1
|
Nikolovska K, Seidler UE, Stock C. The Role of Plasma Membrane Sodium/Hydrogen Exchangers in Gastrointestinal Functions: Proliferation and Differentiation, Fluid/Electrolyte Transport and Barrier Integrity. Front Physiol 2022; 13:899286. [PMID: 35665228 PMCID: PMC9159811 DOI: 10.3389/fphys.2022.899286] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/18/2022] [Accepted: 04/19/2022] [Indexed: 12/11/2022] Open
Abstract
The five plasma membrane Na+/H+ exchanger (NHE) isoforms in the gastrointestinal tract are characterized by distinct cellular localization, tissue distribution, inhibitor sensitivities, and physiological regulation. NHE1 (Slc9a1) is ubiquitously expressed along the gastrointestinal tract in the basolateral membrane of enterocytes, but so far, an exclusive role for NHE1 in enterocyte physiology has remained elusive. NHE2 (Slc9a2) and NHE8 (Slc9a8) are apically expressed isoforms with ubiquitous distribution along the colonic crypt axis. They are involved in pHi regulation of intestinal epithelial cells. Combined use of a knockout mouse model, intestinal organoid technology, and specific inhibitors revealed previously unrecognized actions of NHE2 and NHE8 in enterocyte proliferation and differentiation. NHE3 (Slc9a3), expressed in the apical membrane of differentiated intestinal epithelial cells, functions as the predominant nutrient-independent Na+ absorptive mechanism in the gut. The new selective NHE3 inhibitor (Tenapanor) allowed discovery of novel pathophysiological and drug-targetable NHE3 functions in cystic-fibrosis associated intestinal obstructions. NHE4, expressed in the basolateral membrane of parietal cells, is essential for parietal cell integrity and acid secretory function, through its role in cell volume regulation. This review focuses on the expression, regulation and activity of the five plasma membrane Na+/H+ exchangers in the gastrointestinal tract, emphasizing their role in maintaining intestinal homeostasis, or their impact on disease pathogenesis. We point to major open questions in identifying NHE interacting partners in central cellular pathways and processes and the necessity of determining their physiological role in a system where their endogenous expression/activity is maintained, such as organoids derived from different parts of the gastrointestinal tract.
Collapse
|
2
|
Pathophysiological role of ion channels and transporters in gastrointestinal mucosal diseases. Cell Mol Life Sci 2021; 78:8109-8125. [PMID: 34778915 PMCID: PMC8629801 DOI: 10.1007/s00018-021-04011-5] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/18/2021] [Revised: 09/10/2021] [Accepted: 10/23/2021] [Indexed: 11/13/2022]
Abstract
The incidence of gastrointestinal (GI) mucosal diseases, including various types of gastritis, ulcers, inflammatory bowel disease and GI cancer, is increasing. Therefore, it is necessary to identify new therapeutic targets. Ion channels/transporters are located on cell membranes, and tight junctions (TJs) affect acid–base balance, the mucus layer, permeability, the microbiota and mucosal blood flow, which are essential for maintaining GI mucosal integrity. As ion channel/transporter dysfunction results in various GI mucosal diseases, this review focuses on understanding the contribution of ion channels/transporters to protecting the GI mucosal barrier and the relationship between GI mucosal disease and ion channels/transporters, including Cl−/HCO3− exchangers, Cl− channels, aquaporins, Na+/H+ exchangers, and K+ channels. Here, we provide novel prospects for the treatment of GI mucosal diseases.
Collapse
|
3
|
Cao L, Yuan Z, Liu M, Stock C. (Patho-)Physiology of Na +/H + Exchangers (NHEs) in the Digestive System. Front Physiol 2020; 10:1566. [PMID: 32009977 PMCID: PMC6974801 DOI: 10.3389/fphys.2019.01566] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/15/2019] [Accepted: 12/12/2019] [Indexed: 02/06/2023] Open
Abstract
Na+/H+ exchangers (NHEs) are expressed in virtually all human tissues and organs. Two major tasks of those NHE isoforms that are located in plasma membranes are cell volume control by Na+-uptake and cellular pH regulation by H+-extrusion. Several NHEs, particularly NHE 1–4 and 8, are involved in the pathogenesis of diseases of the digestive system such as inflammatory bowel disease (ulcerative colitis, Crohn’s disease) and gastric and colorectal tumorigenesis. In the present review, we describe the physiological purposes, possible malfunctions and pathophysiological effects of the different NHE isoforms along the alimentary canal from esophagus to colon, including pancreas, liver and gallbladder. Particular attention is paid to the functions of NHEs in injury repair and to the role of NHE1 in Barrett’s esophagus. The impact of NHEs on gut microbiota and intestinal mucosal integrity is also dealt with. As the hitherto existing findings are not always consistent, sometimes even controversial, they are compared and critically discussed.
