1
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Beito MR, Ashraf S, Odogwu D, Harmancey R. Role of Ectopic Olfactory Receptors in the Regulation of the Cardiovascular-Kidney-Metabolic Axis. Life (Basel) 2024; 14:548. [PMID: 38792570 PMCID: PMC11122380 DOI: 10.3390/life14050548] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/02/2024] [Revised: 04/19/2024] [Accepted: 04/22/2024] [Indexed: 05/26/2024] Open
Abstract
Olfactory receptors (ORs) represent one of the largest yet least investigated families of G protein-coupled receptors in mammals. While initially believed to be functionally restricted to the detection and integration of odors at the olfactory epithelium, accumulating evidence points to a critical role for ectopically expressed ORs in the regulation of cellular homeostasis in extranasal tissues. This review aims to summarize the current state of knowledge on the expression and physiological functions of ectopic ORs in the cardiovascular system, kidneys, and primary metabolic organs and emphasizes how altered ectopic OR signaling in those tissues may impact cardiovascular-kidney-metabolic health.
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Affiliation(s)
| | | | | | - Romain Harmancey
- Division of Cardiology, Department of Internal Medicine, McGovern Medical School, The University of Texas Health Science Center at Houston, Houston, TX 77030, USA; (M.R.B.); (S.A.); (D.O.)
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2
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Xu R, Cong X, Zheng Q, Xu L, Ni MJ, de March CA, Matsunami H, Golebiowski J, Ma M, Yu Y. Interactions among key residues regulate mammalian odorant receptor trafficking. FASEB J 2022; 36:e22384. [PMID: 35639289 DOI: 10.1096/fj.202200116rr] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/20/2022] [Revised: 05/17/2022] [Accepted: 05/19/2022] [Indexed: 11/11/2022]
Abstract
Odorant receptors (ORs) expressed in mammalian olfactory sensory neurons are essential for the sense of smell. However, structure-function studies of many ORs are hampered by unsuccessful heterologous expression. To understand and eventually overcome this bottleneck, we performed heterologous expression and functional assays of over 80 OR variants and chimeras. Combined with literature data and machine learning, we found that the transmembrane domain 4 (TM4) and its interactions with neighbor residues are important for OR functional expression. The data highlight critical roles of T4.62 therein. ORs that fail to reach the cell membrane can be rescued by modifications in TM4. Consequently, such modifications in MOR256-3 (Olfr124) also alter OR responses to odorants. T1614.62 P causes the retention of MOR256-3 in the endoplasmic reticulum (ER), while T1614.62 P/T1484.49 A reverses the retention and makes receptor trafficking to cell membrane. This study offers new clues toward wide-range functional studies of mammalian ORs.
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Affiliation(s)
- Rui Xu
- School of Life Sciences, Shanghai University, Shanghai, People's Republic of China
| | - Xiaojing Cong
- Institut de Chimie de Nice UMR7272, CNRS, Université Côte d'Azur, Nice, France.,Institut de Génomique Fonctionnelle, University of Montpellier, CNRS, INSERM, Montpellier Cedex 5, 34094, France
| | - Qian Zheng
- School of Life Sciences, Shanghai University, Shanghai, People's Republic of China
| | - Lun Xu
- Ear, Nose & Throat Institute, Department of Otolaryngology, Eye, Ear, Nose & Throat Hospital, Fudan University, Shanghai, People's Republic of China
| | - Mengjue J Ni
- Department of Molecular Genetics and Microbiology, Duke University Medical Center, Durham, North Carolina, USA.,Department of Neurobiology, Duke University Medical Center, Durham, North Carolina, USA
| | - Claire A de March
- Department of Molecular Genetics and Microbiology, Duke University Medical Center, Durham, North Carolina, USA.,Department of Neurobiology, Duke University Medical Center, Durham, North Carolina, USA
| | - Hiroaki Matsunami
- Department of Molecular Genetics and Microbiology, Duke University Medical Center, Durham, North Carolina, USA.,Department of Neurobiology, Duke University Medical Center, Durham, North Carolina, USA
| | - Jérôme Golebiowski
- Institut de Chimie de Nice UMR7272, CNRS, Université Côte d'Azur, Nice, France.,Department of Brain and Cognitive Sciences, Daegu Gyeongbuk Institute of Science and Technology, Daegu, South Korea
| | - Minghong Ma
- Department of Neuroscience, University of Pennsylvania Perelman School of Medicine, Philadelphia, Pennsylvania, USA
| | - Yiqun Yu
- Ear, Nose & Throat Institute, Department of Otolaryngology, Eye, Ear, Nose & Throat Hospital, Fudan University, Shanghai, People's Republic of China.,Clinical and Research Center for Olfactory Disorders, Eye, Ear, Nose & Throat Hospital, Fudan University, Shanghai, People's Republic of China
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3
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Haag F, Di Pizio A, Krautwurst D. The key food odorant receptive range of broadly tuned receptor OR2W1. Food Chem 2021; 375:131680. [PMID: 34857413 DOI: 10.1016/j.foodchem.2021.131680] [Citation(s) in RCA: 12] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/18/2021] [Revised: 11/22/2021] [Accepted: 11/22/2021] [Indexed: 11/28/2022]
Abstract
Mammals perceive a multitude of odorants by their chemical sense of olfaction, a high-dimensional stimulus-detection system, with hundreds of narrowly or broadly tuned receptors, enabling pattern recognition by the brain. Cognate receptor-agonist information, however, is sparse, and the role of broadly tuned odorant receptors for encoding odor quality remains elusive. Here, we screened IL-6-HaloTag®-OR2W1 and haplotypes against 187 out of 230 defined key food odorants using the GloSensor™ system in HEK-293 cells, yielding 48 new agonists. Altogether, key food odorants represent about two-thirds of now 153 reported agonists of OR2W1, the highest number of agonists known for a mammalian odorant receptor. In summary, we characterized OR2W1 as a human odorant receptor, with a chemically diverse but exclusive receptive range, complementary to chemical subgroups covered by evolutionary younger, highly selective receptors. Our data suggest OR2W1 to be suited for participating in the detection of many foodborne odorants.
