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Paradoxical activation of endothelial nitric oxide synthase by NADPH oxidase.

ABSTRACT: Increased formation of reactive oxygen species (ROS) has been identified as a causative factor in endothelial dysfunction by reducing NO bioavailability and uncoupling endothelial nitric oxide synthase (eNOS). However, the specific contribution of ROS to endothelial function is not well understood.A major source of intracellular ROS is the NADPH oxidase (Nox) family of enzymes. The goal of the current study was to directly assess the contribution of NADPH oxidase derived superoxide to eNOS function by expressing Nox5, a single gene product that constitutively produces superoxide within cells. Paradoxically, we found that instead of inhibiting eNOS, coexpression of Nox5 increased NO release from both bovine and human endothelial cells. To establish the functional significance of this observation in intact blood vessels, the endothelium of mouse aorta was transduced with Nox5 or control adenoviruses. Nox5 potently inhibited Ach-induced relaxation and potentiated contractile responses to phenylephrine. In precontracted aortae, acute exposure to superoxide dismutase induced significant vascular relaxation in vessels exposed to Nox5 versus control and unmasked the ability of Nox5 to activate eNOS in blood vessel endothelium.These findings suggest that ROS inhibit eNOS function via consumption of NO rather than direct inhibition of enzymatic activity.

SUBMITTER: Zhang Q

PROVIDER: S-EPMC2771553 | biostudies-other | 2008 Sep

REPOSITORIES: biostudies-other

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Paradoxical activation of endothelial nitric oxide synthase by NADPH oxidase.

Zhang Qian Q Malik Pulkit P Pandey Deepesh D Gupta Sonali S Jagnandan Davin D Belin de Chantemele Eric E Banfi Botond B Marrero Mario B MB Rudic R Daniel RD Stepp David W DW Fulton David J R DJ

Arteriosclerosis, thrombosis, and vascular biology 20080612 9

<h4>Objective</h4>Increased formation of reactive oxygen species (ROS) has been identified as a causative factor in endothelial dysfunction by reducing NO bioavailability and uncoupling endothelial nitric oxide synthase (eNOS). However, the specific contribution of ROS to endothelial function is not well understood.<h4>Methods and results</h4>A major source of intracellular ROS is the NADPH oxidase (Nox) family of enzymes. The goal of the current study was to directly assess the contribution of ...[more]

PMID: 18556569

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Project description:We have previously shown that NADPH oxidase (NOX) lies upstream of uncoupled endothelial nitric oxide synthase (eNOS), which is known to occur in diabetic endothelium. However, it remains unclear which specific NOX isoform(s) is responsible for eNOS uncoupling and endothelial dysfunction in diabetic mouse models. The aim of the present study was to test the hypothesis that one or more NOX isoform(s) mediate(s) diabetic uncoupling of eNOS, which has been shown to occur in patients with diabetes to contribute to endothelial dysfunction.Diabetes was induced by streptozotocin administration. The N (?)-nitro-L-arginine methyl ester (L-NAME)-sensitive superoxide production of aortic segments, reflective of eNOS uncoupling activity, was determined by electron spin resonance.The L-NAME-sensitive superoxide production was more than doubled in wild-type diabetic mice, implicating uncoupling of eNOS. This was abolished in diabetic p47 ( phox-/-) (also known as Ncf1 (-/-)) mice, but preserved in Nox2 (-/y) (also known as Cybb (-/-)) mice made diabetic. The eNOS uncoupling activity was markedly attenuated in diabetic mice transfected with Nox1 or Nox1 organiser 1 (Noxo1) short interfering RNA (siRNA), and abolished in Nox1 (-/y) diabetic mice. Diabetes-induced impairment in endothelium-dependent vasorelaxation was also significantly attenuated in the Nox1 (-/y) mice made diabetic. By contrast, Nox4 siRNA, or inhibition of mitochondrial complex I or III with rotenone or siRNA, respectively, had no effect on diabetic uncoupling of eNOS. Overexpression of Dhfr, or oral administration of folic acid to improve dihydrofolate reductase (DHFR) function, recoupled eNOS in diabetes to improve endothelial function.Our data demonstrate for the first time that the p47(phox) and NOXO1-dependent activation of NOX1, but not that of NOX2, NOX4 or mitochondrion, mediates diabetic uncoupling of eNOS. NOX1-null mice are protected from diabetic endothelial dysfunction. Novel approaches to inhibit NOX1 and/or improve DHFR function, may prove to have therapeutic potential for diabetic endothelial dysfunction.

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Paradoxical activation of endothelial nitric oxide synthase by NADPH oxidase.

Publications

Paradoxical activation of endothelial nitric oxide synthase by NADPH oxidase.

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