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McKay DM, Defaye M, Rajeev S, MacNaughton WK, Nasser Y, Sharkey KA. Neuroimmunophysiology of the gastrointestinal tract. Am J Physiol Gastrointest Liver Physiol 2024; 326:G712-G725. [PMID: 38626403 DOI: 10.1152/ajpgi.00075.2024] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/07/2024] [Revised: 04/11/2024] [Accepted: 04/15/2024] [Indexed: 04/18/2024]
Abstract
Gut physiology is the epicenter of a web of internal communication systems (i.e., neural, immune, hormonal) mediated by cell-cell contacts, soluble factors, and external influences, such as the microbiome, diet, and the physical environment. Together these provide the signals that shape enteric homeostasis and, when they go awry, lead to disease. Faced with the seemingly paradoxical tasks of nutrient uptake (digestion) and retarding pathogen invasion (host defense), the gut integrates interactions between a variety of cells and signaling molecules to keep the host nourished and protected from pathogens. When the system fails, the outcome can be acute or chronic disease, often labeled as "idiopathic" in nature (e.g., irritable bowel syndrome, inflammatory bowel disease). Here we underscore the importance of a holistic approach to gut physiology, placing an emphasis on intercellular connectedness, using enteric neuroimmunophysiology as the paradigm. The goal of this opinion piece is to acknowledge the pace of change brought to our field via single-cell and -omic methodologies and other techniques such as cell lineage tracing, transgenic animal models, methods for culturing patient tissue, and advanced imaging. We identify gaps in the field and hope to inspire and challenge colleagues to take up the mantle and advance awareness of the subtleties, intricacies, and nuances of intestinal physiology in health and disease by defining communication pathways between gut resident cells, those recruited from the circulation, and "external" influences such as the central nervous system and the gut microbiota.
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Affiliation(s)
- Derek M McKay
- Snyder Institute for Chronic Diseases, University of Calgary, Calgary, Alberta, Canada
- Gastrointestinal Research Group, University of Calgary, Calgary, Alberta, Canada
- Inflammation Research Network, University of Calgary, Calgary, Alberta, Canada
- Department of Physiology and Pharmacology, Cumming School of Medicine, University of Calgary, Calgary, Alberta, Canada
| | - Manon Defaye
- Snyder Institute for Chronic Diseases, University of Calgary, Calgary, Alberta, Canada
- Gastrointestinal Research Group, University of Calgary, Calgary, Alberta, Canada
- Inflammation Research Network, University of Calgary, Calgary, Alberta, Canada
- Department of Physiology and Pharmacology, Cumming School of Medicine, University of Calgary, Calgary, Alberta, Canada
| | - Sruthi Rajeev
- Snyder Institute for Chronic Diseases, University of Calgary, Calgary, Alberta, Canada
- Gastrointestinal Research Group, University of Calgary, Calgary, Alberta, Canada
- Inflammation Research Network, University of Calgary, Calgary, Alberta, Canada
- Department of Physiology and Pharmacology, Cumming School of Medicine, University of Calgary, Calgary, Alberta, Canada
| | - Wallace K MacNaughton
- Snyder Institute for Chronic Diseases, University of Calgary, Calgary, Alberta, Canada
- Gastrointestinal Research Group, University of Calgary, Calgary, Alberta, Canada
- Inflammation Research Network, University of Calgary, Calgary, Alberta, Canada
- Department of Physiology and Pharmacology, Cumming School of Medicine, University of Calgary, Calgary, Alberta, Canada
- Alberta Children's Hospital Research Institute, University of Calgary, Calgary, Alberta, Canada
| | - Yasmin Nasser
- Snyder Institute for Chronic Diseases, University of Calgary, Calgary, Alberta, Canada
- Gastrointestinal Research Group, University of Calgary, Calgary, Alberta, Canada
- Inflammation Research Network, University of Calgary, Calgary, Alberta, Canada
- Department of Medicine, Cumming School of Medicine, University of Calgary, Calgary, Alberta, Canada
| | - Keith A Sharkey
- Snyder Institute for Chronic Diseases, University of Calgary, Calgary, Alberta, Canada
- Gastrointestinal Research Group, University of Calgary, Calgary, Alberta, Canada
- Department of Physiology and Pharmacology, Cumming School of Medicine, University of Calgary, Calgary, Alberta, Canada
- Hotchkiss Brain Institute, University of Calgary, Calgary, Alberta, Canada
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2
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Wang B, Iglesias-Ledon L, Bishop M, Chadha A, Rudolph SE, Longo BN, Cairns DM, Chen Y, Kaplan DL. Impact of Micro- and Nano-Plastics on Human Intestinal Organoid-Derived Epithelium. Curr Protoc 2024; 4:e1027. [PMID: 38588063 DOI: 10.1002/cpz1.1027] [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] [Indexed: 04/10/2024]
Abstract
