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The Shaggy Dog Story of Enteric Signaling: Serotonin, a Molecular Megillah. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2022; 1383:307-318. [PMID: 36587168 DOI: 10.1007/978-3-031-05843-1_28] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Abstract
Historically and quantitatively, the enteric site of serotonin (5-HT) storage has primacy over those of any other organ. 5-HT, by the name of "enteramine", was first discovered in the bowel, and the gut produces most of the body's 5-HT. Not only does the bowel secrete 5-HT prodigiously but it also expresses a kaleidoscopic abundance of 5-HT receptors. The larger of two enteric 5-HT stores is mucosal, biosynthetically dependent upon tryptophan hydroxylase1 (TPH1), and located in EC cells. Mechanical stimuli, nutrients, luminal bacteria, and neurotransmitters such as acetylcholine and norepinephrine are all able to stimulate EC cells. Paracrine actions of 5-HT allow the mucosa to signal to neurons to initiate peristaltic and secretory reflexes as well as to inflammatory cells to promote intestinal inflammation. Endocrine effects of 5-HT allow EC cells to influence distant organs, including bone, liver, and endocrine pancreas. The smaller enteric 5-HT store is biosynthetically dependent upon TPH2 and is located within a small subset of myenteric neurons. 5-HT is responsible for slow excitatory neurotransmission manifested primarily in type II/AH neurons. Importantly, neuronal 5-HT also promotes enteric nervous system (ENS) neurogenesis, both pre- and postnatally, through 5-HT2B and especially 5-HT4 receptors. The early birth of serotonergic neurons allows these cells to function as sculptors of the mature ENS. The inactivation of secreted 5-HT depends on transmembrane transport mediated by a serotonin transporter (SERT; SLC6A4). The importance of SERT in control of 5-HT's function means that pharmacological inhibition of SERT, as well as gain- or loss-of-function mutations in SLC6A4, can exert profound effects on development and function of the ENS. Extra-enteric, TPH1-derived 5-HT from yolk sac and placenta promotes neurogenesis before enteric neurons synthesize 5-HT and contribute to ENS patterning. The impressive multi-functional nature of enteric 5-HT has made the precise identification of individual physiological roles difficult and sometimes controversial.
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Engevik M, Ruan W, Visuthranukul C, Shi Z, Engevik KA, Engevik AC, Fultz R, Schady DA, Spinler JK, Versalovic J. Limosilactobacillus reuteri ATCC 6475 metabolites upregulate the serotonin transporter in the intestinal epithelium. Benef Microbes 2021; 12:583-599. [PMID: 34550056 DOI: 10.3920/bm2020.0216] [Citation(s) in RCA: 13] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
The serotonin transporter (SERT) readily takes up serotonin (5-HT), thereby regulating the availability of 5-HT within the intestine. In the absence of SERT, 5-HT remains in the interstitial space and has the potential to aberrantly activate the many 5-HT receptors distributed on the epithelium, immune cells and enteric neurons. Perturbation of SERT is common in many gastrointestinal disorders as well as mouse models of colitis. Select commensal microbes regulate intestinal SERT levels, but the mechanism of this regulation is poorly understood. Additionally, ethanol upregulates SERT in the brain and dendritic cells, but its effects in the intestine have never been examined. We report that the intestinal commensal microbe Limosilactobacillus (previously classified as Lactobacillus) reuteri ATCC PTA 6475 secretes 83.4 mM ethanol. Consistent with the activity of L. reuteri alcohol dehydrogenases, we found that L. reuteri tolerated various levels of ethanol. Application of L. reuteri conditioned media or exogenous ethanol to human colonic T84 cells was found to upregulate SERT at the level of mRNA. A 4-(4-(dimethylamino) phenyl)-1-methylpyridinium (APP+) uptake assay confirmed the functional activity of SERT. These findings were mirrored in mouse colonic organoids, where L. reuteri metabolites and ethanol were found to upregulate SERT at the apical membrane. Finally, in a trinitrobenzene sulphonic acid model of acute colitis, we observed that mice treated with L. reuteri maintained SERT at the colon membrane compared with mice receiving phosphate buffered saline vehicle control. These data suggest that L. reuteri metabolites, including ethanol, can upregulate SERT and may be beneficial for maintaining intestinal homeostasis with respect to serotonin signalling.
