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Aquaporins Display a Diversity in their Substrates. J Membr Biol 2023; 256:1-23. [PMID: 35986775 DOI: 10.1007/s00232-022-00257-7] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/29/2021] [Accepted: 07/13/2022] [Indexed: 02/07/2023]
Abstract
Aquaporins constitute a family of transmembrane proteins that function to transport water and other small solutes across the cell membrane. Aquaporins family members are found in diverse life forms. Aquaporins share the common structural fold consisting of six transmembrane alpha helices with a central water-transporting channel. Four such monomers assemble together to form tetramers as their biological unit. Initially, aquaporins were discovered as water-transporting channels, but several studies supported their involvement in mediating the facilitated diffusion of different solutes. The so-called water channel is able to transport a variety of substrates ranging from a neutral molecule to a charged molecule or a small molecule to a bulky molecule or even a gas molecule. This article gives an overview of a diverse range of substrates conducted by aquaporin family members. Prime focus is on human aquaporins where aquaporins show a wide tissue distribution and substrate specificity leading to various physiological functions. This review also highlights the structural mechanisms leading to the transport of water and glycerol. More research is needed to understand how one common fold enables the aquaporins to transport an array of solutes.
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Solenov EI, Baturina GS, Katkova LE, Yang B, Zarogiannis SG. Methods to Measure Water Permeability. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2023; 1398:343-361. [PMID: 36717506 DOI: 10.1007/978-981-19-7415-1_24] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Abstract
Water permeability is a key feature of the cell plasma membranes, and it has seminal importance for several cell functions such as cell volume regulation, cell proliferation, cell migration, and angiogenesis to name a few. The transport of water occurs mainly through plasma membrane water channels, aquaporins. Aquaporins have very important function in physiological and pathophysiological states. Due to the above, the experimental assessment of the water permeability of cells and tissues is necessary. The development of new methodologies of measuring water permeability is a vibrant scientific field that constantly develops during the last three decades along with the advances in imaging mainly. In this chapter we describe and critically assess several methods that have been developed for the measurement of water permeability both in living cells and in tissues with a focus in the first category.
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Affiliation(s)
- Evgeniy I Solenov
- Institute of Cytology and Genetics, SB RAS, Novosibirsk, Russia.
- Novosibirsk State Technical University, Novosibirsk, Russia.
| | | | | | - Baoxue Yang
- School of Basic Medical Sciences, Peking University, Beijing, China
| | - Sotirios G Zarogiannis
- Department of Physiology, Faculty of Medicine, University of Thessaly, BIOPOLIS, Larissa, Greece
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Jackson L, Woodward M, Coward RJ. The molecular biology of pelvi-ureteric junction obstruction. Pediatr Nephrol 2018; 33:553-571. [PMID: 28286898 PMCID: PMC5859056 DOI: 10.1007/s00467-017-3629-0] [Citation(s) in RCA: 20] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/11/2016] [Revised: 02/16/2017] [Accepted: 02/17/2017] [Indexed: 12/17/2022]
Abstract
Over recent years routine ultrasound scanning has identified increasing numbers of neonates as having hydronephrosis and pelvi-ureteric junction obstruction (PUJO). This patient group presents a diagnostic and management challenge for paediatric nephrologists and urologists. In this review we consider the known molecular mechanisms underpinning PUJO and review the potential of utilising this information to develop novel therapeutics and diagnostic biomarkers to improve the care of children with this disorder.
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Affiliation(s)
- Laura Jackson
- Bristol Renal Group, University of Bristol, Dorothy Hodgkin Building, Whitson Street, Bristol, BS1 3NY, UK. .,Bristol Royal Hospital for Children, Bristol, UK.
