National Science Foundation Research Experiences for Undergraduates Structure and Function of Proteins

Blood flow throughout the vascular circuit exerts a tangential force called shear stress upon all vessel walls. Under homeostatic conditions, shear stress is maintained within a narrow range. It has been shown that an alteration from this normal range of shear stress activates a biochemical signaling cascade in a process termed mechanotransduction. Although the signaling mechanism has not been well defined, endothelial NADPH oxidase is known to be involved. Variation from the physiological values of shear stress results in an increase in NADPH oxidasegenerated reactive oxygen species. Superoxide, the principal species generated, has numerous atherogenic effects when present in abnormally high quantities. Thus, vascular susceptibility to atherosclerotic plaque formation is closely related to shear stress. Vessel geometry studies have shown that initial sites of atherosclerotic plaque formation coincide with vessel bifurcations. At such branching regions, the flow of blood at certain points becomes nonlaminar, resulting in an oscillatory shear stress which range exceeds that applied to a vessel wall subject to laminar flow. These portions of the vascular wall highly subject to plaque formation are characterized by increased endothelial NADPH oxidase activity. In phagocytic cells, the NADPH oxidase subunit gp91 is able to generate reactive oxygen species by itself. We wished to determine whether the gp91 expressed in endothelial cells is also the key player in the NADPH oxidase generation of reactive oxygen species, which would imply a crucial role for gp91 in the mechanotransduction pathway. We designed experiments to compare the expression of gp91 in MPAECs grown in static culture and those grown in an artificial capillary system and adapted to shear stress via fluid flow. Static culture of MPAECs mimics the sites of bifurcation in the vessel wall that are subjected to oscillatory shear stress with a net value of zero. Results indicated that gp91 expression is downregulated in flow-adapted cells as compared to those grown in static culture, suggesting that the level of gp91 expression may be an important factor in atherogenic and atheroprotective mechanisms.