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The Adenosine System at the Crossroads of Intestinal Inflammation and Neoplasia. Int J Mol Sci 2020; 21:ijms21145089. [PMID: 32708507 PMCID: PMC7403993 DOI: 10.3390/ijms21145089] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/30/2020] [Revised: 07/13/2020] [Accepted: 07/16/2020] [Indexed: 12/14/2022] Open
Abstract
Adenosine is a purine nucleoside, resulting from the degradation of adenosine triphosphate (ATP). Under adverse conditions, including hypoxia, ischemia, inflammation, or cancer, the extracellular levels of adenosine increase significantly. Once released, adenosine activates cellular signaling pathways through the engagement of the four known G-protein-coupled receptors, adenosine A1 receptor subtype (A1), A2A, A2B, and A3. These receptors, expressed virtually on all immune cells, mitigate all aspects of immune/inflammatory responses. These immunosuppressive effects contribute to blunt the exuberant inflammatory responses, shielding cells, and tissues from an excessive immune response and immune-mediated damage. However, a prolonged persistence of increased adenosine concentrations can be deleterious, participating in the creation of an immunosuppressed niche, ideal for neoplasia onset and development. Based on this evidence, the present review has been conceived to provide a comprehensive and critical overview of the involvement of adenosine system in shaping the molecular mechanisms underlying the enteric chronic inflammation and in promoting the generation of an immunosuppressive niche useful for the colorectal tumorigenesis.
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Hydralazine Sensitizes to the Antifibrotic Effect of 5-Aza-2'-deoxycytidine in Hepatic Stellate Cells. BIOLOGY 2020; 9:biology9060117. [PMID: 32503264 PMCID: PMC7345531 DOI: 10.3390/biology9060117] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 03/19/2020] [Revised: 05/21/2020] [Accepted: 05/27/2020] [Indexed: 11/17/2022]
Abstract
BACKGROUND Hepatic stellate cell (HSC) activation is essential for the development of liver fibrosis. Epigenetic machinery, such as DNA methylation, is largely involved in the regulation of gene expression during HSC activation. Although the pharmacological DNA demethylation of HSC using 5-aza-2'-deoxycytidine (5-aza-dC) yielded an antifibrotic effect, this drug has been reported to induce excessive cytotoxicity at a high dose. Hydralazine (HDZ), an antihypertensive agent, also exhibits non-nucleoside demethylating activity. However, the effect of HDZ on HSC activation remains unclear. In this study, we performed a combined treatment with 5-aza-dC and HDZ to obtain an enhanced antifibrotic effect with lower cytotoxicity. METHODS HSC-T6 cells were used as a rat HSC cell line in this study. The cells were cultivated together with 1 µM 5-Aza-dC and/or 10 µg/mL of HDZ, which were refreshed every 24 h until the 96 h treatment ended. Cell proliferation was measured using the WST-1 assay. The mRNA expression levels of peptidylprolyl isomerase A (Ppia), an internal control gene, collagen type I alpha 1 (Cola1), RAS protein activator like 1 (Rasal1), and phosphatase and tensin homolog deleted from chromosome 10 (Pten) were analyzed using quantitative reverse transcription polymerase chain reaction. RESULTS The percentage cell viability with 5-aza-dC, HDZ, and combined treatment vs. the vehicle-only control was 101.4 ± 2.5, 95.2 ± 5.7, and 79.2 ± 0.7 (p < 0.01 for 5-aza-dC and p < 0.01 for HDZ), respectively, in the 48 h treatment, and 52.4 ± 5.6, 65.9 ± 3.4, and 29.9 ± 1.3 (p < 0.01 for 5-aza-dC and p < 0.01 for HDZ), respectively, in the 96 h treatment. 5-Aza-dC and the combined treatment markedly decreased Cola1 mRNA levels. Accordingly, the expression levels of Rasal1 and Pten, which are antifibrotic genes, were increased by treatment after the 5-aza-dC and combined treatments. Moreover, single treatment with HDZ did not affect the expression levels of Cola1, Rasal1, or Pten. These results suggest that HDZ sensitizes to the antifibrotic effect of 5-aza-dC in HSC-T6 cells. The molecular mechanism underlying the sensitization to the antifibrotic effect of 5-aza-dC by HDZ remains to be elucidated. The expression levels of rat equilibrative nucleoside transporter genes (rEnt1, rEnt2, and rEnt3) were not affected by HDZ in this study. CONCLUSIONS Further confirmation using primary HSCs and in vivo animal models is desirable, but combined treatment with 5-aza-dC and HDZ may be an effective therapy for liver fibrosis without severe adverse effects.
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Ko J, Rounds S, Lu Q. Sustained adenosine exposure causes endothelial mitochondrial dysfunction via equilibrative nucleoside transporters. Pulm Circ 2020; 10:2045894020924994. [PMID: 32523687 PMCID: PMC7235668 DOI: 10.1177/2045894020924994] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/21/2020] [Accepted: 04/16/2020] [Indexed: 12/12/2022] Open
Abstract
Adenosine is a potent signaling molecule that has paradoxical effects on lung diseases. We have previously demonstrated that sustained adenosine exposure by inhibition of adenosine degradation impairs lung endothelial barrier integrity and causes intrinsic apoptosis through equilibrative nucleoside transporter1/2-mediated intracellular adenosine signaling. In this study, we further demonstrated that sustained adenosine exposure increased mitochondrial reactive oxygen species and reduced mitochondrial respiration via equilibrative nucleoside transporter1/2, but not via adenosine receptor-mediated signaling. We have previously shown that sustained adenosine exposure activates p38 and c-Jun N-terminal kinases in mitochondria. Here, we show that activation of p38 and JNK partially contributed to sustained adenosine-induced mitochondrial reactive oxygen species production. We also found that sustained adenosine exposure promoted mitochondrial fission and increased mitophagy. Finally, mitochondria-targeted antioxidants prevented sustained adenosine exposure-induced mitochondrial fission and improved cell survival. Our results suggest that inhibition of equilibrative nucleoside transporter1/2 and mitochondria-targeted antioxidants may be potential therapeutic approaches for lung diseases associated with sustained elevated adenosine.
