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Pálsson TG, Gilliam-Vigh H, Jensen BAH, Jeppesen PB, Lund AB, Knop FK, Nielsen CK. Targeting the GLP-2 receptor in the management of obesity. Peptides 2024; 177:171210. [PMID: 38579917 DOI: 10.1016/j.peptides.2024.171210] [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: 12/22/2023] [Revised: 03/27/2024] [Accepted: 04/01/2024] [Indexed: 04/07/2024]
Abstract
Recent advancements in understanding glucagon-like peptide 2 (GLP-2) biology and pharmacology have sparked interest in targeting the GLP-2 receptor (GLP-2R) in the treatment of obesity. GLP-2 is a proglucagon-derived 33-amino acid peptide co-secreted from enteroendocrine L cells along with glucagon-like peptide 1 (GLP-1) and has a range of actions via the GLP-2R, which is particularly expressed in the gastrointestinal tract, the liver, adipose tissue, and the central nervous system (CNS). In humans, GLP-2 evidently induces intestinotrophic effects (i.e., induction of intestinal mucosal proliferation and improved gut barrier function) and promotes mesenteric blood flow. However, GLP-2 does not seem to have appetite or food intake-reducing effects in humans, but its gut barrier-promoting effect may be of interest in the context of obesity. Obesity is associated with reduced gut barrier function, increasing the translocation of proinflammatory gut content to the circulation. This phenomenon constitutes a strong driver of obesity-associated systemic low-grade inflammation, which in turn plays a major role in the development of most obesity-associated complications. Thus, the intestinotrophic and gut barrier-improving effect of GLP-2, which in obese rodent models shows strong anti-inflammatory potential, may, in combination with food intake-reducing strategies, e.g., GLP-1 receptor (GLP-1) agonism, be able to rectify core pathophysiological mechanism of obesity. Here, we provide an overview of GLP-2 physiology in the context of obesity pathophysiology and review the pharmacological potential of GLP-2R activation in the management of obesity and related comorbidities.
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Affiliation(s)
- Thorir G Pálsson
- Center for Clinical Metabolic Research, Copenhagen University Hospital - Herlev and Gentofte, Hellerup, Denmark
| | - Hannah Gilliam-Vigh
- Center for Clinical Metabolic Research, Copenhagen University Hospital - Herlev and Gentofte, Hellerup, Denmark
| | - Benjamin A H Jensen
- Department of Biomedical Sciences, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
| | - Palle B Jeppesen
- Department of Clinical Medicine, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark; Department of Intestinal Failure and Liver Diseases, Rigshospitalet, Copenhagen University Hospital, Copenhagen, Denmark
| | - Asger B Lund
- Center for Clinical Metabolic Research, Copenhagen University Hospital - Herlev and Gentofte, Hellerup, Denmark; Steno Diabetes Center Copenhagen, Copenhagen University Hospital, Herlev, Denmark
| | - Filip K Knop
- Center for Clinical Metabolic Research, Copenhagen University Hospital - Herlev and Gentofte, Hellerup, Denmark; Department of Clinical Medicine, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark; Steno Diabetes Center Copenhagen, Copenhagen University Hospital, Herlev, Denmark
| | - Casper K Nielsen
- Center for Clinical Metabolic Research, Copenhagen University Hospital - Herlev and Gentofte, Hellerup, Denmark.
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2
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Gadgaard S, van der Velden WJC, Schiellerup SP, Hunt JE, Gabe MBN, Windeløv JA, Boer GA, Kissow H, Ørskov C, Holst JJ, Hartmann B, Rosenkilde MM. Novel agonist- and antagonist-based radioligands for the GLP-2 receptor - useful tools for studies of basic GLP-2R pharmacology. Br J Pharmacol 2021; 179:1998-2015. [PMID: 34855984 PMCID: PMC9303331 DOI: 10.1111/bph.15766] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/18/2020] [Revised: 10/22/2021] [Accepted: 11/10/2021] [Indexed: 11/27/2022] Open
Abstract
Background Glucagon‐like peptide‐2 (GLP‐2) is a pro‐glucagon‐derived hormone secreted from intestinal enteroendocrine L cells with actions on gut and bones. GLP‐2(1–33) is cleaved by DPP‐4, forming GLP‐2(3–33), having low intrinsic activity and competitive antagonism properties at GLP‐2 receptors. We created radioligands based on these two molecules. Experimental approach The methionine in position 10 of GLP‐2(1–33) and GLP‐2(3–33) was substituted with tyrosine (M10Y) enabling oxidative iodination, creating [125I]‐hGLP‐2(1–33,M10Y) and [125I]‐hGLP‐2(3–33,M10Y). Both were characterized by competition binding, on‐and‐off‐rate determination and receptor activation. Receptor expression was determined by target‐tissue autoradiography and immunohistochemistry. Key results Both M10Y‐substituted peptides induced cAMP production via the GLP‐2 receptor comparable to the wildtype peptides. GLP‐2(3–33,M10Y) maintained the antagonistic properties of GLP‐2(3–33). However, hGLP‐2(1–33,M10Y) had lower arrestin recruitment than hGLP‐2(1–33). High affinities for the hGLP‐2 receptor were observed using [125I]‐hGLP‐2(1–33,M10Y) and [125I]‐hGLP‐2(3–33,M10Y) with KD values of 59.3 and 40.6 nM. The latter (with antagonistic properties) had higher Bmax and faster on and off rates compared to the former (full agonist). Both bound the hGLP‐1 receptor with low affinity (Ki of 130 and 330 nM, respectively). Autoradiography in wildtype mice revealed strong labelling of subepithelial myofibroblasts, confirmed by immunohistochemistry using a GLP‐2 receptor specific antibody that in turn was confirmed in GLP‐2 receptor knock‐out mice. Conclusion and implications Two new radioligands with different binding kinetics, one a full agonist and the other a weak partial agonist with antagonistic properties were developed and subepithelial myofibroblasts identified as a major site for GLP‐2 receptor expression.
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Affiliation(s)
- Sarina Gadgaard
- Laboratory of Molecular Pharmacology, Department of Biomedical Sciences, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark.,Bainan Biotech, Copenhagen, Denmark
| | - Wijnand J C van der Velden
- Laboratory of Molecular Pharmacology, Department of Biomedical Sciences, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark.,Present address: Department of Computational & Quantitative Medicine, Beckman Research Institute of the City of Hope, Duarte, California, USA
| | - Sine P Schiellerup
- Laboratory of Molecular Pharmacology, Department of Biomedical Sciences, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
| | - Jenna Elizabeth Hunt
- Endocrinology and Metabolism, Department of Biomedical Sciences, Faculty of Health and Medical Sciences, University of Copenhagen, Denmark
| | - Maria B N Gabe
- Laboratory of Molecular Pharmacology, Department of Biomedical Sciences, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
| | - Johanne Agerlin Windeløv
- Novo Nordisk Foundation Center for Basic Metabolic Research, University of Copenhagen, Copenhagen, Denmark
| | - Geke Aline Boer
- Endocrinology and Metabolism, Department of Biomedical Sciences, Faculty of Health and Medical Sciences, University of Copenhagen, Denmark
| | - Hannelouise Kissow
- Endocrinology and Metabolism, Department of Biomedical Sciences, Faculty of Health and Medical Sciences, University of Copenhagen, Denmark
| | - Cathrine Ørskov
- Endocrinology and Metabolism, Department of Biomedical Sciences, Faculty of Health and Medical Sciences, University of Copenhagen, Denmark
| | - Jens J Holst
- Endocrinology and Metabolism, Department of Biomedical Sciences, Faculty of Health and Medical Sciences, University of Copenhagen, Denmark.,Novo Nordisk Foundation Center for Basic Metabolic Research, University of Copenhagen, Copenhagen, Denmark
| | - Bolette Hartmann
- Endocrinology and Metabolism, Department of Biomedical Sciences, Faculty of Health and Medical Sciences, University of Copenhagen, Denmark.,Novo Nordisk Foundation Center for Basic Metabolic Research, University of Copenhagen, Copenhagen, Denmark
| | - Mette M Rosenkilde
- Laboratory of Molecular Pharmacology, Department of Biomedical Sciences, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
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3
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Moo EV, van Senten JR, Bräuner-Osborne H, Møller TC. Arrestin-Dependent and -Independent Internalization of G Protein-Coupled Receptors: Methods, Mechanisms, and Implications on Cell Signaling. Mol Pharmacol 2021; 99:242-255. [PMID: 33472843 DOI: 10.1124/molpharm.120.000192] [Citation(s) in RCA: 45] [Impact Index Per Article: 15.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/27/2020] [Accepted: 01/07/2021] [Indexed: 01/05/2023] Open
Abstract
Agonist-induced endocytosis is a key regulatory mechanism for controlling the responsiveness of the cell by changing the density of cell surface receptors. In addition to the role of endocytosis in signal termination, endocytosed G protein-coupled receptors (GPCRs) have been found to signal from intracellular compartments of the cell. Arrestins are generally believed to be the master regulators of GPCR endocytosis by binding to both phosphorylated receptors and adaptor protein 2 (AP-2) or clathrin, thus recruiting receptors to clathrin-coated pits to facilitate the internalization process. However, many other functions have been described for arrestins that do not relate to their role in terminating signaling. Additionally, there are now more than 30 examples of GPCRs that internalize independently of arrestins. Here we review the methods, pharmacological tools, and cellular backgrounds used to determine the role of arrestins in receptor internalization, highlighting their advantages and caveats. We also summarize key examples of arrestin-independent GPCR endocytosis in the literature and their suggested alternative endocytosis pathway (e.g., the caveolae-dependent and fast endophilin-mediated endocytosis pathways). Finally, we consider the possible function of arrestins recruited to GPCRs that are endocytosed independently of arrestins, including the catalytic arrestin activation paradigm. Technological improvements in recent years have advanced the field further, and, combined with the important implications of endocytosis on drug responses, this makes endocytosis an obvious parameter to include in molecular pharmacological characterization of ligand-GPCR interactions. SIGNIFICANCE STATEMENT: G protein-coupled receptor (GPCR) endocytosis is an important means to terminate receptor signaling, and arrestins play a central role in the widely accepted classical paradigm of GPCR endocytosis. In contrast to the canonical arrestin-mediated internalization, an increasing number of GPCRs are found to be endocytosed via alternate pathways, and the process appears more diverse than the previously defined "one pathway fits all."