Collapse
Affiliation(s)
- Li Cao
- Department of Gastroenterology, Tongji Hospital, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, China
| | - Zhenglin Yuan
- Department of Stomatology, Union Hospital, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, China
| | - Mei Liu
- Department of Gastroenterology, Tongji Hospital, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, China
| | - Christian Stock
- Department of Gastroenterology, Hepatology and Endocrinology, Hannover Medical School, Hanover, Germany
| |
Collapse
|
4
|
Kurteva E, Lindley KJ, Hill SM, Köglmeier J. Mucosal Abnormalities in Children With Congenital Chloride Diarrhea-An Underestimated Phenotypic Feature? Front Pediatr 2020; 8:365. [PMID: 32850522 PMCID: PMC7403178 DOI: 10.3389/fped.2020.00365] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/02/2020] [Accepted: 06/01/2020] [Indexed: 01/12/2023] Open
Abstract
Objectives and Study: Congenital chloride diarrhea (CCD) is a rare, autosomal recessive disorder caused by mutations in the SLC26A3 gene encoding a transmembrane chloride/bicarbonate ion exchanger mainly expressed in the apical brush border of the ileal and colonic epithelium. Lifelong, secretory, chloride-rich diarrhea and hypochloremic, hypokalemic metabolic alkalosis are characteristic. Histological evidence of bowel inflammation is not typically described in CCD and has only been reported in a few patients. Methods: We report four cases of CCD who received adequate resuscitation with appropriate replacement of their fecal salt and water losses. Three had associated inflammatory bowel changes at endoscopy. The index case of CCD who developed frankly bloodstained diarrhea aged 7 months was found to have histologically confirmed colitis at endoscopy. An electronic search of the hospital database to identify all patients with confirmed CCD was performed. A further three children underwent de novo diagnostic evaluation and treatment. A retrospective case note review was undertaken to determine the incidence and subtype of inflammatory bowel disease (IBD) by clinical, endoscopic, and histological means. Results: Four children with genetically confirmed CCD were identified, two being female. The first girl had a granulomatous colitis with ulceration. She went into remission with a combination of steroids and azathioprine. Immunosuppression was subsequently discontinued without a further flare of colitis. A second girl was found to have patchy inflammatory changes in the small bowel and focal active colitis. A third patient, a boy, demonstrated mild inflammatory changes in the small bowel with apoptotic debris and mild inflammation in the colon. A fourth patient did not develop intestinal inflammation. Conclusion: Our case series highlights the potential association of CCD with panenteric inflammation. While our cohort was small, CCD is rare and three out of four children referred to our tertiary referral center were affected. While early diagnosis and adequate salt replacement therapy are crucial in CCD management, the clinician should also be aware of bowel inflammation as a potential cause of failure of CCD therapy to control bowel symptomatology. Further insight is needed to understand the underlying patho-mechanism giving rise to bowel inflammation in this group.
Collapse
Affiliation(s)
- Elena Kurteva
- Great Ormond Street Hospital for Children NHS Foundation Trust, London, United Kingdom
| | - Keith J Lindley
- Great Ormond Street Hospital for Children NHS Foundation Trust, London, United Kingdom
| | - Susan M Hill
- Great Ormond Street Hospital for Children NHS Foundation Trust, London, United Kingdom
| | - Jutta Köglmeier
- Great Ormond Street Hospital for Children NHS Foundation Trust, London, United Kingdom
| |
Collapse
|
5
|
Subramanian VS, Sabui S, Subramenium GA, Marchant JS, Said HM. Tumor necrosis factor alpha reduces intestinal vitamin C uptake: a role for NF-κB-mediated signaling. Am J Physiol Gastrointest Liver Physiol 2018; 315:G241-G248. [PMID: 29631379 PMCID: PMC6139644 DOI: 10.1152/ajpgi.00071.2018] [Citation(s) in RCA: 33] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
Sodium-dependent vitamin C transporter-1 (SVCT-1) is the major transporter mediating intestinal vitamin C uptake. Intestinal inflammation and prolonged infection are associated with increased serum and intestinal mucosa levels of tumor necrosis factor-α (TNF-α), which also exerts profound effects on the intestinal absorption process. Elevated levels of TNF-α have been linked to the pathogenesis of inflammatory bowel disease (IBD) and malabsorption of nutrients, and patients with this condition have low levels of vitamin C. To date, little is known about the effect of TNF-α on intestinal absorption of vitamin C. We studied the impact of TNF-α on ascorbic acid (AA) transport using a variety of intestinal preparations. The expression level of human SVCT-1 mRNA is significantly lower in patients with IBD. TNF-α treated Caco-2 cells and mice showed a significant inhibition of intestinal 14C-AA uptake. This inhibition was associated with significant decreases in SVCT-1 protein, mRNA, and heterogeneous nuclear RNA levels in TNF-α treated Caco-2 cells, mouse jejunum, and enteroids. Also, TNF-α caused a significant inhibition in the SLC23A1 promoter activity. Furthermore, treatment of Caco-2 cells with celastrol (NF-κB inhibitor) blocked the inhibitory effect caused by TNF-α on AA uptake, SVCT-1 protein, and mRNA expression, as well as the activity of SLC23A1 promoter. Treatment of TNF-α also led to a significant decrease in the expression of hepatocyte nuclear factor-1-α, which drives the basal activity of SLC23A1 promoter, and this effect was reversed by celastrol. Together, these findings show that TNF-α inhibits intestinal AA uptake, and this effect is mediated, at least in part, at the level of transcription of the SLC23A1 gene via the NF-κB pathway. NEW & NOTEWORTHY Our findings show that tumor necrosis factor-α inhibits intestinal ascorbic acid uptake in both in vitro and in vivo systems, and this inhibitory effect is mediated, at least in part, at the level of transcription of the SLC23A1 (sodium-dependent vitamin C transporter-1) gene via the NF-κB pathway.
