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Yan R, Cai H, Zhou X, Bao G, Bai Z, Ge RL. Hypoxia-inducible factor-2α promotes fibrosis in non-alcoholic fatty liver disease by enhancing glutamine catabolism and inhibiting yes-associated protein phosphorylation in hepatic stellate cells. Front Endocrinol (Lausanne) 2024; 15:1344971. [PMID: 38501098 PMCID: PMC10946064 DOI: 10.3389/fendo.2024.1344971] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/27/2023] [Accepted: 01/25/2024] [Indexed: 03/20/2024] Open
Abstract
Non-alcoholic fatty liver disease (NAFLD) has a high global prevalence and affects approximately one-third of adults, owing to high-fat dietary habits and a sedentary lifestyle. The role of hypoxia-inducible factor 2α (HIF-2α) in NAFLD progression remains unknown. This study aimed to investigate the effects of chronic hypoxia on NAFLD progression by examining the role of hypoxia-inducible factor 2α (HIF-2α) activation and that of hepatic stellate cell (HSC)-derived myofibroblasts through glutaminolysis. We hypothesised that hypoxia exacerbates NAFLD by promoting HIF-2α upregulation and inhibiting phosphorylated yes-associated protein (YAP), and that increasing YAP expression enhances HSC-derived myofibroblasts. We studied patients with NAFLD living at high altitudes, as well as animal models and cultured cells. The results revealed significant increases in HSC-derived myofibroblasts and collagen accumulation caused by HIF-2α and YAP upregulation, both in patients and in a mouse model for hypoxia and NAFLD. HIF-2α and HIF-2α-dependent YAP downregulation reduced HSC activation and myofibroblast levels in persistent chronic hypoxia. Furthermore, hypoxia-induced HIF-2α upregulation promoted YAP and inhibited YAP phosphorylation, leading to glutaminase 1 (GLS1), SLC38A1, α-SMA, and Collagen-1 overexpression. Additionally, hypoxia restored mitochondrial adenosine triphosphate production and reactive oxygen species (ROS) overproduction. Thus, chronic hypoxia-induced HIF-2α activation enhances fibrosis and NAFLD progression by restoring mitochondrial ROS production and glutaminase-1-induced glutaminolysis, which is mediated through the inhibition of YAP phosphorylation and increased YAP nuclear translocation. In summary, HIF-2α plays a pivotal role in NAFLD progression during chronic hypoxia.
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Affiliation(s)
- Ranran Yan
- Qinghai-Utah Joint Key Lab for High-altitude Medicine, Medical College of Qinghai University, Xining, China
- Research Center for High Altitude Medicine, Medical College of Qinghai University, Xining, China
- Key Laboratory of High-Altitude Medicine in Qinghai University, Ministry of Education, Xining, China
- Key Laboratory for Application of High-Altitude Medicine in Qinghai Province, Xining, China
| | - Hao Cai
- Oncology Department, The Fifth People’s Hospital of Qinghai Provincial, Xining, China
| | - Xiaofeng Zhou
- Affiliated Hospital of Qinghai University, Xining, China
| | - Guodan Bao
- Qinghai-Utah Joint Key Lab for High-altitude Medicine, Medical College of Qinghai University, Xining, China
- Research Center for High Altitude Medicine, Medical College of Qinghai University, Xining, China
- Key Laboratory of High-Altitude Medicine in Qinghai University, Ministry of Education, Xining, China
- Affiliated Hospital of Qinghai University, Xining, China
| | - Zhenzhong Bai
- Qinghai-Utah Joint Key Lab for High-altitude Medicine, Medical College of Qinghai University, Xining, China
- Research Center for High Altitude Medicine, Medical College of Qinghai University, Xining, China
- Key Laboratory of High-Altitude Medicine in Qinghai University, Ministry of Education, Xining, China
- Key Laboratory for Application of High-Altitude Medicine in Qinghai Province, Xining, China
| | - Ri-li Ge
- Qinghai-Utah Joint Key Lab for High-altitude Medicine, Medical College of Qinghai University, Xining, China
- Research Center for High Altitude Medicine, Medical College of Qinghai University, Xining, China
- Key Laboratory of High-Altitude Medicine in Qinghai University, Ministry of Education, Xining, China
- Key Laboratory for Application of High-Altitude Medicine in Qinghai Province, Xining, China
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2