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Affiliation(s)
- M Engevik
- Department of Pathology & Immunology, Baylor College of Medicine, 1 Baylor Plaza, Houston, TX 77030, USA
- Department of Regenerative Medicine & Cell Biology, Medical University of South Carolina, 173 Ashely Ave, BSB 626, Charleston, SC 29425, USA
| | - W Ruan
- Department of Pediatrics, Baylor College of Medicine, 6701 Fannin Street, Houston, TX 77030, USA
- Section of Gastroenterology, Hepatology, and Nutrition, Texas Children's Hospital, 6701 Fannin St, Houston, TX 77030, USA
| | - C Visuthranukul
- Department of Pathology & Immunology, Baylor College of Medicine, 1 Baylor Plaza, Houston, TX 77030, USA
- Pediatric Nutrition Research Unit, Department of Pediatrics, Faculty of Medicine, Chulalongkorn University, Bangkok, Thailand
| | - Z Shi
- Department of Pathology & Immunology, Baylor College of Medicine, 1 Baylor Plaza, Houston, TX 77030, USA
- Department of Pathology, Texas Children's Hospital, 6621 Fannin St, Houston, TX 77030, USA
| | - K A Engevik
- Department of Molecular Virology & Microbiology, Baylor College of Medicine, 1 Baylor Plaza, Houston, TX 7703, USA
| | - A C Engevik
- Departments of Surgery, Vanderbilt University Medical Center, 1211 Medical Center Dr, Nashville, TN 37232, USA
| | - R Fultz
- Department of Neuroscience, Cell Biology, and Anatomy, University of Texas Medical Branch, 301 University Boulevard, Galveston, TX 77555-0625, USA
| | - D A Schady
- Department of Pathology & Immunology, Baylor College of Medicine, 1 Baylor Plaza, Houston, TX 77030, USA
- Department of Pathology, Texas Children's Hospital, 6621 Fannin St, Houston, TX 77030, USA
| | - J K Spinler
- Department of Pathology & Immunology, Baylor College of Medicine, 1 Baylor Plaza, Houston, TX 77030, USA
- Department of Pathology, Texas Children's Hospital, 6621 Fannin St, Houston, TX 77030, USA
| | - J Versalovic
- Department of Pathology & Immunology, Baylor College of Medicine, 1 Baylor Plaza, Houston, TX 77030, USA
- Department of Pathology, Texas Children's Hospital, 6621 Fannin St, Houston, TX 77030, USA
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Gennari L, Merlotti D, Figura N, Mingiano C, Franci MB, Lucani B, Picchioni T, Alessandri M, Campagna MS, Gonnelli S, Bianciardi S, Materozzi M, Caffarelli C, Gonnelli S, Nuti R. Infection by CagA-Positive Helicobacter pylori Strains and Bone Fragility: A Prospective Cohort Study. J Bone Miner Res 2021; 36:80-89. [PMID: 32790186 DOI: 10.1002/jbmr.4162] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/25/2020] [Revised: 07/31/2020] [Accepted: 08/05/2020] [Indexed: 02/06/2023]
Abstract
Helicobacter pylori (HP) infection is a common and persistent disorder acting as a major cofactor for the development of upper gastrointestinal diseases and several extraintestinal disorders including osteoporosis. However, no prospective study assessed the effects of HP on bone health and fracture risk. We performed a HP screening in a population-based cohort of 1149 adults followed prospectively for up to 11 years. The presence of HP infection was assessed by serologic testing for serum antibodies to HP and the cytotoxin associated gene-A (CagA). The prevalence of HP infection did not differ among individuals with normal bone mineral density (BMD), osteoporosis, and osteopenia. However, HP infection by CagA-positive strains was significantly increased in osteoporotic (30%) and osteopenic (26%) patients respect to subjects with normal BMD (21%). Moreover, anti-CagA antibody levels were significantly and negatively associated with lumbar and femoral BMD. Consistent with these associations, patients affected by CagA-positive strains had a more than fivefold increased risk to sustain a clinical vertebral fracture (HR 5.27; 95% CI, 2.23-12.63; p < .0001) and a double risk to sustain a nonvertebral incident fracture (HR 2.09; 95% CI, 1.27-2.46; p < .005). Reduced estrogen and ghrelin levels, together with an impaired bone turnover balance after the meal were also observed in carriers of CagA-positive HP infection. HP infection by strains expressing CagA may be considered a risk factor for osteoporosis and fractures. Further studies are required to clarify in more detail the underlying pathogenetic mechanisms of this association. © 2020 American Society for Bone and Mineral Research (ASBMR).
