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Ansari S, Kolivand S, Salmanian S, Saghaeian Jazi M, Najafi SMA. Gαq Signaling Activates β-Catenin-Dependent Gene Transcription. IRANIAN BIOMEDICAL JOURNAL 2023; 27:183-90. [PMID: 37481708 PMCID: PMC10507289 DOI: 10.52547/ibj.3890] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Subscribe] [Scholar Register] [Received: 01/21/2023] [Accepted: 05/28/2023] [Indexed: 07/24/2023]
Abstract
Background The canonical Wnt signal transduction or the Wnt/β-catenin pathway plays a crucial role in both carcinogenesis and development of animals. Activation of the Gαq class of Gα proteins positively regulates Wnt/β-catenin pathway, and expression of Gαq in human embryonic kidney 293 (HEK293T) cells or Xenopus oocytes leads to the inhibition of glycogen synthase kinase-3 beta and cellular accumulation of β-catenin. This study investigated whether Gαq-mediated cellular accumulation of β-catenin could affect the transcriptional activity of this protein. Methods HEK-293T and HT-29 cells were used for cell culture and transfection. Protein localization and quantification were assessed by using immunofluorescence microscopy, cell fractionation assay, and Western blotting analysis. Gene expression at the transcription level was examined by quantitative reverse transcriptase/real-time PCR method. Results Transcription of two cellular β-catenin target genes (c-MYC and CCND1) and the β-catenin/ T-cell factor reporter luciferase gene (TopFlash plasmid) significantly increased by Gαq activation. The Gαq-mediated increase in the expression level of the β-catenin-target genes was sensitive to the expression of a minigene encoding a specific Gαq blocking peptide. The results of cell fractionation and Western blotting experiments showed that activation of Gαq signaling increased the intracellular β-catenin protein level, but it blocked its membrane localization. Conclusion Our results reveal that the Gαq-dependent cellular accumulation of β-catenin can enhance β-catenin transcriptional activity.
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Affiliation(s)
| | | | | | | | - S Mahmoud A Najafi
- Department of Cell and Molecular Biology, School of Biology, College of Sciences, University of Tehran, P.O.Box 14155-6455, Tehran, Iran
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Ansari S, Kolivand S, Salmanian S, Saghaeian Jazi M, Najafi SMA. Gαq Signaling Activates β-Catenin-Dependent Gene Transcription. IRANIAN BIOMEDICAL JOURNAL 2023; 27:183-90. [PMID: 37481708 PMCID: PMC10507289 DOI: 10.61186/ibj.3890] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 01/21/2023] [Accepted: 05/28/2023] [Indexed: 12/17/2023]
Abstract
Background The canonical Wnt signal transduction or the Wnt/β-catenin pathway plays a crucial role in both carcinogenesis and development of animals. Activation of the Gαq class of Gα proteins positively regulates Wnt/β-catenin pathway, and expression of Gαq in human embryonic kidney 293 (HEK293T) cells or Xenopus oocytes leads to the inhibition of glycogen synthase kinase-3 beta and cellular accumulation of β-catenin. This study investigated whether Gαq-mediated cellular accumulation of β-catenin could affect the transcriptional activity of this protein. Methods HEK-293T and HT-29 cells were used for cell culture and transfection. Protein localization and quantification were assessed by using immunofluorescence microscopy, cell fractionation assay, and Western blotting analysis. Gene expression at the transcription level was examined by quantitative reverse transcriptase/real-time PCR method. Results Transcription of two cellular β-catenin target genes (c-MYC and CCND1) and the β-catenin/ T-cell factor reporter luciferase gene (TopFlash plasmid) significantly increased by Gαq activation. The Gαq-mediated increase in the expression level of the β-catenin-target genes was sensitive to the expression of a minigene encoding a specific Gαq blocking peptide. The results of cell fractionation and Western blotting experiments showed that activation of Gαq signaling increased the intracellular β-catenin protein level, but it blocked its membrane localization. Conclusion Our results reveal that the Gαq-dependent cellular accumulation of β-catenin can enhance β-catenin transcriptional activity.
