1
|
Huo X, Yu Z, Zhao F, Chen Y, Chen P, Xing L, Qiao Y, Peng Y, Tian M, Zhou M, Wu F, Wang Y, Wang C, Tian X, Lv D, Zhang B, Shi L, Ma X, Ma T. Hepatocyte aquaporin 8-mediated water transport facilitates bile dilution and prevents gallstone formation in mice. J Hepatol 2024:S0168-8278(24)02563-7. [PMID: 39326676 DOI: 10.1016/j.jhep.2024.09.023] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/01/2024] [Revised: 09/09/2024] [Accepted: 09/17/2024] [Indexed: 09/28/2024]
Abstract
BACKGROUND & AIMS Although water channel aquaporin-8 (AQP8) has been implicated in hepatic bile formation and liver diseases associated with abnormal bile flow in human and animal studies, direct evidence of its involvement in bile secretion is still lacking. This study aimed to determine the role of AQP8 in bile secretion and gallstone formation. METHODS We generated various transgenic knock-in and knockout mouse models and assessed liver AQP8 expression by immunostaining and immunoblotting, hepatic bile secretion by cannulation of the common bile duct, cholesterol gallstone formation by feeding a high-fat lithogenic diet, and identified regulatory small molecules by screening the organic fractions of cholagogic Chinese herbs and performing biochemical characterization. RESULTS We identified a novel expression pattern of AQP8 protein in the canalicular membrane of approximately 50% of the liver lobules. AQP8-deficient mice exhibited impaired hepatic bile formation, characterized by the secretion of concentrated bile with a lower flow rate and higher levels of bile lipids than that of wild-type littermates. Aqp8-/- mice showed accelerated gallstone formation, which was rescued by AAV-mediated hepatic expression of AQP8 or AQP1. Moreover, we identified a small molecule, scutellarin, that upregulates hepatocyte AQP8 expression in vitro and in vivo. In Aqp8+/+ mice, scutellarin significantly increased bile flow, decreased bile lipid concentrations, and prevented gallstone formation compared to Aqp8-/- mice. Molecular studies revealed that scutellarin promoted the ubiquitination and degradation of HIF-1α, a transcriptional negative regulator of AQP8, by disrupting its interactions with HSP90. CONCLUSIONS AQP8 plays a crucial role in facilitating water transport and bile dilution during hepatic bile formation, thereby mitigating gallstone formation in mice. Small-molecule intervention validated hepatocyte AQP8 as a promising drug target for gallstone therapy. IMPACT AND IMPLICATIONS The incidence of gallstone disease is high, and current drug treatments for gallstones are very limited, necessitating the identification of novel drug targets for therapeutic development with universal applicability. To our knowledge, this is the first study to provide direct evidence that the hepatic water channel AQP8 plays a key role in bile dilution and gallstone formation. Modulation of hepatic water transport may provide a universal therapeutic strategy for all types of gallstone diseases.
Collapse
Affiliation(s)
- Xiaokui Huo
- Pharmaceutical Research Center, Second Affiliated Hospital, Dalian Medical University, Dalian, China
| | - Zhenlong Yu
- Dalian Key Laboratory of Metabolic Target Characterization and Traditional Chinese Medicine Intervention, College of Basic Medical Sciences, Institute of Integrative Medicine, Dalian Medical University, Dalian, China
| | - Feng Zhao
- Dalian Key Laboratory of Metabolic Target Characterization and Traditional Chinese Medicine Intervention, College of Basic Medical Sciences, Institute of Integrative Medicine, Dalian Medical University, Dalian, China
| | - Yang Chen
- School of Medicine & Holistic Integrative Medicine, Nanjing University of Chinese Medicine, Nanjing, China
| | - Peng Chen
- School of Medicine & Holistic Integrative Medicine, Nanjing University of Chinese Medicine, Nanjing, China
| | - Lina Xing
- Dalian Key Laboratory of Metabolic Target Characterization and Traditional Chinese Medicine Intervention, College of Basic Medical Sciences, Institute of Integrative Medicine, Dalian Medical University, Dalian, China
| | - Yanling Qiao
- Pharmaceutical Research Center, Second Affiliated Hospital, Dalian Medical University, Dalian, China; Harbin Medical University, Harbin, China
| | - Yulin Peng
- Dalian Key Laboratory of Metabolic Target Characterization and Traditional Chinese Medicine Intervention, College of Basic Medical Sciences, Institute of Integrative Medicine, Dalian Medical University, Dalian, China
| | - Manman Tian
- Pharmaceutical Research Center, Second Affiliated Hospital, Dalian Medical University, Dalian, China
| | - Meirong Zhou
- Pharmaceutical Research Center, Second Affiliated Hospital, Dalian Medical University, Dalian, China
| | - Fan Wu
- Pharmaceutical Research Center, Second Affiliated Hospital, Dalian Medical University, Dalian, China
| | - Yan Wang
- Dalian Key Laboratory of Metabolic Target Characterization and Traditional Chinese Medicine Intervention, College of Basic Medical Sciences, Institute of Integrative Medicine, Dalian Medical University, Dalian, China
| | - Chao Wang
- Dalian Key Laboratory of Metabolic Target Characterization and Traditional Chinese Medicine Intervention, College of Basic Medical Sciences, Institute of Integrative Medicine, Dalian Medical University, Dalian, China
| | - Xiangge Tian
- Pharmaceutical Research Center, Second Affiliated Hospital, Dalian Medical University, Dalian, China
| | - Dongyue Lv
- School of Medicine & Holistic Integrative Medicine, Nanjing University of Chinese Medicine, Nanjing, China
| | - Bo Zhang
- School of Medicine & Holistic Integrative Medicine, Nanjing University of Chinese Medicine, Nanjing, China
| | - Lei Shi
- Dalian Key Laboratory of Metabolic Target Characterization and Traditional Chinese Medicine Intervention, College of Basic Medical Sciences, Institute of Integrative Medicine, Dalian Medical University, Dalian, China.
| | - Xiaochi Ma
- Pharmaceutical Research Center, Second Affiliated Hospital, Dalian Medical University, Dalian, China; Dalian Key Laboratory of Metabolic Target Characterization and Traditional Chinese Medicine Intervention, College of Basic Medical Sciences, Institute of Integrative Medicine, Dalian Medical University, Dalian, China.
| | - Tonghui Ma
- School of Medicine & Holistic Integrative Medicine, Nanjing University of Chinese Medicine, Nanjing, China.
| |
Collapse
|
2
|
Bourgeois S, Houillier P. State of knowledge on ammonia handling by the kidney. Pflugers Arch 2024; 476:517-531. [PMID: 38448728 PMCID: PMC11006756 DOI: 10.1007/s00424-024-02940-1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2023] [Revised: 02/28/2024] [Accepted: 03/01/2024] [Indexed: 03/08/2024]
Abstract
The disposal of ammonia, the main proton buffer in the urine, is important for acid-base homeostasis. Renal ammonia excretion is the predominant contributor to renal net acid excretion, both under basal condition and in response to acidosis. New insights into the mechanisms of renal ammonia production and transport have been gained in the past decades. Ammonia is the only urinary solute known to be produced in the kidney and selectively transported through the different parts of the nephron. Both molecular forms of total ammonia, NH3 and NH4+, are transported by specific proteins. Proximal tubular ammoniagenesis and the activity of these transport processes determine the eventual fate of total ammonia produced and excreted by the kidney. In this review, we summarized the state of the art of ammonia handling by the kidney and highlighted the newest processes described in the last decade.
Collapse
Affiliation(s)
- Soline Bourgeois
- Institut of Physiology, University of Zurich, Zurich, Switzerland.
| | - Pascal Houillier
- Centre de Recherche Des Cordeliers, INSERM, Sorbonne Université, Université Paris Cité, Paris, France
- Centre National de La Recherche Scientifique (CNRS), EMR 8228, Paris, France
| |
Collapse
|
3
|
Xu Z, Li X, Ding L, Zhang Z, Sun Y. The dietary inflammatory index and new-onset hypertension in Chinese adults: a nationwide cohort study. Food Funct 2023; 14:10759-10769. [PMID: 37975169 DOI: 10.1039/d3fo03767c] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2023]
Abstract
Purpose: The development of hypertension is shown to be triggered by chronic low-grade inflammation. The dietary inflammatory index (DII) is a parameter for assessing the potential of a diet to cause inflammation. The prospective association between the DII and new-onset hypertension in Chinese adults remains unclear. Materials and methods: The nationwide cohort study included 10694 participants from 7 rounds of the China Health and Nutrition Survey. Dietary nutrient intake data were collected by 3-day 24 h dietary recalls and used to calculate the DII. The time-dependent Cox regression model was used to calculate hazard ratios (HRs) and 95% confidence intervals (CIs) for studying the risk of new-onset hypertension, and stratified analyses were used to examine factors that may modify the association. Restricted cubic spline (RCS) regression was used to examine the non-linear relationship between the DII and new-onset hypertension. The relationship between the DII and physical activity was analyzed with the time-dependent Cox regression model. Results: The highest quartile of the DII had a significantly higher risk of new-onset hypertension compared to the lowest quartile (adjusted HR, 1.13; 95% CI, 1.02, 1.24). RCS regression results showed that the risk of new-onset hypertension increased significantly after the DII above 1.09 (P for non-linearity <0.001). The interaction results showed that the DII may play a better role (P < 0.05) in the female, age < 45 years, baseline SBP < 130 mmHg, DBP < 80 mmHg, BMI < 24 kg m-2 and moderate/heavy physical activity level subgroup. Stratified analysis results showed that the baseline SBP, DBP, obesity, and physical activity level modified the association between the DII and hypertension (P for interaction < 0.05). Conclusion: Reducing the inflammatory potential of the diet is an effective strategy to prevent hypertension in Chinese adults.
Collapse
Affiliation(s)
- Ze Xu
- Department of Nutrition and Food Hygiene, School of Public Health, Qingdao University, Qingdao 266071, China.
| | - Xue Li
- Department of Big Data in Health Science, School of Public Health and The Second Affiliated Hospital, Zhejiang University School of Medicine, Hangzhou 310058, China
| | - Li Ding
- Qingdao West Coast New District Health Bureau, Huangdao District, Qingdao 266000, China
| | - Zhaofeng Zhang
- Department of Nutrition and Food Hygiene, School of Public Health, Peking University Health Science Center, Beijing 100191, China.
- Key Laboratory of Food Safety Toxicology Research and Evaluation, Beijing 100191, China
| | - Yongye Sun
- Department of Nutrition and Food Hygiene, School of Public Health, Qingdao University, Qingdao 266071, China.
| |
Collapse
|
4
|
Ceci L, Han Y, Krutsinger K, Baiocchi L, Wu N, Kundu D, Kyritsi K, Zhou T, Gaudio E, Francis H, Alpini G, Kennedy L. Gallstone and Gallbladder Disease: Biliary Tract and Cholangiopathies. Compr Physiol 2023; 13:4909-4943. [PMID: 37358507 DOI: 10.1002/cphy.c220028] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/27/2023]
Abstract
Cholestatic liver diseases are named primarily due to the blockage of bile flow and buildup of bile acids in the liver. Cholestasis can occur in cholangiopathies, fatty liver diseases, and during COVID-19 infection. Most literature evaluates damage occurring to the intrahepatic biliary tree during cholestasis; however, there may be associations between liver damage and gallbladder damage. Gallbladder damage can manifest as acute or chronic inflammation, perforation, polyps, cancer, and most commonly gallstones. Considering the gallbladder is an extension of the intrahepatic biliary network, and both tissues are lined by biliary epithelial cells that share common mechanisms and properties, it is worth further evaluation to understand the association between bile duct and gallbladder damage. In this comprehensive article, we discuss background information of the biliary tree and gallbladder, from function, damage, and therapeutic approaches. We then discuss published findings that identify gallbladder disorders in various liver diseases. Lastly, we provide the clinical aspect of gallbladder disorders in liver diseases and ways to enhance diagnostic and therapeutic approaches for congruent diagnosis. © 2023 American Physiological Society. Compr Physiol 13:4909-4943, 2023.
