Rapid development of vein graft atheroma in ApoE-deficient mice.

Several animal models manifesting lesions resembling neointimal hyperplasia of human vein grafts have been developed, but no spontaneous atheromatous lesions in their vein grafts have been observed. We developed and here characterize a new animal model of vein graft atheroma, a maturated atherosclerotic plaque, in apoE-deficient mice. The lesion displayed classical complex morphological features and heterogeneous cellular compositions and consisted of a fibrous cap, infiltrated mononuclear cells, foam cells, cholesterol crystal structure, necrotic core with calcification, and neovasculature. Cell component analysis revealed smooth muscle cells (SMCs) localized in the cap region, macrophages which made up a large portion of the lesions, and CD4+ T cells scattered under the cap. Importantly, apoptotic/necrotic cells determined by TUNEL assay in vein grafts into apoE-/- mice were significantly higher than wild-type mice, although a similar number of proliferating cell nuclear antigen-positive cells in both types of lesions was found. Interestingly, vascular SMCs cultivated from aortas of apoE-deficient mice showed a high rate of spontaneous apoptosis/necrosis and a higher rate of cell death stimulated by a nitric oxide donor, sodium nitroprusside, H(2)O(2), and oxidized low density lipoprotein (LDL), although no difference in proliferation of both SMCs incubated with platelet-derived growth factor, angiotensin II, LDL, and oxidized LDL was seen. Thus, the pathogenic mechanisms of vein graft atheroma involve increased intimal cell death initiated by biomechanical stress and amplified by hypercholesterolemia, which leads to continuous recruitment of blood mononuclear cells to constitute atheromatous lesions. This mouse model resembling human vein graft disease has many advantages over other animal models.

Biomechanical stress-induced apoptosis in vein grafts involves p38 mitogen-activated protein kinases.

The present study was designed to investigate whether apoptosis occurs in early-stage vein grafts and to determine the mechanisms by which mechanical stress contributes to apoptosis in vascular smooth muscle cells (SMCs). Apoptosis in vessel walls of mouse vein grafts was confirmed by morphological changes and by terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end labeling (TUNEL). TUNEL(+) cells in vein grafts 1, 4, and 8 wk postoperatively was 13%, 29%, and 21%, respectively, and apoptosis occurred mainly in veins grafted to arteries, remaining unchanged in vein-to-vein grafts. When mouse, rat, and human arterial SMCs were cultured on a flexible membrane and subjected to cyclic strain stress, apoptosis was observed in a time- and strength-dependent manner. All three types of SMCs showed apoptotic death as confirmed by TUNEL, propidium iodide, and annexin V staining. To further study the signal pathways leading to apoptosis, activities of p38, a subfamily of mitogen-activated protein kinases (MAPKs), were determined. Mechanical stress resulted in p38 MAPK activation, reaching high levels within 8 min. SB 202190, a specific inhibitor for p38 MAPKs, prevented SMC apoptosis in response to mechanical stress. SMC lines stably transfected with a dominant negative rac, an upstream signal transducer, or overexpressing MAPK phosphatase-1, a negative regulator for MAPKs, completely inhibited mechanical stress stimulated p38 activation and abolished mechanical stress-induced apoptosis. Thus, we provide solid evidence that one of the earliest events in venous bypass grafts is apoptosis, in which mechanical stress-induced p38-MAPK activation is responsible for transducing signals leading to apoptosis.-Mayr, M., Li, C., Zou, Y., Huemer, U., Hu, Y., Xu, Q. Biomechanical stress-induced apoptosis in vein grafts involves p38 mitogen-activated protein kinases.