1
|
Iloki Assanga SB, Lewis Luján LM, McCarty MF. Targeting beta-catenin signaling for prevention of colorectal cancer - Nutraceutical, drug, and dietary options. Eur J Pharmacol 2023; 956:175898. [PMID: 37481200 DOI: 10.1016/j.ejphar.2023.175898] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/11/2023] [Revised: 06/09/2023] [Accepted: 06/29/2023] [Indexed: 07/24/2023]
Abstract
Progressive up-regulation of β-catenin signaling is very common in the transformation of colorectal epithelium to colorectal cancer (CRC). Practical measures for opposing such signaling hence have potential for preventing or slowing such transformation. cAMP/PKA activity in colon epithelium, as stimulated by COX-2-generated prostaglandins and β2-adrenergic signaling, boosts β-catenin activity, whereas cGMP/PKG signaling has the opposite effect. Bacterial generation of short-chain fatty acids (as supported by unrefined high-carbohydrate diets, berberine, and probiotics), dietary calcium, daily aspirin, antioxidants opposing cox-2 induction, and nicotine avoidance, can suppress cAMP production in colonic epithelium, whereas cGMP can be boosted via linaclotides, PDE5 inhibitors such as sildenafil or icariin, and likely high-dose biotin. Selective activation of estrogen receptor-β by soy isoflavones, support of adequate vitamin D receptor activity with UV exposure or supplemental vitamin D, and inhibition of CK2 activity with flavanols such as quercetin, can also oppose β-catenin signaling in colorectal epithelium. Secondary bile acids, the colonic production of which can be diminished by low-fat diets and berberine, can up-regulate β-catenin activity by down-regulating farnesoid X receptor expression. Stimulation of PI3K/Akt via insulin, IGF-I, TLR4, and EGFR receptors boosts β-catenin levels via inhibition of glycogen synthase-3β; plant-based diets can down-regulate insulin and IGF-I levels, exercise training and leanness can keep insulin low, anthocyanins and their key metabolite ferulic acid have potential for opposing TLR4 signaling, and silibinin is a direct antagonist for EGFR. Partially hydrolyzed phytate can oppose growth factor-mediated down-regulation of β-catenin by inhibiting Akt activation. Multifactorial strategies for safely opposing β-catenin signaling can be complemented with measures that diminish colonic mutagenesis and DNA hypomethylation - such as avoidance of heme-rich meat and charred or processed meats, consumption of phase II-inductive foods and nutraceuticals (e.g., Crucifera), and assurance of adequate folate status.
Collapse
Affiliation(s)
- Simon Bernard Iloki Assanga
- Departamento de Ciencias Químico Biológicas, Universidad de Sonora, Blvd Luis Encinas y Rosales S/N Col. Centro, Hermosillo, Sonora, C.P. 83000, Mexico.
| | - Lidianys María Lewis Luján
- Technological Institute of Hermosillo (ITH), Ave. Tecnológico y Periférico Poniente S/N, Col. Sahuaro, Hermosillo, Sonora, C.P. 83170, México.
| | | |
Collapse
|
2
|
Mo L, Su G, Su H, Huang W, Luo X, Tao C. Effect of IL-10 in the pathogenesis of HIV/AIDS patients with cryptococcal meningitis. Mol Cell Biochem 2023; 478:1-11. [PMID: 35708865 DOI: 10.1007/s11010-022-04488-z] [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: 10/11/2021] [Accepted: 05/31/2022] [Indexed: 02/08/2023]
Abstract
This study aimed to explore the role of IL-10 in the pathogenesis of HIV/AIDS patients with cryptococcal meningitis (CM).Patients were assigned into 4 groups (n = 40/group): group A (HIV/AIDS with CM), group B (HIV/AIDS with tuberculosis), group C (HIV/AIDS), and group D (CM). The levels of IL-10 and associated indicators were measured and the correlations were analyzed by Pearson correlation and partial correlation method. In plasma and cerebrospinal fluid (CSF), no significant difference was observed on IL-10 level between group A and other groups (P > 0.050). R values for IL-10 and relevant indicators in blood were as follows (P < 0.050): group A, IFN-γ (-0.377), IL-12 (0.743), IL-4 (0.881), and IL-6 (0.843); group B, IL-12 (0.740), IL-4 (0.573), and IL-6 (0.900); group C, IL-12 (0.402) and IL-4 (0.896); group D, IL-12 (0.575), IL-4 (0.852), and CD8 (0.325). R values for IL-10 and related indicators in CSF were as follows (P < 0.050): group A, TNF-α (0.664), IL-4 (0.852), white blood cells (WBCs, 0.321) and total protein (TP, 0.330); group B, TNF-α (0.566), IL-4 (0.702), and lactate dehydrogenase (LDH, 0.382); group D, IFN-γ (0.807) and IL-4 (0.441). IL-10 level was positively correlated with IL-4, IL-6, IL-12, TNF-α, WBC, and TP in blood or CSF, and negatively correlated with IFN-γ in blood, suggesting that IL-10 affected both pro-inflammatory and anti-inflammatory activities in the pathogenesis of HIV/AIDS with CM.
Collapse
Affiliation(s)
- Lida Mo
- Department of Laboratory Medicine, Nanning Fourth People's Hospital, Guangxi AIDS Clinical Treatment Center (Nanning), Nanning Infectious Disease Hospital Affiliated to Guangxi Medical University, Nanning, 530023, China
| | - Guosheng Su
- Department of Laboratory Medicine, West China Hospital, Sichuan University, No. 37, Guoxue Lane, Wuhou District, Chengdu, 610041, Sichuan, China.,Department of Laboratory Medicine, People's Hospital of Guangxi-ASEAN Economic and Technological Development Zone, The Tenth People's Hospital of Nanning, Nanning, 530105, Guangxi, China
| | - Hanzhen Su
- Department of Laboratory Medicine, Nanning Fourth People's Hospital, Guangxi AIDS Clinical Treatment Center (Nanning), Nanning Infectious Disease Hospital Affiliated to Guangxi Medical University, Nanning, 530023, China
| | - Wanhong Huang
- Department of Laboratory Medicine, Nanning Fourth People's Hospital, Guangxi AIDS Clinical Treatment Center (Nanning), Nanning Infectious Disease Hospital Affiliated to Guangxi Medical University, Nanning, 530023, China
| | - Xiaolu Luo
- Department of Laboratory Medicine, Nanning Fourth People's Hospital, Guangxi AIDS Clinical Treatment Center (Nanning), Nanning Infectious Disease Hospital Affiliated to Guangxi Medical University, Nanning, 530023, China.
| | - Chuanmin Tao
- Department of Laboratory Medicine, West China Hospital, Sichuan University, No. 37, Guoxue Lane, Wuhou District, Chengdu, 610041, Sichuan, China.
| |
Collapse
|
3
|
Sousa FBM, Nolêto IRSG, Chaves LS, Pacheco G, Oliveira AP, Fonseca MMV, Medeiros JVR. A comprehensive review of therapeutic approaches available for the treatment of cholera. J Pharm Pharmacol 2020; 72:1715-1731. [DOI: 10.1111/jphp.13344] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/14/2020] [Accepted: 07/04/2020] [Indexed: 12/15/2022]
Abstract
Abstract
Objectives
The oral rehydration solution is the most efficient method to treat cholera; however, it does not interfere in the action mechanism of the main virulence factor produced by Vibrio cholerae, the cholera toxin (CT), and this disease still stands out as a problem for human health worldwide. This review aimed to describe therapeutic alternatives available in the literature, especially those related to the search for molecules acting upon the physiopathology of cholera.
Key findings
New molecules have offered a protection effect against diarrhoea induced by CT or even by infection from V. cholerae. The receptor regulator cystic fibrosis channel transmembrane (CFTR), monosialoganglioside (GM1), enkephalinase, AMP-activated protein kinase (AMPK), inhibitors of expression of virulence factors and activators of ADP-ribosylarginine hydrolase are the main therapeutic targets studied. Many of these molecules or extracts still present unclear action mechanisms.
Conclusions
Knowing therapeutic alternatives and their molecular mechanisms for the treatment of cholera could guide us to develop a new drug that could be used in combination with the rehydration solution.
Collapse
Affiliation(s)
- Francisca B M Sousa
- Laboratory of Pharmacology of Inflammation and Gastrointestinal Disorders (Lafidg), Post-graduation Program in Biotechnology, Federal University of Parnaíba Delta, Parnaíba, Brazil
- Northeast Biotechnology Network (RENORBIO), Federal University of Piauí, Teresina, Brazil
| | - Isabela R S G Nolêto
- Laboratory of Pharmacology of Inflammation and Gastrointestinal Disorders (Lafidg), Post-graduation Program in Biotechnology, Federal University of Parnaíba Delta, Parnaíba, Brazil
- Northeast Biotechnology Network (RENORBIO), Federal University of Piauí, Teresina, Brazil
| | - Leticia S Chaves
- Laboratory of Pharmacology of Inflammation and Gastrointestinal Disorders (Lafidg), Post-graduation Program in Biotechnology, Federal University of Parnaíba Delta, Parnaíba, Brazil
- Post-graduation Program in Biomedical Sciences, Federal University of Piauí, Parnaíba, Brazil
| | - Gabriella Pacheco
- Laboratory of Pharmacology of Inflammation and Gastrointestinal Disorders (Lafidg), Post-graduation Program in Biotechnology, Federal University of Parnaíba Delta, Parnaíba, Brazil
| | - Ana P Oliveira
- Laboratory of Pharmacology of Inflammation and Gastrointestinal Disorders (Lafidg), Post-graduation Program in Biotechnology, Federal University of Parnaíba Delta, Parnaíba, Brazil
- Northeast Biotechnology Network (RENORBIO), Federal University of Piauí, Teresina, Brazil
| | - Mikhail M V Fonseca
- Institute of Higher Education of Vale do Parnaíba (IESVAP), Parnaíba, Brazil
| | - Jand V R Medeiros
- Laboratory of Pharmacology of Inflammation and Gastrointestinal Disorders (Lafidg), Post-graduation Program in Biotechnology, Federal University of Parnaíba Delta, Parnaíba, Brazil
- Northeast Biotechnology Network (RENORBIO), Federal University of Piauí, Teresina, Brazil
| |
Collapse
|
4
|
King SJ, Bunz M, Chappell A, Scharl M, Docherty M, Jung B, Lytle C, McCole DF. AMPK mediates inhibition of electrolyte transport and NKCC1 activity by reactive oxygen species. Am J Physiol Gastrointest Liver Physiol 2019; 317:G171-G181. [PMID: 31070932 PMCID: PMC6734373 DOI: 10.1152/ajpgi.00317.2018] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
Reactive oxygen species such as H2O2 are believed to play a prominent role in the injury and loss of transport function that affect the intestinal epithelium in inflammatory conditions such as inflammatory bowel diseases. Defects in intestinal epithelial ion transport regulation contribute to dysbiosis and inflammatory phenotypes. We previously showed that H2O2 inhibits Ca2+-dependent Cl- secretion across intestinal epithelial cells (IECs) via a phosphatidylinositol 3-kinase (PI3K)- and extracellular signal-regulated kinase (ERK)-dependent mechanism that occurs, at least in part, through inhibition of the basolateral Na+-K+-2Cl- cotransporter NKCC1. NKCC1 governs Cl- entry into crypt IECs and thus plays a critical role in maintaining the driving force for Cl- secretion. Electrolyte transport consumes large amounts of cellular energy, and direct pharmacological activation of the cellular energy sensor AMP-activated protein kinase (AMPK) has been shown to inhibit a number of ion transport proteins. Here, we show that H2O2 activates AMPK in human IEC lines and ex vivo human colon. Moreover, we demonstrate that the inhibitory effect of H2O2 on Ca2+-dependent Cl- secretion and NKCC1 activity is AMPK-dependent. This inhibitory effect is associated with a physical interaction between AMPK and NKCC1, as well as increased phosphorylation (Thr212,217) of NKCC1, without causing NKCC1 internalization. These data identify a key role for AMPK-NKCC1 interaction as a point of convergence for suppression of colonic epithelial ion transport by inflammatory reactive oxygen species.NEW & NOTEWORTHY H2O2 inhibition of intestinal epithelial Ca2+-dependent Cl- secretion involves recruitment of AMP-activated protein kinase (AMPK) downstream of ERK and phosphatidylinositol 3-kinase signaling pathways, physical interaction of AMPK with the Na+-K+-2Cl- cotransporter NKCC1, and AMPK-dependent suppression of NKCC1-mediated electrolyte influx without causing NKCC1 internalization. It is intriguing that, in human intestinal epithelial cell lines and human colon, H2O2 activation of AMPK increased phosphorylation of NKCC1 residues required for promoting, not inhibiting, NKCC1 activity. These data identify an elevated complexity of AMPK regulation of NKCC1 in the setting of an inflammatory stimulus.
