Up-regulation of endothelial nitric oxide synthase via phosphatidylinositol 3-kinase pathway contributes to ischemic tolerance in the CA1 subfield of gerbil hippocampus

We here investigated endothelial nitric oxide synthase (eNOS) expression after 10 minutes of forebrain ischemia. Real-time polymerase chain reaction, immunoblots and immunohistochemical studies revealed up-regulation of eNOS expression in the hippocampal CA1 subfield of gerbil. Immunoreactivity of eNOS significantly increased in endothelium but neither in neurons nor astrocytes after 6 to 168 hours of reperfusion. An increased Akt activity preceded the postischemic eNOS up-regulation. Intracerebroventricular injection (i.c.v.) of wortmannin, an inhibitor of phosphatidylinositol 3-kinase (PI-3K), significantly inhibited the increases in both eNOS mRNA and its protein with concomitant inhibition of Akt activation. The significant increase in the eNOS expression was also evident following preconditioning 2-minute ischemia. Both eNOS up-regulation and acquisition of ischemic tolerance observed at 3 days after preconditioning ischemia were significantly inhibited by pretreatment with wortmannin. Administration (i.c.v.) of N-nitro-L-arginine methyl ester, but not 7-nitroindazole, 30 minutes prior to lethal 10-minute ischemia, significantly abolished the acquired tolerance. Intraperitoneal injections of aminoguanidine at immediately after, 24, and 48 hours after preconditioning had no effects on the tolerance. These results suggest that eNOS expression is up-regulated in the endothelium via PI-3K pathways after transient forebrain ischemia, and that preconditioning-induced eNOS expression plays an important role in neuroprotection in the ischemic tolerance.

Endothelial Nitric Oxide Synthase

Advances in our understanding of the molecular mechanisms involved in the constitutive and regulated expression of endothelial nitric oxide synthase (eNOS) mRNA expression present a new level of complexity to the study of endothelial gene regulation in health and disease. Recent studies highlight the contribution of both transcription and RNA stability to net steady-state mRNA levels of eNOS in vascular endothelium, introducing a new paradigm to gene regulation in the injured blood vessel. Constitutive eNOS expression is dependent on basal transcription machinery in the core promoter, involving positive and negative protein–protein and protein–DNA interactions. Chromatin-based mechanisms and epigenetic events also regulate expression of eNOS at the transcriptional level in a cell-restricted fashion. Although constitutively active, important physiological and pathophysiologic stimuli alter eNOS gene transcription rates. For instance, eNOS transcription rates increase in response to lysophosphatidylcholine, shear stress, and TGF-β, among others. Under basal conditions, eNOS mRNA is extremely stable. Surprisingly, posttranscriptional mechanisms have emerged as important regulatory pathways in the observed decreases in eNOS expression in some settings. In models of inflammation, proliferation/injury, oxidized low-density lipoprotein treatment, and hypoxia, eNOS mRNA destabilization plays a significant role in the rapid downregulation of eNOS mRNA levels.

Interferon-gamma induces characteristics of central sensitization in spinal dorsal horn neurons in vitro

Hyperexcitability of spinal dorsal horn neurons, also known as 'central sensitization', is a component of pain associated with pathological conditions in the nervous system. The aim of the present study was to analyze if the pro-inflammatory cytokine, interferon-gamma (IFN-gamma), which can be released for extended periods of time in the nervous system during inflammatory and infectious events, can alter synaptic activity in dorsal horn neurons and thereby contribute to such hyperexcitability. Treatment of cultured dorsal horn neurons with IFN-gamma for 2 weeks resulted in a significantly reduced clustering of alpha-amino-3-hydroxy-5-methylisoxazole (AMPA) receptor subunit 1 (GluR1) that was dependent on nitric oxide. The neurons displayed an increased frequency and amplitude of excitatory postsynaptic currents (EPSCs) upon IFN-gamma treatment. Treated dorsal horn neurons also exhibited increased responsiveness to stimulation of dorsal root ganglia (DRG) axons in a two-compartment model. Furthermore, disinhibition by the GABA(A) receptor antagonist picrotoxin (PTX) significantly increased EPSC frequency and induced bursting in untreated cultures but did not significantly increase the frequency in treated neurons, which displayed bursting even without PTX. GABA(A) agonists reduced activity more strongly in treated cultures and immunochemical staining for GABA(A) receptors showed no difference from controls. Since GluR1-containing AMPA receptors (AMPARs) occur predominantly on inhibitory neurons in the dorsal horn, we suggest that the IFN-gamma-mediated increase in spontaneous activity and responsiveness to DRG axon stimulation, decrease in sensitivity to PTX and tendency for EPSC bursting result from a reduced expression of GluR1 on these neurons and not from a reduction in active GABA(A) receptors in the network. IFN-gamma thereby likely causes disinhibition of synaptic activity and primary afferent input in the dorsal horn, which consequently results in central sensitization.

Dexamethasone lacks effect on blood pressure in mice with a disrupted endothelial NO synthase gene

Cushing's syndrome and systemic administration of glucocorticoids are associated with hypertension, but the underlying molecular mechanism is only partially understood. We have shown previously that dexamethasone downregulates the expression of the endothelial NO synthase (eNOS) gene in human endothelial cells and in the rat and that this may contribute to the blood pressure-raising effect of the steroid [Proc. Natl. Acad. Sci. USA 96 (1999) 13357]. In the current communication, we demonstrated that dexamethasone increased mean arterial blood pressure in wild-type C-57 Bl6 mice (eNOS+/+ mice), but had no effect on blood pressure in mice with a disrupted eNOS gene (eNOS-/- mice) derived from the same strain. The NOS inhibitor ethylisothiourea, used for control purposes, showed a hypertensive effect in eNOS+/+ mice, but no such effect in eNOS-/- mice. Serum NO2-/NO3- levels, an indicator of total body NO synthesis, decreased significantly when eNOS+/+ mice were treated with dexamethasone. eNOS-/- mice had lower serum NO2-/NO3- levels per se, which were not changed significantly by dexamethasone. Dexamethasone decreased the expression of eNOS in three major organs of the mouse investigated, namely the heart, the liver, and the kidney. We conclude that the expressional downregulation of eNOS and the ensuing reduction in vascular NO production contributes to the hypertension caused by glucocorticoids.

Neuronal Nitric Oxide Synthase as a Novel Anti-Atherogenic Factor

Nitric oxide (NO) has multiple important actions that contribute to the maintenance of vascular homeostasis. NO is synthesized by three different isoforms of NO synthase (NOS), all of which have been reported to be expressed in human atherosclerotic vascular lesions. Although the regulatory roles of endothelial NOS (eNOS) and inducible NOS (iNOS) on the development of atherosclerosis have been described, little is known about the role of neuronal NOS (nNOS). Recent studies have demonstrated that nNOS also exerts important vasculoprotective effects in vivo. In a carotid artery ligation model, nNOS-knockout mice exhibited accelerated neointimal formation and constrictive vascular remodeling caused by blood flow disruption. In a rat balloon injury model, the selective inhibition of nNOS activity potently enhanced vasoconstrictor responses to a variety of calcium-mobilizing stimuli, and exacerbated neointimal formation. Moreover, in apolipoprotein E-knockout mice, deficiency of nNOS induced progression of aortic vascular lesion formation. In these models, nNOS was up-regulated in vascular lesions, and was predominantly expressed in the neointima and medial smooth muscle cells. These results provide the first direct evidence that nNOS plays important roles in suppressing arteriosclerotic vascular lesion formation. Thus, nNOS could be regarded as a novel anti-atherogenic factor.

