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Cultured vascular endothelial cell (EC) exposure to steady laminar shear stress results in peroxynitrite ([ONOO.sup.-]) formation intramitochondrially and inactivation of the electron transport chain. We examined whether the 'hyperoxic state' of 21% [O.sub.2], compared with more physiological [O.sub.2] tensions (P[O.sub.2]), increases the shear-induced nitric oxide (NO) synthesis and mitochondrial superoxide ([O.sub.2*.sup.-]) generation leading to [ONOO.sup.-] formation and suppression of respiration. Electron paramagnetic resonance oximetry was used to measure [O.sub.2] consumption rates of bovine aortic ECs sheared (10 dyn/[cm.sup.2], 30 min) at 5%, 10%, or 21% [O.sub.2] or left static at 5% or 21% [O.sub.2]. Respiration was inhibited to a greater extent when ECs were sheared at 21% [O.sub.2] than at lower P[O.sub.2] or left static at different P[O.sub.2]. Flow in the presence of an endothelial NO synthase (eNOS) inhibitor or a [ONOO.sup.-] scavenger abolished the inhibitory effect. EC transfection with an adenovirus that expresses manganese superoxide dismutase in mitochondria, and not a control virus, blocked the inhibitory effect. Intracellular and mitochondrial [O.sub.2*.sup.-] production was higher in ECs sheared at 21% than at 5% [O.sub.2], as determined by dihydroethidium and MitoSOX red fluorescence, respectively, and the latter was, at least in part, NO-dependent. Accumulation of NO metabolites in media of ECs sheared at 21% [O.sub.2] was modestly increased compared with ECs sheared at lower P[O.sub.2], suggesting that eNOS activity may be higher at 21% [O.sub.2]. Hence, the hyperoxia of in vitro EC flow studies, via increased NO and mitochondrial [O.sub.2*.sup.-] production, leads to enhanced [ONOO.sup.-] formation intramitochondrially and suppression of respiration. shear stress; endothelium; mitochondria; reactive oxygen species

There is evidence that nitric oxide (NO), superoxide ([O.sub.2.sup.*-]), and their associated reactive nitrogen species (RNS) produced by vascular endothelial cells (ECs) in response to hemodynamic forces play a role in cell signaling. NO is known to impair mitochondrial respiration. We sought to determine whether exposure of human umbilical vein ECs (HUVECs) to steady laminar shear stress and the resultant NO production modulate electron transport chain (ETC) enzymatic activities. The activities of respiratory complexes I, II/III, and IV were dependent on the presence of serum and growth factor supplement in the medium. EC exposure to steady laminar shear stress (10 dyn/[cm.sup.2]) resulted in a gradual inhibition of each of the complexes starting as early as 5 min from the flow onset and lasting up to 16 h. Ramp flow resulted in inhibition of the complexes similar to that of step flow. When ECs were sheared in the presence of the NO synthase inhibitor [N.sup.G]-nitro-L-arginine methyl ester (L-NAME: 100 [micro]M), the NO scavenger 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (c-PTIO; 100 [micro]M), or the peroxynitrite (ONO[O.sup.-]) scavenger uric acid (UA; 50 [micro]M), the flow-inhibitory effect on mitochondrial complexes was attenuated. In particular, L-NAME and UA abolished the flow effect on complex IV. Increased tyrosine nitration was observed in the mitochondria of sheared ECs, and UA blocked the shear-induced nitrotyrosine staining. In summary, shear stress induces mitochondrial RNS formation that inhibits the electron flux of the ETC at multiple sites. This may be a critical mechanism by which shear stress modulates EC signaling and function. oxidative stress; mitochondria; endothelium

Adhesion of flowing monocytes to hypoxia-reoxygenation-exposed endothelial cells: role of Rac1, ROS, and VCAM-1. Am J Physiol Cell Physiol 283: C93-C102, 2002. First published March 6, 2002; 10.1152/ajpcell.00301.2001.--Production of reactive oxygen species (ROS) by ischemic tissue after ischemia-reperfusion (I/RP) is an important factor that contributes to tissue injury. The small GTPase Rac1 mediates the oxidative burst, and ROS act on signaling pathways involved in expression of inflammatory genes. Because there is evidence implicating monocytes in the pathogenesis of I/RP injury, our objective was to determine the molecular mechanisms that regulate adhesive interactions between monocytes and hypoxia-reoxygenation (H/RO)-exposed cultured endothelial cells (ECs). When U937 cells were perfused over human umbilical vein ECs at 1 dyn/[cm.sup.2], H (1 h at 1% [O.sub.2])/RO (13 h) significantly increased the fluxes of rolling and stably adherent U937 cells. Either EC treatment with the antioxidant pyrrolidine dithiocarbamate (PDTC) or infection with AdRac1N17, which results in expression of the dominant-negative form of Rac1, abolished H/RO-induced ROS production, attenuated rolling, and abolished stable adhesion of U937 cells to H/RO-exposed ECs. Infection with AdRac1N17 also abolished H/RO-induced upregulation of vascular cell adhesion molecule (VCAM)-1. In turn, blocking VCAM-1 abolished U937 cell stable adhesion and slightly increased rolling. We concluded that the Rac1-dependent ROS partially regulate rolling and exclusively regulate stable adhesion of monocytic cells to ECs after H/RO and that stable adhesion, but not rolling, is mediated by ROS-induced expression of VCAM-1. reactive oxygen species; shear stress; endothelial cell adhesion molecules