Collapse
Affiliation(s)
- Stephanie J. King
- 1Division of Biomedical Sciences, University of California, Riverside, Riverside, California
| | - Michael Bunz
- 2Division of Gastroenterology, School of Medicine, University of California, San Diego, La Jolla, California,3Kreisklinik Woert an der Donau, Department of Anaesthesiology and Intensive Care Medicine, Woerth an der Donau, Germany
| | - Alfred Chappell
- 2Division of Gastroenterology, School of Medicine, University of California, San Diego, La Jolla, California
| | - Michael Scharl
- 2Division of Gastroenterology, School of Medicine, University of California, San Diego, La Jolla, California,4Division of Gastroenterology and Hepatology, Zurich Center for Integrative Human Physiology, University Hospital and University of Zurich, Zurich, Switzerland
| | - Michael Docherty
- 2Division of Gastroenterology, School of Medicine, University of California, San Diego, La Jolla, California
| | - Barbara Jung
- 2Division of Gastroenterology, School of Medicine, University of California, San Diego, La Jolla, California
| | - Christian Lytle
- 1Division of Biomedical Sciences, University of California, Riverside, Riverside, California
| | - Declan F. McCole
- 1Division of Biomedical Sciences, University of California, Riverside, Riverside, California
| |
Collapse
|
5
|
Stephens CE, Whittamore JM, Hatch M. 125 Iodide as a surrogate tracer for epithelial chloride transport by the mouse large intestine in vitro. Exp Physiol 2019; 104:334-344. [PMID: 30615234 PMCID: PMC6397055 DOI: 10.1113/ep087445] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/25/2018] [Accepted: 01/02/2019] [Indexed: 12/25/2022]
Abstract
NEW FINDINGS What is the central question of this study? The tracer 36 Cl- , currently used to measure transepithelial Cl- fluxes, has become prohibitively expensive, threatening its future use. 125 Iodide, previously validated alongside 36 Cl- as a tracer of Cl- efflux by cells, has not been tested as a surrogate for 36 Cl- across epithelia. What is the main finding and its importance? We demonstrate that 125 I- can serve as an inexpensive replacement for measuring Cl- transport across mouse large intestine, tracking Cl- transport in response to cAMP stimulation (inducing Cl- secretion) in the presence and absence of the main gastrointestinal Cl- -HCO3- exchanger, DRA. ABSTRACT Chloride transport is important for driving fluid secretion and absorption by the large intestine, with dysregulation resulting in diarrhoea-associated pathologies. The radioisotope 36 Cl- has long been used as a tracer to measure epithelial Cl- transport but is prohibitively expensive. 125 Iodide has been used as an alternative to 36 Cl- in some transport assays but has never been validated as an alternative for tracing bidirectional transepithelial Cl- fluxes. The goal of this study was to validate 125 I- as an alternative to 36 Cl- for measurement of Cl- transport by the intestine. Simultaneous fluxes of 36 Cl- and 125 I- were measured across the mouse caecum and distal colon. Net Cl- secretion was induced by the stimulation of cAMP with a cocktail of forskolin (FSK) and 3-isobutyl-1-methylxanthine (IBMX). Unidirectional fluxes of 125 I- correlated well with 36 Cl- fluxes after cAMP-induced net Cl- secretion, occurring predominantly through a reduction in the absorptive mucosal-to-serosal Cl- flux rather than by stimulation of the secretory serosal-to-mucosal Cl- flux. Correlations between 125 I- fluxes and 36 Cl- fluxes were maintained in epithelia from mice lacking DRA (Slc26a3), the main Cl- -HCO3- exchanger responsible for Cl- absorption by the large intestine. Lower rates of Cl- and I- absorption in the DRA knockout intestine suggest that DRA might have a previously unrecognized role in iodide uptake. This study validates that 125 I- traces transepithelial Cl- fluxes across the mouse large intestine, provides insights into the mechanism of net Cl- secretion and suggests that DRA might be involved in intestinal iodide absorption.
Collapse
Affiliation(s)
- Christine E Stephens
- Department of Pathology, Immunology, and Laboratory Medicine, College of Medicine, University of Florida, Gainesville, FL, USA
| | - Jonathan M Whittamore
- Department of Pathology, Immunology, and Laboratory Medicine, College of Medicine, University of Florida, Gainesville, FL, USA
| | - Marguerite Hatch
- Department of Pathology, Immunology, and Laboratory Medicine, College of Medicine, University of Florida, Gainesville, FL, USA
| |
Collapse
|
6
|
Romero-Calvo I, Ocón B, Gámez-Belmonte R, Hernández-Chirlaque C, de Jonge HR, Bijvelds MJ, Martínez-Augustin O, Sánchez de Medina F. Adenylyl cyclase 6 is involved in the hyposecretory status of experimental colitis. Pflugers Arch 2018; 470:1705-1717. [PMID: 30094477 DOI: 10.1007/s00424-018-2187-z] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/23/2018] [Revised: 07/12/2018] [Accepted: 07/24/2018] [Indexed: 12/12/2022]
Abstract
One of the cardinal symptoms of intestinal inflammation is diarrhea. Acute intestinal inflammation is associated with inhibition of ion absorption and increased secretion, along with fluid leakage due to epithelial injury and changes in permeability. However, in the chronic situation, a downregulation of both absorptive and secretory transport has been reported. We investigated how experimental colitis reduces cAMP levels in intestinal epithelial cells through modulation of adenylyl cyclases (AC). Primary colonic epithelial cells obtained from rats with trinitrobenzenesulfonic acid colitis and non-colitic controls were analyzed for AC expression by RT-qPCR and Western blot, following a preliminary microarray analysis. AC6 and AC5 were found to be expressed in colonocytes, and downregulated by inflammation, with the former exhibiting considerably higher mRNA levels in both cases. To test the hypothesis that inflammatory cytokines may account for this effect, Caco 2 cells were treated with IL-1β, TNF-α, or IFN-γ. All three cytokines inhibited forskolin evoked short-circuit currents in Ussing chambers and lowered intracellular cAMP, but failed to alter AC6 mRNA levels. AC5/AC6 expression was however inhibited in mouse jejunal organoids treated with IFN-γ and TNF-α, but not IL-1β. Gene knockdown of AC6 resulted in a significant decrease of ion secretion in T84 cells. We conclude that the disturbances in ion secretion observed in rat TNBS colitis are associated with low intracellular levels of cAMP in the epithelium, which may be explained in part by the downregulation of AC5/AC6 expression by proinflammatory cytokines.
Collapse
Affiliation(s)
- Isabel Romero-Calvo
- Department of Biochemistry and Molecular Biology II, School of Pharmacy, Campus de Cartuja s/n, 18071, Granada, Spain
| | - Borja Ocón
- Department of Pharmacology, CIBERehd, School of Pharmacy, Instituto de Investigación Biosanitaria ibs.GRANADA, University of Granada, Granada, Spain
| | - Reyes Gámez-Belmonte
- Department of Pharmacology, CIBERehd, School of Pharmacy, Instituto de Investigación Biosanitaria ibs.GRANADA, University of Granada, Granada, Spain
| | - Cristina Hernández-Chirlaque
- Department of Biochemistry and Molecular Biology II, School of Pharmacy, Campus de Cartuja s/n, 18071, Granada, Spain
| | - Hugo R de Jonge
- Department of Gastroenterology and Hepatology, Erasmus MC University Medical Center, Rotterdam, The Netherlands
| | - Marcel J Bijvelds
- Department of Gastroenterology and Hepatology, Erasmus MC University Medical Center, Rotterdam, The Netherlands
| | - Olga Martínez-Augustin
- Department of Biochemistry and Molecular Biology II, School of Pharmacy, Campus de Cartuja s/n, 18071, Granada, Spain.
| | - Fermín Sánchez de Medina
- Department of Pharmacology, CIBERehd, School of Pharmacy, Instituto de Investigación Biosanitaria ibs.GRANADA, University of Granada, Granada, Spain
| |
Collapse
|
7
|
H 2S is a key antisecretory molecule against cholera toxin-induced diarrhoea in mice: Evidence for non-involvement of the AC/cAMP/PKA pathway and AMPK. Nitric Oxide 2017; 76:152-163. [PMID: 28943473 DOI: 10.1016/j.niox.2017.09.007] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/24/2017] [Revised: 09/18/2017] [Accepted: 09/20/2017] [Indexed: 01/18/2023]
Abstract
Hydrogen sulphide (H2S) is a gasotransmitter that participates in various physiological and pathophysiological processes within the gastrointestinal tract. We studied the effects and possible mechanism of action of H2S in secretory diarrhoea caused by cholera toxin (CT). The possible mechanisms of action of H2S were investigated using an intestinal fluid secretion model in isolated intestinal loops on anaesthetized mice treated with CT. NaHS and Lawesson's reagent and l-cysteine showed antisecretory activity through reduction of intestinal fluid secretion and loss of Cl- induced by CT. Pretreatment with an inhibitor of cystathionine-γ-lyase (CSE), dl-propargylglycine (PAG), reversed the effect of l-cysteine and caused severe intestinal secretion. Co-treatment with PAG and a submaximal dose of CT increased intestinal fluid secretion, thus supporting the role of H2S in the pathophysiology of cholera. CT increased the expression of CSE and the production of H2S. Pretreatment with PAG did not reverse the effect of SQ 22536 (an AC inhibitor), bupivacaine (inhibitor of cAMP production), KT-5720 (a PKA inhibitor), and AICAR (an AMPK activator). The treatment with Forskolin does not reverse the effects of the H2S donors. Co-treatment with either NaHS or Lawesson's reagent and dorsomorphin (an AMPK inhibitor) did not reverse the effect of the H2S donors. H2S has antisecretory activity and is an essential molecule for protection against the intestinal secretion induced by CT. Thus, H2S donor drugs are promising candidates for cholera therapy. However, more studies are needed to elucidate the possible mechanism of action.
Collapse
|
8
|
Barrett KE, McCole DF. Hydrogen peroxide scavenger, catalase, alleviates ion transport dysfunction in murine colitis. Clin Exp Pharmacol Physiol 2017; 43:1097-1106. [PMID: 27543846 DOI: 10.1111/1440-1681.12646] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/08/2016] [Revised: 08/11/2016] [Accepted: 08/18/2016] [Indexed: 12/16/2022]
Abstract
Reactive oxygen species (ROS) such as hydrogen peroxide (H2 O2 ) contribute to epithelial damage and ion transport dysfunction (key events in inflammatory diarrhoea) in inflammatory bowel disease (IBD). The aim of this study was to identify if H2 O2 mediates suppression of colonic ion transport function in the murine dextran sulfate sodium (DSS) colitis model by using the H2 O2 degrading enzyme, catalase. Colitis was induced by administering DSS (4%) in drinking water for 5 days followed by 3 days on normal H2 O. Mice were administered either pegylated catalase or saline at day -1, 0 and +1 of DSS treatment. Ion transport responses to the Ca2+ -dependent agonist, carbachol (CCh), or the cAMP-dependent agonist, forskolin, were measured across distal colonic mucosa mounted in Ussing chambers. Parameters of DSS-induced inflammation (loss in body weight, decreased colon length, altered stool consistency), were only partially alleviated by catalase while histology was only minimally improved. However, catalase significantly reversed the DSS-induced reduction in baseline ion transport as well as colonic Isc responses to CCh. However, ion transport responses to forskolin were not significantly restored. Catalase also reduced activation of ERK MAP kinase in the setting of colitis, and increased expression of the Na+ -K+ -2Cl- cotransporter, NKCC1, consistent with restoration of ion transport function. Ex vivo treatment of inflamed colonic mucosae with catalase also partially restored ion transport function. Therefore, catalase partially prevents, and rescues, the loss of ion transport properties in DSS colitis even in the setting of unresolved tissue inflammation. These findings indicate a prominent role for ROS in ion transport dysfunction in colitis and may suggest novel strategies for the treatment of inflammatory diarrhoea.
