Protein-protein interactions controlling nitric oxide synthases

Identification of Partner Proteins of the Algae Klebsormidium nitens NO Synthases: Toward a Better Understanding of NO Signaling in Eukaryotic Photosynthetic Organisms

In animals, NO is synthesized from L-arginine by three isoforms of nitric oxide synthase (NOS) enzyme. NO production and effects have also been reported in plants but the identification of its sources, especially the enzymatic ones, remains one of the critical issues in the field. NOS-like activities have been reported, although there are no homologs of mammalian NOS in the land plant genomes sequenced so far. However, several NOS homologs have been found in algal genomes and transcriptomes. A first study has characterized a functional NOS in the chlorophyte Ostreococcus tauri and the presence of NOS homologs was later confirmed in a dozen algae. These results raise the questions of the significance of the presence of NOS and their molecular diversity in algae. We hypothesize that comparisons among protein structures of the two KnNOS, together with the identification of their interacting partner proteins, might allow a better understanding of the molecular diversification and functioning of NOS in different physiological contexts and, more generally, new insights into NO signaling in photosynthetic organisms. We recently identified two NOS homologs sequences in the genome of the streptophyte Klebsormidium nitens, a model alga in the study of plant adaptation to terrestrial life. The first sequence, named KnNOS1, contains canonical NOS signatures while the second, named KnNOS2, presents a large C-ter extension including a globin domain. In order to identify putative candidates for KnNOSs partner proteins, we draw the protein-protein interaction networks of the three human NOS using the BioGRID database and hypothesized on the biological role of K. nitens orthologs. Some of these conserved partners are known to be involved in mammalian NOSs regulation and functioning. In parallel, our methodological strategy for the identification of partner proteins of KnNOS1 and KnNOS2 by in vitro pull-down assay is presented.

Bioactive Flavonoids Icaritin and Icariin Protect against Cerebral Ischemia-Reperfusion-Associated Apoptosis and Extracellular Matrix Accumulation in an Ischemic Stroke Mouse Model

Stroke, which is the second leading cause of mortality in the world, is urgently needed to explore the medical strategies for ischemic stroke treatment. Both icariin (ICA) and icaritin (ICT) are the major active flavonoids extracted from Herba epimedii that have been regarded as the neuroprotective agents in disease models. In this study, we aimed to investigate and compare the neuroprotective effects of ICA and ICT in a middle cerebral artery occlusion (MCAO) mouse model. Male ICR mice were pretreated with both ICA and ICT, which ameliorated body weight loss, neurological injury, infarct volume, and pathological change in acute ischemic stroke mice. Furthermore, administration of both ICA and ICT could also protect against neuronal cell apoptotic death, oxidative and nitrosative stress, lipid peroxidation, and extracellular matrix (ECM) accumulation in the brains. The neuroprotective effects of ICT are slightly better than that of ICA in acute cerebral ischemic stroke mice. These results suggest that pretreatment with both ICA and ICT improves the neuronal cell apoptosis and responses of oxidative/nitrosative stress and counteracts the ECM accumulation in the brains of acute cerebral ischemic stroke mice. Both ICA and ICT treatment may serve as a useful therapeutic strategy for acute ischemic stroke.

The heart is lost without the hypothalamus

Neuroanatomic and functional studies show the paraventricular (PVN) of the hypothalamus to have a central role in the autonomic control that supports cardiovascular regulation. Direct and indirect projections from the PVN preautonomic neurons to the sympathetic preganglionic neurons in the spinal cord modulate sympathetic activity. The preautonomic neurons of the PVN adjust their level of activation in response to afferent signals arising from peripheral viscerosensory receptors relayed through the nucleus tractus solitarius. The prevailing sympathetic tone is a balance between excitatory and inhibitory influences that arises from the preautonomic PVN neurons. Under physiologic conditions, tonic sympathetic inhibition driven by a nitric oxide-γ-aminobutyric acid-mediated mechanism is dominant, but in pathologic situation such as heart failure there is a switch from inhibition to sympathoexcitation driven by glutamate and angiotensin II. Angiotensin II, reactive oxygen species, and hypoxia as a result of myocardial infarction/ischemia alter the tightly regulated posttranslational protein-protein interaction of CAPON (carboxy-terminal postsynaptic density protein ligand of neuronal nitric oxide synthase (NOS1)) and PIN (protein inhibitor of NOS1) signaling mechanism. Within the preautonomic neurons of the PVN, the disruption of CAPON and PIN signaling leads to a downregulation of NOS1 expression and reduced NO bioavailability. These data support the notion that CAPON-PIN dysregulation of NO bioavailability is a major contributor to the pathogenesis of sympathoexcitation in heart failure.

Expression of CAMK1 and its association with clinicopathologic characteristics in pancreatic cancer

Calcium/calmodulin‐dependent protein kinase (CAMKs) can control a wide range of cancer‐related functions in multiple tumour types. Herein, we explore the expressions and clinical significances of calcium/calmodulin‐dependent protein kinase 1 (CAMK1) in pancreatic cancer (PC). The expression of CAMK1 in PC was analysed by Gene Expression Profiling Interactive Analysis 2 (GEPIA 2) database and the Oncomine database. For further validation, the protein level of CAMK1 in PC tissues was also detected in the Human Protein Atlas (HPA) database and the tissue microarray (TMA)‐based immunohistochemistry (IHC). GEPIA 2 and Kaplan‐Meier Plotter (KM Plotter) databases were used to explore the prognostic significances of CAMK1 in overall survival (OS) and disease‐free survival (DFS) of PC at mRNA level. The relationship between CAMK1 expression and the clinicopathological characteristics of PC was further explored. Additionally, the Search Tool for the Retrieval of Interacting Genes (STRING) database was used to analyse protein‐protein interactions (PPI). We found CAMK1 was highly expressed in PC both in bioinformatics analyses and TMA‐IHC results. The prognostic analyses from the public databases also showed consistent results with follow‐up data. The PPI network suggested that CALM1, CALM3, CREB1, CALM2, SYN1, NOS3, ATF1, GAPDH, PPM1F and FBXL12 were important significant genes associated with CAMK1. Our finding revealed CAMK1 has prognostic value in PC patients, suggesting that CAMK1 may has a distinct role in PC patients and can be used as a candidate marker for investigating clinical prognosis of PC.

Caveolin-1 suppresses tumor formation through the inhibition of the unfolded protein response

Caveolin-1 (CAV1), is a broadly expressed, membrane-associated scaffolding protein that acts both, as a tumor suppressor and a promoter of metastasis, depending on the type of cancer and stage. CAV1 is downregulated in human tumors, tumor cell lines and oncogene-transformed cells. The tumor suppressor activity of CAV1 is generally associated with its presence at the plasma membrane, where it participates, together with cavins, in the formation of caveolae and also has been suggested to interact with and inhibit a wide variety of proteins through interactions mediated by the scaffolding domain. However, a pool of CAV1 is also located at the endoplasmic reticulum (ER), modulating the secretory pathway in a manner dependent on serine-80 (S80) phosphorylation. In melanoma cells, CAV1 expression suppresses tumor formation, but the protein is largely absent from the plasma membrane and does not form caveolae. Perturbations to the function of the ER are emerging as a central driver of cancer, highlighting the activation of the unfolded protein response (UPR), a central pathway involved in stress mitigation. Here we provide evidence indicating that the expression of CAV1 represses the activation of the UPR in vitro and in solid tumors, reflected in the attenuation of PERK and IRE1α signaling. These effects correlated with increased susceptibility of cells to ER stress and hypoxia. Interestingly, the tumor suppressor activity of CAV1 was abrogated by site-directed mutagenesis of S80, correlating with a reduced ability to repress the UPR. We conclude that the tumor suppression by CAV1 involves the attenuation of the UPR, and identified S80 as essential in this context. This suggests that intracellular CAV1 regulates cancer through alternative signaling outputs.

