Nitric oxide attenuates vascular smooth muscle cell activation by interferon-gamma. The role of constitutive NF-kappa B activity

Atherogenesis involves cellular immune responses and altered vascular smooth muscle cell (SMC) function. Cytokines such as interleukin (IL)-1 alpha and interferon-gamma (IFN-gamma) may contribute to this process by activating SMC. To determine whether the anti-atherogenic mediator, nitric oxide (.NO), can modulate cytokine-induced SMC activation, we investigated the effects of various .NO-generating compounds on the expression of intercellular and vascular cell adhesion molecules (ICAM-1 and VCAM-1). Induction of ICAM-1 expression by IL-1 alpha and VCAM-1 expression by IFN-gamma was attenuated by .NO donors but not by cGMP analogues. Nuclear run-on assays and transfection studies using various VCAM-1 promoter constructs linked to the chloramphenicol acetyl-transferase reporter gene showed that .NO repressed IFN-gamma-induced VCAM-1 gene transcription, in part, through inhibition of nuclear factor-kappa B (NF-kappa B). Electrophoretic mobility shift assay revealed that SMC possess basal constitutive NF-kappa B activity, which was augmented by treatment with IL-1 alpha. In contrast, IFN-gamma induced and activated interferon regulatory factor (IRF)-1 but had little effect on basal constitutive NF-kappa B activity. .NO donors had no inhibitory effect on IRF-1 activation but did inhibit basal and IL-1 alpha-stimulated NF-kappa B activation. These findings suggest that the induction of ICAM-1 and VCAM-1 expression requires NF-kappa B activation and that .NO attenuates IFN-gamma-induced VCAM-1 expression primarily by inhibiting basal constitutive NF-kappa B activity in SMC.

Regulation of bovine endothelial constitutive nitric oxide synthase by oxygen

Oxygen (O2) may regulate pulmonary vascular resistance through changes in endothelial nitric oxide (NO) production. To determine whether constitutive NO synthase (cNOS) is regulated by O2, we assessed cNOS expression and activity in bovine pulmonary artery endothelial cells exposed to different concentrations of O2. In a time-dependent manner, changes in O2 concentration from 95 to 3% produced a progressive decrease in cNOS mRNA and protein levels resulting in 4.8- and 4.3-fold reductions after 24h, respectively. This correlated with changes in cNOS activity as determined by nitrite measurements. Compared with 20% O2, cNOS activity was increased 1.5-fold in 95% O2 and decreased 1.9-fold in 3% O2. A decrease in O2 concentration from 94 to 3% shortened cNOS mRNA half-life from 46 to 24 h and caused a 20-fold repression of cNOS gene transcription. Treatment with cycloheximide produced a threefold increase in cNOS mRNA at all O2 concentrations, suggesting that cNOS mRNA expression is negatively regulated under basal condition. We conclude that O2 upregulates cNOS expression through transcriptional and post-transcriptional mechanisms. A decrease in cNOS activity in the presence of low O2 levels, therefore, may contribute to hypoxia-induced vasoconstriction in the pulmonary circulation.

Nitric oxide inhibits macrophage-colony stimulating factor gene transcription in vascular endothelial cells

Macrophage-colony stimulating factor (M-CSF) contributes to atherogenesis by regulating macrophage-derived foam cells in atherosclerotic lesions. Here we report that nitric oxide (NO) inhibits the expression of M-CSF in human vascular endothelial cells independent of guanylyl cyclase activation. The induction of M-CSF mRNA expression by either oxidized low density lipoprotein (ox-LDL) or tumor necrosis factor-alpha (TNF alpha) was attenuated by NO donors, S-nitrosoglutathione (GSNO), sodium nitroprusside (SNP), and 3-morpholinosydnonimine, but not by cGMP analogues, glutathione, or nitrite. Inhibition of endogenous NO production by N-monomethyl-L-arginine (L-NMA) also increased M-CSF expression in control and TNF alpha-stimulated cells. Nuclear run-on assays and transfection studies using M-CSF promoter constructs linked to chloramphenicol acetyltransferase reporter gene indicated that NO repressed M-CSF gene transcription through nuclear factor-kappa B (NF-kappa B). Electrophoretic mobility shift assays demonstrated that activation of NF-kappa B by L-NMA, ox-LDL, and TNF alpha was attenuated by GSNO and SNP, but not by glutathione or cGMP analogues. Since the induction of M-CSF expression depends upon NF-kappa B activation, the ability of NO to inhibit NF-kappa B activation and M-CSF expression may contribute to some of NO's antiatherogenic properties.

