Type II TGFβ receptor modulates chondrocyte phenotype

Aging is one of the major risk factors of osteoarthritis. This pathology during which chondrocytes undergo modifications of their phenotype may result from alteration of transforming growth factor beta (TGF beta) signaling. This study investigates the role of TGF beta response in the process of chondrocyte dedifferentiation/redifferentiation. Dedifferentiation was induced by successive passages of human articular chondrocytes, whereas their redifferentiation was performed by three-dimensional culture in alginate. Human mesenchymal stem cells were obtained from bone marrow and differentiated into chondrocyte-like phenotype by three-dimensional culture, embedded in the same scaffold. Protein and mRNA levels were analyzed by Western blot and real-time reverse transcription PCR. Regulatory mechanism was investigated using specific inhibitors (mithramycin), mRNA silencing or decoy oligonucleotides, and expression vectors. Chondrocyte dedifferentiation interfered with TGF beta signaling by decreasing T beta RII mRNA and protein levels and subsequent TGF beta response. T beta RII ectopic expression in passaged chondrocytes permitted to increase the expression of several matrix genes, such as aggrecan or type II collagen. Redifferentiation of passaged chondrocytes permitted to restore, at least in part, T beta RII expression and was related to differentiation of human bone marrow mesenchymal stem cells toward chondrocytes, where both specific protein 1 (Sp1) and T beta RII mRNA levels were increased. Moreover, Sp1 manipulation by silencing or ectopic expression and pharmacologic inhibition revealed a link between expression levels of this transcriptional factor, which is crucial for constitutive expression of T beta RII in cartilage, and TGF beta response. Therefore, these data permit us to suggest an important role of T beta RII expression in the maintenance of chondrocyte phenotype, which is altered with age, and bring new insights in our understanding of chondrogenesis process.