Collapse
Affiliation(s)
- Ludovica Ceci
- Division of Gastroenterology and Hepatology, Department of Medicine, Indiana University School of Medicine, Indianapolis, Indiana, USA
- Department of Anatomical, Histological, Forensic Medicine and Orthopedics Sciences, Sapienza University of Rome, Rome, Italy
| | - Yuyan Han
- School of Biological Sciences, University of Northern Colorado, Greeley, Colorado, USA
| | - Kelsey Krutsinger
- School of Biological Sciences, University of Northern Colorado, Greeley, Colorado, USA
| | | | - Nan Wu
- Division of Gastroenterology and Hepatology, Department of Medicine, Indiana University School of Medicine, Indianapolis, Indiana, USA
| | - Debjyoti Kundu
- Division of Gastroenterology and Hepatology, Department of Medicine, Indiana University School of Medicine, Indianapolis, Indiana, USA
| | - Konstantina Kyritsi
- Division of Gastroenterology and Hepatology, Department of Medicine, Indiana University School of Medicine, Indianapolis, Indiana, USA
| | - Tianhao Zhou
- Division of Gastroenterology and Hepatology, Department of Medicine, Indiana University School of Medicine, Indianapolis, Indiana, USA
| | - Eugenio Gaudio
- Department of Anatomical, Histological, Forensic Medicine and Orthopedics Sciences, Sapienza University of Rome, Rome, Italy
| | - Heather Francis
- Division of Gastroenterology and Hepatology, Department of Medicine, Indiana University School of Medicine, Indianapolis, Indiana, USA
- Department of Research, Richard L. Roudebush VA Medical Center, Indianapolis, Indiana, USA
| | - Gianfranco Alpini
- Division of Gastroenterology and Hepatology, Department of Medicine, Indiana University School of Medicine, Indianapolis, Indiana, USA
- Department of Research, Richard L. Roudebush VA Medical Center, Indianapolis, Indiana, USA
| | - Lindsey Kennedy
- Division of Gastroenterology and Hepatology, Department of Medicine, Indiana University School of Medicine, Indianapolis, Indiana, USA
- Department of Research, Richard L. Roudebush VA Medical Center, Indianapolis, Indiana, USA
| |
Collapse
|
5
|
Harris AN, Skankar M, Melanmed M, Batlle D. An Update on Kidney Ammonium Transport Along the Nephron. ADVANCES IN KIDNEY DISEASE AND HEALTH 2023; 30:189-196. [PMID: 36868733 DOI: 10.1053/j.akdh.2022.12.005] [Citation(s) in RCA: 8] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/02/2022] [Accepted: 12/14/2022] [Indexed: 03/05/2023]
Abstract
Acid-base homeostasis is critical to the maintenance of normal health. The kidneys have a central role in bicarbonate generation, which occurs through the process of net acid excretion. Renal ammonia excretion is the predominant component of renal net acid excretion under basal conditions and in response to acid-base disturbances. Ammonia produced in the kidney is selectively transported into the urine or the renal vein. The amount of ammonia produced by the kidney that is excreted in the urine varies dramatically in response to physiological stimuli. Recent studies have advanced our understanding of ammonia metabolism's molecular mechanisms and regulation. Ammonia transport has been advanced by recognizing that the specific transport of NH3 and NH4+ by specific membrane proteins is critical to ammonia transport. Other studies show that proximal tubule protein, NBCe1, specifically the A variant, significantly regulates renal ammonia metabolism. This review discusses these critical aspects of the emerging features of ammonia metabolism and transport.
Collapse
Affiliation(s)
- Autumn N Harris
- Department of Small Animal Clinical Science, University of Florida College of Veterinary Medicine, Gainesville, FL; Division of Nephrology, Hypertension and Renal Transplantation, University of Florida College of Medicine, Gainesville, FL.
| | - Mythri Skankar
- Department of Nephrology, Institute of Nephro-urology, Bengaluru, India
| | - Michal Melanmed
- Albert Einstein College of Medicine/ Montefiore Medical Center, Bronx, NY
| | - Daniel Batlle
- Northwestern University Feinberg School of Medicine, Chicago, IL
| |
Collapse
|
6
|
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.
Collapse
|
7
|
The aquaporin 8 (AQP8) membrane channel gene is present in the elasmobranch dogfish (Squalus acanthias) genome and is expressed in brain but not in gill, kidney or intestine. Comp Biochem Physiol B Biochem Mol Biol 2022; 260:110730. [PMID: 35248695 DOI: 10.1016/j.cbpb.2022.110730] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/28/2022] [Revised: 02/27/2022] [Accepted: 03/01/2022] [Indexed: 11/23/2022]
Abstract
The transport mechanisms for water, ammonia and urea in elasmobranch gill, kidney and gastrointestinal tract remain to be fully elucidated. Aquaporin 8 (AQP8) is a known water, ammonia and urea channel that is expressed in the kidney and respiratory and gastrointestinal tracts of mammals and teleost fish. However, at the initiation of this study in late 2019, there was no copy of an elasmobranch aquaporin 8 gene identified in the genebank even for closely related holocephalon species such as elephant fish (Callorhinchus milii) or for the elasmobranch little skate (Leucoraja erinacea). A transcriptomic study in spiny dogfish (Squalus acanthias) also failed to identify a copy. Hence this study has remedied this and identified the AQP8 cDNA sequence using degenerate PCR. Agarose electrophoresis of degenerate PCR reactions from dogfish tissues showed a strong band from brain cDNA and faint bands of a similar size in gill and liver. 5' and 3' RACE was used to complete the AQP8 cDNA sequence. Primers were then designed for further PCR reactions to determine the distribution of AQP8 mRNA expression in dogfish tissues. This showed that AQP8 is only expressed in dogfish brain and AQP8 therefore clearly can play no role in water, ammonia and urea transport in the gill, kidney or gastrointestinal tract. The role of AQP8 in dogfish brain remains to be determined.
Collapse
|
8
|
Escudero-Hernández C, Münch A, Østvik AE, Granlund AVB, Koch S. The Water Channel Aquaporin 8 is a Critical Regulator of Intestinal Fluid Homeostasis in Collagenous Colitis. J Crohns Colitis 2020; 14:962-973. [PMID: 32016376 PMCID: PMC7393183 DOI: 10.1093/ecco-jcc/jjaa020] [Citation(s) in RCA: 21] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
BACKGROUND AND AIMS Diarrhoea is a common, debilitating symptom of gastrointestinal disorders. Pathomechanisms probably involve defects in trans-epithelial water transport, but the role of aquaporin [AQP] family water channels in diarrhoea-predominant diseases is unknown. We investigated the involvement of AQPs in the pathobiology of collagenous colitis [CC], which features chronic, watery diarrhoea despite overtly normal intestinal epithelial cells [IECs]. METHODS We assessed the expression of all AQP family members in mucosal samples of CC patients before and during treatment with the corticosteroid drug budesonide, steroid-refractory CC patients and healthy controls. Samples were analysed by genome-wide mRNA sequencing [RNA-seq] and quantitative real-time PCR [qPCR]. In some patients, we performed tissue microdissection followed by RNA-seq to explore the IEC-specific CC transcriptome. We determined changes in the protein levels of the lead candidates in IEC by confocal microscopy. Finally, we investigated the regulation of AQP expression by corticosteroids in model cell lines. RESULTS Using qPCR and RNA-seq, we identified loss of AQP8 expression as a hallmark of active CC, which was reverted by budesonide treatment in steroid-responsive but not refractory patients. Consistently, decreased AQP8 mRNA and protein levels were observed in IECs of patients with active CC, and steroid drugs increased AQP8 expression in model IECs. Moreover, low APQ8 expression was strongly associated with higher stool frequency in CC patients. CONCLUSION Down-regulation of epithelial AQP8 may impair water resorption in active CC, resulting in watery diarrhoea. Our results suggest that AQP8 is a potential drug target for the treatment of diarrhoeal disorders.
Collapse
Affiliation(s)
| | - Andreas Münch
- Department of Biomedical and Clinical Sciences [BKV), Linköping University, Linköping, Sweden,Division of Gastroenterology and Hepatology, Department of Biomedical and Clinical Sciences [BKV), Faculty of Health Science, Linköpings University, Linköping, Sweden,Corresponding authors: Andreas Münch, MD PhD, Division of Gastroenterology and Hepatology, Department of Biomedical and Clinical Sciences [BKV), Faculty of Health Sciences, Linköping University, Linköping, 58185, Sweden. Tel: +46 100130000; ; Stefan Koch, PhD, BKV/MII—Plan 13, s-581 83 Linköping, Sweden. Tel: +46 13 282969;
| | - Ann-Elisabet Østvik
- Department of Clinical and Molecular Medicine, Faculty of Medicine and Health Sciences, Norwegian University of Science and Technology (NTNU), Trondheim, Norway,Department of Gastroenterology and Hepatology, St Olav’s University Hospital, Trondheim, Norway,Clinic of Medicine, St Olav’s University Hospital, Trondheim, Norway
| | - Atle van Beelen Granlund
- Department of Clinical and Molecular Medicine, Faculty of Medicine and Health Sciences, Norwegian University of Science and Technology (NTNU), Trondheim, Norway,Clinic of Medicine, St Olav’s University Hospital, Trondheim, Norway,Centre of Molecular Inflammation Research, Department of Clinical and Molecular Medicine, Faculty of Medicine and Health Sciences, Norwegian University of Science and Technology (NTNU), Trondheim, Norway
| | - Stefan Koch
- Department of Biomedical and Clinical Sciences [BKV), Linköping University, Linköping, Sweden,Wallenberg Centre for Molecular Medicine (WCMM), Linköping University, Linköping, Sweden,Corresponding authors: Andreas Münch, MD PhD, Division of Gastroenterology and Hepatology, Department of Biomedical and Clinical Sciences [BKV), Faculty of Health Sciences, Linköping University, Linköping, 58185, Sweden. Tel: +46 100130000; ; Stefan Koch, PhD, BKV/MII—Plan 13, s-581 83 Linköping, Sweden. Tel: +46 13 282969;
| |
Collapse
|
9
|
Weiner ID, Verlander JW. Emerging Features of Ammonia Metabolism and Transport in Acid-Base Balance. Semin Nephrol 2020; 39:394-405. [PMID: 31300094 DOI: 10.1016/j.semnephrol.2019.04.008] [Citation(s) in RCA: 25] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
Ammonia metabolism has a critical role in acid-base homeostasis and in other cellular functions. Kidneys have a central role in bicarbonate generation, which occurs through the process of net acid excretion; ammonia metabolism is the quantitatively greatest component of net acid excretion, both under basal conditions and in response to acid-base disturbances. Several recent studies have advanced our understanding substantially of the molecular mechanisms and regulation of ammonia metabolism. First, the previous paradigm that ammonia transport could be explained by passive NH3 diffusion and NH4+ trapping has been advanced by the recognition that specific transport of NH3 and of NH4+ by specific membrane proteins is critical to ammonia transport. Second, significant advances have been made in the understanding of the regulation of ammonia metabolism. Novel studies have shown that hyperkalemia directly inhibits ammonia metabolism, thereby leading to the metabolic acidosis present in type IV renal tubular acidosis. Other studies have shown that the proximal tubule protein NBCe1, specifically the A variant NBCe1-A, has a major role in regulating renal ammonia metabolism. Third, there are important sex differences in ammonia metabolism that involve structural and functional differences in the kidney. This review addresses these important aspects of ammonia metabolism and transport.