Nitrosative Stress Is Associated with Dopaminergic Dysfunction in the HIV-1 Transgenic Rat

Advances in antiretroviral therapy have resulted in significantly decreased HIV-related mortality. HIV-associated neurocognitive disorders, however, continue to be a major problem in infected patients. The neuropathology underlying HIV-associated neurocognitive disorders has not been well characterized, and evidence suggests different contributing mechanisms. One potential mechanism is the induction of oxidative stress. Using the HIV-1 transgenic (Tg) rat model of HIV, we found increased striatal NADPH oxidase-4 and neuronal nitric oxide synthase expression in the adult (7- to 9-month-old) Tg rat compared with control rats but not in the young (1-month-old) Tg rats. This was accompanied by increased 3-nitrotyrosine (3-NT) immunostaining in the adult Tg rats, which worsened significantly in the old Tg rats (18 to 20 months old). There was, however, no concurrent induction of the antioxidant systems because there was no change in the expression of the nuclear factor-erythroid 2-related factor 2 and its downstream targets (thioredoxin and glutathione antioxidant systems). Colocalization of 3-NT staining with neurofilament proteins and evidence of decreased tyrosine hydroxylase and dopamine transporter expression in the old rats support dopaminergic involvement. We conclude that the HIV-1 Tg rat brain shows evidence of nitrosative stress without appropriate oxidation-reduction adaptation, whereas 3-NT modification of striatal neurofilament proteins likely points to the ensuing dopaminergic neuronal loss and dysfunction in the aging HIV-1 Tg rat.

Maternal Smoking Highly Affects the Function, Membrane Integrity, and Rheological Properties in Fetal Red Blood Cells

An understanding of the basic pathophysiological mechanisms of neonatal diseases necessitates detailed knowledge about the wide range of complications in the circulating fetal RBCs. Recent publications on adult red blood cells (RBCs) provide evidence that RBCs carry an active nitric oxide synthase (NOS3) enzyme and contribute to vascular functioning and integrity via their active nitric oxide synthesis. The aim of this study was to determine the effect of maternal smoking on the phenotypical appearance and functionality of fetal RBCs, based on morphological and molecular studies. We looked for possible links between vascular dysfunction and NOS3 expression and activation and its regulation by arginase (ARG1). Significant morphological and functional differences were found between fetal RBCs isolated from the arterial cord blood of neonates born to nonsmoking (RBC-NS, n = 62) and heavy-smoking (RBC-S, n = 51) mothers. Morphological variations were quantified by Advanced Cell Classifier, microscopy-based intelligent analysis software. To investigate the relevance of the newly suggested “erythrocrine” function in fetal RBCs, we measured the levels of NOS3 and its phosphorylation in parallel with the level of ARG1, as one of the major influencers of NOS3 dimerization, by fluorescence-activated cell sorting. Fetal RBCs, even the “healthy-looking” biconcave-shaped type, exhibited impaired NOS3 activation in the RBC-S population, which was paralleled with elevated ARG1 level, thus suggesting an increased redox burden. Our molecular data indicate that maternal smoking can exert marked effects on the circulating fetal RBCs, which could have a consequence on the outcome of in utero development. We hypothesize that any endothelial dysfunction altering NO production/bioavailability can be sensed by circulating fetal RBCs. Hence, we are putting forward the idea that neonatal RBC could serve as a real-time sensor for not only monitoring RBC-linked anomalies but also predicting the overall status of the vascular microenvironment.

Combined effects of cigarette smoking, alcohol drinking and eNOS Glu298Asp polymorphism on blood pressure in Chinese male hypertensive subjects

INTRODUCTION

Genetic factors and lifestyle exposures, as well as their combinations, play important roles in the development of hypertension. We examined whether cigarette smoking, alcohol drinking and the Glu298Asp polymorphism of the endothelial nitric oxide synthase (eNOS) gene generate combined effects on blood pressure (BP) in hypertensive subjects.

METHODS

A total of 342 essential hypertensive subjects were recruited from Susong community in Anhui province, China, from July 2017 to January 2018, and the plasma biochemical parameters and the genotype on Glu298Asp polymorphism were determined.

RESULTS

There were no gender differences in the distributions of alleles and genotypes in hypertensive subjects. The proportions of cigarette smoking and alcohol drinking in male hypertensive subjects were remarkably higher than those in the females (p<0.001). The systolic blood pressure (SBP) and diastolic blood pressure (DBP) levels of mutant genotypes (Glu/Asp and Asp/Asp) were significantly higher than those of wild genotype (Glu/Glu) (p=0.013 and 0.026, respectively) in male hypertensive subjects. Moreover, the SBP and DBP levels of the mutant genotype were remarkably higher than those of wild genotype in both cigarette smoking and alcohol drinking male hypertensive subjects (p=0.034 and 0.043, respectively).

CONCLUSIONS

Cigarette smoking, alcohol drinking and the Glu298Asp polymorphism of the eNOS gene generate combined effects that increase the susceptibility of the mutant genotype to BP in Chinese male hypertensive subjects.

Caveolae, caveolin-1 and lung diseases of aging

INTRODUCTION

Flask-shaped plasma membrane (PM) invaginations called caveolae and their constitutive caveolin and cavin proteins regulate cellular function via plasma membrane and intracellular signal transduction pathways. Caveolae are present in a variety of cells in the lung including airway smooth muscle (ASM) where they interact with other proteins, receptors, and ion channels and thereby have the potential to affect both normal and disease processes such as inflammation, contractility, and fibrosis. Given their involvement in cell signaling, caveolae may play important roles in mediating and modulating aging processes, and contribute to lung diseases of aging. Areas covered: This review provides a broad overview of the current state of knowledge regarding caveolae and their constituent proteins in lung diseases in the elderly and identifies potential mechanisms that can be targeted for future therapies. Expert Commentary: Caveolin-1 may play a protective role in lung disease. What is less clear is whether altered caveolin-1 with aging is a natural process, or a biomarker of disease progression in the elderly.

The ACE2/Angiotensin-(1-7)/MAS Axis of the Renin-Angiotensin System: Focus on Angiotensin-(1-7)

The renin-angiotensin system (RAS) is a key player in the control of the cardiovascular system and hydroelectrolyte balance, with an influence on organs and functions throughout the body. The classical view of this system saw it as a sequence of many enzymatic steps that culminate in the production of a single biologically active metabolite, the octapeptide angiotensin (ANG) II, by the angiotensin converting enzyme (ACE). The past two decades have revealed new functions for some of the intermediate products, beyond their roles as substrates along the classical route. They may be processed in alternative ways by enzymes such as the ACE homolog ACE2. One effect is to establish a second axis through ACE2/ANG-(1-7)/MAS, whose end point is the metabolite ANG-(1-7). ACE2 and other enzymes can form ANG-(1-7) directly or indirectly from either the decapeptide ANG I or from ANG II. In many cases, this second axis appears to counteract or modulate the effects of the classical axis. ANG-(1-7) itself acts on the receptor MAS to influence a range of mechanisms in the heart, kidney, brain, and other tissues. This review highlights the current knowledge about the roles of ANG-(1-7) in physiology and disease, with particular emphasis on the brain.

The low affinity neurotensin receptor antagonist levocabastine impairs brain nitric oxide synthesis and mitochondrial function by independent mechanisms

Neurotensin is known to inhibit neuronal Na⁺ , K⁺ -ATPase, an effect that is rescued by nitric oxide (NO) synthase inhibition. However, whether the neurotensinergic and the nitrergic systems are independent pathways, or are mechanistically linked, remains unknown. Here, we addressed this issue and found that the administration of low affinity neurotensin receptor (NTS2) antagonist, levocabastine (50 μg/kg, i.p.) inhibited NO synthase (NOS) activity by 74 and 42% after 18 h in synaptosomal and mitochondrial fractions isolated from the Wistar rat cerebral cortex, respectively; these effects disappeared 36 h after levocabastine treatment. Intriguingly, whereas neuronal NOS protein abundance decreased (by 56%) in synaptosomes membranes, it was enhanced (by 86%) in mitochondria 18 h after levocabastine administration. Levocabastine enhanced the respiratory rate of synaptosomes in the presence of oligomycin, but it failed to alter the spare respiratory capacity; furthermore, the mitochondrial respiratory chain (MRC) complexes I-IV activities were severely diminished by levocabastine administration. The inhibition of NOS and MRC complexes activities were also observed after incubation of synaptosomes and mitochondria with levocabastine (1 μM) in vitro. These data indicate that the NTS2 antagonist levocabastine regulates NOS expression and activity at the synapse, suggesting an interrelationship between the neurotensinergic and the nitrergic systems. However, the bioenergetics effects of NTS2 activity inhibition are likely to be independent from the regulation of NO synthesis.

Role of transient receptor potential vanilloid 1 in regulating erythropoietin-induced activation of endothelial nitric oxide synthase

AIMS

Erythropoietin (EPO), the key hormone involved in erythropoiesis, beneficially affects endothelial cells (ECs), but the detailed mechanisms are yet to be completely understood. In this study, we investigated the role of transient receptor potential vanilloid type 1 (TRPV1), a ligand-gated non-selective calcium (Ca²⁺ ) channel, in EPO-mediated endothelial nitric oxide synthase (eNOS) activation and angiogenesis.

