Migration of adventitial myofibroblasts following vascular balloon injury: insights from in vivo gene transfer to rat carotid arteries

OBJECTIVES: Migration of adventitial fibroblasts, in addition to smooth muscle cell proliferation, plays a role in neointima formation following vascular injury. Previous studies have not directly addressed whether endogenous adventitial cells migrate towards the intima following balloon injury in the absence of medial dissection. We have employed an in vivo gene transfer technique to the rat carotid artery to directly label adventitial fibroblasts prior to balloon injury. METHODS: An adenoviral vector coordinating expression of nuclear targeted beta-galactosidase (AdLacZ) suspended in pluronic gel was applied to the perivascular surface of left carotid arteries of male Sprague-Dawley rats. Balloon catheter mediated vascular injury was performed on these arteries 4 days later and animals killed at 3, 7 and 14 days after injury. RESULTS: Expression of LacZ up to 14 days after application of the adenovirus was restricted only to the adventitia of uninjured arteries and absent from untransfected right carotid arteries. However, following balloon catheter injury, LacZ positive cells were observed within the medial layer of vessels by 3 days, and contributed to the population of cells within the neointima at 7-14 days. Adventitial cells in uninjured arteries did not express smooth muscle alpha-actin but after injury, LacZ positive cells migrating towards the lumen exhibited alpha-actin immunostaining, suggesting their change to a myofibroblastic phenotype. CONCLUSIONS: These findings provide direct evidence that adventitial fibroblasts migrate and contribute to neointima formation after balloon injury and show that in vivo gene transfer to the adventitia results in sustained transgene expression capable of labelling migrating adventitial cells within the media and neointima of injured vessels.