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Affiliation(s)
- Ee Von Moo
- Department of Drug Design and Pharmacology, University of Copenhagen, Copenhagen, Denmark
| | - Jeffrey R van Senten
- Department of Drug Design and Pharmacology, University of Copenhagen, Copenhagen, Denmark
| | - Hans Bräuner-Osborne
- Department of Drug Design and Pharmacology, University of Copenhagen, Copenhagen, Denmark
| | - Thor C Møller
- Department of Drug Design and Pharmacology, University of Copenhagen, Copenhagen, Denmark
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4
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Gobron B, Bouvard B, Legrand E, Chappard D, Mabilleau G. GLP-2 administration in ovariectomized mice enhances collagen maturity but did not improve bone strength. Bone Rep 2020; 12:100251. [PMID: 32071954 PMCID: PMC7013338 DOI: 10.1016/j.bonr.2020.100251] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/28/2019] [Revised: 02/03/2020] [Accepted: 02/04/2020] [Indexed: 02/07/2023] Open
Abstract
Osteoporosis and bone fragility are progressing worldwide. Previous published literature reported a possible beneficial role of gut hormones, and especially glucagon-like peptide-2 (GLP-2), in modulating bone remodeling. As now (Gly2)GLP-2 is approved in the treatment of short bowel syndrome, we thought to investigate whether such molecule could be beneficial in bone fragility. MC3T3 and Raw 264.7 were cultured in presence of ascending concentrations of (Gly2)GLP-2. Collagen crosslinks, maturity, lysyl oxidase activity and osteoclastogenesis were then analyzed. Furthermore, (Gly2)GLP-2, at the clinical approved dose of 50 μg/kg/day, was also administered to ovariectomized Balb/c mice for 8 weeks. Hundred μg/kg zoledronic acid (once iv) was also used as a positive comparator. Bone strength, microarchitectures and bone tissue composition were analyzed by 3-point bending, compression test, microCT and Fourier transform infrared imaging, respectively. In vitro, (Gly2)GLP-2 was potent in enhancing bone matrix gene expression but also to dose-dependently enhanced collagen maturation and post-processing. (Gly2)GLP-2 was also capable of reducing dose-dependently the number of newly generated osteoclasts. However, in vivo, (Gly2)GLP-2 was not capable of improving neither bone strength, at the femur diaphysis or lumbar vertebrae, nor bone microarchitecture. On the other hand, at the tissue material level, (Gly2)GLP-2 significantly enhances collagen maturity and reduce phosphate/amide ratio. Overall, this study highlights that despite modification of bone tissue composition, (Gly2)GLP-2, at the clinical approved dose of 50 μg/kg/day, did not provide real beneficial effects in improving bone strength in a mouse model of bone fragility. Further studies are recommended to validate the best dose and regimen of administration to significantly enhance bone strength. In vitro, (Gly2)GLP-2 enhances dose-dependently bone matrix deposition and quality. In vitro, (Gly2)GLP-2 reduces dose-dependently osteoclast formation. In vivo, (Gly2)GLP-2 failed to improve bone strength in ovariectomy-induced bone loss. In vivo, (Gly2)GLP-2 failed to improve bone microarchitecture. In vivo, (Gly2)GLP-2 increased collagen maturity and phosphate/amide ratios.
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Affiliation(s)
- B Gobron
- Groupe études remodelage osseux et biomatériaux, GEROM, UPRES EA4658, UNIV Angers, SFR 42-08, Institut de Biologie en Santé, CHU d'Angers, 49933 Angers cedex, France.,Service de Rhumatologie, CHU d'Angers, 49933 Angers cedex, France
| | - B Bouvard
- Groupe études remodelage osseux et biomatériaux, GEROM, UPRES EA4658, UNIV Angers, SFR 42-08, Institut de Biologie en Santé, CHU d'Angers, 49933 Angers cedex, France.,Service de Rhumatologie, CHU d'Angers, 49933 Angers cedex, France
| | - E Legrand
- Groupe études remodelage osseux et biomatériaux, GEROM, UPRES EA4658, UNIV Angers, SFR 42-08, Institut de Biologie en Santé, CHU d'Angers, 49933 Angers cedex, France.,Service de Rhumatologie, CHU d'Angers, 49933 Angers cedex, France
| | - D Chappard
- Groupe études remodelage osseux et biomatériaux, GEROM, UPRES EA4658, UNIV Angers, SFR 42-08, Institut de Biologie en Santé, CHU d'Angers, 49933 Angers cedex, France.,Service commun d'imageries et d'analyses microscopiques, SCIAM, UNIV Angers, SFR 42-08, Institut de Biologie en Santé, CHU d'Angers, 49933 Angers cedex, France.,UF de Pathologie osseuse, CHU d'Angers, 49933 Angers cedex, France
| | - G Mabilleau
- Groupe études remodelage osseux et biomatériaux, GEROM, UPRES EA4658, UNIV Angers, SFR 42-08, Institut de Biologie en Santé, CHU d'Angers, 49933 Angers cedex, France.,Service commun d'imageries et d'analyses microscopiques, SCIAM, UNIV Angers, SFR 42-08, Institut de Biologie en Santé, CHU d'Angers, 49933 Angers cedex, France.,UF de Pathologie osseuse, CHU d'Angers, 49933 Angers cedex, France
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5
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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]
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6
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Yang J, Shen Z, Jiang X, Yang H, Huang H, Jin L, Chen Y, Shi L, Zhou N. Agonist-Activated Bombyx Corazonin Receptor Is Internalized via an Arrestin-Dependent and Clathrin-Independent Pathway. Biochemistry 2016; 55:3874-87. [PMID: 27348044 DOI: 10.1021/acs.biochem.6b00250] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Agonist-induced internalization plays a key role in the tight regulation of the extent and duration of G protein-coupled receptor signaling. Previously, we have shown that the Bombyx corazonin receptor (BmCrzR) activates both Gαq- and Gαs-dependent signaling cascades. However, the molecular mechanisms involved in the regulation of the internalization and desensitization of BmCrzR remain to be elucidated. Here, vectors for expressing BmCrzR fused with enhanced green fluorescent protein (EGFP) at the C-terminal end were used to further characterize BmCrzR internalization. We found that the BmCrzR heterologously expressed in HEK-293 and BmN cells was rapidly internalized from the plasma membrane into the cytoplasm in a concentration- and time-dependent manner via a β-arrestin (Kurtz)-dependent and clathrin-independent pathway in response to agonist challenge. While most of the internalized receptors were recycled to the cell surface via early endosomes, some others were transported to lysosomes for degradation. Assays using RNA interference revealed that both GRK2 and GRK5 were essentially involved in the regulation of BmCrzR phosphorylation and internalization. Further investigations indicated that the identified cluster of Ser/Thr residues ((411)TSS(413)) was responsible for GRK-mediated phosphorylation and internalization. This is the first detailed investigation of the internalization and trafficking of Bombyx corazonin receptors.
