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Sbrini G, Mutti V, Bono F, Tomasoni Z, Fadel D, Missale C, Fiorentini C. 17-β-estradiol potentiates the neurotrophic and neuroprotective effects mediated by the dopamine D3/acetylcholine nicotinic receptor heteromer in dopaminergic neurons. Eur J Pharmacol 2024; 976:176678. [PMID: 38821163 DOI: 10.1016/j.ejphar.2024.176678] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/13/2024] [Revised: 05/10/2024] [Accepted: 05/27/2024] [Indexed: 06/02/2024]
Abstract
Dopaminergic neurons express a heteromer composed of the dopamine D3 receptor and the α4β2 nicotinic acetylcholine receptor, the D3R-nAChR heteromer, activated by both nicotine and dopamine D2 and D3 receptors agonists, such as quinpirole, and crucial for dopaminergic neuron homeostasis. We now report that D3R-nAChR heteromer activity is potentiated by 17-β-estradiol which acts as a positive allosteric modulator by binding a specific domain on the α4 subunit of the nicotinic receptor protomer. In mouse dopaminergic neurons, in fact, 17-β-estradiol significantly increased the ability of nicotine and quinpirole in promoting neuron dendritic remodeling and in protecting neurons against the accumulation of α-synuclein induced by deprivation of glucose, with a mechanism that does not involve the classical estrogen receptors. The potentiation induced by 17-β-estradiol required the D3R-nAChR heteromer since either nicotinic receptor or dopamine D3 receptor antagonists and interfering TAT-peptides, but not the estrogen receptor antagonist fulvestrant, specifically prevented 17-β-estradiol effects. Evidence of estrogens neuroprotection, mainly mediated by genomic mechanisms, have been provided, which is in line with epidemiological data reporting that females are less likely to develop Parkinson's Disease than males. Therefore, potentiation of D3R-nAChR heteromer activity may represent a further mechanism by which 17-β-estradiol reduces dopaminergic neuron vulnerability.
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Affiliation(s)
- Giulia Sbrini
- Department of Molecular and Translational Medicine, University of Brescia, Viale Europa 11, 25123 Brescia, Italy
| | - Veronica Mutti
- Department of Molecular and Translational Medicine, University of Brescia, Viale Europa 11, 25123 Brescia, Italy
| | - Federica Bono
- Department of Molecular and Translational Medicine, University of Brescia, Viale Europa 11, 25123 Brescia, Italy
| | - Zaira Tomasoni
- Department of Molecular and Translational Medicine, University of Brescia, Viale Europa 11, 25123 Brescia, Italy
| | - Dounia Fadel
- Department of Molecular and Translational Medicine, University of Brescia, Viale Europa 11, 25123 Brescia, Italy
| | - Cristina Missale
- Department of Molecular and Translational Medicine, University of Brescia, Viale Europa 11, 25123 Brescia, Italy
| | - Chiara Fiorentini
- Department of Molecular and Translational Medicine, University of Brescia, Viale Europa 11, 25123 Brescia, Italy.
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2
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Wells AC, Mojica C, Lotfipour S. Hypersensitivity of the nicotinic acetylcholine receptor subunit (CHRNA2 L9'S/L9'S) in female adolescent mice produces deficits in nicotine-induced facilitation of hippocampal-dependent learning and memory. Neurobiol Learn Mem 2024; 213:107959. [PMID: 38964600 DOI: 10.1016/j.nlm.2024.107959] [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: 03/15/2024] [Revised: 06/24/2024] [Accepted: 07/01/2024] [Indexed: 07/06/2024]
Abstract
Adolescence is characterized by a critical period of maturation and growth, during which regions of the brain are vulnerable to long-lasting cognitive disturbances. Adolescent exposure to nicotine can lead to deleterious neurological and psychological outcomes. Moreover, the nicotinic acetylcholine receptor (nAChR) has been shown to play a functionally distinct role in the development of the adolescent brain. CHRNA2 encodes for the α2 subunit of nicotinic acetylcholine receptors associated with CA1 oriens lacunosum moleculare GABAergic interneurons and is associated with learning and memory. Previously, we found that adolescent male hypersensitive CHRNA2L9'S/L9' mice had impairments in learning and memory during a pre-exposure-dependent contextual fear conditioning task that could be rescued by low-dose nicotine exposure. In this study, we assessed learning and memory in female adolescent hypersensitive CHRNA2L9'S/L9' mice exposed to saline or a subthreshold dose of nicotine using a hippocampus-dependent task of pre-exposure-dependent contextual fear conditioning. We found that nicotine-treated wild-type female mice had significantly greater improvements in learning and memory than both saline-treated wild-type mice and nicotine-treated CHRNA2L9'S/L9' female mice. Thus, hyperexcitability of CHRNA2 in female adolescent mice ablated the nicotine-mediated potentiation of learning and memory seen in wild-types. Our results indicate that nicotine exposure during adolescence mediates sexually dimorphic patterns of learning and memory, with wild-type female adolescents being more susceptible to the effects of sub-threshold nicotine exposure. To understand the mechanism underlying sexually dimorphic behavior between hyperexcitable CHRNA2 mice, it is critical that further research be conducted.