Collapse
Affiliation(s)
- Kim E Barrett
- Division of Gastroenterology, University of California, San Diego School of Medicine, La Jolla, CA, USA
| | - Declan F McCole
- Division of Biomedical Sciences, School of Medicine, University of California Riverside, Riverside, CA, USA.
| |
Collapse
|
9
|
Fatty acid and mineral receptors as drug targets for gastrointestinal disorders. Future Med Chem 2017; 9:315-334. [DOI: 10.4155/fmc-2016-0205] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
Nutrient-sensing receptors, including fatty acid receptors (FFA1–FFA4), Ca2+-sensing receptors and Zn2+-sensing receptors, are involved in several biological processes. These receptors are abundantly expressed in the GI tract, where they have been shown to play crucial roles in regulating GI function. This review provides an overview of the GI functions of fatty acid and mineral receptors, including the regulation of gastric and enteroendocrine functions, GI motility, ion transport and cell growth. Recently, several lines of evidence have implicated these receptors as promising therapeutic targets for the treatment of GI disorders, for example, inflammatory bowel disease, colorectal cancer, metabolic syndrome and diarrheal diseases. A future perspective on drug discovery research targeting these receptors is discussed.
Collapse
|
10
|
Lazo-Fernández Y, Baile G, Meade P, Torcal P, Martínez L, Ibañez C, Bernal ML, Viollet B, Giménez I. Kidney-specific genetic deletion of both AMPK α-subunits causes salt and water wasting. Am J Physiol Renal Physiol 2016; 312:F352-F365. [PMID: 28179232 DOI: 10.1152/ajprenal.00169.2016] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/17/2016] [Revised: 11/07/2016] [Accepted: 11/07/2016] [Indexed: 11/22/2022] Open
Abstract
AMP-activated kinase (AMPK) controls cell energy homeostasis by modulating ATP synthesis and expenditure. In vitro studies have suggested AMPK may also control key elements of renal epithelial electrolyte transport but in vivo physiological confirmation is still insufficient. We studied sodium renal handling and extracellular volume regulation in mice with genetic deletion of AMPK catalytic subunits. AMPKα1 knockout (KO) mice exhibit normal renal sodium handling and a moderate antidiuretic state. This is accompanied by higher urinary aldosterone excretion rates and reduced blood pressure. Plasma volume, however, was found to be increased compared with wild-type mice. Thus blood volume is preserved despite a significantly lower hematocrit. The lack of a defect in renal function in AMPKα1 KO mice could be explained by a compensatory upregulation in AMPK α2-subunit. Therefore, we used the Cre-loxP system to knock down AMPKα2 expression in renal epithelial cells. Combining this approach with the systemic deletion of AMPKα1 we achieved reduced renal AMPK activity, accompanied by a shift to a moderate water- and salt-wasting phenotype. Thus we confirm the physiologically relevant role of AMPK in the kidney. Furthermore, our results indicate that in vivo AMPK activity stimulates renal sodium and water reabsorption.
Collapse
Affiliation(s)
| | - Goretti Baile
- Department of Pharmacology and Physiology, University of Zaragoza, Zaragoza, Spain
| | - Patricia Meade
- Department of Cellular Biology and Biochemistry University of Zaragoza, Zaragoza, Spain.,IIS Aragón. Instituto Aragonés de Ciencias de la Salud, Zaragoza, Spain
| | - Pilar Torcal
- IIS Aragón. Instituto Aragonés de Ciencias de la Salud, Zaragoza, Spain
| | - Laura Martínez
- IIS Aragón. Instituto Aragonés de Ciencias de la Salud, Zaragoza, Spain
| | - Carmen Ibañez
- Department of Pharmacology and Physiology, University of Zaragoza, Zaragoza, Spain
| | - Maria Luisa Bernal
- Department of Pharmacology and Physiology, University of Zaragoza, Zaragoza, Spain
| | - Benoit Viollet
- INSERM, U1016, Institut Cochin, Paris, France.,CNRS (UMR 8104), Paris, France; and.,Université Paris Descartes, Sorbonne Paris Cité, Paris, France
| | - Ignacio Giménez
- Department of Pharmacology and Physiology, University of Zaragoza, Zaragoza, Spain; .,IIS Aragón. Instituto Aragonés de Ciencias de la Salud, Zaragoza, Spain
| |
Collapse
|
11
|
McClure ML, Barnes S, Brodsky JL, Sorscher EJ. Trafficking and function of the cystic fibrosis transmembrane conductance regulator: a complex network of posttranslational modifications. Am J Physiol Lung Cell Mol Physiol 2016; 311:L719-L733. [PMID: 27474090 DOI: 10.1152/ajplung.00431.2015] [Citation(s) in RCA: 26] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/15/2015] [Accepted: 07/26/2016] [Indexed: 12/19/2022] Open
Abstract
Posttranslational modifications add diversity to protein function. Throughout its life cycle, the cystic fibrosis transmembrane conductance regulator (CFTR) undergoes numerous covalent posttranslational modifications (PTMs), including glycosylation, ubiquitination, sumoylation, phosphorylation, and palmitoylation. These modifications regulate key steps during protein biogenesis, such as protein folding, trafficking, stability, function, and association with protein partners and therefore may serve as targets for therapeutic manipulation. More generally, an improved understanding of molecular mechanisms that underlie CFTR PTMs may suggest novel treatment strategies for CF and perhaps other protein conformational diseases. This review provides a comprehensive summary of co- and posttranslational CFTR modifications and their significance with regard to protein biogenesis.
Collapse
Affiliation(s)
- Michelle L McClure
- Cystic Fibrosis Research Center, University of Alabama at Birmingham, Birmingham, Alabama
| | - Stephen Barnes
- Department of Pharmacology and Toxicology, University of Alabama at Birmingham, Birmingham, Alabama
| | - Jeffrey L Brodsky
- Department of Biological Sciences, University of Pittsburgh, Pittsburgh, Pennsylvania; and
| | - Eric J Sorscher
- Department of Pediatrics, Emory University, Atlanta, Georgia
| |
Collapse
|
12
|
Kozan PA, McGeough MD, Peña CA, Mueller JL, Barrett KE, Marchelletta RR, Sivagnanam M. Mutation of EpCAM leads to intestinal barrier and ion transport dysfunction. J Mol Med (Berl) 2014; 93:535-45. [PMID: 25482158 PMCID: PMC4408367 DOI: 10.1007/s00109-014-1239-x] [Citation(s) in RCA: 36] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/05/2014] [Revised: 11/11/2014] [Accepted: 11/14/2014] [Indexed: 12/11/2022]
Abstract
UNLABELLED Congenital tufting enteropathy (CTE) is a devastating diarrheal disease seen in infancy that is typically associated with villous changes and the appearance of epithelial tufts. We previously found mutations in epithelial cell adhesion molecule (EpCAM) to be causative in CTE. We developed a knock-down cell model of CTE through transfection of an EpCAM shRNA construct into T84 colonic epithelial cells to elucidate the in vitro role of EpCAM in barrier function and ion transport. Cells with EpCAM deficiency exhibited decreased electrical resistance, increased permeability, and decreased ion transport. Based on mutations in CTE patients, an in vivo mouse model was developed, with tamoxifen-inducible deletion of exon 4 in Epcam resulting in mutant protein with decreased expression. Tamoxifen treatment of Epcam (Δ4/Δ4) mice resulted in pathological features of villous atrophy and epithelial tufts, similar to those in human CTE patients, within 4 days post induction. Epcam (Δ4/Δ4) mice also showed decreased expression of tight junctional proteins, increased permeability, and decreased ion transport in the intestines. Taken together, these findings reveal mechanisms that may underlie disease in CTE. KEY MESSAGES Knock-down EpCAM cell model of congenital tufting enteropathy was developed. In vivo inducible mouse model was developed resulting in mutant EpCAM protein. Cells with EpCAM deficiency demonstrated barrier and ion transport dysfunction. Tamoxifen-treated Epcam (Δ4/Δ4) mice demonstrated pathological features. Epcam (Δ4/Δ4) mice showed improper barrier function and ion transport.
Collapse
Affiliation(s)
- Philip A Kozan
- Division of Gastroenterology, Department of Medicine, University of California San Diego, San Diego, CA, USA
| | | | | | | | | | | | | |
Collapse
|
13
|
Ward JBJ, Keely SJ, Keely SJ. Oxygen in the regulation of intestinal epithelial transport. J Physiol 2014; 592:2473-89. [PMID: 24710059 DOI: 10.1113/jphysiol.2013.270249] [Citation(s) in RCA: 39] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022] Open
Abstract
The transport of fluid, nutrients and electrolytes to and from the intestinal lumen is a primary function of epithelial cells. Normally, the intestine absorbs approximately 9 l of fluid and 1 kg of nutrients daily, driven by epithelial transport processes that consume large amounts of cellular energy and O2. The epithelium exists at the interface of the richly vascularised mucosa, and the anoxic luminal environment and this steep O2 gradient play a key role in determining the expression pattern of proteins involved in fluid, nutrient and electrolyte transport. However, the dynamic nature of the splanchnic circulation necessitates that the epithelium can evoke co-ordinated responses to fluctuations in O2 availability, which occur either as a part of the normal digestive process or as a consequence of several pathophysiological conditions. While it is known that hypoxia-responsive signals, such as reactive oxygen species, AMP-activated kinase, hypoxia-inducible factors, and prolyl hydroxylases are all important in regulating epithelial responses to altered O2 supply, our understanding of the molecular mechanisms involved is still limited. Here, we aim to review the current literature regarding the role that O2 plays in regulating intestinal transport processes and to highlight areas of research that still need to be addressed.
Collapse
Affiliation(s)
- Joseph B J Ward
- Department of Molecular Medicine, Royal College of Surgeons in Ireland, Dublin, Ireland
| | - Simon J Keely
- School of Biomedical Sciences and Pharmacy, University of Newcastle, Newcastle NSW, Australia
| | - Stephen J Keely
- Department of Molecular Medicine, Royal College of Surgeons in Ireland, Dublin, Ireland
| |
Collapse
|
14
|
Rogers AC, Huetter L, Hoekstra N, Collins D, Collaco A, Baird AW, Winter DC, Ameen N, Geibel JP, Kopic S. Activation of AMPK inhibits cholera toxin stimulated chloride secretion in human and murine intestine. PLoS One 2013; 8:e69050. [PMID: 23935921 PMCID: PMC3728293 DOI: 10.1371/journal.pone.0069050] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/28/2013] [Accepted: 06/03/2013] [Indexed: 02/07/2023] Open
Abstract
Increased intestinal chloride secretion through chloride channels, such as the cystic fibrosis transmembrane conductance regulator (CFTR), is one of the major molecular mechanisms underlying enterotoxigenic diarrhea. It has been demonstrated in the past that the intracellular energy sensing kinase, the AMP-activated protein kinase (AMPK), can inhibit CFTR opening. We hypothesized that pharmacological activation of AMPK can abrogate the increased chloride flux through CFTR occurring during cholera toxin (CTX) mediated diarrhea. Chloride efflux was measured in isolated rat colonic crypts using real-time fluorescence imaging. AICAR and metformin were used to activate AMPK in the presence of the secretagogues CTX or forskolin (FSK). In order to substantiate our findings on the whole tissue level, short-circuit current (SCC) was monitored in human and murine colonic mucosa using Ussing chambers. Furthermore, fluid accumulation was measured in excised intestinal loops. CTX and forskolin (FSK) significantly increased chloride efflux in isolated colonic crypts. The increase in chloride efflux could be offset by using the AMPK activators AICAR and metformin. In human and mouse mucosal sheets, CTX and FSK increased SCC. AICAR and metformin inhibited the secretagogue induced rise in SCC, thereby confirming the findings made in isolated crypts. Moreover, AICAR decreased CTX stimulated fluid accumulation in excised intestinal segments. The present study suggests that pharmacological activation of AMPK effectively reduces CTX mediated increases in intestinal chloride secretion, which is a key factor for intestinal water accumulation. AMPK activators may therefore represent a supplemental treatment strategy for acute diarrheal illness.
