Atherosclerosis is an inflammatory disease, occurring preferentially in branched or curved arterial regions exposed to disturbed flow conditions including oscillatory shear stress (OS). In contrast, straight portions exposed to undisturbed laminar shear stress (LS) are relatively lesion free. The opposite effects of atheroprotective LS and proatherogenic OS are likely to be determined by differential expression of genes and proteins, including redox regulating factors. OS induces inflammation via mechanisms involving increased reactive oxygen species (ROS) production from the NADPH oxidases. Through a transcript profiling study and subsequent verification and functional studies, the authors discovered that OS induces inflammation by producing bone morphogenic protein 4 (BMP4) in endothelial cells. BMP4 stimulates expression and activity of NADPH oxidase requiring p47phox and Nox-1 in an autocrine-like manner. The NADPH oxidase activation by BMP4 then leads to ROS production, NF-kappaB activation, intercellular adhesion molecule 1 (ICAM-1) expression, and subsequent increased monocyte adhesivity of endothelial cells. It is proposed that endothelial NADPH oxidases play a critical role in disturbed flow- and BMP4-dependent inflammation, which is the critical early atherogenic response occurring in atheroprone areas. This emerging field of shear stress, BMP4, NADPH oxidases, inflammation, and atherosclerosis is reviewed.

Shear stress plays a significant role in endothelial cell biology and atherosclerosis development. Previous work by our group has shown that fluid flow stimulates important functional changes in cells through protein expression regulation. Peroxiredoxins (PRX) are a family of antioxidant enzymes but have yet to be investigated in response to shear stress. Studies have shown that oscillatory shear stress (OS) increases reactive oxygen species (ROS) levels in endothelial cells, whereas laminar shear stress (LS) blocks this response. We hypothesized that PRX are responsible for the anti-oxidative effect of LS. To test this hypothesis, bovine aortic endothelial cells (BAEC) were subjected to LS (15 dyn/cm 2 ), OS (؎5 dyn/cm 2 , 1 Hz), or static conditions for 24 h. Using Western blot and immunofluorescence staining, all six isoforms of PRX were identified in BAEC. When compared with OS and static, exposure to chronic LS up-regulated PRX 1 levels intracellularly. LS also increased expression of PRX 5 relative to static controls, but not OS. PRX exhibited broad subcellular localization, with distribution in the cytoplasm, Golgi, mitochondria, and intermediate filaments. In addition, PRX 1 knock down, using specific small interference RNA, attenuated LS-dependent reactive oxygen species reduction in BAEC. However, PRX 5 depletion did not. Together, these results suggest that PRX 1 is a novel mechanosensitive antioxidant, playing an important role in shear-dependent regulation of endothelial biology and atherosclerosis.Shear stress acting on the blood vessel wall plays an important role in the development of atherosclerosis. Straight regions of the arterial tree are considered "protected" from atherogenesis by high levels of unidirectional laminar shear stress (LS) 3 (1, 2). In contrast, plaque-prone areas in curves and bifurcations of the vasculature correspond to locales exposed to low or unstable shear stress, including oscillatory shear stress (OS) (2-4). These local mechanical forces have been correlated to the behavior of the exposed endothelium.Endothelial cells exposed to disturbed flow experience oxidative stress, inflammatory molecule expression, and monocyte recruitment as early signatures of atherosclerosis (5-9). In vitro studies have established that OS is a potent stimulator of reactive oxygen species (ROS) production in endothelial cells, and quantitative measurements by our group showed a significant increase in both OS-dependent superoxide (O 2 . ) and hydrogen peroxide (H 2 O 2 ) production (9 -12). We found that OS-stimulated ROS occurs in an NADPH oxidase-dependent manner and leads to inflammatory responses (ICAM-1) (intercellular adhesion molecule 1) expression and monocyte adhesion (10, 11). Conversely, LS acts to reduce ROS production and subsequent inflammatory response (10). Nevertheless, the mechanism by which LS restricts oxidative stress remains unclear. Antioxidant defense systems are critical to the protection of cellular macromolecules. They work to maintain a reductive cytosolic enviro...

Abstract-Vascular endothelial growth factor (VEGF) is a critical regulator of endothelial cell biology and vascular function. Chronic VEGF treatment has been shown to inhibit tumor necrosis factor-induced apoptosis in endothelial cells. However, the mechanism for this cell survival is unclear. Interestingly, VEGF also enhances the expression of X-linked inhibitor of apoptosis (XIAP), a well-established antiapoptotic factor. XIAP has been shown to suppress apoptosis by blocking caspase activity in cancer cells, but it remains under studied in the endothelium. Therefore, we hypothesized that VEGF affects important endothelial functions, such as apoptosis and cell migration, by regulating XIAP expression and downstream caspase activity. To test this hypothesis, caspase activity, apoptosis, and cell migration were assessed following XIAP overexpression or depletion in bovine aortic endothelial cells. Much like VEGF treatment, ectopic expression of XIAP blocked tumor necrosis factor-induced apoptosis. Surprisingly, the mechanism was caspase-independent. In addition, XIAP-associated cell survival was the result of enhanced nitric oxide (NO) production, and XIAP was partially localized in caveolae. In these lipid rafts, XIAP interacted with a regulator of NO production, caveolin-1, via a binding motif (FtFgtwiY, where the bold letters represent aromatic amino acids) in the baculoviral IAP repeat-3 domain. Endothelial NO synthase binding to caveolin-1 was competitively inhibited by XIAP, suggesting that XIAP acts as a modulator of NO production by releasing endothelial NO synthase from caveolin-1. Further studies showed that endothelial cell migration was also controlled by XIAP-dependent NO. Taken Key Words: VEGF Ⅲ XIAP Ⅲ caveolin-1 Ⅲ nitric oxide Ⅲ apoptosis E xtensive study of apoptosis has revealed a dichotomy of functions in the vascular system. In the endothelium, apoptosis contributes significantly to vascular pathology, as well as normal physiological function. In atherosclerotic plaques, apoptosis weakens the endothelial cell layer, promoting plaque rupture and atherothrombosis. 1 In contrast, apoptosis also acts as an important physiological mediator, eliminating unbalanced, harmful cells and maintaining vascular homeostasis. 2 Thus, the definition of apoptosis as an either physiological or pathological phenomenon requires careful dissection of distinct vascular apoptotic processes.Vascular endothelial growth factor (VEGF) is an endothelial cytokine that acts through the activation of VEGF receptor tyrosine kinases, eg, flkA/KDR and flt-1. 3 It is an important regulator of angiogenesis 4 and cell survival, or antiapoptosis, [5][6][7] and has been shown to act as a survival factor for newly formed blood vessels. Additional studies have found that VEGF also upregulates antiapoptotic proteins such as the inhibitors of apoptosis (IAPs) in human umbilical vein endothelial cells (HUVECs). 8 Cellular IAP homologs have been identified in many organisms, from yeasts to higher-order animals. 9 An important family m...