Trafficking and activation of eNOS in epithelial cells

HSP90 Modulates T2R Bitter Taste Receptor Nitric Oxide Production and Innate Immune Responses in Human Airway Epithelial Cells and Macrophages

Bitter taste receptors (T2Rs) are G protein-coupled receptors (GPCRs) expressed in various cell types including ciliated airway epithelial cells and macrophages. T2Rs in these two innate immune cell types are activated by bitter products, including those secreted by Pseudomonas aeruginosa, leading to Ca2+-dependent activation of endothelial nitric oxide (NO) synthase (eNOS). NO enhances mucociliary clearance and has direct antibacterial effects in ciliated epithelial cells. NO also increases phagocytosis by macrophages. Using biochemistry and live-cell imaging, we explored the role of heat shock protein 90 (HSP90) in regulating T2R-dependent NO pathways in primary sinonasal epithelial cells, primary monocyte-derived macrophages, and a human bronchiolar cell line (H441). Immunofluorescence showed that H441 cells express eNOS and T2Rs and that the bitter agonist denatonium benzoate activates NO production in a Ca2+- and HSP90-dependent manner in cells grown either as submerged cultures or at the air-liquid interface. In primary sinonasal epithelial cells, we determined that HSP90 inhibition reduces T2R-stimulated NO production and ciliary beating, which likely limits pathogen clearance. In primary monocyte-derived macrophages, we found that HSP-90 is integral to T2R-stimulated NO production and phagocytosis of FITC-labeled Escherichia coli and pHrodo-Staphylococcus aureus. Our study demonstrates that HSP90 serves as an innate immune modulator by regulating NO production downstream of T2R signaling by augmenting eNOS activation without impairing upstream Ca2+ signaling. These findings suggest that HSP90 plays an important role in airway antibacterial innate immunity and may be an important target in airway diseases such as chronic rhinosinusitis, asthma, or cystic fibrosis.

Morphological Alterations and Stress Protein Variations in Lung Biopsies Obtained from Autopsies of COVID-19 Subjects

Molecular chaperones, many of which are heat shock proteins, play a role in cell stress response and regulate the immune system in various ways, such as in inflammatory/autoimmune reactions. It would be interesting to study the involvement of these molecules in the damage done to COVID-19-infected lungs. In our study, we performed a histological analysis and an immunomorphological evaluation on lung samples from subjects who succumbed to COVID-19 and subjects who died from other causes. We also assessed Hsp60 and Hsp90 distribution in lung samples to determine their location and post-translational modifications. We found histological alterations that could be considered pathognomonic for COVID-19-related lung disease. Hsp60 and Hsp90 immunopositivity was significantly higher in the COVID-19 group compared to the controls, and immunolocalization was in the plasma membrane of the endothelial cells in COVID-19 subjects. The colocalization ratios for Hsp60/3-nitrotyrosine and Hsp60/acetylate-lisine were significantly increased in the COVID-19 group compared to the control group, similar to the colocalization ratio for Hsp90/acetylate-lisine. The histological and immunohistochemical findings led us to hypothesize that Hsp60 and Hsp90 might have a role in the onset of the thromboembolic phenomena that lead to death in a limited number of subjects affected by COVID-19. Further studies on a larger number of samples obtained from autopsies would allow to confirm these data as well as discover new biomarkers useful in the battle against this disease.

Osteoprotegerin and RANKL-RANK-OPG-TRAIL signalling axis in heart failure and other cardiovascular diseases

Osteoprotegerin (OPG) is a glycoprotein involved in the regulation of bone remodelling. OPG regulates osteoclast activity by blocking the interaction between the receptor activator of nuclear factor kappa B (RANK) and its ligand (RANKL). More and more studies confirm the relationship between OPG and cardiovascular diseases. Numerous studies have confirmed that a high plasma concentration of OPG and a low concentration of tumour necrosis factor–related apoptosis inducing ligand (TRAIL) together with a high OPG/TRAIL ratio are predictors of poor prognosis in patients with myocardial infarction. A high plasma OPG concentration and a high ratio of OPG/TRAIL in the acute myocardial infarction are a prognostic indicator of adverse left ventricular remodelling and of the development of heart failure. Ever more data indicates the participation of OPG in the regulation of the function of vascular endothelial cells and the initiation of the atherosclerotic process in the arteries. Additionally, it has been shown that TRAIL has a protective effect on blood vessels and exerts an anti-atherosclerotic effect. The mechanisms of action of both OPG and TRAIL within the cells of the vascular wall are complex and remain largely unclear. However, these mechanisms of action as well as their interaction in the local vascular environment are of great interest to researchers. This article presents the current state of knowledge on the mechanisms of action of OPG and TRAIL in the circulatory system and their role in cardiovascular diseases. Understanding these mechanisms may allow their use as a therapeutic target in cardiovascular diseases in the future.