Collapse
Affiliation(s)
- Veedamali S. Subramanian
- 1Department of Medicine, University of California, Irvine, California,2Department of Physiology and Biophysics, University of California, Irvine, California,3Department of Veterans Affairs Medical Center, Long Beach, California
| | - Subrata Sabui
- 1Department of Medicine, University of California, Irvine, California,2Department of Physiology and Biophysics, University of California, Irvine, California,3Department of Veterans Affairs Medical Center, Long Beach, California
| | - Ganapathy A. Subramenium
- 1Department of Medicine, University of California, Irvine, California,2Department of Physiology and Biophysics, University of California, Irvine, California,3Department of Veterans Affairs Medical Center, Long Beach, California
| | - Jonathan S. Marchant
- 4Department of Cell Biology, Neurobiology and Anatomy, Medical College of Wisconsin, Milwaukee, Wisconsin
| | - Hamid M. Said
- 1Department of Medicine, University of California, Irvine, California,2Department of Physiology and Biophysics, University of California, Irvine, California,3Department of Veterans Affairs Medical Center, Long Beach, California
| |
Collapse
|
6
|
Abstract
Inflammatory bowel diseases broadly categorized into Crohn's disease (CD) and ulcerative colitis (UC), are chronic inflammatory disorders of the gastrointestinal tract with increasing prevalence worldwide. The etiology of the disease is complex and involves a combination of genetic, environmental, immunological and gut microbial factors. Recurring and bloody diarrhea is the most prevalent and debilitating symptom in IBD. The pathogenesis of IBD-associated diarrhea is multifactorial and is essentially an outcome of mucosal damage caused by persistent inflammation resulting in dysregulated intestinal ion transport, impaired epithelial barrier function and increased accessibility of the pathogens to the intestinal mucosa. Altered expression and/or function of epithelial ion transporters and channels is the principle cause of electrolyte retention and water accumulation in the intestinal lumen leading to diarrhea in IBD. Aberrant barrier function further contributes to diarrhea via leak-flux mechanism. Mucosal penetration of enteric pathogens promotes dysbiosis and exacerbates the underlying immune system further perpetuating IBD associated-tissue damage and diarrhea. Here, we review the mechanisms of impaired ion transport and loss of epithelial barrier function contributing to diarrhea associated with IBD.
Collapse
Affiliation(s)
- Arivarasu N Anbazhagan
- a Division of Gastroenterology and Hepatology, Department of Medicine, University of Illinois at Chicago , Chicago , IL , USA
| | - Shubha Priyamvada
- a Division of Gastroenterology and Hepatology, Department of Medicine, University of Illinois at Chicago , Chicago , IL , USA
| | - Waddah A Alrefai
- a Division of Gastroenterology and Hepatology, Department of Medicine, University of Illinois at Chicago , Chicago , IL , USA.,b Jesse Brown VA Medical Center , Chicago , IL , USA
| | - Pradeep K Dudeja
- a Division of Gastroenterology and Hepatology, Department of Medicine, University of Illinois at Chicago , Chicago , IL , USA.,b Jesse Brown VA Medical Center , Chicago , IL , USA
| |
Collapse
|
7
|
Xu H, Ghishan FK, Kiela PR. SLC9 Gene Family: Function, Expression, and Regulation. Compr Physiol 2018; 8:555-583. [PMID: 29687889 DOI: 10.1002/cphy.c170027] [Citation(s) in RCA: 38] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
The Slc9 family of Na+ /H+ exchangers (NHEs) plays a critical role in electroneutral exchange of Na+ and H+ in the mammalian intestine as well as other absorptive and secretory epithelia of digestive organs. These transport proteins contribute to the transepithelial Na+ and water absorption, intracellular pH and cellular volume regulation as well as the electrolyte, acid-base, and fluid volume homeostasis at the systemic level. They also influence the function of other membrane transport mechanisms, affect cellular proliferation and apoptosis as well as cell migration, adherence to the extracellular matrix, and tissue repair. Additionally, they modulate the extracellular milieu to facilitate other nutrient absorption and to regulate the intestinal microbial microenvironment. Na+ /H+ exchange is inhibited in selected gastrointestinal diseases, either by intrinsic factors (e.g., bile acids, inflammatory mediators) or infectious agents and associated bacterial toxins. Disrupted NHE activity may contribute not only to local and systemic electrolyte imbalance but also to the disease severity via multiple mechanisms. In this review, we describe the cation proton antiporter superfamily of Na+ /H+ exchangers with a particular emphasis on the eight SLC9A isoforms found in the digestive tract, followed by a more integrative description in their roles in each of the digestive organs. We discuss regulatory mechanisms that determine the function of Na+ /H+ exchangers as pertinent to the digestive tract, their regulation in pathological states of the digestive organs, and reciprocally, the contribution of dysregulated Na+ /H+ exchange to the disease pathogenesis and progression. © 2018 American Physiological Society. Compr Physiol 8:555-583, 2018.
Collapse
Affiliation(s)
- Hua Xu
- Department of Pediatrics, Steele Children's Research Center, University of Arizona, Tucson, Arizona, USA
| | - Fayez K Ghishan
- Department of Pediatrics, Steele Children's Research Center, University of Arizona, Tucson, Arizona, USA
| | - Pawel R Kiela
- Department of Pediatrics, Steele Children's Research Center, University of Arizona, Tucson, Arizona, USA.,Department of Immunobiology, University of Arizona, Tucson, Arizona, USA
| |
Collapse
|
8
|
Kumar A, Chatterjee I, Gujral T, Alakkam A, Coffing H, Anbazhagan AN, Borthakur A, Saksena S, Gill RK, Alrefai WA, Dudeja PK. Activation of Nuclear Factor-κB by Tumor Necrosis Factor in Intestinal Epithelial Cells and Mouse Intestinal Epithelia Reduces Expression of the Chloride Transporter SLC26A3. Gastroenterology 2017; 153:1338-1350.e3. [PMID: 28823863 PMCID: PMC5669803 DOI: 10.1053/j.gastro.2017.08.024] [Citation(s) in RCA: 30] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/09/2017] [Revised: 07/26/2017] [Accepted: 08/02/2017] [Indexed: 12/02/2022]
Abstract
BACKGROUND & AIMS Diarrhea associated with inflammatory bowel diseases has been associated with increased levels of inflammatory cytokines, including tumor necrosis factor (TNF). The intestinal mucosa of patients with inflammatory bowel diseases has reduced expression of solute carrier family 26 member 3 (SLC26A3, also called DRA). We investigated whether TNF directly affects expression of DRA in human intestinal epithelial cells (IECs) and in the intestines of mice, and studied the mechanisms of these effects. METHODS We performed quantitative reverse transcription polymerase chain reaction, immunofluorescence, and immunoblot analyses in Caco-2, HT-29, and T-84 cells human IECs cultured in 2 or 3 dimensions with or without TNF (50 ng/mL for 6-24 hours). We purified nuclear extracts and quantified nuclear factor-κB (NF-κB) activation and DNA binding. We isolated intestinal crypts from C57BL/6 mice, cultured enteroids, incubated these with TNF (50 ng/mL, 24 hours), and quantified messenger RNAs. DRA-mediated exchange of Cl- for HCO3- was measured by uptake of 125I. Expression of the NF-κB inhibitor α (IkBa) was knocked down in Caco-2 cells with small interfering RNAs. Activation of NF-κB in response to TNF was measured by luciferase reporter assays; binding of the NF-κB subunit p65 in cells was analyzed in chromatin immunoprecipitation assays. DRA promoter activity was measured in a luciferase reporter assay. C57BL/6 mice were injected with TNF (5 μg/mouse for 3-6 hours) or vehicle (control); intestines were collected and analyzed by immunofluorescence, or RNA and protein were collected from the mucosa. RESULTS Incubation of IECs with TNF reduced expression of DRA. Knockdown of NF-κB inhibitor α in IECs led to nuclear translocation of the NF-κB subunit p65 and reduced levels of DRA messenger RNA and protein. Expression of a transgene encoding p65 or p50 in IECs led to significant reductions in the promoter activity of DRA and its expression. In chromatin immunoprecipitation assays, p65 bound directly to the promoter of DRA, at the regions of -935 to -629 and -375 to -84. Injection of mice with TNF or incubation of crypt-derived enteroids with TNF reduced their expression of DRA messenger RNA and protein. CONCLUSIONS In human IECs and intestinal tissues from mice, we found TNF to activate NF-κB, which reduced expression of the Cl- / HCO3- exchanger DRA (SLC26A3), via direct binding to the promoter of DRA. This pathway is an important therapeutic target for inflammatory bowel disease-associated diarrhea.
