c-Src induces phosphorylation and translocation of p47phox: role in superoxide generation by angiotensin II in human vascular smooth muscle cells

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.

Vascular inflammation in hypertension and diabetes: molecular mechanisms and therapeutic interventions

More than 80% of patients with type 2 diabetes mellitus develop hypertension, and approx. 20% of patients with hypertension develop diabetes. This combination of cardiovascular risk factors will account for a large proportion of cardiovascular morbidity and mortality. Lowering elevated blood pressure in diabetic hypertensive individuals decreases cardiovascular events. In patients with hypertension and diabetes, the pathophysiology of cardiovascular disease is multifactorial, but recent evidence points toward the presence of an important component dependent on a low-grade inflammatory process. Angiotensin II may be to a large degree responsible for triggering vascular inflammation by inducing oxidative stress, resulting in up-regulation of pro-inflammatory transcription factors such as NF-kappaB (nuclear factor kappaB). These, in turn, regulate the generation of inflammatory mediators that lead to endothelial dysfunction and vascular injury. Inflammatory markers (e.g. C-reactive protein, chemokines and adhesion molecules) are increased in patients with hypertension and metabolic disorders, and predict the development of cardiovascular disease. Lifestyle modification and pharmacological approaches (such as drugs that target the renin-angiotensin system) may reduce blood pressure and inflammation in patients with hypertension and metabolic disorders, which will reduce cardiovascular risk, development of diabetes and cardiovascular morbidity and mortality.

Vascular signaling through cholesterol-rich domains: implications in hypertension

PURPOSE OF REVIEW

Lipid rafts are emerging as key players in the integration of cellular responses. Alterations in these highly regulated signaling cascades are important in structural, mechanical and functional abnormalities that underlie vascular pathological processes. The present review focuses on recent advances in signal transduction through caveolae/lipid rafts, implicated in hypertensive processes.

RECENT FINDINGS

Caveolae/lipid rafts function as sites of dynamic regulatory events in receptor-induced signal transduction. Mediators of vascular function, including G-protein coupled receptors, Src family tyrosine kinases, receptor tyrosine kinases, protein phosphatases and nitric oxide synthase, are concentrated within these microdomains. The assembly of functionally active nicotinamide adenine dinucleotide phosphate oxidase and subsequent reactive oxygen species production are also dependent on interactions within the caveolae/lipid rafts. Recent findings have also demonstrated the importance of actin-cytoskeleton and focal adhesion sites for protein interactions with caveolae/lipid raft.

SUMMARY

Many vascular signaling processes are altered in hypertension. Whether these events involve lipid rafts/caveolae remains unclear. A better understanding of how signaling molecules compartmentalize in lipid rafts/caveolae will provide further insights into molecular mechanisms underlying vascular damage in cardiovascular disease.

Quercetin and isorhamnetin prevent endothelial dysfunction, superoxide production, and overexpression of p47phox induced by angiotensin II in rat aorta

The dietary flavonoid quercetin reduces blood pressure and improves endothelial function in several rat models of hypertension. We analyzed the effects of quercetin and its methylated metabolite isorhamnetin on the aortic endothelial dysfunction induced by incubation with angiotensin II (AngII) in vitro for 6 h. AngII diminished the relaxant responses to acetylcholine in phenylephrine-contracted aorta. Coincubation with quercetin or isorhamnetin, or addition of superoxide (O(2)(-)) dismutase or apocynin to the assay medium, prevented these inhibitory effects. At 6 h, AngII induced a marked increase in O(2)(-) production as measured by dihydroethidium fluorescence, which was prevented by quercetin and isorhamnetin. AngII also increased the expression of p47(phox), a regulatory subunit of the membrane NADPH oxidase. Immunohistochemical analysis revealed that overexpression of p47(phox) occurred mainly in the medial layer. p47(phox) overexpression was also prevented by quercetin and isorhamnetin. Taken together, these results show for the first time, to our knowledge, that quercetin and isorhamnetin prevent AngII-induced endothelial dysfunction by inhibiting the overexpression of p47(phox) and the subsequent increased O(2)(-) production, resulting in increased nitric oxide bioavailability.

Angiotensin II-induced NADPH oxidase activation impairs insulin signaling in skeletal muscle cells

The renin-angiotensin system (RAS) and reactive oxygen species (ROS) have been implicated in the development of insulin resistance and its related complications. There is also evidence that angiotensin II (Ang II)-induced generation of ROS contributes to the development of insulin resistance in skeletal muscle, although the precise mechanisms remain unknown. In the present study, we found that Ang II markedly enhanced NADPH oxidase activity and consequent ROS generation in L6 myotubes. These effects were blocked by the angiotensin II type 1 receptor blocker losartan, and by the NADPH oxidase inhibitor apocynin. Ang II also promoted the translocation of NADPH oxidase cytosolic subunits p47phox and p67phox to the plasma membrane within 15 min. Furthermore, Ang II abolished insulin-induced tyrosine phosphorylation of insulin receptor substrate 1 (IRS1), activation of protein kinase B (Akt), and glucose transporter-4 (GLUT4) translocation to the plasma membrane, which was reversed by pretreating myotubes with losartan or apocynin. Finally, small interfering RNA (siRNA)-specific gene silencing targeted specifically against p47phox (p47siRNA), in both L6 and primary myotubes, reduced the cognate protein expression, decreased NADPH oxidase activity, restored Ang II-impaired IRS1 and Akt activation as well as GLUT4 translocation by insulin. These results suggest a pivotal role for NADPH oxidase activation and ROS generation in Ang II-induced inhibition of insulin signaling in skeletal muscle cells.

Inhibition of the renin angiotensin system: implications for the endothelium

The endothelium is critically involved in modulating vascular tone through the release of vasodilator (mainly nitric oxide; NO) and vasoconstrictor agents. Under normal conditions the endothelium induces NO-mediated vasodilation, and opposes cell adhesion and thrombosis. Angiotensin II-induced generation of reactive oxygen species plays a key role in the pathophysiology of endothelial dysfunction by reducing NO bioavailability. Endothelial dysfunction is associated with several pathologic conditions, including hypertension and diabetes, and is characterized by altered vascular tone, inflammation, and thrombosis in the vascular wall. Inhibition of the renin-angiotensin-aldosterone system has induced beneficial effects on endothelial function in animals and humans. Angiotensin-converting enzyme inhibitors, angiotensin receptor blockers, and mineralocorticoid receptor antagonists have improved endothelial function in hypertension and diabetes, slowed the progression of atherosclerosis, and reduced the risk associated with cardiovascular disease.

Noxa1 is a central component of the smooth muscle NADPH oxidase in mice

NADPH oxidase is the most important source of oxygen-derived radicals (ROS) in the vascular wall. In vascular smooth muscle cells (VSMC), NADPH oxidase is characterized by the expression of the membrane subunit Nox1, which is activated by cytoplasmic proteins binding to its activation domain. We set out to identify the cytoplasmic protein involved in NADPH oxidase activation in mouse VSMC. Western blot analysis revealed that human endothelial cells and leukocytes but not VSMC from the aorta of the rat and the mouse express the classic NADPH oxidase activator p67phox. In mouse VSMC, however, the p67phox homologue Noxa1 was detected. Using antibodies generated against mouse Noxa1, the protein was observed in the cytosolic fraction of mouse VSMC with a molecular weight of about 51 kDa. Immunohistochemistry revealed that Noxa1 is expressed in the smooth muscle layer but not in endothelium or the adventitia of the mouse carotid artery. Fluorescent fusion proteins of Noxa1 were observed to be expressed in the cytoplasm of VSMC and coexpression of the NADPH oxidase organizer Noxo1 targeted the complex to membrane. An antisense plasmid of Noxa1 attenuated the endogenous Noxa1 protein expression in VSMC. This plasmid attenuated the ROS formation in mouse VSMC as detected using L012 chemiluminescence and prevented the agonist-induced ROS production in response to basic fibroblast growth factor and epidermal growth factor. In conclusion, these data indicate that Noxa1 replaces p67phox in VSMC and plays a central role in the activation of the NADPH oxidase in the vascular wall.

Reactive oxygen species signaling in vascular smooth muscle cells

Reactive oxygen species (ROS) have been shown to function as important signaling molecules in the cardiovascular system. Vascular smooth muscle cells (VSMCs) contain several sources of ROS, among which the NADPH oxidases are predominant. In VSMCs, ROS mediate many pathophysiological processes, such as growth, migration, apoptosis and secretion of inflammatory cytokines, as well as physiological processes, such as differentiation, by direct and indirect effects at multiple signaling levels. Therefore, it becomes critical to understand the different roles ROS play in the physiology and pathophysiology of VSMCs.

