The HMG-CoA reductase inhibitor simvastatin activates the protein kinase Akt and promotes angiogenesis in normocholesterolemic animals

Recent studies suggest that statins can function to protect the vasculature in a manner that is independent of their lipid-lowering activity. We show here that statins rapidly activate the protein kinase Akt/PKB in endothelial cells. Accordingly, simvastatin enhanced phosphorylation of the endogenous Akt substrate endothelial nitric oxide synthase (eNOS), inhibited apoptosis and accelerated vascular structure formation in vitro in an Akt-dependent manner. Similar to vascular endothelial growth factor (VEGF) treatment, both simvastatin administration and enhanced Akt signaling in the endothelium promoted angiogenesis in ischemic limbs of normocholesterolemic rabbits. Therefore, activation of Akt represents a mechanism that can account for some of the beneficial side effects of statins, including the promotion of new blood vessel growth.

Acute modulation of endothelial Akt/PKB activity alters nitric oxide-dependent vasomotor activity in vivo

The serine/threonine protein kinase Akt (protein kinase B) phosphorylates endothelial cell nitric oxide synthase (eNOS) and enhances its ability to generate nitric oxide (NO). Because NO is an important regulator of vasomotor tone, we investigated whether Akt can regulate endothelium-dependent vasomotion in vivo using a rabbit femoral artery model of gene transfer. The endothelium of isolated femoral arteries was infected with replication-defective adenoviral constructs expressing beta-galactosidase, constitutively-active Akt (myr-Akt), or dominant-negative Akt (dn-Akt). Femoral arteries transduced with myr-Akt showed a significant increase in resting diameter and blood flow, as assessed by angiography and Doppler flow measurements, respectively. L-NAME, an eNOS inhibitor, blocked myr-Akt-mediated vasodilatation. In contrast, endothelium-dependent vasodilatation in response to acetylcholine was attenuated in vessels transduced with dn-Akt, although these vessels showed normal responses to nitroglycerin, an endothelium-independent vasodilator. Similarly, relaxation of murine aorta ex vivo in response to acetylcholine, but not nitroglycerin, was inhibited by transduction of dn-Akt to the endothelium. These data provide evidence that Akt functions as key regulator of vasomotor tone in vivo.

Reconstitution of an endothelial nitric-oxide synthase (eNOS), hsp90, and caveolin-1 complex in vitro. Evidence that hsp90 facilitates calmodulin stimulated displacement of eNOS from caveolin-1

The activity of endothelial nitric-oxide synthase (eNOS) is regulated by its subcellular localization, phosphorylation and through its interaction with different proteins. The association of eNOS with caveolin-1 (Cav) is believed to maintain eNOS in an inactive state; however, increased association of eNOS to heat shock protein 90 (hsp90) is observed following activation. In this study, we investigate the relationship between caveolin and hsp90 as opposing regulatory proteins on eNOS function. Immunoprecipitation of Cav-1 from bovine lung microvascular endothelial cells shows that eNOS and hsp90 are present in the Cav-1 complex. eNOS and hsp90 from the lysate also interact with exogenous glutathione S-transferase-linked caveolin-1 (GST-Cav), and the addition of calcium-activated calmodulin (CaM) to the GST-Cav complex partially inhibited the association of eNOS and hsp90. Purified eNOS associates with GST-Cav specifically through the caveolin-scaffolding domain (residues 82-101); however, the addition of CaM slightly, but nonstatistically, reduces eNOS binding to GST-Cav. When hsp90 is present in the binding reaction, the addition of increasing concentrations of CaM significantly displaces eNOS and hsp90 from GST-Cav. eNOS enzymatic activity is also less sensitive to inhibition by the caveolin scaffolding peptide (residues 82-101) when eNOS is prebound to hsp90. Collectively, our results show that the actions of CaM on eNOS dissociation from caveolin are facilitated in the presence of hsp90.

Temporal events underlying arterial remodeling after chronic flow reduction in mice: correlation of structural changes with a deficit in basal nitric oxide synthesis

To define the cellular events of vascular remodeling in mice, we measured blood flow and analyzed the morphology of remodeled vessels at defined points after a flow-reducing remodeling stimulus for 3, 7, 14, and 35 days. Acute ligation of the left external carotid artery reduced blood flow in the left common carotid artery (LC) compared with sham and contralateral right common carotid arteries (RCs). In morphometric analyses, the decrease in diameter in LCs was reversible by vasodilator perfusion 3 days after ligation, whereas ligation for 7 days or greater resulted in a permanent diameter reduction. Coincident with structural remodeling at day 7 was an increase in cell death in remodeled LCs. Functionally, rings from remodeled LCs contracted to prostaglandin F(2alpha) and relaxed to acetylcholine in a manner identical to that of control arteries. However, remodeled LCs were hypersensitive to the nitrovasodilator sodium nitroprusside (at day 7) and exhibited a marked reduction in basal NO synthesis at 7 and 14 days after ligation. The impairment of endothelial NO synthase function was likely due to post-translational mechanisms, given that endothelial NO synthase mRNA and protein levels did not change in remodeled LCs. These data define the ontogeny of flow-triggered luminal remodeling in adult mice and suggest that endothelial dysfunction occurs during reorganization of the vessel wall.

Vascular endothelial growth factor-stimulated actin reorganization and migration of endothelial cells is regulated via the serine/threonine kinase Akt

Vascular endothelial growth factor (VEGF) induces endothelial cell proliferation, migration, and actin reorganization, all necessary components of an angiogenic response. However, the distinct signal transduction mechanisms leading to each angiogenic phenotype are not known. In this study, we examined the ability of VEGF to stimulate cell migration and actin rearrangement in microvascular endothelial cells infected with adenoviruses encoding beta-galactosidase (beta-gal), activation-deficient Akt (AA-Akt), or constitutively active Akt (myr-Akt). VEGF increased cell migration in cells transduced with beta-gal, whereas AA-Akt blocked VEGF-induced cell locomotion. Interestingly, myr-Akt transduction of bovine lung microvascular endothelial cells stimulated cytokinesis in the absence of VEGF, suggesting that constitutively active Akt, per se, can initiate the process of cell migration. Treatment of beta-gal-infected endothelial cells with an inhibitor of NO synthesis blocked VEGF-induced migration but did not influence migration initiated by myr-Akt. In addition, VEGF stimulated remodeling of the actin cytoskeleton into stress fibers, a response abrogated by infection with dominant-negative Akt, whereas transduction with myr-Akt alone caused profound reorganization of F-actin. Collectively, these data demonstrate that Akt is critically involved in endothelial cell signal transduction mechanisms leading to migration and that the Akt/endothelial NO synthase pathway is necessary for VEGF-stimulated cell migration.

Angiopoietin-1 inhibits endothelial cell apoptosis via the Akt/survivin pathway

A productive angiogenic response must couple to the survival machinery of endothelial cells to preserve the integrity of newly formed vessels. Angiopoietin-1 (Ang-1) is an endothelium-specific ligand essential for embryonic vascular stabilization, branching morphogenesis, and post-natal angiogenesis, but its contribution to endothelial cell survival has not been completely elucidated. Here we show that Ang-1 acting via the Tie 2 receptor induces phosphorylation of the survival serine-threonine kinase, Akt (or protein kinase B). This is associated with up-regulation of the apoptosis inhibitor, survivin, in endothelial cells and protection of endothelium from death-inducing stimuli. Moreover, dominant negative survivin negates the ability of Ang-1 to protect cells from undergoing apoptosis. The activation of anti-apoptotic pathways mediated by Akt and survivin in endothelial cells may contribute to Ang-1 stabilization of vascular structures during angiogenesis, in vivo.