The development of patient-derived intestinal organoids represents an invaluable model for simulating the native human intestinal epithelium. These stem cell-rich cultures outperform commonly used cell lines like Caco-2 and HT29-MTX in reflecting the cellular diversity of the native intestinal epithelium after differentiation. In our recent study examining the effects of polystyrene (PS), microplastics (MPs), and nanoplastics (NPs), widespread pollutants in our environment and food chain, on the human intestinal epithelium, these organoids have been instrumental in elucidating the absorption mechanisms and potential biological impacts of plastic particles. Building on previously established protocols in human intestinal organoid culture, we herein detail a streamlined protocol for the cultivation, differentiation, and generation of organoid-derived monolayers. This protocol is tailored to generate monolayers incorporating microfold cells (M cells), key for intestinal particle uptake but often absent in current in vitro models. We provide validated protocols for the characterization of MPs/NPs via scanning electron microscopy (SEM) for detailed imaging and their introduction to intestinal epithelial monolayer cells via confocal immunostaining. Additionally, protocols to test the impacts of MP/NP exposure on the functions of the intestinal barrier using transendothelial electrical resistance (TEER) measurements and assessing inflammatory responses using cytokine profiling are detailed. Overall, our protocols enable the generation of human intestinal organoid monolayers, complete with the option of including or excluding M cells, offering crucial techniques for observing particle uptake and identifying inflammatory responses in intestinal epithelial cells to advance our knowledge of the potential effects of plastic pollution on human gut health. These approaches are also amendable to the study of other gut-related chemical and biological exposures and physiological responses due to the robust nature of the systems. © 2024 Wiley Periodicals LLC. Basic Protocol 1: Human intestinal organoid culture and generation of monolayers with and without M cells Support Protocol 1: Culture of L-WRN and production of WRN-conditioned medium Support Protocol 2: Neuronal cell culture and integration into intestinal epithelium Support Protocol 3: Immune cell culture and integration into intestinal epithelium Basic Protocol 2: Scanning electron microscopy: sample preparation and imaging Basic Protocol 3: Immunostaining and confocal imaging of MP/NP uptake in organoid-derived monolayers Basic Protocol 4: Assessment of intestinal barrier function via TEER measurements Basic Protocol 5: Cytokine profiling using ELISA post-MP/NP exposure.
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Affiliation(s)
- Brooke Wang
- Department of Biomedical Engineering, Tufts University, Medford, Massachusetts
| | | | - Matthew Bishop
- Department of Biomedical Engineering, Tufts University, Medford, Massachusetts
| | - Anushka Chadha
- Department of Biomedical Engineering, Tufts University, Medford, Massachusetts
| | - Sara E Rudolph
- Department of Biomedical Engineering, Tufts University, Medford, Massachusetts
| | - Brooke N Longo
- Department of Biomedical Engineering, Tufts University, Medford, Massachusetts
| | - Dana M Cairns
- Department of Biomedical Engineering, Tufts University, Medford, Massachusetts
| | - Ying Chen
- Department of Biomedical Engineering, Tufts University, Medford, Massachusetts
| | - David L Kaplan
- Department of Biomedical Engineering, Tufts University, Medford, Massachusetts
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Mairal A, Mehrotra S, Kumar A, Maiwal R, Marsal J, Kumar A. Hyaluronic Acid-Conjugated Thermoresponsive Polymer-Based Bioformulation Enhanced Wound Healing and Gut Barrier Repair of a TNBS-Induced Colitis Injury Ex Vivo Model in a Dynamic Perfusion Device. ACS APPLIED MATERIALS & INTERFACES 2024; 16:5382-5400. [PMID: 38266010 DOI: 10.1021/acsami.3c14113] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/26/2024]
Abstract
Impairment of intestinal epithelium is a typical feature of inflammatory bowel disease (IBD) that causes leakage of bacteria and antigens from the intestinal lumen and thus results in persistent immune activation. Hence, healing and regeneration of the damaged gut mucosa is a promising therapeutic approach to achieve deep remission in IBD. Currently, available systemic therapies have moderate effects and are often associated with numerous side effects and malignancies. In this study, we aimed to develop a topical therapy by chemically conjugating a temperature-responsive polymer, i.e., poly(N-isopropylacrylamide), along with hyaluronic acid to obtain a sprayable therapeutic formulation that upon colon instillation adheres to the damaged gut mucosa due to its temperature-induced phase transition and mucoadhesive properties. An ex vivo adhesion experiment demonstrates that this therapeutic formulation forms a thin physical coating on the mucosal lining at a physiological temperature within 5 min. Physicochemical characterization of (P(NIPAM-co-NTBAM)-HA) established this formulation to be biocompatible, hemo-compatible, and non-immunogenic. Prednisolone was encapsulated within the polymer formulation to achieve maximum therapeutic efficacy in the case of IBD-like conditions as assessed in a custom-fabricated perfusion-based ex vivo model system. Histological analysis suggests that the prednisolone-encapsulated polymer formulation nearly restored the mucosal architecture after 2,4,6-trinitrobenzenesulfonic acid-induced damage. Furthermore, a significant (p ≤ 0.001) increase in mRNA levels of Muc-2 and ZO-1 in treated groups further confirmed the mucosal epithelial barrier restoration.