NADPH oxidase-derived reactive oxygen species in cardiac pathophysiology

Chronic heart failure, secondary to left ventricular hypertrophy or myocardial infarction, is a condition with increasing morbidity and mortality. Although the mechanisms underlying the development and progression of this condition remain a subject of intense interest, there is now growing evidence that redox-sensitive pathways play an important role. This article focuses on the involvement of reactive oxygen species derived from a family of superoxide-generating enzymes, termed NADPH oxidases (NOXs), in the pathophysiology of ventricular hypertrophy, the accompanying interstitial fibrosis and subsequent heart failure. In particular, the apparent ability of the different NADPH oxidase isoforms to define the response of a cell to a range of physiological and pathophysiological stimuli is reviewed. If confirmed, these data would suggest that independently targeting different members of the NOX family may hold the potential for therapeutic intervention in the treatment of cardiac disease.

Endothelin-A and -B receptors, superoxide, and Ca2+ signaling in afferent arterioles

It is unknown if endothelin-A and -B receptors (ET(A)R and ET(B)R) activate the production of superoxide via NAD(P)H oxidase and subsequently stimulate the formation of cyclic adenine diphosphate ribose (cADPR) in afferent arterioles. Vessels were isolated from rat kidney and loaded with fura 2. Endothelin-1 (ET-1) rapidly increased cytosolic Ca(2+) concentration ([Ca(2+)](i)) by 303 nM. The superoxide dismutase mimetic tempol, the NAD(P)H oxidase inhibitor apocynin, and nicotinamide, an inhibitor of ADPR cyclase, diminished the response by approximately 60%. The ET(B)R agonist sarafotoxin 6c (S6c) increased peak [Ca(2+)](i) by 117 nM. Subsequent addition of ET-1 in the continued presence of S6c caused an additional [Ca(2+)](i) peak of 225 nM. Neither nicotinamide or 8-bromo- (8-Br) cADPR nor apocynin decreased the [Ca(2+)](i) response to S6c, but inhibited the subsequent [Ca(2+)](i) response to ET-1. The ET(B)R blockers BQ-788 and A-192621 prevented the S6c [Ca(2+)](i) peak and reduced the ET-1 response by more than one-half, suggesting an ET(B)R/ET(A)R interaction. In contrast, the ET(A)R blocker BQ-123 had no effect on the S6c [Ca(2+)](i) peak and obliterated the subsequent ET-1 response. ET-1 immediately stimulated superoxide formation (measured with TEMPO-9-AC, 68 arbitrary units) that was inhibited 95% by apocynin or diphenyl iodonium. S6c or IRL-1620 increased superoxide by 8% of that caused by subsequent ET-1 addition. We conclude that ET(A)R activation of afferent arterioles increases the formation of superoxide that accounts for approximately 60% of subsequent Ca(2+) signaling. ET(B)R activation appears to result in only minor increases in superoxide production. Nicotinamide and 8-Br-cADPR results suggest that ET-1 (and primarily ET(A)R) causes the activation of vascular smooth muscle cell-ADPR cyclase.

Adventitial delivery of dominant-negative p67phox attenuates neointimal hyperplasia of the rat carotid artery

Several essential components of NADPH oxidase, including p22phox, gp91phox (nox2) and its homologs nox1 and nox4, p47phox, p67phox, and rac1, are present in the vasculature. We previously reported that p67phox is essential for adventitial fibroblast NADPH oxidase O2- production. Thus we postulated that inhibition of adventitial p67phox activity would attenuate angioplasty-induced hyperplasia. To test this hypothesis, we treated the adventitia of carotid arteries with a control adenovirus (Ad-control), a virus expressing dominant-negative p67phox (Ad-p67dn), or a virus expressing a competitive peptide (gp91ds) targeting the p47phox-gp91phox interaction (Ad-gp91ds). Common carotid arteries (CCAs) from male Sprague-Dawley rats were transfected with Ad-control, Ad-p67dn, or Ad-gp91ds in pluronic gel. After 2 days, a 2-F (Fogarty) catheter was used to injure CCAs in vivo. After 14 days, CCAs were perfusion-fixed and analyzed. In 13 experiments, digital morphometry suggested a reduction of neointimal hyperplasia with Ad-p67dn compared with Ad-control; however, the reduction did not reach statistical significance (P = 0.058). In contrast, a significant reduction was achieved with Ad-gp91ds (P = 0.006). No changes in medial area or remodeling were observed with either treatment. Moreover, adventitial fibroblast proliferation in vitro was inhibited by Ad-gp91ds but not by Ad-p67dn, despite confirmation that Ad-p67dn inhibits NADPH oxidase in fibroblasts. These data appear to suggest that a multicomponent vascular NADPH oxidase plays a role in neointimal hyperplasia. However, inhibition of p47phox may be more effective than inhibition of p67phox at attenuating neointimal growth.

Aldosterone mediates angiotensin II-induced interstitial cardiac fibrosis via a Nox2-containing NADPH oxidase

Angiotensin (ANG) II (AngII) and aldosterone contribute to the development of interstitial cardiac fibrosis. We investigated the potential role of a Nox2-containing NADPH oxidase in aldosterone-induced fibrosis and the involvement of this mechanism in AngII-induced effects. Nox2-/- mice were compared with matched wild-type controls (WT). In WT mice, subcutaneous (s.c.) AngII (1.1 mg/kg/day for 2 wk) significantly increased NADPH oxidase activity, interstitial fibrosis (11.5+/-1.0% vs. 7.2+/-0.7%; P<0.05), expression of fibronectin, procollagen I, and connective tissue growth factor mRNA, MMP-2 activity, and NF-kB activation. These effects were all inhibited in Nox2-/- hearts. The mineralocorticoid receptor antagonist spironolactone inhibited AngII-induced increases in NADPH oxidase activity and the increase in interstitial fibrosis. In a model of mineralocorticoid-dependent hypertension involving chronic aldosterone infusion (0.2 mg/kg/day) and a 1% Na Cl diet ("ALDO"), WT animals exhibited increased NADPH oxidase activity, pro-fibrotic gene expression, MMP-2 activity, NF-kB activation, and significant interstitial cardiac fibrosis (12.0+/-1.7% with ALDO vs. 6.3+/-0.3% without; P<0.05). These effects were inhibited in Nox2-/- ALDO mice (e.g., fibrosis 6.8+/-0.8% with ALDO vs. 5.8+/-1.0% without ALDO; P=NS). These results suggest that aldosterone-dependent activation of a Nox2-containing NADPH oxidase contributes to the profibrotic effect of AngII in the heart as well as the fibrosis seen in mineralocorticoid-dependent hypertension.

Exercise and the coronary circulation-alterations and adaptations in coronary artery disease

Coronary vasorelaxation depends on nitric oxide (NO) bioavailability, which is a function of endothelial nitric oxide synthase-derived NO production and NO inactivation by reactive oxygen species. This fine-tuned balance is disrupted in coronary artery disease (CAD). The impairment of NO production in conjunction with excessive oxidative stress promotes the loss of endothelial cells by apoptosis, leads to a further aggravation of endothelial dysfunction and triggers myocardial ischemia in CAD. In healthy individuals, increased release of NO from the vasculature in response to exercise training results from changes in endothelial nitric oxide synthase expression, phosphorylation, and conformation. However, exercise training has assumed a role in cardiac rehabilitation of patients with CAD, as well, because it reduces mortality and increases myocardial perfusion. This has been largely attributed to exercise training-mediated correction of coronary endothelial dysfunction in CAD. Indeed, regular physical activity restores the balance between NO production and NO inactivation by reactive oxygen species in CAD, thereby enhancing the vasodilatory capacity in different vascular beds. Because endothelial dysfunction has been identified as a predictor of cardiovascular events, the partial reversal of endothelial dysfunction secondary to exercise training might be the most likely mechanism responsible for the exercise training-induced reduction in cardiovascular morbidity and mortality in patients with CAD.

Targeting reactive oxygen species in hypertension

PURPOSE OF REVIEW

Hypertension is a major risk factor for vascular diseases such as stroke, myocardial infarction, and renal microvascular disease. The mechanism by which vascular disease develops is complex, and growing evidence suggests that an increase in reactive oxygen species during hypertension is a major contributing factor. NADPH oxidase, the primary source of reactive oxygen species in the cardiovascular system, is a strong candidate for the development of therapeutic agents to ameliorate hypertension and end-organ damage.