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Affiliation(s)
- Jingwen Yang
- National Engineering Research Center of Marine Facilities Aquaculture, Zhejiang Ocean University , Zhoushan, Zhejiang 316022, China.,Department of Economic Zoology, College of Animal Sciences, Zhejiang University , Hangzhou, Zhejiang 310058, China
| | - Zhangfei Shen
- Department of Economic Zoology, College of Animal Sciences, Zhejiang University , Hangzhou, Zhejiang 310058, China
| | - Xue Jiang
- Department of Economic Zoology, College of Animal Sciences, Zhejiang University , Hangzhou, Zhejiang 310058, China
| | - Huipeng Yang
- College of Life Sciences, Zhejiang University , Zijingang Campus, Hangzhou, Zhejiang, China
| | - Haishan Huang
- Zhejiang Provincial Key Laboratory of Medical Genetics, School of Laboratory Medicine and Life Science, Wenzhou Medical University , Wenzhou, Zhejiang 325035, China
| | - Lili Jin
- College of Life Sciences, Zhejiang University , Zijingang Campus, Hangzhou, Zhejiang, China
| | - Yajie Chen
- Department of Economic Zoology, College of Animal Sciences, Zhejiang University , Hangzhou, Zhejiang 310058, China
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7
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Qian J, Wu C, Chen X, Li X, Ying G, Jin L, Ma Q, Li G, Shi Y, Zhang G, Zhou N. Differential requirements of arrestin-3 and clathrin for ligand-dependent and -independent internalization of human G protein-coupled receptor 40. Cell Signal 2014; 26:2412-23. [DOI: 10.1016/j.cellsig.2014.07.019] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/22/2014] [Revised: 06/06/2014] [Accepted: 07/10/2014] [Indexed: 10/25/2022]
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8
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Munesue S, Yamamoto Y, Urushihara R, Inomata K, Saito H, Motoyoshi S, Watanabe T, Yonekura H, Yamamoto H. Low-molecular weight fractions of Japanese soy sauce act as a RAGE antagonist via inhibition of RAGE trafficking to lipid rafts. Food Funct 2014; 4:1835-42. [PMID: 24191276 DOI: 10.1039/c2fo30359k] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
Advanced glycation end-products (AGE) have been implicated in aging and the pathogenesis of diabetic complications, inflammation, Alzheimer's disease, and cancer. AGE engage the cell surface receptor for AGE (RAGE), which in turn elicits intracellular signaling, leading to activation of NF-κB to cause deterioration of tissue homeostasis. AGE are not only formed within our bodies but are also derived from foods, endowing them with flavor. In the present study, we assessed the agonistic/antagonistic effects of food-derived AGE on RAGE signaling in a reporter assay system and found that low-molecular weight AGE can antagonize the action of AGE-BSA. Foods tested were Japanese soy sauce, coffee, cola, and red wine, all of which showed fluorescence characteristics of AGE. Soy sauce and coffee contained N(ε)-carboxymethyl-lysine (CML). Soy sauce, coffee, and red wine inhibited the RAGE ligand-induced activation of NF-κB, whereas cola had no effect on the ligand induction of NF-κB. The liquids were then fractionated into high-molecular weight (HMW) fractions and low-molecular weight (LMW) fractions. Soy sauce-, coffee-, and red wine-derived LMW fractions consistently inhibited the RAGE ligand induction of NF-κB, whereas the HMW fractions of these foods activated RAGE signaling. Using the LMW fraction of soy sauce as a model food-derived RAGE antagonist, we performed a plate-binding assay and found that the soy sauce LMW fractions competitively inhibited AGE-RAGE association. Further, this fraction significantly reduced AGE-dependent monocyte chemoattractant protein-1 (MCP-1) secretion from murine peritoneal macrophages. The LMF from soy sauce suppressed the AGE-induced RAGE trafficking to lipid rafts. These results indicate that small components in some, if not all, foods antagonize RAGE signaling and could exhibit beneficial effects on RAGE-related diseases.
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Affiliation(s)
- Seiichi Munesue
- Department of Biochemistry and Molecular Vascular Biology, Graduate School of Medical Sciences, Kanazawa University, 13-1 Takara-machi, Kanazawa 920-8640, Japan.
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9
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Drucker DJ, Yusta B. Physiology and pharmacology of the enteroendocrine hormone glucagon-like peptide-2. Annu Rev Physiol 2013; 76:561-83. [PMID: 24161075 DOI: 10.1146/annurev-physiol-021113-170317] [Citation(s) in RCA: 225] [Impact Index Per Article: 20.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Abstract
Glucagon-like peptide-2 (GLP-2) is a 33-amino-acid proglucagon-derived peptide secreted from enteroendocrine L cells. GLP-2 circulates at low basal levels in the fasting period, and plasma levels rise rapidly after food ingestion. Renal clearance and enzymatic inactivation control the elimination of bioactive GLP-2. GLP-2 increases mesenteric blood flow and activates proabsorptive pathways in the gut, facilitating nutrient absorption. GLP-2 also enhances gut barrier function and induces proliferative and cytoprotective pathways in the small bowel. The actions of GLP-2 are transduced via a single G protein-coupled receptor (GLP-2R), expressed predominantly within the gastrointestinal tract. Disruption of GLP-2R signaling increases susceptibility to gut injury and impairs the adaptive mucosal response to refeeding. Sustained augmentation of GLP-2R signaling reduces the requirement for parenteral nutrition in human subjects with short-bowel syndrome. Hence GLP-2 integrates nutrient-derived signals to optimize mucosal integrity and energy absorption.
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Affiliation(s)
- Daniel J Drucker
- Department of Medicine, Mount Sinai Hospital, Lunenfeld Tanenbaum Research Institute, University of Toronto, Toronto, Ontario, Canada M5G 1X5; ,
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10
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Taylor-Edwards CC, Burrin DG, Holst JJ, McLeod KR, Harmon DL. Glucagon-like peptide-2 (GLP-2) increases small intestinal blood flow and mucosal growth in ruminating calves. J Dairy Sci 2011; 94:888-98. [PMID: 21257057 DOI: 10.3168/jds.2010-3540] [Citation(s) in RCA: 43] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/16/2010] [Accepted: 10/03/2010] [Indexed: 01/27/2023]
Abstract
Glucagon-like peptide-2 (GLP-2) increases small intestinal mass and blood flow in nonruminants but its effect in ruminants is unknown. Eight Holstein calves with an ultrasonic flow probe around the superior mesenteric artery and catheters in the carotid artery and mesenteric vein were paired by age and randomly assigned to treatment of a control (0.5% of BSA in saline; n=4) or GLP-2 (50 μg/kg of body weight of bovine GLP-2 in BSA; n=4) given subcutaneously every 12h for 10 d. Blood flow was measured on d 0 (acute) and d 10 (chronic) and included 3 periods: baseline (saline infusion), treatment (infusion of BSA or 1,000 pmol of GLP-2/kg of body weight per h), and recovery (saline infusion). On d 11, calves were killed 2h after injection of 5-bromo-2'-deoxyuridine (BrdU). Gastrointestinal tissues were weighed and epithelial samples were obtained to determine villus height, crypt depth, and BrdU staining. Infusion of GLP-2 increased superior mesenteric artery blood flow to 175% of baseline on d 0 but to only 137% of baseline after chronic treatment. Compared with that of the control, GLP-2 increased small intestinal mass by 24% by increasing epithelial mass in the jejunum and ileum. Additionally, GLP-2 increased villus height, crypt depth, and BrdU-labeling in small intestinal segments. These results demonstrate that GLP-2 induces similar increases in small intestinal blood flow and growth in ruminants to those observed in nonruminants. Furthermore, GLP-2 increases small intestinal blood flow in ruminants but this response is attenuated after 10 d of GLP-2 administration. In cattle, GLP-2 may be an important hormone in the regulation of intestinal blood flow and epithelial growth.