Collapse
Affiliation(s)
- I David Weiner
- Division of Nephrology, Hypertension and Renal Transplantation, University of Florida College of Medicine, Gainesville, FL; Nephrology and Hypertension Section, Gainesville Veterans Affairs Medical Center, Gainesville, FL.
| | - Jill W Verlander
- Division of Nephrology, Hypertension and Renal Transplantation, University of Florida College of Medicine, Gainesville, FL
| |
Collapse
|
10
|
Zhou J, Liu X, Chen T, Cheng G, Cai S. Preventive effect of ethanol extract from Chinese sumac fruits against tetrachloromethane-induced liver fibrosis in mice. Food Funct 2020; 11:7061-7072. [DOI: 10.1039/d0fo00548g] [Citation(s) in RCA: 16] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
Chinese sumac (Rhus chinensis Mill.) fruits effectively prevent CCl4-induced liver fibrosis in mice.
Collapse
Affiliation(s)
- Jiexin Zhou
- Faculty of Agriculture and Food
- Yunnan Institute of Food Safety
- Kunming University of Science and Technology
- Kunming
- People's Republic of China
| | - Xiaojing Liu
- Faculty of Agriculture and Food
- Yunnan Institute of Food Safety
- Kunming University of Science and Technology
- Kunming
- People's Republic of China
| | - Taiming Chen
- Faculty of Agriculture and Food
- Yunnan Institute of Food Safety
- Kunming University of Science and Technology
- Kunming
- People's Republic of China
| | - Guiguang Cheng
- Faculty of Agriculture and Food
- Yunnan Institute of Food Safety
- Kunming University of Science and Technology
- Kunming
- People's Republic of China
| | - Shengbao Cai
- Faculty of Agriculture and Food
- Yunnan Institute of Food Safety
- Kunming University of Science and Technology
- Kunming
- People's Republic of China
| |
Collapse
|
11
|
Chapp AD, Schum S, Behnke JE, Hahka T, Huber MJ, Jiang E, Larson RA, Shan Z, Chen QH. Measurement of cations, anions, and acetate in serum, urine, cerebrospinal fluid, and tissue by ion chromatography. Physiol Rep 2019; 6:e13666. [PMID: 29654634 PMCID: PMC5899179 DOI: 10.14814/phy2.13666] [Citation(s) in RCA: 23] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/31/2018] [Accepted: 02/12/2018] [Indexed: 01/17/2023] Open
Abstract
Accurate quantification of cations and anions remains a major diagnostic tool in understanding diseased states. The current technologies used for these analyses are either unable to quantify all ions due to sample size/volume, instrument setup/method, or are only able to measure ion concentrations from one physiological sample (liquid or solid). Herein, we adapted a common analytical chemistry technique, ion chromatography and applied it to measure the concentration of cations; sodium, potassium, calcium, and magnesium (Na+, K+, Ca2+, and Mg2+) and anions; chloride, and acetate (Cl−, −OAc) from physiological samples. Specifically, cations and anions were measured in liquid samples: serum, urine, and cerebrospinal fluid, as well as tissue samples: liver, cortex, hypothalamus, and amygdala. Serum concentrations of Na+, K+, Ca2+, Mg2+, Cl−, and −OAc (mmol/L): 138.8 ± 4.56, 4.05 ± 0.21, 4.07 ± 0.26, 0.98 ± 0.05, 97.7 ± 3.42, and 0.23 ± 0.04, respectively. Cerebrospinal fluid concentrations of Na+, K+, Ca2+, Mg2+, Cl−, and −OAc (mmol/L): 145.1 ± 2.81, 2.41 ± 0.26, 2.18 ± 0.38, 1.04 ± 0.11, 120.2 ± 3.75, 0.21 ± 0.05, respectively. Tissue Na+, K+, Ca2+, Mg2+, Cl−, and −OAc were also measured. Validation of the ion chromatography method was established by comparing chloride concentration between ion chromatography with a known method using an ion selective chloride electrode. These results indicate that ion chromatography is a suitable method for the measurement of cations and anions, including acetate from various physiological samples.
Collapse
Affiliation(s)
- Andrew D Chapp
- Department of Kinesiology and Integrative Physiology, Michigan Technological University, Houghton, Michigan.,Department of Biological Sciences, Michigan Technological University, Houghton, Michigan
| | - Simeon Schum
- Department of Chemistry, Michigan Technological University, Houghton, Michigan
| | - Jessica E Behnke
- Department of Kinesiology and Integrative Physiology, Michigan Technological University, Houghton, Michigan.,Department of Biological Sciences, Michigan Technological University, Houghton, Michigan
| | - Taija Hahka
- Department of Kinesiology and Integrative Physiology, Michigan Technological University, Houghton, Michigan.,Department of Biological Sciences, Michigan Technological University, Houghton, Michigan
| | - Michael J Huber
- Department of Kinesiology and Integrative Physiology, Michigan Technological University, Houghton, Michigan.,Department of Biological Sciences, Michigan Technological University, Houghton, Michigan
| | - Enshe Jiang
- Department of Kinesiology and Integrative Physiology, Michigan Technological University, Houghton, Michigan
| | - Robert A Larson
- Department of Kinesiology and Integrative Physiology, Michigan Technological University, Houghton, Michigan.,Department of Internal Medicine, Carver College of Medicine, University of Iowa, Iowa City, Iowa
| | - Zhiying Shan
- Department of Kinesiology and Integrative Physiology, Michigan Technological University, Houghton, Michigan.,Department of Biological Sciences, Michigan Technological University, Houghton, Michigan
| | - Qing-Hui Chen
- Department of Kinesiology and Integrative Physiology, Michigan Technological University, Houghton, Michigan.,Department of Biological Sciences, Michigan Technological University, Houghton, Michigan
| |
Collapse
|
12
|
Abstract
Acid-base homeostasis is critical to maintenance of normal health. Renal ammonia excretion is the quantitatively predominant component of renal net acid excretion, both under basal conditions and in response to acid-base disturbances. Although titratable acid excretion also contributes to renal net acid excretion, the quantitative contribution of titratable acid excretion is less than that of ammonia under basal conditions and is only a minor component of the adaptive response to acid-base disturbances. In contrast to other urinary solutes, ammonia is produced in the kidney and then is selectively transported either into the urine or the renal vein. The proportion of ammonia that the kidney produces that is excreted in the urine varies dramatically in response to physiological stimuli, and only urinary ammonia excretion contributes to acid-base homeostasis. As a result, selective and regulated renal ammonia transport by renal epithelial cells is central to acid-base homeostasis. Both molecular forms of ammonia, NH3 and NH4+, are transported by specific proteins, and regulation of these transport processes determines the eventual fate of the ammonia produced. In this review, we discuss these issues, and then discuss in detail the specific proteins involved in renal epithelial cell ammonia transport.
Collapse
Affiliation(s)
- I David Weiner
- Division of Nephrology, Hypertension and Renal Transplantation, University of Florida College of Medicine, Gainesville, Florida; and Nephrology and Hypertension Section, North Florida/South Georgia Veterans Health System, Gainesville, Florida
| | - Jill W Verlander
- Division of Nephrology, Hypertension and Renal Transplantation, University of Florida College of Medicine, Gainesville, Florida; and Nephrology and Hypertension Section, North Florida/South Georgia Veterans Health System, Gainesville, Florida
| |
Collapse
|
13
|
Bernardino RL, Marinelli RA, Maggio A, Gena P, Cataldo I, Alves MG, Svelto M, Oliveira PF, Calamita G. Hepatocyte and Sertoli Cell Aquaporins, Recent Advances and Research Trends. Int J Mol Sci 2016; 17:ijms17071096. [PMID: 27409609 PMCID: PMC4964472 DOI: 10.3390/ijms17071096] [Citation(s) in RCA: 24] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/04/2016] [Revised: 06/22/2016] [Accepted: 07/04/2016] [Indexed: 12/30/2022] Open
Abstract
Aquaporins (AQPs) are proteinaceous channels widespread in nature where they allow facilitated permeation of water and uncharged through cellular membranes. AQPs play a number of important roles in both health and disease. This review focuses on the most recent advances and research trends regarding the expression and modulation, as well as physiological and pathophysiological functions of AQPs in hepatocytes and Sertoli cells (SCs). Besides their involvement in bile formation, hepatocyte AQPs are involved in maintaining energy balance acting in hepatic gluconeogenesis and lipid metabolism, and in critical processes such as ammonia detoxification and mitochondrial output of hydrogen peroxide. Roles are played in clinical disorders including fatty liver disease, diabetes, obesity, cholestasis, hepatic cirrhosis and hepatocarcinoma. In the seminiferous tubules, particularly in SCs, AQPs are also widely expressed and seem to be implicated in the various stages of spermatogenesis. Like in hepatocytes, AQPs may be involved in maintaining energy homeostasis in these cells and have a major role in the metabolic cooperation established in the testicular tissue. Altogether, this information represents the mainstay of current and future investigation in an expanding field.
Collapse
Affiliation(s)
- Raquel L Bernardino
- Department of Microscopy, Laboratory of Cell Biology, Institute of Biomedical Sciences Abel Salazar (ICBAS) and Unit for Multidisciplinary Research in Biomedicine (UMIB), University of Porto, 4050-313 Porto, Portugal.
| | - Raul A Marinelli
- Instituto de Fisiología Experimental-CONICET, Facultad de Ciencias Bioquímicas y Farmacéuticas-Universidad Nacional de Rosario, 531 S2002LRK Rosario, Santa Fe, Argentina.
| | - Anna Maggio
- Department of Biosciences, Biotechnologies and Biopharnaceutics, University of Bari "Aldo Moro", 70125 Bari, Italy.
| | - Patrizia Gena
- Department of Biosciences, Biotechnologies and Biopharnaceutics, University of Bari "Aldo Moro", 70125 Bari, Italy.
| | - Ilaria Cataldo
- Department of Biosciences, Biotechnologies and Biopharnaceutics, University of Bari "Aldo Moro", 70125 Bari, Italy.
| | - Marco G Alves
- CICS-UBI, Health Sciences Research Centre, University of Beira Interior, 6201-506 Covilhã, Portugal.
| | - Maria Svelto
- Department of Biosciences, Biotechnologies and Biopharnaceutics, University of Bari "Aldo Moro", 70125 Bari, Italy.
| | - Pedro F Oliveira
- Department of Microscopy, Laboratory of Cell Biology, Institute of Biomedical Sciences Abel Salazar (ICBAS) and Unit for Multidisciplinary Research in Biomedicine (UMIB), University of Porto, 4050-313 Porto, Portugal.
- Instituto de Investigação e Inovação em Saúde, Universidade do Porto, 4200-135 Porto, Portugal.
| | - Giuseppe Calamita
- Department of Biosciences, Biotechnologies and Biopharnaceutics, University of Bari "Aldo Moro", 70125 Bari, Italy.
| |
Collapse
|
14
|
Taatjes DJ, Roth J. The Histochemistry and Cell Biology omnium-gatherum: the year 2015 in review. Histochem Cell Biol 2016; 145:239-74. [DOI: 10.1007/s00418-016-1417-8] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 02/01/2016] [Indexed: 02/07/2023]
|
15
|
Kitchen P, Day RE, Salman MM, Conner MT, Bill RM, Conner AC. Beyond water homeostasis: Diverse functional roles of mammalian aquaporins. Biochim Biophys Acta Gen Subj 2015; 1850:2410-21. [PMID: 26365508 DOI: 10.1016/j.bbagen.2015.08.023] [Citation(s) in RCA: 109] [Impact Index Per Article: 12.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/17/2015] [Revised: 08/25/2015] [Accepted: 08/30/2015] [Indexed: 01/02/2023]
Abstract
BACKGROUND Aquaporin (AQP) water channels are best known as passive transporters of water that are vital for water homeostasis. SCOPE OF REVIEW AQP knockout studies in whole animals and cultured cells, along with naturally occurring human mutations suggest that the transport of neutral solutes through AQPs has important physiological roles. Emerging biophysical evidence suggests that AQPs may also facilitate gas (CO2) and cation transport. AQPs may be involved in cell signalling for volume regulation and controlling the subcellular localization of other proteins by forming macromolecular complexes. This review examines the evidence for these diverse functions of AQPs as well their physiological relevance. MAJOR CONCLUSIONS As well as being crucial for water homeostasis, AQPs are involved in physiologically important transport of molecules other than water, regulation of surface expression of other membrane proteins, cell adhesion, and signalling in cell volume regulation. GENERAL SIGNIFICANCE Elucidating the full range of functional roles of AQPs beyond the passive conduction of water will improve our understanding of mammalian physiology in health and disease. The functional variety of AQPs makes them an exciting drug target and could provide routes to a range of novel therapies.
