1
|
Barton JR, Londregan AK, Alexander TD, Entezari AA, Covarrubias M, Waldman SA. Enteroendocrine cell regulation of the gut-brain axis. Front Neurosci 2023; 17:1272955. [PMID: 38027512 PMCID: PMC10662325 DOI: 10.3389/fnins.2023.1272955] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/04/2023] [Accepted: 10/16/2023] [Indexed: 12/01/2023] Open
Abstract
Enteroendocrine cells (EECs) are an essential interface between the gut and brain that communicate signals about nutrients, pain, and even information from our microbiome. EECs are hormone-producing cells expressed throughout the gastrointestinal epithelium and have been leveraged by pharmaceuticals like semaglutide (Ozempic, Wegovy), terzepatide (Mounjaro), and retatrutide (Phase 2) for diabetes and weight control, and linaclotide (Linzess) to treat irritable bowel syndrome (IBS) and visceral pain. This review focuses on role of intestinal EECs to communicate signals from the gut lumen to the brain. Canonically, EECs communicate information about the intestinal environment through a variety of hormones, dividing EECs into separate classes based on the hormone each cell type secretes. Recent studies have revealed more diverse hormone profiles and communication modalities for EECs including direct synaptic communication with peripheral neurons. EECs known as neuropod cells rapidly relay signals from gut to brain via a direct communication with vagal and primary sensory neurons. Further, this review discusses the complex information processing machinery within EECs, including receptors that transduce intraluminal signals and the ion channel complement that govern initiation and propagation of these signals. Deeper understanding of EEC physiology is necessary to safely treat devastating and pervasive conditions like irritable bowel syndrome and obesity.
Collapse
Affiliation(s)
- Joshua R. Barton
- Department of Pharmacology, Physiology, and Cancer Biology, Thomas Jefferson University, Philadelphia, PA, United States
| | - Annie K. Londregan
- Department of Pharmacology, Physiology, and Cancer Biology, Thomas Jefferson University, Philadelphia, PA, United States
| | - Tyler D. Alexander
- Department of Neurosciences, Thomas Jefferson University, Philadelphia, PA, United States
| | - Ariana A. Entezari
- Department of Pharmacology, Physiology, and Cancer Biology, Thomas Jefferson University, Philadelphia, PA, United States
| | - Manuel Covarrubias
- Department of Neurosciences, Thomas Jefferson University, Philadelphia, PA, United States
| | - Scott A. Waldman
- Department of Pharmacology, Physiology, and Cancer Biology, Thomas Jefferson University, Philadelphia, PA, United States
- Sidney Kimmel Cancer Center, Thomas Jefferson University, Philadelphia, PA, United States
| |
Collapse
|
2
|
Brubaker PL. The Molecular Determinants of Glucagon-like Peptide Secretion by the Intestinal L cell. Endocrinology 2022; 163:6717959. [PMID: 36156130 DOI: 10.1210/endocr/bqac159] [Citation(s) in RCA: 4] [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: 08/24/2022] [Indexed: 11/19/2022]
Abstract
The intestinal L cell secretes a diversity of biologically active hormones, most notably the glucagon-like peptides, GLP-1 and GLP-2. The highly successful introduction of GLP-1-based drugs into the clinic for the treatment of patients with type 2 diabetes and obesity, and of a GLP-2 analog for patients with short bowel syndrome, has led to the suggestion that stimulation of the endogenous secretion of these peptides may serve as a novel therapeutic approach in these conditions. Situated in the intestinal epithelium, the L cell demonstrates complex relationships with not only circulating, paracrine, and neural regulators, but also ingested nutrients and other factors in the lumen, most notably the microbiota. The integrated input from these numerous secretagogues results in a variety of temporal patterns in L cell secretion, ranging from minutes to 24 hours. This review combines the findings of traditional, physiological studies with those using newer molecular approaches to describe what is known and what remains to be elucidated after 5 decades of research on the intestinal L cell and its secreted peptides, GLP-1 and GLP-2.
Collapse
Affiliation(s)
- Patricia L Brubaker
- Department of Physiology, University of Toronto, Toronto, ON M5S 1A8, Canada
- Department of Medicine, University of Toronto, Toronto, ON M5S 1A8, Canada
| |
Collapse
|
3
|
Martchenko A, Biancolin AD, Martchenko SE, Brubaker PL. Nobiletin ameliorates high fat-induced disruptions in rhythmic glucagon-like peptide-1 secretion. Sci Rep 2022; 12:7271. [PMID: 35508494 PMCID: PMC9068808 DOI: 10.1038/s41598-022-11223-7] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/22/2022] [Accepted: 04/20/2022] [Indexed: 02/06/2023] Open
Abstract
The incretin hormone glucagon-like peptide-1 (GLP-1) is secreted by the intestinal L cell in response to nutrient intake. However, GLP-1 secretion also follows a circadian rhythm which is disrupted by the saturated fatty acid palmitate in vitro and high-fat diet (HFD) feeding in vivo. The flavonoid nobiletin is a clock enhancer which improves metabolic homeostasis. Therefore, the aim of this study was to elucidate whether and how nobiletin mitigates the negative effects of palmitate and HFD-feeding on rhythmic GLP-1 release. Pre-treatment of murine GLUTag L cells with palmitate dampened the GLP-1 secretory response at the normal peak of secretion, while nobiletin co-treatment restored GLP-1 secretion and upregulated the ‘metabolic pathway’ transcriptome. Mice fed a HFD also lost their GLP-1 secretory rhythm in association with markedly increased GLP-1 levels and upregulation of L cell transcriptional pathways related to ‘sensing’ and ‘transducing’ cellular stimuli at the normal peak of GLP-1 release. Nobiletin co-administration reduced GLP-1 levels to more physiological levels and upregulated L cell ‘oxidative metabolism’ transcriptional pathways. Furthermore, nobiletin improved colonic microbial 16S rRNA gene diversity and reduced the levels of Proteobacteria in HFD-fed mice. Collectively, this study establishes that nobiletin improves the normal rhythm in GLP-1 secretion following fat-induced disruption.
Collapse
Affiliation(s)
- Alexandre Martchenko
- Department of Physiology, University of Toronto, Rm 3366 Medical Sciences Building, 1 King's College Circle, Toronto, ON, M5S 1A8, Canada
| | - Andrew D Biancolin
- Department of Physiology, University of Toronto, Rm 3366 Medical Sciences Building, 1 King's College Circle, Toronto, ON, M5S 1A8, Canada
| | - Sarah E Martchenko
- Department of Physiology, University of Toronto, Rm 3366 Medical Sciences Building, 1 King's College Circle, Toronto, ON, M5S 1A8, Canada
| | - Patricia L Brubaker
- Department of Physiology, University of Toronto, Rm 3366 Medical Sciences Building, 1 King's College Circle, Toronto, ON, M5S 1A8, Canada. .,Department of Medicine, University of Toronto, Toronto, ON, Canada.
| |
Collapse
|
4
|
Liu C, Liu Y, Xin Y, Wang Y. Circadian secretion rhythm of GLP-1 and its influencing factors. Front Endocrinol (Lausanne) 2022; 13:991397. [PMID: 36531506 PMCID: PMC9755352 DOI: 10.3389/fendo.2022.991397] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/11/2022] [Accepted: 11/22/2022] [Indexed: 12/04/2022] Open
Abstract
Circadian rhythm is an inherent endogenous biological rhythm in living organisms. However, with the improvement of modern living standards, many factors such as prolonged artificial lighting, sedentarism, short sleep duration, intestinal flora and high-calorie food intake have disturbed circadian rhythm regulation on various metabolic processes, including GLP-1 secretion, which plays an essential role in the development of various metabolic diseases. Herein, we focused on GLP-1 and its circadian rhythm to explore the factors affecting GLP-1 circadian rhythm and its potential mechanisms and propose some feasible suggestions to improve GLP-1 secretion.