Dual role of the L-arginine-ADMA-NO pathway in systemic hypoxic vasodilation and pulmonary hypoxic vasoconstriction

In healthy vascular endothelium, nitric oxide acts as a vasodilator paracrine mediator on adjacent smooth muscle cells. By activating soluble guanylyl cyclase, nitric oxide stimulates cyclic guanosine monophosphate (cGMP) which causes relaxation of vascular smooth muscle (vasodilation) and inhibition of platelet aggregation. This mechanism is active in both, the systemic and pulmonary circulation. In the systemic circulation, hypoxia results in local vasodilation, which has been shown to be brought about by stabilization of hypoxia-inducible factor-1α (HIF1α) and concomitant upregulation of endothelial nitric oxide synthase. By contrast, the physiological response to hypoxia in the pulmonary circulation is vasoconstriction. Hypoxia in the lung primarily results from hypoventilation of circumscript areas of the lung, e.g. by bronchial tree obstruction or inflammatory infiltration. Therefore, hypoxic pulmonary vasoconstriction is a mechanism preventing distribution of blood to hypoventilated areas of the lungs, thereby maintaining maximal oxygenation of blood. The exact molecular mechanism of hypoxic pulmonary vasoconstriction is less well understood than hypoxic vasodilation in the systemic circulation. While alveolar epithelial cells may be key in sensing low oxygen concentration, and pulmonary vascular smooth muscle cells obviously are the effectors of vasoconstriction, the pulmonary vascular endothelium plays a crucial role as an intermediate between these cell types. Indeed, dysfunctional endothelial nitric oxide release was observed in humans exposed to acute hypoxia, and animal studies suggest that hypoxic pulmonary vasoconstriction is enhanced by nitric oxide synthase inhibition. This may be caused, in part, by elevation of asymmetric dimethylarginine, an endogenous inhibitor of nitric oxide synthesis. High asymmetric dimethylarginine levels are associated with endothelial dysfunction, vascular disease, and hypertension.

Reciprocal regulation of eNOS and caveolin-1 functions in endothelial cells

We hypothesized that the maintenance of vascular homeostasis is critically dependent on the expression and reciprocal regulation of caveolin-1 (Cav-1) and endothelial nitric oxide synthase (eNOS) in endothelial cells (ECs). Skeletal muscle biopsies from subjects with type 2 diabetes showed 50% less Cav-1 and eNOS than those from lean healthy controls. The Cav-1:eNOS expression ratio was 200:1 in primary culture human ECs. Cav-1 small interfering RNA (siRNA) reduced eNOS protein and gene expression in association with a twofold increase in eNOS phosphorylation and nitrate production per molecule of eNOS, which was reversed in cells overexpressing Adv-Cav-1-GFP. Upon addition of the Ca²⁺ ionophore A23187 to activate eNOS, we observed eNOS Ser1177 phosphorylation, its translocation to β-catenin-positive cell–cell junctions, and increased colocalization of eNOS and Cav-1 within 5 min. We also observed Cav-1 S-nitrosylation and destabilization of Cav-1 oligomers in cells treated with A23187 as well as insulin or albumin, and this could be blocked by L-NAME, PP2, or eNOS siRNA. Finally, caveola-mediated endocytosis of albumin or insulin was reduced by Cav-1 or eNOS siRNA, and the effect of Cav-1 siRNA was rescued by Adv-Cav-1-GFP. Thus, Cav-1 stabilizes eNOS expression and regulates its activity, whereas eNOS-derived NO promotes caveola-mediated endocytosis.

Inhibition of endothelial nitric oxide synthase in cholangiocarcinoma cell lines - a new strategy for therapy

The isoform of nitric oxide synthase (NOS) found in endothelial cells (eNOS) plays a crucial role in vasodilation. We recently reported the activation of eNOS in cholangiocarcinoma (CCA) tissues and cell lines. Moreover, we also reported that the abundance of eNOS and phosphorylated eNOS (p-eNOS), as well as its upstream regulator proteins, is significantly associated with the metastatic status of CCA patients. However, the function of eNOS in CCA progression has not been addressed. Therefore, the present study aimed to investigate the function of eNOS involved in the migration and invasion ability of CCA cell lines. The results reveal that eNOS activation significantly increases migration and invasion ability of CCA cells via the up-regulation of phosphorylated vasodilator-stimulated protein (p-VASP). A combination treatment with recombinant human vascular endothelial growth factor C and eNOS inhibitor (N^ω-nitro-l-arginine methyl ester hydrochloride) resulted in the down-regulation of p-VASP, as well as a decreased migration and invasion ability of the CCA cell line. Thus, this work suggests that eNOS can serve as an attractive target to inhibit the progression of CCA.