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Affiliation(s)
| | | | | | | | - S Mahmoud A Najafi
- Department of Cell and Molecular Biology, School of Biology, College of Sciences, University of Tehran, P.O.Box 14155-6455, Tehran, Iran
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JUNSI M, SIRIPONGVUTIKORN S. Anti-insecticides activity in cell-lines model of Thunbergia laurifolia leaf extract aiming for functional drink. FOOD SCIENCE AND TECHNOLOGY 2022. [DOI: 10.1590/fst.10722] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
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Abstract
Hydrogen to deuterium isotopic substitution has only a minor effect on physical and chemical properties of water and, as such, is not supposed to influence its neutral taste. Here we conclusively demonstrate that humans are, nevertheless, able to distinguish D2O from H2O by taste. Indeed, highly purified heavy water has a distinctly sweeter taste than same-purity normal water and can add to perceived sweetness of sweeteners. In contrast, mice do not prefer D2O over H2O, indicating that they are not likely to perceive heavy water as sweet. HEK 293T cells transfected with the TAS1R2/TAS1R3 heterodimer and chimeric G-proteins are activated by D2O but not by H2O. Lactisole, which is a known sweetness inhibitor acting via the TAS1R3 monomer of the TAS1R2/TAS1R3, suppresses the sweetness of D2O in human sensory tests, as well as the calcium release elicited by D2O in sweet taste receptor-expressing cells. The present multifaceted experimental study, complemented by homology modelling and molecular dynamics simulations, resolves a long-standing controversy about the taste of heavy water, shows that its sweet taste is mediated by the human TAS1R2/TAS1R3 taste receptor, and opens way to future studies of the detailed mechanism of action. Ben Abu, Mason and colleagues use molecular dynamics, cell-based experiments, mouse models, and human subjects to determine that, unlike ordinary water, heavy water tastes sweet to humans, but not mice. Mechanistically, this effect is mediated by the human TAS1R/TAS1R3 sweet taste receptor.
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Abstract
Hydrogen to deuterium isotopic substitution has only a minor effect on physical and chemical properties of water and, as such, is not supposed to influence its neutral taste. Here we conclusively demonstrate that humans are, nevertheless, able to distinguish D2O from H2O by taste. Indeed, highly purified heavy water has a distinctly sweeter taste than same-purity normal water and can add to perceived sweetness of sweeteners. In contrast, mice do not prefer D2O over H2O, indicating that they are not likely to perceive heavy water as sweet. HEK 293T cells transfected with the TAS1R2/TAS1R3 heterodimer and chimeric G-proteins are activated by D2O but not by H2O. Lactisole, which is a known sweetness inhibitor acting via the TAS1R3 monomer of the TAS1R2/TAS1R3, suppresses the sweetness of D2O in human sensory tests, as well as the calcium release elicited by D2O in sweet taste receptor-expressing cells. The present multifaceted experimental study, complemented by homology modelling and molecular dynamics simulations, resolves a long-standing controversy about the taste of heavy water, shows that its sweet taste is mediated by the human TAS1R2/TAS1R3 taste receptor, and opens way to future studies of the detailed mechanism of action.