RECENT FINDINGS

Various scavengers and inhibitors of reactive oxygen species have been proposed for use in animal as well as human studies. While many of these agents are effective at lowering tissue reactive oxygen species levels, their specificity is a serious concern. Our laboratory has developed cell-permeant peptidic inhibitors targeting key interactions among the different NAD(P)H oxidase homologues. One of these inhibitors targeting nox2 and p47-phox interaction has proven useful in attenuating target neoplasia and hypertrophy.

SUMMARY

Strategies aimed at specifically inhibiting NAD(P)H oxidase have proven effective in attenuating cardiovascular oxidative stress. The development of new inhibitors targeting novel oxidase homologues appears to hold significant promise for clarifying the physiologic role of these homologues as well as for the development of new antioxidant therapies.

Elastic fibres and vascular structure in hypertension

Blood vessels are dynamic structures composed of cells and extracellular matrix (ECM), which are in continuous cross-talk with each other. Thus, cellular changes in phenotype or in proliferation/death rate affect ECM synthesis. In turn, ECM elements not only provide the structural framework for vascular cells, but they also modulate cellular function through specific receptors. These ECM-cell interactions, together with neurotransmitters, hormones and the mechanical forces imposed by the heart, modulate the structural organization of the vascular wall. It is not surprising that pathological states related to alterations in the nervous, humoral or haemodynamic environment-such as hypertension-are associated with vascular wall remodeling, which, in the end, is deleterious for cardiovascular function. However, the question remains whether these structural alterations are simply a consequence of the disease or if there are early cellular or ECM alterations-determined either genetically or by environmental factors-that can predispose to vascular remodeling independent of hypertension. Elastic fibres might be key elements in the pathophysiology of hypertensive vascular remodeling. In addition to the well known effects of hypertension on elastic fibre fatigue and accelerated degradation, leading to loss of arterial wall resilience, recent investigations have highlighted new roles for individual components of elastic fibres and their degradation products. These elements can act as signal transducers and regulate cellular proliferation, migration, phenotype, and ECM degradation. In this paper, we review current knowledge regarding components of elastic fibres and discuss their possible pathomechanistic associations with vascular structural abnormalities and with hypertension development or progression.

The interrelation of the angiotensin and endothelin systems on the modulation of NAD(P)H oxidaseThis paper is one of a selection of papers published in this Special issue, entitled Young Investigator's Forum

The NAD(P)H oxidase is an enzyme assembled at the cellular membrane able to produce superoxide anion from NADH or NAD(P)H (nicotinamide adenine dinucleotide phosphate). It is one of the main sources of superoxide anion in cardiovascular tissues and its role in a variety of cardiovascular disorders such as atherosclerosis, cardiac hypertrophy, and endothelial dysfunction was recently proposed. Although, many factors and receptors were shown to lead to the activation of the enzyme, particulary the type 1 angiotensin receptor, the pathways involved are still widely unknown. Despite the identification of factors such as c-Src and protein kinase C implicated in the acute activation of NAD(P)H oxidase, the signalling involved in the sustained activation of the enzyme is probably far more complex than was previously envisioned. In this review, we describe the role of endothelin-1 in NAD(P)H oxidase signalling after a sustained stimulation by angiotensin II. Since most pathologies caused by an NAD(P)H oxidase overactivation develop over a relatively long period of time, it is necessary to better understand the long-term signalling of the enzyme for the development or use of more specific therapeutic tools.

Impact of regular physical activity on the NAD(P)H oxidase and angiotensin receptor system in patients with coronary artery disease

BACKGROUND

In patients with stable coronary artery disease, physical exercise training (ET) improves endothelial dysfunction. A potential mechanism mediating the enhanced vasomotor function is a reduced breakdown of endothelium-derived nitric oxide by reactive oxygen species (ROS). The aim of the present study was to analyze the impact of ET on sources of ROS generation in the left internal mammary artery of patients with symptomatic coronary artery disease.

METHODS AND RESULTS

In left internal mammary artery rings sampled during bypass surgery from 45 patients randomized to either a training (n=22) or an inactive control (n=23) group, the mRNA expression of NAD(P)H oxidase subunits, NAD(P)H oxidase activity, and ROS production were assessed. In addition, endothelial function, expression of angiotensin II (Ang II) receptor type 1 and 2 (AT1-R and AT2-R), and Ang II-mediated vasoconstriction were determined. ET resulted in a significant lower expression of gp91phox (23.1+/-0.5 versus 69.1+/-18.1 arbitrary units, training versus control), p22phox (0.7+/-0.3 versus 2.0+/-0.5 arbitrary units), and Nox4 (2.7+/-1.2 versus 5.4+/-1.0 arbitrary units). Enzymatic activity (2.1+/-0.3 versus 4.9+/-0.4 mU/mg) and ROS generation (0.02+/-0.01 versus 0.06+/-0.02 arbitrary units) were significantly lower in the training compared with the control group. On a functional level, ET resulted in improved acetylcholine-mediated vasodilatation and a 49% reduction in Ang II-induced vasoconstriction, accompanied by lower AT1-R (3.7+/-0.8 versus 16.6+/-5.7 arbitrary units, training versus control) and higher AT2-R (7.8+/-2.5 versus 1.6+/-0.7 arbitrary units) mRNA expression.

CONCLUSIONS

ET reduces vascular expression of NAD(P)H oxidase and AT1-R, resulting in decreased local ROS generation. These molecular effects converge in a reduced Ang II-mediated vasoconstriction.

Expression of functionally phagocyte-type NAD(P)H oxidase in pericytes: effect of angiotensin II and high glucose

BACKGROUND INFORMATION

A growing body of evidence demonstrates the involvement of the oxidative stress in the development of vascular complications associated with diabetes, such as hypertension, retinopathy, nephropathy, neuropathy and atherosclerosis. However, the molecular mechanisms accountable for the increased production of reactive oxygen species (ROS) remain uncertain. Among others, the NAD(P)H oxidase is one of the most important sources of superoxide anion (O2-) that induce dysfunction of vascular cells. Pericytes (PCs) have an essential role in the capillary dysfunction in retinopathy and other vascular complications in diabetes. We questioned whether PCs express a functional phagocyte-type NAD(P)H oxidase, and examined the role of angiotensin II and high glucose on the activity of the oxidase complex and expression of the essential subunit p22(phox).

RESULTS

The mRNA expression of p22(phox), p47(phox), p67(phox) and NOX 1 subunits, and the lack of gp91(phox) component, were detected in PCs by reverse transcriptase PCR. Western-blotting analysis demonstrated the protein expression of p22(phox), p47(phox) and p67(phox) subunits. As compared with the normal condition, stimulation of PCs with angiotensin II or high glucose induced: (i) an increase in ROS production and NAD(P)H oxidase activity, and (ii) an up-regulation of p22(phox) mRNA and protein expression.

CONCLUSIONS

Taken together, the present study provides the first evidence that PCs express a functional phagocyte-type NAD(P)H oxidase, which is up-regulated by both angiotensin II and high glucose. Given the importance of ROS in vascular physiology and pathology, the NAD(P)H oxidase complex could be an important therapeutic target in the treatment of microvascular disorders.

Angiotensin II, reactive oxygen species, and Ca2+signaling in afferent arterioles

In afferent arteriolar vascular smooth muscle cells, ANG II induces a rise in cytosolic Ca2+([Ca2+]i) via inositol trisphosphate receptor (IP3R) stimulation and by activation of the adenine diphosphate ribose (ADPR) cyclase to form cyclic ADPR, which sensitizes the ryanodine receptor (RyR) to Ca2+. We hypothesize that ANG II stimulation of NAD(P)H oxidases leads to the formation of superoxide anion (O2−·), which, in turn, activates ADPR cyclase. Afferent arterioles were isolated from rat kidney with the magnetized microsphere and sieving technique and loaded with fura-2 to measure [Ca2+]i. ANG II rapidly increased [Ca2+]iby 124 ± 12 nM. In the presence of apocynin, a specific inhibitor of NAD(P)H oxidase assembly, the [Ca2+]iresponse was reduced to 35 ± 5 nM ( P < 0.01). Tempol, a superoxide dismutase mimetic, did not alter the [Ca2+]iresponse to ANG II at a concentration of 10−4M (99 ± 12 nM), but 10−3M tempol reduced the response to 32 ± 3 nM ( P < 0.01). The addition of nicotinamide, an inhibitor of ADPR cyclase, to apocynin or tempol (10−3M) resulted in no further inhibition. Measurement of superoxide production with the fluorescent probe tempo 9-AC showed that ANG II caused an increase of 48 ± 20 arbitrary units; apocynin or diphenyl iodonium (an inhibitor of flavoprotein oxidases) inhibited the response by 94%. Hydrogen peroxide (H2O2) was studied at physiological (10−7M) and higher concentrations. In the presence of H2O2(10−7M), neither baseline [Ca2+]inor the response to ANG II was altered (125 ± 15 nM), whereas H2O2(10−6and 10−5M) inhibited the [Ca2+]iresponse to ANG II by 35 and 46%, respectively. We conclude that ANG II rapidly activates NAD(P)H oxidases of afferent arterioles, leading to the formation of O2−·, which then stimulates ADPR cyclase to form cADPR. cADPR, by sensitizing the RyR to Ca2+, augments the Ca2+response (calcium-induced calcium release) initiated by activation of the IP3R.