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Affiliation(s)
- Franziska Haag
- Leibniz-Institute for Food Systems Biology at the Technical University of Munich, Lise-Meitner-Str. 34, 85354 Freising, Germany
| | - Antonella Di Pizio
- Leibniz-Institute for Food Systems Biology at the Technical University of Munich, Lise-Meitner-Str. 34, 85354 Freising, Germany
| | - Dietmar Krautwurst
- Leibniz-Institute for Food Systems Biology at the Technical University of Munich, Lise-Meitner-Str. 34, 85354 Freising, Germany.
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4
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Zhang S, Li L, Li H. Role of ectopic olfactory receptors in glucose and lipid metabolism. Br J Pharmacol 2021; 178:4792-4807. [PMID: 34411276 DOI: 10.1111/bph.15666] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/27/2020] [Revised: 05/25/2021] [Accepted: 08/11/2021] [Indexed: 12/25/2022] Open
Abstract
The metabolic syndrome has become one of the major public health challenges in the world, and adjusting glucose and lipid levels to their normal values is crucial for treating the metabolic syndrome. Olfactory receptors (ORs) expressed in extra-nasal tissues participate in diverse biological processes, including the regulation of glucose and lipid metabolism. Ectopic ORs can regulate a variety of metabolic events including insulin secretion, glucagon secretion, fatty acid oxidation, lipogenesis and thermogenesis. Understanding the physiological function and deciphering the olfactory recognition code by suitable ligands make ectopic ORs potential targets for the treatment of the metabolic syndrome. In this review, we delineate the roles and mechanisms of ectopic ORs in the regulation of glucose and lipid metabolism, summarize the corresponding natural ligands, and discuss existing problems and the therapeutic potential of targeting ORs in the metabolic syndrome.
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Affiliation(s)
- Siyu Zhang
- Institute of Pharmacology, Department of Pharmaceutical Sciences, Zhejiang University of Technology, Hangzhou, China
| | - Linghuan Li
- Institute of Pharmacology, Department of Pharmaceutical Sciences, Zhejiang University of Technology, Hangzhou, China
| | - Hanbing Li
- Institute of Pharmacology, Department of Pharmaceutical Sciences, Zhejiang University of Technology, Hangzhou, China.,Section of Endocrinology, School of Medicine, Yale University, New Haven, Connecticut, USA
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5
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Manzini I, Schild D, Di Natale C. Principles of odor coding in vertebrates and artificial chemosensory systems. Physiol Rev 2021; 102:61-154. [PMID: 34254835 DOI: 10.1152/physrev.00036.2020] [Citation(s) in RCA: 30] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Abstract
The biological olfactory system is the sensory system responsible for the detection of the chemical composition of the environment. Several attempts to mimic biological olfactory systems have led to various artificial olfactory systems using different technical approaches. Here we provide a parallel description of biological olfactory systems and their technical counterparts. We start with a presentation of the input to the systems, the stimuli, and treat the interface between the external world and the environment where receptor neurons or artificial chemosensors reside. We then delineate the functions of receptor neurons and chemosensors as well as their overall I-O relationships. Up to this point, our account of the systems goes along similar lines. The next processing steps differ considerably: while in biology the processing step following the receptor neurons is the "integration" and "processing" of receptor neuron outputs in the olfactory bulb, this step has various realizations in electronic noses. For a long period of time, the signal processing stages beyond the olfactory bulb, i.e., the higher olfactory centers were little studied. Only recently there has been a marked growth of studies tackling the information processing in these centers. In electronic noses, a third stage of processing has virtually never been considered. In this review, we provide an up-to-date overview of the current knowledge of both fields and, for the first time, attempt to tie them together. We hope it will be a breeding ground for better information, communication, and data exchange between very related but so far little connected fields.
