Peroxide generation by p47phox-Src activation of Nox2 has a key role in protein kinase C-induced arterial smooth muscle contraction

NADPH oxidase derived ROS promote arterial contraction in early postnatal rats by activation of L-type voltage-gated Ca2+ channels

Reactive oxygen species (ROS) produced by NADPH oxidase promote contraction of peripheral arteries, which is especially pronounced in early postnatal period in comparison to adulthood, but the mechanisms of such vasomotor influence are poorly understood. We tested the hypothesis that Rho-kinase and protein kinase C (PKC) mediate procontractile influence of NADPH oxidase derived ROS in peripheral artery of early postnatal rats. In addition, we evaluated the involvement Src-kinase and L-type voltage-gated Ca2+ channels (LTCC) into procontractile influence of ROS, produced by NADPH oxidase, because of their known interplay with Rho-kinase and PKC pathways. Saphenous arteries from 11- to 15-day-old male rats were studied using quantitative PCR, isometric myography and lucigenin-enhanced chemiluminescence. Arterial tissue of early postnatal rats contained Nox2, Nox4, Duox1 and Duox2 mRNAs, among which Nox2 mRNA was the most abundant. Pan-NADPH oxidase inhibitor VAS2870 (10 µM) significantly reduced arterial contractile responses to methoxamine. The inhibitors of Rho-kinase (Y27632, 3 µM), PKC (GF109203X, 10 µM) and Src-kinase (PP2, 10 µM), as well as LTCC blockers (nimodipine, 0.1 µM, and verapamil, 0.1 μM) also reduced methoxamine-induced contraction. Importantly, the effect of VAS2870 persisted in the presence of Rho-kinase, PKC or Src-kinase inhibitors, but not in the presence of LTCC blocker. Notably, the blockade of LTCC did not affect either basal or NADPH-induced O2•- production. Our data show that LTCC, but not Rho-kinase, PKC or Src-kinase are involved into procontractile effect of ROS, produced by NADPH oxidase, in saphenous artery of young rats. Сalcium influx through LTCC does not activate ROS production by NADPH oxidase.

Perinatal hypoxia augments contractile impact of NADPH oxidase-derived ROS in early postnatal rat arteries

BACKGROUND

 Reactive oxygen species (ROS), including those produced by NADPH oxidase (NOX), play an important vasomotor role, especially at early postnatal period. Mechanisms for regulating vascular tone can change significantly due to neonatal asphyxia and accompanying hypoxia. We tested the hypothesis that normobaric hypoxia (8% O2) for 2 h at the second day of life changes the functional contribution of NOX-derived ROS to the regulation of agonist-induced contraction in early postnatal rats.

METHODS

We studied saphenous arteries from 11- to 14-day-old male offspring using isometric myography and Western blotting and assessed the content of biochemical parameters in blood serum.

RESULTS

 The values of main biochemical parameters in blood serum and the protein content of NOXs and superoxide dismutases in arterial tissue did not differ between "Control" and "Hypoxia" pups. The NOX inhibitor VAS2870 equally reduced the contractile responses of arteries to α1-adrenoceptor agonist methoxamine in "Control" and "Hypoxia" pups, but its effect was more pronounced in the arteries from "Hypoxia" pups when vasocontraction was evoked by the agonist of thromboxane A2 receptors U46619.

CONCLUSION

 Perinatal hypoxia at the second day of life increases procontractile influence of NOX-derived ROS to the regulation of U46619-induced vasocontraction in the systemic arteries at early postnatal ontogenesis.

IMPACT

Nothing is known about programming effects of perinatal hypoxia, including birth asphyxia, on the ROS-mediated regulation of contraction in systemic arteries of early postnatal organism. 2-h normobaric hypoxia (8% O2) in rats at the second day of life increases the procontractile contribution of NOX-produced ROS to the regulation of U46619-induced vasocontraction in the systemic arteries at early postnatal ontogenesis. This fact may serve as a risk factor for the development of various disorders at later developmental stages and should be considered regarding the therapy for newborns who have suffered neonatal asphyxia.

Phospholipase C-β3 is dispensable for vascular constriction but indispensable for vascular hyperplasia

Angiotensin II (AngII) induces the contraction and proliferation of vascular smooth muscle cells (VSMCs). AngII activates phospholipase C-β (PLC-β), thereby inducing Ca2+ mobilization as well as the production of reactive oxygen species (ROS). Since contraction is a unique property of contractile VSMCs, signaling cascades related to the proliferation of VSMCs may differ. However, the specific molecular mechanism that controls the contraction or proliferation of VSMCs remains unclear. AngII-induced ROS production, migration, and proliferation were suppressed by inhibiting PLC-β3, inositol trisphosphate (IP3) receptor, and NOX or by silencing PLC-β3 or NOX1 but not by NOX4. However, pharmacological inhibition or silencing of PLC-β3 or NOX did not affect AngII-induced VSMC contraction. Furthermore, the AngII-dependent constriction of mesenteric arteries isolated from PLC-β3∆SMC, NOX1-/-, NOX4-/- and normal control mice was similar. AngII-induced VSMC contraction and mesenteric artery constriction were blocked by inhibiting the L-type calcium channel Rho-associated kinase 2 (ROCK2) or myosin light chain kinase (MLCK). The activation of ROCK2 and MLCK was significantly induced in PLC-β3∆SMC mice, whereas the depletion of Ca2+ in the extracellular medium suppressed the AngII-induced activation of ROCK2, MLCK, and vasoconstriction. AngII-induced hypertension was significantly induced in NOX1-/- and PLC-β3∆SMC mice, whereas LCCA ligation-induced neointima formation was significantly suppressed in NOX1-/- and PLC-β3∆SMC mice. These results suggest that PLC-β3 is essential for vascular hyperplasia through NOX1-mediated ROS production but is nonessential for vascular constriction or blood pressure regulation.

Role of c-Src and reactive oxygen species in cardiovascular diseases

Oxidative stress, caused by the over production of oxidants or inactivity of antioxidants, can modulate the redox state of several target proteins such as tyrosine kinases, mitogen-activated protein kinases and tyrosine phosphatases. c-Src is one such non-receptor tyrosine kinase which activates NADPH oxidases (Noxs) in response to various growth factors and shear stress. Interaction between c-Src and Noxs is influenced by cell type and primary messengers such as angiotensin II, which binds to G-protein coupled receptor and activates the intracellular signaling cascade. c-Src stimulated activation of Noxs results in elevated release of intracellular and extracellular reactive oxygen species (ROS). These ROS species disturb vascular homeostasis and cause cardiac hypertrophy, coronary artery disease, atherosclerosis and hypertension. Interaction between c-Src and ROS in the pathobiology of cardiac fibrosis is hypothesized to be influenced by cell type and stimuli. c-Src and ROS have a bidirectional relationship, thus increased ROS levels due to c-Src mediated activation of Noxs can further activate c-Src by promoting the oxidation and sulfenylation of critical cysteine residues. This review highlights the role of c-Src and ROS in mediating downstream signaling pathways underlying cardiovascular diseases. Furthermore, due to the central role of c-Src in activation of various signaling proteins involved in differentiation, migration, proliferation, and cytoskeletal reorganization of vascular cells, it is presented as therapeutic target for treating cardiovascular diseases except cardiac fibrosis.

Reactive Oxygen Species Scavenging Nanomedicine for the Treatment of Ischemic Heart Disease

Ischemic heart disease (IHD) is the leading cause of disability and mortality worldwide. Reactive oxygen species (ROS) have been shown to play key roles in the progression of diabetes, hypertension, and hypercholesterolemia, which are independent risk factors that lead to atherosclerosis and the development of IHD. Engineered biomaterial-based nanomedicines are under extensive investigation and exploration, serving as smart and multifunctional nanocarriers for synergistic therapeutic effect. Capitalizing on cell/molecule-targeting drug delivery, nanomedicines present enhanced specificity and safety with favorable pharmacokinetics and pharmacodynamics. Herein, the roles of ROS in both IHD and its risk factors are discussed, highlighting cardiovascular medications that have antioxidant properties, and summarizing the advantages, properties, and recent achievements of nanomedicines that have ROS scavenging capacity for the treatment of diabetes, hypertension, hypercholesterolemia, atherosclerosis, ischemia/reperfusion, and myocardial infarction. Finally, the current challenges of nanomedicines for ROS-scavenging treatment of IHD and possible future directions are discussed from a clinical perspective.