Collapse
Affiliation(s)
- Philip Kitchen
- Molecular Organisation and Assembly in Cells Doctoral Training Centre, University of Warwick, Coventry CV4 7AL, UK
| | - Rebecca E Day
- Biomedical Research Centre, Sheffield Hallam University, Howard Street, Sheffield S1 1WB, UK
| | - Mootaz M Salman
- Biomedical Research Centre, Sheffield Hallam University, Howard Street, Sheffield S1 1WB, UK
| | - Matthew T Conner
- Biomedical Research Centre, Sheffield Hallam University, Howard Street, Sheffield S1 1WB, UK
| | - Roslyn M Bill
- School of Life & Health Sciences and Aston Research Centre for Healthy Ageing, Aston University, Aston Triangle, Birmingham B4 7ET, UK
| | - Alex C Conner
- Institute of Clinical Sciences, University of Birmingham, Edgbaston, Birmingham B15 2TT, UK.
| |
Collapse
|
16
|
Gregoire F, Lucidi V, Zerrad-Saadi A, Virreira M, Bolaky N, Delforge V, Lemmers A, Donckier V, Devière J, Demetter P, Perret J, Delporte C. Analysis of aquaporin expression in liver with a focus on hepatocytes. Histochem Cell Biol 2015; 144:347-63. [PMID: 26126651 DOI: 10.1007/s00418-015-1341-3] [Citation(s) in RCA: 32] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 06/16/2015] [Indexed: 12/30/2022]
Abstract
A deeper understanding of aquaporins (AQPs) expression and transcriptional regulation will provide useful information for liver pathophysiology. We established a complete AQPs mRNA expression profile in human and mouse liver, as well as protein localization of expressed AQPs. Additionally, the modulation of AQPs mRNA levels in response to various agents was determined in human HuH7 cells and in primary culture of mouse hepatocytes. AQP1, AQP3, AQP7, AQP8, and AQP9 mRNA and protein expressions were detected in human liver, while only AQP6 and AQP11 mRNAs were detected. We reported for the first time the localization of AQP3 in Kupffer cells, AQP7 in hepatocytes and endothelial cells, and AQP9 in cholangiocytes. In addition, we confirmed the localization of AQP1 in endothelial cells, and of AQP8 and AQP9 in hepatocytes. On HuH7 cells, we reported the presence of AQP4 mRNA, confirmed the presence of AQP3, AQP7, and AQP11 mRNAs, but not of AQP8 mRNA. On primary culture of murine hepatocytes, AQP1 and AQP7 mRNAs were identified, while the presence of AQP3, AQP8, AQP9, and AQP11 mRNAs was confirmed. At the protein level, murine endothelial liver cells expressed AQP1 and AQP9, while hepatocytes expressed AQP3, AQP7, AQP8, and AQP9, and macrophages expressed AQP3. Dexamethasone, forskolin, AICAR, rosiglitazone, octanoylated, and non-octanoylated ghrelin regulated some AQP expression in primary culture of murine hepatocytes and human HuH7 cells. Additional studies will be required to further assess the role of AQPs expression in human and murine liver and understand the transcriptional regulation of AQPs in hepatocytes under pathophysiological conditions.
Collapse
Affiliation(s)
- Françoise Gregoire
- Laboratory of Pathophysiological and Nutritional Biochemistry, Université Libre de Bruxelles, Brussels, Belgium
| | - Valério Lucidi
- Digestive Oncology Department, Erasme Hospital, Brussels, Belgium
| | - Amal Zerrad-Saadi
- Laboratory of Pathophysiological and Nutritional Biochemistry, Université Libre de Bruxelles, Brussels, Belgium
| | - Myrna Virreira
- Laboratory of Pathophysiological and Nutritional Biochemistry, Université Libre de Bruxelles, Brussels, Belgium
| | - Nargis Bolaky
- Laboratory of Pathophysiological and Nutritional Biochemistry, Université Libre de Bruxelles, Brussels, Belgium
| | - Valérie Delforge
- Laboratory of Pathophysiological and Nutritional Biochemistry, Université Libre de Bruxelles, Brussels, Belgium
| | - Arnaud Lemmers
- Gastroenterology Department, Erasme Hospital, Brussels, Belgium
| | - Vincent Donckier
- Digestive Oncology Department, Erasme Hospital, Brussels, Belgium
| | - Jacques Devière
- Gastroenterology Department, Erasme Hospital, Brussels, Belgium
| | - Pieter Demetter
- Anatomopathology Department, Erasme Hospital, Brussels, Belgium
| | - Jason Perret
- Laboratory of Pathophysiological and Nutritional Biochemistry, Université Libre de Bruxelles, Brussels, Belgium
| | - Christine Delporte
- Laboratory of Pathophysiological and Nutritional Biochemistry, Université Libre de Bruxelles, Brussels, Belgium.
| |
Collapse
|
17
|
Larsen EH, Deaton LE, Onken H, O'Donnell M, Grosell M, Dantzler WH, Weihrauch D. Osmoregulation and Excretion. Compr Physiol 2014; 4:405-573. [DOI: 10.1002/cphy.c130004] [Citation(s) in RCA: 127] [Impact Index Per Article: 12.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
|
18
|
Abstract
Aquaporins (AQPs) are a family of membrane water channels that basically function as regulators of intracellular and intercellular water flow. To date, thirteen aquaporins have been characterized. They are distributed wildly in specific cell types in multiple organs and tissues. Each AQP channel consists of six membrane-spanning alpha-helices that have a central water-transporting pore. Four AQP monomers assemble to form tetramers, which are the functional units in the membrane. Some of AQPs also transport urea, glycerol, ammonia, hydrogen peroxide, and gas molecules. AQP-mediated osmotic water transport across epithelial plasma membranes facilitates transcellular fluid transport and thus water reabsorption. AQP-mediated urea and glycerol transport is involved in energy metabolism and epidermal hydration. AQP-mediated CO2 and NH3 transport across membrane maintains intracellular acid-base homeostasis. AQPs are also involved in the pathophysiology of a wide range of human diseases (including water disbalance in kidney and brain, neuroinflammatory disease, obesity, and cancer). Further work is required to determine whether aquaporins are viable therapeutic targets or reliable diagnostic and prognostic biomarkers.
Collapse
|
19
|
Out of balance--systemic iron homeostasis in iron-related disorders. Nutrients 2013; 5:3034-61. [PMID: 23917168 PMCID: PMC3775241 DOI: 10.3390/nu5083034] [Citation(s) in RCA: 114] [Impact Index Per Article: 10.4] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/18/2013] [Revised: 07/16/2013] [Accepted: 07/19/2013] [Indexed: 02/06/2023] Open
Abstract
Iron is an essential element in our daily diet. Most iron is required for the de novo synthesis of red blood cells, where it plays a critical role in oxygen binding to hemoglobin. Thus, iron deficiency causes anemia, a major public health burden worldwide. On the other extreme, iron accumulation in critical organs such as liver, heart, and pancreas causes organ dysfunction due to the generation of oxidative stress. Therefore, systemic iron levels must be tightly balanced. Here we focus on the regulatory role of the hepcidin/ferroportin circuitry as the major regulator of systemic iron homeostasis. We discuss how regulatory cues (e.g., iron, inflammation, or hypoxia) affect the hepcidin response and how impairment of the hepcidin/ferroportin regulatory system causes disorders of iron metabolism.
Collapse
|
20
|
Soria LR, Marrone J, Calamita G, Marinelli RA. Ammonia detoxification via ureagenesis in rat hepatocytes involves mitochondrial aquaporin-8 channels. Hepatology 2013; 57:2061-71. [PMID: 23299935 DOI: 10.1002/hep.26236] [Citation(s) in RCA: 55] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/03/2012] [Accepted: 11/27/2012] [Indexed: 12/26/2022]
Abstract
UNLABELLED Hepatocyte mitochondrial ammonia detoxification via ureagenesis is critical for the prevention of hyperammonemia and hepatic encephalopathy. Aquaporin-8 (AQP8) channels facilitate the membrane transport of ammonia. Because AQP8 is expressed in hepatocyte inner mitochondrial membranes (IMMs), we studied whether mitochondrial AQP8 (mtAQP8) plays a role in ureagenesis from ammonia. Primary cultured rat hepatocytes were transfected with small interfering RNAs (siRNAs) targeting two different regions of the rat AQP8 molecule or with scrambled control siRNA. After 48 hours, the levels of mtAQP8 protein decreased by approximately 80% (P < 0.05) without affecting cell viability. mtAQP8 knockdown cells in the presence of ammonium chloride showed a decrease in ureagenesis of approximately 30% (P < 0.05). Glucagon strongly stimulated ureagenesis in control hepatocytes (+120%, P < 0.05) but induced no significant stimulation in mtAQP8 knockdown cells. Contrarily, mtAQP8 silencing induced no significant change in basal and glucagon-induced ureagenesis when glutamine or alanine was used as a source of nitrogen. Nuclear magnetic resonance studies using 15N-labeled ammonia confirmed that glucagon-induced 15N-labeled urea synthesis was markedly reduced in mtAQP8 knockdown hepatocytes (-90%, P < 0.05). In vivo studies in rats showed that under glucagon-induced ureagenesis, hepatic mtAQP8 protein expression was markedly up-regulated (+160%, P < 0.05). Moreover, transport studies in liver IMM vesicles showed that glucagon increased the diffusional permeability to the ammonia analog [(14) C]methylamine (+80%, P < 0.05). CONCLUSION Hepatocyte mtAQP8 channels facilitate the mitochondrial uptake of ammonia and its metabolism into urea, mainly under glucagon stimulation. This mechanism may be relevant to hepatic ammonia detoxification and in turn, avoid the deleterious effects of hyperammonemia.