Nitric oxide decreases cytokine-induced endothelial activation. Nitric oxide selectively reduces endothelial expression of adhesion molecules and proinflammatory cytokines

To test the hypothesis that nitric oxide (NO) limits endothelial activation, we treated cytokine-stimulated human saphenous vein endothelial cells with several NO donors and assessed their effects on the inducible expression of vascular cell adhesion molecule-1 (VCAM-1). In a concentration-dependent manner, NO inhibited interleukin (IL)-1 alpha-stimulated VCAM-1 expression by 35-55% as determined by cell surface enzyme immunoassays and flow cytometry. This inhibition was paralleled by reduced monocyte adhesion to endothelial monolayers in nonstatic assays, was unaffected by cGMP analogues, and was quantitatively similar after stimulation by either IL-1 alpha, IL-1 beta, IL-4, tumor necrosis factor (TNF alpha), or bacterial lipopolysaccharide. NO also decreased the endothelial expression of other leukocyte adhesion molecules (E-selectin and to a lesser extent, intercellular adhesion molecule-1) and secretable cytokines (IL-6 and IL-8). Inhibition of endogenous NO production by L-N-monomethyl-arginine also induced the expression of VCAM-1, but did not augment cytokine-induced VCAM-1 expression. Nuclear run-on assays, transfection studies using various VCAM-1 promoter reporter gene constructs, and electrophoretic mobility shift assays indicated that NO represses VCAM-1 gene transcription, in part, by inhibiting NF-kappa B. We propose that NO's ability to limit endothelial activation and inhibit monocyte adhesion may contribute to some of its antiatherogenic and antiinflammatory properties within the vessel wall.

Induction and stabilization of I kappa B alpha by nitric oxide mediates inhibition of NF-kappa B

To determine the mechanism(s) by which the endogenous mediator nitric oxide (NO) inhibits the activation of transcription factor NF-kappa B, we stimulated human vascular endothelial cells with tumor necrosis factor-alpha in the presence of two NO donors, sodium nitroprusside and S-nitrosoglutathione. Electrophoretic mobility shift assays demonstrated that both NO donors inhibited NF-kappa B activation by tumor necrosis factor-alpha. This effect was not mediated by guanylyl cyclase activation since the cGMP analogue 8-bromo-cGMP had no similar effect. Inhibition of endogenous constitutive NO production by L-N-monomethylarginine, however, activated NF-kappa B, suggesting tonic inhibition of NF-kappa B under basal conditions. NO had little or no effects on other nuclear binding proteins such as AP-1 and GATA. Immunoprecipitation studies showed that NO stabilized the NF-kappa B inhibitor, I kappa B alpha, by preventing its degradation from NF-kappa B. NO also increased the mRNA expression of I kappa B alpha, but not NF-kappa B subunits, p65 or p50, and transfection experiments with a chloramphenicol acetyltransferase reporter gene linked to the I kappa B alpha promoter suggested transcriptional induction of I kappa B alpha by NO. We propose that the induction and stabilization of I kappa B alpha by NO are important mechanisms by which NO inhibits NF-kappa B and attenuate atherogenesis.

Regulation of G-protein alpha i2 subunit expression by oxidized low-density lipoprotein

Oxidized low-density lipoprotein (LDL) inhibits signalling pathways mediated by pertussis toxin-sensitive guanine nucleotide-binding proteins (Gi proteins). To determine whether this inhibition is due to altered G protein alpha i subunit expression, mRNA and protein levels of alpha i isoforms were assessed in bovine aortic endothelial cells treated with oxidized LDL (0-100 micrograms/ml, 0-72 h). Oxidized LDL did not affect the expression of alpha i3, but did cause time- and concentration-dependent decrease in alpha i2 mRNA and protein resulting in a 3.2- and 3.5-fold reduction, respectively, after 72 h. This decrease in alpha i2 coincided with a 86% decrease in alpha i2 GTPase activity. Nuclear run-off studies did not show any significant effect of oxidized LDL on alpha i2 or alpha i3 transcription. In the presence of actinomycin D, oxidized LDL shortened the t1/2 of alpha i2 mRNA from 16 h to 8 h which was attenuated by cycloheximide. In addition, pulse-chase labelling with [35S]methionine revealed that oxidized LDL reduced the t1/2 of alpha i2 protein from 27 to 14 h. Our results indicate that oxidized LDL can modulate receptor-Gi coupling by downregulating the expression of alpha i2, but not alpha i3. The mechanism involves both mRNA destabilization and protein degradation.