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Affiliation(s)
- Junsuk Ko
- Vascular Research Laboratory, Providence Veterans Affairs Medical Center, Providence, RI, USA.,MD Anderson Cancer Center and University of Texas Health Science at Houston Graduate School, Houston, TX, USA.,Department of Biochemistry and Molecular Biology, McGovern Medical School, Houston, TX, USA
| | - Sharon Rounds
- Vascular Research Laboratory, Providence Veterans Affairs Medical Center, Providence, RI, USA.,Department of Medicine, Alpert Medical School of Brown University, Providence, RI, USA
| | - Qing Lu
- Vascular Research Laboratory, Providence Veterans Affairs Medical Center, Providence, RI, USA.,Department of Medicine, Alpert Medical School of Brown University, Providence, RI, USA
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4
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Chambers ED, White A, Vang A, Wang Z, Ayala A, Weng T, Blackburn M, Choudhary G, Rounds S, Lu Q. Blockade of equilibrative nucleoside transporter 1/2 protects against Pseudomonas aeruginosa-induced acute lung injury and NLRP3 inflammasome activation. FASEB J 2020; 34:1516-1531. [PMID: 31914698 PMCID: PMC7045807 DOI: 10.1096/fj.201902286r] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/10/2019] [Revised: 11/13/2019] [Accepted: 11/14/2019] [Indexed: 11/11/2022]
Abstract
Pseudomonas aeruginosa infections are increasingly multidrug resistant and cause healthcare-associated pneumonia, a major risk factor for acute lung injury (ALI)/acute respiratory distress syndrome (ARDS). Adenosine is a signaling nucleoside with potential opposing effects; adenosine can either protect against acute lung injury via adenosine receptors or cause lung injury via adenosine receptors or equilibrative nucleoside transporter (ENT)-dependent intracellular adenosine uptake. We hypothesized that blockade of intracellular adenosine uptake by inhibition of ENT1/2 would increase adenosine receptor signaling and protect against P. aeruginosa-induced acute lung injury. We observed that P. aeruginosa (strain: PA103) infection induced acute lung injury in C57BL/6 mice in a dose- and time-dependent manner. Using ENT1/2 pharmacological inhibitor, nitrobenzylthioinosine (NBTI), and ENT1-null mice, we demonstrated that ENT blockade elevated lung adenosine levels and significantly attenuated P. aeruginosa-induced acute lung injury, as assessed by lung wet-to-dry weight ratio, BAL protein levels, BAL inflammatory cell counts, pro-inflammatory cytokines, and pulmonary function (total lung volume, static lung compliance, tissue damping, and tissue elastance). Using both agonists and antagonists directed against adenosine receptors A2AR and A2BR, we further demonstrated that ENT1/2 blockade protected against P. aeruginosa -induced acute lung injury via activation of A2AR and A2BR. Additionally, ENT1/2 chemical inhibition and ENT1 knockout prevented P. aeruginosa-induced lung NLRP3 inflammasome activation. Finally, inhibition of inflammasome prevented P. aeruginosa-induced acute lung injury. Our results suggest that targeting ENT1/2 and NLRP3 inflammasome may be novel strategies for prevention and treatment of P. aeruginosa-induced pneumonia and subsequent ARDS.
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Affiliation(s)
- Eboni D. Chambers
- Vascular Research Laboratory, Providence Veterans Affairs Medical Center, Alpert Medical School of Brown University, Providence, RI 02908
| | - Alexis White
- Vascular Research Laboratory, Providence Veterans Affairs Medical Center, Alpert Medical School of Brown University, Providence, RI 02908
| | - Alexander Vang
- Vascular Research Laboratory, Providence Veterans Affairs Medical Center, Alpert Medical School of Brown University, Providence, RI 02908
| | - Zhengke Wang
- Vascular Research Laboratory, Providence Veterans Affairs Medical Center, Alpert Medical School of Brown University, Providence, RI 02908
| | - Alfred Ayala
- Division of Surgical Research, Rhode Island Hospital, Alpert Medical School of Brown University, Providence, RI 02908
| | - Tingting Weng
- Departments of Biochemistry and Molecular Biology, University of Texas-Houston Medical School, Houston, TX 77030
| | - Michael Blackburn
- Departments of Biochemistry and Molecular Biology, University of Texas-Houston Medical School, Houston, TX 77030
| | - Gaurav Choudhary
- Vascular Research Laboratory, Providence Veterans Affairs Medical Center, Alpert Medical School of Brown University, Providence, RI 02908
| | - Sharon Rounds
- Vascular Research Laboratory, Providence Veterans Affairs Medical Center, Alpert Medical School of Brown University, Providence, RI 02908
| | - Qing Lu
- Vascular Research Laboratory, Providence Veterans Affairs Medical Center, Alpert Medical School of Brown University, Providence, RI 02908
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Miller SG, Hafen PS, Brault JJ. Increased Adenine Nucleotide Degradation in Skeletal Muscle Atrophy. Int J Mol Sci 2019; 21:E88. [PMID: 31877712 PMCID: PMC6981514 DOI: 10.3390/ijms21010088] [Citation(s) in RCA: 32] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/03/2019] [Revised: 12/17/2019] [Accepted: 12/19/2019] [Indexed: 12/23/2022] Open
Abstract
Adenine nucleotides (AdNs: ATP, ADP, AMP) are essential biological compounds that facilitate many necessary cellular processes by providing chemical energy, mediating intracellular signaling, and regulating protein metabolism and solubilization. A dramatic reduction in total AdNs is observed in atrophic skeletal muscle across numerous disease states and conditions, such as cancer, diabetes, chronic kidney disease, heart failure, COPD, sepsis, muscular dystrophy, denervation, disuse, and sarcopenia. The reduced AdNs in atrophic skeletal muscle are accompanied by increased expression/activities of AdN degrading enzymes and the accumulation of degradation products (IMP, hypoxanthine, xanthine, uric acid), suggesting that the lower AdN content is largely the result of increased nucleotide degradation. Furthermore, this characteristic decrease of AdNs suggests that increased nucleotide degradation contributes to the general pathophysiology of skeletal muscle atrophy. In view of the numerous energetic, and non-energetic, roles of AdNs in skeletal muscle, investigations into the physiological consequences of AdN degradation may provide valuable insight into the mechanisms of muscle atrophy.