c-Src–Dependent Nongenomic Signaling Responses to Aldosterone Are Increased in Vascular Myocytes From Spontaneously Hypertensive Rats

Aldosterone plays an important role in the pathogenesis of hypertension. We previously demonstrated that nongenomic signaling by aldosterone in vascular smooth muscle cells occurs through c-Src–dependent pathways. Here we tested the hypothesis that upregulation of c-Src by aldosterone plays a role in increased mitogen-activated protein (MAP) kinase activation, [ 3 H]-proline incorporation, and NADPH-driven generation of reactive oxygen species, thereby inducing cell growth, collagen production, and inflammation, respectively, in vascular smooth muscle cells from spontaneously hypertensive rats. The time course of c-Src phosphorylation by aldosterone was shifted to the left in vascular myocytes from hypertensive animals. Aldosterone rapidly increased phosphorylation of p38 MAP kinase and extracellular signal–regulated kinase with significantly greater effects in cells from spontaneously hypertensive rats versus control cells ( P <0.05). Aldosterone increased NADPH oxidase activity with significantly greater responses in vascular smooth muscle cells from hypertensive animals ( P <0.05). These events were associated with enhanced [ 3 H]proline incorporation (index of collagen synthesis) in cells from spontaneously hypertensive rats ( P <0.05). The NADPH oxidase activity increase, collagen synthesis, c-Src, and MAP kinase phosphorylation induced by aldosterone were significantly reduced by eplerenone (selective mineralocorticoid receptor blocker) and PP2 (selective c-Src inhibitor). In conclusion, nongenomic signaling by exogenous aldosterone, mediated through c-Src, is increased in vascular smooth muscle cells from spontaneously hypertensive rats. Upregulation of c-Src signaling may be important in the profibrotic and proinflammatory actions of aldosterone in this genetic model of hypertension.

Regulation of NAD(P)H oxidase by associated protein disulfide isomerase in vascular smooth muscle cells

NAD(P)H oxidase, the main source of reactive oxygen species in vascular cells, is known to be regulated by redox processes and thiols. However, the nature of thiol-dependent regulation has not been established. Protein disulfide isomerase (PDI) is a dithiol/disulfide oxidoreductase chaperone of the thioredoxin superfamily involved in protein processing and translocation. We postulated that PDI regulates NAD(P)H oxidase activity of rabbit aortic smooth muscle cells (VSMCs). Western blotting confirmed robust PDI expression and shift to membrane fraction after incubation with angiotensin II (AII, 100 nm, 6 h). In VSMC membrane fraction, PDI antagonism with bacitracin, scrambled RNase, or neutralizing antibody led to 26-83% inhibition (p < 0.05) of oxidase activity. AII incubation led to significant increase in oxidase activity, accompanied by a 6-fold increase in PDI refolding isomerase activity. AII-induced NAD(P)H oxidase activation was inhibited by 57-71% with antisense oligonucleotide against PDI (PDIasODN). Dihydroethidium fluorescence showed decreased superoxide generation due to PDIasODN. Confocal microscopy showed co-localization between PDI and the oxidase subunits p22(phox), Nox1, and Nox4. Co-immunoprecipitation assays supported spatial association between PDI and oxidase subunits p22(phox), Nox1, and Nox4 in VSMCs. Moreover, in HEK293 cells transfected with green fluorescent protein constructs for Nox1, Nox2, and Nox4, each of these subunits co-immunoprecipitated with PDI. Akt phosphorylation, a known downstream pathway of AII-driven oxidase activation, was significantly reduced by PDIasODN. These results suggest that PDI closely associates with NAD(P)H oxidase and acts as a novel redox-sensitive regulatory protein of such enzyme complex, potentially affecting subunit traffic/assembling.

Pleiotropic AT1 receptor signaling pathways mediating physiological and pathogenic actions of angiotensin II

Angiotensin II (Ang II) activates a wide spectrum of signaling responses via the AT1 receptor (AT1R) that mediate its physiological control of blood pressure, thirst, and sodium balance and its diverse pathological actions in cardiovascular, renal, and other cell types. Ang II-induced AT1R activation via Gq/11 stimulates phospholipases A2, C, and D, and activates inositol trisphosphate/Ca2+ signaling, protein kinase C isoforms, and MAPKs, as well as several tyrosine kinases (Pyk2, Src, Tyk2, FAK), scaffold proteins (G protein-coupled receptor kinase-interacting protein 1, p130Cas, paxillin, vinculin), receptor tyrosine kinases, and the nuclear factor-kappaB pathway. The AT1R also signals via Gi/o and G11/12 and stimulates G protein-independent signaling pathways, such as beta-arrestin-mediated MAPK activation and the Jak/STAT. Alterations in homo- or heterodimerization of the AT1R may also contribute to its pathophysiological roles. Many of the deleterious actions of AT1R activation are initiated by locally generated, rather than circulating, Ang II and are concomitant with the harmful effects of aldosterone in the cardiovascular system. AT1R-mediated overproduction of reactive oxygen species has potent growth-promoting, proinflammatory, and profibrotic actions by exerting positive feedback effects that amplify its signaling in cardiovascular cells, leukocytes, and monocytes. In addition to its roles in cardiovascular and renal disease, agonist-induced activation of the AT1R also participates in the development of metabolic diseases and promotes tumor progression and metastasis through its growth-promoting and proangiogenic activities. The recognition of Ang II's pathogenic actions is leading to novel clinical applications of angiotensin-converting enzyme inhibitors and AT1R antagonists, in addition to their established therapeutic actions in essential hypertension.

Reactive oxygen species as mediators of calcium signaling by angiotensin II: implications in vascular physiology and pathophysiology

Reactive oxygen species (ROS), including superoxide anion, hydrogen peroxide, and hydroxyl radical, and reactive nitrogen species, such as nitric oxide and peroxynitrite, are biologically relevant O2 derivatives increasingly being recognized as important in vascular biology through their oxidation/reduction (redox) potential. All vascular cell types produce ROS primarily via membrane-associated NAD(P)H oxidase. ROS influence vascular function by modulating contraction/dilation, cell growth, apoptosis/anoikis, migration, inflammation, and fibrosis. An imbalance in redox state where prooxidants overwhelm antioxidant capacity results in oxidative stress. Oxidative excess and associated oxidative damage are mediators of altered vascular tone and structural remodeling in many cardiovascular diseases. ROS elicit these effects by influencing intracellular signaling events. In addition to modulating protein tyrosine kinases, protein phosphatases, mitogen-activated protein kinases, and transcription factors, ROS are important regulators of intracellular Ca2+ homeostasis and RhoA/Rho kinase signaling. ROS increase vascular [Ca2+]i by stimulating inositol trisphosphate-mediated Ca2+ mobilization, by increasing cytosolic Ca2+ accumulation through sarcoplasmic/endoplasmic reticulum Ca2+-ATPase inhibition, and by stimulating Ca2+ influx through Ca2+ channels. Increased ROS generation enhances Ca2+ signaling and up-regulates RhoA/Rho kinase, thereby altering vascular contractility and tone. The present review discusses the importance of ROS in angiotensin II signaling in vascular biology and focuses specifically on the role of oxidative stress in Ca2+ signaling in the vasculature.

Redox-dependent protein kinase regulation by angiotensin II: mechanistic insights and its pathophysiology

Reactive oxygen species (ROS) are proposed to induce cardiovascular diseases, such as atherosclerosis, hypertension, restenosis, and fibrosis, through several mechanisms. One such mechanism involves ROS acting as intracellular second messengers, which lead to induction of unique signal transductions. Angiotensin II (AngII), a potent cardiovascular pathogen, stimulates ROS production through the G protein-coupled AngII type 1 receptor expressed in its target organs, such as vascular tissues, heart, and kidney. Recent accumulating evidence indicates that through ROS production, AngII activates downstream ROS-sensitive kinases that are critical in mediating cardiovascular remodeling. Each of these ROS-sensitive kinases could potentially mediate its own specific function. In this review, we will focus our discussion on the current findings that suggest novel mechanisms of how AngII mediates activation of these redox-sensitive kinases in target organs, as well as the pathological significance of their activation.