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Khajavi M, Zhou Y, Schiffer AJ, Bazinet L, Birsner AE, Zon L, D'Amato RJ. Identification of Basp1 as a novel angiogenesis-regulating gene by multi-model system studies. FASEB J 2021; 35:e21404. [PMID: 33899275 DOI: 10.1096/fj.202001936rrr] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/17/2020] [Revised: 01/13/2021] [Accepted: 01/15/2021] [Indexed: 01/23/2023]
Abstract
We have previously used the genetic diversity available in common inbred mouse strains to identify quantitative trait loci (QTLs) responsible for the differences in angiogenic response using the corneal micropocket neovascularization (CoNV) assay. Employing a mouse genome-wide association study (GWAS) approach, the region on chromosome 15 containing Basp1 was identified as being significantly associated with angiogenesis in inbred strains. Here, we developed a unique strategy to determine and verify the role of BASP1 in angiogenic pathways. Basp1 expression in cornea had a strong correlation with a haplotype shared by mouse strains with varied angiogenic phenotypes. In addition, inhibition of BASP1 demonstrated a dosage-dependent effect in both primary mouse brain endothelial and human microvascular endothelial cell (HMVEC) migration. To investigate its role in vivo, we knocked out basp1 in transgenic kdrl:zsGreen zebrafish embryos using a widely adopted CRISPR-Cas9 system. These embryos had severely disrupted vessel formation compared to control siblings. We further show that basp1 promotes angiogenesis by upregulating β-catenin gene and the Dll4/Notch1 signaling pathway. These results, to the best of our knowledge, provide the first in vivo evidence to indicate the role of Basp1 as an angiogenesis-regulating gene and opens the potential therapeutic avenues for a wide variety of systemic angiogenesis-dependent diseases.
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Affiliation(s)
- Mehrdad Khajavi
- Department of Surgery, Vascular Biology Program, Boston Children's Hospital, Harvard Medical School, Boston, MA, USA
| | - Yi Zhou
- Division of Hematology/Oncology, Boston Children's Hospital, Harvard Stem Cell Institute, Harvard Medical School, Boston, MA, USA
| | - Alex J Schiffer
- Department of Surgery, Vascular Biology Program, Boston Children's Hospital, Harvard Medical School, Boston, MA, USA
| | - Lauren Bazinet
- Department of Surgery, Vascular Biology Program, Boston Children's Hospital, Harvard Medical School, Boston, MA, USA
| | - Amy E Birsner
- Department of Surgery, Vascular Biology Program, Boston Children's Hospital, Harvard Medical School, Boston, MA, USA
| | - Leonard Zon
- Division of Hematology/Oncology, Boston Children's Hospital, Harvard Stem Cell Institute, Harvard Medical School, Boston, MA, USA.,Howard Hughes Medical Institute, Boston, MA, USA
| | - Robert J D'Amato
- Department of Surgery, Vascular Biology Program, Boston Children's Hospital, Harvard Medical School, Boston, MA, USA.,Department of Ophthalmology, Harvard Medical School, Boston, MA, USA
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Dikalova AE, Aschner JL, Zhang Y, Kaplowitz MR, Fike CD. Reactive oxygen species modulate Na +-coupled neutral amino acid transporter 1 expression in piglet pulmonary arterial endothelial cells. Am J Physiol Heart Circ Physiol 2019; 316:H911-H919. [PMID: 30794434 DOI: 10.1152/ajpheart.00674.2018] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
We have previously shown that Na+-coupled neutral amino acid transporter 1 (SNAT1) modulates nitric oxide (NO) production in pulmonary arterial endothelial cells (PAECs) from newborn piglets. Specifically, the ability to increase NO production in response to the l-arginine-NO precursor l-citrulline is dependent on SNAT1 expression. Elucidating factors that regulate SNAT1 expression in PAECs could provide new insights and therapeutic targets relevant to NO production. Our major goals were to determine if reactive oxygen species (ROS) modulate SNAT1 expression in PAECs from newborn piglets and to evaluate the role of NADPH oxidase 1 (NOX1) and uncoupled endothelial NO synthase, enzymatic sources of ROS, in hypoxia-induced increases in SNAT1 expression. Treatment with either H2O2 or xanthine plus xanthine oxidase increased SNAT1 expression in PAECs from newborn piglets cultured under normoxic conditions. Hypoxia-induced increases in SNAT1 expression were inhibited by treatments with the ROS-removing