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Affiliation(s)
- Ayushi Mairal
- Department of Biological Sciences and Bioengineering; Indian Institute of Technology Kanpur, Kanpur 208016, UP, India
| | - Shreya Mehrotra
- Department of Biological Sciences and Bioengineering; Indian Institute of Technology Kanpur, Kanpur 208016, UP, India
- Centre for Environmental Science and Engineering, Indian Institute of Technology Kanpur, Kanpur 208016, UP, India
| | - Anupam Kumar
- Department of Molecular and Cellular Medicine, Institute of Liver and Biliary Sciences, Vasant Kunj, New Delhi 110070, Delhi, India
| | - Rakhi Maiwal
- Department of Hepatology, Institute of Liver and Biliary Sciences, Vasant Kunj, New Delhi 110070, Delhi, India
| | - Jan Marsal
- Department of Clinical Sciences, Lund University and Skåne University Hospital, SE-22185 Lund, Sweden
| | - Ashok Kumar
- Department of Biological Sciences and Bioengineering; Indian Institute of Technology Kanpur, Kanpur 208016, UP, India
- Centre for Environmental Science and Engineering, Indian Institute of Technology Kanpur, Kanpur 208016, UP, India
- The Mehta Family Centre for Engineering in Medicine, Indian Institute of Technology Kanpur, Kanpur 208016, UP, India
- Centre for Nanosciences, Indian Institute of Technology Kanpur, Kanpur 208016, UP, India
- Centre of Excellence for Orthopedics and Prosthetics, Gangwal School of Medical Sciences and Technology, Indian Institute of Technology Kanpur, Kanpur 208016, UP, India
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Wang D, Jiang Q, Dong Z, Meng T, Hu F, Wang J, Yuan H. Nanocarriers transport across the gastrointestinal barriers: The contribution to oral bioavailability via blood circulation and lymphatic pathway. Adv Drug Deliv Rev 2023; 203:115130. [PMID: 37913890 DOI: 10.1016/j.addr.2023.115130] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/20/2023] [Revised: 09/27/2023] [Accepted: 10/27/2023] [Indexed: 11/03/2023]
Abstract
Oral administration is the preferred route of drug delivery in clinical practice due to its noninvasiveness, safety, convenience, and high patient compliance. The gastrointestinal tract (GIT) plays a crucial role in facilitating the targeted delivery of oral drugs. However, the GIT presents multiple barriers that impede drug absorption, including the gastric barrier in the stomach and the mucus and epithelial barriers in the intestine. In recent decades, nanotechnology has emerged as a promising approach for overcoming these challenges by utilizing nanocarrier-based drug delivery systems such as liposomes, micelles, polymeric nanoparticles, solid lipid nanoparticles, and inorganic nanoparticles. Encapsulating drugs within nanocarriers not only protects them from degradation but also enhances their transport and absorption across the GIT, ultimately improving oral bioavailability. The aim of this review is to elucidate the mechanisms underlying nanocarrier-mediated transportation across the GIT into systemic circulation via both the blood circulation and lymphatic pathway.
