Identification of the tyrosine nitration sites in human endothelial nitric oxide synthase by liquid chromatography-mass spectrometry

Nitric oxide and hydrogen sulfide modulate the NADPH-generating enzymatic system in higher plants

Nitric oxide (NO) and hydrogen sulfide (H2S) are two key molecules in plant cells that participate, directly or indirectly, as regulators of protein functions through derived post-translational modifications, mainly tyrosine nitration, S-nitrosation, and persulfidation. These post-translational modifications allow the participation of both NO and H2S signal molecules in a wide range of cellular processes either physiological or under stressful circumstances. NADPH participates in cellular redox status and it is a key cofactor necessary for cell growth and development. It is involved in significant biochemical routes such as fatty acid, carotenoid and proline biosynthesis, and the shikimate pathway, as well as in cellular detoxification processes including the ascorbate-glutathione cycle, the NADPH-dependent thioredoxin reductase (NTR), or the superoxide-generating NADPH oxidase. Plant cells have diverse mechanisms to generate NADPH by a group of NADP-dependent oxidoreductases including ferredoxin-NADP reductase (FNR), NADP-glyceraldehyde-3-phosphate dehydrogenase (NADP-GAPDH), NADP-dependent malic enzyme (NADP-ME), NADP-dependent isocitrate dehydrogenase (NADP-ICDH), and both enzymes of the oxidative pentose phosphate pathway, designated as glucose-6-phosphate dehydrogenase (G6PDH) and 6-phosphogluconate dehydrogenase (6PGDH). These enzymes consist of different isozymes located in diverse subcellular compartments (chloroplasts, cytosol, mitochondria, and peroxisomes) which contribute to the NAPDH cellular pool. We provide a comprehensive overview of how post-translational modifications promoted by NO (tyrosine nitration and S-nitrosation), H2S (persulfidation), and glutathione (glutathionylation), affect the cellular redox status through regulation of the NADP-dependent dehydrogenases.

Electrophilic Signaling: The Role of Reactive Carbonyl Compounds

Reactive carbonyl compounds (RCC) are a group of compounds with clearly pronounced electrophilic properties that facilitate their spontaneous reactions with numerous nucleophilic reaction sites in proteins, lipids, and nucleic acids. The biological functions of RCC are determined by their concentration and governed by the hormesis (biphasic reaction) principle. At low concentrations, RCC act as signaling molecules activating defense systems against xenobiotics and oxidizers, and at high concentrations, they exhibit the cytotoxic effect. RCC participate in the formation of cell adaptive response via intracellular signaling pathways involving regulation of gene expression and cytoplasmic mechanisms related to the structure-functional rearrangements of proteins. Special attention in this review is given to the functioning of electrophiles as mediators of cell general adaption syndrome manifested as the biphasic response. The hypothesis is proposed that electrophilic signaling can be a proto-signaling system.

Transcriptional and Posttranslational Regulation of eNOS in the Endothelium

Nitric oxide (NO) is a highly reactive free radical gas and these unique properties have been adapted for a surprising number of biological roles. In neurons, NO functions as a neurotransmitter; in immune cells, NO contributes to host defense; and in endothelial cells, NO is a major regulator of blood vessel homeostasis. In the vasculature, NO is synthesized on demand by a specific enzyme, endothelial nitric oxide synthase (eNOS) that is uniquely expressed in the endothelial cells that form the interface between the circulating blood and the various tissues of the body. NO regulates endothelial and blood vessel function via two distinct pathways, the activation of soluble guanylate cyclase and cGMP-dependent signaling and the S-nitrosylation of proteins with reactive thiols (S-nitrosylation). The chemical properties of NO also serve to reduce oxidation and regulate mitochondrial function. Reduced synthesis and/or compromised biological activity of NO precede the development of cardiovascular disease and this has generated a high level of interest in the mechanisms controlling the synthesis and fate of NO in the endothelium. The amount of NO produced results from the expression level of eNOS, which is regulated at the transcriptional and posttranscriptional levels as well as the acute posttranslational regulation of eNOS. The goal of this chapter is to highlight and integrate past and current knowledge of the mechanisms regulating eNOS expression in the endothelium and the posttranslational mechanisms regulating eNOS activity in both health and disease.