Activation of Coronary Arteriolar PKCβ2 Impairs Endothelial NO-Mediated Vasodilation: Role of JNK/Rho Kinase Signaling and Xanthine Oxidase Activation

Protein kinase C (PKC) activation can evoke vasoconstriction and contribute to coronary disease. However, it is unclear whether PKC activation, without activating the contractile machinery, can lead to coronary arteriolar dysfunction. The vasoconstriction induced by the PKC activator phorbol 12,13-dibutyrate (PDBu) was examined in isolated porcine coronary arterioles. The PDBu-evoked vasoconstriction was sensitive to a broad-spectrum PKC inhibitor but not affected by inhibiting PKCβ2 or Rho kinase. After exposure of the vessels to a sub-vasomotor concentration of PDBu (1 nmol/L, 60 min), the endothelium-dependent nitric oxide (NO)-mediated dilations in response to serotonin and adenosine were compromised but the dilation induced by the NO donor sodium nitroprusside was unaltered. PDBu elevated superoxide production, which was blocked by the superoxide scavenger Tempol. The impaired NO-mediated vasodilations were reversed by Tempol or inhibition of PKCβ2, xanthine oxidase, c-Jun N-terminal kinase (JNK) and Rho kinase but were not affected by a hydrogen peroxide scavenger or inhibitors of NAD(P)H oxidase and p38 kinase. The PKCβ2 protein was detected in the arteriolar wall and co-localized with endothelial NO synthase. In conclusion, activation of PKCβ2 appears to compromise NO-mediated vasodilation via Rho kinase-mediated JNK signaling and superoxide production from xanthine oxidase, independent of the activation of the smooth muscle contractile machinery.

Reactive Oxygen Species: Modulators of Phenotypic Switch of Vascular Smooth Muscle Cells

Reactive oxygen species (ROS) are natural byproducts of oxygen metabolism in the cell. At physiological levels, they play a vital role in cell signaling. However, high ROS levels cause oxidative stress, which is implicated in cardiovascular diseases (CVD) such as atherosclerosis, hypertension, and restenosis after angioplasty. Despite the great amount of research conducted to identify the role of ROS in CVD, the image is still far from being complete. A common event in CVD pathophysiology is the switch of vascular smooth muscle cells (VSMCs) from a contractile to a synthetic phenotype. Interestingly, oxidative stress is a major contributor to this phenotypic switch. In this review, we focus on the effect of ROS on the hallmarks of VSMC phenotypic switch, particularly proliferation and migration. In addition, we speculate on the underlying molecular mechanisms of these cellular events. Along these lines, the impact of ROS on the expression of contractile markers of VSMCs is discussed in depth. We conclude by commenting on the efficiency of antioxidants as CVD therapies.

NADPH oxidase in the vasculature: Expression, regulation and signalling pathways; role in normal cardiovascular physiology and its dysregulation in hypertension

The last 20-25 years have seen an explosion of interest in the role of NADPH oxidase (NOX) in cardiovascular function and disease. In vascular smooth muscle and endothelium, NOX generates reactive oxygen species (ROS) that act as second messengers, contributing to the control of normal vascular function. NOX activity is altered in response to a variety of stimuli, including G-protein coupled receptor agonists, growth-factors, perfusion pressure, flow and hypoxia. NOX-derived ROS are involved in smooth muscle constriction, endothelium-dependent relaxation and smooth muscle growth, proliferation and migration, thus contributing to the fine-tuning of blood flow, arterial wall thickness and vascular resistance. Through reversible oxidative modification of target proteins, ROS regulate the activity of protein tyrosine phosphatases, kinases, G proteins, ion channels, cytoskeletal proteins and transcription factors. There is now considerable, but somewhat contradictory evidence that NOX contributes to the pathogenesis of hypertension through oxidative stress. Specific NOX isoforms have been implicated in endothelial dysfunction, hyper-contractility and vascular remodelling in various animal models of hypertension, pulmonary hypertension and pulmonary arterial hypertension, but also have potential protective effects, particularly NOX4. This review explores the multiplicity of NOX function in the healthy vasculature and the evidence for and against targeting NOX for antihypertensive therapy.

GPCR transactivation signalling in vascular smooth muscle cells: role of NADPH oxidases and reactive oxygen species

The discovery and extension of G-protein-coupled receptor (GPCR) transactivation-dependent signalling has enormously broadened the GPCR signalling paradigm. GPCRs can transactivate protein tyrosine kinase receptors (PTKRs) and serine/threonine kinase receptors (S/TKRs), notably the epidermal growth factor receptor (EGFR) and transforming growth factor-β type 1 receptor (TGFBR1), respectively. Initial comprehensive mechanistic studies suggest that these two transactivation pathways are distinct. Currently, there is a focus on GPCR inhibitors as drug targets, and they have proven to be efficacious in vascular diseases. With the broadening of GPCR transactivation signalling, it is therefore important from a therapeutic perspective to find a common transactivation pathway of EGFR and TGFBR1 that can be targeted to inhibit complex pathologies activated by the combined action of these receptors. Reactive oxygen species (ROS) are highly reactive molecules and they act as second messengers, thus modulating cellular signal transduction pathways. ROS are involved in different mechanisms of GPCR transactivation of EGFR. However, the role of ROS in GPCR transactivation of TGFBR1 has not yet been studied. In this review, we will discuss the involvement of ROS in GPCR transactivation-dependent signalling.

Signalling pathways involved in p47phox -dependent reactive oxygen species in platelets of endotoxemic rats

Thrombocytopenia during sepsis is associated with a less favourable clinical outcome. Overproduction of reactive oxygen species (ROS) by different cell types contributes to sepsis. Platelets generate ROS, but the upstream pathways of NADPH oxidase activation are not completely understood. Here, we designed experiments in washed platelets from lipopolysaccharide (LPS)-treated rats to investigate the p47^phox activation and ROS generation, and its modulation by c-Src family kinase (c-Src), phosphoinositide 3-kinase (PI3K), protein kinase C (PKC) and protein kinase G (PKG). Rats were injected intraperitoneally with LPS (1 mg/kg), and at 48 hours thereafter, arterial blood was collected and washed platelets were obtained. Washed platelets were pre-incubated with different inhibitors and subsequently activated or not with ADP. Flow cytometry, Western blotting and ELISA were performed. We found that LPS significantly increased the p47^phox phosphorylation and ROS generation compared with the control group (P < 0.05). The enhanced ROS production in the LPS group was unaffected by the non-selective SFKs inhibitor PP2, the PI3K inhibitor wortmannin or the Akt inhibitor PPI-1. The cyclic GMP levels were 115% higher in activated platelets of LPS compared with the saline group (P < 0.05). Moreover, in the LPS group, the sGC inhibitor ODQ, the PKG inhibitor Rp-8-Br and the PKC inhibitor GF109203X abrogated the increased p47^phox phosphorylation and reduced the ROS levels. In conclusion, selective inhibitors of cGMP-PKG and PKC-p47^phox pathways that regulate ROS generation by LPS in platelets may help control the redox balance in sepsis improving the survival of patients.

Vascular dysfunction in the stroke-prone spontaneously hypertensive rat is dependent on constrictor prostanoid activity and Y chromosome lineage

Vascular dysfunction is a hallmark of hypertension and the strongest risk factor to date for coronary artery disease. As Y chromosome lineage has emerged as one of the strongest genetic predictors of cardiovascular disease risk to date, we investigated if Y chromosome lineage modulated this important facet in the stroke-prone spontaneously hypertensive rat (SHRSP) using consomic strains. Here, we show that vascular dysfunction in the SHRSP is attributable to differential cyclooxygenase (COX) activity with nitric oxide (NO) levels playing a less significant role. Measurement of prostacyclin, the most abundant product of COX in the vasculature, confirmed the augmented COX activity in the SHRSP aorta. This was accompanied by functional impairment of the vasodilatory prostacyclin (IP) receptor, while inhibition of the thromboxane (TP) receptor significantly ameliorated vascular dysfunction in the SHRSP, suggesting this is the downstream target responsible for constrictor prostanoid activity. Importantly, Y chromosome lineage was shown to modulate vascular function in the SHRSP through influencing COX activity, prostacyclin levels and IP dysfunction. Vascular dysfunction in the renal and intrarenal arteries was also found to be prostanoid and Y chromosome dependent. Interestingly, despite no apparent differences in agonist-stimulated NO levels, basal NO levels were compromised in the SHRSP aorta, which was also Y chromosome dependent. Thus, in contrast with the widely held view that COX inhibition is deleterious for the vasculature due to inhibition of the vasodilator prostacyclin, we show that COX inhibition abolishes vascular dysfunction in three distinct vascular beds, with IP dysfunction likely being a key mechanism underlying this effect. We also delineate a novel role for Y chromosome lineage in regulating vascular function through modulation of COX and basal NO levels.

Gene Expressions Underlying Mishandled Calcium Clearance and Elevated Generation of Reactive Oxygen Species in the Coronary Artery Smooth Muscle Cells of Chronic Heart Failure Rats

BACKGROUND

The calcium clearance and reactive oxygen species (ROS) generations in the coronary artery smooth muscle cells in chronic heart failure (HF) have not been fully investigated. Therefore, we attempted to understand the gene expressions underlying the mishandling of calcium clearance and the accumulations of ROS.