Role of the Golgi Apparatus in the Blood-Brain Barrier: Golgi Protection May Be a Targeted Therapy for Neurological Diseases

The blood-brain barrier (BBB) protects the brain from toxic material in the blood, provides nutrients for brain tissues, and screens harmful substances from the brain. The specific brain microvascular endothelial cells (BMVECs), tight junction between endothelial cells, and astrocytes ensure proper function of the central nervous system (CNS). Pathological factors disrupt the integrity of the BBB by destroying the normal function of endothelial cells and decreasing the production of tight junction proteins or the expression of proteins specifically localized on astrocytes. Interestingly, fragmentation of the Golgi apparatus is observed in neurological diseases and is involved in the destruction of the BBB function. The Golgi acts as a processing center in which proteins are transported after being processed in the endoplasmic reticulum. Besides reprocessing, classifying, and packaging proteins, the Golgi apparatus (GA) also acts as a signaling platform and calcium pool. In this review, we summarized the current literature on the potential relationship between the Golgi and endothelial cells, tight junction, and astrocytes. The normal function of the BBB is maintained as long as the normal function and morphology of the GA are not disturbed. Furthermore, we speculate that protecting the Golgi may be a novel therapeutic approach to protect the BBB and treat neurological diseases due to BBB dysfunction.

Renal nitric oxide synthase and antioxidant preservation in Cyp1a1-Ren-2 transgenic rats with inducible malignant hypertension

BACKGROUND

Dietary administration of 0.30% indole-3-carbinol (I3C) to Cyp1a1-Ren2 transgenic rats (TGRs) generates angiotensin II (ANG II)-dependent malignant hypertension (HTN) and increased renal vascular resistance. However, TGRs with HTN maintain a normal or slightly reduced glomerular filtration rate. We tested the hypothesis that maintenance of renal function in hypertensive Cyp1a1-Ren2 TGRs is due to preservation of the intrarenal nitric oxide (NO) and antioxidant systems.

METHODS

Kidney cortex, kidney medulla, aortic endothelial (e) and neuronal (n) nitric oxide synthase (NOS), superoxide dismutases (SODs), and p22phox (nicotinamide adenine dinucleotide phosphate-oxidase subunit) protein abundances were measured along with kidney cortex total antioxidant capacity (TAC) and NOx. TGRs were fed a normal diet that contained 0.3% I3C or 0.3% I3C + candesartan (AT1 receptor antagonist; 25mg/L in drinking water) (n = 5-6 per group) for 10 days.

RESULTS

Blood pressure increased and body weight decreased in I3C-induced TGRs, while candesartan blunted these responses. Abundances of NOS, SOD, and p22phox as well as TAC were maintained in the kidney cortex of I3C-induced TGRs with and without candesartan, while kidney cortex NOx production increased in both groups. Kidney medulla eNOS and extracellular (EC) SOD decreased and nNOS were unchanged in both groups of I3C-induced TGRs. In addition, a compensatory increase occurred in kidney medulla Mn SOD in I3C-induced TGRs + candesartan. Aortic eNOS and nNOS∝ fell and p22phox and Mn SOD increased in hypertensive I3C-induced TGRs; all changes were reversed with candesartan.

CONCLUSIONS

The preservation of renal cortical NO and antioxidant capacity is associated with preserved renal function in Cyp1a1-Ren2 TGRs with ANG II-dependent malignant HTN.

Role of exercise in the prevention of cardiovascular disease: results, mechanisms, and new perspectives

On an empirical basis, exercise has been regarded as a fundamental pre-requisite for human well-being and physical integrity since classical times. Only in the last decades, however, scientific evidence has accumulated proving its role in the prevention and treatment of multiple chronic diseases beyond any reasonable doubt. Few treatment strategies in medicine have been tested so rigorously in large cohorts of patients as regular physical exercise. With the advent of molecular biology, the underlying mechanisms, such as NO bioavailability and mobilization of progenitor cells, could be identified. This enhances our understanding of this therapeutic tool. Unfortunately, the low compliance rate of the patients is the major drawback of the intervention exercise training (ET). The objective of this manuscript is to summarize the current knowledge with respect to ET on cardiovascular disease (CVD) and the molecular changes elicited by ET. Finally, we will critically assess reasons why ET as therapeutic option is not as effective at the population level in preventing CVD and what we may change in the future to make ET the most effective intervention to fight the development of CVD.

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.

Localization of eNOS in the olfactory epithelium of the rat

Nitric oxide (NO) is a free radical and produced from L-arginine by nitric oxide synthase (NOS). Since NO is recently suggested to be involved in olfactory perception, the expression of eNOS, an isoform of NOS, was examined in the rat olfactory epithelium. The activity of NADPH-diaphorase was also examined as a marker of NOS. In the dorsomedial region of the nasal cavity, intensely positive reactions for NADPH-diaphorase were observed in the entire cytoplasm of sensory cells (olfactory cells). By immunohistochemistry, intensely positive reactions for eNOS were also found in the dorsomedial region of the nasal cavity. These reactions were observed on the free border of the olfactory epithelium. By immunoelectron microscopy, positive reactions for eNOS were found in the cilia of olfactory cells. In addition, in situ hybridization analysis of the olfactory epithelium revealed the expression of eNOS mRNA in the olfactory cells. These results indicate the presence of eNOS in the olfactory cells of the rat, and differential expression of eNOS in the olfactory epithelium depending on the regions of the nasal cavity. In addition, NO produced by eNOS may be involved in olfactory perception in the cilia of olfactory cells.

