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Xu R, Höß C, Swiercz JM, Brandt DT, Lutz V, Petersen N, Li R, Zhao D, Oleksy A, Creigh-Pulatmen T, Trokter M, Fedorova M, Atzberger A, Strandby RB, Olsen AA, Achiam MP, Matthews D, Huber M, Gröne HJ, Offermanns S, Worzfeld T. A semaphorin-plexin-Rasal1 signaling pathway inhibits gastrin expression and protects against peptic ulcers. Sci Transl Med 2022; 14:eabf1922. [PMID: 35857828 DOI: 10.1126/scitranslmed.abf1922] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
Peptic ulcer disease is a frequent clinical problem with potentially serious complications such as bleeding or perforation. A decisive factor in the pathogenesis of peptic ulcers is gastric acid, the secretion of which is controlled by the hormone gastrin released from gastric G cells. However, the molecular mechanisms regulating gastrin plasma concentrations are poorly understood. Here, we identified a semaphorin-plexin signaling pathway that operates in gastric G cells to inhibit gastrin expression on a transcriptional level, thereby limiting food-stimulated gastrin release and gastric acid secretion. Using a systematic siRNA screening approach combined with biochemical, cell biology, and in vivo mouse experiments, we found that the RasGAP protein Rasal1 is a central mediator of plexin signal transduction, which suppresses gastrin expression through inactivation of the small GTPase R-Ras. Moreover, we show that Rasal1 is pathophysiologically relevant for the pathogenesis of peptic ulcers induced by nonsteroidal anti-inflammatory drugs (NSAIDs), a main risk factor of peptic ulcers in humans. Last, we show that application of recombinant semaphorin 4D alleviates peptic ulcer disease in mice in vivo, demonstrating that this signaling pathway can be harnessed pharmacologically. This study unravels a mode of G cell regulation that is functionally important in gastric homeostasis and disease.
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Affiliation(s)
- Rui Xu
- Institute of Pharmacology, University of Marburg, Marburg 35043, Germany.,Department of Pharmacology, Max Planck Institute for Heart and Lung Research, Bad Nauheim 61231, Germany
| | - Carsten Höß
- Institute of Pharmacology, University of Marburg, Marburg 35043, Germany
| | - Jakub M Swiercz
- Department of Pharmacology, Max Planck Institute for Heart and Lung Research, Bad Nauheim 61231, Germany
| | - Dominique T Brandt
- Institute of Pharmacology, University of Marburg, Marburg 35043, Germany
| | - Veronika Lutz
- Institute for Medical Microbiology and Hospital Hygiene, University of Marburg, Marburg 35043, Germany
| | - Natalia Petersen
- Novo Nordisk Foundation Center for Basic Metabolic Research, Faculty of Health Sciences, University of Copenhagen, Copenhagen 2200, Denmark
| | - Rui Li
- Department of Pharmacology, Max Planck Institute for Heart and Lung Research, Bad Nauheim 61231, Germany
| | - Dandan Zhao
- Institute of Pharmacology, University of Marburg, Marburg 35043, Germany
| | | | | | | | | | - Ann Atzberger
- Flow Cytometry Facility, Max Planck Institute for Heart and Lung Research, Bad Nauheim 61231, Germany
| | - Rune B Strandby
- Department of Surgical Gastroenterology, Rigshospitalet, University of Copenhagen, Copenhagen 2100, Denmark
| | - August A Olsen
- Department of Surgical Gastroenterology, Rigshospitalet, University of Copenhagen, Copenhagen 2100, Denmark
| | - Michael P Achiam
- Department of Surgical Gastroenterology, Rigshospitalet, University of Copenhagen, Copenhagen 2100, Denmark
| | | | - Magdalena Huber
- Institute for Medical Microbiology and Hospital Hygiene, University of Marburg, Marburg 35043, Germany
| | - Hermann-Josef Gröne
- Institute of Pharmacology, University of Marburg, Marburg 35043, Germany.,Medical Faculty, University of Heidelberg, Heidelberg 69120, Germany
| | - Stefan Offermanns
- Department of Pharmacology, Max Planck Institute for Heart and Lung Research, Bad Nauheim 61231, Germany.,Medical Faculty, University of Frankfurt, Frankfurt 60590, Germany
| | - Thomas Worzfeld
- Institute of Pharmacology, University of Marburg, Marburg 35043, Germany.,Department of Pharmacology, Max Planck Institute for Heart and Lung Research, Bad Nauheim 61231, Germany
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2
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ElObeid AS, Haseeb A. Treating ENT symptoms and diseases induced by extraesophageal acidity using plant extracted melanin. Med Hypotheses 2020; 144:110126. [PMID: 32758902 DOI: 10.1016/j.mehy.2020.110126] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/12/2020] [Accepted: 07/18/2020] [Indexed: 10/23/2022]
Affiliation(s)
| | - Adil Haseeb
- Department of Physics, Faculty of Science, University of Khartoum, Sudan
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3
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Abstract
Gastric acid secretion (i) facilitates digestion of protein as well as absorption of micronutrients and certain medications, (ii) kills ingested microorganisms, including Helicobacter pylori, and (iii) prevents bacterial overgrowth and enteric infection. The principal regulators of acid secretion are the gastric peptides gastrin and somatostatin. Gastrin, the major hormonal stimulant for acid secretion, is synthesized in pyloric mucosal G cells as a 101-amino acid precursor (preprogastrin) that is processed to yield biologically active amidated gastrin-17 and gastrin-34. The C-terminal active site of gastrin (Trp-Met-Asp-Phe-NH2 ) binds to gastrin/CCK2 receptors on parietal and, more importantly, histamine-containing enterochromaffin-like (ECL) cells, located in oxyntic mucosa, to induce acid secretion. Histamine diffuses to the neighboring parietal cells where it binds to histamine H2 -receptors coupled to hydrochloric acid secretion. Gastrin is also a trophic hormone that maintains the integrity of gastric mucosa, induces proliferation of parietal and ECL cells, and is thought to play a role in carcinogenesis. Somatostatin, present in D cells of the gastric pyloric and oxyntic mucosa, is the main inhibitor of acid secretion, particularly during the interdigestive period. Somatostatin exerts a tonic paracrine restraint on gastrin secretion from G cells, histamine secretion from ECL cells, and acid secretion from parietal cells. Removal of this restraint, for example by activation of cholinergic neurons during ingestion of food, initiates and maximizes acid secretion. Knowledge regarding the structure and function of gastrin, somatostatin, and their respective receptors is providing novel avenues to better diagnose and manage acid-peptic disorders and certain cancers. Published 2020. Compr Physiol 10:197-228, 2020.
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Affiliation(s)
- Mitchell L Schubert
- Division of Gastroenterology, Department of Medicine, Virginia Commonwealth University Health System, Richmond, Virginia, USA.,Hunter Holmes McGuire Veterans Affairs Medical Center, Richmond, Virginia, USA
| | - Jens F Rehfeld
- Department of Clinical Biochemistry, Rigshospitalet, University of Copenhagen, Copenhagen, Denmark
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4
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Xian Y, Zhao X, Wang C, Kang C, Ding L, Zhu W, Hang S. Phenylalanine and tryptophan stimulate gastrin and somatostatin secretion and H +-K +-ATPase activity in pigs through calcium-sensing receptor. Gen Comp Endocrinol 2018; 267:1-8. [PMID: 29782837 DOI: 10.1016/j.ygcen.2018.05.022] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/16/2018] [Revised: 04/28/2018] [Accepted: 05/17/2018] [Indexed: 11/20/2022]
Abstract
In rodents and humans, aromatic amino acids increase gut hormone secretion and H+-K+-ATPase activity by modulating calcium-sensing receptor (CaSR). However, the role of CaSR and its related signaling molecules in amino acid-induced gut hormone secretion in swine has not been investigated. Here, we examined whether a CaSR-dependent pathway modulated gastrin and somatostatin (SS) secretion and H+-K+-ATPase activity in pigs. Perfusion of pig stomach tissues in the presence of extracellular 80 mM l-phenylalanine (Phe) or 20 mM l-tryptophan (Trp) and a CaSR agonist cinacalcet triggered gastrin and SS secretion and H+-K+-ATPase activity (P < 0.05) and increased CaSR expression (P < 0.05). This effect of Phe and Trp was dependent on Ca2+ (P < 0.05) and was abolished after treatment with NPS 2143, an inhibitor of CaSR, and 2-aminoethyl diphenyl borinate, an inhibitor of CaSR downstream signaling molecule inositol 1,4,5-triphosphate receptor (IP3R). These findings indicate that Phe and Trp induce Ca2+-dependent gastrin and SS secretion and H+-K+-ATPase activity through CaSR and its downstream signaling molecule IP3R.
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Affiliation(s)
- Yihan Xian
- Laboratory of Gastrointestinal Microbiology, Nanjing Agriculture University, Nanjing, Jiangsu 210095, China
| | - Xiuying Zhao
- Laboratory of Gastrointestinal Microbiology, Nanjing Agriculture University, Nanjing, Jiangsu 210095, China
| | - Chao Wang
- Laboratory of Gastrointestinal Microbiology, Nanjing Agriculture University, Nanjing, Jiangsu 210095, China
| | - Cuicui Kang
- Laboratory of Gastrointestinal Microbiology, Nanjing Agriculture University, Nanjing, Jiangsu 210095, China
| | - Liren Ding
- Laboratory of Gastrointestinal Microbiology, Nanjing Agriculture University, Nanjing, Jiangsu 210095, China
| | - Weiyun Zhu
- Laboratory of Gastrointestinal Microbiology, Nanjing Agriculture University, Nanjing, Jiangsu 210095, China
| | - Suqin Hang
- Laboratory of Gastrointestinal Microbiology, Nanjing Agriculture University, Nanjing, Jiangsu 210095, China.
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5
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Calcium-sensing receptor in nutrient sensing: an insight into the modulation of intestinal homoeostasis. Br J Nutr 2018; 120:881-890. [DOI: 10.1017/s0007114518002088] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
AbstractThe animal gut effectively prevents the entry of hazardous substances and microbes while permitting the transfer of nutrients, such as water, electrolytes, vitamins, proteins, lipids, carbohydrates, minerals and microbial metabolites, which are intimately associated with intestinal homoeostasis. The gut maintains biological functions through its nutrient-sensing receptors, including the Ca-sensing receptor (CaSR), which activates a variety of signalling pathways, depending on cellular context. CaSR coordinates food digestion and nutrient absorption, promotes cell proliferation and differentiation, regulates energy metabolism and immune response, stimulates hormone secretion, mitigates secretory diarrhoea and enhances intestinal barrier function. Thus, CaSR is crucial to the maintenance of gut homoeostasis and protection of intestinal health. In this review, we focused on the emerging roles of CaSR in the modulation of intestinal homoeostasis including related underlying mechanisms. By elucidating the relationship between CaSR and animal gut homoeostasis, effective and inexpensive methods for treating intestinal health imbalance through nutritional manipulation can be developed. This article is expected to provide experimental data of the effects of CaSR on animal or human health.