Paradoxical roles of different nitric oxide synthase isoforms in colonic injury

Nitric oxide (NO) is a free radical that is largely produced by three isoforms of NO synthase (NOS): neuronal (nNOS), endothelial (eNOS), and inducible (iNOS). NO regulates numerous processes in the gastrointestinal tract; however, the overall role that NO plays in intestinal inflammation is unclear. NO is upregulated in both ulcerative colitis and Crohn's disease as well as in animal models of colitis. There have been conflicting reports on whether NO protects or exacerbates injury in colitis or is simply a marker of inflammation. To determine whether the site, timing, and level of NO production modulate the effect on the inflammatory responses, the dextran sodium sulfate model of colitis was assessed in murine lines rendered deficient in iNOS, nNOS, eNOS, or e/nNOS by targeted gene disruption. The loss of nNOS resulted in more severe disease and increased mortality, whereas the loss of eNOS or iNOS was protective. Furthermore, concomitant loss of eNOS reversed the susceptibility found in nNOS-/- mice. Deficiencies in specific NOS isoforms led to distinctive alterations of inflammatory responses, including changes in leukocyte recruitment and alterations in colonic lymphocyte populations. The present studies indicate that NO produced by individual NOS isoforms plays different roles in modulating an inflammatory process.

17β-Estradiol regulates nNOS and eNOS activity in the hippocampus

Estrogen treatment in symptomatic postmenopausal women appears to improve cognitive performance including memory, an effect which may involve enhanced nitric oxide formation in hippocampal neurons. To study whether 17beta-estradiol (E2) affects NO synthase activity in the hippocampus, we investigated the influence of E2 on hippocampal NO synthase expression and activity in female rats. Ovariectomy, which significantly decreased E2 serum levels, reduced neuronal (nNOS) and endothelial NO synthase (eNOS) expression and Ca(2+)-dependent NOS activity. E2 substitution reversed these effects. It is concluded that E2 increases nNOS and eNOS expression and activity in female hippocampus and thus improves hippocampal function.

Multiple variable first exons: a mechanism for cell- and tissue-specific gene regulation

A large family of neural protocadherin (Pcdh) proteins is encoded by three closely linked mammalian gene clusters (alpha, beta, and gamma). Pcdh alpha and gamma clusters have a striking genomic organization. Specifically, each "variable" exon is spliced to a common set of downstream "constant" exons within each cluster. Recent studies demonstrated that the cell-specific expression of each Pcdh gene is determined bya combination of variable-exon promoter activation and cis-splicing of the corresponding variable exon to the first constant exon. To determine whether there are other similarly organized gene clusters in mammalian genomes, we performed a genome-wide search and identified a large number of mammalian genes containing multiple variable first exons. Here we describe several clusters that contain about a dozen variable exons arrayed in tandem, including UDP glucuronosyltransferase (UGT1), plectin, neuronal nitric oxide synthase (NOS1), and glucocorticoid receptor (GR) genes. In all these cases, multiple variable first exons are each spliced to a common set of downstream constant exons to generate diverse functional mRNAs. As an example, we analyzed the tissue-specific expression profile of the mouse UGT1 repertoire and found that multiple isoforms are expressed in a tissue-specific manner. Therefore, this variable and constant genomic organization provides a genetic mechanism for directing distinct cell- and tissue-specific patterns of gene expression.

Endothelial dysfunction in acute and chronic coronary syndromes: evidence for a pathogenetic role of oxidative stress

The past two decades have highlighted the pivotal role of the endothelium in preserving vascular homeostasis. Among others, nitric oxide (NO) is currently believed to be the main component responsible for endothelium dependent vasorelaxation and therefore for endothelial function integrity. Reduced NO bioavailability causes the so-called "endothelial dysfunction," which seems to be the common molecular disorder comprising stable atherosclerotic narrowing lesions or acute plaque rupture causing unstable angina or myocardial infarction. Compelling evidence is accumulating, stressing the role of oxidative stress in causing reduced NO bioavailability and subsequently endothelial dysfunction (ED). More recently, the role of endothelial cell (EC) apoptosis as a possible final stage of ED and plaque activation has been suggested. In vitro and in vivo evidence suggests a role of oxidative stress also as a putative mechanism finally leading to plaque denudation and activation through increased EC apoptosis. Thus, oxidative stress, irrespective of atherosclerotic disease stages, seems to represent a key phenomenon in vascular disease progression and possible prevention.

Lovastatin inhibits Rho-regulated expression of E-selectin by TNFalpha and attenuates tumor cell adhesion

E-selectin mediated cell-cell adhesion plays an important role in inflammatory processes and extravasation of tumor cells. Tumor necrosis factor-alpha (TNF-alpha) induces E-selectin gene and protein expression in primary human endothelial cells (HUVEC) and in an endothelial cell line (EA.hy-926). As shown by ELISA and FACS analyses, HMG-CoA reductase inhibitors (e.g., lovastatin) impair the TNF-alpha stimulated increase in E-selectin protein expression. Similar results were obtained for E-selectin mRNA expression and promoter activity, indicating that the effect of lovastatin is based on inhibition of gene expression. The effective inhibitory concentration of lovastatin was in a physiologically relevant range (IC50<0.1 microM). Lovastatin-mediated block of TNF-alpha induced E-selectin expression is due to inhibition of protein geranylgeranylation rather than farnesylation. Down-regulation of Rho signaling by coexpression of dominant-negative Rho mutants (i.e RhoA, RhoB and Rac) impaired TNF-alpha driven E-selectin gene expression, indicating Rho signaling to be essential for transcriptional activation of the E-selectin gene. Inhibition of E-selectin expression by lovastatin gives rise to a significant reduction in TNF-alpha stimulated adhesion of colon carcinoma cells to HUVEC. Furthermore, low concentration of lovastatin (i.e., < or =1 microM) attenuated TNF-alpha induced tumor cell invasion in vitro. The data support the view that statins might be clinically useful in protection against E-selectin mediated metastasis.

Identification of a plant nitric oxide synthase gene involved in hormonal signaling

Nitric oxide (NO) serves as a signal in plants. An Arabidopsis mutant (Atnos1) was identified that had impaired NO production, organ growth, and abscisic acid-induced stomatal movements. Expression of AtNOS1 with a viral promoter in Atnos1 mutant plants resulted in overproduction of NO. Purified AtNOS1 protein used the substrates arginine and nicotinamide adenine dinucleotide phosphate and was activated by Ca2+ and calmodulin-like mammalian endothelial nitric oxide synthase and neuronal nitric oxide synthase, yet it is a distinct enzyme with no sequence similarities to any mammalian isoform. Thus, AtNOS1 encodes a distinct nitric oxide synthase that regulates growth and hormonal signaling in plants.

TNF-alpha induces a decrease in eNOS promoter activity

We determined whether TNF-alpha induces a decrease in activity of the promoter for the endothelial nitric oxide synthase (eNOS) gene in pulmonary microvessel endothelial monolayers (PMEM). eNOS promoter activity was assessed in PMEM transfected with plasmids coding the wild-type (F1: -1600 nt from transcription start site) and truncated (F2: -1189, F4: -779, F5: -494, F6: -166) human eNOS promoters linked to a luciferase reporter. PMEM lysates were analyzed for the luciferase/galactosidase ratio (Luc/Gal) after incubation with TNF-alpha (50 ng/ml) for 0.5 or 4 h. TNF-alpha caused a decrease in the Luc/Gal ratio in the PMEM transfected with wild-type F1 and truncated F2, F4, and F5 plasmids but not with truncated F6 plasmid. Truncated-promoter analysis indicated the response elements (-370)CACCC, (-231)GATA, and (-186)CACCC may regulate the effect of TNF-alpha on the eNOS promoter. DNA-binding activity of (32)P-labeled oligonucleotide probes that span the GATA-binding site ((-239)-[(-231)GATA]-(-219)) and the two different CACCC-binding regions ((-379)-[(-370)CACCC]-(-358) and (-196)-[(-186) CACCC]-(-176)) were assessed using EMSA. In response to TNF-alpha treatment for 4 h, nuclear protein binding to (32)P oligonucleotides was characterized as: 1) a significant increase in binding to (-370)CACCC, 2) a significant decrease in binding to (-231)GATA, and 3) no change in (-186)CACCC binding. EMSA supershift analysis indicated that the transcription factor protein GATA-4 bound to the (-231)GATA site, and Sp3 bound to the (-370)CACCC site. Our data indicate TNF causes a decrease in eNOS promoter activity that may be mediated by GATA-4 and Sp3.