METHODS

We initially established an animal model of chronic HF by making the left anterior descending coronary artery ligation (CAL) in rats, and then isolated the coronary artery vascular smooth muscle cells from the ischemic and the nonischemic parts of the coronary artery vessels in 12 weeks after CAL operation. The intracellular calcium concentration and ROS level were measured using flow cytometry, and the gene expressions of sarco/endoplasmic reticulum Ca2+-ATPase (SERCA2a), encoding sarcoplasmic reticulum Ca2+-ATPase 2a, encoding sodium-calcium exchanger (NCX), and p47phox encoding a subunit of the nicotinamide adenine dinucleotide phosphate (NADPH) oxidase were examined using real-time quantitative reverse transcription polymerase chain reaction and Western blotting, respectively.

RESULTS

We found that the calcium accumulation and ROS generation in the coronary artery smooth muscle cells isolated from either the ischemic or the nonischemic part of the CAL coronary artery vessel were significantly increased irrespective of blood supply (all P < 0.01). Moreover, these were accompanied by the increased expressions of NCX and p47phox, the decreased expression of SERCA2a, and the increased amount of phosphorylated forms of p47phox in NADPH oxidase (all P < 0.05).

CONCLUSIONS

Our results demonstrated that the disordered calcium clearance and the increased ROS generation occurred in the coronary artery smooth muscle cells in rats with chronic HF produced by ligation of the left anterior descending coronary artery (CAL), and which was found to be disassociated from blood supply, and the increased generation of ROS in the cells was found to make concomitancy to the increased activity of NADPH oxidase in cytoplasm.

NADPH oxidase activation played a critical role in the oxidative stress process in stable coronary artery disease

OBJECTIVES

The study was designed to investigate the oxidative stress levels of endothelial progenitor cells (EPCs) in stable coronary artery disease (CAD) and to explore the underlying mechanisms of NADPH oxidase activation and subsequent EPCs dysfunction.

METHODS

EPCs were isolated from patients with stable CAD (n=50) and matched healthy volunteers (n=50). NADPH oxidase activation was detected by measuring the expression of each subunit using western blotting and qPCR analyses and the membrane translocation of p47^phox using immunofluorescence. The in vivo angiogenesis capacity was evaluated using immunofluorescence by transplanting EPCs into a rat hind limb ischemia model. The PKC inhibitor GÖ-6983 was used to determine the role of PKC in NADPH oxidase activation.

RESULTS

Oxidative stress level was increased and the in vivo angiogenesis capacity was impaired in EPCs obtained from CAD subjects with the activation of NADPH oxidase. P47^phox membrane translocation increased in CAD group vs controls. These effects were resolved by NADPH oxidase inhibition. Up-regulation of PKCα/β2 was found in EPCs from CAD subjects, PKC inhibition GÖ-6983 could reduce the expression and activity of NADPH oxidation.

CONCLUSIONS

NADPH oxidase activation via p47^phox membrane translocation played a critical role in the initiation and progression of CAD, and the PKCα/β2 signaling pathway might be involved.

The NADPH Oxidases DUOX1 and NOX2 Play Distinct Roles in Redox Regulation of Epidermal Growth Factor Receptor Signaling

The epidermal growth factor receptor (EGFR) plays a critical role in regulating airway epithelial homeostasis and responses to injury. Activation of EGFR is regulated by redox-dependent processes involving reversible cysteine oxidation by reactive oxygen species (ROS) and involves both ligand-dependent and -independent mechanisms, but the precise source(s) of ROS and the molecular mechanisms that control tyrosine kinase activity are incompletely understood. Here, we demonstrate that stimulation of EGFR activation by ATP in airway epithelial cells is closely associated with dynamic reversible oxidation of cysteine residues via sequential sulfenylation and S-glutathionylation within EGFR and the non-receptor-tyrosine kinase Src. Moreover, the intrinsic kinase activity of recombinant Src or EGFR was in both cases enhanced by H₂O₂ but not by GSSG, indicating that the intermediate sulfenylation is the activating modification. H₂O₂-induced increase in EGFR tyrosine kinase activity was not observed with the C797S variant, confirming Cys-797 as the redox-sensitive cysteine residue that regulates kinase activity. Redox-dependent regulation of EGFR activation in airway epithelial cells was found to strongly depend on activation of either the NADPH oxidase DUOX1 or the homolog NOX2, depending on the activation mechanism. Whereas DUOX1 and Src play a primary role in EGFR transactivation by wound-derived signals such as ATP, direct ligand-dependent EGFR activation primarily involves NOX2 with a secondary role for DUOX1 and Src. Collectively, our findings establish that redox-dependent EGFR kinase activation involves a dynamic and reversible cysteine oxidation mechanism and that this activation mechanism variably involves DUOX1 and NOX2.

Functional Heterogeneity of Nadph Oxidases in Atherosclerotic and Aneurysmal Diseases

NADPH oxidases (NOX) are enzymes that catalyze the production of reactive oxygen species (ROS). Four species of NOX catalytic homologs (NOX1, NOX2, NOX4, and NOX5) are reportedly expressed in vascular tissues. The pro-atherogenic roles of NOX1, NOX2, and their organizer protein p47^phox were manifested, and it was noted that the hydrogen peroxide-generating enzyme NOX4 possesses atheroprotective effects. Loss of NOX1 or p47^phox appears to ameliorate murine aortic dissection and subsequent aneurysmal diseases; in contrast, the ablation of NOX2 exacerbates the aneurysmal diseases. It is possible that the loss of NOX2 activates inflammatory cascades in macrophages in the lesions. Roles of NOX5 in vascular functions are currently undetermined, owing to the absence of this enzyme in rodents and the limitation of the experimental procedure. Thus, it is possible that the NOX family of enzymes exhibits heterogeneity in the atherosclerotic diseases. In this aspect, subtype-selective NOX inhibitor may be promising when NOX systems serve as a molecular target for atherosclerotic and aneurysmal diseases.

Potential role of mitochondrial superoxide decreasing ferrochelatase and heme in coronary artery soluble guanylate cyclase depletion by angiotensin II

Oxidation of the soluble guanylate cyclase (sGC) heme promotes loss of regulation by nitric oxide (NO) and depletion of sGC. We hypothesized that angiotensin II (ANG II) stimulation of mitochondrial superoxide by its type 1 receptor could function as a potential inhibitor of heme biosynthesis by ferrochelatase, and this could decrease vascular responsiveness to NO by depleting sGC. These processes were investigated in a 24-h organoid culture model of bovine coronary arteries (BCA) with 0.1 μM ANG II. Treatment of BCA with ANG II increased mitochondrial superoxide, depleted mitochondrial superoxide dismutase (SOD2), ferrochelatase, and cytochrome oxidase subunit 4, and sGC, associated with impairment of relaxation to NO. These processes were attenuated by organoid culture with 8-bromo-cGMP and/or δ-aminolevulinic acid (a stimulator of sGC by protoporphyrin IX generation and heme biosynthesis). Organoid culture with Mito-TEMPOL, a scavenger of mitochondrial matrix superoxide, also attenuated ANG II-elicited ferrochelatase depletion and loss of relaxation to NO, whereas organoid culture with Tempol, an extramitochondrial scavenger of superoxide, attenuated the loss of relaxation to NO by ANG II, but not ferrochelatase depletion, suggesting cytosolic superoxide could be an initiating factor in the loss of sGC regulation by NO. The depletion of cytochrome oxidase subunit 4 and sGC (but not catalase) suggests that sGC expression may be very sensitive to depletion of heme caused by ANG II disrupting ferrochelatase activity by increasing mitochondrial superoxide. In addition, cGMP-dependent activation of protein kinase G appears to attenuate these ANG II-stimulated processes through both preventing SOD2 depletion and increases in mitochondrial and extramitochondrial superoxide.

Chronic aldosterone administration causes Nox2-mediated increases in reactive oxygen species production and endothelial dysfunction in the cerebral circulation

OBJECTIVES

An elevated plasma aldosterone level is an independent cardiovascular risk factor. Although excess aldosterone promotes cardiovascular disease, no studies have examined the effect of increased plasma aldosterone on the cerebral circulation. A major source of vascular reactive oxygen species (ROS) during cardiovascular disease is the NADPH oxidases. Because Nox2-containing NADPH oxidase (Nox2 oxidase) is highly expressed in the cerebral endothelium, we postulated that it might contribute to ROS generation and vascular dysfunction in response to aldosterone. Here, we examined the effect of aldosterone and Nox2 oxidase on ROS production and endothelial dysfunction in the cerebral circulation, and whether the effects of aldosterone are exacerbated in aged mice.