METHODS AND RESULTS

In ECs, EPO time dependently increased intracellular levels of calcium; this increase was abrogated by the Ca²⁺ chelators and pharmacological inhibitors of TRPV1 in bovine aortic ECs (BAECs) and TRPV1-transfected HEK293 cells. In addition, EPO-induced nitrite oxide (NO) production, phosphorylation of eNOS, Akt and AMP-activated protein kinase (AMPK) and the formation of TRPV1-Akt-AMPK-eNOS complex as well as tube formation were diminished by the pharmacological inhibition of TRPV1 in BAECs. Moreover, EPO time dependently induced the phosphorylation of phospholipase C-γ1 (PLC-γ1). Inhibition of PLC-γ1 activity blunted the EPO-induced Ca²⁺ influx, eNOS phosphorylation, TRPV1-eNOS complex formation and NO production. The phosphorylated level of eNOS increased in the aortas of EPO-treated wild-type (WT) mice or EPO-transgenic (Tg) mice but not in those of EPO-treated TRPV1-deficient (TRPV1^-/- ) mice or EPO-Tg/TRPV1^-/- mice. Matrigel plug assay showed that EPO-induced angiogenesis was abrogated in TRPV1 antagonist capsazepine-treated WT mice and TRPV1^-/- mice.

CONCLUSION

These findings indicate the EPO-induced Ca²⁺ influx via the activation of the PLC-γ1 signalling pathway, which leads to TRPV1 activation and consequently increases the association of the TRPV1-Akt-AMPK-eNOS complex, eNOS activation, NO production and angiogenesis.

Post-translational regulation of neuronal nitric oxide synthase: implications for sympathoexcitatory states

INTRODUCTION

Nitric oxide (NO) synthesized via neuronal nitric oxide synthase (nNOS) plays a significant role in regulation/modulation of autonomic control of circulation. Various pathological states are associated with diminished nNOS expression and blunted autonomic effects of NO in the central nervous system (CNS) including heart failure, hypertension, diabetes mellitus, chronic renal failure etc. Therefore, elucidation of the molecular mechanism/s involved in dysregulation of nNOS is essential to understand the pathogenesis of increased sympathoexcitation in these diseased states. Areas covered: nNOS is a highly regulated enzyme, being regulated at transcriptional and posttranslational levels via protein-protein interactions and modifications viz. phosphorylation, ubiquitination, and sumoylation. The enzyme activity of nNOS also depends on the optimal concentration of substrate, cofactors and association with regulatory proteins. This review focuses on the posttranslational regulation of nNOS in the context of normal and diseased states within the CNS. Expert opinion: Gaining insight into the mechanism/s involved in the regulation of nNOS would provide novel strategies for manipulating nNOS directed therapeutic modalities in the future, including catalytically active dimer stabilization and protein-protein interactions with intracellular protein effectors. Ultimately, this is expected to provide tools to improve autonomic dysregulation in various diseases such as heart failure, hypertension, and diabetes.

Activation peptide of coagulation factor IX regulates endothelial permeability

Endothelial hyperpermeability is involved in several critical illnesses, and its regulatory mechanisms have been intensively investigated. It was recently reported that the activation peptide of coagulation factor IX enhances cell matrix and intercellular adhesion. The aim of this study was to investigate the role of activation peptide of coagulation factor IX in intercellular adhesion of endothelial cells and evaluate its effects on endothelial permeability. In the presence of activation peptide, cells spread with lamellipodium-like broad protrusions multidirectionally, increasing the area of adhesion to matrix by 16% within 30 minutes. In intercellular adhesion, treatment with activation peptide induced overlapping of adjacent cell edges and remodeling of intercellular adhesion sites, with colocalization of the adherens junction proteins VE-cadherin and β-catenin and a marker protein of the lateral border recycling compartment, PECAM. Activation peptide decreased gaps between cells by 66% in cultured endothelial cells and suppressed increased endothelial cell monolayer permeability induced by interleukin-1β in a dose-dependent manner. Treatment with activation peptide decreased eNOS protein expression and altered its subcellular distribution, decreasing intracellular cGMP. An analogue of cGMP suppressed the effects of activation peptide on cell spreading. In addition, the effect of activation peptide on hyperpermeability was investigated in mice injected with lipopolysaccharide. Intravenous injection of lipopolysaccharide increased lung weight by 28%, and treatment with activation peptide significantly suppressed the increase in lung weight to 5%. Our results indicate that activation peptide of factor IX regulates endothelial intercellular adhesion and thus could be used in the treatment of vascular hyperpermeability.

Research progress in NOS1AP in neurological and psychiatric diseases

Nitric Oxide Synthase 1 Adaptor Protein (NOS1AP, previously named CAPON) was firstly identified in rat brain in 1998. Structurally, NOS1AP consists of a phosphotyrosine-binding (PTB) domain at its N-terminal and a PDZ (PSD-95/discs-large/ZO-1) ligand motif at its C-terminal. The PTB domain of NOS1AP mediates the interactions with Dexras1, scribble, and synapsins. The PDZ ligand motif of NOS1AP binds to the PDZ domain of NOS1, the enzyme responsible for nitric oxide synthesis in the nervous system. NOS1AP is implicated in Dexras1 activation, neuronal nitric oxide production, Hippo pathway signaling, and dendritic development through the association with these important partners. An increasing body of evidence is pointing to the significant roles of NOS1AP in excitotoxic neuronal damage, traumatic nervous system injury, bipolar disorder, and schizophrenia. However, the study progress in NOS1AP in neurological or psychiatric diseases, has not been systematically reviewed. Here we introduce the expression, structure, and isoforms of NOS1AP, then summarize the physiological roles of NOS1AP, and discuss the relationships between NOS1AP alterations and the pathophysiology of some neurological and psychiatric disorders. The review will promote the further investigation of NOS1AP in brain disorders and the development of drugs targeting the NOS1AP PTB domain or PDZ-binding motif in the future.

Serine 1179 Phosphorylation of Endothelial Nitric Oxide Synthase Increases Superoxide Generation and Alters Cofactor Regulation

Endothelial nitric oxide synthase (eNOS) is responsible for maintaining systemic blood pressure, vascular remodeling and angiogenesis. In addition to producing NO, eNOS can also generate superoxide (O2-.) in the absence of the cofactor tetrahydrobiopterin (BH4). Previous studies have shown that bovine eNOS serine 1179 (Serine 1177/human) phosphorylation critically modulates NO synthesis. However, the effect of serine 1179 phosphorylation on eNOS superoxide generation is unknown. Here, we used the phosphomimetic form of eNOS (S1179D) to determine the effect of S1179 phosphorylation on superoxide generating activity, and its sensitivity to regulation by BH4, Ca2+, and calmodulin (CAM). S1179D eNOS exhibited significantly increased superoxide generating activity and NADPH consumption compared to wild-type eNOS (WT eNOS). The superoxide generating activities of S1179D eNOS and WT eNOS did not differ significantly in their sensitivity to regulation by either Ca2+ or CaM. The sensitivity of the superoxide generating activity of S1179D eNOS to inhibition by BH4 was significantly reduced compared to WT eNOS. In eNOS-overexpressing 293 cells, BH4 depletion with 10mM DAHP for 48 hours followed by 50ng/ml VEGF for 30 min to phosphorylate eNOS S1179 increased ROS accumulation compared to DAHP-only treated cells. Meanwhile, MTT assay indicated that overexpression of eNOS in HEK293 cells decreased cellular viability compared to control cells at BH4 depletion condition (P<0.01). VEGF-mediated Serine 1179 phosphorylation further decreased the cellular viability in eNOS-overexpressing 293 cells (P<0.01). Our data demonstrate that eNOS serine 1179 phosphorylation, in addition to enhancing NO production, also profoundly affects superoxide generation: S1179 phosphorylation increases superoxide production while decreasing sensitivity to the inhibitory effect of BH4 on this activity.

