Objective-Localization of atherosclerotic plaques typically correlates with areas of biomechanical strain where shear stress is decreased while stretch, thought to promote atherogenesis through enhanced oxidative stress, is increased. Methods and Results-In human cultured endothelial cells, nitric oxide synthase expression was exclusively shear stress-dependent whereas expression of glutathione peroxidase-1 (GPx-1), but not that of Cu 2ϩ /Zn 2ϩ -superoxide dismutase or Mn 2ϩ -superoxide dismutase, was upregulated solely in response to cyclic stretch. GPx-1 expression was also enhanced in isolated mouse arteries perfused at high pressure. Combined pharmacological and decoy oligodeoxynucleotide blockade revealed that activation of p38 MAP kinase followed by nuclear translocation of CCAAT/enhancer binding protein plays a pivotal role in stretch-induced GPx-1 expression in human endothelial cells. Antisense oligodeoxynucleotide knockdown of GPx-1 reinforced both their capacity to generate hydrogen peroxide and the transient stretch-induced expression of CD40, monocyte chemoatractant protein-1, and vascular cell adhesion molecule-1. Consequently, THP-1 monocyte adhesion to the GPx-1-depleted cells was augmented. Conclusions-Stretch-induced proatherosclerotic gene expression in human endothelial cells seems to be hydrogen peroxide-mediated. The concomitant rise in GPx-1 expression, but not that of other antioxidant enzymes, may comprise an adaptive mechanism through which the cells maintain their antiatherosclerotic properties in spite of a decreased bioavailability of nitric oxide. Key Words: glutathione peroxidase Ⅲ oxidative stress Ⅲ cyclic stretch Ⅲ endothelial cells Ⅲ atherosclerosis A therosclerotic plaques are often located at arterial bifurcations and curvatures. 1,2 Although the primary risk factors for atherosclerosis (ie, diabetes, dyslipidemia, hypertension, and cigarette smoking) contribute to pathophysiological mechanisms which affect the endothelium in general, they do not explain the focal nature of the disease. Otherwise, it is well known that biomechanical forces exerted on the vessel wall by the flowing blood tend to vary at these predilection sites due to oscillations in blood flow. 3 As a result, laminar shear stress is reduced, whereas volume (pressure)-dependent deformation of the vessel wall is enhanced. 3 Whereas laminar shear stress protects arteries from developing atherosclerosis by maintaining endothelial cell nitric oxide (NO) synthesis, cyclic deformation promotes atherosclerosis through an increased formation of reactive oxygen species (ROS), namely superoxide anions (O 2 Ϫ ). Both radicals rapidly neutralize each other, hence reducing the level of biologically active NO even further. 4 Whereas cyclic stretch in endothelial cells, presumably through activation of protein kinase C and subsequent assembly of NOX-2, 5,6 initially triggers the formation of O 2 Ϫ , this is rapidly converted to hydrogen peroxide (H 2 O 2 ) by the various superoxide dismutases (SOD) present in these cells....

Certain progestins, including MPA, attenuate the 17beta-E-induced NO-mediated inhibition of platelet aggregation by endothelial cells through preventing both eNOS and GTPCH I expression most likely via activation of glucocorticoid receptors.

Hormone replacement therapy with estroprogestin preparations is associated with an increased risk of venous and arterial thromboembolic events in postmenopausal women. This study examined whether progestins affect the formation of NO in endothelial cells, and, if so, to determine the underlying mechanism. Experiments were performed with human umbilical vein endothelial cells. Endothelial nitric oxide synthase (eNOS) expression was assessed by real-time polymerase chain reaction (PCR) and Western blot analysis, NO formation by electron spin resonance spectroscopy, nuclear translocation of the glucocorticoid receptor by immunofluorescence microscopy, and platelet aggregation by an aggregometer. Medroxyprogesterone acetate (MPA) and progesterone markedly decreased the eNOS mRNA and protein levels, whereas levonorgestrel and nomegestrol acetate had only small effects. This effect was associated with a decreased NO formation leading to a reduced ability of endothelial cells to prevent platelet aggregation and was prevented by knockdown of the glucocorticoid receptor using siRNA. MPA and progesterone, but not levonorgestrel and nomegestrol acetate, caused nuclear translocation of the glucocorticoid receptor. The present findings indicate that certain progestins, including MPA, reduce the antiaggregatory effect of endothelial cells by decreasing the expression of eNOS and the formation of NO in endothelial cells, an effect that is mediated via activation of glucocorticoid receptors.