Angiotensin preconditioning of the heart

Angiotensin II (Ang II) has been found to exert preconditioning-like effect on mammalian hearts. Diverse mechanisms are known to exist to explain the cardioprotective abilities of Ang II preconditioning. The present study hypothesized, based on the recent report that Ang II generates reactive oxygen species (ROS) through NADPH oxidase, that Ang II preconditioning occurs through redox cycling. To test this hypothesis, a group of rat hearts was treated with Ang II in the absence or presence of an NADPH oxidase inhibitor, apocynin; or a cell-permeable ROS scavenger, N-acetyl cysteine (NAC). Ang II pretreatment improved postischemic ventricular recovery; reduced myocardial infarction; and decreased the number of cardiomyocyte apoptosis, indicating its ability to precondition the heart against ischemic injury. Both apocynin and NAC almost abolished the preconditioning ability of Ang II. Ang II resulted in increase in ROS activity in the heart, which was reduced by either NAC or apocynin. Ang II also increased both the NADPH oxidase subunits gp91 phox and p22phox mRNA expression, which was abolished with apocynin and NAC. Our results thus demonstrate that the Ang II preconditioning was associated with enhanced ROS activities and increased NADPH oxidase subunits p22phox and gp91phox expression. Both NAC and apocynin reduced ROS activities simultaneously abolishing preconditioning ability of Ang II, suggesting that Ang II preconditioning occurs through redox cycling. That both NAC and apocynin reduced ROS activities and abolished Ang II-mediated increase in p22phox and gp91phox activity further suggest that such redox cycling occurs via both NADPH oxidase-dependent and -independent pathways.     

Angiotensin II-induced skeletal muscle insulin resistance mediated by NF-kappaB activation via NADPH oxidase

Reduced insulin sensitivity is a key factor in the pathogenesis of type 2 diabetes and hypertension. Skeletal muscle insulin resistance is particularly important for its major role in insulin-mediated glucose disposal. Angiotensin II (ANG II) is integral in regulating blood pressure and plays a role in the pathogenesis of hypertension. In addition, we have documented that ANG II-induced skeletal muscle insulin resistance is associated with generation of reactive oxygen species (ROS). However, the linkage between ROS and insulin resistance in skeletal muscle remains unclear. To explore potential mechanisms, we employed the transgenic TG(mRen2)27 (Ren-2) hypertensive rat, which harbors the mouse renin transgene and exhibits elevated tissue ANG II levels, and skeletal muscle cell culture. Compared with Sprague-Dawley normotensive control rats, Ren-2 skeletal muscle exhibited significantly increased oxidative stress, NF-kappaB activation, and TNF-alpha expression, which were attenuated by in vivo treatment with an angiotensin type 1 receptor blocker (valsartan) or SOD/catalase mimetic (tempol). Moreover, ANG II treatment of L6 myotubes induced NF-kappaB activation and TNF-alpha production and decreased insulin-stimulated Akt activation and GLUT-4 glucose transporter translocation to plasma membranes. These effects were markedly diminished by treatment of myotubes with valsartan, the antioxidant N-acetylcysteine, NADPH oxidase-inhibiting peptide (gp91 ds-tat), or NF-kappaB inhibitor (MG-132). Similarly, NF-kappaB p65 small interfering RNA reduced NF-kappaB p65 subunit expression and nuclear translocation and TNF-alpha production but improved insulin-stimulated phosphorylation (Ser(473)) of Akt and translocation of GLUT-4. These findings suggest that NF-kappaB plays an important role in ANG II/ROS-induced skeletal muscle insulin resistance.     

NADPH oxidase-derived superoxide anion-induced apoptosis is mediated via the JNK-dependent activation of NF-κB in cardiomyocytes exposed to high glucose