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Affiliation(s)
- Luigi Gennari
- Department of Medicine, Surgery and Neurosciences, University of Siena, Siena, Italy
| | - Daniela Merlotti
- Department of Medicine, Surgery and Neurosciences, University of Siena, Siena, Italy
| | - Natale Figura
- Department of Medicine, Surgery and Neurosciences, University of Siena, Siena, Italy
| | - Christian Mingiano
- Department of Medicine, Surgery and Neurosciences, University of Siena, Siena, Italy
| | - Maria Beatrice Franci
- Department of Medicine, Surgery and Neurosciences, University of Siena, Siena, Italy
| | - Barbara Lucani
- Department of Medicine, Surgery and Neurosciences, University of Siena, Siena, Italy
| | - Tommaso Picchioni
- Department of Medicine, Surgery and Neurosciences, University of Siena, Siena, Italy
| | - Mario Alessandri
- Department of Medicine, Surgery and Neurosciences, University of Siena, Siena, Italy
| | - Maria Stella Campagna
- Department of Medicine, Surgery and Neurosciences, University of Siena, Siena, Italy
| | - Sara Gonnelli
- Department of Medicine, Surgery and Neurosciences, University of Siena, Siena, Italy
| | - Simone Bianciardi
- Department of Medicine, Surgery and Neurosciences, University of Siena, Siena, Italy
| | - Maria Materozzi
- Department of Medicine, Surgery and Neurosciences, University of Siena, Siena, Italy.,Department of Medical Biotechnologies, University of Siena, Siena, Italy
| | - Carla Caffarelli
- Department of Medicine, Surgery and Neurosciences, University of Siena, Siena, Italy
| | - Stefano Gonnelli
- Department of Medicine, Surgery and Neurosciences, University of Siena, Siena, Italy
| | - Ranuccio Nuti
- Department of Medicine, Surgery and Neurosciences, University of Siena, Siena, Italy
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van Bodegraven AA, Bravenboer N. Perspective on skeletal health in inflammatory bowel disease. Osteoporos Int 2020; 31:637-646. [PMID: 31822927 PMCID: PMC7075921 DOI: 10.1007/s00198-019-05234-w] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/02/2018] [Accepted: 11/14/2019] [Indexed: 12/18/2022]
Abstract
Osteopenia and osteoporosis are common features in inflammatory bowel disease (IBD), comprising both Crohn's disease and ulcerative colitis. Moreover, Crohn's disease is associated with increased fracture risk. The etiology of bone loss in IBD is multifactorial. It includes insufficient intake or absorption of calcium, vitamin D, and potassium; smoking; a low peak bone mass; a low body mass index; and decreased physical activity. In several studies, it has been shown that elevated concentrations of systemic and local pro-inflammatory cytokines, including tumor necrosis factor alpha (TNF-α), interferon-γ (IFNγ), interleukin (IL)-1β, IL-4, IL-5, IL-6, IL-13, and IL-17, present in IBD patients are potentially detrimental for bone metabolism and may be responsible for bone loss and increased fracture risk. This perspective aims to review the current literature on the role of inflammatory factors in the pathophysiology of skeletal problems in IBD and to suggest potential treatment to improve bone health, based on a combination of evidence and clinical and pathophysiological reasoning.
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Affiliation(s)
- A. A. van Bodegraven
- Department of Gastroenterology, Geriatrics, Internal and Intensive Care Medicine(Co-MIK), Zuyderland MC, Sittard-Geleen-Heerlen, Dr H van der Hoffplein 1, 6162 BG Geleen, Netherlands
- Department of Gastroenterology, Amsterdam UMC, Location Vrije Universiteit, PO Box 7057, 1007 MB Amsterdam, Netherlands
| | - N. Bravenboer
- Department of Clinical Chemistry, Research Institute Amsterdam Movement Sciences Amsterdam UMC, Location Vrije Universiteit, PO Box 7057, 1007 MB Amsterdam, Netherlands
- Department of Internal Medicine, Endocrinology Section, Centre for Bone Quality LUMC, Albinusdreef 2, Leiden, 2333 ZA Netherlands
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Pan Q, Liu Q, Wan R, Kalavagunta PK, Liu L, Lv W, Qiao T, Shang J, Wu H. Selective inhibition of intestinal 5-HT improves neurobehavioral abnormalities caused by high-fat diet mice. Metab Brain Dis 2019; 34:747-761. [PMID: 30931486 DOI: 10.1007/s11011-019-0392-x] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/22/2018] [Accepted: 01/28/2019] [Indexed: 12/16/2022]
Abstract