Collapse
|
5
|
Martchenko SE, Martchenko A, Biancolin AD, Waller A, Brubaker PL. L-cell Arntl is required for rhythmic glucagon-like peptide-1 secretion and maintenance of intestinal homeostasis. Mol Metab 2021; 54:101340. [PMID: 34520858 PMCID: PMC8489154 DOI: 10.1016/j.molmet.2021.101340] [Citation(s) in RCA: 11] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/14/2021] [Revised: 09/03/2021] [Accepted: 09/07/2021] [Indexed: 12/13/2022] Open
Abstract
OBJECTIVE Recent studies using whole-body clock-disrupted animals identified a disruption in the circadian rhythm of the intestinal L-cell incretin hormone, glucagon-like peptide-1 (GLP-1). Although GLP-1 plays an essential role in metabolism through enhancement of both glucose-stimulated insulin secretion and satiety, recent evidence has also demonstrated its importance in regulating intestinal and microbial homeostasis. Therefore, using in vivo and in vitro models, this study assessed the role of the core circadian clock gene Arntl in the regulation of time-dependent GLP-1 secretion and its impact on the intestinal environment. METHODS Oral glucose tolerance tests were conducted at zeitgeber time 2 and 14 in control and inducible Gcg-Arntl knockout (KO) mice. Colonic intraepithelial lymphocytes were isolated, mucosal gene expression analysis was conducted, and 16S rRNA gene sequencing of colonic feces as well as analysis of microbial metabolites were performed. Time-dependent GLP-1 secretion and transcriptomic analysis were conducted in murine (m) GLUTag L-cells following siRNA-mediated knockdown of Arntl. RESULTS Gcg-Arntl KO mice displayed disrupted rhythmic release of GLP-1 associated with reduced secretion at the established peak time point. Analysis of the intestinal environment in KO mice revealed a decreased proportion of CD4+ intraepithelial lymphocytes in association with increased proinflammatory cytokine gene expression and increased colonic weight. Moreover, increased Actinobacteria within the colonic microbiome was found following L-cell Arntl disruption, as well as reductions in the microbial products, short chain fatty acids, and bile acids. Finally, siRNA-mediated knockdown of Arntl in mGLUTag L-cells resulted in both impaired time-dependent GLP-1 secretion and the disruption of pathways related to key cellular processes. CONCLUSIONS These data establish, for the first time, the essential role of Arntl in the intestinal L-cell in regulating time-dependent GLP-1 secretion. Furthermore, this study revealed the integral role of L-cell Arntl in mediating the intestinal environment, which ultimately may provide novel insight into the development of therapeutics for the treatment of intestinal and metabolic disorders.
Collapse
Affiliation(s)
| | | | | | - Alison Waller
- Department of Biological Sciences, Brock University, St. Catharines, ON, Canada
| | - Patricia L Brubaker
- Department of Physiology, University of Toronto, Canada; Department of Medicine, University of Toronto, Toronto, ON, Canada.
| |
Collapse
|
6
|
Zhang X, Li N, Zhang J, Zhang Y, Yang X, Luo Y, Zhang B, Xu Z, Zhu Z, Yang X, Yan Y, Lin B, Wang S, Chen D, Ye C, Ding Y, Lou M, Wu Q, Hou Z, Zhang K, Liang Z, Wei A, Wang B, Wang C, Jiang N, Zhang W, Xiao G, Ma C, Ren Y, Qi X, Han W, Wang C, Rao F. 5-IP 7 is a GPCR messenger mediating neural control of synaptotagmin-dependent insulin exocytosis and glucose homeostasis. Nat Metab 2021; 3:1400-1414. [PMID: 34663975 DOI: 10.1038/s42255-021-00468-7] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/03/2020] [Accepted: 09/02/2021] [Indexed: 11/08/2022]
Abstract
5-diphosphoinositol pentakisphosphate (5-IP7) is a signalling metabolite linked to various cellular processes. How extracellular stimuli elicit 5-IP7 signalling remains unclear. Here we show that 5-IP7 in β cells mediates parasympathetic stimulation of synaptotagmin-7 (Syt7)-dependent insulin release. Mechanistically, vagal stimulation and activation of muscarinic acetylcholine receptors triggers Gαq-PLC-PKC-PKD-dependent signalling and activates IP6K1, the 5-IP7 synthase. Whereas both 5-IP7 and its precursor IP6 compete with PIP2 for binding to Syt7, Ca2+ selectively binds 5-IP7 with high affinity, freeing Syt7 to enable fusion of insulin-containing vesicles with the cell membrane. β-cell-specific IP6K1 deletion diminishes insulin secretion and glucose clearance elicited by muscarinic stimulation, whereas mice carrying a phosphorylation-mimicking, hyperactive IP6K1 mutant display augmented insulin release, congenital hyperinsulinaemia and obesity. These phenotypes are absent in mice lacking Syt7. Our study proposes a new conceptual framework for inositol pyrophosphate physiology in which 5-IP7 acts as a GPCR second messenger at the interface between peripheral nervous system and metabolic organs, transmitting Gq-coupled GPCR stimulation to unclamp Syt7-dependent, and perhaps other, exocytotic events.
Collapse
Affiliation(s)
- Xiaozhe Zhang
- School of Life Sciences, Southern University of Science and Technology, Shenzhen, China
| | - Na Li
- School of Life Sciences, Southern University of Science and Technology, Shenzhen, China
| | - Jun Zhang
- School of Life Sciences, Southern University of Science and Technology, Shenzhen, China
| | - Yanshen Zhang
- Ministry of Education Key Laboratory for Membraneless Organelles & Cellular Dynamics, Hefei National Laboratory for Physical Sciences at the Microscale, School of Life Sciences, Division of Life Sciences and Medicine, University of Science and Technology of China, Hefei, China
- Department of Neurology, the First Affiliated Hospital of USTC, Division of Life Sciences and Medicine, University of Science and Technology of China, Hefei, China
| | - Xiaoli Yang
- School of Life Sciences, Southern University of Science and Technology, Shenzhen, China
| | - Yifan Luo
- School of Life Sciences, Southern University of Science and Technology, Shenzhen, China
| | - Bobo Zhang
- School of Life Sciences, Southern University of Science and Technology, Shenzhen, China
| | - Zhixue Xu
- School of Life Sciences, Southern University of Science and Technology, Shenzhen, China
| | - Zhenhua Zhu
- School of Life Sciences, Southern University of Science and Technology, Shenzhen, China
| | - Xiuyan Yang
- School of Life Sciences, Southern University of Science and Technology, Shenzhen, China
| | - Yuan Yan
- School of Life Sciences, Southern University of Science and Technology, Shenzhen, China
| | - Biao Lin
- School of Life Sciences, Southern University of Science and Technology, Shenzhen, China
| | - Shen Wang
- Key Laboratory of Molecular Biophysics of the Ministry of Education, College of Life Science and Technology, Huazhong University of Science and Technology, Wuhan, China
| | - Da Chen
- Ministry of Education Key Laboratory for Membraneless Organelles & Cellular Dynamics, Hefei National Laboratory for Physical Sciences at the Microscale, School of Life Sciences, Division of Life Sciences and Medicine, University of Science and Technology of China, Hefei, China
- Department of Neurology, the First Affiliated Hospital of USTC, Division of Life Sciences and Medicine, University of Science and Technology of China, Hefei, China
| | - Caichao Ye
- Department of Physics and Shenzhen Institute for Quantum Science & Technology, Southern University of Science and Technology, Shenzhen, China
| | - Yan Ding
- National Institute of Biological Sciences, Beijing, China
| | - Mingliang Lou
- National Institute of Biological Sciences, Beijing, China
| | - Qingcui Wu
- National Institute of Biological Sciences, Beijing, China
| | - Zhanfeng Hou
- National Institute of Biological Sciences, Beijing, China
| | - Keren Zhang
- BGI-Shenzhen, Beishan Industrial Zone 11th building, Shenzhen, China
| | - Ziming Liang
- Department of Hepatic Surgery, the Third People's Hospital of Shenzhen and the Second Affiliated Hospital of Southern University of Science and Technology, Shenzhen, China
