the light and electron microscope level, even though cells from the nucleus and inner annulus appeared chondrocyte-like, being rounded and enclosed in a capsule. The function of these processes is at present unknown. We suggest that they may serve to sense mechanical strain.

We investigated the immunohistochemical localisation of types II and X collagen as well as the cytochemical localisation of alkaline phosphatase in the developing condylar cartilage of the fetal mouse mandible on d 14–16 of pregnancy. On d 14 of pregnancy, although no immunostaining for types II and X collagen was observed, alkaline phosphatase activity was detected in all cells in the anlage of the future condylar process. On d 15 of pregnancy, immunostaining for both collagen types was simultaneously detected in the primarily formed condylar cartilage. Alkaline phosphatase activity was also detected in chondrocytes at this stage. By d 16 of pregnancy, the hypertrophic cell zone rapidly increased in size. These findings strongly support a periosteal origin for the condylar cartilage of the fetal mouse mandible, and show that progenitor cells for condylar cartilage rapidly or directly differentiate into hypertrophic chondrocytes.

Changes in the 3-dimensional arrangement of the articular cartilage matrix during growth of the rabbit tibial plateau were studied. Knees from newborn, and 1, 2 and 6 wk-old rabbits were compared with those of adults by light and electron microscopy. The specimens were fixed, embedded en bloc in epoxy resin and sectioned vertically/coronally through the point where the articular cartilage was thickest in the adult medial tibial plateau. At birth, the proximal tibial epiphysis was cartilaginous, but nascent articular cartilage was recognisable as a densely cellular layer covering the tibial condyle. Within 30 μm of the articular surface, the chondrocytes were flattened and collagen fibres ran among these cells in a direction parallel to the surface. Deeper in the articular cartilage, rounded cells were evenly distributed within a random collagen fibril network. At the centre of the plateau, the tangential layer changed little during growth, whereas the subjacent cellular layer grew in thickness and steadily achieved a more vertical character in the organisation of its constituent collagen and cellular elements. At 1 wk, cells were separated into clusters by acellular regions filled with collagen fibrils. At 2 wk, cells within the forming radial zone were aligned in columns bracketed by vertical collagen fibres. Continuity of these vertical fibres with those in the tangential surface layer was evident at this age. The chondrocytes were surrounded by fibrous capsules typical of chondrons. By 6 wk, the bases of the radial collagen fibres in the very centre of the condyle had calcified, as had the adjacent hypertrophic hyaline cartilage. A solid subchondral plate and tidemark did not appear until skeletal maturity. From birth to age 6 wk, maximum thickness of the layer identified as primordial articular cartilage increased from 0.13 mm to 0.70 mm, and was 1.5 mm in the adult. Throughout growth, however, the thickness of the tangential layer in the centre of the plateau never exceeded 0.05 μm. In the patella, femoral head and peripheral tibial plateau, cartilage development followed the same general sequence. In contrast to the central tibial plateau, the tangential layer also grew in thickness, but at a slower rate than that of the radial zone. At all ages, the developing articular cartilage was structurally distinct from the deeper hyaline cartilage which contributed to growth of the ossification centre through enchondral ossification. The collagen matrix of articular cartilage acquires a characteristic, orderly 3-dimensional structure soon after birth. Growth in cartilage thickness occurs primarily through enlargement of the radial zone.

The chondrocyte and its pericellular microenvironment together represent the chondron, historically considered the primary structural, functional and metabolic unit of articular and other hyaline cartilages. This review summarises research over the last 10 years to establish the molecular anatomy, functional properties and metabolic contribution of the chondron in articular cartilage homeostasis, and its failure during the initiation and progression of degenerative osteoarthritis.

An ultrastructural study was undertaken on cartilage resorption at the site of initial endochondral bone formation in the mouse mandibular condyle on d 16 of pregnancy. After resorbing the bone collar, the osteoclasts extended their cell processes into the cartilage matrix and made contact with hypertrophic chondrocytes. By means of cell processes or vacuolar structures, these osteoclasts entrapped the calcified cartilage matrices, cell debris, and the degraded uncalcified cartilage matrices. In particular, since the calcified cartilage matrices were sometimes seen to be disrupted within the osteoclastic vacuolar structures, they were probably disposed of by the osteoclasts. Invading endothelial cells giving rise to capillaries also directly surrounded the degraded uncalcified cartilage matrices and small deposits of cell debris. In addition, hypertrophic chondrocytes that had attached to or were in the process of attaching to the invading osteoclasts often enclosed the small calcified cartilage matrices. Other cell types that have often been reported in other regions of cartilage resorption were not seen at the site of initial endochondral bone formation in this study. Our findings in relation to cartilage resorption may therefore represent unique features of the site of initial endochondral bone formation site. We consider that the manner of cartilage resorption is likely to vary by site, age, and species.