Autocrine stimulation by insulin‐like growth factor 1 and insulin‐like growth factor 2 mediates chondrocyte survival in vitro

Objective To determine the role of autocrine stimulation by insulin‐like growth factor 1 (IGF‐1) and IGF‐2 in mediating chondrocyte survival and to determine whether chondrocytes from older individuals are more susceptible to cell death when IGF action is blocked. Methods Survival was assessed in human and monkey chondrocytes cultured in suspension in alginate under serum‐free conditions. The role of IGFs in mediating survival was determined by treating cultures with neutralizing antibodies to IGF‐1 and IGF‐2, an antibody that blocks the type 1 IGF receptor, and antisense oligonucleotides to inhibit IGF‐1 production. Survival was measured in chondrocyte cultures from young and old adult monkeys in the presence and absence of the IGF receptor blocking antibody and ceramide to induce cell death. Results Cell survival of >90% was noted when chondrocytes were cultured for as long as 107 days in alginate in a supplemented serum‐free medium. Compared with controls, survival was significantly reduced by treatment with neutralizing antibodies to IGF‐1 (25% cell death), neutralizing antibodies to IGF‐2 (18% cell death), antibody to the IGF receptor (45% cell death), and IGF‐1 antisense oligonucleotides (28% cell death). Cell death from inhibition of the type 1 IGF receptor was associated with an increase in caspase 3 activity and with positive DNA fragmentation, consistent with apoptotic cell death. Chondrocytes from old adult monkeys were more susceptible to cell death than were those from young adult monkeys when the IGF receptor was blocked and cell death was further stimulated by ceramide. Conclusion Autocrine production of IGFs helps to maintain chondrocyte survival in vitro and could play a similar role in vivo. With aging, chondrocytes may become more susceptible to factors that induce cell death.