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Guo Y, Yang X, He J, Liu J, Yang S, Dong H. Important roles of the Ca 2+-sensing receptor in vascular health and disease. Life Sci 2018; 209:217-227. [PMID: 30098342 DOI: 10.1016/j.lfs.2018.08.016] [Citation(s) in RCA: 29] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/23/2018] [Revised: 07/30/2018] [Accepted: 08/06/2018] [Indexed: 02/07/2023]
Abstract
Ca2+-sensing receptor (CaSR), a member of G protein-coupled receptor family, is widely expressed in the vascular system, including perivascular neurons, vascular endothelial cells (VECs) and vascular smooth muscle cells (VSMCs). When stimulated, CaSR can further increase the cytosolic Ca2+ concentration ([Ca2+]cyt) in two ways: intracellular Ca2+ release from endo/sarcoplasmic reticulum (ER/SR) and extracellular Ca2+ entry through Ca2+-permeable cation channels. In endothelium, increased Ca2+ subsequently activate nitric oxide synthase (NOS) and intermediate conductance Ca2+-activated K+ channels (IKCa), resulting in vasodilation through NOS-mediated NO release or membrane hyperpolarization. In VSMCs, CaSR-induced intracellular Ca2+ increase causes blood vessel constriction. CaSR activation predominantly induces vasorelaxation of whole vascular tissues through VECs-dependent mechanisms; however, CaSR-induced Ca2+ signaling in VSMCs may play a braking role in CaSR-mediated vasorelaxation. Emerging evidence reveals the importance of CaSR in the regulation of vascular tone and blood pressure. Here, we summarized recent advances in CaSR-mediated vascular reaction and the underlying mechanisms in different species, including humans. In addition, several studies have demonstrated that CaSR dysfunction may be associated with some fatal vascular diseases, such as pulmonary arterial hypertension, primary hypertension, diabetes, acute myocardial infarction and vascular calcification. With the advance of studies on CaSR in vascular health and disease, it is expected positive modulators or negative modulators of CaSR used for the treatment of specific diseases may be promising therapeutic options for the prevention and/or treatment of vascular diseases.
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Affiliation(s)
- Yanjun Guo
- Department of Gastroenterology, Xinqiao Hospital, Army Medical University, Chongqing, China
| | - Xin Yang
- Department of Gastroenterology, Xinqiao Hospital, Army Medical University, Chongqing, China
| | - Jialin He
- Department of Gastroenterology, Xinqiao Hospital, Army Medical University, Chongqing, China
| | - Jingjing Liu
- Department of Gastroenterology, Xinqiao Hospital, Army Medical University, Chongqing, China
| | - Shiming Yang
- Department of Gastroenterology, Xinqiao Hospital, Army Medical University, Chongqing, China
| | - Hui Dong
- Department of Gastroenterology, Xinqiao Hospital, Army Medical University, Chongqing, China.
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7
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Kitay AM, Schneebacher MT, Schmitt A, Heschl K, Kopic S, Alfadda T, Alsaihati A, Link A, Geibel JP. Modulations in extracellular calcium lead to H +-ATPase-dependent acid secretion: a clarification of PPI failure. Am J Physiol Gastrointest Liver Physiol 2018. [PMID: 29517927 DOI: 10.1152/ajpgi.00132.2017] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
The H+,K+-ATPase was identified as the primary proton secretory pathway in the gastric parietal cell and is the pharmacological target of agents suppressing acid secretion. Recently, we identified a second acid secretory protein expressed in the parietal cell, the vacuolar H+-ATPase (V-type ATPase). The aim of the present study was to further characterize H+-ATPase activation by modulations in extracellular calcium via the calcium sensing receptor (CaSR). Isolated gastric glands were loaded with the pH indicator dye BCECF-AM [2',7'-bis-(2-carboxyethyl)-5-(and-6)-carboxyfluorescein acetoxymethyl ester] to measure intracellular pH. Experiments were conducted in the absence of sodium and potassium to monitor H+-ATPase-specific transport activity. CaSR was activated with the calcimimetic R568 (400 nM) and/or by modulations in extracellular Ca2+. Elevation in calcium concentrations increased proton extrusion from the gastric parietal cell. Allosteric modification of the CaSR via R568 and calcium increased vacuolar H+-ATPase activity significantly (ΔpH/minlowCa2+(0.1mM) = 0.001 ± 0.001, ΔpH/minnormalCa2+(1.0mM) = 0.033 ± 0.004, ΔpH/minhighCa2+(5.0mM) = 0.051 ± 0.005). Carbachol significantly suppressed calcium-induced gastric acid secretion via the H+-ATPase under sodium- and potassium-free conditions. We conclude that the V-type H+-ATPase is tightly linked to CaSR activation. We observed that proton pump inhibitor (PPI) exposure does not modulate H+-ATPase activity. This elevated blood calcium activation of the H+-ATPase could provide an explanation for recurrent reflux symptoms while taking a PPI therapy. NEW & NOTEWORTHY This study emphasizes the role of the H+-ATPase in acid secretion. We further demonstrate the modification of this proton excretion pathway by extracellular calcium and the activation of the calcium sensing receptor CaSR. The novelty of this paper is based on the modulation of the H+-ATPase via both extracellular Ca (activation) and the classical secretagogues histamine and carbachol (inactivation). Both activation and inactivation of this proton pump are independent of PPI modulation.
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Affiliation(s)
- Alice Miriam Kitay
- Department of Surgery, Yale University School of Medicine , New Haven, Connecticut.,Department of Gastroenterology, Hepatology and Infectious Diseases, Otto-von-Guericke University, Magdeburg, Gemany
| | | | - Anne Schmitt
- Department of Surgery, Yale University School of Medicine , New Haven, Connecticut
| | - Katharina Heschl
- Department of Surgery, Yale University School of Medicine , New Haven, Connecticut
| | - Sascha Kopic
- Department of Surgery, Yale University School of Medicine , New Haven, Connecticut.,Department of Cellular and Molecular Physiology, Yale University School of Medicine , New Haven, Connecticut
| | - Tariq Alfadda
- Department of Surgery, Yale University School of Medicine , New Haven, Connecticut
| | - Abrar Alsaihati
- Department of Surgery, Yale University School of Medicine , New Haven, Connecticut
| | - Alexander Link
- Department of Gastroenterology, Hepatology and Infectious Diseases, Otto-von-Guericke University, Magdeburg, Gemany
| | - John Peter Geibel
- Department of Surgery, Yale University School of Medicine , New Haven, Connecticut.,Department of Cellular and Molecular Physiology, Yale University School of Medicine , New Haven, Connecticut
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8
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Kitay AM, Geibel JP. Stomach and Bone. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2017; 1033:97-131. [DOI: 10.1007/978-3-319-66653-2_6] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
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9
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Zhang C, Miller CL, Gorkhali R, Zou J, Huang K, Brown EM, Yang JJ. Molecular Basis of the Extracellular Ligands Mediated Signaling by the Calcium Sensing Receptor. Front Physiol 2016; 7:441. [PMID: 27746744 PMCID: PMC5043022 DOI: 10.3389/fphys.2016.00441] [Citation(s) in RCA: 37] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/03/2016] [Accepted: 09/16/2016] [Indexed: 12/20/2022] Open
Abstract
Ca2+-sensing receptors (CaSRs) play a central role in regulating extracellular calcium concentration ([Ca2+]o) homeostasis and many (patho)physiological processes in multiple organs. This regulation is orchestrated by a cooperative response to extracellular stimuli such as small changes in Ca2+, Mg2+, amino acids, and other ligands. In addition, CaSR is a pleiotropic receptor regulating several intracellular signaling pathways, including calcium mobilization and intracellular calcium oscillation. Nearly 200 mutations and polymorphisms have been found in CaSR in relation to a variety of human disorders associated with abnormal Ca2+ homeostasis. In this review, we summarize efforts directed at identifying binding sites for calcium and amino acids. Both homotropic cooperativity among multiple calcium binding sites and heterotropic cooperativity between calcium and amino acid were revealed using computational modeling, predictions, and site-directed mutagenesis coupled with functional assays. The hinge region of the bilobed Venus flytrap (VFT) domain of CaSR plays a pivotal role in coordinating multiple extracellular stimuli, leading to cooperative responses from the receptor. We further highlight the extensive number of disease-associated mutations that have also been shown to affect CaSR's cooperative action via several types of mechanisms. These results provide insights into the molecular bases of the structure and functional cooperativity of this receptor and other members of family C of the G protein-coupled receptors (cGPCRs) in health and disease states, and may assist in the prospective development of novel receptor-based therapeutics.
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Affiliation(s)
- Chen Zhang
- Department of Chemistry, Georgia State University Atlanta, GA, USA
| | | | - Rakshya Gorkhali
- Department of Chemistry, Georgia State University Atlanta, GA, USA
| | - Juan Zou
- Department of Chemistry, Georgia State University Atlanta, GA, USA
| | - Kenneth Huang
- Department of Chemistry, Georgia State University Atlanta, GA, USA
| | - Edward M Brown
- Center for Diagnostics and Therapeutics, Georgia State UniversityAtlanta, GA, USA; Division of Endocrinology, Diabetes and Hypertension, Department of Medicine, Brigham and Women's HospitalBoston, MA, USA
| | - Jenny J Yang
- Department of Chemistry, Georgia State University Atlanta, GA, USA
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10
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Tang L, Cheng CY, Sun X, Pedicone AJ, Mohamadzadeh M, Cheng SX. The Extracellular Calcium-Sensing Receptor in the Intestine: Evidence for Regulation of Colonic Absorption, Secretion, Motility, and Immunity. Front Physiol 2016; 7:245. [PMID: 27458380 PMCID: PMC4914593 DOI: 10.3389/fphys.2016.00245] [Citation(s) in RCA: 24] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/23/2016] [Accepted: 06/03/2016] [Indexed: 12/14/2022] Open
Abstract
Different from other epithelia, the intestinal epithelium has the complex task of providing a barrier impeding the entry of toxins, food antigens, and microbes, while at the same time allowing for the transfer of nutrients, electrolytes, water, and microbial metabolites. These molecules/organisms are transported either transcellularly, crossing the apical and basolateral membranes of enterocytes, or paracellularly, passing through the space between enterocytes. Accordingly, the intestinal epithelium can affect energy metabolism, fluid balance, as well as immune response and tolerance. To help accomplish these complex tasks, the intestinal epithelium has evolved many sensing receptor mechanisms. Yet, their roles and functions are only now beginning to be elucidated. This article explores one such sensing receptor mechanism, carried out by the extracellular calcium-sensing receptor (CaSR). In addition to its established function as a nutrient sensor, coordinating food digestion, nutrient absorption, and regulating energy metabolism, we present evidence for the emerging role of CaSR in the control of intestinal fluid homeostasis and immune balance. An additional role in the modulation of the enteric nerve activity and motility is also discussed. Clearly, CaSR has profound effects on many aspects of intestinal function. Nevertheless, more work is needed to fully understand all functions of CaSR in the intestine, including detailed mechanisms of action and specific pathways involved. Considering the essential roles CaSR plays in gastrointestinal physiology and immunology, research may lead to a translational opportunity for the development of novel therapies that are based on CaSR's unique property of using simple nutrients such as calcium, polyamines, and certain amino acids/oligopeptides as activators. It is possible that, through targeting of intestinal CaSR with a combination of specific nutrients, oral solutions that are both inexpensive and practical may be developed to help in conditioning the gut microenvironment and in maintaining digestive health.
