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Crabtree MJ, Channon KM. Synthesis and recycling of tetrahydrobiopterin in endothelial function and vascular disease. Nitric Oxide 2011; 25:81-8. [PMID: 21550412 PMCID: PMC5357050 DOI: 10.1016/j.niox.2011.04.004] [Citation(s) in RCA: 148] [Impact Index Per Article: 11.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/04/2010] [Revised: 04/14/2011] [Accepted: 04/17/2011] [Indexed: 01/08/2023]
Abstract
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.
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Ge ZD, Ionova IA, Vladic N, Pravdic D, Hirata N, Vásquez-Vivar J, Pratt PF, Warltier DC, Pieper GM, Kersten JR. Cardiac-specific overexpression of GTP cyclohydrolase 1 restores ischaemic preconditioning during hyperglycaemia. Cardiovasc Res 2011; 91:340-9. [PMID: 21422102 PMCID: PMC3125073 DOI: 10.1093/cvr/cvr079] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/02/2010] [Revised: 03/07/2011] [Accepted: 03/16/2011] [Indexed: 02/07/2023] Open
Abstract
AIMS Hyperglycaemia (HG) decreases intracellular tetrahydrobiopterin (BH(4)) concentrations, and this action may contribute to injury during myocardial ischaemia and reperfusion. We investigated whether increased BH(4) by cardiomyocyte-specific overexpression of the GTP cyclohydrolase (GTPCH) 1 gene rescues myocardial and mitochondrial protection by ischaemic preconditioning (IPC) during HG through a nitric oxide (NO)-dependent pathway. METHODS AND RESULTS Mice underwent 30 min of myocardial ischaemia followed by 2 h of reperfusion with or without IPC elicited with four cycles of 5 min ischaemia/5 min of reperfusion in the presence or absence of HG produced by d-glucose. In C57BL/6 wild-type mice, IPC increased myocardial BH(4) and NO concentrations and decreased myocardial infarct size (30 ± 3% of risk area) compared with control (56 ± 5%) experiments. This protective effect was inhibited by HG (48 ± 3%) but not hyperosmolarity. GTPCH-1 overexpression increased myocardial BH(4) and NO concentrations and restored cardioprotection by IPC during HG (32 ± 4%). In contrast, a non-selective NO synthase inhibitor N(G)-nitro-l-arginine methyl ester attenuated the favourable effects of GTPCH-1 overexpression (52 ± 3%) during HG. Mitochondria isolated from myocardium subjected to IPC required significantly higher in vitro Ca(2+) concentrations (184 ± 14 µmol mg(-1) protein) to open the mitochondrial permeability transition pore when compared with mitochondria isolated from control experiments (142 ± 10 µmol mg(-1) protein). This beneficial effect of IPC was reversed by HG and rescued by GTPCH-1 overexpression. CONCLUSION Increased BH(4) by cardiomyocyte-specific overexpression of GTPCH-1 preserves the ability of IPC to elicit myocardial and mitochondrial protection that is impaired by HG, and this action appears to be dependent on NO.
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Chen W, Li L, Brod T, Saeed O, Thabet S, Jansen T, Dikalov S, Weyand C, Goronzy J, Harrison DG. Role of increased guanosine triphosphate cyclohydrolase-1 expression and tetrahydrobiopterin levels upon T cell activation. J Biol Chem 2011; 286:13846-51. [PMID: 21343293 PMCID: PMC3077585 DOI: 10.1074/jbc.m110.191023] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/02/2010] [Revised: 01/25/2011] [Indexed: 12/27/2022] Open
Abstract
Tetrahydrobiopterin (BH(4)) is an essential co-factor for the nitric-oxide (NO) synthases, and in its absence these enzymes produce superoxide (O(2)(·-)) rather than NO. The rate-limiting enzyme for BH(4) production is guanosine triphosphate cyclohydrolase-1 (GTPCH-1). Because endogenously produced NO affects T cell function, we sought to determine whether antigen stimulation affected T cell GTPCH-1 expression and ultimately BH(4) levels. Resting T cells had minimal expression of inducible NOS (NOS2), endothelial NOS (NOS3), and GTPCH-1 protein and nearly undetectable levels of BH(4). Anti-CD3 stimulation of T cells robustly stimulated the coordinated expression of NOS2, NOS3, and GTPCH-1 and markedly increased both GTPCH-1 activity and T cell BH(4) levels. The newly expressed GTPCH-1 was phosphorylated on serine 72 and pharmacological inhibition of casein kinase II reduced GTPCH-1 phosphorylation and blunted the increase in T cell BH(4). Inhibition of GTPCH-1 with diaminohydroxypyrimidine (1 mmol/liter) prevented T cell BH(4) accumulation, reduced NO production, and increased T cell O(2)(·-) production, due to both NOS2 and NOS3 uncoupling. GTPCH-1 inhibition also promoted TH(2) polarization in memory CD4 cells. Ovalbumin immunization of mice transgenic for an ovalbumin receptor (OT-II mice) confirmed a marked increase in T cell BH(4) in vivo. These studies identify a previously unidentified consequence of T cell activation, promoting BH(4) levels, NO production, and modulating T cell cytokine production.