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Sabbir MG. CAMKK2-CAMK4 signaling regulates transferrin trafficking, turnover, and iron homeostasis. Cell Commun Signal 2020; 18:80. [PMID: 32460794 PMCID: PMC7251913 DOI: 10.1186/s12964-020-00575-0] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/06/2020] [Accepted: 04/02/2020] [Indexed: 12/20/2022] Open
Abstract
Background Circulatory iron is a hazardous biometal. Therefore, iron is transported in a redox-safe state by a serum glycoprotein - transferrin (TF). Different organs acquire iron from the systemic circulation through a tightly regulated mechanism at the blood-tissue interface which involves receptor-mediated internalization of TF. Thus, abnormal TF trafficking may lead to iron dyshomeostasis associated with several diseases including neurodegeneration. Iron -induced toxicity can cause neuronal damage to iron-sensitive brain regions. Recently, it was discovered that CAMKK2, a calcium (Ca2+)/calmodulin-activated kinase, controls receptor-mediated TF trafficking in mouse tissues, specifically in the brain. The biological function of CAMKK2 is mediated through multiple downstream effectors. Both CAMKK2 and one of its downstream kinase, CAMK4, exhibit overlapping expression in mouse brain. The role of CAMK4 in vesicular transport has been reported and loss of CAMKK2 or CAMK4 leads to cognitive defects in mouse. Therefore, it was hypothesized that CAMKK2-CAMK4 signaling regulates receptor-mediated TF trafficking and iron homeostasis which may be responsible for the neuronal malfunction observed in CAMKK2- or CAMK4-deficient mice. Methods CAMK4−/− mouse was used to study tissue-specific turnover of TF, TF-receptor (TFRC) and iron. CRISPR/Cas9-based CAMKK2 and/or CAMK4 deleted human embryonic kidney-derived HEK293 cell clones were used to study the molecular defects in receptor-mediated TF trafficking. Further, a “zero functional G protein” condition in HEK293 cell was exploited to study CAMKK2-CAMK4 signaling-mediated regulation of intracellular Ca2+ homeostasis which was linked to calcium signaling during TF trafficking. Results Loss of CAMK4 leads to abnormal post-translational modifications (PTMs) and turnover of TF in mouse cerebellum and liver which was associated with iron dyshomeostasis in these tissues. The HEK293 cell-based study revealed that the absence of CAMKK2-CAMK4 signaling altered intracellular Ca2+ homeostasis and lead to abnormal calcium signaling during TF trafficking. Also, CAMKK2-CAMK4 signaling deficiency affected the molecular interaction of TF and TF-receptor-associated protein complexes which indicated a potential failure in the recruitment of interacting proteins due to differential PTMs in TF. Conclusion Overall, this study established a novel mechanistic link between intracellular Ca2+ level, receptor-mediated TF trafficking, and iron homeostasis, all regulated by CAMKK2-CAMK4 signaling. Video Abstract
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Affiliation(s)
- Mohammad Golam Sabbir
- Canadian Centre for Agri-Food Research in Health and Medicine, St. Boniface Albrechtsen Research Centre, Room R2034 - 351 Taché Avenue, Winnipeg, MB, R2H 2A6, Canada. .,Alzo Biosciences Inc., San Diego, CA, USA.
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Sabbir MG. Loss of Ca 2+/Calmodulin Dependent Protein Kinase Kinase 2 Leads to Aberrant Transferrin Phosphorylation and Trafficking: A Potential Biomarker for Alzheimer's Disease. Front Mol Biosci 2018; 5:99. [PMID: 30525042 PMCID: PMC6256988 DOI: 10.3389/fmolb.2018.00099] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/14/2018] [Accepted: 10/25/2018] [Indexed: 01/19/2023] Open
Abstract
Ca2+/calmodulin-dependent protein kinase kinase 2 (CaMKK2) is a serine/threonine kinase that is activated following an increase in the intracellular Ca2+ concentration and activates multiple signaling cascades that control physiologically important neuronal processes. CaMKK2 has been implicated in schizophrenia, bipolar disease, neurodegeneration, and cancer. Using isoelectric focusing (IEF) and mass spectrometry-based proteomic analysis, it was found that knockdown (KD) of CaMKK2 in cultured adult primary dorsal root ganglion (DRG) neurons resulted in the reduction of transferrin (TF) phosphorylation at multiple functionally relevant residues which corresponded to loss of an acidic fraction (pH~3-4) of TF. In vitro studies using CRISPR/Cas9 based CaMKK2 knockout (KO) HEK293 and HepG2 cells lines validated previous findings and revealed that loss of CaMKK2 interfered with TF trafficking and turnover. TF is an iron transporter glycoprotein. Abnormal accumulation of iron and/or deregulated Ca2+ homeostasis leads to neurodegeneration in Alzheimer's disease (AD). Therefore, it was hypothesized that aberrant CaMKK2 in AD may lead to aberrant phosphorylated transferrin (P-TF: pH~3-4 fraction) which may serve as a hallmark biomarker for AD. A significant reduction of P-TF in the brain and serum of CaMKK2 KO mice and a triple-transgenic mouse model of AD (3xTg-AD) supported this hypothesis. In addition, analysis of early (< 65 years) and late-stage (>65 years) postmortem human AD cerebrospinal fluid (CSF) and serum samples revealed that aberrant P-TF (pH~3-4 fraction) profile was associated with both early and late-stage AD compared to age-matched controls. This indicates P-TF (pH~3-4 fraction) profile may be useful as a minimally invasive biomarker for AD. In addition, this study provides a link between aberrant CaMKK2 with TF trafficking and turnover which provides a novel insight into the neurodegeneration process.