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Affiliation(s)
- Lieqi Tang
- Department of Pediatrics, Gastroenterology, Hepatology, and Nutrition, University of Florida Gainesville, FL, USA
| | - Catherine Y Cheng
- Department of Pediatrics, Gastroenterology, Hepatology, and Nutrition, University of Florida Gainesville, FL, USA
| | - Xiangrong Sun
- Department of Pediatrics, Gastroenterology, Hepatology, and Nutrition, University of Florida Gainesville, FL, USA
| | - Alexandra J Pedicone
- Department of Pediatrics, Gastroenterology, Hepatology, and Nutrition, University of Florida Gainesville, FL, USA
| | - Mansour Mohamadzadeh
- Department of Medicine, Center for Inflammation and Mucosal Immunology, University of Florida Gainesville, FL, USA
| | - Sam X Cheng
- Department of Pediatrics, Gastroenterology, Hepatology, and Nutrition, University of Florida Gainesville, FL, USA
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Abstract
The present review examines the pig as a model for physiological studies in human subjects related to nutrient sensing, appetite regulation, gut barrier function, intestinal microbiota and nutritional neuroscience. The nutrient-sensing mechanisms regarding acids (sour), carbohydrates (sweet), glutamic acid (umami) and fatty acids are conserved between humans and pigs. In contrast, pigs show limited perception of high-intensity sweeteners and NaCl and sense a wider array of amino acids than humans. Differences on bitter taste may reflect the adaptation to ecosystems. In relation to appetite regulation, plasma concentrations of cholecystokinin and glucagon-like peptide-1 are similar in pigs and humans, while peptide YY in pigs is ten to twenty times higher and ghrelin two to five times lower than in humans. Pigs are an excellent model for human studies for vagal nerve function related to the hormonal regulation of food intake. Similarly, the study of gut barrier functions reveals conserved defence mechanisms between the two species particularly in functional permeability. However, human data are scant for some of the defence systems and nutritional programming. The pig model has been valuable for studying the changes in human microbiota following nutritional interventions. In particular, the use of human flora-associated pigs is a useful model for infants, but the long-term stability of the implanted human microbiota in pigs remains to be investigated. The similarity of the pig and human brain anatomy and development is paradigmatic. Brain explorations and therapies described in pig, when compared with available human data, highlight their value in nutritional neuroscience, particularly regarding functional neuroimaging techniques.
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12
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Regulation of α-Transducin and α-Gustducin Expression by a High Protein Diet in the Pig Gastrointestinal Tract. PLoS One 2016; 11:e0148954. [PMID: 26871573 PMCID: PMC4752509 DOI: 10.1371/journal.pone.0148954] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/19/2015] [Accepted: 01/25/2016] [Indexed: 11/29/2022] Open
Abstract
Background The expression of taste receptors (TASRs) and their signalling molecules in the gastrointestinal (GI) epithelial cells, including enteroendocrine cells (EECs), suggests they participate in chemosensing mechanisms influencing GI physiology via the release of endocrine messengers. TASRs mediate gustatory signalling by interacting with different transducers, including α-gustducin (Gαgust) and α-transducin (Gαtran) G protein subunits. This study tested whether Gαtran and Gαgust immunoreactive (-IR) cells are affected by a short-term (3 days) and long-term (30 days) high protein (Hp) diet in the pig GI tract. Result In the stomach, Gαgust and Gαtran-IR cells contained serotonin (5-HT) and ghrelin (GHR), while in the small and large intestine, Gαgust and Gαtran-IR colocalized with 5-HT-, cholecystokinin (CCK)- and peptide YY (PYY)-IR. There was a significant increase in the density of Gαtran-IR cells in the pyloric mucosa in both short- and long-term Hp diet groups (Hp3 and Hp30) vs. the control group (Ctr) (P<0.05), while the increase of Gαgust-IR cells in the pyloric mucosa was significant in Hp30 group vs. Ctr and vs. Hp3 (P<0.05); these cells included Gαtran / 5HT-IR and Gαtran / GHR-IR cells (P<0.05 and P<0.001 vs. Ctr, respectively) as well as Gαgust /5-HT-IR or Gαgust / GHR-IR cells (P<0.05 and P<0.01 vs. Ctr, respectively). In the small intestine, we recorded a significant increase in Gαtran-IR cells in the duodenal crypts and a significant increase of Gαgust-IR cells in the jejunal crypts in Hp3 group compared to HP30 (P<0.05). With regard to the number of Gαtran-Gαgust IR cells colocalized with CCK or 5-HT, there was only a significant increase of Gαtran / CCK-IR cells in Hp3 group compared to Ctr (P = 0.01). Conclusion This study showed an upregulation of selected subpopulations of Gαgust / Gαtran-IR cells in distinct regions of the pig GI tract by short- and long-term Hp diet lending support to TASR-mediated effects in metabolic homeostasis and satiety mechanisms.
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13
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Jeong S, Kim JH, Kim MG, Han N, Kim IW, Kim T, Oh JM. Genetic polymorphisms of CASR and cancer risk: evidence from meta-analysis and HuGE review. Onco Targets Ther 2016; 9:655-69. [PMID: 26929638 PMCID: PMC4755434 DOI: 10.2147/ott.s97602] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022] Open
Abstract
Background CASR gene appears to be involved in cancer biology and physiology. However, a number of studies investigating CASR polymorphisms and cancer risks have presented inconclusive results. Thus, a systematic review and a meta-analysis of the effect of CASR polymorphisms on several cancer risks were performed to suggest a statistical evidence for the association of CASR polymorphisms with cancer risks. Methods MEDLINE, EMBASE, Web of Science, Scopus, and the HuGE databases were searched. Nineteen articles of case–control and cohort studies were included for the final analysis. Results The colorectal cancer risk was reduced in proximal (odds ratio [OR] =0.679, P=0.001) and distal (OR =0.753, P=0.026) colon sites with GG genotype of CASR rs1042636 and increased in distal colon site (OR =1.418, P=0.039) with GG genotype of rs1801726 by additive genetic model. The rs17251221 demonstrated noticeable associations that carrying a homozygote variant increases breast and prostate cancer risk considerably. Conclusion The significant association of CASR polymorphisms with several cancer risks was observed in this review. In particular, the act of CASR polymorphisms as a tumor suppressor or an oncogene differs by cancer site and can be the research target for tumorigenesis.
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Affiliation(s)
- Sohyun Jeong
- College of Pharmacy and Research Institute of Pharmaceutical Sciences, Seoul National University, Seoul, South Korea
| | - Jae Hyun Kim
- College of Pharmacy and Research Institute of Pharmaceutical Sciences, Seoul National University, Seoul, South Korea
| | - Myeong Gyu Kim
- College of Pharmacy and Research Institute of Pharmaceutical Sciences, Seoul National University, Seoul, South Korea
| | - Nayoung Han
- College of Pharmacy and Research Institute of Pharmaceutical Sciences, Seoul National University, Seoul, South Korea
| | - In-Wha Kim
- College of Pharmacy and Research Institute of Pharmaceutical Sciences, Seoul National University, Seoul, South Korea
| | - Therasa Kim
- College of Pharmacy and Research Institute of Pharmaceutical Sciences, Seoul National University, Seoul, South Korea
| | - Jung Mi Oh
- College of Pharmacy and Research Institute of Pharmaceutical Sciences, Seoul National University, Seoul, South Korea
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Tae CH, Shim KN, Kim HI, Joo YH, Lee JH, Cho MS, Moon CM, Kim SE, Jung HK, Jung SA. Significance of calcium-sensing receptor expression in gastric cancer. Scand J Gastroenterol 2016; 51:67-72. [PMID: 26153034 DOI: 10.3109/00365521.2015.1064993] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
OBJECTIVE The calcium-sensing receptor (CaSR) is known to have differential expression in various carcinomas and normal tissues. It has been shown to be involved in carcinogenesis or tumor suppression. However, its role in gastric cancer remains unknown. This study was performed to determine the CaSR expression level in gastric cancer and non-tumor gastric tissues and to examine the related clinicopathological factors. MATERIALS AND METHODS Thirty-one pairs of gastric cancer tissues and matched non-tumor gastric tissues were obtained from surgical tissues after gastrectomy. Using real-time polymerase chain reaction, we measured CaSR mRNA expression. We evaluated the association between CaSR mRNA expression and clinicopathological variables based on the downregulation or upregulation of CaSR mRNA expression in gastric cancer tissues compared to those of matched non-tumor gastric tissues. By immunohistochemistry, we confirmed CaSR expression levels in gastric cancer tissues. RESULTS Downregulation of CaSR mRNA was observed in 77.4% of gastric cancer tissues compared to their matched normal tissues. Downregulated CaSR was associated with a tendency for deeper invasion into the proper muscle (p = 0.028) and more advanced stage (II-IV; p = 0.012). CONCLUSION We conclude that downregulation of CaSR may contribute to the prevention or suppression of tumor outgrowth.
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Affiliation(s)
- Chung Hyun Tae
- a 1 Department of Health Promotion Medicine, Ewha Womans University School of Medicine, Ewha Medical Research Institute , Seoul, Korea
| | - Ki-Nam Shim
- b 2 Department of Internal Medicine, Ewha Womans University School of Medicine, Ewha Medical Research Institute , Seoul, Korea
| | - Hye In Kim
- b 2 Department of Internal Medicine, Ewha Womans University School of Medicine, Ewha Medical Research Institute , Seoul, Korea
| | - Yang-Hee Joo
- b 2 Department of Internal Medicine, Ewha Womans University School of Medicine, Ewha Medical Research Institute , Seoul, Korea
| | - Joo-Ho Lee
- c 3 Department of Surgery, Ewha Womans University School of Medicine, Ewha Medical Research Institute , Seoul, Korea
| | - Min-Sun Cho
- d 4 Department of Pathology, Ewha Womans University School of Medicine, Ewha Medical Research Institute , Seoul, Korea
| | - Chang Mo Moon
- b 2 Department of Internal Medicine, Ewha Womans University School of Medicine, Ewha Medical Research Institute , Seoul, Korea
| | - Seong-Eun Kim
- b 2 Department of Internal Medicine, Ewha Womans University School of Medicine, Ewha Medical Research Institute , Seoul, Korea
| | - Hye-Kyung Jung
- b 2 Department of Internal Medicine, Ewha Womans University School of Medicine, Ewha Medical Research Institute , Seoul, Korea
| | - Sung-Ae Jung
- b 2 Department of Internal Medicine, Ewha Womans University School of Medicine, Ewha Medical Research Institute , Seoul, Korea
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Symonds EL, Peiris M, Page AJ, Chia B, Dogra H, Masding A, Galanakis V, Atiba M, Bulmer D, Young RL, Blackshaw LA. Mechanisms of activation of mouse and human enteroendocrine cells by nutrients. Gut 2015; 64:618-26. [PMID: 25015642 PMCID: PMC4392230 DOI: 10.1136/gutjnl-2014-306834] [Citation(s) in RCA: 74] [Impact Index Per Article: 8.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/18/2014] [Revised: 05/16/2014] [Accepted: 06/06/2014] [Indexed: 01/05/2023]
Abstract
OBJECTIVE Inhibition of food intake and glucose homeostasis are both promoted when nutrients stimulate enteroendocrine cells (EEC) to release gut hormones. Several specific nutrient receptors may be located on EEC that respond to dietary sugars, amino acids and fatty acids. Bypass surgery for obesity and type II diabetes works by shunting nutrients to the distal gut, where it increases activation of nutrient receptors and mediator release, but cellular mechanisms of activation are largely unknown. We determined which nutrient receptors are expressed in which gut regions and in which cells in mouse and human, how they are associated with different types of EEC, how they are activated leading to hormone and 5-HT release. DESIGN AND RESULTS mRNA expression of 17 nutrient receptors and EEC mediators was assessed by quantitative PCR and found throughout mouse and human gut epithelium. Many species similarities emerged, in particular the dense expression of several receptors in the distal gut. Immunolabelling showed specific colocalisation of receptors with EEC mediators PYY and GLP-1 (L-cells) or 5-HT (enterochromaffin cells). We exposed isolated proximal colonic mucosa to specific nutrients, which recruited signalling pathways within specific EEC extracellular receptor-regulated kinase (p-ERK) and calmodulin kinase II (pCAMKII), as shown by subsequent immunolabelling, and activated release of these mediators. Aromatic amino acids activated both pathways in mouse, but in humans they induced only pCAMKII, which was colocalised mainly with 5-HT expression. Activation was pertussis toxin-sensitive. Fatty acid (C12) potently activated p-ERK in human in all EEC types and evoked potent release of all three mediators. CONCLUSIONS Specific nutrient receptors associate with distinct activation pathways within EEC. These may provide discrete, complementary pharmacological targets for intervention in obesity and type II diabetes.