Post-translational regulation of endothelial nitric oxide synthase in vascular endothelium

Nitric oxide (NO) is a short-lived gaseous signaling molecule. In blood vessels, it is synthesized in a dynamic fashion by endothelial nitric oxide synthase (eNOS) and influences vascular function via two distinct mechanisms, the activation of soluble guanylyl cyclase (sGC)/cyclic guanosine monophosphate (cGMP)-dependent signaling and the S-nitrosylation of proteins with reactive thiols (S-nitrosylation). The regulation of eNOS activity and NO bioavailability is critical to maintain blood vessel function. The activity of eNOS and ability to generate NO is regulated at the transcriptional, posttranscriptional, and posttranslational levels. Post-translational modifications acutely impact eNOS activity and dysregulation of these mechanisms compromise eNOS activity and foster the development of cardiovascular diseases (CVDs). This review will intergrate past and current literature on the post-translational modifications of eNOS in both health and disease.

Bosentan inhibits oxidative and nitrosative stress and rescues occlusive pulmonary hypertension

Pulmonary arterial hypertension (PH) is a fatal disease marked by excessive pulmonary vascular cell proliferation. Patients with idiopathic PH express endothelin-1 (ET-1) at high levels in their lungs. As the activation of both types of ET-1 receptor (ETA and ETB) leads to increased generation of superoxide and hydrogen peroxide, this may contribute to the severe oxidative stress found in PH patients. As a number of pathways may induce oxidative stress, the particular role of ET-1 remains unclear. The aim of this study was to determine whether inhibition of ET-1 signaling could reduce pulmonary oxidative stress and attenuate the progression of disease in rats with occlusive-angioproliferative PH induced by a single dose of SU5416 (200 mg/kg) and subsequent exposure to hypoxia for 21 days. Using this regimen, animals developed severe PH as evidenced by a progressive increase in right-ventricle (RV) peak systolic pressure (RVPSP), severe RV hypertrophy, and pulmonary endothelial and smooth muscle cell proliferation, resulting in plexiform vasculopathy. PH rats also had increased oxidative stress, correlating with endothelial nitric oxide synthase uncoupling and NADPH oxidase activation, leading to enhanced protein nitration and increases in markers of vascular remodeling. Treatment with the combined ET receptor antagonist bosentan (250 mg/kg/day; day 10 to 21) prevented further increase in RVPSP and RV hypertrophy, decreased ETA/ETB protein levels, reduced oxidative stress and protein nitration, and resulted in marked attenuation of pulmonary vascular cell proliferation. We conclude that inhibition of ET-1 signaling significantly attenuates the oxidative and nitrosative stress associated with PH and prevents its progression.

Oxidative stress and the development of endothelial dysfunction in congenital heart disease with increased pulmonary blood flow: lessons from the neonatal lamb

Congenital heart diseases associated with increased pulmonary blood flow commonly leads to the development of pulmonary hypertension. However, most patients who undergo histological evaluation have advanced pulmonary hypertension, and therefore it has been difficult to investigate aberrations in signaling cascades that precede the development of overt vascular remodeling. This review discusses the role played by both oxidative and nitrosative stress in the lung and their impact on the signaling pathways that regulate vasodilation, vessel growth, and vascular remodeling in the neonatal lung exposed to increased pulmonary blood flow.

An exclusion list based label-free proteome quantification approach using an LTQ Orbitrap

RATIONALE

Label-based mass spectrometry is a powerful tool for large-scale protein identification and quantification. However, it requires the chemical or metabolic incorporation of the labeled compound(s) which can be difficult to attain, e.g. for non-cultivable organisms or scarce sample, such as biopsies. Therefore, we set out to develop and validate an efficient label-free liquid chromatography/tandem mass spectrometry (LC/MS/MS) workflow based on optimized instrument settings and incremental exclusion lists.

METHODS

To increase the number of quantified peptides an incremental exclusion list was incorporated along with optimized instrument settings for the used LTQ Orbitrap. As a proof of concept, label-free quantification data from this optimized approach were compared to the results of control measurements without exclusion lists and of an in vivo metabolic labeling GeLC/MS/MS experiment. The data were drawn from Staphylococcus aureus whole cell lysates of non-stressed and nitric oxide (NO)-stressed cells.