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Affiliation(s)
- Mohammad Golam Sabbir
- Division of Neurodegenerative Disorders, St. Boniface Hospital Albrechtsen Research Centre, Winnipeg, MB, Canada
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Hening P, Mataram Auriva MB, Wijayanti N, Kusindarta DL, Wihadmadyatami H. The neuroprotective effect of Ocimum sanctum Linn. ethanolic extract on human embryonic kidney-293 cells as in vitro model of neurodegenerative disease. Vet World 2018; 11:1237-1243. [PMID: 30410227 PMCID: PMC6200556 DOI: 10.14202/vetworld.2018.1237-1243] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/13/2018] [Accepted: 07/24/2018] [Indexed: 11/22/2022] Open
Abstract
Aim: This study aimed to analyze the neuroprotective effect of Ocimum sanctum Linn. ethanolic extract (OSE) on human embryonic kidney-293 (HEK-293) cells as the in vitro model of neurodegenerative diseases. Materials and Methods: In this research, HEK-293 cells divided into five groups consisting of normal and healthy cells (NT), cells treated with Camptothecin 500 µM as the negative control, cells treated with trimethyltin 10 µM (TMT), cells treated with OSE 75 µg/ml, and cells pre-treated with OSE 75 µg/ml then induced by TMT 10 µM (OSE+TMT). MTT assay and phase contrast microscopy were applied to observe the cell viability quantitatively and morphological after Ocimum sanctum Linn extract treatment. Finally, the reverse transcription polymerase chain reaction was employed to study the expression of choline acetyltransferase (ChAT). Results: The MTT assay and phase contrast microscopy showed that OSE pre-treatment significantly increased the viability of TMT-induced apoptotic cells and maintained cell viability of the normal HEK-293 cells. Expression of ChAT markedly reduced on TMT treatment group, but OSE administration stabilized ChAT expression in TMT-induced HEK-293 cells. Conclusion: This present study proved that OSE administration has neuroprotective effect by increased HEK-293 cells viability and maintain ChAT expression.
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Affiliation(s)
- Puspa Hening
- Research Center of Biotechnology, Universitas Gadjah Mada, Yogyakarta, 55281, Indonesia
| | - Made Bagus Mataram Auriva
- Department of Anatomy, Faculty of Veterinary Medicine, Universitas Gadjah Mada, Yogyakarta, 55281, Indonesia
| | - Nastiti Wijayanti
- Department of Animal Physiology, Faculty of Biology, Universitas Gadjah Mada, Yogyakarta, 55281, Indonesia
| | - Dwi Liliek Kusindarta
- Department of Anatomy, Faculty of Veterinary Medicine, Universitas Gadjah Mada, Yogyakarta, 55281, Indonesia
| | - Hevi Wihadmadyatami
- Department of Anatomy, Faculty of Veterinary Medicine, Universitas Gadjah Mada, Yogyakarta, 55281, Indonesia
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Gonzalez-Suarez AM, Peña-del Castillo JG, Hernández-Cruz A, Garcia-Cordero JL. Dynamic Generation of Concentration- and Temporal-Dependent Chemical Signals in an Integrated Microfluidic Device for Single-Cell Analysis. Anal Chem 2018; 90:8331-8336. [DOI: 10.1021/acs.analchem.8b02442] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Affiliation(s)
- Alan M. Gonzalez-Suarez
- Unidad Monterrey, Centro de Investigación y de Estudios Avanzados del Instituto Politécnico Nacional, Parque PIIT, Apodaca, Nuevo León, 66628, México