METHODS AND RESULTS

In adult (average age ∼24-25 weeks) wild-type and Nox2-deficient (Nox2(/y)) mice, neither vehicle nor aldosterone (0.28  mg/kg per day for 14 days) affected blood pressure (measured using tail-cuff). By contrast, aldosterone treatment reduced dilation of the basilar artery (measured using myography) to the endothelium-dependent agonist acetylcholine in wild-type mice (P < 0.05), but had no such effect in Nox2(/y) mice (P > 0.05). Aldosterone increased basal and phorbol dibutyrate-stimulated superoxide production (measured using L-012-enhanced chemiluminesence) in cerebral arteries from wild-type but not from Nox2(/y) mice. In aged wild-type mice (average age ∼70 weeks), aldosterone treatment increased blood pressure, but had a similar effect on cerebral artery superoxide levels as in adult wild-type mice.

CONCLUSION

These data indicate that Nox2 oxidase mediates aldosterone-induced increases in ROS production and endothelial dysfunction in cerebral arteries from adult mice independently of blood pressure changes. Aldosterone-induced hypertension is augmented during aging.

ET-1 mediates the release of reactive oxygen species and TNF-α in lung tissue by protein kinase C α and β1

BACKGROUND

The aim of this study was to determine the involvement of protein kinase C (PKC) in the ET-1 induced generation of reactive oxygen species and TNF-α in rat lungs.

METHODS

Experiments were performed on 6 groups of rats: Group I: saline-treated control; Group II: saline followed by endothelin-1 (ET-1) (3μg/kg); Group III: saline followed by selective PKC αβ1 inhibitor (Gö6976) (2μg/kg); Group IV: Gö6976 (2μg/kg) administered 30min before ET-1 (3μg/kg); Group V: saline followed by the PKC activator phorbol 12-myristate 13-acetate (PMA) (50μg/kg); Group VI: Gö6976 (2μg/kg) administered 30min before PMA (50μg/kg). After 5h, the animals were euthanized and their lungs were isolated for measurements.

RESULTS

ET-1 resulted in increase in thiobarbituric acid reactive substances (TBARS) and hydrogen peroxide (H2O2) levels and lung edema, as well as a decrease in GSH/GSSG ratio compared to the controls. The level of TNF-α also was elevated in the presence of ET-1. Administration of Gö6976 30min before ET-1 injection significantly decreased lung edema, as well as the concentrations of TBARS, H2O2 and TNF-α, but increased the GSH/GSSG redox ratio compared to ET-1. Conversely, PMA elevated lung edema and TBARS, H2O2 and TNF-α concentrations, but decreased the GSH/GSSG redox ratio compared to the control group. Treatment with Gö6976 significantly ameliorated the PMA-induced oxidative stress parameters, decreased tissue TNF-α level, and lung edema.

CONCLUSION

Endothelin-1 induces ROS generation, increases TNF-α level and lung edema via activation of PKC αβ1.

Insulin elicits a ROS-activated and an IP₃-dependent Ca²⁺ release, which both impinge on GLUT4 translocation

Insulin signaling includes generation of low levels of H2O2; however, its origin and contribution to insulin-stimulated glucose transport are unknown. We tested the impact of H2O2 on insulin-dependent glucose transport and GLUT4 translocation in skeletal muscle cells. H2O2 increased the translocation of GLUT4 with an exofacial Myc-epitope tag between the first and second transmembrane domains (GLUT4myc), an effect additive to that of insulin. The anti-oxidants N-acetyl L-cysteine and Trolox, the p47(phox)-NOX2 NADPH oxidase inhibitory peptide gp91-ds-tat or p47(phox) knockdown each reduced insulin-dependent GLUT4myc translocation. Importantly, gp91-ds-tat suppressed insulin-dependent H2O2 production. A ryanodine receptor (RyR) channel agonist stimulated GLUT4myc translocation and insulin stimulated RyR1-mediated Ca(2+) release by promoting RyR1 S-glutathionylation. This pathway acts in parallel to insulin-mediated stimulation of inositol-1,4,5-trisphosphate (IP3)-activated Ca(2+) channels, in response to activation of phosphatidylinositol 3-kinase and its downstream target phospholipase C, resulting in Ca(2+) transfer to the mitochondria. An inhibitor of IP3 receptors, Xestospongin B, reduced both insulin-dependent IP3 production and GLUT4myc translocation. We propose that, in addition to the canonical α,β phosphatidylinositol 3-kinase to Akt pathway, insulin engages both RyR-mediated Ca(2+) release and IP3-receptor-mediated mitochondrial Ca(2+) uptake, and that these signals jointly stimulate glucose uptake.

Regulation of NADPH oxidase 5 by protein kinase C isoforms

NADPH oxidase5 (Nox5) is a novel Nox isoform which has recently been recognized as having important roles in the pathogenesis of coronary artery disease, acute myocardial infarction, fetal ventricular septal defect and cancer. The activity of Nox5 and production of reactive oxygen species is regulated by intracellular calcium levels and phosphorylation. However, the kinases that phosphorylate Nox5 remain poorly understood. Previous studies have shown that the phosphorylation of Nox5 is PKC dependent, but this contention was based on the use of pharmacological inhibitors and the isoforms of PKC involved remain unknown. Thus, the major goals of this study were to determine whether PKC can directly regulate Nox5 phosphorylation and activity, to identify which isoforms are involved in the process, and to understand the functional significance of this pathway in disease. We found that a relatively specific PKCα inhibitor, Ro-32-0432, dose-dependently inhibited PMA-induced superoxide production from Nox5. PMA-stimulated Nox5 activity was significantly reduced in cells with genetic silencing of PKCα and PKCε, enhanced by loss of PKCδ and the silencing of PKCθ expression was without effect. A constitutively active form of PKCα robustly increased basal and PMA-stimulated Nox5 activity and promoted the phosphorylation of Nox5 on Ser490, Thr494, and Ser498. In contrast, constitutively active PKCε potently inhibited both basal and PMA-dependent Nox5 activity. Co-IP and in vitro kinase assay experiments demonstrated that PKCα directly binds to Nox5 and modifies Nox5 phosphorylation and activity. Exposure of endothelial cells to high glucose significantly increased PKCα activation, and enhanced Nox5 derived superoxide in a manner that was in prevented by a PKCα inhibitor, Go 6976. In summary, our study reveals that PKCα is the primary isoform mediating the activation of Nox5 and this maybe of significance in our understanding of the vascular complications of diabetes and other diseases with increased ROS production.

Contractile protein expression is upregulated by reactive oxygen species in aorta of Goto-Kakizaki rat

Although it is known that blood vessels undergo remodeling in type 2 diabetes (T2D), the signaling pathways that underlie the structural and functional changes seen in diabetic arteries remain unclear. Our objective was to determine whether the remodeling in type 2 diabetic Goto-Kakizaki (GK) rats is evoked by elevated reactive oxygen species (ROS). Our results show that aortas from GK rats produced greater force (P < 0.05) in response to stimulation with KCl and U46619 than aortas from Wistar rats. Associated with these changes, aortic expression of contractile proteins (measured as an index of remodeling) and the microRNA (miR-145), which act to upregulate transcription of contractile protein genes, was twofold higher (P < 0.05) in GK than Wistar (age-matched control) rats, and there was a corresponding increase in ROS and decrease in nitric oxide signaling. Oral administration of the antioxidant Tempol (1 mmol/l) to Wistar and GK rats reduced (P < 0.05) myocardin and calponin expression. Tempol (1 mmol/l) decreased expression of miR-145 in Wistar and GK rat aorta. To elucidate the mechanism through which ROS increases miR-145, we measured their levels in freshly isolated aorta and cultured aortic smooth muscle cells incubated for 12 h in the presence of H2O2 (300 μmol/l). H2O2 increased expression of miR-145, and there were corresponding nuclear increases in myocardin, a miR-145 target protein. Intriguingly, H2O2-induced expression of miR-145 was decreased by U0126 (10 μmol/l), a MEK1/2 inhibitor, and myocardin was decreased by anti-miR-145 (50 nmol/l) and U0126 (10 μmol/l). Our novel findings demonstrate that ROS evokes vascular wall remodeling and dysfunction by enhancing expression of contractile proteins in T2D.

Reactive oxygen species, vascular Noxs, and hypertension: focus on translational and clinical research

SIGNIFICANCE

Reactive oxygen species (ROS) are signaling molecules that are important in physiological processes, including host defense, aging, and cellular homeostasis. Increased ROS bioavailability and altered redox signaling (oxidative stress) have been implicated in the onset and/or progression of chronic diseases, including hypertension.

RECENT ADVANCES

Although oxidative stress may not be the only cause of hypertension, it amplifies blood pressure elevation in the presence of other pro-hypertensive factors, such as salt loading, activation of the renin-angiotensin-aldosterone system, and sympathetic hyperactivity, at least in experimental models. A major source for ROS in the cardiovascular-renal system is a family of nicotinamide adenine dinucleotide phosphate oxidases (Noxs), including the prototypic Nox2-based Nox, and Nox family members: Nox1, Nox4, and Nox5.