Current concepts in diabetic gastroparesis

Diabetic gastroparesis is a common and debilitating condition affecting millions of patients with diabetes mellitus worldwide. Although gastroparesis in diabetes has been known clinically for more than 50 years, treatment options remain very limited. Until recently, the scientific literature has offered few clues regarding the precise aetiology of gastric dysfunction in diabetes.Up to 50% of patients with diabetes may experience postprandial abdominal pain, nausea, vomiting and bloating secondary to gastric dysfunction. There is no clear association between length of disease and the onset of delayed gastric emptying. Gastroparesis affects both type 1 (insulin dependent) and type 2 (non- insulin dependent) forms of diabetes. Diagnosis requires identifying the proper symptom complex, while excluding other entities (peptic ulcer disease, rheumatological diseases, medication effects). The diagnosis of gastroparesis may be confirmed by demonstrating gastric emptying delay during a 4-hour scintigraphic study. Treatment options are limited and rely on dietary modifications, judicious use of available pharmacological agents, and occasionally surgical or endoscopic placement of gastrostomies or jejunostomies. Gastric pacing offers promise for patients with medically refractory gastroparesis but awaits further investigation. Current pharmacological agents for treating gastroparesis include metoclopramide, erythromycin, cisapride (only available via a company-sponsored programme) and domperidone (not US FDA approved). All of these drugs act as promotility agents that increase the number or the intensity of gastric contractions. These medications are not uniformly effective and all have adverse effects that limit their use. Cisapride has been removed from the open market as a result of over 200 reported cases of cardiac toxicity attributed to its use. Unfortunately, there is a paucity of clinical studies that clearly define the efficacy of these agents in diabetic gastroparesis and there are no studies that compare these drugs to each other. The molecular pathophysiology of diabetic gastroparesis is unknown, limiting the development of rational therapies. New studies, primarily in animals, point to a defect in the enteric nervous system as a major molecular cause of abnormal gastric motility in diabetes. This defect is characterised by a loss of nitric oxide signals from nerves to muscles in the gut resulting in delayed gastric emptying. Novel therapies designed to augment nitric oxide signalling are being studied.

Molecular cloning and characterization of alternatively spliced mRNA isoforms from psoriatic skin encoding a novel member of the S100 family

In an effort to identify psoriasis-associated genes, we compared gene expression in normal and psoriatic skin, using differential display RT-PCR technique. Sequence analysis of a 650-bp cDNA fragment (clone 110) that was highly up-regulated in lesional skin revealed homology to a noncoding cDNA (NICE-2). By subsequent cDNA cloning, using RNA from psoriatic skin, we have identified two alternatively spliced mRNA-isoforms (0.5 and 4.4 kb), which differ in composition of their untranslated regions. By sequence comparison, we have mapped the novel gene, named S100A15, to the S100 gene cluster within the epidermal differentiation complex (chromosome 1q21). Analysis of the deduced amino acid sequence revealed a protein of 101 amino acids containing two potential EF-hand motifs with high homology to the S100A7. Northern blot hybridization and semiquantitative RT-PCR analysis confirmed the S100A15 overexpression in psoriasis, showing different levels of expression of the S100A15 mRNA isoforms. In situ hybridization of the S100A15 revealed a markedly increased staining of basal and suprabasal epidermal layers of psoriatic skin compared with healthy tissue. Our data suggest an involvement of the novel S100A15 in epidermal differentiation and inflammation and might therefore be important for the pathogenesis of psoriasis and other diseases.

Mice with targeted disruption of p8 gene show increased sensitivity to lipopolysaccharide and DNA microarray analysis of livers reveals an aberrant gene expression response

BACKGROUND

p8 is a DNA-binding protein induced in many tissues in response to LPS treatment. Hence, p8 could be a mediator of LPS-associated effects or, on the contrary, p8 expression may be part of the protective mechanism of the tissues in response to LPS. Finally, p8 expression in response to LPS could also be a simple epiphenomenon.

METHODS

To investigate the role of p8 in vivo, we generated p8-deficient mice by gene targeting. Because p8 is a stress protein, we analyzed the response of p8-/- mice to a systemic stress induced by LPS injection. Liver was chosen as model organ to monitor alterations in gene expression.

RESULTS

LPS resulted in higher serum TNF-alpha concentration and higher mortality rate in p8-deficient mice than in wild-type. Also, liver and pancreas, but not lung, from p8-/- mice showed increased amounts of MPO and HPO. To gain insight into the molecular bases of such susceptibility, we used high density DNA microarrays consisting of ~6000 genes and ESTs to compare gene regulation in response to LPS in p8+/+ and p8-/- livers. In wild-type, 105 genes and 73 ESTs were up-regulated and 232 genes and 138 ESTs down-regulated. By contrast, 212 genes and 125 ESTs were found up-regulated and 90 genes and 85 ESTs down regulated in p8-/- mice. Among them, only 93 (51 induced and 42 repressed) corresponded to the wild-type pattern, demonstrating that p8 deficiency hinders the normal response to LPS, which may account for the increased sensitivity of p8-/-mice to the endotoxin.

CONCLUSIONS

The large number of genes showing abnormal regulation after LPS suggests that p8 is an important regulatory factor involved in many cellular defence pathways.

A technique to estimate the rate of whole body nitric oxide formation in conscious mice

OBJECTIVE

We have established a technique to estimate the total rate of nitric oxide (NO) formation in mice, based on inhalation of a stable oxygen isotope (18O(2)). Changes of NO production with age were also studied.

METHODS

The experiments were performed in eight-week- (n=6) and eight-month-old (n=6-7), respectively, female (C57/Bl6xCBAca) mice. Pairs of conscious mice were kept in an air-tight closed system allowing breathing of a mixture containing 18O(2). The 18O(2)-technique was validated by L-NAME (10mg/kg) and lipopolysaccharide (LPS, 8 mg/kg) administration. The concentrations of O(2) and CO(2) in the system were controlled and plasma nitrate analyzed by GC/MS technique.

RESULTS

NO formation was similar in young and old mice (young=7.68+/-1.47 vs. old = 6.25+/-1.49 micromol/kg/h, n.s.). Total NO production was reduced after L-NAME treatment in young animals by 91% and in old animals by 71% (p<0.05 for both), whereas LPS administration increased NO production (114+/-17%, p<0.05).Conclusion. NO formation is unaltered with age in mice. The 18O(2)-technique is a valid and specific technique to estimate whole body NO production in conscious mice.

Effects of acute hypoxia and lipopolysaccharide on nitric oxide synthase-2 expression in acute lung injury

The potential role of nitric oxide synthase-2 (NOS2) in acute lung injury (ALI) has gained increasing attention. This study evaluates the effects of hypoxia, an important feature of ALI, on NOS2 expression in a rat model of ALI caused by exposure to hypoxia and LPS. Exposure to hypoxia alone had no effect on the expression of NOS2 in rat lungs. LPS treatment resulted in a significant increase in NOS2 in the lungs, which was further enhanced by concomitant exposure to hypoxia. Immunohistochemical analysis and in situ hybridization showed no changes in the expression of NOS2 in lung resident cells under any conditions. The increase in NOS2 levels is mainly due to the influx of NOS2-expressing inflammatory cells. By morphologic analysis, these inflammatory cells were identified as neutrophils, lymphocytes, and monocytes. In vitro experiments of lung epithelial and endothelial cell lines showed no detectable expression of NOS2 with any of the treatments. In a macrophage cell line, LPS-induced NOS2 expression was not affected by the concomitant exposure to hypoxia. In conclusion, LPS increases NOS2 expression in rat lungs through the recruitment of NOS2-producing leukocytes. Simultaneous exposure to LPS and hypoxia results in a greater influx of inflammatory cells that further enhances NOS2 expression.