Gaseous neurotransmitters and their role in anapyrexia

Mammals keep their body temperature (Tb) relatively constant even under a wide range of ambient temperature variation. However, in some particular situations it may be beneficial to increase or to decrease Tb. For instance, under hypoxic conditions, a regulated drop in Tb (anapyrexia) takes place which has been reported to be crucial for survival in a number of different species. This review highlights major advances in the research about nitric oxide (NO) and carbon monoxide (CO- where data are relatively less abundant), before focusing on the role played by these gaseous neuromediators in thermoregulation, under the conditions of euthermia and anapyrexia. Available data are consistent with the notion that both NO and CO, acting on the CNS, participate in thermoregulation, with NO decreasing Tb and CO increasing it. However further studies are required before definitive conclusions can be made as to their physiological mechanisms of action.

Functional role of HSP90 complexes with endothelial nitric-oxide synthase (eNOS) and calpain on nitric oxide generation in endothelial cells

Although several reports have indicated that eNOS is a highly sensitive calpain substrate, the occurrence of a concomitant Ca(2+)-dependent activation of the synthase and of the protease has never been analyzed in specific direct experiments. In this study, we have explored in vivo how eNOS can undergo Ca(2+)-dependent translocation and activation, protected against degradation by activated calpain. Here we demonstrate that following a brief exposure to Ca(2+)-loading, the cytosolic eNOS-HSP90 complex recruits calpain in a form in which the chaperone and the synthase are almost completely resistant to digestion by the protease. Furthermore, in the presence of the HSP90 inhibitor geldanamycin, a significant decrease in NO production and an extensive degradation of eNOS protein occurs, indicating that dissociation from membranes and association with the chaperone is correlated to the protection of the synthase. Experiments with isolated membrane preparations confirm the primary role of HSP90 in dissociation of eNOS from caveolae. Prolonged exposure of cells to Ca(2+)-loading resulted in an extensive degradation of both eNOS and HSP90, accompanied by a large suppression of NO production. We propose that the protective effect exerted by HSP90 on eNOS degradation mediated by calpain represents a novel and critical mechanism that assures the reversibility of the intracellular trafficking and activation of the synthase.

Can rodent models of diabetic kidney disease clarify the significance of early hyperfiltration?: recognizing clinical and experimental uncertainties

In the past, hyperfiltration and increased glomerular capillary pressure have been identified as important determinants of the development of DN (diabetic nephropathy). Recently, some basic research and clinical reviews on DN have omitted identifying hyperfiltration as an important risk factor. At the same time, different rodent models of DN have been described without and with documented hyperfiltration. In the present review, the importance of hyperfiltration is reassessed, reviewing key clinical and research studies, including the first single nephron studies in a mouse model of DN. From clinical studies of Type 1 and Type 2 diabetes mellitus, it is clear that many patients do not have early hyperfiltration and, even when present, its contribution to subsequent DN remains uncertain. Key mechanisms underlying hyperfiltration in rodent models are reviewed. Findings on intrarenal NO metabolism and the control of single-nephron GFR (glomerular filtration rate) in rodent models of DN are also presented. Characterization of valid experimental models of DN should include a careful delineation of the absence or presence of early hyperfiltration, with special efforts made to establish the specific role hyperfiltration may play in the emergence of DN.

Expression, regulation and function of trail in atherosclerosis

Atherosclerosis is a condition where vascular smooth muscle cells (VSMCs), inflammatory cells, lipids, cholesterol and cellular waste accumulate in the inner lining of an artery, producing a fibro-fatty plaque and resulting in the thickening of the arterial wall. The tumor necrosis factor (TNF) family of cytokines plays a major role in the progression of atherosclerosis. Recently, TNF-related apoptosis-inducing ligand (TRAIL), a member of the TNF superfamily, has been implicated in the development of atherosclerosis since it has been detected in normal and diseased atherosclerotic tissue. Not only is TRAIL involved in apoptosis and immune regulation, recent studies have provided a new function of TRAIL on vascular cells, such that TRAIL can promote endothelial cell (EC) and VSMCs migration and proliferation. In addition, TRAIL is implicated in regulating vascular tone. This review discusses our current understanding of TRAIL expression, regulation and function, and summarises the recent data implicating a role for TRAIL in atherosclerosis.