Collapse
Affiliation(s)
- Anoop Kumar
- Division of Gastroenterology and Hepatology, University of Illinois at Chicago, Chicago, Illinois
| | - Ishita Chatterjee
- Division of Gastroenterology and Hepatology, University of Illinois at Chicago, Chicago, Illinois
| | - Tarunmeet Gujral
- Division of Gastroenterology and Hepatology, University of Illinois at Chicago, Chicago, Illinois
| | - Anas Alakkam
- Division of Gastroenterology and Hepatology, University of Illinois at Chicago, Chicago, Illinois
| | - Hayley Coffing
- Department of Microbiology and Immunology, Department of Medicine, University of Illinois at Chicago, Chicago, Illinois
| | - Arivarasu N Anbazhagan
- Division of Gastroenterology and Hepatology, University of Illinois at Chicago, Chicago, Illinois
| | - Alip Borthakur
- Division of Gastroenterology and Hepatology, University of Illinois at Chicago, Chicago, Illinois
| | - Seema Saksena
- Division of Gastroenterology and Hepatology, University of Illinois at Chicago, Chicago, Illinois; Jesse Brown Veterans Affairs Medical Center, Chicago, Illinois
| | - Ravinder K Gill
- Division of Gastroenterology and Hepatology, University of Illinois at Chicago, Chicago, Illinois
| | - Waddah A Alrefai
- Division of Gastroenterology and Hepatology, University of Illinois at Chicago, Chicago, Illinois; Jesse Brown Veterans Affairs Medical Center, Chicago, Illinois
| | - Pradeep K Dudeja
- Division of Gastroenterology and Hepatology, University of Illinois at Chicago, Chicago, Illinois; Jesse Brown Veterans Affairs Medical Center, Chicago, Illinois.
| |
Collapse
|
9
|
Soleiman AA, Thameem F, Khan I. Mechanism of down regulation of Na-H exchanger-2 in experimental colitis. PLoS One 2017; 12:e0176767. [PMID: 28493993 PMCID: PMC5426621 DOI: 10.1371/journal.pone.0176767] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/23/2016] [Accepted: 04/17/2017] [Indexed: 11/18/2022] Open
Abstract
BACKGROUND The Na-H exchanger [NHE] performs an electroneutral uptake of NaCl and water from the lumen of the gastrointestinal tract. There are several distinct NHE isoforms, some of which show an altered expression in the inflammatory bowel diseases (IBD). In this study, we examined a role of NHE-2 in experimental colitis. METHODS Colitis was induced in male Sprague-Dawley rats by intra-rectal administration of trinitrobenzenesulphonic acid (TNBS). On day 6 post-TNBS, the animals were sacrificed, colonic and ileal segments were taken out, cleaned with phosphate buffered saline and used in this study. RESULTS There was a significant decrease in the level of NHE-2 protein as measured by ECL western blot analysis and confocal immunofluorescence microscopy. The levels of NHE-2 mRNA and heteronuclear RNA measured by an end-point RT-PCR and a real time PCR were also decreased significantly in the inflamed colon. However, there was no change in the level of NHE-2 protein in response to in vitro TNF-α treatment of uninflamed rat colonic segment. These changes were selective and localized to the colon as actin, an internal control, remained unchanged. Confocal immunofluorescence microscopy revealed co-localization of NHE-2 and NHE-3 in the brush borders of colonic epithelial cells. Inflamed colon showed a significant increase in myeloperoxidase activity and colon hypertrophy. In addition, there was a significant decrease in body weight and goblet cells' mucin staining in the TNBS treated colon. These changes were not conspicuous in the non-inflamed ileum. CONCLUSIONS These findings demonstrate suppression of NHE-2 expression on the brush borders in the colonic epithelial cells which is regulated transcriptionally. However a role of TNF-α in the regulation of NHE-2 is discounted in the present model of colitis. This decrease in the NHE-2 expression will lead to a loss of electrolyte and water uptake thus contributing to the symptoms associated with IBD.