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Affiliation(s)
- Ding Wang
- College of Pharmaceutical Science, Zhejiang University, Hangzhou 310058, PR China
| | - Qi Jiang
- College of Pharmaceutical Science, Zhejiang University, Hangzhou 310058, PR China
| | - Zhefan Dong
- College of Pharmaceutical Science, Zhejiang University, Hangzhou 310058, PR China
| | - Tingting Meng
- College of Pharmaceutical Science, Zhejiang University, Hangzhou 310058, PR China
| | - Fuqiang Hu
- College of Pharmaceutical Science, Zhejiang University, Hangzhou 310058, PR China
| | - Jianwei Wang
- The Second Affiliated Hospital Zhejiang University School of Medicine, Hangzhou, 310009, PR China
| | - Hong Yuan
- College of Pharmaceutical Science, Zhejiang University, Hangzhou 310058, PR China; China Jinhua Institute of Zhejiang University, Jinhua 321299, PR China.
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Masloh S, Culot M, Gosselet F, Chevrel A, Scapozza L, Zeisser Labouebe M. Challenges and Opportunities in the Oral Delivery of Recombinant Biologics. Pharmaceutics 2023; 15:pharmaceutics15051415. [PMID: 37242657 DOI: 10.3390/pharmaceutics15051415] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/24/2023] [Revised: 04/22/2023] [Accepted: 04/24/2023] [Indexed: 05/28/2023] Open
Abstract
Recombinant biological molecules are at the cutting-edge of biomedical research thanks to the significant progress made in biotechnology and a better understanding of subcellular processes implicated in several diseases. Given their ability to induce a potent response, these molecules are becoming the drugs of choice for multiple pathologies. However, unlike conventional drugs which are mostly ingested, the majority of biologics are currently administered parenterally. Therefore, to improve their limited bioavailability when delivered orally, the scientific community has devoted tremendous efforts to develop accurate cell- and tissue-based models that allow for the determination of their capacity to cross the intestinal mucosa. Furthermore, several promising approaches have been imagined to enhance the intestinal permeability and stability of recombinant biological molecules. This review summarizes the main physiological barriers to the oral delivery of biologics. Several preclinical in vitro and ex vivo models currently used to assess permeability are also presented. Finally, the multiple strategies explored to address the challenges of administering biotherapeutics orally are described.
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Affiliation(s)
- Solene Masloh
- Laboratoire de la Barrière Hémato-Encéphalique (LBHE), Faculté des sciences Jean Perrin, University of Artois, UR 2465, Rue Jean Souvraz, 62300 Lens, France
- Affilogic, 24 Rue de la Rainière, 44300 Nantes, France
- School of Pharmaceutical Sciences, University of Geneva, 1 Rue Michel Servet, 1201 Geneva, Switzerland
- Institute of Pharmaceutical Sciences of Western Switzerland, University of Geneva, 1 Rue Michel Servet, 1201 Geneva, Switzerland
| | - Maxime Culot
- Laboratoire de la Barrière Hémato-Encéphalique (LBHE), Faculté des sciences Jean Perrin, University of Artois, UR 2465, Rue Jean Souvraz, 62300 Lens, France
| | - Fabien Gosselet
- Laboratoire de la Barrière Hémato-Encéphalique (LBHE), Faculté des sciences Jean Perrin, University of Artois, UR 2465, Rue Jean Souvraz, 62300 Lens, France
| | - Anne Chevrel
- Affilogic, 24 Rue de la Rainière, 44300 Nantes, France
| | - Leonardo Scapozza
- School of Pharmaceutical Sciences, University of Geneva, 1 Rue Michel Servet, 1201 Geneva, Switzerland
- Institute of Pharmaceutical Sciences of Western Switzerland, University of Geneva, 1 Rue Michel Servet, 1201 Geneva, Switzerland
| | - Magali Zeisser Labouebe
- School of Pharmaceutical Sciences, University of Geneva, 1 Rue Michel Servet, 1201 Geneva, Switzerland
- Institute of Pharmaceutical Sciences of Western Switzerland, University of Geneva, 1 Rue Michel Servet, 1201 Geneva, Switzerland
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Valiei A, Aminian-Dehkordi J, Mofrad MRK. Gut-on-a-chip models for dissecting the gut microbiology and physiology. APL Bioeng 2023; 7:011502. [PMID: 36875738 PMCID: PMC9977465 DOI: 10.1063/5.0126541] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/16/2022] [Accepted: 01/23/2023] [Indexed: 03/04/2023] Open
Abstract
Microfluidic technologies have been extensively investigated in recent years for developing organ-on-a-chip-devices as robust in vitro models aiming to recapitulate organ 3D topography and its physicochemical cues. Among these attempts, an important research front has focused on simulating the physiology of the gut, an organ with a distinct cellular composition featuring a plethora of microbial and human cells that mutually mediate critical body functions. This research has led to innovative approaches to model fluid flow, mechanical forces, and oxygen gradients, which are all important developmental cues of the gut physiological system. A myriad of studies has demonstrated that gut-on-a-chip models reinforce a prolonged coculture of microbiota and human cells with genotypic and phenotypic responses that closely mimic the in vivo data. Accordingly, the excellent organ mimicry offered by gut-on-a-chips has fueled numerous investigations on the clinical and industrial applications of these devices in recent years. In this review, we outline various gut-on-a-chip designs, particularly focusing on different configurations used to coculture the microbiome and various human intestinal cells. We then elaborate on different approaches that have been adopted to model key physiochemical stimuli and explore how these models have been beneficial to understanding gut pathophysiology and testing therapeutic interventions.
