Tetrahydrobiopterin synthesis is induced by LPS in vascular smooth muscle and is rate-limiting for nitric oxide production

Probiotic, Bacillus subtilis E20 alters the immunity of white shrimp, Litopenaeus vannamei via glutamine metabolism and hexosamine biosynthetic pathway

The purpose of this study was to profile the mechanisms of action of probiotic, Bacillus subtilis E20 in activating the immunity of white shrimp, Litopenaeus vannamei. Two groups of shrimp were studied. One group was fed a control diet without probiotic supplementation and the other was fed a probiotic-containing diet at a level of 10⁹ cfu kg diet^-1. After the 8-week feeding regimen, the metabolite composition in the hepatopancreas of shrimp were investigated using ¹H nuclear magnetic resonance (¹H NMR) based metabolomic analysis. Results from the ¹H NMR analysis revealed that 16 hepatopancreatic metabolites were matched and identified among groups, of which 2 metabolites, creatinine and glutamine were significantly higher in probiotic group than in the control group. This result was confirmed by the reverse-phase high-performance liquid chromatography (RP-HPLC) and spectrophotometric analysis. Transcriptome analysis indicated the expressions of 10 genes associated with antioxidant enzymes, pattern recognition proteins and antimicrobial molecules, more active expression in the shrimp fed a diet supplemented with probiotic as compared to that of shrimp in control. In addition, the expressions of 4 genes involved with hexosamine biosynthesis pathway (HBP) and UDP-N-acetylglucosamine-peptide N-acetylglucosaminyltransferase for protein O-glycosylation were also higher in hepatopancreas of probiotic-treated shrimp than in shrimp fed a control diet. Western blot and enzyme-linked immunosorbent assay showed that heat shock factor 1, heat shock protein 70, and protein O-glycosylation in hepatopancreas were higher in probiotic group than the control group. These findings suggest that probiotic, B. subtilis E20 promotes the digestibility of glutamine in the diet, and that the increased glutamine in shrimp can be used as fuel for immune cells or may be used to regulate immune molecule expressions and protein O-glycosylation via the HBP to increase protein O-glycosylation, thereby improving the health of shrimp.

Gasotransmitter Heterocellular Signaling

SIGNIFICANCE

The family of gasotransmitter molecules, nitric oxide (NO), carbon monoxide (CO), and hydrogen sulfide (H₂S), has emerged as an important mediator of numerous cellular signal transduction and pathophysiological responses. As such, these molecules have been reported to influence a diverse array of biochemical, molecular, and cell biology events often impacting one another. Recent Advances: Discrete regulation of gasotransmitter molecule formation, movement, and reaction is critical to their biological function. Due to the chemical nature of these molecules, they can move rapidly throughout cells and tissues acting on targets through reactions with metal groups, reactive chemical species, and protein amino acids.

CRITICAL ISSUES

Given the breadth and complexity of gasotransmitter reactions, this field of research is expanding into exciting, yet sometimes confusing, areas of study with significant promise for understanding health and disease. The precise amounts of tissue and cellular gasotransmitter levels and where they are formed, as well as how they react with molecular targets or themselves, all remain poorly understood.

FUTURE DIRECTIONS

Elucidation of specific molecular targets, characteristics of gasotransmitter molecule heterotypic interactions, and spatiotemporal formation and metabolism are all important to better understand their true pathophysiological importance in various organ systems. Antioxid. Redox Signal. 26, 936-960.