Recent literature reported the adverse effects of high-fat diet (HFD) on animal's emotional and cognitive function. An HFD-induced obesity/hyperlipidemia is accompanied by hormonal and neurochemical changes that can lead to depression. The important roles of gut-derived serotonin (5-Hydroxytryptamine, 5-HT) during this processing have been increasingly focused. Hence, to determine the potential role of gut-derived serotonin, HFD model was established in C57BL/6 mice. At the 4th week of feeding, a pharmacologic inhibitor of gut-derived 5-HT synthesis LP533401 (12.5 mg/kg/day), simvastatin (SIM) (5 mg/kg/day) and benzafibrate (BZ) (75 mg/kg/day) were administered for two weeks by oral gavage. Then, intraperitoneal glucose tolerance test (IPGTT), open field test (OFT), tail suspension test (TST), forced swim test (FST), sucrose preference test (SPT) were used to evaluate metabolic and neurobehavioral performances. Immunohistochemical staining, real-time quantitative PCR and other methods were to explore possible mechanisms. It was found that HFD feeding and drug treatments had some significant effects on neurobehaviors and brain: (1) All administrations reduced the total cholesterol (TC) and triglyceride (TG) parametric abnormality caused by HFD. LP533401 and SIM could significantly improve the impaired glucose tolerance, while BZ had no significant effect. (2) LP533401, SIM and BZ alleviated depression-like behavior of HFD mice in OFT, TST, FST and SPT. (3) LP533401 and SIM reversed the inhibition of Tryptophan Hydroxylase 2, Tph2 gene expression and the activation of Indoleamine 2,3-dioxy-Genase, IDO expression in HFD-treated brain, whereas BZ did not. (4) LP533401, SIM and BZ restored the inhibitory expression of 5-HT1A receptor in HFD hippocampus. Conclusions: Selective inhibition of intestinal 5-HT can attenuate depressive-like behavior, reduce 5-HT1AR impairment in hippocampus and correct abnormal 5-HT pathway in brain while ameliorating HFD-induced glucose intolerance. Further experiments are warranted to define the adequate strategy of targeting peripheral 5-HT for the treatment of such co-morbidity.
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Affiliation(s)
- Qi Pan
- State Key Laboratory of Natural Medicines, China Pharmaceutical University, Nanjing, 210009, China
- Jiangsu Key Laboratory of TCM Evaluation and Translational Research, China Pharmaceutical University, Nanjing, 211198, China
- School of Traditional Chinese Pharmacy, China Pharmaceutical University, Nanjing, 211198, China
| | - Qiongzhen Liu
- State Key Laboratory of Natural Medicines, China Pharmaceutical University, Nanjing, 210009, China
- Jiangsu Key Laboratory of TCM Evaluation and Translational Research, China Pharmaceutical University, Nanjing, 211198, China
| | - Renling Wan
- State Key Laboratory of Natural Medicines, China Pharmaceutical University, Nanjing, 210009, China
- Jiangsu Key Laboratory of TCM Evaluation and Translational Research, China Pharmaceutical University, Nanjing, 211198, China
- School of Traditional Chinese Pharmacy, China Pharmaceutical University, Nanjing, 211198, China
| | - Praveen Kumar Kalavagunta
- State Key Laboratory of Natural Medicines, China Pharmaceutical University, Nanjing, 210009, China
- Jiangsu Key Laboratory of TCM Evaluation and Translational Research, China Pharmaceutical University, Nanjing, 211198, China
- School of Traditional Chinese Pharmacy, China Pharmaceutical University, Nanjing, 211198, China
| | - Li Liu
- State Key Laboratory of Natural Medicines, China Pharmaceutical University, Nanjing, 210009, China
- Jiangsu Key Laboratory of TCM Evaluation and Translational Research, China Pharmaceutical University, Nanjing, 211198, China
- School of Traditional Chinese Pharmacy, China Pharmaceutical University, Nanjing, 211198, China
| | - Wenting Lv
- State Key Laboratory of Natural Medicines, China Pharmaceutical University, Nanjing, 210009, China
- Jiangsu Key Laboratory of TCM Evaluation and Translational Research, China Pharmaceutical University, Nanjing, 211198, China
- School of Traditional Chinese Pharmacy, China Pharmaceutical University, Nanjing, 211198, China
| | - Tong Qiao
- Vascular Surgery Department, Nanjing Drum Tower Hospital, Nanjing, 210008, China
| | - Jing Shang
- State Key Laboratory of Natural Medicines, China Pharmaceutical University, Nanjing, 210009, China.
- Jiangsu Key Laboratory of TCM Evaluation and Translational Research, China Pharmaceutical University, Nanjing, 211198, China.
- School of Traditional Chinese Pharmacy, China Pharmaceutical University, Nanjing, 211198, China.
- Qinghai Key Laboratory of Tibetan Medicine Pharmacology and Safety Evaluation, Northwest, Xining, Qinghai, China.
| | - Huali Wu
- State Key Laboratory of Natural Medicines, China Pharmaceutical University, Nanjing, 210009, China.