Oxidized low-density lipoprotein decreases the expression of endothelial nitric oxide synthase

The atherogenic effects of low-density lipoprotein (LDL) may be mediated, in part, by its effect(s) on endothelial-derived nitric oxide (NO). To determine whether LDL can modulate NO production by changing NO synthase expression, we treated human saphenous vein endothelial cells with increasing concentrations of native or oxidized LDL (0-100 micrograms/ml) for various durations (0-72 h). Oxidized, but not native LDL caused a time-dependent decrease in steady-state NO synthase mRNA levels. This coincided with a maximal 56% decrease in NOS activity was determined by [3H]arginine to [3H]citrulline conversion. In the presence of actinomycin D, treatment with oxidized LDL reduced the half-life of NO synthase mRNA from 36 to 10 h. This decrease in NO synthase mRNA correlated with the degree of LDL oxidation and was attenuated by pretreatment with cycloheximide. Nuclear run-off studies showed a biphasic transcriptional pattern of NO synthase gene with an initial 25% decrease during the first 6 h followed by a maximal 2.2-fold increase over baseline during the subsequent 18 h. These results indicate that oxidized LDL regulates endothelial NOS expression through a combination of early transcriptional inhibition and post-transcriptional mRNA destabilization.

Inhibition of Gi proteins by low density lipoprotein attenuates bradykinin-stimulated release of endothelial-derived nitric oxide

The mechanism(s) by which low density lipoprotein (LDL) attenuates the release of endothelial-derived nitric oxide (EDNO) is not known but may involve inhibition of membrane signal transduction. To test this hypothesis, we treated bovine aortic endothelial cells with LDL (0-500 micrograms/ml, 72 h) to determine its effect on G proteins (G(i) and Gq) which are known to couple the bradykinin receptor to EDNO release. Bradykinin-stimulated EDNO release was measured by perfusion bioassay and showed a maximal 56% decrease which was unaffected by cotreatment with pertussis toxin (PTX, 100 ng/ml, 16 h). Although radioligand binding studies and Western blotting did not detect any significant changes in the amount of bradykinin receptor, alpha i2, alpha i3, and alpha q, both agonist-stimulated GTPase activity and phosphatidylinositol 4,5-bisphosphate (PIP2) hydrolysis were reduced by LDL treatment (77 and 70%, respectively). When G(i) and Gq function in LDL-treated membranes were assessed by PTX and COOH-terminal antisera to alpha i2 (P4), alpha i3 (JL14), and alpha q (Q17), only the Q17 antisera caused a further reduction in GTPase activity and PIP2 hydrolysis while treatment with PTX alone or in combination with the P4 and JL14 antisera had no further inhibitory effect. These results suggest that LDL attenuates EDNO release by preferentially inhibiting the function of Gi.

The G proteins of the G alpha i and G alpha q family couple the bradykinin receptor to the release of endothelium-derived relaxing factor

Bradykinin stimulates diverse functions in endothelial cells including the release of endothelium-derived relaxing factor (EDRF). Little is known, however, regarding the identity of the G protein(s) involved. Here we demonstrate that G proteins of the G alpha i and G alpha q family are coupled to the bradykinin receptor (BKR) in bovine aortic endothelial cells by using specific antisera directed against the COOH-terminal region of G alpha i2 (P4), G alpha i3 (EC), and G alpha q (QL). These antisera are specific since their effects are blocked by the decapeptides from which they were derived. The degree of receptor-G protein coupling was assessed by the formation of high affinity agonist binding sites (HABS) and GTP hydrolysis. In a concentration-dependent manner, the QL antisera reduced HABS and GTPase activity by 65 and 60%, respectively, and effectively abolished them in membranes from pertussis toxin-treated cells. The combination of P4 and EC antisera produced a loss of HABS (41%) and GTPase activity (40%) comparable to the effects of pertussis toxin. These findings indicate that G alpha i and G alpha q proteins mediate the cellular responses to bradykinin in bovine aortic endothelial cells and support the observation that bradykinin-stimulated EDRF release is relatively insensitive to pertussis toxin.