| | - Mark Woodward
- 0000 0004 0399 4960grid.415172.4Bristol Royal Hospital for Children, Bristol, UK
| | - Richard J. Coward
- 0000 0004 1936 7603grid.5337.2Bristol Renal Group, University of Bristol, Dorothy Hodgkin Building, Whitson Street, Bristol, BS1 3NY UK ,0000 0004 0399 4960grid.415172.4Bristol Royal Hospital for Children, Bristol, UK
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Li Y, Wang W, Jiang T, Yang B. Aquaporins in Urinary System. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2017; 969:131-148. [PMID: 28258571 DOI: 10.1007/978-94-024-1057-0_9] [Citation(s) in RCA: 24] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
Several aquaporin (AQP )-type water channels are expressed in kidney: AQP1 in the proximal tubule, thin descending limb of Henle, and vasa recta; AQP2 -6 in the collecting duct; AQP7 in the proximal tubule; AQP8 in the proximal tubule and collecting duct; and AQP11 in the endoplasmic reticulum of proximal tubule cells. AQP2 is the vasopressin-regulated water channel that is important in hereditary and acquired diseases affecting urine-concentrating ability. The roles of AQPs in renal physiology and transepithelial water transport have been determined using AQP knockout mouse models. This chapter describes renal physiologic insights revealed by phenotypic analysis of AQP knockout mice and the prospects for further basic and clinical studies.
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Affiliation(s)
- Yingjie Li
- Department of Pharmacology, School of Basic Medical Sciences, Peking University, Beijing, 100191, China
| | - Weiling Wang
- State Key Laboratory of Natural and Biomimetic Drugs, and Department of Pharmacology, School of Basic Medical Sciences, Peking University, Beijing, 100191, China
| | - Tao Jiang
- Department of Pharmacology, School of Basic Medical Sciences, Peking University, Beijing, 100191, China
| | - Baoxue Yang
- Department of Pharmacology, School of Basic Medical Sciences, Peking University, Beijing, 100191, China.
- State Key Laboratory of Natural and Biomimetic Drugs, Peking University, Beijing, 100191, China.
- Key Laboratory of Molecular Cardiovascular Sciences, Ministry of Education, Peking University, Beijing, 100191, China.
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Geilswijk M, Thomsen KL, Pedersen EB, Vilstrup H, Grønbæk H. Urinary aquaporin-2 excretion before and after transjugular intrahepatic portosystemic shunt insertion for refractory ascites. Scand J Gastroenterol 2015; 50:454-61. [PMID: 25637473 DOI: 10.3109/00365521.2014.962610] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
OBJECTIVE The role of renal aquaporin-2 (AQP2) water channel turnover in patients with liver cirrhosis, portal hypertension and water retention remains unclear. Transjugular intrahepatic portosystemic shunt (TIPS) insertion reduces portal hypertension, improves water excretion and lowers plasma vasopressin. The aim of this study was to establish whether TIPS insertion decreases urinary AQP2 excretion (uAQP2) in parallel with improved water excretion. MATERIAL AND METHODS Fourteen cirrhosis patients with refractory ascites were studied before TIPS insertion and 4 and 12 weeks after insertion. A 24-h urine collection was followed by an oral water load (20 ml/kg body weight) with a 4-h blood and urine sampling. RESULTS TIPS reduced the portal pressure gradient from a median 18(4) (25-75% InterQuartile-range) to 7(2) mmHg, p < 0.05 and the need for diuretics (p < 0.05). TIPS increased plasma sodium from 136(6) mmol/l to 139(4), (p < 0.05) and diuresis from 1650(1043) ml/24 h to 2230(560) (p < 0.05), although the 24-h urinary sodium excretion did not change. There was no change in the baseline uAQP2 before 274(249) ng/(mmol creatinine/24 h) and 12 weeks after TIPS 242(201). There were no systematic changes in uAQP2, plasma vasopressin or other vasoactive substances during the water loads, before or after TIPS. CONCLUSION The effective amelioration of portal hypertension improved the patient's water excretion and plasma sodium, but there was no change in renal AQP2 trafficking or vasopressin. These findings do not support a primary role for renal AQP2 water channels in portal hypertensive water retention.