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Affiliation(s)
| | | | - Jeffrey J. Brault
- Indiana Center for Musculoskeletal Health, Indiana University School of Medicine, Department of Anatomy, Cell Biology & Physiology, 635 Barnhill Dr., Van Nuys Medical Science Bldg. 5035, Indianapolis, IN 46202, USA; (S.G.M.); (P.S.H.)
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Pulmonary Endothelial Cell Apoptosis in Emphysema and Acute Lung Injury. ADVANCES IN ANATOMY EMBRYOLOGY AND CELL BIOLOGY 2019; 228:63-86. [PMID: 29288386 DOI: 10.1007/978-3-319-68483-3_4] [Citation(s) in RCA: 49] [Impact Index Per Article: 9.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
Apoptosis plays an essential role in homeostasis and pathogenesis of a variety of human diseases. Endothelial cells are exposed to various environmental and internal stress and endothelial apoptosis is a pathophysiological consequence of these stimuli. Pulmonary endothelial cell apoptosis initiates or contributes to progression of a number of lung diseases. This chapter will focus on the current understanding of the role of pulmonary endothelial cell apoptosis in the development of emphysema and acute lung injury (ALI) and the factors controlling pulmonary endothelial life and death.
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Bernareggi A, Sciancalepore M, Lorenzon P. Interplay Between Cholinergic and Adenosinergic Systems in Skeletal Muscle. Neuroscience 2019; 439:41-47. [PMID: 31121259 DOI: 10.1016/j.neuroscience.2019.05.020] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/30/2019] [Revised: 05/06/2019] [Accepted: 05/07/2019] [Indexed: 02/06/2023]
Abstract
Since the pioneering works of Ricardo Miledi, the neuromuscular junction represents the best example of a synapse where ACh is the neurotransmitter acting on nicotinic ACh receptors. ATP, co-released with ACh, is promptly degraded to Ado, which acts as a modulator of the cholinergic synaptic activity. Consequently, both ACh and adenosine play a crucial role in controlling the nerve-muscle communication. Apart from their role in the context of synaptic transmission, ACh and adenosine are autocrinally released by skeletal muscle cells, suggesting also a non nerve-driven function of these molecules. Indeed, the existence of cholinergic and adenosinergic systems has been widely described in many other non neuronal cell types. In this review, we will describe the two systems and their interplay in non-innervated differentiating skeletal muscle cells, and in innervated adult skeletal muscle fibers. We believe that the better comprehension of the interactions between the activity of nAChRs and adenosine could help the knowledge of skeletal muscle physiology. This article is part of a Special Issue entitled: Honoring Ricardo Miledi - outstanding neuroscientist of XX-XXI centuries.
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Affiliation(s)
- Annalisa Bernareggi
- Department of Life Sciences, University of Trieste, Trieste, Italy; B.R.A.I.N., Centre for Neuroscience, Trieste, Italy.
| | - Marina Sciancalepore
- Department of Life Sciences, University of Trieste, Trieste, Italy; B.R.A.I.N., Centre for Neuroscience, Trieste, Italy
| | - Paola Lorenzon
- Department of Life Sciences, University of Trieste, Trieste, Italy; B.R.A.I.N., Centre for Neuroscience, Trieste, Italy
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Transport of ribavirin across the rat and human placental barrier: Roles of nucleoside and ATP-binding cassette drug efflux transporters. Biochem Pharmacol 2019; 163:60-70. [DOI: 10.1016/j.bcp.2019.01.024] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/20/2018] [Accepted: 01/31/2019] [Indexed: 12/27/2022]
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Yang C, Leung GPH. Equilibrative Nucleoside Transporters 1 and 4: Which One Is a Better Target for Cardioprotection Against Ischemia-Reperfusion Injury? J Cardiovasc Pharmacol 2015; 65:517-21. [PMID: 26070128 PMCID: PMC4461397 DOI: 10.1097/fjc.0000000000000194] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/07/2014] [Accepted: 11/14/2014] [Indexed: 01/04/2023]
Abstract
The cardioprotective effects of adenosine and adenosine receptor agonists have been studied extensively. However, their therapeutic outcomes in ischemic heart disease are limited by systemic side effects such as hypotension, bradycardia, and sedation. Equilibrative nucleoside transporter (ENT) inhibitors may be an alternative. By reducing the uptake of extracellular adenosine, ENT1 inhibitors potentiate the cardioprotective effect of endogenous adenosine. They have fewer systemic side effects because they selectively increase the extracellular adenosine levels in ischemic tissues undergoing accelerated adenosine formation. Nonetheless, long-term inhibition of ENT1 may adversely affect tissues that have low capacity for de novo nucleotide biosynthesis. ENT1 inhibitors may also affect the cellular transport, and hence the efficacy, of anticancer and antiviral nucleoside analogs used in chemotherapy. It has been proposed that ENT4 may also contribute to the regulation of extracellular adenosine in the heart, especially under the acidotic conditions associated with ischemia. Like ENT1 inhibitors, ENT4 inhibitors should work specifically on ischemic tissues. Theoretically, ENT4 inhibitors do not affect tissues that rely on ENT1 for de novo nucleotide synthesis. They also have no interaction with anticancer and antiviral nucleosides. Development of specific ENT4 inhibitors may open a new avenue in research on ischemic heart disease therapy.