| | - Anqi Wei
- Neuroscience Research Center, Institute of Mitochondrial Biology and Medicine, Key Laboratory of Biomedical Information Engineering of Ministry of Education, School of Life Science and Technology, Xi'an Jiaotong University, Xi'an, China
| | - Bianbian Wang
- Neuroscience Research Center, Institute of Mitochondrial Biology and Medicine, Key Laboratory of Biomedical Information Engineering of Ministry of Education, School of Life Science and Technology, Xi'an Jiaotong University, Xi'an, China
| | - Changhe Wang
- Neuroscience Research Center, Institute of Mitochondrial Biology and Medicine, Key Laboratory of Biomedical Information Engineering of Ministry of Education, School of Life Science and Technology, Xi'an Jiaotong University, Xi'an, China
| | - Nan Jiang
- Department of Hepatic Surgery, the Third People's Hospital of Shenzhen and the Second Affiliated Hospital of Southern University of Science and Technology, Shenzhen, China
| | - Wenqing Zhang
- Department of Physics and Shenzhen Institute for Quantum Science & Technology, Southern University of Science and Technology, Shenzhen, China
| | - Guozhi Xiao
- Department of Biochemistry, School of Medicine, Southern University of Science and Technology, Guangdong Provincial Key Laboratory of Cell Microenvironment and Disease Research, Shenzhen Key Laboratory of Cell Microenvironment, Shenzhen, China
| | - Cong Ma
- Key Laboratory of Molecular Biophysics of the Ministry of Education, College of Life Science and Technology, Huazhong University of Science and Technology, Wuhan, China
| | - Yan Ren
- BGI-Shenzhen, Beishan Industrial Zone 11th building, Shenzhen, China
| | - Xiangbing Qi
- National Institute of Biological Sciences, Beijing, China
| | - Weiping Han
- Institute of Molecular and Cell Biology, Agency for Science, Technology, and Research, Singapore, Singapore
- Center for Neuro-Metabolism and Regeneration Research, Guangzhou Regenerative Medicine and Health Guangdong Laboratory, Guangzhou, China
| | - Chao Wang
- Ministry of Education Key Laboratory for Membraneless Organelles & Cellular Dynamics, Hefei National Laboratory for Physical Sciences at the Microscale, School of Life Sciences, Division of Life Sciences and Medicine, University of Science and Technology of China, Hefei, China.
- Department of Neurology, the First Affiliated Hospital of USTC, Division of Life Sciences and Medicine, University of Science and Technology of China, Hefei, China.
| | - Feng Rao
- School of Life Sciences, Southern University of Science and Technology, Shenzhen, China.
| |
Collapse
|
7
|
Fujiwara Y, Yamane S, Harada N, Ikeguchi-Ogura E, Usui R, Nakamura T, Iwasaki K, Suzuki K, Yabe D, Hayashi Y, Inagaki N. Carbonic anhydrase 8 (CAR8) negatively regulates GLP-1 secretion from enteroendocrine cells in response to long-chain fatty acids. Am J Physiol Gastrointest Liver Physiol 2021; 320:G617-G626. [PMID: 33533304 DOI: 10.1152/ajpgi.00312.2020] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/27/2020] [Accepted: 01/30/2021] [Indexed: 01/31/2023]
Abstract
Glucagon-like peptide-1 (GLP-1) is an incretin secreted from enteroendocrine preproglucagon (PPG)-expressing cells (traditionally known as L cells) in response to luminal nutrients that potentiates insulin secretion. Augmentation of endogenous GLP-1 secretion might well represent a novel therapeutic target for diabetes treatment in addition to the incretin-associated drugs currently in use. In this study, we found that PPG cells substantially express carbonic anhydrase 8 (CAR8), which has been reported to inhibit inositol 1,4,5-trisphosphate (IP3) binding to the IP3 receptor and subsequent Ca2+ efflux from the endoplasmic reticulum in neuronal cells. In vitro experiments using STC-1 cells demonstrated that Car8 knockdown increases long-chain fatty acid (LCFA)-stimulated GLP-1 secretion. This effect was reduced in the presence of phospholipase C (PLC) inhibitor; in addition, Car8 knockdown increased the intracellular Ca2+ elevation caused by α-linolenic acid, indicating that CAR8 exerts its effect on GLP-1 secretion via the PLC/IP3/Ca2+ pathway. Car8wdl null mutant mice showed significant increase in GLP-1 response to oral corn oil administration compared with that in wild-type littermates, with no significant change in intestinal GLP-1 content. These results demonstrate that CAR8 negatively regulates GLP-1 secretion from PPG cells in response to LCFAs, suggesting the possibility of augmentation of postprandial GLP-1 secretion by CAR8 inhibition.NEW & NOTEWORTHY This study focused on the physiological significance of carbonic anhydrase 8 (CAR8) in GLP-1 secretion from enteroendocrine preproglucagon (PPG)-expressing cells. We found an inhibitory role of CAR8 in LCFA-induced GLP-1 secretion in vitro and in vivo, suggesting a novel therapeutic approach to diabetes and obesity through augmentation of postprandial GLP-1 secretion by CAR8 inhibition.
Collapse
Affiliation(s)
- Yuta Fujiwara
- Department of Diabetes, Endocrinology, and Nutrition, Graduate School of Medicine, Kyoto University, Kyoto, Japan
| | - Shunsuke Yamane
- Department of Diabetes, Endocrinology, and Nutrition, Graduate School of Medicine, Kyoto University, Kyoto, Japan
| | - Norio Harada
- Department of Diabetes, Endocrinology, and Nutrition, Graduate School of Medicine, Kyoto University, Kyoto, Japan
| | - Eri Ikeguchi-Ogura
- Department of Diabetes, Endocrinology, and Nutrition, Graduate School of Medicine, Kyoto University, Kyoto, Japan
| | - Ryota Usui
- Department of Diabetes, Endocrinology, and Nutrition, Graduate School of Medicine, Kyoto University, Kyoto, Japan
| | - Toshihiro Nakamura
- Department of Diabetes, Endocrinology, and Nutrition, Graduate School of Medicine, Kyoto University, Kyoto, Japan
| | - Kanako Iwasaki
- Department of Diabetes, Endocrinology, and Nutrition, Graduate School of Medicine, Kyoto University, Kyoto, Japan
| | - Kazuyo Suzuki
- Department of Diabetes, Endocrinology, and Nutrition, Graduate School of Medicine, Kyoto University, Kyoto, Japan
| | - Daisuke Yabe
- Department of Diabetes and Endocrinology, Gifu University Graduate School of Medicine, Gifu, Japan
| | - Yoshitaka Hayashi
- Department of Endocrinology, Research Institute of Environmental Medicine, Nagoya University, Nagoya, Japan
| | - Nobuya Inagaki
- Department of Diabetes, Endocrinology, and Nutrition, Graduate School of Medicine, Kyoto University, Kyoto, Japan
| |
Collapse
|
8
|
Yang M, Reimann F, Gribble FM. Chemosensing in enteroendocrine cells: mechanisms and therapeutic opportunities. Curr Opin Endocrinol Diabetes Obes 2021; 28:222-231. [PMID: 33449572 DOI: 10.1097/med.0000000000000614] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
PURPOSE OF REVIEW Enteroendocrine cells (EECs) are scattered chemosensory cells in the intestinal epithelium that release hormones with a wide range of actions on intestinal function, food intake and glucose homeostasis. The mechanisms by which gut hormones are secreted postprandially, or altered by antidiabetic agents and surgical interventions are of considerable interest for future therapeutic development. RECENT FINDINGS EECs are electrically excitable and express a repertoire of G-protein coupled receptors that sense nutrient and nonnutrient stimuli, coupled to intracellular Ca2+ and cyclic adenosine monophosphate. Our knowledge of EEC function, previously developed using mouse models, has recently been extended to human cells. Gut hormone release in humans is enhanced by bariatric surgery, as well as by some antidiabetic agents including sodium-coupled glucose transporter inhibitors and metformin. SUMMARY EECs are important potential therapeutic targets. A better understanding of their chemosensory mechanisms will enhance the development of new therapeutic strategies to treat metabolic and gastrointestinal diseases.