Role of phosphatase activity of soluble epoxide hydrolase in regulating simvastatin-activated endothelial nitric oxide synthase

Soluble epoxide hydrolase (sEH) has C-terminal epoxide hydrolase and N-terminal lipid phosphatase activity. Its hydrolase activity is associated with endothelial nitric oxide synthase (eNOS) dysfunction. However, little is known about the role of sEH phosphatase in regulating eNOS activity. Simvastatin, a clinical lipid-lowering drug, also has a pleiotropic effect on eNOS activation. However, whether sEH phosphatase is involved in simvastatin-activated eNOS activity remains elusive. We investigated the role of sEH phosphatase activity in simvastatin-mediated activation of eNOS in endothelial cells (ECs). Simvastain increased the phosphatase activity of sEH, which was diminished by pharmacological inhibitors of sEH phosphatase. In addition, pharmacological inhibition of sEH phosphatase or overexpressing the inactive phosphatase domain of sEH enhanced simvastatin-induced NO bioavailability, tube formation and phosphorylation of eNOS, Akt, and AMP-activated protein kinase (AMPK). In contrast, overexpressing the phosphatase domain of sEH limited the simvastatin-increased NO biosynthesis and eNOS phosphorylation at Ser1179. Simvastatin evoked epidermal growth factor receptor–c-Src–increased Tyr phosphorylation of sEH and formation of an sEH–Akt–AMPK–eNOS complex, which was abolished by the c-Src kinase inhibitor PP1 or c-Src dominant-negative mutant K298M. These findings suggest that sEH phosphatase activity negatively regulates simvastatin-activated eNOS by impeding the Akt–AMPK–eNOS signaling cascade.

The essential role of transient receptor potential vanilloid 1 in simvastatin-induced activation of endothelial nitric oxide synthase and angiogenesis

AIMS

We investigated the role of transient receptor potential vanilloid receptor type 1 (TRPV1) in simvastatin-mediated activation of endothelial nitric oxide synthase (eNOS) and angiogenesis.

METHODS

Fluo-8 NW assay was for Ca(2+) detection; Griess's assay was for NO bioavailability; Western blotting and immunoprecipitation were for protein phosphorylation and interaction; tube formation and Matrigel plug assay were for angiogenesis.

RESULTS

In endothelial cells (ECs), treatment with simvastatin time-dependently increased intracellular level of Ca(2+). Pharmacological inhibition or genetic disruption of TRPV1 abrogated simvastatin-mediated elevation of intracellular Ca(2+) in ECs or TRPV1-transfected HEK293 cells. Loss of TRPV1 function abolished simvastatin-induced NO production and phosphorylation of eNOS and calmodulin protein kinase II (CaMKII) in ECs and in aortas of mice. Inhibition of TRPV1 activation prevented the simvastatin-elicited increase in the formation of TRPV1-Akt-CaMKII-AMPK-eNOS complex. In mice, Matrigel plug assay showed that simvastatin-evoked angiogenesis was abolished by TRPV1 antagonist and genetic ablation of TRPV1. Additionally, our results demonstrated that TRP ankyrin 1 (TRPA1) is the downstream effector in the simvastatin-activated TRPV1-Ca(2+) signalling and in the consequent NO production and angiogenesis as evidence by that re-expression of TRPA1 further augmented simvastatin-elicited Ca(2+) influx in TRPV1-expressed HEK293 cells and ablation of TRPA1 function profoundly inhibited the simvastatin-induced increase in the phosphorylation of eNOS and CaMKII, formation of TRPV1-Akt-CaMKII-AMPK-eNOS complex, NO bioavailability, tube formation and angiogenesis in ECs or mice.

CONCLUSION

Simvastatin-induced Ca(2+) influx may through the activation of TRPV1-TRPA1 signalling, which leads to phosphorylation of CaMKII, increases in the formation of TRPV1-CaMKII-AMPK-eNOS complex, eNOS activation, NO production and, ultimately, angiogenesis in ECs.

Effect of novobiocin on the viability of human gingival fibroblasts (HGF-1)

Background

Novobiocin is a coumarin antibiotic, which affects also eukaryotic cells inhibiting activity of Heat shock protein 90 (Hsp90). The Hsp90 represents a molecular chaperone critical for stabilization and activation of many proteins, particularly oncoproteins that drive cancer progression. Currently, Hsp90 inhibitors focus a significant attention since they form a potentially new class of drugs in therapy of cancer. However, in the process of tumorigenesis a significant role is played also by the microenvironment of the tumour, and, in particular, by cancer-associated fibroblasts (CAFs). This study aimed at examination of the effect played by novobiocin on viability of human gingival fibroblasts (HGF-1).

Methods

The studies were conducted using 24 h cultures of human gingival fibroblasts – HGF-1 (CRL-2014) in Chamber Slides, in presence of 0.1, 0.5, 1.0, 2.5 or 5.0 mM novobiocin. Cell viability was evaluated using fluorescence test, ATP assay and LDH release.

Results

Viability of HGF-1 was drastically reduced after 5 hour treatment with novobiocin in concentrations of 1 mM or higher. In turn, the percentage of LDH-releasing cells after 5 h did not differ from control value although it significantly increased after 10 h incubation with 1 mM and continued to increase till the 20th hour.

Conclusions

The obtained data indicate that novobiocin may induce death of human gingival fibroblasts. Therefore, application of the Hsp90 inhibitor in neoplastic therapy seems controversial: on one hand novobiocin reduces tumour-associated CAFs but, on the other, it may induce a significant destruction of periodontium.

Administration of telmisartan reduced systolic blood pressure and oxidative stress probably through the activation of PI3K/Akt/eNOS pathway and NO release in spontaneously hypertensive rats

We investigated the effects of telmisartan, the blocker of angiotensin II receptor 1, on the regulation of systolic blood pressure (SBP) and oxidative stress through endothelial nitric oxide (NO) release in spontaneously hypertensive rats (SHRs). SHRs randomly received placebo, oral feeding of telmisartan (5 mg/kg or 10 mg/kg) every day and Wistar-Kyoto rats (WKYs) served as normotensive control. The SBP of rat was measured before and weekly thereafter. After a total of 8-week treatment, rats were killed for experimental measurements. Parameters that subject to measurements in isolated aorta endothelial cells include: NO concentration, protein expression levels of angiotensin II receptor 1, nitrotyrosine, 8-isoprostane, SOD, PI3K, Akt, AMPK and eNOS. In addition, L-NMMA, a general inhibitor of nitric oxide synthase, was also applied to test the inhibition of NO concentration. We found that SBPs were significantly lower in telmisartan therapy group than in placebo treated hypertensive rats and WKYs (p<0.05). The NO concentration was significantly higher in telmisartan-treated group with increased activity of the PI3K/Akt pathway and activated eNOS signaling. Blockade of Akt activity reversed such effects. Activation of AMPK also contributed to the phosphorylation of eNOS. L-NMMA treatment reduced less NO concentration in SHR rats than the telmisartan co-treated groups. Oxidative stress in SHRs was also attenuated by telmisartan administration, shown by reduced formation of nitrotyrosine, 8-isoprostane, and recovered SOD protein level. Telmisartan enhanced NO release by activating the PI3K/Akt system, AMPK phosphorylation and eNOS expression, which attenuated the blood pressure and oxidative stress in SHRs.

Is there a role for neuronal nitric oxide synthase (nNOS) in cytokine toxicity to pancreatic beta cells?

Nitric oxide (NO), produced by the action of the inducible NO synthase, plays a crucial role in cytokine toxicity to pancreatic beta cells during type 1 diabetes development. It was the aim of this study to analyze the role of the neuronal NOS (nNOS) in proinflammatory cytokine-mediated beta cell toxicity. Expression of different isoforms of nitric oxide synthase in insulin-secreting INS1E cells and rat islets was analyzed by quantitative real-time PCR and Western blotting. The expression of nNOS in insulin-secreting INS1E cells was similar to that found in rat brain, while two other isoforms, namely the endothelial eNOS and inducible iNOS were not expressed in untreated cells. IL-1β alone or in combination with TNF-α and/or IFNγ induced iNOS but not eNOS expression. In contrast, nNOS expression was strongly decreased by the mixture of the three proinflammatory cytokines (IL-1β, TNF-α and IFNγ) both on the gene and protein level in INS1E cells and rat islet cells. The effects of cytokines on glucose-induced insulin-secretion followed the pattern of nNOS expression reduction and, on the other hand, of the iNOS induction. The data indicate that a low level of nitric oxide originating from the constitutive expression of nNOS in pancreatic beta cells is not deleterious. In particular since proinflammatory cytokines reduce this expression. This nNOS suppression can compensate for NO generation by low concentrations of IL-1β through iNOS induction. Thus, this basal nNOS expression level in pancreatic beta cells represents a protective element against cytokine toxicity.