Collapse
Affiliation(s)
- Ailín C. Rogers
- University College Dublin and St. Vincent's University Hospital, Dublin, Ireland
| | - Lisa Huetter
- Institute of Physiology and Pathophysiology, Paracelsus Medical University, Salzburg, Austria
- Department of Surgery, Yale University, School of Medicine, New Haven, Connecticut, United States of America
| | - Nadia Hoekstra
- Department of Pediatrics, Yale University, School of Medicine, New Haven, Connecticut, United States of America
| | - Danielle Collins
- University College Dublin and St. Vincent's University Hospital, Dublin, Ireland
| | - Anne Collaco
- Department of Pediatrics, Yale University, School of Medicine, New Haven, Connecticut, United States of America
| | - Alan W. Baird
- University College Dublin and St. Vincent's University Hospital, Dublin, Ireland
| | - Desmond C. Winter
- University College Dublin and St. Vincent's University Hospital, Dublin, Ireland
| | - Nadia Ameen
- Department of Pediatrics, Yale University, School of Medicine, New Haven, Connecticut, United States of America
- Department of Cellular and Molecular Physiology, Yale University, School of Medicine, New Haven, Connecticut, United States of America
| | - John P. Geibel
- Department of Surgery, Yale University, School of Medicine, New Haven, Connecticut, United States of America
- Department of Cellular and Molecular Physiology, Yale University, School of Medicine, New Haven, Connecticut, United States of America
| | - Sascha Kopic
- Department of Surgery, Yale University, School of Medicine, New Haven, Connecticut, United States of America
- Department of Cellular and Molecular Physiology, Yale University, School of Medicine, New Haven, Connecticut, United States of America
- * E-mail:
| |
Collapse
|
15
|
|
16
|
Keely S, Kelly CJ, Weissmueller T, Burgess A, Wagner BD, Robertson CE, Harris JK, Colgan SP. Activated fluid transport regulates bacterial-epithelial interactions and significantly shifts the murine colonic microbiome. Gut Microbes 2012; 3:250-60. [PMID: 22614705 PMCID: PMC3427217 DOI: 10.4161/gmic.20529] [Citation(s) in RCA: 48] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/03/2023] Open
Abstract
Within the intestinal mucosa, epithelial cells serve multiple functions to partition the lumen from the lamina propria. As part of their natural function, intestinal epithelial cells actively transport electrolytes with passive water movement as a mechanism for mucosal hydration. Here, we hypothesized that electrogenic Cl(-) secretion, and associated mucosal hydration, influences bacterial-epithelial interactions and significantly influences the composition of the intestinal microbiota. An initial screen of different epithelial secretagogues identified lubiprostone as the most potent agonist for which to define these principles. In in vitro studies using cultured T84 cells, lubiprostone decreased E. coli translocation in a concentration-dependent manner (p < 0.001) and decreased S. typhimurium internalization and translocation by as much as 71 ± 6% (p < 0.01). Such decreases in bacterial translocation were abolished by inhibition of electrogenic Cl(-) secretion and water transport using the Na/K/Cl(-) antagonist bumetanide (p < 0.01). Extensions of these findings to microbiome analysis in vivo revealed that lubiprostone delivered orally to mice fundamentally shifted the intestinal microbiota, with notable changes within the Firmicutes and Bacteroidetes phyla of resident colonic bacteria. Such findings document a previously unappreciated role for epithelial Cl(-) secretion and water transport in influencing bacterial-epithelial interactions and suggest that active mucosal hydration functions as a primitive innate epithelial defense mechanism.
Collapse
Affiliation(s)
- Simon Keely
- Mucosal Inflammation Program; Department of Medicine; University of Colorado School of Medicine; Aurora, CO USA,School of Biomedical Sciences and Pharmacy; University of Newcastle; New Castle, Australia
| | - Caleb J. Kelly
- Mucosal Inflammation Program; Department of Medicine; University of Colorado School of Medicine; Aurora, CO USA
| | - Thomas Weissmueller
- Mucosal Inflammation Program; Department of Medicine; University of Colorado School of Medicine; Aurora, CO USA,Department of Anesthesiology and Perioperative Pain; Brigham and Women’s Hospital and Harvard Medical School; Boston, MA USA
| | - Adrianne Burgess
- Mucosal Inflammation Program; Department of Medicine; University of Colorado School of Medicine; Aurora, CO USA
| | - Brandie D. Wagner
- Department of Biostatistics and Informatics; Colorado School of Public Health; University of Colorado Denver; Aurora, CO USA
| | - Charles E. Robertson
- Department of Molecular; Cellular and Developmental Biology; University of Colorado; Boulder, CO USA
| | - J. Kirk Harris
- Department of Pediatrics, Pulmonary Medicine; Children’s Hospital Colorado; Aurora, CO USA
| | - Sean P. Colgan
- Mucosal Inflammation Program; Department of Medicine; University of Colorado School of Medicine; Aurora, CO USA,Correspondence to: Sean P. Colgan,
| |
Collapse
|
17
|
|
18
|
Abstract
Diarrhoea is a hallmark of intestinal inflammation. The mechanisms operating in acute inflammation of the intestine are well characterized and are related to regulatory changes induced by inflammatory mediators such as prostaglandins, cytokines or reactive oxygen species, along with leakage due to epithelial injury and changes in permeability. In chronic colitis, however, the mechanisms are less well known, but it is generally accepted that both secretory and absorptive processes are inhibited. These disturbances in ionic transport may be viewed as an adaptation to protracted inflammation of the intestine, since prolonged intense secretion may be physiologically unacceptable in the long term. Mechanistically, the changes in transport may be due to adjustments in the regulation of the different processes involved, to broader epithelial alterations or frank damage, or to modulation of the transportome in terms of expression. In the present review, we offer a summary of the existing evidence on the status of the transportome in chronic intestinal inflammation.
Collapse
|
19
|
Langhans W, Leitner C, Arnold M. Dietary fat sensing via fatty acid oxidation in enterocytes: possible role in the control of eating. Am J Physiol Regul Integr Comp Physiol 2011; 300:R554-65. [DOI: 10.1152/ajpregu.00610.2010] [Citation(s) in RCA: 51] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Various mechanisms detect the presence of dietary triacylglycerols (TAG) in the digestive tract and link TAG ingestion to the regulation of energy homeostasis. We here propose a novel sensing mechanism with the potential to encode dietary TAG-derived energy by translating enterocyte fatty acid oxidation (FAO) into vagal afferent signals controlling eating. Peripheral FAO has long been implicated in the control of eating ( 141 ). The prevailing view was that mercaptoacetate (MA) and other FAO inhibitors stimulate eating by modulating vagal afferent signaling from the liver. This concept has been challenged because hepatic parenchymal vagal afferent innervation is scarce and because experimentally induced changes in hepatic FAO often fail to affect eating. Nevertheless, intraperitoneally administered MA acts in the abdomen to stimulate eating because this effect was blocked by subdiaphragmatic vagal deafferentation ( 21 ), a surgical technique that eliminates all vagal afferents from the upper gut. These and other data support a role of the small intestine rather than the liver as a FAO sensor that can influence eating. After intrajejunal infusions, MA also stimulated eating in rats through vagal afferent signaling, and after infusion into the superior mesenteric artery, MA increased the activity of celiac vagal afferent fibers originating in the proximal small intestine. Also, pharmacological interference with TAG synthesis targeting the small intestine induced a metabolic profile indicative of increased FAO and inhibited eating in rats on a high-fat diet but not on chow. Finally, cell culture studies indicate that enterocytes oxidize fatty acids, which can be modified pharmacologically. Thus enterocytes may sense dietary TAG-derived fatty acids via FAO and influence eating through changes in intestinal vagal afferent activity. Further studies are necessary to identify the link between enterocyte FAO and vagal afferents and to examine the specificity and potential physiological relevance of such a mechanism.
Collapse
Affiliation(s)
- Wolfgang Langhans
- Physiology and Behavior Laboratory, Institute of Food, Nutrition and Health, Swiss Federal Institute of Technology, Zurich, Schwerzenbach, Switzerland
| | - Claudia Leitner
- Physiology and Behavior Laboratory, Institute of Food, Nutrition and Health, Swiss Federal Institute of Technology, Zurich, Schwerzenbach, Switzerland
| | - Myrtha Arnold
- Physiology and Behavior Laboratory, Institute of Food, Nutrition and Health, Swiss Federal Institute of Technology, Zurich, Schwerzenbach, Switzerland
| |
Collapse
|
20
|
Activating AMP-activated protein kinase (AMPK) slows renal cystogenesis. Proc Natl Acad Sci U S A 2011; 108:2462-7. [PMID: 21262823 DOI: 10.1073/pnas.1011498108] [Citation(s) in RCA: 235] [Impact Index Per Article: 18.1] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022] Open
Abstract
Renal cyst development and expansion in autosomal dominant polycystic kidney disease (ADPKD) involves both fluid secretion and abnormal proliferation of cyst-lining epithelial cells. The chloride channel of the cystic fibrosis transmembrane conductance regulator (CFTR) participates in secretion of cyst fluid, and the mammalian target of rapamycin (mTOR) pathway may drive proliferation of cyst epithelial cells. CFTR and mTOR are both negatively regulated by AMP-activated protein kinase (AMPK). Metformin, a drug in wide clinical use, is a pharmacological activator of AMPK. We find that metformin stimulates AMPK, resulting in inhibition of both CFTR and the mTOR pathways. Metformin induces significant arrest of cystic growth in both in vitro and ex vivo models of renal cystogenesis. In addition, metformin administration produces a significant decrease in the cystic index in two mouse models of ADPKD. Our results suggest a possible role for AMPK activation in slowing renal cystogenesis as well as the potential for therapeutic application of metformin in the context of ADPKD.
Collapse
|
21
|
Alesutan I, Föller M, Sopjani M, Dërmaku-Sopjani M, Zelenak C, Fröhlich H, Velic A, Fraser S, Kemp BE, Seebohm G, Völkl H, Lang F. Inhibition of the heterotetrameric K+ channel KCNQ1/KCNE1 by the AMP-activated protein kinase. Mol Membr Biol 2011; 28:79-89. [PMID: 21231794 DOI: 10.3109/09687688.2010.520037] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023]
Abstract
The heterotetrameric K(+)-channel KCNQ1/KCNE1 is expressed in heart, skeletal muscle, liver and several epithelia including the renal proximal tubule. In the heart, it contributes to the repolarization of cardiomyocytes. The repolarization is impaired in ischemia. Ischemia stimulates the AMP-activated protein kinase (AMPK), a serine/threonine kinase, sensing energy depletion and stimulating several cellular mechanisms to enhance energy production and to limit energy utilization. AMPK has previously been shown to downregulate the epithelial Na(+) channel ENaC, an effect mediated by the ubiquitin ligase Nedd4-2. The present study explored whether AMPK regulates KCNQ1/KCNE1. To this end, cRNA encoding KCNQ1/KCNE1 was injected into Xenopus oocytes with and without additional injection of wild type AMPK (AMPKα1 + AMPKβ1 + AMPKγ1), of the constitutively active (γR70Q)AMPK (α1β1γ1(R70Q)), of the kinase dead mutant (αK45R)AMPK (α1(K45R)β1γ1), or of the ubiquitin ligase Nedd4-2. KCNQ1/KCNE1 activity was determined in two electrode voltage clamp experiments. Moreover, KCNQ1 abundance in the cell membrane was determined by immunostaining and subsequent confocal imaging. As a result, wild type and constitutively active AMPK significantly reduced KCNQ1/KCNE1-mediated currents and reduced KCNQ1 abundance in the cell membrane. Similarly, Nedd4-2 decreased KCNQ1/KCNE1-mediated currents and KCNQ1 protein abundance in the cell membrane. Activation of AMPK in isolated perfused proximal renal tubules by AICAR (10 mM) was followed by significant depolarization. In conclusion, AMPK is a potent regulator of KCNQ1/KCNE1.