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Affiliation(s)
- Cui Yang
- Ethnic Drug Screening & Pharmacology Center, Key Laboratory of Chemistry in Ethnic Medicinal Resources, State Ethnic Affairs Commission & Ministry of Education, Yunnan Minzu University, Kunming, China; and
| | - George P. H. Leung
- Department of Pharmacology and Pharmacy, The University of Hong Kong, Hong Kong, China
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10
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Bone DB, Antic M, Vilas G, Hammond JR. Oxidative stress modulates nucleobase transport in microvascular endothelial cells. Microvasc Res 2014; 95:68-75. [DOI: 10.1016/j.mvr.2014.06.008] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/15/2014] [Revised: 06/07/2014] [Accepted: 06/10/2014] [Indexed: 12/23/2022]
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11
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Pharmacologic manipulation of coronary vascular physiology for the evaluation of coronary artery disease. Pharmacol Ther 2013; 140:121-32. [DOI: 10.1016/j.pharmthera.2013.06.004] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/21/2013] [Accepted: 05/23/2013] [Indexed: 11/24/2022]
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12
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Lu Q, Sakhatskyy P, Newton J, Shamirian P, Hsiao V, Curren S, Gabino Miranda GA, Pedroza M, Blackburn MR, Rounds S. Sustained adenosine exposure causes lung endothelial apoptosis: a possible contributor to cigarette smoke-induced endothelial apoptosis and lung injury. Am J Physiol Lung Cell Mol Physiol 2013; 304:L361-70. [PMID: 23316066 DOI: 10.1152/ajplung.00161.2012] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022] Open
Abstract
Pulmonary endothelial cell (EC) apoptosis has been implicated in the pathogenesis of emphysema. Cigarette smoke (CS) causes lung EC apoptosis and emphysema. In this study, we show that CS exposure increased lung tissue adenosine levels in mice, an effect associated with increased lung EC apoptosis and the development of emphysema. Adenosine has a protective effect against apoptosis via adenosine receptor-mediated signaling. However, sustained elevated adenosine increases alveolar cell apoptosis in adenosine deaminase-deficient mice. We established an in vitro model of sustained adenosine exposure by incubating lung EC with adenosine in the presence of an adenosine deaminase inhibitor, deoxycoformicin. We demonstrated that sustained adenosine exposure caused lung EC apoptosis via nucleoside transporter-facilitated intracellular adenosine uptake, subsequent activation of p38 and JNK in mitochondria, and ultimately mitochondrial defects and activation of the mitochondria-mediated intrinsic pathway of apoptosis. Our results suggest that sustained elevated adenosine may contribute to CS-induced lung EC apoptosis and emphysema. Our data also reconcile the paradoxical effects of adenosine on apoptosis, demonstrating that prolonged exposure causes apoptosis via nucleoside transporter-mediated intracellular adenosine signaling, whereas acute exposure protects against apoptosis via activation of adenosine receptors. Inhibition of adenosine uptake may become a new therapeutic target in treatment of CS-induced lung diseases.
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Affiliation(s)
- Qing Lu
- Vascular Research Laboratory, Providence Veterans Affairs Medical Center, Department of Medicine, Alpert Medical School of Brown University, Providence, RI 02908, USA.
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Lu Q, Newton J, Hsiao V, Shamirian P, Blackburn MR, Pedroza M. Sustained adenosine exposure causes lung endothelial barrier dysfunction via nucleoside transporter-mediated signaling. Am J Respir Cell Mol Biol 2012; 47:604-13. [PMID: 22744860 DOI: 10.1165/rcmb.2012-0012oc] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023] Open
Abstract
Previous studies by our group as well as others have shown that acute adenosine exposure enhances lung vascular endothelial barrier integrity and protects against increased permeability lung edema. In contrast, there is growing evidence that sustained adenosine exposure has detrimental effects on the lungs, including lung edema. It is well established that adenosine modulates lung inflammation. However, little is known concerning the effect of sustained adenosine exposure on lung endothelial cells (ECs), which are critical to the maintenance of the alveolar-capillary barrier. We show that exogenous adenosine plus adenosine deaminase inhibitor caused sustained elevation of adenosine in lung ECs. This sustained adenosine exposure decreased EC barrier function, elevated cellular reactive oxygen species levels, and activated p38, JNK, and RhoA. Inhibition of equilibrative nucleoside transporters (ENTs) prevented sustained adenosine-induced p38 and JNK activation and EC barrier dysfunction. Inhibition of p38, JNK, or RhoA also partially attenuated sustained adenosine-induced EC barrier dysfunction. These data indicate that sustained adenosine exposure causes lung EC barrier dysfunction via ENT-dependent intracellular adenosine uptake and subsequent activation of p38, JNK, and RhoA. The antioxidant N-acetylcysteine and the NADPH inhibitor partially blunted sustained adenosine-induced JNK activation but were ineffective in attenuation of p38 activation or barrier dysfunction. p38 was activated exclusively in mitochondria, whereas JNK was activated in mitochondria and cytoplasm by sustained adenosine exposure. Our data further suggest that sustained adenosine exposure may cause mitochondrial oxidative stress, leading to activation of p38, JNK, and RhoA in mitochondria and resulting in EC barrier dysfunction.
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Affiliation(s)
- Qing Lu
- Alpert Medical School of Brown University, Providence VA Medical Center, Research Services, 830 Chalkstone Avenue, Providence, RI 02908, USA.