Collapse
Affiliation(s)
- Amal Ali Soleiman
- Department of Biochemistry, Faculty of Medicine, Kuwait University, Jabriya, Kuwait
| | - Farook Thameem
- Department of Biochemistry, Faculty of Medicine, Kuwait University, Jabriya, Kuwait
| | - Islam Khan
- Department of Biochemistry, Faculty of Medicine, Kuwait University, Jabriya, Kuwait
- * E-mail:
| |
Collapse
|
10
|
Magalhães D, Cabral JM, Soares-da-Silva P, Magro F. Role of epithelial ion transports in inflammatory bowel disease. Am J Physiol Gastrointest Liver Physiol 2016; 310:G460-76. [PMID: 26744474 DOI: 10.1152/ajpgi.00369.2015] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/22/2015] [Accepted: 01/02/2016] [Indexed: 02/06/2023]
Abstract
Inflammatory bowel disease (IBD) is a chronic inflammatory disorder with a complex pathogenesis. Diarrhea is a highly prevalent and often debilitating symptom of IBD patients that results, at least in part, from an intestinal hydroelectrolytic imbalance. Evidence suggests that reduced electrolyte absorption is more relevant than increased secretion to this disequilibrium. This systematic review analyses and integrates the current evidence on the roles of epithelial Na(+)-K(+)-ATPase (NKA), Na(+)/H(+) exchangers (NHEs), epithelial Na(+) channels (ENaC), and K(+) channels (KC) in IBD-associated diarrhea. NKA is the key driving force of the transepithelial ionic transport and its activity is decreased in IBD. In addition, the downregulation of apical NHE and ENaC and the upregulation of apical large-conductance KC all contribute to the IBD-associated diarrhea by lowering sodium absorption and/or increasing potassium secretion.
Collapse
Affiliation(s)
- Diogo Magalhães
- Department of Pharmacology and Therapeutics, Faculty of Medicine, Porto, Portugal; and MedInUP-Center for Drug Discovery and Innovative Medicines, University of Porto, Porto, Portugal
| | - José Miguel Cabral
- Department of Pharmacology and Therapeutics, Faculty of Medicine, Porto, Portugal; and MedInUP-Center for Drug Discovery and Innovative Medicines, University of Porto, Porto, Portugal
| | - Patrício Soares-da-Silva
- Department of Pharmacology and Therapeutics, Faculty of Medicine, Porto, Portugal; and MedInUP-Center for Drug Discovery and Innovative Medicines, University of Porto, Porto, Portugal
| | - Fernando Magro
- Department of Pharmacology and Therapeutics, Faculty of Medicine, Porto, Portugal; and MedInUP-Center for Drug Discovery and Innovative Medicines, University of Porto, Porto, Portugal
| |
Collapse
|
11
|
Xu H, McCoy A, Li J, Zhao Y, Ghishan FK. Sodium butyrate stimulates NHE8 expression via its role on activating NHE8 basal promoter activity. Am J Physiol Gastrointest Liver Physiol 2015; 309:G500-5. [PMID: 26159698 PMCID: PMC4572406 DOI: 10.1152/ajpgi.00194.2015] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/19/2015] [Accepted: 07/06/2015] [Indexed: 01/31/2023]
Abstract
Butyrate is a major metabolite in colonic lumen. It is produced from bacterial fermentation of dietary fiber. Butyrate has been shown to stimulate electroneutral sodium absorption through its regulation on sodium/hydrogen exchanger 3 (NHE3). Although NHE8, the newest addition of intestinal NHE family, is involved in sodium absorption in the intestinal tract, whether butyrate modulates NHE8 expression in the intestinal epithelial cells is not known. In the current study, we showed that butyrate treatment strongly induced NHE8 protein and NHE8 mRNA expression in human intestinal epithelial cells. Transfection with the human NHE8 promoter reporter constructs showed that butyrate treatment stimulated reporter gene expression at an amount comparable with its stimulation of NHE8 mRNA expression. Interestingly, a similar result was also observed in human NHE8 promoter transfected cells after trichostatin (TSA) treatment. Gel mobility shift assay identified an enhanced Sp3 protein binding on the human NHE8 basal promoter region upon butyrate stimulation. Furthermore, Sp3 acetylation modification is involved in butyrate-mediated NHE8 activation in Caco-2 cells. Our findings suggest that the mechanism of butyrate action on NHE8 expression involves enhanced Sp3 interaction at the basal promoter region of the human NHE8 gene promoter to activate NHE8 gene transcription. Thus butyrate is involved in intestinal regulation of NHE8 resulting enhanced sodium absorption.
Collapse
Affiliation(s)
- Hua Xu
- University of Arizona, Tucson, Arizona
| | | | - Jing Li
- University of Arizona, Tucson, Arizona
| | - Yang Zhao
- University of Arizona, Tucson, Arizona
| | | |
Collapse
|
12
|
Muthusamy S, Cheng M, Jeong JJ, Kumar A, Dudeja PK, Malakooti J. Extracellular acidosis stimulates NHE2 expression through activation of transcription factor Egr-1 in the intestinal epithelial cells. PLoS One 2013; 8:e82023. [PMID: 24376510 PMCID: PMC3871166 DOI: 10.1371/journal.pone.0082023] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/26/2013] [Accepted: 10/29/2013] [Indexed: 01/28/2023] Open
Abstract
Na(+)/H(+) exchangers (NHEs) play important roles in regulating internal pH (pHi), cell volume and neutral Na(+) absorption in the human intestine. Earlier studies have shown that low extracellular pH (pHe) and metabolic acidosis increases the expression and function of NHE1-3 genes. However, transcriptional mechanisms involved remained unknown. Therefore, we investigated the molecular mechanisms underlying acid-induced NHE2 expression in C2BBe1 and SK-CO15 intestinal epithelial cells. Assessing total RNA and protein by RT-PCR and Western blot analysis, respectively, displayed significant increases in the NHE2 mRNA and protein levels in cells exposed to acidic media (pH 6.5 and 6.7) compared to normal medium. Acid treatment was also associated with a significant enhancement in NHE2 transport activity. Quantification of the heterogeneous nuclear RNA indicated that the rate of NHE2 transcription was increased in response to acid. Furthermore, acid caused a significant increase in NHE2 promoter activity confirming transcriptional upregulation. Through functional and mutational studies the acid-response element was mapped to a 15-nucleotide GC-rich sequence at bp -337 to -323 upstream from the transcription start site. We previously identified this element as an overlapping Egr-1/Sp1/Egr-1 motif that was essential for the NHE2 upregulation by mitogen-induced transcription factor Egr-1. Cells exposed to acid exhibited a temporal increase in Egr-1 mRNA and protein expression. These events were followed by Egr-1 nuclear accumulation, as detected by immunofluorescence microscopy, and potentiated its in vitro and in vivo interaction with the NHE2 promoter. Disruption of ESE motif and knockdown of Egr-1 expression by targeted small interfering RNA abrogated the acid-induced NHE2 transcriptional activity. These data indicate that the acid-dependent NHE2 stimulation is implemented by transcriptional upregulation of NHE2 via acid-induced Egr-1 in the intestinal epithelial cells.