Nitric oxide production by endotoxin preparations in TLR4-deficient mice

Sepsis and septic shock result from an exacerbated systemic inflammatory reaction to infection. Their incidence is rising, and they have recently become the main cause of death in intensive care units. Septic shock is defined as sepsis accompanied by life-threatening refractory hypotension, for which excessive nitric oxide (NO), produced by inducible NO synthase iNOS, is thought responsible. LPS, a vital outer membrane component of Gram-negative bacteria, mimics most of the septic effects and is widely used as a model for septic shock. TLR4 is the signal-transducing receptor for LPS, evidenced by the resistance of TLR4-deficient C3H/HeJ and C57BL/10ScNJ mice. As expected, we found that TLR4 deficiency precludes LPS-induced cytokine production, independent of the purity of the LPS preparation. However, various conventional LPS preparations induced NO in TLR4-deficient mice to the same level as in control animals, while ultrapure LPS did not, indicating the presence of NO-producing contaminant(s). Nevertheless, despite identical iNOS induction pattern and systemic NO levels, the contaminant does not cause hypotension, hypothermia, or any other sign of morbidity. Using mice deficient for TLR2, TRL3, TLR4, TRL2x4, TLR9, MyD88 or TRIF, we found that the contaminant signals via TLR2 and MyD88. In conclusion, conventional LPS preparations generally used in endotoxic shock research contain TLR2 agonists that induce iNOS and high levels of systemic NO as such, and synergize with LPS towards the production of pro-inflammatory cytokines, morbidity and mortality. Surprisingly, the excessive iNOS-derived systemic NO production induced by impure LPS in TLR4⁻/⁻ is not accompanied by hypotension or morbidity.

Nitric oxide synthases in heart failure

SIGNIFICANCE

The regulation of myocardial function by constitutive nitric oxide synthases (NOS) is important for the maintenance of myocardial Ca(2+) homeostasis, relaxation and distensibility, and protection from arrhythmia and abnormal stress stimuli. However, sustained insults such as diabetes, hypertension, hemodynamic overload, and atrial fibrillation lead to dysfunctional NOS activity with superoxide produced instead of NO and worse pathophysiology.

RECENT ADVANCES

Major strides in understanding the role of normal and abnormal constitutive NOS in the heart have revealed molecular targets by which NO modulates myocyte function and morphology, the role and nature of post-translational modifications of NOS, and factors controlling nitroso-redox balance. Localized and differential signaling from NOS1 (neuronal) versus NOS3 (endothelial) isoforms are being identified, as are methods to restore NOS function in heart disease.

CRITICAL ISSUES

Abnormal NOS signaling plays a key role in many cardiac disorders, while targeted modulation may potentially reverse this pathogenic source of oxidative stress.

FUTURE DIRECTIONS

Improvements in the clinical translation of potent modulators of NOS function/dysfunction may ultimately provide a powerful new treatment for many hearts diseases that are fueled by nitroso-redox imbalance.

Synthesis and recycling of tetrahydrobiopterin in endothelial function and vascular disease

Nitric oxide, generated by the nitric oxide synthase (NOS) enzymes, plays pivotal roles in cardiovascular homeostasis and in the pathogenesis of cardiovascular disease. The NOS cofactor, tetrahydrobiopterin (BH4), is an important regulator of NOS function, since BH4 is required to maintain enzymatic coupling of L-arginine oxidation, to produce NO. Loss or oxidation of BH4 to 7,8-dihydrobiopterin (BH2) is associated with NOS uncoupling, resulting in the production of superoxide rather than NO. In addition to key roles in folate metabolism, dihydrofolate reductase (DHFR) can 'recycle' BH2, and thus regenerate BH4. It is therefore likely that net BH4 cellular bioavailability reflects the balance between de novo BH4 synthesis, loss of BH4 by oxidation to BH2, and the regeneration of BH4 by DHFR. Recent studies have implicated BH4 recycling in the direct regulation of eNOS uncoupling, showing that inhibition of BH4 recycling using DHFR-specific siRNA and methotrexate treatment leads to eNOS uncoupling in endothelial cells and the hph-1 mouse model of BH4 deficiency, even in the absence of oxidative stress. These studies indicate that not only BH4 level, but the recycling pathways regulating BH4 bioavailability represent potential therapeutic targets and will be discussed in this review.

