Factors controlling smooth-muscle cell proliferation

Injury to the arterial wall normally elicits a rapid and significant increase in smooth-muscle cell (SMC) replication with the subsequent development of intimal lesions. A variety of factors have been proposed to control SMC replication, but recent work has highlighted the role of basic fibroblast growth factor (bFGF) and platelet-derived growth factor in this process. In the carotid artery of the uninjured rat, we have shown that the SMCs express mRNA for bFGF and that bFGF can be readily extracted from these arteries. Following mechanical injury to the artery, ie, after balloon injury, we suggested that bFGF is released from damaged cells and then stimulates adjacent SMCs. In support of this concept, the infusion of a blocking antibody to bFGF was found to significantly inhibit the early SMC replication induced by use of a balloon catheter. The addition of the antibody at the time of injury, however, did not inhibit the development of intimal lesions. In contrast, studies by us and other investigators have shown that platelet-derived growth factor is not directly important for SMC replication after balloon injury, but that it plays a key role in stimulating the migration of SMCs into the intima. Intimal SMC replication was not inhibited with antibodies to either bFGF or platelet-derived growth factor. Therefore, while significant inroads have been made in understanding the initial events, we still do not fully understand all the processes involved in the proliferation of arterial intimal lesions.