| | - Johanna G. Peña-del Castillo
- Departamento de Neurociencia Cognitiva y Laboratorio Nacional de Canalopatías, Instituto de Fisiología Celular, Circuito de la Investigación Científica s/n Ciudad Universitaria, Universidad Nacional Autónoma de México, Ciudad de México 04510, México
| | - Arturo Hernández-Cruz
- Departamento de Neurociencia Cognitiva y Laboratorio Nacional de Canalopatías, Instituto de Fisiología Celular, Circuito de la Investigación Científica s/n Ciudad Universitaria, Universidad Nacional Autónoma de México, Ciudad de México 04510, México
| | - Jose L. Garcia-Cordero
- Unidad Monterrey, Centro de Investigación y de Estudios Avanzados del Instituto Politécnico Nacional, Parque PIIT, Apodaca, Nuevo León, 66628, México
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Ethanolic extract Ocimum sanctum. Enhances cognitive ability from young adulthood to middle aged mediated by increasing choline acetyl transferase activity in rat model. Res Vet Sci 2018; 118:431-438. [DOI: 10.1016/j.rvsc.2018.04.005] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/24/2017] [Revised: 03/31/2018] [Accepted: 04/13/2018] [Indexed: 01/05/2023]
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Qian J, Mummalaneni S, Larsen J, Grider JR, Spielman AI, Özdener MH, Lyall V. Nicotinic acetylcholine receptor (CHRN) expression and function in cultured human adult fungiform (HBO) taste cells. PLoS One 2018. [PMID: 29513745 PMCID: PMC5841828 DOI: 10.1371/journal.pone.0194089] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Abstract
In rodents, CHRNs are involved in bitter taste transduction of nicotine and ethanol. Currently, it is not clear if CHRNs are expressed in human taste cells and if they play a role in transducing the bitter taste of nicotine and ethanol or in the synthesis and release of neurohumoral peptides. Accordingly, we investigated the expression and functional role of CHRNs in HBO cells. Using molecular techniques, we demonstrate that a subset of HBO cells express CHRNs that also co-express TRPM5, T1R3 or T2R38. Exposing HBO cells to nicotine or ethanol acutely or to nicotine chronically induced a differential increase in the expression of CHRN mRNA and protein in a dose- and time-dependent manner. Acutely exposing HBO cells to a mixture containing nicotine plus ethanol induced a smaller increase in CHRN mRNAs relative to nicotine or ethanol treatment alone. A subset of HBO cells responded to nicotine, acetylcholine and ATP with a transient increase in [Ca2+]i. Nicotine effects on [Ca2+]i were mecamylamine sensitive. Brain-derived neurotrophic factor (BDNF) protein was detected in HBO cells using ELISA. Acute nicotine exposure decreased BDNF in HBO cells and increased BDNF release in the medium. CHRNs were also detected in HEK293 cells by RT-PCR. Unlike HBO cells, CHRNs were localized in most of HEK293 cells and majority of HEK293 cells responded to nicotine and ethanol stimulation with a transient increase in [Ca2+]i. BDNF levels in HEK293 cells were significantly higher than in HBO cells but the nicotine induced release of BDNF in the media was a fraction of the BDNF cellular content. We conclude that CHRNs are expressed in TRPM5 positive HBO cells. CHRN mRNA expression is modulated by exposure to nicotine and ethanol in a dose- and time-dependent manner. Nicotine induces the synthesis and release of BDNF in HBO cells.
