Chondrogenic potential of bone marrow- and adipose tissue-derived adult human mesenchymal stem cells

Regarding cartilage repair, tissue engineering is currently focusing on the use of adult mesenchymal stem cells (MSC) as an alternative to autologous chondrocytes. The potential of stem cells from various tissues to differentiate towards the chondrogenic phenotype has been investigated and it appears that the most common and studied sources are bone marrow (BM) and adipose tissue (AT) for historical and easy access reasons. In addition to three dimensional environment, the presence of member(s) of the transforming growth factor (TGF-β family and low oxygen tension have been reported to promote the in vitro differentiation of MSCs. Our work aimed at characterizing and comparing the degree of chondrogenic differentiation of MSCs isolated from BM and AT cultured in the same conditions. We also further aimed at and at determining whether hypoxia (2% oxygen) could affect the chondrogenic potential of AT-MSCs. Cells were first expanded in the presence of FGF-2, then harvested and centrifuged to allow formation of cell pellets, which were cultured in the presence of TGF-β3 and/or Bone Morphogenetic Protein-2 (BMP-2) and with 2 or 20% oxygen tension, for 24 days. Markers of the chondrocyte (COL2A1, AGC1, Sox9) and hypertrophic chondrocyte (COL10A1, MMP-13) were monitored by real-time PCR and/or by immunohistological staining. Our data show that BMP-2/TGF-β3 combination is the best culture condition to induce the chondrocyte phenotype in pellet cultures of BM and AT-MSCs. Particularly, a switch in the expression of the pre-chondrogenic type IIA form to the cartilage-specific type IIB form of COL2A1 was observed. A parallel increase in gene expression of COL10A1 and MMP-13 was also recorded. However when AT-MSCs were cultured in hypoxia, the expression of markers of hypertrophic chondrocytes decreased when BMP-2/TGF-β3 were present in the medium. Thus it seems that hypoxia participates to the control of AT-MSCs chondrogenesis. Altogether, these cellular model systems will help us to investigate further the potential of different adult stem cells for cartilage engineering.