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Affiliation(s)
- Marianne Geilswijk
- Department of Hepatology and Gastroenterology, Aarhus University Hospital , 44 Nørrebrogade, 8000 Aarhus C , Denmark
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Insights into structural mechanisms of gating induced regulation of aquaporins. PROGRESS IN BIOPHYSICS AND MOLECULAR BIOLOGY 2014; 114:69-79. [DOI: 10.1016/j.pbiomolbio.2014.01.002] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/21/2014] [Revised: 01/21/2014] [Accepted: 01/26/2014] [Indexed: 11/19/2022]
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Janosi L, Ceccarelli M. The gating mechanism of the human aquaporin 5 revealed by molecular dynamics simulations. PLoS One 2013; 8:e59897. [PMID: 23565173 PMCID: PMC3614956 DOI: 10.1371/journal.pone.0059897] [Citation(s) in RCA: 56] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/09/2012] [Accepted: 02/19/2013] [Indexed: 11/29/2022] Open
Abstract
Aquaporins are protein channels located across the cell membrane with the role of conducting water or other small sugar alcohol molecules (aquaglyceroporins). The high-resolution X-ray structure of the human aquaporin 5 (HsAQP5) shows that HsAQP5, as all the other known aquaporins, exhibits tetrameric structure. By means of molecular dynamics simulations we analyzed the role of spontaneous fluctuations on the structural behavior of the human AQP5. We found that different conformations within the tetramer lead to a distribution of monomeric channel structures, which can be characterized as open or closed. The switch between the two states of a channel is a tap-like mechanism at the cytoplasmic end which regulates the water passage through the pore. The channel is closed by a translation of the His67 residue inside the pore. Moreover, water permeation rate calculations revealed that the selectivity filter, located at the other end of the channel, regulates the flow rate of water molecules when the channel is open, by locally modifying the orientation of His173. Furthermore, the calculated permeation rates of a fully open channel are in good agreement with the reported experimental value.
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Affiliation(s)
- Lorant Janosi
- Department of Physics, University of Cagliari, Cagliari, Italy.
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Tamma G, Procino G, Svelto M, Valenti G. Cell culture models and animal models for studying the patho-physiological role of renal aquaporins. Cell Mol Life Sci 2012; 69:1931-46. [PMID: 22189994 PMCID: PMC11114724 DOI: 10.1007/s00018-011-0903-3] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/03/2011] [Revised: 11/07/2011] [Accepted: 11/29/2011] [Indexed: 12/29/2022]
Abstract
Aquaporins (AQPs) are key players regulating urinary-concentrating ability. To date, eight aquaporins have been characterized and localized along the nephron, namely, AQP1 located in the proximal tubule, thin descending limb of Henle, and vasa recta; AQP2, AQP3 and AQP4 in collecting duct principal cells; AQP5 in intercalated cell type B; AQP6 in intercalated cells type A in the papilla; AQP7, AQP8 and AQP11 in the proximal tubule. AQP2, whose expression and cellular distribution is dependent on vasopressin stimulation, is involved in hereditary and acquired diseases affecting urine-concentrating mechanisms. Due to the lack of selective aquaporin inhibitors, the patho-physiological role of renal aquaporins has not yet been completely clarified, and despite extensive studies, several questions remain unanswered. Until the recent and large-scale development of genetic manipulation technology, which has led to the generation of transgenic mice models, our knowledge on renal aquaporin regulation was mainly based on in vitro studies with suitable renal cell models. Transgenic and knockout technology approaches are providing pivotal information on the role of aquaporins in health and disease. The main goal of this review is to update and summarize what we can learn from cell and animal models that will shed more light on our understanding of aquaporin-dependent renal water regulation.