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Affiliation(s)
- Erin L Symonds
- Nerve-Gut Research Laboratory, Hanson Institute, Royal Adelaide Hospital, Adelaide, South Australia, Australia
| | - Madusha Peiris
- Wingate Institute of Neurogastroenterology, Blizard Institute, Barts and The London School of Medicine & Dentistry, Queen Mary, University of London, London, UK
| | - Amanda J Page
- Nerve-Gut Research Laboratory, Hanson Institute, Royal Adelaide Hospital, Adelaide, South Australia, Australia
- Discipline of Medicine, University of Adelaide, Adelaide, South Australia, Australia
| | - Bridgette Chia
- Nerve-Gut Research Laboratory, Hanson Institute, Royal Adelaide Hospital, Adelaide, South Australia, Australia
| | - Harween Dogra
- Wingate Institute of Neurogastroenterology, Blizard Institute, Barts and The London School of Medicine & Dentistry, Queen Mary, University of London, London, UK
| | - Abigail Masding
- Wingate Institute of Neurogastroenterology, Blizard Institute, Barts and The London School of Medicine & Dentistry, Queen Mary, University of London, London, UK
| | - Vasileios Galanakis
- Wingate Institute of Neurogastroenterology, Blizard Institute, Barts and The London School of Medicine & Dentistry, Queen Mary, University of London, London, UK
| | - Michael Atiba
- Wingate Institute of Neurogastroenterology, Blizard Institute, Barts and The London School of Medicine & Dentistry, Queen Mary, University of London, London, UK
| | - David Bulmer
- Wingate Institute of Neurogastroenterology, Blizard Institute, Barts and The London School of Medicine & Dentistry, Queen Mary, University of London, London, UK
| | - Richard L Young
- Nerve-Gut Research Laboratory, Hanson Institute, Royal Adelaide Hospital, Adelaide, South Australia, Australia
- Discipline of Medicine, University of Adelaide, Adelaide, South Australia, Australia
| | - L Ashley Blackshaw
- Wingate Institute of Neurogastroenterology, Blizard Institute, Barts and The London School of Medicine & Dentistry, Queen Mary, University of London, London, UK
- Discipline of Medicine, University of Adelaide, Adelaide, South Australia, Australia
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16
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Zhang C, Miller CL, Brown EM, Yang JJ. The calcium sensing receptor: from calcium sensing to signaling. SCIENCE CHINA-LIFE SCIENCES 2015; 58:14-27. [DOI: 10.1007/s11427-014-4779-y] [Citation(s) in RCA: 32] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/17/2014] [Accepted: 10/21/2014] [Indexed: 12/14/2022]
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Leach K, Sexton PM, Christopoulos A, Conigrave AD. Engendering biased signalling from the calcium-sensing receptor for the pharmacotherapy of diverse disorders. Br J Pharmacol 2014; 171:1142-55. [PMID: 24111791 DOI: 10.1111/bph.12420] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/29/2013] [Revised: 08/22/2013] [Accepted: 08/26/2013] [Indexed: 12/14/2022] Open
Abstract
The human calcium-sensing receptor (CaSR) is widely expressed in the body, where its activity is regulated by multiple orthosteric and endogenous allosteric ligands. Each ligand stabilizes a unique subset of conformational states, which enables the CaSR to couple to distinct intracellular signalling pathways depending on the extracellular milieu in which it is bathed. Differential signalling arising from distinct receptor conformations favoured by each ligand is referred to as biased signalling. The outcome of CaSR activation also depends on the cell type in which it is expressed. Thus, the same ligand may activate diverse pathways in distinct cell types. Given that the CaSR is implicated in numerous physiological and pathophysiological processes, it is an ideal target for biased ligands that could be rationally designed to selectively regulate desired signalling pathways in preferred cell types.
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Affiliation(s)
- K Leach
- Pharmaceutical Sciences, Monash University, Melbourne, Vic., Australia
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18
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Emerging roles of the extracellular calcium-sensing receptor in nutrient sensing: control of taste modulation and intestinal hormone secretion. Br J Nutr 2014; 111 Suppl 1:S16-22. [PMID: 24382107 DOI: 10.1017/s0007114513002250] [Citation(s) in RCA: 37] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
The extracellular Ca-sensing receptor (CaSR) is a sensor for a number of key nutrients within the body, including Ca ions (Ca²⁺) and L-amino acids. The CaSR is expressed in a number of specialised cells within the gastrointestinal (GI) tract, and much work has been done to examine CaSR's role as a nutrient sensor in this system. This review article examines two emerging roles for the CaSR within the GI tract--as a mediator of kokumi taste modulation in taste cells and as a regulator of dietary hormone release in response to L-amino acids in the intestine.
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19
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Zhang C, Huang Y, Jiang Y, Mulpuri N, Wei L, Hamelberg D, Brown EM, Yang JJ. Identification of an L-phenylalanine binding site enhancing the cooperative responses of the calcium-sensing receptor to calcium. J Biol Chem 2014; 289:5296-309. [PMID: 24394414 DOI: 10.1074/jbc.m113.537357] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022] Open
Abstract
Functional positive cooperative activation of the extracellular calcium ([Ca(2+)]o)-sensing receptor (CaSR), a member of the family C G protein-coupled receptors, by [Ca(2+)]o or amino acids elicits intracellular Ca(2+) ([Ca(2+)]i) oscillations. Here, we report the central role of predicted Ca(2+)-binding site 1 within the hinge region of the extracellular domain (ECD) of CaSR and its interaction with other Ca(2+)-binding sites within the ECD in tuning functional positive homotropic cooperativity caused by changes in [Ca(2+)]o. Next, we identify an adjacent L-Phe-binding pocket that is responsible for positive heterotropic cooperativity between [Ca(2+)]o and L-Phe in eliciting CaSR-mediated [Ca(2+)]i oscillations. The heterocommunication between Ca(2+) and an amino acid globally enhances functional positive homotropic cooperative activation of CaSR in response to [Ca(2+)]o signaling by positively impacting multiple [Ca(2+)]o-binding sites within the ECD. Elucidation of the underlying mechanism provides important insights into the longstanding question of how the receptor transduces signals initiated by [Ca(2+)]o and amino acids into intracellular signaling events.
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Affiliation(s)
- Chen Zhang
- From the Department of Chemistry, Center for Diagnostics and Therapeutics, Georgia State University, Atlanta, Georgia 30303 and
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20
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Squires PE, Jones PM, Younis MYG, Hills CE. The calcium-sensing receptor and β-cell function. VITAMINS AND HORMONES 2014; 95:249-67. [PMID: 24559921 DOI: 10.1016/b978-0-12-800174-5.00010-7] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/06/2022]
Abstract
In addition to its central role controlling systemic calcium homeostasis, the extracellular calcium-sensing receptor (CaSR) can be found on multiple cell types not associated with controlling plasma calcium. The endocrine pancreas is one such tissue, and it is apparent that the receptor plays an important role in regulating β-cell function. During exocytosis, divalent cations are coreleased with insulin and their concentration within the restricted intercellular compartments of the pancreatic islet increases sufficiently to activate the CaSR on neighboring cells. Acute and chronic activation of the receptor has multiple effects on the β-cell, from increasing cadherin-based cell-cell adhesion to directly altering the expression and function of various potassium and voltage-dependent calcium channels. The promiscuous activation of multiple binding partners improves cell adhesion, cell coupling, and cell-to-cell communication within the islet and is the basis for the effect of the CaSR on β-cell function and improved glucose responsiveness.
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Affiliation(s)
- Paul E Squires
- School of Life Sciences, University of Warwick, Coventry, United Kingdom.
| | - Peter M Jones
- Diabetes & Nutritional Sciences Division, School of Medicine, King's College London, London, United Kingdom
| | - Mustafa Y G Younis
- School of Life Sciences, University of Warwick, Coventry, United Kingdom
| | - Claire E Hills
- School of Life Sciences, University of Warwick, Coventry, United Kingdom
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21
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Wauson EM, Lorente-Rodríguez A, Cobb MH. Minireview: Nutrient sensing by G protein-coupled receptors. Mol Endocrinol 2013; 27:1188-97. [PMID: 23820899 DOI: 10.1210/me.2013-1100] [Citation(s) in RCA: 64] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023] Open
Abstract
G protein-coupled receptors (GPCRs) are membrane proteins that recognize molecules in the extracellular milieu and transmit signals inside cells to regulate their behaviors. Ligands for many GPCRs are hormones or neurotransmitters that direct coordinated, stereotyped adaptive responses. Ligands for other GPCRs provide information to cells about the extracellular environment. Such information facilitates context-specific decision making that may be cell autonomous. Among ligands that are important for cellular decisions are amino acids, required for continued protein synthesis, as metabolic starting materials and energy sources. Amino acids are detected by a number of class C GPCRs. One cluster of amino acid-sensing class C GPCRs includes umami and sweet taste receptors, GPRC6A, and the calcium-sensing receptor. We have recently found that the umami taste receptor heterodimer T1R1/T1R3 is a sensor of amino acid availability that regulates the activity of the mammalian target of rapamycin. This review focuses on an array of findings on sensing amino acids and sweet molecules outside of neurons by this cluster of class C GPCRs and some of the physiologic processes regulated by them.
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Affiliation(s)
- Eric M Wauson
- Department of Pharmacology, University of Texas Southwestern Medical Center at Dallas, Dallas, Texas 75390-9041, USA
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22
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Epithelial calcium-sensing receptor activation by eosinophil granule protein analog stimulates collagen matrix contraction. Pediatr Res 2013; 73:414-9. [PMID: 23269116 PMCID: PMC4321999 DOI: 10.1038/pr.2012.198] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
BACKGROUND Eosinophils reside in normal gastrointestinal tracts and increase during disease states. Receptors for eosinophil-derived granule proteins (EDGPs) have not been identified, but highly cationic molecules, similar to eosinophil proteins, bind extracellular calcium-sensing receptors (CaSRs). We hypothesized that stimulation of CaSRs by eosinophil proteins activates epithelial cells. METHODS Caco2 intestinal epithelial cells, AML14.3D10 eosinophils, wild-type (WT) human embryonic kidney 293 (HEK293) cells not expressing CaSRs (HEK-WT), and CaSR-transfected HEK293 cells (HEK-CaSR) were stimulated with an eosinophil protein analog poly-L-arginine (PA) and phosphorylated extracellular signal-regulated kinase (pERK)1 and pERK2 were measured. Functional activation was measured with collagen lattice contraction assays. RESULTS Coculture of Caco2 cells with AML14.3D10 eosinophils augmented lattice contraction as compared with lattices containing Caco2 cells alone. PA stimulation of Caco2 lattices augmented contraction. HEK-CaSR stimulation with PA or Ca(2+) resulted in greater pERK activation than that of stimulated HEK-WT cells. PA stimulated greater HEK-CaSR lattice contraction than unstimulated lattices. Contraction of PA-stimulated and PA-unstimulated HEK-WT lattices did not differ. CONCLUSION Exposure of intestinal epithelia to the EDGP analog PA stimulates CaSR-dependent ERK phosphorylation and epithelial-mediated collagen lattice contraction. We speculate that EDGP release within the epithelial layers activates the CaSR receptor, leading to matrix contraction and tissue fibrosis.
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23
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Kopic S, Geibel JP. Gastric acid, calcium absorption, and their impact on bone health. Physiol Rev 2013; 93:189-268. [PMID: 23303909 DOI: 10.1152/physrev.00015.2012] [Citation(s) in RCA: 102] [Impact Index Per Article: 9.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
Calcium balance is essential for a multitude of physiological processes, ranging from cell signaling to maintenance of bone health. Adequate intestinal absorption of calcium is a major factor for maintaining systemic calcium homeostasis. Recent observations indicate that a reduction of gastric acidity may impair effective calcium uptake through the intestine. This article reviews the physiology of gastric acid secretion, intestinal calcium absorption, and their respective neuroendocrine regulation and explores the physiological basis of a potential link between these individual systems.
