Background: Myofibroblasts are a prominent cell type in wound healing. The goal of this study was to examine the extent to which myofibroblasts contribute to structural changes in saphenous vein bypass grafts.
Methods and results: Control veins and reversed saphenous vein bypass conduits of porcine carotid arteries were examined 2 to 4, 7 to 14, and 30 to 90 days after surgery with immunohistochemical markers of cellular proliferation (proliferating cell nuclear antigen), cytoskeletal protein production (alpha-smooth muscle actin and desmin), and histochemistry (Verhoeff's stain). Control veins demonstrated an extremely low level of cellular proliferation and no evidence of myofibroblasts in the adventitia, media, or intima. After bypass grafting, cellular proliferation was followed by myofibroblast formation, which occurred in the perivascular area and within the media. This was evidenced by a dense, but transient, expression of alpha-smooth muscle actin and a variable expression of desmin at 1 to 2 weeks, and with a significant increase in collagenous tissue by 1 to 3 months. Major cytoskeletal protein changes also occurred in the intima, with the appearance of alpha-smooth muscle actin positive cells at 7 to 14 days. alpha-Smooth muscle actin was still present in the neointima at 1 to 3 months, which is compatible with a persistent myofibroblast formation.
Conclusion: Myofibroblast formation occurs around and within saphenous veins after bypass grafting. This phenomenon is associated with significant remodeling of the vein grafts. The histologic changes are strikingly similar to events that occur during wound healing and may have implications for the development of neointimal hyperplasia and late vein graft disease.