Transforming growth factor beta signaling is essential for the autonomous formation of cartilage-like tissue by expanded chondrocytes.

Cartilage is a tissue with limited self-healing potential. Hence, cartilage defects require surgical attention to prevent or postpone the development of osteoarthritis. For cell-based cartilage repair strategies, in particular autologous chondrocyte implantation, articular chondrocytes are isolated from cartilage and expanded in vitro to increase the number of cells required for therapy. During expansion, the cells lose the competence to autonomously form a cartilage-like tissue, that is in the absence of exogenously added chondrogenic growth factors, such as TGF-βs. We hypothesized that signaling elicited by autocrine and/or paracrine TGF-β is essential for the formation of cartilage-like tissue and that alterations within the TGF-β signaling pathway during expansion interfere with this process. Primary bovine articular chondrocytes were harvested and expanded in monolayer culture up to passage six and the formation of cartilage tissue was investigated in high density pellet cultures grown for three weeks. Chondrocytes expanded for up to three passages maintained the potential for autonomous cartilage-like tissue formation. After three passages, however, exogenous TGF-β1 was required to induce the formation of cartilage-like tissue. When TGF-β signaling was blocked by inhibiting the TGF-β receptor 1 kinase, the autonomous formation of cartilage-like tissue was abrogated. At the initiation of pellet culture, chondrocytes from passage three and later showed levels of transcripts coding for TGF-β receptors 1 and 2 and TGF-β2 to be three-, five- and five-fold decreased, respectively, as compared to primary chondrocytes. In conclusion, the autonomous formation of cartilage-like tissue by expanded chondrocytes is dependent on signaling induced by autocrine and/or paracrine TGF-β. We propose that a decrease in the expression of the chondrogenic growth factor TGF-β2 and of the TGF-β receptors in expanded chondrocytes accounts for a decrease in the activity of the TGF-β signaling pathway and hence for the loss of the potential for autonomous cartilage-like tissue formation.

Rapport de Formation: Formation test pour l'application du Guide de formation en EIE pour les communes rurales: Commune Rurale Bemanonga Morondava 9 - 25 Novembre 2004

Rapport de la formation test réalisée pour l'application du Guide de formation en EIE pour les communes rurales dans la commune de Bemanonga Morondava : participants, programme, résultats des exercices, évaluation, conclusions.

Micromass co-culture of human articular chondrocytes and human bone marrow mesenchymal stem cells to investigate stable neocartilage tissue formation in vitro

Cell therapies for articular cartilage defects rely on expanded chondrocytes. Mesenchymal stem cells (MSC) represent an alternative cell source should their hypertrophic differentiation pathway be prevented. Possible cellular instruction between human articular chondrocytes (HAC) and human bone marrow MSC was investigated in micromass pellets. HAC and MSC were mixed in different percentages or incubated individually in pellets for 3 or 6 weeks with and without TGF-beta1 and dexamethasone (±T±D) as chondrogenic factors. Collagen II, collagen X and S100 protein expression were assessed using immunohistochemistry. Proteoglycan synthesis was evaluated applying the Bern score and quantified using dimethylmethylene blue dye binding assay. Alkaline phosphatase activity (ALP) was detected on cryosections and soluble ALP measured in pellet supernatants. HAC alone generated hyaline-like discs, while MSC formed spheroid pellets in ±T±D. Co-cultured pellets changed from disc to spheroid shape with decreasing number of HAC, and displayed random cell distribution. In -T-D, HAC expressed S100, produced GAG and collagen II, and formed lacunae, while MSC did not produce any cartilage-specific proteins. Based on GAG, collagen type II and S100 expression chondrogenic differentiation occurred in -T-D MSC co-cultures. However, quantitative experimental GAG and DNA values did not differ from predicted values, suggesting only HAC contribution to GAG production. MSC produced cartilage-specific matrix only in +T+D but underwent hypertrophy in all pellet cultures. In summary, influence of HAC on MSC was restricted to early signs of neochondrogenesis. However, MSC did not contribute to the proteoglycan deposition, and HAC could not prevent hypertrophy of MSC induced by chondrogenic stimuli.

Neocartilage formation in 1 g, simulated, and microgravity environments: implications for tissue engineering

The aim of this study was to analyze and compare the deposition of cartilage-specific extracellular matrix components and cellular organization in scaffold-free neocartilage produced in microgravity and simulated microgravity.

Chondrogenic differentiation of bovine synovium: bone morphogenetic proteins 2 and 7 and transforming growth factor beta1 induce the formation of different types of cartilaginous tissue

OBJECTIVE: To compare the potential of bone morphogenetic proteins 2 and 7 (BMP-2 and BMP-7) and transforming growth factor beta1 (TGFbeta1) to effect the chondrogenic differentiation of synovial explants by analyzing the histologic, biochemical, and gene expression characteristics of the cartilaginous tissues formed. METHODS: Synovial explants derived from the metacarpal joints of calves were cultured in agarose. Initially, BMP-2 was used to evaluate the chondrogenic potential of the synovial explants under different culturing conditions. Under appropriate conditions, the chondrogenic effects of BMP-2, BMP-7, and TGFbeta1 were then compared. The differentiated tissue was characterized histologically, histomorphometrically, immunohistochemically, biochemically, and at the gene expression level. RESULTS: BMP-2 induced the chondrogenic differentiation of synovial explants in a dose- and time-dependent manner under serum- and dexamethasone-free conditions. The expression levels of cartilage-related genes increased in a time-dependent manner. BMP-7 was more potent than BMP-2 in inducing chondrogenesis, but the properties of the differentiated tissue were similar in each case. The type of cartilaginous tissue formed under the influence of TGFbeta1 differed in terms of both cell phenotype and gene expression profiles. CONCLUSION: The 3 tested members of the TGFbeta superfamily have different chondrogenic potentials and induce the formation of different types of cartilaginous tissue. To effect the full differentiation of synovial explants into a typically hyaline type of articular cartilage, further refinement of the stimulation conditions is required. This might be achieved by the simultaneous application of several growth factors.

