| Arterial tortuosity is associated with cardiovascular diseases such as hypertension, atherosclerosis, and aneurysms. However, the process of tortuous development is poorly understood. Previous studies suggested that mechanical buckling of arteries under mechanical stress may relate to vessel tortuosity(Han 2011). One possibility is that arterial tortuosity develops due to artery remodeling initiated by buckling. However, the effect of buckling on arterial wall remodeling remains unclear. The objective of this study was to investigate the possible link between buckling and arterial tortuosity by evaluating cell proliferation and extracellular matrix remodeling in buckled arteries. We used an ex vivo organ culture model that allowed us to compare straight and buckled arteries while maintaining the same pressure and flow. Arteries were cultured for 3 days and 7 days, under a pressure of 200+/-20 mmHg and stretch ratio of 1.5. To examine arterial remodeling, endothelial cell and smooth muscle cell proliferation, collagen I content, elastin content, MMP9, fibronectin, arterial structure, local stress in the arterial wall were examined using BrdU staining, western blot, histological staining and mechanical analysis. Our results showed that after 3 days cell proliferation on the inner curve of buckled arteries and MMP9 levels on the outer curve of buckled arteries were significantly higher compared to the control group. No significant difference was observed for cell proliferation or MMP9 after 7 days in organ culture. Collagen I protein level, measured by western blot, did not change in both 3 day and 7 day organ culture; however, the trichrome stain showed that total collagen ratio significantly increased in the inner curve of the buckled artery after 7 days in organ culture. At the same time, stress analysis indicated that shear stress, circumferential stress, axial stress and radial stress were lower in the inner curve of buckled arteries compared to the control arteries, while the outer curve affords the highest shear stress and wall stress. Multiple linear regression analysis indicated that circumferential stress was significantly related with smooth muscle cell proliferation in the inner media. Fibronectin level, elastin content, wall thickness, deflection and curvature did not significantly change after 3-day and 7-day organ culture although deflection did increase gradually with days in organ culture. In conclusion, our results demonstrated, artery buckling stimulates cell proliferation as well as extracellular matrix remodeling, which could be factors contributing to the development of tortuosity. Shear stress is one possible stimulus of endothelial cell proliferation and MMP9 secretion, while circumferential stress correlates with smooth muscle cell proliferation. Our results improve our understanding of the mechanics of tortuosity formation, though further studies are needed to investigate longer term effect. |