Enhanced electron flux and reduced calmodulin dissociation may explain "calcium-independent" eNOS activation by phosphorylation

Bovine endothelial nitric oxide synthase (eNOS) is phosphorylated directly by the protein kinase Akt at serine 1179. Mutation of this residue to the negatively charged aspartate (S1179D eNOS) increases nitric oxide (NO) production constitutively, in the absence of agonist challenge. Here, we examine the potential mechanism of how aspartate at 1179 increases eNOS activity using purified proteins. Examination of NO production and cytochrome c reduction resulted in no substantial changes in the K(m)/EC(50) for L-arginine, calmodulin, and calcium, whereas there was a 2-fold increase in the rate of NO production for S1179D and a 2-4-fold increase in reductase activity (based on cytochrome c reduction). The observed increase in activity for both assays of NOS function indicates that a faster rate of electron flux through the reductase domain is likely the rate-limiting step in NO formation from eNOS. In addition, S1179D eNOS did show an increased resistance to inactivation by EGTA compared with wild type eNOS. These results suggest that a negative charge imposed at serine 1179, either by phosphorylation or by replacement with aspartate, increases eNOS catalytic activity by increasing electron flux at the reductase domain and by reducing calmodulin dissociation from activated eNOS when calcium levels are low.

Estrogen stimulates heat shock protein 90 binding to endothelial nitric oxide synthase in human vascular endothelial cells. Effects on calcium sensitivity and NO release

Estradiol (E(2)) causes endothelium-dependent vasodilation, mediated, in part, by enhanced nitric oxide (NO) release. We have previously shown that E(2)-induced activation of endothelial nitric oxide synthase (eNOS) reduces its calcium dependence. This pathway of eNOS activation is unique to a limited number of stimuli, including shear stress, the response to which is herbimycin-inhibitable. Consistent with this, herbimycin and geldanamycin pretreatment of human umbilical vein endothelial cells (HUVEC) abrogated E(2)-stimulated NO release and cGMP production, respectively. These benzoquinone ansamycins are potent inhibitors of Hsp90 function, which has recently been shown to play a role in stimulus-dependent eNOS activation. As in response to shear, E(2) induced an Hsp90-eNOS association, peaking at 30 min and completely inhibited by the conventional estrogen receptor antagonist ICI 182,780. These findings suggest that Hsp90 plays an important role in the rapid, estrogen receptor-mediated modulation of eNOS activation by estrogen.

Quantification of eNOS mRNA in the canine cardiac vasculature by competitive PCR

The goal of the present study was to develop a competitive PCR assay to measure changes in the expression of endothelial nitric oxide synthase (eNOS) mRNA levels throughout the canine vascular tree. A partial sequence of canine eNOS cDNA (1.86 kb), inducible NOS (1.95 kb), and neuronal NOS (1.16 kb) was cultured from canine aortic endothelial cells, LPS-treated canine splenic vein endothelial cells, and from canine left ventricle, respectively. Competitor eNOS cDNA (eNOS-C) was constructed via recombinant PCR. Thus, with the use of a standard curve competitive PCR with eNOS-C, the amount of eNOS mRNA in 500 ng of total RNA was greatest in the circumflex > right coronary artery > left anterior descending coronary artery > aorta. The isolation of coronary microvessels from the left ventricle was associated with an enrichment of endothelial cell markers such as eNOS, von Willebrand factor, and caveolin-1, an observation supported by the detection of up to 15-fold higher levels of eNOS mRNA in coronary microvessels relative to the larger arteries. The ability to quantify changes in eNOS mRNA levels throughout the canine vasculature should provide greater insight into the molecular mechanisms of how this gene is regulated in physiological and pathophysiological states.

Vasomotor control in arterioles of the mouse cremaster muscle

Recent advances in transgenic mouse technology provide novel models to study cardiovascular physiology and pathophysiology. In light of these developments, there is an increasing need for understanding cardiovascular function and blood flow control in normal mice. To this end we have used intravital microscopy to investigate vasomotor control in arterioles of the superfused cremaster muscle preparation of anesthetized C57Bl6 mice. Spontaneous resting tone increased with branch order and was enhanced by oxygen. Norepinephrine and acetylcholine (ACh) caused concentration-dependent vasoconstriction and vasodilation, respectively. Microiontophoresis of ACh evoked vasodilation that conducted along arterioles; the local (direct) response was inhibited by N(omega)-nitro-L-arginine (LNA), and both local and conducted responses were inhibited by 17-octadecynoic acid (17-ODYA). Microejection of KCl evoked a biphasic response: a transient conducted vasoconstriction (inhibited by nifedipine), followed by a conducted vasodilation that was insensitive to LNA, indomethacin, and 17-ODYA. Phenylephrine evoked focal vasoconstriction that did not conduct. Perivascular sympathetic nerve stimulation evoked constriction along arterioles that was inhibited by tetrodotoxin. These findings indicate that for arterioles in the mouse cremaster muscle, nitric oxide and endothelial-derived hyperpolarizing factor (as shown by LNA and 17-ODYA interventions, respectively) mediate vasodilatory responses to ACh but not to KCl, and that vasomotor responses spread along arterioles by multiple pathways of cell-to-cell communication.

Impaired endothelial nitric oxide synthase activity associated with enhanced caveolin binding in experimental cirrhosis in the rat

BACKGROUND & AIMS

A reduction in nitric oxide (NO) has been implicated as a cause of intrahepatic vasoconstriction in cirrhosis, but the regulatory mechanisms remain undefined. The aim of this study was to examine a contributory role for caveolin-1, a putative negative regulator of endothelial NO synthase, in mediating deficient intrahepatic NO production in the intact cirrhotic liver.

METHODS

Cirrhosis was induced by carbon tetrachloride inhalation. Flow regulation of NO production and perfusion pressure was examined in the perfused rat liver. Protein expression of endothelial NO synthase (eNOS), caveolin, and calmodulin was examined by Western blotting and immunohistochemistry. NOS activity and NO production were assessed by citrulline generation and chemiluminescence, respectively. Protein-protein interactions were examined using whole tissue protein immunoprecipitation.

RESULTS

In response to incremental increases in flow, cirrhotic animals produced significantly less NO(x) than control animals. NOS activity was significantly reduced in liver tissue from cirrhotic animals compared with control animals in the presence of similar eNOS protein levels. Deficient eNOS activity was associated with a severalfold increase in binding of eNOS with caveolin. Protein levels of caveolin-1 were markedly increased in the cirrhotic liver.

CONCLUSIONS

These studies provide evidence that enhanced expression and interaction of caveolin with eNOS contribute to impaired NO production, reduced NOS activity, and vasoconstriction in the intact cirrhotic liver.

Codistribution of NOS and caveolin throughout peripheral vasculature and skeletal muscle of hamsters

In isolated cell systems, nitric oxide synthase (NOS) activity is regulated by caveolin (CAV), a resident caveolae coat protein. Because little is known of this interaction in vivo, we tested whether NOS and caveolin are distributed together in the intact organism. Using immunohistochemistry, we investigated the localization of constitutive neuronal (nNOS) and endothelial (eNOS) enzyme isoforms along with caveolin-1 (CAV-1) and caveolin-3 (CAV-3) throughout the systemic vasculature and peripheral tissues of the hamster. The carotid artery, abdominal aorta, vena cava, femoral artery and vein, feed artery and collecting vein of the cheek pouch retractor muscle, capillaries and muscle fibers of retractor and cremaster muscles, and arterioles and venules of the cheek pouch were studied. In endothelial cells, eNOS and CAV-1 were present throughout the vasculature, whereas nNOS and CAV-3 were absent except in capillaries, which reacted for nNOS. In smooth muscle cells, nNOS and CAV-1 were also expressed systemically, whereas eNOS was absent; CAV-3 was present in the arterial but not the venous vasculature. Both nNOS and CAV-3 were located at the sarcolemma of skeletal muscle fibers, which were devoid of eNOS and CAV-1. These immunolabeling patterns suggest functional interactions between eNOS and CAV-1 throughout the endothelium, regional differences in the modulation of nNOS by caveolin isoforms in vascular smooth muscle, and modulation of nNOS by CAV-3 in skeletal muscle.

Molecular control of nitric oxide synthases in the cardiovascular system

Nitric oxide plays an important role in cardiovascular homeostasis. In this review, the regulation of the three nitric oxide synthase isoforms in the cardiovascular system are examined at molecular and cellular levels. In addition, recent information gleaned from the use of NOS knockout mice are discussed.