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Affiliation(s)
- G Tamma
- Department of Biosciences, Biotechnologies and Pharmacological Sciences, University of Bari, Italy
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Mahler B, Kamperis K, Schroeder M, Frøkiær J, Djurhuus JC, Rittig S. Sleep deprivation induces excess diuresis and natriuresis in healthy children. Am J Physiol Renal Physiol 2012; 302:F236-43. [DOI: 10.1152/ajprenal.00283.2011] [Citation(s) in RCA: 44] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Urine production is reduced at night, allowing undisturbed sleep. This study was undertaken to show the effect of sleep deprivation (SD) on urine production in healthy children. Special focus was on gender and children at an age where enuresis is still prominent. Twenty healthy children (10 girls) underwent two 24-h studies, randomly assigned to either sleep or SD on the first study night. Diet and fluid intake were standardized. Blood samples were drawn every 4 h during daytime and every 2 h at night. Urine was fractionally collected. Blood pressure and heart rate were noninvasively monitored. Blood was analyzed for plasma antidiuretic hormone (AVP), atrial natriuretic peptide (ANP), angiotensin II, aldosterone, and renin. Urine was analyzed for aquaporin-2 and PGE2. Successful SD was achieved in all participants with a minimum of 4 h 50 min, and full-night SD was obtained in 50% of the participants. During SD, both boys and girls produced markedly larger amounts of urine than during normal sleep (477 ± 145 vs. 291 ± 86 ml, P < 0.01). SD increased urinary excretion of sodium (0.17 ± 0.05 vs. 0.10 ± 0.03 mmol·kg−1·h−1) whereas solute-free water reabsorption remained unchanged. SD induced a significant fall in nighttime plasma AVP ( P < 0.01), renin ( P < 0.05), angiotensin II ( P < 0.001), and aldosterone ( P < 0.05) whereas plasma ANP levels remained uninfluenced ( P = 0.807). Nighttime blood pressure and heart rate were significantly higher during SD (mean arterial pressure: 78.5 ± 8.0 vs. 74.7 ± 8.7 mmHg, P < 0.001). SD leads to natriuresis and excess diuresis in healthy children. The underlying mechanism could be a reduced nighttime dip in blood pressure and a decrease in renin-angiotensin-aldosterone system levels during sleep deprivation.
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Affiliation(s)
- B. Mahler
- Institute of Clinical Medicine,
- Department of Pediatrics,
| | | | | | - J. Frøkiær
- Department of Clinical Physiology, and
- Water and Salt Research Center, Aarhus University, Aarhus University Hospital, Skejby, Aarhus N, Denmark
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Xin L, Su H, Nielsen CH, Tang C, Torres J, Mu Y. Water permeation dynamics of AqpZ: A tale of two states. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2011; 1808:1581-6. [DOI: 10.1016/j.bbamem.2011.02.001] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/31/2010] [Revised: 01/27/2011] [Accepted: 02/01/2011] [Indexed: 11/30/2022]
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Li Y, Zelenina M, Plat-Willson G, Marcoux MO, Aperia A, Casper C. Urinary aquaporin-2 excretion during ibuprofen or indomethacin treatment in preterm infants with patent ductus arteriosus. Acta Paediatr 2011; 100:59-66. [PMID: 21143292 DOI: 10.1111/j.1651-2227.2010.01943.x] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
AIM Water channel AQP2 is the target for vasopressin (AVP) and a major determinant of urinary concentrating capacity. In mature kidneys, prostaglandins counteract the effect of AVP on AQP2 expression at functional sites. We investigated whether disturbances in water homeostasis in infants with patent ductus arteriosus (PDA) treated with prostaglandin inhibitors can be attributed to activation of AQP2. METHODS In 53 infants with symptomatic PDA (gestational age 24-33 weeks), 30 receiving ibuprofen and 23 indomethacin starting at 2-15 days of life, clinical and biochemical data were collected before treatment and after each dose of the drugs. Urinary AQP2 was determined by dot immunoblotting. RESULTS Urinary AQP2 level and osmolality were decreased in both groups. Urinary osmolality was overall low and correlated inversely with fluid uptake. In ibuprofen group, there was no correlation of AQP2 level with urinary osmolality. CONCLUSION There was no AQP2 upregulation in the infants. The low urinary osmolality and dissociation between urinary osmolality and urinary AQP2 level indicate that the fluid retention sometimes observed in PDA infants treated with prostaglandin inhibitors is not caused by increased levels of functional AQP2. Thus, knowledge about the renal physiology of the adult cannot always be transferred to the infant kidney.
