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Abstract-High blood pressure induces a mechanical stress on vascular walls and evokes oxidative stress and vascular dysfunction. The aim of this study was to characterize the intracellular signaling causing vascular oxidative stress in response to pressure. In carotid arteries subjected to high pressure levels, we observed not only an impaired vasorelaxation, increased superoxide production, and NADPH oxidase activity, but also a concomitant activation of Rac-1, a small G protein. Key Words: high pressure Ⅲ oxidative stress Ⅲ mechanotransduction Ⅲ integrin signaling Ⅲ endothelial dysfunction H ypertension is strictly associated with changes in cardiovascular structure and function that affect morbidity and mortality. 1,2 In particular, at the vascular level hypertension induces an impaired endothelial vasorelaxation, one of the main determinants of cardiovascular risk. 3,4 The increase in pressure within the vasculature generates a biomechanical stress, which is perceived and transmitted to the intracellular compartment through various mechanosensors, and it has been associated with increased production of reactive oxygen species (ROS), which is responsible for vascular dysfunction in hypertension. [5][6][7][8][9] Thus, it could be noteworthy to characterize the intracellular signaling conditioning the cellular machinery toward an increased ROS production in response to biomechanical stress induced by high blood pressure levels. Among the main sources of ROS in the vascular wall, NADPH oxidase seems the most relevant for the vascular dysfunction in hypertension. 7,10 NADPH oxidase is a multisubunit enzyme made up of a membraneassociated catalytic moiety and cytosolic regulatory components that must assemble to form the active oxidase. Activation of NADPH oxidase requires Rac-1, a small G protein, which migrates from cytosol to the plasma membrane, where it favors the assembly of NADPH oxidase subunits. 11,12 Interestingly, an intracellular signaling converging on Rac-1 can be activated not only by agonists binding to G-protein and tyrosine-kinase receptors but also by integrins, 13-15 a class of membrane receptors that link the extracellular matrix to intracellular space. So far, the activation of these latter molecules has been involved in actin polymerization and the rearrangement of the cytoskeleton induced by mechanical forces. 16 -19 Thus, integrins could sense the mechanical force induced by blood pressure on the cell surface and generate an intracellular signaling contributing to the enhanced vascular oxidative stress. 20,21 The aim of this study was to clarify the mechanical stress-induced intracellular signaling toward vascular oxida-

Overall our findings suggest that PI3Kγ inhibition could be a novel tool to modulate calcium influx in vascular smooth muscle cells, thus relaxing resistance arteries and lowering blood pressure.

OBJECTIVE-Since vascular dysfunction is a main trait of obese subjects, in the present study we evaluated the vascular impact of resistin, a recently discovered hormone markedly increased in obesity.RESEARCH DESIGN AND METHODS-We performed our analysis on aortic and mesenteric segments from young and old C57BL/6 mice and on cultured endothelial cells. Resistin-induced vascular effect was evaluated in vitro and in vivo. Molecular analyses were performed by immunoprecipitation and Western blotting.RESULTS-Recombinant murine resistin did not induce changes in either basal vascular tone or phenylephrine-induced vascular contraction. In contrast, both in vivo and in vitro administration of resistin significantly impaired dose-dependent insulin-evoked vasodilation by reducing endothelial nitric oxide synthase (eNOS) enzymatic activity. This effect of resistin was selective for insulin vascular action, since vasodilatation induced by increasing doses of acetylcholine or nitroglycerin was not influenced by the hormone. Molecular analysis of endothelial cells further detailed resistin-induced vascular resistance by showing impairment of insulin-evoked AKT and eNOS phosphorylations after exposure to resistin. Even this latter abnormality is selective of insulin signaling since AKT/eNOS phosphorylations are normally activated during acetylcholine stimulation. More important, the resistin-induced endothelial dysfunction depends on resistin's ability to alter insulin receptor substrate (IRS)-1 tyrosine/serine phosphorylation and its consequent interaction with phosphatidylinositol 3-kinase.CONCLUSIONS-Our results demonstrate that resistin is able to induce a selective vascular insulin resistance-impairing endothelial IRS-1 signaling pathway that leads to eNOS activation and vasodilation. Diabetes 57:577-583, 2008

Abstract-Hypertension can lead to subarachnoid hemorrhage and eventually to cerebral vasospasm. It has been suggested that the latter could be the result of oxidative stress and an inflammatory response evoked by subarachnoid hemorrhage.Because an unavoidable consequence of hemorrhage is lysis of red blood cells, we first tested the hypothesis on carotid arteries that the proinflammatory cytokine tumor necrosis factor-␣ contributes to vascular oxidative stress evoked by hemolysis. We observed that hemolysis induces a significant increase in tumor necrosis factor-␣ both in blood and in vascular tissues, where it provokes Rac-1/NADPH oxidase-mediated oxidative stress and vasoconstriction. Furthermore, we extended our observations to cerebral vessels, demonstrating that tumor necrosis factor-␣ triggered this mechanism on the basilar artery. Finally, in an in vivo model of subarachnoid hemorrhage obtained by the administration of hemolyzed blood in the cisterna magna, we demonstrated, by high-resolution ultrasound analysis, that tumor necrosis factor-␣ inhibition prevented and resolved acute cerebral vasoconstriction. Moreover, tumor necrosis factor-␣ inhibition rescued the hemolysis-induced brain injury, evaluated with the method of 2,3,5-triphenyltetrazolium chloride and by the histological analysis of pyknotic nuclei. In conclusion, our results demonstrate that tumor necrosis factor-␣ plays a crucial role in the onset of hemolysis-induced vascular injury and can be used as a novel target of the therapeutic strategy against cerebral vasospasm.