Trafficking of endothelial nitric-oxide synthase in living cells. Quantitative evidence supporting the role of palmitoylation as a kinetic trapping mechanism limiting membrane diffusion

To examine endothelial nitric-oxide synthase (eNOS) trafficking in living endothelial cells, the eNOS-deficient endothelial cell line ECV304 was stably transfected with an eNOS-green fluorescent protein (GFP) fusion construct and characterized by functional, biochemical, and microscopic analysis. eNOS-GFP was colocalized with Golgi and plasma membrane markers and produced NO in response to agonist challenge. Localization in the plasma membrane was dependent on the palmitoylation state, since the palmitoylation mutant of eNOS (C15S/C26S eNOS-GFP) was excluded from the plasma membrane and was concentrated in a diffuse perinuclear pattern. Fluorescence recovery after photobleaching (FRAP) revealed eNOS-GFP in the perinuclear region moving 3 times faster than the plasmalemmal pool, suggesting that protein-lipid or protein-protein interactions are different in these two cellular domains. FRAP of the palmitoylation mutant was two times faster than that of wild-type eNOS-GFP, indicating that palmitoylation was influencing the rate of trafficking. Interestingly, FRAP of C15S/C26S eNOS-GFP but not wild-type eNOS-GFP fit a model of protein diffusion in a lipid bilayer. These data suggest that the regulation of eNOS trafficking within the plasma membrane and Golgi are probably different mechanisms and not due to simple diffusion of the protein in a lipid bilayer.

Hsp90 regulation of endothelial nitric oxide synthase contributes to vascular control in portal hypertension

The molecular chaperone, heat shock protein 90 (Hsp90), acts as an intermediate in the signaling cascades leading to activation of endothelial nitric oxide synthase (eNOS). In this study, we examine the participation of this pathway in nitric oxide (NO)-dependent vasodilation in the rat mesentery in vitro. In normal animals, immunoprecipitation of eNOS from intact mesentery coimmunoprecipitates Hsp90 and, additionally, both eNOS and Hsp90 colocalize to the endothelial lining of mesenteric vessels. In the perfused mesenteric vasculature of normal animals, geldanamycin (GA), a specific inhibitor of Hsp90 signaling, attenuates ACh-dependent vasodilation but does not affect vasodilation in response to sodium nitroprusside. Next, studies were performed in animals with experimental portal hypertension induced by portal vein ligation (PVL). In PVL animals, NOS catalytic activity is markedly enhanced in mesenteric tissue and the perfused mesentery is hyporesponsive to the vasoconstrictor methoxamine (MTX). GA significantly potentiates MTX-induced vasoconstriction after PVL, thereby partially reversing the hyporeactivity to this agent exhibited in the mesenteric vasculature after PVL. These studies suggest that Hsp90 can act as a signaling mediator of NO-dependent responses in the mesenteric circulation and indicate that the excessive NO production observed in portal hypertension is mediated in part through Hsp90 signaling.

Regulation of endothelium-derived nitric oxide production by the protein kinase Akt

Endothelial nitric oxide synthase (eNOS) is the nitric oxide synthase isoform responsible for maintaining systemic blood pressure, vascular remodelling and angiogenesis. eNOS is phosphorylated in response to various forms of cellular stimulation, but the role of phosphorylation in the regulation of nitric oxide (NO) production and the kinase(s) responsible are not known. Here we show that the serine/threonine protein kinase Akt (protein kinase B) can directly phosphorylate eNOS on serine 1179 and activate the enzyme, leading to NO production, whereas mutant eNOS (S1179A) is resistant to phosphorylation and activation by Akt. Moreover, using adenovirus-mediated gene transfer, activated Akt increases basal NO release from endothelial cells, and activation-deficient Akt attenuates NO production stimulated by vascular endothelial growth factor. Thus, eNOS is a newly described Akt substrate linking signal transduction by Akt to the release of the gaseous second messenger NO.

NO overproduction by eNOS precedes hyperdynamic splanchnic circulation in portal hypertensive rats

Chronic high blood flow and the hyperdynamic circulatory syndrome in portal hypertension are associated with endothelial constitutive nitric oxide (NO) synthase (eNOS) upregulation and increased NO release. In portal vein-ligated (PVL) rats the splanchnic circulation is not yet hyperdynamic on day 3 postoperatively. In vitro perfused superior mesenteric arteries (SMAs) of day 3 PVL and sham rats were challenged with increasing flow rates or the alpha-adrenoreceptor agonist methoxamine (30 and 100 microM) before and after incubation with the NO inhibitor, Nomega-nitro-L-arginine (L-NNA, 10(-4) M). Perfusate NO metabolite (NOx) concentrations were measured by chemiluminescence. PVL rats expressed a significant hyporesponsiveness to increases in flow rate or methoxamine that was overcome by incubation with L-NNA. The PVL vasculature showed significantly higher slopes of NOx production vs. flow-induced shear stress, higher increases in perfusate NOx concentration in response to methoxamine, and higher eNOS protein levels (Western blot) compared with sham rats. In conclusion, eNOS-upregulation and increased NO release by the SMA endothelium occur before the development of the hyperdynamic splanchnic circulation, suggesting a primary role of NO in the pathogenesis of arterial vasodilatation.

A vascular bed-specific pathway

The endothelial nitric oxide synthase (eNOS) gene is induced by a variety of extracellular signals under both in vitro and in vivo conditions. To gain insight into the mechanisms underlying environmental regulation of eNos expression, transgenic mice were generated with the 1,600-bp 5' flanking region of the human eNos promoter coupled to the coding region of the LacZ gene. In multiple independent lines of mice, transgene expression was detected within the endothelium of the brain, heart, skeletal muscle, and aorta. beta-galactosidase activity was consistently absent in the vascular beds of the liver, kidney, and spleen. In stable transfection assays of murine endothelial progenitor cells, the 1,600-bp promoter region was selectively induced by conditioned media from cardiac myocytes, skeletal myocytes, and brain astrocytes. Cardiac myocyte-mediated induction was partly abrogated by neutralizing anti-platelet-derived growth factor (PDGF) antibodies. In addition, promoter activity was upregulated by PDGF-AB. Analysis of promoter deletions revealed that a PDGF response element lies between -744 and -1,600 relative to the start site of transcription, whereas a PDGF-independent cardiac myocyte response element is present within the first 166 bp of the 5' flanking region. Taken together, these results suggest that the eNos gene is regulated in the cardiac endothelium by both a PDGF-dependent and PDGF-independent microvascular bed-specific signaling pathway.

Direct actions of angiopoietin-1 on human endothelium: evidence for network stabilization, cell survival, and interaction with other angiogenic growth factors

Angiopoietin-1 (Ang-1) is a recently described angiogenic protein that activates the endothelial Tie 2 receptor. Disruption of the Ang-1 gene shows that it has an indispensable role in blood vessel development, but it is not clear what specific effects, if any, Ang-1 has on endothelial cell (EC) phenotypes. Here, we show that Ang-1 dose-dependently stabilizes HUVEC network organization for up to 48 hours; this action of Ang-1 is dependent on Tie-2 receptor activation, because a soluble form of the Tie2-, but not the Tie1-receptor, completely blocks the effects of Ang-1. Moreover, we show that Ang-1 potentiates the actions of other angiogenic growth factors. Ang-1 markedly increases the survival of vascular networks (up to 96 hours) exposed to either vascular endothelial growth factor or endothelial cell growth supplement, a form of acidic fibroblast growth factor. In addition, Ang-1 prevents apoptotic death in HUVEC triggered by withdrawal of endothelial cell growth supplement. Collectively, these data are consistent with the idea that Ang-1 directly acts on human EC and interacts with other angiogenic molecules to stabilize vascular structures by promoting the survival of differentiated ECs.