Collapse
Affiliation(s)
- Leandro R Soria
- Instituto de Fisiología Experimental, Consejo Nacional de Investigaciones Científicas y Técnicas, Facultad de Ciencias Bioquímicas y Farmacéuticas, Universidad Nacional de Rosario, Rosario, Argentina
| | | | | | | |
Collapse
|
21
|
Geyer RR, Musa-Aziz R, Qin X, Boron WF. Relative CO(2)/NH(3) selectivities of mammalian aquaporins 0-9. Am J Physiol Cell Physiol 2013; 304:C985-94. [PMID: 23485707 DOI: 10.1152/ajpcell.00033.2013] [Citation(s) in RCA: 71] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
Previous work showed that aquaporin 1 (AQP1), AQP4-M23, and AQP5 each has a characteristic CO(2)/NH(3) and CO(2)/H(2)O permeability ratio. The goal of the present study is to characterize AQPs 0-9, which traffic to the plasma membrane when heterologously expressed in Xenopus oocytes. We use video microscopy to compute osmotic water permeability (P(f)) and microelectrodes to record transient changes in surface pH (ΔpH(S)) caused by CO(2) or NH(3) influx. Subtracting respective values for day-matched, H(2)O-injected control oocytes yields the channel-specific values P(f)* and ΔpH(S)*. We find that P(f)* is significantly >0 for all AQPs tested except AQP6. (ΔpH(S)*)(CO(2)) is significantly >0 for AQP0, AQP1, AQP4-M23, AQP5, AQP6, and AQP9. (ΔpH(S)*)(NH(3)) is >0 for AQP1, AQP3, AQP6, AQP7, AQP8, and AQP9. The ratio (ΔpH(S)*)(CO(2))/P(f)* falls in the sequence AQP6 (∞) > AQP5 > AQP4-M23 > AQP0 ≅ AQP1 ≅ AQP9 > others (0). The ratio (ΔpH(S)*)(NH(3))/P(f)* falls in the sequence AQP6 (∞) > AQP3 ≅ AQP7 ≅ AQP8 ≅ AQP9 > AQP1 > others (0). Finally, the ratio (ΔpH(S)*)(CO(2))/(-ΔpH(S)*)(NH(3)) falls in the sequence AQP0 (∞) ≅ AQP4-M23 ≅ AQP5 > AQP6 > AQP1 > AQP9 > AQP3 (0) ≅ AQP7 ≅ AQP8. The ratio (ΔpH(S)*)(CO(2))/(-ΔpH(S)*)(NH(3)) is indeterminate for both AQP2 and AQP4-M1. In summary, we find that mammalian AQPs exhibit a diverse range of selectivities for CO(2) vs. NH(3) vs. H(2)O. As a consequence, by expressing specific combinations of AQPs, cells could exert considerable control over the movements of each of these three substances.
Collapse
Affiliation(s)
- R Ryan Geyer
- Department of Physiology and Biophysics, Case Western Reserve University, Cleveland, OH 44106, USA.
| | | | | | | |
Collapse
|
22
|
Intertissue Differences for the Role of Glutamate Dehydrogenase in Metabolism. Neurochem Res 2013; 39:516-26. [DOI: 10.1007/s11064-013-0998-z] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/26/2012] [Revised: 01/24/2013] [Accepted: 02/01/2013] [Indexed: 11/26/2022]
|
23
|
Abstract
Renal ammonia metabolism and transport mediates a central role in acid-base homeostasis. In contrast to most renal solutes, the majority of renal ammonia excretion derives from intrarenal production, not from glomerular filtration. Renal ammoniagenesis predominantly results from glutamine metabolism, which produces 2 NH4(+) and 2 HCO3(-) for each glutamine metabolized. The proximal tubule is the primary site for ammoniagenesis, but there is evidence for ammoniagenesis by most renal epithelial cells. Ammonia produced in the kidney is either excreted into the urine or returned to the systemic circulation through the renal veins. Ammonia excreted in the urine promotes acid excretion; ammonia returned to the systemic circulation is metabolized in the liver in a HCO3(-)-consuming process, resulting in no net benefit to acid-base homeostasis. Highly regulated ammonia transport by renal epithelial cells determines the proportion of ammonia excreted in the urine versus returned to the systemic circulation. The traditional paradigm of ammonia transport involving passive NH3 diffusion, protonation in the lumen and NH4(+) trapping due to an inability to cross plasma membranes is being replaced by the recognition of limited plasma membrane NH3 permeability in combination with the presence of specific NH3-transporting and NH4(+)-transporting proteins in specific renal epithelial cells. Ammonia production and transport are regulated by a variety of factors, including extracellular pH and K(+), and by several hormones, such as mineralocorticoids, glucocorticoids and angiotensin II. This coordinated process of regulated ammonia production and transport is critical for the effective maintenance of acid-base homeostasis.
Collapse
Affiliation(s)
- I David Weiner
- Nephrology and Hypertension Section, NF/SGVHS, Gainesville, Florida, USA.
| | | |
Collapse
|
24
|
Engelund MB, Chauvigné F, Christensen BM, Finn RN, Cerdà J, Madsen SS. Differential expression and novel permeability properties of three aquaporin 8 paralogs from seawater-challenged Atlantic salmon smolts. J Exp Biol 2013; 216:3873-85. [DOI: 10.1242/jeb.087890] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
Summary
Aquaporins may facilitate transepithelial water absorption in the intestine of seawater (SW) acclimated fish. Here we have characterized three full-length aqp8 paralogs from Atlantic salmon (Salmo salar). Bayesian inference revealed that each paralog is a representative of the three major classes of aqp8aa, aqp8ab and aqp8b genes found in other teleosts. The permeability properties were studied by heterologous expression in Xenopus laevis oocytes, and the expression levels examined by qPCR, immunofluorescence and immunoelectron microscopy, and immunoblotting of membrane fractions from intestines of SW challenged smolts. All three Aqp8 paralogs were permeable to water and urea, whereas Aqp8ab and -8b were, surprisingly, also permeable to glycerol. The mRNA tissue distribution of each paralog was distinct although some tissues, such as the intestine showed redundant expression of more than one paralog. Immunofluorescence microscopy localized Aqp8aa(1+2) to intracellular compartments of the liver and intestine, and Aqp8ab and Aqp8b to apical plasma membrane domains of the intestinal epithelium, with Aqp8b also in goblet cells. In a control experiment with rainbow trout, immunoelectron microscopy confirmed abundant labeling of Aqp8ab and -8b at apical plasma membranes of enterocytes in the middle intestine and also in subapical vesicular structures. During SW-challenge, Aqp8ab showed significantly increased levels of protein expression in plasma membrane enriched fractions of the intestine. These data indicate that the Atlantic salmon Aqp8 paralogs have neofunctionalized on a transcriptional as well as on a functional level, and that Aqp8ab may play a central role in the intestinal transcellular uptake of water during SW acclimation.
Collapse
Affiliation(s)
| | - François Chauvigné
- Institut de Recerca i Tecnologia Agroalimentàries - Institut de Ciències del Mar, CSIC
| | | | | | - Joan Cerdà
- Institut de Recerca i Tecnologia Agroalimentàries - Institut de Ciències del Mar, CSIC
| | | |
Collapse
|
25
|
Soyfoo MS, Bolaky N, Depoortere I, Delporte C. Relationship between aquaporin-5 expression and saliva flow in streptozotocin-induced diabetic mice? Oral Dis 2012; 18:501-5. [PMID: 22273265 DOI: 10.1111/j.1601-0825.2011.01902.x] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022]
Abstract
OBJECTIVE To investigate the expression and distribution of AQP5 in submandibular acinar cells from sham- and streptozotocin (STZ)-treated mice in relation to the salivary flow. METHODS Mice were sham or STZ injected. Distribution of AQP5 subcellular expression in submandibular glands was determined by immunohistochemistry. AQP5 labelling indices (LI), reflecting AQP5 subcellular distribution, were determined in acinar cells. Western blotting was performed to determine the expression of AQP5 in submandibular glands. Blood glycaemia and osmolality and saliva flow rates were also determined. RESULTS AQP5 immunoreactivity was primarily located at the apical and apical-basolateral membranes of submandibular gland acinar cells from sham- and STZ-treated mice. No significant differences in AQP5 protein levels were observed between sham- and STZ-treated mice. Compared to sham-treated mice, STZ-treated mice had significant increased glycaemia, while no significant differences in blood osmolality were observed. Saliva flow rate was significantly decreased in STZ-treated mice as compared to sham-treated mice. CONCLUSIONS In STZ-treated mice, significant reduction in salivary flow rate was observed without any concomitant modification in AQP5 expression and localization.
Collapse
Affiliation(s)
- M S Soyfoo
- Laboratory of Biological Chemistry and Nutrition, Université Libre de Bruxelles, Brussels, Belgium
| | | | | | | |
Collapse
|
26
|
Molinas SM, Trumper L, Marinelli RA. Mitochondrial aquaporin-8 in renal proximal tubule cells: evidence for a role in the response to metabolic acidosis. Am J Physiol Renal Physiol 2012; 303:F458-66. [PMID: 22622463 DOI: 10.1152/ajprenal.00226.2012] [Citation(s) in RCA: 42] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Mitochondrial ammonia synthesis in proximal tubules and its urinary excretion are key components of the renal response to maintain acid-base balance during metabolic acidosis. Since aquaporin-8 (AQP8) facilitates transport of ammonia and is localized in inner mitochondrial membrane (IMM) of renal proximal cells, we hypothesized that AQP8-facilitated mitochondrial ammonia transport in these cells plays a role in the response to acidosis. We evaluated whether mitochondrial AQP8 (mtAQP8) knockdown by RNA interference is able to impair ammonia excretion in the human renal proximal tubule cell line, HK-2. By RT-PCR and immunoblotting, we found that AQP8 is expressed in these cells and is localized in IMM. HK-2 cells were transfected with short-interfering RNA targeting human AQP8. After 48 h, the levels of mtAQP8 protein decreased by 53% (P < 0.05). mtAQP8 knockdown decreased the rate of ammonia released into culture medium in cells grown at pH 7.4 (-31%, P < 0.05) as well as in cells exposed to acid (-90%, P < 0.05). We also evaluated mtAQP8 protein expression in HK-2 cells exposed to acidic medium. After 48 h, upregulation of mtAQP8 (+74%, P < 0.05) was observed, together with higher ammonia excretion rate (+73%, P < 0.05). In vivo studies in NH(4)Cl-loaded rats showed that mtAQP8 protein expression was also upregulated after 7 days of acidosis in renal cortex (+51%, P < 0.05). These data suggest that mtAQP8 plays an important role in the adaptive response of proximal tubule to acidosis possibly facilitating mitochondrial ammonia transport.
Collapse
Affiliation(s)
- Sara M Molinas
- Instituto de Fisiología Experimental. Facultad de Ciencias Bioquímicas y Farmacéuticas. Universidad Nacional de Rosario, Suipacha 570, 2000 Rosario, Santa Fe, Argentina.
| | | | | |
Collapse
|
27
|
Wright G, Noiret L, Olde Damink SWM, Jalan R. Interorgan ammonia metabolism in liver failure: the basis of current and future therapies. Liver Int 2011; 31:163-75. [PMID: 20673233 DOI: 10.1111/j.1478-3231.2010.02302.x] [Citation(s) in RCA: 105] [Impact Index Per Article: 8.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/13/2023]
Abstract
Hepatic encephalopathy complicates the course of both acute and chronic liver disease and its treatment remains an unmet clinical need. Ammonia is thought to be central in its pathogenesis and remains an important target of current and future therapeutic approaches. In liver failure, the main detoxification pathway of ammonia metabolism is compromised leading to hyperammonaemia. In this situation, the other ammonia-regulating pathways in multiple organs assume important significance. The present review focuses upon interorgan ammonia metabolism in health and disease describing the role of the key enzymes, glutamine synthase and glutaminase. Better understanding of these alternative pathways are leading to the development of new therapeutic approaches.
