Concomitant Proliferation and Caspase-3 Mediated Apoptosis in Response to Low Shear Stress and Balloon Injury

Background Arterial remodeling occurs as a response to hemodynamic change and direct vessel wall injury through the process of neointimal hyperplasia (NH). A concomitant response of vascular smooth muscle cell (VSMC) proliferation and apoptosis exists. The purpose of this study is to assess the cellular response of vessels following exposure to low shear stress (τ) and balloon injury in order to further elucidate the mechanisms underlying vascular injury. Our hypothesis is that the combination of low τ and balloon injury results in NH approximating that seen in clinical arterial restenosis, and that quantitative analysis of VSMC proliferation and apoptosis correlates with the associated increase in arterial remodeling. Methods and Results New Zealand White rabbits underwent surgery on the carotid artery creating low τ ( n =11), balloon injury ( n = 11), combined low τ and balloon injury ( n =11), and sham ( n = 13) groups. Experiments were terminated at 1, 3, and 28 d. Day 1 and 3 arteries were analyzed with immunohistochemistry for apoptotic markers, terminal transferase dUTP nick end labeling (TUNEL), and activated caspase-3, and a cellular proliferation marker, accumulated proliferating cell nuclear antigen (PCNA), as well as immunoblot analysis for activated caspase-3 and PCNA at day 3. There was significantly greater apoptosis in the combined group as compared with the other groups assessed by quantitative TUNEL and activated caspase-3 levels at both days 1 and 3. Similarly, an increase in cellular proliferation assessed by PCNA expression, was significantly greater in the combined group as compared with the other groups. At 28 d there was no difference in NH observed in the low τ (26 ± 3 μm) and balloon injury (51 ± 17 μm) groups. However, significantly more NH was observed in the combined group (151 ± 35 μm) as compared with the other groups. Conclusions An increase in VSMC apoptosis via a caspase-3 dependent pathway is up-regulated by 24 h in the face of combined low shear stress and balloon-induced vessel wall injury. Paradoxically, this increase in VSMC apoptosis is associated with a significant increase in neointimal thickening at 28 d. The concomitant increase of both apoptosis and proliferation are indicative of a robust arterial remodeling response.