agents catalase and superoxide dismutase, NOX1 siRNA, and the NO synthase inhibitor NG-nitro-l-arginine methyl ester. Both tetrahydropbiopterin (BH4) and l-citrulline, two therapies that decrease ROS by recoupling endothelial NO synthase, reduced the hypoxia-induced increase in SNAT1 expression. BH4 and l-citrulline treatment improved NO production in hypoxic PAECs despite a reduction in SNAT1 expression. In conclusion, SNAT1 expression is modulated by ROS in PAECs from newborn piglets. However, ROS-mediated decreases in SNAT1 expression per se do not implicate a reduction in NO production. Although SNAT1 may be critical to l-citrulline-induced increases in NO production, therapies designed to alter SNAT1 expression may not lead to a concordant change in NO production. NEW & NOTEWORTHY Na+-coupled neutral amino acid transporter 1 (SNAT1) modulates nitric oxide (NO) production in piglet pulmonary arterial endothelial cells. Factors that regulate SNAT1 expression in pulmonary arterial endothelial cells are unclear. Here, we show that ROS-reducing strategies inhibit hypoxia-induced increases in SNAT1 expression. l-Citrulline and tetrahydropbiopterin decrease SNAT1 expression but increase NO production. Although SNAT1 is modulated by ROS, changes in SNAT1 expression may not cause a concordant change in NO production.
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Affiliation(s)
- Anna E Dikalova
- Department of Pediatrics, Vanderbilt University Medical Center , Nashville, Tennessee.,Department of Medicine, Vanderbilt University Medical Center , Nashville, Tennessee
| | - Judy L Aschner
- Department of Pediatrics, Albert Einstein College of Medicine, The Bronx, New York
| | - Yongmei Zhang
- Department of Pediatrics, Vanderbilt University Medical Center , Nashville, Tennessee.,Department of Pediatrics, University of Utah Health , Salt Lake City, Utah
| | - Mark R Kaplowitz
- Department of Pediatrics, Vanderbilt University Medical Center , Nashville, Tennessee.,Department of Pediatrics, University of Utah Health , Salt Lake City, Utah
| | - Candice D Fike
- Department of Pediatrics, Vanderbilt University Medical Center , Nashville, Tennessee.,Department of Pediatrics, University of Utah Health , Salt Lake City, Utah
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Pedersen J, Hedegaard ER, Simonsen U, Krüger M, Infanger M, Grimm D. Current and Future Treatments for Persistent Pulmonary Hypertension in the Newborn. Basic Clin Pharmacol Toxicol 2018; 123:392-406. [PMID: 29855164 DOI: 10.1111/bcpt.13051] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/20/2018] [Accepted: 05/27/2018] [Indexed: 01/18/2023]
Abstract
Persistent pulmonary hypertension in newborn (PPHN) is a serious and possibly fatal syndrome characterized by sustained foetal elevation of pulmonary vascular resistance at birth. PPHN may manifest secondary to other conditions as meconium aspiration syndrome, infection and congenital diaphragmatic hernia. This MiniReview provides the reader with an overview of current and future treatment options for patients with PPHN without congenital diaphragmatic hernia. The study is based on systematic searches in the databases PubMed and Cochrane Library and registered studies on Clinicaltrials.gov investigating PPHN. Inhaled nitric oxide (iNO) is well documented for treatment of PPHN, but 30% fail to respond to iNO. Other current treatment options could be sildenafil, milrinone, prostaglandin analogues and bosentan. There are several ongoing trials with sildenafil, but evidence is lacking for the other treatments and/or for the combination with iNO. Currently, there is no evidence for effect in PPHN of other treatments, for example tadalafil, macitentan, ambrisentan, riociguat and selexipag used for pulmonary arterial hypertension in adults. Experimental studies in animal models for PPHN suggest effect of a series of approaches including recombinant human superoxide dismutase, L-citrulline, Rho-kinase inhibitors and peroxisome proliferator-activated receptor-γ agonists. We conclude that iNO is the most investigated and the only approved pulmonary vasodilator for infants with PPHN. In the iNO non-responders, sildenafil currently seems to be the best alternative either alone or in combination with iNO. Systematic and larger clinical studies are required for testing the other potential treatments of PPHN.