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Affiliation(s)
- Ivan Manzini
- Animal Physiology and Molecular Biomedicine, Justus-Liebig-University Gießen, Gießen, Germany
| | - Detlev Schild
- Institute of Neurophysiology and Cellular Biophysics, University Medical Center, University of Göttingen, Göttingen, Germany
| | - Corrado Di Natale
- Department of Electronic Engineering, University of Rome Tor Vergata, Rome, Italy
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6
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Corey EA, Zolotukhin S, Ache BW, Ukhanov K. Mixture interactions at mammalian olfactory receptors are dependent on the cellular environment. Sci Rep 2021; 11:9278. [PMID: 33927269 PMCID: PMC8085013 DOI: 10.1038/s41598-021-88601-0] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/07/2020] [Accepted: 04/07/2021] [Indexed: 02/02/2023] Open
Abstract
Functional characterization of mammalian olfactory receptors (ORs) remains a major challenge to ultimately understanding the olfactory code. Here, we compare the responses of the mouse Olfr73 ectopically expressed in olfactory sensory neurons using AAV gene delivery in vivo and expressed in vitro in cell culture. The response dynamics and concentration-dependence of agonists for the ectopically expressed Olfr73 were similar to those reported for the endogenous Olfr73, however the antagonism previously reported between its cognate agonist and several antagonists was not replicated in vivo. Expressing the OR in vitro reproduced the antagonism reported for short odor pulses, but not for prolonged odor exposure. Our findings suggest that both the cellular environment and the stimulus dynamics shape the functionality of Olfr73 and argue that characterizing ORs in 'native' conditions, rather than in vitro, provides a more relevant understanding of ligand-OR interactions.
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Affiliation(s)
- Elizabeth A Corey
- Whitney Laboratory, University of Florida, Gainesville, FL, USA
- Center for Smell and Taste, University of Florida, Gainesville, FL, USA
| | - Sergei Zolotukhin
- Department of Pediatrics, University of Florida, Gainesville, FL, USA
- Center for Smell and Taste, University of Florida, Gainesville, FL, USA
| | - Barry W Ache
- Whitney Laboratory, University of Florida, Gainesville, FL, USA
- Department of Biology and Neuroscience, University of Florida, Gainesville, FL, USA
- Center for Smell and Taste, University of Florida, Gainesville, FL, USA
- McKnight Brain Institute, University of Florida, Gainesville, FL, USA
| | - Kirill Ukhanov
- Department of Pharmacology and Therapeutics, University of Florida, Gainesville, FL, USA.
- Center for Smell and Taste, University of Florida, Gainesville, FL, USA.
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7
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Zapiec B, Mombaerts P. The Zonal Organization of Odorant Receptor Gene Choice in the Main Olfactory Epithelium of the Mouse. Cell Rep 2021; 30:4220-4234.e5. [PMID: 32209480 DOI: 10.1016/j.celrep.2020.02.110] [Citation(s) in RCA: 23] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/06/2019] [Revised: 01/16/2020] [Accepted: 02/27/2020] [Indexed: 12/15/2022] Open
Abstract
A mature olfactory sensory neuron (OSN) of the main olfactory epithelium (MOE) typically expresses one allele of one odorant receptor (OR) gene. It is widely thought that the great majority of the 1,141 intact mouse OR genes are expressed in one of four MOE zones (or bands or stripes), which are largely non-overlapping. Here, we develop a multiplex method to map, in 3D and MOE-wide, the expression areas of multiple OR genes in individual, non-genetically modified mice by three-color fluorescence in situ hybridization, semi-automated image segmentation, and 3D reconstruction. We classify the expression areas of 68 OR genes into 9 zones. These zones are highly overlapping and strikingly complex when viewed in 3D reconstructions. There could well be more zones. We propose that zones reflect distinct OSN types that are each restricted in their choice to a subset of the OR gene repertoire.
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Affiliation(s)
- Bolek Zapiec
- Max Planck Research Unit for Neurogenetics, Max-von-Laue-Strasse 4, 60438 Frankfurt, Germany
| | - Peter Mombaerts
- Max Planck Research Unit for Neurogenetics, Max-von-Laue-Strasse 4, 60438 Frankfurt, Germany.