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Affiliation(s)
- C C Taylor-Edwards
- Department of Animal and Food Sciences, University of Kentucky, Lexington 40546, USA
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11
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Leen JLS, Izzo A, Upadhyay C, Rowland KJ, Dubé PE, Gu S, Heximer SP, Rhodes CJ, Storm DR, Lund PK, Brubaker PL. Mechanism of action of glucagon-like peptide-2 to increase IGF-I mRNA in intestinal subepithelial fibroblasts. Endocrinology 2011; 152:436-46. [PMID: 21159855 PMCID: PMC3384785 DOI: 10.1210/en.2010-0822] [Citation(s) in RCA: 47] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
IGF-I, a known secretory product of intestinal subepithelial myofibroblasts (ISEMFs), is essential for the intestinotropic effects of glucagon-like peptide-2 (GLP-2). Furthermore, GLP-2 increases IGF-I mRNA transcript levels in vitro in heterogeneous fetal rat intestinal cultures, as well as in vivo in the rodent small intestine. To determine the mechanism underlying the stimulatory effect of GLP-2 on intestinal IGF-I mRNA, murine ISEMF cells were placed into primary culture. Immunocytochemistry showed that the ISEMF cells appropriately expressed α-smooth muscle actin and vimentin but not desmin. The cells also expressed GLP-2 receptor and IGF-I mRNA transcripts. Treatment of ISEMF cells with (Gly2)GLP-2 induced IGF-I mRNA transcripts by up to 5-fold of basal levels after treatment with 10(-8) m GLP-2 for 2 h (P < 0.05) but did not increase transcript levels for other intestinal growth factors, such as ErbB family members. Immunoblot revealed a 1.6-fold increase in phospho (p)-Akt/total-(t)Akt with 10(-8) m GLP-2 treatment (P < 0.05) but no changes in cAMP, cAMP-dependent β-galactosidase expression, pcAMP response element-binding protein/tcAMP response element-binding protein, pErk1/2/tErk1/2, or intracellular calcium. Furthermore, pretreatment of ISEMF cells with the phosphatidylinositol 3 kinase (PI3K) inhibitors, LY294002 and wortmannin, abrogated the IGF-I mRNA response to GLP-2, as did overexpression of kinase-dead Akt. The role of PI3K/Akt in GLP-2-induced IGF-I mRNA levels in the murine jejunum was also confirmed in vivo. These findings implicate the PI3K/Akt pathway in the stimulatory effects of GLP-2 to enhance intestinal IGF-I mRNA transcript levels and provide further evidence in support of a role for IGF-I produced by the ISEMF cells in the intestinotropic effects of GLP-2.
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Affiliation(s)
- Jason L S Leen
- Department of Physiology,University of Toronto, Toronto, Ontario, Canada
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12
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Amato A, Rotondo A, Cinci L, Baldassano S, Vannucchi MG, Mulè F. Role of cholinergic neurons in the motor effects of glucagon-like peptide-2 in mouse colon. Am J Physiol Gastrointest Liver Physiol 2010; 299:G1038-44. [PMID: 20705903 DOI: 10.1152/ajpgi.00282.2010] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
Glucagon-like peptide-2 (GLP-2) reduces mouse gastric tone and small intestine transit, but its action on large intestine motility is still unknown. The purposes of the present study were 1) to examine the influence of GLP-2 on spontaneous mechanical activity and on neurally evoked responses, by recording intraluminal pressure from mouse isolated colonic segments; 2) to characterize GLP-2 mechanism of action; and 3) to determine the distribution of GLP-2 receptor (GLP-2R) in the mouse colonic muscle coat by immunohistochemistry. Exogenous GLP-2 (0.1-300 nM) induced a concentration-dependent reduction of the spontaneous mechanical activity, which was abolished by the desensitization of GLP-2 receptor or by tetrodotoxin, a voltage-dependent Na(+)-channel blocker. GLP-2 inhibitory effect was not affected by N(ω)-nitro-l-arginine methyl ester (a nitric oxide synthase inhibitor), apamin (a blocker of small conductance Ca(2+)-dependent K(+) channels), or [Lys1,Pro2,5,Arg3,4,Tyr6]VIP(7-28) (a VIP receptor antagonist), but it was prevented by atropine or pertussis toxin (PTX), a G(i/o) protein inhibitor. Proximal colon responses to electrical field stimulation were characterized by nitrergic relaxation, which was followed by cholinergic contraction. GLP-2 reduced only the cholinergic evoked contractions. This effect was almost abolished by GLP-2 receptor desensitization or PTX. GLP-2 failed to affect the contractile responses to exogenous carbachol. GLP-2R immunoreactivity (IR) was detected only in the neuronal cells of both plexuses of the colonic muscle coat. More than 50% of myenteric GLP-2R-IR neurons shared the choline acetyltransferase IR. In conclusion, the activation of GLP-2R located on cholinergic neurons may modulate negatively the colonic spontaneous and electrically evoked contractions through inhibition of acetylcholine release. The effect is mediated by G(i) protein.
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Affiliation(s)
- Antonella Amato
- Dipartimento di Biologia cellulare e dello Sviluppo, Università di Palermo, Palermo, Italy
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13
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Cong P, Pricolo V, Biancani P, Behar J. Effects of cholesterol on CCK-1 receptors and caveolin-3 proteins recycling in human gallbladder muscle. Am J Physiol Gastrointest Liver Physiol 2010; 299:G742-50. [PMID: 20558763 PMCID: PMC2950694 DOI: 10.1152/ajpgi.00064.2010] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
The contraction of gallbladders (GBs) with cholesterol stones is impaired due to high cholesterol concentrations in caveolae compared with GBs with pigment stones. The reduced contraction is caused by a lower cholecystokinin (CCK)-8 binding to CCK-1 receptors (CCK-1R) due to caveolar sequestration of receptors. We aimed to examine the mechanism of cholesterol-induced sequestration of receptors. Muscle cells from human and guinea pig GBs were studied. Antibodies were used to examine CCK-1R, antigens of early and recycling endosomes, and total (CAV-3) and phosphorylated caveolar-3 protein (pCAV-3) by Western blots. Contraction was measured in muscle cells transfected with CAV3 mRNA or clathrin heavy-chain small-interfering RNA (siRNA). CCK-1R returned back to the bulk plasma membrane (PM) 30 min after CCK-8 recycled by endosomes, peaking at 5 min in early endosomes and at 20 min in recycling endosomes. Pretreatment with cholesterol-rich liposomes inhibited the transfer of CCK-1R and of CAV-3 in the endosomes by blocking CAV-3 phosphorylation. 4-Amino-5-(4-chloro-phenyl)-7-(t-butyl)pyrazolo[3,4-d]pyrimidine (inhibitor of tyrosine kinase) reproduced these effects by blocking pCAV-3 formation, increasing CAV-3 and CCK-1R sequestration in the caveolae and impairing CCK-8-induced contraction. CAV-3 siRNA reduced CAV-3 protein expression, decreased CCK-8-induced contraction, and accumulated CCK-1R in the caveolae. Abnormal concentrations of caveolar cholesterol had no effect on met-enkephalin that stimulates a delta-opioid receptor that internalizes through clathrin. We found that impaired muscle contraction in GBs with cholesterol stones is due to high caveolar levels of cholesterol that inhibits pCAV-3 generation. Caveolar cholesterol increases the caveolar sequestration of CAV-3 and CCK-1R caused by their reduced recycling to the PM.
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Affiliation(s)
- P. Cong
- Departments of 1Medicine and
| | - V. Pricolo
- 2Surgery, Rhode Island Hospital and Brown University Medical School, Providence, Rhode Island
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Gylfason GA, Knútsdóttir E, Asgeirsson B. Isolation and biochemical characterisation of lipid rafts from Atlantic cod (Gadus morhua) intestinal enterocytes. Comp Biochem Physiol B Biochem Mol Biol 2009; 155:86-95. [PMID: 19854289 DOI: 10.1016/j.cbpb.2009.10.006] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/06/2009] [Revised: 10/15/2009] [Accepted: 10/15/2009] [Indexed: 01/21/2023]
Abstract
Lipid rafts are glycosphingolipid/cholesterol-enriched membrane microdomains that have been extensively studied during the past two decades. Our aim was to isolate and perform biochemical characterization of lipid rafts from the intestinal brush border membrane (BBM) of Atlantic cod (Gadus morhua) to confirm their existence in a cold-water species and compare their characteristics with lipid rafts from other species in terms of lipid and protein content. To validate the isolation process, we assayed marker enzymes for subcellular organelles, including alkaline phosphatase (AP) and leucine aminopeptidase (LAP), both well-known marker enzymes for BBM and lipid rafts. All biochemical methods showed enrichment of AP in both the BBM and lipid raft fractions. Proteomic studies were performed by MALDI-TOF mass spectrometry using trypsin digested SDS-PAGE samples. Various proteins were associated with the cod intestinal lipid raft preparation such as aminopeptidase-N, prohibitin, and beta-actin. Lipid analysis with (31)P NMR and thin layer chromatography on BBMs and lipid rafts samples gave higher content of sphingomyelin than previously reported in the BBM and lower content of phosphatidylcholine. Furthermore, sphingomyelin was highly dominant in the lipid rafts together with cholesterol. The existence of lipid rafts containing previously reported lipid raft characteristics from the cod intestine has, therefore, been confirmed in a ray-finned fish for the first time to the best of our knowledge.