Effects of stress on endocrine and metabolic processes and redirection: cross talk between subcellular compartments

Recent advances in genome analysis and biochemical pathway mapping have advanced our understanding of how biological systems have evolved over time. Protein and DNA marker comparisons suggest that several of these systems are both ancient in origin but highly conserved into today's evolved species. However, remnants of some of the more ancient functions of these chemical systems can run in conflict with the functions that those same pathways serve in complex organisms and tissue systems today. Relevant to the present topic, nitric oxide (NO) and superoxide anion (O(2)(•-)), ancient cellular molecules in evolutionary terms, are recognized today as both necessary for the well-being and stable health of cells but also injurious to cells as elaborated in conjunction with the cellular stress response. Why the dichotomy? This question underlies one of the basic issues challenging researchers as well as practitioners in their approach to disease management. The fundamental proinflammatory response of the innate immune system of the host is needed for pathogen control but can be injurious to tissues from "collateral damage" from NO- and O(2)(•-)-derived reactive molecules capable of affecting protein function via post-translational chemical modification. This review highlights newer aspects of the biochemistry of the NO- and O(2)(•-)-mediated innate proinflammatory response and further show how protein and tissue damage via overproduction of reactive nitrogen and oxygen intermediary molecules such as peroxynitrite (ONOO(-)) might be targeted to specific epitopes of proteins. Changes in the regulation of metabolism in response to proinflammatory disease states are discussed for GH signal transduction and tissue specificity.

Hsp90β inhibition modulates nitric oxide production and nitric oxide-induced apoptosis in human chondrocytes

Background

Hsp90β is a member of the Hsp90 family of protein chaperones. This family plays essential roles in the folding, maturation and activity of many proteins that are involved in signal transduction and transcriptional regulation. The role of this protein in chondrocytes is not well understood, although its increase in osteoarthritic cells has been reported. The present study aimed to explore the role of Hsp90β in key aspects of OA pathogenesis.

Methods

Human OA chondrocytes were isolated from cartilage obtained from patients undergoing joint replacement surgery, and primary cultured. Cells were stimulated with proinflammatory cytokines (IL-1β or TNF-α) and nitric oxide donors (NOC-12 or SNP). For Hsp90β inhibition, two different chemical inhibitors (Geldanamycin and Novobiocin) were employed, or siRNA transfection procedures were carried out. Gene expression was determined by real-time PCR, apoptosis was quantified by flow cytometry and ELISA, and nitric oxide (NO) production was evaluated by the Griess method. Indirect immunofluorescence assays were performed to evaluate the presence of Hsp90β in stimulated cells.

Results

Hsp90β was found to be increased by proinflammatory cytokines. Inhibition of Hsp90β by the chemicals Geldanamycin (GA) and Novobiocin (NB) caused a dose-dependent decrease of the NO production induced by IL-1β in chondrocytes, up to basal levels. Immunofluorescence analyses demonstrate that the NO donors NOC-12 and SNP also increased Hsp90β. Chemical inhibition or specific gene silencing of this chaperone reduced the DNA condensation and fragmentation, typical of death by apoptosis, that is induced by NO donors in chondrocytes.

Conclusions

The present results show how Hsp90β modulates NO production and NO-mediated cellular death in human OA chondrocytes.

Estrogen increases nitric-oxide production in human bronchial epithelium

Although sex differences in asthma severity are recognized, the mechanisms by which sex steroids such as estrogen influence the airway are still under investigation. Airway tone, a key aspect of asthma, represents a balance between bronchoconstriction and dilation. Nitric oxide (NO) from the bronchial epithelium is an endogenous bronchodilator. We hypothesized that estrogens facilitate bronchodilation by generating NO in bronchial epithelium. In acutely dissociated human bronchial epithelial cells from female patients exposure to 17β-estradiol (E(2); 10 pM-100 nM) resulted in rapid increase of diaminofluorescein fluorescence (NO indicator) within minutes, comparable with that induced by ATP (20 μM). Estrogen receptor (ER) isoform-specific agonists (R,R)-5,11-diethyl-5,6,11,12-tetrahydro-2,8-chrysenediol (THC) (ERα) and diaryl-propionitrile (DPN) (ERβ) stimulated NO production to comparable levels and at comparable rates, whereas the ER antagonist 7α,17β-[9-[(4,4,5,5,5-pentafluoropentyl)sulfinyl]nonyl]estra-1,3,5(10)-triene-3,17-diol (ICI 182,780) (1 μM) was inhibitory. Estrogen effects on NO were mediated via caveolin-1 (blocked using the caveolin-1 scaffolding domain peptide) and by increased intracellular calcium concentration [prevented by 20 μM 1,2-bis(o-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid tetra(acetoxymethyl) ester but not by blocking Ca(2+) influx using LaCl(3)]. Estrogen increased endothelial NO synthase activation (inhibited by 100 μM N(G)-nitro-l-arginine methyl ester) and phosphorylated Akt. In epithelium-intact human bronchial rings contracted with acetylcholine (1 μM), E(2), THC, and DPN all produced acute bronchodilation in a dose-dependent fashion. Such bronchodilatory effects were substantially reduced by epithelial denudation. Overall, these data indicate that estrogens, acting via ERα or ERβ, can acutely produce NO in airway epithelium (akin to vascular endothelium). Estrogen-induced NO and its impairment may contribute to altered bronchodilation in women with asthma.

Antioxidants to enhance fertility: role of eNOS and potential benefits

The use of antioxidants is now often used as a pharmacological adjunct to limit infertility. Indeed, the lay public rightly perceives oxidative stress and, thus, antioxidant treatment as important modulators of infertility. While the direct effects of antioxidant treatment on the quality of semen and oocytes are still under investigation, a significant body of evidence points to loss of vascular tone as a root-cause of erectile dysfunction and, possibly, alterations to female reproduction. In this article, we will critically review the often neglected link between vascular dysfunction and infertility. A particular emphasis will be on the potential use of antioxidants to increase fertility and promote conception.

Radix Astragali extract promotes angiogenesis involving vascular endothelial growth factor receptor-related phosphatidylinositol 3-kinase/Akt-dependent pathway in human endothelial cells

Angiogenesis plays an important role in a wide range of physiological processes and many diseases are associated with dysregulation of angiogenesis. Radix Astragali, commonly used in traditional Chinese medicine, is a potential candidate for treating such diseases. However, the biological effects of Radix Astragali on angiogenesis and its underlying mechanisms are yet to be elucidated fully. This study describes the angiogenic effects of Radix Astragali extract (RAE) on human umbilical vein endothelial cells (HUVEC) in vitro. It was shown that RAE treatment stimulated HUVEC to proliferate. A significant increase in migration was observed in RAE-treated HUVEC using the wound healing migration assay. In addition, a significant increase in the number of branching points was observed during endothelial cell capillary formation after RAE treatment. It was shown that RAE enhances vascular endothelial growth factor (VEGF) mRNA expression, and that a specific blocker of VEGF receptor 2 (KDR/Flk) inhibited the RAE-induced HUVEC proliferation. In addition, a decrease in the RAE-induced HUVEC proliferation was observed after treatment with inhibitors of phosphatidylinositol 3-kinase (PI3K), Akt and endothelial nitric oxide synthase (eNOS). Taken together, these data suggest that RAE is a potent stimulator of angiogenesis and that its pro-angiogenic effects involve the VEGF-KDR/Flk and PI3K-Akt-eNOS pathways.

Telmisartan inhibits vasoconstriction via PPARγ-dependent expression and activation of endothelial nitric oxide synthase

AIMS

Telmisartan activates peroxisome proliferator-activated receptor-γ (PPARγ) in addition to serving as an angiotensin II type 1 receptor (AT(1)R) blocker. The PPARγ activity of telmisartan on resistance arteries has remained largely unknown. The present study investigated the hypothesis that telmisartan inhibited vascular tension in mouse mesenteric resistance arteries, which was attributed to an increased nitric oxide (NO) production through the PPARγ-dependent augmentation of expression and activity of endothelial nitric oxide synthase (eNOS).