Lung endothelial cell proliferation with decreased shear stress is mediated by reactive oxygen species

Acute cessation of flow (ischemia) leads to depolarization of the endothelial cell (EC) membrane mediated by K(ATP) channels and followed by production of reactive oxygen species (ROS) from NADPH oxidase. We postulated that ROS are a signal for initiating EC proliferation associated with the loss of shear stress. Flow cytometry was used to identify proliferating CD31-positive pulmonary microvascular endothelial cells (mPMVECs) from wild-type, Kir6.2-/-, and gp91phox-/- mice. mPMVECs were labeled with PKH26 and cultured in artificial capillaries for 72 h at 5 dyn/cm2 (flow adaptation), followed by 24 h of stop flow or continued flow. ROS production during the first hour of ischemia was markedly diminished compared with wild-type mice in both types of gene-targeted mPMVECs. Cell proliferation was defined as the proliferation index (PI). After 72 h of flow, >98% of PKH26-labeled wild-type mPMVECs were at a single peak (PI 1.0) and the proportion of cells in the S+G2/M phases were at 5.8% on the basis of cell cycle analysis. With ischemia (24 h), PI increased to 2.5 and the ratio of cells in S+G2/M phases were at 35%. Catalase, diphenyleneiodonium, and cromakalim markedly inhibited ROS production and cell proliferation in flow-adapted wild-type mPMVECs. Significant effects of ischemia were not observed in Kir6.2-/- and gp91phox-/- cells. ANG II activation of NADPH oxidase was unaffected by KATP gene deletion. Thus loss of shear stress in flow-adapted mPMVECs results in cell division associated with ROS generated by NADPH oxidase. This effect requires a functioning cell membrane KATP channel.

Protein kinases in vascular smooth muscle tone--role in the pulmonary vasculature and hypoxic pulmonary vasoconstriction

Hypoxic pulmonary vasoconstriction (HPV) is an adaptive mechanism that in the normal animal diverts blood away from poorly ventilated areas of the lung, thereby maintaining optimal ventilation-perfusion matching. In global hypoxia however, such as in respiratory disease or at altitude, it causes detrimental increases in pulmonary vascular resistance and pulmonary artery (PA) pressure. The precise intracellular pathways and mechanisms underlying HPV remain unclear, although it is now recognised that both an elevation in smooth muscle intracellular [Ca2+] and a concomitant increase in Ca2+ sensitivity are involved. Several key intracellular protein kinases have been proposed as components of the signal transduction pathways leading to development of HPV, specifically Rho kinase, non-receptor tyrosine kinases (NRTK), p38 mitogen activated protein (MAP) kinase, and protein kinase C (PKC). All of these have been implicated to a greater or lesser extent in pathways leading to Ca2+ sensitisation, and in some cases regulation of intracellular [Ca2+] as well. In this article, we review the role of these key protein kinases in the regulation of vascular smooth muscle (VSM) constriction, applying what is known in the systemic circulation to the pulmonary circulation and HPV. We conclude that the strongest evidence for direct involvement of protein kinases in the mechanisms of HPV concerns a central role for Rho kinase in Ca2+ sensitisation, and a potential role for Src-family kinases in both modulation of Ca2+ entry via capacitative Ca2+ entry (CCE) and activation of Rho kinase, though others are likely to have indirect or modulatory influences. In addition, we speculate that Src family kinases may provide a central interface between the proposed hypoxia-induced generation of reactive oxygen species by mitochondria and both the elevation in intracellular [Ca2+] and Rho kinase mediated Ca2+ sensitisation.

Angiotensin II-induced over-activation of p47phox in fibroblasts from hypertensives: which role in the enhanced ERK1/2 responsiveness to angiotensin II?

BACKGROUND

Fibroblasts are involved in the remodeling of the heart and of the vasculature associated to arterial hypertension, and an abnormal extracellular signal-regulated kinase 1/2 (ERK1/2) activation by angiotensin II (Ang II) plays a pivotal role in this process. However, the intracellular pathways leading to cell hypertrophy and hyperplasia, as well as to collagen production, are still incompletely known.

OBJECTIVE

To investigate the role of superoxide anion (O2) and of nicotinamide adenine dinucleotide phosphate (NAD(P)H) oxidase in Ang II-stimulated ERK1/2 over-activation in fibroblasts from hypertensive patients.

METHODS

O2 production was measured in skin fibroblasts from hypertensives (HT, n = 11) and from normotensive controls (NT, n = 10) by electron spin resonance technique. ERK1/2 phosphorylation and p47phox NAD(P)H oxidase subunit translocation were measured by western blot.

RESULTS

Ang II (1 micromol/l) induced a larger p47phox subunit translocation and increased intracellular O2 production to a larger extent in HT in comparison to NT and this effect was blocked by apocynin, an inhibitor of the NAD(P)H oxidase. Ang II increased ERK1/2 phosphorylation more in HT than in NT. The Ang II-induced ERK1/2 phosphorylation was inhibited by apocynin in a dose-dependent manner in NT, but not in HT.

CONCLUSIONS

The chain of cellular events leading to increased ERK1/2 responsiveness to Ang II in hypertension include an exaggerated response of p47phox, NAD(P)H oxidase and O2, but it is partially resistant to apocynin. Therefore, NAD(P)H-dependent reactive oxygen species (ROS) production is not the only determinant of the exaggerated ERK1/2 responsiveness in fibroblasts of hypertensives (HT).

Mechanisms for suppressing NADPH oxidase in the vascular wall

Oxidative stress underlies many forms of vascular disease as well as tissue injury following ischemia and reperfusion. The major source of oxidative stress in the artery wall is an NADPH oxidase. This enzyme complex as expressed in vascular cells differs from that in phagocytic leucocytes both in biochemical structure and functions. The crucial flavin-containing catalytic subunits, Nox1 and Nox4, are not found in leucocytes, but are highly expressed in vascular cells and upregulated with vascular remodeling, such as that found in hypertension and atherosclerosis. The difference in catalytic subunits offers the opportunity to develop "vascular specific" NADPH oxidase inhibitors that do not compromise the essential physiological signaling and phagocytic functions carried out by reactive oxygen and nitrogen species. Nitric oxide and targeted inhibitors of NADPH oxidase that block the source of oxidative stress in the vasculature are more likely to prevent the deterioration of vascular function that leads to stroke and heart attack, than are conventional antioxidants. The roles of Nox isoforms in other inflammatory conditions are yet to be explored.

Stimulation of NADPH oxidase by angiotensin II in human neutrophils is mediated by ERK, p38 MAP-kinase and cytosolic phospholipase A2

OBJECTIVE

The present research was designed to study the involvement of ERK and p38 MAP-kinase in cytosolic phospholipase A2 (cPLA2) and NADPH-oxidase activation by angiotensin II (Ang II) in human neutrophils.

METHODS

NADPH-oxidase activity was measured by reduction of cytochrome C. cPLA2 activity was measured in cell lysate using sonicated dispersions of 1-stearoyl-2-[C]arachidonyl phosphatidylcholine. Cells were incubated with MEK inhibitor UO126 or with p38 MAP-kinase inhibitor SB202190 prior to stimulation with Ang II. Translocation of p47, p67 and cPLA2 and phosphorylation of ERK and p38 MAP-kinase were measured by immunoblot analysis.

RESULTS

Ang II induced a dose-dependent activation of NADPH oxidase in neutrophils and monocytes as well as in differentiated PLB-985 cells towards neutrophil or monocyte lineages, but not in cPLA2-deficient differentiated PLB-985 cells. An immediate activation of both ERK and p38 MAP-kinase and of cPLA2 was induced by Ang II in human neutrophils. In addition, Ang II induced translocation of the cytosolic oxidase components, detected by translocation of p47, which preceded the translocation of cPLA2 induced by this agonist. The p38 MAP-kinase inhibitor SB202190 or the MEK-ERK pathway inhibitor UO126 totally inhibited the activation of both NADPH oxidase and cPLA2 as well as the translocation of cytosolic oxidase components and of cPLA2 to the membrane fractions.

CONCLUSIONS

These results suggest that either ERK or p38 MAP-kinase are involved in the activation of both cPLA2 and NADPH oxidase, and that cPLA2 is required for activation of the NADPH oxidase by Ang II in human neutrophils.

