Integrin expression and collagen type II implicated in maintenance of chondrocyte shape in monolayer culture: an immunomorphological study.

Chondrocytes grown in monolayer culture at low density, with serum added, either dedifferentiate after several days whereby their cell shape or they are overgrown by fibroblast-like cells. The aim of this study was to optimize the cultivation of chondrocytes in monolayer culture and to slow down their transformation or their overgrowth by fibroblast-like cells. For this purpose freshly isolated chondrocytes of cartilage anlagen from 17-day-old mouse embryos were grown on plastic or collagen type II-coated substrates. With this model: (a) chondrocytes grown on plastic substrates had almost completely changed to fibroblast-like cells after 5 days in culture. (b) When grown on collagen type II, the chondrocytes maintained their round phenotype for more than 2 weeks in culture. (c) Immunomorphological investigations showed that chondrocytes produce collagen type II and fibronectin and express specific surface receptors (integrins of the beta 1-group) on the membrane from day 1 until the end of the culture period when grown on collagen type II. (d) Treatment with beta 1-integrin antibodies clearly reduces chondrocyte adhesion on collagen type II by about 70%. Hence, these data indicate that the most probable influence of collagen type II on cellular behaviour depends on the integrins participating in a chondrocyte-collagen type II interaction, and this model represents a pure chondrocyte culture which allows cell growth for an extended period.