Induction of nitric oxide synthase mRNA by shear stress requires intracellular calcium and G-protein signals and is modulated by PI 3 kinase

We have investigated the signaling pathways by which shear stress induces accumulation of endothelial nitric oxide synthase (eNOS) mRNA in bovine aortic endothelial cells (BAEC). Steady laminar fluid shear stress (20 dyn/cm2) induced a time-dependent increase in eNOS mRNA levels that did not require de novo protein synthesis and was in part transcriptional. Shear responsiveness was conferred on a luciferase reporter by a portion of the eNOS gene promoter encoding the 5'-flanking region between nt -1600 and -779. Shear-mediated induction of eNOS mRNA was abolished by chelation of intracellular calcium ([Ca2+]i) with BAPTA-AM, and inhibited by blockade of calcium entry with SKF96535. In contrast, eNOS mRNA upregulation by shear was potentiated by thapsigargin-mediated depletion of Ca2+i stores. Pertussis toxin (PTX) inhibited both the shear-induced elevation in [Ca2+]i and the subsequent increase in eNOS mRNA, implicating a PTX-sensitive G-protein in both responses. Shear-induced upregulation of eNOS mRNA was unaffected by the calmodulin inhibitor W-7 and by the tyrosine kinase inhibitor herbimycin A, suggesting that neither calmodulin nor tyrosine kinases are required. However, eNOS mRNA upregulation was potentiated by the PI 3-kinase inhibitors wortmannin and LY294002, suggesting that PI 3-kinase inhibits the shear response. Although microtubule integrity is required for the shear-induced regulation of endothelin-1 mRNA and the morphological and cytoskeletal responses to flow, neither microtubule dissolution with nocodazole nor microtubule stabilization with taxol altered shear-induced [Ca2+]i elevation or upregulation of eNOS mRNA. In conclusion, shear stress of BAEC increases eNOS transcriptional rate and upregulates eNOS mRNA levels by a process that requires calmodulin-independent [Ca2+]i signaling and a PTX-sensitive G-protein, is inhibited by PI 3-kinase, and is independent of microtubule integrity and tyrosine kinase activity.

Biological action of leptin as an angiogenic factor

Leptin is a hormone that regulates food intake, and its receptor (OB-Rb) is expressed primarily in the hypothalamus. Here, it is shown that OB-Rb is also expressed in human vasculature and in primary cultures of human endothelial cells. In vitro and in vivo assays revealed that leptin has angiogenic activity. In vivo, leptin induced neovascularization in corneas from normal rats but not in corneas from fa/fa Zucker rats, which lack functional leptin receptors. These observations indicate that the vascular endothelium is a target for leptin and suggest a physiological mechanism whereby leptin-induced angiogenesis may facilitate increased energy expenditure.

Neuronal nitric oxide synthase is expressed in principal cell of collecting duct

We used the RT-PCR technique and immunocytochemical methods to determine the expression of endothelial nitric oxide synthase (eNOS) or neuronal nitric oxide synthase (nNOS) in the cortical collecting duct (CCD) in rats on high-K+ diet. The microdissected CCDs of the rat kidney were lysed, and RT-PCR was carried out using rat nNOS and eNOS gene-specific primers. Southern analysis showed the presence of mRNA of nNOS but not eNOS in the CCD. The presence of nNOS in the CCD was further confirmed by light microscopy. We used the polyclonal nNOS antibody in immunocytochemical studies of the isolated CCD. We found that immunoreactivity to nNOS was present in the CCD and heterogeneous with positive and negative immunostaining. We performed the immunocytochemical studies in the split-open CCD and found that the immunoreactivity to nNOS was detected only in principal cells but not in intercalated cells. We conclude that nNOS is expressed in the rat CCD in rats on high-K+ diet. The presence of nNOS in the CCD is heterogeneous and mainly located in principal cells.

Dynamic activation of endothelial nitric oxide synthase by Hsp90

Heat-shock protein 90 (Hsp90) coordinates the trafficking and regulation of diverse signalling proteins, but its precise role in regulating specific cellular targets is not known. Here we show that Hsp90 associates with endothelial nitric oxide synthase (eNOS) and is rapidly recruited to the eNOS complex by agonists that stimulate production of nitric oxide, namely vascular endothelial growth factor, histamine and fluid shear stress. Moreover, the binding of Hsp90 to eNOS enhances the activation of eNOS. Inhibition of signalling through Hsp90 attenuates both agonist-stimulated production of nitric oxide and endothelium-dependent relaxation of isolated blood vessels. Our results indicate that Hsp90 facilitates signalling mediated by growth-factor, G-protein and mechanotransduction pathways that lead to the activation of eNOS. These observations indicate that in addition to its role as a molecular chaperone involved in protein folding and maturation, Hsp90 may also be recruited to cellular targets depending on the activation state of the cell.

Hypotension and inflammatory cytokine gene expression triggered by factor Xa-nitric oxide signaling

The signaling pathway initiated by factor Xa on vascular endothelial cells was investigated. Factor Xa stimulated a 5- to 10-fold increased release of nitric oxide (NO) in a dose-dependent reaction (0.1-2.5 microG/ml) unaffected by the thrombin inhibitor hirudin but abolished by active site inhibitors, tick anticoagulant peptide, or Glu-Gly-Arg-chloromethyl ketone. In contrast, the homologous clotting protease factor IXa or another endothelial cell ligand, fibrinogen, was ineffective. A factor Xa inter-epidermal growth factor synthetic peptide L (83)FTRKL(88) (G) blocking ligand binding to effector cell protease receptor-1 inhibited NO release by factor Xa in a dose-dependent manner, whereas a control scrambled peptide KFTGRLL was ineffective. Catalytically active factor Xa induced hypotension in rats and vasorelaxation in the isolated rat mesentery, which was blocked by the NO synthase inhibitor L-N(G)-nitroarginine methyl ester (L-NAME) but not by D-NAME. Factor Xa/NO signaling also produced a dose-dependent endothelial cell release of interleukin 6 (range 0.55-3.1 ng/ml) in a reaction inhibited by L-NAME and by the inter-epidermal growth factor peptide Leu(83)-Leu(88) but unaffected by hirudin. Maximal induction of interleukin 6 mRNA required a brief, 30-min stimulation with factor Xa, unaffected by subsequent addition of tissue factor pathway inhibitor. These data suggest that factor Xa-induced NO release modulates endothelial cell-dependent vasorelaxation and cytokine gene expression. This pathway requiring factor Xa binding to effector cell protease receptor-1 and a secondary step of ligand-dependent proteolysis may preserve an anti-thrombotic phenotype of endothelium but also trigger acute phase responses during activation of coagulation in vivo.

Bladder instillation and intraperitoneal injection of Escherichia coli lipopolysaccharide up-regulate cytokines and iNOS in rat urinary bladder

Systemic bacterial lipopolysaccharides (LPS) induce inflammatory responses characteristic of sepsis. Instillation of LPS into rat bladder produces a localized inflammatory response similar to that seen in urinary tract infections (UTIs). Four hours after intravesical instillation of LPS, neutrophils infiltrate into the bladder, and mRNA for inducible nitric oxide synthase (iNOS) and the cytokines, interleukin (IL)-6 and IL-10, is detected in rat bladder but not in the kidney. Induction of iNOS protein is inferred because urinary nitrate and cGMP levels are increased 4 hr after LPS intravesical instillation and remain elevated for at least 24 hr. When LPS is injected intraperitoneally, iNOS and IL-6 mRNA are induced both in the bladder and in the kidney. These data are consistent with the effects of intravesical instillation of LPS remaining localized, iNOS activity increases in both particulate and soluble bladder fractions when measured 4 hr after intravesical instillation of LPS. The magnitude of these increases in iNOS activity in the bladder is not as great as when LPS is injected intraperitoneally. Intravesical instillation of LPS induces no increase in lung or kidney NOS activity. The localized inflammatory response produced by intravesical instillation of LPS demonstrates the importance of LPS as a mediator of the host response in UTIs and supports the use of urinary measurements of nitrate and cGMP in humans as indicative of the localized induction of iNOS in UTIs.

The synergistic activity of alphavbeta3 integrin and PDGF receptor increases cell migration

Integrins and growth factor receptors act synergistically to modulate cellular functions. The alphavbeta3 integrin and the platelet-derived growth factor receptor have both been shown to play a positive role in cell migration. We show here that a platelet derived growth factor-BB gradient stimulated migration of rat microvascular endothelial cells on vitronectin (9.2-fold increase compared to resting cells) in a alphavbeta3 and RGD-dependent manner. In contrast, this response was not observed on a beta1 integrin ligand, laminin; background levels of migration, in response to a platelet derived growth factor-BB gradient, were observed on this substrate or on bovine serum albumin (2.4- or 2.0-fold, respectively). Comparable results were obtained using NIH-3T3 cells. Platelet derived growth factor-BB did not change the cells' ability to adhere to vitronectin, nor did it stimulate a further increase in proliferation on vitronectin versus laminin. In addition, platelet derived growth factor-BB stimulation of NIH-3T3 cells did not alter the ability of alphavbeta3 to bind RGD immobilized on Sepharose. The alphavbeta3 integrin and the platelet derived growth factor receptor-beta associate in both microvascular endothelial cells and NIH-3T3 cells, since they coprecipitated using two different antibodies to either alphavbeta3 or to the platelet derived growth factor receptor-beta. In contrast, beta1 integrins did not coprecipitate with the platelet derived growth factor receptor-beta. These results point to a novel pathway, mediated by the synergistic activity of alphavbeta3 and the platelet derived growth factor receptor-beta, that regulates cell migration and, therefore, might play a role during neovessel formation and tissue infiltration.

