AGE-RELATED DECREASE IN THE RESPONSIVENESS OF RAT ARTICULAR CHONDROCYTES TO EGF IS ASSOCIATED WITH DIMINISHED NUMBER AND AFFINITY FOR THE LIGAND OF CELL-SURFACE BINDING-SITES

The effect of age on the responsiveness of articular chondrocytes (AC) to epidermal growth factor (EGF) was examined. Cells were isolated by digesting cartilage fragments from the humeral and femoral heads of 2 1-day old, 8- and 14-month old rats with collagenase. The cells were c ultured under standard conditions, as monolayers. DNA synthesis was me asured by [H-3]thymidine incorporation and cell proliferation by the D NA content of subconfluent cultures. [I-125]EGF binding and the amount s of EGF and EGF-receptor mRNAs were determined using confluent cells. DNA synthesis was decreased with age of animals. EGF stimulated DNA s ynthesis in cultures in 1- and 8-month old rats at low serum concentra tions (< 5%), and in cultures in 14-month old animals at high serum co ncentrations. It also increased 5-day DNA content of cultures compared to serum-treated controls but this effect was weak in cultures in 14- month old rats. The number of high affinity binding sites for [I-125]E GF decreased from 37 800 in the 1-month old to 1950 in the 14-month ol d rat AC. The apparent dissociation constant (K-d) also decreased with age: 0.18 nmol/l in the 1-month old; 0.12 nmol/l in the 8-month old; and 0.07 nmol/l in the 14-month old cells. AC in older rats contained more EGF mRNA and less EGF-receptor mRNA. Incubation of the cells with EGF resulted in down regulation of the EGF-and upregulation of EGF-re ceptor mRNA expressions. These findings show the age-related quantitat ive and qualitative alterations in EGF and EGF-receptor which may acco unt, at least in part, for the diminished responsiveness of senescent AC to EGF. (C) 1998 Elsevier Science Ireland Ltd.