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14
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Effects of exercise and antioxidant supplementation on endothelial gene expression. Int J Cardiol 2012; 158:59-65. [DOI: 10.1016/j.ijcard.2010.12.104] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/18/2010] [Revised: 11/04/2010] [Accepted: 12/30/2010] [Indexed: 11/20/2022]
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Abstract
BACKGROUND Nucleoside/nucleobase transporters have been investigated since the 1960s. In particular, equilibrative nucleoside transporters were thought to be valuable drug targets, since they are involved in various kinds of viral and parasitic diseases as well as cancers. DISCUSSION In the postgenomic era multiple transporters, including different subtypes, have been cloned and characterized on the molecular level. In this article we summarize recent advances regarding structure, function and localization of nucleoside/nucleobase transporters as well as the pharmacological profile of selected drugs. CONCLUSION Knowledge of the different kinetic properties and structural features of nucleoside transporters can either be used for the rational design of therapeutics directly targeting the transporter itself or for the delivery of drugs using the transporter as a port of entry into the target cell. Equilibrative nucleoside transporters are of considerable pharmacological interest as drug targets for the development of drugs tailored to each patient's need for the treatment of cardiac disease, cancer and viral infections.
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Guzmán-Gutiérrez E, Sandoval C, Nova E, Castillo J, Vera J, Lamperti L, Krause B, Salomón C, Sepúlveda C, Aguayo C, Sobrevia L. Differential expression of functional nucleoside transporters in non-differentiated and differentiated human endothelial progenitor cells. Placenta 2010; 31:928-36. [DOI: 10.1016/j.placenta.2010.07.016] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/11/2010] [Revised: 07/26/2010] [Accepted: 07/29/2010] [Indexed: 01/19/2023]
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Marvi M, Rose JB, Bang A, Moon BC, Pozeg Z, Ibrahim M, Peniston C, Coe IR. Nucleoside transporter expression profiles in human cardiac tissue show striking individual variability with overall predominance of hENT1. Eur J Pharm Sci 2010; 41:685-91. [PMID: 20883780 DOI: 10.1016/j.ejps.2010.09.013] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/23/2010] [Revised: 09/17/2010] [Accepted: 09/21/2010] [Indexed: 11/25/2022]
Abstract
Nucleoside transporters (NTs) are integral membrane transport proteins that modulate the flux of nucleosides such as adenosine across cell membranes. Two families of NTs exist, the concentrative NTs (CNTs, SLC28) and the equilibrative NTs (ENTs, SLC29). CNTs and ENTs transport anti-cancer and anti-viral nucleoside analog drugs and ENTs are also targets of drugs used to treat cardiac pathologies. Levels of some NT profiles have been shown to relate to clinical outcomes in the use of nucleoside analog drugs. However, currently, patient NT profile is not assessed prior to pharmacological administration of analog drugs. Here we describe a reliable method to determine a complete individual NT expression profile from human tissue using quantitative real-time PCR. We developed this assay on tissue (right atrial appendage, left internal mammary, aorta) from individuals undergoing cardiac surgery and compared these findings to the NT expression profiles in pooled whole heart tissue (normal and diseased). Data show that hENT1 is the most abundantly expressed NT, with highest expression levels in the aorta. However, NT expression profiles are highly variable among individuals and changes in NT expression between normal and diseased tissues were observed. These data are the first to describe the RNA expression patterns of all seven NT isoforms in the human heart. The methodology described here may be useful for quantitatively characterizing complete NT expression profiles in any human target tissue.
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Affiliation(s)
- Melissa Marvi
- Department of Biology, Muscle Health Research Centre, York University, Toronto, ON, Canada
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Bone DBJ, Choi DS, Coe IR, Hammond JR. Nucleoside/nucleobase transport and metabolism by microvascular endothelial cells isolated from ENT1−/− mice. Am J Physiol Heart Circ Physiol 2010; 299:H847-56. [DOI: 10.1152/ajpheart.00018.2010] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Nucleoside and nucleobase uptake is integral to mammalian cell function, and its disruption has significant effects on the cardiovasculature. The predominant transporters in this regard are the equilibrative nucleoside transporter subtypes 1 (ENT1) and 2 (ENT2). To examine the role of ENT1 in more detail, we have assessed the mechanisms by which microvascular endothelial cells (MVECs) from ENT1−/− mice transport and metabolize nucleosides and nucleobases. Wild-type murine MVECs express mainly the ENT1 subtype with only trace levels of ENT2. These cells also have a Na+-independent equilibrative nucleobase transport mechanism for hypoxanthine (ENBT1). In the ENT1−/− cells, there is no change in ENT2 or ENBT1, resulting in a very low level of nucleoside uptake in these cells, but a high capacity for nucleobase accumulation. Whereas there were no significant changes in nucleoside transporter subtype expression, there was a dramatic increase in adenosine deaminase and adenosine A2a receptors (both transcript and protein) in the ENT1−/− tissues compared with WT. These changes in adenosine deaminase and A2a receptors likely reflect adaptive cellular mechanisms in response to reduced adenosine flux across the membranes of ENT1−/− cells. Our study also revealed that mouse MVECs have a nucleoside/nucleobase transport profile that is more similar to human MVECs than to rat MVECs. Thus mouse MVECs from transgenic animals may prove to be a useful preclinical model for studies of the effects of purine metabolite modifiers on vascular function.