Direct evidence for the importance of endothelium-derived nitric oxide in vascular remodeling

The vascular endothelium mediates the ability of blood vessels to alter their architecture in response to hemodynamic changes; however, the specific endothelial-derived factors that are responsible for vascular remodeling are poorly understood. Here we show that endothelial-derived nitric oxide (NO) is a major endothelial-derived mediator controlling vascular remodeling. In response to external carotid artery ligation, mice with targeted disruption of the endothelial nitric oxide synthase gene (eNOS) did not remodel their ipsilateral common carotid arteries whereas wild-type mice did. Rather, the eNOS mutant mice displayed a paradoxical increase in wall thickness accompanied by a hyperplastic response of the arterial wall. These findings demonstrate a critical role for endogenous NO as a negative regulator of vascular smooth muscle proliferation in response to a remodeling stimulus. Furthermore, our data suggests that a primary defect in the NOS/NO pathway can promote abnormal remodeling and may facilitate pathological changes in vessel wall morphology associated with complex diseases such as hypertension and atherosclerosis.

Nitric oxide production contributes to the angiogenic properties of vascular endothelial growth factor in human endothelial cells

Vascular endothelial growth factor (VEGF) is a regulator of vasculogenesis and angiogenesis. To investigate the role of nitric oxide (NO) in VEGF-induced proliferation and in vitro angiogenesis, human umbilical vein endothelial cells (HUVEC) were used. VEGF stimulated the growth of HUVEC in an NO-dependent manner. In addition, VEGF promoted the NO-dependent formation of network-like structures in HUVEC cultured in three dimensional (3D) collagen gels. Exposure of cells to VEGF led to a concentration-dependent increase in cGMP levels, an indicator of NO production, that was inhibited by nitro-L-arginine methyl ester. VEGF-stimulated NO production required activation of tyrosine kinases and increases in intracellular calcium, since tyrosine kinase inhibitors and calcium chelators attenuated VEGF-induced NO release. Moreover, two chemically distinct phosphoinositide 3 kinase (PI-3K) inhibitors attenuated NO release after VEGF stimulation. In addition, HUVEC incubated with VEGF for 24 h showed an increase in the amount of endothelial NO synthase (eNOS) protein and the release of NO. In summary, both short- and long-term exposure of human EC to VEGF stimulates the release of biologically active NO. While long-term exposure increases eNOS protein levels, short-term stimulation with VEGF promotes NO release through mechanisms involving tyrosine and PI-3K kinases, suggesting that NO mediates aspects of VEGF signaling required for EC proliferation and organization in vitro.

Liver sinusoidal endothelial cells are responsible for nitric oxide modulation of resistance in the hepatic sinusoids

The mechanisms that regulate vascular resistance in the liver are an area of active investigation. Previously, we have shown that nitric oxide (NO) modulates hepatic vascular tone in the normal rat liver. In this study, the production of NO is examined in further detail by isolating sinusoidal endothelial cells (SEC) from the rat liver. Endothelial NO synthase (eNOS) was present in SEC based on Western blotting and confocal immunofluorescence microscopy. Exposure of SEC to flow increased the release of NO. To investigate the relevance of these in vitro findings to the intact liver, we modified an in situ perfusion system to allow for direct measurement of NO release from the hepatic vasculature. NO was released from the hepatic vasculature in a time-dependent manner, and administration of N-monomethyl-L-arginine reduced NO release and increased portal pressure. Immunostaining of intact liver demonstrated eNOS localization to endothelial cells lining the hepatic sinusoids. These findings demonstrate that SEC in vitro and in vivo express eNOS and produce NO basally, and increase their production in response to flow. Additionally, an increase in portal pressure concomitant with the blockade of NO release directly demonstrates that endogenous endothelial-derived NO modulates portal pressure.

17 beta-estradiol regulation of human endothelial cell basal nitric oxide release, independent of cytosolic Ca2+ mobilization

Estradiol retards the development of atherosclerosis. Animal models have suggested that NO may be a critical effector molecule in this cardiovascular protection. In this study, female human umbilical vein endothelial cells (HUVECs) were propagated in phenol red-free gonadal hormone-free medium and pretreated with 17 beta-estradiol (E2). Reduced NO2- and NO3- (NOx) concentration, determined by chemiluminescence, demonstrated a rapid increase in basal HUVEC NO release in response to physiological concentrations of E2. The estrogen receptor (ER) antagonist ICI 164,384 inhibited the augmented NO release, demonstrating an ER-mediated component of this response. Because endothelial NO synthase (eNOS) activity is largely regulated by cytosolic Ca2+, relative [Ca2+]i in response to E2 was determined in a fluorometric assay. E2 did not promote HUVEC Ca2+ fluxes. Furthermore, eNOS activity in E2-pretreated endothelial whole-cell lysates was not dependent on additional Ca2+. Despite involving the ER, this is a nongenomic effect E2, as demonstrated by maintained responses in transcriptionally inhibited cells and by the rapidly (10 minutes) of cGMP formation in an NO bioassay. We demonstrate, for the first time, that independent of cytosolic Ca2+ mobilization, there is augmentation of eNOS activity with a resultant increase in HUVEC basal NO release in response to short-term estradiol exposure. Implications for the cardiovascular protective role of estrogen are discussed.

Dissecting the interaction between nitric oxide synthase (NOS) and caveolin. Functional significance of the nos caveolin binding domain in vivo

Endothelial nitric oxide synthase (eNOS) is a dually acylated peripheral membrane protein that targets to the Golgi region and caveolae of endothelial cells. Recent evidence has shown that eNOS can co-precipitate with caveolin-1, the resident coat protein of caveolae, suggesting a direct interaction between these two proteins. To test this idea, we examined the interactions of eNOS with caveolin-1 in vitro and in vivo. Incubation of endothelial cell lysates or purified eNOS with glutathione S-transferase (GST)-caveolin-1 resulted in the direct interaction of the two proteins. Utilizing a series of GST-caveolin-1 deletion mutants, we identified two cytoplasmic domains of caveolin-1 that interact with eNOS, the scaffolding domain (amino acids 61-101) and to a lesser extent the C-terminal tail (amino acids 135-178). Incubation of pure eNOS with peptides derived from the scaffolding domains of caveolin-1 and -3, but not the analogous regions from caveolin-2, resulted in inhibition of eNOS, inducible NOS (iNOS), and neuronal NOS (nNOS) activities. These results suggest a common mechanism and site of inhibition. Utilizing GST-eNOS fusions, the site of caveolin binding was localized between amino acids 310 and 570. Site-directed mutagenesis of the predicted caveolin binding motif within eNOS blocked the ability of caveolin-1 to suppress NO release in co-transfection experiments. Thus, our data demonstrate a novel functional role for caveolin-1 in mammalian cells as a potential molecular chaperone that directly inactivates NOS. This suggests that the direct binding of eNOS to caveolin-1, per se, and the functional consequences of eNOS targeting to caveolae are likely temporally and spatially distinct events that regulate NO production in endothelial cells. Additionally, the inactivation of eNOS and nNOS by the scaffolding domain of caveolin-3 suggests that eNOS in cardiac myocytes and nNOS in skeletal muscle are likely subject to negative regulation by this muscle-specific caveolin isoform.