Hyperglycemia-induced generation of reactive oxygen species (ROS) can lead to cardiomyocyte apoptosis and cardiac dysfunction. However, the mechanism by which high glucose causes cardiomyocyte apoptosis is not clear. In this study, we investigated the signaling pathways involved in NADPH oxidase-derived ROS-induced apoptosis in cardiomyocytes under hyperglycemic conditions. H9c2 cells were treated with 5.5 or 33 mM glucose for 36 h. We found that 33 mM glucose resulted in a time-dependent increase in ROS generation as well as a time-dependent increase in protein expression of p22(phox), p47(phox), gp91(phox), phosphorylated IκB, c-Jun N-terminal kinase (JNK) and p38, as well as the nuclear translocation of NF-kB. Treatment with apocynin or diphenylene iodonium (DPI), NADPH oxidase inhibitors, resulted in reduced expression of p22(phox), p47(phox), gp91(phox), phosphorylated IκB, c-Jun N-terminal kinase (JNK) and p38. In addition, treatment with JNK and NF-kB siRNAs blocked the activity of caspase-3. Furthermore, treatment with JNK, but not p38, siRNA inhibited the glucose-induced activation of NF-κB. Similar results were obtained in neonatal cardiomyocytes exposed to high glucose concentrations. Therefore, we propose that NADPH oxidase-derived ROS-induced apoptosis is mediated via the JNK-dependent activation of NF-κB in cardiomyocytes exposed to high glucose.     

Apocynin prevents cyclooxygenase 2 expression in human monocytes through NADPH oxidase and glutathione redox-dependent mechanisms

In the present study we report the preventive effect of apocynin, an active constituent of the Himalayan herb Picrorhiza kurrooa, on cyclooxygenase-2 (Cox-2) synthesis and activity in human adherent monocytes exposed to serum treated zymosan (STZ) and phorbol myristate acetate (PMA). Apocynin markedly decreases the intracellular reduced/oxidized glutathione ratio (GSH/GSSG) and prevents nuclear factor-kappaB (NF-kappaB) activation in stimulated monocytes. Moreover, it reduces intracellular reactive oxygen species (ROS) generation, NADPH oxidase activity in monocyte homogenates and translocation of p47phox subunit in monocyte membranes. p47phox levels are also reduced in lysates of apocynin-treated monocytes. The inhibition of Cox-2 by apocynin is completely abrogated by GSH provision. Results from this study indicate that apocynin inhibits Cox-2 synthesis and activity induced in monocytes by an increased oxidative tone and provide an explanation for the protective effect exerted by this compound in numerous cell and animal models of inflammation. Attenuation of NADPH oxidase derived ROS coupled with GSH/GSSG reduction and suppression of NF-kappaB activation are highlighted as the molecular mechanisms responsible for Cox-2 inhibition.     

Peroxiredoxin 6 phosphorylation and subsequent phospholipase A2 activity are required for agonist-mediated activation of NADPH oxidase in mouse pulmonary microvascular endothelium and alveolar macrophages

Peroxiredoxin 6 (Prdx6), a bifunctional enzyme with glutathione peroxidase and phospholipase A2 (PLA(2)) activities, participates in the activation of NADPH oxidase 2 (NOX2) in neutrophils, but the mechanism for this effect is not known. We now demonstrate that Prdx6 is required for agonist-induced NOX2 activation in pulmonary microvascular endothelial cells (PMVEC) and that the effect requires the PLA(2) activity of Prdx6. Generation of reactive oxygen species (ROS) in response to angiotensin II (Ang II) or phorbol 12-myristate 13-acetate was markedly reduced in perfused lungs and isolated PMVEC from Prdx6 null mice. Rac1 and p47(phox), cytosolic components of NOX2, translocated to the endothelial cell membrane after Ang II treatment in wild-type but not Prdx6 null PMVEC. MJ33, an inhibitor of Prdx6 PLA(2) activity, blocked agonist-induced PLA(2) activity and ROS generation in PMVEC by >80%, whereas inhibitors of other PLA(2)s were ineffective. Transfection of Prx6 null cells with wild-type and C47S mutant Prdx6, but not with mutants of the PLA(2) active site (S32A, H26A, and D140A), "rescued" Ang II-induced PLA(2) activity and ROS generation. Ang II treatment of wild-type cells resulted in phosphorylation of Prdx6 and its subsequent translocation from the cytosol to the cell membrane. Phosphorylation as well as PLA(2) activity and ROS generation were markedly reduced by the MAPK inhibitor, U0126. Thus, agonist-induced MAPK activation leads to Prdx6 phosphorylation and translocation to the cell membrane, where its PLA(2) activity facilitates assembly of the NOX2 complex and activation of the oxidase.     