Constitutive NO synthase regulates the Na+/Ca2+ exchanger in human T cells: role of [Ca2+]i and tyrosine phosphorylation

For many types of cells, heat stress leads to an increase in intracellular free calcium concentration ([Ca2+](i)) that has been shown to trigger a wide variety of cellular responses. In T lymphocytes, for example, heat stress stimulates pathways that make them more susceptible to Fas/CD95-mediated apoptosis. Because of our interest in understanding more about the response of lymphocytes to various stressors, we used human peripheral and Jurkat T lymphocytes to investigate the effect of heat stress on calcium homeostasis. We found that peripheral and Jurkat T cells both exhibit cNOs activity but not iNOs activity. Heat stress increased NO production, which was inhibited by LNNA (a cNOs inhibitor) but not L-NIL (an iNOs inhibitor). Heat stress increased [Ca2+](i) in Jurkat T cells by decreasing the K(m) of the cell surface membrane Na+/Ca2+ exchanger for extracellular Ca2+. Heating also increased cNOs phosphorylation at tyrosine residues. In cells incubated with LNNA, heat stress promoted an increase in [Ca2+](i) and a decrease in [Na+](i) greater than in cells heated without LNNA, a larger decrease in K(m) of the Na+/Ca2+ exchanger for extracellular Ca2+, and decreased phosphorylation of cNOs. Our results suggest that cNOs plays an important regulatory role after heat stress. Heating appears to increase the phosphorylation of cNOs that is complexed with the Na+/Ca2+ exchanger to decrease its activity. This process is related to increased expression of Fas/CD95 on the cell surface, which might explain the apoptotic diathesis of lymphocytes after heat stress.

Nitric oxide produced by the enterocyte is involved in the cellular regulation of ion transport

The role of nitric oxide (NO) in the intestinal basal ion transport and under conditions of enterotoxin-induced ion secretion is controversial. Namely it is not clear whether NO enhances or counteracts intestinal ion secretion and whether the effects on transport result from a direct interaction with the enterocyte. The cell origin of NO is also unclear. We have tested the hypothesis that NO produced by the enterocyte directly regulates ion transport processes either in basal condition or in response to cholera toxin-induced secretion. Electrical variables reflecting transepithelial ion transport were measured in Caco-2 cell monolayers mounted in Ussing chambers exposed to the NO synthase inhibitor Nomega-nitro-l-arginine methyl ester, in the presence or absence of cholera toxin. cAMP concentrations were also measured. NO release was determined by nitrite-nitrate concentration. NO synthase activities were assayed by Western blot analysis. Nomega-nitro-l-arginine methyl ester had a secretory effect, as judged by increased basal short-circuit current and cAMP concentration. It also increased cholera toxin-induced electrical response and cAMP production. Either cholera toxin or the cAMP analog 8-bromo-cAMP induced a rapidly progressive and Ca2+-dependent increase in NO concentration, suggesting a homeostatic up-regulation of the constitutive form of NO synthase. Western blot analysis showed an increase in constitutive NO synthase enzyme isoform. These results indicate that the enterocyte regulates its own ion transport processes, either in basal condition or in the presence of active secretion, through the activation of a constitutive NO synthase-NO pathway, functioning as a braking force of cAMP-induced ion secretion.

Insulin enhances the expression of the endothelial nitric oxide synthase in native endothelial cells: a dual role for Akt and AP-1

Insulin-induced vasodilatation in vivo has been attributed to the activation of the endothelial nitric oxide (NO) synthase (eNOS). The present study addressed the effects of insulin on the activity and expression of eNOS in native and cultured endothelial cells. Insulin applied to native porcine aortic endothelial cells elicited the tyrosine phosphorylation of the insulin receptor and receptor substrate, the subsequent activation of phosphatidylinositol 3-kinase (PI 3-K), Akt (protein kinase B), and ERK1/2. Insulin did not activate eNOS in cultured endothelial cells nor relax endothelium-intact arterial segments. However, 4h after application of insulin to native endothelial cells eNOS mRNA was increased 2-fold. A comparable increase in eNOS protein was detected after 18-24h and associated with an increase in intracellular cyclic GMP. In native endothelial cells, insulin enhanced the DNA-binding activity of Sp1 and AP-1, but not that of NF-kappaB. The insulin-induced increase in eNOS expression was prevented by wortmannin as well as by AP-1 decoy oligonucleotides. The MEK1 inhibitor, PD 98059, also enhanced eNOS expression in native and cultured endothelial cells, an effect which was independent of ERK1/2 and associated with an increase in the DNA-binding activity of AP-1 and Sp1. These results demonstrate that insulin activates multiple signalling pathways in endothelial cells but does not acutely activate eNOS. Insulin however enhances eNOS mRNA and protein by a mechanism involving the combined activation of a PI 3-K- and AP-1-dependent pathway.

Genetic Models in Applied Physiology. Differential role of nitric oxide synthase isoforms in fever of different etiologies: studies using Nos gene-deficient mice

Male C57BL/6J mice deficient in nitric oxide synthase (NOS) genes (knockout) and control (wild-type) mice were implanted intra-abdominally with battery-operated miniature biotelemeters (model VMFH MiniMitter, Sunriver, OR) to monitor changes in body temperature. Intravenous injection of lipopolysaccharide (LPS; 50 microg/kg) was used to trigger fever in response to systemic inflammation in mice. To induce a febrile response to localized inflammation, the mice were injected subcutaneously with pure turpentine oil (30 microl/animal) into the left hindlimb. Oral administration (gavage) of N(G)-monomethyl-l-arginine (l-NMMA) for 3 days (80 mg. kg(-1). day(-1) in corn oil) before injection of pyrogens was used to inhibit all three NOSs (N(G)-monomethyl-d-arginine acetate salt and corn oil were used as control). In normal male C57BL/6J mice, l-NMMA inhibited the LPS-induced fever by approximately 60%, whereas it augmented fever by approximately 65% in mice injected with turpentine. Challenging the respective NOS knockout mice with LPS and with l-NMMA revealed that inducible NOS and neuronal NOS isoforms are responsible for the induction of fever to LPS, whereas endothelial NOS (eNOS) is not involved. In contrast, none of the NOS isoforms appeared to trigger fever to turpentine. Inhibition of eNOS, however, exacerbates fever in mice treated with l-NMMA and turpentine, indicating that eNOS participates in the antipyretic mechanism. These data support the hypothesis that nitric oxide is a regulator of fever. Its action differs, however, depending on the pyrogen used and the NOS isoform.

Anti-epileptic drugs as possible neuroprotectants in cerebral ischemia

Many similarities exist between cerebral ischemia and epilepsy regarding brain-damaging and auto-protective mechanisms that are activated following the injurious insult. Therefore, drugs that are effective in minimizing seizure-induced brain damage may also be useful in minimizing ischemic injury. Use of such drugs in stroke victims may have important clinical and financial advantages. Therefore, the authors conducted a Medline search of studies involving the use of anti-epileptic drugs (AEDs) as possible neuroprotectants and summarize the data. Most AEDs have been tested in animal models of focal or global ischemia and some were already tested in humans, for a possible neuroprotective effect. The existing data is rather scant and insufficient but it appears that only drugs that have multiple mechanisms of action seem to have some potential in conferring a degree of neuroprotection that could be clinically applicable to stroke patients. In conclusion, some of the newer AEDs show promise as possible neuroprotectants in the setup of acute ischemic stroke but more studies are needed before clinical trials in humans could be undertaken.