Collapse
Affiliation(s)
- Saminathan Muthusamy
- Division of Gastroenterology and Hepatology, Department of Medicine, University of Illinois at Chicago, Chicago, Illinois, United States of America
| | - Ming Cheng
- Division of Gastroenterology and Hepatology, Department of Medicine, University of Illinois at Chicago, Chicago, Illinois, United States of America
| | - Jong-Jin Jeong
- Division of Gastroenterology and Hepatology, Department of Medicine, University of Illinois at Chicago, Chicago, Illinois, United States of America
| | - Anoop Kumar
- Division of Gastroenterology and Hepatology, Department of Medicine, University of Illinois at Chicago, Chicago, Illinois, United States of America
| | - Pradeep K. Dudeja
- Division of Gastroenterology and Hepatology, Department of Medicine, University of Illinois at Chicago, Chicago, Illinois, United States of America
- * E-mail:
| | - Jaleh Malakooti
- Division of Gastroenterology and Hepatology, Department of Medicine, University of Illinois at Chicago, Chicago, Illinois, United States of America
| |
Collapse
|
13
|
McCracken C, Zane A, Knight DA, Dutta PK, Waldman WJ. Minimal intestinal epithelial cell toxicity in response to short- and long-term food-relevant inorganic nanoparticle exposure. Chem Res Toxicol 2013; 26:1514-25. [PMID: 24028186 DOI: 10.1021/tx400231u] [Citation(s) in RCA: 65] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
Toxicity of commercial nanoparticles of titania, silica, and zinc oxides is being investigated in this in vitro study. Particles of these compositions are found in many food items, and thus this study is directed toward particle behavior in simulated digestion media and their interaction with intestinal epithelial cell line C2BBe1, a clone of Caco-2 cells, originally isolated from a human colon cancer. Even though the primary particle size of all three particles was below 50 nm, the particles appeared as aggregates in culture media with a negatively charged surface. In the presence of pepsin (pH 2), the charge on the titania became positive, and silica was almost neutral and aggregated extensively, whereas ZnO dissolved. For silica and titania, treatment with simulated intestinal digestive solution led to a strongly negatively charged surface and particle sizes approaching values similar to those in media. On the basis of infrared spectroscopy, we concluded that the surface of silica and titania was covered with bile salts/proteins after this treatment. Transmission electron microscopy indicated that the C2BBe1 cells internalized all three particles. Toxicity assays included investigation of necrosis, apoptosis, membrane damage, and mitochondrial activity. Titania and SiO₂ particles suspended in media at loading levels of 10 μg/cm² exhibited no toxicity. With ZnO at the same loading level, mild toxicity was observed based only on the LDH assay and decrease of mitochondrial activity and not necrosis or apoptosis. Titania particles exposed to the simulated digestion media exhibited mild toxicity based on decrease of mitochondrial activity, likely due to transport of toxic bile salts via adsorption on the particle surface.
Collapse
Affiliation(s)
- Christie McCracken
- Department of Pathology, The Ohio State University College of Medicine , Columbus, Ohio 43210, United States
| | | | | | | | | |
Collapse
|
14
|
Nanau RM, Neuman MG. Metabolome and inflammasome in inflammatory bowel disease. Transl Res 2012; 160:1-28. [PMID: 22687960 DOI: 10.1016/j.trsl.2011.08.006] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/03/2011] [Revised: 08/22/2011] [Accepted: 08/22/2011] [Indexed: 02/07/2023]
Abstract
Inflammatory bowel disease (IBD) encompasses several chronic inflammatory disorders leading to the damage of the gastrointestinal tract. The 2 principal forms of these disorders are ulcerative colitis (UC) and Crohn's disease (CD). Bacteria are involved in the etiology of IBD. Many microorganisms have been put forward as causative factors in IBD, but the primary etiologic agents are still not known. The underlying genetic, environmental, and lifestyle issues can affect the individual's predisposition to these diseases. Immune factors identified in IBD are: dysregulation of the innate and adaptive immune system directed against luminal bacteria or their products found in the intestinal lumen and inappropriate immune responses to organisms in the intestine that normally do not elicit a response, possibly because of intrinsic alterations in mucosal barrier function. However, recent advances in basic science research revealed new insights into the role of specific immune cells and their mediators in intestinal inflammation. The inflammatory mediators known as "inflammasome" are a consequence of the metabolic products (metabolom) of cells and commensal or pathogenic bacteria. Elucidation of inflammasome and metabolom has led to the development of biomarkers specific for each disease that are involved into management strategies targeted at altering specific pathogenic mechanisms that have the potential to modify or change the natural course of these disease entities. The review discusses the potential role of biomarkers in monitoring the inflammasome and therefore the severity of intestinal damage. The microbial ecosystem in the human gut in different microhabitats and metabolic niches contribute to the bowel metabolome.In addition, this review will focus on our expanding understanding of microbial factors associated with both the initiation and maintenance of IBD. New insights acquired from murine genetic models of inflammatory bowel disease will also be discussed.