Collapse
Affiliation(s)
- Gavin Wright
- UCL Institute of Hepatology, Division of Medicine, University College London, London, UK
| | | | | | | |
Collapse
|
28
|
Weiner ID, Verlander JW. Role of NH3 and NH4+ transporters in renal acid-base transport. Am J Physiol Renal Physiol 2011; 300:F11-23. [PMID: 21048022 PMCID: PMC3023229 DOI: 10.1152/ajprenal.00554.2010] [Citation(s) in RCA: 98] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/20/2010] [Accepted: 11/01/2010] [Indexed: 11/22/2022] Open
Abstract
Renal ammonia excretion is the predominant component of renal net acid excretion. The majority of ammonia excretion is produced in the kidney and then undergoes regulated transport in a number of renal epithelial segments. Recent findings have substantially altered our understanding of renal ammonia transport. In particular, the classic model of passive, diffusive NH3 movement coupled with NH4+ "trapping" is being replaced by a model in which specific proteins mediate regulated transport of NH3 and NH4+ across plasma membranes. In the proximal tubule, the apical Na+/H+ exchanger, NHE-3, is a major mechanism of preferential NH4+ secretion. In the thick ascending limb of Henle's loop, the apical Na+-K+-2Cl- cotransporter, NKCC2, is a major contributor to ammonia reabsorption and the basolateral Na+/H+ exchanger, NHE-4, appears to be important for basolateral NH4+ exit. The collecting duct is a major site for renal ammonia secretion, involving parallel H+ secretion and NH3 secretion. The Rhesus glycoproteins, Rh B Glycoprotein (Rhbg) and Rh C Glycoprotein (Rhcg), are recently recognized ammonia transporters in the distal tubule and collecting duct. Rhcg is present in both the apical and basolateral plasma membrane, is expressed in parallel with renal ammonia excretion, and mediates a critical role in renal ammonia excretion and collecting duct ammonia transport. Rhbg is expressed specifically in the basolateral plasma membrane, and its role in renal acid-base homeostasis is controversial. In the inner medullary collecting duct (IMCD), basolateral Na+-K+-ATPase enables active basolateral NH4+ uptake. In addition to these proteins, several other proteins also contribute to renal NH3/NH4+ transport. The role and mechanisms of these proteins are discussed in depth in this review.
Collapse
Affiliation(s)
- I David Weiner
- Division of Nephrology, Hypertension and Transplantation, University of Florida College of Medicine, Gainesville, FL 32610, USA.
| | | |
Collapse
|
29
|
Magdeldin S, Li H, Yoshida Y, Satokata I, Maeda Y, Yokoyama M, Enany S, Zhang Y, Xu B, Fujinaka H, Yaoita E, Yamamoto T. Differential proteomic shotgun analysis elucidates involvement of water channel aquaporin 8 in presence of α-amylase in the colon. J Proteome Res 2010; 9:6635-46. [PMID: 20939500 DOI: 10.1021/pr100789v] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
Abstract
Aquaporin (AQP) family plays a pivotal role in fluid secretion and absorption, especially in the digestive system and secretory glands. Within this family, AQP8 was reported to be widely expressed in the epithelia of the digestive tract, liver, and pancreas. In two parallel experimental platforms with different analytical and comparative approaches, in-gel tryptic digestion with macro-embedded spreadsheet analysis and in-solution tryptic digestion with LC-MS alignment based approach, we compared wild-type and AQP8 knockout mice colon proteomes. Shared result between both experiments revealed down-regulation of α-amylase 2 in AQP8-deleted mice model. Verification on both transcriptional and translational levels confirmed the involvement of AQP8 in α-amylase 2 regulation. Given the profound role of AQP8 as a water and solutes transporter, it might be important in modulating α-amylase 2 synthesis by colonic epithelial cells as well. Here, we also proved the capability of our coupled approaches for selecting the most reliable and significant candidates, an applicable process for initial screening of biological biomarkers in complex specimens and tissue extracts.
Collapse
Affiliation(s)
- Sameh Magdeldin
- Department of Structural Pathology, Institute of Nephrology, Graduate School of Medical and Dental Sciences, Niigata University, Japan.
| | | | | | | | | | | | | | | | | | | | | | | |
Collapse
|
30
|
Chen LM, Zhao J, Musa-Aziz R, Pelletier MF, Drummond IA, Boron WF. Cloning and characterization of a zebrafish homologue of human AQP1: a bifunctional water and gas channel. Am J Physiol Regul Integr Comp Physiol 2010; 299:R1163-74. [PMID: 20739606 DOI: 10.1152/ajpregu.00319.2010] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The mammalian aquaporins AQP1, AQP4, and AQP5 have been shown to function not only as water channels but also as gas channels. Zebrafish have two genes encoding an AQP1 homologue, aqp1a and aqp1b. In the present study, we cloned the cDNA that encodes the zebrafish protein Aqp1a from the 72-h postfertilization (hpf) embryo of Danio rerio, as well as from the swim bladder of the adult. The deduced amino-acid sequence of aqp1a consists of 260 amino acids and is 59% identical to human AQP1. By analyzing the genomic DNA sequence, we identified four exons in the aqp1a gene. By in situ hybridization, aqp1a is expressed transiently in the developing vasculature and in erythrocytes from 16 to 48 h of development. Later, at 72 hpf, aqp1a is expressed in dermal ionocytes and in the swim bladder. Western blot analysis of adult tissues reveals that Aqp1a is most highly expressed in the eye and swim bladder. Xenopus oocytes expressing aqp1a have a channel-dependent (*) osmotic water permeability (P(f)(*)) that is indistinguishable from that of human AQP1. On the basis of the magnitude of the transient change in surface pH (ΔpH(S)) that were recorded as the oocytes were exposed to either CO(2) or NH(3), we conclude that zebrafish Aqp1a is permeable to both CO(2) and NH(3). The ratio (ΔpH(S)(*))((CO)2)/P(f)(*) is about half that of human AQP1, and the ratio (ΔpH(S)(*))(NH3)/P(f)(*) is about one-quarter that of human AQP1. Thus, compared with human AQP1, zebrafish Aqp1a has about twice the selectivity for CO(2) over NH(3).
Collapse
Affiliation(s)
- Li-Ming Chen
- Department of Biological Sciences, Key Laboratory of Molecular Biophysics of the Ministry of Education, Huazhong University of Science & Technology School of Life Science and Technology, Wuhan, Hubei Province, China
| | | | | | | | | | | |
Collapse
|
31
|
Rato L, Socorro S, Cavaco JEB, Oliveira PF. Tubular Fluid Secretion in the Seminiferous Epithelium: Ion Transporters and Aquaporins in Sertoli Cells. J Membr Biol 2010; 236:215-24. [DOI: 10.1007/s00232-010-9294-x] [Citation(s) in RCA: 74] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/02/2010] [Accepted: 07/20/2010] [Indexed: 01/01/2023]
|
32
|
Comparison of two dimensional electrophoresis mouse colon proteomes before and after knocking out Aquaporin 8. J Proteomics 2010; 73:2031-40. [PMID: 20619372 DOI: 10.1016/j.jprot.2010.06.010] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/15/2010] [Revised: 06/09/2010] [Accepted: 06/23/2010] [Indexed: 12/28/2022]
Abstract
Aquaporin (AQP) family plays a fundamental role in transmembrane water and small solutes movement. Within this family, aquaporin 8 (AQP8), showed to be widely distributed in the digestive system especially colon. To investigate the possible protein alterations involved in AQP8 regulation and trafficking, we extensively compared between wild type and AQP8 knockout mouse colon using semi-quantitative fluorescence- stained two dimensional gel electrophoresis (2-DE) coupled with nano LC-Ms/Ms. Our analysis revealed identification and regulation of 21 proteins, most notably, actin-related family which suggests its possible involvement in regulating AQP8 secretory vesicles migration to be integrated as a cell membrane protein.
Collapse
|
33
|
Aquaporin-8-facilitated mitochondrial ammonia transport. Biochem Biophys Res Commun 2010; 393:217-21. [DOI: 10.1016/j.bbrc.2010.01.104] [Citation(s) in RCA: 78] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/15/2010] [Accepted: 01/26/2010] [Indexed: 11/21/2022]
|
34
|
Ludewig U, Dynowski M. Plant aquaporin selectivity: where transport assays, computer simulations and physiology meet. Cell Mol Life Sci 2009; 66:3161-75. [PMID: 19565186 PMCID: PMC11115745 DOI: 10.1007/s00018-009-0075-6] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/22/2009] [Revised: 06/08/2009] [Accepted: 06/10/2009] [Indexed: 10/20/2022]
Abstract
Plants contain a large number of aquaporins with different selectivity. These channels generally conduct water, but some additionally conduct NH(3), CO(2) and/or H(2)O(2). The experimental evidence and molecular basis for the transport of a given solute, the validation with molecular dynamics simulations and the physiological impact of the selectivity are reviewed here. The aromatic/arginine (ar/R) constriction is most important for solute selection, but the exact pore requirements for efficient conduction of small solutes remain difficult to predict. Yeast growth assays are valuable for screening substrate selectivity and are explicitly shown for hydrogen peroxide and methylamine, a transport analog of ammonia. Independent assays need to address the relevance of different substrates for each channel in its physiological context. This is emphasized by the fact that several plant NIP channels, which conduct several solutes, are specifically involved in the transport of metalloids, such as silicic acid, arsenite, or boric acid in planta.
Collapse
Affiliation(s)
- Uwe Ludewig
- Institute of Botany, Darmstadt University of Technology, Schnittspahnstr. 10, 64287, Darmstadt, Germany.
| | | |
Collapse
|
35
|
Verkman AS. Aquaporins: translating bench research to human disease. ACTA ACUST UNITED AC 2009; 212:1707-15. [PMID: 19448080 DOI: 10.1242/jeb.024125] [Citation(s) in RCA: 121] [Impact Index Per Article: 8.1] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
There is considerable potential for translating knowledge of aquaporin structure, function and physiology to the clinic. One area is in aquaporin-based diagnostics. The discovery of AQP4 autoantibodies as a marker of the neuromyelitis optica form of multiple sclerosis has allowed precise diagnosis of this disease. Other aquaporin-based diagnostics are possible. Another area is in aquaporin-based genetics. Genetic diseases caused by loss-of-function mutations in aquaporins include nephrogenic diabetes insipidus and cataracts, and functionally significant aquaporin polymorphisms are beginning to be explored. Perhaps of greatest translational potential is aquaporin-based therapeutics. Information largely from aquaporin knockout mice has implicated key roles of aquaporin-facilitated water transport in transepithelial fluid transport (urinary concentrating, gland fluid secretion), water movement into and out of the brain, cell migration (angiogenesis, tumor metastasis, wound healing) and neural function (sensory signaling, seizures). A subset of aquaporins that transport both water and glycerol, the 'aquaglyceroporins', regulate glycerol content in epidermal, fat and other tissues, and are involved in skin hydration, cell proliferation, carcinogenesis and fat metabolism. Aquaporin-based modulator drugs are predicted to be of broad potential utility in the treatment of edematous states, cancer, obesity, wound healing, epilepsy and glaucoma. These exciting possibilities and their associated challenges are reviewed.
Collapse
Affiliation(s)
- A S Verkman
- Department of Medicine, Cardiovascular Research Institute, University of California, San Francisco, CA 94143, USA.
| |
Collapse
|
36
|
Bowman RV, Wright CM, Davidson MR, Francis SMS, Yang IA, Fong KM. Epigenomic targets for the treatment of respiratory disease. Expert Opin Ther Targets 2009; 13:625-40. [PMID: 19409032 DOI: 10.1517/14728220902926119] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
Abstract
BACKGROUND A number of processes lead to epigenetic and epigenomic modifications. OBJECTIVE To address the importance of epigenomics in respiratory disease. METHODS Studies of epigenomics were analysed in relation to chronic respiratory diseases. RESULTS/CONCLUSION In lung cancer and mesothelioma, a number of genes involved in carcinogenesis have been demonstrated to be hypermethylated, implicating epigenomic changes in the aetiology of these cancers. Hypermethylated genes have also been associated with lung cancer recurrence, indicating epigenomic regulation of metastasis. In airway diseases, modulation of histone function may activate inflammatory mechanisms in chronic obstructive pulmonary disease patients and lead to relative steroid resistance. There is emerging evidence for the role of epigenetic changes in chronic lung diseases such as asthma, including responses to environmental exposures in utero and to the effects of air pollution. Insight into epigenomics will lead to the development of novel biomarkers and treatment targets in respiratory diseases.