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8
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Dewan A. Olfactory signaling via trace amine-associated receptors. Cell Tissue Res 2020; 383:395-407. [PMID: 33237477 DOI: 10.1007/s00441-020-03331-5] [Citation(s) in RCA: 14] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/24/2020] [Accepted: 10/28/2020] [Indexed: 01/30/2023]
Abstract
Trace amine-associated receptors (TAARs) are a family of G protein-coupled receptors that function as odorant receptors in the main olfactory system of vertebrates. TAARs are monoallelically expressed in primary sensory neurons where they couple to the same transduction cascade as canonical olfactory receptors and are mapped onto glomeruli within a specific region of the olfactory bulb. TAARs have a high affinity for volatile amines, a class of chemicals that are generated during the decomposition of proteins and are ubiquitous physiological metabolites that are found in body fluids. Thus, amines are proposed to play an important role in intra- and interspecific communication such as signaling the sex of the conspecific, the quality of the food source, or even the proximity of a predator. TAARs have a crucial role in the perception of these behaviorally relevant compounds as the genetic deletion of all or even individual olfactory TAARs can alter the behavioral response and reduce the sensitivity to amines. The small size of this receptor family combined with the ethological relevance of their ligands makes the TAARs an attractive model system for probing olfactory perception. This review will summarize the current knowledge on the olfactory TAARs and discuss whether they represent a unique subsystem within the main olfactory system.
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Affiliation(s)
- Adam Dewan
- Department of Psychology, Florida State University, 1107 W. Call St, Tallahassee, FL, 32306, USA.
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9
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Degl’Innocenti A, Meloni G, Mazzolai B, Ciofani G. A purely bioinformatic pipeline for the prediction of mammalian odorant receptor gene enhancers. BMC Bioinformatics 2019; 20:474. [PMID: 31521109 PMCID: PMC6744719 DOI: 10.1186/s12859-019-3012-1] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/26/2018] [Accepted: 07/29/2019] [Indexed: 12/30/2022] Open
Abstract
BACKGROUND In most mammals, a vast array of genes coding for chemosensory receptors mediates olfaction. Odorant receptor (OR) genes generally constitute the largest multifamily (> 1100 intact members in the mouse). From the whole pool, each olfactory neuron expresses a single OR allele following poorly characterized mechanisms termed OR gene choice. OR genes are found in genomic aggregations known as clusters. Nearby enhancers, named elements, are crucial regulators of OR gene choice. Despite their importance, searching for new elements is burdensome. Other chemosensory receptor genes responsible for smell adhere to expression modalities resembling OR gene choice, and are arranged in genomic clusters - often with chromosomal linkage to OR genes. Still, no elements are known for them. RESULTS Here we present an inexpensive framework aimed at predicting elements. We redefine cluster identity by focusing on multiple receptor gene families at once, and exemplify thirty - not necessarily OR-exclusive - novel candidate enhancers. CONCLUSIONS The pipeline we introduce could guide future in vivo work aimed at discovering/validating new elements. In addition, our study provides an updated and comprehensive classification of all genomic loci responsible for the transduction of olfactory signals in mammals.
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Affiliation(s)
- Andrea Degl’Innocenti
- Smart Bio-Interfaces, Istituto Italiano di Tecnologia, Viale Rinaldo Piaggio 34, 56025 Pontedera (Pisa), Italy
- Max Planck Institute for Biophysics, Max-Planck-Gesellschaft, Max-von-Laue-Straße 3, D-60438 Frankfurt am Main, Germany
| | - Gabriella Meloni
- Center for Micro-BioRobotics, Istituto Italiano di Tecnologia, Viale Rinaldo Piaggio 34, 56025 Pontedera (Pisa), Italy
- The BioRobotics Institute, Scuola Superiore Sant’Anna, Viale Rinaldo Piaggio 34, 56025 Pontedera (Pisa), Italy
| | - Barbara Mazzolai
- Center for Micro-BioRobotics, Istituto Italiano di Tecnologia, Viale Rinaldo Piaggio 34, 56025 Pontedera (Pisa), Italy
| | - Gianni Ciofani
- Smart Bio-Interfaces, Istituto Italiano di Tecnologia, Viale Rinaldo Piaggio 34, 56025 Pontedera (Pisa), Italy
- Department of Mechanical and Aerospace Engineering, Politecnico di Torino, Corso Duca degli Abruzzi 24, 10129 Torino, Italy
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10
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Zhang R, Pan Y, Ahmed L, Block E, Zhang Y, Batista VS, Zhuang H. A Multispecific Investigation of the Metal Effect in Mammalian Odorant Receptors for Sulfur-Containing Compounds. Chem Senses 2019; 43:357-366. [PMID: 29659735 DOI: 10.1093/chemse/bjy022] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Metal-coordinating compounds are generally known to have strong smells, a phenomenon that can be attributed to the fact that odorant receptors for intense-smelling compounds, such as those containing sulfur, may be metalloproteins. We previously identified a mouse odorant receptor (OR), Olfr1509, that requires copper ions for sensitive detection of a series of metal-coordinating odorants, including (methylthio)methanethiol (MTMT), a strong-smelling component of male mouse urine that attracts female mice. By combining mutagenesis and quantum mechanics/molecular mechanics (QM/MM) modeling, we identified candidate binding sites in Olfr1509 that may bind to the copper-MTMT complex. However, whether there are other receptors utilizing metal ions for ligand-binding and other sites important for receptor activation is still unknown. In this study, we describe a second mouse OR for MTMT with a copper effect, namely Olfr1019. In an attempt to investigate the functional changes of metal-coordinating ORs in multiple species and to decipher additional sites involved in the metal effect, we cloned various mammalian orthologs of the 2 mouse MTMT receptors, and a third mouse MTMT receptor, Olfr15, that does not have a copper effect. We found that the function of all 3 MTMT receptors varies greatly among species and that the response to MTMT always co-occurred with the copper effect. Furthermore, using ancestral reconstruction and QM/MM modeling combined with receptor functional assay, we found that the amino acid residue R260 in Olfr1509 and the respective R261 site in Olfr1019 may be important for receptor activation.