Site-1 protease is essential for endochondral bone formation in mice

Site-1 protease (S1P) has an essential function in the conversion of latent, membrane-bound transcription factors to their free, active form. In mammals, abundant expression of S1P in chondrocytes suggests an involvement in chondrocyte function. To determine the requirement of S1P in cartilage and bone development, we have created cartilage-specific S1P knockout mice (S1P(cko)). S1P(cko) mice exhibit chondrodysplasia and a complete lack of endochondral ossification even though Runx2 expression, Indian hedgehog signaling, and osteoblastogenesis is intact. However, there is a substantial increase in chondrocyte apoptosis in the cartilage of S1P(cko) mice. Extraction of type II collagen is substantially lower from S1P(cko) cartilage. In S1P(cko) mice, the collagen network is disorganized and collagen becomes entrapped in chondrocytes. Ultrastructural analysis reveals that the endoplasmic reticulum (ER) in S1P(cko) chondrocytes is engorged and fragmented in a manner characteristic of severe ER stress. These data suggest that S1P activity is necessary for a specialized ER stress response required by chondrocytes for the genesis of normal cartilage and thus endochondral ossification.

Tissue neogenesis and STRO-1 expression in immature and mature articular cartilage

This study determined the potential for neotissue formation and the role of STRO-1+ cells in immature versus mature articular cartilage. Cartilage explants from immature and mature bovine knee joints were cultured for up to 12 weeks and stained with safranin-O, for type II collagen and STRO-1. Bovine chondrocyte pellet cultures and murine knee joints at the age of 2 weeks and 3 months, and surgically injured cartilage, were analyzed for changes in STRO-1 expression patterns. Results show that immature explants contained more STRO-1+ cells than mature explants. After 8 weeks in culture, immature explants showed STRO-1+ cell proliferation and newly formed tissue, which contained glycosaminoglycan and type II collagen. Mature cartilage explants showed only minimal cell expansion and neotissue formation. Pellet cultures with chondrocytes from immature cartilage showed increased glycosaminoglycan synthesis and STRO-1+ staining, as compared to pellets with mature chondrocytes. The frequency of STRO-1+ cells in murine knee joints significantly declined with joint maturation. Following surgical injury, immature explants had higher potential for tissue repair than mature explants. In conclusion, these findings suggest that the high percentage of STRO-1+ cells in immature cartilage changes with joint maturation. STRO-1+ cells have the potential to form new cartilage spontaneously and after tissue injury. (c) 2009 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res.

Inégalités de formation lors de l’accès à l’enseignement supérieur selon le sexe et le contexte migratoire: résultats de l’analyse des situations suisse, allemande et française

La présente contribution porte sur le passage dans le degré tertiaire en tenant compte de l’intrication des inégalités liées au sexe et au contexte migratoire. L’étude, qui repose sur des concepts de la théorie décisionnelle, s’articule principalement sur une comparaison entre la Suisse (TREE), l’Allemagne (élèves pouvant prétendre aux études supérieures 2002 HIS) et la France (Panel d'élèves du second degré 1995). Les résultats révèlent qu’en Suisse et en Allemagne, indépendamment de l’origine sociale, les jeunes hommes appartenant à certains groupes de migrants socialement défavorisés (2e génération) affichent un taux de passage dans le supérieur plus élevé que leurs camarades nationaux. Ils mettent par ailleurs en évidence que, ni en Suisse, ni en Allemagne, ni en France, les migrantes de deuxième génération issues de pays fortement marqués par le modèle patriarcal sont désavantagées.

Gentrification alpine : Lorsque le village de montagne devient un arrondissement métropolitain. Les nouveaux résidents partagés entre amour du paysage et capital symbolique

Cet article aborde la transformation de régions de montagne en lieux de résidence remplaçant des secteurs économiques plus anciens (agriculture, industrie manufacturière, tourisme) dans les montagnes européennes. Il se place dans la perspective du développement régional et de son impact sur les ressources régionales fixes, le « capital territorial ». Cette nouvelle tendance affecte les montagnes européennes de deux manières, et participe à la formation de régions métropolitaines qui combinent centres métropolitains et environnements de loisirs fondés sur les attraits du paysage pour constituer de nouvelles entités intégrées. Au cours du processus, le paysage devient un bien de consommation nouveau et rare, qui joue un rôle dans l’accumulation du capital investi. L’article établit que les concepts d’esthétique du paysage et d’agréments ne suffisent pas à expliquer cette nouvelle dynamique, car ils méconnaissent les processus spatio-économiques ainsi que le rôle de la marchandisation du paysage pour les nouveaux résidents. Ces nouveaux résidents ont un profil plus « multilocal » que migrant. La multilocalité et l’usage sélectif des produits du paysage freinent le processus d’intégration, crucial pour entretenir et développer le capital territorial. On peut poser que la présence non permanente des nouveaux résidents risque d’affaiblir et non de renforcer les structures locales existantes. Il semble donc nécessaire de déployer des efforts particuliers auprès de chaque groupe de nouveaux résidents pour que de simples résidents à temps partiel deviennent des acteurs régionaux (au moins à temps partiel). De plus, le concept du développement régional centré sur les acteurs innovants doit être remis en question dans la mesure où l’aspect « consommation » domine le rapport du paysage.