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Affiliation(s)
- Jonas Pedersen
- Department of Biomedicine, Pharmacology, Aarhus University, Aarhus, Denmark
| | - Elise R Hedegaard
- Department of Biomedicine, Pharmacology, Aarhus University, Aarhus, Denmark
| | - Ulf Simonsen
- Department of Biomedicine, Pharmacology, Aarhus University, Aarhus, Denmark
| | - Marcus Krüger
- Clinic for Plastic, Aesthetic and Hand Surgery, Otto-von-Guericke-University Magdeburg, Magdeburg, Germany
| | - Manfred Infanger
- Clinic for Plastic, Aesthetic and Hand Surgery, Otto-von-Guericke-University Magdeburg, Magdeburg, Germany
| | - Daniela Grimm
- Department of Biomedicine, Pharmacology, Aarhus University, Aarhus, Denmark.,Clinic for Plastic, Aesthetic and Hand Surgery, Otto-von-Guericke-University Magdeburg, Magdeburg, Germany
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5
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Fike CD, Dikalova A, Kaplowitz MR, Cunningham G, Summar M, Aschner JL. Rescue Treatment with L-Citrulline Inhibits Hypoxia-Induced Pulmonary Hypertension in Newborn Pigs. Am J Respir Cell Mol Biol 2015; 53:255-64. [PMID: 25536367 DOI: 10.1165/rcmb.2014-0351oc] [Citation(s) in RCA: 38] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023] Open
Abstract
Infants with cardiopulmonary disorders associated with hypoxia develop pulmonary hypertension. We previously showed that initiation of oral L-citrulline before and continued throughout hypoxic exposure improves nitric oxide (NO) production and ameliorates pulmonary hypertension in newborn piglets. Rescue treatments, initiated after the onset of pulmonary hypertension, better approximate clinical strategies. Mechanisms by which L-citrulline improves NO production merit elucidation. The objective of this study was to determine whether starting L-citrulline after the onset of pulmonary hypertension inhibits disease progression and improves NO production by recoupling endothelial NO synthase (eNOS). Hypoxic and normoxic (control) piglets were studied. Some hypoxic piglets received oral L-citrulline starting on Day 3 of hypoxia and continuing throughout the remaining 7 days of hypoxic exposure. Catheters were placed for hemodynamic measurements, and pulmonary arteries were dissected to assess NO production and eNOS dimer-to-monomer ratios (a measure of eNOS coupling). Pulmonary vascular resistance was lower in L-citrulline-treated hypoxic piglets than in untreated hypoxic piglets but was higher than in normoxic controls. NO production and eNOS dimer-to-monomer ratios were greater in pulmonary arteries from L-citrulline-treated than from untreated hypoxic animals but were lower than in normoxic controls. When started after disease onset, oral L-citrulline treatment improves NO production by recoupling eNOS and inhibits the further development of chronic hypoxia-induced pulmonary hypertension in newborn piglets. Oral L-citrulline may be a novel strategy to halt or reverse pulmonary hypertension in infants suffering from cardiopulmonary conditions associated with hypoxia.