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Affiliation(s)
- Gudjón Andri Gylfason
- Department of Biochemistry, Science Institute, University of Iceland, Dunhagi 3, 107 Reykjavik, Iceland
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15
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Velázquez E, Blázquez E, Ruiz-Albusac JM. Synergistic effect of glucagon-like peptide 2 (GLP-2) and of key growth factors on the proliferation of cultured rat astrocytes. Evidence for reciprocal upregulation of the mRNAs for GLP-2 and IGF-I receptors. Mol Neurobiol 2009; 40:183-93. [PMID: 19672727 DOI: 10.1007/s12035-009-8080-1] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/25/2009] [Accepted: 07/27/2009] [Indexed: 12/29/2022]
Abstract
The aim of this work was to determine whether the stimulating effect of glucagon-like peptide (GLP)-2 on astrocyte proliferation could be reinforced by proliferating substances, including growth factors such as EGF, platelet-derived growth factor, insulin-like growth factor type I (IGF-I) or a hormone such as insulin. Both DNA synthesis and astrocyte density, as well as the expression of c-Fos, Ki-67, proliferating cell nuclear antigen and glial fibrillary acidic proteins, were found to be higher in the presence of GLP-2 than in its absence. In an attempt to get a better understanding of this process, intracellular cyclic adenosine monophosphate (cAMP) production, extracellular signal-regulated kinase (ERK) 1/2 phosphorylation and the expression of GLP-2R and IGF-I receptor (IGF-IR) mRNAs were studied in response to growth factors. Our results indicate that, in the presence of different growth factors, GLP-2 does not increase cAMP production but raises ERK 1/2 phosphorylation. In addition, GLP-2R mRNA expression was increased by IGF-I, whilst mRNA expression of IGF-IR was higher in cells incubated with GLP-2 than in control cells. These results suggest for the first time that GLP-2 and several growth factors show synergistic effects on the proliferation of rat astrocytes, a process in which an enhanced expression of GLP-2R and IGF-IR may be involved, providing additional insights into the physiological role of this novel neuropeptide, specially during astroglial regeneration.
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Affiliation(s)
- Esther Velázquez
- Department of Biochemistry and Molecular Biology, Faculty of Medicine, Complutense University, Madrid, Spain
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Böhme I, Beck-Sickinger AG. Illuminating the life of GPCRs. Cell Commun Signal 2009; 7:16. [PMID: 19602276 PMCID: PMC2726148 DOI: 10.1186/1478-811x-7-16] [Citation(s) in RCA: 60] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/08/2009] [Accepted: 07/14/2009] [Indexed: 01/19/2023] Open
Abstract
The investigation of biological systems highly depends on the possibilities that allow scientists to visualize and quantify biomolecules and their related activities in real-time and non-invasively. G-protein coupled receptors represent a family of very dynamic and highly regulated transmembrane proteins that are involved in various important physiological processes. Since their localization is not confined to the cell surface they have been a very attractive "moving target" and the understanding of their intracellular pathways as well as the identified protein-protein-interactions has had implications for therapeutic interventions. Recent and ongoing advances in both the establishment of a variety of labeling methods and the improvement of measuring and analyzing instrumentation, have made fluorescence techniques to an indispensable tool for GPCR imaging. The illumination of their complex life cycle, which includes receptor biosynthesis, membrane targeting, ligand binding, signaling, internalization, recycling and degradation, will provide new insights into the relationship between spatial receptor distribution and function. This review covers the existing technologies to track GPCRs in living cells. Fluorescent ligands, antibodies, auto-fluorescent proteins as well as the evolving technologies for chemical labeling with peptide- and protein-tags are described and their major applications concerning the GPCR life cycle are presented.
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Affiliation(s)
- Ilka Böhme
- Institute of Biochemistry, Faculty of Biosciences, Pharmacy and Psychology, Leipzig University, Brüderstr, 34, 04103 Leipzig, Germany.
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Drozdowski L, Thomson ABR. Intestinal hormones and growth factors: effects on the small intestine. World J Gastroenterol 2009; 15:385-406. [PMID: 19152442 PMCID: PMC2653359 DOI: 10.3748/wjg.15.385] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
There are various hormones and growth factors which may modify the intestinal absorption of nutrients, and which might thereby be useful in a therapeutic setting, such as in persons with short bowel syndrome. In part I, we focus first on insulin-like growth factors, epidermal and transferring growth factors, thyroid hormones and glucocorticosteroids. Part II will detail the effects of glucagon-like peptide (GLP)-2 on intestinal absorption and adaptation, and the potential for an additive effect of GLP2 plus steroids.
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Park JY, Kim KS, Lee SB, Ryu JS, Chung KC, Choo YK, Jou I, Kim J, Park SM. On the mechanism of internalization of alpha-synuclein into microglia: roles of ganglioside GM1 and lipid raft. J Neurochem 2009; 110:400-11. [PMID: 19457104 DOI: 10.1111/j.1471-4159.2009.06150.x] [Citation(s) in RCA: 107] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
ALpha-synuclein (alpha-syn) has been known to be a key player of the pathogenesis of Parkinson's disease and has recently been detected in extracellular biological fluids and shown to be rapidly secreted from cells. The penetration of alpha-syn into cells has also been observed. In this study, we observed that dl-threo-1-phenyl-2-decanoylamino-3-morpholino-1-propanol, a glucosyltransferase inhibitor, and proteinase K inhibited the internalization of extracellular monomeric alpha-syn into BV-2 cells, and the addition of monosialoganglioside GM1 ameliorated the inhibition of alpha-syn internalization in dl-threo-1-phenyl-2-decanoylamino-3-morpholino-1-propanol-treated BV-2 cells. Furthermore, inhibition of clathrin-, caveolae-, and dynamin-dependent endocytosis did not prevent the internalization of alpha-syn, but disruption of lipid raft inhibited it. Inhibition of macropinocytosis and disruption of actin and microtubule structures also did not inhibit the internalization of alpha-syn. In addition, we further confirmed these observations by co-culture system of BV-2 cells and alpha-syn-over-expressing SH-SY5Y cells. These findings suggest that extracellular alpha-syn is internalized into microglia via GM1 as well as hitherto-unknown protein receptors in clathrin-, caveolae-, and dynamin-independent, but lipid raft-dependent manner. Elucidation of the mechanism involved in internalization of alpha-syn should be greatly helpful in the development of new treatments of alpha-syn-related neurodegenerative diseases.
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Affiliation(s)
- Ji-Young Park
- Chronic Inflammatory Disease Research Center, Ajou University School of Medicine, Suwon, Korea
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19
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Temporal Changes in the Intestinal Growth Promoting Effects of Glucagon-Like Peptide 2 Following Intestinal Resection. J Surg Res 2009; 152:271-80. [DOI: 10.1016/j.jss.2008.05.007] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/01/2007] [Revised: 04/15/2008] [Accepted: 05/18/2008] [Indexed: 12/19/2022]
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Amato A, Baldassano S, Serio R, Mulè F. Glucagon-like peptide-2 relaxes mouse stomach through vasoactive intestinal peptide release. Am J Physiol Gastrointest Liver Physiol 2009; 296:G678-84. [PMID: 19109404 DOI: 10.1152/ajpgi.90587.2008] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
Glucagon-like peptide-2 (GLP-2) influences different aspects of the gastrointestinal function, including epithelial growth, digestion, absorption, motility, and blood flow. Intraluminal pressure from isolated mouse stomach was recorded to investigate whether GLP-2 affects gastric tone and to analyze its mechanism of action. Regional differences between diverse parts of the stomach were also examined using circular muscular strips from fundus and antrum. In the whole stomach, GLP-2 (0.3-100 nM) produced concentration-dependent relaxation with a maximum that was about 75% of relaxation to 1 microM isoproterenol (IC50=2.5 nM). This effect was virtually abolished by desensitization of GLP-2 receptors or by alpha-chymotrypsin. The relaxant response to GLP-2 was not affected by tetrodotoxin, a blocker of neuronal voltage-dependent Na+ channels, but it was significantly reduced by omega-conotoxin GVIA, a blocker of neuronal N-type voltage-operated Ca2+ channels. Nomega-nitro-L-arginine methyl ester, a blocker of nitric oxide synthase, or apamin, a blocker of Ca2+-dependent potassium channels, failed to affect the gastric response to the peptide. However, the relaxation was significantly antagonized by [Lys1,Pro2,5,Arg3,4,Tyr6]VIP7-28, a vasoactive intestinal peptide (VIP) receptor antagonist (GLP-2 maximum effect=45% of relaxation to 1 microM isoproterenol), and virtually abolished by desensitization of the VIP receptors. GLP-2 induced concentration-dependent relaxation in carbachol-precontracted fundic strips but not in antral strips. These results provide the first experimental evidence that GLP-2 is able to induce gastric relaxation acting peripherally on the mouse stomach. The effect appears to be mediated by prejunctional neural release of VIP and confined to fundic region.