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Affiliation(s)
- Alicia C Wells
- School of Medicine, University of California, Irvine, CA 92697, USA.
| | - Celina Mojica
- Graduate Division, University of California, Irvine, CA 92697, USA
| | - Shahrdad Lotfipour
- School of Medicine, University of California, Irvine, CA 92697, USA; Department of Emergency Medicine, Pharmaceutical Sciences, Pathology and Laboratory Medicine, University of California, Irvine, CA 92697, USA
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3
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Joglekar R, Cauley M, Lipsich T, Corcoran DL, Patisaul HB, Levin ED, Meyer JN, McCarthy MM, Murphy SK. Developmental nicotine exposure and masculinization of the rat preoptic area. Neurotoxicology 2022; 89:41-54. [PMID: 35026373 PMCID: PMC8917982 DOI: 10.1016/j.neuro.2022.01.005] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/04/2021] [Revised: 12/22/2021] [Accepted: 01/06/2022] [Indexed: 11/24/2022]
Abstract
Nicotine is a neuroteratogenic component of tobacco smoke, e-cigarettes, and other products and can exert sex-specific effects in the developing brain, likely mediated through sex hormones. Estradiol modulates expression of nicotinic acetylcholine receptors in rats, and plays critical roles in neurodevelopmental processes, including sexual differentiation of the brain. Here, we examined the effects of developmental nicotine exposure on the sexual differentiation of the preoptic area (POA), a brain region that normally displays robust structural sexual dimorphisms and controls adult mating behavior in rodents. Using a rat model of gestational exposure, developing pups were exposed to nicotine (2 mg/kg/day) via maternal osmotic minipump (subcutaneously, sc) throughout the critical window for brain sexual differentiation. At postnatal day (PND) 4, a subset of offspring was analyzed for epigenetic effects in the POA. At PND40, all offspring were gonadectomized, implanted with a testosterone-releasing capsule (sc), and assessed for male sexual behavior at PND60. Following sexual behavior assessment, the area of the sexually dimorphic nucleus of the POA (SDN-POA) was measured using immunofluorescent staining techniques. In adults, normal sex differences in male sexual behavior and in the SDN-POA area were eliminated in nicotine-treated animals. Using novel analytical approaches to evaluate overall masculinization of the adult POA, we identified significant masculinization of the nicotine-treated female POA. In neonates (PND4), nicotine exposure induced trending alterations in methylation-dependent masculinizing gene expression and DNA methylation levels at sexually-dimorphic differentially methylated regions, suggesting that developmental nicotine exposure is capable of triggering masculinization of the rat POA via epigenetic mechanisms.