Collapse
Affiliation(s)
- Radu M Nanau
- In Vitro Drug Safety and Biotechnology, University of Toronto, Toronto, Canada
| | | |
Collapse
|
15
|
Muthusamy S, Shukla S, Amin MR, Cheng M, Orenuga T, Dudeja PK, Malakooti J. PKCδ-dependent activation of ERK1/2 leads to upregulation of the human NHE2 transcriptional activity in intestinal epithelial cell line C2BBe1. Am J Physiol Gastrointest Liver Physiol 2012; 302:G317-25. [PMID: 22052014 PMCID: PMC3287399 DOI: 10.1152/ajpgi.00363.2011] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
The apical Na+/H+ exchanger (NHE) isoform NHE2 is involved in transepithelial Na+ absorption in the intestine. Our earlier studies have shown that mitogenic agent phorbol 12-myristate 13-acetate (PMA) induces the expression of NHE2 through activation of transcription factor early growth response-1 (Egr-1) and its interactions with the NHE2 promoter. However, the signaling pathways involved in transcriptional stimulation of NHE2 in response to PMA in the intestinal epithelial cells are not known. Chemical inhibitors and genetic approaches were used to investigate the signaling pathways responsible for the stimulation of NHE2 expression by PMA via Egr-1 induction. We show that, in response to PMA, PKCδ, a member of novel PKC isozymes, and MEK-ERK1/2 pathway of mitogen-activated protein kinases stimulate the NHE2 expression in C2BBe1 intestinal epithelial cells. PMA rapidly and transiently induced activation of PKCδ. Small inhibitory RNA-mediated knockdown of PKCδ blocked the stimulatory effect of PMA on the NHE2 promoter activity. In addition, blockade of PKCδ by rottlerin, a PKCδ-specific inhibitor, and ERK1/2 by U0126, a MEK-ERK inhibitor, abrogated PMA-induced Egr-1 expression. Immunofluorescence studies revealed that inhibition of ERK1/2 activation prevents translocation of PMA-induced Egr-1 into the nucleus. Consistent with these data, PMA-induced Egr-1 interaction with the NHE2 promoter region was prevented in nuclear extracts from U0126-pretreated cells. In conclusion, our data provide the first evidence that the stimulatory effect of PMA on NHE2 expression is mediated through the initial activation of PKCδ, subsequent PKCδ-dependent activation of MEK-ERK1/2 signaling pathway, and stimulation of Egr-1 expression. Furthermore, we show that transcription factor Egr-1 acts as an intermediate effector molecule that links the upstream signaling cues to the long-term stimulation of NHE2 expression by PMA in C2BBe1 cells.
Collapse
Affiliation(s)
- Saminathan Muthusamy
- Section of Digestive Diseases and Nutrition, Department of Medicine, University of Illinois at Chicago, Chicago, Illinois
| | - Sagar Shukla
- Section of Digestive Diseases and Nutrition, Department of Medicine, University of Illinois at Chicago, Chicago, Illinois
| | - Md. Ruhul Amin
- Section of Digestive Diseases and Nutrition, Department of Medicine, University of Illinois at Chicago, Chicago, Illinois
| | - Ming Cheng
- Section of Digestive Diseases and Nutrition, Department of Medicine, University of Illinois at Chicago, Chicago, Illinois
| | - Temitope Orenuga
- Section of Digestive Diseases and Nutrition, Department of Medicine, University of Illinois at Chicago, Chicago, Illinois
| | - Pradeep K. Dudeja
- Section of Digestive Diseases and Nutrition, Department of Medicine, University of Illinois at Chicago, Chicago, Illinois
| | - Jaleh Malakooti
- Section of Digestive Diseases and Nutrition, Department of Medicine, University of Illinois at Chicago, Chicago, Illinois
| |
Collapse
|
16
|
Xiao F, Juric M, Li J, Riederer B, Yeruva S, Singh AK, Zheng L, Glage S, Kollias G, Dudeja P, Tian DA, Xu G, Zhu J, Bachmann O, Seidler U. Loss of downregulated in adenoma (DRA) impairs mucosal HCO3(-) secretion in murine ileocolonic inflammation. Inflamm Bowel Dis 2012; 18:101-11. [PMID: 21557395 PMCID: PMC5426909 DOI: 10.1002/ibd.21744] [Citation(s) in RCA: 69] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/17/2011] [Accepted: 03/28/2011] [Indexed: 12/12/2022]
Abstract
BACKGROUND Ileocolonic luminal pH has been reported to be abnormally low in inflammatory bowel disease (IBD) patients, and one of the causative factors may be reduced epithelial HCO(3)(-) secretory rate (J(HCO3)(-)). Disturbances in J(HCO3)(-) may occur due to inflammation-induced changes in the crypt and villous architecture, or due to the effect of proinflammatory cytokines on epithelial ion transporters. METHODS To discriminate between these possibilities, the tumor necrosis factor alpha (TNF-α) overexpressing (TNF(+/ΔARE)) mouse model was chosen, which displays high proinflammatory cytokine levels in both ileum and colon, but develops only mild colonic histopathology and diarrhea. HCO(3)(-) secretion, mRNA expression, immunohistochemistry, and fluid absorptive capacity were measured in ileal and mid-colonic mucosa of TNF(+/ΔARE) and wildtype (WT) (TNF(+/+)) mice in Ussing chambers, and in anesthetized mice in vivo. RESULTS The high basal J(HCO3)(-) observed in WT ileal and mid-colonic mucosa were luminal Cl(-) -dependent and strongly decreased in TNF(+/ΔARE) mice. Downregulated in adenoma (DRA) mRNA and protein expression was strongly decreased in TNF(+/ΔARE) ileocolon, whereas cystic fibrosis transmembrane conductance regulator (CFTR), Na(+) /H(+) exchanger 3 (NHE3), Na(+) /HCO(3)(-) cotransporter (NBC), and epithelial sodium channel (ENaC) expression was not significantly altered. This indicates that the severe defect in ileocolonic J(HCO3)(-) was due to DRA downregulation. Fluid absorption was severely depressed in the ileum but only mildly affected in the mid-distal colon, preventing the development of overt diarrhea. CONCLUSIONS Even mild ileocolonic inflammation may result in a decrease of epithelial HCO(3)(-) secretion, which may contribute to alterations in surface pH, intestinal flora, and mucus barrier properties.