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Affiliation(s)
- Antonella Amato
- Dipartimento di Biologia cellulare e dello Sviluppo, Laboratorio di Fisiologia generale, Università di Palermo, Viale delle Scienze, 90128 Palermo, Italy
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21
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Langlois S, Cowan KN, Shao Q, Cowan BJ, Laird DW. Caveolin-1 and -2 interact with connexin43 and regulate gap junctional intercellular communication in keratinocytes. Mol Biol Cell 2007; 19:912-28. [PMID: 18162583 DOI: 10.1091/mbc.e07-06-0596] [Citation(s) in RCA: 98] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
Connexin43 (Cx43) has been reported to interact with caveolin (Cav)-1, but the role of this association and whether other members of the caveolin family bind Cx43 had yet to be established. In this study, we show that Cx43 coimmunoprecipitates and colocalizes with Cav-1 and Cav-2 in rat epidermal keratinocytes. The colocalization of Cx43 with Cav-1 was confirmed in keratinocytes from human epidermis in vivo. Our mutation and Far Western analyses revealed that the C-terminal tail of Cx43 is required for its association with Cavs and that the Cx43/Cav-1 interaction is direct. Our results indicate that newly synthesized Cx43 interacts with Cavs in the Golgi apparatus and that the Cx43/Cavs complex also exists at the plasma membrane in lipid rafts. Using overexpression and small interfering RNA approaches, we demonstrated that caveolins regulate gap junctional intercellular communication (GJIC) and that the presence of Cx43 in lipid raft domains may contribute to the mechanism modulating GJIC. Our results suggest that the Cx43/Cavs association occurs during exocytic transport, and they clearly indicate that caveolin regulates GJIC.
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Affiliation(s)
- Stéphanie Langlois
- Department of Anatomy and Cell Biology, University of Western Ontario, London, ON N6A 5C1, Canada
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22
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Abstract
Glucagon-like peptide-2 (GLP-2) is a pleiotropic hormone that affects multiple facets of intestinal physiology, including growth, barrier function, digestion, absorption, motility, and blood flow. The mechanisms through which GLP-2 produces these actions are complex, involving unique signaling mechanisms and multiple indirect mediators. As clinical trials have begun for the use of GLP-2 in a variety of intestinal disorders, the elucidation of such mechanisms is vital. The GLP-2 receptor (GLP-2R) is a G protein-coupled receptor, signaling through multiple G proteins to affect the cAMP and mitogen-activated protein kinase pathways, leading to both proliferative and antiapoptotic cellular responses. The GLP-2R also demonstrates unique mechanisms for receptor trafficking. Expression of the GLP-2R in discrete sets of intestinal cells, including endocrine cells, subepithelial myofibroblasts, and enteric neurons, has led to the hypothesis that GLP-2 acts indirectly through multiple mediators to produce its biological effects. Indeed, several studies have now provided important mechanistic data illustrating several of the indirect pathways of GLP-2 action. Thus, insulin-like growth factor I has been demonstrated to be required for GLP-2-induced crypt cell proliferation, likely involving activation of beta-catenin signaling. Furthermore, vasoactive intestinal polypeptide modulates the actions of GLP-2 in models of intestinal inflammation, while keratinocyte growth factor is required for GLP-2-induced colonic mucosal growth and mucin expression. Finally, enteric neural GLP-2R signaling affects intestinal blood flow through a nitric oxide-dependent mechanism. Determining how GLP-2 produces its full range of biological effects, which mediators are involved, and how these mediators interact is a continuing area of active research.
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Affiliation(s)
- Philip E Dubé
- Department of Physiology, University of Toronto, Toronto, Ontario, Canada
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23
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Nelson DW, Sharp JW, Brownfield MS, Raybould HE, Ney DM. Localization and activation of glucagon-like peptide-2 receptors on vagal afferents in the rat. Endocrinology 2007; 148:1954-62. [PMID: 17234710 DOI: 10.1210/en.2006-1232] [Citation(s) in RCA: 80] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
Glucagon-like peptide-2 (GLP-2) is a nutrient-dependent proglucagon-derived hormone that stimulates intestinal growth through poorly understood paracrine and/or neural pathways. The relationship between GLP-2 action and a vagal pathway is unclear. Our aims were to determine whether 1) the GLP-2 receptor (GLP-2R) is expressed on vagal afferents by localizing it to the nodose ganglia; 2) exogenous GLP-2 stimulates the vagal afferent pathway by determining immunoreactivity for c-fos protein in the nucleus of the solitary tract (NTS); and 3) functional ablation of vagal afferents attenuates GLP-2-mediated intestinal growth in rats maintained with total parenteral nutrition (TPN). A polyclonal antibody against the N terminus of the rat GLP-2R was raised and characterized. The GLP-2R was localized to vagal afferents in the nodose ganglia and confirmed in enteroendocrine cells, enteric neurons, and nerve fibers in the myenteric plexus using immunohistochemistry. Activation of the vagal afferent pathway, as indicated by c-fos protein immunoreactivity in the NTS, was determined by immunohistochemistry after ip injection of 200 microg human GLP-2. GLP-2 induced a significant 5-fold increase in the number of c-fos protein immunoreactive neurons in the NTS compared with saline. Ablation of vagal afferent function by perivagal application of capsaicin, a specific afferent neurotoxin, abolished c-fos protein immunoreactivity, suggesting that activation of the NTS due to GLP-2 is dependent on vagal afferents. Exogenous GLP-2 prevented TPN-induced mucosal atrophy, but ablation of vagal afferent function with capsaicin did not attenuate this effect. This suggests that vagal-independent pathways are responsible for GLP-2 action in the absence of luminal nutrients during TPN, possibly involving enteric neurons or endocrine cells. This study shows for the first time that the GLP-2R is expressed by vagal afferents, and ip GLP-2 activates the vagal afferent pathway.
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Affiliation(s)
- David W Nelson
- Department of Nutritional Sciences, University of Wisconsin-Madison, Madison, Wisconsin 53706, USA
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Gallant MA, Slipetz D, Hamelin E, Rochdi MD, Talbot S, de Brum-Fernandes AJ, Parent JL. Differential regulation of the signaling and trafficking of the two prostaglandin D2 receptors, prostanoid DP receptor and CRTH2. Eur J Pharmacol 2007; 557:115-23. [PMID: 17207480 DOI: 10.1016/j.ejphar.2006.11.058] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/13/2006] [Revised: 11/10/2006] [Accepted: 11/16/2006] [Indexed: 11/28/2022]
Abstract
Prostaglandin D2 (PGD2) exerts its actions on two G protein-coupled receptors, the prostanoid DP receptor and CRTH2 (chemoattractant homologous receptor expressed on TH2 cells). Here, we characterize the regulation of the signaling and trafficking of the prostanoid DP receptor and CRTH2. Time-course and dose-response curves showed that both receptors expressed in HEK293 cells internalized maximally after 2 h of stimulation with 1 microM PGD2. Co-expression of the G protein-coupled receptor kinases GRK2, GRK5 or GRK6 increased agonist-induced internalization of CRTH2, while only GRK2 had an effect on the internalization of the prostanoid DP receptor. Protein kinase C (PKC) activation stimulated the internalization of both receptors. Interestingly, only PGD2-induced internalization of CRTH2, and not of prostanoid DP receptor, was decreased by inhibition of PKC or protein kinase A (PKA). Our data also indicate that CRTH2 is subjected to basal phosphorylation by PKA, which appears to be involved in CRTH2 internalization. Prostanoid DP receptor internalization was promoted by co-expression of arrestin-2 and -3, while the internalization of CRTH2 was increased by co-expression of arrestin-3 only. The detection of prostanoid DP receptor and CRTH2 internalization was reduced by the co-expression of Rab4 and Rab11, respectively, suggesting differential regulation of receptor recycling. Moreover, immunofluorescence microscopy experiments showed that the prostanoid DP receptor specifically co-localized with Rab4, and CRTH2 with Rab11. The signaling of the prostanoid DP receptor was regulated by GRK2 overexpression, while that of CRTH2 was modulated by overexpression of GRK2, -5 and -6. Our results show a differential regulation of the prostanoid DP receptor and CRTH2, two receptors for PGD2.