CRITICAL ISSUES

Although extensive experimental data support a role for increased ROS levels and altered redox signaling in the pathogenesis of hypertension, the role in clinical hypertension is unclear, as a direct causative role of ROS in blood pressure elevation has yet to be demonstrated in humans. Nevertheless, what is becoming increasingly evident is that abnormal ROS regulation and aberrant signaling through redox-sensitive pathways are important in the pathophysiological processes which is associated with vascular injury and target-organ damage in hypertension.

FUTURE DIRECTIONS

There is a paucity of clinical information related to the mechanisms of oxidative stress and blood pressure elevation, and a few assays accurately measure ROS directly in patients. Such further ROS research is needed in humans and in the development of adequately validated analytical methods to accurately assess oxidative stress in the clinic.

Src tyrosine kinase mediates platelet-derived growth factor BB-induced and redox-dependent migration in metanephric mesenchymal cells

The adult kidney is derived from the interaction between the metanephric blastema and the ureteric bud. Platelet-derived growth factor (PDGF) receptor β is essential for the development of the mature glomerular tuft, as mice deficient for this receptor lack mesangial cells. This study investigated the role of Src tyrosine kinase in PDGF-mediated reactive oxygen species (ROS) generation and migration of metanephric mesenchymal cells (MMCs). Cultured embryonic MMCs from wild-type and PDGF receptor-deficient embryos were established. Migration was determined via wound-healing assay. Unlike PDGF AA, PDGF BB-induced greater migration in MMCs with respect to control. This was abrogated by neutralizing an antibody to PDGF BB. Phosphatidylinositol 3-kinase (PI3K) inhibitors suppressed PDGF BB-induced migration. Conversely, mitogen-activated protein kinase/extracellular signal-regulated kinase (MEK) inhibitors had no effect. Src inhibitors inhibited PDGF-induced cell migration, PI3K activity, and Akt phosphorylation. Adenoviral dominant negative Src (AD DN Src) abrogated PDGF BB-induced Akt phosphorylation. Hydrogen peroxide stimulated cell migration. PDGF BB-induced wound closure was inhibited by the antioxidants N-acetyl-l-cysteine, tiron, and the flavoprotein inhibitor diphenyleneiodonium. These cells express the NADPH oxidase homolog Nox4. Inhibiting Nox4 with antisense oligonucleotides or small interfering RNA (siRNA) suppressed PDGF-induced wound closure. Inhibition of Src with siRNA reduced PDGF BB-induced ROS generation as assessed by 2',7'-dichlorodihydrofluorescein diacetate fluorescence. Furthermore, PDGF BB-stimulated ROS generation and migration were similarly suppressed by Ad DN Src. In MMCs, PDGF BB-induced migration is mediated by PI3K and Src in a redox-dependent manner involving Nox4. Src may be upstream to PI3K and Nox4.

Polymerase delta interacting protein 2 sustains vascular structure and function

OBJECTIVE

On the basis of previous evidence that polymerase delta interacting protein 2 (Poldip2) increases reduced nicotinamide adenine dinucleotide phosphate (NADPH) oxidase 4 (Nox4) activity in vascular smooth muscle cells, we hypothesized that in vivo knockdown of Poldip2 would inhibit reactive oxygen species production and alter vascular function.

APPROACH AND RESULTS

Because homozygous Poldip2 deletion is lethal, Poldip2(+/-) mice were used. Poldip2 mRNA and protein levels were reduced by ≈50% in Poldip2(+/-) aorta, with no change in p22phox, Nox1, Nox2, and Nox4 mRNAs. NADPH oxidase activity was also inhibited in Poldip2(+/-) tissue. Isolated aortas from Poldip2(+/-) mice demonstrated impaired phenylephrine and potassium chloride-induced contractions, increased stiffness, and reduced compliance associated with disruption of elastic lamellae and excessive extracellular matrix deposition. Collagen I secretion was elevated in cultured vascular smooth muscle cells from Poldip2(+/-) mice and restored by H2O2 supplementation, suggesting that this novel function of Poldip2 is mediated by reactive oxygen species. Furthermore, Poldip2(+/-) mice were protected against aortic dilatation in a model of experimental aneurysm, an effect consistent with increased collagen secretion.

CONCLUSIONS

Poldip2 knockdown reduces H2O2 production in vivo, leading to increases in extracellular matrix, greater vascular stiffness, and impaired agonist-mediated contraction. Thus, unaltered expression of Poldip2 is necessary for vascular integrity and function.

Cell signaling through protein kinase C oxidation and activation

Due to the growing importance of cellular signaling mediated by reactive oxygen species (ROS), proteins that are reversibly modulated by these reactant molecules are of high interest. In this context, protein kinases and phosphatases, which act coordinately in the regulation of signal transduction through the phosphorylation and dephosphorylation of target proteins, have been described to be key elements in ROS-mediated signaling events. The major mechanism by which these proteins may be modified by oxidation involves the presence of key redox-sensitive cysteine residues. Protein kinase C (PKC) is involved in a variety of cellular signaling pathways. These proteins have been shown to contain a unique structural feature that is susceptible to oxidative modification. A large number of scientific studies have highlighted the importance of ROS as a second messenger in numerous cellular processes, including cell proliferation, gene expression, adhesion, differentiation, senescence, and apoptosis. In this context, the goal of this review is to discuss the mechanisms by which PKCs are modulated by ROS and how these processes are involved in the cellular response.

Oxidative stress, Noxs, and hypertension: experimental evidence and clinical controversies

Reactive oxygen species (ROS) are signaling molecules that influence many physiological processes. Increased ROS bioavailability and altered redox signaling (oxidative stress) have been implicated in chronic diseases including hypertension. Although oxidative stress may not be the sole cause of hypertension, it amplifies blood pressure elevation in the presence of other prohypertensive factors (salt, renin-angiotensin system, sympathetic hyperactivity). A major source for cardiovascular ROS is a family of non-phagocytic NADPH oxidases (Nox1, Nox2, Nox4, Nox5). Other sources of ROS involve mitochondrial electron transport enzymes, xanthine oxidase, and uncoupled nitric oxide synthase. Although evidence from experimental and animal studies supports a role for oxidative stress in the pathogenesis of hypertension, there is still no convincing proof that oxidative stress is a cause of human hypertension. However, what is clear is that oxidative stress is important in the molecular mechanisms associated with cardiovascular and renal injury in hypertension and that hypertension itself can contribute to oxidative stress. The present review addresses the putative function of ROS in the pathogenesis of hypertension and focuses on the role of Noxs in ROS generation in vessels and the kidney. Implications of oxidative stress in human hypertension are discussed, and clinical uncertainties are highlighted.

Constriction of retinal arterioles to endothelin-1: requisite role of rho kinase independent of protein kinase C and L-type calcium channels

PURPOSE

Although endothelin-1 (ET-1) is a potent vasoconstrictor peptide implicated in several retinal pathologies, the underlying mechanism of vasoconstriction is understood incompletely. We addressed this issue by assessing the contributions of extracellular calcium (Ca²⁺), L-type voltage-operated calcium channels (L-VOCCs), Rho kinase (ROCK), and protein kinase C (PKC) to ET-1-induced constriction of porcine retinal arterioles, all of which have been implicated commonly in vascular smooth muscle contraction.

METHODS

Porcine retinal arterioles (~50-100 μm) were isolated for vasomotor study and molecular assessment of ROCK isoforms.

RESULTS

Isolated arterioles developed stable basal tone at 55 cmH₂O luminal pressure and constricted to ET-1 (0.1 nM) with a 40 ± 6% reduction in resting diameter in 20 minutes. In the absence of extraluminal Ca²⁺, arterioles lost basal tone and failed to constrict to ET-1. Although L-VOCC inhibitor nifedipine reduced basal tone and blocked vasoconstriction to PKC activator PDBu, vasoconstriction to ET-1 was unaffected. The broad-spectrum PKC inhibitor Gö-6983 abolished vasoconstriction to PDBu, but did not alter ET-1-induced vasoconstriction or basal tone. Incubation of arterioles with ROCK inhibitor H-1152 abolished basal tone and vasoconstrictions to ET-1 and PDBu. Both ROCK1 and ROCK2 isoforms were expressed in the retinal arteriolar wall.

CONCLUSIONS

Extracellular Ca²⁺ entry via L-VOCCs and basal ROCK activity play important roles in the maintenance of basal tones of porcine retinal arterioles. ET-1-induced constriction is mediated by extracellular Ca²⁺ entry independent of L-VOCCs and by ROCK activation without the involvement of PKC. However, direct PKC activation can cause vasoconstriction via L-VOCC and ROCK signaling.