NADPH oxidase modulates myocardial Akt, ERK1/2 activation, and angiogenesis after hypoxia-reoxygenation

Recent studies have demonstrated that reactive oxygen species (ROS) mediate myocardial ischemia-reperfusion (I/R) and angiogenesis via the mitogen-activated protein kinases and the serine-threonine kinase Akt/protein kinase B pathways. NADPH oxidases are major sources of ROS in endothelial cells and cardiomyocytes. In the present study, we investigated the role of NADPH oxidase-derived ROS in hypoxia-reoxygenation (H/R)-induced Akt and ERK1/2 activation and angiogenesis using porcine coronary artery endothelial cells (PCAECs) and a mouse myocardial I/R model. Our data demonstrate that exposure of PCAECs to hypoxia for 2 h followed by 1 h of reoxygenation significantly increased ROS formation. Pretreatment with the NADPH oxidase inhibitors, diphenyleneiodonium (DPI, 10 microM) and apocynin (Apo, 200 and 600 microM), significantly attenuated H/R-induced ROS formation. Furthermore, exposure of PCAECs to H/R caused a significant increase in Akt and ERK1/2 activation. Exposure of PCAEC spheroids and mouse aortic rings to H/R significantly increased endothelial spheroid sprouting and vessel outgrowth, whereas pharmacological inhibition of NADPH oxidase or genetic deletion of the NADPH oxidase subunit, p47(phox) (p47(phox-/-)), significantly suppressed these changes. With the use of a mouse I/R model, our data further show that the increases in myocardial Akt and ERK1/2 activation and vascular endothelial growth factor (VEGF) expression were markedly blunted in the p47(phox-/-) mouse subjected to myocardial I/R compared with the wild-type mouse. Our findings underscore the important role of NADPH oxidase and its subunit p47(phox) in modulating Akt and ERK1/2 activation, angiogenic growth factor expression, and angiogenesis in myocardium undergoing I/R.     

Role of the actin cytoskeleton in angiotensin II signaling in human vascular smooth muscle cells

Angiotensin II (Ang II) regulates vascular smooth muscle cell (VSMC) function by activating signaling cascades that promote vasoconstriction, growth, and inflammation. Subcellular mechanisms coordinating these processes are unclear. In the present study, we questioned the role of the actin cytoskeleton in Ang II mediated signaling through mitogen-activated protein (MAP) kinases and reactive oxygen species (ROS) in VSMCs. Human VSMCs were studied. Cells were exposed to Ang II (10-7 mol/L) in the absence and presence of cytochalasin B (10-6 mol/L, 60 min), which disrupts the actin cytoskeleton. Phosphorylation of p38MAP kinase, JNK, and ERK1/2 was assessed by immuno blotting. ROS generation was measured using the fluoroprobe chloromethyl-2',7'-dichlorodihydrofluorescein diacetate (4 micromol/L). Interaction between the cytoskeleton and NADPH oxidase was determined by evaluating the presence of p47phox in the Triton X-100 insoluble membrane fraction. Ang II significantly increased phosphorylation of p38MAP kinase, JNK, and ERK1/2 (two- to threefold above control, p < 0.05). Cytochalasin B pretreatment attenuated p38MAP kinase and JNK effects (p < 0.05) without altering ERK1/2 phosphorylation. ROS formation, which was increased in Ang II stimulated cells, was significantly reduced by cytochalasin B (p < 0.01). p47phox, critically involved in NADPH oxidase activation, colocalized with the actin cytoskeleton in Ang II stimulated cells. Our data demonstrate that Ang II mediated ROS formation and activation of p38MAP kinase and JNK, but not ERK1/2, involves the actin cytoskeleton in VSMCs. In addition, Ang II promotes interaction between actin and p47phox. These data indicate that the cytoskeleton is involved in differential MAP kinase signaling and ROS generation by Ang II in VSMCs. Together, these studies suggest that the cytoskeleton may be a central point of crosstalk in growth- and redox-signaling pathways by Ang II, which may be important in the regulation of VSMC function.     

Maturation of the regulation of GLUT4 activity by p38 MAPK during L6 cell myogenesis