Collapse
Affiliation(s)
- Ioana Alesutan
- Department of Physiology, University of Tübingen, Tübingen, Germany
| | | | | | | | | | | | | | | | | | | | | | | |
Collapse
|
22
|
Scharl M, Rudenko I, McCole DF. Loss of protein tyrosine phosphatase N2 potentiates epidermal growth factor suppression of intestinal epithelial chloride secretion. Am J Physiol Gastrointest Liver Physiol 2010; 299:G935-45. [PMID: 20689057 PMCID: PMC2957338 DOI: 10.1152/ajpgi.00106.2010] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
The Crohn's disease candidate gene, protein tyrosine phosphatase nonreceptor type 2 (PTPN2), has been shown to regulate epidermal growth factor (EGF)-induced phosphatidylinositol 3-kinase (PI3K) activation in fibroblasts. In intestinal epithelial cells (IECs), EGF-induced EGF receptor (EGFR) activation and recruitment of PI3K play a key role in regulating many cellular functions including Ca(2+)-dependent Cl(-) secretion. Moreover, EGFR also serves as a conduit for signaling by other non-growth factor receptor ligands such as the proinflammatory cytokine, IFN-γ. Here we investigated a possible role for PTPN2 in the regulation of EGFR signaling and Ca(2+)-dependent Cl(-) secretion in IECs. PTPN2 knockdown enhanced EGF-induced EGFR tyrosine phosphorylation in T(84) cells. In particular, PTPN2 knockdown promoted EGF-induced phosphorylation of EGFR residues Tyr-992 and Tyr-1068 and led subsequently to increased association of the catalytic PI3K subunit, p110, with EGFR and elevated phosphorylation of the downstream marker, Akt. As a functional consequence, loss of PTPN2 potentiated EGF-induced inhibition of carbachol-stimulated Ca(2+)-dependent Cl(-) secretion. In contrast, PTPN2 knockdown affected neither IFN-γ-induced EGFR transactivation nor EGF- or IFN-γ-induced phosphorylation of ERK1/2. In summary, our data establish a role for PTPN2 in the regulation of EGFR signaling in IECs in response to EGF but not IFN-γ. Knockdown of PTPN2 directs EGFR signaling toward increased PI3K activation and increased suppression of epithelial chloride secretory responses. Moreover, our findings suggest that PTPN2 dysfunction in IECs leads to altered control of intestinal epithelial functions regulated by EGFR.
Collapse
Affiliation(s)
- Michael Scharl
- Department of Medicine, University of California, San Diego, School of Medicine, La Jolla, California
| | - Ivan Rudenko
- Department of Medicine, University of California, San Diego, School of Medicine, La Jolla, California
| | - Declan F. McCole
- Department of Medicine, University of California, San Diego, School of Medicine, La Jolla, California
| |
Collapse
|
23
|
Alzamora R, Gong F, Rondanino C, Lee JK, Smolak C, Pastor-Soler NM, Hallows KR. AMP-activated protein kinase inhibits KCNQ1 channels through regulation of the ubiquitin ligase Nedd4-2 in renal epithelial cells. Am J Physiol Renal Physiol 2010; 299:F1308-19. [PMID: 20861072 DOI: 10.1152/ajprenal.00423.2010] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023] Open
Abstract
The KCNQ1 K(+) channel plays a key role in the regulation of several physiological functions, including cardiac excitability, cardiovascular tone, and body electrolyte homeostasis. The metabolic sensor AMP-activated protein kinase (AMPK) has been shown to regulate a growing number of ion transport proteins. To determine whether AMPK regulates KCNQ1, we studied the effects of AMPK activation on KCNQ1 currents in Xenopus laevis oocytes and collecting duct epithelial cells. AMPK activation decreased KCNQ1 currents and channel surface expression in X. laevis oocytes, but AMPK did not phosphorylate KCNQ1 in vitro, suggesting an indirect regulatory mechanism. As it has been recently shown that the ubiquitin-protein ligase Nedd4-2 inhibits KCNQ1 plasma membrane expression and that AMPK regulates epithelial Na(+) channels via Nedd4-2, we examined the role of Nedd4-2 in the AMPK-dependent regulation of KCNQ1. Channel inhibition by AMPK was blocked in oocytes coexpressing either a dominant-negative or constitutively active Nedd4-2 mutant, or a Nedd4-2 interaction-deficient KCNQ1 mutant, suggesting that Nedd4-2 participates in the regulation of KCNQ1 by AMPK. KCNQ1 is expressed at the basolateral membrane in mouse polarized kidney cortical collecting duct (mpkCCD(c14)) cells and in rat kidney. Treatment with the AMPK activators AICAR (2 mM) or metformin (1 mM) reduced basolateral KCNQ1 currents in apically permeabilized polarized mpkCCD(c14) cells. Moreover, AICAR treatment of rat kidney slices ex vivo induced AMPK activation and intracellular redistribution of KCNQ1 from the basolateral membrane in collecting duct principal cells. AICAR treatment also induced increased ubiquitination of KCNQ1 immunoprecipitated from kidney slice homogenates. These results indicate that AMPK inhibits KCNQ1 activity by promoting Nedd4-2-dependent channel ubiquitination and retrieval from the plasma membrane.
Collapse
Affiliation(s)
- Rodrigo Alzamora
- Renal-Electrolyte Division, Department of Medicine, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania 15261, USA
| | | | | | | | | | | | | |
Collapse
|
24
|
Hallows KR, Mount PF, Pastor-Soler NM, Power DA. Role of the energy sensor AMP-activated protein kinase in renal physiology and disease. Am J Physiol Renal Physiol 2010; 298:F1067-77. [PMID: 20181668 PMCID: PMC2867412 DOI: 10.1152/ajprenal.00005.2010] [Citation(s) in RCA: 117] [Impact Index Per Article: 8.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/05/2010] [Accepted: 02/18/2010] [Indexed: 11/22/2022] Open
Abstract
The ultrasensitive energy sensor AMP-activated protein kinase (AMPK) orchestrates the regulation of energy-generating and energy-consuming pathways. AMPK is highly expressed in the kidney where it is reported to be involved in a variety of physiological and pathological processes including ion transport, podocyte function, and diabetic renal hypertrophy. Sodium transport is the major energy-consuming process in the kidney, and AMPK has been proposed to contribute to the coupling of ion transport with cellular energy metabolism. Specifically, AMPK has been identified as a regulator of several ion transporters of significance in renal physiology, including the cystic fibrosis transmembrane conductance regulator (CFTR), the epithelial sodium channel (ENaC), the Na(+)-K(+)-2Cl(-) cotransporter (NKCC), and the vacuolar H(+)-ATPase (V-ATPase). Identified regulators of AMPK in the kidney include dietary salt, diabetes, adiponectin, and ischemia. Activation of AMPK in response to adiponectin is described in podocytes, where it reduces albuminuria, and in tubular cells, where it reduces glycogen accumulation. Reduced AMPK activity in the diabetic kidney is associated with renal accumulation of triglyceride and glycogen and the pathogenesis of diabetic renal hypertrophy. Acute renal ischemia causes a rapid and powerful activation of AMPK, but the functional significance of this observation remains unclear. Despite the recent advances, there remain significant gaps in the present understanding of both the upstream regulating pathways and the downstream substrates for AMPK in the kidney. A more complete understanding of the AMPK pathway in the kidney offers potential for improved therapies for several renal diseases including diabetic nephropathy, polycystic kidney disease, and ischemia-reperfusion injury.
Collapse
Affiliation(s)
- Kenneth R Hallows
- Renal-Electrolyte Division, Department of Medicine, University of Pittsburgh, Pittsburgh, Pennsylvania, USA
| | | | | | | |
Collapse
|
25
|
Lim A, Park SH, Sohn JW, Jeon JH, Park JH, Song DK, Lee SH, Ho WK. Glucose deprivation regulates KATP channel trafficking via AMP-activated protein kinase in pancreatic beta-cells. Diabetes 2009; 58:2813-9. [PMID: 19720793 PMCID: PMC2780861 DOI: 10.2337/db09-0600] [Citation(s) in RCA: 69] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
OBJECTIVE AMP-activated protein kinase (AMPK) and the ATP-sensitive K(+) (K(ATP)) channel are metabolic sensors that become activated during metabolic stress. AMPK is an important regulator of metabolism, whereas the K(ATP) channel is a regulator of cellular excitability. Cross talk between these systems is poorly understood. RESEARCH DESIGN AND METHODS Rat pancreatic beta-cells or INS-1 cells were pretreated for 2 h at various concentrations of glucose. Maximum K(ATP) conductance (G(max)) was monitored by whole-cell measurements after intracellular ATP washout using ATP-free internal solutions. K(ATP) channel activity (NPo) was monitored by inside-out patch recordings in the presence of diazoxide. Distributions of K(ATP) channel proteins (Kir6.2 and SUR1) were examined using immunofluorescence imaging and surface biotinylation studies. Insulin secretion from rat pancreatic islets was measured using an enzyme immunoassay. RESULTS G(max) and NPo in cells pretreated with glucose-free or 3 mmol/l glucose solutions were significantly higher than in cells pretreated in 11.1 mmol/l glucose solutions. Immunofluorescence imaging and biotinylation studies revealed that glucose deprivation induced an increase in the surface level of Kir6.2 without affecting the total cellular amount. Increases in G(max) and the surface level of Kir6.2 were inhibited by compound C, an AMPK inhibitor, and siAMPK transfection. The effects of glucose deprivation on K(ATP) channels were mimicked by an AMPK activator. Glucose deprivation reduced insulin secretion, but this response was attenuated by compound C. CONCLUSIONS K(ATP) channel trafficking is regulated by energy status via AMPK, and this mechanism may play a key role in inhibiting insulin secretion under low energy status.