Impaired vasomodulation is associated with reduced neuronal nitric oxide synthase in skeletal muscle of ovariectomized rats

In exercising skeletal muscle, vasoconstrictor responses to alpha-adrenoceptor activation are attenuated in part by nitric oxide (NO) produced by the neuronal isoform of NO synthase (nNOS), which is expressed constitutively in skeletal muscle cells. In skeletal muscle of pregnant animals, nNOS mRNA is upregulated, suggesting that muscle nNOS expression is modulated by the steroid hormone oestrogen. Whether oestrogen-induced changes in nNOS expression have measurable effects on vasoregulation in skeletal muscle is unknown. In this study, we hypothesized that oestrogen deficiency would reduce muscle nNOS expression, resulting in impaired modulation of sympathetic vasoconstriction in exercising skeletal muscle. Compared to gonadally intact rats, we found that ovariectomized (OVX) rats were characterized by greater sympathetic vasoconstriction in contracting hindlimb and reduced nNOS, but not eNOS, in skeletal muscle. In addition, NOS inhibition resulted in a greater enhancement of sympathetic vasoconstriction in contracting hindlimbs of intact compared to OVX rats. These effects of oestrogen deficiency were prevented by chronic treatment of OVX rats with 17beta-oestradiol, but not with chronic progesterone or acute oestradiol. Further analysis revealed that skeletal muscle nNOS correlated directly with plasma 17beta-oestradiol and inversely with the magnitude of sympathetic vasoconstrictor responses in contracting hindlimbs. These data indicate that NO-dependent attenuation of sympathetic vasoconstriction in contracting skeletal muscle is impaired in oestrogen-deficient female rats, and suggest that this impairment may be mediated by reduced skeletal muscle nNOS expression.

Vascular network of the rat hippocampus is not homogeneous along the septotemporal axis

Qualitative and quantitative image analysis of hippocampal vascular bed, after transcardial perfusion of India ink, reveals significant differences among hippocampal subfields and along the septotemporal axis of the rat hippocampus. Ventral hippocampus exhibits significantly higher levels of vascularization compared to dorsal hippocampus, which, however, is characterized by significantly higher capillary density. These results may explain the selective ischemia vulnerability of hippocampus along its septotemporal axis.

Intraluminal pressure increases vascular neuronal nitric oxide synthase expression

BACKGROUND

Development of high blood pressure (BP) is associated with an increased expression of neuronal nitric oxide synthase (nNOS) in vascular smooth muscle cells.

METHODS

We investigated whether or not changes in intraluminal pressure affect nNOS expression in carotid arteries of normotensive rats. Expression of nNOS and other NOS isoforms was determined by Western blot analysis in rat carotid arteries maintained up to 24 h at different levels of intraluminal pressure in an organ culture system.

RESULTS

Expression of nNOS in arteries exposed to 80 mmHg was stable for the duration of the experiment. Increasing intraluminal pressure to 200 mmHg transiently augmented nNOS expression at 9 h, both in intact arteries and in arteries where the endothelium and the adventitia were removed. The expression of endothelial NOS (eNOS) was also augmented under similar experimental conditions, but only after 24 h exposure. The ERK1/2 kinase cascade inhibitor PD 98059 significantly impaired the expression of nNOS in arteries exposed to 200 mmHg for 9 h. However, the angiotensin AT(1) antagonist candesartan and the angiotensin converting enzyme inhibitor perindoprilat did not have any effect under the same experimental conditions. Finally, the preferential nNOS inhibitor S-methyl-L-thiocitrulline significantly augmented the contraction evoked by angiotensin II in arteries exposed to 200 mmHg, but not in those maintained at 80 mmHg intraluminal pressure for 9 h.

CONCLUSION

These results show that transmural pressure increases nNOS expression and NO release in rat smooth muscle cells by a mechanism involving the mitogen-activated protein kinase pathway, but independent from the local formation of angiotensin II.

Activation of endothelial nitric oxide synthase in contralateral testis during unilateral testicular torsion in rats

There are controversies about the injury of the contralateral testis during unilateral testicular torsion (UTT). An autonomic reflex arc between bilateral testes has been proposed. The authors focused on the involvement of nitric oxide (NO) in the contralateral testis during UTT. Eight-week-old male Wistar rats underwent unilateral torsion (1 h)-detorsion (up to 24 h). NO synthase (NOS) activity was detected as NADPH-diaphorase activity after fixation by paraformaldehyde. N-nitro-L-Arginine methyl ester (L-NAME, 20 mg/kg) was injected intravenously to the other group of rats. To evaluate the testicular injury, proteolysis of alpha-fodrin production was detected by Western blotting. Apoptosis of the germ cells was evaluated by TUNEL. Long-term effect on spermatogenesis was evaluated by flow cytometry at 60 days after UTT. Transient activation of NOS was detected following the proteolysis of alpha-fodrin in the contralateral testis. L-NAME inhibited these alterations. NADPH-diaphorase activity and eNOS immunoreactivity were co-localized in the endothelial cells. These reactions were not observed in other organs. There was neither enhanced apoptosis nor deteriorated spermatogenesis in the contralateral testis during and 60 days after UTT. In the contralateral testis, eNOS-derived NO regulates the vasomotor function against unilateral testicular torsion, whereas it acts slightly cytotoxic. These results suggest the possible involvement of a testis-specific neurovasomotor reflex between the bilateral testes.

Modulation of baroreceptor activity by gene transfer of nitric oxide synthase to carotid sinus adventitia

Administration of nitric oxide (NO) or NO donors to isolated carotid sinus and carotid bodies inhibits the activity of baroreceptor and chemoreceptor afferent nerves. Furthermore, NO synthase (NOS) is present in endothelial cells and in sensory nerves innervating the carotid sinus region. The major goal of this study was to determine whether overexpression of NOS in carotid sinus modulates baroreceptor activity. Rabbits were anesthetized, and adenoviral vectors (5 x 10(8) plaque-forming units) encoding genes for either beta-galactosidase (beta-Gal) or endothelial type III NOS (eNOS) were applied topically to the adventitial surface of one carotid sinus. In some experiments, the NOS inhibitor N(G)-nitro-l-arginine methyl ester (l-NAME) was applied to the carotid sinus immediately after the vector. Four to five days later, baroreceptor activity and carotid sinus diameter were measured from the vascularly isolated carotid sinus of the anesthetized rabbits. Transgene expression was confirmed by X-Gal staining of beta-Gal and measurement of NOS activity by citrulline assay. The expression was restricted to the carotid sinus adventitia. Baroreceptor activity was decreased significantly, and the pressure-activity curve was shifted to higher pressures in eNOS-transduced (n = 5) compared with beta-Gal-transduced (n = 5) carotid sinuses. The pressure corresponding to 50% of maximum activity averaged 55 +/- 6 and 76 +/- 7 mmHg in beta-Gal- and eNOS-transduced carotid sinuses, respectively (P < 0.05). Decreased baroreceptor activity was accompanied by a significant increase in carotid diameter in the eNOS-transduced carotid sinuses (n = 5). l-NAME prevented the inhibition of baroreceptor activity and the increase in carotid diameter in eNOS-transduced carotid sinuses (n = 5). We conclude that adenoviral-mediated gene transfer of eNOS to carotid sinus adventitia causes sustained, NO-dependent inhibition of baroreceptor activity and resetting of the baroreceptor function curve to higher pressures.

Oxidative stress and endothelial nitric oxide bioactivity

The endothelium plays an important role in the maintenance of vascular homeostasis. Central to this role is the endothelial production of nitric oxide (NO), synthesized by the constitutively expressed endothelial isoform of nitric oxide synthase. Vascular diseases, including hypertension, diabetes, and atherosclerosis, are characterized by impaired endothelium-derived NO bioactivity that may contribute to clinical cardiovascular events. Growing evidence indicates that impaired endothelium-derived NO bioactivity is due, in part, to excess vascular oxidative stress. This review outlines how different forms of oxidative stress can impact on NO bioactivity and discusses strategies to prevent oxidative stress-induced endothelial dysfunction.