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Affiliation(s)
- Sascha Kopic
- Department of Surgery and Cellular and Molecular Physiology, Yale School of Medicine, New Haven, Connecticut, USA
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24
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Abstract
PURPOSE OF REVIEW This review summarizes the past year's literature regarding the regulation of gastric exocrine and endocrine secretion, both basic science and clinical. RECENT FINDINGS Gastric acid secretion facilitates the digestion of protein as well as the absorption of iron, calcium, vitamin B12, and certain medications as well as prevents bacterial overgrowth, enteric infection, and possibly community-acquired pneumonia, spontaneous bacterial peritonitis, and IgE-mediated food allergy. It is regulated by neural (e.g., pituitary adenylate cyclase-activating peptide), hormonal (e.g., gastrin, ghrelin, and apelin), and paracrine (e.g., histamine) pathways as well as by chemical (e.g., amino acids) and bacterial stimuli (e.g., Helicobacter pylori). Novel peptides, which may possess physiologic function, have been identified in gastric mucosal neuroendocrine cells including parathyroid hormone-like hormone in histamine-secreting enterochromaffin-like cells and hepcidin in acid-secreting parietal cells. The secretion of hydrochloric acid by parietal cells involves translocation of the proton pump, HK-ATPase, to the apical membrane along with activation of apical chloride and potassium channels. Serum markers include chromogranin A for neuroendocrine tumors, pepsinogen I for gastric atrophy, and pepsinogen II for H. pylori infection. SUMMARY We continue to make progress in our understanding of the regulation of gastric acid secretion in health and disease.
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25
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Page AJ, Symonds E, Peiris M, Blackshaw LA, Young RL. Peripheral neural targets in obesity. Br J Pharmacol 2012; 166:1537-58. [PMID: 22432806 PMCID: PMC3419899 DOI: 10.1111/j.1476-5381.2012.01951.x] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/25/2011] [Revised: 02/20/2012] [Accepted: 02/22/2012] [Indexed: 12/15/2022] Open
Abstract
Interest in pharmacological treatments for obesity that act in the brain to reduce appetite has increased exponentially over recent years, but failures of clinical trials and withdrawals due to adverse effects have so far precluded any success. Treatments that do not act within the brain are, in contrast, a neglected area of research and development. This is despite the fact that a vast wealth of molecular mechanisms exists within the gut epithelium and vagal afferent system that could be manipulated to increase satiety. Here we discuss mechano- and chemosensory pathways from the gut involved in appetite suppression, and distinguish between gastric and intestinal vagal afferent pathways in terms of their basic physiology and activation by enteroendocrine factors. Gastric bypass surgery makes use of this system by exposing areas of the intestine to greater nutrient loads resulting in greater satiety hormone release and reduced food intake. A non-surgical approach to this system is preferable for many reasons. This review details where the opportunities may lie for such approaches by describing nutrient-sensing mechanisms throughout the gastrointestinal tract.
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Affiliation(s)
- Amanda J Page
- Nerve-Gut Research Laboratory, Discipline of Medicine, South Australia, Australia
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Mace OJ, Schindler M, Patel S. The regulation of K- and L-cell activity by GLUT2 and the calcium-sensing receptor CasR in rat small intestine. J Physiol 2012; 590:2917-36. [PMID: 22495587 DOI: 10.1113/jphysiol.2011.223800] [Citation(s) in RCA: 183] [Impact Index Per Article: 15.3] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
Intestinal enteroendocrine cells (IECs) secrete gut peptides in response to both nutrients and non-nutrients. Glucose and amino acids both stimulate gut peptide secretion. Our hypothesis was that the facilitative glucose transporter, GLUT2, could act as a glucose sensor and the calcium-sensing receptor, CasR, could detect amino acids in the intestine to modify gut peptide secretion. We used isolated loops of rat small intestine to study the secretion of gluco-insulinotropic peptide (GIP), glucagon-like peptide-1 (GLP-1) and peptide tyrosine tyrosine (PYY) secretion stimulated by luminal perfusion of nutrients or bile acid. Inhibition of the sodium-dependent glucose cotransporter 1 (SGLT1) with phloridzin partially inhibited GIP, GLP-1 and PYY secretion by 45%, suggesting another glucose sensor might be involved in modulating peptide secretion. The response was completely abolished in the presence of the GLUT2 inhibitors phloretin or cytochalasin B. Given that GLUT2 modified gut peptide secretion stimulated by glucose, we investigated whether it was involved in the secretion of gut peptide by other gut peptide secretagogues. Phloretin completely abolished gut peptide secretion stimulated by artificial sweetener (sucralose), dipeptide (glycylsarcosine), lipid (oleoylethanolamine), short chain fatty acid (propionate) and major rat bile acid (taurocholate) indicating a fundamental position for GLUT2 in the gut peptide secretory mechanism. We investigated how GLUT2 was able to influence gut peptide secretion mediated by a diverse range of stimulators and discovered that GLUT2 affected membrane depolarisation through the closure of K+(ATP)-sensitive channels. In the absence of SGLT1 activity (or presence of phloridzin), the secretion of GIP, GLP-1 and PYY was sensitive to K+(ATP)-sensitive channel modulators tolbutamide and diazoxide. L-amino acids phenylalanine (Phe), tryptophan (Trp), asparagine (Asn), arginine (Arg) and glutamine (Gln) also stimulated GIP, GLP-1 and PYY secretion, which was completely abolished when extracellular Ca2+ was absent. The gut peptide response stimulated by the amino acids was also blocked by the CasR inhibitor Calhex 231 and augmented by the CasR agonist NPS-R568. GLUT2 and CasR regulate K- and L-cell activity in response to nutrient and non-nutrient stimuli.
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Haid DC, Jordan-Biegger C, Widmayer P, Breer H. Receptors responsive to protein breakdown products in g-cells and d-cells of mouse, swine and human. Front Physiol 2012; 3:65. [PMID: 22514536 PMCID: PMC3322525 DOI: 10.3389/fphys.2012.00065] [Citation(s) in RCA: 46] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/27/2012] [Accepted: 03/05/2012] [Indexed: 11/13/2022] Open
Abstract
Monitoring the luminal content in the stomach is of vital importance for adjusting the gastric activities, including the release of gastric hormones such as gastrin. Our previous studies have shown that in mice the gastrin-secreting G-cells express receptor types which are responsive to amino acids. Since the pig is considered as more suitable model for studying gastro-physiological aspects relevant for men, in this study we have analyzed the distribution of G-cells and D-cells in the gastric antrum of men, swine, and mouse and the expression of receptor types which may render these cells responsiveness to protein breakdown products. The results indicate that the number of G-cells per antral invagination was significantly higher in swine and human compared to mice and also the distribution pattern of G-cells differed between the species. The molecular phenotyping revealed that the receptors GPRC6A and CaSR were also expressed in G-cells and in a subpopulation of D-cells from swine and men. As an additional receptor type, the peptone-receptor GPR92, was found to be expressed in G-cells and a subpopulation of D-cells; this receptor type may be particular suitable for sensing protein breakdown products and thus be a key element to adjust the activity of G-cells and D-cells according to the progress of the digestive processes in the stomach. In search for elements of an intracellular signaling cascade it was found that G-cells express the G-protein subunit Gαq as well as the phospholipase C subtype PLCβ3; in contrast, D-cells expressed the subtype PLCβ2 and neither Gαq. These results indicate that there are significant species differences concerning the number and distribution pattern, but not concerning the molecular phenotype of the gastric endocrine cells. However, G-cells and D-cells significantly differ from each other regarding the repertoire of receptors and signaling elements.
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Signaling through the extracellular calcium-sensing receptor (CaSR). ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2012; 740:103-42. [PMID: 22453940 DOI: 10.1007/978-94-007-2888-2_5] [Citation(s) in RCA: 79] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
The extracellular calcium ([Formula: see text])-sensing receptor (CaSR) was the first GPCR identified whose principal physiological ligand is an ion, namely extracellular Ca(2+). It maintains the near constancy of [Formula: see text] that complex organisms require to ensure normal cellular function. A wealth of information has accumulated over the past two decades about the CaSR's structure and function, its role in diseases and CaSR-based therapeutics. This review briefly describes the CaSR and key features of its structure and function, then discusses the extracellular signals modulating its activity, provides an overview of the intracellular signaling pathways that it controls, and, finally, briefly describes CaSR signaling both in tissues participating in [Formula: see text] homeostasis as well as those that do not. Factors controlling CaSR signaling include various factors affecting the expression of the CaSR gene as well as modulation of its trafficking to and from the cell surface. The dimeric cell surface CaSR, in turn, links to various heterotrimeric and small molecular weight G proteins to regulate intracellular second messengers, lipid kinases, various protein kinases, and transcription factors that are part of the machinery enabling the receptor to modulate the functions of the wide variety of cells in which it is expressed. CaSR signaling is impacted by its interactions with several binding partners in addition to signaling elements per se (i.e., G proteins), including filamin-A and caveolin-1. These latter two proteins act as scaffolds that bind signaling components and other key cellular elements (e.g., the cytoskeleton). Thus CaSR signaling likely does not take place randomly throughout the cell, but is compartmentalized and organized so as to facilitate the interaction of the receptor with its various signaling pathways.
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Abstract
PURPOSE OF REVIEW The review summarizes the past year's literature regarding the regulation of gastric exocrine and endocrine secretion, both basic science and clinical. RECENT FINDINGS Gastric acid secretion is an elaborate and dynamic process that is regulated by neural (efferent and afferent), hormonal (e.g. gastrin), and paracrine (e.g. histamine, ghrelin, somatostatin) pathways as well as mechanical (e.g. distension) and chemical (e.g. amino acids) stimuli. Secretion of hydrochloric acid (HCl) by parietal cells involves translocation of HK-ATPase-containing cytoplasmic tubulovesicles to the apical membrane with subsequent electroneutral transport of hydronium ions in exchange for potassium. The main apical potassium channel is KCNQ1 which, when activated, assembles with its β-subunit KCNE2 to function as a constitutively open, voltage-insensitive, and acid-resistant luminal potassium channel. Proton pump inhibitors block acid secretion by covalently binding to cysteine residues accessible from the luminal surface of the HK-ATPase. Potassium-competitive ATPase blockers (P-CABs) act by competing for K on the luminal surface of HK-ATPase. As they are acid-stable and do not require acid-dependent activation, P-CABs hold promise for rapid and prolonged inhibition of acid secretion. SUMMARY We continue to make progress in our understanding of the physiologic regulation of gastric acid secretion. A better understanding of the pathways and mechanisms regulating acid secretion should lead to improved management of patients with acid-induced disorders.
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Liou AP, Sei Y, Zhao X, Feng J, Lu X, Thomas C, Pechhold S, Raybould HE, Wank SA. The extracellular calcium-sensing receptor is required for cholecystokinin secretion in response to L-phenylalanine in acutely isolated intestinal I cells. Am J Physiol Gastrointest Liver Physiol 2011; 300:G538-46. [PMID: 21252045 PMCID: PMC3074990 DOI: 10.1152/ajpgi.00342.2010] [Citation(s) in RCA: 125] [Impact Index Per Article: 9.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
The extracellular calcium-sensing receptor (CaSR) has recently been recognized as an L-amino acid sensor and has been implicated in mediating cholecystokinin (CCK) secretion in response to aromatic amino acids. We investigated whether direct detection of L-phenylalanine (L-Phe) by CaSR results in CCK secretion in the native I cell. Fluorescence-activated cell sorting of duodenal I cells from CCK-enhanced green fluorescent protein (eGFP) transgenic mice demonstrated CaSR gene expression. Immunostaining of fixed and fresh duodenal tissue sections confirmed CaSR protein expression. Intracellular calcium fluxes were CaSR dependent, stereoselective for L-Phe over D-Phe, and responsive to type II calcimimetic cinacalcet in CCK-eGFP cells. Additionally, CCK secretion by an isolated I cell population was increased by 30 and 62% in response to L-Phe in the presence of physiological (1.26 mM) and superphysiological (2.5 mM) extracellular calcium concentrations, respectively. While the deletion of CaSR from CCK-eGFP cells did not affect basal CCK secretion, the effect of L-Phe or cinacalcet on intracellular calcium flux was lost. In fact, both secretagogues, as well as superphysiological Ca(2+), evoked an unexpected 20-30% decrease in CCK secretion compared with basal secretion in CaSR(-/-) CCK-eGFP cells. CCK secretion in response to KCl or tryptone was unaffected by the absence of CaSR. The present data suggest that CaSR is required for hormone secretion in the specific response to L-Phe by the native I cell, and that a receptor-mediated mechanism may inhibit hormone secretion in the absence of a fully functional CaSR.