Collapse
Affiliation(s)
- Ming Yang
- University of Cambridge, Institute of Metabolic Science and MRC Metabolic Diseases Unit, Addenbrooke's Hospital, Cambridge, UK
| | | | | |
Collapse
|
9
|
Martchenko A, Martchenko SE, Biancolin AD, Brubaker PL. Circadian Rhythms and the Gastrointestinal Tract: Relationship to Metabolism and Gut Hormones. Endocrinology 2020; 161:5909225. [PMID: 32954405 PMCID: PMC7660274 DOI: 10.1210/endocr/bqaa167] [Citation(s) in RCA: 13] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/16/2020] [Accepted: 09/16/2020] [Indexed: 02/08/2023]
Abstract
Circadian rhythms are 24-hour biological rhythms within organisms that have developed over evolutionary time due to predefined environmental changes, mainly the light-dark cycle. Interestingly, metabolic tissues, which are largely responsible for establishing diurnal metabolic homeostasis, have been found to express cell-autonomous clocks that are entrained by food intake. Disruption of the circadian system, as seen in individuals who conduct shift work, confers significant risk for the development of metabolic diseases such as type 2 diabetes and obesity. The gastrointestinal (GI) tract is the first point of contact for ingested nutrients and is thus an essential organ system for metabolic control. This review will focus on the circadian function of the GI tract with a particular emphasis on its role in metabolism through regulation of gut hormone release. First, the circadian molecular clock as well as the organization of the mammalian circadian system is introduced. Next, a brief overview of the structure of the gut as well as the circadian regulation of key functions important in establishing metabolic homeostasis is discussed. Particularly, the focus of the review is centered around secretion of gut hormones; however, other functions of the gut such as barrier integrity and intestinal immunity, as well as digestion and absorption, all of which have relevance to metabolic control will be considered. Finally, we provide insight into the effects of circadian disruption on GI function and discuss chronotherapeutic intervention strategies for mitigating associated metabolic dysfunction.
Collapse
Affiliation(s)
| | | | | | - Patricia L Brubaker
- Department of Physiology, University of Toronto, Toronto, ON, Canada
- Department of Medicine, University of Toronto, Toronto, ON, Canada
- Correspondence: P.L. Brubaker, Rm 3366 Medical Sciences Building, University of Toronto, 1 King’s College Circle, Toronto, ON M5S 1A8 Canada. E-mail:
| |
Collapse
|
10
|
Martchenko SE, Martchenko A, Cox BJ, Naismith K, Waller A, Gurges P, Sweeney ME, Philpott DJ, Brubaker PL. Circadian GLP-1 Secretion in Mice Is Dependent on the Intestinal Microbiome for Maintenance of Diurnal Metabolic Homeostasis. Diabetes 2020; 69:2589-2602. [PMID: 32928871 DOI: 10.2337/db20-0262] [Citation(s) in RCA: 33] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/17/2020] [Accepted: 09/07/2020] [Indexed: 11/13/2022]
Abstract
The incretin glucagon-like peptide 1 (GLP-1) is secreted by the intestinal L cell upon nutrient ingestion. GLP-1 also exhibits a circadian rhythm, with highest release at the onset of the feeding period. Similarly, microbial composition and function exhibit circadian rhythmicity with fasting-feeding. The circadian pattern of GLP-1 release was found to be dependent on the oral route of glucose administration and was necessary for the rhythmic release of insulin and diurnal glycemic control in normal male and female mice. In mice fed a Western (high-fat/high-sucrose) diet for 16 weeks, GLP-1 secretion was markedly increased but arrhythmic over the 24-h day, whereas levels of the other incretin, glucose-dependent insulinotropic polypeptide, were not as profoundly affected. Furthermore, the changes in GLP-1 secretion were shown to be essential for the maintenance of normoglycemia in this obesogenic environment. Analysis of the primary L-cell transcriptome, as well as of the intestinal microbiome, also demonstrated time-of-day- and diet-dependent changes paralleling GLP-1 secretion. Finally, studies in antibiotic-induced microbial depleted and in germ-free mice with and without fecal microbial transfer, provided evidence for a role of the microbiome in diurnal GLP-1 release. In combination, these findings establish a key role for microbiome-dependent circadian GLP-1 secretion in the maintenance of 24-h metabolic homeostasis.
Collapse
Affiliation(s)
- Sarah E Martchenko
- Department of Physiology, University of Toronto, Toronto, Ontario, Canada
| | | | - Brian J Cox
- Department of Physiology, University of Toronto, Toronto, Ontario, Canada
- Department of Obstetrics and Gynecology, University of Toronto, Toronto, Ontario, Canada
| | - Kendra Naismith
- Department of Physiology, University of Toronto, Toronto, Ontario, Canada
| | - Alison Waller
- Department of Biological Sciences, Brock University, St. Catharines, Ontario, Canada
| | - Patrick Gurges
- Department of Physiology, University of Toronto, Toronto, Ontario, Canada
| | - Maegan E Sweeney
- Department of Physiology, University of Toronto, Toronto, Ontario, Canada
| | - Dana J Philpott
- Department of Immunology, University of Toronto, Toronto, Ontario, Canada
| | - Patricia L Brubaker
- Department of Physiology, University of Toronto, Toronto, Ontario, Canada
- Department of Medicine, University of Toronto, Toronto, Ontario, Canada
| |
Collapse
|
11
|
Campbell JR, Martchenko A, Sweeney ME, Maalouf MF, Psichas A, Gribble FM, Reimann F, Brubaker PL. Essential Role of Syntaxin-Binding Protein-1 in the Regulation of Glucagon-Like Peptide-1 Secretion. Endocrinology 2020; 161:5788420. [PMID: 32141504 PMCID: PMC7124137 DOI: 10.1210/endocr/bqaa039] [Citation(s) in RCA: 16] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/21/2019] [Accepted: 02/28/2020] [Indexed: 12/12/2022]
Abstract
Circadian secretion of the incretin, glucagon-like peptide-1 (GLP-1), correlates with expression of the core clock gene, Bmal1, in the intestinal L-cell. Several SNARE proteins known to be circadian in pancreatic α- and β-cells are also necessary for GLP-1 secretion. However, the role of the accessory SNARE, Syntaxin binding protein-1 (Stxbp1; also known as Munc18-1) in the L-cell is unknown. The aim of this study was to determine whether Stxbp1 is under circadian regulation in the L-cell and its role in the control of GLP-1 secretion. Stxbp1 was highly-enriched in L-cells, and STXBP1 was expressed in a subpopulation of L-cells in mouse and human intestinal sections. Stxbp1 transcripts and protein displayed circadian patterns in mGLUTag L-cells line, while chromatin-immunoprecipitation revealed increased interaction between BMAL1 and Stxbp1 at the peak time-point of the circadian pattern. STXBP1 recruitment to the cytosol and plasma membrane within 30 minutes of L-cell stimulation was also observed at this time-point. Loss of Stxbp1 in vitro and in vivo led to reduced stimulated GLP-1 secretion at the peak time-point of circadian release, and impaired GLP-1 secretion ex vivo. In conclusion, Stxbp1 is a circadian regulated exocytotic protein in the intestinal L-cell that is an essential regulatory component of GLP-1 secretion.