METHODS AND RESULTS

Second-order mesenteric arteries were isolated from male C57BL/6J, eNOS knockout and PPARγ knockout mice and changes in vascular tension were determined by isometric force measurement with a myograph. Expression and activation of relevant proteins were analysed by Western blotting. Real-time NO production was measured by confocal microscopy using the dye DAF. Telmisartan inhibited 9,11-dideoxy-11α,9α-epoxymethanoprostaglandin F(2α) (U46619)- or endothelin-1-induced contractions. An NOS inhibitor, N(G)-nitro-L-arginine methyl ester (l-NAME), or an inhibitor of soluble guanylate cyclase, 1H-[1,2,4]-oxadizolo[4,3-a]quinoxalin-1-one (ODQ), prevented telmisartan-induced inhibition of U46619 contractions. A PPARγ antagonist, GW9662, abolished telmisartan-induced inhibition. Likewise, the PPARγ antagonist rosiglitazone attenuated U46619-induced contractions. The effects of telmisartan and rosiglitazone were prevented by actinomycin-D, a transcription inhibitor. In contrast, losartan, olmesartan, and irbesartan did not inhibit contractions. The inhibition was absent in mesenteric arteries from eNOS knockout or PPARγ knockout mice. Telmisartan augmented eNOS expression, phosphorylation, and NO production, which were reversed by the co-treatment with GW9662.

CONCLUSIONS

The present results suggest that telmisartan-induced inhibition of vasoconstriction in resistance arteries is mediated through a PPARγ-dependent increase in eNOS expression and activity that is unrelated to AT₁R blockade.

Looking at the blood-brain barrier: molecular anatomy and possible investigation approaches

The blood-brain barrier (BBB) is a dynamic and complex interface between blood and the central nervous system that strictly controls the exchanges between the blood and brain compartments, therefore playing a key role in brain homeostasis and providing protection against many toxic compounds and pathogens. In this review, the unique properties of brain microvascular endothelial cells and intercellular junctions are examined. The specific interactions between endothelial cells and basement membrane as well as neighboring perivascular pericytes, glial cells and neurons, which altogether constitute the neurovascular unit and play an essential role in both health and function of the central nervous system, are also explored. Some relevant pathways across the endothelium, as well as mechanisms involved in the regulation of BBB permeability, and the emerging role of the BBB as a signaling interface are addressed as well. Furthermore, we summarize some of the experimental approaches that can be used to monitor BBB properties and function in a variety of conditions and have allowed recent advances in BBB knowledge. Elucidation of the molecular anatomy and dynamics of the BBB is an essential step for the development of new strategies directed to maintain or restore BBB integrity and barrier function and ultimately preserve the delicate interstitial brain environment.

Nitric oxide regulation of autonomic function in heart failure

Nitric oxide (NO) functions at all levels of the autonomic nervous system to influence sympathetic and parasympathetic control of cardiovascular function. It modulates the excitability of peripheral sensory and motor neurons of cardiovascular reflexes and the central neurons that integrate their function. Its effects within this system are diverse and site specific and are (at many levels) not well defined. However, most evidence suggests that the neuromodulator's influence acts to restrain sympathetic outflow and facilitate parasympathetic outflow. In chronic heart failure, these functional effects of NO are impaired or downregulated and contribute to the state of sympathetic overactivation and parasympathetic deactivation characterized by the disease. The cellular and molecular mechanisms regulating NO production and signaling in the autonomic nervous system in the normal and chronic heart failure state are summarized and discussed in light of their therapeutic implications. This review also emphasizes questions of regulation of NO function in the autonomic nervous system that remain unresolved.

Neutralizing a surface charge on the FMN subdomain increases the activity of neuronal nitric-oxide synthase by enhancing the oxygen reactivity of the enzyme heme-nitric oxide complex

Nitric-oxide synthases (NOSs) are calmodulin-dependent flavoheme enzymes that oxidize l-Arg to nitric oxide (NO) and l-citrulline. Their catalytic behaviors are complex and are determined by their rates of heme reduction (k(r)), ferric heme-NO dissociation (k(d)), and ferrous heme-NO oxidation (k(ox)). We found that point mutation (E762N) of a conserved residue on the enzyme's FMN subdomain caused the NO synthesis activity to double compared with wild type nNOS. However, in the absence of l-Arg, NADPH oxidation rates suggested that electron flux through the heme was slower in E762N nNOS, and this correlated with the mutant having a 60% slower k(r). During NO synthesis, little heme-NO complex accumulated in the mutant, compared with approximately 50-70% of the wild-type nNOS accumulating as this complex. This suggested that the E762N nNOS is hyperactive because it minimizes buildup of an inactive ferrous heme-NO complex during NO synthesis. Indeed, we found that k(ox) was 2 times faster in the E762N mutant than in wild-type nNOS. The mutational effect on k(ox) was independent of calmodulin. Computer simulation and experimental measures both indicated that the slower k(r) and faster k(ox) of E762N nNOS combine to lower its apparent K(m,O(2)) for NO synthesis by at least 5-fold, which in turn increases its V/K(m) value and enables it to be hyperactive in steady-state NO synthesis. Our work underscores how sensitive nNOS activity is to changes in the k(ox) and reveals a novel means for the FMN module or protein-protein interactions to alter nNOS activity.

Assessing reliability of protein-protein interactions by integrative analysis of data in model organisms

Background

Protein-protein interactions play vital roles in nearly all cellular processes and are involved in the construction of biological pathways such as metabolic and signal transduction pathways. Although large-scale experiments have enabled the discovery of thousands of previously unknown linkages among proteins in many organisms, the high-throughput interaction data is often associated with high error rates. Since protein interaction networks have been utilized in numerous biological inferences, the inclusive experimental errors inevitably affect the quality of such prediction. Thus, it is essential to assess the quality of the protein interaction data.

Results

In this paper, a novel Bayesian network-based integrative framework is proposed to assess the reliability of protein-protein interactions. We develop a cross-species in silico model that assigns likelihood scores to individual protein pairs based on the information entirely extracted from model organisms. Our proposed approach integrates multiple microarray datasets and novel features derived from gene ontology. Furthermore, the confidence scores for cross-species protein mappings are explicitly incorporated into our model. Applying our model to predict protein interactions in the human genome, we are able to achieve 80% in sensitivity and 70% in specificity. Finally, we assess the overall quality of the experimentally determined yeast protein-protein interaction dataset. We observe that the more high-throughput experiments confirming an interaction, the higher the likelihood score, which confirms the effectiveness of our approach.

Conclusion

This study demonstrates that model organisms certainly provide important information for protein-protein interaction inference and assessment. The proposed method is able to assess not only the overall quality of an interaction dataset, but also the quality of individual protein-protein interactions. We expect the method to continually improve as more high quality interaction data from more model organisms becomes available and is readily scalable to a genome-wide application.

Valsartan regulates the interaction of angiotensin II type 1 receptor and endothelial nitric oxide synthase via Src/PI3K/Akt signalling

AIMS

Valsartan, a selective angiotensin II type 1 receptor (AT1R) blocker, has beneficial effects in the cardiovascular system in part by its increase of nitric oxide (NO) bioavailability, yet the mechanisms are unclear. We investigated the molecular mechanisms underlying this effect in endothelial cells (ECs).

METHODS AND RESULTS

NO production was examined by Griess reagent assay, DAF-2 DA fluorescence staining and cGMP ELISA kits. Protein interaction was determined by western blotting and immunoprecipitation. Treating bovine or human aortic ECs with valsartan increased NO production, as evidenced by elevated level of stable NO metabolites and intracellular cGMP. Valsartan increased the phosphorylation but not the protein level of endothelial NO synthase (eNOS). Inhibition of phosphoinositide-3 kinase (PI3K)/Akt and Src pathways by specific inhibitors suppressed valsartan-induced NO release. In addition, valsartan increased the tyrosine residue phosphorylation of AT1R, which was attenuated by inhibition of Src but not PI3K activities. Valsartan also suppressed the interaction of eNOS and AT1R, which was blocked by Src or PI3K inhibition.

CONCLUSION

Valsartan-induced NO production in ECs is mediated through Src/PI3K/Akt-dependent phosphorylation of eNOS. Valsartan-induced AT1R phosphorylation depends on Src but not PI3K, whereas valsartan-induced suppression of AT1R-eNOS interaction depends on Src/PI3K/Akt signalling. These results indicate a novel vasoprotective mechanism of valsartan in upregulating NO production in ECs.