Collapse
Affiliation(s)
- Ajin Lim
- National Research Laboratory for Cell Physiology, Seoul National University College of Medicine, Seoul, Korea
- Department of Physiology, Seoul National University College of Medicine, Seoul, Korea
| | - Sun-Hyun Park
- National Research Laboratory for Cell Physiology, Seoul National University College of Medicine, Seoul, Korea
- Department of Physiology, Seoul National University College of Medicine, Seoul, Korea
| | - Jong-Woo Sohn
- National Research Laboratory for Cell Physiology, Seoul National University College of Medicine, Seoul, Korea
- Department of Physiology, Seoul National University College of Medicine, Seoul, Korea
| | - Ju-Hong Jeon
- Department of Physiology, Seoul National University College of Medicine, Seoul, Korea
| | - Jae-Hyung Park
- Department of Physiology and Chronic Disease Research Center, Keimyung University School of Medicine, Daegu, Korea
| | - Dae-Kyu Song
- Department of Physiology and Chronic Disease Research Center, Keimyung University School of Medicine, Daegu, Korea
| | - Suk-Ho Lee
- National Research Laboratory for Cell Physiology, Seoul National University College of Medicine, Seoul, Korea
- Department of Physiology, Seoul National University College of Medicine, Seoul, Korea
| | - Won-Kyung Ho
- National Research Laboratory for Cell Physiology, Seoul National University College of Medicine, Seoul, Korea
- Department of Physiology, Seoul National University College of Medicine, Seoul, Korea
- Corresponding author: Won-Kyung Ho,
| |
Collapse
|
26
|
Scharl M, Paul G, Barrett KE, McCole DF. AMP-activated protein kinase mediates the interferon-gamma-induced decrease in intestinal epithelial barrier function. J Biol Chem 2009; 284:27952-27963. [PMID: 19654324 DOI: 10.1074/jbc.m109.046292] [Citation(s) in RCA: 84] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
Impaired epithelial barrier function plays a crucial role in the pathogenesis of inflammatory bowel disease. Elevated levels of the pro-inflammatory cytokine, interferon-gamma (IFNgamma), are believed to be prominently involved in the pathogenesis of Crohn disease. Treatment of T(84) intestinal epithelial cells with IFNgamma severely impairs their barrier properties measured as transepithelial electrical resistance (TER) or permeability and reduces the expression of tight junction proteins such as occludin and zonula occludens-1 (ZO-1). However, little is known about the signaling events that are involved. The cellular energy sensor, AMP-activated protein kinase (AMPK), is activated in response to cellular stress, as occurs during inflammation. The aim of this study was to investigate a possible role for AMPK in mediating IFNgamma-induced effects on the intestinal epithelial barrier. We found that IFNgamma activates AMPK by phosphorylation, independent of intracellular energy levels. Inhibition of AMPK prevents, at least in part, the IFNgamma-induced decrease in TER. Furthermore, AMPK knockdown prevented the increased epithelial permeability, the decreased TER, and the decrease in occludin and ZO-1 caused by IFNgamma treatment of T(84) cells. However, AMPK activity alone was not sufficient to cause alterations in epithelial barrier function. These data show a novel role for AMPK, in concert with other signals induced by IFNgamma, in mediating reduced epithelial barrier function in a cell model of chronic intestinal inflammation. These findings may implicate AMPK in the pathogenesis of chronic intestinal inflammatory conditions, such as inflammatory bowel disease.
Collapse
Affiliation(s)
- Michael Scharl
- Department of Medicine, University of California, San Diego, School of Medicine, La Jolla, California 92093
| | - Gisela Paul
- Department of Medicine, University of California, San Diego, School of Medicine, La Jolla, California 92093
| | - Kim E Barrett
- Department of Medicine, University of California, San Diego, School of Medicine, La Jolla, California 92093
| | - Declan F McCole
- Department of Medicine, University of California, San Diego, School of Medicine, La Jolla, California 92093.
| |
Collapse
|
27
|
Myerburg MM, King JD, Oyster NM, Fitch AC, Magill A, Baty CJ, Watkins SC, Kolls JK, Pilewski JM, Hallows KR. AMPK agonists ameliorate sodium and fluid transport and inflammation in cystic fibrosis airway epithelial cells. Am J Respir Cell Mol Biol 2009; 42:676-84. [PMID: 19617399 DOI: 10.1165/2009-0147oc] [Citation(s) in RCA: 87] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
The metabolic sensor AMP-activated kinase (AMPK) inhibits both the cystic fibrosis (CF) transmembrane conductance regulator (CFTR) Cl(-) channel and epithelial Na(+) channel (ENaC), and may inhibit secretion of proinflammatory cytokines in epithelia. Here we have tested in primary polarized CF and non-CF human bronchial epithelial (HBE) cells the effects of AMPK activators, metformin and 5-aminoimidazole-4-carboxamide-1-beta-D-riboside (AICAR), on various parameters that contribute to CF lung disease: ENaC-dependent short-circuit currents (I(sc)), airway surface liquid (ASL) height, and proinflammatory cytokine secretion. AMPK activation after overnight treatment with either metformin (2-5 mM) or AICAR (1 mM) substantially inhibited ENaC-dependent I(sc) in both CF and non-CF airway cultures. Live-cell confocal images acquired 60 minutes after apical addition of Texas Red-dextran-containing fluid revealed significantly greater ASL heights after AICAR and metformin treatment relative to controls, suggesting that AMPK-dependent ENaC inhibition slows apical fluid reabsorption. Both metformin and AICAR decreased secretion of various proinflammatory cytokines, both with and without prior LPS stimulation. Finally, prolonged exposure to more physiologically relevant concentrations of metformin (0.03-1 mM) inhibited ENaC currents and decreased proinflammatory cytokine levels in CF HBE cells in a dose-dependent manner. These findings suggest that novel therapies to activate AMPK in the CF airway may be beneficial by blunting excessive sodium and ASL absorption and by reducing excessive airway inflammation, which are major contributors to CF lung disease.
Collapse
Affiliation(s)
- Michael M Myerburg
- Renal-Electrolyte Division, Department of Medicine, University of Pittsburgh School of Medicine, S976 Scaife Hall, 3550 Terrace Street, Pittsburgh, PA 15261, USA
| | | | | | | | | | | | | | | | | | | |
Collapse
|
28
|
Murphy BA, Fakira KA, Song Z, Beuve A, Routh VH. AMP-activated protein kinase and nitric oxide regulate the glucose sensitivity of ventromedial hypothalamic glucose-inhibited neurons. Am J Physiol Cell Physiol 2009; 297:C750-8. [PMID: 19570894 DOI: 10.1152/ajpcell.00127.2009] [Citation(s) in RCA: 107] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Abstract
The mechanisms by which glucose regulates the activity of glucose-inhibited (GI) neurons in the ventromedial hypothalamus (VMH) are largely unknown. We have previously shown that AMP-activated protein kinase (AMPK) increases nitric oxide (NO) production in VMH GI neurons. We hypothesized that AMPK-mediated NO signaling is required for depolarization of VMH GI neurons in response to decreased glucose. In support of our hypothesis, inhibition of neuronal nitric oxide synthase (nNOS) or the NO receptor soluble guanylyl cyclase (sGC) blocked depolarization of GI neurons to decreased glucose from 2.5 to 0.7 mM or to AMPK activation. Conversely, activation of sGC or the cell-permeable analog of cGMP, 8-bromoguanosine 3',5'-cyclic monophosphate (8-Br-cGMP), enhanced the response of GI neurons to decreased glucose, suggesting that stimulation of NO-sGC-cGMP signaling by AMPK is required for glucose sensing in GI neurons. Interestingly, the AMPK inhibitor compound C completely blocked the effect of sGC activation or 8-Br-cGMP, and 8-Br-cGMP increased VMH AMPKalpha2 phosphorylation. These data suggest that NO, in turn, amplifies AMPK activation in GI neurons. Finally, inhibition of the cystic fibrosis transmembrane regulator (CFTR) Cl(-) conductance blocked depolarization of GI neurons to decreased glucose or AMPK activation, whereas decreased glucose, AMPK activation, and 8-Br-cGMP increased VMH CFTR phosphorylation. We conclude that decreased glucose triggers the following sequence of events leading to depolarization in VMH GI neurons: AMPK activation, nNOS phosphorylation, NO production, and stimulation of sGC-cGMP signaling, which amplifies AMPK activation and leads to closure of the CFTR.
Collapse
Affiliation(s)
- Beth Ann Murphy
- Dept. of Pharmacology and Physiology, New Jersey Medical School, PO Box 1709, Newark, NJ 07101-1709, USA
| | | | | | | | | |
Collapse
|
29
|
Bajwa PJ, Lee JW, Straus DS, Lytle C. Activation of PPARgamma by rosiglitazone attenuates intestinal Cl- secretion. Am J Physiol Gastrointest Liver Physiol 2009; 297:G82-9. [PMID: 19443733 DOI: 10.1152/ajpgi.90640.2008] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
The thiazolidinedione (TZD) drugs rosiglitazone (Ro) and pioglitazone (Po) are PPARgamma agonists in widespread clinical use as insulin-sensitizing agents in Type 2 diabetes. On the basis of recent evidence implicating PPARgamma as a positive modulator of intestinal epithelial differentiation, we hypothesized that TZD drugs might attenuate intestinal secretory function. To evaluate this possibility, we examined the effects of Ro and Po on electrogenic Cl- secretion [short-circuit current (I(sc))] in mouse intestinal segments and in cultured human intestinal epithelial cells (HT29-Cl.19A). As hypothesized, oral administration of Ro (20 mg.kg(-1).day(-1)) to mice for 8 days markedly reduced intestinal I(sc) responses to cAMP (forskolin)- and Ca2+ (carbachol)-dependent stimuli. In these Ro-treated mice, cholera toxin-induced intestinal fluid accumulation was reduced 65%. With continued Ro treatment, the I(sc) response to carbachol recovered significantly, whereas that to forskolin remained attenuated. Treatment of HT29 cells for 5 days with 10 muM Ro or Po in vitro brought about a similar hyposecretory state. In HT29 cells, the loss of cAMP-dependent Cl- secretion was attributable to a reduced expression of CFTR Cl- channel, KCNQ1 K+ channel, and Na-K-2Cl cotransporter-1 proteins. The transient loss of Ca2+-dependent Cl- secretion involved an impairment of basolateral Ca2+-stimulated K+ channel activity without a detectable loss of K(Ca)3.1 channel protein. Our results establish TZD drugs as important modulators of intestinal Cl- secretory function.
Collapse
Affiliation(s)
- Poonam J Bajwa
- Division of Biomedical Sciences, University of California, Riverside, CA 92521-0121, USA
| | | | | | | |
Collapse
|
30
|
Activation of AMP-activated kinase as a strategy for managing autosomal dominant polycystic kidney disease. Med Hypotheses 2009; 73:1008-10. [PMID: 19570618 DOI: 10.1016/j.mehy.2009.05.043] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/12/2008] [Revised: 09/12/2008] [Accepted: 05/29/2009] [Indexed: 12/21/2022]
Abstract
There is evidence that overactivity of both mammalian target of rapamycin (mTOR) and cystic fibrosis transmembrane conductance regulator (CFTR) contributes importantly to the progressive expansion of renal cysts in autosomal dominant polycystic kidney disease (ADPKD). Recent research has established that AMP-activated kinase (AMPK) can suppress the activity of each of these proteins. Clinical AMPK activators such as metformin and berberine may thus have potential in the clinical management of ADPKD. The traditional use of berberine in diarrhea associated with bacterial infections may reflect, in part, the inhibitory impact of AMPK on chloride extrusion by small intestinal enterocytes.
Collapse
|
31
|
Martínez-Augustin O, Romero-Calvo I, Suárez MD, Zarzuelo A, de Medina FS. Molecular bases of impaired water and ion movements in inflammatory bowel diseases. Inflamm Bowel Dis 2009; 15:114-27. [PMID: 18626965 DOI: 10.1002/ibd.20579] [Citation(s) in RCA: 49] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
The intestine is dedicated to the absorption of water and nutrients. Fine tuning of this process is necessary to maintain an adequate balance and inflammation disrupts the equilibrium. This review summarizes the current evidence in this field. Classical mechanisms proposed include alteration of epithelial integrity, augmented secretion, and reduced absorption. In addition, intestinal inflammation is associated with defects in epithelial barrier function. However, our understanding of the phenomenon has been complicated by the fact that ionic secretion is in fact diminished in vivo, even after inflammation has subsided. Inhibited ionic secretion can be reversed partially or totally in vitro by maneuvers such as blockade of inducible nitric oxide synthase or removal of the submucosal layer. Disturbances in ionic absorption are less well characterized but clearly involve both electroneutral and electrogenic Na(+) absorption. Altered ionic transport is associated with changes in the expression and function of the transporters, including the Na(+)/K(+) ATPase, the sodium/potassium/chloride cotransporter 1 (NKCC1), the sodium/hydrogen exchanger 3 (NHE3), and the epithelial sodium channel (ENaC), as well as to the modulation of intracellular signaling. Further investigation is needed in this area in order to provide an integrated paradigm of ionic transport in the inflamed intestine. In particular, we do not know exactly how diarrhea ensues in inflammation and, consequently, we do not have specific pharmacological tools to combat this condition effectively and without side effects. Moreover, whether transport disturbances are reversible independently of inflammatory control is unknown.