GTP cyclohydrolase I expression, protein, and activity determine intracellular tetrahydrobiopterin levels, independent of GTP cyclohydrolase feedback regulatory protein expression

GTP cyclohydrolase I (GTPCH) is a key enzyme in the synthesis of tetrahydrobiopterin (BH4), a required cofactor for nitricoxide synthases and aromatic amino acid hydroxylases. Alterations of GTPCH activity and BH4 availability play an important role in human disease. GTPCH expression is regulated by inflammatory stimuli, in association with reduced expression of GTP cyclohydrolase feedback regulatory protein (GFRP). However, the relative importance of GTPCH expression versus GTPCH activity and the role of GFRP in relation to BH4 bioavailability remain uncertain. We investigated these relationships in a cell line with tet-regulated GTPCH expression and in the hph-1 mouse model of GTPCH deficiency. Doxycycline exposure resulted in a dose-dependent decrease in GTPCH protein and activity, with a strong correlation between GTPCH expression and BH4 levels (r(2) = 0.85, p < 0.0001). These changes in GTPCH and BH4 had no effect on GFRP expression or protein levels. GFRP overexpression and knockdown in tet-GCH cells did not alter GTPCH activity or BH4 levels, and GTPCH-specific knockdown in sEnd.1 endothelial cells had no effect on GFRP protein. In mouse liver we observed a graded reduction of GTPCH expression, protein, and activity, from wild type, heterozygote, to homozygote littermates, with a striking linear correlation between GTPCH expression and BH4 levels (r(2) = 0.82, p < 0.0001). Neither GFRP expression nor protein differed between wild type, heterozygote, nor homozygote mice, despite the substantial differences in BH4. We suggest that GTPCH expression is the primary regulator of BH4 levels, and changes in GTPCH or BH4 are not necessarily accompanied by changes in GFRP expression.

Downregulation by lipopolysaccharide of Notch signaling, via nitric oxide

The Notch signaling pathway appears to perform an important function in inflammation. Here, we present evidence to suggest that lipopolysaccharide (LPS) suppresses Notch signaling via the direct modification of Notch by the nitration of tyrosine residues in macrophages. In the RAW264.7 macrophage cell line and in rat primary alveolar macrophages, LPS was found to inhibit Notch1 intracellular domain (Notch1-IC) transcription activity, which could then be rescued by treatment with N(G)-nitro-l-arginine, a nitric oxide synthase (NOS) inhibitor. Nitric oxide (NO), which was produced in cells that stably express endothelial NOS (eNOS) and brain NOS (bNOS), also induced the inhibition of Notch1 signaling. The NO-induced inhibition of Notch1 signaling remained unchanged after treatment with 1H-[1,2,4]oxadiazolo[4,3-alpha]quinoxalin-1-one (ODQ), a guanylyl-cyclase inhibitor, and was not found to be mimicked by 8-bromo-cyclic GMP in the primary alveolar macrophages. With regards to the control of Notch signaling, NO appears to have a significant negative influence, via the nitration of Notch1-IC, on the binding that occurs between Notch1-IC and RBP-Jk, both in vitro and in vivo. By intrinsic fluorescence, we also determined that nitration could mediate conformational changes of Notch1-IC. The substitution of phenylalanine for tyrosine at residue 1905 in Notch1-IC abolished the nitration of Notch1-IC by LPS. Overall, our data suggest that an important relationship exists between LPS-mediated inflammation and the Notch1 signaling pathway, and that this relationship intimately involves the nitration of Notch1-IC tyrosine residues.

Transcriptional profiling of the peripheral blood response during tularemia

Tularemia is a febrile disease caused by the highly contagious bacterium Francisella tularensis. We undertook an analysis of the transcriptional response in peripheral blood during the course of ulceroglandular tularemia by use of Affymetrix microarrays comprising 14,500 genes. Samples were obtained from seven individuals at five occasions during 2 weeks after the first hospital visit and convalescent samples 3 months later. In total, 265 genes were differentially expressed, 95 of which at more than one time point. The differential expression was verified with real-time quantitative polymerase chain reaction for 36 genes (R(2)=0.590). The most prominent changes were noted in samples drawn on days 2-3 and a considerable proportion of the upregulated genes appeared to represent an interferon-gamma-induced response and also a proapoptotic response. Genes involved in the generation of innate and acquired immune responses were found to be downregulated, presumably a pathogen-induced event. A logistic regression analysis revealed that seven genes were good predictors of the early phase of tularemia. This is the first description of the transcriptional host response to ulceroglandular tularemia and the study has identified gene subsets relevant to the pathogenesis of the disease and subsets that may serve as early diagnostic biomarkers.