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Affiliation(s)
- Amin Valiei
- Molecular Cell Biomechanics Laboratory, Departments of Bioengineering and Mechanical Engineering, University of California, Berkeley, California 94720, USA
| | - Javad Aminian-Dehkordi
- Molecular Cell Biomechanics Laboratory, Departments of Bioengineering and Mechanical Engineering, University of California, Berkeley, California 94720, USA
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Lechuga S, Braga-Neto MB, Naydenov NG, Rieder F, Ivanov AI. Understanding disruption of the gut barrier during inflammation: Should we abandon traditional epithelial cell lines and switch to intestinal organoids? Front Immunol 2023; 14:1108289. [PMID: 36875103 PMCID: PMC9983034 DOI: 10.3389/fimmu.2023.1108289] [Citation(s) in RCA: 7] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/25/2022] [Accepted: 02/01/2023] [Indexed: 02/18/2023] Open
Abstract
Disruption of the intestinal epithelial barrier is a hallmark of mucosal inflammation. It increases exposure of the immune system to luminal microbes, triggering a perpetuating inflammatory response. For several decades, the inflammatory stimuli-induced breakdown of the human gut barrier was studied in vitro by using colon cancer derived epithelial cell lines. While providing a wealth of important data, these cell lines do not completely mimic the morphology and function of normal human intestinal epithelial cells (IEC) due to cancer-related chromosomal abnormalities and oncogenic mutations. The development of human intestinal organoids provided a physiologically-relevant experimental platform to study homeostatic regulation and disease-dependent dysfunctions of the intestinal epithelial barrier. There is need to align and integrate the emerging data obtained with intestinal organoids and classical studies that utilized colon cancer cell lines. This review discusses the utilization of human intestinal organoids to dissect the roles and mechanisms of gut barrier disruption during mucosal inflammation. We summarize available data generated with two major types of organoids derived from either intestinal crypts or induced pluripotent stem cells and compare them to the results of earlier studies with conventional cell lines. We identify research areas where the complementary use of colon cancer-derived cell lines and organoids advance our understanding of epithelial barrier dysfunctions in the inflamed gut and identify unique questions that could be addressed only by using the intestinal organoid platforms.
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Affiliation(s)
- Susana Lechuga
- Department of Inflammation and Immunity, Lerner Research Institute, Cleveland Clinic Foundation, Cleveland, OH, United States
| | - Manuel B. Braga-Neto
- Department of Gastroenterology, Hepatology and Nutrition, Digestive Diseases and Surgery Institute, Cleveland Clinic Foundation, Cleveland, OH, United States
| | - Nayden G. Naydenov
- Department of Inflammation and Immunity, Lerner Research Institute, Cleveland Clinic Foundation, Cleveland, OH, United States
| | - Florian Rieder
- Department of Inflammation and Immunity, Lerner Research Institute, Cleveland Clinic Foundation, Cleveland, OH, United States
- Department of Gastroenterology, Hepatology and Nutrition, Digestive Diseases and Surgery Institute, Cleveland Clinic Foundation, Cleveland, OH, United States
| | - Andrei I. Ivanov
- Department of Inflammation and Immunity, Lerner Research Institute, Cleveland Clinic Foundation, Cleveland, OH, United States
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Nie J, Liao W, Zhang Z, Zhang M, Wen Y, Capanoglu E, Sarker MMR, Zhu R, Zhao C. A 3D co-culture intestinal organoid system for exploring glucose metabolism. Curr Res Food Sci 2022; 6:100402. [DOI: 10.1016/j.crfs.2022.11.021] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/23/2022] [Revised: 11/02/2022] [Accepted: 11/25/2022] [Indexed: 11/30/2022] Open
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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.
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