Osteogenic differentiation of human mesenchymal bone marrow cells in silk scaffolds is regulated by nitric oxide

Bone marrow-derived mesenchymal stem cells (BMSC) are a powerful tool for tissue engineering and can be used in the regeneration of bone and other tissues. Nitric oxide (NO) produced by the endothelial NO synthase (eNOS) plays an important role in bone development and healing. We hypothesized that NO plays a role in osteogenic differentiation of BMSC cultured in three-dimensional silk scaffolds. eNOS protein was measured by Western Analysis and its activity was assessed by measuring nitrite in culture supernatants. Mineralization was evaluated through calcium deposition and the expression of genes associated with osteogenic differentiation (collagen I, RUNX2, and osteocalcin) was quantified using real-time RT-PCR. eNOS was consistently expressed with minor fluctuations, but NO production significantly increased at later time points (weeks 4 and 5). Addition of a competitive NOS inhibitor (L-NAME) resulted in a modest decrease in calcium deposition, which became statistically significant in week 5. This was preceded by a dramatic decrease in RUNX2 and osteocalcin expression in week 4. These results support our hypothesis and implicate NO as an important player in bone tissue engineering.

The developmental stage and cell type dependent phosphorylation of eNOS in murine enteric mucosa and myenteric plexus

In order to clarify the developmental regulation of the eNOS activity in intestine by phosphorylation, we examined the immunohistochemical localizations of the eNOS phosphorylation sites at Ser(1177), Ser(116) and at Thr(495) in cells of the mouse enteric mucosa and myenteric plexus at E13.5, E14.5, E16.5, E18.5, E20.5 and P3. In addition, in cells of the E16.5 stage the protein levels of eNOS and the phosphorylation sites of eNOS at Ser(1177), Ser(116) and at Thr(495) were investigated by immunoblot. From E14.5 to P3, phosphorylation residues of eNOS at Ser(1177) and at Ser(116) were detected with different staining intensities in the enteric mucosa epithelium. In ganglion cells of the myenteric plexus Ser(116) was identified at E18.5 to P3. The absence of phosphorylated Thr(495) in cells of intestine during all developmental stages, was confirmed by immunoblot at E16.5. The immunoblot levels of eNOS and eNOS phosphorylated at Ser(1177) and at Ser(116) were comparable with the immunohistochemical results of E16.5 mouse intestine. It was concluded that development of epithelial cells of the enteric mucosa may be modulated by phosphorylation of eNOS at Ser(1177) and at Ser(116). The phosphorylation of eNOS in cells of the myenteric plexus is modulated at Ser(116). These data suggest that there is a developmental stage and cell type dependent phosphorylation of eNOS.

Haplotype analysis of endothelial nitric oxide synthase (NOS3) genetic variants and tardive dyskinesia in patients with schizophrenia

OBJECTIVES

Several studies have indicated the involvement of nitric oxide (NO) in the pathogenesis of tardive dyskinesia (TD), an incapacitating adverse movement disorder associated with long-term antipsychotic treatment. In human brain, the NO could be generated by endothelial nitric oxide synthase (NOS3). In this study, we studied whether the genetic variants in human NOS3 gene is associated with TD in patients with schizophrenia.

METHODS

Two hundred and eighty-two chronic inpatients with schizophrenia treated with typical antipsychotics were recruited in this study. The patients were further grouped by the presence of TD or not according to the Research and Diagnostic Criteria for TD. The genetic variants in the NOS3 gene investigated in this study were -786T > C in the promotor region, 27-bp variable number of tandem repeats (27-bp VNTR) in intron 4, and Glu298Asp in exon 7. The frequencies of genotypes, alleles and haplotypes of the three markers were compared between the TD (n = 153) and non-TD (n = 129) groups.

RESULTS

There were no significant associations between the genotypes and alleles of the three markers and TD. However, in the haplotype-based case-control analysis, the frequency of haplotype T-4b-Glu was significantly higher in non-TD than in TD group (TD vs. non-TD = 72.7% vs. 81.0%, permutation P value = 0.021, OR = 0.648, 95% CI = 0.432-0.973).

CONCLUSIONS

We found that the haplotype T-4b-Glu represents a protective haplotype against TD after long-term antipsychotic treatment. This finding suggests that human NOS3 gene may be involved in the pathogenesis of TD.

Translocation of endothelial nitric-oxide synthase involves a ternary complex with caveolin-1 and NOSTRIN

Recently, we characterized a novel endothelial nitric-oxide synthase (eNOS)-interacting protein, NOSTRIN (for eNOS-trafficking inducer), which decreases eNOS activity upon overexpression and induces translocation of eNOS away from the plasma membrane. Here, we show that NOSTRIN directly binds to caveolin-1, a well-established inhibitor of eNOS. Because this interaction occurs between the N terminus of caveolin (positions 1-61) and the central domain of NOSTRIN (positions 323-434), it allows for independent binding of each of the two proteins to eNOS. Consistently, we were able to demonstrate the existence of a ternary complex of NOSTRIN, eNOS, and caveolin-1 in Chinese hamster ovary (CHO)-eNOS cells. In human umbilical vein endothelial cells (HUVECs), the ternary complex assembles at the plasma membrane upon confluence or thrombin stimulation. In CHO-eNOS cells, NOSTRIN-mediated translocation of eNOS involves caveolin in a process most likely representing caveolar trafficking. Accordingly, trafficking of NOSTRIN/eNOS/caveolin is affected by altering the state of actin filaments or cholesterol levels in the plasma membrane. During caveolar trafficking, NOSTRIN functions as an adaptor to recruit mediators such as dynamin-2 essential for membrane fission. We propose that a ternary complex between NOSTRIN, caveolin-1, and eNOS mediates translocation of eNOS, with important implications for the activity and availability of eNOS in the cell.