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Affiliation(s)
- Rashmi Joglekar
- Duke University Nicholas School of the Environment, Durham, NC 27708 USA
| | - Marty Cauley
- Duke University Medical Center, Department of Psychiatry and Behavioral Sciences, Durham, NC 27708 USA
| | - Taylor Lipsich
- Duke University Medical Center, Department of Obstetrics & Gynecology, Durham, NC 27708 USA
| | - David L. Corcoran
- Duke Center for Genomic and Computational Biology, Durham, NC 27708 USA
| | - Heather B. Patisaul
- North Carolina State University, Department of Biological Sciences, Raleigh, NC 27695 USA
| | - Edward D. Levin
- Duke University Medical Center, Department of Psychiatry and Behavioral Sciences, Durham, NC 27708 USA
| | - Joel N. Meyer
- Duke University Nicholas School of the Environment, Durham, NC 27708 USA
| | - Margaret M. McCarthy
- University of Maryland School of Medicine, Department of Pharmacology, Baltimore, MD 21201 USA
| | - Susan K. Murphy
- Duke University Medical Center, Department of Obstetrics & Gynecology, Durham, NC 27708 USA
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4
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Pan Z, Zhao M, Peng Y, Wang J. Functional divergence analysis of vertebrate neuronal nicotinic acetylcholine receptor subunits. J Biomol Struct Dyn 2018; 37:2938-2948. [PMID: 30044167 DOI: 10.1080/07391102.2018.1500945] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/28/2022]
Abstract
Nicotinic acetylcholine receptors (nAChRs) are pentamers formed by subunits from a large multigene family and are highly variable in kinetic, electrophysiological and pharmacological properties. Due to the essential roles of nAChRs in many physiological procedures and diversity in function, identifying the function-related sites specific to each subunit is not only necessary to understand the properties of the receptors but also useful to design potential therapeutic compounds that target these macromolecules for treating a series of central neuronal disorders. By conducting a detailed function divergence analysis on nine neuronal nAChR subunits from representative vertebrate species, we revealed the existence of significant functional variation between most subunit pairs. Specifically, 44 unique residues were identified for the α7 subunit, while another 22 residues that were likely responsible for the specific features of other subunits were detected. By mapping these sites onto the 3 D structure of the human α7 subunit, a structure-function relationship profile was revealed. Our results suggested that the functional divergence related sites clustered in the ligand binding domain, the β2-β3 linker close to the N-terminal α-helix, the intracellular linkers between transmembrane domains, and the "transition zone" may have experienced altered evolutionary rates. The former two regions may be potential binding sites for the α7* subtype-specific allosteric modulators, while the latter region is likely to be subtype-specific allosteric modulations of the heteropentameric descendants such as the α4β2* nAChRs. Communicated by Ramaswamy H. Sarma.
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Affiliation(s)
- Zhenhua Pan
- a School of Biomedical Engineering , Tianjin Medical University , Tianjin , China.,b Tianjin Key Laboratory of Lung Cancer Metastasis and Tumor Microenvironment , Tianjin Lung Cancer Institute, Tianjin Medical University General Hospital , Tianjin , China
| | - Mengwen Zhao
- a School of Biomedical Engineering , Tianjin Medical University , Tianjin , China
| | - Yonglin Peng
- a School of Biomedical Engineering , Tianjin Medical University , Tianjin , China
| | - Ju Wang
- a School of Biomedical Engineering , Tianjin Medical University , Tianjin , China
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5
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Cross SJ, Linker KE, Leslie FM. Sex-dependent effects of nicotine on the developing brain. J Neurosci Res 2017; 95:422-436. [PMID: 27870426 DOI: 10.1002/jnr.23878] [Citation(s) in RCA: 62] [Impact Index Per Article: 8.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/06/2016] [Revised: 07/08/2016] [Accepted: 07/14/2016] [Indexed: 02/06/2023]
Abstract
The use of tobacco products represents a major public health concern, especially among women. Epidemiological data have consistently demonstrated that women have less success quitting tobacco use and a higher risk for developing tobacco-related diseases. The deleterious effects of nicotine are not restricted to adulthood, as nicotinic acetylcholine receptors regulate critical aspects of neural development. However, the exact mechanisms underlying the particular sensitivity of women to develop tobacco dependence have not been well elucidated. In this mini-review, we show that gonadal hormone-mediated sexual differentiation of the brain may be an important determinant of sex differences in the effects of nicotine. We highlight direct interactions between sex steroid hormones and ligand-gated ion channels critical for brain maturation, and discuss the extended and profound sexual differentiation of the brain. We emphasize that nicotine exposure during the perinatal and adolescent periods interferes with normal sexual differentiation and can induce long-lasting, sex-dependent alterations in neuronal structure, cognitive and executive function, learning and memory, and reward processing. We stress important age and sex differences in nicotine's effects and emphasize the importance of including these factors in preclinical research that models tobacco dependence. © 2016 Wiley Periodicals, Inc.