Intracellular mechanisms involved in vascular remodelling of resistance arteries in hypertension: role of angiotensin II

Resistance arteries undergo structural changes (vascular remodelling) in hypertension. These changes involve media thickening, reduced lumen diameter and consequent increased media:lumen ratio. Cellular processes underlying these events include altered vascular smooth muscle cell (VSMC) growth, migration, differentiation and increased extracellular matrix abundance. Another factor contributing to remodelling is inflammation, associated with macrophage infiltration, fibrosis and increased expression of redox-sensitive pro-inflammatory genes. Among the factors involved in arterial remodelling, angiotensin (Ang) II appears to be one of the most important. Ang II, a multifunctional peptide with pleiotropic actions, modulates vasomotor tone, cell growth, apoptosis/anoikis, cell migration and extracellular matrix deposition. It is pro-inflammatory and it stimulates production of growth factors and vasoactive agents. The multiple actions of Ang II are mediated via complex intracellular signalling pathways including stimulation of the phosholipase C (PLC)-inositol 1,4,5-trisphosphate (IP3)-1,2-diacylglycerol (DAG) cascade, mitogen-activated protein (MAP) kinases, tyrosine kinases and RhoA/Rho kinase. Furthermore, Ang II elicits many of its (patho)physiological effects by stimulating reactive oxygen species (*O2- and H2O2) generation through activation of vascular NAD(P)H oxidase. *O2- and H2O2 in turn influence downstream signalling molecules including transcription factors, tyrosine kinases/phosphatases, Ca2+ channels and MAP kinases. Interaction between these systems is complex and dysregulation at any level may contribute to vascular remodelling. Targeting such molecules/pathways could prevent or induce regression of hypertensive vascular damage thereby ameliorating development of hypertension and preventing target organ damage. The present review discusses the role of Ang II in remodelling of resistance arteries, focusing on some signalling pathways involved in vascular growth and inflammation in hypertension.

Src-mediated Tyrosine Phosphorylation of p47 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.

A redox-sensitive pathway mediates oxidized LDL-induced downregulation of insulin-like growth factor-1 receptor

Oxidized low density lipoprotein (OxLDL) has multiple proatherogenic effects, including induction of apoptosis. We have recently shown that OxLDL markedly downregulates insulin-like growth factor-1 receptor (IGF-1R) in human aortic smooth muscle cells, and that IGF-1R overexpression blocks OxLDL-induced apoptosis. We hypothesized that specific OxLDL-triggered signaling events led to IGF-1R downregulation and apoptosis. We examined OxLDL signaling pathways and found that neither IGF-1R downregulation nor the proapoptotic effect was blocked by inhibition of OxLDL-triggered extracellular signal-regulated kinase, p38 mitogen-activated protein kinase (MAPK), or peroxisome proliferator-activated receptor gamma (PPARgamma) signaling pathways, as assessed using specific inhibitors. However, antioxidants, polyethylene glycol catalase, superoxide dismutase, and Trolox completely blocked OxLDL downregulation of IGF-1R and OxLDL-induced apoptosis. Nordihydroguaiaretic acid, AA-861, and baicalein, which are lipoxygenase inhibitors and also have antioxidant activity, blocked IGF-1R downregulation and apoptosis as well as reactive oxygen species (ROS) production. These results suggest that OxLDL enhances ROS production possibly through lipoxygenase activity, leading to IGF-1R downregulation and apoptosis. Furthermore, anti-CD36 scavenger receptor antibody markedly inhibited OxLDL-induced IGF-1R downregulation and apoptosis as well as ROS production. In conclusion, our data demonstrate that OxLDL downregulates IGF-1R via redox-sensitive pathways that are distinct from OxLDL signaling through MAPK- and PPARgamma-involved pathways but may involve a CD36-dependent mechanism.

Aldosterone Activates Vascular p38MAP Kinase and NADPH Oxidase Via c-Src

Increasing evidence indicates that aldosterone elicits vascular effects through nongenomic signaling pathways. We tested the hypothesis that aldosterone induces activation of vascular mitogen-activated protein (MAP) kinases and NADPH oxidase via c-Src–dependent mechanisms in vascular smooth muscle cells (VSMCs). Aldosterone effects on activation of c-Src, p38MAP kinase, and NADPH oxidase, and incorporation of [ 3 H]proline, an index of collagen synthesis, were assessed in cultured rat VSMCs. Studies were performed in the absence and presence of eplerenone, a selective mineralocorticoid receptor blocker, PP2, a selective Src inhibitor, and SB212190, a selective p38MAPK inhibitor. Phosphorylation of c-Src was dose-dependently increased by aldosterone, with maximal responses obtained at 10 −7 mol/L. Aldosterone increased p38MAP kinase phosphorylation, NAD(P)H oxidase activation, and [ 3 H]proline incorporation. These responses were abrogated by eplerenone and almost abolished by PP2. Aldosterone-stimulated incorporation of [ 3 H]proline was significantly reduced by SB212190, indicating that p38MAP kinase plays a role in profibrotic actions of aldosterone. To unambiguously demonstrate the importance of aldosterone in c-Src signaling, VSMCs from c-Src +/+ and c-Src +/− mice were also studied. Aldosterone increased phosphorylation of c-Src, p38MAP kinase, and cortactin, a Src-specific substrate, in c-Src +/+ VSMCs, but not in c-Src-deficient cells. Taken together, our findings demonstrate that nongenomic signaling by aldosterone occurs through c-Src–dependent pathways. These processes may play an important role in profibrotic actions of aldosterone.

Angiotensin II-Dependent Chronic Hypertension and Cardiac Hypertrophy Are Unaffected by gp91phox-Containing NADPH Oxidase

The gp91phox-containing NADPH oxidase is the major source of reactive oxygen species (ROS) in the cardiovascular system and inactivation of gp91phox has been reported to blunt hypertension and cardiac hypertrophy seen in angiotensin (Ang) II-infused animals. In the current study, we sought to determine the role of gp91phox-derived ROS on cardiovascular outcomes of chronic exposure to Ang II. The gp91phox-deficient mice were crossed with transgenic mice expressing active human renin in the liver (TTRhRen). TTRhRen mice exhibit chronic Ang II–dependent hypertension and frank cardiac hypertrophy by age 10 to 12 weeks. Four genotypes of mice were generated: control, TTRhRen trangenics (TTRhRen), gp91phox-deficient (gp91 − ), and TTRhRen transgenic gp91phox-deficient (TTRhRen/gp91 − ). Eight to 10 mice/group were studied. ROS levels were significantly reduced ( P <0.05) in the heart and aorta of TTRhRen/gp91 − and gp91 − mice compared with control counterparts, and this was associated with reduced cardiac, aortic, and renal NADPH oxidase activity ( P <0.05). Systolic blood pressure (SBP), cardiac mass, and cardiac fibrosis were increased in TTRhRen versus controls. In contrast to its action on ROS generation, gp91phox inactivation had no effect on development of hypertension or cardiac hypertrophy in TTRhRen mice, although interstitial fibrosis was reduced. Cardiac and renal expression of gp91phox homologues, Nox1 and Nox4, was not different between groups. Thus, although eliminating gp91phox-associated ROS production may be important in cardiovascular consequences in acute insult models, it does not prevent the development of hypertension and cardiac hypertrophy in a model in which the endogenous renin-angiotensin system is chronically upregulated.