Collapse
Affiliation(s)
| | | | - Maegan E Sweeney
- Departments of Physiology, University of Toronto, Toronto, ON, Canada
| | - Michael F Maalouf
- Departments of Physiology, University of Toronto, Toronto, ON, Canada
| | - Arianna Psichas
- Departments of Medicine, University of Toronto, Toronto, ON, Canada
| | - Fiona M Gribble
- Departments of Medicine, University of Toronto, Toronto, ON, Canada
| | - Frank Reimann
- Departments of Medicine, University of Toronto, Toronto, ON, Canada
| | - Patricia L Brubaker
- Departments of Physiology, University of Toronto, Toronto, ON, Canada
- Wellcome Trust-MRC Institute of Metabolic Science – Metabolic Research Laboratories (IMS-MRL), University of Cambridge, Cambridge, UK
- Correspondence: P.L. Brubaker, Rm. 3366 Medical Sciences Building, University of Toronto, 1 King’s College Circle, Toronto, ON M5S 1A8. E-mail:
| |
Collapse
|
12
|
Guan Z, Quiñones-Frías MC, Akbergenova Y, Littleton JT. Drosophila Synaptotagmin 7 negatively regulates synaptic vesicle release and replenishment in a dosage-dependent manner. eLife 2020; 9:e55443. [PMID: 32343229 PMCID: PMC7224696 DOI: 10.7554/elife.55443] [Citation(s) in RCA: 17] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/24/2020] [Accepted: 04/28/2020] [Indexed: 01/03/2023] Open
Abstract
Synchronous neurotransmitter release is triggered by Ca2+ binding to the synaptic vesicle protein Synaptotagmin 1, while asynchronous fusion and short-term facilitation is hypothesized to be mediated by plasma membrane-localized Synaptotagmin 7 (SYT7). We generated mutations in Drosophila Syt7 to determine if it plays a conserved role as the Ca2+ sensor for these processes. Electrophysiology and quantal imaging revealed evoked release was elevated 2-fold. Syt7 mutants also had a larger pool of readily-releasable vesicles, faster recovery following stimulation, and intact facilitation. Syt1/Syt7 double mutants displayed more release than Syt1 mutants alone, indicating SYT7 does not mediate the residual asynchronous release remaining in the absence of SYT1. SYT7 localizes to an internal membrane tubular network within the peri-active zone, but does not enrich at active zones. These findings indicate the two Ca2+ sensor model of SYT1 and SYT7 mediating all phases of neurotransmitter release and facilitation is not applicable at Drosophila synapses.
Collapse
Affiliation(s)
- Zhuo Guan
- The Picower Institute for Learning and Memory, Department of Biology and Department of Brain and Cognitive Sciences, Massachusetts Institute of TechnologyCambridgeUnited States
| | - Monica C Quiñones-Frías
- The Picower Institute for Learning and Memory, Department of Biology and Department of Brain and Cognitive Sciences, Massachusetts Institute of TechnologyCambridgeUnited States
| | - Yulia Akbergenova
- The Picower Institute for Learning and Memory, Department of Biology and Department of Brain and Cognitive Sciences, Massachusetts Institute of TechnologyCambridgeUnited States
| | - J Troy Littleton
- The Picower Institute for Learning and Memory, Department of Biology and Department of Brain and Cognitive Sciences, Massachusetts Institute of TechnologyCambridgeUnited States
| |
Collapse
|
13
|
Biancolin AD, Martchenko A, Mitova E, Gurges P, Michalchyshyn E, Chalmers JA, Doria A, Mychaleckyj JC, Adriaenssens AE, Reimann F, Gribble FM, Gil-Lozano M, Cox BJ, Brubaker PL. The core clock gene, Bmal1, and its downstream target, the SNARE regulatory protein secretagogin, are necessary for circadian secretion of glucagon-like peptide-1. Mol Metab 2020; 31:124-137. [PMID: 31918914 PMCID: PMC6920326 DOI: 10.1016/j.molmet.2019.11.004] [Citation(s) in RCA: 32] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/28/2019] [Revised: 10/24/2019] [Accepted: 11/01/2019] [Indexed: 12/16/2022] Open
Abstract
OBJECTIVES The incretin hormone glucagon-like peptide-1 (GLP-1) is secreted from intestinal L-cells upon nutrient intake. While recent evidence has shown that GLP-1 is released in a circadian manner in rats, whether this occurs in mice and if this pattern is regulated by the circadian clock remain to be elucidated. Furthermore, although circadian GLP-1 secretion parallels expression of the core clock gene Bmal1, the link between the two remains largely unknown. Secretagogin (Scgn) is an exocytotic SNARE regulatory protein that demonstrates circadian expression and is essential for insulin secretion from β-cells. The objective of the current study was to establish the necessity of the core clock gene Bmal1 and the SNARE protein SCGN as essential regulators of circadian GLP-1 secretion. METHODS Oral glucose tolerance tests were conducted at different times of the day on 4-hour fasted C57BL/6J, Bmal1 wild-type, and Bmal1 knockout mice. Mass spectrometry, RNA-seq, qRT-PCR and/or microarray analyses, and immunostaining were conducted on murine (m) and human (h) primary L-cells and mGLUTag and hNCI-H716 L-cell lines. At peak and trough GLP-1 secretory time points, the mGLUTag cells were co-stained for SCGN and a membrane-marker, ChIP was used to analyze BMAL1 binding sites in the Scgn promoter, protein interaction with SCGN was tested by co-immunoprecipitation, and siRNA was used to knockdown Scgn for GLP-1 secretion assay. RESULTS C57BL/6J mice displayed a circadian rhythm in GLP-1 secretion that peaked at the onset of their feeding period. Rhythmic GLP-1 release was impaired in Bmal1 knockout (KO) mice as compared to wild-type controls at the peak (p < 0.05) but not at the trough secretory time point. Microarray identified SNARE and transport vesicle pathways as highly upregulated in mGLUTag L-cells at the peak time point of GLP-1 secretion (p < 0.001). Mass spectrometry revealed that SCGN was also increased at this time (p < 0.001), while RNA-seq, qRT-PCR, and immunostaining demonstrated Scgn expression in all human and murine primary L-cells and cell lines. The mGLUTag and hNCI-H716 L-cells exhibited circadian rhythms in Scgn expression (p < 0.001). The ChIP analysis demonstrated increased binding of BMAL1 only at the peak of Scgn expression (p < 0.01). Immunocytochemistry showed the translocation of SCGN to the cell membrane after stimulation at the peak time point only (p < 0.05), while CoIP showed that SCGN was pulled down with SNAP25 and β-actin, but only the latter interaction was time-dependent (p < 0.05). Finally, Scgn siRNA-treated cells demonstrated significantly blunted GLP-1 secretion (p < 0.01) in response to stimulation at the peak time point only. CONCLUSIONS These data demonstrate, for the first time, that mice display a circadian pattern in GLP-1 secretion, which is impaired in Bmal1 knockout mice, and that Bmal1 regulation of Scgn expression plays an essential role in the circadian release of the incretin hormone GLP-1.
Collapse
Affiliation(s)
| | | | - Emilia Mitova
- Department of Physiology, University of Toronto, Toronto, ON, Canada
| | - Patrick Gurges
- Department of Physiology, University of Toronto, Toronto, ON, Canada
| | | | | | - Alessandro Doria
- Department of Medicine, Harvard Medical School, Boston, MA, USA; Research Division, Joslin Diabetes Center, Boston, MA, USA
| | - Josyf C Mychaleckyj
- Center for Public Health Genomics, University of Virginia, Charlottesville, VA, USA
| | - Alice E Adriaenssens
- Wellcome Trust-MRC Institute of Metabolic Science, University of Cambridge, Cambridge, UK
| | - Frank Reimann
- Wellcome Trust-MRC Institute of Metabolic Science, University of Cambridge, Cambridge, UK
| | - Fiona M Gribble
- Wellcome Trust-MRC Institute of Metabolic Science, University of Cambridge, Cambridge, UK
| | - Manuel Gil-Lozano
- Department of Physiology, University of Toronto, Toronto, ON, Canada
| | - Brian J Cox
- Department of Physiology, University of Toronto, Toronto, ON, Canada; Department of Obstetrics and Gynecology, University of Toronto, Toronto, ON, Canada
| | - Patricia L Brubaker
- Department of Physiology, University of Toronto, Toronto, ON, Canada; Department of Medicine, University of Toronto, Toronto, ON, Canada.
