Effects of mechanical environment on regulation of structure and function in vascular endothelial cells

Abstract

Vascular endothelial cells (VEC) are continuously exposed to hemodynamic forces of tensile stress due to blood vessel dilations, and shear stress and pressure due to blood flow. These hemodynamic forces play an important role in VEC physiology and are closely related to the cardiovascular diseases. One such example is the atherosclerosis caused by an unusually low shear stress due to abnormal flow patterns in the blood vessel. Alterations in the shear stress caused by non-physiological flow conditions induce various changes in the structure and function of VEC by regulating the cytoskeleton and intercellular junction proteins. Therefore it is important to investigate the correlation between these protein expressions and the various flow conditions. We first develop a parallel plate flow chamber designed based on 3-D CFD (computational fluid dynamics) technique. In cultured VEC, the effects of various shear stresses and flow chamber geometries on junction and cytoskeleton proteins are observed using immunostaining and conventional microscopy. Experimental results show that cells have tendency of migrating against the flow and orienting more parallel to the direction of flow in a higher stress than a lower stress as time progresses. Moreover, cells divide less frequently as the magnitude of shear stress increases. In addition, the longer and thicker actin stress fibers form across the cytoplasm and connexin43 shows up-regulated expression as the duration of stress increases. In a set of experiments with hemodynamic features of atherosclerotic lesion-prone region, the cells near zero shear stress regions round up and become abnormally aggregated. Our findings provide new insights into the role of the mechanical stress on cytoskeleton rearrangement and the junction protein expression in regions prone to the pathogenesis of cardiovascular diseases such as atherosclerosis.