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Affiliation(s)
- Ruina Zhang
- Department of Pathophysiology, Key Laboratory of Cell Differentiation and Apoptosis of the Chinese Ministry of Education, Shanghai Jiaotong University School of Medicine, Huangpu District, Shanghai, P. R. China
| | - Yi Pan
- Department of Pathophysiology, Key Laboratory of Cell Differentiation and Apoptosis of the Chinese Ministry of Education, Shanghai Jiaotong University School of Medicine, Huangpu District, Shanghai, P. R. China
| | - Lucky Ahmed
- Department of Chemistry, Yale University, New Haven, CT, USA
| | - Eric Block
- Department of Chemistry, University at Albany, State University of New York, NY, USA
| | - Yuetian Zhang
- Department of Pathophysiology, Key Laboratory of Cell Differentiation and Apoptosis of the Chinese Ministry of Education, Shanghai Jiaotong University School of Medicine, Huangpu District, Shanghai, P. R. China
| | | | - Hanyi Zhuang
- Department of Pathophysiology, Key Laboratory of Cell Differentiation and Apoptosis of the Chinese Ministry of Education, Shanghai Jiaotong University School of Medicine, Huangpu District, Shanghai, P. R. China
- Institute of Health Sciences, Shanghai Jiaotong University School of Medicine/Shanghai Institutes for Biological Sciences of Chinese Academy of Sciences, Xuhui District, Shanghai, P. R. China
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11
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Odor-Induced Electrical and Calcium Signals from Olfactory Sensory Neurons In Situ. Methods Mol Biol 2019. [PMID: 29884944 DOI: 10.1007/978-1-4939-8609-5_12] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register]
Abstract
Electrophysiological recording and optical imaging enable the characterization of membrane and odorant response properties of olfactory sensory neurons (OSNs) in the nasal neuroepithelium. Here we describe a method to record the responses of mammalian OSNs to odorant stimulations in an ex vivo preparation of intact olfactory epithelium. The responses of individual OSNs with defined odorant receptor types can be monitored via patch-clamp recording or calcium imaging.
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12
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Block E. Molecular Basis of Mammalian Odor Discrimination: A Status Report. JOURNAL OF AGRICULTURAL AND FOOD CHEMISTRY 2018; 66:13346-13366. [PMID: 30453735 DOI: 10.1021/acs.jafc.8b04471] [Citation(s) in RCA: 35] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
Humans have 396 unique, intact olfactory receptors (ORs), G-protein coupled receptors (GPCRs) containing receptor-specific binding sites; other mammals have more. Activation of these transmembrane proteins by an odorant initiates a signaling cascade, evoking an action potential leading to perception of a smell. Because the number of distinguishable odorants vastly exceeds the number of ORs, research has focused on mechanisms of recognition and signaling processes for classes of odorants. In this review, selected recent examples will be presented of "deorphaned" mammalian receptors, where the OR ligands (odorants) as well as key aspects of receptor-odorant interactions were identified using odorant-mediated receptor activation data together with site-directed mutagenesis and molecular modeling. Based on cumulative evidence from OR deorphaning and olfactory receptor neuron activation studies, a receptor-ligand docking model rather than an alternative bond vibration model is suggested to best explain the molecular basis of the exquisitely sensitive odor discrimination in mammals.
