Objective: Repair of focal articular cartilage lesions is usually performed by employing cell-based therapeutic strategies such as autologous chondrocyte implantation (ACI). The aim of this study was to determine whether periosteum exerts pro-chondrogenic effects on the transplanted cells beyond its biomechanical role in ACI.
Methods: Micromass pellets of human articular chondrocytes were cocultured for up to 28 days with human periosteal explants either with physical contact or separated by a membrane allowing paracrine interactions only. Quantitative reverse transcription (RT)-PCR, ELISA, immunohistochemistry and collagen isolation were used to analyse the expression and secretion of TGF-beta1, collagens I and II and chondrogenic differentiation markers such as MIA (CD-RAP) and aggrecan.
Results: TGF-beta1 gene expression was induced significantly in paracrine cocultures in periosteum, whereas it was repressed in physical contact cocultures. However, a higher TGF-beta1 secretion rate was observed in physical contact cocultures compared with periosteal monocultures. The expression of COL2A1, melanoma inhibitory activity (cartilage-derived retinoic acid-sensitive protein) [MIA (CD-RAP)] and aggrecan was mainly unaffected by culture conditions, whereas COL1A1 gene expression was increased in periosteal paracrine cocultures. Collagen I staining was induced in micromass pellets from paracrine cocultures, whereas it was repressed in chondrocytes from physical contact cocultures.
Conclusions: We found evidence for a bidirectional regulating system with paracrine signalling pathways between periosteum and articular chondrocytes. Stimulation of TGF-beta1 and COL1A1 gene expression in periosteal paracrine cocultures and the increased release of TGF-beta1 protein in physical contact conditions indicate an anabolic, and not merely chondrogenic micro-environment in this in vitro model for periosteal-based ACI.