Regulation of NAD(P)H oxidases by AMPK in cardiovascular systems

Reactive oxygen species (ROS) and reactive nitrogen species (RNS) are ubiquitously produced in cardiovascular systems. Under physiological conditions, ROS/RNS function as signaling molecules that are essential in maintaining cardiovascular function. Aberrant concentrations of ROS/RNS have been demonstrated in cardiovascular diseases owing to increased production or decreased scavenging, which have been considered common pathways for the initiation and progression of cardiovascular diseases such as atherosclerosis, hypertension, (re)stenosis, and congestive heart failure. NAD(P)H oxidases are primary sources of ROS and can be induced or activated by all known cardiovascular risk factors. Stresses, hormones, vasoactive agents, and cytokines via different signaling cascades control the expression and activity of these enzymes and of their regulatory subunits. But the molecular mechanisms by which NAD(P)H oxidase is regulated in cardiovascular systems remain poorly characterized. Investigations by us and others suggest that adenosine monophosphate-activated protein kinase (AMPK), as an energy sensor and modulator, is highly sensitive to ROS/RNS. We have also obtained convincing evidence that AMPK is a physiological suppressor of NAD(P)H oxidase in multiple cardiovascular cell systems. In this review, we summarize our current understanding of how AMPK functions as a physiological repressor of NAD(P)H oxidase.

Redox regulation of protein kinases as a modulator of vascular function

Reactive oxygen species (ROS) are continuously generated in vascular tissues by various oxidoreductase enzymes. They contribute to normal cell signaling, and modulate vascular smooth muscle tone and endothelial permeability in response to physiological agonists and to various cellular stresses and environmental factors, such as hypoxia. While concentrations of ROS are normally tightly controlled by cellular redox buffer systems, if produced in excess they may contribute to vascular disease. Protein kinases are essential components of most cell signaling pathways, including those involving ROS. The functioning of several members of this highly diverse group of enzymes, which include receptor and nonreceptor tyrosine kinases, protein kinase C, mitogen-activated kinases, and Rho-kinase, are modified by ROS, either through direct oxidative modification or indirectly through modification of associated proteins such as tyrosine phosphatases and monomeric G proteins. In this review, we discuss the molecular mechanisms of redox modification of these proteins, the downstream pathways affected, the often complex interaction between major kinase pathways, and feedback to ROS production itself. We also discuss complicating factors such as differential actions of superoxide anion and hydrogen peroxide, questions concerning concentration dependence, and the significance of signaling microdomains.

Impairment by hypoxia or hypoxia/reoxygenation of nitric oxide-mediated relaxation in isolated monkey coronary artery: the role of intracellular superoxide

To investigate the effect of hypoxia or hypoxia/reoxygenation on vascular smooth muscle function, mechanical response of monkey coronary artery without endothelium was studied under normoxia, hypoxia, and hypoxia/reoxygenation. Hypoxia or hypoxia/reoxygenation impaired the relaxation by nitroglycerin or isosorbide dinitrate but not that by 8-bromoguanosine-3',5'-cyclic monophosphate or isoproterenol. Tempol restored the impaired relaxation by nitroglycerin or isosorbide dinitrate, but superoxide dismutase had no effect. Apocynin, an NADPH oxidase inhibitor, improved the nitroglycerin-induced relaxation under hypoxia, but not under reoxygenation. Under combined treatment of apocynin with oxypurinol (xanthine oxidase inhibitor), rotenone (mitochondria electron transport inhibitor), or both, hypoxic impairment of vasorelaxation was restored more effectively. Similarly, impairment of the nitroglycerin-induced vasorelaxation under hypoxia/reoxygenation was restored by combined treatment with three inhibitors, apocynin, oxypurinol, and rotenone. Increase in superoxide production under hypoxia tended to be inhibited by apocynin and that under hypoxia/reoxygenation was abolished by combined treatment with three inhibitors. These findings suggest that increased intracellular superoxide production under hypoxia or hypoxia/reoxygenation attenuates vasodilation mediated with a nitric oxide/soluble guanylyl cyclase, but not adenylyl cyclase, signaling pathway. The main source of superoxide production under hypoxia seems to be different from that under reoxygenation: superoxide is produced by NADPH oxidase during hypoxia, whereas it is produced by xanthine oxidase, mitochondria, or both during reoxygenation.[Supplementary Figure: available only at http://dx.doi.org/10.1254/jphs.11031FP].

Mechanism of glucose-6-phosphate dehydrogenase-mediated regulation of coronary artery contractility

We previously identified glucose-6-phosphate dehydrogenase (G6PD) as a regulator of vascular smooth muscle contraction. In this study, we tested our hypothesis that G6PD activated by KCl via a phosphatase and tensin homologue deleted on chromosome 10 (PTEN)-protein kinase C (PKC) pathway increases vascular smooth muscle contraction and that inhibition of G6PD relaxes smooth muscle by decreasing intracellular Ca(2+) ([Ca(2+)](i)) and Ca(2+) sensitivity to the myofilament. Here we show that G6PD is activated by membrane depolarization via PKC and PTEN pathway and that G6PD inhibition decreases intracellular free calcium ([Ca(2+)](i)) in vascular smooth muscle cells and thus arterial contractility. In bovine coronary artery (CA), KCl (30 mmol/l) increased PKC activity and doubled G6PD V(max) without affecting K(m). KCl-induced PKC and G6PD activation was inhibited by bisperoxo(pyridine-2-carboxyl)oxovanadate (Bpv; 10 μmol/l), a PTEN inhibitor, which also inhibited (P < 0.05) KCl-induced CA contraction. The G6PD blockers 6-aminonicotinamide (6AN; 1 mmol/l) and epiandrosterone (EPI; 100 μmol/l) inhibited KCl-induced increases in G6PD activity, [Ca(2+)](i), Ca(2+)-dependent myosin light chain (MLC) phosphorylation, and contraction. Relaxation of precontracted CA by 6AN and EPI was not blocked by calnoxin (10 μmol/l), a plasma membrane Ca(2+) ATPase inhibitor or by lowering extracellular Na(+), which inhibits the Na(+)/Ca(2+) exchanger (NCX), but cyclopiazonic acid (200 μmol/l), a sarcoplasmic reticulum Ca(2+) ATPase inhibitor, reduced (P < 0.05) 6AN- and EPI-induced relaxation. 6AN also attenuated phosphorylation of myosin phosphatase target subunit 1 (MYPT1) at Ser855, a site phosphorylated by Rho kinase, inhibition of which reduced (P < 0.05) KCl-induced CA contraction and 6AN-induced relaxation. By contrast, 6AN increased (P < 0.05) vasodilator-stimulated phosphoprotein (VASP) phosphorylation at Ser239, indicating that inhibition of G6PD increases PKA or PKG activity. Inhibition of PKG by RT-8-Br-PET-cGMPs (100 nmol/l) diminished 6AN-evoked VASP phosphorylation (P < 0.05), but RT-8-Br-PET-cGMPs increased 6AN-induced relaxation. These findings suggest G6PD inhibition relaxes CA by decreasing Ca(2+) influx, increasing Ca(2+) sequestration, and inhibiting Rho kinase but not by increasing Ca(2+) extrusion or activating PKG.

Glucose-6-phosphate dehydrogenase is a regulator of vascular smooth muscle contraction

Glucose-6-phosphate dehydrogenase (G6PD) is the rate-limiting enzyme in the pentose phosphate pathway and a major source of nicotinamide adenine dinucleotide phosphate reduced (NADPH), which regulates numerous enzymatic (including glutathione reductase and NADPH oxidase that, respectively, generates reduced glutathione and reactive oxygen species) reactions involved in various cellular actions, yet its physiological function is seldom investigated. We, however, recently showed that inhibiting G6PD causes precontracted coronary artery (CA) to relax in an endothelium-derived relaxing factor- and second messenger-independent manner. Here we assessed the role of G6PD in regulating CA contractility. Treating bovine CAs for 20 min with potassium chloride (KCl; 30 mM), amphotericin B (50 μM), or U46619 (100 nM) significantly (p < 0.05) increased both G6PD activity and glucose flux through the pentose phosphate pathway. The effect was Ca(2+) independent, and there was a corresponding increase in protein kinase C (PKC) activity. Activation of G6PD by KCl was blocked by the PKCδ inhibitor rottlerin (10 μM) or by knocking down PKCδ expression using siRNA. Phorbol 12, 13-dibutyrate (10 μM), a PKC activator, significantly increased G6PD phosphorylation and activity, whereas single (S210A, T266A) and double (S210A/T266A) mutations at sites flanking the G6PD active site significantly inhibited phosphorylation, shifted the isoelectric point, and reduced enzyme activity. Knocking down G6PD decreased NADPH and reactive oxygen species generation, and reduced KCl-evoked increases in [Ca(2+)](i) and myosin light chain phosphorylation, thereby reducing CA contractility. Similarly, aortas from G6PD-deficient mice developed less KCl/phorbol 12, 13-dibutyrate-evoked force than those from their wild-type littermates. Conversely, overexpression of G6PD augmented KCl-evoked increases in [Ca(2+)](i), thereby augmenting CA contraction. Our findings demonstrate that G6PD activity and NADPH is increased in activated CA in a PKCδ-dependent manner and that G6PD modulates Ca(2+) entry and CA contractions evoked by membrane depolarization.