Insulin stimulates glucose uptake in skeletal muscle cells and fat cells by promoting the rapid translocation of GLUT4 glucose transporters to the plasma membrane. Recent work from our laboratory supports the concept that insulin also stimulates the intrinsic activity of GLUT4 through a signaling pathway that includes p38 MAPK. Here we show that regulation of GLUT4 activity by insulin develops during maturation of skeletal muscle cells into myotubes in concert with the ability of insulin to stimulate p38 MAPK. In L6 myotubes expressing GLUT4 that carries an exofacial myc-epitope (L6-GLUT4myc), insulin-stimulated GLUT4myc translocation equals in magnitude the glucose uptake response. Inhibition of p38 MAPK with SB203580 reduces insulin-stimulated glucose uptake without affecting GLUT4myc translocation. In contrast, in myoblasts, the magnitude of insulin-stimulated glucose uptake is significantly lower than that of GLUT4myc translocation and is insensitive to SB203580. Activation of p38 MAPK by insulin is considerably higher in myotubes than in myoblasts, as is the activation of upstream kinases MKK3/MKK6. In contrast, the activation of all three Akt isoforms and GLUT4 translocation are similar in myoblasts and myotubes. Furthermore, GLUT4myc translocation and phosphorylation of regulatory sites on Akt in L6-GLUT4myc myotubes are equally sensitive to insulin, whereas glucose uptake and phosphorylation of regulatory sites on p38 MAPK show lower sensitivity to the hormone. These observations draw additional parallels between Akt and GLUT4 translocation and between p38 MAPK and GLUT4 activation. Regulation of GLUT4 activity by insulin develops upon muscle cell differentiation and correlates with p38 MAPK activation by insulin.     

Novel role for non-muscle myosin light chain kinase (MLCK) in hyperoxia-induced recruitment of cytoskeletal proteins, NADPH oxidase activation, and reactive oxygen species generation in lung endothelium

We recently demonstrated that hyperoxia (HO) activates lung endothelial cell NADPH oxidase and generates reactive oxygen species (ROS)/superoxide via Src-dependent tyrosine phosphorylation of p47(phox) and cortactin. Here, we demonstrate that the non-muscle ~214-kDa myosin light chain (MLC) kinase (nmMLCK) modulates the interaction between cortactin and p47(phox) that plays a role in the assembly and activation of endothelial NADPH oxidase. Overexpression of FLAG-tagged wild type MLCK in human pulmonary artery endothelial cells enhanced interaction and co-localization between cortactin and p47(phox) at the cell periphery and ROS production, whereas abrogation of MLCK using specific siRNA significantly inhibited the above. Furthermore, HO stimulated phosphorylation of MLC and recruitment of phosphorylated and non-phosphorylated cortactin, MLC, Src, and p47(phox) to caveolin-enriched microdomains (CEM), whereas silencing nmMLCK with siRNA blocked recruitment of these components to CEM and ROS generation. Exposure of nmMLCK(-/-) null mice to HO (72 h) reduced ROS production, lung inflammation, and pulmonary leak compared with control mice. These results suggest a novel role for nmMLCK in hyperoxia-induced recruitment of cytoskeletal proteins and NADPH oxidase components to CEM, ROS production, and lung injury.     

NADPH oxidase is involved in angiotensin II-induced apoptosis in H9C2 cardiac muscle cells: effects of apocynin

Angiotensin II stimulates NADPH oxidase activity in vascular cells. However, it is not fully understood whether angiotensin II, which plays an important role in heart failure, stimulates NADPH oxidase activation and expression in cardiac myocytes. Previous studies have shown that angiotensin II induces myocyte apoptosis, but whether the change is mediated via NADPH oxidase remains to be elucidated. In this study we proposed to determine whether angiotensin II stimulated NADPH oxidase activation and NADPH oxidase subunit p47-phox expression in H9C2 cardiac muscle cells. If so, we would determine whether the NADPH oxidase inhibitor apocynin prevented angiotensin II-induced apoptosis. The results showed that angiotensin II increased NADPH oxidase activity, p47-phox protein and mRNA expression, intracellular reactive oxygen species, and apoptosis in H9C2 cells. Angiotensin II elevated p38 mitogen-activated protein kinase (MAPK) activity, decreased Bcl-2 protein, and increased Bax protein and caspase-3 activity. Apocynin treatment inhibited angiotensin II-induced NADPH oxidase activation and increases in p47-phox expression, intracellular reactive oxygen species, and apoptosis. The effect of apocynin on apoptosis was associated with reduced p38 MAPK activity, increased Bcl-2 protein, and decreased Bax protein and caspase-3 activity. These results suggest that angiotensin II-induced apoptosis is mediated via NADPH oxidase activation probably through p38 MAPK activation, a decrease in Bcl-2 protein, and caspase activation.     