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Affiliation(s)
- Derek B. J. Bone
- Department of Physiology and Pharmacology, University of Western Ontario, London, Canada
| | - Doo-Sup Choi
- Molecular Pharmacology and Experimental Therapeutics, Mayo Clinic, Rochester, Minnesota; and
| | - Imogen R. Coe
- Department of Biology, York University, Toronto, Canada
| | - James R. Hammond
- Department of Physiology and Pharmacology, University of Western Ontario, London, Canada
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Giordano C, Sebastiani M, De Giorgio R, Travaglini C, Tancredi A, Valentino ML, Bellan M, Cossarizza A, Hirano M, d'Amati G, Carelli V. Gastrointestinal dysmotility in mitochondrial neurogastrointestinal encephalomyopathy is caused by mitochondrial DNA depletion. THE AMERICAN JOURNAL OF PATHOLOGY 2008; 173:1120-8. [PMID: 18787099 PMCID: PMC2543079 DOI: 10.2353/ajpath.2008.080252] [Citation(s) in RCA: 82] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
Chronic intestinal pseudo-obstruction is a life-threatening condition of unknown pathogenic mechanisms. Chronic intestinal pseudo-obstruction can be a feature of mitochondrial disorders, such as mitochondrial neurogastrointestinal encephalomyopathy (MNGIE), a rare autosomal-recessive syndrome, resulting from mutations in the thymidine phosphorylase gene. MNGIE patients show elevated circulating levels of thymidine and deoxyuridine, and accumulate somatic mitochondrial DNA (mtDNA) defects. The present study aimed to clarify the molecular basis of chronic intestinal pseudo-obstruction in MNGIE. Using laser capture microdissection, we correlated the histopathological features with mtDNA defects in different tissues from the gastrointestinal wall of five MNGIE and ten control patients. We found mtDNA depletion, mitochondrial proliferation, and smooth cell atrophy in the external layer of the muscularis propria, in the stomach and in the small intestine of MNGIE patients. In controls, the lowest amounts of mtDNA were present at the same sites, as compared with other layers of the gastrointestinal wall. We also observed mitochondrial proliferation and mtDNA depletion in small vessel endothelial and smooth muscle cells. Thus, visceral mitochondrial myopathy likely causes gastrointestinal dysmotility in MNGIE patients. The low baseline abundance of mtDNA molecules may predispose smooth muscle cells of the muscularis propria external layer to the toxic effects of thymidine and deoxyuridine, and exposure to high circulating levels of nucleosides may account for the mtDNA depletion observed in the small vessel wall.
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Affiliation(s)
- Carla Giordano
- Dipartimento di Medicina Sperimentale, Sapienza, Università di Roma, Roma, Italy
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20
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Rose JB, Coe IR. Physiology of Nucleoside Transporters: Back to the Future. . . . Physiology (Bethesda) 2008; 23:41-8. [DOI: 10.1152/physiol.00036.2007] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Nucleoside transporters (NTs) are integral membrane proteins responsible for mediating and facilitating the flux of nucleosides and nucleobases across cellular membranes. NTs are also responsible for the uptake of nucleoside analog drugs used in the treatment of cancer and viral infections, and they are the target of certain compounds used in the treatment of some types of cardiovascular disease. The important role of NTs as drug transporters and therapeutic targets has necessarily led to intense interest into their structure and function and the relationship between these proteins and drug efficacy. In contrast, we still know relatively little about the fundamental physiology of NTs. In this review, we discuss various aspects of the physiology of NTs in mammalian systems, particularly noting tissues and cells where there has been little recent research. Our central thesis is reference back to some of the older literature, combined with current findings, will provide direction for future research into NT physiology that will lead to a fuller understanding of the role of these intriguing proteins in the everyday lives of cells, tissues, organs, and whole animals.
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Affiliation(s)
- Jennifer B. Rose
- Department of Biology, York University, Toronto, Ontario, Canada,
| | - Imogen R. Coe
- Department of Biology, York University, Toronto, Ontario, Canada,
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21
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Robillard KR, Bone DBJ, Hammond JR. Hypoxanthine uptake and release by equilibrative nucleoside transporter 2 (ENT2) of rat microvascular endothelial cells. Microvasc Res 2007; 75:351-7. [PMID: 18048066 DOI: 10.1016/j.mvr.2007.10.002] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/03/2007] [Accepted: 10/09/2007] [Indexed: 12/21/2022]
Abstract
The cardioprotective actions of adenosine are terminated by its uptake into endothelial cells with subsequent metabolism through hypoxanthine to uric acid. This process involves xanthine oxidase-mediated generation of reactive oxygen species (ROS), which have been implicated in the vascular dysfunction observed in ischemia-reperfusion injury. The equilibrative nucleoside transporter, ENT2, mediates the transfer of hypoxanthine into cells. We hypothesize that ENT2 also mediates the cellular release of hypoxanthine, which would limit the amount of intracellular hypoxanthine available for xanthine oxidase-mediated ROS production. Rat microvascular endothelial cells (MVECs) were isolated from skeletal muscle by lectin-affinity purification. The transport of [(3)H]hypoxanthine was assessed using an oil-stop method, and hypoxanthine metabolites were identified by thin-layer chromatography. MVECs accumulated hypoxanthine with a K(m) of 300 microM and a V(max) of 2.8 pmol microl(-1) s(-1). ATP-depleted cells loaded with [(3)H]hypoxanthine released the radiolabel with kinetics similar to that obtained for [(3)H]hypoxanthine influx. The uptake and release of [(3)H]hypoxanthine were both blocked by ENT2 inhibitors with similar order of potency. Thus, ENT2 mediates both the influx and efflux of hypoxanthine. Inhibition of ENT2 in MVECs might be expected to increase the amount of intracellular hypoxanthine available for metabolism by xanthine oxidase and enhance the intracellular production of ROS.
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Affiliation(s)
- Kevin R Robillard
- Department of Physiology and Pharmacology, M216 Medical Sciences Building, University of Western Ontario London, ON, Canada N6A 5C1
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22
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Van Linden A, Eltzschig HK. Role of pulmonary adenosine during hypoxia: extracellular generation, signaling and metabolism by surface adenosine deaminase/CD26. Expert Opin Biol Ther 2007; 7:1437-47. [PMID: 17727332 DOI: 10.1517/14712598.7.9.1437] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
Abstract
Numerous parallels exist between limited oxygen availability (hypoxia) and acute inflammation. The lungs in particular are prone to acute inflammation during hypoxia, resulting in pulmonary edema, vascular leakage and neutrophil infiltration. The innate response elicited by hypoxia is associated with increased extracellular adenosine effects. Although studies on acute pulmonary hypoxia show a protective role of extracellular adenosine by attenuating pulmonary edema and excessive inflammation, chronic elevation of pulmonary adenosine may be detrimental. Adenosine deaminase (ADA)-deficient mice, for example, develop signs of chronic pulmonary injury in association with highly elevated levels of adenosine. Thus, the authors hypothesized the existence of hypoxia-elicited clearance mechanisms to offset deleterious influences of chronically elevated adenosine. Such studies indicated a second response to hypoxia characterized by pulmonary induction of ADA and CD26. In fact, hypoxia-inducible ADA is enzymatically active and tethered on the outside of the membrane via CD26 to form a complex capable of degrading extracellular adenosine to inosine. This paper reviews metabolic and transcriptional changes of extracellular adenosine generation, signaling and degradation during acute and prolonged pulmonary hypoxia.