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Affiliation(s)
- Eric Block
- Department of Chemistry , University at Albany, SUNY , Albany , New York 12222 , United States
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13
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Sevenster D, de Oliveira Alvares L, D’Hooge R. Pre-exposure and retrieval effects on generalization of contextual fear. LEARNING AND MOTIVATION 2018. [DOI: 10.1016/j.lmot.2017.11.003] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
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14
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Abstract
In many species, survival depends on olfaction, yet the mechanisms that underlie olfactory sensitivity are not well understood. Here we examine how a conserved subset of olfactory receptors, the trace amine-associated receptors (TAARs), determine odor detection thresholds of mice to amines. We find that deleting all TAARs, or even single TAARs, results in significant odor detection deficits. This finding is not limited to TAARs, as the deletion of a canonical odorant receptor reduced behavioral sensitivity to its preferred ligand. Remarkably, behavioral threshold is set solely by the most sensitive receptor, with no contribution from other highly sensitive receptors. In addition, increasing the number of sensory neurons (and glomeruli) expressing a threshold-determining TAAR does not improve detection, indicating that sensitivity is not limited by the typical complement of sensory neurons. Our findings demonstrate that olfactory thresholds are set by the single highest affinity receptor and suggest that TAARs are evolutionarily conserved because they determine the sensitivity to a class of biologically relevant chemicals. Odorous chemicals broadly activate subsets of olfactory receptors in the nose, but how individual receptors contribute to behavioral sensitivity is not clear. Here, the authors demonstrate that detection thresholds in mice are set solely by the highest affinity receptor for a given odorant.
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15
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G-protein coupled receptors Mc4r and Drd1a can serve as surrogate odorant receptors in mouse olfactory sensory neurons. Mol Cell Neurosci 2018; 88:138-147. [PMID: 29407371 DOI: 10.1016/j.mcn.2018.01.010] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/09/2017] [Revised: 01/26/2018] [Accepted: 01/29/2018] [Indexed: 01/11/2023] Open
Abstract
In the mouse, most mature olfactory sensory neurons (OSNs) express one allele of one gene from the repertoire of ~1100 odorant receptor (OR) genes, which encode G-protein coupled receptors (GPCRs). Axons of OSNs that express a given OR coalesce into homogeneous glomeruli, which reside at conserved positions in the olfactory bulb. ORs are intimately involved in ensuring the expression of one OR per OSN and the coalescence of OSN axons into glomeruli. But the mechanisms whereby ORs accomplish these diverse functions remain poorly understood. An experimental approach that has been informative is to substitute an OR genetically with another GPCR that is normally not expressed in OSNs, in order to determine in which aspects this GPCR can serve as surrogate OR in mouse OSNs. Thus far only the β2-adrenergic receptor (β2AR, Ardb2) has been shown to be able to serve as surrogate OR in OSNs; the β2AR could substitute for the M71 OR in all aspects examined. Can other non-olfactory GPCRs function equally well as surrogate ORs in OSNs? Here, we have generated and characterized two novel gene-targeted mouse strains in which the mouse melanocortin 4 receptor (Mc4r) or the mouse dopamine receptor D1 (Drd1a) is coexpressed with tauGFP in OSNs that express the OR locus M71. These alleles and strains are abbreviated as Mc4r → M71-GFP and Drd1a → M71-GFP. We detected strong Mc4r or Drd1a immunoreactivity in axons and dendritic knobs and cilia of OSNs that express Mc4r or Drd1a from the M71 locus. These OSNs responded physiologically to cognate agonists for Mc4r (Ro27-3225) or Drd1a (SKF81297), and not to the M71 ligand acetophenone. Axons of OSNs expressing Mc4r → M71-GFP coalesced into glomeruli. Axons of OSNs expressing Drd1a → M71-GFP converged onto restricted areas of the olfactory bulb but did not coalesce into glomeruli. Thus, OR functions in OSNs can be substituted by Mc4r or Drd1a, but not as well as by β2AR. We attribute the weak performance of Drd1a as surrogate OR to poor OSN maturation.
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16
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Maier AM, Breer H, Strotmann J. Structural Features of an OR37 Glomerulus: A Comparative Study. Front Neuroanat 2018; 11:125. [PMID: 29326560 PMCID: PMC5741646 DOI: 10.3389/fnana.2017.00125] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/10/2017] [Accepted: 12/05/2017] [Indexed: 11/13/2022] Open
Abstract
In the olfactory bulb (OB) a sophisticated neuronal network mediates the primary processing of sensory information and extensive investigations over the past decades have greatly improved our understanding of the morphology and neuronal organization of the OB. However, efforts have mostly been focused on the different radial layers, typical for the OB and little attention has been paid to individual odorant receptor specific glomeruli, the first relay station of sensory information. It has been assumed that glomeruli processing odorant information out of different contextual fields might require accordingly specialized neuronal networks. In this study, we have analyzed and compared the structural features as well as cell types in the periglomerular (PG) region of three odorant receptor specific glomeruli. The investigations were focused on glomeruli of the receptor type OR37A, a member of the unique OR37 subsystem, in comparison to glomeruli of OR18-2, a class I odorant receptor and OR256-17, a class II receptor. Each of the odorant receptor types is known to be activated by distinct odorants and their glomeruli are located in different regions of the bulb. We found significant differences in the size of the glomeruli as well as in the variability of the glomerulus size in individual mice, whereby the OR37A glomeruli featured a remarkably stable size. The number of cells surrounding a given glomerulus correlated strongly with its size which allowed comparative analyses of the surrounding cell types for individual glomeruli. The proportion of PG cells labeled by NeuN as well as putative GABAergic neurons labeled by GAD65 was quite similar for the different glomerulus types. However, the number of cells expressing distinct calcium-binding proteins, namely parvalbumin (PV), calbindin (CB) or calretinin (CR) varied significantly among the three glomerulus types. These data suggest that each odorant receptor specific glomerulus type may be surrounded by a unique network of PG cells.