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Berbee M, Fu Q, Boerma M, Pathak R, Zhou D, Kumar KS, Hauer-Jensen M. Reduction of radiation-induced vascular nitrosative stress by the vitamin E analog γ-tocotrienol: evidence of a role for tetrahydrobiopterin. Int J Radiat Oncol Biol Phys 2011; 79:884-91. [PMID: 20950957 PMCID: PMC3023840 DOI: 10.1016/j.ijrobp.2010.08.032] [Citation(s) in RCA: 42] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/05/2010] [Revised: 08/19/2010] [Accepted: 08/20/2010] [Indexed: 01/13/2023]
Abstract
PURPOSE The vitamin E analog γ-tocotrienol (GT3) is a powerful radioprotector. GT3 reduces postradiation vascular peroxynitrite production, an effect dependent on inhibition of hydroxy-methylglutaryl-coenzyme A reductase. Hydroxy-methylglutaryl-coenzyme A reductase inhibitors mediate their pleiotropic effects via endothelial nitric oxide synthase that requires the cofactor tetrahydrobiopterin (BH4). This study investigated the effects of radiation on BH4 bioavailability and of GT3 on BH4 metabolism. METHODS AND MATERIALS Mice were exposed to 8.5 Gy of total body irradiation (TBI). Lung BH4 and total biopterin concentrations were measured 0, 3.5, 7, 14, and 21 days after TBI by use of differential oxidation followed by high-performance liquid chromatography. The effect of exogenous GT3 and BH4 treatment on postradiation vascular oxidative stress and bone marrow colony-forming units were assessed in vivo. The effect of GT3 on endothelial cell apoptosis and endothelial expression of guanosine triphosphate (GTP) cyclohydrolase 1 (GTPCH), GTPCH feedback regulatory protein (GFRP), GFRP transcription, GFRP protein levels, and GFRP-GTPCH protein binding was determined in vitro. RESULTS Compared with baseline levels, lung BH4 concentrations decreased by 24% at 3.5 days after TBI, an effect that was reversed by GT3. At 14 and 21 days after TBI, compensatory increases in BH4 (58% and 80%, respectively) were observed. Relative to vehicle-treated controls, both GT3 and BH4 supplementation reduced postirradiation vascular peroxynitrite production at 3.5 days (by 66% and 33%, respectively), and BH4 resulted in a 68% increase in bone marrow colony-forming units. GT3 ameliorated endothelial cell apoptosis and reduced endothelial GFRP protein levels and GFRP-GTPCH binding by decreasing transcription of the GFRP gene. CONCLUSIONS BH4 bioavailability is reduced in the early postradiation phase. Exogenous administration of BH4 reduces postirradiation vascular oxidative stress. GT3 potently reduces the expression of GFRP, one of the key regulatory proteins in the BH4 pathway, and may thus exert some of its beneficial effects on postradiation free radical production partly by counteracting the decrease in BH4.
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Kang KT, Sullivan JC, Spradley FT, d'Uscio LV, Katusic ZS, Pollock JS. Antihypertensive therapy increases tetrahydrobiopterin levels and NO/cGMP signaling in small arteries of angiotensin II-infused hypertensive rats. Am J Physiol Heart Circ Physiol 2011; 300:H718-24. [PMID: 21148769 PMCID: PMC3064310 DOI: 10.1152/ajpheart.00393.2010] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/20/2010] [Accepted: 12/07/2010] [Indexed: 02/07/2023]
Abstract
We previously reported that small mesenteric arteries from hypertensive rats have increased NOS-derived H(2)O(2) and reduced NO/cGMP signaling. We hypothesized that antihypertensive therapy lowers blood pressure through a tetrahydrobiopterin (BH(4))-dependent mechanism restoring NO/cGMP signaling and endothelial NOS (NOS3; eNOS) phosphorylation in small arteries. To test this hypothesis, small mesenteric arteries from normotensive rats (NORM), angiotensin II-infused rats (ANG), ANG rats with triple therapy (reserperine, hydrochlorothiazide, and hydralazine), or ANG rats with oral BH(4) therapy were studied. Both triple therapy and oral BH(4) therapy attenuated the rise in systolic blood pressure in ANG rats and restored NO/cGMP signaling in small arteries similarly. Triple therapy significantly increased vascular BH(4) levels and BH(4)-to-BH(2) ratio similar to ANG rats with BH(4) supplementation. Furthermore, triple therapy (but not oral BH(4) therapy) significantly increased GTP cyclohydrolase I (GTPCH I) activity in small arteries without a change in expression. NOS3 phosphorylation at Ser1177 was reduced in small arteries from ANG compared with NORM, while NOS3 phosphorylation at Ser633 and Thr495 were similar in ANG and NORM. NOS3 phosphorylation at Ser1177 was restored with triple therapy or oral BH(4) in ANG rats. In conclusion, antihypertensive therapy regulates NO/cGMP signaling in small arteries through increasing BH(4) levels and NOS3 phosphorylation at Ser1177.
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Stephens LL, Shonhai A, Blatch GL. Co-expression of the Plasmodium falciparum molecular chaperone, PfHsp70, improves the heterologous production of the antimalarial drug target GTP cyclohydrolase I, PfGCHI. Protein Expr Purif 2011; 77:159-65. [PMID: 21262365 DOI: 10.1016/j.pep.2011.01.005] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/19/2010] [Revised: 01/17/2011] [Accepted: 01/18/2011] [Indexed: 11/19/2022]
Abstract
Molecular chaperones have been used for the improved expression of target proteins within heterologous systems; however, the chaperone and target protein have seldom been matched in terms of origin. We have developed a heterologous co-expression system that allows independent expression of the plasmodial chaperone, PfHsp70, and a plasmodial target protein. In this study, the target was Plasmodium falciparum GTP cyclohydrolase I (PfGCHI), the first enzyme in the plasmodial folate pathway. The sequential expression of the molecular chaperone followed by the target protein increased the expression of soluble functional PfGCHI. His-tagged PfGCHI was successfully purified using nickel affinity chromatography, and the specific activity was determined by high performance liquid chromatography with spectrofluorometeric detection to be 5.93nmol/h/mg. This is the first report of a heterologous co-expression system in which a plasmodial chaperone is harnessed for the improved production and purification of a plasmodial target protein.
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Ferdousy F, Bodeen W, Summers K, Doherty O, Wright O, Elsisi N, Hilliard G, O'Donnell JM, Reiter LT. Drosophila Ube3a regulates monoamine synthesis by increasing GTP cyclohydrolase I activity via a non-ubiquitin ligase mechanism. Neurobiol Dis 2010; 41:669-77. [PMID: 21147225 DOI: 10.1016/j.nbd.2010.12.001] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/26/2010] [Revised: 11/13/2010] [Accepted: 12/02/2010] [Indexed: 11/18/2022] Open
Abstract
The underlying defects in Angelman syndrome (AS) and autism spectrum disorder (ASD) may be in part due to basic defects in synaptic plasticity and function. In some individuals serotonin reuptake inhibitors, which decrease pre-synaptic re-uptake of serotonin, can ameliorate symptoms, as can resperidone, which blocks both dopamine and serotonin receptors. Loss of maternal UBE3A expression causes AS, while maternal duplications of chromosome 15q11.2-q13 that include the UBE3A gene cause ASD, implicating the maternally expressed UBE3A gene in the ASD phenotype. In a Drosophila screen for proteins regulated by UBE3A, we identified a key regulator of monoamine synthesis, the gene Punch, or GCH1, encoding the enzyme GTP cyclohydrolase I. Here we show that Dube3a, the fly UBE3A orthologue, regulates Punch/GCH1 in the fly brain. Over-expression of Dube3a elevates tetrahydrobiopterin (THB), the rate-limiting cofactor in monoamine synthesis while loss of Dube3a has the opposite effect. The fluctuations in dopamine levels were associated with hyper- and hypoactivity, respectively, in flies. We show that changes in Punch/GCH1 and dopamine levels do not depend on the ubiquitin ligase catalytic domain of Dube3a. In addition, both wild type Dube3a and a ubiquitination-defective Dube3a-C/A form were found at high levels in nuclear fractions and appear to be poly-ubiquitinated in vivo by endogenous Dube3a. We propose that the transcriptional co-activation function of Dube3a may regulate GCH1 activity in the brain. These results provide a connection between monoamine synthesis (dopamine/serotonin) and Dube3a expression that may explain why some individuals with ASD or AS respond better to selective serotonin reuptake inhibitors than others.