- Department of Pharmacology, China Pharmaceutical University, Nanjing, 210009, China.
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Pernow Y, Shahror R, Acharya S, Jahnson L, Vumma R, Venizelos N. Aberrant tryptophan transport in cultured fibroblast from patients with Male Idiopathic Osteoporosis: An in vitro study. Bone Rep 2018; 8:25-28. [PMID: 29379847 PMCID: PMC5787622 DOI: 10.1016/j.bonr.2018.01.002] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/24/2017] [Revised: 12/21/2017] [Accepted: 01/02/2018] [Indexed: 11/28/2022] Open
Abstract
It has been demonstrated, that long-term chronic tryptophan deficiency, results in decreased serotonin synthesis, which may lead to low bone mass and low bone formation. Findings from studies in male patients with idiopathic osteoporosis suggested a decreased transport of tryptophan in erythrocytes of osteoporotic patients, indicating that serotonin system defects may be involved in the etiology of low bone mass. Tryptophan is the precursor of serotonin, and a disturbed transport of tryptophan is implicated in altered serotonin synthesis. However, no study has investigated the tryptophan transport kinetics in MIO patients. The aim of this study is to investigate the kinetic parameters of tryptophan transport in fibroblasts derived from MIO patients compared to age and sex matched controls. Fibroblast cells were cultured from skin biopsies obtained from 14 patients diagnosed with Male Idiopathic Osteoporosis and from 13 healthy age-sex matched controls, without a diagnosis of osteoporosis. Transport of the amino acid tryptophan across the cell membrane was measured by the cluster tray method. The kinetic parameters, maximal transport capacity (Vmax) and affinity constant (Km) were determined by using the Lineweaver-Burke plot equation. The results of this study have shown a significantly lower mean value for Vmax (p = 0.0138) and lower Km mean value (p = 0.0009) of tryptophan transport in fibroblasts of MIO patients compared to the control group. A lower Vmax implied a decreased tryptophan transport availability in MIO patients. In conclusion, reduced cellular tryptophan availability in MIO patients might result in reduced brain serotonin synthesis and its endogenous levels in peripheral tissues, and this may contribute to low bone mass/formation. The findings of the present study could contribute to the etiology of idiopathic osteoporosis and for the development of novel approaches for diagnosis, treatment and management strategies of MIO.
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Affiliation(s)
- Ylva Pernow
- Department of Molecular Medicine and Surgery, Endocrine and Diabetes Unit, Karolinska Institutet and Karolinska University Hospital, Stockholm, Sweden
| | - Rami Shahror
- NGBI, Neuropsychiatric Research Laboratory, Faculty of Medicine and Health, School of Medical Sciences, Örebro University, SE 701 82 Örebro, Sweden
| | - Shikha Acharya
- NGBI, Neuropsychiatric Research Laboratory, Faculty of Medicine and Health, School of Medical Sciences, Örebro University, SE 701 82 Örebro, Sweden
| | - Lena Jahnson
- Department of Internal Medicine, Örebro University Hospital, SE 701 85 Örebro, Sweden
| | - Ravi Vumma
- Faculty of Health and Life Sciences, Department of Chemistry and Biomedical Sciences, Linnaeus University, SE-391 82 Kalmar, Sweden
| | - Nikolaos Venizelos
- NGBI, Neuropsychiatric Research Laboratory, Faculty of Medicine and Health, School of Medical Sciences, Örebro University, SE 701 82 Örebro, Sweden
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Kaneko Y, Onda N, Watanabe Y, Shibutani M. Identification of 5-hydroxytryptamine-producing cells by detection of fluorescence in paraffin-embedded tissue sections. Eur J Histochem 2016; 60:2684. [PMID: 27734992 PMCID: PMC5062634 DOI: 10.4081/ejh.2016.2684] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/15/2016] [Revised: 08/09/2016] [Accepted: 08/18/2016] [Indexed: 01/25/2023] Open
Abstract
5-Hydroxytryptamine (5-HT) produced by enterochromaffin (EC) cells is an important enteric mucosal signaling ligand and has been implicated in several gastrointestinal diseases, including inflammatory bowel disease and functional disorders such as irritable bowel syndrome. The present study reports a new, simple and rapid visualization method of 5-HT-producing EC cells utilizing detection of fluorescence in paraffin-embedded tissue sections after formalin fixation. In human samples, there was a high incidence of fluorescence+ cells in the 5-HT+ cells in the pyloric, small intestinal and colonic glands, while co-localization was lacking between fluorescence+ and gastrin+ cells in the pyloric and small intestinal glands. Fluorescence+ EC cells were detected in the colon of mice and rats. Fluorescence+ cells were also observed in 5-HT+ β cells in the pancreatic islets of Langerhans in pregnant mice, while non-pregnant mouse pancreatic islet cells showed no 5-HT immunoreactivity or fluorescence. These results suggest that fluorescence+ cells are identical to 5-HT+ cells, and the source of fluorescence may be 5-HT itself or molecules related to its synthesis or degradation. This fluorescence signal detection method may be applicable for monitoring of inflammatory status of inflammatory bowel diseases in both the experimental and clinical settings.