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Affiliation(s)
- Anna-Maria Maier
- Institute of Physiology, University of Hohenheim, Stuttgart, Germany
| | - Heinz Breer
- Institute of Physiology, University of Hohenheim, Stuttgart, Germany
| | - Jörg Strotmann
- Institute of Physiology, University of Hohenheim, Stuttgart, Germany
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Izquierdo C, Gómez-Tamayo JC, Nebel JC, Pardo L, Gonzalez A. Identifying human diamine sensors for death related putrescine and cadaverine molecules. PLoS Comput Biol 2018; 14:e1005945. [PMID: 29324768 PMCID: PMC5783396 DOI: 10.1371/journal.pcbi.1005945] [Citation(s) in RCA: 25] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/25/2017] [Revised: 01/24/2018] [Accepted: 12/28/2017] [Indexed: 12/21/2022] Open
Abstract
Pungent chemical compounds originating from decaying tissue are strong drivers of animal behavior. Two of the best-characterized death smell components are putrescine (PUT) and cadaverine (CAD), foul-smelling molecules produced by decarboxylation of amino acids during decomposition. These volatile polyamines act as ‘necromones’, triggering avoidance or attractive responses, which are fundamental for the survival of a wide range of species. The few studies that have attempted to identify the cognate receptors for these molecules have suggested the involvement of the seven-helix trace amine-associated receptors (TAARs), localized in the olfactory epithelium. However, very little is known about the precise chemosensory receptors that sense these compounds in the majority of organisms and the molecular basis of their interactions. In this work, we have used computational strategies to characterize the binding between PUT and CAD with the TAAR6 and TAAR8 human receptors. Sequence analysis, homology modeling, docking and molecular dynamics studies suggest a tandem of negatively charged aspartates in the binding pocket of these receptors which are likely to be involved in the recognition of these small biogenic diamines. The distinctive dead smell comes largely from molecules like cadaverine and putrescine that are produced during decomposition of organic tissues. These volatile compounds act as powerful chemical signals important for the survival of a wide range of species. Previous studies have identified the trace amine-associated receptor 13c (or TAAR13c) in zebrafish as the cognate receptor of cadaverine in bony fishes. In this work, we employed computational strategies to disclose the human TAAR6 and TAAR8 receptors as sensors of the putrescine and cadaverine molecules. Our results indicate that several negatively charged residues in the ligand binding pocket of these receptors constitute the molecular basis for recognition of these necromones in humans.
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Affiliation(s)
- Cristina Izquierdo
- Laboratori de Medicina Computacional, Unitat de Bioestadística, Facultat de Medicina, Universitat Autònoma de Barcelona, E-08193 Bellaterra, Spain
| | - José C. Gómez-Tamayo
- Laboratori de Medicina Computacional, Unitat de Bioestadística, Facultat de Medicina, Universitat Autònoma de Barcelona, E-08193 Bellaterra, Spain
| | - Jean-Christophe Nebel
- Faculty of Science, Engineering and Computing, Kingston University, London, United Kingdom
| | - Leonardo Pardo
- Laboratori de Medicina Computacional, Unitat de Bioestadística, Facultat de Medicina, Universitat Autònoma de Barcelona, E-08193 Bellaterra, Spain
| | - Angel Gonzalez
- Laboratori de Medicina Computacional, Unitat de Bioestadística, Facultat de Medicina, Universitat Autònoma de Barcelona, E-08193 Bellaterra, Spain
- * E-mail:
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18
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Kepchia D, Sherman B, Haddad R, Luetje CW. Mammalian odorant receptor tuning breadth persists across distinct odorant panels. PLoS One 2017; 12:e0185329. [PMID: 28945824 PMCID: PMC5612731 DOI: 10.1371/journal.pone.0185329] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/21/2017] [Accepted: 09/11/2017] [Indexed: 11/19/2022] Open
Abstract
The molecular receptive range (MRR) of a mammalian odorant receptor (OR) is the set of odorant structures that activate the OR, while the distribution of these odorant structures across odor space is the tuning breadth of the OR. Variation in tuning breadth is thought to be an important property of ORs, with the MRRs of these receptors varying from narrowly to broadly tuned. However, defining the tuning breadth of an OR is a technical challenge. For practical reasons, a screening panel that broadly covers odor space must be limited to sparse coverage of the many potential structures in that space. When screened with such a panel, ORs with different odorant specificities, but equal tuning breadths, might appear to have different tuning breadths due to chance. We hypothesized that ORs would maintain their tuning breadths across distinct odorant panels. We constructed a new screening panel that was broadly distributed across an estimated odor space and contained compounds distinct from previous panels. We used this new screening panel to test several murine ORs that were previously characterized as having different tuning breadths. ORs were expressed in Xenopus laevis oocytes and assayed by two-electrode voltage clamp electrophysiology. MOR256-17, an OR previously characterized as broadly tuned, responded to nine novel compounds from our new screening panel that were structurally diverse and broadly dispersed across an estimated odor space. MOR256-22, an OR previously characterized as narrowly tuned, responded to a single novel compound that was structurally similar to a previously known ligand for this receptor. MOR174-9, a well-characterized receptor with a narrowly tuned MRR, did not respond to any novel compounds in our new panel. These results support the idea that variation in tuning breadth among these three ORs is not an artifact of the screening protocol, but is an intrinsic property of the receptors.