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Affiliation(s)
- Annemie Van Linden
- University of Colorado Health Science Center, Mucosal Inflammation Program, Department of Anesthesiology, Perioperative Care and Pain Medicine, Biochemistry Research Building (BRB), Room 852, 4200 E. 9th Avenue, Campus Box B113, Denver, CO 80262, USA
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23
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Bone DBJ, Hammond JR. Nucleoside and nucleobase transporters of primary human cardiac microvascular endothelial cells: characterization of a novel nucleobase transporter. Am J Physiol Heart Circ Physiol 2007; 293:H3325-32. [PMID: 17921321 DOI: 10.1152/ajpheart.01006.2007] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Levels of cardiovascular active metabolites, like adenosine, are regulated by nucleoside transporters of endothelial cells. We characterized the nucleoside and nucleobase transport capabilities of primary human cardiac microvascular endothelial cells (hMVECs). hMVECs accumulated 2-[3H]chloroadenosine via the nitrobenzylmercaptopurine riboside-sensitive equilibrative nucleoside transporter 1 (ENT1) at a V(max) of 3.4 +/- 1 pmol.microl(-1).s(-1), with no contribution from the nitrobenzylmercaptopurine riboside-insensitive ENT2. Inhibition of 2-chloroadenosine uptake by ENT1 blockers produced monophasic inhibition curves, which are also compatible with minimal ENT2 expression. The nucleobase [3H]hypoxanthine was accumulated within hMVECs (K(m) = 96 +/- 37 microM; V(max) = 1.6 +/- 0.3 pmol.microl(-1).s(-1)) despite the lack of a known nucleobase transport system. This novel transporter was dipyridamole-insensitive but could be inhibited by adenine (K(i) = 19 +/- 7 microM) and other purine nucleobases, including chemotherapeutic analogs. A variety of other cell types also expressed the nucleobase transporter, including the nucleoside transporter-deficient PK(15) cell line (PK15NTD). Further characterization of [3H]hypoxanthine uptake in the PK15NTD cells showed no dependence on Na(+) or H(+). PK15NTD cells expressing human ENT2 accumulated 4.5-fold more [3H]hypoxanthine in the presence of the ENT2 inhibitor dipyridamole than did PK15NTD cells or hMVECs, suggesting trapping of ENT2-permeable metabolites. Understanding the nucleoside and nucleobase transporter profiles in the vasculature will allow for further study into their roles in pathophysiological conditions such as hypoxia or ischemia.
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Affiliation(s)
- Derek B J Bone
- Department of Physiology and Pharmacology, University of Western Ontario, London, Ontario, Canada
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24
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Abdulla P, Coe IR. Characterization and functional analysis of the promoter for the human equilibrative nucleoside transporter gene, hENT1. NUCLEOSIDES NUCLEOTIDES & NUCLEIC ACIDS 2007; 26:99-110. [PMID: 17162590 DOI: 10.1080/15257770601052331] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
Abstract
Equilibrative nucleoside transporters (ENTs) are membrane proteins that transport nucleosides, nucleobases and analogs across membranes. ENT genes and the regulation of their expression are poorly understood. Therefore, we isolated and functionally characterized the promoter of the prototypic human ENT, hENT1. A single transcriptional initiation site 58 bp downstream of the TATA box and 272 bp upstream of the translation initiation site is present. Limited sequence similarity exists between the hENT1 and mouse ENT1 (mENT1) promoters suggesting conservation of ENT1 transcriptional regulators in mammals. Putative consensus sites for transcription factors exist within the hENT1 promoter. Reporter assays revealed similar but not identical transcriptional activity profiles in human cells.
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Affiliation(s)
- Parween Abdulla
- Department of Biology, York University, Toronto, Ontario, Canada
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25
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Löffler M, Morote-Garcia JC, Eltzschig SA, Coe IR, Eltzschig HK. Physiological roles of vascular nucleoside transporters. Arterioscler Thromb Vasc Biol 2007; 27:1004-13. [PMID: 17332491 DOI: 10.1161/atvbaha.106.126714] [Citation(s) in RCA: 129] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023]
Abstract
Nucleoside transporters (NTs) comprise 2 widely expressed families, the equilibrative nucleoside transporters (diffusion-limited channels) and concentrative nucleoside transporters (sodium-dependent transporters). Because of their anatomic position at the blood-tissue interface, vascular NTs are in an ideal position to influence vascular nucleoside levels, particularly adenosine, which among others plays an important role in tissue protection during acute injury. For example, endothelial NTs contribute to preserving the vascular integrity during conditions of limited oxygen availability (hypoxia). Indeed, hypoxia-inducible factor-1-dependent repression of NTs results in enhanced extracellular adenosine signaling and thus attenuates hypoxia-associated increases in vascular leakage. In addition, vascular NTs also contribute to cardiac ischemic preconditioning, coronary vasodilation, and inhibition of platelet aggregation. Moreover, vascular nucleoside uptake via NTs is important for nucleoside recovery, particularly in cells lacking de novo nucleotide synthesis pathways (erythrocytes, leukocytes). Taken together, vascular NTs are critical in modulating adenosine-mediated responses during conditions such as inflammation or hypoxia.