Regulation of hyperoxia-induced NADPH oxidase activation in human lung endothelial cells by the actin cytoskeleton and cortactin

Although the actin cytoskeleton has been implicated in the control of NADPH oxidase in phagocytosis, very little is known about the cytoskeletal regulation of endothelial NADPH oxidase assembly and activation. Here, we report a role for cortactin and the tyrosine phosphorylation of cortactin in hyperoxia-induced NADPH oxidase activation and ROS production in human pulmonary artery ECs (HPAECs). Exposure of HPAECs to hyperoxia for 3 h induced NADPH oxidase activation, as demonstrated by enhanced superoxide production. Hyperoxia also caused a thickening of the subcortical dense peripheral F-actin band and increased the localization of cortactin in the cortical regions and lamellipodia at cell-cell borders that protruded under neighboring cells. Pretreatment of HPAECs with the actin-stabilizing agent phallacidin attenuated hyperoxia-induced cortical actin thickening and ROS production, whereas cytochalasin D and latrunculin A enhanced basal and hyperoxia-induced ROS formation. In HPAECs, a 3-h hyperoxic exposure enhanced the tyrosine phosphorylation of cortactin and interaction between cortactin and p47(phox), a subcomponent of the EC NADPH oxidase, when compared with normoxic cells. Furthermore, transfection of HPAECs with cortactin small interfering RNA or myristoylated cortactin Src homology domain 3 blocking peptide attenuated ROS production and the hyperoxia-induced translocation of p47(phox) to the cell periphery. Similarly, down-regulation of Src with Src small interfering RNA attenuated the hyperoxia-mediated phosphorylation of cortactin tyrosines and blocked the association of cortactin with actin and p47(phox). In addition, the hyperoxia-induced generation of ROS was significantly lower in ECs expressing a tyrosine-deficient mutant of cortactin than in vector control or wild-type cells. These data demonstrate a novel function for cortactin and actin in hyperoxia-induced activation of NADPH oxidase and ROS generation in human lung endothelial cells.     

Acute tumor necrosis factor alpha signaling via NADPH oxidase in microvascular endothelial cells: role of p47phox phosphorylation and binding to TRAF4

Tumor necrosis factor alpha (TNF-alpha) receptor-associated factors (TRAFs) play important roles in TNF-alpha signaling by interacting with downstream signaling molecules, e.g., mitogen-activated protein kinases (MAPKs). However, TNF-alpha also signals through reactive oxygen species (ROS)-dependent pathways. The interrelationship between these pathways is unclear; however, a recent study suggested that TRAF4 could bind to the NADPH oxidase subunit p47phox. Here, we investigated the potential interaction between p47phox phosphorylation and TRAF4 binding and their relative roles in acute TNF-alpha signaling. Exposure of human microvascular endothelial cells (HMEC-1) to TNF-alpha (100 U/ml; 1 to 60 min) induced rapid (within 5 min) p47phox phosphorylation. This was paralleled by a 2.7- +/- 0.5-fold increase in p47phox-TRAF4 association, membrane translocation of p47phox-TRAF4, a 2.3- +/- 0.4-fold increase in p47phox-p22phox complex formation, and a 3.2- +/- 0.2-fold increase in NADPH-dependent O2- production (all P < 0.05). TRAF4-p47phox binding was accompanied by a progressive increase in extracellular signal-regulated kinases 1 and 2 (ERK1/2) and p38(MAPK) activation, which was inhibited by an O2- scavenger, tiron. TRAF4 predominantly bound the phosphorylated form of p47phox, in a protein kinase C-dependent process. Knockdown of TRAF4 expression using siRNA had no effect on p47phox phosphorylation or binding to p22phox but inhibited TNF-alpha-induced ERK1/2 activation. In coronary microvascular EC from p47phox-/- mice, TNF-alpha-induced NADPH oxidase activation, ERK1/2 activation, and cell surface intercellular adhesion molecule 1 (ICAM-1) expression were all inhibited. Thus, both p47phox phosphorylation and TRAF4 are required for acute TNF-alpha signaling. The increased binding between p47phox and TRAF4 that occurs after p47phox phosphorylation could serve to spatially confine ROS generation from NADPH oxidase and subsequent MAPK activation and cell surface ICAM-1 expression in EC.     