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Affiliation(s)
- Devin Kepchia
- Department of Molecular and Cellular Pharmacology, University of Miami Miller School of Medicine, Miami, Florida, United States of America
| | - Benjamin Sherman
- Department of Molecular and Cellular Pharmacology, University of Miami Miller School of Medicine, Miami, Florida, United States of America
| | - Rafi Haddad
- The Leslie & Susan Goldschmied (Gonda) Multidisciplinary Brain Research Center, Bar-Ilan University, Ramat-Gan, Israel
| | - Charles W. Luetje
- Department of Molecular and Cellular Pharmacology, University of Miami Miller School of Medicine, Miami, Florida, United States of America
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19
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Abstract
Natural olfactory stimuli are volatile-chemical mixtures in which relative perceptual saliencies determine which odor-components are identified. Odor identification also depends on rapid selective adaptation, as shown for 4 odor stimuli in an earlier experimental simulation of natural conditions. Adapt-test pairs of mixtures of water-soluble, distinct odor stimuli with chemical features in common were studied. Identification decreased for adapted components but increased for unadapted mixture-suppressed components, showing compound identities were retained, not degraded to individual molecular features. Four additional odor stimuli, 1 with 2 perceptible odor notes, and an added "water-adapted" control tested whether this finding would generalize to other 4-compound sets. Selective adaptation of mixtures of the compounds (odors): 3 mM benzaldehyde (cherry), 5 mM maltol (caramel), 1 mM guaiacol (smoke), and 4 mM methyl anthranilate (grape-smoke) again reciprocally unmasked odors of mixture-suppressed components in 2-, 3-, and 4-component mixtures with 2 exceptions. The cherry note of "benzaldehyde" (itself) and the shared note of "methyl anthranilate and guaiacol" (together) were more readily identified. The pervasive mixture-component dominance and dynamic perceptual salience may be mediated through peripheral adaptation and central mutual inhibition of neural responses. Originating in individual olfactory receptor variants, it limits odor identification and provides analytic properties for momentary recognition of a few remaining mixture-components.
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Affiliation(s)
- Marion E Frank
- Oral Health & Diagnostic Sciences, School of Dental Medicine, UConn Health, MC 1715, 263 Farmington Avenue, Farmington, CT 06030, USA
| | - Dane B Fletcher
- Oral Health & Diagnostic Sciences, School of Dental Medicine, UConn Health, MC 1715, 263 Farmington Avenue, Farmington, CT 06030, USA
| | - Thomas P Hettinger
- Oral Health & Diagnostic Sciences, School of Dental Medicine, UConn Health, MC 1715, 263 Farmington Avenue, Farmington, CT 06030, USA
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20
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Abstract
The mechanisms by which odors induce instinctive behaviors are largely unknown. Odor detection in the mouse nose is mediated by >1, 000 different odorant receptors (ORs) and trace amine-associated receptors (TAARs). Odor perceptions are encoded combinatorially by ORs and can be altered by slight changes in the combination of activated receptors. However, the stereotyped nature of instinctive odor responses suggests the involvement of specific receptors and genetically programmed neural circuits relatively immune to extraneous odor stimuli and receptor inputs. Here, we report that, contrary to expectation, innate odor-induced behaviors can be context-dependent. First, different ligands for a given TAAR can vary in behavioral effect. Second, when combined, some attractive and aversive odorants neutralize one another's behavioral effects. Both a TAAR ligand and a common odorant block aversion to a predator odor, indicating that this ability is not unique to TAARs and can extend to an aversive response of potential importance to survival. In vitro testing of single receptors with binary odorant mixtures indicates that behavioral blocking can occur without receptor antagonism in the nose. Moreover, genetic ablation of a single receptor prevents its cognate ligand from blocking predator odor aversion, indicating that the blocking requires sensory input from the receptor. Together, these findings indicate that innate odor-induced behaviors can depend on context, that signals from a single receptor can block innate odor aversion, and that instinctive behavioral responses to odors can be modulated by interactions in the brain among signals derived from different receptors.
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