Reactive oxygen species and vascular biology: implications in human hypertension

Increased vascular production of reactive oxygen species (ROS; termed oxidative stress) has been implicated in various chronic diseases, including hypertension. Oxidative stress is both a cause and a consequence of hypertension. Although oxidative injury may not be the sole etiology, it amplifies blood pressure elevation in the presence of other pro-hypertensive factors. Oxidative stress is a multisystem phenomenon in hypertension and involves the heart, kidneys, nervous system, vessels and possibly the immune system. Compelling experimental and clinical evidence indicates the importance of the vasculature in the pathophysiology of hypertension and as such much emphasis has been placed on the (patho)biology of ROS in the vascular system. A major source for cardiovascular, renal and neural ROS is a family of non-phagocytic nicotinamide adenine dinucleotide phosphate (NADPH) oxidases (Nox), including the prototypic Nox2 homolog-based NADPH oxidase, as well as other Noxes, such as Nox1 and Nox4. Nox-derived ROS is important in regulating endothelial function and vascular tone. Oxidative stress is implicated in endothelial dysfunction, inflammation, hypertrophy, apoptosis, migration, fibrosis, angiogenesis and rarefaction, important processes involved in vascular remodeling in hypertension. Despite a plethora of data implicating oxidative stress as a causative factor in experimental hypertension, findings in human hypertension are less conclusive. This review highlights the importance of ROS in vascular biology and focuses on the potential role of oxidative stress in human hypertension.

Redox regulation of responses to hypoxia and NO-cGMP signaling in pulmonary vascular pathophysiology

Pulmonary vascular responses elicited by hypoxia and NO-cGMP signaling are potentially influenced by ROS and redox mechanisms that change during the progression of disease processes. Our studies in endothelium-rubbed bovine pulmonary arteries suggest increased glucose-6-phosphate dehydrogenase levels (compared to coronary arteries) seem to maintain a tonic peroxide-mediated relaxation removed by hypoxia through NADPH fueling superoxide generation from Nox oxidase. The activities of glucose-6-phosphate dehydrogenase, oxidases (i.e., Nox4), and systems metabolizing superoxide and peroxide markedly influence hypoxic pulmonary vasoconstriction (HPV). Activation of soluble guanylate cyclase and cGMP protein kinase seems to participate in peroxide-elicited relaxation. Endogenous NO helps maintain low pulmonary arterial pressure and suppresses HPV. Multiple redox processes potentially occurring during the progression of pulmonary hypertension may also attenuate NO-mediated relaxation beyond its scavenging by superoxide, including oxidation of guanylate cyclase heme and thiols normally maintained by cytosolic NADPH redox control.

Hypoxic relaxation of penile arteries: involvement of endothelial nitric oxide and modulation by reactive oxygen species

Although obesity-related cardiovascular disease and hypoxia are associated with erectile dysfunction, little is known about the direct effects of hypoxia on penile arteries. In the present study, the effects of acute hypoxia (Po(2) = approximately 10 Torr, 20 min) were investigated in isolated penile arteries to determine the influence of endothelium removal, nitric oxide (NO) synthase (NOS), cyclooxygenase (COX), NADPH oxidase, changes in reactive oxygen species (ROS), and a high-fat diet. Hypoxia-relaxed penile arteries contracted with phenylephrine by approximately 50%. Relaxation to hypoxia and acetylcholine was reduced by endothelium removal and by inhibition of NOS (N(omega)-nitro-l-arginine) and COX (indomethacin) but was enhanced by Tempol and by NADPH oxidase inhibition with apocynin and gp91ds-tat. Basal superoxide levels detected by lucigenin chemiluminescence were reduced by Tempol and gp91ds-tat and were enhanced by NOS blockade. Hypoxic relaxant responses were enhanced by catalase and ebselen. Exogenous peroxide evoked relaxations of penile arteries, which were partially inhibited by endothelium removal and by the inhibition of COX and extracellular signal-regulated mitogen-activated protein kinase (MAPK) but enhanced by p38 MAPK blockade. The NO-dependent component of relaxation to hypoxia was impaired in penile arteries from high-fat diet-fed, obese rats associated with increased superoxide production. Thus hypoxic relaxation of penile arteries is partially mediated by endothelial NO in a manner that is normally attenuated by endogenous ROS production. Obesity further increases superoxide production and impairs the influence of NO. Therefore, cardiovascular disease involving decreased NO bioavailability and/or enhanced ROS generation may contribute to erectile dysfunction through impairing the relaxation of penile arteries to hypoxia.

Vascular dysfunction in cerebrovascular disease: mechanisms and therapeutic intervention

The endothelium plays a crucial role in the control of vascular homoeostasis through maintaining the synthesis of the vasoprotective molecule NO* (nitric oxide). Endothelial dysfunction of cerebral blood vessels, manifested as diminished NO* bioavailability, is a common feature of several vascular-related diseases, including hypertension, hypercholesterolaemia, stroke, subarachnoid haemorrhage and Alzheimer's disease. Over the past several years an enormous amount of research has been devoted to understanding the mechanisms underlying endothelial dysfunction. As such, it has become apparent that, although the diseases associated with impaired NO* function are diverse, the underlying causes are similar. For example, compelling evidence indicates that oxidative stress might be an important mechanism of diminished NO* signalling in diverse models of cardiovascular 'high-risk' states and cerebrovascular disease. Although there are several sources of vascular ROS (reactive oxygen species), the enzyme NADPH oxidase is emerging as a strong candidate for the excessive ROS production that is thought to lead to vascular oxidative stress. The purpose of the present review is to outline some of the mechanisms thought to contribute to endothelial dysfunction in the cerebral vasculature during disease. More specifically, we will highlight current evidence for the involvement of ROS, inflammation, the RhoA/Rho-kinase pathway and amyloid beta-peptides. In addition, we will discuss currently available therapies for improving endothelial function and highlight future therapeutic strategies.

Roles for Nox4 in the contractile response of bovine pulmonary arteries to hypoxia

Hypoxia appears to promote contraction [hypoxic pulmonary vasoconstriction (HPV)] of bovine pulmonary arteries (BPA) through removal of a peroxide-mediated relaxation. This study examines the roles of BPA Nox oxidases and mitochondria in the HPV response. Inhibitors of Nox2 (0.1 mM apocynin and 50 muM gp91-dstat) and mitochondrial electron transport (10 muM antimycin and rotenone) decreased superoxide generation in BPA without affecting contraction to 25 mM KCl or the HPV response. Transfection of BPA with small inhibitory RNA (siRNA) for Nox2 and Nox4 decreased Nox2 and Nox4 protein expression, respectively, associated with an attenuation of superoxide detection, without affecting 25 mM KCl contraction. However, Nox4 siRNA, but not Nox2, attenuated HPV in BPA. A Nox4 inhibitor plumbagin (10 muM) increased basal force, decreased superoxide detection and peroxide release, and caused BPA to relax under hypoxia. Although acute removal of peroxide with 0.1 mM ebselen increased 25 mM KCl contraction and decreased hypoxic contraction, prolonged treatment with ebselen only decreased hypoxic contraction without affecting 25 mM KCl contraction, suggesting basal peroxide levels also maintain a contractile mechanism not removed by acute hypoxia. Organ culture of BPA with transforming growth factor (TGF)-beta1 (4 nM) increased Nox4 expression, superoxide, peroxide, and the HPV response. Thus Nox2 and mitochondria are sources for superoxide generation in BPA, which do not appear to influence the HPV response. However, peroxide derived from superoxide generated by Nox4 appears to maintain a basal relaxation in BPA under normoxic conditions, which is removed under hypoxia leading to HPV. Peroxide generated by Nox4 may also function to maintain a contractile mechanism, which is not reversed by acute hypoxia.

Redox control of vascular smooth muscle migration

Vascular smooth muscle cell migration is important during vascular development and contributes to lesion formation in the adult vasculature. The mechanisms regulating migration of this cell type are therefore of great interest. Recent work has shown that reactive oxygen species (ROS) derived from NADPH oxidases are important mediators of promigratory signaling pathways. ROS regulate the intracellular signals responsible for lamellipodia formation, actin cytoskeleton remodeling, focal adhesion turnover, and contraction of the cell body. In addition, they contribute to matrix remodeling, a critical step to initiate and support vascular smooth muscle cell motility. Despite these recent advances in our understanding of the redox mechanisms that contribute to migration, additional work is needed to evaluate fully the potential of ROS-sensitive molecular signals as therapeutic targets to prevent inappropriate smooth muscle cell migration.