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Affiliation(s)
- Sarah J Cross
- Department of Anatomy and Neurobiology, School of Medicine, University of California, Irvine, California
| | - Kay E Linker
- Department of Anatomy and Neurobiology, School of Medicine, University of California, Irvine, California
| | - Frances M Leslie
- Department of Anatomy and Neurobiology, School of Medicine, University of California, Irvine, California.,Department of Pharmacology, School of Medicine, University of California, Irvine, California
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6
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Jin X, Germann AL, Shin DJ, Akk G, Steinbach JH. Determination of the Residues in the Extracellular Domain of the Nicotinic α Subunit Required for the Actions of Physostigmine on Neuronal Nicotinic Receptors. Mol Pharmacol 2017; 92:318-326. [PMID: 28630263 PMCID: PMC5548365 DOI: 10.1124/mol.117.108894] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/21/2017] [Accepted: 06/14/2017] [Indexed: 11/22/2022] Open
Abstract
Physostigmine can potentiate and inhibit neuronal nicotinic receptors, in addition to inhibiting the activity of acetylcholinesterase. We found that receptors containing three copies of the α2 subunit are inhibited by low concentrations of physostigmine in contrast to receptors containing three copies of the α4 subunit that are potentiated. We exploited this observation to determine the regions required for the actions of physostigmine. Chimeric constructs of the α2 and α4 subunits located two regions in the extracellular amino-terminal domain of the subunit: the E loop (a loop of the transmitter-binding domain) and a region closer to the amino-terminus that collectively could completely determine the different effects of physostigmine. Point mutations then identified a single residue, α2(I92) versus α4(R92), that, when combined with transfer of the E loop, could convert the inhibition seen with α2 subunits to potentiation and the potentiation seen with α4 subunits to inhibition. In addition, other point mutations could affect the extent of potentiation or inhibition, indicating that a more extensive set of interactions in the amino-terminal domain plays some role in the actions of physostigmine.
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Affiliation(s)
- Xiaochun Jin
- Department of Anesthesiology, Washington University School of Medicine in St. Louis, St. Louis, Missouri (X.J., A.L.G., D.J.S., G.A., J.H.S.); and Taylor Family Institute for Innovative Psychiatric Research, Washington University School of Medicine in St. Louis, St. Louis, Missouri (G.A., J.H.S.)
| | - Allison L Germann
- Department of Anesthesiology, Washington University School of Medicine in St. Louis, St. Louis, Missouri (X.J., A.L.G., D.J.S., G.A., J.H.S.); and Taylor Family Institute for Innovative Psychiatric Research, Washington University School of Medicine in St. Louis, St. Louis, Missouri (G.A., J.H.S.)
| | - Daniel J Shin
- Department of Anesthesiology, Washington University School of Medicine in St. Louis, St. Louis, Missouri (X.J., A.L.G., D.J.S., G.A., J.H.S.); and Taylor Family Institute for Innovative Psychiatric Research, Washington University School of Medicine in St. Louis, St. Louis, Missouri (G.A., J.H.S.)
| | - Gustav Akk
- Department of Anesthesiology, Washington University School of Medicine in St. Louis, St. Louis, Missouri (X.J., A.L.G., D.J.S., G.A., J.H.S.); and Taylor Family Institute for Innovative Psychiatric Research, Washington University School of Medicine in St. Louis, St. Louis, Missouri (G.A., J.H.S.)
| | - Joe Henry Steinbach
- Department of Anesthesiology, Washington University School of Medicine in St. Louis, St. Louis, Missouri (X.J., A.L.G., D.J.S., G.A., J.H.S.); and Taylor Family Institute for Innovative Psychiatric Research, Washington University School of Medicine in St. Louis, St. Louis, Missouri (G.A., J.H.S.)
