Cellular and molecular events during chondrogenesis of human mesenchymal stromal cells grown in a three-dimensional hyaluronan based scaffold

Mesenchymal stromal cells (MSCs) seem to be a good alternative to chondrocytes for cartilage regeneration. To obtain new information on the sequence of cellular and molecular events during in vitro chondrogenic differentiation we analysed MSCs on a widely used hyaluronic acid biomaterial (Hyaff(g) -11). Cellular differentiation was induced using two different concentrations of TGF beta 1 (10 and 20 ng/ml) and the process was analysed at different time points (24 h, and 7, 14 21 and 28 days) using techniques of light and electron microscopy, real-time PCR and immunohistochemistry. We found that without TGF beta MSCs did not survive while in the presence of TGF beta the cells significantly proliferated from day 7 until day 28. Light and electron microscopy showed that TGF beta at 20 ng/ml better induced the formation of cartilage-like tissue. Real-time PCR showed an increased expression of collagen type II, IX and aggrecan associated to a down-regulation of collagen type I. Immunohistochemical analysis confirmed that collagen type I was down-modulated while collagen type II increased from day 14 to day 28. These data clearly showed that higher concentrations of TGF beta (20 ng/ml) induce chondrogenesis of MSCs on Hyaff(g)-11 scaffold better than 10 ng/ml of TGF beta. This process is characterized by a sequence of cellular and molecular events that deal with the in vitro formation of a cartilage-like tissue.