Contractile smooth muscle cell apoptosis early after saphenous vein grafting

Background. The media of saphenous veins is composed of two cell populations: smooth muscle (SMC) and non-smooth muscle (NSMC) cells. Previous studies demonstrate a loss of SMCs by 3 days after grafting, despite an increase in cell proliferation. The purpose of this study is to determine the rates of apoptotic cell death versus cell proliferation for the two major cell populations of the media. Methods. Veins (six/time point) were examined at 0.5, 1, 2, 4, 8, 24, and 48 hours after grafting in crossbred pigs. Terminal transferase-mediated dUTP nick end labeling (TUNEL) and proliferating cell nuclear antigen (PCNA) stains were used to assess apoptosis and proliferation. Apoptosis was also corroborated with confocal and electron microscopy. Results. Apoptosis was high in both cell populations: at 8 hours, SMC and NSMC apoptosis peaked at 14.5% ± 3.5% and 49.9% ± 7.8%, respectively. In contrast, cell proliferation was different between the two populations. SMC proliferation was low at all time points, whereas NSMC proliferation rose to 22% ± 5.4% by 48 hours. Conclusions. Medial SMCs are removed through apoptosis and appear to be replaced by fibrous tissue (NSMCs) early after vein grafting. This reciprocal change between the medial SMC and NSMC populations may contribute to late vein graft degeneration.