Articular Chondrocytes Produce Factors That Inhibit Maturation of Sternal Chondrocytes in Serum-Free Agarose Cultures: A TGF-β Independent Process

Abstract

Under normal conditions, articular chondrocytes persist throughout postnatal life, whereas "transient" chondrocytes, which constitute the bulk of prenatal and early postnatal cartilaginous skeleton, undergo maturation, hypertrophy, and replacement by bone cells. The mechanisms regulating the markedly different behavior and fate of articular and transient chondrocytes are largely unclear. In the present study, we asked whether articular chondrocytes possess dominant antimaturation properties which may subtend their ability to persist throughout life. Adult chicken articular chondrocytes and transient maturing chondrocytes from the core region of day 17 chick embryo cephalic sternum were cultured or cocultured in serum-free agarose conditions. When the sternal cells were grown by themselves, they quickly developed into hypertrophic type X collagen-synthesizing cells; however, when they were cocultured with as few as 10% articular chondrocytes or fed with articular chondrocyteconditioned medium, their maturation was markedly impaired, as revealed by a sharp drop in type X collagen synthesis. A similar, albeit less potent, antimaturation activity characterized resting and proliferating immature chondrocytes isolated from other regions of embryonic sternum. Transforming growth factor-␤2 (TGF-␤2) was previously suggested to be an inhibitor of chondrocyte maturation. We found, however, that treatment with a neutralizing antiserum to TGF-␤ did not counteract the inhibition of maturation in cocultures of articular and maturing core sternal chondrocytes. Indeed, articular chondrocytes produced and accumulated relatively low levels of TGF-␤ in their culture medium, about 15 ng/ml/48 h, of which over 90% was latent; surprisingly, maturing sternal core chondrocytes accumulated over 10-fold more TGF-␤ in the medium, about 150 ng/ml/48 h, of which over 20% was endogenously active. These results indicate that articular chondrocytes do possess dominant antimaturation properties which appear to be TGF-␤ independent. The TGF-␤s may thus have a more prominent role in the terminal phases of chondrocyte maturation, as indicated by their abundance and greater activity in

Human articular chondrocytes secrete parathyroid hormone–related protein and inhibit hypertrophy of mesenchymal stem cells in coculture during chondrogenesis

“…Resting chondrocytes in the growth plate and articular chondrocytes maintain their nonhypertrophic phenotype by active inhibition of terminal differentiation, and soluble factors have been discussed as the main mediators of this action (17)(18)(19)30). This encouraged us to evaluate whether articular chondrocytes can teach MSCs to become stable chondrocytes, either by direct or indirect coculture, during TGF␤-driven in vitro chondrogenesis.…”

“…Interestingly, coculture experiments have demonstrated that immature or articular chondrocytes produce soluble factors that are able to suppress the terminal differentiation of maturing growth plate chondrocytes in vitro (17)(18)(19). This indicates that resting chondrocytes maintain their stable phenotype by actively inhibiting terminal differentiation and could potentially teach differentiating MSCs to become stable chondrocytes in coculture.…”

“…This indicates that resting chondrocytes maintain their stable phenotype by actively inhibiting terminal differentiation and could potentially teach differentiating MSCs to become stable chondrocytes in coculture. It has been suggested that coculture-induced mechanisms may rely on the soluble factors TGF␤2 and fibroblast growth factor 2 (FGF-2) acting in synergy (17), whereas other postulated mechanisms are TGF␤-independent (18).…”

Coculture of Human Mesenchymal Stem Cells and Articular Chondrocytes Reduces Hypertrophy and Enhances Functional Properties of Engineered Cartilage

“…Factors such as mechanical loading, controlling cell and matrix interactions, and engineered biomaterials have been investigated toward this end, yet only modest improvements have been seen. 9 Recent studies indicate that paracrine factors released by articular chondrocytes are able to induce the chondrogenesis of MSCs [10][11][12] and inhibit the terminal differentiation of growth plate chondrocytes 13,14 as well as hypertrophy of MSCs in coculture. 11,15 However, there have been few studies examining the effects of human MSC/chondrocyte coculture on the development of the functional properties of tissue engineered cartilage as well as MSC hypertrophy using a 3D scaffold system such as these HA hydrogels.…”

Effects of 5-Aza-2’ Deoxycytidine on Proliferation and Differentiation of Embryonic Chick Caudal Region Chondrocytes in Culture

“…The cephalic and Caudal (one third part of the tip region) of sterna were dissected as described by [12]. Tissues were finely diced and pre-incubated for 30 min at 37 o C with Bacterial collagenase type 1A (10mg/ml) purchased from Sigma chemical Co., Dorset U.K. and Trypsin (0.4mg/ml) GIBCO (BRL) in minimal essential medium.…”