The utility of melatonin in reducing cerebral damage resulting from ischemia and reperfusion

The brain is highly susceptible to focal or global ischemia. Unless ischemia is promptly reversed, reperfusion produces further cerebral damage. Acute thrombolysis or defibrinogenation is effective only in selective patients with ischemic stroke and carries a significant risk of bleeding complications. Whereas numerous neuroprotectants were shown to be effective in experimental studies, none of them have been shown to work in clinical trials. The major pathogenetic mechanisms of ischemia/reperfusion injury include excitotoxicity, disturbed calcium ion homeostasis, overproduction of nitric oxide and other free radicals, inflammation, and apoptosis. Nitric oxide and other free radicals, the key mediators of excitotoxicity and disturbed calcium ion homeostasis, cause direct injury and also indirectly damage via inflammation and apoptosis. Melatonin is a potent free radical scavenger and an indirect antioxidant. This mini review summarizes the in vivo and in vitro evidence that melatonin protects against ischemia/reperfusion injury. There is convincing evidence from the literature that melatonin treatment is highly effective in different in vivo and in vitro models of excitotoxicity or ischemia/reperfusion in multiple animal species. Melatonin is safe and non-toxic in humans, and its administration via the oral route or intravenous injection is convenient. While more experimental studies should be conducted to further explore the neuroprotective mechanisms and to document any synergistic or additive protection from combining melatonin with thrombolysis, defibrinogenation or other neuroprotectants, interested clinical scientists should consider planning phase II and III studies to confirm the benefit of melatonin as an acute stroke treatment or a preventive measure for stroke patients.

Transcription of different exons 1 of the human neuronal nitric oxide synthase gene is dynamically regulated in a cell- and stimulus-specific manner

An extensive screening of the human neuronal nitric oxide synthase (nNOS) mRNAs in various human tissues and cell lines unraveled an extreme complexity in the transcription of this gene. Using 5' rapid amplification of cDNA ends (5'-RACE), ten different exons 1 (named 1a-1l) were identified. They were spliced in a cell-specific manner to a common exon 2, which bears the translational start site. Three first exons (1d, 1g and 1f) were used predominantly for the transcription of the nNOS gene (146 out of 197 5'-RACE clones contained these exons). Exon 1k was found alone, but in many instances was interposed between exons 1b, 1d, 1g, 1i or 1j and the common exon 2. In addition to the cell-specific heterogeneity of human nNOS transcripts, nNOS is highly regulated at the transcriptional level. In resting A673 neuroepithelioma cells, the prevalent nNOS transcript was the exon 1g mRNA (with minor expression of exons 1d+1k and exon 1f mRNAs). When the cells were treated with dibutyryl-cAMP, nNOS mRNA was markedly upregulated. This upregulation was solely due to an increase in exon 1f mRNA, while the expression of the other mRNA species remained unchanged. Human HaCat keratinocyte-like cells expressed the exon 1i+1k and 1i nNOS transcripts under basal conditions. When stimulated with epidermal growth factor, only the exon 1i+1k transcript was upregulated. Although these nNOS transcripts do not differ in their translated region, the various mRNAs may trigger post-transcriptional effects such as changes in mRNA stability and translation efficiency.

Sexual dimorphism in the aging kidney: Effects on injury and nitric oxide system

BACKGROUND

Male gender confers enhanced susceptibility to development of age-dependent kidney damage. In other models of progressive renal disease, development of injury is linked to declines in renal nitric oxide synthase (NOS) capacity.

METHODS

We investigated the in vitro characteristics of the renal NOS system in young (3 to 5 months), middle-aged (11 to 13 months) and old (18 to 22 months) male and female Sprague-Dawley rats.

RESULTS

NOS activity (pmol [3H]-arginine converted to [3H]-citrulline/mg protein/minute) is reduced in the soluble fraction of renal cortex from old versus young males but not females. In contrast, NOS activity in the soluble fraction of cerebellum is not altered by age or gender. The abundance of endothelial NOS (eNOS) and neuronal (nNOS) is reduced in renal cortex of old versus young males but is unchanged in female cortex. In renal medulla, eNOS protein is reduced with age in both males and females. We found no difference in abundance of either eNOS or nNOS protein in the cortex of young male and female rats. The incidence and severity of glomerular damage increases markedly with age in the male and only slightly in the female.

CONCLUSION

These findings indicate that a relative reduction occurs in renal NOS in the male kidney with advancing age, whereas NOS protein and activity is maintained during aging in females. This, together with the marked age-dependent kidney damage seen in the male, suggests that the renal NO deficiency in the aging male rat may contribute to the age-dependent kidney damage.

Nitrergic dendrites in the superficial layers of the rat superior colliculus: retinal afferents and alternatively spliced isoforms in normal and deafferented animals

The superficial layers of the rat superior colliculus (sSC) receive innervation from the retina and include nitrergic neurons. We have shown previously that in sSC, eye enucleation reduces NADPH diaphorase staining considerably in all but the most proximal dendrites of nitrergic neurons. We have used immunocytochemistry for neuronal nitric oxide synthase (nNOS) at light and electron microscopic levels and bilateral eye enucleation with varied survival times to determine the regulatory changes imposed by the direct and indirect loss of retinal input on apparent nNOS amount and subcellular distribution. In addition, we have used SDS-PAGE and immunoblotting to test alternatively spliced isoforms in normal and deafferented animals. Our results show that unambiguously identified retinal terminals contact nitrergic neurons. In normal dendrites, nNOS immunoreactivity was distributed almost completely within the cytoplasm of the dendrite and along the postsynaptic membrane at synaptic junctions, in association with endoplasmic reticulum, ribosomes and external mitochondrial membranes. In contrast, nNOS labeling was greatly reduced in sSC deprived of retinal projections, and could only be observed in association with mitochondrial membranes and postsynaptic densities. Immunoblots of the soluble fraction from sSC revealed a surprisingly high proportion of the beta isoform with respect to the alpha counterpart in normal colliculi, suggesting an increase in isoform proportion after enucleation, or at least maintenance of the same proportion. It is suggested that ultrastructural alterations observed in sSC cells of enucleated animals may be consequent to plastic reactions of the sSC cells in response to the removal of retinal afferents.

Endothelial nitric oxide synthase variants in cystic fibrosis lung disease

Variants in the genes encoding for the nitric oxide synthases may act as disease modifier loci in cystic fibrosis, affecting both an individual's nitric oxide level and pulmonary function. In this study, the 894G/T variant in exon 7 of the endothelial nitric oxide synthase gene was related to exhaled nitric oxide and pulmonary function in 70 cystic fibrosis patients who were aged 14.8 +/- 6.9 years (mean +/- SD), with a FEV1 of 69.4 +/- 24.8% predicted. Although there was no association between endothelial nitric oxide synthase genotypes and exhaled nitric oxide in males, nitric oxide levels were significantly higher in female cystic fibrosis patients with an 894T mutant allele, compared with female patients homozygous for the 894G wild-type allele (7.0 +/- 4.4 versus 3.6 +/- 1.9 parts per billion, p = 0.02). Furthermore, in female patients, colonization of airways with Pseudomonas aeruginosa was significantly (p < 0.05) less frequent when carrying an 894T mutant allele as compared with wild type. These data suggest that the 894T variant in the endothelial nitric oxide synthase gene is associated with increased airway nitric oxide formation in female cystic fibrosis patients, possibly affecting colonization of airways with P. aeruginosa.

Endothelial nitric oxide synthase gene polymorphisms and the shedding of circulating tumour cells in the blood of prostate cancer patients

The involvement of endothelial nitric oxide synthase (ecNOS) gene polymorphisms (ecNOS4a/b and Glu-Asp298) on the shedding of tumor cells in the blood of 61 patients with prostate cancer (PCa), was analyzed. Hematogenous micrometastasis with blood circulating tumor cells (CTCs) may be an early event in the natural history of PCa metastization. CTCs can be detected by the presence of messenger RNA prostate specific membrane antigen by reverse transcription-polymerase chain reaction. We found an association between ecNOS4a/b genotypes presenting the a allele (ab/aa) with the presence of CTCs in the blood of PCa under the age of 67 years (P=0.003) and with localized disease (P=0.012). This association was not found for Glu-Asp298 genotypes. In summary, we have identified a nitric oxide related genetic factor associated with micrometastization of prostate cancer. We hypothesize that genotypes with the a allele of the ecNOS4a/b polymorphism may facilitate the survival of CTCs in the blood of cancer patients.