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Affiliation(s)
- Alice P. Liou
- 1Digestive Diseases Branch, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, Maryland; ,2School of Veterinary Medicine, Department of Anatomy, Physiology, and Cell Biology, University of California, Davis, Davis, California; and
| | - Yoshitatsu Sei
- 1Digestive Diseases Branch, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, Maryland;
| | - Xilin Zhao
- 1Digestive Diseases Branch, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, Maryland;
| | - Jianying Feng
- 1Digestive Diseases Branch, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, Maryland;
| | - Xinping Lu
- 1Digestive Diseases Branch, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, Maryland;
| | - Craig Thomas
- 3Chemical Genomics Center, National Human Genome Research Institute, and
| | - Susanne Pechhold
- 4Diabetes Branch, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, Maryland
| | - Helen E. Raybould
- 2School of Veterinary Medicine, Department of Anatomy, Physiology, and Cell Biology, University of California, Davis, Davis, California; and
| | - Stephen A. Wank
- 1Digestive Diseases Branch, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, Maryland;
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Wang Y, Chandra R, Samsa LA, Gooch B, Fee BE, Cook JM, Vigna SR, Grant AO, Liddle RA. Amino acids stimulate cholecystokinin release through the Ca2+-sensing receptor. Am J Physiol Gastrointest Liver Physiol 2011; 300:G528-37. [PMID: 21183662 PMCID: PMC3074989 DOI: 10.1152/ajpgi.00387.2010] [Citation(s) in RCA: 125] [Impact Index Per Article: 9.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
Cholecystokinin (CCK) is produced by discrete endocrine cells in the proximal small intestine and is released following the ingestion of food. CCK is the primary hormone responsible for gallbladder contraction and has potent effects on pancreatic secretion, gastric emptying, and satiety. In addition to fats, digested proteins and aromatic amino acids are major stimulants of CCK release. However, the cellular mechanism by which amino acids affect CCK secretion is unknown. The Ca(2+)-sensing receptor (CaSR) that was originally identified on parathyroid cells is not only sensitive to extracellular Ca(2+) but is activated by extracellular aromatic amino acids. It has been postulated that this receptor may be involved in gastrointestinal hormone secretion. Using transgenic mice expressing a CCK promoter driven/enhanced green fluorescent protein (GFP) transgene, we have been able to identify and purify viable intestinal CCK cells. Intestinal mucosal CCK cells were enriched >200-fold by fluorescence-activated cell sorting. These cells were then used for real-time PCR identification of CaSR. Immunohistochemical staining with an antibody specific for CaSR confirmed colocalization of CaSR to CCK cells. In isolated CCK cells loaded with a Ca(2+)-sensitive dye, the amino acids phenylalanine and tryptophan, but not nonaromatic amino acids, caused an increase in intracellular Ca(2+) ([Ca(2+)](i)). The increase in [Ca(2+)](i) was blocked by the CaSR inhibitor Calhex 231. Phenylalanine and tryptophan stimulated CCK release from intestinal CCK cells, and this stimulation was also blocked by CaSR inhibition. Electrophysiological recordings from isolated CCK-GFP cells revealed these cells to possess a predominant outwardly rectifying potassium current. Administration of phenylalanine inhibited basal K(+) channel activity and caused CCK cell depolarization, consistent with changes necessary for hormone secretion. These findings indicate that amino acids have a direct effect on CCK cells to stimulate CCK release by activating CaSR and suggest that CaSR is the physiological mechanism through which amino acids regulate CCK secretion.
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Affiliation(s)
- Yu Wang
- Department of Medicine, Duke University and Durham Veterans Affairs Medical Centers, Durham, North Carolina
| | - Rashmi Chandra
- Department of Medicine, Duke University and Durham Veterans Affairs Medical Centers, Durham, North Carolina
| | - Leigh Ann Samsa
- Department of Medicine, Duke University and Durham Veterans Affairs Medical Centers, Durham, North Carolina
| | - Barry Gooch
- Department of Medicine, Duke University and Durham Veterans Affairs Medical Centers, Durham, North Carolina
| | - Brian E. Fee
- Department of Medicine, Duke University and Durham Veterans Affairs Medical Centers, Durham, North Carolina
| | - J. Michael Cook
- Department of Medicine, Duke University and Durham Veterans Affairs Medical Centers, Durham, North Carolina
| | - Steven R. Vigna
- Department of Medicine, Duke University and Durham Veterans Affairs Medical Centers, Durham, North Carolina
| | - Augustus O. Grant
- Department of Medicine, Duke University and Durham Veterans Affairs Medical Centers, Durham, North Carolina
| | - Rodger A. Liddle
- Department of Medicine, Duke University and Durham Veterans Affairs Medical Centers, Durham, North Carolina
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Abstract
Luminal amino acids and lack of luminal acidity as a result of acid neutralization by intragastric foodstuffs are powerful signals for acid secretion. Although the hormonal and neural pathways underlying this regulatory mechanism are well understood, the nature of the gastric luminal pH sensor has been enigmatic. In clinical studies, high pH, tryptic peptides, and luminal divalent metals (Ca2+ and Mg2+) increase gastrin release and acid production. The calcium-sensing receptor (CaSR), first described in the parathyroid gland but expressed on gastric G cells, is a logical candidate for the gastric acid sensor. Because CaSR ligands include amino acids and divalent metals, and because extracellular pH affects ligand binding in the pH range of the gastric content, its pH, metal, and nutrient-sensing functions are consistent with physiologic observations. The CaSR is thus an attractive candidate for the gastric luminal sensor that is part of the neuroendocrine negative regulatory loop for acid secretion.
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Affiliation(s)
- Tyralee Goo
- Greater Los Angeles Veteran Affairs Healthcare System, West Los Angeles VA Medical Center, Los Angeles, CA 90073, USA
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Abstract
Compelling evidence of a cell surface receptor sensitive to extracellular calcium was observed as early as the 1980s and was finally realized in 1993 when the calcium-sensing receptor (CaR) was cloned from bovine parathyroid tissue. Initial studies relating to the CaR focused on its key role in extracellular calcium homeostasis, but as the amount of information about the receptor grew it became evident that it was involved in many biological processes unrelated to calcium homeostasis. The CaR responds to a diverse array of stimuli extending well beyond that merely of calcium, and these stimuli can lead to the initiation of a wide variety of intracellular signaling pathways that in turn are able to regulate a diverse range of biological processes. It has been through the examination of the molecular characteristics of the CaR that we now have an understanding of how this single receptor is able to convert extracellular messages into specific cellular responses. Recent CaR-related reviews have focused on specific aspects of the receptor, generally in the context of the CaR's role in physiology and pathophysiology. This review will provide a comprehensive exploration of the different aspects of the receptor, including its structure, stimuli, signalling, interacting protein partners, and tissue expression patterns, and will relate their impact on the functionality of the CaR from a molecular perspective.
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Affiliation(s)
- Aaron L Magno
- Department of Endocrinology and Diabetes, First Floor, C Block, Sir Charles Gairdner Hospital, Hospital Avenue, Nedlands 6009, Western Australia, Australia
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Abstract
The upper gastrointestinal (GI) mucosa is exposed to endogenous and exogenous chemicals, including gastric acid, CO₂ and nutrients. Mucosal chemical sensors are necessary to exert physiological responses such as secretion, digestion, absorption and motility. We propose the mucosal chemosensing system by which luminal chemicals are sensed to trigger mucosal defence mechanisms via mucosal acid sensors and taste receptors. Luminal acid/CO₂ is sensed via ecto- and cytosolic carbonic anhydrases and ion transporters in the epithelial cells and via acid sensors on the afferent nerves in the duodenum and the oesophagus. Gastric acid sensing is differentially mediated via endocrine cell acid sensors and afferent nerves. Furthermore, a luminal l-glutamate signal is mediated via epithelial l-glutamate receptors, including metabotropic glutamate receptors and taste receptor 1 family heterodimers, with activation of afferent nerves and cyclooxygenase, whereas luminal Ca²(+) is differently sensed via the calcium-sensing receptor in the duodenum. These luminal chemosensors help to activate mucosal defence mechanisms in order to maintain the mucosal integrity and physiological responses of the upper GI tract. Stimulation of luminal chemosensing in the upper GI mucosa may prevent mucosal injury, affect nutrient metabolism and modulate sensory nerve activity.
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Affiliation(s)
- Y Akiba
- Department of Medicine, University of California Los Angeles, Brentwood Biomedical Research Institute, USA.
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Calcium-sensing receptor is a physiologic multimodal chemosensor regulating gastric G-cell growth and gastrin secretion. Proc Natl Acad Sci U S A 2010; 107:17791-6. [PMID: 20876097 DOI: 10.1073/pnas.1009078107] [Citation(s) in RCA: 106] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023] Open
Abstract
The calcium-sensing receptor (CaR) is the major sensor and regulator of extracellular Ca(2+), whose activity is allosterically regulated by amino acids and pH. Recently, CaR has been identified in the stomach and intestinal tract, where it has been proposed to function in a non-Ca(2+) homeostatic capacity. Luminal nutrients, such as Ca(2+) and amino acids, have been recognized for decades as potent stimulants for gastrin and acid secretion, although the molecular basis for their recognition remains unknown. The expression of CaR on gastrin-secreting G cells in the stomach and their shared activation by Ca(2+), amino acids, and elevated pH suggest that CaR may function as the elusive physiologic sensor regulating gastrin and acid secretion. The genetic and pharmacologic studies presented here comparing CaR-null mice and wild-type littermates support this hypothesis. Gavage of Ca(2+), peptone, phenylalanine, Hepes buffer (pH 7.4), and CaR-specific calcimimetic, cinacalcet, stimulated gastrin and acid secretion, whereas the calcilytic, NPS 2143, inhibited secretion only in the wild-type mouse. Consistent with known growth and developmental functions of CaR, G-cell number was progressively reduced between 30 and 90 d of age by more than 65% in CaR-null mice. These studies of nutrient-regulated G-cell gastrin secretion and growth provide definitive evidence that CaR functions as a physiologically relevant multimodal sensor. Medicinals targeting diseases of Ca(2+) homeostasis should be reviewed for effects outside traditional Ca(2+)-regulating tissues in view of the broader distribution and function of CaR.
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Konturek SJ, Bielanski W, Konturek PC, Brzozowski T. Endogenous gastric mediators: patho-physiological role and measurements. CURRENT PROTOCOLS IN TOXICOLOGY 2010; Chapter 21:Unit 21.6. [PMID: 20967748 DOI: 10.1002/0471140856.tx2106s45] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/30/2023]
Abstract
The protocols described in this unit are designed to present the major endogenous gastric mediators involved in the control of gastric acid secretion, namely gastrin and histamine, and in the regulation of gastric motility, which include motilin and ghrelin, under physiological and pathological conditions. The measurement of these mediators in plasma or serum of humans and animals by radioimmunoassay are described and their pathophysiological role is discussed.
