EXPRESSION OF CARTILAGE-SPECIFIC MOLECULES IS RETAINED ON LONG-TERM CULTURE OF HUMAN ARTICULAR CHONDROCYTES

Normal human adult articular chondrocytes were used to determine how t he chondrocyte phenotype is modulated by culture conditions following long-term culture. We report here for the first time that human articu lar chondrocytes have a lifespan in the range of 34-37 population doub lings. While chondrocytes cultured as monolayers displayed a fibroblas toid morphology and grew faster, those cultured as suspensions over ag arose adopted a round morphology and formed clusters of cells reminisc ent of chondrocyte differentiation in intact cartilage, with little or no DNA synthesis. These morphologies were independent of the age of t he culture. Despite, these morphological differences, however, chondro cytes expressed markers at mRNA and protein levels characteristic of c artilage: namely, types II and IX collagens and the large aggregating proteoglycans, aggrecan, versican and link protein, but not syndecan, under both culture conditions. However, they also expressed type I col lagen alpha 1(I) and alpha 2(I) chains. It has been suggested that exp ression of collagen alpha 1(I) by chondrocytes cultured as monolayers is a marker of the loss of the chondrocyte phenotype. However, we show here, using reverse transcriptase/polymerase chain reaction, that nor mal fresh intact human articular cartilage expresses collagen alpha 1( I). The data show that following long-term culture human articular cho ndrocytes retain their differentiated characteristics and that cell sh ape does not correlate with the expression of the chondrocyte phenotyp e. It is proposed that loss of the chondrocyte phenotype is marked by the loss of one or more cartilage-specific molecules rather than by th e appearance of non-cartilage-specific molecules.