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Affiliation(s)
- Michaela Löffler
- Department of Anesthesiology and Intensive Care Medicine, Tübingen University Hospital, Waldhörnle Str. 22, 72072, Tübingen, Germany
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26
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Leung GPH, Tse CM, Man RYK. Characterization of adenosine transport in H9c2 cardiomyoblasts. Int J Cardiol 2006; 116:186-93. [PMID: 16824629 DOI: 10.1016/j.ijcard.2006.03.044] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/26/2005] [Revised: 03/20/2006] [Accepted: 03/25/2006] [Indexed: 11/20/2022]
Abstract
Adenosine plays a significant role in various physiological processes including cardioprotection. Nucleoside transporters modulate adenosine levels in the vicinity of adenosine receptors, which in turn modulate adenosine functional efficacy. In the current study, adenosine transport in the rat heart myoblast cell line H9c2 was characterized. Kinetic analysis of adenosine transport in H9c2 cells revealed a Km of 8.9+/-0.001 microM and a Vmax of 32.1+/-0.65 pmol/mg protein/min. Adenosine transport in H9c2 cells was Na+-independent. About 6% of the total adenosine uptake was sensitive to nitrobenzylmercaptopurine riboside (NBMPR); however, 94% was insensitive, suggesting that adenosine uptake by H9c2 cells was predominantly mediated by the equilibrative nucleoside transporter (ENT)-2 and only mildly by ENT-1. Results of RT-PCR demonstrated the presence of mRNA for ENT-1, ENT-2 and ENT-3. Upon culture in a cell differentiation medium containing fetal bovine serum (1%) and retinoic acid (10 nM), both the activity and mRNA expression of ENT-1 increased 3-fold, however, ENT-2 was unaffected. Pharmacological studies revealed that ENT-1 activity was stimulated by PKA and PKC-delta/epsilon, however, ENT-2 activity was unaffected. Taken together, the exceptionally high expression level of ENT-2 in H9c2 cells raises questions regarding the use of H9c2 cells as a model for physiological adenosine activity in the heart. Furthermore, this study may form the basis for further investigation into the effect of cell differentiation and protein kinases on the regulation of nucleoside transporters.
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Affiliation(s)
- George P H Leung
- Department of Pharmacology, The University of Hong Kong, Hong Kong.
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27
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Eltzschig HK, Abdulla P, Hoffman E, Hamilton KE, Daniels D, Schönfeld C, Löffler M, Reyes G, Duszenko M, Karhausen J, Robinson A, Westerman KA, Coe IR, Colgan SP. HIF-1-dependent repression of equilibrative nucleoside transporter (ENT) in hypoxia. ACTA ACUST UNITED AC 2006; 202:1493-505. [PMID: 16330813 PMCID: PMC2213326 DOI: 10.1084/jem.20050177] [Citation(s) in RCA: 274] [Impact Index Per Article: 15.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
Extracellular adenosine (Ado) has been implicated as central signaling molecule during conditions of limited oxygen availability (hypoxia), regulating physiologic outcomes as diverse as vascular leak, leukocyte activation, and accumulation. Presently, the molecular mechanisms that elevate extracellular Ado during hypoxia are unclear. In the present study, we pursued the hypothesis that diminished uptake of Ado effectively enhances extracellular Ado signaling. Initial studies indicated that the half-life of Ado was increased by as much as fivefold after exposure of endothelia to hypoxia. Examination of expressional levels of the equilibrative nucleoside transporter (ENT)1 and ENT2 revealed a transcriptionally dependent decrease in mRNA, protein, and function in endothelia and epithelia. Examination of the ENT1 promoter identified a hypoxia inducible factor 1 (HIF-1)–dependent repression of ENT1 during hypoxia. Using in vitro and in vivo models of Ado signaling, we revealed that decreased Ado uptake promotes vascular barrier and dampens neutrophil tissue accumulation during hypoxia. Moreover, epithelial Hif1α mutant animals displayed increased epithelial ENT1 expression. Together, these results identify transcriptional repression of ENT as an innate mechanism to elevate extracellular Ado during hypoxia.
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Affiliation(s)
- Holger K Eltzschig
- Department of Anesthesiology and Intensive Care Medicine, Tübingen University Hospital, Tübingen, Germany
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28
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Pinto-Duarte A, Coelho JE, Cunha RA, Ribeiro JA, Sebastião AM. Adenosine A
2A
receptors control the extracellular levels of adenosine through modulation of nucleoside transporters activity in the rat hippocampus. J Neurochem 2005; 93:595-604. [PMID: 15836618 DOI: 10.1111/j.1471-4159.2005.03071.x] [Citation(s) in RCA: 67] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Adenosine, a neuromodulator of the CNS, activates inhibitory-A1 receptors and facilitatory-A2A receptors; its synaptic levels are controlled by the activity of bi-directional equilibrative nucleoside transporters. To study the relationship between the extracellular formation/inactivation of adenosine and the activation of adenosine receptors, we investigated how A1 and A2A receptor activation modifies adenosine transport in hippocampal synaptosomes. The A2A receptor agonist, CGS 21680 (30 nm), facilitated adenosine uptake through a PKC-dependent mechanism, but A1 receptor activation had no effect. CGS 21680 (30 nm) also increased depolarization-induced release of adenosine. Both effects were prevented by A2A receptor blockade. A2A receptor-mediated enhancement of adenosine transport system is important for formatting adenosine neuromodulation according to the stimulation frequency, as: (1) A1 receptor antagonist, DPCPX (250 nm), facilitated the evoked release of [(3)H]acetylcholine under low-frequency stimulation (2 Hz) from CA3 hippocampal slices, but had no effect under high-frequency stimulation (50 Hz); (2) either nucleoside transporter or A2A receptor blockade revealed the facilitatory effect of DPCPX (250 nm) on [3H]acetylcholine evoked-release triggered by high-frequency stimulation. These results indicate that A2A receptor activation facilitates the activity of nucleoside transporters, which have a preponderant role in modulating the extracellular adenosine levels available to activate A1 receptors.
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Affiliation(s)
- António Pinto-Duarte
- Institute of Pharmacology and Neurosciences, Faculty of Medicine and Institute of Molecular Medicine, University of Lisbon, Lisbon, Portugal
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