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Xie HH, Zhou S, Chen D, Channon KM, Su DF, Chen AF. GTP cyclohydrolase I/BH4 pathway protects EPCs via suppressing oxidative stress and thrombospondin-1 in salt-sensitive hypertension. Hypertension 2010; 56:1137-44. [PMID: 21059996 PMCID: PMC3003666 DOI: 10.1161/hypertensionaha.110.160622] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
Endothelial progenitor cells (EPCs) are both reduced and dysfunctional in hypertension that correlates inversely with its mortality, but the mechanisms are poorly understood. Endothelial nitric oxide synthase (eNOS) critically regulates EPC mobilization and function but is uncoupled in salt-sensitive hypertension because of the reduced cofactor tetrahydrobiopterin (BH4). We tested the hypothesis that GTP cyclohydrolase I (GTPCH I), the rate-limiting enzyme of BH4 de novo synthesis, protects EPCs and its function in deoxycorticosterone acetate (DOCA)-salt mice. EPCs were isolated from peripheral blood and bone marrow of wild-type (WT), WT DOCA-salt, endothelial-specific GTPCH transgenic (Tg-GCH), GTPCH transgenic DOCA-salt, and BH4-deficient hph-1 mice. In WT DOCA-salt and hph-1 mice, EPCs were significantly decreased with impaired angiogenesis and adhesion, which were restored in Tg-GCH DOCA-salt mice. Superoxide (O₂⁻) and nitric oxide (NO) levels in EPCs were elevated and reduced, respectively, in WT DOCA-salt and hph-1 mice; both were rescued in Tg-GCH DOCA-salt mice. eNOS(-/-)/GCH(+/-) hybrid mice demonstrated that GTPCH preserved the circulating EPC number, reduced intracellular O₂⁻ in EPCs, and ameliorated EPC dysfunction independent of eNOS in DOCA-salt hypertension. Secreted thrombospondin-1 (TSP-1; a potent angiogenesis inhibitor) from EPCs was elevated in WT DOCA-salt and hph-1 but not DOCA-salt Tg-GCH mice. In vitro treatment with BH4, polyethylene glycol-superoxide dismutase (PEG-SOD), or Nomega-nitro-L-arginine (L-NNA) significantly augmented NO and reduced TSP-1 and O₂⁻ levels from EPCs of WT DOCA-salt mice. These results demonstrated, for the first time, that the GTPCH/BH4 pathway critically regulates EPC number and function in DOCA-salt hypertensive mice, at least in part, via suppressing TSP-1 expression and oxidative stress.
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Mayahi L, Mason L, Bleasdale-Barr K, Donald A, Trender-Gerhard I, Sweeney MG, Davis MB, Wood N, Mathias CJ, Watson L, Pellerin D, Heales S, Deanfield JE, Bhatia K, Murray-Rust J, Hingorani AD. Endothelial, sympathetic, and cardiac function in inherited (6R)-L-erythro-5,6,7,8-tetrahydro-L-biopterin deficiency. CIRCULATION. CARDIOVASCULAR GENETICS 2010; 3:513-22. [PMID: 20937667 DOI: 10.1161/circgenetics.110.957605] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
BACKGROUND (6R)-5,6,7,8-Tetrahydro-l-biopterin (BH4) is a cofactor for enzymes involved in catecholamine and nitric oxide generation whose synthesis is initiated by GTP cyclohydrolase I (GTPCH-1), encoded by GCH1. In the absence of a potent, specific GTPCH-1 inhibitor, natural BH4 deficiency caused by mutations in GCH1 in the rare movement disorder, DOPA-responsive dystonia (OMIM DYT5), offers the opportunity to study the role of endogenous BH4 in humans. METHODS AND RESULTS In 16 DOPA-responsive dystonia patients with mutations predicted to affect GTPCH-1 expression or function and in age- and sex-matched control subjects, we measured plasma biopterin and nitrogen oxides by high-performance liquid chromatography and the Griess reaction, respectively, endothelial function by brachial artery flow-mediated dilation (FMD), sympathetic function by measurement of plasma norepinephrine, epinephrine, and heart rate and blood pressure in response. Cardiac function and structure were assessed by echocardiography. Plasma biopterin was lower in patients (5.76±0.53 versus 8.43±0.85 nmol/L, P=0.03), but plasma NO(2)(-)/NO(3)(-) (NOx) (median, 9.06 [interquartile range, 5.35 to 11.04] versus 8.40 [interquartile range, 5.28 to 11.44] μmol/L, P=1) and FMD were not lower (7.7±0.8% versus 7.9±0.9%, P=0.91). In patients but not control subjects, FMD was insensitive to nitric oxide synthase inhibition (FMD at baseline, 6.7±2.1%; FMD during l-NMMA infusion, 6.2±2.5, P=0.68). The heart rate at rest was higher in patients, but the heart rate and blood pressure response to sympathetic stimulation did not differ in patients and control subjects despite lower concentrations of norepinepherine (264±8 pg/mL versus 226±9 pg/mL, P=0.006) and epinephrine (33.8±5.2 pg/mL versus 17.8±4.6 pg/mL, P=0.03) in patients. There was also no difference in cardiac function and structure. CONCLUSIONS Sympathetic, cardiac, and endothelial functions are preserved in patients with GCH1 mutations despite a neurological phenotype, reduced plasma biopterin, and norepinepherine and epinephrine concentrations. Lifelong endogenous BH4 deficiency may elicit developmental adaptation through mechanisms that are inaccessible during acquired BH4 deficiency in adulthood.