RESULTS

Compared to MS analysis without exclusion lists the new approach resulted in an increased number of identified peptides, enabling label-free quantification of more than 990 S. aureus proteins. With respect to the number of quantified proteins and differences in protein levels between the control and NO-treated samples the results of the new method were consistent with those of the GeLC/MS/MS experiment.

CONCLUSIONS

The application of exclusion lists and optimized instrument settings in LC/MS/MS analysis significantly enhances the sensitivity and resolution of label-free protein identification and quantification. Therefore, the new workflow is a powerful alternative to label-based quantification methods.

GTP cyclohydrolase I expression is regulated by nitric oxide: role of cyclic AMP

Our previous studies have demonstrated that nitric oxide (NO) leads to nitric oxide synthase (NOS) uncoupling and an increase in NOS-derived superoxide. However, the cause of this uncoupling has not been adequately resolved. The pteridine cofactor tetrahydrobiopterin (BH(4)) is a critical determinant of endothelial NOS (eNOS) activity and coupling, and GTP cyclohydrolase I (GCH1) is the rate-limiting enzyme in its generation. Thus the initial purpose of this study was to determine whether decreases in BH(4) could underlie, at least in part, the NO-mediated uncoupling of eNOS we have observed both in vitro and in vivo. Initially we evaluated the effect of inhaled NO levels on GCH1 expression and BH(4) levels in the intact lamb. Contrary to our hypothesis, we found that there was a significant increase in both plasma BH4 levels and peripheral lung GCH1 protein levels. Furthermore, in vitro, we found that exposure to the NO donor spermine NONOate (SPNONO) led to an increase in GCH1 protein and BH(4) levels in both COS-7 and pulmonary arterial endothelial cells. However, SPNONO treatment also caused a significant increase in phospho-cAMP response element binding protein (CREB) levels, as detected by Western blot analysis, and significantly increased cAMP levels, as detected by enzyme immunoassay. Furthermore, utilizing GCH1 promoter fragments fused to a luciferase reporter gene, we found that GCH1 promoter activity was enhanced by SPNONO in a CREB-dependent manner, and electromobility shift assays revealed an NO-dependent increase in the nuclear binding of CREB. These data suggest that NO increases BH(4) levels through a cAMP/CREB-mediated increase in GCH1 transcription and that the eNOS uncoupling associated with exogenous NO does not involved reduced BH(4) levels.

Progressive dysfunction of nitric oxide synthase in a lamb model of chronically increased pulmonary blood flow: a role for oxidative stress

Cardiac defects associated with increased pulmonary blood flow result in pulmonary vascular dysfunction that may relate to a decrease in bioavailable nitric oxide (NO). An 8-mm graft (shunt) was placed between the aorta and pulmonary artery in 30 late gestation fetal lambs; 27 fetal lambs underwent a sham procedure. Hemodynamic responses to ACh (1 microg/kg) and inhaled NO (40 ppm) were assessed at 2, 4, and 8 wk of age. Lung tissue nitric oxide synthase (NOS) activity, endothelial NOS (eNOS), neuronal NOS (nNOS), inducible NOS (iNOS), and heat shock protein 90 (HSP90), lung tissue and plasma nitrate and nitrite (NO(x)), and lung tissue superoxide anion and nitrated eNOS levels were determined. In shunted lambs, ACh decreased pulmonary artery pressure at 2 wk (P < 0.05) but not at 4 and 8 wk. Inhaled NO decreased pulmonary artery pressure at each age (P < 0.05). In control lambs, ACh and inhaled NO decreased pulmonary artery pressure at each age (P < 0.05). Total NOS activity did not change from 2 to 8 wk in control lambs but increased in shunted lambs (ANOVA, P < 0.05). Conversely, NO(x) levels relative to NOS activity were lower in shunted lambs than controls at 4 and 8 wk (P < 0.05). eNOS protein levels were greater in shunted lambs than controls at 4 wk of age (P < 0.05). Superoxide levels increased from 2 to 8 wk in control and shunted lambs (ANOVA, P < 0.05) and were greater in shunted lambs than controls at all ages (P < 0.05). Nitrated eNOS levels were greater in shunted lambs than controls at each age (P < 0.05). We conclude that increased pulmonary blood flow results in progressive impairment of basal and agonist-induced NOS function, in part secondary to oxidative stress that decreases bioavailable NO.