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Affiliation(s)
- Yanhong Li
- Nordic Centre of Excellence for Research in Water Imbalance Related Disorders, Department of Women's and Children's Health, Karolinska Institutet, Stockholm, Sweden
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Kazory A. Emergence of blood urea nitrogen as a biomarker of neurohormonal activation in heart failure. Am J Cardiol 2010; 106:694-700. [PMID: 20723648 DOI: 10.1016/j.amjcard.2010.04.024] [Citation(s) in RCA: 134] [Impact Index Per Article: 9.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/03/2010] [Revised: 04/07/2010] [Accepted: 04/07/2010] [Indexed: 11/27/2022]
Abstract
The nonosmotic release of arginine vasopressin, concurrent with the activation of the sympathetic nervous system and renin-angiotensin-aldosterone system, is thought to represent the maladaptive response that is central to the pathophysiology of heart failure (HF). The degree of neurohormonal activation correlates with the severity of the disease and can predict the outcomes. However, quantification of components of neurohormonal axis (e.g., serum arginine vasopressin level) is mainly reserved for research purposes rather than routine practice. The results of several recent HF trials have shed light on the differential role of blood urea nitrogen (BUN) and creatinine in predicting the outcomes in this setting. These studies suggest that BUN could indeed represent a surrogate marker for "renal response" to neurohormonal activation in this setting, above and beyond its role in the estimation of renal function. In this report, the relevant physiologic mechanisms underlying urea and water transport in the kidney are first reviewed. Then, the activation of the neurohormonal axis and the impact of its components on renal urea transport, independent of changes in renal function, are explained. Finally, the unique role of BUN as a biomarker of neurohormonal activation in the setting of HF is discussed, and the potential clinical implication of this novel concept is emphasized. In conclusion, this review explains the pathophysiologic basis for the emerging role of BUN as a biomarker in HF.
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Törnroth-Horsefield S, Hedfalk K, Fischer G, Lindkvist-Petersson K, Neutze R. Structural insights into eukaryotic aquaporin regulation. FEBS Lett 2010; 584:2580-8. [DOI: 10.1016/j.febslet.2010.04.037] [Citation(s) in RCA: 103] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/07/2010] [Accepted: 04/14/2010] [Indexed: 01/24/2023]
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Abstract
BACKGROUND End-stage liver disease is often complicated by hyponatremia. Cirrhotic patients with hyponatremia admitted to intensive care units (ICUs) have high mortality rates. This study analyzed the outcomes of critically ill cirrhotic patients and identified the prognostic value of serum sodium concentration. METHODS One hundred twenty-six consecutive cirrhotic patients admitted to the ICU of a tertiary center during a 1.5-year period were enrolled in this study. Demographic, clinical, and laboratory variables on the first day of ICU admission were prospectively recorded for post hoc analysis. RESULTS Overall hospital mortality was 65.1%. Comparing with serum sodium >135 mmol/L, patients with serum sodium <or=135 mmol/L had a greater frequency of ascites, illness severity scores, hepatic encephalopathy, sepsis, renal failure, and in-hospital mortality (55.9% vs. 73.1%, P=0.043). Multiple Cox proportional hazards analysis revealed that serum sodium levels, hepatocellular carcinoma, and sequential organ failure assessment scores on the first day of ICU admission were independent risk factors for 6-month mortality. Cumulative survival rates at 6-month follow-up after hospital discharge differed significantly (P<0.05) between patients with serum sodium >135 mmol/L versus those with serum sodium <or=135 mmol/L. CONCLUSIONS Low serum sodium levels in critically ill cirrhotic patients are associated with high complications of liver cirrhosis, in-hospital mortality, and poor short-term prognosis. The serum sodium concentration is important predictor of survival among candidates for liver transplantation. Future research with sequential application of serum sodium may reflect the dynamic aspects of clinical conditions, thus providing complete data for mortality risk.