Dystrophins carrying spectrin-like repeats 16 and 17 anchor nNOS to the sarcolemma and enhance exercise performance in a mouse model of muscular dystrophy

Sarcolemma-associated neuronal NOS (nNOS) plays a critical role in normal muscle physiology. In Duchenne muscular dystrophy (DMD), the loss of sarcolemmal nNOS leads to functional ischemia and muscle damage; however, the mechanism of nNOS subcellular localization remains incompletely understood. According to the prevailing model, nNOS is recruited to the sarcolemma by syntrophin, and in DMD this localization is altered. Intriguingly, the presence of syntrophin on the membrane does not always restore sarcolemmal nNOS. Thus, we wished to determine whether dystrophin functions in subcellular localization of nNOS and which regions may be necessary. Using in vivo transfection of dystrophin deletion constructs, we show that sarcolemmal targeting of nNOS was dependent on the spectrin-like repeats 16 and 17 (R16/17) within the rod domain. Treatment of mdx mice (a DMD model) with R16/17-containing synthetic dystrophin genes effectively ameliorated histological muscle pathology and improved muscle strength as well as exercise performance. Furthermore, sarcolemma-targeted nNOS attenuated alpha-adrenergic vasoconstriction in contracting muscle and improved muscle perfusion during exercise as measured by Doppler and microsphere circulation. In summary, we have identified the dystrophin spectrin-like repeats 16 and 17 as a novel scaffold for nNOS sarcolemmal targeting. These data suggest that muscular dystrophy gene therapies based on R16/17-containing dystrophins may yield better clinical outcomes than the current therapies.

Differential effects of nitric oxide synthesis on pulmonary vascular function during lung ischemia-reperfusion injury

Lung ischemia-reperfusion (IR) injury causes alveolar, epithelial and endothelial cell dysfunction which often results in decreased alveolar perfusion, characteristic of an acute respiratory distress syndrome. Nitric oxide (NO) from endothelium-derived NO synthase (eNOS) helps maintain a low pulmonary vascular resistance. Paradoxically, during acute lung injury, overproduction of NO via inducible NO synthase (iNOS) and oxidative stress lead to reactive oxygen and nitrogen species (ROS and RNS) formation and vascular dysfunction. RNS potentiate vascular and cellular injury by oxidation, by decreasing NO bioavailability, and by regulating NOS isoforms. RNS potentiate their own production by uncoupling NO production through eNOS by oxidation and disruption of Akt-mediated phosphorylation of eNOS. This review focuses on effects of NO which cause vascular dysfunction in the unique environment of the lung and presents a hypothesis for interplay between eNOS and iNOS activation with implications for development of new strategies to treat vascular dysfunction associated with IR.

Modulation of PKCdelta signaling alters the shear stress-mediated increases in endothelial nitric oxide synthase transcription: role of STAT3

We have previously shown that the regulation of endothelial nitric oxide synthase (eNOS) in endothelial cells isolated from fetal lamb under static conditions is positively regulated by PKCdelta. In this study, we explore the role of PKCdelta in regulating shear-induced upregulation of eNOS. We found that shear caused a decrease in PKCdelta activation. Modulation of PKCdelta before shear with a dominant negative mutant of PKCdelta (DN PKCdelta) or bryostatin (a known PKCdelta activator) demonstrated that PKCdelta inhibition potentiates the shear-mediated increases in eNOS expression and activity, while PKCdelta activation inhibited these events. To gain insight into the mechanism by which PKCdelta inhibits shear-induced eNOS expression, we examined activation of STAT3, a known target for PKCdelta phosphorylation. We found that shear decreased the phosphorylation of STAT3. Further the transfection of cells with DN PKCdelta reduced, while PKCdelta activation enhanced, STAT3 phosphorylation in the presence of shear. Transfection of cells with a dominant negative mutant of STAT3 enhanced eNOS promoter activity and nitric oxide production in response to shear. Finally, we found that mutating the STAT3 binding site sequence within the eNOS promoter increased promoter activity in response to shear and that this was no longer inhibited by bryostatin. In conclusion, shear decreases PKCdelta activity and, subsequently, reduces STAT3 binding to the eNOS promoter. This signaling pathway plays a previously unidentified role in the regulation of eNOS expression by shear stress.

Endothelial nitric oxide (NO) and its pathophysiologic regulation

Nitric oxide (NO) is a gaseous lipophilic free radical generated by three distinct isoforms of nitric oxide synthases (NOS), type 1 or neuronal (nNOS), type 2 or inducible (iNOS) and type 3 or endothelial NOS (eNOS). Expression of eNOS is altered in many types of cardiovascular disease, such as atherosclerosis, diabetes and hypertension. The ubiquitous chaperone heat shock protein 90 (hsp90) associates with NOS and is important for its proper folding and function. Current studies point toward a therapeutic potential by modulating hsp90-NOS association in various vascular diseases. Here we review the transcriptional regulation of endothelial NOS and factors affecting eNOS activity and function, as well as the important vascular pathologies associated with altered NOS function, focusing on the regulatory role of hsp90 and other factors in NO-associated pathogenesis of these diseases.

In vivo degradation of nitric oxide synthase (NOS) and heat shock protein 90 (HSP90) by calpain is modulated by the formation of a NOS-HSP90 heterocomplex

We have shown previously that isolated heat shock protein 90 (HSP90) and nitric oxide synthase (NOS), once associated in a heterocomplex, become completely resistant to calpain digestion. In this study, it is shown that, in vivo, under conditions of calpain activation, the protection of NOS degradation occurs. In addition, the extent of NOS degradation is a function of the level of HSP90 expression. Thus, in rat brain, which contains a large excess of HSP90, almost all neuronal NOS is associated with the chaperone protein. In this condition, neuronal NOS retains its full catalytic activity, although limited proteolytic conversion to still active low-molecular-mass (130 kDa) products takes place. In contrast, in aorta, which contains much smaller amounts of HSP90, endothelial NOS is not completely associated with the chaperone, and undergoes extensive degradation with a loss of protein and catalytic activity. On the basis of these findings, we propose a novel role of the HSP90-NOS heterocomplex in protecting in vivo NOS from proteolytic degradation by calpain. The efficiency of this effect is directly related to the level of intracellular HSP90 expression, generating a high HSP90 to NOS ratio, which favours both the formation and stabilization of the HSP90-NOS heterocomplex. This condition seems to occur in rat brain, but not in aorta, thus explaining the higher vulnerability to proteolytic degradation of endothelial NOS relative to neuronal NOS.

Racial differences in nitric oxide-dependent vasorelaxation

Along with the growing heterogeneity of the American population, ethnic/racial disparity is becoming a clear health issue in the United States. The awareness of ethnic/racial disparities has been growing because of considerable data gathered from recent clinical and epidemiological studies. These studies have highlighted the importance of addressing these differences in the diagnosis and treatment of various diseases potentially according to race. It is becoming particularly clear that there is a 2- to 3-fold racial difference in certain cardiovascular diseases (eg, preeclampsia) associated with dysfunctional nitric oxide-mediated vasodilation. In this review, the authors summarize the current literature on racial disparities in nitric oxide-mediated vasodilation in relation to cardiovascular health with an emphasis on vascular nitric oxide bioavailability as a balance between production via endothelial nitric oxide synthase and degradation through reactive oxygen species. The major hypotheses postulated on the biological basis of these differences are also highlighted.

Proteolytic degradation of nitric oxide synthase isoforms by calpain is modulated by the expression levels of HSP90

Ca2+ loading of Jurkat and bovine aorta endothelium cells induces the degradation of the neuronal and endothelial nitric oxide synthases that are selectively expressed in these cell lines. For neuronal nitric oxide synthase, this process involves a conservative limited proteolysis without appreciable loss of catalytic activity. By contrast, endothelial nitic oxide synthase digestion proceeds through a parallel loss of protein and catalytic activity. The chaperone heat shock protein 90 (HSP90) is present in a large amount in Jurkat cells and at significantly lower levels in bovine aorta endothelium cells. The differing ratios of HSP90/nitric oxide synthase (NOS) occurring in the two cell types are responsible for the conservative or nonconservative digestion of NOS isozymes. Consistently, we demonstrate that, in the absence of Ca2+, HSP90 forms binary complexes with NOS isozymes or with calpain. When Ca2+ is present, a ternary complex containing the three proteins is produced. In this associated state, HSP90 and NOS forms are almost completely resistant to calpain digestion, probably due to a structural hindrance and a reduction in the catalytic efficiency of the protease. Thus, the recruitment of calpain in the HSP90-NOS complexes reduces the extent of the proteolysis of these two proteins. We have also observed that calpastatin competes with HSP90 for the binding of calpain in reconstructed systems. Digestion of the proteins present in the complexes can occur only when free active calpain is present in the system. This process can be visualized as a novel mechanism involving the association of NOS with HSP90 and the concomitant recruitment of active calpain in ternary complexes in which the proteolysis of both NOS isozymes and HSP90 is significantly reduced.