Collapse
Affiliation(s)
- Fang Xiao
- Department of Gastroenterology, Hannover Medical School, Hannover, Germany
| | - Marina Juric
- Department of Gastroenterology, Hannover Medical School, Hannover, Germany
| | - Junhua Li
- Department of Gastroenterology, Hannover Medical School, Hannover, Germany,Department of Nephrology, Tongji Hospital, Huazhong University of Science & Technology, China
| | - Brigitte Riederer
- Department of Gastroenterology, Hannover Medical School, Hannover, Germany
| | - Sunil Yeruva
- Department of Gastroenterology, Hannover Medical School, Hannover, Germany
| | - Anurag Kumar Singh
- Department of Gastroenterology, Hannover Medical School, Hannover, Germany
| | - Lifei Zheng
- Department of Gastroenterology, Hannover Medical School, Hannover, Germany,Department of Physiology, Capital Medical University, China
| | - Silke Glage
- Institute of Laboratory Animal Science, Hannover Medical School, Hannover, Germany
| | - George Kollias
- Biomedical Sciences Research Center Alexander Fleming, Greece
| | - Pradeep Dudeja
- Department of Medicine, University of Illinois, Champaign, Illinois
| | - De-An Tian
- Department of Gastroenterology, Tongji Hospital, Huazhong University of Science & Technology, China
| | - Gang Xu
- Department of Nephrology, Tongji Hospital, Huazhong University of Science & Technology, China
| | - Jinxia Zhu
- Department of Physiology, Capital Medical University, China
| | - Oliver Bachmann
- Department of Gastroenterology, Hannover Medical School, Hannover, Germany
| | - Ursula Seidler
- Department of Gastroenterology, Hannover Medical School, Hannover, Germany
| |
Collapse
|
17
|
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
|
18
|
Tang Y, Forsyth CB, Keshavarzian A. New molecular insights into inflammatory bowel disease-induced diarrhea. Expert Rev Gastroenterol Hepatol 2011; 5:615-25. [PMID: 21910579 PMCID: PMC3227675 DOI: 10.1586/egh.11.64] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
Diarrhea is one of the common symptoms that significantly affects quality of life in patients with inflammatory bowel disease (IBD). The clinical manifestation of diarrhea is mainly dependant on the type of IBD and the location, extent and severity of intestinal inflammation. Understanding the pathophysiologic mechanisms of diarrhea in patients with IBD will be beneficial to developing effective treatments for IBD-associated diarrhea. In recent years, modern molecular techniques have been used intensively to dissect the role of the intestinal microbiota, epithelial barrier and the host immune system in the mechanisms of IBD-induced diarrhea. These studies have significantly advanced our knowledge of the mechanisms of IBD-induced diarrhea. In this article, we focus on the new and critical molecular insights into the contributions of the intestinal microbiota, epithelial tight junctions, proinflammatory cytokines and microRNA as potential mechanisms underlying to IBD-induced diarrhea.
Collapse
Affiliation(s)
- Yueming Tang
- Department of Internal Medicine, Division of Digestive Disease and Nutrition, Rush University Medical Center, Chicago, IL 60612, USA.
| | - Christopher B Forsyth
- Department of Internal Medicine, Division of Digestive Disease and Nutrition, Rush University Medical Center, Chicago, IL 60612, USA,Department of Biochemistry, Division of Digestive Disease and Nutrition, Rush University Medical Center, Chicago, IL 60612, USA
| | - Ali Keshavarzian
- Department of Internal Medicine, Division of Digestive Disease and Nutrition, Rush University Medical Center, Chicago, IL 60612, USA,Department of Pharmacology, Division of Digestive Disease and Nutrition, Rush University Medical Center, Chicago, IL 60612, USA,Department of Molecular Biophysics and Physiology, Division of Digestive Disease and Nutrition, Rush University Medical Center, Chicago, IL 60612, USA
| |
Collapse
|
19
|
Abstract
The epithelial apical membrane Na+/H+ exchangers [NHE (sodium hydrogen exchanger)2 and NHE3] and Cl-/HCO3- exchangers [DRA (down-regulated in adenoma) and PAT-1 (putative anion transporter 1)] are key luminal membrane transporters involved in electroneutral NaCl absorption in the mammalian intestine. During the last decade, there has been a surge of studies focusing on the short-term regulation of these electrolyte transporters, particularly for NHE3 regulation. However, the long-term regulation of the electrolyte transporters, involving transcriptional mechanisms and transcription factors that govern their basal regulation or dysregulation in diseased states, has only now started to unfold with the cloning and characterization of their gene promoters. The present review provides a detailed analysis of the core promoters of NHE2, NHE3, DRA and PAT-1 and outlines the transcription factors involved in their basal regulation as well as in response to both physiological (butyrate, protein kinases and probiotics) and pathophysiological (cytokines and high levels of serotonin) stimuli. The information available on the transcriptional regulation of the recently identified NHE8 isoform is also highlighted. Therefore the present review bridges a gap in our knowledge of the transcriptional mechanisms underlying the alterations in the gene expression of intestinal epithelial luminal membrane Na+ and Cl- transporters involved in electroneutral NaCl absorption. An understanding of the mechanisms of the modulation of gene expression of these transporters is important for a better assessment of the pathophysiology of diarrhoea associated with inflammatory and infectious diseases and may aid in designing better management protocols.
Collapse
|