The NO − K+ Channel Axis in Pulmonary Arterial Hypertension

The prognosis of patients with pulmonary arterial hypertension (PAH) is poor. Available therapies (Ca(++)-channel blockers, epoprostenol, bosentan) have limited efficacy or are expensive and associated with significant complications. PAH is characterized by vasoconstriction, thrombosis in-situ and vascular remodeling. Endothelial-derived nitric oxide (NO) activity is decreased, promoting vasoconstriction and thrombosis. Voltage-gated K+ channels (Kv) are downregulated, causing depolarization, Ca(++)-overload and PA smooth muscle cell (PASMC) contraction and proliferation. Augmenting the NO and Kv pathways should cause pulmonary vasodilatation and regression of PA remodeling. Several inexpensive oral treatments may be able to enhance the NO axis and/or K+ channel expression/function and selectively decrease pulmonary vascular resistance (PVR). Oral L-Arginine, NOS' substrate, improves NO synthesis and functional capacity in humans with PAH. Most of NO's effects are mediated by cyclic guanosine-monophosphate (c-GMP). cGMP causes vasodilatation by activating K+ channels and lowering cytosolic Ca++. Sildenafil elevates c-GMP levels by inhibiting type-5 phosphodiesterase, thereby opening BK(Ca). channels and relaxing PAs. In PAH, sildenafil (50 mg-po) is as effective and selective a pulmonary vasodilator as inhaled NO. These benefits persist after months of therapy leading to improved functional capacity. 3) Oral Dichloroacetate (DCA), a metabolic modulator, increases expression/function of Kv2.1 channels and decreases remodeling and PVR in rats with chronic-hypoxic pulmonary hypertension, partially via a tyrosine-kinase-dependent mechanism. These drugs appear safe in humans and may be useful PAH therapies, alone or in combination.

Molecular mechanisms involved in the regulation of the endothelial nitric oxide synthase

The endothelial nitric oxide synthase (eNOS), the expression of which is regulated by a range of transcriptional and posttranscriptional mechanisms, generates nitric oxide (NO) in response to a number of stimuli. The physiologically most important determinants for the continuous generation of NO and thus the regulation of local blood flow are fluid shear stress and pulsatile stretch. Although eNOS activity is coupled to changes in endothelial cell Ca(2+) levels, an increase in Ca(2+) alone is not sufficient to affect enzyme activity because the binding of calmodulin (CaM) and the flow of electrons from the reductase to the oxygenase domain of the enzyme is dependent on protein phosphorylation and dephosphorylation. Two amino acids seem to be particularly important in regulating eNOS activity and these are a serine residue in the reductase domain (Ser(1177)) and a threonine residue (Thr(495)) located within the CaM-binding domain. Simultaneous alterations in the phosphorylation of Ser(1177) and Thr(495) in response to a variety of stimuli are regulated by a number of kinases and phosphatases that continuously associate with and dissociate from the eNOS signaling complex. eNOS associated proteins, such as caveolin, heat shock protein 90, eNOS interacting protein, and possibly also motor proteins provide the scaffold for the formation of the protein complex as well as its intracellular localization.

Modulation of cardiac contraction, relaxation and rate by the endothelial nitric oxide synthase (eNOS): lessons from genetically modified mice

The modulatory role of endothelial nitric oxide synthase (eNOS) on heart contraction, relaxation and rate is examined in light of recent studies using genetic deletion or overexpression in mice under specific conditions. Unstressed eNOS-/- hearts in basal conditions exhibit a normal inotropic and lusitropic function, with either decreased or unchanged heart rate. Under stimulation with catecholamines, eNOS-/- mice predominantly show a potentiation in their beta-adrenergic inotropic and lusitropic responsiveness. A similar phenotype is observed in beta 3-adrenoceptor deficient mice, pointing to a key role of this receptor subtype for eNOS coupling. The effect of eNOS on the muscarinic cholinergic modulation of cardiac function probably operates in conjunction with other NO-independent mechanisms, the persistence of which may explain the apparent dispensability of this isoform for the effect of acetylcholine in some eNOS-/- mouse strains. eNOS-/- hearts submitted to short term ischaemia-reperfusion exhibit variable alterations in systolic and diastolic function and infarct size, while those submitted to myocardial infarction present a worsened ventricular remodelling, increased 1 month mortality and loss of benefit from ACE inhibitor or angiotensin II type I receptor antagonist therapy. Although non-conditional eNOS gene deletion may engender phenotypic adaptations (e.g. ventricular hypertrophy resulting from chronic hypertension, or upregulation of the other NOS isoforms) potentially confounding the interpretation of comparative studies, the use of eNOS-/- mice has undoubtedly advanced (and will probably continue to improve) our understanding of the complex role of eNOS (in conjunction with the other NOSs) in the regulation of cardiac function. The challenge is now to confirm the emerging paradigms in human cardiac physiology and hopefully translate them into therapy.

Chronic inhibition of endothelial nitric oxide synthase activity in nucleus tractus solitarii enhances baroreceptor reflex in conscious rats

In acute experiments, we demonstrated previously that nitric oxide (NO) donors exogenously applied to the nucleus tractus solitarii (NTS) depressed the baroreceptor cardiac reflex. In this study, we determined a role for endogenous endothelial nitric oxide synthase (eNOS) activity in the NTS for chronically regulating baroreceptor reflex function in conscious rats. A recombinant adenoviral vector directing expression of a truncated form of eNOS was microinjected bilaterally into the NTS to inhibit endogenous eNOS activity. Arterial pressure was monitored continuously using radio-telemetry in freely moving animals and spontaneous baroreceptor reflex gain (sBRG) determined by a time-series method. sBRG showed a gradual increase from day 7 to 21 after gene transfer and the value at day 21 (1.68 +/- 0.20 ms mmHg(-1), n = 6) was significantly higher than that before gene transfer (1.13 +/- 0.09 ms mmHg(-1), P < 0.001). This value was also significantly higher than that in rats in which enhanced green fluorescent protein (eGFP) was expressed in the NTS (1.04 +/- 0.21 ms mmHg(-1); n = 6, P < 0.01) and saline-treated groups (1.12 +/- 0.15 ms mmHg(-1); n = 4, P < 0.05), which did not change from control levels. In addition, heart rate decreased from 336 +/- 6 to 318 +/- 8 b.p.m. (P < 0.05) 21 days after gene transfer. This value was also significantly lower than that in control groups (eGFP: 348 +/- 9 b.p.m., n = 6, P < 0.01; saline: 347 +/- 5 b.p.m., n = 4, P < 0.05). Gene transfer did not affect arterial pressure. These findings suggest that in the conscious rat eNOS is constitutively active within the NTS and is a factor regulating baroreceptor reflex gain and heart rate.

NOSTRIN: a protein modulating nitric oxide release and subcellular distribution of endothelial nitric oxide synthase

Activity and localization of endothelial nitric oxide synthase (eNOS) is regulated in a remarkably complex fashion, yet the complex molecular machinery mastering stimulus-induced eNOS translocation and trafficking is poorly understood. In a search by the yeast two-hybrid system using the eNOS oxygenase domain as bait, we have identified a previously uncharacterized eNOS-interacting protein, dubbed NOSTRIN (for eNOS traffic inducer). NOSTRIN contains a single polypeptide chain of 506-aa residues of 58 kDa with an N-terminal cdc15 domain and a C-terminal SH3 domain. NOSTRIN mRNA is abundant in highly vascularized tissues such as placenta, kidney, lung, and heart, and NOSTRIN protein is expressed in vascular endothelial cells. Coimmunoprecipitation experiments demonstrated the eNOS-NOSTRIN interaction in vitro and in vivo, and NOSTRIN's SH3 domain was essential and sufficient for eNOS binding. NOSTRIN colocalized extensively with eNOS at the plasma membrane of confluent human umbilical venous endothelial cells and in punctate cytosolic structures of CHO-eNOS cells. NOSTRIN overexpression induced a profound redistribution of eNOS from the plasma membrane to vesicle-like structures matching the NOSTRIN pattern and at the same time led to a significant inhibition of NO release. We conclude that NOSTRIN contributes to the intricate protein network controlling activity, trafficking, and targeting of eNOS.