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Xia N, Daiber A, Habermeier A, Closs EI, Thum T, Spanier G, Lu Q, Oelze M, Torzewski M, Lackner KJ, Münzel T, Förstermann U, Li H. Resveratrol reverses endothelial nitric-oxide synthase uncoupling in apolipoprotein E knockout mice. J Pharmacol Exp Ther 2010; 335:149-54. [PMID: 20610621 DOI: 10.1124/jpet.110.168724] [Citation(s) in RCA: 122] [Impact Index Per Article: 8.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023] Open
Abstract
A crucial cause of the decreased bioactivity of nitric oxide (NO) in cardiovascular diseases is the uncoupling of the endothelial NO synthase (eNOS) caused by the oxidative stress-mediated deficiency of the NOS cofactor tetrahydrobiopterin (BH(4)). The reversal of eNOS uncoupling might represent a novel therapeutic approach. The treatment of apolipoprotein E knockout (ApoE-KO) mice with resveratrol resulted in the up-regulation of superoxide dismutase (SOD) isoforms (SOD1-SOD3), glutathione peroxidase 1 (GPx1), and catalase and the down-regulation of NADPH oxidases NOX2 and NOX4 in the hearts of ApoE-KO mice. This was associated with reductions in superoxide, 3-nitrotyrosine, and malondialdehyde levels. In parallel, the cardiac expression of GTP cyclohydrolase 1 (GCH1), the rate-limiting enzyme in BH(4) biosynthesis, was enhanced by resveratrol. This enhancement was accompanied by an elevation in BH(4) levels. Superoxide production from ApoE-KO mice hearts was reduced by the NOS inhibitor L-N(G)-nitro-arginine methyl ester, indicating eNOS uncoupling in this pathological model. Resveratrol treatment resulted in a reversal of eNOS uncoupling. Treatment of human endothelial cells with resveratrol led to an up-regulation of SOD1, SOD2, SOD3, GPx1, catalase, and GCH1. Some of these effects were preventable with sirtinol, an inhibitor of the protein deacetylase sirtuin 1. In summary, resveratrol decreased superoxide production and enhanced the inactivation of reactive oxygen species. The resulting reduction in BH(4) oxidation, together with the enhanced biosynthesis of BH(4) by GCH1, probably was responsible for the reversal of eNOS uncoupling. This novel mechanism (reversal of eNOS uncoupling) might contribute to the protective effects of resveratrol.
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Ionova IA, Vásquez-Vivar J, Cooley BC, Khanna AK, Whitsett J, Herrnreiter A, Migrino RQ, Ge ZD, Regner KR, Channon KM, Alp NJ, Pieper GM. Cardiac myocyte-specific overexpression of human GTP cyclohydrolase I protects against acute cardiac allograft rejection. Am J Physiol Heart Circ Physiol 2010; 299:H88-96. [PMID: 20418482 PMCID: PMC2904123 DOI: 10.1152/ajpheart.00203.2010] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/26/2010] [Accepted: 04/20/2010] [Indexed: 12/31/2022]
Abstract
GTP cyclohydrolase I (GTPCH) is the rate-limiting enzyme for tetrahydrobiopterin (BH(4)) synthesis. Decreases in GTPCH activity and expression have been shown in late stages of acute cardiac rejection, suggesting a deficit in BH(4). We hypothesized that increasing intracellular levels of BH(4) by cardiac myocyte-targeted overexpression of GTPCH would diminish acute cardiac allograft rejection. Transgenic mice overexpressing GTPCH in the heart were generated and crossed on C57BL6 background. Wild-type and transgenic mouse donor hearts were transplanted into BALB/c recipient mice. Left ventricular (LV) function, histological rejection, BH(4) levels, and inflammatory cytokine gene expression (mRNA) were examined. Expression of human GTPCH was documented by PCR, Western analysis, and function by a significant (P < 0.001) increase in cardiac BH(4) levels. GTPCH transgene decreased histological rejection (46%; P < 0.003) and cardiac myocyte injury (eosin autofluorescence; 56%; P < 0.0001) independent of changes in inflammatory cytokine expression or nitric oxide content. GTPCH transgene decreased IL-2 (88%; P < 0.002), IL-1R2 (42%; P < 0.0001), and programmed cell death-1 (67%; P < 0.0001) expression, whereas it increased fms-like tyrosine kinase 3 (156%; P < 0.0001) and stromal-derived factor-1 (2; 190%; P < 0.0001) expression. There was no difference in ejection fraction or fractional shortening; however, LV mass was significantly increased (P < 0.05) only in wild-type grafts. The decreases in LV mass, cardiac injury, and histological rejection support a protective role of cardiac GTPCH overexpression and increased BH(4) synthesis in cardiac allografts. The mechanism of the decreased rejection appears related to decreased T cell proliferation and modulation of immune function by higher expression of genes involved in hematopoietic/stromal cell development and recruitment.
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Hiroi T, Wajima T, Kaneko Y, Kiuchi Y, Shimizu S. An important role of increase in tetrahydrobiopterin via H2O2-JAK2 signalling pathway in late phase of ischaemic preconditioning. Exp Physiol 2010; 95:609-21. [PMID: 20139166 DOI: 10.1113/expphysiol.2009.051417] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2023]
Abstract
The goal of this study was to elucidate whether there is an increase in myocardial tetrahydrobiopterin (BH4), which is a cofactor for nitric oxide synthase, during the late phase of ischaemic preconditioning (IPC) leading to cardioprotection against myocardial infarction and, if so, to examine the induction mechanisms of BH4 synthesis. Rats were preconditioned with four cycles of 3 min left main coronary artery (LCA) occlusion followed by 10 min reperfusion. Twenty-four hours later, the rats were subjected to 20 min ischaemia by LCA ligation and 2 h reperfusion, and the infarct size was determined by 2,3,5-triphenyltetrazolium chloride staining. The IPC protocol reduced the infarct size, and increased the BH4 content and expression of GTP-cyclohydrolase I (GTPCH), which is the rate-limiting enzyme for BH4 synthesis. Administration of a GTPCH inhibitor attenuated both the reduction in infarct size and the increase in BH4 levels. Moreover, the increase in BH4 content was reduced by administration of catalase or a Janus tyrosine kinase-2 (JAK2) inhibitor. These observations suggest that upregulation of BH4 synthesis in the heart contributes to an acquisition of ischaemic tolerance in late IPC, and the increase in myocardial BH4 content seems to be mediated by the induction of GTPCH via the H(2)O(2)-JAK2 pathway.
