| Background and objectiveAtherosclerotic disease is one of the major hazards to human health. The pathogenic mechanism of atherosclerosis has been the focus of cardiovascular research field. Atherosclerotic plaques often appear in the low velocity blood flow and recirculation zone. Theory of lipid infiltration, thrombosis theory, doctrine and injury response of monoclonal theory can not well explain localization of atherosclerosis. Hemodynamic factors have a major role in incidence of atherosclerosis, and hemodynamic theory provides a new perspective for recognizing the the causes and pathogenesis of focal atherosclerosis. The time-related blood flow shear stress, especially low shear stress, plays a key role in the occurrence and development of atherosclerosis by causing vascular remodeling, upregulation the expression of endothelial adhesion molecules and lead to endothelial inflammation.Normal blood flow shear stress has an important regulatory role for the maintenance of vascular homeostasis, including anti-thrombosis, its barrier function and vascular homeostasis, etc. Changes in blood flow will lead to the occurrence of revascularization due to the destruction of vascular homeostasis. Vascular reconstruction is occurring changes in vascular structure and functions to meet internal or external environment, especially the mechanical environment changes, including adaptive rearrangement in early stage and pathological reconstruction in advanced stage which is the shared pathological basis of cardiovascular and cerebrovascular diseases. However, vascular remodeling mechanism is not clear in the field of cellular and molecular biology. Hemodynamic theory hold that, uniform laminar shear stress can induced endothelial anti-atherogenic gene expression selectively to offset the harmful effects of systemic risk factors, yet the abnormal shear stress will reduce the atherosclerosis resistant molecules and promote the expression of inflammatory cytokines of endothelium. Then accelerate the development of artery inflammation through activating the appropriate signal transduction pathways.Leukocyte is hard to adhesion to endothelium under normal circumstances, only when the interaction between external factors and endothelial cell increased endothelial adhesion molecules expression could help leukocyte adhesion to endothelium and transfer across the wall, which is the first step in the formation mechanism of atherosclerosis. In which P-selectin plays a decisive role in the initial adhesion and maintain the inflammatory state of early arterial lesions. Vascular cell adhesion molecule-1(VCAM-1) mainly play a role in the subsequent close adhesion of leukocytes and endothelial cells, and mediated leukocyte exudative and migration process, is also critical to maintain the endothelial inflammation by promote endothelial damage. To detect hemodynamic indicator early and study the vascular biological effects induced by shear stress deep will be great theoretical and practical significance for further revealing the nature of atherosclerosis and exploring the prevention and treatment methods.In the present study, we will create an animal model for local change of shear stress to analyze the arterial wall response at different patterns of fluid shear stress and evaluate the dynamic changes of vascular structure and adhesion molecules in endothelial cell under low shear stress. Methods1. Experimental animals and groups.20 Kunming mice were randomly divided into four groups:three short time stenosis groups (n=15) and sham operated group (n=5).25 Kunming mice were randomly divided into five groups:four long time stenosis groups (n=20) and sham operated group (n=5).2. Prepartion of mice model of abdominal aortic stenosis.we used a cast to induce standardized changes in shear stress. The cast imposes a fixed geometry on the vessel wall and thereby causes a stenosis, resulting a decrease in blood flow and consequently a lowered shear stress region upstream from the cast, and a vortex downstream from the cast (oscillatory blood flow). The upstream reduction in blood flow is caused by a device-induced. The downstream vortex is generated by a boundary separation immediately downstream from the cast, which is induced by a combination of velocity acceleration at the beginning of the cast, inertia of the blood, and the angle of the streamline at the end of the cast. For surgery, the test group mice were anesthetized with isoflurane, and the cast were placed around the abdominal aortic and fixed with a suture. The control group underwent sham operation without a cast. Artery samples were taken at 1 hour to 28 days after surgery and Determination of hemodynamic parameter, and reserved in -80℃.3. Determination of hemodynamic parameter.The shear stress values have been derived from measurements of vessel diameter and the velocity of blood flow which detected by Color Doppler Ultrasound, and capillary viscometer measured the viscosity of blood in 4 hours. The wall shear stress was calculated by Poiseiulle hydrodynamics formula (τm=η×4×Vm/D).4. Hematoxylin and eosin staining and morphological analysis of arterial.Pathological examination were performed to observe the arterial morphological changes. Using routine H&E staining of frozen sections. Sections were stained with hematoxylin and eosin. The intimal-media thickness and adventitia thickness of the aorta were measured. Morphology's analysis was made on the HE's photomicrograph by AutoCad picture analysis system. 5. Immunohistochemical staining and quantitative analysis.The immunohistochemical staining were performed for P-seletin and VCAM-1. All groups used two-step test:under the same conditions. The distribution of the positive cells was observed under the optical microscope, and were analyzed by Image-pro plus auto picture analysis system. One-way ANOVA was performed by using of SPSS 13.0 statistical package, data were expressed as mean±standard error.ResultsRegions of low shear stress and oscillatory shear stress were created upstream and downstream of the cast respectively. Vascular remodeling and P-selectin expression in the upstream arterial wall were much more severe than those in the downstream in all observed time-points (P<0.05). As compared with the control, with the increase of observed time, the changes of both wall thickness and the ratio of wall thickness to inner diameter were gradually greater at the area of low shear stress (P<0.05). The up-regulated expression of endothelial P-selectin was seen from 1 to 28 days at the area of low shear stress, the peak was at 7 days and above that the up-regulation attenuated (P<0.05). While the up-regulation of VCAM-1 was noted until 7 days (P<0.05), above 14 days the plateau was reached.Conclusions1. Vascular remodeling and endothelial P-selectin expression could happened in a relative short time when it exposured under low shear stress.2. Variant patterns of fluid shear stress may play different roles in the pathological process of artery.3. Low shear stress may play significantly initial roles in the pathological process of atherosclerosis resulting from endothelial inflammation... |
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