Migration of Medial Smooth Muscle Cells to the Intima after Balloon Injury

Migration to the intima and other responses of M-SMC in the rat carotid artery and abdominal aorta after balloon injury were investigated in vivo. Migration occurred intensively between the second and fifth days after injury. About 80% of the cells were in the G1 and S phases of the cell cycle. The majority of the migrating cells were therefore simultaneously proliferating. Positive values of 42.3%, 48.9%, 44.4%, and 32.8% of the migrating cells on the fifth day in the carotid artery for PDGF-B, elastase III B, MMP-I, and MMP-9, were observed, respectively. Many of the cells expressed messages of PDGF-A and elastases II and III B by in situ hybridization. Fine structures of the migrating cells were characterized as a synthetic phenotype of the smooth muscle cell with reduced attachment to their surrounding ECM. A biphasic proliferative response of the M-SMC appeared on the second and fifth days. Migration occurred correspondingly in the proliferative period. The populations of M-SMC positive in immunostainings for PDGFs, their receptors, elastase III B, and MMP-1 and MMP-9 also increased biphasically, around 12 h and five days after the injury. The results of these studies suggest that the migrating cells were proliferative and synthesizing PDGFs, elastases, and collagenases.