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Affiliation(s)
- Candice D Fike
- 1 Department of Pediatrics, Vanderbilt University Medical Center, Nashville, Tennessee.,2 Monroe Carell Jr. Children's Hospital at Vanderbilt, Nashville, Tennessee
| | - Anna Dikalova
- 1 Department of Pediatrics, Vanderbilt University Medical Center, Nashville, Tennessee
| | - Mark R Kaplowitz
- 1 Department of Pediatrics, Vanderbilt University Medical Center, Nashville, Tennessee
| | - Gary Cunningham
- 3 Division of Genetics and Metabolism, Children's National Medical Center, Washington, District of Columbia; and
| | - Marshall Summar
- 3 Division of Genetics and Metabolism, Children's National Medical Center, Washington, District of Columbia; and
| | - Judy L Aschner
- 4 Department of Pediatrics, Albert Einstein College of Medicine and the Children's Hospital at Montefiore, New York, New York
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Zielińska M, Obara-Michlewska M, Hilgier W, Albrecht J. Citrulline uptake in rat cerebral cortex slices: modulation by Thioacetamide -Induced hepatic failure. Metab Brain Dis 2014; 29:1053-60. [PMID: 24385142 PMCID: PMC4234898 DOI: 10.1007/s11011-013-9472-5] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/05/2013] [Accepted: 12/13/2013] [Indexed: 11/01/2022]
Abstract
L-citrulline (Cit) is a co-product of NO synthesis and a direct L-arginine (Arg) precursor for de novo NO synthesis. Acute liver failure (ALF) is associated with increased nitric oxide (NO) and cyclic GMP (cGMP) synthesis in the brain, indirectly implicating a role for active transport of Cit. In the present study we characterized [(3)H]Cit uptake to the cortical brain slices obtained from control rats and rats with thioacetamide (TAA)-induced ALF ("TAA slices"). In both control and TAA slices the uptake was partially Na(+)-dependent and markedly inhibited by substrates of systems L and N, including L-glutamine (Gln), which accumulates in excess in brain during ALF. Cit uptake was not affected by Arg, the y(+)/y(+)L transport system substrate, nor by amino acids taken up by systems A, xc (-)or XAG. The Vmax of the uptake in TAA slices was ~60 % higher than in control slices. Chromatographic (HPLC) analysis revealed a ~30 % increase of Cit concentration in the cerebral cortical homogenates of TAA rats. The activity of argininosuccinate synthase (ASS) and argininosuccinate lyase (ASL), the two enzymes of Cit-NO cycle catalyzing synthesis of Arg, showed an increase in TAA rats, consistent with increased ASS and ASL protein expression, by ~30 and ~20 %, respectively. The increased Cit-NO cycle activity was paralleled by increased expression of mRNA coding for inducible nitric oxide synthase (iNOS). Taken together, the results suggest a role for Cit in the activation of cerebral NO synthesis during ALF.
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Affiliation(s)
- Magdalena Zielińska
- Department of Neurotoxicology, Medical Research Centre, Polish Academy of Sciences, Pawinskiego 5, 02-106 Warsaw, Poland
| | - Marta Obara-Michlewska
- Department of Neurotoxicology, Medical Research Centre, Polish Academy of Sciences, Pawinskiego 5, 02-106 Warsaw, Poland
| | - Wojciech Hilgier
- Department of Neurotoxicology, Medical Research Centre, Polish Academy of Sciences, Pawinskiego 5, 02-106 Warsaw, Poland
| | - Jan Albrecht
- Department of Neurotoxicology, Medical Research Centre, Polish Academy of Sciences, Pawinskiego 5, 02-106 Warsaw, Poland
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Fike CD, Summar M, Aschner JL. L-citrulline provides a novel strategy for treating chronic pulmonary hypertension in newborn infants. Acta Paediatr 2014; 103:1019-26. [PMID: 24862864 DOI: 10.1111/apa.12707] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/22/2013] [Revised: 03/23/2014] [Accepted: 05/23/2014] [Indexed: 02/05/2023]
Abstract
UNLABELLED Effective therapies are urgently needed for infants with forms of pulmonary hypertension that develop or persist beyond the first week of life. The L-arginine nitric oxide (NO) precursor, L-citrulline, improves NO signalling and ameliorates pulmonary hypertension in newborn animals. In vitro studies demonstrate that manipulating L-citrulline transport alters NO production. CONCLUSION Strategies that increase the supply and transport of L-citrulline merit pursuit as novel approaches to managing infants with chronic, progressive pulmonary hypertension.