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Oberg F, Ekvall M, Nyblom M, Backmark A, Neutze R, Hedfalk K. Insight into factors directing high production of eukaryotic membrane proteins; production of 13 human AQPs in Pichia pastoris. Mol Membr Biol 2009; 26:215-27. [PMID: 19384754 DOI: 10.1080/09687680902862085] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/20/2022]
Abstract
Membrane proteins are key players in all living cells. To achieve a better understanding of membrane protein function, significant amounts of purified protein are required for functional and structural analyses. Overproduction of eukaryotic membrane proteins, in particular, is thus an essential yet non-trivial task. Hence, improved understanding of factors which direct a high production of eukaryotic membrane proteins is desirable. In this study we have compared the overproduction of all human aquaporins in the eukaryotic host Pichia pastoris. We report quantitated production levels of each homologue and the extent of their membrane localization. Our results show that the protein production levels vary substantially, even between highly homologous aquaporins. A correlation between the extents of membrane insertion with protein function also emerged, with a higher extent of membrane insertion for pure water transporters compared to aquaporin family members with other substrate specificity. Nevertheless, the nucleic acid sequence of the second codon appears to play an important role in overproduction. Constructs containing guanine at the first position of this codon (being part of the mammalian Kozak sequence) are generally produced at a higher level, which is confirmed for hAQP8. In addition, mimicking the yeast consensus sequence (ATGTCT) apparently has a negative influence on the production level, as shown for hAQP1. Moreover, by mutational analysis we show that the yield of hAQP4 can be heavily improved by directing the protein folding pathway as well as stabilizing the aquaporin tetramer.
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Affiliation(s)
- Fredrik Oberg
- Department of Chemistry/Biochemistry, Göteborg University, Göteborg, Sweden
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Heo J, Meng F, Hua SZ. Contribution of aquaporins to cellular water transport observed by a microfluidic cell volume sensor. Anal Chem 2008; 80:6974-80. [PMID: 18698799 PMCID: PMC2612540 DOI: 10.1021/ac8008498] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/23/2023]
Abstract
Here we demonstrate that an impedance-based microfluidic cell volume sensor can be used to study the roles of aquaporin (AQP) in cellular water permeability and screen AQP-specific drugs. Human embryonic kidney (HEK-293) cells were transiently transfected with AQP3- or AQP4-encoding genes to express AQPs in plasma membranes. The swelling of cells in response to hypotonic stimulation was traced in real time using the sensor. Two time constants were obtained by fitting the swelling curves with a two-exponential function, a fast time constant associated with osmotic water permeability of AQP-expressing cells and a slow phase time constant associated mainly with water diffusion through lipid bilayers in the nontransfected cells. The AQP-expressing cells showed at least 10× faster osmotic water transport than control cells. Using the volume sensor, we examined the effects of Hg2+ and Ni2+ on the water transport via AQPs. Hg2+ inhibited the water flux in AQP3-expressing cells irreversibly, while Ni2+ blocked the AQP3 channels reversibly. Neither of the two ions blocked the AQP4 channels. The microfluidic volume sensor can sense changes in cell volume in real time, which enables perfusion of various reagents sequentially. It provides a convenient tool for studying the effect of reagents on the function and regulation mechanism of AQPs.
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Affiliation(s)
- Jinseok Heo
- Department of Mechanical & Aerospace Engineering, SUNY-Buffalo, Buffalo, New York 14260, USA
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Decreased expression of endometrial vessel AQP1 and endometrial epithelium AQP2 related to anovulatory uterine bleeding in premenopausal women. Menopause 2008; 15:648-54. [DOI: 10.1097/gme.0b013e31816086ef] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2022]
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Hedfalk K, Törnroth-Horsefield S, Nyblom M, Johanson U, Kjellbom P, Neutze R. Aquaporin gating. Curr Opin Struct Biol 2006; 16:447-56. [PMID: 16837191 DOI: 10.1016/j.sbi.2006.06.009] [Citation(s) in RCA: 86] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/02/2006] [Revised: 06/02/2006] [Accepted: 06/27/2006] [Indexed: 10/24/2022]
Abstract
An acceleration in the rate at which new aquaporin structures are determined means that structural models are now available for mammalian AQP0, AQP1, AQP2 and AQP4, bacterial GlpF, AqpM and AQPZ, and the plant SoPIP2;1. With an apparent consensus emerging concerning the mechanism of selective water transport and proton extrusion, emphasis has shifted towards the issues of substrate selectivity and the mechanisms of aquaporin regulation. In particular, recently determined structures of plant SoPIP2;1, sheep and bovine AQP0, and Escherichia coli AQPZ provide new insights into the underlying structural mechanisms by which water transport rates are regulated in diverse organisms. From these results, two distinct pictures of 'capping' and 'pinching' have emerged to describe aquaporin gating.