Nitric oxide synthase expression and nitric oxide toxicity in oligodendrocytes

Oligodendrocytes (OLG) have more complex interactions with nitric oxide (NO) than initially suspected. Historically, OLG were seen only as targets of high NO levels released from other cells. Expression of nitric oxide synthase type II (NOS-2) in primary cultures of OLGs stimulated by cytokines led to controversy due to the presence of small numbers of microglia, cells also inducible for NOS-2 expression. The present review summarizes the findings that immature OLG express NOS-2, but that they do not in their most mature stage in culture as membrane sheet-bearing cells. This raises questions about the regulation of NOS-2 expression in OLG. Additionally, novel data are presented on NOS-3 expression in cultured OLG. If confirmed in vivo, this finding suggests that constitutive NOS-3 expression may play a key role in OLG injury due to its activation by calcium, in interaction with pathways mediating glutamate toxicity. The authors discuss in vivo NO levels to place in vitro findings in context, and compare OLG sensitivity to NO with that of other brain cells. Lastly, the multiple interactions of NO are considered with regard to glutamate cytotoxicity, the antioxidant glutathione, mitochondrial function, and myelin architecture.

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) regulates endothelial nitric oxide synthase (eNOS) activity and its localization within the human vein endothelial cells (HUVEC) in culture

We have recently demonstrated that tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) increases endothelial nitric oxide synthase (eNOS) phosphorylation, NOS activity, and nitric oxide (NO) synthesis in cultured human umbilical vein endothelial cells (HUVEC), without inducing apoptotic cell death. Although an important factor that regulates eNOS activity is its localization within the cells, little is known about the role of TRAIL in the regulation of eNOS trafficking among cellular compartments and the cytoskeleton involvement in this machinery. Then, we did both quantitative and semi-quantitative evaluations with biochemical assays and immune fluorescence microscopy in the presence of specific inhibitors of NOS activity as well as of cytoskeletal microtubule structures. In our cellular model, TRAIL treatment not only increased NO levels but also caused a time-dependent NO migration of fluorescent spots from the plasma membrane to the inner part of the cells. In unstimulated cells, most of the eNOS was localized at the cell membranes. However, within 10 min following addition of TRAIL, nearly all the cells showed an increased cytoplasm localization of eNOS which appeared co-localized with the Golgi apparatus at a higher extent than in unstimulated cells. These effects were associated to an increased formation of trans-cytoplasm stress fibers with no significant changes of the microtubule network. Conversely, microtubule disruption and Golgi scattering induced with Nocodazole treatment inhibited TRAIL-increased NOS activity, indicating that, on cultured HUVEC, TRAIL ability to affect NO production by regulating eNOS sub-cellular distribution is mediated by cytoskeleton and Golgi complex modifications.

NOSTRIN functions as a homotrimeric adaptor protein facilitating internalization of eNOS

Intracellular trafficking of endothelial nitric oxide synthase (eNOS) between different compartments is incompletely understood. Recently, we described a novel eNOS-interacting protein, NOSTRIN, which upon overexpression drives eNOS away from the plasma membrane towards intracellular compartments. Sequence similarity of NOSTRIN and pacsins/syndapins suggested a role for NOSTRIN in endocytosis. Accordingly, we show here that NOSTRIN interacts with the large GTPase dynamin and the actin nucleation promoting factor N-WASP by means of its SH3 domain, which also represents the docking site for eNOS. Via a coiled-coil region in the C-terminal portion of the protein, NOSTRIN oligomerizes, mainly forming trimers, which would allow simultaneous interaction with multiple binding partners of the SH3 domain. Consistent with this notion, expression of dynamin-2-GFP in CHO cells stably expressing eNOS (CHO-eNOS) results in recruitment of eNOS to dynamin-positive structures, only when NOSTRIN is present as well. Similarly, when N-WASP-GFP and NOSTRIN are co-expressed in CHO-eNOS cells, both proteins strongly co-localize with eNOS and are recruited to structures running along actin filaments. If, however, the actin cytoskeleton is depolymerized by cytochalasin D, NOSTRIN and eNOS are associated with extended structures in the cell periphery, possibly being unable to leave the plasma membrane. Together, these results indicate that NOSTRIN may facilitate endocytosis of eNOS by coordinating the function of dynamin and N-WASP.

Nitric oxide and cGMP mediate alpha1D-adrenergic receptor-Stimulated protein secretion and p42/p44 MAPK activation in rat lacrimal gland

PURPOSE

To determine whether alpha(1)-adrenergic receptors use the nitric oxide (NO)/cGMP pathway to stimulate protein secretion by rat lacrimal gland.