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7
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Lotfipour S, Mojica C, Nakauchi S, Lipovsek M, Silverstein S, Cushman J, Tirtorahardjo J, Poulos A, Elgoyhen AB, Sumikawa K, Fanselow MS, Boulter J. α2* Nicotinic acetylcholine receptors influence hippocampus-dependent learning and memory in adolescent mice. ACTA ACUST UNITED AC 2017; 24:231-244. [PMID: 28507032 PMCID: PMC5435881 DOI: 10.1101/lm.045369.117] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/21/2017] [Accepted: 03/31/2017] [Indexed: 11/24/2022]
Abstract
The absence of α2* nicotinic acetylcholine receptors (nAChRs) in oriens lacunosum moleculare (OLM) GABAergic interneurons ablate the facilitation of nicotine-induced hippocampal CA1 long-term potentiation and impair memory. The current study delineated whether genetic mutations of α2* nAChRs (Chrna2L9′S/L9′S and Chrna2KO) influence hippocampus-dependent learning and memory and CA1 synaptic plasticity. We substituted a serine for a leucine (L9′S) in the α2 subunit (encoded by the Chrna2 gene) to make a hypersensitive nAChR. Using a dorsal hippocampus-dependent task of preexposure-dependent contextual fear conditioning, adolescent hypersensitive Chrna2L9′S/L9′S male mice exhibited impaired learning and memory. The deficit was rescued by low-dose nicotine exposure. Electrophysiological studies demonstrated that hypersensitive α2 nAChRs potentiate acetylcholine-induced ion channel flux in oocytes and acute nicotine-induced facilitation of dorsal/intermediate CA1 hippocampal long-term potentiation in Chrna2L9′S/L9′S mice. Adolescent male mice null for the α2 nAChR subunit exhibited a baseline deficit in learning that was not reversed by an acute dose of nicotine. These effects were not influenced by locomotor, sensory or anxiety-related measures. Our results demonstrated that α2* nAChRs influenced hippocampus-dependent learning and memory, as well as nicotine-facilitated CA1 hippocampal synaptic plasticity.
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Affiliation(s)
- Shahrdad Lotfipour
- Department of Psychiatry, University of California, Los Angeles, Los Angeles, California 90095, USA
| | - Celina Mojica
- Department of Psychiatry, University of California, Los Angeles, Los Angeles, California 90095, USA
| | - Sakura Nakauchi
- Department of Neurobiology and Behavior, University of California, Irvine, Irvine, California 92612, USA
| | - Marcela Lipovsek
- Instituto de Investigaciones en Ingeniería Genética y Biología Molecular, Dr. Héctor N Torres, CONICET, Buenos Aires, C1428ADN, Argentina
| | - Sarah Silverstein
- Department of Psychiatry, University of California, Los Angeles, Los Angeles, California 90095, USA
| | - Jesse Cushman
- Department of Psychology, University of California, Los Angeles, Los Angeles, California 90095, USA
| | | | - Andrew Poulos
- Department of Psychology, University of California, Los Angeles, Los Angeles, California 90095, USA
| | - Ana Belén Elgoyhen
- Instituto de Investigaciones en Ingeniería Genética y Biología Molecular, Dr. Héctor N Torres, CONICET, Buenos Aires, C1428ADN, Argentina
| | - Katumi Sumikawa
- Department of Neurobiology and Behavior, University of California, Irvine, Irvine, California 92612, USA
| | - Michael S Fanselow
- Department of Psychiatry, University of California, Los Angeles, Los Angeles, California 90095, USA.,Department of Psychology, University of California, Los Angeles, Los Angeles, California 90095, USA
| | - Jim Boulter
- Department of Psychiatry, University of California, Los Angeles, Los Angeles, California 90095, USA
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8
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Jin X, McCollum MM, Germann AL, Akk G, Steinbach JH. The E Loop of the Transmitter Binding Site Is a Key Determinant of the Modulatory Effects of Physostigmine on Neuronal Nicotinic α4β2 Receptors. Mol Pharmacol 2017; 91:100-109. [PMID: 27895161 PMCID: PMC5267520 DOI: 10.1124/mol.116.106484] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/11/2016] [Accepted: 11/23/2016] [Indexed: 11/22/2022] Open
Abstract