Manganese modulates pro-inflammatory gene expression in activated glia

Redox-active metals are of paramount importance for biological functions. Their impact and cellular activities participate in the physiological and pathophysiological processes of the central nervous system (CNS), including inflammatory responses. Manganese is an essential trace element and it is required for normal biological activities and ubiquitous enzymatic reactions. However, excessive chronic exposure to manganese results in neurobehavioral deficits. Recent evidence suggests that manganese neurotoxicity involves activation of microglia or astrocytes, representative CNS immune cells. In this study, we assessed the molecular basis of the effects of manganese on the modulation of pro-inflammatory cytokines and nitric oxide (NO) production in primary rat cortical glial cells. Cultured glial cells consisted of 85% of astrocytes and 15% of microglia. Within the assayed concentrations, manganese was unable to induce tumor necrosis factor alpha (TNF-alpha) and inducible nitric oxide synthase (iNOS) expression, whereas it potentiated iNOS and TNF-alpha gene expression by lipopolysaccharide/interferon-gamma-activated glial cells. The enhancement was accompanied by elevation of free manganese, generation of oxidative stress, activation of mitogen-activated protein kinases, and increased NF-kappaB and AP-1 binding activities. The potentiated degradation of inhibitory molecule IkappaB-alpha was one of underlying mechanisms for the increased activation of NF-kappaB by manganese. However, manganese decreased iNOS enzymatic activity possibly through the depletion of cofactor since exogenous tetrahydrobiopterin reversed manganese's action. These data indicate that manganese could modulate glial inflammation through variable strategies.

Argininosuccinate Synthetase is Reversibly Inactivated by S-Nitrosylation in Vitro and in Vivo

Prior studies have demonstrated that the substrate for NO synthesis, l-arginine, can be regenerated from the NOS co-product l-citrulline. This requires the sequential action of two enzymes, argininosuccinate synthetase (AS) and argininosuccinate lyase (AL). AS activity has been shown to be rate-limiting for high output NO synthesis by immunostimulant-activated cells and represents a potential site for metabolic control of NO synthesis. We now demonstrate that NO mediates reversible S-nitrosylation and inactivation of AS in vitro and in lipopolysaccharide-treated cells and mice. Using a novel mass spectrometry-based method, we show that Cys-132 in human AS is the sole target for S-nitrosylation among five Cys residues. Mutagenesis studies confirm that S-nitrosylation of Cys-132 is both necessary and sufficient for the inhibition of AS by NO donors. S-nitroso-AS content is regulated by cellular glutathione levels and selectively influences NO production when citrulline is provided to cells as a protosubstrate of NOS but not when l-arginine is provided. A phylogenetic comparison of AS sequences suggests that Cys-132 evolved as a site for post-translational regulation of activity in the AS in NOS-expressing species, endowing NO with the capacity to limit its own synthesis by restricting arginine availability.

Diminished production of nitric oxide synthase cofactor tetrahydrobiopterin by rosiglitazone in adipocytes

Increased nitric oxide (NO) synthesis has been proposed to participate in the generation of insulin resistance in adipose and muscle tissues. Therefore, we examined the potential rate-limiting role of tetrahydrobiopterin (BH4) in cytokine-induced NO synthesis, and the effect of peroxisome proliferator activated receptor-gamma (PPARgamma) activation using the insulin-sensitizer rosiglitazone on cytokine-induced BH4 synthesis in 3T3-L1 adipocytes. Our data indicate that modulated availability of the mandatory nitric oxide synthase (NOS) cofactor BH4 affected cytokine-induced NO generation. Semiquantitative linear range reverse transcription polymerase chain reaction (RT-PCR) analysis demonstrated that rosiglitazone not only reduced inducible nitric oxide synthase (iNOS) mRNA transcription, but also guanosine triphosphate cyclohydrolase (GTPCH), the rate-limiting and controlling step of BH4 synthesis. Accordingly, intracellular BH4 concentration was reduced by 45% following rosiglitazone treatment. Furthermore, we observed a transient inhibitory effect of natural PPARgamma ligand 15-deoxy-Delta(12,14)-prostaglandin J2 (15d-PJ2) on cytokine-mediated iNOS and GTPCH induction. Thus, the inhibition of cytokine-induced NO synthesis by rosiglitazone is at least in part attributable to reduced availability of BH4, the synthesis of which might represent a potential new target in the treatment of type 2 diabetes and insulin resistance.