Collapse
Affiliation(s)
- Rayleen V Bowman
- The Prince Charles Hospital, Department of Thoracic Medicine, Brisbane, Australia.
| | | | | | | | | | | |
Collapse
|
37
|
Abstract
The human aquaporins,AQP3,AQP7, AQP8,AQP9, and possibly AQP10, are permeable to ammonia, and AQP7, AQP9, and possibly AQP3, are permeable to urea. In humans, these aquaporins supplement the ammonia transport of the Rhesus (Rh) proteins and the urea transporters (UTs). The mechanism by which ammonium is transported by aquaporins is not fully resolved. A comparison of transport equations, models, and experimental data shows that ammonia is transported in its neutral form, NH(3). In the presence of NH(3), the aquaporin stimulates H(+) transport. Consequently, this transport of H(+) is only significant at alkaline pH. It is debated whether the H(+) ion passes via the aquaporin or by some external route; the investigation of this problem requires the aquaporin-expressing cell to be voltage-clamped. The ammonia-permeable aquaporins differ from other aquaporins by having a less restrictive aromatic/arginine region, and an exclusively water-permeable aquaporin can be transformed into an ammonia-permeable aquaporin by single point mutations in this region. The ammonia-permeable aquaporins fall into two groups: those that are permeable (AQP3, 7, 9, 10) and those that are impermeable (AQP8) to glycerol. The two groups differ in the amino acid composition of their aromatic/arginine regions. The location of the ammonia-permeable aquaporins in the body parallels that of the Rh proteins. This applies to erythrocytes and to cells associated with nitrogen homeostasis and high rates of anabolism. In the liver, AQPs 8 and 9 are found together with Rh proteins in cells exposed to portal blood coming from the intestine. In the kidney, AQP3 might participate in the excretion of NH(4) (+) in the collecting duct. The interplay between the ammonia-permeable aquaporins and the other types of ammonia- and urea-permeable proteins is not well understood.
Collapse
Affiliation(s)
- Thomas Litman
- Exiqon A/S, Department of Biomarker Discovery, Bygstubben 16, Vedbaek, 2950, Denmark
| | | | | |
Collapse
|
38
|
Abstract
The study of water transport began long before the molecular identification of water channels with studies of water-permeable tissues. The discovery of the first aquaporin, AQP1, occurred during experiments focused on the identity of the Rh blood group antigens. Since then the field has expanded dramatically to study aquaporins in all types of organisms. In mammals, some of the aquaporins transport only water. However, there are some family members that collectively transport a diverse set of solutes. The aquaporins can be regulated by factors that affect channel permeability or subcellular localization. An extensive set of studies examines the physiological role of many of the mammalian aquaporins. However, much is still to be discovered about the physiological role of this membrane protein family.
Collapse
|
39
|
Gao MH, Tang T, Guo T, Miyanohara A, Yajima T, Pestonjamasp K, Feramisco JR, Hammond HK. Adenylyl cyclase type VI increases Akt activity and phospholamban phosphorylation in cardiac myocytes. J Biol Chem 2008; 283:33527-35. [PMID: 18838385 PMCID: PMC2586283 DOI: 10.1074/jbc.m805825200] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/29/2008] [Revised: 09/09/2008] [Indexed: 12/21/2022] Open
Abstract
Increased expression of adenylyl cyclase VI has beneficial effects on the heart, but strategies that increase cAMP production in cardiac myocytes usually are harmful. Might adenylyl cyclase VI have beneficial effects unrelated to increased beta-adrenergic receptor-mediated signaling? We previously reported that adenylyl cyclase VI reduces cardiac phospholamban expression. Our focus in the current studies is how adenylyl cyclase VI influences phospholamban phosphorylation. In cultured cardiac myocytes, increased expression of adenylyl cyclase VI activates Akt by phosphorylation at serine 473 and threonine 308 and is associated with increased nuclear phospho-Akt. Activated Akt phosphorylates phospholamban, a process that does not require beta-adrenergic receptor stimulation or protein kinase A activation. These previously unrecognized signaling events would be predicted to promote calcium handling and increase contractile function of the intact heart independently of beta-adrenergic receptor activation. We speculate that phospholamban phosphorylation, through activation of Akt, may be an important mechanism by which adenylyl cyclase VI increases the function of the failing heart.
Collapse
Affiliation(s)
- Mei Hua Gao
- Veterans Administration San Diego Healthcare System, University of California, San Diego, La Jolla, California 92093, USA
| | | | | | | | | | | | | | | |
Collapse
|
40
|
Loppnow H, Werdan K, Buerke M. Vascular cells contribute to atherosclerosis by cytokine- and innate-immunity-related inflammatory mechanisms. Innate Immun 2008; 14:63-87. [PMID: 18713724 DOI: 10.1177/1753425908091246] [Citation(s) in RCA: 62] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
Cardiovascular diseases are the human diseases with the highest death rate and atherosclerosis is one of the major underlying causes of cardiovascular diseases. Inflammatory and innate immune mechanisms, employing monocytes, innate receptors, innate cytokines, or chemokines are suggested to be involved in atherogenesis. Among the inflammatory pathways the cytokines are central players. Plasma levels of cytokines and related proteins, such as CRP, have been investigated in cardiovascular patients, tissue mRNA expression was analyzed and correlations to vascular diseases established. Consistent with these findings the generation of cytokine-deficient animals has provided direct evidence for a role of cytokines in atherosclerosis. In vitro cell culture experiments further support the suggestion that cytokines and other innate mechanisms contribute to atherogenesis. Among the initiation pathways of atherogenesis are innate mechanisms, such as toll-like-receptors (TLRs), including the endotoxin receptor TLR4. On the other hand, innate cytokines, such as IL-1 or TNF, or even autoimmune triggers may activate the cells. Cytokines potently activate multiple functions relevant to maintain or spoil homeostasis within the vessel wall. Vascular cells, not least smooth muscle cells, can actively contribute to the inflammatory cytokine-dependent network in the blood vessel wall by: (i) production of cytokines; (ii) response to these potent cell activators; and (iii) cytokine-mediated interaction with invading cells, such as monocytes, T-cells, or mast cells. Activation of these pathways results in accumulation of cells and increased LDL- and ECM-deposition which may serve as an 'immunovascular memory' resulting in an ever-growing response to subsequent invasions. Thus, vascular cells may potently contribute to the inflammatory pathways involved in development and acceleration of atherosclerosis.
Collapse
Affiliation(s)
- Harald Loppnow
- Martin-Luther-Universität Halle-Wittenberg, Universitätsklinik und Poliklinik für Innere Medizin , Halle (Saale), Germany.
| | | | | |
Collapse
|
41
|
Invertebrate aquaporins: a review. J Comp Physiol B 2008; 178:935-55. [DOI: 10.1007/s00360-008-0288-2] [Citation(s) in RCA: 113] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/01/2008] [Revised: 06/03/2008] [Accepted: 06/10/2008] [Indexed: 10/25/2022]
|
42
|
Davies MJ, Hawkins CL, Pattison DI, Rees MD. Mammalian heme peroxidases: from molecular mechanisms to health implications. Antioxid Redox Signal 2008; 10:1199-234. [PMID: 18331199 DOI: 10.1089/ars.2007.1927] [Citation(s) in RCA: 423] [Impact Index Per Article: 26.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
A marked increase in interest has occurred over the last few years in the role that mammalian heme peroxidase enzymes, primarily myeloperoxidase, eosinophil peroxidase, and lactoperoxidase, may play in both disease prevention and human pathologies. This increased interest has been sparked by developments in our understanding of polymorphisms that control the levels of these enzymes, a greater understanding of the basic chemistry and biochemistry of the oxidants formed by these species, the development of specific biomarkers that can be used in vivo to detect damage induced by these oxidants, the detection of active forms of these peroxidases at most, if not all, sites of inflammation, and a correlation between the levels of these enzymes and a number of major human pathologies. This article reviews recent developments in our understanding of the enzymology, chemistry, biochemistry and biologic roles of mammalian peroxidases and the oxidants that they generate, the potential role of these oxidants in human disease, and the use of the levels of these enzymes in disease prognosis.
Collapse
Affiliation(s)
- Michael J Davies
- The Heart Research Institute, Camperdown, University of Sydney, Sydney, Australia., Faculty of Medicine, University of Sydney, Sydney, Australia.
| | | | | | | |
Collapse
|
43
|
Abstract
AIM Hyaluronan (HA) is involved in renomedullary water handling through its water-binding capacity. This study addressed the effect of hormones involved in regulating fluid-electrolyte homeostasis on renomedullary HA content in vivo and in vitro. METHODS The kidneys from rats treated with L-NAME, indomethacin, vasopressin (AVP) or methylprednisolone (MP) during euvolaemia or water loading were analysed for HA by RIA, ELISA and histochemical staining. HA was measured in renomedullary interstitial cells treated with AVP, angiotensin II (Ang II) or a combination of AVP and Ang II. RESULTS Baseline renal cortical and medullary HA content was unaffected by 2 h of intravenous treatment with L-NAME (NOS inhibitor) or indomethacin (cyclo-oxygenase inhibitor), whereas AVP reduced medullary HA by 33%. During 2 h of acute water loading, diuresis was accompanied by an increase in renomedullary HA (+45%), but cortical HA was unaffected. In both L-NAME- and indomethacin-treated animals, the water loading-induced increase in renomedullary HA was absent, indicating involvement of NO and prostaglandins. After 7 days of MP treatment, medullary HA was reduced by 40%, but the water loading-induced elevation in HA remained. In cultured renomedullary interstitial cells, AVP reduced the HA content in the supernatant by 63%, and simultaneous treatment with Ang II reduced the HA content even further (95%). CONCLUSION AVP reduces HA content, and NO and prostaglandins are needed for the increase in HA during water loading.
Collapse
Affiliation(s)
- L Rügheimer
- Division of Integrative Physiology, Department of Medical Cell Biology, Uppsala University, Uppsala, Sweden.
| | | | | | | |
Collapse
|
44
|
Mammalian aquaporins: diverse physiological roles and potential clinical significance. Expert Rev Mol Med 2008; 10:e13. [PMID: 18482462 DOI: 10.1017/s1462399408000690] [Citation(s) in RCA: 105] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
Aquaporins have multiple distinct roles in mammalian physiology. Phenotype analysis of aquaporin-knockout mice has confirmed the predicted role of aquaporins in osmotically driven transepithelial fluid transport, as occurs in the urinary concentrating mechanism and glandular fluid secretion. Aquaporins also facilitate water movement into and out of the brain in various pathologies such as stroke, tumour, infection and hydrocephalus. A major, unexpected cellular role of aquaporins was revealed by analysis of knockout mice: aquaporins facilitate cell migration, as occurs in angiogenesis, tumour metastasis, wound healing, and glial scar formation. Another unexpected role of aquaporins is in neural function - in sensory signalling and seizure activity. The water-transporting function of aquaporins is likely responsible for these roles. A subset of aquaporins that transport both water and glycerol, the 'aquaglyceroporins', regulate glycerol content in epidermal, fat and other tissues. Mice lacking various aquaglyceroporins have several interesting phenotypes, including dry skin, resistance to skin carcinogenesis, impaired cell proliferation, and altered fat metabolism. The various roles of aquaporins might be exploited clinically by development of drugs to alter aquaporin expression or function, which could serve as diuretics, and in the treatment of brain swelling, glaucoma, epilepsy, obesity and cancer.