Physostigmine is a well known inhibitor of acetylcholinesterase, which can also activate, potentiate, and inhibit acetylcholine receptors, including neuronal nicotinic receptors comprising α4 and β2 subunits. We have found that the two stoichiometric forms of this receptor differ in the effects of physostigmine. The form containing three copies of α4 and two of β2 was potentiated at low concentrations of acetylcholine chloride (ACh) and physostigmine, whereas the form containing two copies of α4 and three of β2 was inhibited. Chimeric constructs of subunits indicated that the presence of inhibition or potentiation depended on the source of the extracellular ligand binding domain of the subunit. Further sets of chimeric constructs demonstrated that a portion of the ACh binding domain, the E loop, is a key determinant. Transferring the E loop from the β2 subunit to the α4 subunit resulted in strong inhibition, whereas the reciprocal transfer reduced inhibition. To control the number and position of the incorporated chimeric subunits, we expressed chimeric constructs with subunit dimers. Surprisingly, incorporation of a subunit with an altered E loop had similar effects whether it contributed either to an intersubunit interface containing a canonical ACh binding site or to an alternative interface. The observation that the α4 E loop is involved suggests that physostigmine interacts with regions of subunits that contribute to the ACh binding site, whereas the lack of interface specificity indicates that interaction with a particular ACh binding site is not the critical factor.
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Affiliation(s)
- Xiaochun Jin
- Department of Anesthesiology (X.J., M.M.C., A.L.G., G.A., J.H.S.) and Taylor Family Institute for Innovative Psychiatric Research (G.A., J.H.S.), Washington University School of Medicine, St. Louis, Missouri
| | - Megan M McCollum
- Department of Anesthesiology (X.J., M.M.C., A.L.G., G.A., J.H.S.) and Taylor Family Institute for Innovative Psychiatric Research (G.A., J.H.S.), Washington University School of Medicine, St. Louis, Missouri
| | - Allison L Germann
- Department of Anesthesiology (X.J., M.M.C., A.L.G., G.A., J.H.S.) and Taylor Family Institute for Innovative Psychiatric Research (G.A., J.H.S.), Washington University School of Medicine, St. Louis, Missouri
| | - Gustav Akk
- Department of Anesthesiology (X.J., M.M.C., A.L.G., G.A., J.H.S.) and Taylor Family Institute for Innovative Psychiatric Research (G.A., J.H.S.), Washington University School of Medicine, St. Louis, Missouri
| | - Joe Henry Steinbach
- Department of Anesthesiology (X.J., M.M.C., A.L.G., G.A., J.H.S.) and Taylor Family Institute for Innovative Psychiatric Research (G.A., J.H.S.), Washington University School of Medicine, St. Louis, Missouri
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9
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Alcaino C, Musgaard M, Minguez T, Mazzaferro S, Faundez M, Iturriaga-Vasquez P, Biggin PC, Bermudez I. Role of the Cys Loop and Transmembrane Domain in the Allosteric Modulation of α4β2 Nicotinic Acetylcholine Receptors. J Biol Chem 2016; 292:551-562. [PMID: 27864368 DOI: 10.1074/jbc.m116.751206] [Citation(s) in RCA: 24] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/31/2016] [Revised: 11/04/2016] [Indexed: 11/06/2022] Open
Abstract
Allosteric modulators of pentameric ligand-gated ion channels are thought to act on elements of the pathways that couple agonist binding to channel gating. Using α4β2 nicotinic acetylcholine receptors and the α4β2-selective positive modulators 17β-estradiol (βEST) and desformylflustrabromine (dFBr), we have identified pathways that link the binding sites for these modulators to the Cys loop, a region that is critical for channel gating in all pentameric ligand-gated ion channels. Previous studies have shown that the binding site for potentiating βEST is in the C-terminal (post-M4) region of the α4 subunit. Here, using homology modeling in combination with mutagenesis and electrophysiology, we identified the binding site for potentiating dFBr on the top half of a cavity between the third (M3) and fourth transmembrane (M4) α-helices of the α4 subunit. We found that the binding sites for βEST and dFBr communicate with the Cys loop, through interactions between the last residue of post-M4 and Phe170 of the conserved FPF sequence of the Cys loop, and that these interactions affect potentiating efficacy. In addition, interactions between a residue in M3 (Tyr309) and Phe167, a residue adjacent to the Cys loop FPF motif, also affect dFBr potentiating efficacy. Thus, the Cys loop acts as a key control element in the allosteric transduction pathway for potentiating βEST and dFBr. Overall, we propose that positive allosteric modulators that bind the M3-M4 cavity or post-M4 region increase the efficacy of channel gating through interactions with the Cys loop.