Reduction of blood pressure, plasma cholesterol, and atherosclerosis by elevated endothelial nitric oxide

In the vascular system, nitric oxide is generated by endothelial NO synthase (eNOS). NO has pleiotropic effects, most of which are believed to be atheroprotective. Therefore, it has been argued that patients suffering from cardiovascular disease could benefit from an increase in eNOS activity. However, increased NO production can cause oxidative damage, cell toxicity, and apoptosis and hence could be atherogenic rather than beneficial. To study the in vivo effects of increased eNOS activity, we created transgenic mice overexpressing human eNOS. Aortic blood pressure was approximately 20 mm Hg lower in the transgenic mice compared with control mice because of lower systemic vascular resistance. The effects of eNOS overexpression on diet-induced atherosclerosis were studied in apolipoprotein E-deficient mice. Elevation of eNOS activity decreased blood pressure ( approximately 20 mm Hg) and plasma levels of cholesterol ( approximately 17%), resulting in a reduction in atherosclerotic lesions by 40%. We conclude that an increase in eNOS activity is beneficial and provides protection against atherosclerosis.

Rho GTPase/Rho kinase negatively regulates endothelial nitric oxide synthase phosphorylation through the inhibition of protein kinase B/Akt in human endothelial cells

Endothelial nitric oxide synthase (eNOS) is an important regulator of cardiovascular homeostasis by production of nitric oxide (NO) from vascular endothelial cells. It can be activated by protein kinase B (PKB)/Akt via phosphorylation at Ser-1177. We are interested in the role of Rho GTPase/Rho kinase (ROCK) pathway in regulation of eNOS expression and activation. Using adenovirus-mediated gene transfer in human umbilical vein endothelial cells (HUVECs), we show here that both active RhoA and ROCK not only downregulate eNOS gene expression as reported previously but also inhibit eNOS phosphorylation at Ser-1177 and cellular NO production with concomitant suppression of PKB activation. Moreover, coexpression of a constitutive active form of PKB restores the phosphorylation but not gene expression of eNOS in the presence of active RhoA. Furthermore, we show that thrombin inhibits eNOS phosphorylation, as well as expression via Rho/ROCK pathway. Expression of the active PKB reverses eNOS phosphorylation but has no effect on downregulation of eNOS expression induced by thrombin. Taken together, these data demonstrate that Rho/ROCK pathway negatively regulates eNOS phosphorylation through inhibition of PKB, whereas it downregulates eNOS expression independent of PKB.

Smad2 mediates transforming growth factor-beta induction of endothelial nitric oxide synthase expression

Transforming growth factor-beta (TGF-beta) increases expression of endothelial nitric oxide synthase (eNOS), although the precise mechanism by which it does so is unclear. We report that Smad2, a transcription factor activated by TGF-beta, mediates TGF-beta induction of eNOS in endothelial cells. TGF-beta induces Smad2 translocation from cytoplasm to nucleus, where it directly interacts with a specific region of the eNOS promoter. Overexpression of Smad2 increases basal levels of eNOS, and further increases TGF-beta stimulation of eNOS expression. Ectopic expression of Smurf, an antagonizer of Smad2, decreases Smad2 expression and blocks TGF-beta induction of eNOS. Because Smad2 can interact with a variety of transcription factors, coactivators, and corepressors, Smad2 may thus act as an integrator of multiple signals in the regulation of eNOS expression.

Nitric oxide production stimulated by the basic fibroblast growth factor requires the synthesis of ceramide

Nitric oxide (NO) is an intracellular and intercellular mediator involved in the modulation of many physiologic and pathologic processes including the regulation of neoangiogenesis. We analyzed the effects of basic fibroblast growth factor (bFGF) on NO production in CHO-K1 cells and the intracellular mechanisms involved. bFGF induces NO production through activation of the endothelial NO synthase (eNOS), causing a subsequent increase in cGMP levels. In most systems, eNOS activation is a Ca(2+)-calmodulin-dependent process. In CHO-K1 cells, NO production by bFGF is Ca(2+) and MAP kinase independent, because it was not reverted by pretreatment with intracellular Ca(2+) chelators or MEK inhibitors. Translocation of the eNOS from the plasma membrane, where it is bound to caveolin 1, to the cytosol is the crucial step in the synthesis of NO. We demonstrate that the cytosolic translocation of eNOS is caused by increased synthesis of ceramide dependent by the bFGF activation of sphingomyelinase. Indeed, in the presence of the sphingomyelinase inhibitors D609 or desipramine, bFGF-dependent NO production is abrogated. To support this evidence we evaluated ceramide concentration using HPLC-electrospray ionization-mass spectrometry in controls and in bFGF-treated cells: after bFGF stimulation, a substantial increase in ceramide levels was observed. These data were further confirmed by the lack of NO production in response to fibroblast growth factor in fibroblasts derived from Niemann Pick patients who genetically lack the enzyme sphingomyelinase. In conclusion, ceramide in CHO-K1 cells is responsible for a novel Ca(2+)/calmodulin-independent mechanism for eNOS activation after fibroblast growth factor stimulation.

Inhibitory effect of glucocorticoid on coronary artery endothelial function

Acute and chronic stresses are implicated in cardiovascular diseases including coronary artery disease. The present study was designed to examine the direct effects of the stress hormone cortisol on nitric oxide (NO) release and endothelial NO synthase (eNOS) expression in cultured bovine coronary artery endothelial cells (BCAEC). Nitrate, nitrite, and NO (NO(x)) were measured by the chemiluminescence method. At 24 h after treatment, cortisol (1 nM-10 microM) produced a dose-dependent decrease in NO(x) release, which was attenuated in the presence of the 11beta-hydroxysteroid dehydrogenase inhibitor carbenoxolone (3 microM). In accordance, eNOS protein levels were significantly decreased by cortisol in a dose-dependent manner. Cortisol pretreatment significantly increased the rate of eNOS protein degradation in the presence of cycloheximide. In addition, cortisol pretreatment decreased ATP-induced intracellular Ca(2+) elevation and NO(x) release in BCAEC. The presence of glucocorticoid receptors in BCAEC was demonstrated by Western blot. The results suggest that cortisol, through activation of glucocorticoid receptors, suppresses NO(x) release in BCAEC by downregulating eNOS proteins and inhibiting intracellular Ca(2+) mobilization. Decreased NO(x) is likely to result in an increase in contraction of coronary arteries, leading to a decrease in coronary blood flow.

Human peripheral blood polymorphonuclear leukocytes at the ovulatory period are in an activated state

The ovulatory process has been compared with inflammation. We investigated the state of female peripheral polymorphonuclear leukocytes (PMN) during menstrual cycles, and found that PMN contained high levels of superoxide, hydrogen peroxide and nitric oxide (NO) during at the peri-ovulatory period. Assuming the cause of this elevation to be a luteinizing hormone (LH), the surge of which preceded the ovulation, we examined the responsiveness of PMN to pituitary LH. The results revealed that this hormone elevated dose-dependently the production of reactive oxygen intermediates (ROI). Furthermore, we demonstrated the mRNA expression of LH receptors and their presence on PMN. The data indicated that the LH surge before on the ovulatory day resulted in general activation of PMN, suggesting that this state of PMN may be a necessary step for initiation of ovulation, rather than a defensive role against infection.