Collapse
|
45
|
Qiu L, Wu X, Chau JFL, Szeto IYY, Tam WY, Guo Z, Chung SK, Oates PJ, Chung SSM, Yang JY. Aldose reductase regulates hepatic peroxisome proliferator-activated receptor alpha phosphorylation and activity to impact lipid homeostasis. J Biol Chem 2008; 283:17175-83. [PMID: 18445591 DOI: 10.1074/jbc.m801791200] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023] Open
Abstract
Aldose reductase (AR) is implicated in the development of a number of diabetic complications, but the underlying mechanisms remain to be fully elucidated. We performed this study to determine whether and how AR might influence hepatic peroxisome proliferator-activated receptor alpha (PPARalpha) activity and lipid metabolism. Our results in mouse hepatocyte AML12 cells show that AR overexpression caused strong suppression of PPARalpha/delta activity (74%, p < 0.001) together with significant down-regulation of mRNA expression for acetyl-CoA oxidase and carnitine palmitoyltransferase-1. These suppressive effects were attenuated by the selective AR inhibitor zopolrestat. Furthermore, AR overexpression greatly increased the levels of phosphorylated PPARalpha and ERK1/2. Moreover, AR-induced suppression of PPARalpha activity was attenuated by treatment with an inhibitor for ERK1/2 but not that for phosphoinositide 3-kinase, p38, or JNK. Importantly, similar effects were observed for cells exposed to 25 mm glucose. In streptozotocin-diabetic mice, AR inhibitor treatment or genetic deficiency of AR resulted in significant dephosphorylation of both PPARalpha and ERK1/2. With the dephosphorylation of PPARalpha, hepatic acetyl-CoA oxidase and apolipoprotein C-III mRNA expression was greatly affected and that was associated with substantial reductions in blood triglyceride and nonesterified fatty acid levels. These data indicate that AR plays an important role in the regulation of hepatic PPARalpha phosphorylation and activity and lipid homeostasis. A significant portion of the AR-induced modulation is achieved through ERK1/2 signaling.
Collapse
Affiliation(s)
- Longxin Qiu
- Ministry of Education Key Laboratory for Cell Biology and Tumor Cell Engineering and Department of Biomedical Sciences, School of Life Sciences, Xiamen University, Xiamen 361005, China
| | | | | | | | | | | | | | | | | | | |
Collapse
|
46
|
Maciver B, Smith CP, Hill WG, Zeidel ML. Functional characterization of mouse urea transporters UT-A2 and UT-A3 expressed in purified Xenopus laevis oocyte plasma membranes. Am J Physiol Renal Physiol 2008; 294:F956-64. [PMID: 18256317 DOI: 10.1152/ajprenal.00229.2007] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Urea is a small solute synthesized by many terrestrial organisms as part of the catabolism of protein. In mammals it is transported across cellular membranes by specific urea transporter (UT) proteins that are the products of two separate, but closely related genes, referred to as UT-A and UT-B. Three major UT-A isoforms are found in the kidney, namely UT-A1, UT-A2, and UT-A3. UT-A2 is found in the thin, descending limb of the loop of Henle, whereas UT-A1 and UT-A3 are concentrated in the inner medullary collecting duct. UT-A2 and UT-A3 effectively represent two halves of the whole UT-A gene and, when joined together by 73 hydrophilic amino acids, constitute UT-A1. A biophysical characterization of mouse UT-A2 and UT-A3 was undertaken by expression in Xenopus laevis oocytes and subsequent preparation of highly enriched plasma membrane vesicles for use in stopped-flow fluorometry. Both isoforms were found to be highly specific for urea, and did not permeate water, ammonia, or other molecules closely related to urea (formamide, acetamide, methylurea, and dimethylurea). Single transporter flux rates of 46,000 +/- 10,000 and 59,000 +/- 15,000 (means +/- SE) urea molecules/s/channel for UT-A2 and UT-A3, respectively, were obtained. Overall, the UT-A2 and UT-A3 isoforms appear to have identical functional kinetics.
Collapse
Affiliation(s)
- Bryce Maciver
- Beth Israel Deaconess Medical Center and Harvard Medical School, 840 Memorial Drive, Cambridge MA 02139, USA.
| | | | | | | |
Collapse
|
47
|
Wang D, Lu S, Dong Z. Regulation of TGF-beta1 gene transcription in human prostate cancer cells by nitric oxide. Prostate 2007; 67:1825-33. [PMID: 17941092 DOI: 10.1002/pros.20669] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
BACKGROUND Overexpression of transforming growth factor (TGF)-beta1 is associated with advanced prostate cancer. Our previous studies showed an inverse correlation between the expressions of TGF-beta1 and inducible nitric oxide synthase (iNOS) in prostatic tumors in mice. The purpose of this study was to investigate regulation of TGF-beta1 expression in human prostate cancer cells by nitric oxide (NO). METHODS Expression of TGF-beta1 in the three well-characterized lines of human prostate cancer cells (PC-3MM2, LNCaP, and DU145) was determined by using the enzyme-linked immunoabsorbance assay (ELISA), real-time reverse-transcriptase PCR (RT-PCR), nuclear run-on, and promoter activity analyses. RESULTS Expression of both TGF-beta1 protein and mRNA was inhibited in both dose- and time-dependent manners by NO donors sodium nitroprusside (SNP), S-nitroso-N-acetylpenicilamine (SNAP), S-nitrosoglutathione (GSNO), and (+/-)-(E)-methyl-2-[(E)-hydroxyimino]-5-nitro-6-methoxy-3-hexeneamide (NOR-1) and by transfection of iNOS. The inhibitory effects of SNP and iNOS on TGF-beta1 expression were reduced in cells treated with NO scavengers N-dithiocarboxysarcosine (DTCS), 2-phenyl-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (PTIO), and hemoglobin, or with the iNOS inhibitor N-methyl-arginine (NMA). SNP downregulated the in vitro transcription of TGF-beta1 mRNA, inhibited TGF-beta1 promoter activity, but had no significant effects on TGF-beta1 mRNA stability. CONCLUSION These results show that NO downregulates TGF-beta1 expression in prostate cancer cells at transcription level by suppressing the de novo synthesis of TGF-beta1 mRNA.
Collapse
Affiliation(s)
- Daren Wang
- Division of Experimental Hematology, Cincinnati Children's Hospital Medical Center, Cincinnati, Ohio, USA.
| | | | | |
Collapse
|
48
|
Rahman I, Kode A, Biswas SK. Assay for quantitative determination of glutathione and glutathione disulfide levels using enzymatic recycling method. Nat Protoc 2007; 1:3159-65. [PMID: 17406579 DOI: 10.1038/nprot.2006.378] [Citation(s) in RCA: 1538] [Impact Index Per Article: 90.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
The spectrophotometric/microplate reader assay method for glutathione (GSH) involves oxidation of GSH by the sulfhydryl reagent 5,5'-dithio-bis(2-nitrobenzoic acid) (DTNB) to form the yellow derivative 5'-thio-2-nitrobenzoic acid (TNB), measurable at 412 nm. The glutathione disulfide (GSSG) formed can be recycled to GSH by glutathione reductase in the presence of NADPH. The assay is composed of two parts: the preparation of cell cytosolic/tissue extracts and the detection of total glutathione (GSH and GSSG). The method is simple, convenient, sensitive and accurate. The lowest detection for GSH and GSSG is 0.103 nM in a 96-well plate. This method is rapid and the whole procedure takes no longer than 15 min including reagent preparation. The method can assay GSH in whole blood, plasma, serum, lung lavage fluid, cerebrospinal fluid, urine, tissues and cell extracts and can be extended for drug discovery/pharmacology and toxicology protocols to study the effects of drugs and toxic compounds on glutathione metabolism.
Collapse
Affiliation(s)
- Irfan Rahman
- Department of Environmental Medicine, Lung Biology and Disease Program, University of Rochester Medical Center, Rochester, New York, USA.
| | | | | |
Collapse
|
49
|
Soyfoo MS, De Vriese C, Debaix H, Martin-Martinez MD, Mathieu C, Devuyst O, Steinfeld SD, Delporte C. Modified aquaporin 5 expression and distribution in submandibular glands from NOD mice displaying autoimmune exocrinopathy. ACTA ACUST UNITED AC 2007; 56:2566-74. [PMID: 17665453 DOI: 10.1002/art.22826] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
OBJECTIVE To investigate the expression and localization of aquaporin 5 (AQP5) in salivary glands and salivary gland function in the NOD mouse. METHODS All experiments were performed using NOD and BALB/c mice (ages 8 weeks and 24 weeks). Real-time reverse transcription-polymerase chain reaction, Western blotting, and immunohistochemical analysis were used to study the expression and distribution of AQP5 in salivary glands. In addition, salivary gland function was determined. RESULTS Compared with the levels in BALB/c mice, relative AQP5 messenger RNA levels were not significantly modified in the parotid glands from NOD mice of both ages but were significantly increased in the submandibular glands from NOD mice of both ages. Western blot analyses of both salivary gland membranes revealed that the level of AQP5 protein was increased in 24-week-old NOD mice. Important inflammatory infiltrates were observed in the submandibular glands, but not in the parotid glands, from 24-week-old NOD mice. The 8-week-old and 24-week-old BALB/c mice and the 8-week-old NOD mice showed AQP5 primarily at the apical membrane of the salivary gland acinus. In contrast, in acini from the submandibular glands (but not the parotid glands) from 24-week-old NOD mice, AQP5 staining was reduced at the apical membrane but was increased at the basal membrane. A moderately statistically significant decrease in pilocarpine-stimulated salivary flow was observed in 24-week-old NOD mice compared with that in age-matched BALB/c mice. CONCLUSION Submandibular glands from 24-week-old NOD mice displayed inflammatory infiltrates, increased AQP5 protein expression, and impaired AQP5 distribution. However, the moderately statistically significant decrease in the salivary flow rate in these mice did not match the extent of AQP5 misdistribution.
Collapse
Affiliation(s)
- Muhammad S Soyfoo
- Laboratory of Biochemistry, Université Libre de Bruxelles, Route de Lennik 808, B-1070 Brussels, Belgium
| | | | | | | | | | | | | | | |
Collapse
|
50
|
Xu Y, Farmer SR, Smith BD. Peroxisome proliferator-activated receptor gamma interacts with CIITA x RFX5 complex to repress type I collagen gene expression. J Biol Chem 2007; 282:26046-56. [PMID: 17611194 DOI: 10.1074/jbc.m703652200] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Recent reports demonstrate that peroxisome proliferator-activated receptor gamma (PPARgamma), a member of the nuclear receptor superfamily, acts as a repressor of type I collagen synthesis. Our data demonstrate that exogenously expressed PPARgamma down-regulates collagen expression in a dose-responsive manner in human lung fibroblast cells. Silencing PPARgamma using lentiviruses expressing short hairpin RNAs partially reverses interferon-gamma (IFN-gamma)-induced repression and activates collagen mRNA levels. Previous studies indicate that IFN-gamma represses collagen gene expression and induces major histocompatibility complex II (MHC II) expression by activating the formation of a regulatory factor for X-box 5 (RFX5) complex with class II transactivator (CIITA). This report demonstrates that PPARgamma is within the RFX5.CIITA complex as judged by co-immunoprecipitation and DNA affinity precipitation studies. Most importantly, occupancy of PPARgamma on the collagen transcription start site and MHC II promoter increases with IFN-gamma treatment. The PPARgamma agonist, troglitazone, sensitizes the cells to IFN-gamma treatment by increasing recruitment of PPARgamma to collagen gene while repressing collagen expression, and these effects are blocked by the PPARgamma antagonist T0070907. PPARgamma may mediate IFN-gamma-stimulated collagen transcription down-regulation and MHC II up-regulation by interacting with CIITA as well as regulating CIITA expression. Therefore, PPARgamma is a critical target for investigations into therapeutics of diseases involving extracellular matrix remodeling and the immune response.
Collapse
Affiliation(s)
- Yong Xu
- Department of Biochemistry, Boston University School of Medicine, Boston, Massachusetts 02118, USA
| | | | | |
Collapse
|