Objective-Proinflammatory mediators influence atherosclerosis by inducing adhesion molecules (eg, VCAM-1) on endothelial cells (ECs) via signaling intermediaries including p38 MAP kinase. Regions of arteries exposed to high shear stress are protected from inflammation and atherosclerosis, whereas low-shear regions are susceptible. Here we investigated whether the transcription factor Nrf2 regulates EC activation in arteries. Methods and Results-En face staining revealed that Nrf2 was activated in ECs at an atheroprotected region of the murine aorta where it negatively regulated p38 -VCAM-1 signaling, but was expressed in an inactive form in ECs at an atherosusceptible site. Treatment with sulforaphane, a dietary antioxidant, activated Nrf2 and suppressed p38 -VCAM-1 signaling at the susceptible site in wild-type but not Nrf2 Ϫ/Ϫ animals, indicating that it suppresses EC activation via Nrf2. Studies of cultured ECs revealed that Nrf2 inactivates p38 by suppressing an upstream activator MKK3/6 and by enhancing the activity of the negative regulator MKP-1. Key Words: Nrf2 Ⅲ arterial endothelium Ⅲ shear stress Ⅲ sulforaphane Ⅲ proinflammatory activation Ⅲ p38 Ⅲ MKK3/6 Ⅲ MKP-1 E arly atherosclerotic lesions contain monocytes and T-lymphocytes which are recruited from the circulation by adhesion to activated vascular endothelial cells (ECs). 1 This process is triggered by proinflammatory mediators (eg, TNF␣) which induce cellular adhesion molecules (eg, VCAM-1) via signaling intermediaries including p38 mitogen-activated protein (MAP) kinase, which is activated by phosphorylation by MAP kinase kinases 3 and 6 (MKK 3/6). 2,3 Vascular inflammation and atherosclerosis develop predominantly at distinct sites of the arterial tree located near branches and bends which are exposed to nonuniform blood flow, which exerts relatively low shear stress on vascular endothelium, whereas regions of arteries that are exposed to unidirectional high shear stress are protected. 4 -6 Proinflammatory activation of ECs is reduced at high-shear sites compared to low-shear regions, thus providing a potential explanation for the distinct spatial localization of vascular inflammation and lesion formation. 5,7-10 Similarly, the application of unidirectional high shear stress can suppress proinflammatory activation of cultured ECs, whereas low or oscillatory shear can act as a positive regulator of EC activation. 5,10 -15 The molecular mechanisms underlying the antiinflammatory effects of shear stress are uncertain, but previous studies of cultured cells have suggested a role for the transcription factor nuclear factor erythroid 2-related factor 2 (Nrf2). 16 -20 In unstimulated cells, Nrf2 is suppressed by kelch-like ECH-associated protein 1 (Keap1) which targets it for ubiquitination and proteasomal processing. Nrf2 can be activated by shear stress, dietary antioxidants (eg, sulforaphane) and other physiological stimuli which disrupt Keap1-Nrf2 interactions leading to stabilization and nuclear translocation of Nrf2. 16 -22 A previous study...

Cardiovascular pathologies are still the primary cause of death worldwide. The molecular mechanisms behind these pathologies have not been fully elucidated. Unravelling them will bring us closer to therapeutic strategies to prevent or treat cardiovascular disease. One of the major transcription factors that has been linked to both cardiovascular health and disease is NF-kappaB (nuclear factor kappaB). The NF-kappaB family controls multiple processes, including immunity, inflammation, cell survival, differentiation and proliferation, and regulates cellular responses to stress, hypoxia, stretch and ischaemia. It is therefore not surprising that NF-kappaB has been shown to influence numerous cardiovascular diseases including atherosclerosis, myocardial ischaemia/reperfusion injury, ischaemic preconditioning, vein graft disease, cardiac hypertrophy and heart failure. The function of NF-kappaB is largely dictated by the genes that it targets for transcription and varies according to stimulus and cell type. Thus NF-kappaB has divergent functions and can protect cardiovascular tissues from injury or contribute to pathogenesis depending on the cellular and physiological context. The present review will focus on recent studies on the function of NF-kappaB in the cardiovascular system.