Collapse
Affiliation(s)
- Olga Martínez-Augustin
- Department of Biochemistry and Molecular Biology II, School of Pharmacy, University of Granada, Granada, Spain
| | | | | | | | | |
Collapse
|
32
|
Kongsuphol P, Cassidy D, Hieke B, Treharne KJ, Schreiber R, Mehta A, Kunzelmann K. Mechanistic insight into control of CFTR by AMPK. J Biol Chem 2008; 284:5645-53. [PMID: 19095655 PMCID: PMC2645823 DOI: 10.1074/jbc.m806780200] [Citation(s) in RCA: 65] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
The cystic fibrosis transmembrane conductance regulator (CFTR) is a cAMP
and protein kinase A (PKA)-regulated Cl– channel in the
apical membrane of epithelial cells. The metabolically regulated and adenosine
monophosphate-stimulated kinase (AMPK) is colocalized with CFTR and attenuates
its function. However, the sites for CFTR phosphorylation and the precise
mechanism of inhibition of CFTR by AMPK remain obscure. We demonstrate that
CFTR normally remains closed at baseline, but nevertheless, opens after
inhibition of AMPK. AMPK phosphorylates CFTR in vitro at two
essential serines (Ser737 and Ser768) in the R domain,
formerly identified as “inhibitory” PKA sites. Replacement of both
serines by alanines (i) reduced phosphorylation of the R domain, with
Ser768 having dramatically greater impact, (ii) produced CFTR
channels that were partially open in the absence of any stimulation, (iii)
significantly augmented their activation by IBMX/forskolin, and (iv)
eliminated CFTR inhibition post AMPK activation. Attenuation of CFTR by AMPK
activation was detectable in the absence of cAMP-dependent stimulation but
disappeared in maximally stimulated oocytes. Our data also suggest that AMP is
produced by local phosphodiesterases in close proximity to CFTR. Thus we
propose that CFTR channels are kept closed in nonstimulated epithelia with
high baseline AMPK activity but CFTR may be basally active in tissues with
lowered endogenous AMPK activity.
Collapse
Affiliation(s)
- Patthara Kongsuphol
- Department of Physiology, University of Regensburg, 93053 Regensburg, Germany
| | | | | | | | | | | | | |
Collapse
|
33
|
Zheng W, Kuhlicke J, Jäckel K, Eltzschig HK, Singh A, Sjöblom M, Riederer B, Weinhold C, Seidler U, Colgan SP, Karhausen J. Hypoxia inducible factor-1 (HIF-1)-mediated repression of cystic fibrosis transmembrane conductance regulator (CFTR) in the intestinal epithelium. FASEB J 2008; 23:204-13. [PMID: 18779379 DOI: 10.1096/fj.08-110221] [Citation(s) in RCA: 71] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
Diarrhea is widespread in intestinal diseases involving ischemia and/or hypoxia. Since hypoxia alters stimulated Cl(-) and water flux, we investigated the influence of such a physiologically and pathophysiologically important signal on expression of the cystic fibrosis transmembrane conductance regulator (CFTR). Located on the apical membrane, this cAMP-activated Cl(-) channel determines salt and fluid transport across mucosal surfaces. Our studies revealed depression of CFTR mRNA, protein, and function in hypoxic epithelia. Chromatin immunoprecipitation identified a previously unappreciated binding site for the hypoxia inducible factor-1 (HIF-1), and promoter studies established its relevance by loss of repression following point mutation. Consequently, HIF-1 overexpressing cells exhibited significantly reduced transport capacity in colorimetric Cl(-) efflux studies, altered short circuit measurements, and changes in transepithelial fluid movement. Whole-body hypoxia in wild-type mice resulted in significantly reduced small intestinal fluid and HCO(3)(-) secretory responses to forskolin. Experiments performed in Cftr(-/-) and Nkcc1(-/-) mice underlined the role of altered CFTR expression for these functional changes, and work in conditional Hif1a mutant mice verified HIF-1-dependent CFTR regulation in vivo. In summary, our study clarifies CFTR regulation and introduces the concept of a HIF-1-orchestrated response designed to regulate ion and fluid movement across hypoxic intestinal epithelia.
Collapse
Affiliation(s)
- Wen Zheng
- Abteilung Gastroenterologie, Hepatologie und Endokrinologie, Medizinische Hochschule Hannover, Hannover,
| | | | | | | | | | | | | | | | | | | | | |
Collapse
|
34
|
Regulation of Cl(-) secretion by AMPK in vivo. Pflugers Arch 2008; 457:1071-8. [PMID: 18752001 DOI: 10.1007/s00424-008-0577-3] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/15/2008] [Accepted: 08/09/2008] [Indexed: 10/21/2022]
Abstract
Previous in vitro studies suggested that Cl(-) currents produced by the cystic fibrosis transmembrane conductance regulator (CFTR; ABCC7) are inhibited by the alpha1 isoform of the adenosine monophosphate (AMP)-stimulated kinase (AMPK). AMPK is a serine/threonine kinase that is activated during metabolic stress. It has been proposed as a potential mediator for transport-metabolism coupling in epithelial tissues. All previous studies have been performed in vitro and thus little is known about the regulation of Cl(-) secretion by AMPK in vivo. Using AMPKalpha1(-/-) mice and wild-type littermates, we demonstrate that phenformin, an activator of AMPK, strongly inhibits cAMP-activated Cl(-) secretion in mouse airways and colon, when examined in ex vivo in Ussing chamber recordings. However, phenformin was equally effective in AMPKalpha1(-/-) and wild-type animals, suggesting additional AMPK-independent action of phenformin. Phenformin inhibited CFTR Cl(-) conductance in basolaterally permeabilized colonic epithelium from AMPKalpha1(+/+) but not AMPKalpha1(-/-) mice. The inhibitor of AMPK compound C enhanced CFTR-mediated Cl(-) secretion in epithelial tissues of AMPKalpha1(-/-) mice, but not in wild-type littermates. There was no effect on Ca(2+)-mediated Cl(-) secretion, activated by adenosine triphosphate or carbachol. Moreover CFTR-dependent Cl(-) secretion was enhanced in the colon of AMPKalpha1(-/-) mice, as indicated in Ussing chamber ex vivo and rectal PD measurements in vivo. Taken together, these data suggest that epithelial Cl(-) secretion mediated by CFTR is controlled by AMPK in vivo.
Collapse
|
35
|
Chappell AE, Bunz M, Smoll E, Dong H, Lytle C, Barrett KE, McCole DF. Hydrogen peroxide inhibits Ca2+-dependent chloride secretion across colonic epithelial cells via distinct kinase signaling pathways and ion transport proteins. FASEB J 2008; 22:2023-36. [PMID: 18211955 DOI: 10.1096/fj.07-099697] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
Reactive oxygen species (ROS) are key mediators in a number of inflammatory conditions, including inflammatory bowel disease (IBD). ROS, including hydrogen peroxide (H(2)O(2)), modulate intestinal epithelial ion transport and are believed to contribute to IBD-associated diarrhea. Intestinal crypt fluid secretion, driven by electrogenic Cl(-) secretion, hydrates and sterilizes the crypt, thus reducing bacterial adherence. Here, we show that pathophysiological concentrations of H(2)O(2) inhibit Ca(2+)-dependent Cl(-) secretion across T(84) colonic epithelial cells by elevating cytosolic Ca(2+), which contributes to activation of two distinct signaling pathways. One involves recruitment of the Ca(2+)-responsive kinases, Src and Pyk-2, as well as extracellular signal-regulated kinase (ERK). A separate pathway recruits p38 MAP kinase and phosphoinositide 3-kinase (PI3-K) signaling. The ion transport response to Ca(2+)-dependent stimuli is mediated in part by K(+) efflux through basolateral K(+) channels and Cl(-) uptake by the Na(+)-K(+)-2Cl(-) cotransporter, NKCC1. We demonstrate that H(2)O(2) inhibits Ca(2+)-dependent basolateral K(+) efflux and also inhibits NKCC1 activity independently of inhibitory effects on apical Cl(-) conductance. Thus, we have demonstrated that H(2)O(2) inhibits Ca(2+)-dependent Cl(-) secretion through multiple negative regulatory signaling pathways and inhibition of specific ion transporters. These findings increase our understanding of mechanisms by which inflammation disturbs intestinal epithelial function and contributes to intestinal pathophysiology.
Collapse
Affiliation(s)
- Alfred E Chappell
- Division of Gastroenterology, University of California, San Diego, 9500 Gilman Dr., La Jolla, CA 92093-0063, USA
| | | | | | | | | | | | | |
Collapse
|
36
|
Fukuda T, Ishii K, Nanmoku T, Isobe K, Kawakami Y, Takekoshi K. 5-Aminoimidazole-4-carboxamide-1-beta-4-ribofuranoside stimulates tyrosine hydroxylase activity and catecholamine secretion by activation of AMP-activated protein kinase in PC12 cells. J Neuroendocrinol 2007; 19:621-31. [PMID: 17620104 DOI: 10.1111/j.1365-2826.2007.01570.x] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
Abstract
The activity of AMP-activated protein kinase (AMPK) is regulated by the metabolic and nutritional state of the cell. 5-Aminoimidazole-4-carboxamide-1-beta-4-ribofuranoside (AICAR) is transformed into riboside monophosphate (ZMP) via phosphorylation by adenosine kinase inside the cell and exerts it effect by stimulating AMPK. AICAR significantly induces an increase in AMPK activity in a dose- and time-dependent manner in the rat pheochromocytoma cell line PC12. In addition, compound C, an AMPK inhibitor, as well as 5'-amino-5'-dAdo, an adenosine kinase inhibitor, inhibits the AICAR-induced AMPK activity. AICAR significantly stimulates tyrosine hydroxylase (TH) (the rate-limiting enzyme in the biosynthesis of catecholamine) activity and the corresponding mRNA level, which closely matches with the TH protein level. In addition, AICAR provokes a rapid and long-lasting increase in the phosphorylation of TH at Ser19, Ser31 and Ser40. AICAR also markedly activates ERKs, JNK and p38. The MEK-1-inhibitor (PD-098059) causes a partial, but significant, inhibition of AICAR-induced TH enzyme activity by phosphorylation of Ser31 without affecting phosphorylation at the two other sites. By contrast, neither the JNK-inhibitor nor the p38-inhibitor affects TH enzyme activity and phosphorylation. Similarly, PD-098059 partially, but significantly, inhibits the AICAR-induced increase in the TH mRNA level. Furthermore, AICAR increases the level of cAMP in PC12 cells. The present study also shows that H89, a protein kinase A inhibitor, abolishes the AICAR-induced increase in the level of TH mRNA, as well as the corresponding enzyme activity and Ser40 phosphorylation. Finally, AICAR significantly increases dopamine secretion from PC12 cells. These findings indicate that AICAR activates catecholamine synthesis and secretion through AMPK activation in chromaffin cells.