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Affiliation(s)
- Maxime A Gallant
- Division of Rheumatology, Département de Médecine, Faculté de Médecine and Centre de Recherche Clinique-Etienne Lebel, Université de Sherbrooke, Sherbrooke, Québec, Canada
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25
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Abstract
Multiple peptide hormones produced within the gastrointestinal system aid in the regulation of energy homeostasis and metabolism. Among these is the intestinotrophic peptide glucagon-like peptide-2 (GLP-2), which is released following food intake and plays a significant role in the adaptive regulation of bowel mass and mucosal integrity. The discovery of GLP-2's potent growth-promoting and cytoprotective effects in the gastrointestinal (GI) tract stimulated interest in its use as a therapeutic agent for the treatment of GI diseases involving malabsorption, inflammation, and/or mucosal damage. Current research has focused on determining the physiological mechanisms contributing to the effects of GLP-2 and factors regulating its biological mechanisms of action. This chapter provides an overview of the biology of GLP-2 with a focus on the most recent findings on the role of this peptide hormone in the normal and diseased GI tract.
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Affiliation(s)
- Jennifer L Estall
- Department of Laboratory Medicine and Pathobiology, The Banting and Best Diabetes Center, Toronto General Hospital, University of Toronto, Ontario, Canada, M5G 2C4
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26
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Merlen C, Fabrega S, Desbuquois B, Unson CG, Authier F. Glucagon-mediated internalization of serine-phosphorylated glucagon receptor and Gsalpha in rat liver. FEBS Lett 2006; 580:5697-704. [PMID: 17010343 DOI: 10.1016/j.febslet.2006.09.021] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/06/2006] [Revised: 07/25/2006] [Accepted: 09/12/2006] [Indexed: 10/24/2022]
Abstract
To assess glucagon receptor compartmentalization and signal transduction in liver parenchyma, we have studied the functional relationship between glucagon receptor endocytosis, phosphorylation and coupling to the adenylate cyclase system. Following administration of a saturating dose of glucagon to rats, a rapid internalization of glucagon receptor was observed coincident with its serine phosphorylation both at the plasma membrane and within endosomes. Co-incident with glucagon receptor endocytosis, a massive internalization of both the 45- and 47-kDa Gsalpha proteins was also observed. In contrast, no change in the subcellular distribution of adenylate cyclase or beta-arrestin 1 and 2 was observed. In response to des-His(1)-[Glu(9)]glucagon amide, a glucagon receptor antagonist, the extent and rate of glucagon receptor endocytosis and Gsalpha shift were markedly reduced compared with wild-type glucagon. However, while the glucagon analog exhibited a wild-type affinity for endosomal acidic glucagonase activity and was processed at low pH with similar kinetics and rates, its proteolysis at neutral pH was 3-fold lower. In response to tetraiodoglucagon, a glucagon receptor agonist of enhanced biological potency, glucagon receptor endocytosis and Gsalpha shift were of higher magnitude and of longer duration, and a marked and prolonged activation of adenylate cyclase both at the plasma membrane and in endosomes was observed. The subsequent post-endosomal fate of internalized Gsalpha was evaluated in a cell-free rat liver endosome-lysosome fusion system following glucagon injection. A sustained endo-lysosomal transfer of the two 45- and 47-kDa Gsalpha isoforms was observed. Therefore, these results reveal that within hepatic target cells and consequent to glucagon-mediated internalization of the serine-phosphorylated glucagon receptor and the Gsalpha protein, extended signal transduction may occur in vivo at the locus of the endo-lysosomal apparatus.
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Affiliation(s)
- Clémence Merlen
- Institut National de la Santé et de la Recherche Médicale Unité 756, Faculté de Pharmacie Paris XI, 92296 Châtenay-Malabry, France
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Syme CA, Zhang L, Bisello A. Caveolin-1 regulates cellular trafficking and function of the glucagon-like Peptide 1 receptor. Mol Endocrinol 2006; 20:3400-11. [PMID: 16931572 DOI: 10.1210/me.2006-0178] [Citation(s) in RCA: 93] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022] Open
Abstract
The glucagon-like peptide 1 receptor (GLP-1R) mediates important effects on beta-cell function and glucose homeostasis and is one of the most promising therapeutic targets for type 2, and possibly type 1, diabetes. Yet, little is known regarding the molecular and cellular mechanisms that regulate its function. Therefore, we examined the cellular trafficking of the GLP-1R and the relation between receptor localization and signaling activity. In resting human embryonic kidney 293 and insulinoma MIN6 cells, a fully functional green fluorescent protein-tagged GLP-1R was localized both at the cell membrane and in highly mobile intracellular compartments. Real-time confocal fluorescence microscopy allowed direct visualization of constitutive cycling of the receptor. Overexpression of K44A-dynamin increased the number of functional receptors at the cell membrane. Immunoprecipitation, sucrose sedimentation, and microscopy observations demonstrated that the GLP-1R localizes in lipid rafts and interacts with caveolin-1. This interaction is necessary for membrane localization of the GLP-1R, because overexpression of a dominant-negative form of caveolin-1 (P132L-cav1) or specific mutations within the putative GLP-1R's caveolin-1 binding domain completely inhibited GLP-1 binding and activity. Upon agonist stimulation, the GLP-1R underwent rapid and extensive endocytosis independently from arrestins but in association with caveolin-1. Finally, GLP-1R-stimulated activation of ERK1/2, which involves transactivation of epidermal growth factor receptors, required lipid raft integrity. In summary, the interaction of the GLP-1R with caveolin-1 regulates subcellular localization, trafficking, and signaling activity. This study provides further evidence of the key role of accessory proteins in specifying the cellular behavior of G protein-coupled receptors.
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Affiliation(s)
- Colin A Syme
- Division of Endocrinology and Metabolism, Department of Medicine, University of Pittsburgh School of Medicine, E1140 Biomedical Science Tower, 200 Lothrop Street, Pittsburgh, Pennsylvania 15261, USA
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Ueda Y, Neel NF, Schutyser E, Raman D, Richmond A. Deletion of the COOH-terminal domain of CXC chemokine receptor 4 leads to the down-regulation of cell-to-cell contact, enhanced motility and proliferation in breast carcinoma cells. Cancer Res 2006; 66:5665-75. [PMID: 16740704 PMCID: PMC2664111 DOI: 10.1158/0008-5472.can-05-3579] [Citation(s) in RCA: 50] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
The CXC chemokine receptor 4 (CXCR4) contributes to the metastasis of human breast cancer cells. The CXCR4 COOH-terminal domain (CTD) seems to play a major role in regulating receptor desensitization and down-regulation. We expressed either wild-type CXCR4 (CXCR4-WT) or CTD-truncated CXCR4 (CXCR4-DeltaCTD) in MCF-7 human mammary carcinoma cells to determine whether the CTD is involved in CXCR4-modulated proliferation of mammary carcinoma cells. CXCR4-WT-transduced MCF-7 cells (MCF-7/CXCR4-WT cells) do not differ from vector-transduced MCF-7 control cells in morphology or growth rate. However, CXCR4-DeltaCTD-transduced MCF-7 cells (MCF-7/CXCR4-DeltaCTD cells) exhibit a higher growth rate and altered morphology, potentially indicating an epithelial-to-mesenchymal transition. Furthermore, extracellular signal-regulated kinase (ERK) activation and cell motility are increased in these cells. Ligand induces receptor association with beta-arrestin for both CXCR4-WT and CXCR4-DeltaCTD in these MCF-7 cells. Overexpressed CXCR4-WT localizes predominantly to the cell surface in unstimulated cells, whereas a significant portion of overexpressed CXCR4-DeltaCTD resides intracellularly in recycling endosomes. Analysis with human oligomicroarray, Western blot, and immunohistochemistry showed that E-cadherin and Zonula occludens are down-regulated in MCF-7/CXCR4-DeltaCTD cells. The array analysis also indicates that mesenchymal marker proteins and certain growth factor receptors are up-regulated in MCF-7/CXCR4-DeltaCTD cells. These observations suggest that (a) the overexpression of CXCR4-DeltaCTD leads to a gain-of-function of CXCR4-mediated signaling and (b) the CTD of CXCR4-WT may perform a feedback repressor function in this signaling pathway. These data will contribute to our understanding of how CXCR4-DeltaCTD may promote progression of breast tumors to metastatic lesions.
