The initial attachment of transplanted chondrocytes to the surface of a cartilage defect is crucial for the success of chondrocyte transplantation. The purpose of this study was to investigate the early interaction of chondrocytes with the deep or calcified zones of cartilage or the subchondral bone, joint surfaces to which transplanted chondrocytes might have to attach in vivo.
Freshly isolated (primary) or passaged (P1) chondrocytes were seeded on the top of bone plugs having either a surface composed of mid-deep zone hyaline cartilage or calcified cartilage or bone only. The percent of cells that attached, the role of integrins in cell attachment, and gene expression after placement of the cells on the different surfaces were determined.
Both primary and passaged chondrocytes attached efficiently to all three surfaces (over 88% of seeded cells). The chondrocytes showed a punctate distribution of beta 1-integrin and vinculin, which in areas co-localized with actin, suggesting that the cells formed focal adhesions. The primary chondrocytes had a different shape, appearance of focal contacts, and actin distribution when compared to passaged cells and these did not appear to be influenced by the type of surface to which the cells attached. Blocking either beta 1-integrin or alpha v beta 5 integrin partially inhibited (between 27 to 48% and 26 to 37% respectively) attachment of both primary and passaged chondrocytes to all surfaces. Blocking alpha v beta 3 had no effect on adhesion. There was expression of type II collagen and aggrecan core protein mRNA by 2h. The different surfaces did not appear to affect the expression of these genes up to 24h although gene levels were lower in passaged cells.
Chondrocytes, either freshly isolated or passaged, have the potential to adhere to the different joint surfaces that could be exposed in a cartilage defect. Understanding how chondrocytes adhere and interact with damaged joint surfaces may help identify methods to enhance the retention of transplanted cells in the defect site and cartilage tissue formation.