No abstract

Hemodynamic shear stress, the blood flow-generated frictional force acting on the vascular endothelial cells, is essential for endothelial homeostasis under normal physiological conditions. Mechanosensors on endothelial cells detect shear stress and transduce it into biochemical signals to trigger vascular adaptive responses. Among the various shear-induced signaling molecules, reactive oxygen species (ROS) and nitric oxide (NO) have been implicated in vascular homeostasis and diseases. In this review, we explore the molecular, cellular, and vascular processes arising from shear-induced signaling (mechanotransduction) with emphasis on the roles of ROS and NO, and also discuss the mechanisms that may lead to excessive vascular remodeling and thus drive pathobiologic processes responsible for atherosclerosis. Current evidence suggests that NADPH oxidase is one of main cellular sources of ROS generation in endothelial cells under flow condition. Flow patterns and magnitude of shear determine the amount of ROS produced by endothelial cells, usually an irregular flow pattern (disturbed or oscillatory) producing higher levels of ROS than a regular flow pattern (steady or pulsatile). ROS production is closely linked to NO generation and elevated levels of ROS lead to low NO bioavailability, as is often observed in endothelial cells exposed to irregular flow. The low NO bioavailability is partly caused by the reaction of ROS with NO to form peroxynitrite, a key molecule which may initiate many pro-atherogenic events. This differential production of ROS and RNS (reactive nitrogen species) under various flow patterns and conditions modulates endothelial gene expression and thus results in differential vascular responses. Moreover, ROS/RNS are able to promote specific post-translational modifications in regulatory proteins (including S-glutathionylation, S-nitrosylation and tyrosine nitration), which constitute chemical signals that are relevant in cardiovascular pathophysiology. Overall, the dynamic interplay between local hemodynamic milieu and the resulting oxidative and S-nitrosative modification of regulatory proteins is important for ensuing vascular homeostasis. Based on available evidence, it is proposed that a regular flow pattern produces lower levels of ROS and higher NO bioavailability, creating an anti-atherogenic environment. On the other hand, an irregular flow pattern results in higher levels of ROS and yet lower NO bioavailability, thus triggering pro-atherogenic effects.

No abstract

In addition, data from tumor xenografts and human cancer specimens indicate that AGO1-mediated translational desuppression of VEGF may be associated with tumor angiogenesis and poor prognosis. These findings provide evidence for an angiogenic pathway involving HRMs that target AGO1 and suggest that this pathway may be a suitable target for anti-or proangiogenesis strategies.

Our data suggest that ROS are involved in Ang II-induced proliferation and ET-1 gene expression. Our findings imply that the combination of AT(I) and ET(A) receptor antagonists plus antioxidants may be beneficial in preventing the formation of excessive cardiac fibrosis.

Since endothelial cells are constantly subjected to pressure-induced strain, we examined how cyclic strain affects the expression of intercellular adhesion molecule-1 (ICAM-1). Endothelial cells grown on a flexible membrane base were deformed by different sinusoidal negative pressures (-10, -15, or -20 kPa) to produce an average strain of 9%, 11%, and 12%, respectively, for various times. The release of the soluble form of ICAM-1 from strained endothelial cells increased in a time- and strain-dependent manner. Using flow cytometric analysis, we showed the induction of ICAM-1 expression on the endothelial cell surface to depend on both time and the amount of strain. Northern blot analysis revealed a sustained, approximately 1.8-fold increase in ICAM-1 mRNA levels in 11% strained cells. Strain-induced expression of ICAM-1 correlated with a strain-dependent increase in adhesion of monocytic cells to strained cells. This increase in monocytic cell adhesion could be partially inhibited by pretreatment of strained cells with antibody to ICAM-1. These results indicate that mechanical strain can stimulate the expression of ICAM-1 by endothelial cells and thus contribute to the increased adhesion of monocytes to strained cells. Such strain-induced expression of ICAM-1 may contribute to the trapping of monocytes on local vascular walls where strain is high and to the initiation of atherogenesis, thus providing a possible link between hypertension and atherogenesis.

Abstract-Angiotensin II (Ang II) is involved in the pathogenesis of atrial fibrillation (AF). L-type calcium channel (LCC)expression is altered in AF remodeling. We investigated whether Ang II modulates LCC current through transcriptional regulation, by using murine atrial HL-1 cells, which have a spontaneous calcium transient, and an in vivo rat model. Ang II increased LCC ␣1C subunit mRNA and protein levels and LCC current density, which resulted in an augmented calcium transient in atrial myocytes. An Ϸ2-kb promoter region of LCC ␣1C subunit gene was cloned to the pGL3 luciferase vector. Ang II significantly increased promoter activity in a concentration-and time-dependent manner.Truncation and mutational analysis of the LCC ␣1C subunit gene promoter showed that cAMP response element (CRE) (Ϫ1853 to Ϫ1845) was an important cis element in Ang II-induced LCC ␣1C subunit gene expression. Transfection of dominant-negative CRE binding protein (CREB) (pCMV-CREBS133A) abolished the Ang II effect. Ang II (1 mol/L, 2 hours) induced serine 133 phosphorylation of CREB and binding of CREB to CRE and increased LCC ␣1C subunit gene promoter activity through a protein kinase C/NADPH oxidase/reactive oxygen species pathway, which was blocked by the Ang II type 1 receptor blocker losartan and the antioxidant simvastatin. In the rat model, Ang II infusion increased LCC ␣1C subunit expression and serine 133 phosphorylation of CREB, which were attenuated by oral losartan and simvastatin. In summary, Ang II induced LCC ␣1C subunit expression via a protein kinase C-, reactive oxygen species-, and CREB-dependent pathway and was blocked by losartan and simvastatin. [2][3][4] Moreover, blockade of the renin-angiotensin system has been shown to be an effective treatment of AF. 5 Ang II increases spontaneous calcium sparks 6,7 and L-type calcium channel (LCC) current (I CaL ) in cardiomyocytes. 7,8 However, downregulation of I CaL 9 and channel expression 10,11 are observed in AF. Whether Ang II increases or decreases I CaL channel subunit expression in atrial myocytes and the detailed signaling mechanisms are unknown. Accordingly, in the present study, we explored the chronic effect of Ang II on the transcriptional regulation of LCC channel subunits in atrial myocytes. We used a murine atrial cell line HL-1, which is the only available atrial myocyte cell line that continuously divides and maintains a differentiated cardiac phenotype with spontaneous depolarization. 10 We also used an in vivo rat model of Ang II infusion to verify the results obtained in the cellular study. We first found that Ang II increased LCC channel ␣1C subunit expression and augmented I CaL and calcium transient amplitude in HL-1 atrial myocytes. The detailed signaling mechanisms by which Ang II regulates the expression of LCC ␣1C subunits were also studied. Materials and Methods Culture and Transfection of HL-1 CardiomyocytesHL-1 myocytes were cultured in the Claycomb medium. Transient transfection of the HL-1 myocytes was performed using Lipo-

Post-translational S-nitrosylation of proteins in ECs can be detected by a reliable CyDye switch method. This flow-induced S-nitrosylation of endothelial proteins may be essential for the adaptation and remodelling of ECs under flow conditions.