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Young SH, Rey O, Sternini C, Rozengurt E. Amino acid sensing by enteroendocrine STC-1 cells: role of the Na+-coupled neutral amino acid transporter 2. Am J Physiol Cell Physiol 2010; 298:C1401-13. [PMID: 20219951 PMCID: PMC2889636 DOI: 10.1152/ajpcell.00518.2009] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/23/2009] [Accepted: 03/04/2010] [Indexed: 12/22/2022]
Abstract
The results presented here show that STC-1 cells, a model of intestinal endocrine cells, respond to a broad range of amino acids, including l-proline, l-serine, l-alanine, l-methionine, l-glycine, l-histidine, and alpha-methyl-amino-isobutyric acid (MeAIB) with a rapid increase in the intracellular Ca(2+) concentration ([Ca(2+)](i)). We sought to identify the mechanism by which amino acids induce Ca(2+) signaling in these cells. Several lines of evidence suggest that amino acid transport through the Na(+)-coupled neutral amino acid transporter 2 (SNAT2) is a major mechanism by which amino acids induced Ca(2+) signaling in STC-1 cells: 1) the amino acid efficacy profile for inducing Ca(2+) signaling in STC-1 cells closely matches the amino acid specificity of SNAT2; 2) amino acid-induced Ca(2+) signaling in STC-1 cells was suppressed by removing Na(+) from the medium; 3) the nonmetabolized synthetic substrate of amino acid transport MeAIB produced a marked increase in [Ca(2+)](i); 4) transfection of small interfering RNA targeting SNAT2 produced a marked decrease in Ca(2+) signaling in response to l-proline in STC-1 cells; 5) amino acid-induced increase in [Ca(2+)](i) was associated with membrane depolarization and mediated by Ca(2+) influx, since it depended on extracellular Ca(2+); 6) the increase in [Ca(2+)](i) in response to l-proline, l-alanine, or MeAIB was abrogated by either nifedipine (1-10 muM) or nitrendipine (1 muM), which block L-type voltage-sensitive Ca(2+) channels. We hypothesize that the inward current of Na(+) associated with the function of SNAT2 leads to membrane depolarization and activation of voltage-sensitive Ca(2+) channels that mediate Ca(2+) influx, thereby leading to an increase in the [Ca(2+)](i) in enteroendocrine STC-1 cells.
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Affiliation(s)
- Steven H Young
- Department of Medicine, David Geffen School of Medicine, University of California, Los Angeles, CA 90095-1786, USA
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Riccardi D, Finney BA, Wilkinson WJ, Kemp PJ. Novel regulatory aspects of the extracellular Ca2+-sensing receptor, CaR. Pflugers Arch 2009; 458:1007-22. [PMID: 19484257 DOI: 10.1007/s00424-009-0681-z] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/23/2009] [Revised: 04/30/2009] [Accepted: 05/05/2009] [Indexed: 01/15/2023]
Abstract
The capacity to sense and adapt to changes in environmental cues is of paramount importance for every living organism. From yeast to man, cells must be able to match cellular activities to growth environment and nutrient availability. Key to this process is the development of membrane-bound systems that can detect modifications in the extracellular environment and to translate these into biological responses. Evidence gathered over the last 15 years has demonstrated that many of these cell surface "sensors" belong to the G protein-coupled receptor superfamily. Crucial to our understanding of nutrient sensing in mammalian species has been the identification of the extracellular Ca(2+)/cation-sensing receptor, CaR. CaR was the first ion-sensing molecule identified in man and genetic studies in humans have revealed the importance of the CaR in mineral ion metabolism. Latter, it has become apparent that the CaR also plays an important role outside the Ca(2+) homeostatic system, as an integrator of multiple environmental signals for the regulation of many vital cellular processes, from cell-to-cell communication to secretion and cell survival/cell death. Recently, novel aspects of receptor function reveal an unexpected role for the CaR in the regulation of growth and development in utero.
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Egbuna O, Quinn S, Kantham L, Butters R, Pang J, Pollak M, Goltzman D, Brown E. The full-length calcium-sensing receptor dampens the calcemic response to 1alpha,25(OH)2 vitamin D3 in vivo independently of parathyroid hormone. Am J Physiol Renal Physiol 2009; 297:F720-8. [PMID: 19474191 DOI: 10.1152/ajprenal.00164.2009] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
1Alpha,25(OH)(2) vitamin D(3) [1,25(OH)(2)D(3)] increases serum Ca(2+) concentration in vivo, an action counteracted by activation of the Ca(2+)-sensing receptor (CaSR), which decreases parathyroid hormone (PTH) secretion and increases renal Ca(2+) excretion. Relatively little is known of the role the CaSR plays in this response through its potentially direct actions in kidney, gut, and bone independently of PTH. We report PTH-independent roles of the CaSR in modulating the response to exogenous 1,25(OH)(2)D(3) in mice with targeted disruption of both the CaSR and PTH genes (C(-)P(-)) compared with that in mice with disruption of the PTH gene alone (C(+)P(-)) or wild-type mice (C(+)P(+)). After intraperitoneal injection of 0.5 ng/g body wt 1,25(OH)(2)D(3), peak calcemic responses were observed at 24 h in all three genotypes in association with 1) a greater increase in serum Ca(2+) in C(-)P(-) mice than in the other genotypes on a Ca(2+)-replete diet that was attenuated by a Ca(2+)-deficient diet and pamidronate, 2) increased urinary Ca(2+)-to-creatinine ratios (UCa/Cr) in the C(+)P(-) and C(+)P(+) mice but a lowered ratio in the C(-)P(-) mice on a Ca(2+)-replete diet, and 3) no increase in calcitonin (CT) secretion in the C(+)P(+) and C(+)P(-) mice and a small increase in the C(-)P(-) mice. PTH deficiency had the anticipated effects on the expression of key genes involved in Ca(2+) transport at baseline in the duodenum and kidney, and injection of 1,25(OH)(2)D(3) increased gene expression 8 h later. However, the changes in the genes evaluated did not fully explain the differences in serum Ca(2+) seen among the genotypes. In conclusion, mice lacking the full-length CaSR have increased sensitivity to the calcemic action of 1,25(OH)(2)D(3) in the setting of PTH deficiency. This is principally from enhanced 1,25(OH)(2)D(3)-mediated gut Ca(2+) absorption and decreased renal Ca(2+) excretion, without any differences in bone-related release of Ca(2+) or CT secretion among the three genotypes that could explain the differences in their calcemic responses.
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Affiliation(s)
- Ogo Egbuna
- Division of Endocrinology, Diabetes and Hypertension, Brigham and Women's Hospital and Harvard Medical School, Boston, MA 02115, USA.
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Toke J, Patócs A, Gergics P, Bertalan R, Tóth M, Rácz K, Tulassay Z. [Extracellular calcium sensing under normal and pathological conditions]. Orv Hetil 2009; 150:781-90. [PMID: 19362934 DOI: 10.1556/oh.2009.28602] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
Ionic calcium has been known as an important intracellular second messenger for many decades. In addition, a whole series of experimental and clinical studies from the past fifteen years have provided evidence that extracellular ionic calcium itself is also a first messenger, since it is the ligand of a cell surface G-protein coupled receptor called calcium-sensing receptor. This review summarizes the current knowledge on the role of calcium-sensing receptor in the maintenance of calcium homeostasis, its functions in various tissues and some of the most important disorders characterized by defective calcium sensing. The inherited disorders of the calcium-sensing receptors may be classified as the results of loss-of-function and gain-of-function mutations of the calcium-sensing receptor gene. Loss-of-function heterozygous mutations lead to familial hypocalciuric hypercalcemia while homozygous mutations result in the frequently life-threatening disorder called neonatal severe hyperparathyroidism. Gain-of-function mutations of this receptor's gene cause the disorder called autosomal dominant hypocalcemia. The authors briefly highlight the clinical features, laboratory characteristics and therapeutic implications of these disorders. Also, they discuss briefly the molecular mechanisms resulting defective calcium-sensing in of patients with primary and secondary hyperparathyroidism, and summarize the results of some recent investigations on the functional consequences of genetic variants of the calcium-sensing receptor gene.
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Affiliation(s)
- Judit Toke
- Semmelweis Egyetem, Altalános Orvostudományi Kar, II. Belgyógyászati Klinika, Budapest
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Geibel JP, Hebert SC. The Functions and Roles of the Extracellular Ca2+–Sensing Receptor along the Gastrointestinal Tract. Annu Rev Physiol 2009; 71:205-17. [DOI: 10.1146/annurev.physiol.010908.163128] [Citation(s) in RCA: 99] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Affiliation(s)
- John P. Geibel
- Department of Surgery, Yale University School of Medicine, New Haven, Connecticut 06520;
| | - Steven C. Hebert
- Department of Cellular and Molecular Physiology, Yale University School of Medicine, New Haven, Connecticut 06520
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Burkitt MD, Varro A, Pritchard DM. Importance of gastrin in the pathogenesis and treatment of gastric tumors. World J Gastroenterol 2009; 15:1-16. [PMID: 19115463 PMCID: PMC2653300 DOI: 10.3748/wjg.15.1] [Citation(s) in RCA: 71] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/07/2023] Open
Abstract
In addition to regulating acid secretion, the gastric antral hormone gastrin regulates several important cellular processes in the gastric epithelium including proliferation, apoptosis, migration, invasion, tissue remodelling and angiogenesis. Elevated serum concentrations of this hormone are caused by many conditions, particularly hypochlorhydria (as a result of autoimmune or Helicobacter pylori (H pylori)-induced chronic atrophic gastritis or acid suppressing drugs) and gastrin producing tumors (gastrinomas). There is now accumulating evidence that altered local and plasma concentrations of gastrin may play a role during the development of various gastric tumors. In the absence of H pylori infection, marked hypergastrinemia frequently results in the development of gastric enterochromaffin cell-like neuroendocrine tumors and surgery to remove the cause of hypergastrinemia may lead to tumor resolution in this condition. In animal models such as transgenic INS-GAS mice, hypergastrinemia has also been shown to act as a cofactor with Helicobacter infection during gastric adenocarcinoma development. However, it is currently unclear as to what extent gastrin also modulates human gastric adenocarcinoma development. Therapeutic approaches targeting hypergastrinemia, such as immunization with G17DT, have been evaluated for the treatment of gastric adenocarcinoma, with some promising results. Although the mild hypergastrinemia associated with proton pump inhibitor drug use has been shown to cause ECL-cell hyperplasia and to increase H pylori-induced gastric atrophy, there is currently no convincing evidence that this class of agents contributes towards the development of gastric neuroendocrine tumors or gastric adenocarcinomas in human subjects.
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Ceglia L, Harris SS, Rasmussen HM, Dawson-Hughes B. Activation of the calcium sensing receptor stimulates gastrin and gastric acid secretion in healthy participants. Osteoporos Int 2009; 20:71-8. [PMID: 18536954 PMCID: PMC2716662 DOI: 10.1007/s00198-008-0637-8] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/08/2008] [Accepted: 03/11/2008] [Indexed: 11/29/2022]
Abstract
UNLABELLED In 17 adults on a fixed metabolic diet, an 11-day course of cinacalcet increased serum gastrin and basal gastric acid output, but not maximal gastric acid output, compared with a placebo. These findings indicate that the calcium sensor receptor plays a role in the regulation of gastric acid. INTRODUCTION Gastric acid secretion is a complex process regulated by neuronal and hormonal pathways. Ex vivo studies in human gastric tissues indicate that the calcium sensing receptor (CaR), expressed on the surface of G and parietal cells, may be involved in this regulation. We sought to determine whether cinacalcet, a CaR allosteric agonist, increases serum gastrin and gastric acid secretion. METHODS Seventeen healthy adults with normal gastric acid output were placed on an 18-day metabolic diet. On day 8 (baseline), participants were given cinacalcet (15 then 30 mg/day) or placebo for 11 days. Changes in gastric acid output, serum gastrin, and other measures were compared in the two groups. RESULTS Changes in serum gastrin and basal acid output (adjusted for baseline body weight) were significantly more positive in the cinacalcet group compared with placebo (P = 0.004 and P = 0.039 respectively). Change in maximal acid output was similar in the two groups (P = 0.995). As expected, cinacalcet produced significant decreases in serum PTH (P < 0.001) and ionized calcium levels (P = 0.032), and increases in serum phosphorus levels (P = 0.001) and urinary calcium (P = 0.023). CONCLUSIONS This study provides in vivo evidence that activation of the CaR increases serum gastrin levels and basal gastric acid secretion in healthy adults.
