Calcineurin inhibitors promote chondrogenic marker expression of dedifferentiated human adult chondrocytes via stimulation of endogenous TGFbeta1 production

In vitro chondrocyte expansion is required for several cell-based approaches for the repair of chondral lesions. During expansion, loss of chondrogenic phenotype takes place (dedifferentiation). The objective of this study was to investigate calcineurin (Cn) as a potential target to improve chondrocyte phenotype for cartilage repair purposes. Cn activity in human articular chondrocytes was significantly increased during dedifferentiation and decreased during redifferentiation in vitro. Inhibition of Cn activity by FK506 increased the expression of chondrogenic markers collagen type 2, aggrecan, and SOX9 in culture-expanded cells. Addition of FK506 increased endogenous transforming growth factor 2 (TGF) beta1 expression on both mRNA and protein level. The effect of FK506 on chondrogenic markers was abolished by addition of anti-TGFbeta1 antibody, indicating that the endogenous TGFbeta1 was necessary to increase chondrogenic marker expression. We also showed that chondrocyte redifferentiation by TGFbeta requires calcium influx and does not depend on changes in Cn activity. In conclusion, inhibition of Cn activity by FK506 increases the expression of chondrogenic markers via endogenous TGFbeta1 production in human articular chondrocytes. Cn inhibitors might be an alternative for the application of (recombinant) TGFbeta, to promote chondrocyte phenotype for cell-based cartilage repair procedures.