Stimulation of tetrahydrobiopterin synthesis by cyclosporin A in mouse brain microvascular endothelial cells

We examined the effect of the immunosuppressant, cyclosporin A (CsA) on the synthesis of tetrahydrobiopterin (BH4), a cofactor for nitric oxide (NO) synthase and a scavenger of reactive oxygen species (ROS), in mouse brain microvascular endothelial cells. Treatment with CsA increased the BH4 content and the expression of mRNA level of GTP cyclohydrolase I, the rate-limiting enzyme of BH4 synthesis. 2,4-Diamino-6-hydroxypyrimidine, an inhibitor of GTP cyclohydrolase I, strongly reduced the CsA-induced increase in BH4 content. Cycloheximide (CHX), a protein synthesis inhibitor, also reduced CsA-induced BH4 synthesis. These findings suggest that CsA stimulates BH4 synthesis via a de novo pathway with the induction of GTP cyclohydrolase I. Moreover, CsA-induced the mRNA level of the inducible type of NO synthase, and stimulated the L-citrulline formation from L-arginine, which is a marker for NO synthesis. The CsA-stimulated L-citrulline formation was attenuated by the co-treatment with GTP cyclohydrolase I inhibitor. The expression of the endothelial type of NO synthase was low under basal condition, and was not affected by the treatment with CsA. These findings suggest that increase in BH4 content induced by CsA is coupled with NO production by inducible type of NO synthase.

An inducible nitric-oxide synthase (NOS)-associated protein inhibits NOS dimerization and activity

A variety of transcriptional and post-transcriptional mechanisms regulate the expression of the inducible nitric-oxide synthase (iNOS, or NOS2). Although neurons and endothelial cells express proteins that interact with and inhibit neuronal NOS and endothelial NOS, macrophage proteins that inhibit NOS2 have not been identified. We show that murine macrophages express a 110-kDa protein that interacts with NOS2, which we call NOS-associated protein-110 kDa (NAP110). NAP110 directly interacts with the amino terminus of NOS2, and inhibits NOS catalytic activity by preventing formation of NOS2 homodimers. Expression of NAP110 may be a mechanism by which macrophages expressing NOS2 protect themselves from cytotoxic levels of nitric oxide.

Regulation of 6-pyruvoyltetrahydropterin synthase activity and messenger RNA abundance in human vascular endothelial cells

BACKGROUND

The nitric oxide synthase cofactor tetrahydrobiopterin (BH4) is involved in the regulation of endothelium-dependent vascular functions mediated by nitric oxide. Vascular endothelial cells synthesize and secrete large amounts of BH4 on cytokine activation. There is scant knowledge about molecular mechanisms of cytokine-triggered BH4 production in endothelial cells.

METHODS AND RESULTS

Pteridine production, mRNA expression of GTP cyclohydrolase (GTPCH) and 6-pyruvoyltetrahydropterin synthase (PTPS) (both key enzymes of BH4 biosynthesis), and PTPS activity were studied in human umbilical vein endothelial cells (HUVECs) exposed to inflammatory cytokines. BH4 levels were </=140-fold enhanced on treatment of HUVECs with combined interferon-gamma/tumor necrosis factor-alpha/interleukin-1 (IFN/TNF/IL-1). Specific PTPS activity was approximately 3-fold higher in cytokine-treated HUVECs than in untreated cells. Reverse-transcription/limiting-dilution polymerase chain reaction analysis showed that in response to IFN/TNF/IL-1, mRNA abundance of GTPCH and PTPS was increased approximately 64-fold and 10-fold, respectively.

CONCLUSIONS

The present study demonstrates for the first time the cytokine-dependent regulation of PTPS, the second enzyme in BH4 synthesis. Although GTPCH is believed to be the rate-limiting step, control of endothelial PTPS expression by cytokines may play an important role in regulating BH4-dependent nitric oxide production in the vascular system.