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Raghupathi R, Jessup CF, Lumsden AL, Keating DJ. Fusion Pore Size Limits 5-HT Release From Single Enterochromaffin Cell Vesicles. J Cell Physiol 2015; 231:1593-600. [PMID: 26574734 DOI: 10.1002/jcp.25256] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/28/2015] [Accepted: 11/13/2015] [Indexed: 12/15/2022]
Abstract
Enterochromaffin cells are the major site of serotonin (5-HT) synthesis and secretion providing ∼95% of the body's total 5-HT. 5-HT can act as a neurotransmitter or hormone and has several important endocrine and paracrine roles. We have previously demonstrated that EC cells release small amounts of 5-HT per exocytosis event compared to other endocrine cells. We utilized a recently developed method to purify EC cells to demonstrate the mechanisms underlying 5-HT packaging and release. Using the fluorescent probe FFN511, we demonstrate that EC cells express VMAT and that VMAT plays a functional role in 5-HT loading into vesicles. Carbon fiber amperometry studies illustrate that the amount of 5-HT released per exocytosis event from EC cells is dependent on both VMAT and the H(+)-ATPase pump, as demonstrated with reserpine or bafilomycin, respectively. We also demonstrate that increasing the amount of 5-HT loaded into EC cell vesicles does not result in an increase in quantal release. As this indicates that fusion pore size may be a limiting factor involved, we compared pore diameter in EC and chromaffin cells by assessing the vesicle capture of different-sized fluorescent probes to measure the extent of fusion pore dilation. This identified that EC cells have a reduced fusion pore expansion that does not exceed 9 nm in diameter. These results demonstrate that the small amounts of 5-HT released per fusion event in EC cells can be explained by a smaller fusion pore that limits 5-HT release capacity from individual vesicles.
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Affiliation(s)
- Ravinarayan Raghupathi
- Department of Human Physiology and Centre for Neuroscience, Flinders University, Adelaide, Australia
| | - Claire F Jessup
- Department of Anatomy and Histology and Centre for Neuroscience, Flinders University, Adelaide, Australia.,Discipline of Medicine, University of Adelaide, Adelaide, Australia
| | - Amanda L Lumsden
- Department of Human Physiology and Centre for Neuroscience, Flinders University, Adelaide, Australia
| | - Damien J Keating
- Department of Human Physiology and Centre for Neuroscience, Flinders University, Adelaide, Australia.,South Australian Health and Medical Research Institute, Adelaide, Australia
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A unified model for bone-renal mineral and energy metabolism. Curr Opin Pharmacol 2015; 22:64-71. [PMID: 25880364 DOI: 10.1016/j.coph.2015.03.006] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/30/2015] [Revised: 03/27/2015] [Accepted: 03/30/2015] [Indexed: 01/09/2023]
Abstract
The beginning of the millennium saw the discovery of a new bone-matrix protein, Matrix Extracellular PhosphoglycoprotEin (MEPE) and an associated C-terminal motif called ASARM. This motif and other distinguishing features occur in a group of proteins called SIBLINGs. These proteins include dentin matrix protein 1 (DMP1), osteopontin, dentin-sialophosphoprotein (DSPP), statherin, bone sialoprotein (BSP) and MEPE. MEPE, DMP1 and ASARM-motifs regulate expression of a phosphate regulating cytokine FGF23. Further, a trimeric interaction between phosphate regulating endopeptidase homolog X-linked (PHEX), DMP1, and α5β3-integrin that occurs on the plasma-membrane of the osteocyte mediates FGF23 regulation (FAP pathway). ASARM-peptides competitively inhibit the trimeric complex and increase FGF23. A second pathway involves specialized structures, matrix vesicles pathway (MVP). This review will discuss the FAP and MVP pathways and present a unified model for mineral and energy metabolism.
