Regulation of vascular function by fluid mechanical forces. Development of a new vascular experimental platform for integrative physiological and molecular biological studies of living conduit vessels

Abstract

The vascular endothelium is a multifunctional interface between blood flow and target organs and is continuously exposed to fluid mechanical forces such as shear stress, compressive, and tensile forces. Both in vivo and in vitro data indicate that biomechanical forces exert important modulating effects on key vascular functions. However, previous studies have provided limited data on the direct links between cellular and molecular mechanisms, on the one hand, and physiology at the level of the whole vessel, on the other.In the present work, a new vascular experimental platform for integrative physiological and molecular biological studies of intact conduit vessels was developed. This model is based on a computerized biomechanical vascular perfusion model, in which intact human conduit vessels could be exposed to well-defined fluid mechanical forces under controlled metabolic conditions. Based on this model, we performed initial biological studies of the differential effects of shear stress and intraluminal pressure on some key vascular regulatory systems at the levels of gene and protein expression, enzyme activity, and vasomotor behavior. Reverse transcriptase real-time PCR, quantitative immunohistochemistry, Western blot, on-line NO measurement, and hemodynamic measurements are major methods used in the thesis to evaluate the vascular responses.We have shown that shear stress and intraluminal pressure exert differential effects on vascular NO and ET-1 pathways. Chronic shear stress in combination with physiological pressure level up-regulates NO system at the levels of gene expression and enzyme synthesis, and these changes are of functional significance for the vessel´s vasomotor behavior. The intact vascular wall responds to acute elevation of intraluminal pressure by a sub-acute compensatory vasodilation, which is associated with up-regulated NO and down-regulated ET-1 expression. Sustained elevation of pressure alters the balance between the NO and ET-1 systems by inducing an elevated ET-1 expression, which diminishes the initial vasodilation. We could also demonstrate an independent role of biomechanical forces on the regulation of VEGF expression and thereby provide the first direct data to indicate that fluid mechanical forces are involved in long-term remodeling of the vascular network architecture. Further, we found that shear stress and intraluminal pressure exert distinct effects on several immediate-early genes encoding proteins in AP-1 transcription factor family, which appears to mediate the differential transcriptional regulatory effects of biomechanical forces. Taken together, fluid mechanical forces such as shear stress and blood pressure exert significant modulating effects on many critical vascular functions. The computerized biomechanical vascular perfusion model provides a new experimental platform for integrative physiological and molecular biological studies at the level of intact vessels. Increased knowledge about these basic and important physiological regulation systems may promote understanding of pathophysiological mechanisms behind several major cardiovascular diseases such as atherosclerosis, hypertension, and thromboembolic diseases, which potentially may help to generate new therapeutic strategies.