Abstract

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Blood flow influences atherosclerosis by generating wall shear stress, which alters endothelial cell (EC) physiology. Low shear stress induces dedifferentiation of EC through a process termed endothelial-to-mesenchymal transition (EndMT). The mechanisms underlying shear stress-regulation of EndMT are uncertain. Here we investigated the role of the transcription factor Snail in low shear stress-induced EndMT. Studies of cultured EC exposed to flow revealed that low shear stress induced Snail expression. Using gene silencing it was demonstrated that Snail positively regulated the expression of EndMT markers (Slug, N-cadherin, α-SMA) in EC exposed to low shear stress. Gene silencing also revealed that Snail enhanced the permeability of endothelial monolayers to macromolecules by promoting EC proliferation and migration. En face staining of the murine aorta or carotid arteries modified with flow-altering cuffs demonstrated that Snail was expressed preferentially at low shear stress sites that are predisposed to atherosclerosis. Snail was also expressed in EC overlying atherosclerotic plaques in coronary arteries from patients with ischemic heart disease implying a role in human arterial disease. We conclude that Snail is an essential driver of EndMT under low shear stress conditions and may promote early atherogenesis by enhancing vascular permeability.

During cardiovascular development, fluid shear stress patterns change dramatically due to extensive remodeling. This biomechanical force has been shown to drive gene expression in endothelial cells and, consequently, is considered to play a role in cardiovascular development. The mechanism by which endothelial cells sense shear stress is still unidentified. In this study, we postulate that primary cilia function as fluid shear stress sensors of endothelial cells. Such a function already has been attributed to primary cilia on epithelial cells of the adult kidney and of Hensen's node in the embryo where they transduce mechanical signals into an intracellular Ca 2ϩ signaling response. Recently, primary cilia were observed on human umbilical vein endothelial cells. These primary cilia disassembled when subjected to high shear stress levels. Whereas endocardial-endothelial cells have been reported to be more shear responsive than endothelial cells, cilia are not detected, thus far, on endocardial cells. In the present study, we use field emission scanning electron microscopy to show shear stress-related regional differences in cell protrusions within the cardiovasculature of the developing chicken. Furthermore, we identify one of these cell protrusions as a monocilium with monoclonal antibodies against acetylated and detyrosinated alphatubulin. The distribution pattern of the monocilia was compared to the chicken embryonic expression pattern of the high shear stress marker Krü ppel-like factor-2. We demonstrate the presence of monocilia on endocardial-endothelial cells in areas of low shear stress and postulate that they are immotile primary cilia, which function as fluid shear stress sensors.

Primary cilia are mechanosensors for fluid shear stress, and are involved in a number of syndromes and congenital anomalies. We identified endothelial cilia in areas of low shear stress in the embryonic heart. The objective of the present study was to demonstrate the role of primary cilia in mechanosensing. Ciliated embryonic endothelial cells were cultured from the heart, and non-ciliated cells from the arteries. Nonciliated cells that were subjected to fluid shear stress showed significantly less induction of the shear marker Krü ppel-Like Factor-2, as compared to ciliated cells. In addition, ciliated cells from which the cilia were chemically removed show a similar decrease in flow response. This shows that primary cilia sensitize endothelial cells for fluid shear stress. In addition, we targeted and stabilized the connection of the cilium to the cytoplasm by treatment with Colchicine and Taxol/Paclitaxel, respectively, and show that microtubular integrity is essential to sense shear stress. Developmental Dynamics 237:725-735, 2008.

In this review, the role of wall shear stress in the chicken embryonic heart is analyzed to determine its effect on cardiac development through regulating gene expression. Therefore, background information is provided for fluid dynamics, normal chicken and human heart development, cardiac malformations, cardiac and vitelline blood flow, and a chicken model to induce cardiovascular anomalies. A set of endothelial shear stress-responsive genes coding for endothelin-1 (ET-1), lung Krüppel-like factor (LKLF/KLF2), and endothelial nitric oxide synthase (eNOS/NOS-3) are active in development and are specifically addressed.