In vitro and in vivo differentiation of mesenchymal stem cells into chondrocytes

Mesenchymal stem cells are multipotent cells that have the potential to differentiate toward multiple lineages, such as adipocytes, myocytes, osteocytes and chondrocytes. Both primary stem cells originating from bone marrow and immortalised cell lines retain their differentiation capacities when cultured in vitro under specific conditions. Growth factors of the TFG-β superfamily have been shown to have the properties of inducing in vitro osteogenic and chondrogenic differentiation. The purpose of this work was to compare the potential of different growth factors (BMP-2, CDMP-1 and CDMP-2) and the Sox-9 chondrocyte-specific transcription factor to induce the chondrogenic differentiation of mesenchymal stem cells both in vitro and in vivo.

To this aim, we first derived mesenchymal stem cells (from the murine C3H10T1/2 line) constitutively expressing either one of the growth or transcription factor. The chondrogenic potential of these factors was then assessed in vitro using the micropellet culture system both by RT-PCR and immunohistochemistry. Those cells were then embedded in a type I collagen matrix and subcutaneously implanted in SCID mice. The matrices were retrieved after 20 days and processed for routine histology and immunohistochemistry analysis. Parallely, BMP-2-expressing stem cells were injected into the intra-articular space of SCID mouse knee joints to determine their capacities of in situ differentiation and cartilaginous matrix formation.

Intra-articular injection of mesenchymal stem cells engineered to express BMP-2 gave rise to the formation of bone in the knee joint and at extra-articular sites, particularly in muscle. The need for differentiation factors, specific for cartilage, is underlined.