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Li L, Rezvan A, Salerno JC, Husain A, Kwon K, Jo H, Harrison DG, Chen W. GTP cyclohydrolase I phosphorylation and interaction with GTP cyclohydrolase feedback regulatory protein provide novel regulation of endothelial tetrahydrobiopterin and nitric oxide. Circ Res 2010; 106:328-36. [PMID: 19926872 PMCID: PMC2818799 DOI: 10.1161/circresaha.109.210658] [Citation(s) in RCA: 45] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
RATIONALE GTP cyclohydrolase I (GTPCH-1) is the rate-limiting enzyme involved in de novo biosynthesis of tetrahydrobiopterin (BH(4)), an essential cofactor for NO synthases and aromatic amino acid hydroxylases. GTPCH-1 undergoes negative feedback regulation by its end-product BH(4) via interaction with the GTP cyclohydrolase feedback regulatory protein (GFRP). Such a negative feedback mechanism should maintain cellular BH(4) levels within a very narrow range; however, we recently identified a phosphorylation site (S81) on human GTPCH-1 that markedly increases BH(4) production in response to laminar shear. OBJECTIVE We sought to define how S81 phosphorylation alters GTPCH-1 enzyme activity and how this is modulated by GFRP. METHODS AND RESULTS Using prokaryotically expressed proteins, we found that the GTPCH-1 phospho-mimetic mutant (S81D) has increased enzyme activity, reduced binding to GFRP and resistance to inhibition by GFRP compared to wild-type GTPCH-1. Using small interfering RNA or overexpressing plasmids, GFRP was shown to modulate phosphorylation of GTPCH-1, BH(4) levels, and NO production in human endothelial cells. Laminar, but not oscillatory shear stress, caused dissociation of GTPCH-1 and GFRP, promoting GTPCH-1 phosphorylation. We also found that both GTPCH-1 phosphorylation and GFRP downregulation prevents endothelial NO synthase uncoupling in response to oscillatory shear. Finally oscillatory shear was associated with impaired GTPCH-1 phosphorylation and reduced BH(4) levels in vivo. CONCLUSIONS These studies provide a new mechanism for regulation of endothelial GTPCH-1 by its phosphorylation and interplay with GFRP. This mechanism allows for escape from GFRP negative feedback and permits large amounts of BH(4) to be produced in response to laminar shear stress.
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Nurkiewicz TR, Wu G, Li P, Boegehold MA. Decreased arteriolar tetrahydrobiopterin is linked to superoxide generation from nitric oxide synthase in mice fed high salt. Microcirculation 2010; 17:147-57. [PMID: 20163541 PMCID: PMC3402363 DOI: 10.1111/j.1549-8719.2009.00014.x] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
OBJECTIVE Impaired endothelium-dependent arteriolar dilation in mice fed high salt (HS) is due to local oxidation of nitric oxide (NO) by superoxide anion (O(2) (-)). We explored the possibility that "uncoupled" endothelial nitric oxide synthase (eNOS) is the source of this O(2) (-). METHODS Levels of L-arginine (L-Arg), tetrahydrobiopterin (BH(4)), and O(2) (-) (hydroethidine oxidation) were measured in spinotrapezius muscle arterioles of mice fed normal salt (0.45%, NS) or (4%, HS) diets for 4 weeks, with or without dietary L-Arg supplementation. The contribution of NO to endothelium-dependent dilation was determined from the effect of N(omega)-nitro-L-arginine methyl ester (L-NAME) on responses to acetylcholine (ACh). RESULTS Arterioles in HS mice had lower [BH(4)] and higher O(2) (-) levels than those in NS mice. ACh further increased arteriolar O(2) (-) in HS mice only. L-Arg supplementation prevented the reduction in [BH(4)] in arterioles of HS mice, and O(2) (-) was not elevated in these vessels. Compared to NS mice, arteriolar ACh responses were diminished and insensitive to L-NAME in HS mice, but not in HS mice supplemented with L-Arg. CONCLUSIONS These findings suggest that eNOS uncoupling due to low [BH(4)] is responsible for O(2) (-) generation and reduced NO-dependent dilation in arterioles of mice fed a HS diet.
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Naylor AM, Pojasek KR, Hopkins AL, Blagg J. The tetrahydrobiopterin pathway and pain. CURRENT OPINION IN INVESTIGATIONAL DRUGS (LONDON, ENGLAND : 2000) 2010; 11:19-30. [PMID: 20047156] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Subscribe] [Scholar Register] [Indexed: 05/28/2023]
Abstract
Novel approaches for treating chronic pain are required to address a widely recognized, yet largely underserved and unmet, clinical need. The recently discovered link between tetrahydrobiopterin (BH4) synthesis and pain in preclinical models and humans provides a promising new approach for treating neuropathic and other forms of chronic pain. The rate-limiting enzyme in BH4 synthesis, guanosine triphosphate cyclohydrolase 1 (GCH1), and sepiapterin reductase (SPR) are both promising drug targets based on initial active-site characterization of the SARs of these two enzymes. Reducing the elevated BH4 levels associated with pain to baseline, while maintaining sufficient BH4 levels to limit side effects is the goal of discovery programs for novel therapeutics targeting GCH1 or SPR.
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Du J, Wei N, Xu H, Ge Y, Vásquez-Vivar J, Guan T, Oldham KT, Pritchard KA, Shi Y. Identification and functional characterization of phosphorylation sites on GTP cyclohydrolase I. Arterioscler Thromb Vasc Biol 2009; 29:2161-8. [PMID: 19762783 PMCID: PMC2798731 DOI: 10.1161/atvbaha.109.194464] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
OBJECTIVE The posttranslational regulation of GTP cyclohydrolase I (GCH-1), the rate-limiting enzyme for tetrahydrobiopterin (BH4) synthesis, remains elusive. Here, we identified specific phosphorylation sites on GCH-1 and characterized the function of these sites. METHODS AND RESULTS Mass spectrometry studies showed overexpressed rat GCH-1 was phosphorylated at serine (S) 51, S167, and threonine (T) 231 in HEK293 cells, whereas a computational analysis of GCH-1 revealed 8 potential phosphorylation sites (S51, S72, T85, T91, T103, S130, S167 and T231). GCH-1 activity and BH4 were significantly decreased in cells transfected with the phospho-defective mutants (S72A, T85A, T91A, T103A, or S130A) and increased in cells transfected with the T231A mutant. BH4 and BH2 were increased in cells transfected with S51E, S72E, T85E, T91E, T103D, or T130D mutants, but decreased in cells transfected with the T231D mutant, whereas cells transfected with the S167A or the S167E mutant had increased BH2. Additionally, cells transfected with the T231A mutant had reduced GCH-1 nuclear localization and nuclear GCH-1 activity. CONCLUSIONS Our data suggest GCH-1 activity is regulated either positively by phosphorylation S51, S72, T85, T91, T103, and S130, or negatively at T231. Such information might be useful in designing new therapies aiming at improving BH4 bioavailability.