| |
Collapse
|
14
|
Brubaker PL. Glucagon‐like Peptide‐2 and the Regulation of Intestinal Growth and Function. Compr Physiol 2018; 8:1185-1210. [DOI: 10.1002/cphy.c170055] [Citation(s) in RCA: 51] [Impact Index Per Article: 8.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
|
15
|
Wheeler SE, Stacey HM, Nahaei Y, Hale SJ, Hardy AB, Reimann F, Gribble FM, Larraufie P, Gaisano HY, Brubaker PL. The SNARE Protein Syntaxin-1a Plays an Essential Role in Biphasic Exocytosis of the Incretin Hormone Glucagon-Like Peptide 1. Diabetes 2017; 66:2327-2338. [PMID: 28596237 PMCID: PMC6237272 DOI: 10.2337/db16-1403] [Citation(s) in RCA: 24] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/14/2016] [Accepted: 06/01/2017] [Indexed: 02/02/2023]
Abstract
Exocytosis of the hormone glucagon-like peptide 1 (GLP-1) by the intestinal L cell is essential for the incretin effect after nutrient ingestion and is critical for the actions of dipeptidyl peptidase 4 inhibitors that enhance GLP-1 levels in patients with type 2 diabetes. Two-photon microscopy revealed that exocytosis of GLP-1 is biphasic, with a first peak at 1-6 min and a second peak at 7-12 min after stimulation with forskolin. Approximately 75% of the exocytotic events were represented by compound granule fusion, and the remainder were accounted for by full fusion of single granules under basal and stimulated conditions. The core SNARE protein syntaxin-1a (syn1a) was expressed by murine ileal L cells. At the single L-cell level, first-phase forskolin-induced exocytosis was reduced to basal (P < 0.05) and second-phase exocytosis abolished (P < 0.05) by syn1a knockout. L cells from intestinal-epithelial syn1a-deficient mice demonstrated a 63% reduction in forskolin-induced GLP-1 release in vitro (P < 0.001) and a 23% reduction in oral glucose-stimulated GLP-1 secretion (P < 0.05) in association with impairments in glucose-stimulated insulin release (by 60%; P < 0.01) and glucose tolerance (by 20%; P < 0.01). The findings identify an exquisite mechanism of metered secretory output that precisely regulates release of the incretin hormone GLP-1 and hence insulin secretion after a meal.
Collapse
Affiliation(s)
- Sarah E Wheeler
- Department of Physiology, University of Toronto, Toronto, Ontario, Canada
| | - Holly M Stacey
- Department of Physiology, University of Toronto, Toronto, Ontario, Canada
| | - Yasaman Nahaei
- Department of Physiology, University of Toronto, Toronto, Ontario, Canada
| | - Stephen J Hale
- Department of Physiology, University of Toronto, Toronto, Ontario, Canada
| | | | - Frank Reimann
- Wellcome Trust-MRC Institute of Metabolic Science, Metabolic Research Laboratories, University of Cambridge, Addenbrooke's Hospital, Cambridge, U.K
| | - Fiona M Gribble
- Wellcome Trust-MRC Institute of Metabolic Science, Metabolic Research Laboratories, University of Cambridge, Addenbrooke's Hospital, Cambridge, U.K
| | - Pierre Larraufie
- Wellcome Trust-MRC Institute of Metabolic Science, Metabolic Research Laboratories, University of Cambridge, Addenbrooke's Hospital, Cambridge, U.K
| | - Herbert Y Gaisano
- Department of Physiology, University of Toronto, Toronto, Ontario, Canada
- Department of Medicine, University of Toronto, Toronto, Ontario, Canada
| | - Patricia L Brubaker
- Department of Physiology, University of Toronto, Toronto, Ontario, Canada
- Department of Medicine, University of Toronto, Toronto, Ontario, Canada
| |
Collapse
|
16
|
Dusaulcy R, Handgraaf S, Skarupelova S, Visentin F, Vesin C, Heddad-Masson M, Reimann F, Gribble F, Philippe J, Gosmain Y. Functional and Molecular Adaptations of Enteroendocrine L-Cells in Male Obese Mice Are Associated With Preservation of Pancreatic α-Cell Function and Prevention of Hyperglycemia. Endocrinology 2016; 157:3832-3843. [PMID: 27547850 PMCID: PMC7228810 DOI: 10.1210/en.2016-1433] [Citation(s) in RCA: 38] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
Glucose homeostasis depends on the coordinated secretion of glucagon, insulin, and Glucagon-like peptide (GLP)-1 by pancreas and intestine. Obesity, which is associated with an increased risk of developing insulin resistance and type 2 diabetes, affects the function of these organs. Here, we investigate the functional and molecular adaptations of proglucagon-producing cells in obese mice to better define their involvement in type 2 diabetes development. We used GLU-Venus transgenic male mice specifically expressing Venus fluorochrome in proglucagon-producing cells. Mice were subjected to 16 weeks of low-fat diet or high-fat diet (HFD) and then subdivided by measuring glycated hemoglobin (HbA1c) in 3 groups: low-fat diet mice and I-HFD (glucose-intolerant) mice with similar HbA1c and H-HFD (hyperglycemic) mice, which exhibited higher HbA1c. At 16 weeks, both HFD groups exhibited similar weight gain, hyperinsulinemia, and insulin resistance. However, I-HFD mice exhibited better glucose tolerance compared with H-HFD mice. I-HFD mice displayed functional and molecular adaptations of enteroendocrine L-cells resulting in increased intestinal GLP-1 biosynthesis and release as well as maintained pancreatic α- and β-cell functions. By contrast, H-HFD mice exhibited dysfunctional L, α- and β-cells with increased β- and L-cell numbers. Administration of the GLP-1R antagonist Exendin9-39 in I-HFD mice led to hyperglycemia and alterations of glucagon secretion without changes in insulin secretion. Our results highlight the cross-talk between islet and intestine endocrine cells and indicate that a compensatory adaptation of L-cell function in obesity plays an important role in preserving glucose homeostasis through the control of pancreatic α-cell functions.