Reactive oxygen species as mediators of angiogenesis signaling: role of NAD(P)H oxidase

Angiogenesis, a process of new blood vessel growth, contributes to various pathophysiologies such as cancer, diabetic retinopathy and atherosclerosis. Accumulating evidence suggests that cardiovascular diseases are associated with increased oxidative stress in blood vessels. Reactive oxygen species (ROS) such as superoxide and H2O2 cause blood vessels to thicken, produce inflammation in the vessel wall, and thus are regarded as "risk factors" for vascular disease, whereas ROS also act as signaling molecules in many aspects of growth factor-mediated physiological responses. Recent reports suggest that ROS play an important role in angiogenesis; however, its underlying molecular mechanisms remain unknown. Vascular endothelial growth factor (VEGF) induces angiogenesis by stimulating endothelial cell (EC) proliferation and migration primarily through the receptor tyrosine kinase VEGF receptor2 (Flk1/KDR). VEGF binding initiates tyrosine phosphorylation of KDR, which results in activation of downstream signaling enzymes including ERK1/2, Akt and eNOS, which contribute to angiogenic-related responses in EC. Importantly, the major source of ROS in EC is a NAD(P)H oxidase and EC express all the components of phagocytic NAD(P)H oxidase including gp91phox, p22phox, p47phox, p67phox and the small G protein Rac1. We have recently demonstrated that ROS derived from NAD(P)H oxidase are critically important for VEGF signaling in vitro and angiogenesis in vivo. Furthermore, a peptide hormone, angiotensin II, a major stimulus for vascular NAD(P)H oxidase, also plays an important role in angiogenesis. Because EC migration and proliferation are primary features of the process of myocardial angiogenesis, we would like to focus on the recent progress that has been made in the emerging area of NAD(P)H oxidase-derived ROS-dependent signaling in ECs, and discuss the possible roles in angiogenesis. Understanding these mechanisms may provide insight into the components of NAD(P)H oxidase as potential therapeutic targets for treatment of angiogenesis-dependent diseases such as cancer and atherosclerosis and for promoting myocardial angiogenesis in ischemic heart diseases.

p47phox Associates With the Cytoskeleton Through Cortactin in Human Vascular Smooth Muscle Cells

OBJECTIVE

We tested the hypothesis that p47phox associates with the actin cytoskeleton, enabling site-directed activation of NAD(P)H oxidase, and assessed whether these actions influence reactive oxygen species (ROS) generation and signaling by angiotensin II (Ang II) in vascular smooth muscle cells (VSMCs) from human resistance and coronary arteries.

METHODS AND RESULTS

Electroporation of anti-p47phox antibody into VSMCs abrogated Ang II-mediated O2 generation, establishing the requirement for p47phox in this response. Immunfluorescence confocal microscopy demonstrated a cytosolic distribution of p47phox in basal conditions. After Ang II stimulation, p47phox rearranged in a linear fashion, colocalizing with F-actin. Co-immunoprecipitation studies confirmed an association between p47phox and actin and demonstrated an interaction with the actin-binding protein cortactin. Cytoskeletal disruption with cytochalasin prevented p47phox:actin interaction and attenuated ROS formation and p38MAP kinase and Akt phosphorylation by Ang II. Intracellular ROS generation in response to LY83583 (O2 generator) or exogenous H2O2 and Ang II-induced ERK1/2 activation were unaltered by cytochalasin.

CONCLUSIONS

The p47phox:actin interaction, through cortactin, plays an important role in Ang II-mediated site-directed assembly of functionally active NAD(P)H oxidase, ROS generation, and activation of redox-sensitive p38MAP kinase and Akt, but not ERK1/2. These findings demonstrate the importance of an intact actin-cytoskeleton in NAD(P)H oxidase regulation and redox signaling by Ang II in human VSMCs.

Molecular and cellular mechanisms in vascular injury in hypertension: role of angiotensin II – editorial review

PURPOSE OF REVIEW

Emerging evidence indicates that hypertension is a vascular disease associated with inflammation, induced through redox-sensitive mechanisms that are regulated by angiotensin II. This review focuses on the role of inflammation, oxidative stress and angiotensin II in vascular injury and discusses implications of these processes in hypertension.

RECENT FINDINGS

The dogma that hypertension is primarily a consequence of hemodynamic alterations has changed over the recent past, with compelling evidence that high blood pressure is linked to vascular damage, oxidative stress and inflammation. Of the many factors implicated in hypertensive vascular disease, angiotensin II appears to be one of the most important. Angiotensin II, a multifunctional peptide regulating vascular contraction, growth and fibrosis, has recently been identified as proinflammatory mediator. Angiotensin II increases vascular permeability, promotes recruitment of inflammatory cells into tissues, and directly activates infiltrating immune cells, which further contribute to the inflammatory process. Moreover, angiotensin II participates in tissue repair and remodeling, by stimulating cell growth and fibrosis. Many of these processes are mediated through increased generation of reactive oxygen species (oxidative stress).

SUMMARY

Inflammation, oxidative stress and hypertension are closely interrelated. Here we discuss the (patho)physiology of vascular inflammation in hypertension, focusing specifically on the role of angiotensin II and reactive oxygen species. By understanding molecular and cellular mechanisms of hypertensive vascular disease will allow for more targeted therapy and hopefully improved management and treatment of patients with hypertension.

Resistance to oxidative stress by chronic infusion of angiotensin II in mouse kidney is not mediated by the AT2 receptor

Wild-type mice are resistant to ANG II-induced renal injury and hence form an attractive model to study renal defense against ANG II. The present study tested whether ANG II induces expression of antioxidative genes via the AT2 receptor in renal cortex and thereby counteracts prooxidative forces. ANG II was infused in female C57BL/6J mice for 28 days and a subgroup received AT2 receptor antagonist (PD-123,319) for the last 3 days. ANG II induced hypertension and aortic hypertrophy; proteinuria and renal injury were absent. Urinary nitric oxide metabolites (NOx) were decreased, and lipid peroxide (TBARS) excretion remained unchanged. Expression of NADPH oxidase components was decreased in renal cortex but induced in aorta. Heme oxygenase-1 (HO-1) was induced in both renal cortex and aorta. In contrast, ANG II suggestively increased AT2 receptor expression in kidney but not in aorta. AT2 receptor blockade enhanced hypertension in ANG II-infused mice, reversed ANG II effects on NOx excretion, but did not affect TBARS. Despite its prohypertensive effect, expression of prooxidative genes in the renal cortex decreased rather than increased after short-term AT2 receptor blockade and renal HO-1 induction after ANG II was normalized. Thus chronic ANG II infusion in mice induces hypertension but not oxidative stress. In contrast to the response in aorta, gene expression of components of NADPH-oxidase was not enhanced in renal cortex. Although ANG II administration induced renal cortical AT2 receptor expression, blockade of that receptor did not unveil the AT2 receptor as intrarenal dampening factor of prooxidative forces.

Redox Mechanisms in Blood Vessels

Reactive oxygen species have been implicated in the pathogenesis of virtually every stage of vascular lesion formation, hypertension, and other vascular diseases. We are currently gaining insight into important sources of reactive oxygen species in the vessel wall, including the NADPH oxidases, xanthine oxidase, uncoupled nitric oxide synthase, and mitochondrial sources. Although various reactive oxygen species have pathological roles, some serve as important signaling molecules that modulate vascular tone, growth, and remodeling. In the next several months, a series of articles in Arteriosclerosis, Thrombosis, and Vascular Biology attempt to further elucidate how reactive oxygen species are produced by vascular cells and the roles of these in vascular homeostasis. This series promises to provide a valuable update on a wide variety of issues related to the biochemistry, molecular biology, and physiology of these important and fascinating molecules. Reactive oxygen species have been implicated in the pathogenesis of virtually every stage of vascular lesion formation, hypertension, and other vascular diseases. Upcoming series of articles in Arteriosclerosis, Thrombosis, and Vascular Biology help elucidate how reactive oxygen species are produced by vascular cells and their role in vascular homeostasis.

Tyrosine kinase-mediated activation of NADPH oxidase enhances proliferative capacity of diabetic vascular smooth muscle cells

To investigate a potential molecular basis for a link between diabetes and atherosclerosis, experiments were performed to determine the role of NADPH oxidase in the enhanced proliferative capacity of vascular smooth muscle cells (VSMC) from OLETF rat, an animal model of type 2 diabetes. An enhanced proliferative response to 10% fetal bovine serum with an increased cell cycle progression from G1 to S phase as well as an augmented superoxide generation with an increased NADPH oxidase activity were observed in diabetic versus control VSMC. Both the enhanced proliferation and superoxide generation in diabetic VSMC were significantly attenuated not only by diphenyleneiodonium (10 microM) and apocynin (100 microM), NADPH oxidase inhibitors but also by protein tyrosine kinase inhibitors such as genistein (100 microM) and AG 112 (100 microM). Furthermore, the enhanced NADPH oxidase activity in diabetic VSMC was significantly attenuated by genistein and AG112, but not by daidzein (100 microM), a genistein analogue devoid of protein tyrosine kinase inhibitory properties. Based on these results, it is suggested that the enhanced proliferative capacity of diabetic VSMC is closely related to the activation of NADPH oxidase that is induced through activation of protein tyrosine kinase.

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 µmol/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.Key words: superoxide, NADPH oxidase, p38MAP kinase, JNK, ERK1/2.