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Yang YM, Huang A, Kaley G, Sun D. eNOS uncoupling and endothelial dysfunction in aged vessels. Am J Physiol Heart Circ Physiol 2009; 297:H1829-36. [PMID: 19767531 PMCID: PMC2781386 DOI: 10.1152/ajpheart.00230.2009] [Citation(s) in RCA: 271] [Impact Index Per Article: 18.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/09/2009] [Accepted: 09/15/2009] [Indexed: 02/07/2023]
Abstract
Endothelial nitric oxide synthase (eNOS) uncoupling is a mechanism that leads to endothelial dysfunction. Previously, we reported that shear stress-induced release of nitric oxide in vessels of aged rats was significantly reduced and was accompanied by increased production of superoxide (18, 27). In the present study, we investigated the influence of aging on eNOS uncoupling. Mesenteric arteries were isolated from young (3 mo) and aged (24 mo) C57 BL/6J mice. The expression of eNOS protein in young vs. aged mice was not significantly different. However, the aged mice had remarkable increases in the ratio of eNOS monomers to dimers and N(omega)-nitro-l-arginine methyl ester-inhibitable superoxide formation. The level of nitrotyrosine in the total protein and precipitated eNOS of aged vessels was increased compared with that in young vessels. HPLC analysis indicated a reduced level of tetrahydrobiopterin (BH4), an essential cofactor for eNOS, in the mesenteric arteries of aged mice. Quantitative PCR results implied that the diminished BH4 may result from the decreased expressions of GTP cyclohydrolase I and sepiapterin reductase, enzymes involved in BH4 biosynthesis. When isolated and cannulated second-order mesenteric arteries (approximately 150 microm) from aged mice were treated with sepiapterin, acetylcholine-induced, endothelium-dependent vasodilation improved significantly, which was accompanied by stabilization of the eNOS dimer. These data suggest that eNOS uncoupling and increased nitrosylation of eNOS, decreased expressions of GTP cyclohydrolase I and sepiapterin reductase, and subsequent reduced BH4 bioavailability may be important contributors of endothelial dysfunction in aged vessels.
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An J, Du J, Wei N, Xu H, Pritchard KA, Shi Y. Role of tetrahydrobiopterin in resistance to myocardial ischemia in Brown Norway and Dahl S rats. Am J Physiol Heart Circ Physiol 2009; 297:H1783-91. [PMID: 19717731 PMCID: PMC2781371 DOI: 10.1152/ajpheart.00364.2009] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/14/2009] [Accepted: 08/27/2009] [Indexed: 11/22/2022]
Abstract
Previously we showed that Brown Norway (BN/Mcw) rats are more resistant to myocardial ischemia-reperfusion (I/R) injury than Dahl S (SS/Mcw) rats due to increased nitric oxide (x NO) generation secondary to increased heat shock protein 90 (HSP90) association with endothelial nitric oxide synthase (NOS3). Here we determined whether increased resistance to I/R injury in BN/Mcw hearts is also related to tetrahydrobiopterin (BH(4)) and GTP cyclohydrolase I (GCH-1), the rate-limiting enzyme for BH(4) synthesis. We observed that BH(4) supplementation via sepiapterin (SP) and inhibition of GCH-1 via 2,4-diamino-6-hydroxypyrimidine (DAHP) differentially modulate cardioprotection and that SP alters the association of HSP90 with NOS3. BH(4) levels were significantly higher and 7,8-dihydrobiopterin (BH(2)) levels were significantly lower in BN/Mcw than in SS/Mcw hearts. The BH(4)-to-BH(2) ratio in BN/Mcw was more than two times that in SS/Mcw hearts. After I/R, BH(4) decreased and BH(2) increased in hearts from both strains compared with their preischemia levels. However, the increase in BH(2) in SS/Mcw hearts was significantly higher than in BN/Mcw hearts. Real-time PCR revealed that BN/Mcw hearts contained more GCH-1 transcripts than SS/Mcw hearts. SP increased recovery of left ventricular developed pressure (rLVDP) following I/R as well as decreased superoxide (O(2)(x-)) and increased x NO in SS/Mcw hearts but not in BN/Mcw hearts. DAHP decreased rLVDP as well as increased O(2)(x-) and decreased x NO in BN/Mcw hearts compared with controls but not in SS/Mcw hearts. SP increased the association of HSP90 with NOS3. These data indicate that BH(4) mediates resistance to I/R by acting as a cofactor and enhancing HSP90-NOS3 association.
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Crabtree MJ, Tatham AL, Hale AB, Alp NJ, Channon KM. Critical role for tetrahydrobiopterin recycling by dihydrofolate reductase in regulation of endothelial nitric-oxide synthase coupling: relative importance of the de novo biopterin synthesis versus salvage pathways. J Biol Chem 2009; 284:28128-28136. [PMID: 19666465 PMCID: PMC2788863 DOI: 10.1074/jbc.m109.041483] [Citation(s) in RCA: 167] [Impact Index Per Article: 11.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/08/2009] [Revised: 08/06/2009] [Indexed: 11/06/2022] Open
Abstract
Tetrahyrobiopterin (BH4) is a required cofactor for the synthesis of nitric oxide by endothelial nitric-oxide synthase (eNOS), and BH4 bioavailability within the endothelium is a critical factor in regulating the balance between NO and superoxide production by eNOS (eNOS coupling). BH4 levels are determined by the activity of GTP cyclohydrolase I (GTPCH), the rate-limiting enzyme in de novo BH4 biosynthesis. However, BH4 levels may also be influenced by oxidation, forming 7,8-dihydrobiopterin (BH2), which promotes eNOS uncoupling. Conversely, dihydrofolate reductase (DHFR) can regenerate BH4 from BH2, but the functional importance of DHFR in maintaining eNOS coupling remains unclear. We investigated the role of DHFR in regulating BH4 versus BH2 levels in endothelial cells and in cell lines expressing eNOS combined with tet-regulated GTPCH expression in order to compare the effects of low or high levels of de novo BH4 biosynthesis. Pharmacological inhibition of DHFR activity by methotrexate or genetic knockdown of DHFR protein by RNA interference reduced intracellular BH4 and increased BH2 levels resulting in enzymatic uncoupling of eNOS, as indicated by increased eNOS-dependent superoxide but reduced NO production. In contrast to the decreased BH4:BH2 ratio induced by DHFR knockdown, GTPCH knockdown greatly reduced total biopterin levels but with no change in BH4:BH2 ratio. In cells expressing eNOS with low biopterin levels, DHFR inhibition or knockdown further diminished the BH4:BH2 ratio and exacerbated eNOS uncoupling. Taken together, these data reveal a key role for DHFR in eNOS coupling by maintaining the BH4:BH2 ratio, particularly in conditions of low total biopterin availability.