Collapse
Affiliation(s)
- Rodolphe Dusaulcy
- Molecular Diabetes Laboratory, Division of Endocrinology, Diabetes, Hypertension and Nutrition; University Hospital/Diabetes Center/University of Geneva Medical School, 1211 Geneva, Switzerland
| | - Sandra Handgraaf
- Molecular Diabetes Laboratory, Division of Endocrinology, Diabetes, Hypertension and Nutrition; University Hospital/Diabetes Center/University of Geneva Medical School, 1211 Geneva, Switzerland
| | - Svetlana Skarupelova
- Molecular Diabetes Laboratory, Division of Endocrinology, Diabetes, Hypertension and Nutrition; University Hospital/Diabetes Center/University of Geneva Medical School, 1211 Geneva, Switzerland
| | - Florian Visentin
- Molecular Diabetes Laboratory, Division of Endocrinology, Diabetes, Hypertension and Nutrition; University Hospital/Diabetes Center/University of Geneva Medical School, 1211 Geneva, Switzerland
| | - Christian Vesin
- Department of Cell Physiology and Metabolism, University of Geneva School of Medicine, 1211 Geneva, Switzerland
| | - Mounia Heddad-Masson
- Molecular Diabetes Laboratory, Division of Endocrinology, Diabetes, Hypertension and Nutrition; University Hospital/Diabetes Center/University of Geneva Medical School, 1211 Geneva, Switzerland
| | - Frank Reimann
- Wellcome Trust/MRC Institute of Metabolic Science and MRC Metabolic Diseases Unit, University of Cambridge, Addenbrooke's Hospital, Cambridge, U.K
| | - Fiona Gribble
- Wellcome Trust/MRC Institute of Metabolic Science and MRC Metabolic Diseases Unit, University of Cambridge, Addenbrooke's Hospital, Cambridge, U.K
| | - Jacques Philippe
- Molecular Diabetes Laboratory, Division of Endocrinology, Diabetes, Hypertension and Nutrition; University Hospital/Diabetes Center/University of Geneva Medical School, 1211 Geneva, Switzerland
| | - Yvan Gosmain
- Molecular Diabetes Laboratory, Division of Endocrinology, Diabetes, Hypertension and Nutrition; University Hospital/Diabetes Center/University of Geneva Medical School, 1211 Geneva, Switzerland
- Address correspondence to: Yvan Gosmain, Molecular Diabetes Laboratory, University Hospital, 1211 Geneva 14, Switzerland, Tel. +41 22 372 42 37 ; Fax. +41 22 372 93 26,
| |
Collapse
|
17
|
Wang Y, Han C, Zhu W, Wu Z, Liu Y, Chen L. An optical method to evaluate both mass and functional competence of pancreatic α- and β-cells. J Cell Sci 2016; 129:2462-71. [PMID: 27173492 DOI: 10.1242/jcs.184523] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/09/2015] [Accepted: 04/28/2016] [Indexed: 01/09/2023] Open
Abstract
Imbalanced glucagon and insulin release leads to the onset of type 2 diabetes. To pinpoint the underlying primary driving force, here we have developed a fast, non-biased optical method to measure ratios of pancreatic α- and β-cell mass and function simultaneously. We firstly label both primary α- and β-cells with the red fluorescent probe ZinRhodaLactam-1 (ZRL1), and then highlight α-cells by selectively quenching the ZRL1 signal from β-cells. Based on the signals before and after quenching, we calculate the ratio of the α-cell to β-cell mass within live islets, which we found matched the results from immunohistochemistry. From the same islets, glucagon and insulin release capability can be concomitantly measured. Thus, we were able to measure the ratio of α-cell to β-cell mass and their function in wild-type and diabetic Lepr(db)/Lepr(db) (denoted db/db) mice at different ages. We find that the initial glucose intolerance that appears in 10-week-old db/db mice is associated with further expansion of α-cell mass prior to deterioration in functional β-cell mass. Our method is extendable to studies of islet mass and function in other type 2 diabetes animal models, which shall benefit mechanistic studies of imbalanced hormone secretion during type 2 diabetes progression.
Collapse
Affiliation(s)
- Yi Wang
- College of Life Science and Technology, Huazhong University of Science and Technology, Wuhan 430074, China State Key Laboratory of Membrane Biology, Beijing Key Laboratory of Cardiometabolic Molecular Medicine, Institute of Molecular Medicine, Peking University, Beijing 100871, China
| | - Chengsheng Han
- State Key Laboratory of Membrane Biology, Beijing Key Laboratory of Cardiometabolic Molecular Medicine, Institute of Molecular Medicine, Peking University, Beijing 100871, China
| | - Wenzhen Zhu
- State Key Laboratory of Membrane Biology, Beijing Key Laboratory of Cardiometabolic Molecular Medicine, Institute of Molecular Medicine, Peking University, Beijing 100871, China
| | - Zhengxing Wu
- College of Life Science and Technology, Huazhong University of Science and Technology, Wuhan 430074, China
| | - Yanmei Liu
- State Key Laboratory of Membrane Biology, Beijing Key Laboratory of Cardiometabolic Molecular Medicine, Institute of Molecular Medicine, Peking University, Beijing 100871, China
| | - Liangyi Chen
- State Key Laboratory of Membrane Biology, Beijing Key Laboratory of Cardiometabolic Molecular Medicine, Institute of Molecular Medicine, Peking University, Beijing 100871, China
| |
Collapse
|
18
|
Synaptotagmin-7 phosphorylation mediates GLP-1-dependent potentiation of insulin secretion from β-cells. Proc Natl Acad Sci U S A 2015. [PMID: 26216970 DOI: 10.1073/pnas.1513004112] [Citation(s) in RCA: 56] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022] Open
Abstract
Glucose stimulates insulin secretion from β-cells by increasing intracellular Ca(2+). Ca(2+) then binds to synaptotagmin-7 as a major Ca(2+) sensor for exocytosis, triggering secretory granule fusion and insulin secretion. In type-2 diabetes, insulin secretion is impaired; this impairment is ameliorated by glucagon-like peptide-1 (GLP-1) or by GLP-1 receptor agonists, which improve glucose homeostasis. However, the mechanism by which GLP-1 receptor agonists boost insulin secretion remains unclear. Here, we report that GLP-1 stimulates protein kinase A (PKA)-dependent phosphorylation of synaptotagmin-7 at serine-103, which enhances glucose- and Ca(2+)-stimulated insulin secretion and accounts for the improvement of glucose homeostasis by GLP-1. A phospho-mimetic synaptotagmin-7 mutant enhances Ca(2+)-triggered exocytosis, whereas a phospho-inactive synaptotagmin-7 mutant disrupts GLP-1 potentiation of insulin secretion. Our findings thus suggest that synaptotagmin-7 is directly activated by GLP-1 signaling and may serve as a drug target for boosting insulin secretion. Moreover, our data reveal, to our knowledge, the first physiological modulation of Ca(2+)-triggered exocytosis by direct phosphorylation of a synaptotagmin.
Collapse
|
19
|
Gagnon J, Baggio LL, Drucker DJ, Brubaker PL. Ghrelin Is a Novel Regulator of GLP-1 Secretion. Diabetes 2015; 64:1513-21. [PMID: 25412624 DOI: 10.2337/db14-1176] [Citation(s) in RCA: 80] [Impact Index Per Article: 8.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/30/2014] [Accepted: 11/15/2014] [Indexed: 12/16/2022]
Abstract
GLP-1 is a gastrointestinal L-cell hormone that enhances glucose-stimulated insulin secretion. Hence, strategies that prevent GLP-1 degradation or activate the GLP-1 receptor are used to treat patients with type 2 diabetes. GLP-1 secretion occurs after a meal and is partly regulated by other circulating hormones. Ghrelin is a stomach-derived hormone that plays a key role in whole-body energy metabolism. Because ghrelin levels peak immediately before mealtimes, we hypothesized that ghrelin plays a role in priming the intestinal L-cell for nutrient-induced GLP-1 release. The intraperitoneal injection of ghrelin into mice 15 min before the administration of oral glucose enhanced glucose-stimulated GLP-1 release and improved glucose tolerance, whereas the ghrelin receptor antagonist D-Lys GHRP-6 reduced plasma levels of GLP-1 and insulin and diminished oral glucose tolerance. The ghrelin-mediated improvement in glucose tolerance was lost in mice coinjected with a GLP-1 receptor antagonist as well as in Glp1r(-/-) mice lacking the GLP-1 receptor. The impaired oral glucose tolerance in diet-induced obese mice was also improved by ghrelin preadministration. Importantly, ghrelin directly stimulated GLP-1 release from L-cell lines (murine GLUTag, human NCI-H716) through an extracellular signal-related kinase 1/2-dependent pathway. These studies demonstrate a novel role for ghrelin in enhancing the GLP-1 secretory response to ingested nutrients.