Pulmonary Artery Hypertension

Pulmonary artery hypertension (PAH) is a sequela of a number of disparate diseases, often with a fatal consequence. Endothelial dysfunction is considered to be an early event during the development of PAH. Impaired availability of bioactive nitric oxide (NO) is a key underlying feature in most forms of clinical and experimental PAH. NO, generated by catalytic activity of endothelial NO synthase (eNOS) on l-arginine, modulates vascular function and structure. For optimal activation, eNOS is targeted to caveolae, the flask-shaped invaginations found on the surface of plasmalemmal membrane of a variety of cells, including endothelial cells. Caveolin-1, the major coat protein of caveolae, regulates eNOS activity. Evidence is accumulating to suggest that caveolin-1 may play a significant role in the pathogenesis of PAH. This review is intended to summarize recent findings indicating a role for caveolin-1 and caveolin-1/eNOS interrelationship in PAH.

Neuronal Nitric Oxide Synthase Signaling in the Heart Is Regulated by the Sarcolemmal Calcium Pump 4b

Background— Neuronal nitric oxide synthase (nNOS) has recently been shown to be a major regulator of cardiac contractility. In a cellular system, we have previously shown that nNOS is regulated by the isoform 4b of plasma membrane calcium/calmodulin-dependent ATPase (PMCA4b) through direct interaction mediated by a PDZ domain (PSD 95, Drosophilia Discs large protein and Zona occludens-1) on nNOS and a cognate ligand on PMCA4b. It remains unknown, however, whether this interaction has physiological relevance in the heart in vivo.

Methods and Results— We generated 2 strains of transgenic mice overexpressing either human PMCA4b or PMCA ct120 in the heart. PMCA ct120 is a highly active mutant form of the pump that does not interact with or modulate nNOS function. Calcium was extruded normally from PMCA4b-overexpressing cardiomyocytes, but in vivo, overexpression of PMCA4b reduced the β-adrenergic contractile response. This attenuated response was not observed in ct120 transgenic mice. Treatment with a specific nNOS inhibitor ( N ω-propyl- l -arginine) reduced the β-adrenergic response in wild-type and ct120 transgenic mice to levels comparable to those of PMCA4b transgenic animals. No differences in lusitropic response were observed in either transgenic strain compared with wild-type littermates.

Conclusions— These data demonstrate the physiological relevance of the interaction between PMCA4b and nNOS and suggests its signaling role in the heart.

Increased superoxide generation and decreased stress protein Hsp90 expression in human umbilical cord vein endothelial cells (HUVECs) from pregnancies complicated by preeclampsia

OBJECTIVE

Endothelial dysfunction is associated with increased oxidative stress in the vascular system in women with preeclampsia (PE), a hypertensive disorder occurring during human pregnancy. However, due to the nature of the disease, direct evidence of increased endothelial oxidative stress in the maternal vascular system at an in vivo situation is still lacking. We previously reported that primary cultured endothelial cells (ECs) from umbilical cords (HUVECs) from pregnancies complicated by PE exhibit phenotypic changes compared to those from normal pregnancies such as reduced eNOs expression associated with disorganized endothelial junction protein distribution and increased endothelial permeability. In this study, we sought to determine whether increased oxidative stress was also present in primary cultured HUVECs from women with PE.

METHODS

HUVECs were isolated from normal and PE pregnancies and EC oxidative stress was examined by superoxide generation using positive nuclear dihydroethidium (DHE) staining as an indicator. Since Hsp90 is believed to have protective effects on endothelial function, we also determined mRNA and protein expression for Hsp90. Using Hsp90 inhibitor geldanamycin (GA), we further determined the potential role of Hsp90 in superoxide generation, eNOs expression, and prostacyclin production of altered EC function associated with PE pregnancies.

RESULTS

We found that primary cultured ECs from PE pregnancies showed an increase in DHE positive cells, p < 0.01. Hsp90 protein expression was significantly decreased in ECs from PE compared with that from normal pregnancies, p < 0.05. Inhibition of Hsp90 by GA resulted in an increase in superoxide generation and a decrease in eNOs protein expression. Decreased prostacyclin production was also found in ECs treated with GA.

CONCLUSION

These in vitro HUVEC data suggest that increased endothelial oxidative stress may also occur in the fetal compartment during preeclampsia.

Eicosapentaenoic acid modifies lipid composition in caveolae and induces translocation of endothelial nitric oxide synthase

Endothelial nitric oxide synthase (eNOS) plays a crucial role in the regulation of a variety of cardiovascular functions. Many studies have shown that dietary n-3 polyunsaturated fatty acids (PUFAs) have beneficial effects on coronary atherosclerosis. However, the mechanisms of n-3 PUFAs regulation in eNOS activation remain unknown. In the present study we investigated the effects of eicosapentaenoic acid (EPA, 20:5 n-3) on subcellular distribution of eNOS and lipid composition of caveolae. We demonstrated for the first time that EPA treatment profoundly altered lipid composition and fatty acyl substitutions of phospholipids in caveolae. We found that caveolin-1 was solely located in caveolae fractions in control cells, and EPA treatment displaced caveolin-1 from caveolae. eNOS was detected in the caveolin-enriched fractions and noncaveolae fractions in control cells. EPA treatment induced the translocation of eNOS from caveolae fractions to soluble fractions. P-eNOS was also distributed in both fractions. After EPA treatment, the level of p-eNOS in each fraction was increased but the distribution of which was unaffected. Moreover, the results of immunofluorescence confirmed that EPA could redistribute caveolin-1 and eNOS in plasma membrane. eNOS activity in HUVEC cells was increased after EPA treatment, which was in a dose dependent manner. And incubation with 50 microM EPA had the maximum effect on eNOS activity. Our results suggested that eNOS translocation was paralleled by a stimulated capacity for NO production in the cells. We found that total Akt and p-Akt were primarily presented in heavy membranes in control cells, and the relative level of p-Akt increased but the distribution did not change after EPA treatment. The distribution of CaM was slightly changed after EPA treatment. Our results indicated that n-3 PUFAs profoundly altered caveolae microenvironment, thereby modifying location and function of proteins in caveolae. EPA-induced alterations of lipid and proteins in caveolae may be an important mechanism in the pathophysiologic process of atherosclerosis.

Human heart mitochondria do not produce physiologically relevant quantities of nitric oxide

Previous studies raised the possibility that nitric oxide synthase is present in heart mitochondria (mtNOS) and the existence of such an enzyme became generally accepted. However, original experimental evidence is rather scarce and positive identification of the enzyme is lacking. We aimed to detect an NOS protein in human and mouse heart mitochondria and to measure the level of NO released from the organelles. Western blotting with 7 different anti-NOS antibodies failed to detect a NOS-like protein in mitochondria. Immunoprecipitation or substrate-affinity purification of the samples concentrated NOS in control preparations but not in mitochondria. Release of NO from live respiring human mitochondria was below 2 ppb after 45 min of incubation. In a bioassay system, mitochondrial suspension failed to cause vasodilation of human mammary artery segments. These results indicate that mitochondria do not produce physiologically relevant quantities of NO in the heart and are unlikely to have any physiological importance as NO donors, nor do they contain a recognizable mtNOS enzyme.

Endostatin down-regulates soluble guanylate cyclase (sGC) in endothelial cells in vivo: influence of endostatin on vascular endothelial growth factor (VEGF) signaling

Endostatin was suggested to be an antiangiogenic agent with the potential for clinical use in cancer therapy. Unfortunately, up to now no antiangiogenic effect was seen in clinical trials using this substance. The lack of response might be caused by an incomplete understanding of endostatin signaling. Endostatin is known to influence the vascular endothelial growth factor (VEGF) signaling pathway. It has been reported to bind to the VEGF receptor KDR directly and to decrease the phosphorylation of endothelial nitric oxide synthase (eNOS) at Ser1177 via the protein phosphatase 2A (PP2A). But so far no details of endostatin signaling with regard to NO downstream effectors have been revealed. In the present work the authors demonstrate that endostatin down-regulates the protein level of soluble guanylate cyclase (sGC) in endothelial cells of newly formed blood vessels in 5 day-old wounds (control: 62.5 +/- 33 vessels/mm2, endostatin: 9.2 +/- 3.2 vessels/mm2). This was confirmed in experiments with endothelial tubes of embryoid bodies and endothelial cells derived from embryonic stem cells (eESCs; control: 126 +/- 20, endostatin: 58 +/- 10). The decrease of sGC protein levels in response to endostatin was abolished after preincubation with the PP2A inhibitor okadaic acid. No alterations of sGC mRNA levels could be found under endostatin treatment in eESC. The authors conclude that endostatin affects VEGF signaling in endothelial cells by a post-transcriptional PP2A-dependent down-regulation of sGC protein levels.