Significance of Angiotensin II Receptor Blocker Lipophilicities and Their Protective Effect against Vascular Remodeling

Although the lipophilicities of the various angiotensin II receptor blockers (ARBs) are very different, the relationship between lipophilicity and the protective effect against vascular remodeling is unclear. In this study, we compared the protective effects of a highly lipophilic ARB, telmisartan, and an ARB with low lipophilicity, losartan, on vascular function and oxidative stress in stroke-prone spontaneously hypertensive rats (SHR-SP). SHR-SP received oral placebo, 1 mg/kg telmisartan, or 10 mg/kg losartan for 2 weeks. The blood pressure (BP) in SHR-SP was significantly higher than that in Wistar-Kyoto (WKY) rats before treatment, and the BP was reduced equally in telmisartan- and losartan-treated SHR-SP compared to placebo-treated SHR-SP. Acetylcholine-induced vasorelaxation in isolated carotid arteries was significantly weaker in SHR-SP than in WKY rats, but in both telmisartan- and losartan-treated SHR-SP, acetylcholine-induced vasorelaxation was significantly higher than in placebo-treated SHR-SP. Moreover, acetylcholine-induced vasorelaxation in telmisartan-treated rats was significantly stronger than in losartan-treated SHR-SP. The expression of the endothelial nitric oxide synthase gene was significantly higher in telmisartan- and losartan-treated rats than in placebo-treated SHR-SP, and was significantly higher in telmisartan-treated rats than in losartan-treated rats. In contrast, the expression of the NAD(P)H oxidase subunit p22phox gene in telmisartan-treated SHR-SP was significantly lower than that in losartan-treated SHR-SP. Immunohistochemistry showed that angiotensin II expression in the aorta was significantly lower in telmisartan-treated SHR-SP than in losartan-treated SHR-SP. In conclusion, a highly lipophilic ARB, telmisartan, may be useful for preventing NAD(P)H oxidase activity, and thereby for conferring vascular protection.

c-Src and hydrogen peroxide mediate transforming growth factor-beta1-induced smooth muscle cell-gene expression in 10T1/2 cells

OBJECTIVE

Transforming growth factor-beta1 (TGF-beta1) controls the expression of numerous genes, including smooth muscle cell (SMC)-specific genes and extracellular matrix protein genes. Here we investigated whether c-Src plays a role in TGF-beta1 signaling in mouse embryonic fibroblast C3H10T1/2 cells.

METHODS AND RESULTS

TGF-beta1 induction of the SMC contractile protein SM22alpha gene expression was inhibited by PP1 (an inhibitor of Src family kinases) or by C-terminal Src kinase (a negative regulator of c-Src). Induction of SM22alpha by TGF-beta1 was markedly attenuated in SYF cells (c-Src(-), Yes(-), and Fyn(-)) compared with Src(++) cells (c-Src(++), Yes(-), and Fyn(-)). PP1 also inhibited the TGF-beta1-induced expression of serum response factor (SRF), a transcription factor regulating the SMC marker gene expression. Confocal immunofluorescence analysis showed that TGF-beta1 stimulates production of hydrogen peroxide. Antioxidants such as catalase or NAD(P)H oxidase inhibitors such as apocynin inhibited the TGF-beta1-induced expression of SM22alpha. Furthermore, we demonstrate that TGF-beta1 induction of the plasminogen activator inhibitor-1 (PAI-1) gene, which is known to be dependent on Smad but not on SRF, is inhibited by PP1 and apocynin.

CONCLUSIONS

Our results suggest that TGF-beta1 activates c-Src and generates hydrogen peroxide through NAD(P)H oxidase, and these signaling pathways lead to the activation of specific sets of genes, including SM22alpha and PAI-1. TGF-beta1 controls the expression of numerous genes, including SM22alpha and PAI-1. We investigated whether c-Src plays a role in TGF-beta1 signaling. TGF-beta1 induction of such genes was significantly reduced in Src family tyrosine kinase-deficient cells, and Csk and pharmacological inhibitors for Src family kinases or antioxidants inhibit the effects of TGF-beta1. These results indicate that c-Src and hydrogen peroxide are required for TGF-beta1 signaling.

Oxidative stress and vascular disease

Growing evidence indicates that chronic and acute overproduction of reactive oxygen species (ROS) under pathophysiologic conditions is integral in the development of cardiovascular diseases (CVD). These ROS can be released from nicotinamide adenine dinucleotide (phosphate) oxidase, xanthine oxidase, lipoxygenase, mitochondria, or the uncoupling of nitric oxide synthase in vascular cells. ROS mediate various signaling pathways that underlie vascular inflammation in atherogenesis: from the initiation of fatty streak development through lesion progress to ultimate plaque rupture. Various animal models of oxidative stress support the notion that ROS have a causal role in atherosclerosis and other cardiovascular diseases. Human investigations also support the oxidative stress hypothesis of atherosclerosis. Oxidative stress is the unifying mechanism for many CVD risk factors, which additionally supports its central role in CVD. Despite the demonstrated role of antioxidants in cellular and animal studies, the ineffectiveness of antioxidants in reducing cardiovascular death and morbidity in clinical trials has led many investigators to question the importance of oxidative stress in human atherosclerosis. Others have argued that the prime factor for the mixed outcomes from using antioxidants to prevent CVD may be the lack of specific and sensitive biomarkers by which to assess the oxidative stress phenotypes underlying CVD. A better understanding of the complexity of cellular redox reactions, development of a new class of antioxidants targeted to specific subcellular locales, and the phenotype-genotype linkage analysis for oxidative stress will likely be avenues for future research in this area as we move toward the broader use of pharmacological and regenerative therapies in the treatment and prevention of CVD.

Arterial Pressure Response to the Antioxidant Tempol and ET B Receptor Blockade in Rats on a High-Salt Diet

We hypothesized that increased superoxide contributes to mean arterial pressure (MAP) regulation in male Sprague-Dawley rats fed a high-salt diet and/or during endothelin (ET B ) receptor blockade. Four groups on either a normal- or a high-salt diet were studied for 1 week: (1) control; (2) tempol, a superoxide dismutase mimetic, in their drinking water (1 mmol/L); (3) A-192621, an ET B antagonist, in their food (10 mg/kg daily); or (4) both tempol and A-192621. Without ET B blockade, tempol had no effect on MAP (telemetry) in rats on the normal-salt diet but significantly reduced MAP in rats on the high-salt diet (100±3 vs 112±2 mm Hg, P <0.05). On the normal-salt diet, A-192621 increased MAP with or without tempol. Under high-salt conditions, tempol attenuated the increase in MAP produced by A-192621, but only during the initial days of treatment. Plasma 8-isoprostanes were increased in all rats on the high-salt diet and were further increased after 3 days of A-192621 but not after 7 days; tempol inhibited the increase produced by A-192621 but had no influence on the increase produced by high salt. H 2 O 2 excretion was significantly higher in rats on a high-salt diet for the 7-day drug treatment compared with those on a normal-salt diet. Tempol further increased H 2 O 2 excretion in rats on a high-salt diet, an effect accelerated in A-192621–treated rats. These data suggest that blood pressure lowering by tempol in rats on a high-salt diet may be unrelated to reductions in superoxide and that renal H 2 O 2 may account for the limited ability of tempol to attenuate hypertension produced by ET B receptor blockade.

Association of increased phagocytic NADPH oxidase-dependent superoxide production with diminished nitric oxide generation in essential hypertension

OBJECTIVE

Oxidative stress has been implicated in the pathogenesis of hypertension and its complications through alterations in nitric oxide (NO) metabolism. This study was designed to investigate whether a relationship exists between phagocytic nicotinamide adenine dinucleotide phosphate (NADPH) oxidase-dependent superoxide anion (*O2-) production and NO generation in patients with essential hypertension.

METHODS

Superoxide production was assayed by chemiluminescence under baseline and stimulated conditions on mononuclear cells obtained from hypertensives (n=51) and normotensives (n=43). NO production was evaluated by determining serum NO metabolites, nitrate plus nitrite (NOx).

RESULTS

Although there were no differences in baseline *O2- production between normotensives and hypertensives, the *O2- production in phorbol myristate acetate (PMA)-stimulated mononuclear cells was increased (P <0.05) in hypertensives compared with normotensives. The PMA-induced *O2- production was completely abolished by apocynin, a specific inhibitor of NADPH oxidase. Moreover, stimulation of *O2- production by angiotensin II and endothelin-1 was higher (P <0.05) in cells from hypertensives than in cells from normotensives. In addition, diminished (P <0.001) serum NOx was detected in hypertensives compared with normotensives. Interestingly, an inverse correlation (r=0.493, P <0.01) was found between *O2- production and NOx in hypertensives.

CONCLUSIONS

Generation of *O2- mainly dependent on NADPH oxidase is abnormally enhanced in stimulated mononuclear cells from hypertensives. It is suggested that this alteration could be involved in the diminished NO production observed in these patients.