Collapse
Affiliation(s)
- Jeffrey Gagnon
- Department of Physiology, University of Toronto, Toronto, Ontario, Canada
| | - Laurie L Baggio
- Department of Medicine, University of Toronto, Toronto, Ontario, Canada Lunenfeld-Tanenbaum Research Institute, University of Toronto, Toronto, Ontario, Canada
| | - Daniel J Drucker
- Department of Medicine, University of Toronto, Toronto, Ontario, Canada Lunenfeld-Tanenbaum Research Institute, University of Toronto, Toronto, Ontario, Canada
| | - Patricia L Brubaker
- Department of Physiology, University of Toronto, Toronto, Ontario, Canada Department of Medicine, University of Toronto, Toronto, Ontario, Canada
| |
Collapse
|
20
|
Li SK, Zhu D, Gaisano HY, Brubaker PL. Role of vesicle-associated membrane protein 2 in exocytosis of glucagon-like peptide-1 from the murine intestinal L cell. Diabetologia 2014; 57:809-18. [PMID: 24356748 DOI: 10.1007/s00125-013-3143-2] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/22/2013] [Accepted: 11/22/2013] [Indexed: 12/27/2022]
Abstract
AIMS/HYPOTHESIS Glucagon-like peptide-1 (GLP-1), secreted by the enteroendocrine L cell, is an incretin hormone that potently stimulates insulin secretion. Although signalling pathways promoting GLP-1 release are well characterised, the mechanisms by which GLP-1-containing granules fuse to the L cell membrane are unknown. As soluble NSF attachment proteins (SNAREs) are known to mediate granule-membrane fusion, the role of vesicle-associated membrane proteins (VAMPs) in GLP-1 exocytosis was examined. METHODS SNARE expression was determined in murine GLUTag L cells by RT-PCR and immunoblot and in primary murine L cells by immunofluorescence. Co-immunoprecipitation was used to examine SNARE interactions, while tetanus toxin (TetX)-mediated cleavage of VAMP was used with a GLP-1 secretion assay and total internal reflection fluorescence microscopy to determine the role of VAMP2 in exocytosis. RESULTS VAMP2 was expressed in murine L cells and localised to secretory granules in GLUTag cells. VAMP1/3 and the core membrane proteins syntaxin1a and synaptosomal-associated protein 25 kDa (SNAP25) were also detected. TetX cleaved VAMPs in GLUTag cells. However, only VAMP2 interacted with syntaxin1a, as did SNAP25 and Munc18-1. TetX treatment of GLUTag cells prevented glucose-dependent insulinotrophic peptide- and oleic-acid-stimulated GLP-1 secretion (p < 0.05-0.01), as well as K(+)-stimulated single-cell exocytosis (p < 0.05-0.001), while TetX-resistant VAMP2 expression rescued GLP-1 secretion (p < 0.01-0.001). CONCLUSIONS/INTERPRETATION Together, these findings indicate an essential role for VAMP2 in GLP-1 exocytosis from the GLUTag L cell in response to a variety of established secretagogues. An improved understanding of the mechanisms governing the release of GLP-1 may lead to new therapeutic approaches to enhance the levels of this incretin hormone in patients with type 2 diabetes.
Collapse
Affiliation(s)
- Samantha K Li
- Department of Physiology, Medical Sciences Building, 1 King's College Circle, University of Toronto, Toronto, ON, M5S 1A8, Canada
| | | | | | | |
Collapse
|
21
|
Mani BK, Chuang JC, Kjalarsdottir L, Sakata I, Walker AK, Kuperman A, Osborne-Lawrence S, Repa JJ, Zigman JM. Role of calcium and EPAC in norepinephrine-induced ghrelin secretion. Endocrinology 2014; 155:98-107. [PMID: 24189139 PMCID: PMC3868802 DOI: 10.1210/en.2013-1691] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
Ghrelin is an orexigenic hormone secreted principally from a distinct population of gastric endocrine cells. Molecular mechanisms regulating ghrelin secretion are mostly unknown. Recently, norepinephrine (NE) was shown to enhance ghrelin release by binding to β1-adrenergic receptors on ghrelin cells. Here, we use an immortalized stomach-derived ghrelin cell line to further characterize the intracellular signaling pathways involved in NE-induced ghrelin secretion, with a focus on the roles of Ca(2+) and cAMP. Several voltage-gated Ca(2+) channel (VGCC) family members were found by quantitative PCR to be expressed by ghrelin cells. Nifedipine, a selective L-type VGCC blocker, suppressed both basal and NE-stimulated ghrelin secretion. NE induced elevation of cytosolic Ca(2+) levels both in the presence and absence of extracellular Ca(2+). Ca(2+)-sensing synaptotagmins Syt7 and Syt9 were also highly expressed in ghrelin cell lines, suggesting that they too help mediate ghrelin secretion. Raising cAMP with the phosphodiesterase inhibitor 3-isobutyl-1-methylxanthine also stimulated ghrelin secretion, although such a cAMP-mediated effect likely does not involve protein kinase A, given the absence of a modulatory response to a highly selective protein kinase A inhibitor. However, pharmacological inhibition of another target of cAMP, exchange protein-activated by cAMP (EPAC), did attenuate both basal and NE-induced ghrelin secretion, whereas an EPAC agonist enhanced basal ghrelin secretion. We conclude that constitutive ghrelin secretion is primarily regulated by Ca(2+) influx through L-type VGCCs and that NE stimulates ghrelin secretion predominantly through release of intracellular Ca(2+). Furthermore, cAMP and its downstream activation of EPAC are required for the normal ghrelin secretory response to NE.
Collapse
Affiliation(s)
- Bharath K Mani
- Division of Endocrinology and Metabolism (B.K.M., J.-C.C., I.S., A.K.W., A.K., S.O.-L., J.M.Z.), Department of Internal Medicine; Division of Hypothalamic research (B.K.M., J.-C.C., L.K., I.S., A.K.W., A.K., S.O.-L., J.J.R., J.M.Z.), Department of Internal Medicine; and Departments of Psychiatry (B.K.M., J.-C.C., I.S., A.K.W., A.K., S.O.-L., J.M.Z.) and Physiology (L.K., J.J.R.), University of Texas Southwestern Medical Center, Dallas, Texas 75390
| | | | | | | | | | | | | | | | | |
Collapse
|
22
|
Seipin differentially regulates lipogenesis and adipogenesis through a conserved core sequence and an evolutionarily acquired C-terminus. Biochem J 2013; 452:37-44. [DOI: 10.1042/bj20121870] [Citation(s) in RCA: 36] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
Homozygous mutations in BSCL2 (Berardinelli–Seip congenital lipodystrophy)/seipin cause CGL2 (congenital generalized lipodystrophy type 2). Recent data suggest that seipin regulates LD (lipid droplet) dynamics and adipocyte differentiation, but whether these roles are mechanistically linked remains unclear. To understand how seipin regulates these processes, we investigated the evolutionary changes of seipin orthologues, and studied individual domains in regulating lipid accumulation in non-adipocytes and adipocytes. Mammalian seipins comprise at least two distinct functional domains, a conserved core sequence and an evolutionarily acquired C-terminus. Despite its requirement for adipocyte formation, seipin overexpression inhibited oleate-induced LD formation and accumulation in nonadipocytes, which was mediated by the core sequence. In contrast, seipin overexpression did not inhibit LD accumulation during adipocyte differentiation or the adipogenic process in 3T3-L1 cells. However, adipogenesis and LD accumulation were impaired in 3T3-L1 cells expressing a seipin mutant lacking the C-terminus. Furthermore, expression of the same mutant without the C-terminus failed to rescue the adipogenic defects in seipin-knockdown cells, demonstrating the importance of the C-terminus for seipin's function in adipocyte development. We propose that seipin is involved in lipid homoeostasis by restricting lipogenesis and LD accumulation in non-adipocytes, while promoting adipogenesis to accommodate excess energy storage.
Collapse
|
23
|
Gustavsson N, Wu B, Han W. Calcium sensing in exocytosis. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2012; 740:731-57. [PMID: 22453967 DOI: 10.1007/978-94-007-2888-2_32] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
Neurotransmitters, neuropeptides and hormones are released through regulated exocytosis of synaptic vesicles and large dense core vesicles. This complex and highly regulated process is orchestrated by SNAREs and their associated proteins. The triggering signal for regulated exocytosis is usually an increase in intracellular calcium levels. Besides the triggering role, calcium signaling modulates the precise amount and kinetics of vesicle release. Thus, it is a central question to understand the molecular machineries responsible for calcium sensing in exocytosis. Here we provide an overview of our current understanding of calcium sensing in neurotransmitter release and hormone secretion.
Collapse
Affiliation(s)
- Natalia Gustavsson
- Laboratory of Metabolic Medicine, Singapore Bioimaging Consortium, Agency for Science, Technology and Research, Singapore.
| | | | | |
Collapse
|