The release of endothelium-derived relaxing factor via alpha 2-adrenergic receptor activation is specifically mediated by Gi alpha 2

The purpose of this study is to determine which pertussis toxin-sensitive guanine nucleotide-binding protein (Gi) mediates alpha 2-adrenergic receptor stimulation of endothelium-derived relaxing factor (EDRF) release. Bovine aortic endothelial cells were treated with pertussis toxin (0-100 ng/ml) for 16 h and stimulated with an alpha 2-adrenergic receptor agonist, UK14304, to release EDRF in a bioassay system. Pertussis toxin produced a concentration-dependent decrease in EDRF release with maximal inhibition (80%) occurring at 5 ng/ml. This correlated with a decrease in receptor-G protein coupling as measured by 87% loss of high affinity agonist binding sites and 94% decrease in agonist-stimulated GTPase activity. Immunoprecipitation of [32P]NAD-ribosylated membranes using specific Gi protein antisera demonstrated that complete ADP-ribosylation of Gi alpha 2 occurred at 5 ng/ml compared to 30 ng/ml for Gi alpha 3. When bovine aortic endothelial cell membranes were treated with carboxyl terminus-directed antisera to Gi alpha 2 (P4) and Gi alpha 3 (EC), the P4 antisera abolished 86% of the high affinity agonist binding sites and 93% decrease in agonist-stimulated GTPase activity, while the EC antisera had minimal effect (12%). These results indicate that Gi alpha 2 mediates most of the EDRF released via the alpha 2-adrenergic receptor.

Specific receptor-guanine nucleotide binding protein interaction mediates the release of endothelium-derived relaxing factor

High affinity agonist-binding (HAB) sites are formed from specific receptor interaction with guanine nucleotide-binding (Gi) proteins. To determine whether the release of endothelium-derived relaxing factor (EDRF) is regulated by specific receptor-Gi protein coupling, we treated bovine aortic endothelial cells with 100 ng/ml pertussis toxin (PTX) for 16 hours to effect receptor-Gi protein uncoupling. The degree of receptor uncoupling as measured by the loss of HAB sites for the alpha 2-adrenergic receptor and bradykinin receptor was assessed by radioligand binding studies using partially purified bovine aortic endothelial cell membranes. The release of EDRF in response to UK14304 (an alpha 2-adrenergic receptor agonist) and bradykinin stimulation was measured with a bioassay apparatus. The Gi protein isoforms were characterized by Western blotting, and complete ADP-ribosylation of these proteins was confirmed by PTX-catalyzed [32P]NAD ribosylation. PTX produced a greater inhibition of EDRF release via the alpha 2-adrenergic receptor pathway compared with the bradykinin receptor pathway (80% versus 46%, p less than 0.01). This corresponded to the loss of HAB sites from the alpha 2-adrenergic receptor and bradykinin receptor pathway (72% versus 46%, p less than 0.01) as compared with complete loss of both HAB sites in the presence of GppNHp (0.1 mM). Since loss of HAB sites from PTX-mediated receptor uncoupling parallels the inhibition of EDRF release, these data suggest that Gi proteins contribute to a greater proportion of HAB sites derived from alpha 2-adrenergic receptor rather than bradykinin receptor interaction and that the inhibition of EDRF release by PTX is mainly due to the loss of these HAB sites.(ABSTRACT TRUNCATED AT 250 WORDS)

Differential impairment of vasodilator responsiveness of peripheral resistance and conduit vessels in humans with atherosclerosis

The purpose of this study was to assess the effect of atherosclerosis on the regulation of limb blood flow. To examine this issue, the reactivity of resistance and conduit vessels was evaluated in 11 patients with peripheral atherosclerotic disease and six control subjects. Responsiveness of resistance vessels was measured by venous occlusion plethysmography. Responsiveness of conduit vessels was determined by quantitative angiography to measure the diameter of the superficial femoral artery. To distinguish endothelium-dependent vasodilation from that caused by direct smooth muscle relaxation, each participant received intra-arterial infusions of methacholine and nitroprusside, respectively. Flow-mediated dilation of the superficial femoral artery was determined during reactive hyperemia. Vasoconstrictor function was determined by the infusion of phenylephrine. Methacholine reduced calf vascular resistance in the control subjects but not in the patients with atherosclerosis (-64 +/- 11% versus 6 +/- 18%, p less than 0.01). Nitroprusside decreased calf vascular resistance comparably in each group (-51 +/- 5% versus -42 +/- 4%, p = NS). The vasoconstrictor effect of phenylephrine was similar in each group (105 +/- 30% versus 108 +/- 22%, p = NS). In the superficial femoral artery, the vasodilator responses to both methacholine (20 +/- 4% versus 1 +/- 4%, p less than 0.05) and nitroprusside (19 +/- 4% versus 5 +/- 4%, p less than 0.05) were blunted in the atherosclerotic patients as was the vasoconstrictive response to phenylephrine (-15 +/- 1% versus -1 +/- 5%, p less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)