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Raghupathi R, Duffield MD, Zelkas L, Meedeniya A, Brookes SJH, Sia TC, Wattchow DA, Spencer NJ, Keating DJ. Identification of unique release kinetics of serotonin from guinea-pig and human enterochromaffin cells. J Physiol 2013; 591:5959-75. [PMID: 24099799 PMCID: PMC3872764 DOI: 10.1113/jphysiol.2013.259796] [Citation(s) in RCA: 59] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/07/2013] [Accepted: 10/02/2013] [Indexed: 12/21/2022] Open
Abstract
The major source of serotonin (5-HT) in the body is the enterochromaffin (EC) cells lining the intestinal mucosa of the gastrointestinal tract. Despite the fact that EC cells synthesise ∼95% of total body 5-HT, and that this 5-HT has important paracrine and endocrine roles, no studies have investigated the mechanisms of 5-HT release from single primary EC cells. We have developed a rapid primary culture of guinea-pig and human EC cells, allowing analysis of single EC cell function using electrophysiology, electrochemistry, Ca(2+) imaging, immunocytochemistry and 3D modelling. Ca(2+) enters EC cells upon stimulation and triggers quantal 5-HT release via L-type Ca(2+) channels. Real time amperometric techniques reveal that EC cells release 5-HT at rest and this release increases upon stimulation. Surprisingly for an endocrine cell storing 5-HT in large dense core vesicles (LDCVs), EC cells release 70 times less 5-HT per fusion event than catecholamine released from similarly sized LDCVs in endocrine chromaffin cells, and the vesicle release kinetics instead resembles that observed in mammalian synapses. Furthermore, we measured EC cell density along the gastrointestinal tract to create three-dimensional (3D) simulations of 5-HT diffusion using the minimal number of variables required to understand the physiological relevance of single cell 5-HT release in the whole-tissue milieu. These models indicate that local 5-HT levels are likely to be maintained around the activation threshold for mucosal 5-HT receptors and that this is dependent upon stimulation and location within the gastrointestinal tract. This is the first study demonstrating single cell 5-HT release in primary EC cells. The mode of 5-HT release may represent a unique mode of exocytosis amongst endocrine cells and is functionally relevant to gastrointestinal sensory and motor function.
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Affiliation(s)
- Ravinarayan Raghupathi
- D. Keating: Department of Human Physiology and Centre for Neuroscience, Flinders University, Sturt Road, Adelaide, 5001, Australia.
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Gaudin-Audrain C, Irwin N, Mansur S, Flatt PR, Thorens B, Baslé M, Chappard D, Mabilleau G. Glucose-dependent insulinotropic polypeptide receptor deficiency leads to modifications of trabecular bone volume and quality in mice. Bone 2013; 53:221-30. [PMID: 23220186 DOI: 10.1016/j.bone.2012.11.039] [Citation(s) in RCA: 62] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/13/2012] [Revised: 11/13/2012] [Accepted: 11/28/2012] [Indexed: 12/12/2022]
Abstract
A role for the gastro-intestinal tract in controlling bone remodeling is suspected since serum levels of bone remodeling markers are affected rapidly after a meal. Glucose-dependent insulinotropic polypeptide (GIP) represents a suitable candidate in mediating this effect. The aim of the present study was to investigate the effect of total inhibition of GIP signaling on trabecular bone volume, microarchitecture and quality. We used GIP receptor (GIPR) knockout mice and investigated trabecular bone volume and microarchitecture by microCT and histomorphometry. GIPR-deficient animals at 16 weeks of age presented with a significant (20%) increase in trabecular bone mass accompanied by an increase (17%) in trabecular number. In addition, the number of osteoclasts and bone formation rate was significantly reduced and augmented, respectively in these animals when compared with wild-type littermates. These modifications of trabecular bone microarchitecture are linked to a remodeling in the expression pattern of adipokines in the GIPR-deficient mice. On the other hand, despite significant enhancement in bone volume, intrinsic mechanical properties of the bone matrix was reduced as well as the distribution of bone mineral density and the ratio of mature/immature collagen cross-links. Taken together, these results indicate an increase in trabecular bone volume in GIPR KO animals associated with a reduction in bone quality.