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Affiliation(s)
- Candice D. Fike
- Department of Pediatrics; Vanderbilt University Medical Center; Nashville TN USA
- Monroe Carell Jr. Children's Hospital at Vanderbilt; Nashville TN USA
| | - Marshall Summar
- Division of Genetics and Metabolism; Children's National Medical Center; Washington DC USA
| | - Judy L. Aschner
- Department of Pediatrics; Albert Einstein College of Medicine and the Children's Hospital at Montefiore; New York NY USA
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8
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Cuffe JSM, Walton SL, Singh RR, Spiers JG, Bielefeldt-Ohmann H, Wilkinson L, Little MH, Moritz KM. Mid- to late term hypoxia in the mouse alters placental morphology, glucocorticoid regulatory pathways and nutrient transporters in a sex-specific manner. J Physiol 2014; 592:3127-41. [PMID: 24801305 DOI: 10.1113/jphysiol.2014.272856] [Citation(s) in RCA: 86] [Impact Index Per Article: 8.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022] Open
Abstract
Maternal hypoxia is a common perturbation that can disrupt placental and thus fetal development, contributing to neonatal impairments. Recently, evidence has suggested that physiological outcomes are dependent upon the sex of the fetus, with males more susceptible to hypoxic insults than females. This study investigated the effects of maternal hypoxia during mid- to late gestation on fetal growth and placental development and determined if responses were sex specific. CD1 mice were housed under 21% or 12% oxygen from embryonic day (E) 14.5 until tissue collection at E18.5. Fetuses and placentas were weighed before collection for gene and protein expression and morphological analysis. Hypoxia reduced fetal weight in both sexes at E18.5 by 7% but did not affect placental weight. Hypoxia reduced placental mRNA levels of the mineralocorticoid and glucocorticoid receptors and reduced the gene and protein expression of the glucocorticoid metabolizing enzyme HSD11B2. However, placentas of female fetuses responded differently to maternal hypoxia than did placentas of male fetuses. Notably, morphology was significantly altered in placentas from hypoxic female fetuses, with a reduction in placental labyrinth blood spaces. In addition mRNA expression of Glut1, Igf2 and Igf1r were reduced in placentas of female fetuses only. In summary, maternal hypoxia altered placental formation in a sex specific manner through mechanisms involving placental vascular development, growth factor and nutrient transporter expression and placental glucocorticoid signalling. This study provides insight into how sex differences in offspring disease development may be due to sex specific placental adaptations to maternal insults.
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Affiliation(s)
- J S M Cuffe
- School of Biomedical Sciences, The University of Queensland, St Lucia, Queensland, Australia
| | - S L Walton
- School of Biomedical Sciences, The University of Queensland, St Lucia, Queensland, Australia
| | - R R Singh
- School of Biomedical Sciences, The University of Queensland, St Lucia, Queensland, Australia
| | - J G Spiers
- School of Biomedical Sciences, The University of Queensland, St Lucia, Queensland, Australia
| | - H Bielefeldt-Ohmann
- School of Veterinary Science, The University of Queensland, Gatton, Queensland, Australia
| | - L Wilkinson
- Institute for Molecular Bioscience, The University of Queensland, St Lucia, Queensland, Australia
| | - M H Little
- Institute for Molecular Bioscience, The University of Queensland, St Lucia, Queensland, Australia
| | - K M Moritz
- School of Biomedical Sciences, The University of Queensland, St Lucia, Queensland, Australia
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Sodium-coupled neutral amino acid transporter 1 (SNAT1) modulates L-citrulline transport and nitric oxide (NO) signaling in piglet pulmonary arterial endothelial cells. PLoS One 2014; 9:e85730. [PMID: 24454923 PMCID: PMC3893279 DOI: 10.1371/journal.pone.0085730] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/16/2013] [Accepted: 11/30/2013] [Indexed: 01/22/2023] Open
Abstract
RATIONALE There is evidence that impairments in nitric oxide (NO) signaling contribute to chronic hypoxia-induced pulmonary hypertension. The L-arginine-NO precursor, L-citrulline, has been shown to ameliorate pulmonary hypertension. Sodium-coupled neutral amino acid transporters (SNATs) are involved in the transport of L-citrulline into pulmonary arterial endothelial cells (PAECs). The functional link between the SNATs, L-citrulline, and NO signaling has not yet been explored. OBJECTIVE We tested the hypothesis that changes in SNAT1 expression and transport function regulate NO production by modulating eNOS coupling in newborn piglet PAECs. METHODS AND RESULTS A silencing RNA (siRNA) technique was used to assess the contribution of SNAT1 to NO production and eNOS coupling (eNOS dimer-to-monomer ratios) in PAECs from newborn piglets cultured under normoxic and hypoxic conditions in the presence and absence of L-citrulline. SNAT1 siRNA reduced basal NO production in normoxic PAECs and prevented L-citrulline-induced elevations in NO production in both normoxic and hypoxic PAECs. SNAT1 siRNA reduced basal eNOS dimer-to-monomer ratios in normoxic PAECs and prevented L-citrulline-induced increases in eNOS dimer-to-monomer ratios in hypoxic PAECs. CONCLUSIONS SNAT1 mediated L-citrulline transport modulates eNOS coupling and thus regulates NO production in hypoxic PAECs from newborn piglets. Strategies that increase SNAT1-mediated transport and supply of L-citrulline may serve as novel therapeutic approaches to enhance NO production in patients with pulmonary vascular disease.