Functional linkage as a direction for studies in oxidative stress: α-adrenergic receptorsThis review is one of a selection of papers published in a Special Issue on Oxidative Stress in Health and Disease

The α-adrenergic receptors (adrenoceptors) are activated by the endogenous agonists epinephrine and norepinephrine. They are G protein-coupled receptors that may be broadly classified into α1 (subclasses α1A, α1B, α1D) and α2 (subclasses α2A, α2B, α2C). The α1-adrenoceptors act by binding to Gαq subunits of the G proteins, causing activation of phospholipase C (PLC). PLC converts phosphatidylinositol 4,5-bisphosphate into inositol trisphosphate (IP3) and diacylglycerol (DAG), which have downstream effects on cytosolic Ca2+ concentration. The α2-adrenoceptors bind to Gαi thus inhibiting adenylyl cyclase and decreasing cAMP levels. DAG alters protein kinase C activity and cAMP activates protein kinase A. The downstream pathways of the two receptors may also interact. Activation of α1- and α2-adrenoceptors in vascular smooth muscle results in vasoconstriction. However, the densities of individual receptor subclasses vary between vessel beds or between vessels of various sizes within the same bed. In vasculature, the densities of adrenoceptor subclasses differ between conduit arteries and arterioles. These differences, along with differences in coupling mechanisms, allow for fine regulation of arterial blood flow. This diversity is enhanced by interactions resulting from homo- and heterodimer formation of the receptors, metabolic pathways, and kinases. Reactive oxygen species generated in pathologies may alter α1- and α2-adrenoceptor cascades, change vascular contractility, or cause remodeling of blood vessels. This review emphasizes the need for understanding the functional linkage between α-adrenoceptor subtypes, coupling, cross talk, and oxidative stress in cardiovascular pathologies.

PKC-alpha mediates flow-stimulated superoxide production in thick ascending limbs

We showed that luminal flow increases net superoxide (O(2)(-)) production via NADPH oxidase in thick ascending limbs. Protein kinase C (PKC) activates NADPH oxidase activity in phagocytes, cardiomyocytes, aortic endothelial cells, vascular smooth muscle cells, and renal mesangial cells. However, the flow-activated pathway that induces NADPH oxidase activity in thick ascending limbs is unclear. We hypothesized that PKC mediates flow-stimulated net O(2)(-) production by thick ascending limbs. Initiation of flow (20 nl/min) increased net O(2)(-) production from 4 +/- 1 to 61 +/- 12 AU/s (P < 0.007; n = 5). The NADPH oxidase inhibitor apocynin completely blocked the flow-induced increase in net O(2)(-) production (2 +/- 1 vs. 1 +/- 1 AU/s; P > 0.05; n = 5). Flow-stimulated O(2)(-) was also blocked in p47(phox)-deficient mice. We measured flow-stimulated PKC activity with a fluorescence resonance energy transfer (FRET)-based membrane-targeted PKC activity reporter and found that the FRET ratio increased from 0.87 +/- 0.02 to 0.96 +/- 0.04 AU (P < 0.05; n = 6). In the absence of flow, the PKC activator phorbol 12-myristate 13-acetate (200 nM) enhanced net O(2)(-) production from 5 +/- 2 to 92 +/- 6 AU/s (P < 0.001; n = 6). The PKC-alpha- and betaI-selective inhibitor Gö 6976 (100 nM) decreased flow-stimulated net O(2)(-) production from 54 +/- 15 to 2 +/- 1 AU/s (P < 0.04; n = 5). Flow-induced net O(2)(-) production was inhibited in thick ascending limbs transduced with dominant-negative (dn)PKC-alpha but not dnPKCbetaI or LacZ (Delta = 11 +/- 3 AU/s for dnPKCalpha, 55 +/- 7 AU/s for dnPKCbetaI, and 63 +/- 7 AU/s for LacZ; P < 0.001; n = 6). We concluded that flow stimulates net O(2)(-) production in thick ascending limbs via PKC-alpha-mediated activation of NADPH oxidase.

NADPH oxidases: functions and pathologies in the vasculature

Reactive oxygen species are ubiquitous signaling molecules in biological systems. Four members of the NADPH oxidase (Nox) enzyme family are important sources of reactive oxygen species in the vasculature: Nox1, Nox2, Nox4, and Nox5. Signaling cascades triggered by stresses, hormones, vasoactive agents, and cytokines control the expression and activity of these enzymes and of their regulatory subunits, among which p22phox, p47phox, Noxa1, and p67phox are present in blood vessels. Vascular Nox enzymes are also regulated by Rac, ClC-3, Poldip2, and protein disulfide isomerase. Multiple Nox subtypes, simultaneously present in different subcellular compartments, produce specific amounts of superoxide, some of which is rapidly converted to hydrogen peroxide. The identity and location of these reactive oxygen species, and of the enzymes that degrade them, determine their downstream signaling pathways. Nox enzymes participate in a broad array of cellular functions, including differentiation, fibrosis, growth, proliferation, apoptosis, cytoskeletal regulation, migration, and contraction. They are involved in vascular pathologies such as hypertension, restenosis, inflammation, atherosclerosis, and diabetes. As our understanding of the regulation of these oxidases progresses, so will our ability to alter their functions and associated pathologies.

Mitochondrial-derived hydrogen peroxide inhibits relaxation of bovine coronary arterial smooth muscle to hypoxia through stimulation of ERK MAP kinase

Mitochondrial reactive oxygen species (ROS) are potentially important in vascular oxygen-sensing mechanisms because hypoxia appears to be a stimulus for mitochondrial ROS generation; however, scavenging of endogenous ROS does not alter relaxation of endothelium-denuded bovine coronary arteries (BCA) to hypoxia. The purpose of this study was to investigate the influence of increasing mitochondrial ROS on the relaxation of BCA to hypoxia. Increasing mitochondrial superoxide with inhibitors of electron transport (10 microM rotenone and antimycin) and by opening mitochondrial ATP-dependent K+ channels with 100 microM diazoxide were observed in this study to attenuate relaxation of BCA precontracted with 30 mM KCl to hypoxia by 68-76% and 38%, respectively. This effect of rotenone is not prevented by inhibiting NADPH oxidase (Nox) activation or scavenging superoxide with Peg-SOD; however, it is reversed 85% and 26% by increasing the consumption of intracellular peroxide by 0.1 mM ebselen and 32.5 U/ml Peg-catalase. Because inhibition of extracellular signal-regulated kinase (ERK) mitogen-activated protein (MAP) kinase (10 microM PD-98059), but not src kinase or rho kinase, also reverses the effects of rotenone by 69%, the peroxide-elicited force-enhancing effects of ERK appear to be attenuating the response to hypoxia. Rotenone increased the phosphorylation of ERK (by 163%). Activation of ERK in BCA with 0.1 mM peroxide or endogenous peroxide generated by stimulating Nox2 with a stretch treatment or contraction with 100 nM U-46619 also attenuated relaxation to hypoxia. Thus coronary arterial relaxation to hypoxia may be attenuated by pathophysiological conditions associated with increased peroxide generation by mitochondria or other sources that stimulate ERK.

PKC-dependent superoxide production by the renal medullary thick ascending limb from diabetic rats

Type 1 diabetes (T1D) is a state of oxidative stress accompanied by PKC activation in many tissues. The primary site of O2*- production by the normal rat kidney is the medullary thick ascending limb (mTAL). We hypothesized that T1D increases O2*- production by the mTAL through a PKC-dependent mechanism involving increased expression and translocation of one or more PKC isoforms. mTAL suspensions were prepared from rats with streptozotocin-induced T1D (STZ mTALs) and from normal or sham rats (normal/sham mTALs). O2*- production by STZ mTALs was fivefold higher than normal/sham mTALs (P < 0.05). PMA (30 min) mimicked the effect of T1D on O2*- production. Exposure to calphostin C or chelerythrine (PKC inhibitors), Gö6976 (PKCalpha/beta inhibitor), or rottlerin (PKCdelta inhibitor) decreased O2*- production to <20% of untreated baseline in both normal/sham and STZ mTALs. PKCbeta inhibitors had no effect. PKC activity was increased in STZ mTALs (P < 0.05 vs. normal/sham mTALs) and was unaltered by antioxidant exposure (tempol). PKCalpha protein levels were increased by 70% in STZ mTALs, with a approximately 30% increase in the fraction associated with the membrane (both P < 0.05 vs. sham). PKCbeta protein levels were elevated by 29% in STZ mTALs (P < 0.05 vs. sham) with no change in the membrane-bound fraction. Neither PKCdelta protein levels nor its membrane-bound fraction differed between groups. Thus STZ mTALs display PKC activation, upregulation of PKCalpha and PKCbeta protein levels, increased PKCalpha translocation to the membrane, and accelerated O2*- production that is eradicated by inhibition of PKCalpha or PKCdelta (but not PKCbeta). We conclude that increased PKCalpha expression and activity are primarily responsible for PKC-dependent O2*- production by the mTAL during T1D.