METHODS

Identification and cellular location of endothelial nitric oxide synthase (eNOS) and neuronal nitric oxide synthase (nNOS) were determined by Western blot and immunofluorescence techniques, respectively. Rat lacrimal gland acini were isolated by collagenase digestion, and protein secretion stimulated by phenylephrine, an alpha(1)-adrenergic agonist, was measured with a fluorescence assay system. Acini were preincubated with inhibitors for 20 minutes before addition of phenylephrine (10(-4) M). NO and cGMP were measured in response to phenylephrine stimulation. Activation of p42/p44 MAPK was determined by Western blot analysis with an antibody against phosphorylated (active) p42/p44 MAPK.

RESULTS

eNOS and nNOS were both present in lacrimal gland. eNOS appeared to be localized with caveolae, whereas nNOS was present in the nerves surrounding the acini. Inhibition of eNOS with N(G)-nitro-l-arginine methyl ester (l-NAME; 10(-6) M) completely inhibited phenylephrine-stimulated protein secretion, whereas the inactive isomer d-NAME and inhibition of nNOS with S-methyl-l-thiocitrulline did not. Phenylephrine increased NO production in a time- and concentration-dependent manner, but the increase was abolished by the alpha(1D)-adrenergic receptor inhibitor BMY-7378. Inhibition of guanylate cyclase with oxadiazoloquinoxalin (ODQ) also inhibited phenylephrine-induced protein secretion, whereas phenylephrine caused a 2.2-fold increase in cGMP. In addition, preincubation with l-NAME and ODQ inhibited phenylephrine-stimulated p42/p44 MAPK activation.

CONCLUSIONS

alpha(1D)-Adrenergic agonists stimulate eNOS to produce NO, leading to production of cGMP by guanylate cyclase, to transduce the extracellular signal through the cell and stimulate protein secretion in rat lacrimal gland.

The Basal Phosphorylation Sites of Endothelial Nitric Oxide Synthase at Serine (Ser)1177, Ser116, and Threonine (Thr)495in Rat Molar Epithelial Rests of Malassez

BACKGROUND

The epithelial rests of Malassez (ERM) are derived from the Hertwig's epithelial root sheath during tooth development. The ERM contain endothelial nitric oxide synthase (eNOS), but the existence of phosphorylation site/s of eNOS in the ERM is unclear.

METHODS

Rat molars with periodontium were perfusion- and post-fixed, decalcified, and frozen-sectioned. Free-floating sections were incubated using antisera against total eNOS, eNOS phosphorylated at serine (Ser)1177, Ser116, and threonine (Thr)495. The signal intensities of t-eNOS, p-eNOS at Ser1177 and Ser116 in the ERM were measured by densitometry and statistically analyzed.

RESULTS

In the ERM, localization of total eNOS and the phosphorylation sites of eNOS at Ser1177 and Ser116 were detected, while a basal localization of eNOS phosphorylated at Thr495 in the ERM was undetectable. For p-eNOS at Ser116 regional differences in phosphorylation were detected.

CONCLUSIONS

The basal production of NO by eNOS in the ERM is modulated by phosphorylation of eNOS at Ser1177 and Ser116 residues, while the basal activity of the eNOS is not influenced by phosphorylation of eNOS at Thr495 residue. This provides evidence that phosphorylation plays a key role for regulation of the catalytic activity of eNOS.

Effect of chronic ethanol administration on hepatic eNOS activity and its association with caveolin-1 and calmodulin in female rats

Although chronic and excessive alcohol consumption is associated with liver disease, the mechanism of alcoholic liver injury is still not clear. Whether reduced hepatic production of nitric oxide, which is evident in models of liver injury, is associated with alcohol-induced liver injury has not been investigated. We measured nitric oxide synthase (NOS) activity in the liver of pair-fed rats receiving liquid diet with or without alcohol [3% (vol/vol)] for 12 wk. Compared with control rats, hepatic NOS activity was significantly reduced in alcohol-treated rats along with the evidence of liver injury. Interestingly, there was no difference in the hepatic expression of endothelial NOS (eNOS) between ethanol-fed and pair-fed rats. We then tested the hypothesis that an imbalance between the binding of eNOS with inhibitory and stimulatory proteins may underlie the reduced activity of eNOS because eNOS catalytic activity is regulated partly through dynamic interactions with the inhibitory protein caveolin-1 and the stimulatory protein calmodulin. We found that hepatic caveolin-1 was markedly increased in alcohol-treated rats compared with control rats, whereas calmodulin remained unaltered. The binding of caveolin-1 and calmodulin with eNOS was increased and decreased, respectively, in alcohol-treated rats. Our results suggest that chronic alcohol intake attenuates hepatic eNOS activity by increasing the expression of the inhibitory protein caveolin-1 and enhancing its binding with eNOS.