Collapse
Affiliation(s)
- T Fukuda
- Molecular Laboratory Medicine, Graduate School of Comprehensive Human Sciences, University of Tsukuba, Tsukuba, Ibaraki, Japan
| | | | | | | | | | | |
Collapse
|
37
|
Cinar A, Chen M, Riederer B, Bachmann O, Wiemann M, Manns M, Kocher O, Seidler U. NHE3 inhibition by cAMP and Ca2+ is abolished in PDZ-domain protein PDZK1-deficient murine enterocytes. J Physiol 2007; 581:1235-46. [PMID: 17395628 PMCID: PMC2170846 DOI: 10.1113/jphysiol.2007.131722] [Citation(s) in RCA: 53] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023] Open
Abstract
The PDZ-binding protein PDZK1 (NHERF3/CAP70/PDZ-dc-1) in vitro binds to NHE3, but its role in the regulation of NHE3 activity in native enterocytes is unknown. This study was undertaken to understand the physiological role of PDZK1 in regulating NHE3 activity in native murine colonic enterocytes. NHE3 transport rates were assessed fluorometrically in BCECF-loaded colonic crypts in the NHE3-expressing cryptal openings by measuring acid-activated, Na+-dependent, Hoe 642-insensitive proton efflux rates. NHE3 mRNA expression levels and NHE3 total enterocyte and brush border membrane (BBM) protein abundance were determined by quantitative PCR and Western analysis and immunohistochemistry. In pdzk1-/- colonic surface cells, acid-activated NHE3 transport rates were strongly reduced, and the inhibitory effect of forskolin and ionomcyin was virtually abolished. Hyperosmolarity, on the other hand, still had an inhibitory effect. In addition, the NHE3-selective inhibitor S1611 inhibited acid-activated NHE3 activity in pdzk1-/- and +/+mice, suggesting that functional NHE3 is present in pdzk1-deficient colonocytes. NHE1 and NHE2 activity was not altered in pdzk1-/- colonic crypts. Immunohistochemistry revealed apical NHE3 staining in pdzk1-/- and +/+proximal colon, and Western blot analysis revealed no difference in NHE3 abundance in colonic enterocyte homogenate as well as brush border membrane. Lack of the PDZ-adaptor protein PDZK1 in murine proximal colonic enterocytes does not influence NHE3 abundance or targeting to the apical membrane, but abolishes NHE3 regulation by cAMPergic and Ca2+ -dependent pathways. It leaves NHE3 inhibition by hyperosmolarity intact, suggesting an important and selective role for PDZK1 in the agonist-mediated regulation of intestinal NHE3 activity.
Collapse
Affiliation(s)
- Ayhan Cinar
- Hannover Medical School, Department of Gastroenterology and Hepatology, Carl-Neuberg-Str. 1, 30625 Hannover, Germany
| | | | | | | | | | | | | | | |
Collapse
|
38
|
Guggino WB, Stanton BA. New insights into cystic fibrosis: molecular switches that regulate CFTR. Nat Rev Mol Cell Biol 2006; 7:426-36. [PMID: 16723978 DOI: 10.1038/nrm1949] [Citation(s) in RCA: 332] [Impact Index Per Article: 18.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
Cystic fibrosis transmembrane conductance regulator (CFTR), a Cl(-)-selective ion channel, is a prototypic member of the ATP-binding cassette transporter superfamily that is expressed in several organs. In these organs, CFTR assembles into large, dynamic macromolecular complexes that contain signalling molecules, kinases, transport proteins, PDZ-domain-containing proteins, myosin motors, Rab GTPases, and SNAREs. Understanding how these complexes regulate the intracellular trafficking and activity of CFTR provides a unique insight into the aetiology of cystic fibrosis and other diseases.
Collapse
Affiliation(s)
- William B Guggino
- Department of Physiology and Pediatrics, Johns Hopkins University School of Medicine, Baltimore, Maryland, USA
| | | |
Collapse
|
39
|
Günzel D, Florian P, Richter JF, Troeger H, Schulzke JD, Fromm M, Gitter AH. Restitution of single-cell defects in the mouse colon epithelium differs from that of cultured cells. Am J Physiol Regul Integr Comp Physiol 2006; 290:R1496-507. [PMID: 16397094 DOI: 10.1152/ajpregu.00470.2005] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
Integrity of colon epithelium is of crucial importance and, as small defects occur constantly, rapid repair (restitution) is essential. To investigate the mechanism of restitution, single-cell lesions were induced in mouse colonic surface epithelia by iontophoretic injection of Ca2+. Closure of the resulting defects was monitored using confocal laser scanning microscopy (CLSM), and functional sealing by electrophysiological techniques. Restitution was evaluated as the time constant tau of the exponential decrease in conductance of an induced leak and amounted to 0.28 min under control conditions. After 4 min, the leak was completely sealed. Repair was thus considerably faster than in previously investigated HT-29/B6 cells (tau=5.73 min). As in cultured cells, cytochalasin D delayed restitution in native colon epithelia (tau=0.69 min), indicating the involvement of actin in the healing process; however, no accumulation of actin surrounding the lesion was detected. Long-term incubation of epithelia with IFN-gamma alone or in combination with TNF-alpha increased tau to 0.49 and 0.59 min, respectively. In contrast to cultured cells, TNF-alpha alone did not affect restitution. A brief (<10 min) exposure to the sterile filtered supernatant of hemolytic E. coli O4 cultures did not affect the morphology of the epithelium, but delayed restitution. In CLSM studies, defects were still clearly visible 4 min after the onset of lesion induction. The supernatant of a nonhemolytic E. coli O4 mutant did not exhibit this effect. In conclusion, single-cell defects in native colon cause functional leaks that seal faster than in cell cultures. Proinflammatory cytokines and pathogenic bacteria delay restitution. This suggests a key role of very small lesions at the onset of pathogenic processes in the intestine.
Collapse
Affiliation(s)
- D Günzel
- Department of Clinical Physiology, Charité, Campus Benjamin Franklin, Hindenburgdamm 30, 12200 Berlin, and Jena University of Applied Sciences, Germany.
| | | | | | | | | | | | | |
Collapse
|
40
|
Hallows KR. Emerging role of AMP-activated protein kinase in coupling membrane transport to cellular metabolism. Curr Opin Nephrol Hypertens 2005; 14:464-71. [PMID: 16046906 DOI: 10.1097/01.mnh.0000174145.14798.64] [Citation(s) in RCA: 63] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
PURPOSE OF REVIEW It has long been recognized that the coupling of membrane transport to underlying cellular metabolic status is critical because transport processes consume a large portion of total cellular energy. Recently, the finely tuned metabolic sensor AMP-activated protein kinase (AMPK) has emerged as a membrane transport regulator, which may permit sensitive transport-metabolism crosstalk. This review will discuss how AMPK may play an important role in the regulation of ion and solute transport across the plasma membrane under both physiological and pathological conditions in epithelia and other tissues. RECENT FINDINGS Recent studies have found that AMPK, which becomes activated during cellular metabolic stress, promotes the cellular uptake of fuel sources such as glucose and fatty acids to promote ATP generation and inhibits ion-transport proteins such as the cystic fibrosis transmembrane conductance regulator Cl channel and the epithelial Na channel, thereby limiting the dissipation of transmembrane ion gradients. An understanding of the underlying cellular and molecular mechanisms for AMPK-dependent regulation of transport proteins is beginning to emerge. SUMMARY As earlier studies have focused on the role of nucleotides such as ATP in regulating transport-protein activities, the regulation of membrane transport by AMPK represents a novel and more-sensitive mechanism for the coupling of membrane transport to cellular metabolic status. Identifying new membrane-transport targets of AMPK and elucidating the mechanisms involved in their AMPK-dependent regulation are fruitful areas for new investigation that should yield valuable insights into the pathophysiology of hypoxic and ischemic tissue injury.
Collapse
Affiliation(s)
- Kenneth R Hallows
- Renal-Electrolyte Division, Department of Medicine and Department of Cell Biology and Physiology, University of Pittsburgh School of Medicine, S976 Scaife Hall, 3550 Terrace Street, Pittsburgh, PA 15261, USA.
| |
Collapse
|
41
|
LaRosa C, Downs SM. Stress stimulates AMP-activated protein kinase and meiotic resumption in mouse oocytes. Biol Reprod 2005; 74:585-92. [PMID: 16280415 DOI: 10.1095/biolreprod.105.046524] [Citation(s) in RCA: 50] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
This study examined the effects of three different cellular stresses on oocyte maturation in meiotically arrested mouse oocytes. Cumulus-cell enclosed oocytes (CEO) or denuded oocytes (DO) from immature, eCG-primed mice were cultured for 17-18 h in dbcAMP-containing medium plus increasing concentrations of the metabolic poison, sodium arsenite, or the free radical-generating agent, menadione. Alternatively, oocytes were exposed to osmotic stress by pulsing with sorbitol and returned to control inhibitory conditions for the duration of culture. Arsenite and menadione each dose-dependently induced germinal vesicle breakdown (GVB) in both DO and CEO. DO, but not CEO, pulsed for 60 min with 500 mM sorbitol were stimulated to resume maturation. The lack of effect in CEO suggests that the cumulus cells may be playing a protective role in osmotic stress-induced GVB. The AMP-activated protein kinase (PRKA; formerly known as AMPK) inhibitors, compound C and araA, completely blocked the meiosis-stimulating effects of all the tested stresses. Western blots showed that acetyl-CoA carboxylase, an important substrate of PRKA, was phosphorylated before GVB, supporting a role for PRKA in stress-induced maturation. Together, these data show that a variety of stresses stimulate GVB in meiotically arrested mouse oocytes in vitro and suggest that this effect is mediated through activation of PRKA.
Collapse
Affiliation(s)
- Cean LaRosa
- Biology Department, Marquette University, Milwaukee, Wisconsin 53233, USA
| | | |
Collapse
|
42
|
Walker J, Jijon H, Diaz H, Salehi P, Churchill T, Madsen K. 5-aminoimidazole-4-carboxamide riboside (AICAR) enhances GLUT2-dependent jejunal glucose transport: a possible role for AMPK. Biochem J 2005; 385:485-91. [PMID: 15367103 PMCID: PMC1134720 DOI: 10.1042/bj20040694] [Citation(s) in RCA: 117] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
AMPK (AMP-activated protein kinase) is a key sensor of energy status within the cell. Activated by an increase in the AMP/ATP ratio, AMPK acts to limit cellular energy depletion by down-regulating selective ATP-dependent processes. The purpose of the present study was to determine the role of AMPK in regulating intestinal glucose transport. [3H]3-O-methyl glucose fluxes were measured in murine jejunum in the presence and absence of the AMPK activators AICAR (5-aminoimidazole-4-carboxamide riboside) and metformin and the p38 inhibitor, SB203580. To differentiate between a sodium-coupled (SGLT1) and diffusive (GLUT2) route of entry, fluxes were measured in the presence of the SGLT1 and GLUT2 inhibitors phloridzin and phloretin. Glucose transporter mRNA levels were measured by reverse transcriptase-PCR, and localization by Western blotting. Surface-expressed GLUT2 was assessed by luminal biotinylation. Activation of p38 mitogen-activated protein kinase was analysed by Western blotting. We found that treatment of jejunal tissue with AICAR resulted in enhanced net glucose uptake and was associated with phosphorylation of p38 mitogen-activated protein kinase. Inhibition of p38 abrogated the stimulation of AICAR-stimulated glucose uptake. Phloretin abolished the AICAR-mediated increase in glucose flux, whereas phloridzin had no effect, suggesting the involvement of GLUT2. In addition, AICAR decreased total protein levels of SGLT1, concurrently increasing levels of GLUT2 in the brush-border membrane. The anti-diabetic drug metformin, a known activator of AMPK, also induced the localization of GLUT2 to the luminal surface. We conclude that the activation of AMPK results in an up-regulation of non-energy requiring glucose uptake by GLUT2 and a concurrent down-regulation of sodium-dependent glucose transport.
Collapse
Affiliation(s)
- John Walker
- *Division of Gastroenterology, University of Alberta, 6146 Dentistry Pharmacy Building, Edmonton, Alberta, Canada T6G 2C2
| | - Humberto B. Jijon
- *Division of Gastroenterology, University of Alberta, 6146 Dentistry Pharmacy Building, Edmonton, Alberta, Canada T6G 2C2
| | - Hugo Diaz
- *Division of Gastroenterology, University of Alberta, 6146 Dentistry Pharmacy Building, Edmonton, Alberta, Canada T6G 2C2
| | - Payam Salehi
- †Department of Surgery, University of Alberta, Edmonton, Alberta, Canada T6G 2C2
| | - Thomas Churchill
- †Department of Surgery, University of Alberta, Edmonton, Alberta, Canada T6G 2C2
| | - Karen L. Madsen
- *Division of Gastroenterology, University of Alberta, 6146 Dentistry Pharmacy Building, Edmonton, Alberta, Canada T6G 2C2
- To whom correspondence should be addressed (email )
| |
Collapse
|