AUTOCRINE INDUCTION OF DNA-SYNTHESIS BY MECHANICAL INJURY OF CULTUREDSMOOTH-MUSCLE CELLS - POTENTIAL ROLE OF FGF AND PDGF

To determine whether replication of arterial smooth muscle cells (SMCs ) in response to mechanical injury would occur in the absence of serum and other cells, we created an in vitro model in which confluent, gro wth-arrested cultures of rat SMCs were injured by gentle pressure of a soft plastic tube and then kept in serum-free medium for up to 4 days . Replication of SMCs in and around the injury, as measured by tritiat ed thymidine incorporation, was noted within 24 hours and peaked at 48 hours after injury, whereas noninjured cells remained quiescent. An i ncreased expression of platelet-derived growth factor (PDGF) A mRNA, n oted 6 hours after injury, was followed by an increased PDGF AA immuno reactivity in SMCs in and around the zone of injury at 24 and 48 hours after injury. A PDGF A chain antisense oligonucleotide inhibited 87.0 +/- 4.0% (P<.005) of SMC replication in the injury zone, whereas the corresponding sense oligonucleotide reduced SMC replication by only 37 .2%. An antibody to fibroblast growth factor (FGF) almost completely i nhibited SMC replication in the injured zone, whereas an antibody to P DGF AA was without effect. Incubation of SMCs with FGF increased PDGF A mRNA levels in SMCs, and 5 mu mol/L PDGF A antisense oligonucleotide s reduced FGF-induced SMC replication by 62%. Taken together, these re sults demonstrate that injured rat SMCs in culture release FGF that ac tivates DNA synthesis of neighboring SMCs both by a direct mechanism a nd by stimulating the production of PDGF AA.