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Affiliation(s)
- Yukiko Ueda
- Department of Cancer Biology, Vanderbilt University School of Medicine, Nashville, Tennessee
| | - Nicole F. Neel
- Department of Cancer Biology, Vanderbilt University School of Medicine, Nashville, Tennessee
| | - Evemie Schutyser
- Department of Cancer Biology, Vanderbilt University School of Medicine, Nashville, Tennessee
| | - Dayanidhi Raman
- Department of Cancer Biology, Vanderbilt University School of Medicine, Nashville, Tennessee
| | - Ann Richmond
- Departments of Veterans Affairs, Vanderbilt University School of Medicine, Nashville, Tennessee
- Department of Cancer Biology, Vanderbilt University School of Medicine, Nashville, Tennessee
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Kirkham M, Parton RG. Clathrin-independent endocytosis: new insights into caveolae and non-caveolar lipid raft carriers. BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH 2006; 1745:273-86. [PMID: 16046009 DOI: 10.1016/j.bbamcr.2005.06.002] [Citation(s) in RCA: 191] [Impact Index Per Article: 10.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Subscribe] [Scholar Register] [Received: 03/24/2005] [Revised: 06/06/2005] [Accepted: 06/06/2005] [Indexed: 01/06/2023]
Abstract
A number of recent studies have provided new insights into the complexity of the endocytic pathways originating at the plasma membrane of mammalian cells. Many of the molecules involved in clathrin coated pit internalization are now well understood but other pathways are less well defined. Caveolae appear to represent a low capacity but highly regulated pathway in a restricted set of tissues in vivo. A third pathway, which is both clathrin- and caveolae-independent, may constitute a specialized high capacity endocytic pathway for lipids and fluid. The relationship of this pathway, if any, to macropinocytosis or to the endocytic pathways of lower eukaryotes remains an interesting open question. Our understanding of the regulatory mechanisms and molecular components involved in this pathway are at a relatively primitive stage. In this review, we will consider some of the characteristics of different endocytic pathways in high and lower eukaryotes and consider some of the common themes in endocytosis. One theme which becomes apparent from comparison of these pathways is that apparently different pathways can share common molecular machinery and that pathways considered to be distinct actually represent similar basic pathways to which additional levels of regulatory complexity have been added.
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Affiliation(s)
- Matthew Kirkham
- Institute for Molecular Bioscience, University of Queensland, Queensland 4072, Australia
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30
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Kirkham M, Parton RG. Clathrin-independent endocytosis: new insights into caveolae and non-caveolar lipid raft carriers. BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH 2006; 1746:349-63. [PMID: 16440447 DOI: 10.1016/j.bbamcr.2005.11.007] [Citation(s) in RCA: 111] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
A number of recent studies have provided new insights into the complexity of the endocytic pathways originating at the plasma membrane of mammalian cells. Many of the molecules involved in clathrin coated pit internalization are now well understood but other pathways are less well defined. Caveolae appear to represent a low capacity but highly regulated pathway in a restricted set of tissues in vivo. A third pathway, which is both clathrin- and caveolae-independent, may constitute a specialized high capacity endocytic pathway for lipids and fluid. The relationship of this pathway, if any, to macropinocytosis or to the endocytic pathways of lower eukaryotes remains an interesting open question. Our understanding of the regulatory mechanisms and molecular components involved in this pathway are at a relatively primitive stage. In this review, we will consider some of the characteristics of different endocytic pathways in high and lower eukaryotes and consider some of the common themes in endocytosis. One theme which becomes apparent from comparison of these pathways is that apparently different pathways can share common molecular machinery and that pathways considered to be distinct actually represent similar basic pathways to which additional levels of regulatory complexity have been added.
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Affiliation(s)
- Matthew Kirkham
- Institute for Molecular Bioscience, University of Queensland, 4072, Australia
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Shin ED, Estall JL, Izzo A, Drucker DJ, Brubaker PL. Mucosal adaptation to enteral nutrients is dependent on the physiologic actions of glucagon-like peptide-2 in mice. Gastroenterology 2005; 128:1340-53. [PMID: 15887116 DOI: 10.1053/j.gastro.2005.02.033] [Citation(s) in RCA: 105] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
BACKGROUND & AIMS Our understanding of the intestinotropic actions of glucagon-like peptide-2 (GLP-2)(1-33) is based on pharmacologic studies involving exogenous administration. However, the physiologic role of GLP-2 in mucosal growth and adaptation to nutritional stimulation remains poorly understood. METHODS The properties of GLP-2(3-33), a GLP-2(1-33) metabolite, were determined in baby-hamster kidney cells transfected with the mouse GLP-2 receptor complementary DNA and in isolated murine intestinal muscle strips. To investigate the role of endogenous GLP-2(1-33) in gut adaptation, GLP-2(3-33) was administered to mice that were re-fed for 24 hours after 24 hours of fasting, and the small intestine was analyzed. GLP-2(3-33) also was injected into rats for analysis of circulating GLP-2(1-33) levels. RESULTS GLP-2(3-33) antagonized the actions of GLP-2(1-33) in vitro and ex vivo. Fasting mice exhibited small intestinal atrophy (37% +/- 1% decrease in small intestinal weight, 19% +/- 2% decrease in crypt-villus height, and 99% +/- 35% increase in villus apoptosis, P < .05-.01). Adaptive growth in re-fed mice restored all these parameters, as well as crypt-cell proliferation, to normal control levels (P < .05 vs. fasting); these adaptive changes were prevented partially or completely by co-administration of GLP-2(3-33) to refeeding mice (by 32% +/- 19% to 103% +/- 15%, P < .05-.01 vs re-fed mice). Exogenous GLP-2(3-33) did not affect endogenous GLP-2(1-33) levels. CONCLUSIONS These data show that endogenous GLP-2 regulates the intestinotropic response in re-fed mice through modulation of crypt-cell proliferation and villus apoptosis. GLP-2 is therefore a physiologic regulator of the dynamic adaptation of the gut mucosal epithelium in response to luminal nutrients.
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MESH Headings
- Adaptation, Physiological/drug effects
- Adaptation, Physiological/physiology
- Amino Acid Sequence
- Animals
- Apoptosis/physiology
- Body Weight
- Cell Division/physiology
- Cloning, Molecular
- Drinking/physiology
- Eating/physiology
- Female
- Gene Expression
- Glucagon/genetics
- Glucagon-Like Peptide 2
- Glucagon-Like Peptide-1 Receptor
- Glucagon-Like Peptides
- Intestinal Mucosa/cytology
- Intestinal Mucosa/enzymology
- Intestinal Mucosa/physiology
- Intestine, Small/cytology
- Intestine, Small/enzymology
- Intestine, Small/physiology
- Male
- Mice
- Mice, Inbred C57BL
- Molecular Sequence Data
- Organ Size
- Peptide Fragments/blood
- Peptide Fragments/pharmacology
- Peptide Fragments/physiology
- Proglucagon
- Protein Precursors/genetics
- Rats
- Rats, Wistar
- Receptors, Glucagon/genetics
- Receptors, Glucagon/metabolism
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Affiliation(s)
- Eric D Shin
- Department of Physiology, University of Toronto, Ontario, Canada
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Estall JL, Koehler JA, Yusta B, Drucker DJ. The glucagon-like peptide-2 receptor C terminus modulates beta-arrestin-2 association but is dispensable for ligand-induced desensitization, endocytosis, and G-protein-dependent effector activation. J Biol Chem 2005; 280:22124-34. [PMID: 15817468 DOI: 10.1074/jbc.m500078200] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022] Open
Abstract
Classic models of receptor desensitization and internalization have been largely based on the behavior of Family A G-protein-coupled receptors (GPCRs). The glucagon-like peptide-2 receptor (GLP-2R) is a member of the Family B glucagon-secretin GPCR family, which exhibit significant sequence and structural differences from the Family A receptors in their intracellular and extracellular domains. To identify structural motifs that regulate GLP-2R signaling and cell surface receptor expression, we analyzed the functional properties of a series of mutant GLP-2Rs. The majority of the C-terminal receptor tail was dispensable for GLP-2-induced cAMP accumulation, ERK1/2 activation, and endocytosis in transfected cells. However, progressive truncation of the C terminus reduced cell surface receptor expression, altered agonist-induced GLP-2R trafficking, and abrogated protein kinase A-mediated heterologous receptor desensitization. Elimination of the distal 21 amino acids of the receptor was sufficient to promote constitutive receptor internalization and prevent agonist-induced recruitment of beta-arrestin-2. Site-directed mutagenesis identified specific amino acid residues within the distal GLP-2R C terminus that mediate the stable association with beta-arrestin-2. Surprisingly, although the truncated mutant receptors failed to interact with beta-arrestin-2, they underwent homologous desensitization and subsequent resensitization with kinetics similar to that observed with the wild-type GLP-2R. Our data suggest that, although the GLP-2R C terminus is not required for coupling to cellular machinery regulating signaling or desensitization, it may serve as a sorting signal for intracellular trafficking. Taken together with the previously demonstrated clathrin and dynamin-independent, lipid-raft-dependent pathways for internalization, our data suggest that GLP-2 receptor signaling has evolved unique structural and functional mechanisms for control of receptor trafficking, desensitization, and resensitization.
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Affiliation(s)
- Jennifer L Estall
- Departments of Laboratory Medicine and Pathobiology, and Medicine, University of Toronto, The Banting and Best Diabetes Centre, Toronto General Hospital, University of Toronto, Toronto M5G 2C4, Canada
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