The first 35 amino acids and fatty acylation sites determine the molecular targeting of endothelial nitric oxide synthase into the Golgi region of cells: a green fluorescent protein study

Catalytically active endothelial nitric oxide synthase (eNOS) is located on the Golgi complex and in the caveolae of endothelial cells (EC). Mislocalization of eNOS caused by mutation of the N-myristoylation or cysteine palmitoylation sites impairs production of stimulated nitric oxide (NO), suggesting that intracellular targeting is critical for optimal NO production. To investigate the molecular determinants of eNOS targeting in EC, we constructed eNOS-green fluorescent protein (GFP) chimeras to study its localization in living and fixed cells. The full-length eNOS-GFP fusion colocalized with a Golgi marker, mannosidase II, and retained catalytic activity compared to wild-type (WT) eNOS, suggesting that the GFP tag does not interfere with eNOS localization or function. Experiments with different size amino-terminal fusion partners coupled to GFP demonstrated that the first 35 amino acids of eNOS are sufficient to target GFP into the Golgi region of NIH 3T3 cells. Additionally, the unique (Gly-Leu)5 repeat located between the palmitoylation sites (Cys-15 and -26) of eNOS is necessary for its palmitoylation and thus localization, but not for N-myristoylation, membrane association, and NOS activity. The palmitoylation-deficient mutants displayed a more diffuse fluorescence pattern than did WT eNOS-GFP, but still were associated with intracellular membranes. Biochemical studies also showed that the palmitoylation-deficient mutants are associated with membranes as tightly as WT eNOS. Mutation of the N-myristoylation site Gly-2 (abolishing both N-myristoylation and palmitoylation) caused the GFP fusion protein to distribute throughout the cell as GFP alone, consistent with its primarily cytosolic nature in biochemical studies. Therefore, eNOS targets into the Golgi region of NIH 3T3 cells via the first 35 amino acids, including N-myristoylation and palmitoylation sites, and its overall membrane association requires N-myristoylation but not cysteine palmitoylation. These results suggest a novel role for fatty acylation in the specific compartmentalization of eNOS and most likely, for other dually acylated proteins, to the Golgi complex.

Nitric oxide synthase inhibitors attenuate transforming-growth-factor-beta 1-stimulated capillary organization in vitro

Angiogenesis is a complex process involving endothelial cell (EC) proliferation, migration, differentiation, and organization into patent capillary networks. Nitric oxide (NO), an EC mediator, has been reported to be antigenic as well as proangiogenic in different models of in vivo angiogenesis. Our aim was to investigate the role of NO in capillary organization using rat microvascular ECs (RFCs) grown in three-dimensional (3D) collagen gels. RFCs placed in 3D cultures exhibited extensive tube formation in the presence of transforming growth factor-beta 1. Addition of the NO synthase (NOS) inhibitors L-nitro-arginine methylester (L-NAME, 1 mmol/L) or L-monomethyl-nitro-l-arginine (1 mmol/L) inhibited tube formation and the accumulation of nitrite in the media by approximately 50%. Incubation of the 3D cultures with excess L-arginine reversed the inhibitory effect of L-NAME on tube formation. In contrast to the results obtained in 3D cultures, inhibition of NO synthesis by L-NAME did not influence RFC proliferation in two-dimensional (2D) cultures or antagonize the ability of transforming growth factor-beta 1 to suppress EC proliferation in 2D cultures. Reverse transcriptase-polymerase chain reaction revealed the constitutive expression of all three NOS isoforms, neuronal, inducible, and endothelial NOSs, in 2D and 3D cultures. Moreover, Western blot analysis demonstrated the presence of immunoreactive protein for all NOS isoforms in 3D cultures of RFCs. In addition, in the face of NOS blockade, co-treatment with the NO donor sodium nitroprusside or the stable analog of cGMP, 8-bromo-cGMP, restored capillary tube formation. Thus, the autocrine production of NO and the activation of soluble guanylate cyclase are necessary events in the process of differentiation and in vitro capillary tube organization of RFCs.

Endotoxin impairs biliary glutathione and HCO3- excretion and blocks the choleretic effect of nitric oxide in rat liver

Cholestasis in patients with sepsis has been attributed to the effects of endotoxin (lipopolysaccharides, LPS) and LPS-induced cytokines, which are also potent stimulators of systemic and hepatic nitric oxide (NO) synthesis. NO donors stimulate bile acid-independent bile flow in normal rat liver, but the effects of LPS-induced NO on bile formation remain unclear. To address this question we examined the effects of NO and its mediator guanosine 3',5'-cyclic monophosphate (cGMP) on bile flow and biliary HCO3- and glutathione excretion in isolated perfused rat livers (IPRL) from LPS-treated rats. Portal and systemic NO2- + NO3- plasma levels were increased 47-fold in LPS-treated rats and were also elevated in perfusate (6-fold) and bile (9-fold) after isolating and perfusing livers from these animals. Bile flow, HCO3-, and glutathione output were decreased by 33%, 25%, and 81% in these IPRL, respectively. Stimulation of NO synthesis with L-arginine or inhibition of inducible NO synthesis with aminoguanidine did not change bile flow, although pretreatment with aminoguanidine inhibited NO production by 85%. Moreover, the choleretic effects of infusions of the NO donors sodium nitroprusside (SNP) and S-nitroso-acetyl-penicillamine were markedly reduced in endotoxemic IPRL compared with normal controls, and SNP-induced HCO3- and glutathione excretion were reduced by 61% and 86%, respectively. SNP-induced cyclic GMP production was 2.3-fold lower than in normals, but the choleretic effect of dibutyryl cGMP was only slightly reduced in endotoxemic livers. These findings indicate that LPS reduces bile acid-independent bile flow primarily by inhibiting biliary excretion of glutathione and to a lesser extent HCO3-, whereas LPS-induced NO does not modulate bile formation in endotoxemia. Thus, impairment of the major determinants of bile acid-independent bile flow by LPS may contribute significantly to the pathogenesis of the cholestasis of sepsis.

Characterization of bovine endothelial nitric oxide synthase as a homodimer with down-regulated uncoupled NADPH oxidase activity: tetrahydrobiopterin binding kinetics and role of haem in dimerization

The fatty-acylation-deficient bovine endothelial NO synthase (eNOS) mutant (Gly-2 to Ala-2, G2AeNOS) was purified from a baculovirus overexpression system. The purified protein was soluble and highly active (0.2-0.7 micromol of l-citrulline. mg-1.min-1), contained 0. 77+/-0.01 equivalent of haem per subunit, showed a Soret maximum at 396 nm, and exhibited only minor uncoupling of NADPH oxidation in the absence of l-arginine or tetrahydrobiopterin. Radioligand binding studies revealed KD values of 147+/-24.1 nM and 52+/-9.2 nM for specific binding of tetrahydrobiopterin in the absence and presence of 0.1 mM l-arginine respectively. The positive co-operative effect of l-arginine was due to a pronounced decrease in the rate of tetrahydrobiopterin dissociation (from 1.6+/-0.5 to 0. 3+/-0.1 min-1). Low-temperature SDS gel electrophoresis showed that approx. 80% of the protein migrated as haem-containing dimer after preincubation with l-arginine and tetrahydrobiopterin. Gel-filtration chromatography yielded one peak with a Stokes radius of 6.8+/-0.04 nm, corresponding to a hydrodynamic volume of 1. 32x10(-24) m3, whereas haem-deficient preparations (approx. 0.3 equivalent per subunit) contained an additional protein species with a hydrodynamic radius of 5.1+/-0.2 nm and a corresponding volume of 0.55x10(-24) m3, suggesting that haem availability regulates eNOS dimerization.

Substrate binding and calmodulin binding to endothelial nitric oxide synthase coregulate its enzymatic activity

Endothelial nitric oxide synthase (NOS) is a constitutively expressed flavin-containing heme protein that catalyzes the formation of NO from L-arginine, NADPH, and molecular oxygen. We purified bovine endothelial NOS from transfected embryonic kidney cells by conventional chromatographic techniques and characterized the activity of the detergent-solubilized enzyme. Endothelial NOS displays a much lower specific activity of NO synthesis (143 +/- 11 nmol NO/min/mg enzyme) than the constitutive neuronal NOS or inducible NOS isoforms. Like the neuronal isoform, endothelial NOS requires binding of Ca2+/calmodulin to achieve Vmax NO synthase activity; however, we observed a basal level of NO synthesis even when Ca2+/calmodulin was omitted and 0.5 mM EDTA was present in the assay solution. Moreover, endothelial NOS demonstrates a high-affinity bonding interaction with calmodulin such that the enzyme as purified has a NO synthase activity at about 80% of Vmax. We also observed a more than twofold increase in NADPH consumption by endothelial NOS when it was coupled to arginine oxygenation as opposed to when oxygen is activated in the absence of substrate. Substrate binding was also shown to stimulate heme reduction in the absence of added calmodulin. Thus, the enzymatic synthesis of NO from L-arginine by endothelial NOS appears to be partially regulated by binding of both calmodulin and substrate. These findings for endothelial NOS represent a significant departure from the enzymatic properties of the other constitutive NOS isoform, neuronal NOS, and we interpret this result in terms of the physiological implications.