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Affiliation(s)
- Jie Qian
- Department of Physiology and Biophysics, Virginia Commonwealth University, Richmond, VA, United States of America
| | - Shobha Mummalaneni
- Department of Physiology and Biophysics, Virginia Commonwealth University, Richmond, VA, United States of America
| | - James Larsen
- Department of Physiology and Biophysics, Virginia Commonwealth University, Richmond, VA, United States of America
| | - John R. Grider
- Department of Physiology and Biophysics, Virginia Commonwealth University, Richmond, VA, United States of America
| | | | | | - Vijay Lyall
- Department of Physiology and Biophysics, Virginia Commonwealth University, Richmond, VA, United States of America
- * E-mail:
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GluD1, linked to schizophrenia, controls the burst firing of dopamine neurons. Mol Psychiatry 2018; 23:691-700. [PMID: 28696429 PMCID: PMC5822454 DOI: 10.1038/mp.2017.137] [Citation(s) in RCA: 33] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/18/2016] [Revised: 05/11/2017] [Accepted: 05/15/2017] [Indexed: 01/08/2023]
Abstract
Human mutations of the GRID1 gene encoding the orphan delta1 glutamate receptor-channel (GluD1) are associated with schizophrenia but the explicit role of GluD1 in brain circuits is unknown. Based on the known function of its paralog GluD2 in cerebellum, we searched for a role of GluD1 in slow glutamatergic transmission mediated by metabotropic receptor mGlu1 in midbrain dopamine neurons, whose dysfunction is a hallmark of schizophrenia. We found that an mGlu1 agonist elicits a slow depolarizing current in HEK cells co-expressing mGlu1 and GluD1, but not in cells expressing mGlu1 or GluD1 alone. This current is abolished by additional co-expression of a dominant-negative GluD1 dead pore mutant. We then characterized mGlu1-dependent currents in dopamine neurons from midbrain slices. Both the agonist-evoked and the slow postsynaptic currents are abolished by expression of the dominant-negative GluD1 mutant, pointing to the involvement of native GluD1 channels in these currents. Likewise, both mGlu1-dependent currents are suppressed in GRID1 knockout mice, which reportedly display endophenotypes relevant for schizophrenia. It is known that mGlu1 activation triggers the transition from tonic to burst firing of dopamine neurons, which signals salient stimuli and encodes reward prediction. In vivo recordings of dopamine neurons showed that their spontaneous burst firing is abolished in GRID1 knockout mice or upon targeted expression of the dominant-negative GluD1 mutant in wild-type mice. Our results de-orphanize GluD1, unravel its key role in slow glutamatergic transmission and provide insights into how GRID1 gene alterations can lead to dopaminergic dysfunctions in schizophrenia.
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Hussmann GP, Turner JR, Lomazzo E, Venkatesh R, Cousins V, Xiao Y, Yasuda RP, Wolfe BB, Perry DC, Rezvani AH, Levin ED, Blendy JA, Kellar KJ. Chronic sazetidine-A at behaviorally active doses does not increase nicotinic cholinergic receptors in rodent brain. J Pharmacol Exp Ther 2012; 343:441-50. [PMID: 22899752 DOI: 10.1124/jpet.112.198085] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022] Open
Abstract
Chronic nicotine administration increases α4β2 neuronal nicotinic acetylcholine receptor (nAChR) density in brain. This up-regulation probably contributes to the development and/or maintenance of nicotine dependence. nAChR up-regulation is believed to be triggered at the ligand binding site, so it is not surprising that other nicotinic ligands also up-regulate nAChRs in the brain. These other ligands include varenicline, which is currently used for smoking cessation therapy. Sazetidine-A (saz-A) is a newer nicotinic ligand that binds with high affinity and selectivity at α4β2* nAChRs. In behavioral studies, saz-A decreases nicotine self-administration and increases performance on tasks of attention. We report here that, unlike nicotine and varenicline, chronic administration of saz-A at behaviorally active and even higher doses does not up-regulate nAChRs in rodent brains. We used a newly developed method involving radioligand binding to measure the concentrations and nAChR occupancy of saz-A, nicotine, and varenicline in brains from chronically treated rats. Our results indicate that saz-A reached concentrations in the brain that were ∼150 times its affinity for α4β2* nAChRs and occupied at least 75% of nAChRs. Thus, chronic administration of saz-A did not up-regulate nAChRs despite it reaching brain concentrations that are known to bind and desensitize virtually all α4β2* nAChRs in brain. These findings reinforce a model of nicotine addiction based on desensitization of up-regulated nAChRs and introduce a potential new strategy for smoking cessation therapy in which drugs such as saz-A can promote smoking cessation without maintaining nAChR up-regulation, thereby potentially increasing the rate of long-term abstinence from nicotine.
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Affiliation(s)
- G Patrick Hussmann
- Department of Pharmacology and Physiology, Georgetown University School of Medicine, 3900 Reservoir Road, NW, Washington, DC 20057, USA
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