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Affiliation(s)
- Constanza Alcaino
- From the Department of Biological and Medical Sciences, Oxford Brookes University, Oxford OX3 0BP, United Kingdom
| | - Maria Musgaard
- the Department of Biochemistry, University of Oxford, Oxford OX1 3QU, United Kingdom
| | - Teresa Minguez
- From the Department of Biological and Medical Sciences, Oxford Brookes University, Oxford OX3 0BP, United Kingdom
| | - Simone Mazzaferro
- From the Department of Biological and Medical Sciences, Oxford Brookes University, Oxford OX3 0BP, United Kingdom
| | - Manuel Faundez
- the Faculty of Sciences, University of Chile, Santiago 7800003, Chile, and
| | - Patricio Iturriaga-Vasquez
- the Departamento de Ciencias Quimicas y Recursos Naturales, Facultad de Ingenieria y Ciencias, Universidad de la Frontera, Temuco 4811230, Chile
| | - Philip C Biggin
- the Department of Biochemistry, University of Oxford, Oxford OX1 3QU, United Kingdom
| | - Isabel Bermudez
- From the Department of Biological and Medical Sciences, Oxford Brookes University, Oxford OX3 0BP, United Kingdom,
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10
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Bracamontes JR, Akk G, Steinbach JH. Introduced Amino Terminal Epitopes Can Reduce Surface Expression of Neuronal Nicotinic Receptors. PLoS One 2016; 11:e0151071. [PMID: 26963253 PMCID: PMC4786271 DOI: 10.1371/journal.pone.0151071] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/10/2015] [Accepted: 02/23/2016] [Indexed: 12/05/2022] Open
Abstract
Epitopes accessible on the surface of intact cells are extremely valuable in studies of membrane proteins, allowing quantification and determination of the distribution of proteins as well as identification of cells expressing large numbers of proteins. However for many membrane proteins there are no suitable antibodies to native sequences, due to lack of availability, low affinity or lack of specificity. In these cases the use of an introduced epitope at specific sites in the protein of interest can often provide a suitable tool for studies. However, the introduction of the epitope sequence has the potential to affect protein expression, the assembly of multisubunit proteins or transport to the surface membrane. We find that surface expression of heteromeric neuronal nicotinic receptors containing the α4 and β4 subunits can be affected by introduced epitopes when inserted near the amino terminus of a subunit. The FLAG epitope greatly reduces surface expression when introduced into either α4 or β4 subunits, the V5 epitope has little effect when placed in either, while the Myc epitope reduces expression more when inserted into β4 than α4. These results indicate that the extreme amino terminal region is important for assembly of these receptors, and demonstrate that some widely used introduced epitopes may severely reduce surface expression.
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Affiliation(s)
- John R. Bracamontes
- Department of Anesthesiology, Washington University School of Medicine, Saint Louis, MO, United States of America
| | - Gustav Akk
- Department of Anesthesiology, Washington University School of Medicine, Saint Louis, MO, United States of America
- Taylor Family Institute for Innovative Psychiatric Research, Washington University School of Medicine, Saint Louis, MO, United States of America
| | - Joe Henry Steinbach
- Department of Anesthesiology, Washington University School of Medicine, Saint Louis, MO, United States of America
- Taylor Family Institute for Innovative Psychiatric Research, Washington University School of Medicine, Saint Louis, MO, United States of America
- * E-mail:
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