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Affiliation(s)
- Kristina Hedfalk
- Chalmers University of Technology, Department of Chemistry and Bioscience, SE-405 30 Göteborg, Sweden
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Schrier RW. Body water homeostasis: clinical disorders of urinary dilution and concentration. J Am Soc Nephrol 2006; 17:1820-32. [PMID: 16738014 DOI: 10.1681/asn.2006030240] [Citation(s) in RCA: 137] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Affiliation(s)
- Robert W Schrier
- Department of Medicine, University of Colorado School of Medicine, Denver, CO 80262, USA.
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Abstract
Transgenic mouse models of aquaporin (AQP) deletion and mutation have been instructive in elucidating the role of AQPs in renal physiology. Mice lacking AQP1 are unable to concentrate their urine because of low water permeability in the proximal tubule, thin descending limb of Henle, and outer medullary descending vasa recta, resulting in defective near-isosmolar fluid absorption in the proximal tubule and defective countercurrent multiplication. Mice lacking functional AQP2, AQP3, or AQP4 manifest various degrees of nephrogenic diabetes insipidus resulting from reduced collecting duct water permeability. Mice lacking AQP7 and AQP8 can concentrate their urine fully, although AQP7 null mice manifest an interesting defect in glycerol reabsorption. Two unexpected renal phenotypes of AQP null mice have been discovered recently, including defective proximal tubule cell migration in AQP1 deficiency, and cystic renal disease in AQP11 deficiency. AQPs thus are important in several aspects of the urinary concentrating mechanism and in functions unrelated to tubular fluid transport. The mouse phenotype data suggest the renal AQPs as targets for the development of aquaretics and potentially for therapy of cystic renal disease and acute renal injury.
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Affiliation(s)
- A S Verkman
- Department of Medicine, Cardiovascular Research Institute, University of California, San Francisco, San Francisco, CA 94143-0521, USA.
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Schrier RW, Chen YC, Cadnapaphornchai MA. From finch to fish to man: Role of aquaporins in body fluid and brain water regulation. Neuroscience 2004; 129:897-904. [PMID: 15561406 DOI: 10.1016/j.neuroscience.2004.06.043] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 06/30/2004] [Indexed: 11/28/2022]
Abstract
Charles Darwin, in his Origin of the Species, noted that different species of finches on the Galapagos Islands had adapted their beak size based on where they sought their food. Homer Smith, in his book From Fish to Philosopher, discussed the evolution of the nephron from a single conduit in salt water vertebrates, to nephrons with large glomerular capillaries and proximal and distal tubules in fresh water vertebrates, to smaller glomerular capillaries in amphibians, to nephrons with loops of Henle to allow for urinary concentration and dilution in mammals. The kidney with its million nephrons has emerged as the vital organ for regulating body fluid composition and volume. With the recent discovery of aquaporin water channels, our understanding of volume regulation has been greatly enhanced. This article reviews current knowledge regarding: 1) the unifying hypothesis of body fluid volume regulation; 2) brain aquaporins and their role in pathophysiologic states; and 3) function and regulation of renal aquaporins in the syndrome of inappropriate antidiuretic hormone secretion (SIADH).
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Affiliation(s)
- R W Schrier
- Department of Medicine, Division of Renal Diseases and Hypertension, University of Colorado Health Sciences Center, 4200 East 9th Avenue, Box B173, Denver, CO 80262, USA.
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