Shear stress is known to stimulate an intracellular free calcium concentration ([Ca2+]i) response in vascular endothelial cells (ECs). [Ca2+]i is a key second messenger for signaling that leads to vasodilation and EC survival. Although it is accepted that the shear-induced [Ca2+]i response is, in part, due to Ca2+ release from the endoplasmic reticulum (ER), the role of mitochondria (second largest Ca2+ store) is unknown. We hypothesized that the mitochondria play a role in regulating [Ca2+]i in sheared ECs. Cultured ECs, loaded with a Ca2+-sensitive fluorophore, were exposed to physiological levels of shear stress. Shear stress elicited [Ca2+]i transients in a percentage of cells with a fraction of them displaying oscillations. Peak magnitudes, percentage of oscillating ECs, and oscillation frequencies depended on the shear level. [Ca2+]i transients/oscillations were present when experiments were conducted in Ca2+-free solution (plus lanthanum) but absent when ECs were treated with a phospholipase C inhibitor, suggesting that the ER inositol 1,4,5-trisphosphate receptor is responsible for the [Ca2+]i response. Either a mitochondrial uncoupler or an electron transport chain inhibitor, but not a mitochondrial ATP synthase inhibitor, prevented the occurrence of transients and especially inhibited the oscillations. Knockdown of the mitochondrial Ca2+ uniporter also inhibited the shear-induced [Ca2+]i transients/oscillations compared with controls. Hence, EC mitochondria, through Ca2+ uptake/release, regulate the temporal profile of shear-induced ER Ca2+ release. [Ca2+]i oscillation frequencies detected were within the range for activation of mechanoresponsive kinases and transcription factors, suggesting that dysfunctional EC mitochondria may contribute to cardiovascular disease by deregulating the shear-induced [Ca2+]i response. [ABSTRACT FROM AUTHOR]

There is evidence that nitric oxide (NO), superoxide (O2·-), and their associated reactive nitrogen species (RNS) produced by vascular endothelial cells (ECs) in response to hemodynamic forces play a role in cell signaling. NO is known to impair mitochondrial respiration. We sought to determine whether exposure of human umbilical vein ECs (HUVECs) to steady laminar shear stress and the resultant NO production modulate electron transport chain (ETC) enzymatic activities. The activities of respiratory complexes I, II/III, and IV were dependent on the presence of serum and growth factor supplement in the medium. EC exposure to steady laminar shear stress (10 dyn/cm²) resulted in a gradual inhibition of each of the complexes starting as early as 5 mm from the flow onset and lasting up to 16 h. Ramp flow resulted in inhibition of the complexes similar to that of step flow. When ECs were sheared in the presence of the NO synthase inhibitor NG-nitro-L-arginine methyl ester (L-NAME; 100 µM), the NO scavenger 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazolmne-1-oxyl-3-oxide (c-PTIO; 100 µM), or the peroxynitrite (ONOO-) scavenger uric acid (UA; 50 µM), the flow-inhibitory effect on mitochondrial complexes was attenuated. In particular, L-NAME and UA abolished the flow effect on complex IV. Increased tyrosine nitration was observed in the mitochondria of sheared ECs, and UA blocked the shear-induced nitrotyrosine staining. In summary, shear stress induces mitochondrial RNS formation that inhibits the electron flux of the ETC at multiple sites. This may be a critical mechanism by which shear stress modulates EC signaling and function. [ABSTRACT FROM AUTHOR]

Focuses on the factors influencing the adhesion of flowing monocytes to hypoxia-reoxygenation-exposed endothelial cells. Importance of reactive oxygen species production on tissue injury; Processes involved in the expression of inflammatory genes; Molecular mechanisms regulating adhesive interactions.