Angiopoietin-1-induced angiogenesis is modulated by endothelial NADPH oxidase

Reactive oxygen species (ROS) play a central role in the pathogenesis of many cardiovascular diseases, such as atherosclerosis and hypertension. Endothelial NADPH oxidase is the major source of intracellular ROS. The present study investigated the role of endothelial NADPH oxidase-derived ROS in angiopoietin-1 (Ang-1)-induced angiogenesis. Exposure of porcine coronary artery endothelial cells (PCAECs) to Ang-1 (250 ng/ml) for periods up to 30 min led to a transient and dose-dependent increase in intracellular ROS. Thirty minutes of pretreatment with the NADPH oxidase inhibitors diphenylene iodinium (DPI, 10 microM) and apocynin (200 microM) suppressed Ang-1-stimulated ROS. Pretreatment with either DPI or apocynin also significantly attenuated Ang-1-induced Akt and p44/42 MAPK phosphorylation. In addition, inhibition of NADPH oxidase significantly suppressed Ang-1-induced endothelial cell migration and sprouting from endothelial spheroids. Using mouse heart microvascular endothelial cells from wild-type (WT) mice and mice deficient in the p47(phox) component of NADPH oxidase (p47(phox-/-)), we found that although Ang-1 stimulated intracellular ROS, Akt and p42/44 MAPK phosphorylation, and cell migration in WT cells, the responses were strikingly suppressed in cells from the p47(phox-/-) mice. Furthermore, exposure of aortic rings from p47(phox-/-) mice to Ang-1 demonstrated fewer vessel sprouts than WT mice. Inhibition of the Tie-2 receptor inhibited Ang-1-induced endothelial migration and vessel sprouting. Together, our data strongly suggest that endothelial NADPH oxidase-derived ROS play a critical role in Ang-1-induced angiogenesis.     

Insulin-induced activation of hypoxia-inducible factor-1 requires generation of reactive oxygen species by NADPH oxidase

Hypoxia-inducible factor (HIF)-1 activation in response to hypoxia requires mitochondrial generation of reactive oxygen species (ROS). In contrast, the requirement of ROS for HIF-1 activation by growth factors like insulin remains unexplored. To explore that, insulin-sensitive hepatic cell HepG2 or cardiac muscle cell H9c2 cells were pretreated with NADPH oxidase inhibitor diphenyleneiodonium chloride (DPI) or apocynin and HIF-1 activation was tested by electrophoretic mobility shift and reporter gene assay. Antioxidants DPI or apocynin completely blocked insulin-stimulated HIF-1 activation. The restoration of HIF-1 activation by H(2)O(2) in DPI-pretreated cells not only confirmed the role of ROS but also identified H(2)O(2) as the responsible ROS. The role of NADPH oxidase was further confirmed by greater stimulation of HIF-1 during simultaneous treatment of suboptimal concentration of insulin along with NADPH but not by NADH. The role of oxidant generated by insulin is found to inhibit the protein tyrosine phosphatase as suggested by the following observations. First, tyrosine phosphatase-specific inhibitor sodium vanadate compensates DPI-inhibited HIF-1 activity. Second, sodium vanadate stimulates HIF-1 activation with suboptimal concentration of insulin. Third, DPI and pyrrolidene dithiocarbamate (PDTC) blocks insulin-receptor tyrosine kinase activation. The activity of phosphatidylinositol 3-kinase as evidenced by Akt phosphorylation, involved in HIF-1 activation, is also dependent on ROS generation by insulin. Finally, DPI pretreatment blocked insulin-stimulated expression of genes like VEGF, GLUT1, and ceruloplasmin. Overall, our data provide strong evidence for the essential role of NADPH oxidase-generated ROS in insulin-stimulated activation of HIF-1.     

Src-mediated tyrosine phosphorylation of p47phox in hyperoxia-induced activation of NADPH oxidase and generation of reactive oxygen species in lung endothelial cells