Nitric oxide and superoxide in the renal medulla: a delicate balancing act

PURPOSE OF REVIEW

Endothelial nitric oxide synthase (eNOS) and nicotinamide adenine dinucleotide (phosphate) oxidase [NAD(P)H oxidase] are both expressed in tubular epithelial cells within the renal medulla, particularly the thick ascending limb of the loop of Henle (mTALH). Thick ascending limbs contribute to long-term blood pressure control, both because they reabsorb approximately 30% of filtered sodium, and because they produce paracrine factors like nitric oxide (NO) that control medullary blood flow (MBF), which in turn has a major impact on tubular sodium reabsorption. Herein, we review recent evidence for roles of NO and superoxide (O2*-) in autocrine control of tubular sodium reabsorption, and in paracrine control of MBF.

RECENT FINDINGS

O2*- can have a direct action to reduce MBF, and to enhance sodium reabsorption from mTALH. These actions oppose those of NO produced in mTALH, which inhibits tubular sodium reabsorption (autocrine) and increases MBF (paracrine). NO and O2*- also oppose each other's actions through chemical combination to produce peroxynitrite. Thus, interactions between NO and O2*-, at both the chemical and cellular levels, likely contribute to long-term blood pressure control. This hypothesis is supported by recent data showing that sodium retention and hypertension can develop when the balance of production of these free radicals is tipped towards O2*-, such as in diabetes, atherosclerosis and renin-angiotensin-system activation.

SUMMARY

Interactions between O2*- and NO produced within the mTALH regulate tubular and vascular function in the renal medulla. Dysregulation of these systems in states of oxidative stress likely promotes salt and water retention, and thus hypertension.

Defects in activation of nitric oxide synthases occur during delayed angiogenesis in aging

Angiogenesis, the formation of new vessels from pre-existing vasculature, is impaired in aging. This is due, in part, to a lack of regulatory molecules such as nitric oxide (NO). We wished to test the hypothesis that there are deficits in the pathways that mediate NO production during angiogenesis (as defined by fibrovascular invasion into a polyvinyl alcohol (PVA) sponge implant), in aged mice in comparison to young mice. Sponges were implanted subcutaneously in young (6-8 months old, n=11) and aged (23-25 months old, n=13) mice and sampled at 14 and 19 days. Sections from the implants were stained with antibodies against vascular endothelial growth factor receptor 2 (VEGFR-2), Akt, phosphorylated Akt (p-Akt), endothelial nitric oxide synthase (eNOS), phosphorylated eNOS (p-eNOS), inducible NOS (iNOS), and 3-nitrotyrosine (3-NT, a marker for nitrosylated proteins). Expression of VEGFR-2 was similar in the sponges of young and aged mice. Moreover, there were no significant differences in levels of Akt or its phosphorylated form in sponges from young and aged mice at 14 and 19 d. In marked contrast, levels of eNOS, p-eNOS and iNOS were significantly decreased in sponges from aged mice relative to young mice (p<0.02 for eNOS, p-eNOS and <0.01 for iNOS between young and aged mice). Concomitantly, there was diminished expression of 3-NT in the sponges from aged mice (p<0.05). Our data indicate that defects in the activation of nitric oxide synthases result in decreased NO production in aged tissues relative to young tissues. We propose that the subsequent lack of NO contributes to impaired angiogenesis in aging.

Estrogen induces nitric oxide production via activation of constitutive nitric oxide synthases in human neuroblastoma cells

Although it is becoming increasingly evident that nitric oxide (NO) mediates some of estrogen's actions in the brain, the effects of estrogen on NO production through NO synthases (NOS) in neuronal cells have not yet been identified. Here we assessed changes in NO production induced by 17beta-estradiol (E2) in cells of neuronal origin using human SK-N-SH neuroblastoma cells, which we show express all three isoforms of NOS. Involvement of NOS isoforms in E2-induced NO production was examined using isoform-specific NOS inhibitors. E2 (10(-10)-10(-6) m) induced rapid increases in NO release and changes in endothelial NOS (eNOS) expression, which were blocked by ICI 182,780, an antagonist of estrogen receptors. Increased levels of NO release and NOS activity induced by E2 were blocked by N5-(1-Imino-3-butenyl)-L-ornithine, a neuronal NOS inhibitor, and N(5)-(1-Iminoethyl)-L-ornithine, an eNOS inhibitor, but not by 1400W, an inducible NOS inhibitor. These results demonstrate that E2-stimulated NO production occurs via estrogen receptor-mediated activation of the constitutive NOSs, neuronal NOS and eNOS. The E2-induced NO increase was abolished when extracellular Ca2+ was removed from the medium or after the addition of nifedipine, an L-type channel blocker, and was partially inhibited using 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid acetoxymethyl ester, an intracellular Ca2+ chelator. However, 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid acetoxymethyl ester itself also caused an increase in NO release that was blocked by 1400W, suggesting that inducible NOS mediates this response. Together these data reveal that constitutive NOS activities are responsible for E2-induced NO production in neuroblastoma cells and that differential activation of NOS isoforms in these cells occurs in response to different treatments.