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Björklund T, Hall H, Breysse N, Soneson C, Carlsson T, Mandel RJ, Carta M, Kirik D. Optimization of continuous in vivo DOPA production and studies on ectopic DA synthesis using rAAV5 vectors in Parkinsonian rats. J Neurochem 2009; 111:355-67. [PMID: 19686242 DOI: 10.1111/j.1471-4159.2009.06340.x] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2023]
Abstract
Viral vector-mediated gene transfer is emerging as a novel therapeutic approach with clinical utility in treatment of Parkinson's disease. Recombinant adeno-associated viral (rAAV) vector in particular has been utilized for continuous l-3,4 dihydroxyphenylalanine (DOPA) delivery by expressing the tyrosine hydroxylase (TH) and GTP cyclohydrolase 1 (GCH1) genes which are necessary and sufficient for efficient synthesis of DOPA from dietary tyrosine. The present study was designed to determine the optimal stoichiometric relationship between TH and GCH1 genes for ectopic DOPA production and the cellular machinery involved in its synthesis, storage, and metabolism. For this purpose, we injected a fixed amount of rAAV5-TH vector and increasing amounts of rAAV5-GCH1 into the striatum of rats with complete unilateral dopamine lesion. After 7 weeks the animals were killed for either biochemical or histological analysis. We show that increasing the availability of 5,6,7,8-tetrahydro-l-biopterin (BH4) in the same cellular compartment as the TH enzyme resulted in better efficiency in DOPA synthesis, most likely by hindering inactivation of the enzyme and increasing its stability. Importantly, the BH4 synthesis from ectopic GCH1 expression was saturable, yielding optimal TH enzyme functionality between GCH1 : TH ratios of 1 : 3 and 1 : 7.
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Nunes ACS, Kalkmann DC, Aragão FJL. Folate biofortification of lettuce by expression of a codon optimized chicken GTP cyclohydrolase I gene. Transgenic Res 2009; 18:661-7. [PMID: 19322672 DOI: 10.1007/s11248-009-9256-1] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/27/2009] [Accepted: 03/12/2009] [Indexed: 10/21/2022]
Abstract
Folates are essential coenzymes involved in one-carbon metabolism. Folate deficiency is associated with a higher risk of newborns with neural tube defects, spina bifida, and anencephaly, and an increased risk of cardiovascular diseases, cancer, and impaired cognitive function in adults. In plants folates are synthesized in mitochondria from pterin precursors, which are synthesized from guanosine-5'-triphosphate (GTP) in the cytosol (pterin branch), and p-aminobenzoate (PABA), derived from chorismate in plastids (PABA branch). We generated transgenic lettuce lines expressing a synthetic codon-optimized GTP-cyclohydrolase I gene (gchI) based on native Gallus gallus gene. Immunoblotting analyses confirmed the presence of the gchI in transgenic lines. Twenty-nine transgenic lines were generated and 19 exhibited significant increase in the folate content, ranging from 2.1 to 8.5-fold higher when compared to non-transgenic lines. The folate content in enriched lettuce would provide 26% of the Dietary Reference Intakes for an adult, in a regular serving. Although the lettuce lines generated here exhibited high folate enhancement over the control, better folate enrichment could be further achieved by engineering simultaneously both PABA and pterin pathways.
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Du J, Wei N, Guan T, Xu H, An J, Pritchard KA, Shi Y. Inhibition of CDKS by roscovitine suppressed LPS-induced *NO production through inhibiting NFkappaB activation and BH4 biosynthesis in macrophages. Am J Physiol Cell Physiol 2009; 297:C742-9. [PMID: 19553566 PMCID: PMC2740392 DOI: 10.1152/ajpcell.00138.2009] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/27/2009] [Accepted: 06/23/2009] [Indexed: 11/22/2022]
Abstract
In inflammatory diseases, tissue damage is critically associated with nitric oxide ((*)NO) and cytokines, which are overproduced in response to cellular release of endotoxins. Here we investigated the inhibitory effect of roscovitine, a selective inhibitor of cyclin-dependent kinases (CDKs) on (*)NO production in mouse macrophages. In RAW264.7 cells, we found that roscovitine abolished the production of (*)NO induced by lipopolysaccharide (LPS). Moreover, roscovitine significantly inhibited LPS-induced inducible nitric oxide synthase (iNOS) mRNA and protein expression. Our data also showed that roscovitine attenuated LPS-induced phosphorylation of IkappaB kinase beta (IKKbeta), IkappaB, and p65 but enhanced the phosphorylation of ERK, p38, and c-Jun NH(2)-terminal kinase (JNK). In addition, roscovitine dose dependently inhibited LPS-induced expression of cyclooxygenase-2 (COX)-2, IL-1beta, and IL-6 but not tumor necrosis factor (TNF)-alpha. Tetrahydrobiopterin (BH(4)), an essential cofactor for iNOS, is easily oxidized to 7,8-dihydrobiopterin (BH(2)). Roscovitine significantly inhibited LPS-induced BH(4) biosynthesis and decreased BH(4)-to-BH(2) ratio. Furthermore, roscovitine greatly reduced the upregulation of GTP cyclohydrolase-1 (GCH-1), the rate-limiting enzyme for BH(4) biosynthesis. Using other CDK inhibitors, we found that CDK1, CDK5, and CDK7, but not CDK2, significantly inhibited LPS-induced (*)NO production in macrophages. Similarly, in isolated peritoneal macrophages, roscovitine strongly inhibited (*)NO production, iNOS, and COX-2 upregulation, activation of NFkappaB, and induction of GCH-1 by LPS. Together, our data indicate that roscovitine abolishes LPS-induced (*)NO production in macrophages by suppressing nuclear factor-kappaB activation and BH(4) biosynthesis, which might be mediated by CDK1, CDK5, and CDK7. Our results also suggest that roscovitine may inhibit inflammation and that CDKs may play important roles in the mechanisms by which roscovitine attenuates inflammation.