Superoxide (O(2)(-)) production by nonphagocytes, similar to phagocytes, is by activation of the NADPH oxidase multicomponent system. Although activation of neutrophil NADPH oxidase involves extensive serine phosphorylation of p47(phox), the role of tyrosine phosphorylation of p47(phox) in NADPH oxidase-dependent O(2)(-) production is unclear. We have shown recently that hyperoxia-induced NADPH oxidase activation in human pulmonary artery endothelial cells (HPAECs) is regulated by mitogen-activated protein kinase signal transduction. Here we provided evidence on the role of nonreceptor tyrosine kinase, Src, in hyperoxia-induced tyrosine phosphorylation of p47(phox) and NADPH oxidase activation in HPAECs. Exposure of HPAECs to hyperoxia for 1 h resulted in increased O(2)(-) and reactive oxygen species (ROS) production and enhanced tyrosine phosphorylation of Src as determined by Western blotting with phospho-Src antibodies. Pretreatment of HPAECs with the Src kinase inhibitor PP2 (1 mum) or transient expression of a dominant-negative mutant of Src attenuated hyperoxia-induced tyrosine phosphorylation of Src and ROS production. Furthermore, exposure of cells to hyperoxia enhanced tyrosine phosphorylation of p47(phox) and its translocation to cell peripheries that were attenuated by PP2. In vitro, Src phosphorylated recombinant p47(phox) in a time-dependent manner. Src immunoprecipitates of cell lysates from control cells revealed the presence of immunodetectable p47(phox) and p67(phox), suggesting the association of oxidase components with Src under basal conditions. Moreover, exposure of HPAECs to hyperoxia for 1 h enhanced the association of p47(phox), but not p67(phox), with Src. These results indicated that Src-dependent tyrosine phosphorylation of p47(phox) regulates hyperoxia-induced NADPH oxidase activation and ROS production in HPAECs.     

Puerarin attenuates high-glucose-and diabetes-induced vascular smooth muscle cell proliferation by blocking PKCβ2/Rac1-dependent signaling

Oxidative stress has been implicated in several steps leading to the development of diabetic vascular complications. The purpose of this study was to determine the efficacy and the possible mechanism of puerarin on high-glucose (HG; 25 mM)-induced proliferation of cultured rat vascular smooth muscle cells (VSMCs) and neointimal formation in a carotid arterial balloon injury model of obese Zucker rats. Our data demonstrated that puerarin significantly inhibited rat VSMC proliferation as well as reactive oxygen species (ROS) generation and NADPH oxidase activity induced by HG treatment. Further studies revealed that HG treatment resulted in phosphorylation and membrane translocation of PKCβ2 as well as Rac1, p47phox, and p67phox subunits, leading to NADPH oxidase activation. Puerarin treatment remarkably disrupted the phosphorylation and membrane translocation of PKCβ2 as well as Rac1, p47phox, and p67phox subunits. Blocking PKCβ2 by infection with AdDNPKCβ2 also abolished HG-induced phosphorylation and membrane translocation of Rac1, p47phox, and p67phox subunits as well as ROS production and NADPH oxidase activation in VSMCs. In vivo neointimal formation of obese Zucker rats evoked by balloon injury was evidently attenuated by the administration of puerarin. These results demonstrate that puerarin may exert inhibitory effects on HG-induced VSMC proliferation via interfering with PKCβ2/Rac1-dependent ROS pathways, thus resulting in the attenuation of neointimal formation in the context of hyperglycemia in diabetes mellitus.     

Mechanism of endothelial cell NADPH oxidase activation by angiotensin II. Role of the p47phox subunit

Endothelial cells express a constitutively active phagocyte-type NADPH oxidase whose activity is augmented by agonists such as angiotensin II. We recently reported (Li, J.-M., and Shah, A. M. (2002) J. Biol. Chem. 277, 19952-19960) that in contrast to neutrophils a substantial proportion of the NADPH oxidase in unstimulated endothelial cells exists as preassembled intracellular complexes. Here, we investigate the mechanism of angiotensin II-induced endothelial NADPH oxidase activation. Angiotensin II (100 nmol/liter)-induced reactive oxygen species production (as measured by dichlorohydrofluorescein fluorescence or lucigenin chemiluminescence) was completely absent in coronary microvascular endothelial cells isolated from p47(phox) knockout mice. Transfection of p47(phox) cDNA into p47(phox-/-) cells restored the angiotensin II response, whereas transfection of antisense p47(phox) cDNA into wild-type cells depleted p47(phox) and inhibited the angiotensin II response. In unstimulated human microvascular endothelial cells, there was significant p47(phox)-p22(phox) complex formation but minimal detectable p47(phox) phosphorylation. Angiotensin II induced rapid serine phosphorylation of p47(phox) (within 1 min, peaking at approximately 15 min), a 1.9 +/- 0.1-fold increase in p47(phox)-p22(phox) complex formation and a 1.6 +/- 0.2-fold increase in NADPH-dependent O(2)-* production (p < 0.05). p47(phox) was redistributed to "nuclear" and membrane-enriched cell fractions. These data indicate that angiotensin II-stimulated endothelial NADPH oxidase activity is regulated through serine phosphorylation of p47(phox) and its enhanced binding to p22(phox).