Bacterial infection induces nitric oxide synthase in human neutrophils

The identification of human inflammatory cells that express inducible nitric oxide synthase and the clarification of the role of inducible nitric oxide synthase in human infectious or inflammatory processes have been elusive. In neutrophil-enriched fractions from urine, we demonstrate a 43-fold increase in nitric oxide synthase activity in patients with urinary tract infections compared with that in neutrophil-enriched fractions from noninfected controls. Partially purified inducible nitric oxide synthase is primarily membrane associated, calcium independent, and inhibited by arginine analogues with a rank order consistent with that of purified human inducible nitric oxide synthase. Molecular, biochemical, and immunocytochemical evidence unequivocally identifies inducible nitric oxide synthase as the major nitric oxide synthase isoform found in neutrophils isolated from urine during urinary tract infections. Elevated inducible nitric oxide synthase activity and elevated nitric oxide synthase protein measured in patients with urinary tract infections and treated with antibiotics does not decrease until 6-10 d of antibiotic treatment. The extended elevation of neutrophil inducible nitric oxide synthase during urinary tract infections may have both antimicrobial and proinflammatory functions.

Nitric oxide synthase induction with renal transplant rejection or infection

Nitric oxide (NO) is readily oxidized to nitrate and nitrite and NO activates guanylyl cyclase, increasing cyclic GMP levels. To determine if nitric oxide synthase (NOS) is present in urine collected daily from patients following renal transplantation, we evaluated NOS activity in the leukocyte-rich particulate fraction and measured nitrate, nitrite, and cyclic GMP levels in the supernatant fraction of the urine. Reverse transcriptase-PCR and cDNA sequencing confirmed the presence of inducible NOS (iNOS) in cells obtained from the urine of renal transplant patients with rejection. NOS activity was elevated significantly in renal transplant patients with rejection (6.40 +/- 1.47 pmol citrulline/min/mg protein) or with urinary tract infection (29.56 +/- 11.00 pmol citrulline/min/mg protein), when compared to post-renal transplantation patients without rejection or urinary tract infection (0.51 +/- 0.21 pmol citrulline/min/mg protein). Nitrate levels increased in renal transplant patients with rejection and nitrite levels increased in renal transplant patients with urinary tract infection (UTI). Cyclic GMP levels increased with both rejection and UTI. This study demonstrates the presence of NOS activity and inducible NOS-mRNA in cells isolated from the urine of patients undergoing renal allograft rejection.

Elevated blood pressures in mice lacking endothelial nitric oxide synthase

Nitric oxide produced in endothelial cells affects vascular tone. To investigate the role of endothelial nitric oxide synthase (eNOS) in blood pressure regulation, we have generated mice heterozygous (+/-) or homozygous (-/-) for disruption of the eNOS gene. Immunohistochemical staining with anti-eNOS antibodies showed reduced amounts of eNOS protein in +/- mice and absence of eNOS protein in -/- mutant mice. Male or female mice of all three eNOS genotypes were indistinguishable in general appearance and histology, except that -/- mice had lower body weights than +/+ or +/- mice. Blood pressures tended to be increased (by approximately 4 mmHg) in +/- mice compared with +/+, while -/- mice had a significant increase in pressure compared with +/+ mice (approximately 18 mmHg) or +/- mice (approximately 14 mmHg). Plasma renin concentration in the -/- mice was nearly twice that of +/+ mice, although kidney renin mRNA was modestly decreased in the -/- mice. Heart rates in the -/- mice were significantly lower than in +/- or +/+ mice. Appropriate genetic controls show that these phenotypes in F2 mice are due to the eNOS mutation and are not due to sequences that might differ between the two parental strains (129 and C57BL/6J) and are linked either to the eNOS locus or to an unlinked chromosomal region containing the renin locus. Thus eNOS is essential for maintenance of normal blood pressures and heart rates. Comparisons between the current eNOS mutant mice and previously generated inducible nitric oxide synthase mutants showed that homozygous mutants for the latter differ in having unaltered blood pressures and heart rates; both are susceptible to lipopolysaccharide-induced death.

Endothelial nitric oxide synthase is regulated by tyrosine phosphorylation and interacts with caveolin-1

The regulation of endothelial nitric oxide synthase (eNOS) by phosphorylation is poorly understood. Here, we demonstrate that eNOS is tyrosine-phosphorylated in bovine aortic endothelial cells (BAEC) using 32P metabolic labeling followed by phosphoamino acid analysis and by phosphotyrosine specific Western blotting. Treatment of BAEC with hydrogen peroxide and the protein tyrosine phosphatase inhibitor, sodium orthovanadate, increases eNOS tyrosine phosphorylation. Utilizing a novel immunoNOS assay, the increase in tyrosine phosphorylation is associated with a 50% decrease in the specific activity of the enzyme. Because eNOS is localized in plasmalemma caveolae, we examined if tyrosine phosphorylated eNOS interacts with caveolin-1, the coat protein of caveolae. Immunoprecipitation of eNOS from bovine lung microvascular endothelial cells resulted in the co-precipitation of caveolin-1. Conversely, immunoprecipitation of caveolin-1 resulted in the co-precipitation of tyrosine-phosphorylated eNOS. Thus, tyrosine phosphorylation is a novel regulatory mechanism for eNOS and caveolin-1 is the first eNOS-associated protein. Collectively, these observations provide a novel regulatory mechanism for eNOS and suggest that tyrosine phosphorylation may influence its activity, subcellular trafficking, and interaction with other caveolin-interacting proteins in caveolae.

Palmitoylation of endothelial nitric oxide synthase is necessary for optimal stimulated release of nitric oxide: implications for caveolae localization

Endothelial nitric oxide synthase (eNOS) is dually acylated by N-myristoylation and cysteine palmitoylation and resides in Golgi and caveolae membranes. N-Myristoylation is necessary for its membrane association and targeting into the Golgi complex of transfected cells whereas palmitoylation influences the targeting of eNOS into caveolae. However, the in vivo significance of palmitoylation, membrane association, and the corresponding caveolar localization of eNOS have not been shown. To further examine the nature of membrane association of palmitoylation-deficient forms of eNOS and to address the functional role(s) of palmitoylation in activation of eNOS in vivo, HEk 293 cells stably transfected with wild-type (WT) or palmitoylation-deficient mutants of eNOS were generated. Membrane association of the mutants was biochemically similar to that of the WT protein in terms of their resistance to high salt, high pH, and distribution between Triton X-114 detergent and aqueous phases, suggesting that other hydrophobic factor (s) in eNOS most likely contribute to its membrane association. Most importantly, palmitoylation-deficient mutants of eNOS released less NO from the cells than did WT enzyme, suggesting that palmitoylation plays an important role in determining the optimal release of NO from intact cells. The diminished release of NO from the palmitoylation-deficient mutants was not attributable to alterations in its catalytic properties as the purified mutant and WT enzymes were kinetically identical. Since palmitoylation is necessary for localization of eNOS in caveolae, our data suggest that such localization could regulate the frequency and magnitude of NO release in response to stimuli in vivo.

Inhibition of nitric oxide synthase does not alter ocular dominance shifts in kitten visual cortex

1. Since nitric oxide has been proposed as a feedback factor in plasticity in the hippocampus, we tested whether it might also be a feedback factor in sensory-dependent plasticity in the cat visual cortex. 2. The effects of monocular deprivation were compared between eight hemispheres with infusion of a nitric oxide synthase inhibitor, and eight control hemispheres with either infusion of the inactive isomer, or no infusion. Although nitric oxide synthase activity was reduced significantly, the ocular dominance histograms were not substantially different in the two groups of animals. We conclude that the feedback factor for sensory-dependent plasticity in the visual cortex is likely to be some factor other than nitric oxide.