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Xu J, Wang S, Wu Y, Song P, Zou MH. Tyrosine nitration of PA700 activates the 26S proteasome to induce endothelial dysfunction in mice with angiotensin II-induced hypertension. Hypertension 2009; 54:625-32. [PMID: 19597039 PMCID: PMC2910588 DOI: 10.1161/hypertensionaha.109.133736] [Citation(s) in RCA: 46] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
Abstract
The ubiquitin-proteasome system has been implicated in oxidative stress-induced endothelial dysfunction in cardiovascular diseases. However, the mechanism by which oxidative stress alters the ubiquitin-proteasome system is poorly defined. The present study was conducted to determine whether oxidative modifications of PA700, a 26S proteasome regulatory subunit, contributes to angiotensin II (Ang II)-induced endothelial dysfunction. Exposure of human umbilical vein endothelial cells to low concentrations of Ang II, but not vehicle, for 6 hours significantly decreased the levels of tetrahydro-l-biopterin (BH4), an essential cofactor of endothelial NO synthase, which was accompanied by a decrease in GTP cyclohydrolase I, the rate-limiting enzyme for de novo BH4 synthesis. In addition, Ang II increased both tyrosine nitration of PA700 and the 26S proteasome activity, which were paralleled by increased coimmunoprecipitation of PA700 and the 20S proteasome. Genetic inhibition of NAD(P)H oxidase or administration of uric acid (a peroxynitrite scavenger) or N(G)-nitro-l-arginine methyl ester (nonselective NO synthase inhibitor) significantly attenuated Ang II-induced PA700 nitration, 26S proteasome activation, and reduction of GTP cyclohydrolase I and BH4. Finally, Ang II infusion in mice decreased the levels of both BH4 and GTP cyclohydrolase I and impaired endothelial-dependent relaxation in isolated aortas, and all of these effects were prevented by the administration of MG132, a potent inhibitor for 26S proteasome. We conclude that Ang II increases tyrosine nitration of PA700 resulting in accelerated GTP cyclohydrolase I degradation, BH4 deficiency, and consequent endothelial dysfunction in hypertension.
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Sun X, Kumar S, Tian J, Black SM. Estradiol increases guanosine 5'-triphosphate cyclohydrolase expression via the nitric oxide-mediated activation of cyclic adenosine 5'-monophosphate response element binding protein. Endocrinology 2009; 150:3742-52. [PMID: 19389836 PMCID: PMC2717883 DOI: 10.1210/en.2008-1464] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
A number of studies have demonstrated that estradiol can stimulate endothelial nitric oxide synthase expression and activity, resulting in enhanced nitric oxide (NO) generation. However, its effect on the NO synthase cofactor, tetrahydrobiopterin are less clear. Cellular tetrahydrobiopterin levels are regulated, at least in part, by GTP cyclohydrolase 1 (GCH1). Thus, the purpose of this study was to determine the effect of estradiol on GCH1 expression and the regulatory mechanisms in pulmonary arterial endothelial cells. Our data indicate that 17beta-estradiol (E2) increases GCH1 transcription in a dose- and time-dependent manner, whereas estrogen receptor antagonism or NO synthase inhibition attenuated E2-stimulated GCH1 expression. Analysis of the GCH1 promoter fragment responsive to E2 revealed the presence of a cAMP response element, and we found that E2 triggers a rapid but transient elevation of phospho-cAMP response element-binding protein (CREB; <1 h) followed by a second sustained rise after 6 h. EMSA analysis revealed an increase in the binding of CREB during E2 treatment and mutation of the cAMP response element in the GCH1 promoter attenuated the E2-mediated increase in transcription. Furthermore, inhibition of the cAMP-dependent kinase, protein kinase A (PKA) completely abolished the E2-stimulated GCH1 promoter activity, whereas the stimulation of cAMP levels with forskolin increased GCH1 promoter activity, indicating the key role of cAMP in regulating GCH1 promoter activity. In conclusion, our results demonstrate that estradiol can modulate GCH1 expression via NO-mediated activation of CREB in pulmonary arterial endothelial cells. These findings provide new insight into the vascular protective effect of estradiol.
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Kumar S, Sun X, Sharma S, Aggarwal S, Ravi K, Fineman JR, Black SM. GTP cyclohydrolase I expression is regulated by nitric oxide: role of cyclic AMP. Am J Physiol Lung Cell Mol Physiol 2009; 297:L309-17. [PMID: 19447893 PMCID: PMC2742798 DOI: 10.1152/ajplung.90538.2008] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/27/2008] [Accepted: 05/11/2009] [Indexed: 01/15/2023] Open
Abstract
Our previous studies have demonstrated that nitric oxide (NO) leads to nitric oxide synthase (NOS) uncoupling and an increase in NOS-derived superoxide. However, the cause of this uncoupling has not been adequately resolved. The pteridine cofactor tetrahydrobiopterin (BH(4)) is a critical determinant of endothelial NOS (eNOS) activity and coupling, and GTP cyclohydrolase I (GCH1) is the rate-limiting enzyme in its generation. Thus the initial purpose of this study was to determine whether decreases in BH(4) could underlie, at least in part, the NO-mediated uncoupling of eNOS we have observed both in vitro and in vivo. Initially we evaluated the effect of inhaled NO levels on GCH1 expression and BH(4) levels in the intact lamb. Contrary to our hypothesis, we found that there was a significant increase in both plasma BH4 levels and peripheral lung GCH1 protein levels. Furthermore, in vitro, we found that exposure to the NO donor spermine NONOate (SPNONO) led to an increase in GCH1 protein and BH(4) levels in both COS-7 and pulmonary arterial endothelial cells. However, SPNONO treatment also caused a significant increase in phospho-cAMP response element binding protein (CREB) levels, as detected by Western blot analysis, and significantly increased cAMP levels, as detected by enzyme immunoassay. Furthermore, utilizing GCH1 promoter fragments fused to a luciferase reporter gene, we found that GCH1 promoter activity was enhanced by SPNONO in a CREB-dependent manner, and electromobility shift assays revealed an NO-dependent increase in the nuclear binding of CREB. These data suggest that NO increases BH(4) levels through a cAMP/CREB-mediated increase in GCH1 transcription and that the eNOS uncoupling associated with exogenous NO does not involved reduced BH(4) levels.
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