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Abstract
PURPOSE OF REVIEW Although the gut contains most of the body's 5-hydroxytryptamine (5-HT), many of its most important functions have recently been discovered. This review summarizes and directs attention to this new burst of knowledge. RECENT FINDINGS Enteroendocrine cells have classically been regarded as pressure sensors, which secrete 5-HT to initiate peristaltic reflexes; nevertheless, recent data obtained from studies of mice that selectively lack 5-HT either in enterochromaffin cells (deletion of tryptophan hydroxylase 1 knockout; TPH1KO) or neurons (TPH2KO) imply that neuronal 5-HT is more important for constitutive gastrointestinal transit than that of enteroendocrine cells. The enteric nervous system of TPH2KO mice, however, also lacks a full complement of neurons; therefore, it is not clear whether slow transit in TPH2KO animals is due to their neuronal deficiency or absence of serotonergic neurotransmission. Neuronal 5-HT promotes the growth/maintenance of the mucosa as well as neurogenesis. Enteroendocrine cell derived 5-HT is an essential component of the gastrointestinal inflammatory response; thus, deletion of the serotonin transporter increases, whereas TPH1KO decreases the severity of intestinal inflammation. Enteroendocrine cell derived 5-HT, moreover, is also a hormone, which inhibits osteoblast proliferation and promotes hepatic regeneration. SUMMARY New studies show that enteric 5-HT is a polyfunctional signalling molecule, acting both in developing and mature animals as a neurotransmitter paracrine factor, endocrine hormone and growth factor.
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Affiliation(s)
- Michael D Gershon
- Department of Pathology and Cell Biology, Columbia University, College of Physicians and Surgeons, New York, New York, USA.
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Fu YY, Peng SJ, Lin HY, Pasricha PJ, Tang SC. 3-D imaging and illustration of mouse intestinal neurovascular complex. Am J Physiol Gastrointest Liver Physiol 2013; 304:G1-11. [PMID: 23086917 DOI: 10.1152/ajpgi.00209.2012] [Citation(s) in RCA: 56] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
Because of the dispersed nature of nerves and blood vessels, standard histology cannot provide a global and associated observation of the enteric nervous system (ENS) and vascular network. We prepared transparent mouse intestine and combined vessel painting and three-dimensional (3-D) neurohistology for joint visualization of the ENS and vasculature. Cardiac perfusion of the fluorescent wheat germ agglutinin (vessel painting) was used to label the ileal blood vessels. The pan-neuronal marker PGP9.5, sympathetic neuronal marker tyrosine hydroxylase (TH), serotonin, and glial markers S100B and GFAP were used as the immunostaining targets of neural tissues. The fluorescently labeled specimens were immersed in the optical clearing solution to improve photon penetration for 3-D confocal microscopy. Notably, we simultaneously revealed the ileal microstructure, vasculature, and innervation with micrometer-level resolution. Four examples are given: 1) the morphology of the TH-labeled sympathetic nerves: sparse in epithelium, perivascular at the submucosa, and intraganglionic at myenteric plexus; 2) distinct patterns of the extrinsic perivascular and intrinsic pericryptic innervation at the submucosal-mucosal interface; 3) different associations of serotonin cells with the mucosal neurovascular elements in the villi and crypts; and 4) the periganglionic capillary network at the myenteric plexus and its contact with glial fibers. Our 3-D imaging approach provides a useful tool to simultaneously reveal the nerves and blood vessels in a space continuum for panoramic illustration and analysis of the neurovascular complex to better understand the intestinal physiology and diseases.
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Affiliation(s)
- Ya-Yuan Fu
- Connectomics Research Center, National Tsing Hua University, Hsinchu, Taiwan
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Current world literature. Curr Opin Rheumatol 2012; 24:586-94. [PMID: 22871955 DOI: 10.1097/bor.0b013e32835793df] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
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Abstract
PURPOSE OF REVIEW To discuss current literature and hypotheses pertaining to the pathophysiology of increased bone fragility and fracture in men and women with type 2 diabetes mellitus. RECENT FINDINGS Despite high bone mineral density, studies have shown that men and women with type 2 diabetes mellitus (T2DM) are at increased risk for fracture. Complications of T2DM including retinopathy and autonomic dysfunction may contribute to bone fracture by increasing fall risk. Nephropathy may lead to renal osteodystrophy. Lean mass and potentially fat mass, may additionally contribute to skeletal health in diabetes. There is increasing acknowledgement that the marrow microenvironment is critical to efficient bone remodeling. Medications including thiazolidinediones and selective serotonin reuptake inhibitors may also impair bone remodeling by acting on mesenchymal stem cell differentiation and osteoblastogenesis. T2DM is associated with significant alterations in systemic inflammation, advanced glycation end-product accumulation and reactive oxygen species generation. These systemic changes may also directly and adversely impact the remodeling cycle and lead to bone fragility in T2DM, though more research is needed. SUMMARY Fracture is a devastating event with dismal health consequences. Identifying the extrinsic and intrinsic biochemical causes of bone fracture in T2DM will speed the discovery of effective strategies for fracture prevention and treatment in this at-risk population.
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Affiliation(s)
- Kendall F Moseley
- Division of Endocrinology, Johns Hopkins Bayview Medical Center, Baltimore, Maryland, USA.
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