Targeting of nitric oxide synthase to endothelial cell caveolae via palmitoylation: implications for nitric oxide signaling

The membrane association of endothelial nitric oxide synthase (eNOS) plays an important role in the biosynthesis of nitric oxide (NO) in vascular endothelium. Previously, we have shown that in cultured endothelial cells and in intact blood vessels, eNOS is found primarily in the perinuclear region of the cells and in discrete regions of the plasma membrane, suggesting trafficking of the protein from the Golgi to specialized plasma membrane structures. Here, we show that eNOS is found in Triton X-100-insoluble membranes prepared from cultured bovine aortic endothelial cells and colocalizes with caveolin, a coat protein of caveolae, in cultured bovine lung microvascular endothelial cells as determined by confocal microscopy. To examine if eNOS is indeed in caveolae, we purified luminal endothelial cell plasma membranes and their caveolae directly from intact, perfused rat lungs. eNOS is found in the luminal plasma membranes and is markedly enriched in the purified caveolae. Because palmitoylation of eNOS does not significantly influence its membrane association, we next examined whether this modification can affect eNOS targeting to caveolae. Wild-type eNOS, but not the palmitoylation mutant form of the enzyme, colocalizes with caveolin on the cell surface in transfected NIH 3T3 cells, demonstrating that palmitoylation of eNOS is necessary for its targeting into caveolae. These data suggest that the subcellular targeting of eNOS to caveolae can restrict NO signaling to specific targets within a limited microenvironment at the cell surface and may influence signal transduction through caveolae.

Characterization of bovine endothelial nitric oxide synthase expressed in E. coli

Bovine endothelial constitutive nitric oxide synthase (eNOS) was expressed in E. coli as a soluble, catalytically active enzyme using the pCW expression vector coexpressed with a plasmid, pGroELS, encoding the chaperonins groEL and groES. The E. coli BL21 cultures reproducibly synthesized 6-10 mg of recombinant enzyme per liter of culture. The eNOS protein was purified using 2'5'-ADP Sepharose 4B and appeared as a single band of apparent molecular mass 135 kDa on SDS/PAGE. The recombinant resting enzyme is predominantly high spin with an absorbance maximum at 406 nm. The dithionite-reduced, CO-bound form shows an absorbance maximum at 444 nm. The spectral properties of recombinant eNOS from E. coli are identical to those observed with eNOS from stably transfected HEK 293 cells or from baculovirus expression systems. Enzymatic activity of eNOS from E. coli ranged between 68-135 nmol product formed/min/mg at 25 degrees C, using hemoglobin-NO capture or L-citrulline formation assays. The enzyme is replete with heme and flavins and both activity and [3H]-nitroarginine binding were largely dependent on tetrahydrobiopterin. The heterologous expression of eNOS offers a number of advantages over tissue sources of the protein.

Reduced gene expression of vascular endothelial NO synthase and cyclooxygenase-1 in heart failure

Endothelium-dependent responses are depressed in coronary and peripheral blood vessels after the onset of pacing-induced heart failure in dogs and heart failure of various etiologies in humans. The present study was designed to examine whether these responses were due to decreases in the expression of endothelial cell NO synthase (ecNOS) and cyclooxygenase-1 (COX-1). After 1 month of left ventricular pacing, 8 mongrel dogs were monitored for heart failure as defined by clinical signs and left ventricular end diastolic pressures > 25 mm Hg. Total RNA and protein were isolated from endothelial cells scraped from the thoracic aorta and analyzed by Northern and Western blotting, respectively. Blots probed with 32P-labeled cDNAs for ecNOS and COX-1 were quantified densitometrically, and results were normalized against GAPDH or von Willebrand factor (vWF). In arbitrary units, the ratios of ecNOS to GAPDH were 2.66 +/- 0.77 (mean +/- SEM, n = 17) and 1.12 +/- 0.37 (n = 6 and the ratios of COX-1 to GAPDH were 1.52 +/- 0.52 and 0.56 +/- 0.15 before and after heart failure, respectively. These represent 56% to 64% (P < .05) reductions in ecNOS and COX-1 gene expression. There was no change in the ratios of either COX-1 or ecNOS to vWF. There was also a marked reduction in ecNOS protein after heart failure, estimated at 70%. A marked reduction in nitrite production, a measure of enzyme activity, from thoracic aortas in response to stimulation by either acetylcholine or bradykinin also occurred. To determine whether ecNOS and COX-1 could be independently regulated, an orally active NO-releasing agent, CAS 936, was given to 7 normal dogs for 7 days, and aortic ecNOS and COX-1 mRNAs were analyzed. The ratio of ecNOS to GAPDH was depressed by 52% (P < .05) in aortas from these dogs, whereas the ratio of COX-1 to GAPDH was unchanged. Similar results were found when data were normalized to vWF. These results suggest that at least two endothelial vasodilator gene products are reduced in heart failure, as opposed to a selective defect in NO synthase gene expression.

Biosynthesis and palmitoylation of endothelial nitric oxide synthase: mutagenesis of palmitoylation sites, cysteines-15 and/or -26, argues against depalmitoylation-induced translocation of the enzyme

The presence of myristoylated endothelial nitric oxide synthase (eNOS) in cytosolic fractions of bovine aortic endothelial cells (BAEC) suggests that N-myristoylation of eNOS is not sufficient for membrane localization. Therefore, we examined if posttranslational palmitoylation was another molecular signal for the membrane attachment of eNOS. Metabolic labeling showed incorporation of [3H]palmitic acid into the membrane-bound, but not the cytosolic, form of eNOS. Fatty acid analysis demonstrated the labeled fatty acid incorporated into eNOS was palmitate, linked via a hydroxylamine-labile thioester bond. Biosynthesis and turnover studies show that the turnover of palmitate is much faster than the protein itself. However, the rates of palmitoylation and depalmitoylation were not affected by bradykinin or ionomycin treatment of BAEC. To examine the contribution of palmitoylation to the membrane association of eNOS, we mutated cysteine-15 and -26. Both mutations markedly diminished palmitoylation of eNOS, but did not significantly alter its membrane association. Additionally, [3H]palmitic acid was not incorporated into nonmyristoylated mutant eNOS (G2A eNOS), suggesting that myristoylation is necessary for subsequent palmitoylation of the enzyme. Taken together, our data imply that palmitoylation does not play a major role in membrane association of eNOS and other amino acid sequences, in conjunction with N-myristoylation, are necessary and sufficient for membrane association of the enzyme.

Native low-density lipoprotein increases endothelial cell nitric oxide synthase generation of superoxide anion

To examine mechanisms by which native low-density lipoprotein (n-LDL) perturbs endothelial cell (EC) release of superoxide anion (O2-) and nitric oxide (NO), ECs were incubated with n-LDL at 240 mg cholesterol per deciliter for 4 days with media changes every 24 hours. n-LDL increases EC release of O2- by more than fourfold and increases nitrite production by 57%. In the conditioned media from day-4 incubations, n-LDL increases total nitrogen oxides 20 times control EC (C-EC) levels. However, n-LDL did not alter EC NO synthase (eNOS) enzyme activity as measured by the [3H]citrulline assay. N omega-Nitro-L-arginine methyl ester, a specific inhibitor of eNOS activity, increases C-EC release of O2- by > 300% but decreases LDL-treated EC (LDL-EC) release by > 95%. L-Arginine inhibits the release of O2- from LDL-ECs by > 95% but did not effect C-EC release of O2-. Indomethacin and SKF 525A partially attenuate LDL-induced increases in O2- production by approximately 50% and 30%, respectively. Thus, n-LDL increases O2- and NO production, which increases the likelihood of the formation of peroxynitrite (ONOO-), a potent oxidant. n-LDL increases the levels of nitrotyrosine, a stable oxidation product of ONOO-, and tyrosine by approximately 50%. In spite of this increase in oxidative metabolism, analysis of thiobarbituric acid substances reveals that no significant changes in the oxidation of n-LDL occur during the 24-hour incubations with ECs.(ABSTRACT TRUNCATED AT 250 WORDS)