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Affiliation(s)
- L Ceglia
- Jean Mayer USDA Human Nutrition Research Center on Aging, Tufts University, 711 Washington Street, Boston, MA, 02111, USA,
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Khropycheva R, Uneyama H, Torii K, Zolotarev V. Dietary monosodium glutamate enhances gastric secretion. THE JOURNAL OF MEDICAL INVESTIGATION 2009; 56 Suppl:218-23. [DOI: 10.2152/jmi.56.218] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022]
Affiliation(s)
- Raisa Khropycheva
- Laboratory of Physiology of Digestion, Pavlov Institute of Physiology of the Russian Academy of Sciences
| | - Hisayuki Uneyama
- Physiology and Nutrition Group, Institute of Life Sciences, Ajinomoto Co., Inc
| | - Kunio Torii
- Physiology and Nutrition Group, Institute of Life Sciences, Ajinomoto Co., Inc
| | - Vasiliy Zolotarev
- Laboratory of Physiology of Digestion, Pavlov Institute of Physiology of the Russian Academy of Sciences
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Dong LM, Ulrich CM, Hsu L, Duggan DJ, Benitez DS, White E, Slattery ML, Caan BJ, Potter JD, Peters U. Genetic variation in calcium-sensing receptor and risk for colon cancer. Cancer Epidemiol Biomarkers Prev 2008; 17:2755-65. [PMID: 18843020 DOI: 10.1158/1055-9965.epi-08-0388] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022] Open
Abstract
BACKGROUND Experimental and epidemiologic studies have suggested that high calcium intake is associated with decreased colon cancer risk, yet very limited data are available for candidate genes in the calcium-vitamin D pathway and colon cancer risk. To address this, we evaluated whether calcium-sensing receptor (CASR) single-nucleotide polymorphisms are associated with colon cancer risk. We also examined interactions among CASR, calcium, and vitamin D intake and previously genotyped vitamin D-related genes. METHODS We conducted a large multicenter population-based case-control study of 1,600 cases and 1,949 controls. Seventeen tagging single-nucleotide polymorphisms for CASR were selected from common single-nucleotide polymorphisms (minor allele frequency, >or=5%) based on resequencing data. Haplotypes were estimated and evaluated using HaploStats. RESULTS We did not observe an association between any CASR genotypes or haplotypes and colon cancer risk overall. However, when stratified by anatomic site, statistically significant associations were seen with risk for proximal colon cancer [rs10934578 TT: odds ratio, 1.35; 95% confidence interval (95% CI), 1.01-1.81; rs12485716 AG/AA: odds ratio, 0.84; 95% CI, 0.71-1.00; rs4678174 CT/CC: odds ratio, 0.83; 95% CI, 0.70-0.98; rs2270916 CC: odds ratio, 0.43; 95% CI, 0.19-0.97]. Concordantly, we observed a suggested association for a CASR haplotype (rs4678174, rs2270916) with risk for proximal colon cancer (global P=0.08). We did not observe any meaningful gene-environment (calcium and vitamin D) or gene-gene (CYP24A1, CYP27B1, and VDR) interactions with CASR genotypes and colon cancer risk. CONCLUSION Our study does not provide evidence for an overall association between CASR single-nucleotide polymorphisms and colon cancer; however, results suggest a possible role of CASR on proximal colon cancer, and subsite differences are consistent with known calcium biology. Nonetheless, these findings require confirmation.
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Affiliation(s)
- Linda M Dong
- Fred Hutchinson Cancer Research Center, Seattle, WA 98109, USA
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Tfelt-Hansen J, Brown EM. THE CALCIUM-SENSING RECEPTOR IN NORMAL PHYSIOLOGY AND PATHOPHYSIOLOGY: A Review. Crit Rev Clin Lab Sci 2008; 42:35-70. [PMID: 15697170 DOI: 10.1080/10408360590886606] [Citation(s) in RCA: 173] [Impact Index Per Article: 10.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
Abstract
The discovery of a G protein-coupled, calcium-sensing receptor (CaR) a decade ago and of diseases caused by CaR mutations provided unquestionable evidence of the CaR's critical role in the maintenance of systemic calcium homeostasis. On the cell membrane of the chief cells of the parathyroid glands, the CaR "senses" the extracellular calcium concentration and, subsequently, alters the release of parathyroid hormone (PTH). The CaR is likewise functionally expressed in bone, kidney, and gut--the three major calcium-translocating organs involved in calcium homeostasis. Intracellular signal pathways to which the CaR couples via its associated G proteins include phospholipase C (PLC), protein kinase B (AKT); and mitogen-activated protein kinases (MAPKs). The receptor is widely expressed in various tissues and regulates important cellular functions in addition to its role in maintaining systemic calcium homeostasis, i.e., protection against apoptosis, cellular proliferation, and membrane voltage. Functionally significant mutations in the receptor have been shown to induce diseases of calcium homeostasis owing to changes in the set point for calcium-regulated PTH release as well as alterations in the renal handling of calcium. Gain-of-function mutations cause hypocalcemia, whereas loss-of-function mutations produce hypercalcemia. Recent studies have shown that the latter clinical presentation can also be caused by inactivating autoantibodies directed against the CaR Newly discovered type II allosteric activators of the CaR have been found to be effective as a medical treatment for renal secondary hyperparathyroidism.
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Affiliation(s)
- Jacob Tfelt-Hansen
- Laboratory of Molecular Cardiology, Medical Department B, H:S Rigshospitalet, University of Copenhagen, Copenhagen O, Denmark.
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Conigrave AD, Brown EM, Rizzoli R. Dietary Protein and Bone Health: Roles of Amino Acid–Sensing Receptors in the Control of Calcium Metabolism and Bone Homeostasis. Annu Rev Nutr 2008; 28:131-55. [DOI: 10.1146/annurev.nutr.28.061807.155328] [Citation(s) in RCA: 74] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Affiliation(s)
- A. D. Conigrave
- School of Molecular and Microbial Biosciences, University of Sydney, NSW 2006, Australia;
| | - E. M. Brown
- Division of Endocrinology, Diabetes and Hypertension, Brigham and Women's Hospital, Boston, Massachusetts
| | - R. Rizzoli
- Service of Bone Diseases, WHO Collaborating Center for Osteoporosis Prevention, Department of Rehabilitation and Geriatrics, University Hospital of Geneva, Switzerland
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48
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Schubert ML, Peura DA. Control of gastric acid secretion in health and disease. Gastroenterology 2008; 134:1842-60. [PMID: 18474247 DOI: 10.1053/j.gastro.2008.05.021] [Citation(s) in RCA: 254] [Impact Index Per Article: 15.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/06/2008] [Accepted: 04/28/2008] [Indexed: 12/16/2022]
Abstract
Recent milestones in the understanding of gastric acid secretion and treatment of acid-peptic disorders include the (1) discovery of histamine H(2)-receptors and development of histamine H(2)-receptor antagonists, (2) identification of H(+)K(+)-ATPase as the parietal cell proton pump and development of proton pump inhibitors, and (3) identification of Helicobacter pylori as the major cause of duodenal ulcer and development of effective eradication regimens. This review emphasizes the importance and relevance of gastric acid secretion and its regulation in health and disease. We review the physiology and pathophysiology of acid secretion as well as evidence regarding its inhibition in the management of acid-related clinical conditions.
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Affiliation(s)
- Mitchell L Schubert
- Department of Medicine, Division of Gastroenterology, Virginia Commonwealth University's Medical College of Virginia, McGuire Veterans Affairs Medical Center, Richmond, Virginia 23249, USA.
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49
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Jones PM, Kitsou-Mylona I, Gray E, Squires PE, Persaud SJ. Expression and function of the extracellular calcium-sensing receptor in pancreatic beta-cells. Arch Physiol Biochem 2007; 113:98-103. [PMID: 17852049 DOI: 10.1080/13813450701531185] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 10/20/2022]
Abstract
The extracellular calcium-sensing receptor (CaR) was first identified in tissues involved in systemic Ca2+ homeostasis, where it acts to sense changes in circulating Ca2+. It has since been reported that the CaR is expressed in many tissues that are not associated with Ca2+ homeostasis, including the endocrine cells in pancreatic islets of Langerhans. In the present study we have used an insulin-secreting pancreatic beta-cell line (MIN6) to investigate the expression and function of CaR, using the calcimimetic A568, a CaR agonist that activates the CaR at physiological concentrations of extracellular Ca2+ ([Ca2+]o). Immunocytochemistry, Western blotting and RT-PCR confirmed the expression of CaR in MIN6 cells. CaR activation was associated with rapid and transient increases in [Ca2+]o, which were accompanied by the initiation of a marked but transient insulin secretory response. Stimulation of beta-cell secretory activity had no detectable effect on CaR mRNA levels, but CaR mRNA was markedly reduced by configuring MIN6 cells into islet- like structures. Our data are consistent with an important function for the beta-cell CaR in cell - cell communication within islets to co-ordinate insulin secretory responses.
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Affiliation(s)
- Peter M Jones
- Beta Cell Development and Function Group, Division of Reproduction and Endocrinology, King's College London, London, UK.
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50
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D'Onghia V, Leoncini R, Carli R, Santoro A, Giglioni S, Sorbellini F, Marzocca G, Bernini A, Campagna S, Marinello E, Vannoni D. Circulating gastrin and ghrelin levels in patients with colorectal cancer: correlation with tumour stage, Helicobacter pylori infection and BMI. Biomed Pharmacother 2007; 61:137-41. [PMID: 17258885 DOI: 10.1016/j.biopha.2006.08.007] [Citation(s) in RCA: 49] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/28/2006] [Accepted: 08/23/2006] [Indexed: 12/12/2022] Open
Abstract
Many studies have pointed out a possible role of gut peptides, including gastrin and ghrelin, in the pathogenesis and natural history of gastrointestinal malignancies, one of the most common death cause in the Western world. The objective of this work is to check gastrin and ghrelin serum levels in patients with colorectal cancer according to tumour's location, stage, Helicobacter pylori infection and BMI, in order to understand the two peptides' behaviour through the tumour's natural history and evaluate their assay's use in research and clinical practice. Twenty-nine subjects affected by colorectal cancer and 50 healthy controls were studied. Circulating gastrin and ghrelin levels and H. pylori serum antibodies were assessed by radioimmunologic assay and ELISA method. Gastrin and ghrelin serum levels were respectively slightly higher and significantly lower in colon cancer patients than in controls. Gastrin levels were higher in patients carrying left colon cancer and H. pylori infection while ghrelin levels were lower in both these groups. Both hormones' serum levels decreased from tumour earlier to later stages. Significant differences persisted in the correlation between BMI and ghrelin levels in controls but not in patients. Additional studies are necessary to ascertain the significance of gastrin and ghrelin opposite behaviour in colon cancer probably linked with interferences in endocrine pathways involving other gut peptides in this compromised condition.
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Affiliation(s)
- V D'Onghia
- Dip Di Medicina Interna, Sc. Endocrino metaboliche e Biochimica, Sez. di Biochimica, Università di Siena, Via A. Moro 2, 53100 Siena, Italy
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