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Abstract
Genetically modified mouse models have unparalleled power to determine the mechanisms behind different processes involved in the molecular and physiologic etiology of various classes of human pulmonary hypertension (PH). Processes known to be involved in PH for which there are extensive mouse models available include the following: (1) Regulation of vascular tone through secreted vasoactive factors; (2) regulation of vascular tone through potassium and calcium channels; (3) regulation of vascular remodeling through alteration in metabolic processes, either through alteration in substrate usage or through circulating factors; (4) spontaneous vascular remodeling either before or after development of elevated pulmonary pressures; and (5) models in which changes in tone and remodeling are primarily driven by inflammation. PH development in mice is of necessity faster and with different physiologic ramifications than found in human disease, and so mice make poor models of natural history of PH. However, transgenic mouse models are a perfect tool for studying the processes involved in pulmonary vascular function and disease, and can effectively be used to test interventions designed against particular molecular pathways and processes involved in disease.
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Affiliation(s)
- Mita Das
- Department of Internal Medicine, University of Arkansas Medical Sciences, Little Rock, Arkansas, USA
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Ware LB, Magarik JA, Wickersham N, Cunningham G, Rice TW, Christman BW, Wheeler AP, Bernard GR, Summar ML. Low plasma citrulline levels are associated with acute respiratory distress syndrome in patients with severe sepsis. CRITICAL CARE : THE OFFICIAL JOURNAL OF THE CRITICAL CARE FORUM 2013; 17:R10. [PMID: 23327349 PMCID: PMC4056746 DOI: 10.1186/cc11934] [Citation(s) in RCA: 50] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 07/11/2012] [Accepted: 01/09/2013] [Indexed: 01/11/2023]
Abstract
INTRODUCTION The role of nitric oxide synthase (NOS) in the pathophysiology of acute respiratory distress syndrome (ARDS) is not well understood. Inducible NOS is upregulated during physiologic stress; however, if NOS substrate is insufficient then NOS can uncouple and switch from NO generation to production of damaging peroxynitrites. We hypothesized that NOS substrate levels are low in patients with severe sepsis and that low levels of the NOS substrate citrulline would be associated with end organ damage including ARDS in severe sepsis. METHODS Plasma citrulline, arginine and ornithine levels and nitrate/nitrite were measured at baseline in 135 patients with severe sepsis. ARDS was diagnosed by consensus definitions. RESULTS Plasma citrulline levels were below normal in all patients (median 9.2 uM, IQR 5.2 - 14.4) and were significantly lower in ARDS compared to the no ARDS group (6.0 (3.3 - 10.4) vs. 10.1 (6.2 - 16.6), P = 0.002). The rate of ARDS was 50% in the lowest citrulline quartile compared to 15% in the highest citrulline quartile (P = 0.002). In multivariable analyses, citrulline levels were associated with ARDS even after adjustment for covariates including severity of illness. CONCLUSIONS In severe sepsis, levels of the NOS substrate citrulline are low and are associated with ARDS. Low NOS substrate levels have been shown in other disease states to lead to NOS uncoupling and oxidative injury suggesting a potential mechanism for the association between low citrulline and ARDS. Further studies are needed to determine whether citrulline supplementation could prevent the development of ARDS in patients with severe sepsis and to determine its role in NOS coupling and function.
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